WO2001052719A2 - Detection d'accidents vasculaires cerebraux par tomographie optique diffuse - Google Patents

Detection d'accidents vasculaires cerebraux par tomographie optique diffuse Download PDF

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Publication number
WO2001052719A2
WO2001052719A2 PCT/US2001/002226 US0102226W WO0152719A2 WO 2001052719 A2 WO2001052719 A2 WO 2001052719A2 US 0102226 W US0102226 W US 0102226W WO 0152719 A2 WO0152719 A2 WO 0152719A2
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brain
subject
concentration
dye
peak
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PCT/US2001/002226
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English (en)
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WO2001052719A3 (fr
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David Allan Boas
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The General Hospital Corporation
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Priority claimed from US09/491,595 external-priority patent/US6516214B1/en
Priority claimed from US09/598,422 external-priority patent/US6577884B1/en
Application filed by The General Hospital Corporation filed Critical The General Hospital Corporation
Priority to EP01910346A priority Critical patent/EP1251771A4/fr
Priority to AU2001237963A priority patent/AU2001237963A1/en
Priority to CA002397145A priority patent/CA2397145A1/fr
Publication of WO2001052719A2 publication Critical patent/WO2001052719A2/fr
Publication of WO2001052719A3 publication Critical patent/WO2001052719A3/fr

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    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/6813—Specially adapted to be attached to a specific body part
    • A61B5/6814—Head
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
    • A61B5/0073—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence by tomography, i.e. reconstruction of 3D images from 2D projections
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
    • A61B5/026—Measuring blood flow
    • A61B5/0275—Measuring blood flow using tracers, e.g. dye dilution
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
    • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
    • A61B5/14551—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases
    • A61B5/14553—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters for measuring blood gases specially adapted for cerebral tissue
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/40—Detecting, measuring or recording for evaluating the nervous system
    • A61B5/4076—Diagnosing or monitoring particular conditions of the nervous system
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/41—Detecting, measuring or recording for evaluating the immune or lymphatic systems
    • A61B5/411—Detecting or monitoring allergy or intolerance reactions to an allergenic agent or substance
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02—Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0233—Special features of optical sensors or probes classified in A61B5/00
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00—Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/04—Arrangements of multiple sensors of the same type
    • A61B2562/046—Arrangements of multiple sensors of the same type in a matrix array

Definitions

  • the invention is in the field of diffuse optical tomography and stroke.
  • Victims of stroke caused by an ischemic event in the brain can benefit from treatment with recombinant tissue plasminogen activator, a thrombolytic drug, within three hours of the ischemic event.
  • tissue plasminogen activator a thrombolytic drug
  • thrombolytic drugs are contraindicated.
  • a quick and efficient means of distinguishing an ischemic event from a bleed in a stroke victim would aid a health care provider in managing the treatment of stroke victims.
  • treatment protocols need to be tailored to individual patients. Therefore, continuous monitoring of cerebral perfusion would enable the health care provider to more effectively guide treatment in a patient with a specific pathology.
  • Diffuse optical tomography refers to various non-invasive methods of imaging different tissues of a body or organ.
  • DOT relies on the emission of light from a light source into the body, then detecting the light scattered from various tissues of the body. For example, since light scattered by hemoglobin in blood differs from light scattered by other tissues, DOT has been applied to the imaging of blood within the body.
  • DOT has been used to locate areas of high or low oxygenation in the body by determining decreases or increases in the intensity of scattered light.
  • the application of DOT in various imaging scenarios in the clinic has been limited by the inability to detect light scattered by deep tissues. This can be due to either the inability of the emitted light to reach deep tissues, or the inability to detect and measure the weak intensity of light scattered by the deep tissues (i.e., no measurable contrast between scattered light and background).
  • the invention is based on the recognition that ischemic events deep in the brain can be detected using DOT to monitor collateral blood flow abnormalities in cortical regions of the brain arising from the deep ischemic events using contrast agents, such as blood-borne tracer dyes (also called tracers) and oxygen (e.g., oxyhemoglobin).
  • contrast agents such as blood-borne tracer dyes (also called tracers) and oxygen (e.g., oxyhemoglobin).
  • the invention is also based on the recognition that a brain bleed can be imaged by DOT using a blood-borne tracer dye or oxygen and detecting a localized region of a lower concentration of dye or oxygen or of no dye at all, as compared to an adjacent region in the brain.
  • the imaging of a brain bleed is made possible by recognizing that blood vessel constriction and clotting at the site of the bleed will inhibit the dye or oxygen from infiltrating the region of the bleed while adjacent regions are unaffected.
  • the use of a tracer dye or oxygen increases the contrast in light scattered by blood versus solid tissue deep in the brain, thereby allowing blood volume to be imaged even where the intensity of scattered light is weak.
  • the invention features a method of detecting an ischemic event in a brain in a subject, using a first criterion, by (1) administering a dye bolus into the bloodstream of the subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the dye being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of the dye being different from the light emitted from the brain in the absence of the dye, the magnitude of the difference corresponding to the concentration of the dye; (4) establishing a reference time period corresponding to the time a peak concentration of a dye bolus takes to reach the detection location in a normal brain; (5) determining a subject time period corresponding to the time a peak concentration of the dye bolus takes to reach the detection location in the subject; and (6) comparing the subject time period with the reference time period, where a subject time period 1 or more seconds longer than the reference time period indicates an ischemic event
  • the invention includes a method of detecting an ischemic event in a brain in a subject, using a second criterion, by (1) administering a dye bolus into the bloodstream of the subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the dye being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of dye being different from the light emitted from the brain in the absence of the dye, the magnitude of the difference corresponding to the concentration of the dye; (4) establishing a peak reference concentration of a dye bolus administered to a subject with a normal brain at the detection location; (5) determining a peak subject concentration of the dye bolus at the detection location; and (6) comparing the peak subject concentration with the peak reference concentration, where a peak subject concentration below the peak reference concentration indicates an ischemic event in the brain. If the peak subject concentration is below the peak reference concentration but at least 50% of the peak reference concentration,
  • the invention also includes a method of detecting an ischemic event in a brain in a subject, using a third criterion, by (1) administering a dye bolus into the bloodstream of the subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the dye being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of dye being different from the light emitted from the brain in the absence of the dye, the magnitude of the difference corresponding to the concentration of the dye; (4) establishing a reference time period corresponding to the time for the concentration of a dye bolus to vary from a threshold (e.g., 10, 5, 2, or 1% by volume) concentration to a peak concentration and back to the threshold concentration at the detection location in a normal brain; (5) determining a subject time period corresponding to the time for the concentration of the dye to vary from the threshold concentration to a peak concentration and back to the threshold concentration at the detection location; and
  • the invention includes a method of detecting an ischemic event in a brain in a subject, using a fourth criterion, by (1) administering a dye bolus into the bloodstream of a subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the dye being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of the dye being different from the light emitted from the brain in the absence of the dye, the magnitude of the difference corresponding to the concentration of the dye; (4) establishing a reference map of cortical blood flow in a normal brain; (5) obtaining a subject map of cortical blood flow in the subject; and (6) comparing the reference map with the subject map, where a continuous region of decreased blood flow in the subject map, compared to the reference map indicates an ischemic event in the brain.
  • this method can further include (7) comparing the position of the region of decreased blood flow with a map of known brain vasculature; and (8) extrapolating the position of the ischemic event in the brain of the subject.
  • the invention includes a method of detecting an ischemic event in a brain in a subject using any combination (e.g., all) of the criteria specified above.
  • the methods described above also need not specify all the steps; only the last comparing step is required.
  • the invention further includes a method of detecting a brain bleed in a subject by (1) administering a dye into the bloodstream of the subject; (2) directing light from a light source into the brain of the subject; (3) detecting light emitted from the brain while the dye is present in a portion of the brain, the light emitted from the brain in the presence of the dye being different from the light emitted from the brain in the absence of the dye, the magnitude of the difference corresponding to the concentration of the dye, and the detecting step being performed while the dye is detectable in the blood circulation of the subject; and (4) determining the concentration of the dye in the portion of the brain, where a region of the portion with a lower concentration of the dye than an adjacent region of the portion indicates a brain bleed.
