WO1997040737A2

WO1997040737A2 - X-ray apparatus

Info

Publication number: WO1997040737A2
Application number: PCT/EP1997/002193
Authority: WO
Inventors: Claus Christiansen; Stig MØLLER
Original assignee: Osteometer Meditech A/S
Priority date: 1996-04-29
Filing date: 1997-04-28
Publication date: 1997-11-06
Also published as: AU2773997A; WO1997040737A3; GB9608946D0

Abstract

Apparatus for X-ray bone densitometry of the hip joint in which an image of the hip joint is taken with the patient in a standing position comprising an X-ray source (24) and a detector (48) arranged on opposite sides of a patient receiving space with a height adjustable saddle (56) being provided for the patient to straddle. The appropriate height for the X-ray source and the detector are determined by the positioning of the saddle engaged with the crotch of the patient. Also disclosed is X-ray apparatus comprising a fan beam X-ray source (24) and a detector assembly (48) comprising a linear array of a plurality of detectors extending in the plane of the fan beam with means for scanning the source and the detector such that the source is scanned back and forth in a direction transverse to the plane of the fan beam and the detector array is scanned in said direction to remain in said fan beam and is incrementally indexed in a selected direction in the plane of the fan beam in a series of small steps to bring each detector in said array through a series of overlapping positions in said fan beam and is then indexed through a larger distance in said selected direction to move each detector in said fan beam by a distance equal to said length of said array or a major faction thereof.

Description

X-RAY APPARATUS

The present invention relates to X-ray apparatus with particular but not exclusive relevance to X-ray bone densitometry and the taking of X-ray images of the upper femur or hip joint.

Conventionally, in taking such images or otherwise conducting bone densitometry at this site to assist in assessing the degree of osteoporosis suffered by a patient, the patient is positioned in a supine position and the feet of the patient are rotated inwards by about 5 to 10° to bring the neck of the femur into a correct orientation for imaging. This is an awkward position for a patient to maintain. It is generally necessary to make a preliminary scan by X-ray to ensure that the X-ray source and the detector are correctly positioned, because there is uncertainty about the position of the patient's hip joint. The apparatus is necessarily large because of the need to support the patient in a supine position. Machines have also been proposed in which the patient lies in a supine position with the patient's feet vertical. To accommodate this it is necessary for the X-ray source and detector assembly to be mounted on respective opposite ends of a C-shaped arm which is rocked around the patient to achieve proper alignment with the proximal femur. Such an arrangement is complex and unwieldy.

In a first aspect the present invention now provides apparatus for X-ray bone densitometry, e.g. of the proximal femur, in which in use the patient is positioned in a standing position. Preferably, such apparatus comprises an X-ray source and a detector arranged on opposite sides of a patient receiving space adapted to receive a standing patient.

Thus, the apparatus may comprise a foot plate on which a patient stands in use, said patient receiving space extending upwards from said footplate. Preferably, the apparatus further comprises means for adjusting the height of said X-ray source and said detector, and means for determining when the height of the X-ray source and the height of the detector are appropriate for conducting a desired densitometry measurement on a particular patient, which may be provided by guide means which is adjustable in height with respect to the patient so as to be engageable with the crotch of a patient positioned standing in said space.

