MXPA97003765A - Bone densitometer with better point characterization - Google Patents

Abstract

A bone densitometer with opposite radiation source (129 and a detector (13) placed to obtain a two-dimensional array of image formation blocks having values representing radiation attenuation, a digital computer (18) that assigns category to the blocks of image formation within at least blocks of soft tissue or soft tissue formation, which exhibits the categories of blocks of image formation and which exhibit a diagnostic value based on bone and soft tissue formation blocks. method of measuring bone density of vertebrae of a spine

Description

BONE DENSITOMETER WITH CHARACTERIZATION OF IMPROVED POINT The present invention relates to bone densitometers and in particular, to densitometers that analyze the X-ray attenuation data to distinguish between bone and other materials in the body to identify particular bones and measure those bones.

Background of the Invention digital bone densitometry devices such as DPX machines manufactured by LUNAR Corporation of Madison, Wisconsin or QDR machines manufactured by Hologic, Inc. of Waltham, Massachusetts, are used to generate widely established values of bone character, such as the content of bone mineral ("BMC") or bone mineral density ("BMD"). Such information about the bone character and, in particular, about the characteristics in the spine depends frequently on the diagnosis and treatment of depletive disorders such as osteoporosis. Traditionally, BMC and BMD measurements have been performed by scanning the spine of a patient with a radiation source directed along an anterior-posterior axis ("AP"). One problem with spinal AP scans for BMC and BMD measurement is that the trabecular bone measurements of importance for diagnosis at each vertebra deviate from the contribution of the posterior elements of each vertebra. This is because the bone from the posterior elements projects into the intervertebral space and extends into much of the vertebral body of an AP view. Therefore, most of the bone of the posterior elements were invariably included in the AP measurement. To avoid these problems, manufacturers have resorted to measuring the spine from the lateral position. In the lateral position, it is stated, the region of interest can be easily limited to the vertebral body excluding the posterior elements. Therefore, an impediment has the measurement deviated by the subsequent elements. However, there are significant problems with the side view. Because the thickness of the patient is greater in the lateral view, the resolution is compromised. For the same resolution that is obtained in the AP view, in the side view the flow of the X-ray beam that leads to an increased dose must be increased. If the flow did not increase, the ability to define the margins of the vertebral body was not better and in many cases it was worse than with the AP view. In addition, most of the lateral view of the spine is obstructed by the ribs or hip. Those skilled in the art can appreciate that such an obstruction presents a problem of similar deviation as discussed above with respect to the posterior elements in the AP view.

In the best case, only two vertebrae, L1 and L2, present a blocked lateral view and this is true only for 20 percent of the population. In a small percentage of the population where an unobstructed view is possible, if the vertebrae have a pathology, such as crush fractures, the BMC or BMD measurement of those vertebrae may not be clinically relevant. A device for automated determination and analysis of bone density is described in US-A-5228068. In that description, a matrix of data values is obtained from a lateral vertebral exploration by means of an X-ray beam. The matrix is then investigated by computer to locate the maximum and minimum value that facilitates the determination of the limits of the vertebrae. The determination of these limits allows indications derived from the vertebral conditions. The areas of unusual bone density can also be identified.

Brief Description of the Invention The present invention improves the measurement of bone BMC or BMD in the AP direction by defining a region of measurement of interest (ROI) around a vertebra that avoids areas of the vertebra that are significantly deviated by the superposition of the posterior elements of the vertebrae. The spine. A digital computer analyzes the attenuation values of the acquired data elements and the location of those data elements to identify the high density areas that are similarly originated by the subsequent elements. Those areas are eliminated from the RO measurement Specifically, the vertebrae are scanned with a beam of radiation directed in the AP direction to acquire a matrix of discrete data elements each having a value and a defined location through the vertebra. A digital computer reviews the values of the data elements and their defined locations to identify the individual vertebrae and the data element zones within the individual vertebra where the data elements measure the radiation substantially attenuated by the bone of the center processes spinal and spinal column. These areas can be located by identifying an intervertebral space adjacent to the vertebra and data elements within the intervertebral space that measures radiation substantially attenuated only by the process of the spine and not by the spinal center to produce a reference measurement . The reference measurement can be subtracted from a peak value of the data elements in the vertebrae to establish a limit with those data elements within the vertebrae that have a value greater than the limit defining the zones. The zones are then excluded from a calculation of the physical characteristic of the vertebrae material, which is displayed.