  • the invention includes a method of detecting a brain bleed in a subject by (1) administering a dye into the bloodstream of the subject; (2) directing light from a light source into the brain of the subject; (3) detecting light emitted from the brain while the dye is present in a portion of the brain, the light emitted from the brain in the presence of the dye being different from the light emitted from the brain in the absence of the dye, the magnitude of the difference corresponding to the concentration of the dye, and the detecting step being performed after the initial dye concentration in the blood circulation of the subject has been reduced; and (4) determining the concentration of the dye in the portion of the brain, where a region of the portion with a higher concentration of the dye than an adjacent region of the portion indicates a brain bleed.
  • the dye can be indocyanine green or any other suitable dye described herein
  • the difference in light can be the amplitude of light
  • the subject can be a mammal (e.g., a human).
  • the methods can include directing light into the brain through the scalp of the subject from a plurality of light sources and detecting light emitted from the brain using a plurality of photodetectors (e.g., charged-coupled devices).
  • a system including (1) at
  • the light can be directed by at least two optical sources and detected by at least two optical detectors, the sources coupling light into the brain at spatially separated locations, and the detectors positioned to receive light emitted from the sample at spatially separated locations and generating signals in response to the light from the sources.
  • the invention also features a method of detecting an ischemic event in a brain in a subject, using a first criterion, by (1) administering an oxygen bolus into the bloodstream of the subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the oxygen bolus being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of the oxygen bolus being different from the light emitted from the brain in the absence of the oxygen bolus, the magnitude of the difference corresponding to a difference in the concentration of total oxygen; (4) establishing a reference time period corresponding to a time a peak concentration of the oxygen bolus takes to reach the detection location in a normal brain; (5) determining a subject time period corresponding to a time a peak concentration of the oxygen bolus takes to reach the detection location in the subject; and (6) comparing the
  • the invention includes a method of detecting an ischemic event in a brain in a subject, using a second criterion, by (1) administering an oxygen bolus into the bloodstream of the subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the oxygen bolus being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of the oxygen bolus being different from the light emitted from the brain in the absence of the oxygen bolus, the magnitude of the difference corresponding to a difference in concentration of total oxygen; (4) establishing a peak reference concentration of the oxygen bolus administered to a subject with a normal brain at the detection location; (5) determining a peak subject concentration of the oxygen bolus at the detection location; and (6) comparing the peak subject concentration with the peak reference concentration, where a peak subject concentration below the peak reference concentration indicates an ischemic event in the brain. If the peak subject concentration is below the peak reference
  • the invention also includes a method of detecting an ischemic event in a brain in a subject, using a third criterion, by (1) administering an oxygen bolus into the bloodstream of the subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the oxygen bolus being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of oxygen bolus being different from the light emitted from the brain in the absence of the oxygen bolus, the magnitude of the difference corresponding to the difference in concentration of total oxygen; (4) establishing a reference time period corresponding to the time for the concentration of the oxygen bolus to vary from a threshold concentration (e.g., about 85-95%) oxygen saturation) to a peak concentration and back to the threshold concentration at the detection location in a normal brain; (5) determining a subject time period corresponding to the time for the concentration of the oxygen bolus to vary from the threshold concentration to a peak concentration and
  • the invention includes a method of detecting an ischemic event in a brain in a subject, using a fourth criterion, by (1) administering an oxygen bolus into the bloodstream of a subject; (2) directing light into the brain of the subject; (3) detecting light emitted from the brain over time at a detection location, the oxygen bolus being present in the brain for at least a portion of the detection time, and the light emitted from the brain in the presence of the oxygen bolus being different from the light emitted from the brain in the absence of the oxygen, the magnitude of the difference corresponding to the difference in concentration of total oxygen; (4) establishing a reference map of cortical blood flow in a normal brain; (5) obtaining a subject map of cortical blood flow in the subject; and (6) comparing the reference map with the subject map, where a continuous region of decreased blood flow in the subject map, compared to the reference map indicates an ischemic event in the brain.
  • this method can further include (7) comparing the position of the region of decreased blood flow with a map of known brain vasculature; and (8) extrapolating the position of the ischemic event in the brain of the subject.
  • the invention includes a method of detecting an ischemic event in a brain in a subject using any combination (e.g., all) of the criteria specified above.
  • the methods described above also need not specify all the steps; only the last comparing step is required.
  • the invention further includes a method of detecting a brain bleed in a subject by (1) administering oxygen into the bloodstream of the subject; (2) directing light from a light source into the brain of the subject; (3) detecting light emitted from the brain while the oxygen is present in a portion of the brain, the light emitted from the brain in the presence of the oxygen being different from the light emitted from the brain in the absence of the oxygen, the magnitude of the difference corresponding to the difference in concentration of total oxygen, and the detecting step being performed while the oxygen is detectable in the blood circulation of the subject; and (4) determining the concentration of the oxygen in the portion of the brain, where a region of the portion with a lower concentration of the oxygen than an adjacent region of the portion indicates a brain bleed.
  • the invention includes a method of detecting a brain bleed in a subject by (1) administering oxygen into the bloodstream of the subject; (2) directing light from a light source into the brain of the subject; (3) detecting light emitted from the brain while the oxygen is present in a portion of the brain, the light emitted from the brain in the presence of the oxygen being different from the light emitted from the brain in the absence of the oxygen, the magnitude of the difference corresponding to the difference in concentration of total oxygen, and the detecting step being performed after the initial oxygen concentration in the blood circulation of the subject has been reduced; and (4) determining the concentration of the oxygen in the portion of the brain, where a region of the portion with a higher concentration of the oxygen than an adjacent region of the portion indicates a brain bleed.
  • the oxygen can be administered to the subject by temporary (e.g., for 1 minute) inhalation of oxygen-enriched atmosphere (e.g., 50, 60, 70, 80, 90, or 100% oxygen by volume), the difference in light can be the amplitude of light, and the subject can be a mammal (e.g., a human).
  • the methods can include directing light into the brain through the scalp of the subject from a plurality of light sources and detecting light emitted from the brain using a plurality of photodetectors (e.g., charged-coupled devices).
  • a system including (1) at least two optical sources which during operation emit
  • the light can be directed by at least two optical sources and detected by at least two optical detectors, the sources coupling light into the brain at spatially separated locations, and the detectors positioned to receive light emitted from the sample at spatially separated locations and generating signals in response to the light from the sources.
  • a "normal" brain or region of a brain as used herein is a brain or region suitable to serve as a control or reference tissue for testing of potentially affected tissue in a subject brain.
  • a normal or reference brain or region can be a different brain than that of the brain of a subject under DOT examination, or the same brain as that of the subject.
  • the control or reference tissue can be a matched, symmetric region (e.g., right versus left hemisphere), or a region adjacent to the potentially affected tissue. Due to calibration considerations (discussed below), regions adjacent to the potentially affected tissue serve as better normal portions of the brain than symmetric regions, which in turn are better normal portions than regions of a different brain in a different individual.
  • a "deep” portion or region of a brain is greater than 1 cm below the inner surface of the skull.
  • Oxygen means any form of oxygen, including dissolved oxygen and oxygen complexed with hemoglobin (oxyhemoglobin).
  • Oxygen saturation means the percentage of total hemoglobin that is in the form of oxyhemoglobin.
  • the methods of the invention provide for a quick, non-invasive means of detecting and distinguishing a bleed or ischemic event in the brain of a stroke patient or suspected stroke patient.
  • the methods are particularly applicable for a patient exhibiting a recent onset of one or more symptoms of stroke.
  • distinguishing a bleed from an ischemic event in the shortest amount of time is important for determining the optimal treatment for the patient during the critical first few hours after an ischemic stroke.
  • the methods can be applied continuously to monitor the development of a stroke in a patient for fine tuning of the treatment.
  • FIGs. 1-3 are schematic drawings of systems suitable for implementing the methods of the invention.
