US20160091577A1 - Self-expanding multi-channel rf receiver coil for high resolution intra-cardiac mri and method of use - Google Patents
Self-expanding multi-channel rf receiver coil for high resolution intra-cardiac mri and method of use Download PDFInfo
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- US20160091577A1 US20160091577A1 US14/962,056 US201514962056A US2016091577A1 US 20160091577 A1 US20160091577 A1 US 20160091577A1 US 201514962056 A US201514962056 A US 201514962056A US 2016091577 A1 US2016091577 A1 US 2016091577A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/34084—Constructional details, e.g. resonators, specially adapted to MR implantable coils or coils being geometrically adaptable to the sample, e.g. flexible coils or coils comprising mutually movable parts
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0033—Features or image-related aspects of imaging apparatus classified in A61B5/00, e.g. for MRI, optical tomography or impedance tomography apparatus; arrangements of imaging apparatus in a room
- A61B5/004—Features or image-related aspects of imaging apparatus classified in A61B5/00, e.g. for MRI, optical tomography or impedance tomography apparatus; arrangements of imaging apparatus in a room adapted for image acquisition of a particular organ or body part
- A61B5/0044—Features or image-related aspects of imaging apparatus classified in A61B5/00, e.g. for MRI, optical tomography or impedance tomography apparatus; arrangements of imaging apparatus in a room adapted for image acquisition of a particular organ or body part for the heart
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves
- A61B5/055—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
-
- 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
- A61B5/6846—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive
- A61B5/6847—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be brought in contact with an internal body part, i.e. invasive mounted on an invasive device
- A61B5/6852—Catheters
- A61B5/6858—Catheters with a distal basket, e.g. expandable basket
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/285—Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR
- G01R33/287—Invasive instruments, e.g. catheters or biopsy needles, specially adapted for tracking, guiding or visualization by NMR involving active visualization of interventional instruments, e.g. using active tracking RF coils or coils for intentionally creating magnetic field inhomogeneities
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/563—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution of moving material, e.g. flow contrast angiography
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7271—Specific aspects of physiological measurement analysis
- A61B5/7285—Specific aspects of physiological measurement analysis for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal
Definitions
- the present invention relates generally to MR imaging and, more particularly, to an RF coil assembly capable of self-expansion within a subject to be imaged and capable of minimizing blood flow occlusion by permitting blood flow therethrough.
- polarizing field BO When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field BO), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B 1 ) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B 1 is terminated and this signal may be received by a radio-frequency (RF) coil and processed to form an image.
- RF radio-frequency
- magnetic field gradients (Gx, Gy, and Gz) are employed.
- the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used.
- the resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
- High spatial-resolution or high temporal-resolution imaging of heart anatomy and physiology is desired for a variety of purposes.
- high spatial-resolution imaging may be desired to guide or monitor therapeutic processes in the heart.
- One major determinant in performing such scans is the intrinsic Signal-to-Noise ratio (SNR) of the RF receiver coil.
- SNR Signal-to-Noise ratio
- Current surface mounted RF coils placed on the surface of the torso are limited in SNR due to their physical distance from the heart itself
- the use of large coil elements that image more than the heart may negatively affect SNR.
- surface coils limit image resolution and may not be desirable for cardiac imaging for use in MR-guided interventional procedures that demand fast, high-resolution imaging.
- intra-vascular RF receiver coils have been developed and widely considered preferred for targeted cardiac imaging.
- Intra-vascular RF coils have been shown to significantly improve SNR by placing the receiving coil in proximity to the target tissue.
- blood flow and associated pulsatility during in-vivo intra-vascular imaging have been obstacles to wide-spread implementation. That is, coil motion and tissue motion caused as a result of blood flow can negatively affect image quality and, thus, the diagnostic and probative value of a resulting image.
- known intra-vascular RF coils inhibit blood flow when the coil is positioned in the vasculature. As can be appreciated, prolonged blood flow occlusion is undesirable when imaging coronary arteries and within the heart itself
- the present invention provides a system and method of improved MR image acquisition overcoming the aforementioned drawbacks.
- the invention includes RF coils attached to an expandable housing permitting fluid flow therethrough.
- the expandable housing is constructed to automatically expand from a compressed position to an expanded position when a sheath is retracted therefrom.
- a tracking coil is integrated with the system to allow for actively tracking RF coil movement.
- the known motion of the RF coil may be used to gate data acquisition for high-resolution imaging, which is advantageous when the RF coil moves in a beating heart and/or pulsating blood stream.
- the present invention is particularly useful in conjunction with interventional cardiac therapeutic delivery systems.
- a probe in accordance with one aspect of the invention, includes a self-expanding housing insertable into a subject to be imaged and constructed to permit fluid flow therethrough.
- a plurality of RF coils are included that are attached to the housing.
