A quantitative study of motion estimation methods on 4D cardiac gated SPECT reconstruction

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Image Processing

Background:

• Gated cardiac single photon emission computed tomography (SPECT) image quality is significantly impacted by motion-compensated temporal processing.
• Accurate motion estimation is crucial for improving the quality of reconstructed SPECT images.

Purpose of the Study:

• To investigate the effect of different optical flow estimation (OFE) methods on motion-compensated temporal processing in gated SPECT.
• To determine if improved motion estimation can substantially enhance reconstructed image quality.
• To compare the accuracy of estimated motion with known motion in reconstruction.

Main Methods:

• Compared three motion estimation methods: Horn-Schunck optical flow equation (OFE), a novel periodic OFE, and known motion from the NCAT phantom.
• Evaluated impact on 4D reconstructions using simulated SPECT data with varying noise, geometry, and lesion sizes.
• Quantified results using measures of myocardial error, left ventricle (LV) wall accuracy, time activity curves, and lesion detectability (CHO).

Main Results:

• The periodic OFE method demonstrated superior reconstruction accuracy compared to traditional OFE, nearly matching the performance of known motion.
• Periodic OFE reduced overall myocardial mean-squared error by over 20% and regional LV bias from 20% to 14% (vs. 11% for known motion).
• Improved lesion detectability and more consistent time activity curves and LV wall contours were observed with periodic OFE.

Conclusions:

• Enhanced optical flow estimation significantly improves the accuracy of 4D reconstructed images in gated cardiac SPECT.
• The periodic OFE method offers substantial improvements over traditional OFE and closely approximates the accuracy achieved with known motion.