  • Fig. 4 is a schematic diagram of a source-detector pair for the system shown in Fig. 3.
  • Fig. 5 is a flow chart summarizing the steps of one embodiment of the calibration method described herein.
  • Figs. 6A and 6B are schematic diagrams of blood vessels in a brain with a cortical ischemic event (Fig. 6A) and a brain with a deep ischemic event (Fig. 6B).
  • Fig 7A is a schematic drawing of a human head, showing the spatial distribution of blood flow abnormalities arising from a deep ischemic event.
  • Fig. 7B is a graph of time versus tracer concentration for the abnormality seen in Fig. 7A.
  • Fig. 8A is a schematic drawing of a human head, showing the spatial distribution of blood flow abnormalities arising from a cortical ischemic event.
  • Fig. 8B is a graph of time versus tracer concentration for the abnormality seen in Fig. 8A.
  • Fig. 9A is a schematic representation of a human head, showing a brain bleed (clear region) surrounding a source bleed source (dot), while a dye bolus (hatched region) is present in the brain.
  • the clear region represents a decreased concentration of dye due to an inability of the dye to infiltrate the bleed.
  • Fig. 9B is a graph of position along line A versus tracer concentration for the abnormality seen in Fig. 9A.
  • Fig. 10 is a graph of time versus amplitude in a DOT experiment.
  • Fig. 11 is a schematic diagram of the optical arrangement of the sources and detectors used in Example 5 below.
  • Figs. 12A-12D are reconstructed DOT images of experimental data from Example 5 below.
  • Figs. 13A and 13B are graphs of peak image values derived from the images of Figs. 12A-12D.
  • Fig 14 is an additional reconstructed image of the experimental data from Example 5 below.
  • Fig. 15 is a graph of time versus amplitude obtained in the experiment of Example 6.
  • Figs. 16A-16C are diagrams of a scalp cap for use in the methods of the invention.
  • Fig. 16A is a perspective view of the cap.
  • Fig. 16B is a top view of the cap.
  • Fig. 16C is a portion of a cross-sectional view of the cap taken along line A-A in Fig. 16B, as positioned on the scalp.
  • the invention relates to the use of diffuse optical tomography for detecting a bleed or ischemic event in a brain, or distinguishing one from the other.
  • the various light emitters and detectors, dyes, oxygen, and algorithms used for carrying out DOT are discussed below.
  • perfused brain tissue contains between 5-10%) blood by volume.
  • the region of a bleed contains about 100% blood.
  • the plasma diffuses away, leaving a pool of blood with a greater concentration of hemoglobin and thus higher optical absorption. Therefore, a bleed will offer an intrinsic contrast exceeding a factor of 10-20, and is detectable by static DOT imaging of blood.
  • the blood volume may change by as little as a factor of 2 because ischemia is characterized by reduced, not increased, perfusion.
  • the oxygen saturation will likely drop because of a higher oxygen extraction fraction resulting from the reduced perfusion.
  • the contrast due to a decrease in the ratio of oxyhemoglobin to deoxyhemoglobin can vary from -50%> at 750 nm to +50% at 850 nm. The significantly smaller contrast of an ischemic stroke relative to a bleed has led many to believe that ischemic stroke cannot be detected, monitored, or imaged using DOT.
  • the problem is overcome by recognizing that the reduced perfusion of a deep ischemic stroke has collateral effects extending to the cortex (see Example 1 below).
  • MRI hemodynamic magnetic resonance imaging
  • the magnitude of the delay, as well as the spatial extent (size) of the blood flow abnormality can indicate the severity of an ischemic stroke. Changes in these parameters can also provide valuable feedback on the natural evolution of a stroke and the response of a stroke to treatment.
  • the volume sampled by the scattered light depends on the positioning of the light emitter(s) and collector(s) relative to each other. If the absorption probability increases, e.g., in the presence of an absorbing dye or oxygen, within a tissue, then the amount of light detected will decrease.
  • a major problem in implementing optical methods for monitoring brain hemodynamics is distinguishing scalp signals from brain signals. This is true with static measurements of blood volume (total hemoglobin concentration) and oxygen saturation (proportion of total hemoglobin that is oxyhemoglobin), as well as dynamic bolus kinetic measurements of blood flow.
  • One solution for this problem is to provide a downward force on the optodes so that the optodes make contact with the skin surface. The optodes can then be moved from sided to side along the surface of the scalp to displace any hair blocking the optodes.
  • Another implementation strategy involves extracting small signal changes resulting from small concentrations of the vascular contrast agent (e.g., oxygen or dye).
  • the vascular contrast agent e.g., oxygen or dye.
  • measurements of light intensity or amplitude at the optode emitter wavelength are suitable in DOT
  • measurements at a wavelength different from the optode emitter wavelength are also possible if the dye is a fluorophore.
  • Detection at the fluorophore's emitter wavelength can be used to measure relatively small concentrations of the dye within the blood.
  • the main advantage of fluorescence detection is that smaller concentrations can be injected into the subject for DOT measurements, thereby permitting repeated injections every minute rather than every 10 minutes, as is typical with an absorptive contrast agent.
  • an abso ⁇ tive dye such as indocyanine green (ICG)
  • ICG indocyanine green
  • the baseline level of dye in the circulation would be too high for detecting the next bolus injected into the patient.
  • simultaneous monitoring can be used when a single contrast agent having both significant absorption at the optode emitter wavelength and fluorescence wavelength is injected into a patient as a bolus.
  • simultaneous monitoring can be useful if an abso ⁇ tive dye and a fluorescent dye are injected into the patient, either at the same time or at different times.
  • Photon counting detection methods provide the best signal-to-noise ratio when the number of photons detected per second is small (typically less than 1 x 10 6 per second).
  • the number of photons that reach the center of the brain and escape from the body is much less than the typical background noise of 10 photons per second.
  • This problem is best solved by using lasers with powers greater than 1 W, but fear of tissue burning precludes the use of an emitter having that high power.
  • One solution is to distribute the large optical power across multiple input sites, thereby bringing the total power to levels greater than 1 W without burning the tissue.
  • a catheter can be threaded to the base of the brain. This catheter is then used as a source of light that is detected at the surface of the head.
  • a bolus of dye (also called tracer or contrast agent) can be injected into the blood stream of the patient
  • the injection is usually made intravenously and usually through the arm, taking about 1 second to complete.
  • the bolus can be 1 to 10 ml (e.g., 5 ml) of dye.
  • the bolus travels relatively intact through the brain.
  • the bolus becomes dilute and spatially extended and diffuse. After several passes of the bolus through the heart (each cycle through the body taking about 20-40 seconds), it usually is no longer possible to recognize a spatially coherent contrast.
  • the amplitude of the detected light decreases as the bolus, which absorbs light, flows into the optically sampled volume of tissue. The amplitude then increases back to the baseline as the bolus flows out of the imaged region.
  • the duration of this perturbation is a measure of blood flow, while the magnitude of the perturbation can serve as a measure of perfusion or blood volume.
  • comparison of the onset and offset of the perturbation in different cortical regions of the brain can provide a relative measure of the blood transit time. All of these measures can serve to better characterize the state and evolution of a stroke by providing a spatial map or image of the abnormality in the brain over time.
  • Useful dispersible chromophores include: drugs and dyes such as rifampin (red), ⁇ -carotene (orange), tetracycline (yellow), indocyanine green (such as Cardio-Green®), Evan's blue, methylene blue; soluble inorganic salts such as copper sulfate (green or blue), Cu(NH 3 ) 2+ (dark blue), MnO 4 (pu ⁇ le), NiCl 2 (green), CrO 4 (yellow), Cr 2 O 2" (orange); proteins such as rhodopsin (pu ⁇ le and yellow forms) and green fluorescent protein (fluoresces green under blue light); and any of the Food and Drug Administration (FDA) approved dyes used commonly in foods, pharmaceutical preparations, medical devices, or cosmetics, such as the well-characterized non-toxic sodium salts FD&C Blue No.
