A study of the homogeneity of the trabecular bone mineral density in the calcaneus.

In the past our laboratory has reported a method of measuring trabecular bone mineral density (TBMD) in the calcaneus in vivo by using the coherent-to-Compton scattering ratio. In the present work the distribution of TBMD in the calcaneus has been studied, and the reproducibility of this technique in vivo has been determined. It is found that although the TBMD may vary within the calcaneus, a region exists over which the variation in density is not large. This region coincides with the midportion of the heel and is the site chosen for the measurement of TBMD by the coherent-to-Compton scattering ratio technique. The reproducibility of this technique in vivo has been determined to be 3.4%.

Trabecular bone mineral density measurement in vivo: use of the ratio of coherent to Compton-scattered photons in the calcaneus.

Trabecular bone mineral density (TBMD) was measured in vivo in the calcaneus by a new method that uses the ratio of coherent to Compton-scattered photons arising from irradiation of a small volume of trabecular bone by a gamma ray source with highly collimated geometry. TBMD values for healthy men (22-77 years) were in the range of 180-357 mg/ml, and values for healthy women (18-73 years) were in the range of 160-321 mg/ml. In contrast, values in a small group of paraplegics were in the range of 90-199 mg/ml.

Quantitative assessment of bone mineral by photon scattering: accuracy and precision considerations.

A method to determine the bone mineral density of the calcaneum has been reported earlier by our laboratory. In this method, the calcaneum is irradiated by a 60-keV photon beam from 241Am source and both the coherent and Compton scattered photons are detected by a high-purity Ge detector. The bone mineral density is determined by measuring the ratio of coherent-to-Compton scattered photons. The accuracy and the precision (in vitro) of the method are reported in this paper. The accuracy was determined to be 5%. This was obtained by comparing the bone mineral density values of cadaver calcanea measured directly by Archimedes' volume displacement method with the values measured by the scattering method. The precision was determined to be 3% by measuring the bone mineral density of a calibration phantom intermittently over a ten-month period by the scattering method.

Quantitative assessment of bone mineral by photon scattering: calibration considerations.

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.

The effect of the momentum transfer on the sensitivity of a photon scattering method for the characterization of tissues.

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.

Characterization of tissue via coherent-to-Compton scattering ratio: sensitivity considerations.

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.

The measurement of trabecular bone mineral density using coherent and Compton scattered photons in vitro.

A photon scattering method for measuring the trabecular bone mineral density (TBMD) in vitro is described. This method involves the measurement of the ratio of coherent to Compton 90 degrees scattered photons from Am-241 by using a narrow beam geometry with an intrinsic germanium detector. The feasibility of using smaller scattering angles for better counting efficiency and the associated problems in their application for in-vivo measurements were investigated. Calibration of the system with fresh trabecular bone samples showed a linear relationship between the coherent to Compton ratio R of the detected counts and the TBMD (r = 0.94). The effect of the overlying soft tissue on the R ratio was significant while the effect of self-attenuation by the trabecular bone itself and the cortical layer was negligible. It was found that the marrow fat content could alter the value of the R ratio. Our results show that for a 10% increase in the fat content in the interstices of the trabecular bone there is a 2.5% decrease in the R ratio. This technique together with soft tissue corrections will enable us to measure the TBMD of the calcaneum in vivo, assuming a small variation in the trabecular fat content. The estimated absorbed dose to the bone marrow is about 139 mrad.

Measurement of the velocity of ultrasound in human cortical bone in vivo. Estimation of its potential value in the diagnosis of osteoporosis and metabolic bone disease.

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.

Accuracy of bone mineral data.

The reliability of data obtained from the Norland-Cameron Bone Mineral Analyzer has been questioned and the possibility of an inherent calibration error in the machine has been raised. To make an absolute measurement of the instrumental accuracy, bone mineral content measured by the bone mineral analyzer was compared with an absolute value obtained by the ashing method. The instrument bone mineral content values were found to be higher by about 6.5%. The ash content (%), bone mineral density, and compact bone density in these same bone samples were 62.9%, 1.346 g/cm3, and 2.140 g/cm3, respectively, as determined by direct measurement.

Measurement of the velocity of ultrasound in the human femur in vivo.

A pulse-echo technique for measuring the velocity of ultrasound in the cortex of the femur in vivo is presented. The average result for 27 asymptomatic volunteers is 3250 +/- 190 m/s. The results show no significant differences between proximal and distal femoral sites, right and left femora, males and females. There is also no significant difference between the velocity of sound in the femur and in the radius in normal volunteers. The reproducibility of the time of flight measurement for three volunteers is found to be about 2%, and the total uncertainty of the femoral velocity of ultrasound measurement is determined to be 4% for proximal sites and 7% for distal sites. As the femur is a load-bearing bone, the site of frequent fracture both in the elderly and in the osteoporotic, the measurement of the velocity of sound at this new site may be of great value in investigating these conditions and may ultimately be helpful in assessing "quality" of the femoral cortex in those patients undergoing total hip or knee replacement.

A problem in hemodialysis management: fibromuscular dysplasia of radial and ulnar arteries--report of a case.

Fibromuscular dysplasia (medial type) of the radial and ulna arteries, hitherto unreported, has been demonstrated angiographically following the malfunction of an arteriovenous shunt created for dialysis. Retrograde dilatation of the segmental stenoses caused some improvement in flow. No causal relationship is claimed between fibromuscular dysplasia and the arteriovenous shunt.

Experimental renal artery thromboembolism.

The natural history of experimental renal artery embolism with autogenous thrombus in 16 mongrel dogs has been investigated by sequential selective renal angiography and correlated with examination of the kidneys following autopsy. Angiography in the early (0-24 hr) post-thromboembolism period shows evidence of arterial obstruction and/or spasm which progressively disappears leaving no apparent permanent damage. However, within one or two weeks arterial and nephrographic changes and loss of renal size are discernible by careful comparison with the pre-embolism angiogram. At autopsy multiple disseminated microscopic infarcts involving the convoluted tubules were demonstrable in all cases. Occasionally large wedge-shaped infarcts involving the full thickness of the cortex were superadded. The potential importance of these findings relating to angiographic technique and assessment of treatment of renal thromboembolism is discussed.

Long-term radiographic changes of the kidney following the ileal ureter operation.

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 natural history of the upper renal tracts in adults following ureteroileal diversion (Bricker procedure).

The natural history of the upper tracts (170 renal units) of 87 patients undergoing total cystectomy and ileal loop diversion has been followed roentgenologically for up to seven years. The complications inherent in the procedure are illustrated and the appearances of new upper tract tumors demonstrated. Of 126 renal units which was obstruction of the anastomosis, seen in 29 units. The need for regular contrast material examination of the surgically modified upper tracts is emphasized.

The modulus of elasticity of human cortical bone: an in vivo measurement and its clinical implications.

The modulus of elasticity was derived by combining the velocity of ultrasound measurements and photon absorption (Norland-Cameron method) in human cortical bone (proximal radius) in vivo. The results compare favorably with published values of the elasticity modulus obtained in vitro. Values obtained for a heterogeneous group of patients with bone and joint complaints differed from those of normal volunteers.