- an MRI apparatus in accordance with another aspect of the invention, includes a magnetic resonance imaging (MM) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images.
- the RF coil assembly includes a catheter configured for insertion into a blood flow and is constructed to automatically expand to an expanded position from a compressed position.
- the RF coil assembly also includes a plurality of RF coils connected to the catheter and configured to acquire MR data.
- the RF coil assembly includes a tracking coil connected to the catheter and configured to indicate RF coil assembly location and movement within an imaging subject.
- a method of using an MR imaging device includes inserting an intra-cardiac MR imaging device into a sheath configured for insertion into an imaging subject to be scanned.
- the imaging device includes an MR tracking coil and a pair of RF coils attached to an auto-expandable former.
- the method includes positioning the imaging device within the imaging subject to be scanned and retracting the sheath to allow the former to automatically expand the pair of RF coils to an expanded position.
- the MR tracking coil can function, even with the imaging coil folded, and thus provides a vehicle for properly navigating the catheter to the working region of the anatomy.
- FIG. 1 is a schematic block diagram of an MR imaging system for use with the present invention.
- FIG. 2 is an elevational view of an insertable, intra-vascular probe in accordance with the present invention.
- FIG. 3 is a cross-sectional view of FIG. 2 of a catheter shaft taken along line 3 - 3 of FIG. 2 .
- FIG. 4 is an elevational view of FIG. 2 of a bar assembly taken along line 4 - 4 of FIG. 2 .
- FIG. 5 is side elevational schematic view of the probe in a compressed position in accordance with the present invention.
- FIG. 6 is a side elevational schematic view of the probe in an expanded position in accordance with the present invention.
- FIG. 1 the major components of a preferred magnetic resonance imaging (MRI) system 10 incorporating the present invention are shown.
- the operation of the system is controlled from an operator console 12 which includes a keyboard or other input device 13 , a control panel 14 , and a display screen 16 .
- the console 12 communicates through a link 18 with a separate computer system 20 that enables an operator to control the production and display of images on the display screen 16 .
- the computer system 20 includes a number of modules which communicate with each other through a backplane 20 a . These include an image processor module 22 , a CPU module 24 and a memory module 26 , known in the art as a frame buffer for storing image data arrays.
- the computer system 20 is linked to disk storage 28 and tape drive 30 for storage of image data and programs, and communicates with a separate system control 32 through a high speed serial link 34 .
- the input device 13 can include a mouse, joystick, keyboard, track ball, touch activated screen, light wand, voice control, or any similar or equivalent input device, and may be used for interactive geometry prescription.
- the system control 32 includes a set of modules connected together by a backplane 32 a . These include a CPU module 36 and a pulse generator module 38 which connects to the operator console 12 through a serial link 40 . It is through link 40 that the system control 32 receives commands from the operator to indicate the scan sequence that is to be performed.
- the pulse generator module 38 operates the system components to carry out the desired scan sequence and produces data which indicates the timing, strength and shape of the RF pulses produced, and the timing and length of the data acquisition window.
- the pulse generator module 38 connects to a set of gradient amplifiers 42 , to indicate the timing and shape of the gradient pulses that are produced during the scan.
- the pulse generator module 38 can also receive patient data from a physiological acquisition controller 44 that receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. And finally, the pulse generator module 38 connects to a scan room interface circuit 46 which receives signals from various sensors associated with the condition of the patient and the magnet system. It is also through the scan room interface circuit 46 that a patient positioning system 48 receives commands to move the patient to the desired position for the scan.
- the gradient waveforms produced by the pulse generator module 38 are applied to the gradient amplifier system 42 having Gx, Gy, and Gz amplifiers.
- Each gradient amplifier excites a corresponding physical gradient coil in a gradient coil assembly generally designated 50 to produce the magnetic field gradients used for spatially encoding acquired signals.
- the gradient coil assembly 50 forms part of a magnet assembly 52 which includes a polarizing magnet 54 and a whole-body RF coil 56 .
- a transceiver module 58 in the system control 32 produces pulses which are amplified by an RF amplifier 60 and coupled to the RF coil 56 by a transmit/receive switch 62 .
- the resulting signals emitted by the excited nuclei in the patient may be sensed by the same RF coil 56 and coupled through the transmit/receive switch 62 to a preamplifier 64 .
- the amplified MR signals are demodulated, filtered, and digitized in the receiver section of the transceiver 58 .
- the transmit/receive switch 62 is controlled by a signal from the pulse generator module 38 to electrically connect the RF amplifier 60 to the coil 56 during the transmit mode and to connect the preamplifier 64 to the coil 56 during the receive mode.
- the transmit/receive switch 62 can also enable a separate RF coil (for example, an intra-vascular coil) to be used in either the transmit or receive mode.
- the MR signals picked up by the RF coil 56 are digitized by the transceiver module 58 and transferred to a memory module 66 in the system control 32 .
