Detectability of foci of radioiodine uptake in the thyroid bed and neck comparing pinhole with parallel-hole collimators

ObjectivesThe objective of this study was to evaluate the detection of the foci of radioiodine (RAI) uptake in the thyroid bed and neck of patients with well-differentiated thyroid cancer using a pinhole collimator (PiHC) compared with either whole-body images (WBIs) or individual images obtained using a parallel-hole collimator (PaHC). MethodsA retrospective review was conducted of all RAI scans done at the Washington Hospital Center between June 2000 and December 2006 on patients who had (i) well-differentiated thyroid cancer, (ii) an RAI scan of the thyroid bed and neck before their first RAI ablation or treatment, (iii) individual spot images of the neck (II) taken using both PiHC and PaHC as part of this pretreatment scan, and (iv) WBIs taken using a PaHC. To test for significant differences between the numbers of foci detected by different methods, two sample t-tests for paired groups were used. ResultsOf the 325 patients meeting the above criteria, the mean age was 46 years (range=15–83 years). The mean (range) number of foci identified on WBIs, IIs-PaHC, and IIs-PiHC images was 2.14 (0–8), 2.82 (0–11), and 3.32 (0–14), respectively. The total number of foci detected on WBIs, IIs-PaHC, and IIs-PiHC images was 694, 916, and 1079, respectively. The means (ranges; P values) of the differences in the number foci detected with II-PiHC versus II-PaHC and II-PiHC versus WBI-PaHC were 0.502 (−3 to 6; P<0.001) and 1.185 (−2 to 8; P<0.001), respectively. II-PiHCs showed additional foci of uptake relative to II-PaHCs and WBI-PaHCs in 10% (32) and 33% (108) of patients, respectively. ConclusionII-PiHC showed more foci of RAI uptake in the thyroid bed and neck than either II-PaHC or WBI-PaHC. Pinhole imaging offers the potential to better identify cervical metastases, possibly modify the empiric prescribed activity of RAI, and/or provide a better baseline for future comparison.