Quantitative analysis of technetium-99m-sestamibi uptake and washout in parathyroid scintigraphy supports dual mechanisms of lesion conspicuity.

PURPOSE: Proposed mechanisms of parathyroid localization in 'dual-phase' technetium-99m-sestamibi imaging include increased presence of mitochondria leading to greater uptake and slower washout compared with thyroid tissues owing to reduced expression of P-glycoprotein. Using new techniques of quantitative single-photon emission computed tomography (SPECT)/computed tomography (CT), we have measured MIBI uptake and washout to better understand factors related to conspicuity. PATIENTS AND METHODS: We retrospectively reviewed 125 consecutive patients. Early and delayed SPECT/CT images were reconstructed using a previously validated technique. Maximum standardized uptake values of parathyroid adenomas and thyroid tissue were measured, and corresponding washout rates were calculated. RESULTS: Of 53 patients with localization of parathyroid adenoma (42%), median maximum standardized uptake values were higher for parathyroid adenomas than for thyroid tissue on both early (6.43±3.78 vs. 4.43±1.93, P<0.001) and delayed (3.40±3.09 vs. 1.84±1.05, P<0.001) images, being true on a per-patient basis in 41 (77%) and 48 (91%) patients, respectively. Median washout rates were slower from parathyroid adenomas than from thyroid lobes (0.26±0.16 vs. 0.42±0.18 h, P<0.001), being true on a per-patient basis in 43 (81%) patients. Similar findings were observed in a subgroup of 37 patients with surgically-confirmed adenomas. Of the patients where initial parathyroid uptake did not exceed thyroid uptake, all 12 exhibited slower MIBI washout from the parathyroid adenomas than from the thyroid gland. The characteristics of the thyroid gland did not differ in 67 patients without parathyroid localization. CONCLUSION: Quantitative analysis of 53 patients with localization of parathyroid adenoma revealed both a generally higher initial absolute uptake and slower rate of washout of MIBI in parathyroid adenomas than in thyroid tissue. The findings may support the hypothesis that both mechanisms proposed for parathyroid conspicuity in the dual-phase examination increased mitochondrial binding and slower washout owing to reduced P-glycoprotein expression. The technique of quantitative SPECT/CT represents a powerful tool for measuring tissue uptake to elucidate the contribution of these factors to lesion conspicuity.

Dual time-point quantitative SPECT-CT parathyroid imaging using a single computed tomography: feasibility and operator variability.

OBJECTIVES: Dual-phase parathyroid scan with Tc-sestamibi is a standardized imaging method for diagnosing parathyroid adenoma and hyperplasia. Conventional planar images using a gamma camera are performed routinely in early and delayed time points, followed by a single SPECT-CT. SPECT-CT on both early and delayed time points, although clinically useful, is not commonly performed to avoid extra radiation exposure from computed tomography (CT). This study explores the feasibility of co-registering early and delayed SPECT-CT from a single CT and evaluates the most effective combination of images for co-registration. PATIENTS AND METHODS: Fourteen retrospective patients with early and delayed planar and SPECT-CT images were recruited for this validation study. Results from contemporaneous early and delayed SPECT-CT, with hardware matched registration, are considered the gold standard. Noncontemporaneous early SPECT with delayed CT and vice versa were also processed with manual alignment by an experienced and a novice operator three times each to evaluate interoperator and intraoperator variability. Maximum standardized uptake values (SUVmax) of the thyroid lobes and parathyroid adenomas were measured, and the results in terms of accuracy and precision from noncontemporaneous SPECT-CT acquisitions were evaluated. RESULTS: Good image quality from co-registered SPECT-CT acquired at different time points with the results showed no bias (P>0.5). The co-registration of early SPECT and delayed CT showed higher precision than the alternative combination. Overall, the experienced operator achieved better precision and intraoperator variability than the novice operator (reproducibility coefficient=33% SUV vs. reproducibility coefficient=54% SUV, P<0.001). CONCLUSION: Quantitative SUV measurement from early and delayed parathyroid SPECT-CT imaging is feasible, with the best result achieved by experienced operators using delayed CT in manual registration.