  • drugs and dyes such as rifampin (red), ⁇ -carotene (orange), tetracycline
  • the dispersible chromophores listed above are generally (1) water-soluble at physiological pH, although fat-soluble chromophores (such as ⁇ -carotene) will also work if they are rapidly flushed from tissue, or (2) digestible or metabolizable through enzymatic pathways (such as methylene blue, which is rapidly metabolized by mitochondrial reductases, and proteins which are digested by proteases). In some cases, it may be possible to modify a chromophore to improve its dispersibility.
  • a particular advantage of protein chromophores is that they can be conjugated to degradation inducing moieties, such as degradation signaling polypeptides using standard biochemical techniques. For example, green fluorescent protein can be conjugated to ubiquitin, which facilitates breakdown of the protein into small, invisible peptides by the eukaryotic ubiquitin proteolysis pathway.
  • Oxygen can provide the same benefits as described herein for dyes, with the added advantage that molecular oxygen can be introduced by non-invasive means, e.g., by inhalation.
  • a bolus of an oxygen-containing dye, such as oxyhemoglobin can also be injected into the blood stream as detailed above.
  • a subject that is suspected of having a stroke event can be placed on a standard inhaler or respiratory device for controlling the concentration of oxygen in the inhaled atmosphere. Initially, the subject would breathe an ambient concentration of oxygen (about 20%) or even a slightly enriched oxygen atmosphere. A concentration of oxygen lower than ambient levels may place the subject under some stress, though this is possible as well. At a marked time point, the oxygen concentration will be increased to a substantially higher concentration (e.g., 50, 60, 70, 80, 90, or 100%) for a chosen time period (e.g., for 5 to 30 second, or one or more minutes). The period of time for oxygen inhalation will depend in part on the intended measurement.
  • a substantially higher concentration e.g., 50, 60, 70, 80, 90, or 100%
  • a chosen time period e.g., for 5 to 30 second, or one or more minutes. The period of time for oxygen inhalation will depend in part on the intended measurement.
  • the period should be shorter than the cycle-time of blood (i.e., the time for a particular blood volume to return to the same position in the body, which ranges from 20 to 40 seconds depending on numerous patient-specific factors), to produce a detectable bolus traveling through the blood stream. If only a generally increased concentration of oxygen is desired in the circulating blood, then the subject can be exposed to the increased oxygen atmosphere for longer than the cycle time, e.g., for 1 to 5 minutes.
  • the percentage oxygen saturation can be used as a measure of oxygen concentration.
  • Oxygen saturation is typically expressed as the proportion of total hemoglobin that is oxyhemoglobin and is measured using standard methods known in the art.
  • the baseline arterial oxygen saturation can vary from 85-95%.
  • the concentration of oxygen in the oxygen-enriched air should be high enough to induce a measurable increase in arterial oxygen saturation (e.g., 97% or higher) above baseline in the brain.
  • subjecting an individual to an initially oxygen-poor environment can induce an artificially low base line (e.g., 50% oxygen saturation) over which a bolus can be detected.
  • the particular baseline (or threshold) saturation levels and the peak saturation level for a bolus will vary from subject to subject according to the individual physiological parameters of each subject.
  • the baseline is readily established by monitoring the oxygen saturation of a subject over time and before an oxygen bolus is administered, e.g., by inhalation of an oxygen-enriched environment.
  • oxygen functions as any other dye when administered into the blood stream and provides the same advantages as described herein.
  • DOT measurements There are numerous approaches for taking DOT measurements.
  • a single optode delivers light to the scalp of an individual, and a single optode detects the scattered light.
  • the optodes can be separated by 2.5 to 3.5 cm to maximize the detection of light that has traveled through the skull and into the cortex of the brain before returning to the detecting optode.
  • the detected light likely travels only through the skull. Larger optode separations result in smaller signal-to-noise ratios and a larger volume of tissue sampled, but have poor spatial resolution.
  • the 2.5 to 3.5 cm separation of emitters and detectors permits measurement of flow/mean transit time when a bolus moves through the position imaged by the pair of optodes.
  • a spatial array of measurements are desirable.
  • the array can provide measurements from region to region in the cortex, as well as the spatial extent (size) of any abnormality.
  • the wavelength of the light emitted from the optode should correspond to light that is detectably absorbed by the tissue or local blood to be imaged or that matches the abso ⁇ tion wavelength of a fluorescent or non-fluorescent dye.
  • a bolus of dye can be injected into the patient as described above and used to enhance the abso ⁇ tion of light by the blood in a time-dependent manner. For example, if a bolus of indocyanine green is injected into a patient for DOT, an appropriate wavelength for the light emitted by the optode is 780-800 nm, the peak abso ⁇ tion wavelength of indocyanine green.
  • the optodes can be positioned on a patient's head using any means known in the art.
  • a stiff helmet made of Styrofoam and having holes in various positions around its hemisphere can be used to group, position, and fix the optodes against an individual's scalp.
  • a flexible and elastic cap made of rubber or nylon or the like, similar to a swimmer's cap, can be used to arrange the optodes.
  • a device 400 is formed from a flexible, elastic cap 410 containing holes 420 for placement of a plurality of optodes 430, only two of which are shown in Figs. 16A and 16B.
  • the flexible and elastic nature of the cap helps ensure a fixed, tight fit over an individual's head.
  • the two optodes shown include an optical fiber 432, which delivers light from a laser (not shown) to scalp surface 402, and a photodetector 434 for detecting scattered light. All optodes 430 are flexibly attached to cap 410 by rubber grommets 440.
  • cap 410 When cap 410 is tightly fitted over the head, optodes 430 are pressed against scalp surface 402, with pressure generated by displacement of rubber grommets 440, such as displaced rubber grommet 440a (see Fig. 16C).
  • device 400 can be shifted back and forth while cap 410 is placed over scalp surface 402. This shifting movement causes, for example, optode 432 to move hair fibers 460 away from the scalp area in contact with optical fiber 432 (see Fig. 16C).
  • Other similar arrangements and devices e.g., caps or helmets are suitable for use in the methods of the invention.
  • a second wavelength is useful, for example, to determine the degree of oxygenation (relative amount of oxyhemoglobin) of the blood, while the first wavelength is used to detect the concentration of a dye introduced into the blood stream of a subject as described herein.
  • Monitoring scattered light of the second wavelength can also help calibrate the measurement of dye concentration in blood by accounting for variations in the signals at the first wavelength as a result of changes in blood oxygenation. Circuitry for Detection of Scattered Light
  • FIG. 1 A suitable circuitry for resolving small difference in light intensity returning to one or more optode from the brain is shown in Fig. 1.
  • the circuit enables the use of two wavelengths, though only one wavelength is required for the methods of the invention. For example, a single wavelength of 780 nm would be appropriate when detecting a bolus of indocyanine green passing through the vasculature of the brain.
  • the use of two wavelengths enables more than one dye to be used, each dye having a different abso ⁇ tion and/or fluorescent wavelength. The two dyes then offer collaborating signals that provide more reliable detection of bleeds or ischemic events. Further details regarding such benefits are discusses elsewhere herein.
  • the phase encoding shown in the circuit of Fig. 1 can spatially distinguish light emitted into the head from sources at different locations (e.g., at 5 to 25 locations, particularly at 18 locations) or at the same location but with different wavelengths. This ability is important if the optodes are to be powered continuously to fully resolve the passage of a bolus.
  • a prototype DOT imager having only one light source can only energize one source at a time, which limits the data acquisition rate.
  • a more efficient technique, using the above circuit, is to exploit the phase diversity afforded by coherent detection by modulating each laser wavelength at the same 2 kHz frequency but in phase quadrature with each other.
  • Double-balanced mixers are insensitive to coherent signals which arrive exactly 90° out of phase with the demodulation clock.
  • a quadrature signal passes through the mixer, the DC level of the resulting signal averages out to zero, similar to uncorrelated noise.
  • the mixer fed by a detector signal containing both in-phase and quadrature components (generated by the two laser sources), will demodulate the in-phase signal only, and will completely ignore the quadrature component.
