Correction for patient and organ movement in SPECT: application to exercise thallium-201 cardiac imaging.

We describe a technique for correction of artifacts in exercise 201Tl single photon emission computed tomography (SPECT) images arising from abrupt or gradual translational movement of the heart during acquisition. The procedure involves the tracking of the "center of the heart" in serial projection images using an algorithm which we call "diverging squares". Each projection image is then realigned in the x-y plane so that the heart center conforms to the projected position of a fixed point in space. The shifted projections are reconstructed using the normal filtered backprojection algorithm. In validation studies, the motion correction procedure successfully eliminated movement artifacts in a heart phantom. Image quality was also improved in over one-half of 36 exercise thallium patient studies. The corrected images had smoother and more continuous left ventricular walls, greater clarity of the left ventricular cavity, and reduced streak artifacts. Rest injected or redistribution images, however, were often made worse, due to reduced heart to liver activity ratios and poor tracking of the heart center. Analysis of curves of heart position versus projection angle suggests that translation of the heart is common during imaging after exercise, and results from both abrupt patient movements, and a gradual upward shift of the heart. Our motion correction technique appears to represent a promising new approach for elimination of movement artifacts and enhancement of resolution in exercise 201Tl cardiac SPECT images.