Estimation and correction of irregular respiratory motion of the heart in presence of partial angle effects due to amplitude binning in SPECT

Respiratory motion combined with the “respiratory creep” of the heart can affect the appearance of defects and even conceal them, thereby impacting the diagnostic accuracy of cardiac PET or SPECT perfusion images. Several groups have investigated the use of registration to estimate respiratory motion between 3D reconstructions of respiratory binned projection data in PET, and in SPECT. Motion estimation can be done by first binning the list-mode data into different respiratory gates using an external monitor of respiratory motion. Amplitude binning has been determined to be more accurate than phase-binning thus in general it is favored. However one issue with amplitude binning is that if the patients’ respiratory motion varies greatly with time, it may result in low or no counts in some amplitude bins at some projection angles. In this work we describe a method to overcome the limited-angle effect and estimate 2 DOF (SI and AP direction translation) motion robustly. We tested our method on a (modified) NCAT phantom with and without noise. After the estimation step, we reconstruct the object preserving all the counts, using a motion compensated MLEM algorithm. In our case studies we show that the motion correction help reveal lesions in some cases, and helps to clear up false cooling effect in others.