Automated alignment and sizing of myocardial stress and rest scans to three-dimensional normal templates using an image registration algorithm.

UNLABELLED: To optimize the interpretation of myocardial SPECT, we developed an automated method for alignment, sizing and quantification of images using three-dimensional reference templates.
METHODS: Stress and rest reference templates were built using a hybrid three-dimensional image registration scheme based on principal-axes and simplex-minimization techniques. Normal patient studies were correlated to a common orientation, position and size. Aligned volumes were added to each other to create amalgamated templates. Separate templates were built for normal stress and rest SPECT 99mTc-sestamibi scans of 23 men and 15 women. The same algorithm was used to correlate abnormal test-patient studies with respective normal templates. The robustness of the fitting algorithm was evaluated by registering data with simulated defects and by repeated registrations after arbitrary misalignment of images. To quantify regional count distribution, 18 three-dimensional segments were outlined on the templates, and counts in the segment were evaluated for all test patients.
RESULTS: Our technique provided accurate and reproducible alignment of the images and compensated for varying dimensions of the myocardium by adjusting scaling parameters. The algorithm successfully registered both normal and abnormal studies. The mean registration errors caused by simulated defects were 1.5 mm for position, 1.3 degrees for tilt and 5.3% for sizing (stress images), and 1.4 mm, 2.0 degrees and 3.7% (rest images); these errors were below the limits of visual assessment.
CONCLUSION: Automated three-dimensional image fitting to normal templates can be used for reproducible quantification of myocardial SPECT, eliminating operator-dependence of the results.