Patient motion correction for dynamic cardiac PET: Current status and challenges

Abstract

For dynamic cardiac PET of quantifying myocardial blood flow (MBF), patient motion is a major factor that affects the ROI definition and absolute quantification accuracy. In a recent study, an 82 rubidium ( 82 Rb)-dynamic-tailored motion-correction framework has been proposed to address the voluntary body motion for all the dynamic frames, including both early and late phases. 1 This approach brings us one step closer to the practical and full motion correction for dynamic cardiac PET studies. In this editorial, we discussed the current status and limitations of motion-correction methods for dynamic cardiac PET, including the recent publication at JNC, and also pointed out the remaining challenges for future developments.PET myocardial perfusion imaging has been shown to improve the detection accuracy of coronary artery disease as compared to other non-invasive imaging modalities. 2 Many investigators, in the past two decades, have established methods for absolute quantification of MBF and myocardial flow reserve (MFR) 3 using dynamic PET, which is superior in diagnostic and prognostic value as compared to the conventional relative myocardial perfusion imaging. 4 A prerequisite of accurate quantification in dynamic PET requires appropriate corrections 5 to the original dynamic frame data. In additional to corrections for physical factors such as attenuation, scatter, randoms, and normalization, physiological factors such as patient motion also require correction. Patient motion in cardiac imaging typically includes respiratory motion, cardiac motion, and voluntary body motion. Such motions can cause inaccurate tracer distribution estimation, as well as artifacts introduced by the mismatch between PET and CT-based attenuation map. 6 Comparing to more periodic respiratory motion and cardiac motion, the timing for voluntary body motion is typically unpredictable, thus its impact on the MBF and MFR quantifications can be complicated. 7 Methods for respiratory motion 8 and cardiac motion management 9 have been proposed in the past. The body motion correction has also been studied for several PET applications, especially for brain studies. 10

Motion correction to enhance absolute myocardial blood flow quantitation by PET

“…Evidence supporting this is the far greater fraction of stress studies containing motion than rest studies. 22,23 Proper reconstruction of images when the heart has shifted with respect to the attenuating organs is non-trivial.…”

Moving forward with motion reduction, detection and correction in cardiac PET

“…Image artifact is an artificial finding in an image that should not be there, often leading to an incorrect interpretation and thus an incorrect diagnosis. Three well-documented types of motion artifacts in PET that lead to image artifacts are PET-emission-CTtransmission misregistration, 2-4 motion during dynamic acquisition [5][6][7][8][9] and motion due to breathing. [10][11][12] Emission-transmission misregistration happens when using the CT transmission from a PET/CT scanner to correct for attenuation of the 511 keV photons along the body during PET imaging.…”

Data-Driven Patient Motion Compensation in Cardiac Positron Emission Tomography

“…The effect of patient motion is largely that of inaccurate tracer distribution estimation due to a loss in spatial resolution as well as mis-alignment with PET emission data and corresponding attenuation correction map. 85 When the motion extent is relatively large compared to the spatial resolution of the scanner the effects become more severe which can potentially lead to degradation in image quality which affects the interpretation of the images and, possibly, misdiagnosis of the patient. 84 Moreover, as PET systems continue to advance with respect to hardware and reconstruction techniques the spatial resolution will continue to improve thus leading to greater influence of patient motion on image quality.…”

“…For dynamic cardiac acquisition where absolute blood flow quantification is being performed patient motion can affect not only image quality, as described for MPI, but also the dynamic activity sampling within the blood pool and the myocardium. 85 Incorrect sampling due to patient motion often presents itself in the time-activity curves and manifests as discontinuities or spikes along the measured curves. 77 In a small clinical sample of seven patients, Yu and colleagues demonstrated that respiratory motion correction led to substantial increases in MBF and CFR, e.g.…”

“…The cohort in this study, however, largely does not meet that criterion. Nevertheless, patient motion correction has regularly been identified as a contributing factor to the overall repeatability of MBF estimation 77,81,85,184 and so a robust and automated method with which cases could be classified as those which would benefit from motion correction could be very clinically useful, especially for fringe cases where the motion effects are not obvious.…”