Preferably, said guide means is locatable laterally in a first position to one side of said source and detector in which one of the left or right hip joints of the patient is guided laterally to lie between said source and detector in an appropriate attitude for bone densitometry measurement. Optionally, said guide means may also be locatable laterally in a second position to the other side of said source and detector in which the other of said left and right hip joints of the patient is guided laterally to lie between said source and said detector in an appropriate attitude for bone densitometry measurement. Said guide means may take the form of a saddle having a valley therein for positioning the patient in the fore and aft direction between the source and the detector, e.g. having a forwardly projecting horn and a rearwardly projecting horn angled with respect to one another, suitably at an included angle of from 90 to 150°, more preferably from 110 to 130°, e.g. about 120°. There may be means positionally linking said guide means and said X-ray source and said guide means and said detector, such that the source and said detector are each brought to an appropriate height with respect to the patient for imaging the hip joint of the patient by adjustment of the height of the guide means to engage the guide means with the patient's crotch and optionally there may be means for setting said guide means at the correct height for a patient such as means responsive to resistance to further upward movement of the guide means caused by engagement of the guide means with the crotch of the patient reaching a predetermined level. Said guide means may be driven upward to engage the patient's crotch by an electric motor and said means responsive to said resistance to further upward motion of the guide means reaching said predetermined level may sense as a measure of said resistance the current needed to drive said motion. Many alternative methods for detecting an increase in resistance to upward movement may be used, e.g. a pressure switch.

One or both of the source and the detector may be positioned manually with respect to the height of the guide means by an operator but preferably the guide means is linked to one of said source and said detector mechanically to adjust m height therewith. The guide means may be positionally linked to the other of said source and said detector by a remote linkage means comprising sensor means detecting the position of height adjustment of said guide means and or said one of the source and detector to which the guide means is mechanically linked, said sensor means producing an output signal, drive means connected to the said other of said source and detector for the adjustment of the height thereof, and control means responsive to said output signal to actuate said drive means to adjust the height of the said other of said source and detector to match the height of the said one of the source and detector. Preferably, in use, the source is behind the patient and the detector is in front of the patient.

The apparatus my also comprise means for supporting a patient's arm in a position for bone densitometry measurement of bones of the arm, e.g. an elbow support and means above said elbow support for supporting the hand so that the arm is positioned with the bones of the forearm extending upwardly.

According to a second aspect of the invention, an improved method of scanning a with a relatively wide fan beam uses a relatively low number of detectors in a linear array which is substantially shorter than the fan width. In known fan beam X-ray machines, the linear array of detectors has a length which is essentially equivalent to the width of the fan beam to be recorded at the detector position. In US-A- 5132995 this requires about 30 detectors. As described there, it is known to move the detector array repeatedly by a short distance in the plane of the fan beam, i.e. transverse to the thickness of the beam. A result of this is that the space between detectors in the array in one detector assembly position is covered by a detector during subsequent detector assembly positions. Thus according to the second aspect of the invention, there is provided X-ray apparatus comprising a fan beam X-ray source and a detector assembly for positioning on opposite sides of a member to be X-rayed, wherein said detector assembly comprises a plurality of detectors in a linear array aligned with and extending m the plane of ~he fan beam produced by said source, said array having a length which is less than the width of the fan beam at the detector assembly, and means for scanning said source and said detector assembly such that said source is scanned back and forth m a direction transverse to the plane of said fan beam and said detector array is scanned in said direction to remain in said fan beam and is incrementally indexed in a selected direction in the plane of the fan beam in a series of small steps no bring each detector in said array through a series of overlapping positions in said fan beam, and is then indexed through a larger distance in said selected direction to move each detector in said fan beam by a distance equal to said length of said array or a major fraction thereof. Such X-ray apparatus may of course be apparatus for bone densitometry in accordance with the first aspect of the invention also.

There may be from 3 to 10 steps in said series of small steps between each larger indexing movement and there may be 2 to 10 of said larger indexing movements in a scan.

The apparatus described herein according to any of the aspects of the invention, may be provided with means for receiving the input of results from one or more tests establishing a rate of bone loss for the patient, such as biochemical tests on body fluids or the differences between bone mass measurements over time, and for combining the rate of bone loss with the measurements made in the apparatus of the current condition of the patient to project forward or backward in time to estimate the patient's condition at some future or past time. Preferably, the rate of bone loss is established by measurements of molecular species in body fluids produced specifically by the degradation of bone collagen such as molecular species containing the peptide ammo acid sequence EKAHDGGR or the isomerised sequence EKA*HDGGR, where A* is an aspartic acid bonded not through the alpha carboxylic acid group but through the side chain carboxylic acid group (isoaspartic acid) Such assays are described in WO-A-95/08115, PCT EP 95/04055 and PCT EP96/01228. Such measurements may also include measurements of indicators of bone formation such as osteocalcin.

