RADIOLOGICAL APPARATUS FOR MEASURING BONE DENSITY

Abstract: An apparatus employing radiation for measuring bone density in which the bone can be scanned from different angles. The multidirectional scanning is accomplished by rotating the radiation source and detector about the stationary object being irradiated.

Description: RADIOLOGICAL APPARATUS FOR MEASURING BONE DENSITY Background of the Invention This invention relates to radiologic measuring devices, and more particularly, to the use of radiation in measuring bone structure. The diagnostic use of radiation in evaluating bone structure has recently been applied in assessing bone demineralization that occurs with advancing age. Bone mineral is lost from all parts of the skeleton, and at a linear rate from the lumbar spine, starting at about 35 years of age. The resultant demineralization results in a high risk of fractures with an increased associated mortality and morbidity. In evaluation of the spine, there is a very good correlation between dual photon densito etry measurements of bone density and fracture resistance in excised vertabrae subjected to compression testing. It is also important to evaluate mineral loss in the hip, as appendicular losses often match or exceed spine loss in patients over 70. Dual photon absorptiometry enables non-invasive quantitative analysis of bone mineral in regions of the body that were previously inaccessable using single photon absorptiometry. The use of two photon energies minimizes errors that result from irregular body contour and soft tissue inhomogeneities. Essentially, two photon energies are necessary to allow discrimination of two substances of a given system. In this case between bone mineral and soft tissue. The most commonly used photon energies in dual photon scanning are 44 and 100 KeV. The measurements of the attenuation of this radiation as it passes through the body yields the bone mineral density. ; Summary of the Invention The present invention involves the multidirectional measurement of human bone densities for diagnostic purposes. A radiation source, and a detector used for measuring the radiation transmitted through the object being measured, are rigidly aligned by a bracket or arm. This detector is mounted in a telescoping mechanism to permit control over the source/detector distance. The arm and the attached source and detector, are mounted on an "x-y" table that permits scanning of objects over a predetermined planar area. This apparatus is mounted so that the source, detector, and scanning mechanism can be rotated to view a stationary object from different angles. In a preferred embodiment of the invention, the pivot axis about which the arm rotates is displaceable so that the source will clear the table upon rotation. The rotating apparatus may be mounted in a drawer with guides or rails that telescope out to support the system during rotation. The rotating elements are weighted so that very little pressure is necessary to rotate the system. The weight is distributed so that if the mechanism is stopped at any point during rotation, it will at most slowly accelerate under its own weight. If the center of gravity of the rotating mechanism is approximately along the pivot axis, this condition will be met. One weight is placed in the detector to vertically adjust the center of gravity. A second weight is placed adjacent the scanning assembly to horizontally adjust the center of gravity. Brief Description of the Drawings Figure 1 is a perspective view of the bone densitometer. Figure 2 is a side view of the radiation source and detector in the interior position. Figure 3 is a side view of the apparatus rotated to the lateral position. Figure 4 is a top view of the saddle and drawer assembly. Detailed Description of the Invention Existing scanner assemblies used in bone densito etry generally permit unidirectional scanning of patients only. To obtain lateral or side views, for example, the patient must be turned. This movement of the patient is often difficult or impossible depending upon their physical condition. A dual photon bone densitometer used in diagnosing osteoporosis is illustrated generally in Figure 1. A table 10 on which the patient lies has a drawer assembly 11 which is pulled out from under the. table on the side from which a bracket 12 protrudes. The bracket 12 extends in a "C" shape from the drawer assembly 11 to a detecting apparatus 13. Figure-2 shows, in a cross-sectional view, the relationship between the detector 13 and the contents of the drawer assembly 11. A radiation source 14 is mounted on a moveable platform 15. The source 14 is rigidly aligned with the detector 13 by bracket 12 to insure that radiation emitted from the source is received by the detector regardless of the angle to which the source-detector axis is rotated. The entire rotatable apparatus is mounted on a tray or "saddle" 17. The saddle 17 is rotatably mounted onto the assembly plates 19. The plates 19 in one embodiment constitute the side walls of a drawer which compactly houses the source and scanning apparatus. To rotate the apparatus from the anterior position shown in Figure 2 to the lateral position shown in Figure 3 , the following steps must be taken. The user releases a locking mechanism and pulls the arm horizontally to one side of the table so that the saddle 17 and plates 19 slide the source from under the center of the table to avoid contact with the table during rotation. In one embodiment of the invention the source is approximately one inch below the table during anterior scanning and thus cannot be rov.tated without lateral movement. Source proximity to the table is desirable, as the source and detector are preferably as close to one another as possible to yield the best possible image. The drawer assembly plates 19 telescope out along the glides 20 until the pivot point 18 is astride the.table 10. The plates 19 are then locked in position by a locking mechanism (not shown) . The arm 12 and the attached source and saddle assembly 17 are rotated manually by the user about the axis 18 to the desired position. Note that the pivot axis location must be chosen so that the source and scanning apparatus are rotated into a position just above the plane of the table. This insures that objects positioned on the table can be fully scanned laterally. The pivot location also affects the adjustment of the center of gravity as discussed below. In an alternative embodiment of the invention, the lateral movement of the drawer assembly and/or the rotation may be automatically controlled by adding the necessary motor and control systems. Figures 2 and 3 also illustrate the presence of weights 21 and 24. After initial assembly of the apparatus, the center of gravity of the rotating elements must be adjusted to assure ease of manual rotation. In a preferred embodiment of the invention, the center of gravity of the rotating elements is located along the pivot axis 18. When the center of gravity is so situated the rotating elements will not accelerate under their own weight when the