  • Double-pole post-detection filters are used to attenuate the strong second harmonic component produced by the quadrature source. This use of phase-encoding allows us to sample two sources simultaneously.
  • the circuit 20 shown in Fig. 1 is such a quadrature encoded system, as described immediately above, that places the signals from the two source wavelengths into mutually orthogonal phases at one carrier frequency, centered at about 2 kHz.
  • the electrical signals representing the intensity of each source wavelength are extracted from the single detector channel using synchronous or phase-sensitive detection.
  • the 7555 microprocessor 22 serves as the master clock, which is divided down and split into I and Q (in-phase and quadrature, respectively) outputs 24 and 26.
  • the I and Q outputs 24 and 26 are then used to directly modulate the bias current through the two-laser diode sources 28 and 30, respectively.
  • the demodulator clocks are delayed by the exact same amount using adjustable R-C phase shifters 24a and 26a.
  • the pots are adjusted to maximize the signal level of the main component while nulling the quadrature component to zero.
  • the output of the double-balanced mixers 34 and 36 are then separated by the two-stage lowpass filters 38 and 40 to remove any AC components, and buffered through output buffers 42 and 44, yielding the two synchronously rectified DC signals, "I" output (46) and "Q” output (48).
  • FIG. 2 A schematic of such a system is shown in Fig. 2.
  • the frequency encoded system 50 operates in a manner similar to the circuit 20 shown in Fig. 1, except that each source wavelength 52 and 62 is modulated and demodulated at its own unique frequency. This is essentially the equivalent of two separate single-channel subsystems 50a and 50b operating independently.
  • Each master clock operates at a slightly different frequency. The frequencies must differ by at least three times the baseband (post-detection) bandwidth and should not be within the same distance of any of the frequency harmonics to avoid interchannel cross-talk.
  • Subsystems 50a and 50b are nearly identical and contain components that operate as described above.
  • Subsystem 50a synchronizes a 780 nm laser source 52 with a photo detector 55 using a 2 kHz masterclock 53, in order to improve the signal-to-noise ratio of the detected signal.
  • the signal from photodetector 55 passes through a double-balanced mixer 54, to demodulate the 2 kHz carrier signal to a DC level, before separation by a lowpass filter 56, yielding output 58.
  • subsystem 50b synchronizes a 830 nm laser source 62 with a photo detector 65 using a 2.2 kHz masterclock 63.
  • the signal from photodetector 65 passes through a double-balanced mixer 64 before separation by a lowpass filter 66, yielding output 68.
  • the system 100 includes an array of spatially separated light sources 110 and spatially separated detectors 120.
  • the array of sources and detectors is positioned over a sample 150 to be imaged, e.g., a patient's head to image blood within the brain.
  • a controller 130 connected to light sources 110 sequentially triggers them to couple light into sample 150, which is a highly scattering media (e.g., blood and brain tissue) that causes the light to become diffuse within the sample.
  • sample 150 which is a highly scattering media (e.g., blood and brain tissue) that causes the light to become diffuse within the sample.
  • each detector 120 measures the light that reaches it through sample 150.
  • Controller 130 is also connected to detectors 120 and selectively channels the signals from the detectors.
  • An analyzer 140 is connected to controller 130 and analyzes the signals measured by detectors 120.
  • the signal g(i,j) measured by the/* 1 detector in response to light coupled into the sample by the / ' th source can be expressed as:
  • f(i,j) is the transmittance of the sample from the ⁇ source to the/h detector
  • Dl are coupling coefficients for the ⁇ source to the/ 11 detector, respectively.
  • the transmittance f(ij) depends only on the optical properties, e.g., the spatially varying abso ⁇ tion and scattering coefficients, and can be numerically calculated by a forward calculation if the optical properties are known. Conversely, if the transmittance f(i,j) can be calculated from the measured signals g(ij), an inverse calculation can be performed on f(i,j) to yield the optical properties of the sample (e.g., a brain) and reveal, e.g., the presence of an object (e.g., blood flowing through a blood vessel) hidden in the sample (e.g., a brain).
  • the source coupling coefficient S 1 includes all of the factors associated with coupling light generated from the z m source into the sample.
  • the detector coupling coefficient Dl includes all of the factors associated with coupling light out of the sample to generate an output signal at the/ 11 detector.
  • each source 120 e.g., the i ' " 1 source, includes a diode laser 200 for producing the optical radiation, an optical fiber 210, and a lens 220 for coupling the optical radiation into fiber 210, which includes an end 215 adjacent sample 150 for directing the optical radiation into the sample.
  • Each detector 130 e.g., the/" detector, includes an optical fiber 250 having an end 255 adjacent sample 150 for receiving the optical radiation emitted from sample 150, a photodetector 260 for measuring the intensity of the optical radiation received by fiber 250, and an amplifier 270 for amplifying the output of photodetector
  • the source coupling coefficient S 1 is the product of the fluence L produced by diode laser 200, the coupling coefficient C LF of the lens 220 to the fiber 210, the transmission coefficient 7 LF of fiber 210, and the coupling coefficient C FT at the interface of fiber 210 and sample 150.
  • the detector coupling coefficient Dl is the product of the coupling coefficient C TF at the interface of fiber 250 and sample 150, the transmission coefficient T L ⁇ of fiber 260, and the coupling coefficient of the sample fluence produced by the diode laser P L , the coupling coefficient FD between fiber 260 and photodetector 260, the efficiency ⁇ PE of photodetector 260, and the gain A of amplifier 270.
  • the light source can include a laser other than a diode laser, e.g., an ultrafast laser, or instead it can include an incoherent source.
  • the sources can include a common light source that selectively couples light into one of multiple fibers that deliver the light to spatially separated locations on the sample.
  • the sources need not include optical fibers at all.
  • the lasers themselves can be positioned adjacent the sample or can include beam delivery optics to direct the light to the sample through free space. However, this method does not remove the blood from the scalp as described above.
  • the light sources can provide light at multiple wavelengths by including, e.g., multiple diode lasers.
  • Calibration of signals generated from the methods of the invention can be performed using any means in the art, as well as using the new calibration methods described below.
  • the relationship between abso ⁇ tion and concentration of a natural tracer, such as oxyhemoglobin is described by the Beer-Lambert law and modified versions thereof.
  • the calculation of cerebral blood flow from the concentration of tracer is based on the Fick principle, which states that the rate of accumulation (Q) of tracer in the organ of interest is equal to the difference between the rate of arrival and the rate of departure of the tracer.
  • a measurement of the amount accumulated in an organ can be made at a specific time t (if inducing the tracer at time 0), provided that t is less than the minimum transit time through the organ, i.e., no tracer would be leaving the organ.
  • the accumulation of tracer (Q) can be expressed as:
  • blood flow measurements can be made by near-infrared spectroscopy (NIRS) using oxyhemoglobin as tracer in transmittance mode as described in Edwards et al., J. Appl. Physiol. 75:1885-1889, 1993.
  • NIRS near-infrared spectroscopy
  • the experiment described in the reference immediately above was performed in the forearms of six healthy young adults.
  • Cerebral blood flow can also be measured using the calculations employed in Skov et al., Pediatr. Res. 30:570- 573, 1991; Bucher et al., Pediatr. Res. 33:56-60, 1993; Fallon et al., Ann. Thorac. Surg. 56: 1473- 1477, 1993; and Elwell et al., J. Appl. Physiol. 77:2753-2760, 1994.
  • tracer dyes can be used as a more flexible alternative to oxyhemoglobin in NIRS. Measurements using the dye ICG can produce a relatively high signal-to-noise (S/N) ratio than when using oxyhemoglobin as tracer. See, e.g., Patel et al., supra.
  • the signals still must be calibrated correctly.
  • a calibration is required to convert the measured values for g(i,j) into the transmittance values f(i,j). According to Equation (1), this requires a calibration for the value of SD) for every source-detector pair.
  • analyzer 140 determines self-consistent values for S l Dl based on the set of measured values g(ij) and the results of a numerical calculation for f(i,j) corresponding to an approximate model of the sample.
