Various methodologies for 99m Tc-sestamibi parathyroid scintigraphy are in clinical use. There are few direct comparisons between the different methods and even less evidence supporting the superiority of one over another. Some reports suggest that SPECT is superior to planar imaging. The addition of CT to SPECT may further improve parathyroid adenoma localization. The purpose of our investigation was to compare hybrid SPECT/CT, SPECT, and planar imaging and to determine whether dual-phase imaging is advantageous for the 3 methodologies. Methods: Scintigraphy was performed on 110 patients with primary hyperparathyroidism and no prior neck surgery. Of these, 98 had single adenomas and are the subject of this review. Planar imaging and SPECT/CT were performed at 15 min and 2 h after injection. Six image sets (early and delayed planar imaging, SPECT, and SPECT/CT) and combinations of the 2 image sets were reviewed for adenoma localization at 13 possible sites. Each review was scored for location and certainty of focus by 2 reviewer groups. Surgical location served as the standard. Sensitivity, specificity, area under the curve, positive predictive value, negative predictive value, and k-values were determined for each method. Results: The overall k-coefficient (certainty of adenoma focus) between reading groups was 0.68 (95% confidence interval, 0.66-0.70). The highest values were for dualphase studies that included SPECT/CT. Dual-phase planar imaging, SPECT, and SPECT/CT were statistically significantly superior to single-phase early or delayed imaging in sensitivity, area under the curve, and positive predictive value. Neither single-phase nor dual-phase SPECT was statistically superior to dual-phase planar imaging. Early-phase SPECT/CT in combination with any delayed imaging method was superior to dualphase planar imaging or SPECT for sensitivity, area under the curve, and positive predictive value. Conclusion: Early SPECT/ CT in combination with any delayed imaging method was statistically significantly superior to any single-or dual-phase planar or SPECT study for parathyroid adenoma localization. Localization with dual-phase acquisition was more accurate than with singlephase 99m Tc-sestamibi scintigraphy for planar imaging, SPECT, and SPECT/CT.

The accuracy of myocardial perfusion SPECT improves with attenuation correction. Algorithms for attenuation correction in hybrid SPECT/CT systems have the potential for misregistration of emission and transmission scans because CT and SPECT are obtained sequentially. Misregistration will influence regional tracer distribution and may reduce diagnostic accuracy. This study focused on the role of misregistration in cardiac SPECT/ CT and the performance of a software-based approach for reregistration. Methods: We included 105 consecutive patients who underwent clinical myocardial perfusion imaging on a SPECT/ CT system. Images were quantitatively assessed for misregistration using fusion software. Results were recorded in millimeters in the x-, y-, and z-axes. Regional tracer uptake in 6 segments (anterior, septal, inferior, lateral, anteroapical, and inferoapical) for noncorrected and attenuation-corrected images before and after reregistration was obtained from polar maps. To determine the relative influence of misregistration, we correlated individual differences between noncorrected and attenuation-corrected images, as well as between attenuation-corrected images before and after reregistration, with the degree of misregistration in a multivariate analysis including additional clinical variables such as sex and body weight. Results: The difference in regional radiotracer uptake was significant between noncorrected and attenuationcorrected images in all 6 segments and was most pronounced in the inferior wall. On multivariate analysis, misregistration contributed significantly to changes in radiotracer distribution in the anterior (P 5 0.038), septal (P 5 0.011), and inferior (P 5 0.006) segments. The mean misregistration was 8.6 6 3.8 mm (1.25 6 0.55 pixel). Misregistration of one or more pixels was observed in 64% of studies. Reregistration of misalignment significantly affected regional radiotracer distribution in the segments shown to be influenced by misregistration. Conclusion: Misregistration occurs with SPECT/CT systems and influences regional tracer distribution on attenuation-corrected myocardial images. Reregistration of misaligned studies may be a useful tool for correction. The impact of this strategy on the diagnostic and prognostic accuracy of cardiac hybrid imaging needs to be determined. Formyocardi al perfusion SPECT, professional societies recommend incorporation of attenuation correction to improve diagnostic accuracy (1). On standalone SPECT scanners, the transmission scans necessary for determining tissue density maps for attenuation correction are obtained with an external radionuclide line or point source. With the advent of SPECT/CT hybrid systems, however, CT is now increasingly used for transmission scanning. Advantages of the CT method include higherquality attenuation maps secondary to higher photon flux, lower noise, and improved resolution (2). Additionally, especially when using multislice CT in SPECT/CT systems, coronary calcium scoring or coronary angiography can be performed t...

Forty-two percent of the CT attenuation-corrected myocardial perfusion studies had moderate to severe cardiac misregistration qualitatively. Our data suggest that careful review of attenuation correction maps and registration is needed to avoid reconstruction artifacts due to misregistration.