In a further aspect, the invention includes apparatus for bone densitometry of the proximal femur comprising such means for receiving the results of rate measurements for projecting the patient's condition at a future (or past) time.

The invention will be illustrated by the following description of a preferred embodiment with reference to the accompanying drawings in which: - Figure 1 is a side elevation of apparatus according to the invention,

Figure 2 is a plan view of the apparatus of Figure 1, Figure 3 shows the location of the head of the femur in each hip joint of two differently sized patients positioned on the saddle of the apparatus of Figure 1,

Figure 4 is an enlarged plan view of the saddle and detector mounting arrangement of the apparatus of Figure 1,

Figure 5 is a cross-section on the line A-A of Figure 4;

Figure 6 illustrates the detector array used in the apparatus for Figures 1 to 5 and its scanning pattern,- Figure 7 shows details of modifications to the apparatus of Figure 1; and

Figure 8 shows a further modification to the apparatus of Figure 1. As shown in the drawings, apparatus 10 according to the invention comprises a base 12 having a floor or foot plate 14 upon which a patient may stand. Floor 14 covers a void 16 containing working parts of the apparatus to be described below. From the floor 14 there rises a lead screw 18 and a pair of guide rods 19, each parallel with lead screw 18. A platform 20 is supported in threaded engagement with the lead screw 18 and m sliding bushings containing bearings receives the guide rods 19. Platform 20 carries a tank 22 containing a X-ray source 24. The height of platform 20 is adjustable by rotation of the lead screw 18. A casing 26 mounted on the base 12 encloses the X-ray source tank 22 and the lead screw 18.

At the front end of the base 12 there is provided a second lead screw 30 and a pair of guide rods 32. A yoke 34 has a first aperture 36 through which passes the lead screw 30. A collar 38 is mounted on the yoke 34 above the aperture 36 and carries at its upper end a nut 40 which is fast therewith and which is in threaded engagement with the lead screw 30.

The aperture 36 lies on a plane of symmetry of yoke 34. On either side of said plane there is provided an aperture 42 below which is mounted a bushing 44 containing a bearing 46 enabling the yoke 34 to slide freely on the rods 32. An X-ray detector assembly 48 is provided mounted on the upper surface of the yoke 34 and moving vertically therewith. Below the X-ray source there is positioned a motor 28 connected to drive said lead screws 18 and 30 by toothed belt 29 engaged with a sprocket mounted to the end of each lead screw within the void 16. The motor 28 may be actuated to adjust the height of the X-ray source and detector assembly as described below.

Near each rod 32 there is on the upper surface of the yoke 34 a collar 52 into either of which collars may be pushed 5 a shaft 54 carrying a saddle 56 having a forward horn 58 and rearward horn 60 defining an included angle a of 120° at a central waist. The saddle is suitably approximately 50 mm wide.

An enclosure 68 is provided around the components

10 mounting the detector with slots being provided to accommodate vertical movement of the shaft 54 bearing the saddle 56.

Within the detector assembly there is a detector array 70. Both the detector array and the X-ray source are mounted for scanning movements. The X-ray source is mounted for

15 horizontal scanning movement transversely of the apparatus and across the platform 20. The detector array is mounted for horizontal scanning movement in synchrony with the X-ray source across the yoke 34 and also for vertical movement at each the end of the horizontal scans as described in further

20 detail below. The detector array comprises a plurality of detectors mounted in a vertical line, e.g. 16 detectors each about 15 mm wide in the beam thickness direction, and about 5 mm tall m the beam plane direction. The X-ray source is adapted to produce a vertical fan beam, which at the detector

25 assembly has a vertical spread greater than the length of the detector array. A collimator 72 positioned in front of the X-ray source is mounted for vertical scanning movement in synchrony with the detector array and provides a window through which X-rays are free to pass toward the detector

30 array, while X-rays having too high or too low a path to meet the detector array are blocked. The collimator also shapes the X-ray beam into the required vertical fan beam.

