AUTOMATED INTERSTUDY IMAGE REGISTRATION TECHNIQUE FOR SPECT AND PET

We report the extended application of an automated computer technique for three-dimensional spatial registration of SPECT and PET studies. M ethods: The technique iteratively reslices a misaligned data set until the sum of the absolute differences (SAD) from a reference data set i s minimized. The registration accuracy was assessed in Hoffman brain p hantom studies collected with known misalignments and transmission stu dies of a thorax phantom with fiducial markers. The SAD was compared w ith three other cost functions: stochastic sign change criterion, sum of products and standard deviation (s.d.) of ratios. In clinical neuro logical and myocardial perfusion studies, registration accuracy was es timated from the relative locations of landmarks in the reference and registered data sets. Results: Registration accuracy in the Hoffman br ain phantom studies was -0.07 +/- 0.46 mm (mean +/- s.d.) for translat ions and -0.01 +/- 0.20 degrees for rotations, with maximum translatio n and rotation errors of 1.2 mm and 0.8 degree, respectively. The SAD was the most accurate and reliable cost function. Registration errors in the thorax phantom were 3.1 +/- 1.7 mm. Mean accuracy in the neurol ogical studies, estimated from landmark pairs, was 2.0 +/- 1.1 mm for SPECT to SPECT and 1.8 +/- 1.1 mm for PET to SPECT registrations. Aver age registration accuracy in (TI)-T-201 myocardial perfusion studies w as 2.1 +/- 1.2 mm. Conclusion: Our registration method (a) provided ac curate registrations for phantom and clinical SPECT and PET studies, ( b) is fully automated, (c) simplifies comparison of data sets obtained at different times and with different modalities, and (d) can be appl ied retrospectively.