A major technical advantage of using I-123 for a subtraction technique is that thyroid and parathyroid images can be acquired simultaneously in a dual-energy window. Reported sensitivity for dual-tracer sestamibi and I-123 subtraction scintigraphy ranges from 75% to 94% [54,74- 76], including a retrospective review of 2,681 patients revealing a sensitivity of 87% and PPV of 92% [77]. The latter study showed that negative or inconclusive results had a higher association with MGD and lower serum calcium levels. There is no clear consensus regarding the superiority between dual-tracer subtraction and sestamibi dual-phase planar imaging. One recent study of 63 patients showed greater sensitivity with dual-phase sestamibi (79%) over both dual-tracer (sestamibi and pertechnetate) (69%) and a combined dual-tracer/dual-phase (65%) technique [59]. However, other studies report similar or improved sensitivity of dual-tracer methods (either pertechnetate or I-123, plus sestamibi) over dual-phase sestamibi when utilizing a planar technique [45,54,64,65]. Sestamibi Scan and I-123 Thyroid Scan with SPECT or SPECT/CT Neck Although there are a number of variations in the timing of the SPECT or SPECT/CT acquisition (ie, early, delayed, or both), it is generally accepted that the improved contrast resolution of SPECT or SPECT/CT over planar imaging provides more precise anatomic localization of parathyroid adenomas [68,69]. However, there are conflicting data in the literature as to what extent the addition of SPECT or SPECT/CT changes the sensitivity of the examination. For example, Bhatt et al [74] evaluated a pinhole protocol, SPECT/CT alone, and a combination of Parathyroid Adenoma pinhole/SPECT/CT, revealing sensitivities of 88%, 69%, and 81%, respectively. Other studies have shown superior performance of the combined sestamibi/I-123 plus SPECT/CT protocol with sensitivities ranging from 86% to 95% and PPV from 86% to 100% [45,75,78,79].
Parathyroid Adenoma. A major technical advantage of using I-123 for a subtraction technique is that thyroid and parathyroid images can be acquired simultaneously in a dual-energy window. Reported sensitivity for dual-tracer sestamibi and I-123 subtraction scintigraphy ranges from 75% to 94% [54,74- 76], including a retrospective review of 2,681 patients revealing a sensitivity of 87% and PPV of 92% [77]. The latter study showed that negative or inconclusive results had a higher association with MGD and lower serum calcium levels. There is no clear consensus regarding the superiority between dual-tracer subtraction and sestamibi dual-phase planar imaging. One recent study of 63 patients showed greater sensitivity with dual-phase sestamibi (79%) over both dual-tracer (sestamibi and pertechnetate) (69%) and a combined dual-tracer/dual-phase (65%) technique [59]. However, other studies report similar or improved sensitivity of dual-tracer methods (either pertechnetate or I-123, plus sestamibi) over dual-phase sestamibi when utilizing a planar technique [45,54,64,65]. Sestamibi Scan and I-123 Thyroid Scan with SPECT or SPECT/CT Neck Although there are a number of variations in the timing of the SPECT or SPECT/CT acquisition (ie, early, delayed, or both), it is generally accepted that the improved contrast resolution of SPECT or SPECT/CT over planar imaging provides more precise anatomic localization of parathyroid adenomas [68,69]. However, there are conflicting data in the literature as to what extent the addition of SPECT or SPECT/CT changes the sensitivity of the examination. For example, Bhatt et al [74] evaluated a pinhole protocol, SPECT/CT alone, and a combination of Parathyroid Adenoma pinhole/SPECT/CT, revealing sensitivities of 88%, 69%, and 81%, respectively. Other studies have shown superior performance of the combined sestamibi/I-123 plus SPECT/CT protocol with sensitivities ranging from 86% to 95% and PPV from 86% to 100% [45,75,78,79].