Subtraction Gated Computed Tomography with the Dynamic Spatial Reconstructor

Abstract

Three-dimensional (3-D) dynamic computed tomography of the heart with the dynamic spatial reconstructor (DSR) is being used for studies of cardiovascular function. Formerly, continuous infusion of bilateral bolus injections of contrast medium were required to visualize both sides of the heart simultaneously. The DSR was used to circumvent many of the drawbacks of these methods. In anesthetized dogs a bolus of 1 ml/kg body weight contrast medium was injected into the superior vena cava and 60/s scans were performed during the dextro- and levophases of the resulting angiogram. The recorded scan data were used to generate successive volume (3-D) images with a scan aperture time of 0.06 s each. Each scanned cardiac cycle was thus represented by sequential volume images with either the right or left chambers opacified. Matching equal time intervals from the R wave of the electrocardiogram, the volume images of the left heart phase were digitally subtracted (voxel for voxel) from the images of the right heart phase, with all resulting negative voxel values set to zero. Only the contrast enhanced right ventricle (RV) chamber remained in the subtraction images, whose brightness was then scaled to match the brightness of the opacified left ventricle (LV). The modified RV phase images were then added to the LV phase images. The resulting volume images contain equally enhanced LV and RV chambers and can be used for retrospective analysis, including display of static and dynamic oblique planar images. Verification of the accuracy of this technique was made by estimation of LV muscle mass in five dogs. Dynamic spatial reconstructor estimates from subtracted gated images were compared with postmortem measurements. The correlation was 0.999 with a mean discrepancy of 2.3 ± 0.4% SEM.