Therefore, it is an object of the invention to provide a measurement of bone density in the AP direction that emulates that in the lateral direction without the disadvantages of lateral image formation. This technique can be applied similarly to the location and elimination of the intervertebral spaces from the measurement of the vertebral density. Here the data values in the region of the intervertebral space and the location of the data in conjunction with the known structure of the spine are used to precisely locate the intervertebral spaces and to eliminate those spaces from the measurement of the density . Specifically, the data elements of the vertebrae, acquired as described above, are ordered based on their values in the bone data elements that measure the physical characteristic of the vertebra. The defined locations of these bone elements are used to identify the vertebral column and the intervertebral spaces and a bone integrity value for the vertebrae is determined, which excludes the intervertebral spaces. Therefore, it is another object of the invention to eliminate not only the effects of the denser posterior elements from the vertebral measurement but also the influence of the less dense regions of the intervertebral spaces. A highly flexible and interactive method to select which data elements will be included in the measurement is provided by the use of the "brush" cursor that allows the operator to selectively change the characterization of the data elements by "painting" their image formation blocks over an image of the data elements. Specifically, a two-dimensional arrangement of image forming blocks having values representing radiation attenuation at locations throughout the patient is displayed on a digital computer having a display screen and a cursor controller that provides a select signal and the cursor coordinates in response to the commands of the operator. The digital computer receives the arrangement of image formation blocks and assigns them categories within at least bone imaging blocks, soft tissue imaging blocks and neutral imaging blocks. An image of the image formation blocks is displayed in which at least one category is visually distinguishable from the others. In response to the cursor coordinates from the cursor controller a cursor symbol moves in an image path. The image formation blocks in the path have their categorization changed when the selected signal is received. A diagnostic value is displayed to the operator based on the bone imaging blocks and the bone imaging blocks and the soft tissue imaging blocks but excluding the neutral imaging blocks, since each is affected by the operator under the cursor control. Therefore, it is another object of the invention to allow the operator to accurately select the characterization of each data item in an alternative manner. Other objects, advantages and features of the present invention will become apparent from the following specification when taken in conjunction with the accompanying drawings.

Brief Description of the Di buj os Fig. 1 is a perspective view of an instrument for use in the present invention showing a C-shaped arm that supports at one end an X-ray source that produces a fan beam whose plane is aligned with a plane Transverse of supine patient and received by a linear detector on the other end of the C-shaped arm, the C-shaped arm to be scanned along a lower / upper patient axis to produce a matrix of data elements that They can be displayed on a computer. Fig. 2 is a schematic representation of the array of data elements produced by the instrument of FIG. 1 showing a point typing of each data item as bone or soft tissue; Fig. 3 is a greatly simplified representation of an image of a matrix of data elements acquired by the instrument of FIG. 1 showing the representative vertebrae of the spine as well as portions of the clavicle and the ileum where each data element is represented as a block of image formation on the image; Fig. 4 is a histogram that graphs the frequency of the occurrence of the blocks of image formation in the image of Fig. 3 against the value of its corresponding data element showing the distribution of the image formation blocks in two modes corresponding to bone image formation blocks and soft tissue imaging blocks; Fig. 5 is a flow chart illustrating the refinement steps of the point typing of the data elements of Fig. 2 into multiple categories based on their value, spatial distribution and operator commands; Fig. 6 is a representation of the computer display of Fig. 1 showing the operator inputs to select a type and size of the brush used by the operator to change the dot image typing associated with the image in Fig. 6. . 3; Fig. 7 is a perspective view of a vertebra showing the processes of the spinal center and the dorsal column extending backward; and Fig. 8 is a simplified representation of an AP bone density image as seen in Fig. 3 showing areas of high density caused by overlaying the spinal prosthesis extending back over the spinal center. and identification of a reference area in the intervertebral space used to remove those high density areas from the final density measurement.

