Analysis of thallium-201 "washout" from parametric color coded images.

We developed a parametric washout image which color codes regional washout, and blindly compared enhanced perfusion images in multiple projections with regional washout graphs and images in 25 patients. Washout images permitted true spatial and anatomic assessment of regions viewed en face as well as those seen in tangent, making possible the exclusion of non-coronary irregularities and permitting evaluation of washout over the apparent cavity. "Cavitary" washout was abnormal in 10 of 12 patients with apparent cavitary dilation on the post stress image, but in none without this finding. The distribution and rotation of washout abnormalities seen over the cavity when viewed en face, and the long delay between the termination of stress and post-exercise image acquisition, suggest that apparent cavitary dilation is often related to improved visibility of the 201T1 deficient blood pool due to relative ischemia of the overlying myocardial wall.