  • the same set of measured values g(i,j) can be used to calculate f(i,j) according to Equation (1), from which the analyzer can perform the inverse calculation. Because the same set of measured values are used for the calibration and the inverse calculation, the optical properties determined by the analyzer do not include systematic errors caused by fluctuations in the source and detector coupling coefficients.
  • the sources provide continuous wave (CW) optical radiation and the detectors measure the intensity of the optical radiation, in which case g(ij),f(i,j), S 1 , and Dl are all real-valued.
  • the calibration techniques described herein can also be applied to other diffuse optical measurement techniques in which the sources do not provide CW radiation.
  • the amplitude of the optical radiation provided by the source is modulated to create photon density waves in the sample, and the detectors are configured to measure the amplitude and phase of the photon density waves after propagation through the sample.
  • the values for g(i,j),f(i,j), S 1 , and Dl can be complex.
  • each source provides a temporally coherent light pulse, e.g., a picosecond pulse
  • the detectors are time-gated to measure the temporal delay of the diffuse light pulse in addition to its intensity.
  • time-domain DOT techniques see, e.g., Patterson et al., Appl. Opt. 28: 2331, 1989; and Arridge, Inverse Problems 15:R41-R93, 1999.
  • Equation (2) is the average of all measurements made with source i and Equation (3) is the average of all measurements made with detector j. Substituting Equations (3) and (4) into Equation (2) we obtain a relationship between the source coupling coefficient Si and the detector coupling coefficient corresponding to the tn source and the k tn detector, respectively:
  • L(i,j,k,l) is a function only of the number of sources and detectors, N s and N d , the measurements, g(i,j), and the optical properties of the medium as reflected through (t, ). In other words, L(i,j,k,l) is not dependent on the coupling coefficients.
  • Equation (9) the value for S ⁇ D ⁇ can be calculated by minimizing Equation (9) with respect to S ⁇ D ⁇ .
  • the minimization can be repeated for every source-detector pair, or alternatively, once the value for S ⁇ D ⁇ is determined for the l-k source-detector pair, the other coupling coefficient products can be determined from Equation (7).
  • the calibration is non-linear, with no unique solution for the individual coupling coefficients S 1 and Dl, an exact solution exists for the coupling coefficient product of every source-detector pair, which is all that is needed for the calibration.
  • the minimization of Equation (9) can be performed using standard techniques known in the art, see, e.g., Press et al. in Numerical Recipes in C: The Art of Scientific Computing (Cambridge U. Press, New York, 1988).
  • analyzer 140 makes a numerical forward calculation for ⁇ i ) based on an approximate model of the sample.
  • An initial model can be that the sample is homogenous with a constant abso ⁇ tion coefficient ⁇ ⁇ and a constant reduced scattering coefficient ⁇ .
  • an inverse calculation can provide perturbative corrections to the model to show spatial variations in the optical properties of the sample.
  • Numerical techniques for the forward and inverse calculations are known in the art and will be briefly described in the next section. However, for the simple case of an infinite homogeneous sample, the model forward calculation simplifies to the following expression:
  • r is the distance between the z h source and the/' 1 detector on the sample surface.
  • an iterative procedure can be used to find ⁇ ⁇ , ⁇ ' s , and the coupling coefficients.
  • the procedure involves estimating ⁇ ⁇ and and then minimizing ⁇ (S l D k ) in Equation (9) to find the coupling coefficient S>D k .
  • the procedure is repeated with different values of ⁇ a and ⁇ ' s to minimize F( ⁇ a , ⁇ ' s ⁇ Z)*) with respect to all three parameters.
  • the technique provides an accurate determination of the absolute values of ⁇ ⁇ and ⁇ .
  • step 300 the analyzer receives measured signals g(i,j) from the detectors.
  • an initial model for the sample is input into the analyzer, for example, the initial model may treat the sample as being homogeneous. In this case, values for ⁇ ⁇ and ⁇ ' s are estimated if they are otherwise unknown.
  • the analyzer calculates values for ⁇ j ) based on the sample model and a forward calculation. For example, if the sample is modeled to be homogeneous and infinite, Equation (10) can be used.
  • the coupling coefficient S l D k is determined by minimizing F(S ! D k ) with respect to S'Z)* in Equation (9), the other parameters in Equation (9) being specified by the measurements for g(i,j) and the values for ⁇ ij) from the model forward calculation in step 320.
  • step 340 steps 310-330 are repeated as necessary with additional estimates for ⁇ ⁇ and ⁇ ' s , until values are found for S*D k , ⁇ ⁇ , and ⁇ ' s that optimally minimize F(SfD k ).
  • step 350 the values for all of the remaining coupling coefficients S'D 1 are determined by either: 1) calculating S'D using Equation (7) and the value for S>D k determined in step 340; or 2) replacing the argument SfD k for F in Equation (9) with the coupling coefficients S'D corresponding to each of the remaining source-detector and determining the value S'D that minimizes F.
  • step 360 the calibration coefficients S'D determined in steps 340 and 350, and the measurements g(i,j) from step 300 are used to calculate experimental values for fiij) based on Equation (1).
  • step 370 an inverse calculation is performed on the variation of the experimental values for f(i,j) from the expected values for a homogeneous medium calculated in step 360 to determine spatial variations in the optical properties of the sample, e.g., an object hidden with a highly scattering sample.
  • step 380 if necessary, the model for the sample estimated in step 310 is revised based on the results from step 370, then steps 320, 330, and 350 are repeated, one time, to recalculate the calibration coefficients SD 1 based on the revised sample model.
  • step 390 if necessary, steps 360-370 are repeated, one time, using the recalculated calibration coefficients from step 380 to improve the determination of the spatial variations in the optical properties of the sample. Steps 380-390 can be iteratively repeated as necessary until the spatially varying optical properties determined in step 390 converge to within a desired accuracy.
  • the summations in the Equations above need not be over every source and detector in the experimental apparatus.
  • source-detector measurements between any two sources and any two detectors are sufficient to determine all of the source-detector coupling coefficient products corresponding to that set of sources and detectors.
  • the remaining coupling coefficient products can be determined with relatively fewer additional measurements.
  • Forward and Inverse Calculations Techniques for the forward and inverse calculations of light propagation within the sample are known in the art. See, e.g., Arridge, supra. An exemplary formulation of the calculation is described below.
  • the first-order perturbative solution to the heterogeneous equation, in the limit in which U ⁇ far less than U is given by:
  • M is the amplitude of the source located at r s
  • G(r,r d ) is the Green function solution of the homogeneous equation at detector position r
  • ⁇ is the speed of light in the medium
  • & 0 [(- ⁇ a °+i ⁇ )/D 0 ] 1 2 is the photon density wave number, where ⁇ is the source modulation angular frequency. If an infinite medium is assumed, the Green function is
  • Equation ( 12) exp(ik 0
  • the integral in Equation ( 12) is over the entire sample volume.
  • the source is a CW source without any modulation.
  • ⁇ goes to zero and k 0 is purely imaginary, so that both t/ 0 (r) and U ⁇ (r) are real-valued.
  • the first term in the integral of Equation (12) corresponds to absorbing inhomogeneities, whereas the second term corresponds to scattering inhomogeneities. Where it is known that one or other type of inhomogeneity dominates, the non-dominant term can be dropped from Equation (12).
  • Equation (12) is digitized into a sum over voxels (i.e., volume elements), and equated to a series of the values for
  • the calibration method can be implemented in hardware or software, or a combination of both.
  • the method can be implemented in computer programs using standard programming techniques following the method and figures described herein.
  • Program code is applied to input data to perform the functions described herein and generate output information.
  • the output information is applied to one or more output devices such as a display monitor.
  • Each program is preferably implemented in a high level procedural or object oriented programming language to communicate with a computer system.
  • the programs can be implemented in assembly or machine language, if desired.
  • the language can be a compiled or inte ⁇ reted language.
  • Each such computer program is preferably stored on a storage medium or device (e.g., ROM or magnetic diskette) readable by a general or special purpose programmable computer, for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein.