Description of the Preferred Modality Densitometry Computation Equipment In FIG. 1 there is shown a perspective view of an X-ray-based digital X-ray device 10 of the type employed in the preferred embodiment of the present invention. The digital X-ray device 10 includes a dual-energy X-ray radiation source 12 and a detector 13, both mounted on a rotating C-shaped arm 14, which extends on each side of a supine patient 16 to direct and receiving the radiation along a radiation axis 24 through the patient 16. The C-shaped arm is designed to be rotated in a vertical plane as indicated by the arrows 9 as it is supported by the collar 15 to allow an AP view of the spine or other bones or a side view of it. The C-shaped arm 14 can also move longitudinally along the body of the patient in a scanning direction 19 and can be placed under the control of servo-motors controlled by the computer as is known in the art. The digital X-ray device 10 of the preferred embodiment has the ability to switch from a double energy Z-ray mode to a simple energy X-ray mode. "X-rays of simple energy" refers to ionizing radiation in a narrow band of energies of a few keV in the scale of diagnostic imaging (20-100 keV). "Dual energy X-rays" or "polychromatic X-rays" refers to radiation in two or more energy bands, emitted simultaneously or in rapid succession, or a single broadband energy of more than a few kev over the Diagnostic image formation scale. Switching from double energy to simple energy either by affecting the source, for example, by removing or adding a K-edge filter, or by controlling the switching of energies, that is, between high and low voltage X-ray or, affecting the detector, for example, by selecting only one energy level during a particular study, or a combination of the source and the detector. In the preferred embodiment, a double energy X-ray beam is used for bone character measurements (ie, BMC and BM D) considering that a simple energy can be used for morphometric measurements. Alternatively, a single energy beam can be used only for morphometric measurements without densitometry measurements or a dual energy machine can be used for both morphometric measurements and density. The radiation source 12 can provide an X-ray fan beam 23 which is aligned and oriented towards the vertebra so that the plane of the fan beam 23 is perpendicular to the longitudinal axis of the spine. The orientation of the fan beam 23 perpendicular to the spine allows image formation of the spine or other long bones generally aligned with the spine such as the fem ur, with minimal distortion along the longitudinal axis resulting in ability to measure the vertebral dimensions in this axis with greater precision than possible with a conical beam. For greater precision on the horizontal axis, the fan beam 23 can also be oriented so that the vertebral body or other bone is irradiated by the central portion of the beam instead of the edges that are subject to distortion. Since the center of the fan beam 23 has little angulation, the resulting data are comparable to those obtained with a narrow electronic beam and a much faster scan can still be obtained. The detector 13 is a linear arrangement of the detector elements which subtends the fan beam 23 to provide simultaneous measurements along a number of rays of the fan beam 23 associated with each detector element.

A general-purpose digital computer 18 is programmed for use in the operation of the digital X-ray device 10 and analyzes the data obtained from the detector and includes specialized algorithms for performing the calculations required by the present invention. In addition, the present invention includes a data acquisition system ("DAS") for converting the signals produced by the detector 13 to a form compatible with the computer 18 and a data storage device (none of which is shown) that they can be incorporated into the computer 18. The computer 18 provides an electronic screen for issuing data analysis or data images as will be described. A "mouse" 25 or other cursor control device is provided to allow the operator to control a cursor (not shown in Fig. 1) on the screen 22 in response to movement of the "mouse" 25 on a surface by the operator. The control buttons 26 on the "mouse" allow additional input from the operator associated with the selection of menu items and the modification of images on the screen 22 as will be described in greater detail below. More generally, during the operation of the X-ray device 10, the radiation source 12 emits radiation of a certain level or energy levels along the radiation axis 24 at defined locations along the scan. The radiation passes through the vertebra 20 being scanned and is then received by the detector 13. The analog output of the detector 13 is sampled and digitized to produce a signal consisting of discrete data elements, each associated with a location through the patient, through the DAS. The DAS can transmit the digitized signal to the computer 18 which stores the data in the computer memory (not shown) or in a mass storage device. When the fan beam is poly-energetic, discrimination between the high and low energy attenuation of the patient's X-rays can be made by the detector 13. Two sets of detector elements can be used, each selectively sensitive to high energies or to the low energies Therefore, during scanning the detector 13 produces data for high and low energy images. These two images can be aligned later and mathematically combined to produce the bone density information in accordance with mathematical algorithms known in the art. Referring now to Figs. 1 and 2, at the termination of the scanning of the patient 16 by the radiation source 12 and the detector 13 the computer 18 places the data elements obtained in the scan in a matrix 29 within the memory of the computer. Each data element 31 of the array is associated with a spatial location defined by the position of the C-shaped arm 14 when the data element 31 is acquired during scanning and indicated in the array by the position of the data element 31 in matrix. The spatial separation of the defined locations of the data elements 31 is determined by the distance that the instrument, for example the radiation source and the detector 1 3, moves between the acquisition rows of data elements 31 and by the separation of the detector elements in the detector 13. Each data element 31 has a relative value proportional to the amount of radiation transmitted by the tissue in the corresponding location. The absorption of radiation by a tissue correlates to certain physical properties of that tissue. For example, bone absorbs a greater amount of radiation than soft tissues. The data elements 31 thus obtained are referred to PBM for the pseudo-bone mineral content. The numbers are pseudo values since they are not calibrated and therefore have no dimension. Therefore, at this point in the analysis only the relative differences between the data elements 31 are significant, not their absolute values. While the calibration of each data item 31 could be done at this point, it consumes computer resources and therefore is deferred and the PBM values are used.

