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.

Residual pulmonary embolism as a predictor for recurrence after a first unprovoked episode: Results from the REVERSE cohort study.

BACKGROUND: The optimal duration of oral anticoagulant therapy after a first, unprovoked venous thromboembolism is controversial due to tightly balanced risks and benefits of indefinite anticoagulation. Risk stratification tools may assist in decision making. OBJECTIVES: We sought to determine the relationship between residual pulmonary embolism assessed by baseline ventilation-perfusion scan after completion of 5-7months of oral anticoagulant therapy and the risk of recurrent venous thromboembolism in patients with the first episode of unprovoked pulmonary embolism. METHODS: We conducted a multicentre prospective cohort study of participants with a first, unprovoked venous thromboembolism enrolled after the completion of 5-7months of oral anticoagulation therapy. The participants completed a mean 18-month follow-up. Participants with pulmonary embolism had baseline ventilation-perfusion scan before discontinuation of oral anticoagulant therapy and the percentage of vascular obstruction on baseline ventilation-perfusion scan was determined. During follow-up after discontinuation of oral anticoagulant therapy, all episodes of suspected recurrent venous thromboembolism were independently adjudicated with reference to baseline imaging. MEASUREMENTS AND MAIN RESULTS: During follow-up, 24 of 239 (10.0%) participants with an index event of isolated pulmonary embolism or pulmonary embolism associated with deep vein thrombosis and central assessment of percentage of vascular obstruction on baseline ventilation-perfusion scan had confirmed recurrent venous thromboembolism. As compared to participants with no residual pulmonary embolism on baseline ventilation-perfusion scan, the hazard ratio for recurrent venous thromboembolism was 2.0 (95% CI 0.5-7.3) for participants with percentage of vascular obstruction of 0.1%-4.9%, 2.1 (95% CI 0.5-7.8) for participants with percentage vascular obstruction of 5.0%-9.9% and 5.3 (95% CI 1.8-15.4) for participants with percentage vascular obstruction greater than or equal to 10%. CONCLUSIONS: Residual pulmonary embolism assessed by pulmonary vascular obstruction on baseline ventilation-perfusion performed after 5-7months of oral anticoagulant therapy for the first episode of unprovoked pulmonary embolism was associated with a statistically significant higher risk of subsequent recurrent venous thromboembolism. Percentage of pulmonary vascular obstruction assessment by ventilation-perfusion scans maybe a useful tool to help guide the duration of oral anticoagulant therapy after a first unprovoked pulmonary embolism. TRIAL REGISTRATION: Registered at www.clinicaltrials.gov identifier: NCT00261014.

The Role of Bone Scintigraphy with Single-photon Emission Computed Tomography-computed Tomography in the Diagnosis and Evaluation of Calciphylaxis.

Calciphylaxis, also known as calcific uremic arteriolopathy, is an uncommon disease, typically found in patients with the end-stage renal disease. Pathophysiological features include small vessel vasculopathy with mural calcification, fibrosis, and thrombosis. The clinical presentation varies but often consists of the necrosis of skin and subcutaneous tissues, with or without visceral organ involvement due to small vessel vasculopathy. This condition has a significant morbidity and mortality, making accurate diagnosis imperative. We present a case of calciphylaxis investigated using planar bone scintigraphy and single-photon emission computed tomography-computed tomography (SPECT-CT). This case stresses the value of SPECT-CT to accurately localize the abnormal uptake in subcutaneous soft tissue microcalcifications and confirms the exact location and extent of pathology.

Artifacts and Incidental Findings Encountered on Dual-Energy X-Ray Absorptiometry: Atlas and Analysis.

Bone mineral densitometry (BMD) using dual-energy x-ray absorptiometry (DEXA) has been widely adopted as the standard method of assessing bone density. Although not intended to be a primary imaging modality, the technique generates attenuation map images that are used to guide region-of-interest placement. Artifacts and incidental findings are frequently encountered on the DEXA images, some of which directly affect BMD values and others that are only of incidental importance to clinical practice. We systematically review a variety of artifacts and incidental findings that may be encountered on DEXA, illustrated by a collection of findings from our own practice. Being cognizant of these unexpected abnormalities, and understanding their etiology, will prepare the reader to more readily appreciate significance of these findings when seen in clinical practice.

Discordant response to chemotherapy between lymphadenopathy and bone lesions on gallium-67 scanning in Hodgkin's disease.

A 33-year-old woman with a diagnosis of Hodgkin's disease had a prechemotherapy whole-body Ga-67 scan to document gallium avidity of lesions and to assess response to therapy. A posttherapy scan showed a discordant response with complete resolution of lymphadenopathy and persistence of bone lesions. Radiographic evaluation of the left humerus, radius, and ulna demonstrated typical fibrous dysplasia as a cause for persistence of Ga-67 activity and shoulder activity probably representing arthropathy. She was in remission 3 years later although she fell and fractured the humerus through the bony lesion, and biopsy at the time of internal fixation confirmed fibrous dysplasia.