Parathyroid Imaging: The Importance of Dual-Radiopharmaceutical Simultaneous Acquisition with Tc-99m-Sestamibi and I-123

Our objective was to compare the accuracy of 3 imaging protocols for the detection of parathyroid adenomas: single-tracer, dual-phase imaging with Tc-99m-sestamibi; dual-tracer, single-phase imaging with simultaneous acquisition of Tc-99m-sestamibi and I-123 images; and dual-tracer, dual-phase imaging with simultaneous acquisition of Tc-99m-sestamibi and I-123 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 Tc-99m-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 I-123 followed 2 h later by Tc-99m-sestamibi. Fifteen minutes later, anterior and anterior oblique pinhole images of the Tc-99m-sestamibi and I-123 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 Tc-99m-sestamibi and I-123 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 Tc-99m-sestamibi alone at 15 min and 3 h. The addition of delayed imaging to the dual-tracer protocol did not improve results.