- a scan is complete when an array of raw k-space data has been acquired in the memory module 66 .
- This raw k-space data is rearranged into separate k-space data arrays for each image to be reconstructed, and each of these is input to an array processor 68 which operates to Fourier transform the data into an array of image data.
- This image data is conveyed through the serial link 34 to the computer system 20 where it is stored in memory, such as disk storage 28 .
- this image data may be archived in long term storage, such as on the tape drive 30 , or it may be further processed by the image processor 22 and conveyed to the operator console 12 and presented on the display 16 .
- the probe 70 includes a plurality of expandable bar assemblies 72 .
- Each bar assembly 72 includes a pair of opposing, expandable bars 74 and an RF coil element 76 attached thereto.
- the expandable bars 74 are used as an expandable former.
- the expandable former has a pair of bar assemblies 72 , and the dimensions of the fully expanded former is 2.5 cm. in a minor axis 75 and 6 cm. in a major axis 77 .
- the bar assemblies 72 are constructed so as to reduce a volume occupied thereby to minimize blood flow occlusion when probe 70 , as will be described, is in an expanded position within an intra-vascular system, as shown in FIG. 2 .
- the pair of bar assemblies 72 is also constructed to be positioned in non-parallel planes. In a preferred embodiment, the non-parallel planes are orthogonal to each other.
- MR compatible capacitors 78 are interspersed between sections of the RF coils for RF phase coherency.
- the probe 70 is attached to a distal end 80 of a catheter 82 .
- Catheter 82 preferably has a 6 Fr., 135 cm. shaft.
- Catheter 80 eases intra-vasculature positioning of the probe 70 .
- FIG. 3 a cross-sectional view of FIG. 2 taken along line 3 - 3 is shown.
- the catheter 82 carries two thin coaxial RF lines 84 , 86 connected to the RF coils to transmit received MR data signals to the MM system 10 .
- the coaxial RF lines 84 , 86 have a diameter preferably less than 0.5 mm.
- Two tuning micro-capacitors 88 , 90 are connected to each RF line 84 , 86 to prevent direct current from reaching the RF coils and to approximately tune the RF coils to the resonant frequency of the MM system 10 .
- external circuits may be used to tune and match each of the RF coils to improve RF sensitivity.
- Catheter 82 also carries a thin quarter-wavelength balun 92 to reduce RF noise at the carrier frequency as well as to reduce inter-line coupling through the coaxial line grounds 93 .
- Balun 92 is open-circuited at its distal end and preferably has a diameter less than 0.25 mm.
- Catheter 82 further carries a coaxial line 95 that transmits tracking data received by the tracking coil 94 to the MM system 10 .
- FIG. 4 an elevational view of a bar assembly 72 taken along line 4 - 4 of FIG. 2 is shown.
- An expandable bar 74 provides a support upon which a thin RF coil element 76 is attached.
- the RF coil element 76 is preferably constructed of a copper wire and preferably attaches to an edge of the expandable bar 74 facing away from the opposing expandable bar 74 .
- the expandable bar 74 is constructed of a memory-type material that allows the material to be deformed by a compression force and to automatically return to a non-deformed position when the compression force is removed.
- the expandable bar 74 is constructed of nitinol or similar material(s).
- RF coil element 76 is positioned along expandable bar 74 such that a pre-determined distance or gap 96 is formed therebetween.
- the constant distance is maintained by using a known-thickness of an insulating material with a known dielectric constant. In a preferred embodiment, this is performed by using known-thickness heat-shrink tubing, which is wrapped about the expandable bar. In this manner, an RF field generated by the RF coil element 76 may be increased in a direction away from the surface of probe 70 and into the target tissue.
- Heat-shrink tubing 98 are disposed around the RF coil element 76 and the expandable bar 74 to attach the RF coil element 76 to the expandable bar 74 and to provide a hermetical seal from moisture. Heat-shrink tubing 98 also substantially electrically isolates the expandable bar 74 and the RF coil element 76 from blood or soft-tissue walls.
- FIG. 5 a side elevational schematic view of the probe 70 in a compressed position in accordance with the present invention is shown.
- the bar assemblies 72 are compressible such that probe 70 may be positioned within a sheath 100 for insertion into an imaging subject.
- Sheath 100 is constructed to enclose the bar assemblies 72 and applies a compression force upon the bar assemblies 72 during insertion into the imaging subject and translation to a target tissue to be imaged.
- sheath 100 is a 9 Fr. sheath with a length that exceeds a distance from an insertion point to the target tissue to be imaged.
- Probe 70 is compressed within sheath 100 as the collective assembly is translated through the vasculature to the target tissue or blood flow.
- FIG. 6 a side elevational schematic view of the probe 70 in an expanded position in accordance with the present invention is shown.
- the sheath 100 is retracted to expose probe 70 and to allow the bar assemblies 72 to automatically expand.