Each detector in the array is a dual energy detector having a first phosphor layer adapted to respond predominantly

-35 to softer X-rays and a second phosphor layer adapted to respond predominantly to harder X-rays, optionally with a beam hardening filter between them. As is known in the art, the phosphors may be of the^' same material, the first phosphor being thinner and the second being thicker, or they may be of different materials such that the first phosphor responds preferentially to softer X-rays, as described in ϋS-A-4626688 and US-A-4247774. As is also well known, instead of employing a so-called dual energy detector as just described, one can conduct a dual energy scan using a single energy detector and switching the X-ray source between producing high energy (harder) and low energy (softer) X-rays by alteration of its operating voltage.

In use, the motor 28 is controlled by an operator to drive the detector assembly, the X-ray source and the saddle down to the lowest position shown in Figure 1 (marked A) . A patient is positioned standing on the floor 14 in the position indicated in Figure 2 and the motor 28 is controlled by the operator to raise the saddle to the patient's crotch, e.g. to the position shown at B in Figure 1. By the belt 29, the motor 28 raises the height of the X-ray source to match that of the detector assembly continuously.

As shown in Figure 2, the X-ray source 24 and the detector assembly 48 will now be aligned with the left hip joint of the patient at approximately right-angles to the neck of the femur and in an ideal position for producing an X-ray image of this joint.

The X-ray source is now activated and its position is scanned progressively horizontally repeatedly back and forth in the scan pattern shown in Figure 6. The detector array is illuminated by the beam over an area above 4 mm wide in the beam thickness direction and about 60 mm tall in the beam plane direction and is scanned horizontally in synchrony and is adjusted vertically downwards in a minor movement by less than the height of a single detector of the array at the end of each horizontal run, e.g. by about 1 mm. After a sufficient number of horizontal passes to bring the detector array down by about one detector's height, the detector array is adjusted down in a major movement by the height of the array and the horizontal scanning procedure is continued. This procedure is continued until the whole of the desired area has been scanned, e.g. through four detector array heights.

The collimator is adjusted in height at each major downward movement of the detector array and if desired at each minor downward movement, so as to shield areas of the patient not actively being scanned. Data is acquired from the detectors in respect of position and in respect of the intensity of harder and softer X-ray intensity and an image relating to bone corrected for soft tissue may be constructed in a known manner.

An image of the bone in the area of the scan may be presented to the operator. Automatically or by operator input, the hip axis length of the patient may be determined from the image or the data on which it is based. Automatically or by operator input, a region of interest (ROD may be defined within which to determine the bone densitometry read outs .

There will not be any need for taking a preliminary scan to check the alignment of the detector, X-ray source and joint .

The motor 28 may then be controlled to drop the detector assembly 48 down to position A. The shaft 54 may be withdrawn from the collar 52 and reinserted in the other collar 52 on the other side of the apparatus. The procedure may then be repeated to take an image of the other hip joint.

It will be noted that in comparison to apparatus for a similar purpose designed for use with a supine patient, the apparatus shown in the accompanying drawings is extremely compact, especially m its footprint area.

The apparatus is adapted for use with a wide range of different sizes of patient. As shown in Figure 3, the saddle will automatically centre the hip joints of a large or a small patient equally well. The height adjustment provided by the saddle will guide the X-ray source and detector assembly to the appropriate height and thus as be seen from Figure 2 the neck of the femur will be correctly positioned and correctly angled botn for a very large patient and for a very small patient.

Furthermore, as shown in Figure 8, an elbow receiving cup 83 and finger locators 84 may be provided to enable a patient's arm to be fixated for a wrist scan 82 to be carried out in the same apparatus. As is known in the art, e.g. from US-A-5148455, one or more additional detectors may be positioned to receive X-rays from the source which have not passed through the patient, to act as a reference measurement of the intensity of the source to correct for variations in output due for instance to variations in operating voltage. Reference materials and/or beam hardening filters may be placed between such reference detectors and the X-ray source. For instance a bone like material may be used as such a reference material .