  • the computer program can also reside in cache or main memory during program execution.
  • the calibration method can also be implemented as a computer-readable storage medium, configured with a computer program, where the storage medium so configured causes a computer to operate in a specific and predefined manner to perform the functions described herein.
  • analyzer 140 includes a processor 170, and input/output control card 160, a user interface 190 such as a keyboard and monitor, and a memory 180.
  • the memory stores a program 185 specifying the steps of the calibration method. When executed, the program causes the processor to carry out the steps of the calibration method.
  • the separate data points at each position can be assembled into an image, which is then conveyed via a visual display.
  • the displayed image can indicate an actual or modeled outline of a tissue or organ, with a region of abnormality indicated by a different color or shade of gray.
  • the spatial abnormality can be indicated by a rough outline (e.g., a box) of the affected region, with a caption of text stating the nature of the abnormality (e.g., increased blood volume or delayed blood flow).
  • Other techniques for displaying images containing target structures such as abnormalities are also suitable for use in the invention.
  • a sub-cortical lesion is likely to induce a broad spatial and temporal hemodynamic variation within the cortex.
  • major arteries feeding the brain enter at the organ's center. Blood then flows towards the cortex via branching arterioles (Figs. 6 A and 6B).
  • branching arterioles Figs. 6 A and 6B.
  • each portion of the cortex is fed by more than one set of arterioles and associated capillaries, an architecture that many believe evolved to minimize tissue damage when an ischemic event occurs deep in the brain.
  • an ischemic event deep in the brain will not completely shut off the flow of blood to a cortical region.
  • an ischemic event 510 in a deep portion 550 leads to a diffuse, affected region 520 of decreased and delayed blood flow to cortical portion 530 of a brain 500 due to a longer vessel path taken by the blood in arterioles 540.
  • collateral blood flow will mix tracer from unaffected brain tissue with blood that contains little tracer because of the ischemia, resulting in a less pronounced dilution of the tracer than seen immediately downstream of the ischemic event.
  • a cortical lesion 560 in brain 500 causes a more localized, affected region 570 in cortical portion 530 that exhibits a delay in the transit of a contrast agent (such as a dye or an oxygen bolus) as well as a greater reduction in the quantity of the tracer that moves through local region 570.
  • a contrast agent such as a dye or an oxygen bolus
  • a cortical lesion will cause the tracer peak to be delayed by a small amount and have a significantly reduced peak concentration, while a sub-cortical or deep lesion will cause a longer delay in the peak arrival of the tracer and a smaller reduction in the peak concentration.
  • thresholds on both the temporal and concentration characteristics will enable discernment of deep and cortical lesions.
  • This threshold approach is also supported by the spatial extent (size) of the abnormal blood flow in the cortex. A small spatial extent will be consistent with a cortical lesion, while a large spatial extent will suggest a deep lesion.
  • Thresholds can be set as follows: if (1) the peak delay relative to the normal curve is greater than about 2 seconds, (2) the peak amplitude is reduced by less than about 50%) of the normal peak amplitude, (3) the spatial extent of the blood flow anomaly is greater than about 20 mm in diameter, and/or (4) the minimal period of time required for passage of a dye bolus at a detection point is about 2 or more seconds longer than a normal reference period of time, then a deep ischemic event is indicated.
  • any ischemic event is based on thresholds broader than the ones described immediately above.
  • An ischemic event is detected if (1) the peak delay relative to the normal curve is greater than about 1 second, (2) the peak amplitude is reduced as compared to the normal peak amplitude, (3) a blood flow anomaly is detected, and/or (4) the minimal period of time required for passage of a dye bolus at a detection point is longer than a normal reference period of time.
  • this information can be used to determined which blood vessel and where along its path the blockage has occurred. This is possible because the architecture of brain vasculature is well known and has been exhaustively catalogued in the human population. See, e.g., Kretschmann et al., "Arteries of the Brain and their Vascular Territories," In: Cranial Neuroimaging and Clinical Neuroanatomy, Thieme Medical Publishers, Inc., New York, pp 191- 199, 1992.
  • the locations of lesions 510 and 560 can be deduced from the position and size of affected regions 520 and 570, respectively.
  • a health care provider For a patient suffering from a stroke, a health care provider first withdraws a 1 ml volume of blood from the patient and mixes the blood with 1 ml of a solution containing 0.1 mg/kg body weight of indocyanine green dye (Pulsion-green, Pulsion, Kunststoff, Germany) dissolved in water. After a period of about 15 seconds to allow binding of the dye to plasma proteins, the 2 ml mixture is injected as a bolus into the patient through a venous catheter in the arm.
  • indocyanine green dye Pulsion-green, Pulsion, Kunststoff, Germany
  • the patient's head is first fitted with a helmet containing optodes emitting red light at 780 nm and optode detectors spaced throughout the scalp surface covered by the helmet.
  • Light is emitted by the a laser and passes through the optodes and into the brain through the scalp and skull of the patient. Any light that is reflected and/or scattered by the brain and passes out through the scalp and skull is detected.
  • the amplitude of detected light at a point above the scalp is inversely correlated with the concentration of dye in the cortical region of the brain below that point.
  • a diffuse blood flow abnormality will be evident in a cortical region of the brain.
  • the reference dye bolus trace can be an averaged or estimated normal trace, an actual trace of the patient's brain under normal (i.e., without an ischemic event) conditions, or a trace of a normal matched portion of the brain (e.g., an unaffected hemisphere of the brain).
  • the peak concentration of dye in the affected cortical region is about 55% of the peak normal peak concentration, showing the reduction in the amount of dye moving through the cortical region that would be expected by a deep ischemic event.
  • the deep ischemic event also leads to an increase of about 3 seconds in the time it takes the peak concentration to be detected after the bolus is injected or passes a reference point as compared to a normal peak concentration (ti), showing that the bolus of dye moving through the cortical region of the brain has been delayed by a deep ischemic event.
  • the size of the blood flow abnormality (30 mm at the longest diameter) is indicated by the longer period of time required for the bolus to completely traverse the affected cortical region (t 3 ), as compared to the time required for the bolus to traverse the unaffected region (t 2 ). In this instance, t 3 is about 3 seconds longer than t 2 .
  • Figs. 8A and 8B show several distinguishing characteristics of the abnormal trace of dye concentration.
  • the peak dye concentration is reduced by a greater amount (80%) from normal than is seen for a deep ischemic event (e.g., 45% in Fig. 7B) because the source of the dye flow blockage, rather than its downstream effects, is directly detected by DOT.
  • the increase in the time required for the peak concentration to travel from a reference point, e.g., bolus injection, to the detection site, relative to normal (ti) is only about 1 second because the detected region is closer to the source of the ischemic event.
  • the minimal amount of time needed for the dye concentration to vary from zero to a peak, and back down to zero (t 3 ) is only about 1 second longer than that for the normal trace (t 2 ).
  • a brain bleed can also be detected by DOT following the procedure described in Example 1, except that a measurement is made at a single time point after the dye is distributed uniformly throughout the circulatory system and the brain, instead of measuring the movement of a dye bolus through the brain over time.
  • Figs. 9A and 9B show the head of an individual experiencing a brain bleed and the expected position-dependent trace of the dye concentration, respectively. The dye is shown by the hatched region, and the pooling of blood at the bleed is shown by the clear region within the hatched region, with the source of the bleed indicated as a dot. As traced in the graph of Fig.
  • the dye concentration along line A passing through the source of the bleed differs from a normal trace by the presence of a region of a lower concentration of dye.
  • This phenomenon is caused by the clotting and blood vessel constriction associated with the bleed, which inhibits the dye from infiltrating the bleed region.
  • the clotting and blood vessel constriction would not be apparent immediately after the bleed begins, since some time is required for these physiological and biochemical events to occur. Regions in the brain adjacent to the bleed area are not affected.
