Parathyroid imaging: the importance of dual-radiopharmaceutical simultaneous acquisition with 99mTc-sestamibi and 123I.

UNLABELLED: Our objective was to compare the accuracy of 3 imaging protocols for the detection of parathyroid adenomas: single-tracer, dual-phase imaging with (99m)Tc-sestamibi; dual-tracer, single-phase imaging with simultaneous acquisition of (99m)Tc-sestamibi and (123)I images; and dual-tracer, dual-phase imaging with simultaneous acquisition of (99m)Tc-sestamibi and (123)I images. MATERIALS: Thirty-seven patients with surgical proof of parathyroid adenomas were evaluated. Three different protocols were derived from a single study in each patient, resulting in an intrapatient intrastudy comparison. The first derived protocol was the conventional dual-phase protocol with (99m)Tc-sestamibi consisting of anterior and anterior-oblique pinhole images of the neck at 15 min and 3 h plus parallel-hole images of the neck and upper chest at both imaging times. The second derived protocol was a dual-tracer, single-phase protocol consisting of administration of (123)I followed 2 h later by (99m)Tc-sestamibi. Fifteen minutes later, anterior and anterior oblique pinhole images of the (99m)Tc-sestamibi and (123)I were acquired simultaneously, allowing generation of perfectly coregistered subtraction images. Parallel-hole images of the neck and upper chest were also obtained. The third protocol was the same as the second except that the same imaging protocol was repeated at 3 h. Two experienced nuclear medicine physicians indicated the location of any identified lesion and graded the certainty of diagnosis on a 3-point scale. RESULTS: Thirty-seven patients had 41 parathyroid adenomas. For the 2 observers combined, the localization success rate was 66% for the single-tracer, dual-phase protocol; 94% for the dual-tracer, single-phase protocol; and 90% for the dual-phase, dual-tracer protocol. Both dual-tracer protocols were significantly more accurate than the single-tracer protocol (P < 0.01); there was no significant difference between the 2 dual-tracer protocols. In addition, the degree of certainty of localization was greater with the 2 dual-tracer protocols than the single-tracer protocol (P < 0.001). CONCLUSION: A dual-tracer, single-phase parathyroid imaging protocol consisting of simultaneous acquisition of (99m)Tc-sestamibi and (123)I images with pinhole collimation at 15 min and perfectly coregistered subtraction results in a higher degree of accuracy and a greater degree of diagnostic certainty than the commonly used single-tracer, dual-phase protocol of imaging (99m)Tc-sestamibi alone at 15 min and 3 h. The addition of delayed imaging to the dual-tracer protocol did not improve results.

Brown fat activity is not apparent in subjects with HIV lipodystrophy and increased resting energy expenditure.

The HIV lipodystrophy (LD) syndrome is associated with increased resting energy expenditure (REE), but the basis of this hypermetabolism has not been determined. The objective of this pilot study was to determine if brown fat is activated in subjects with HIV LD and increased REE. In this descriptive study of four subjects with HIV LD and marked hypermetabolism, REE was measured by indirect calorimetry and brown fat activity was determined by (18)F-fluorodeoxyglucose (FDG) positron-emission tomography (PET) combined with anatomic computed tomography (CT). Brown fat activity was not apparent in any subject with HIV LD and resting hypermetabolism. Therefore, brown fat activation is unlikely to be the principal cause of the increased REE associated with the HIV LD syndrome. Evidence of adaptive thermogenesis has been demonstrated in this syndrome, but this study suggests that tissues other than brown adipose tissue (BAT) are responsible. Further understanding of the chronic hypermetabolism associated with HIV LD could provide new insights into the regulation of energy balance.