285 Non-invasive imaging biomarkers 3 lower [99mTc]pertechnetate or radioiodine uptake, benign nodules can be hot as well as cold, while far outnumbering carcinomas. [99mTc]Tc-MIBI uptake is independent of iodine trapping and organification in the thyrocytes. Increased [99mTc]Tc-MIBI uptake and late retention are often observed in malignant nodules [351]. A meta-analysis from 2013 by Treglia et al. showed 82% sensitivity and 63% specificity for [99mTc] Tc-MIBI scintigraphy in clinically suspicious, hypofunctioning, cytologically unselected thyroid nodules [293]. Three studies examined [99mTc]Tc-MIBI scintigraphy in cytologically indeterminate nodules (Bethesda III/IV/pre-Bethesda) [351, 443-447], based on an early image between 10 and 20 minutes post injection and a delayed image between 60 to 120 minutes post injection. The uptake in the nodule and retention on the delayed image were assessed and compared with physiological washout in normal thyroid tissue. Nodules with increased uptake on early images that persisted or increased on the delayed images were suspicious for malignancy. The sensitivities and specificities for visual interpretation ranged from 56% to 96% and from 20% to 95%, respectively. Semiquantitative analysis was performed using the retention index (RI, percentage MIBI uptake reduction in a nodule between the early and the late image, corrected for uptake in the contralateral lobe) and the wash-out index (WOInd, percentage MIBI uptake reduction in a nodule between the early and the late image, corrected for uptake in tissue outside the thyroid). At the cut-off determined, for the RI, the sensitivities were 100% and the specificities ranged from 57% to 90% [443, 446]. For the WOInd, sensitivities were 100% and specificities ranged from 89% to 100% [351, 446, 447]. A recent retrospective multicentre study by Schenke et al. including 365 hypofunctioning Bethesda III and IV nodules in 12 European centres concluded that negative [99mTc]Tc-MIBI result on visual evaluation is an effective tool to rule-out thyroid malignancy in 18% of negative nodules [447]. Semi-quantitative image analysis may considerably improve the overall diagnostic performance at an optimal WOInd cut-off of -19%, with a sensitivity, specificity, PPV, NPV, accuracy, and benign call rate of 100%, 89%, 82%, 100%, 93%, and 61% respectively. These findings cannot be extrapolated to all patients with indeterminate cytology, since preselection of intermediate- or high-risk nodules by EU-TI-RADS and the exclusion of hyperfunctioning nodules, probably by thyroid scintigraphy, is required. Planar gamma camera imaging is globally widely available. Also, the tracer [99mTc]Tc-MIBI can be easily complexed using MIBI-kits and an on-site molybdenum-technetium generator. The average costs of [99mTc]Tc-MIBI scintigraphy range from €119 to €500 in Europe and from $669 to $1156 in the United States [448]. A cost-effectiveness study from 2014 found that [99mTc]Tc-MIBI-based management was more cost-effective than Afirma® gene expression classifier testing from a German perspective [448], but modelled costs for [99mTc]Tc-MIBI scintigraphy and thyroid surgery were likely underestimated and performance parameters were extrapolated from unselected nodules. Disadvantages of [99mTc]Tc-MIBI scintigraphy include the limited spatial resolution of the gamma camera, which limits the test sensitivity in lesions smaller than 30 mm, and the radiation burden is 2 to 6 millisievert for an adult male (20-30% higher for females) [449].
RkJQdWJsaXNoZXIy MTk4NDMw