- the bar assemblies 72 expand and, preferably, to substantially match an inner diameter of a vasculature or other target tissue in which the probe is placed.
- the probe 70 permits fluid or blood flow between the bar assemblies 72 along flow vectors 102 to reduce occlusion that may occur in the vasculature. Allowing blood flow to pass through the probe 70 increases the amount of time in which the probe 70 may be expanded within the vasculature.
- probe 70 movements are actively tracked and monitored using signals received from the MR tracking coil 94 .
- probe 70 movements may be used to gate the data acquisition, and imaging artifacts caused by probe 70 movements within a pulsating vascular volume of interest may be taken into account and, preferably, reduced.
- an RF probe constructed according to the present invention include a sheath-deployable expandable RF coil and the use of RF conductor spacing from a metal surface to force EM field projection outside the probe.
- Other advantages include multi-channel reception in an interventional coil and use of an integrated imaging and tracking coil to reduce motion artifacts or blurring in images taken within moving structures.
- the tracking coil is designed to provide feedback to assist with navigating to the target anatomy when the expandable RF coil is compressed in the sheath. That is, the tracking coil provides feedback independent of the expansion/compression of the RF coil.
- use of the RF probe constructed according to the present invention is particularly advantageous for acquiring MR images of the atrium or ventricles of the heart, and imaging the pulmonary vein anatomy.
- An RF coil constructed according to the present invention is optimally used in a four-channel, or greater-number of channels, phased-array together with a two-channel surface coil.
- the RF coil provides a SNR that allows for faster data acquisitions or higher spatial resolution imaging, which is important in imaging the heart or heart anatomy where imaging times are limited by patient breath-holding tolerance and/or when resolution is limited by the irregularity of cardiac motion over time.
- Image acquisition may be gated by using data received from the MR tracking coil. In this manner, image artifacts may be reduced.
- commercial benefits may be realized with the increased utilization of MR imaging to guide or monitor therapeutic processes in the heart. For commercial applications, high spatial and temporal resolution are required as well as a high contrast-to-noise, for example, tissue temperature monitoring.
- a probe in accordance with one embodiment of the present invention, includes a self-expanding housing insertable into a subject to be imaged and constructed to permit fluid flow therethrough.
- a plurality RF coils are included that are attached to the housing.
- an MRI apparatus in accordance with another embodiment of the present invention, includes a magnetic resonance imaging (MM) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images.
- the RF coil assembly includes a catheter configured for insertion into a blood flow and constructed to automatically expand to an expanded position from a compressed position.
- the RF coil assembly also includes a plurality of RF coils connected to the catheter and configured to acquire MR data. Further, the RF coil assembly also includes a tracking coil connected to the catheter and configured to indicate RF coil assembly location and movement within an imaging subject.
- a method of using an MR imaging device includes inserting an intra-cardiac MR imaging device into a sheath configured for insertion into an imaging subject to be scanned, the imaging device comprising an MR tracking coil and a pair of RF coils attached to an auto-expandable former.
- the method includes positioning the imaging device within the imaging subject to be scanned and retracting the sheath to allow the former to automatically expand the pair of RF coils to an expanded position.
Abstract
A system and method of use for a probe is disclosed that includes a self-expanding housing constructed to permit fluid flow therethrough and constructed for insertion into a subject to be imaged. A plurality of RF coils is attached to the housing to acquire MR data.
Description
- The present application is a continuation of and claims priority to U.S. patent application Ser. No. 10/708,723 filed Mar. 19, 2004, the disclosure of which is incorporated herein in its entirety.
- The present invention relates generally to MR imaging and, more particularly, to an RF coil assembly capable of self-expansion within a subject to be imaged and capable of minimizing blood flow occlusion by permitting blood flow therethrough.
- When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field BO), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, MZ, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received by a radio-frequency (RF) coil and processed to form an image.
- When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
- High spatial-resolution or high temporal-resolution imaging of heart anatomy and physiology is desired for a variety of purposes. For example, high spatial-resolution imaging may be desired to guide or monitor therapeutic processes in the heart. One major determinant in performing such scans is the intrinsic Signal-to-Noise ratio (SNR) of the RF receiver coil. Current surface mounted RF coils placed on the surface of the torso are limited in SNR due to their physical distance from the heart itself Also, the use of large coil elements that image more than the heart may negatively affect SNR. As a result, surface coils limit image resolution and may not be desirable for cardiac imaging for use in MR-guided interventional procedures that demand fast, high-resolution imaging.
