Abstract: A projectional densitometry system performs a scan of an individual's left and right femora by using the location of one femur to estimate a starting location for scanning the opposite femur. The estimated starting location of the second femur scan is based on metric data inputted by the operator or extracted from the first femur scan. Alternatively, the densitometry system performs an initial bone-locating scan of both femora, after which it performs a second, density-measuring scan based on the metric data extracted from the initial scan. A special leg positioning device is used to properly orient both femora for scanning, obviating the need to reposition the individual after scanning the first femur.

Abstract: A method of evaluating bone density around a radiolucent composite prosthesis establishes an implant boundary by fitting a stored template to radio-opaque reference markers embedded in the prosthesis. The implant boundary is used to create a measurement boundary displaced from the implant boundary toward the bone producing a conformal region of interest. Matched histograms of bone density in a lateral and medial such region of interest may be displayed to evaluate symmetrical stress effects. Alternatively, bone density may be displayed plotted along an axis cutting across the medial and lateral sides. Fiducial points are identified from the bone and implant morphology to ensure that either display will have a repeatable reference and hence that such displays will be directly comparable to later and earlier displays thereby aiding in the detection of bone change.

Abstract: A method of evaluating bone density around a prosthesis establishes an implant boundary at the edge of the prosthesis and creates a measurement boundary displaced from this implant boundary toward the bone producing a conformed region of interest. Matched histograms of bone density in a lateral and medial such region of interest may be displayed to evaluate symmetrical stress effects. Alternatively, bone density may be displayed plotted along an axis cutting across the medial and lateral sides. Fiducial points are identified from the bone and implant morphology to ensure that either display will have a repeatable reference and hence that such displays will be directly comparable to later and earlier displays thereby aiding in the detection of bone change.

Abstract: A desitometer gantry may translate in two directions for scanning and may swivel about a vertical axis to allow the radiation angle and the detector-to-patient distance to be altered during a scan so as to provide constant magnification of the image and to align the patient's spine with the radiation beam for more accurate edge measurements. A method of reducing the effects of osteophytes on density measurements applies an iterative threshold based on the density difference between hard and soft tissue.

Abstract: A cylindrical, multiple-anode proportional counter is provided for counting of low-energy photons (<60 keV) at count rates of greater than 10.sup.5 counts/sec. A gas-filled proportional counter cylinder forming an outer cathode is provided with a central coaxially disposed inner cathode and a plurality of anode wires disposed in a cylindrical array in coaxial alignment with and between the inner and outer cathodes to form a virtual cylindrical anode coaxial with the inner and outer cathodes. The virtual cylindrical anode configuration improves the electron drift velocity by providing a more uniform field strength throughout the counter gas volume, thus decreasing the electron collection time following the detection of an ionizing event. This avoids pulse pile-up and coincidence losses at these high count rates. Conventional RC position encoding detection circuitry may be employed to extract the spatial information from the counter anodes.