Densitometry Data Processing Referring now to Fig. 3, the data elements collected during the scan may be displayed as an image 200 where the spatial location of each data item 31 in the patient represents an image forming block 201 having a corresponding spatial location in image 200; and wherein the value of each data element is interpreted as a shadow of gray and / or a color of that image forming block 201. The data elements registering the highest attenuation of the X-ray radiation have given the most luminous gray values in the i 200 image so that the image 200 looks like a conventional X-ray radiograph with areas of bone, which have the highest attenuation, generally illustrated as white and areas of less attenuation such as soft tissue and air generally gloss as black. Typical image 200 will show spine 202 which determines the different vertebrae 20 surrounded by soft tissue 204 and portions of other body bones such as ileum 206 and clavicle 208. In some images 200, the beam of lightning fan X 23 will pass out of the patient's body and image 200 will include air areas 210. When using double energy, this initial image 200 can be created by combining the high and low data values of each location to produce an image effective polyenergética. With reference to Figs. 3 and 4, the values of the data elements will generally be dispersed through the scale of the attenuation values. Furthermore, within those data elements that measure only the bone or only the soft tissue will also vary on a scale of values. The precise computer analysis of that data requires that each data element and therefore each image forming block 201 in the image 200 be identified for its tissue type. This identification or "point typing" is required not only to properly calibrate the algorithms used in the use of double energy measurements (which require reference measurements of tissue types) but also to allow automated measurement of the vertebra by the computer. Referring now also to FIG. 5, a first point typing step is performed by examining the values of the data elements 21 of each image forming block 201 in the image 200 as indicated by the process block 400. In this point typing based on the value, each image forming block 201 of the image 200 is classified according to a plurality of attenuation scales that form the horizontal axis of an effective attenuation histogram 212. The vertical axis of the histogram 212 indicates the number of image forming blocks 201 of the image 200 that have a particular attenuation value. As shown in Fig. 4, typically the image forming blocks 201 will exhibit a bimodal distribution with a first mode of soft tissue 214 and a second mode of bone 216.

The histogram shown in Fig. 4 reflects the fact that there is a scale of image formation block values and in particular image formation block values that remain between modes 214 and 216. A threshold 218 having a value The particular attenuation must therefore be identified between those modes 214 and 216, for example, at the histogram lows 212 between the peaks or maxima of modes 214 and 216. This threshold 218 is used to assign category to each of the image forming blocks 201 of the image 200 either bone or soft tissue based on their value. In images 200 that include image forming blocks associated with data elements 31 that measure only air or that measure a metal implant, additional modes 211 and 213, respectively, will be present outside modes 214 and 216 and attenuations low and high respectively. Those modes 211 and 213 can be used to generate additional thresholds 217 that divide the air image forming blocks 211 of the soft tissue imaging blocks of mode 214 and the threshold 215 that divides the image formation blocks. of mode 213 artifact of the bone image formation blocks of mode 216. Referring to Fig. 2, each data element corresponding to the image forming blocks 201 of the image 200 can be compared to the thresholds 217, 218 and 215 to assign them to a point type 219 on the type 221 matrix in addition to its value. Therefore, the image forming blocks 201 having attenuation values greater than the threshold 218 (but below the threshold value 215) are assigned to the bone category "B", while the image forming blocks 201 having a value less than the threshold 218 (but greater than the threshold 217) are assigned to a tissue value "T". A limit 111 between the bone elements "B" and the tissue elements "T" can therefore be established for further analysis of the bone, by the process block 406 to be described, for the preparation of morphometric measurements of a particular vertebra as shown in FIG. discloses in U.S. Patents 5,228,068 and 5,291,537 assigned to the assignee of the present application. Frequently this point typing based on value is by itself insufficient. This is particularly true when it may be desirable to measure only a certain type of bone, as may be the case when measuring bone loss in individuals. For example, it is considered that the vertebral body of the vertebra, (the spinal center) that has a large portion of trabecular bone is a more sensitive indicator of bone loss than the harder and denser cortical bone found, for example, in the processes of the spine. For this reason, it may be desirable to exclude, as much as possible, the denser spinal processes that effectively dilute the measurement of change in bone density, which remains relatively constant even as trabecular bone is lost.

