J.N. Kritzman

Simultaneous Transmission/Emission Myocardial Perfusion Tomography: Diagnostic Accuracy of Attenuation-Corrected 99mTc-Sestamibi Single-Photon Emission Computed Tomography

BACKGROUND The purpose of the present study was to assess the diagnostic performance of attenuation-corrected (AC) stress 99mTc-sestamibi cardiac single-photon emission computed tomography (SPECT) for the identification of coronary heart disease (CHD). METHODS AND RESULTS With a triple-detector SPECT system with a 241Am transmission line source, simultaneous transmission/emission tomography (TCT/ECT) was performed on 60 patients with angiographic coronary disease and 59 patients with < or = 5% likelihood of CHD. Iteratively reconstructed AC stress 99mTc-sestamibi perfusion images were compared with uncorrected (NC) filtered-backprojection images. Normal database polar maps were constructed from AC and NC images for quantitative analyses. From the low-likelihood patients, the visual and quantitative normalcy rates increased from 0.88 and 0.76 for NC to 0.98 and 0.95 for AC (P < .05). For the detection of CHD, the receiver operating characteristic curves for the AC images demonstrated improved discrimination capacity (P < .05), and sensitivity/specificity values increased from 0.78/0.46 (NC) to 0.84/0.82 (AC) with visual analysis and from 0.84/0.46 (NC) to 0.88/0.82 (AC) with quantitative analysis. For localization of stenosed vessels, visual and quantitative sensitivity values were 0.51 and 0.63 for NC and 0.64 and 0.78 for AC images (P < .05), respectively. CONCLUSIONS TCT/ECT myocardial perfusion imaging significantly improves the diagnostic accuracy of cardiac SPECT for the detection and localization of CHD. Clinical use of TCT/ECT imaging deserves serious consideration.

Dosimetry in 131I internal emitter therapy using voxel dependent integrated time-activities derived from multiple, registered SPECT and CT images

The accuracy of dosimetry calculations in internal emitter therapy applications is often limited by a lack of data describing the time dependence of the spatial activity concentration in patients. In many cases, time-dependent activity data is acquired only for specific regions of interest (ROIs), and measurements of patient anatomy and 3D activity distributions are made at only single time points during tracer studies. When calculating absorbed dose in these applications, this scarcity of data necessitates the approximation that activity distributions can be wholly defined by single spatial measurements, and that all points within given ROIs exhibit uniform time dependence. In the current work, CT and SPECT images have been acquired using a dual-modality scanner at multiple time points after administration of both tracer and therapy activity to follicular lymphoma patients being treated with 131I tositumomab. The data has been registered to a single CT image, and the mutually registered SPECT images have been used to derive integrated time-activities on a voxel-by-voxel basis. Maps of integral time-activity have been used in conjunction with CT images to determine 3D absorbed dose distributions by Monte Carlo computation. Results are presented illustrating the differences between calculations of spatial distributions of integrated activities and absorbed doses made with the current technique and those performed with previous methods.