SPECT blood pool phase analysis can accurately and reproducibly quantify mechanical dyssynchrony.

OBJECTIVES: Phase analysis of SPECT blood pool imaging has the potential to assess mechanical dyssynchrony (MD). However, wall motion of the left ventricle (LV) from SPECT images can be based on either time-activity or time-distance curves. In this paper, these two techniques were compared using receiver-operator characteristics (ROC) analysis at detecting MD patients from a population of normal subjects. METHODS: SPECT phase analysis was performed on 48 normal subjects (LVEF > 55%, normal wall motion, QRS < 120 ms), and 55 MD patients (LVEF < 35%, QRS > 120 ms). ROC analysis was individually performed on each of three phase parameters (phase standard deviation, synchrony, and entropy) for each LV wall motion technique. ROC area differences were assessed using the Student t-test. Intra- and inter-observer reproducibilities were investigated using regression analysis. RESULTS: Time-activity-based phase analysis produced excellent ROC areas of .93 or better for all three phase parameters. The time-distance techniques produced significantly (P < .05) lower ROC areas in the range of .53-.76. Time-activity-based phase analysis had excellent intra- and inter-observer reproducibility with correlation coefficients >.96, compared to values of ~.85 for the time-distance methods. CONCLUSION: SPECT time-activity-based phase analysis had excellent sensitivity and specificity at detecting MD patients with very high intra- and inter-observer reproducibility.

Collimator selection, acquisition speed, and visual assessment of 131I-tositumomab biodistribution in a phantom model.

UNLABELLED: (131)I-Tositumomab has been used in treating patients with non-Hodgkin's lymphoma. It is generally recommended that high-energy collimators be used to image patients before they receive (131)I-tositumomab therapy, to determine the effective half-life for therapeutic dose and gross biodistribution. Because many nuclear medicine departments do not possess high-energy collimators, this study was designed to assess the suitability of using medium-energy collimators. The effect of scanning speed was also investigated, in an attempt to optimize the acquisition time. METHODS: Measurements were taken using an elliptic anthropomorphic torso phantom and an organ-scanning phantom fitted with fillable spheres (1-5 cm in diameter) and organ inserts. Three phantom studies were performed with differing initial (131)I concentrations in the organs, the spheres, and the thoracic and abdominal chambers. Images were acquired with both high-energy and medium-energy collimators and at acquisition speeds of 20 and 100 cm/min. The half-life for each combination (study/collimator/speed) was calculated from a linear fit of the data. The contrast of the tumor sphere was assessed using 2 identical regions, placed on and beside the sphere, and averaged over several time points. Biodistribution and image quality were visually assessed by 2 independent observers. RESULTS: Measured half-life values and visual assessment of biodistribution showed no significant difference between the 2 collimators (P = 0.32) or acquisition speeds (P = 0.85). A significant difference in the contrast of the tumor spheres was observed between the 2 collimators (P < 0.01) but not between acquisition speeds. Visual assessment of the images showed increased noise on the image acquired at 100 cm/min, although this noise did not affect lesion detectability. CONCLUSION: Measured half-life is not significantly different between the 2 collimators; hence, calculation of the residence time would be nearly the same. Medium-energy collimators can be used to accurately calculate the (131)I-tositumomab therapeutic dose and detect alterations in biodistribution.