Value-based typing may also be insufficient due to measurement errors (from noise or quantification) and variations caused by the intervening tissue. For this reason, referring to process block 402 of Figs. 3 and 5, the point typing based on value is increased by a point typing based on model. In the knowledge of the typification of point on a model basis about the shape of a typical spinal vertebra is used to refine the point typing. Generally, point-by-model typing applies rules about the bone shape specific to the bone being investigated. For example, with spine 202, it is known that vertebrae 20 are generally aligned with one another along a slowly varying spinal axis and that their width is relatively constant. This "model" is used to adjust two limit lines 220 towards the left and right limits of spine 202 based on the point typing based on value previously executed in process block 400. Boundary lines 220 are adjusted to the use of well-known curve-fitting algorithms for bone image formation that provide the best fit for a curve described by a polynomial equation of given order points thus identified. Generally, the points to which the curve fits can be identified by examining the point typing of the type 221 matrix through the horizontal lines in the image 200 to identify the limit image formation blocks 201 in which the soft tissue "T" makes a bone "B". Selecting the low order curve, based on the knowledge of the anatomy of a general spine, allows spinal processes 302 that project laterally from the vertebrae in the AP projection to be excluded from the bone measurement. In this point typing based on model, the boundary line bone of 220 is given a neutral characterization which means that it is not classified as bone or soft tissue. A similar model fit can be used to accurately identify the intervertebral spaces 313. Here, the vertical paths through the type 221 matrix are taken and the lower and upper limits of the vertebrae 20 identified by the points in those that the bone characterization "B" makes the characterization of tissue "T" and vice versa. The low-order curves fit at those points and perpendicular to the lines of limit 220 precisely establish the intervertebral spaces 313 that if included in a calculation of bone density can deflect the density calculations. Although the intervertebral spaces are generally not empty of imaging blocks that have a bony classification, in part due to the projection of the posterior spinal processes through the intervertebral spaces, the curve fitting process can be adjusted to Ignore those bone inclusions to provide defined intervertebral limits.

Therefore, with point typing based on value 400 and dot typing based on model 402, a firmer characterization of each point is made within the bone or soft tissue categories. Referring now to Figs. 7 and 8, the information from the values of the data elements 31 and their locations can also be used to identify points of high bone density as it represents an overlap of the spinal processes on the vertebra image. As shown in Fig. 7, the vertebra 20 includes a generally cylindrical spinal center 300 which supports most of the body's load and which includes a high percentage of the trabecular bone. As noted earlier, trabecular bone has been determined to be a sensitive indicator of bone change in the early stages of osteoporosis. Ideally then, measurements of bone density of the spine would first measure the trabecular bone. Extending in the posterior direction from the spinal center 300 are transverse processes 302, the inferior and superior articular processes 303 and the spinal lamina 306. Hereinafter for simplicity, those posterior structures will be collectively designated processes of the spine 305. The bone of the processes of the spine 305 is of greater density than the spinal center 300 and includes little trabecular bone. Referring now to Fig. 8, in an AP 310 bone density image, dorsal spine processes 305 (not directly visible) form areas of higher density 312 superimposed on the image of spinal center 300. Those zones 312, when averaged in the reading of Mean vertebral bone density for vertebrae 20 deviates the average density upwards, probably obscuring the clinically significant loss in trabecular bone mass. For this reason, it is desirable to identify and eliminate those zones 312 from the measurement process. While it is possible to locate those zones 312 with respect to the marks on the vertebra 20 alone, as projected in the image 310, variations in the vertebra 20 makes it preferable that those zones be distinguished by the establishment of certain threshold levels. of bone density indicative of the areas 312. That is, if the density of a data element 31 of the image 310 is above the set threshold, it is assumed that this data element 31 measures, in a significant part, the bone of the bone. spinal processes 305. The particular density threshold, which defines zones 312, will vary depending on the patient. Accordingly, the threshold is determined by a reference density measurement made at an established position with respect to the vertebrae 20. This procedure is executed by the computer 18 which operates on the matrix 29 of the data elements 31 as described previously.