bracket 12 is rotated to any chosen angle, stopped and released. Figure 4 shows a top view of the drawer assembly 11 and illustrates the location of the pivot axis 18, the glides 20 for displacement of the plates 19, and the tracks 26 on which the platform 15 rides. The platform 15, as well as the attached source 14, bracket 12, and detector 13 , are moved in a plane perpendicular to the source-detector axis. The driving mechanism for the scanning motion is a so-called "x-y" table 16. The scanning mechanism is comprised of threaded bars, one running along the longitudinal or "y" axis 26 of the table, the second 25 running perpendicular to the first across the width or "x" axis of the table. The platform 15 has threaded housings which receive, and are driven by, the two threaded bars. The threaded "x" bar 25 is rotated by a motor 23 and the threaded "y" bar 26 is rotated by the motor 22. When the scanning assembly is rotated along with the source and detector, this insures full scanning capability at any angle. In a preferred embodiment of the invention, the scanning mechanism is controlled automatically feeding by the scanning rate and the size of the area to be scanned into a computer, which then triggers the radiation source and coordinates the desired scan. During initial rotation of the system from the vertical position, the weight of the saddle and Q enclosed elements controls the balancing of the bracket 12 and the attached components. The weights 24 are added to the front wall of the saddle to adjust the center of gravity in the horizontal plane. The weight 21 is added to the detector 5 system to adjust the center of gravity in the vertical plane. As the system is rotated through larger angles from the vertical (e.g. 45°-90"), the correct weighting of the bracket and detector by weight 21 becomes more important to maintain ease of I Q manual rotation. By rotating the detector arm, scanning of the lumbar spine in both the anterior and lateral projections is now possible without repositioning the patient. The patient remaining in the supine 15 position for both the lateral and anterior-posterior projection maintains the correct alignment of both projections, permits direct correlation of the two studies, and anatomically is diagnostically correct. Performing the lateral image as the first study 20 may enable the physician to observe extra-osseous calcification in tissue overlying the lumbar spine. In the anterior-posterior projections, such extra-osseous calcification cannot be distinguished from bone, and could therefore interfere with accurate bone density measurements in that projection. The bone being studied may be examined in real time by amplifying the signal output from the detector and displaying it on a C-T screen. While the invention has been particularly shown 3 Q and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims: CLAIMS 1. A radiologic measuring apparatus for scanning bodily tissue characterized by: a radiation source; a detector to detect radiation emitted from the source; a member attached to the source and detector that rigidly aligns the source with the detector; a scanner to scan objects with the source by displacing said member in a plane orthogonal to the alignment of said source and detector; and a translatable support having a pivot axis such that the member and the attached source and detector are translated and rotated relative to the tissue to scan the irradiated tissue at different angles. 2. A radiologic measuring apparatus as defined in Claim 1 wherein the source and detecting means measure the density of the object. 3. A radiologic measuring apparatus as defined in Claim 2 wherein said object is bone such that the density is used to determine the mineral content of the bone. 4. A radiologic measuring apparatus as defined in Claim 1 wherein the distance between the source and said detecting means is adjustable. 5. A radiologic measuring apparatus as defined in Claim 1 wherein said support rotates the member, source, and detector to permit scanning from anterior and lateral views of said tissue. 6. A radiologic measuring apparatus as defined in Claim 5 wherein said support is such that an axis of alignment of the source and detector means is displaced to one side of the tissue before rotating the member about said tissue from the anterior view. 7. A radiologic measuring apparatus as defined in Claim 6 wherein said support is comprised of a drawer such that said rotating means is suspended along the pivot axis within the drawer, and is rotatable about said pivot axis. 8. A radiologic measuring apparatus as defined in Claim 7 wherein said drawer is displaced using telescoping rails in a direction perpendicular to the pivot axis. 9- A radiologic measuring apparatus as defined in Claim 1 wherein the scanner is rigidly attached to, and rotatable with, said member. 10. A radiologic measuring apparatus as defined in Claim 7 further comprising a balance element to balance said member and the attached source and detector during rotation. 11. A radiologic measuring apparatus as defined in Claim 10 wherein said balance element approximately locates the center of gravity of said rotating member along the pivot axis. 12. A radiologic measuring apparatus as defined in Claim 10 wherein said balance element is further comprised of: a first balance distributed adjacent the scanning means; and a second balance distributed adjacent the detecting means. 13. A radiologic measuring apparatus characterized by: a radiation source; a detector to detect radiation emitted from the source; a member rigidly aligning the source with said detector; a scanner to scan objects with the source where said scanner is rigidly attached to the member; and a translatable support rotate said member and scanner about a pivot axis to scan objects at different angles. 14. A method of radiologically scanning objects characterized by the steps of: positioning an object on a horizontal table; scanning said object from one angle with a radiation source and detector which are rigidly aligned by a member along an axis; translating said aligning member such that the axis of alignment is on one side of the table; rotating said aligning member and the attached source and detector about a pivot axis below the plane of the table; and scanning said object with said source from the rotated position. 15. A method of radiologically scanning objects as defined in Claim 14 further comprising determining the density of said object. 16. A method of radiologically scanning objects as defined in Claim 14 wherein said translating step is further comprised of displacing the pivot axis to the side of the table. 17. A method of radiologically scanning objects as defined in Claim 14 wherein said source-detector axis is rotated to a horizontal position above the table around said pivot axis.

Inventors: O'NEIL WILLIAM, WARNE JAMES R, O'NEIL, WILLIAM, WARNE, JAMES, R.
Applicants: MEDICAL & SCIENT ENTERPRISES I, MEDICAL & SCIENTIFIC ENTERPRISES, INC.
Application year: 1988
Main classification: A61B6
IPC codes: A61B6, G01T1