It is known that the ratio (R) of the detected coherent and Compton scattered photons from bone can be used in order to determine its mineral density. This technique utilizes the dependence of the coherent scattering on the effective atomic number (Z) of the scattering medium. It is generally accepted that a small scatter angle is preferred in order to ensure adequate counting statistics by favoring the detection of more coherent photons. Moreover, it has been assumed that a change in the scatter angle does not affect the sensitivity of the measurement. Our theoretical calculations for 60-keV photons and for the range of Z that corresponds to trabecular bone, indicate that increasing the scatter angle results in a stronger power dependence of the measured ratio on Z. This implies that by increasing the scatter angle, smaller changes in the mineral density can be detected, thus improving the sensitivity of the measurement. This effect was investigated experimentally by using a collimated beam of 59.54-keV photons from Am-241 (44.4 GBq) and a collimated intrinsic germanium detector. Solutions of K2HPO4 with different concentrations were used in order to simulate trabecular bone. The scatter spectra were recorded for all solutions at six scatter angles between 37 degrees and 98 degrees and the value of R was computed for each spectrum. The sensitivity of the measurement, evaluated from these experiments increased, with the increase of the scatter angle.
Using a method combining the velocity of ultrasound and photon absorptiometry in the human radius in vivo, the authors measured the speed of sound in bone (U) and bone mineral content (BMC). From these measurements and a "simple" bone model, they then computed the bone mineral density, compact bone density, and modulus of elasticity. The accuracy of these parameters and of the bone model is assessed, and normal values for each parameter are given and compared with published values. The authors feel that a combination of U and BMC permits better discrimination between normal and abnormal in patients with osteoporosis or metabolic bone disease than either parameter alone.
A long-term retrospective evaluation was done on the preoperative and postoperative radiographic studies from patients who had undergone the ileal ureter operation. The comparative studies demonstrated decreased or stable pelviocaliceal dilatation, no measurable parenchymal loss, frequent high pressure vesico-ileac reflux and decreased number of renal calculi. Radiographically there was no evidence of renal morphological deterioration.
The ratio of coherent to Compton photon scattered by a tissue-like material depends on its effective atomic number. This ratio can, therefore, be used for the in vivo characterization of tissues. The intrinsic sensitivity of this measurement is defined as the change in the coherent-to-Compton ratio for a given change in the atomic number. The effect of the scatter angle on the sensitivity has already been described by us in a paper recently submitted to this journal. In this study, the dependence of the sensitivity on the energy of the incident photons is investigated in two ways. The first approach is quasitheoretical and is based on computations of the cross sections of the coherent and Compton scattering for various energies. The second approach is experimental and it involves the measurement of the scatter ratio from a series of K2HPO4 solutions for three primary photon energies: 60, 81, and 140 keV. The combined effect of both the photon energy and the scatter angle on the sensitivity can be described by a single parameter which is the momentum transfer. It is concluded that for the limited range of the atomic numbers which apply to trabecular bone (8 less than or equal to Z less than or equal to 11) the momentum transfer reflects completely the effect of the scatter angle and photon energy on the sensitivity.
The ratio of the coherent-to-Compton photons scattered from bone can be used to measure its mineral density. Conversion of this ratio (R) to bone mineral density (BMD) requires calibration using bone simulating phantoms. The widely used aqueous solution of K2HPO4 proved unsatisfactory for calibration purposes when using the coherent-to-Compton technique. These solutions differ markedly in their scatter spectra and composition from trabecular bone. In this study a new and more realistic series of phantoms is proposed which simulates well the trabecular bone of the calcaneum. These phantoms are made of bone ash suspended in white petrolatum in varying concentrations. A calibration curve has been established using these phantoms with a range of BMD values of 0 to 347 mg/cm3. The scatter spectra, and range of R values and BMD of these phantoms are in very good agreement with those of real trabecular bone. A measuring device has been built for the determination of the BMD of the calcaneum by using the established calibration curve.
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