Momentarily referring to Fig. 3, the left and right spinal limit lines 220 are used to identify the approximate horizontal center of the intervertebral spaces 313. The upper and lower limits of adjacent vertebrae 20, previously detected, are used to determine a vertical center of the intervertebral space 31 3. Therefore, a vertical and horizontal vertebral center 314 is determined. A group of data elements 31 around this center 314 is averaged to determine a density value of the spinal processes 305 without the intervention of the spinal center. 300. This value will be used as a reference measurement to identify the zones 312. Each data item 31 within the vertebra 20 is then identified by the previously described typing and the identification of the limit lines 220. and the intervertebral spaces. These data elements 31 are analyzed to find the data element 31 which indicates the maximum bone density or peak value within the vertebra 20. The previously determined reference value is subtracted after the peak value to provide a density limit that identifies the zones 312. Now only the data elements 31 within the vertebra 20 which have density values below this limit are used in the calculation of the vertebral average bone density for the vertebrae 20 thus effectively excluding the areas 312 from the analysis of vertebral average bone density. The data elements 31 having higher values are considered to be deflected upward by spine processes 305 and ignored. The vertebral average bone density is therefore the sum of the data elements 31 within the vertebrae 20 excluding the zones 312 divided by the area encompassed by those included data elements 31. This density is an area density, for example, grams per cm2. Referring again to FIG. 5, the point typing based on value 400 and the point typing based on model 402 are desirably increased by means of the operator point typing 404 in which the operator changes in a manner interactive the categories of certain blocks of image formation 201. This operator typification ensures superior knowledge of an operator trained in the identification of a bone and soft tissue in the context of an image similar to radiography of bone and soft tissue. The typing of the operator's point also allows the use of the system to form the image and make the measurement of bones for which the model incorporates general knowledge about the bone anatomy that has not been developed. This can occur for other bones in the body or for individuals whose bones do not conform to the generalized rules stored within the equipment. Such flexibility may also be desired if the equipment is used in animal studies.