- In an attempt to achieve higher resolution MR images, intra-vascular RF receiver coils have been developed and widely considered preferred for targeted cardiac imaging. Intra-vascular RF coils have been shown to significantly improve SNR by placing the receiving coil in proximity to the target tissue. However, blood flow and associated pulsatility during in-vivo intra-vascular imaging have been obstacles to wide-spread implementation. That is, coil motion and tissue motion caused as a result of blood flow can negatively affect image quality and, thus, the diagnostic and probative value of a resulting image. Further, known intra-vascular RF coils inhibit blood flow when the coil is positioned in the vasculature. As can be appreciated, prolonged blood flow occlusion is undesirable when imaging coronary arteries and within the heart itself
- It would therefore be desirable to have a system and method capable of acquiring MR data using an intra-vascular probe within a moving image target, while minimizing blood flow occlusion within the image target and utilizing known motion of the system to gate image acquisition to reduce image artifacts and blurring.
- The present invention provides a system and method of improved MR image acquisition overcoming the aforementioned drawbacks. The invention includes RF coils attached to an expandable housing permitting fluid flow therethrough. The expandable housing is constructed to automatically expand from a compressed position to an expanded position when a sheath is retracted therefrom. A tracking coil is integrated with the system to allow for actively tracking RF coil movement. As a result of tracking RF coil movement, the known motion of the RF coil may be used to gate data acquisition for high-resolution imaging, which is advantageous when the RF coil moves in a beating heart and/or pulsating blood stream. The present invention is particularly useful in conjunction with interventional cardiac therapeutic delivery systems.
- Therefore, in accordance with one aspect of the invention, a probe is disclosed that includes a self-expanding housing insertable into a subject to be imaged and constructed to permit fluid flow therethrough. A plurality of RF coils are included that are attached to the housing.
- In accordance with another aspect of the invention, an MRI apparatus is disclosed that includes a magnetic resonance imaging (MM) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images. The RF coil assembly includes a catheter configured for insertion into a blood flow and is constructed to automatically expand to an expanded position from a compressed position. The RF coil assembly also includes a plurality of RF coils connected to the catheter and configured to acquire MR data. Further, the RF coil assembly includes a tracking coil connected to the catheter and configured to indicate RF coil assembly location and movement within an imaging subject.
- In accordance with yet another aspect of the invention, a method of using an MR imaging device is disclosed that includes inserting an intra-cardiac MR imaging device into a sheath configured for insertion into an imaging subject to be scanned. The imaging device includes an MR tracking coil and a pair of RF coils attached to an auto-expandable former. The method includes positioning the imaging device within the imaging subject to be scanned and retracting the sheath to allow the former to automatically expand the pair of RF coils to an expanded position. In a further alternate aspect, the MR tracking coil can function, even with the imaging coil folded, and thus provides a vehicle for properly navigating the catheter to the working region of the anatomy.
- Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.
- The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention.
- In the drawings:
-
FIG. 1 is a schematic block diagram of an MR imaging system for use with the present invention. -
FIG. 2 is an elevational view of an insertable, intra-vascular probe in accordance with the present invention. -
FIG. 3 is a cross-sectional view ofFIG. 2 of a catheter shaft taken along line 3-3 ofFIG. 2 . -
FIG. 4 is an elevational view ofFIG. 2 of a bar assembly taken along line 4-4 ofFIG. 2 . -
FIG. 5 is side elevational schematic view of the probe in a compressed position in accordance with the present invention. -
FIG. 6 is a side elevational schematic view of the probe in an expanded position in accordance with the present invention. - Referring to
FIG. 1 , the major components of a preferred magnetic resonance imaging (MRI)system 10 incorporating the present invention are shown. The operation of the system is controlled from anoperator console 12 which includes a keyboard orother input device 13, a control panel 14, and adisplay screen 16. Theconsole 12 communicates through alink 18 with aseparate computer system 20 that enables an operator to control the production and display of images on thedisplay screen 16. Thecomputer system 20 includes a number of modules which communicate with each other through a backplane 20 a. These include animage processor module 22, aCPU module 24 and amemory module 26, known in the art as a frame buffer for storing image data arrays. Thecomputer system 20 is linked todisk storage 28 andtape drive 30 for storage of image data and programs, and communicates with aseparate system control 32 through a highspeed serial link 34. Theinput device 13 can include a mouse, joystick, keyboard, track ball, touch activated screen, light wand, voice control, or any similar or equivalent input device, and may be used for interactive geometry prescription. - The