  • a brain bleed can be detected by allowing sufficient time for the dye to infiltrate the bleed. Once the dye enters the bleed, the dye is trapped in the bleed by the clotting and blood vessel constriction mentioned above. Meanwhile, the dye in the rest of the circulation is being removed from the body, e.g., by the liver, or degrades. If a measurement of dye concentration is made at this later time point, the presence of a bleed can be seen by an inverse of the phenomenon shown in Figs. 9 A and 9B; namely, that a higher dye concentration is seen in the bleed region, while the rest of the brain exhibits a lower or zero dye concentration. While at this later time (about 10 minutes following bolus injection) the dye concentration in the bleed may be greater than the surrounding tissue, it will always be smaller than the peak concentration observed in the surrounding tissue at earlier times (about 1 minute following injection).
  • IntralipidTM an aqueous suspension of lipid droplets
  • the concentration of IntralipidTM in the solution was adjusted to give the solution light scattering properties similar to that in a human brain
  • the concentration of india ink was adjusted to give the solution light abso ⁇ tion properties similar to that in a human brain.
  • a dilute india ink solution having abso ⁇ tion properties similar to blood was passed through the tubes.
  • the liquid was circulated through the tubes with a pulsatile pump to give a temporal flow distribution similar to that found in arteries.
  • Optodes were then placed on the surface of the slab to deliver light (780 nm) and collect the diffusely remitted light.
  • the separation between optodes was adjusted to 1, 2, 3, and 4 cm for different experiments.
  • a bolus of concentrated india ink (dye) was then injected into the tubes upstream of the position of the optodes. As the dye flowed past the optodes, the light detected decreased in intensity due to the increased abso ⁇ tion of light by the dye. After the dye agent passed the imaging area, the optical signal returned to baseline. The experiment was then repeated at a different flow speed.
  • the amplitude of detected light at the two flow speeds and with a optode separation of 4 cm is graphed in Fig. 10.
  • the "Fast Flow” (shown as the first inverted peak at about 5 seconds) is about 4 times as fast as the "Slow” speed (shown as the second inverted peak at about 17 seconds).
  • "Fast Flow” data points are graphed as solid square symbols, while the "Slow” flow symbols are graphed as solid circles. The graph shows that distinct variations in amplitude could be detected as the bolus passed through the region imaged, indicating that cerebral blood flow could be monitored using DOT.
  • a piglet model was used in this study.
  • the experimental set-up was a hybrid system of diffuse optical tomography and X-ray CT. Measurements were made on the bench of the X-ray scanner.
  • a one-week old piglet weighing 3 kg was sedated, intubated, and ventilated during the experiment.
  • the femoral artery was catheterized for continuous blood pressure monitoring, fluid infusions, and blood extractions. Some of the blood taken from the femoral artery was delivered through two small needles inserted 2 cm through scalp, skull, and brain tissue to produce an artificial brain bleed. The separation of insertion points for the two needles was about 2 cm. The combined thickness of the scalp and skull was about 1 cm, so the blood was injected into the brain at a depth of about 1 cm. The injection speed was controlled by a step motor at a rate of 42 ⁇ l/min. A total of 625 ⁇ l of blood was injected in 15 minutes for each bleed .
  • Bleed A was created first, then bleed B.
  • the optical probe was placed on top of the piglet's head. Referring to Fig. 11, the probe has 16 detectors (large circles) and 9 sources (pairs of small circles) at each of 780 nm and 830 nm. The positions of bleeds A and B relative to the probe are also shown in Fig. 11. Before injecting bleed A, a baseline was measured and used to find the coupling coefficient of each source-detector channel and also the background optical properties.
  • the calculated abso ⁇ tion and effective scattering coefficients were 0.0672 cm “1 and 8.44 cm “1 , respectively, at 780 nm, and 0.0666 cm '1 and 7.61 cm “1 , respectively, at 830 nm. These values correspond to an oxygen saturation (SO 2 ) of 58% and a total hemoglobin content (HbT) of 78 ⁇ l/mol.
  • SO 2 oxygen saturation
  • HbT total hemoglobin content
  • Figs. 12A-12D show the time-course of the reconstructed images of bleed A at both wavelengths, with and without using the calibration method described in detail above to correct the DOT measurements.
  • Figs. 12A-12D show that the application of the calibration method greatly reduces the presence of artifacts in the bottom and right sides of the images. The calibration method also improves the image amplitude.
  • Figs. 13A and 13B show a time-course plot of the peak image value of bleed A at the two wavelengths. Without calibration (Fig 13 A), the plot is noisy with no clear build up of the bleed. After the calibration (Fig. 13B), however, the development of the bleed is clearly visible.
  • Fig. 14 shows time-course images of both bleeds A and B as the volume of bleed B was increased.
  • the base line and coupling coefficient were the same as those used in reconstructing images of bleed A.
  • the respective intensities of the A and B bleeds differ because their depths differ.
  • a 100 mW, 808 nm laser diode coupled to a 1 mm diameter fused silica fiber was used to deliver light to an adult human head.
  • Four diode detectors were coupled to the scalp via 3 mm diameter plastic fibers.
  • the collecting fibers were positioned 1, 2, 3, and 4 cm from the emitting fiber. These four separations were chosen to discriminate between scalp signals and skull signals. Measurements made at 1 and 2 cm separations were sensitive to changes in the optical properties of only the skull and scalp. On the other hand, measurements made at 3 and 4 cm separations were sensitive to changes in the optical properties of the brain, skull, and scalp. The remitted intensity at the four positions was sampled at 4 Hz.
  • Baseline data was collected for 10 seconds, followed by the bolus injection.
  • the bolus consisted of a 2 ml saline solution of 40 mg of indocyanine green injected into a vein in the arm of the volunteer. This injection was immediately followed by a 10 ml saline flush.
  • the data is summarized in the graph of Fig. 15, showing the attenuation of the optical signal caused by passing of the bolus of indocyanine green through the brain of the adult human volunteer.
  • the results indicate that, at 20 seconds following the injection of the dye bolus, the signal at 3 and 4 cm separations dropped significantly, while the drop in the signals at 1 and 2 cm separations was delayed by about 2 seconds.
  • the delay at 1 and 2 cm separations indicated that the signal decay at the 3 and 4 cm separation for the initial 2 seconds was entirely due to the arrival of indocyanine green in the brain.
  • the small increases in each signal at about 34 seconds resulted from the re-circulation of the indocyanine green bolus.
  • the methods of the invention can be accomplished with any combination of one or more fluorescent and/or non-fluorescent dyes injected (e.g., as a bolus) into the blood stream of an individual.

Abstract

L'invention concerne un procédé permettant d'utiliser la tomographie optique diffuse, l'oxygène et un colorant, chez un patient souffrant d'un accident vasculaire cérébral, ou chez un patient dont on suspecte qu'il souffre d'un accident vasculaire cérébral, afin de détecter les événements ischémiques ou les saignements dans l'encéphale.
PCT/US2001/002226 2000-01-24 2001-01-23 Detection d'accidents vasculaires cerebraux par tomographie optique diffuse WO2001052719A2 (fr)

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EP01910346A EP1251771A4 (fr) 2000-01-24 2001-01-23 Detection d'accidents vasculaires cerebraux par tomographie optique diffuse
AU2001237963A AU2001237963A1 (en) 2000-01-24 2001-01-23 Detection of stroke events using diffuse optical tomography
CA002397145A CA2397145A1 (fr) 2000-01-24 2001-01-23 Detection d'accidents vasculaires cerebraux par tomographie optique diffuse

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US09/491,595 US6516214B1 (en) 2000-01-24 2000-01-25 Detection of stroke events using diffuse optical tomography
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US09/598,422 US6577884B1 (en) 2000-06-19 2000-06-19 Detection of stroke events using diffuse optical tomagraphy

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CN1326492C (zh) * 2002-04-19 2007-07-18 维森盖特有限公司 小目标的变速运动光学层析成像技术

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CN1326492C (zh) * 2002-04-19 2007-07-18 维森盖特有限公司 小目标的变速运动光学层析成像技术

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CA2397145A1 (fr) 2001-07-26

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