It is important for the typification of the operator to provide an adequate interface between the operator and the computer to facilitate the re-characterization of the operator of the particular training blocks. Such an interface should, to the extent possible, prevent inadvertent change of the data elements by the operator. The present invention obtains those objectives by adopting a "brush" interface in which the operator maneuvers a brush cursor on the image to change the point typing of the selected data elements. Referring now to Fig. 6, the image 200 is displayed to the operator on the screen 22 together with a menu screen 222 having a brush type menu 224 and a brush size menu 226. Such menu systems are well known in the computer art and graphically provides input to the operator's parameters. In particular, the brush type menu 224 offers five different brushes: bone, fabric, air, artifact and neutral. When a particular type of brush is selected, the material of the selected brush type is enhanced in the image 200 with a blue color in accordance with the current point typing. Therefore, when the bone is selected as indicated in Fig. 6, those image forming blocks 201 previously identified by the point typing of processes 400 and 402 will be highlighted in blue. All materials, including bone, also take a gray scale value based on the values of their data elements 31 as described. Therefore, all the scan data is available to the operator in the elaboration of point type determinations. If the type of tissue brush is selected, the fabric the tissue image forming blocks 201 will be highlighted in blue and the bone tissue will be reverted only to gray, black and white. The categories of air and artifact of the present example would not enhance any tissue since the image forming blocks 201 have not been characterized either as air or artifacts. The neutral characterization will enhance the portions of the ileum 206, the clavicle 208 and the processes 302 previously excluded by the point typing on the basis of value and based on the model of the process blocks 400 and 402. The image forming blocks 201 are selected by the operator by use of a "brush" cursor 228 where the position can be controlled by the "mouse" 25 as previously described with respect to Fig. 1 or other well-known cursor control devices. As the "mouse" 25 moves, the image of the cursor 228 moves in the image 200 providing an interactive real-time control of the point typing of the points by the operator. After the operator moves the cursor 228 to a particular point on the image 200, the "mouse" button 26 can be depressed causing those data elements corresponding to the region of the image 200 covered by the cursor 228 to be changed to the characterization indicated by the brush type menu 224. Preferably, the "mouse" is used dynamically in the manner of a brush with the button 26 being continuously depressed where the swept area of the cursor 228 as it moves over the image 200 in a path defines those image forming blocks 201 changed to a new classification. For example, if the type of bone brush is being used, the image forming blocks 201 selected by the operator will be changed in the bone classification. The brush size can be changed from an example, that is, an image forming block of the image through square shapes up to 9 x 9 samples or image forming blocks 201. Therefore, for the rapid removal of the foreign bone within the neutral classification, a large brush can be used, considering that a small pi ncel can be used for correction of individual point classifications, for example, between the intervertebral spaces. For bone density measurements, this adjustment of the classification operator can significantly increase the clinical value of the measurement with minimal risk of affecting its ability to reproduce. Although the exchange image formation blocks 201 classified as bone in, for example, neutral has the effect of eliminating those image forming blocks 201 from the calculation of the bone density, those image forming blocks are also eliminated. from the divisor used in the density calculation. Therefore, for a homogenous bone re-characterization of some of its image forming blocks 201 as neutral, for example, it will not affect the overall density measurement. On the other hand, the use of the cursor 228 to remove the denser regions of the spinal processes 302 even at the cost of removing some bone that is substantially trabecular can only substantially increase the sensitivity of the density measurement in the detection of loss of bone mass. Referring again to Fig. 5, once the point typing is complete the total bone content for the bone image formation blocks identified for a vertebra 20 can be determined by process block 406 and printed on screen 22. The total bone content is bone density calculated vertebral average (converted to a data item value 31) plus the total number of data items 31 within the vertebrae regardless of whether they are in zones 312 or not the combination of the intervertebral boundaries and the left border lines and right 220 can be used to precisely define a vertebral region that is used to calculate the bone density for that particular vertebra 20. In addition, bone density measurements can be made in particular regions for complete vertebrae or collections of vertebrae within the supine 202 Before these density measurements, point typing can be used to calibrate an algorithm of double energy based on a soft tissue reading to remove the effects of intervening soft tissue superimposed on the bones of interest. It is therefore contemplated that the present invention is subject to many modifications that will become apparent to those skilled in the art. Accordingly, it is intended that the present invention is not limited to the particular embodiment illustrated herein, but encompasses all modified forms thereof as they fall within the scope of the following claims.

Claims (20)

1. A method of measuring a physical characteristic of the vertebrae of a spine, the vertebrae including spinal centers of trabecular bone with denser spinal processes that extend backwards, the method comprising the steps: (a) exploring the vertebrae with a beam radiation (23) directed in the anterior-posterior direction to acquire a matrix of discrete data elements each having a value and a location defined through said vertebra and, where the value of each data element is related to a physical characteristic of the material of the vertebra in the defined location; (b) employ a digital computer (18) to: (1) review the values of the data elements and their defined locations to identify individual vertebrae; (2) identify zones of data elements within the individual vertebra where the data elements measure the radiation substantially attenuated by the bone of the spinal center and the processes of the spine; (3) exclude the zones identified in step (b) (2) from the calculation of the physical characteristic of the material in the vertebra; and (c) exhibit the measurement of the physical characteristic determined in step (3).

2. The method of claim 1, wherein the physical characteristic is bone density.

3. The method of claim 1, wherein the physical characteristic is the bone content.

The method of claim 1, wherein step (2) comprises: (i) using the locations of the vertebra identified in step (b) (1) to locate an intervertebral space adjacent to the vertebra; (ii) identify data elements in the intervertebral space that measures radiation attenuated only substantially by the spinal process and not by the spinal center to produce a reference measurement; (iii) use the reference measurement to identify the data elements within the vertebrae that have significant attenuation by spinal processes; and (iv) identify the zones by means of data elements identified in stage (iii).

The method of claim 4, wherein step (iii) further comprises: subtracting the value of the reference measurement from a peak value of the data elements in the vertebrae to establish a limit; and identify all data elements within the vertebrae that have a value greater than the limit since the data elements within the vertebrae have significant attenuation through the spinal processes.

The method of claim 1, wherein the radiation is double energy X-ray radiation and the values of the discrete data element matrix are double energy measurements of the bone density.

