Issues in the quantitation of reoriented cardiac PET images.

Reorientation of transaxial cardiac PET images into short-axis images has been shown by other investigators to improve visual identifiability of defects in myocardial tracer uptake. However, quantification of physiologic processes from such reoriented images may be complicated by errors introduced during the reorientation process. Therefore, a quantitative characterization of these errors is necessary. An annular phantom of human cardiac dimensions was imaged in a 15-plane positron emission tomograph at six angles (0 degrees, 5 degrees, 25 degrees, 45 degrees, 65 degrees, 85 degrees) and at two different axial sampling densities. In addition, two different reorientation interpolators were employed, one using three-dimensional linear interpolation and the other using a "hybrid" interpolation algorithm. Distortion of linear distances was variable but was minimized with denser axial sampling and the use of hybrid interpolation. Circumferential profile analysis, corrected for inhomogeneities in reoriented image spatial resolution, revealed a maximal loss of region of interest counts at 65 degrees of at least 14.4%. Reorientation errors were minimized by use of dense axial sampling, low angles of reorientation and use of the hybrid interpolation algorithm.

A simplified method for quantification of myocardial blood flow using nitrogen-13-ammonia and dynamic PET.

The utility of Patlak graphical analysis was investigated for quantification of regional myocardial blood flow (MBF) and for generating parametric images of MBF with 13N-ammonia and dynamic PET imaging in dogs and humans. MBF was estimated by a two-compartment model fit of the initial 2 min of the kinetic data and by Patlak graphical analysis of the initial 2, 3, or 4 min of data. In 11 dog studies, MBF by compartmental model fitting linearly correlated with MBF by microspheres (correlation coefficient (r) = 0.99, slope = 0.92) and by Patlak graphical analysis (r = 0.99, slope = 0.90). In 10 normal human studies, MBF obtained by the Patlak graphical analysis agreed well with MBF obtained by the compartmental model fitting (r = 0.96, slope = 1.04). Good agreement of the MBF estimates was also observed in 10 coronary artery disease patient studies (r = 0.96). Patlak graphical analysis permitted generation of parametric images of MBF. The parametric images of MBF, in units of ml/min/g, are of good image quality and have relatively low noise levels. We conclude that regional MBF can be noninvasively and conveniently measured with dynamic 13N-ammonia PET using either a two-compartment model or Patlak graphical analysis. MBF parametric images generated with the Patlak graphical analysis both map the distribution and quantitate the magnitude of myocardial perfusion abnormalities.

Quantification of myocardial blood flow using dynamic nitrogen-13-ammonia PET studies and factor analysis of dynamic structures.

UNLABELLED: In this study, factor analysis of dynamic structures (FADS) was used to extract the "pure" blood-pool time-activity curves (TACs) and to generate parametric myocardial blood flow (MBF) images (pixel unit: ml/min/g). METHODS: Ten dynamic 13N-ammonia dog PET studies (three baseline, five hyperemia and two occlusion) were included. Three factors (TACs) and their corresponding factor images (the right ventricular and left ventricular blood pools and myocardial activities) were extracted from each study. The left ventricular factors matched well with the plasma TACs. The factor images of myocardium were then converted to a parametric images of MBF using a relationship derived from a two-compartment model. RESULTS: MBF estimates obtained from FADS correlated well with MBF estimates obtained with the two-compartment model (r = 0.98, slope = 0.84) and microsphere techniques (r = 0.96, slope = 0.94). FADS-generated MBF parametric images have better image quality and lower noise levels compared to those generated with Patlak graphical analysis. CONCLUSION: Regional MBF can be measured accurately and noninvasively with 13N-ammonia dynamic PET imaging and FADS. The method is simple, accurate and produces parametric images of MBF without requiring blood sampling and spillover correction.

Quantification of regional myocardial blood flow using 13N-ammonia and reoriented dynamic positron emission tomographic imaging.

BACKGROUND: Regional myocardial blood flow has been quantified using transaxial positron emission tomographic (PET) imaging and tracer kinetic modeling. However, the use of transaxial images limits the accuracy of regional partial volume corrections and the localization of the quantified regional flow values. The purpose of the present study was to overcome both problems by calculating regional flows from reoriented short-axis PET images. METHODS AND RESULTS: Twelve experiments were performed in four dogs. 13N-ammonia was injected intravenously while microspheres were administered into the left atrium during baseline, hyperemic, and low-flow conditions. Serial transaxial frames were acquired with a 15-plane PET scanner and reoriented into short-axis frames. The arterial input function and eight regional myocardial tissue activity curves were derived from the reoriented frames. The arterial input functions were corrected for ammonia metabolites, and the myocardial tissue curves were corrected for spillover of activity, partial volume effects, and heterogeneities in the image's spatial resolution introduced during reorientation. Corrections for regional partial volume were based on estimates of the regional myocardial activity thickness derived from reoriented diastolic images of the heart. The myocardial 13N-ammonia kinetics were described with a two-pool compartmental model. Values of regional myocardial blood flow by PET correlated linearly with those by microspheres (slope, 0.94; y intercept, 0.06 ml/min/g; r = 0.93) over a wide range of flows. CONCLUSIONS: Regional myocardial blood flow can be measured accurately and noninvasively from serially acquired and reoriented short-axis 13N-ammonia images, thus overcoming limitations inherent to the use of transaxially acquired images and permitting a more complete evaluation of regional blood flows throughout the left ventricular myocardium.