system control 32 includes a set of modules connected together by a backplane 32 a. These include aCPU module 36 and apulse generator module 38 which connects to theoperator console 12 through aserial link 40. It is throughlink 40 that thesystem control 32 receives commands from the operator to indicate the scan sequence that is to be performed. Thepulse generator module 38 operates the system components to carry out the desired scan sequence and produces data which indicates the timing, strength and shape of the RF pulses produced, and the timing and length of the data acquisition window. Thepulse generator module 38 connects to a set ofgradient amplifiers 42, to indicate the timing and shape of the gradient pulses that are produced during the scan. Thepulse generator module 38 can also receive patient data from a physiological acquisition controller 44 that receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. And finally, thepulse generator module 38 connects to a scanroom interface circuit 46 which receives signals from various sensors associated with the condition of the patient and the magnet system. It is also through the scanroom interface circuit 46 that apatient positioning system 48 receives commands to move the patient to the desired position for the scan. - The gradient waveforms produced by the
pulse generator module 38 are applied to thegradient amplifier system 42 having Gx, Gy, and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil in a gradient coil assembly generally designated 50 to produce the magnetic field gradients used for spatially encoding acquired signals. Thegradient coil assembly 50 forms part of amagnet assembly 52 which includes apolarizing magnet 54 and a whole-body RF coil 56. Atransceiver module 58 in thesystem control 32 produces pulses which are amplified by anRF amplifier 60 and coupled to theRF coil 56 by a transmit/receiveswitch 62. The resulting signals emitted by the excited nuclei in the patient may be sensed by thesame RF coil 56 and coupled through the transmit/receiveswitch 62 to apreamplifier 64. The amplified MR signals are demodulated, filtered, and digitized in the receiver section of thetransceiver 58. The transmit/receiveswitch 62 is controlled by a signal from thepulse generator module 38 to electrically connect theRF amplifier 60 to thecoil 56 during the transmit mode and to connect thepreamplifier 64 to thecoil 56 during the receive mode. The transmit/receiveswitch 62 can also enable a separate RF coil (for example, an intra-vascular coil) to be used in either the transmit or receive mode. - The MR signals picked up by the
RF coil 56 are digitized by thetransceiver module 58 and transferred to amemory module 66 in thesystem control 32. A scan is complete when an array of raw k-space data has been acquired in thememory module 66. This raw k-space data is rearranged into separate k-space data arrays for each image to be reconstructed, and each of these is input to anarray processor 68 which operates to Fourier transform the data into an array of image data. This image data is conveyed through theserial link 34 to thecomputer system 20 where it is stored in memory, such asdisk storage 28. In response to commands received from theoperator console 12, this image data may be archived in long term storage, such as on thetape drive 30, or it may be further processed by theimage processor 22 and conveyed to theoperator console 12 and presented on thedisplay 16. - Referring to
FIG. 2 , an insertable, multi-channelintra-vascular probe 70 in accordance with the present invention and usable with theMM system 10 ofFIG. 1 is shown. Theprobe 70 includes a plurality ofexpandable bar assemblies 72. Eachbar assembly 72 includes a pair of opposing,expandable bars 74 and anRF coil element 76 attached thereto. The expandable bars 74 are used as an expandable former. In a preferred embodiment, the expandable former has a pair ofbar assemblies 72, and the dimensions of the fully expanded former is 2.5 cm. in aminor axis 75 and 6 cm. in amajor axis 77. Thebar assemblies 72 are constructed so as to reduce a volume occupied thereby to minimize blood flow occlusion whenprobe 70, as will be described, is in an expanded position within an intra-vascular system, as shown inFIG. 2 . The pair ofbar assemblies 72 is also constructed to be positioned in non-parallel planes. In a preferred embodiment, the non-parallel planes are orthogonal to each other. MRcompatible capacitors 78 are interspersed between sections of the RF coils for RF phase coherency. Theprobe 70 is attached to adistal end 80 of acatheter 82.Catheter 82 preferably has a 6 Fr., 135 cm. shaft.Catheter 80 eases intra-vasculature positioning of theprobe 70. - Referring to
FIG. 3 , a cross-sectional view ofFIG. 2 taken along line 3-3 is shown. Thecatheter 82 carries two thincoaxial RF lines MM system 10. Thecoaxial RF lines micro-capacitors RF line MM system 10. As the final size of theprobe 70 varies according to the surrounding anatomy, external circuits may be used to tune and match each of the RF coils to improve RF sensitivity. -
Catheter 82 also carries a thin quarter-wavelength balun 92 to reduce RF noise at the carrier frequency as well as to reduce inter-line coupling through thecoaxial line grounds 93.Balun 92 is open-circuited at its distal end and preferably has a diameter less than 0.25 mm.Catheter 82 further carries a coaxial line 95 that transmits tracking data received by the trackingcoil 94 to theMM system 10. - Referring now to
FIG. 4 , an elevational view of abar assembly 72 taken along line 4-4 ofFIG. 2 is shown. Anexpandable bar 74 provides a support upon which a thinRF coil element 76 is attached. TheRF coil element 76 is preferably constructed of a copper wire and preferably attaches to an edge of theexpandable bar 74 facing away from the opposingexpandable bar 74. Theexpandable bar 74 is constructed of a memory-type material that allows the material to be deformed by a compression force and to automatically return to a non-deformed position when the compression force is removed. In a preferred embodiment, theexpandable bar 74 is constructed of nitinol or similar material(s). - For increased RF sensitivity outside the probe,