The method of claim 1, wherein the displayed measurement of bone density is expressed as a bone mass by an identified vertebra.

8. A method of measuring a physical characteristic of a spine in a body, the vertebrae separated by intervertebral spaces to form a spinal column, the method comprising the steps of: (a) scanning the body with a beam of radiation (23) ) directed in the anterior-posterior direction to acquire a matrix of discrete data elements each having a value where each data element corresponds to a defined location in the body and, where the value of each data element is related to a physical characteristic of the material through which the radiation beam passes; (b) employing a digital computer (18) to: (1) classify the data elements based on their values within the bone data elements that measure the physical characteristic of the vertebrae; (2) review the bone data elements and their defined locations to identify the spine and intervertebral spaces; (3) determine a bone integrity based on value on the values of the data elements within the vertebral column excluding the intervertebral spaces; and (c) exhibit the bone integrity value determined in the step (3).

The method of claim 8, wherein the physical characteristic is bone density.

The method of claim 8, wherein the physical characteristic is the total bone content.

The method of claim 8, wherein step b (2) comprises: (i) using the locations of bone data elements identified in step (b) (1) to locate a right and left spinal boundary; (ii) analyze the locations and values of the bone data elements within the left and right spinal boundaries to locate the intervertebral spaces.

The method of claim 8, wherein the radiation is double energy X-ray radiation and values of the discrete data element matrix are double energy measurements of bone density.

13. A densitometer (10) comprising: (a) a source of opposite radiation (12) and a detector (13); (b) a setter (149) supporting the radiation source (12) and the detector (13) and adapted to scan vertebrae with a radiation beam (23) directed in the anterior-posterior direction to acquire a matrix of blocks of discrete image formation each having a value and a defined location through said vertebra and, where the value of each image formation block is related to the density of the material of the vertebra in the defined location; digital computer (18) having a display screen (22) and a cursor controller (25) that provides a select signal and cursor coordinates in response to operator commands, the digital computer (18) that receives a matrix of discrete data elements and that is adapted to: (1) review the values of the image formation blocks and their defined locations to identify the individual vertebra; (2) distinguish categories of training blocks Imaging within the individual vertebra where the imaging blocks measure the radiation substantially attenuated by the bone of the spinal center and the spinal processes; (3) exclude the categories identified in step (c) (2) from a calculation of the density of the material of the vertebra; and (4) displaying, in the form of an image, the measure of the density determined in step (c) (3).

The densitometer (10) of claim 13, wherein the stored program distinguishes the image forming blocks of at least one category in the image by color.

The densitometer (10) of claim 13, wherein at least three categories of blocks of imaging correspond to the physical characteristics selected from the group of: bone, soft tissue, air, artifact and neutral materials.

The densitometer (10) of claim 13, wherein the cursor controller (25) additionally provides a cursor format signal in response to the operator commands that controls the size of the cursor symbol with respect to the blocks of Image formation of the image.

The densitometer (10) of claim 13, wherein step (c) (4) includes the steps of: (i) summing the values of all the image forming blocks into an image forming block category bone after step (c) (3) to produce a total bone content value; (ii) dividing the total bone content value by the number of image formation blocks in the bone image formation block category after step (c) (3).

The densitometer (10) of claim 13, wherein the cursor controller (25) further provides a category signal in response to the operator commands that controls the category within which the indicated image formation blocks are they change when the selected signal is received.

19. An in vivo bone analysis method comprising the steps of: (a) scanning the body with a beam of radiation to acquire a matrix of discrete data elements each having a value where each data element corresponds to a defined location in the body, and where the value of each data item is related to a physical characteristic of the material through which the radiation beam passes; (b) employ a digital computer (18) to: (1) classify the data elements based on their values within bone data categories that indicate the physical characteristic of the vertebrae; (2) review the classified bone data elements and their defined locations to classify the classified data elements into categories of bone data that indicate the physical characteristic of the vertebrae; (3) recategorize the data elements in the bone data categories that indicate the physical characteristic of the vertebra based on the operator review of a screen of the reclassification of stage (2) and a screen of the data elements which indicate their defined values and locations.

20. The method of claim 19, wherein the value of each data element is displayed in step (3) in the form of a brightness of a displayed point in a displayed location corresponding to the defined location of the data element and in where the classification of a data element in step (2) is indicated by a color of the displayed point.