Effect of errors in reangulation on planar and tomographic thallium-201 washout profile curves

Cardiac phantom studies were performed with and without a defect present to test the hypothesis that myocardial ²⁰¹Tl quantitative circumferential washout profile curves calculated from planar and rotating slant hole (RSH) collimator tomographic images are equally affected by errors in axial repositioning. Simulated stress images were acquired with the long axis of the phantom perpendicular to the camera surface and redistribution images were acquired to represent 50% ²⁰¹Tl washout with axial repositioning errors relative to the stress position ranging from 0 to 20° in 5° increments. There was a decrease in the ²⁰¹Tl washout profile curves compared to that expected (50%) in the wall tilted away from the camera surface, and a reciprocal increase in the ²⁰¹Tl washout profile curves in the wall tilted towards the camera surface for both imaging techniques whether a lesion was present or not. This effect became more pronounced as the error in axial repositioning was increased for both the planar (p < 0.001) and the RSH tomographic (p < 0.001) techniques. However, the deviation of the ²⁰¹Tl washout profile curves from that expected (50%) was greater for the planar imaging technqiue with or without a lesion (p < 0.05 to 0.001). Thus, we conclude that ²⁰¹Tl quantitative circumferential washout profile curves calculated using this tomographic imaging technique are less affected by errors in axial repositioning than those calculated using an equivalent projection by standard planar imaging method. These data emphasize the importance which must be placed on the repositioning of patients to obtain valid ²⁰¹Tl washout profile curves for detection and localization of coronary artery disease.