RF coil element 76 is positioned alongexpandable bar 74 such that a pre-determined distance orgap 96 is formed therebetween. The constant distance is maintained by using a known-thickness of an insulating material with a known dielectric constant. In a preferred embodiment, this is performed by using known-thickness heat-shrink tubing, which is wrapped about the expandable bar. In this manner, an RF field generated by theRF coil element 76 may be increased in a direction away from the surface ofprobe 70 and into the target tissue. Several layers of heat-shrink tubing 98 are disposed around theRF coil element 76 and theexpandable bar 74 to attach theRF coil element 76 to theexpandable bar 74 and to provide a hermetical seal from moisture. Heat-shrink tubing 98 also substantially electrically isolates theexpandable bar 74 and theRF coil element 76 from blood or soft-tissue walls. - Referring to
FIG. 5 , a side elevational schematic view of theprobe 70 in a compressed position in accordance with the present invention is shown. Thebar assemblies 72 are compressible such thatprobe 70 may be positioned within asheath 100 for insertion into an imaging subject.Sheath 100 is constructed to enclose thebar assemblies 72 and applies a compression force upon thebar assemblies 72 during insertion into the imaging subject and translation to a target tissue to be imaged. Preferably,sheath 100 is a 9 Fr. sheath with a length that exceeds a distance from an insertion point to the target tissue to be imaged.Probe 70 is compressed withinsheath 100 as the collective assembly is translated through the vasculature to the target tissue or blood flow. - In contrast and referring to
FIG. 6 , a side elevational schematic view of theprobe 70 in an expanded position in accordance with the present invention is shown. When the target tissue within the vascular system is reached, thesheath 100 is retracted to exposeprobe 70 and to allow thebar assemblies 72 to automatically expand. Thebar assemblies 72 expand and, preferably, to substantially match an inner diameter of a vasculature or other target tissue in which the probe is placed. In an expanded position, theprobe 70 permits fluid or blood flow between thebar assemblies 72 alongflow vectors 102 to reduce occlusion that may occur in the vasculature. Allowing blood flow to pass through theprobe 70 increases the amount of time in which theprobe 70 may be expanded within the vasculature. During data acquisition, movements ofprobe 70 are actively tracked and monitored using signals received from theMR tracking coil 94. In this regard, probe 70 movements may be used to gate the data acquisition, and imaging artifacts caused byprobe 70 movements within a pulsating vascular volume of interest may be taken into account and, preferably, reduced. - Advantages in using an RF probe constructed according to the present invention include a sheath-deployable expandable RF coil and the use of RF conductor spacing from a metal surface to force EM field projection outside the probe. Other advantages include multi-channel reception in an interventional coil and use of an integrated imaging and tracking coil to reduce motion artifacts or blurring in images taken within moving structures. In addition, the tracking coil is designed to provide feedback to assist with navigating to the target anatomy when the expandable RF coil is compressed in the sheath. That is, the tracking coil provides feedback independent of the expansion/compression of the RF coil. Furthermore, use of the RF probe constructed according to the present invention is particularly advantageous for acquiring MR images of the atrium or ventricles of the heart, and imaging the pulmonary vein anatomy.
- An RF coil constructed according to the present invention is optimally used in a four-channel, or greater-number of channels, phased-array together with a two-channel surface coil. The RF coil provides a SNR that allows for faster data acquisitions or higher spatial resolution imaging, which is important in imaging the heart or heart anatomy where imaging times are limited by patient breath-holding tolerance and/or when resolution is limited by the irregularity of cardiac motion over time. Image acquisition may be gated by using data received from the MR tracking coil. In this manner, image artifacts may be reduced. Furthermore, commercial benefits may be realized with the increased utilization of MR imaging to guide or monitor therapeutic processes in the heart. For commercial applications, high spatial and temporal resolution are required as well as a high contrast-to-noise, for example, tissue temperature monitoring.
- Therefore, in accordance with one embodiment of the present invention, a probe is disclosed that includes a self-expanding housing insertable into a subject to be imaged and constructed to permit fluid flow therethrough. A plurality RF coils are included that are attached to the housing.
- In accordance with another embodiment of the present invention, an MRI apparatus is disclosed that includes a magnetic resonance imaging (MM) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images. The RF coil assembly includes a catheter configured for insertion into a blood flow and constructed to automatically expand to an expanded position from a compressed position. The RF coil assembly also includes a plurality of RF coils connected to the catheter and configured to acquire MR data. Further, the RF coil assembly also includes a tracking coil connected to the catheter and configured to indicate RF coil assembly location and movement within an imaging subject.
- In accordance with yet another embodiment of the present invention, a method of using an MR imaging device is disclosed that includes inserting an intra-cardiac MR imaging device into a sheath configured for insertion into an imaging subject to be scanned, the imaging device comprising an MR tracking coil and a pair of RF coils attached to an auto-expandable former. The method includes positioning the imaging device within the imaging subject to be scanned and retracting the sheath to allow the former to automatically expand the pair of RF coils to an expanded position.
