Effect of region of interest location on ultrasound measurements of the calcaneus.

Ultrasound (US) measurements of the calcaneus are usually carried out in a region of interest (ROI) at a fixed site relative to a footplate. Recently, US transmission systems have been developed with imaging capability that enable selection of the position of ROI; the region of measurement is always the area of minimum attenuation in the posterior part of the calcaneus. This study compares measurements of broadband ultrasound attenuation (BUA) and speed of sound (SOS) at the variable ROI of minimum attenuation (ROIv) and at fixed coordinates (ROIf). Ultrasound variables were estimated at ROIv and ROIf in 212 female subjects, including 26 patients with osteoporotic fractures. Among the 186 women without fractures, 63 were classified as having osteoporosis on the basis of their vertebral bone density. Precision of BUA and SOS were better at ROIv than at ROIf. BUA was more highly correlated with bone mineral density (BMD) at the lumbar spine and femoral neck at ROIv than ROIf (r = 0.64 for lumbar spine and 0.68 for femoral neck at ROIv versus 0.50 for lumbar spine and 0.54 for femoral neck at ROIf, P < 0.05 for both comparisons). There were no significant differences between the correlations of SOS with axial BMD at ROIv compared with ROIf. Significant difference was found between the areas under the ROC curve for each ultrasound variable at ROIv and ROIf for both groups of patients, subjects with osteoporosis (area under curve = 0.87 for BUA at ROIv versus 0.82 at ROIf, P < 0.05; area under curve = 0.85 for SOS at ROIv versus 0.81 at ROIf, P < 0. 05), and women with fractures (area under curve = 0.93 for BUA at ROIv versus 0.86 at ROIf, P < 0.05; area under curve = 0.91 for SOS at ROIv versus 0.82 at ROIf, P < 0.05). Ultrasound variables measured at ROIv enable improved reproducibility and significantly better differentiation of diseased subjects from healthy individuals as compared with measurements at ROIf.

I-123 metaiodobenzylguanidine--thallium-201 mismatch following myocardial infarction.

Experimental data show that myocardial infarction (MI) results in regional depletion of myocardial catecholamines more extensively than necrosis. To investigate the extent of adrenergic denervation post MI in humans, we examined 16 patients, 59 +/- 12 years old, with recent (7-12 days) MI. Resting thallium-201 (201Tl) single photon emission computerized tomography (SPECT) imaging was performed to assess necrosis; metaiodobenzylguanidine I123 (MIBG) SPECT was used to evaluate adrenergic denervation. 201Tl and I123 MIBG defects were evaluated quantitatively using polar maps, and differences in defects were expressed as percent of total polar map. In all patients, I123 MIBG defect was larger than 201Tl defect, and difference ranged from 19 to 61% (39.5 +/- 13.2%). Thrombolysis and age > 60 did not influence the difference. Anterior MI showed larger differences (44 +/- 13 vs. 32 +/- 11%, p < 0.05); patients with ischemic electrocardiographic (ECG) changes in leads without abnormal Q waves had larger differences (45 +/- 9 vs. 33 +/- 14%, p < 0.05). It was concluded that (a) patients with recent MI present denervation larger than 201Tl perfusion defect, and (b) patients with anterior MI and ischemic ECG changes present a larger area of denervation.

The effect of hydration on the dose to the urinary bladder wall during technetium-99m diethylene triamine penta-acetic acid renography.

A spherical bladder dynamic model for the estimates of the radiation dose to the bladder walls from intravenously injected radionuclides was implemented to investigate in theory the effect of hydration on the reduction of the bladder dose in technetium-99m diethylene triamine penta-acetic acid (99mTc) DTPA renography. This model gives due consideration to the variation with time of the urine flow rate to the bladder, following a known fluid load. According to the model, the estimated dose depends on the renal function, the fluid load, the time elapsed from the fluid load to the i.v. DTPA injection, the micturition volume and the residual urine volume. Experimental data concerning the values of these parameters for normal individuals were obtained from the literature. Calculations cover the time period from i.v. injection up to the time of the ninth postinjection void. Results show that the patient's condition of hydration is critical for the radiation protection of the bladder. It is shown that optimum combinations of the values of the parameters involved in the calculations exist, which minimize the radiation dose. On the basis of these results, a general protocol is proposed, referring to the hydration conditions under which the renal dynamic study may be normally carried out, with a minimal absorbed dose to the bladder walls (less than 0.045 mGy/MBq).