IMPACT OF REORIENTATION ALGORITHMS ON QUANTITATIVE MYOCARDIAL SPECT PERFUSION IMAGING

In myocardial SPECT perfusion imaging, reorientation algorithms from t ransaxial image planes are used to generate short- and long-axis views of myocardial tracer uptake. We performed phantom experiments with Tl -201 to delineate how image reorientation affects the results of quant itative image analysis, Methods: Thirty consecutive patient studies we re analyzed to characterize the distribution of the angle of reorienta tion in a clinical setting. Short-axis SPECT images of a cardiac phant om with and without a 180 degrees cold-spot insert were reconstructed with three different backprojection filters tramp, Metz and Butterwort h) and reoriented through different angles ranging from 45 degrees to 89 degrees. Four interpolation algorithms were used to calculate from the transaxial images the pixel values of the reoriented images: (a) a simple interpolator that averages the pixel values of the eight neigh boring pixels of the transaxial image; (b) a three-dimensional linear interpolator; (c) a hybrid interpolator that combines a two-dimensiona l linear in-plane with a one-dimensional cubic across-plane interpolat ion; and (d) a three-dimensional cubic convolution interpolator. Image s were reoriented twice with opposite angles so that the original and the reoriented images could be directly compared. Circumferential prof ile analysis was applied to determine the root mean square error of co rresponding profiles and the difference of the extent and the severity of perfusion defects. Single and multivariate analyses of variance (A NOVA) were used to compare the effects of the reorientation angle, the backprojection filter and the interpolation algorithm. Results: In th e clinical studies, the angle between the transaxial and reoriented im ages was 75 degrees +/- 10 degrees (s.d.), In 48 phantom experiments, multivariate ANOVA demonstrated that the backprojection filter and the interpolation algorithm significantly affect the circumferential prof iles and the extent and severity of a perfusion defect (p < 0.05). In contrast, the angle of reorientation was not a significant factor (p = ns). By univariate analysis, the three-dimensional cubic interpolator was associated with significantly (p < 0.05) less error than the simp le and three-dimensional linear algorithms. Relative computation times (simple interpolator = 100%) were 119% for the three-dimensional line ar, 136% for the hybrid and 243% for the three-dimensional cubic inter polator. Conclusion: For quantitative analysis of myocardial SPECT per fusion images, a Metz filter for filtered backprojection in combinatio n with a three-dimensional cubic convolution interpolation for image r eorientation appears to offer improved accuracy.