- The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.
Claims (20)
1. A magnetic resonance (MR) imaging apparatus comprising:
an intra-cardiac catheter comprising a self-expanding housing insertable into a subject to be imaged, the housing constructed to permit fluid flow therethrough and comprising a memory-type material moveable between an expanded position and a compressed position; and
a plurality of RF coils attached to the self-expanding housing and configured to acquire MR data, the intra-cardiac catheter configured to automatically expand the plurality of RF coils to an expanded position from a compressed position;
wherein a gap formed between the plurality of RF coils and the self-expanding housing is configured to increase RF sensitivity away from the intra-cardiac catheter.
2. The MR imaging apparatus of claim 1 wherein the gap is filled with an insulating dielectric material.
3. The MR imaging apparatus of claim 2 wherein the insulating dielectric material comprises heat-shrink tubing.
4. The MR imaging apparatus of claim 1 wherein the gap has a uniform thickness.
5. The MR imaging apparatus of claim 1 further comprising:
a first layer of insulating material wrapped about the self-expanding housing and defining a thickness of the gap between the plurality of RF coils and the self-expanding housing; and
a second layer of insulating material coupling the plurality of RF coils to the self-expanding housing.
6. The MR imaging apparatus of claim 5 wherein the second layer of insulating material hermetically seals the plurality of RF coils.
7. The MR imaging apparatus of claim 1 wherein the self-expanding housing comprises at least one bar assembly having a pair of expandable bars.
8. The MR imaging apparatus of claim 7 comprising a first bar assembly having a first pair of expandable bars and a second bar assembly having a second pair of expandable bars, the second pair of expandable bars oriented orthogonal to the first pair of expandable bars.
9. The MR imaging apparatus of claim 7 further comprising an insulating material wrapped about each of the pair of expandable bars and defining a thickness of the gap.
10. The MR imaging apparatus of claim 7 wherein an RF coil is coupled to an edge of one bar of the pair of expandable bars that faces away from the other bar of the pair of expandable bars.
11. The MR imaging apparatus of claim 1 further comprising a tracking coil configured to actively track movement of the intra-cardiac catheter during MR imaging.
12. The MR imaging apparatus of claim 11 wherein the tracking coil is further configured to transmit tracking signals for gating data acquisition independent of expansion or compression of the plurality of RF coils.
13. The MR imaging apparatus of claim 1 further comprising at least one tuning capacitor connected to the plurality RF coils, the at least one tuning capacitor configured to tune the plurality RF coils.
14. The MR imaging apparatus of claim 1 further comprising a retractable sheath constructed to enclose the self-expanding housing during insertion into the subject and translation to a target tissue to be imaged and further constructed to be retracted by a user to allow the self-expanding housing to automatically expand when proximity to the target tissue is reached.
15. A method of using an MR imaging device, the method comprising:
inserting an intra-cardiac MR imaging device into a sheath configured for insertion into an imaging subject to be scanned, wherein the intra-cardiac MR imaging device comprises a pair of RF coils attached to an auto-expandable housing and separated therefrom by a gap defined by a thickness of heat-shrink tubing;
positioning the intra-cardiac MR imaging device within the imaging subject to be scanned; and
retracting the sheath to allow the auto-expandable housing to automatically expand and to cause the pair of RF coils to transition from a compressed position to an expanded position.
16. The method of claim 15 further comprising:
acquiring tracking data from a MR tracking coil representing position and movement of the imaging device during imaging, the MR tracking coil positioned within the sheath when the pair of RF coils is in the compressed and expanded positions; and
gating data acquisition during imaging based on the tracking data to reduce imaging artifacts.
17. The method of claim 16 further comprising the step of receiving tracking feedback from the MR tracking coil while navigating to a target anatomy prior to retracting the sheath therefrom.
18. The method of claim 15 wherein retracting the sheath causes a pair of bar assemblies of the auto-expandable housing to automatically expand to a non-deformed position that permits fluid passage therethrough, each of the pair of bar assemblies comprising a pair of expandable bars.
19. The method of claim 18 wherein retracting the sheath causes one expandable bar of a respective bar assembly of the pair of bar assemblies to expand away from the other expandable bar of the respective bar assembly; and
wherein an RF coil is coupled to an edge of the expandable bar that faces away from the other expandable bar.
20. The method of claim 15 wherein the pair of RF coils is electrically isolated from the imaging subject to be scanned via heat-shrink tubing disposed around the pair of RF coil elements.
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US14/962,056 US20160091577A1 (en) | 2004-03-19 | 2015-12-08 | Self-expanding multi-channel rf receiver coil for high resolution intra-cardiac mri and method of use |
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