Gastric-emptying studies have no accepted standard methodology or reference values. A simplified standardized protocol with a large reference database has been proposed, with imaging obtained at only 0, 1, 2, and 4 h. The rationale for its 4-h length is data suggesting that delayed emptying is detected with higher sensitivity at 4 h than at 2 h. The purpose of the current investigation was to review our 2-y experience using this protocol, to determine the added value of 4-h imaging, and to determine whether the lag phase can predict delayed emptying. Methods: After ingesting a sandwich made with 99m Tc-sulfur colloid egg substitute, 175 patients were imaged immediately, every 10 min for 1 h, and then at 2, 3, and 4 h. Percentage retention was calculated for each interval. Sensitivities, specificities, predictive values, and receiver operating characteristic (ROC) curves were computed for the 1-, 2-, and 3-h intervals on the basis of normal 4-h values. Data were analyzed to determine the added value of the 4-h study. Thresholds were sought that optimized accuracy. ROC analysis was used to determine the predictive value of the lag phase. Results: Gastric emptying was delayed in 20% of patients at 2 h and in 26% at 4 h, a 29% increase in abnormal studies (P , 0.02). Of those normal at 2 h, 13% became abnormal at 4 h. Of those with delayed emptying at 2 h, 24% normalized at 4 h. Compared with the study at 4 h, the study at 2 h had a 59% sensitivity, 94% specificity, 76% PPV, and 87% NPV. ROC analysis showed that the areas under the ROC curve (AUC) were 0.75, 0.93, and 0.97 at 1, 2, and 3 h, respectively. The threshold for optimal accuracy for 3-h data was estimated to be greater than 30% retention. The accuracy of this threshold was 91%. The lag phase AUC for predicting delayed emptying at 4 h was 0.60. Conclusion: This first investigation of a large referral patient population using a standardized protocol found that abnormal emptying is detected with greater sensitivity at 4 h than at 2 h and that the lag phase is not predictive of delayed emptying.

Brown adipose tissue (BAT) is retained into adulthood in some patients. It has been imaged using several radiopharmaceuticals, including 18 F-FDG. Using SPECT/CT, we assessed whether and how frequently uptake of 99m Tc-methoxyisobutylisonitrile ( 99m Tc-MIBI) was present in expected locations of BAT. Methods: A total of 205 SPECT/CT scans using 99m Tc-MIBI for parathyroid imaging were reviewed for the presence of 99m Tc-MIBI uptake in expected locations of BAT. Results: We detected 99m Tc-MIBI uptake in BAT in 13 of 205 patients (6.3%). When BAT was visualized, it was detected on both early and delayed scans. The patients with 99m Tc-MIBI uptake in BAT were younger than the patients with no 99m Tc-MIBI uptake (P 5 0.044). Conclusion: Uptake of 99m Tc-MIBI in BAT is relatively common in this adult patient population and should not be confused with 99m Tc-MIBI-avid-tumors. SPECT/CT can be useful for defining such tracer uptake as a normal physiologic variant. Brown adipose tissue (BAT) is metabolically active in some adults and can cause inaccurate diagnoses on several types of nuclear scans because of substantial tracer uptake, which can be confused with or mask disease. Previously, BAT has been visualized by PET using 18 F-FDG (1,2), and by single-photon imaging using 123 I-metaiodobenzylguanidine (3,4) or 99m Tc-tetrofosmin (5) in humans. 99m Tcmethoxyisobutylisonitrile ( 99m Tc-MIBI) is widely used for many imaging applications, most notably for both cardiac and parathyroid imaging. To our knowledge, there have been 2 case reports (6,7) describing the possible uptake of 99m Tc-MIBI into brown fat in humans. Studies in rodents show clearly an increased uptake of 99m Tc-MIBI into BAT relative to background blood levels (8). Thorough examination of a 99m Tc-MIBI scan of the heart or parathyroid glands includes assessment of the visualized body to exclude incidental incremental tumor involvement, which may be 99m Tc-MIBI-avid. This is particularly important in instances when 99m Tc-MIBI is used for tumor imaging. We suspected that 99m Tc-MIBI might accumulate in BAT and evaluated this possibility, reviewing consecutive SPECT/ CT scans. MATERIALS AND METHODS Patient PopulationWe retrospectively reviewed scintigrams of consecutive patients who were evaluated for parathyroid adenomas from May 2004 to July 2005, using dual-phase (early and late) planar imaging and SPECT/CT. We identified 205 patients (153 female, 52 male; mean age, 59.7 6 13.1 y, range, 23-94 y). Our retrospective study was approved by the Institutional Review Board, and informed consent was waived. Imaging Protocol and AnalysisAll patients were injected intravenously with 925-1,110 MBq of 99m Tc-MIBI. Planar ImagingAt 15 min and 2 h after injection, 10-min anterior, 35°right anterior oblique, and 35°left anterior oblique planar images were acquired in a 128 · 128 matrix, with a 20% window centered around the 140-keV photopeak, using a low-energy, high-resolution parallel collimator. SPECT/CTNeither oral nor intravenous contrast material was used. Hyb...