As also previously known, a reference material may be interposed periodically or intermittently m the measurement beam as a reference for calibration purposes. This may occur at each measuring position of the detector assembly. The interposition of such reference materials, which will normally simulate bony material, is described m US-A-5148455. Means may be provided for varying the intensity of the X-ray exposure of the patient according to the nature or amount of the tissue in the beam as the scan progresses. Thus if the patient is large, the exposure to the X-ray beam may be increased to allow for the greater attenuation caused by the patient's size and this may be done automatically in response to the level sensed by the detector, so as to obtain the optimum exposure for good imaging and bone densitometry. Such adjustments may be made during the course of the scan so that unnecessarily large exposures are not given to parts of the body which are thinner in order to have a proper exposure in thicker regions . Preferably, the variation in exposure is obtained by varying the scan speed according to the attenuation measured on a real time basis.

Means may be provided for conducting a rapid scan through body areas adjacent bone, sensing when the scan reaches bone and slowing the scan to a proper speed for data gathering for bone densitometry while the scan is detecting bone, and reverting to rapid scanning when the scan moves out of bone. This will minimise unnecessary patient exposure. Measurements may be made of bone mineral content (in weight units) and/or of bone mineral density (in weight/area units) as known in the art.

Instead of both the detector assembly and the X-ray source being adjusted in height by a common motor acting through a belt as described above, one of them may be adjusted m height as described and the position of adjustment may be encoded and transmitted to a separate means such as a separate motor adjusting the height of the other.

Such an arrangement is shown in Figure 7 where a shaft encoder 80 detects the position of the lead screw 30 which is driven by a motor 29 and this position is relayed via control circuitry to a motor 28 connected to drive the lead screw 18 carrying the X-ray source. Such a motor may suitably be positioned below the floor 14 at the end of lead screw 18. A further variation shown in Figure 7 is the provision of a load cell or strain gauge 81 at either of the positions 81a or 81b This provides a signal indicative of the saddle 56 engaging with the patient, which signal is transmitted to control circuitry operatively connected to motor 28 (or to motors 28 and 29 if both are provided) to stop the upward movement of the saddle at the correct height.

Many modifications and variations of the invention as described with reference to the accompanying drawings are possible withm the scope of the invention.

Claims

1. Apparatus (10) for X-ray bone densitometry in which in use the patient is positioned in a standing position, comprising an X-ray source (24) and a detector (48) arranged on opposite sides of a patient receiving space adapted to receive a standing patient, characterised in that the apparatus further comprises means (18) for adjusting the height of said X-ray source and said detector, and guide means (56) for determining when the height of the X-ray source and the height of the detector are appropriate for conducting a desired densitometry measurement on a particular patient, wherein which guide means is adjustable in height with respect to the patient so as to be engageable with the crotch of a patient positioned standing in said space.

2. Apparatus as claimed in Claim 1, wherein said apparatus comprises a foot plate (14) on which a patient stands in use, said patient receiving space extending upwards from said footplate.

3. Apparatus as claimed in Claim 1 or Claim 2, wherein said guide means (56) is locatable laterally in a first position to one side of said source and detector in which one of the left or right hip joints of the patient is guided laterally to lie between said source and detector in an appropriate attitude for bone densitometry measurement.

4. Apparatus as claimed in Claim 3, wherein said guide means (56) is locatable laterally in a second position to the other side of said source and detector in which the other of said left and right hip joints of the patient is guided laterally to lie between said source and said detector in an appropriate attitude for bone densitometry measurement.

5. Apparatus as claimed in any one of Claims 1 to 4, wherein said guide means takes the form of a saddle (56) having valley therein for positioning the patient in the fore and aft direction between the source and the detector.

6. Apparatus as claimed in Claim 5, wherein the saddle (56) has a forwardly projecting horn (58) and a rearwardly projecting horn (60) angled with respect to one another at an included angle (x) of from 90 to 150°.

7. Apparatus as claimed in any one of Claims 1 to 6, comprising means (29) positionally linking said guide means (56) and said X-ray source (24} and said guide means (56) and said detector (48) , such that the source and said detector are each brought to an appropriate height with respect to the patient for imaging the hip joint of the patient by adjustment of the height of the guide means to engage the guide means with the patient's crotch.

8. Apparatus as claimed in Claim 7, further comprising means

(28) for setting said guide means at the correct height for a patient.

9. Apparatus as claimed in Claim 8, wherein said means for setting said guide means at the correct height comprises means responsive to resistance to further upward movement of the guide means caused by engagement of the guide means with the crotch of the patient reaching a predetermined level.

10. Apparatus as claimed in Claim 9, wherein said guide means is driven upward to engage the patient's crotch by an electric motor (28) and said means responsive to said resistance to further upward motion of the guide means reaching said predetermined level senses as a measure of said resistance the current needed to drive said motion.

11. Apparatus as claimed in any one of Claims 1 to 10, wherein one or both of the X-ray source (24) and the detector

(48) may be positioned manually with respect to the height of the guide means by an operator.

12. Apparatus as claimed in any one of Claims 2 to 11, wherem the guide means (56) is linked to one of said source and said detector mechanically to adjust m height therewith.

13. Apparatus as claimed in Claim 12, wherein said guide means is positionally linked to the other of said source and said detector by a remote linkage means comprising sensor means detecting the position of height adjustment of said guide means and or said one of the source and detector to which the guide means is mechanically linked, said sensor means producing an output signal, drive means connected to the said other of said source and detector for the adjustment of the height thereof, and control means responsive to said output signal to actuate said drive means to adjust the height of the said other of said source and detector to match the height of the said one of the source and detector.

14. Apparatus as claimed m any one of Claims 1 to 13, wherem, in use, the source is behind the patient and the detector is in front of the patient.

15. Apparatus as claimed in any preceding claim, further comprising means for supporting a patient's arm in a position for bone densitometry measurement of bones of the arm.

16. Apparatus as claimed in Claim 15, wherem said means comprises an elbow support and means above said elbow support for supporting the hand so that the arm is positioned with the bones of the forearm extending upwardly.

17 X-ray apparatus comprising a fan beam X-ray source (24) and a detector assembly (48) for positioning on opposite sides of a member to be X-rayed, wherem said detector assembly comprises a plurality of detectors in a linear array (70) aligned with and extending in the plane of the fan beam produced by said source, said array having a length which is less than the width of the fan beam at the detector assembly, and means for scanning said source and said detector assembly such that said source is scanned back and forth m a direction transverse to the plane of said fan beam and said detector array is scanned m said direction to remain in said fan beam and is incrementally indexed in a selected direction in the plane of the fan beam in a series of small steps to bring each detector m said array through a series of overlapping positions in said fan beam, and is then indexed through a larger distance in said selected direction to move each detector m said fan beam by a distance equal to said length of said array or a major fraction thereof.

18 X-ray apparatus as claimed in Claim 17, being apparatus for bone densitometry as claimed in any one of Claims 1 to 16.

19. X-ray apparatus as claimed in Claim 17 or Claim 18, wherem there are from 3 to 10 steps in said series of small steps between each larger indexing movement.

20. X-ray apparatus as claimed in any one of Claims 17 to 19, wherein there are from 2 to 10 of said larger indexing movements m a scan.

21. Apparatus for bone densitometry of the proximal femur comprising means for receiving the input of results from one or more tests establishing a rate of bone loss for the patient, and for combining the rate of bone loss with the measurements made in the apparatus of the current condition of the patient to project forward or backward in time to estimate the patient's condition at a future or past time.