Influence of patient motion on quantitative accuracy in cardiac 15O-water positron emission tomography

Abstract

Background Patient motion is a common problem during cardiac PET. The purpose of the present study was to investigate to what extent motions influence the quantitative accuracy of cardiac 15O-water PET/CT and to develop a method for automated motion detection. Method Frequency and magnitude of motion was assessed visually using data from 50 clinical 15O-water PET/CT scans. Simulations of 4 types of motions with amplitude of 5 to 20 mm were performed based on data from 10 scans. An automated motion detection algorithm was evaluated on clinical and simulated motion data. MBF and PTF of all simulated scans were compared to the original scan used as reference. Results Patient motion was detected in 68% of clinical cases by visual inspection. All observed motions were small with amplitudes less than half the LV wall thickness. A clear pattern of motion influence was seen in the simulations with a decrease of myocardial blood flow (MBF) in the region of myocardium to where the motion was directed. The perfusable tissue fraction (PTF) trended in the opposite direction. Global absolute average deviation of MBF was 3.1% ± 1.8% and 7.3% ± 6.3% for motions with maximum amplitudes of 5 and 20 mm, respectively. Automated motion detection showed a sensitivity of 90% for simulated motions ≥ 10 mm but struggled with the smaller (≤ 5 mm) simulated (sensitivity 45%) and clinical motions (accuracy 48%). Conclusion Patient motion can impair the quantitative accuracy of MBF. However, at typically occurring levels of patient motion, effects are similar to or only slightly larger than inter-observer variability, and downstream clinical effects are likely negligible.

Detection and correction of patient motion in dynamic 15O-water PET MPI

“…In this part of the study, we investigated the ability to visually detect and manually correct patient motion. Data consisted of myocardial stress 15 O-water PET scans with simulated motion from Nordström et al 6 Of the original 17 simulated motions, five motions with low amplitude were omitted, and instead, 4 new motions were added. Thus, this study included a data set consisting of 16 different simulated motions with an amplitude of 5 to 20 mm applied to data from 10 motion-free clinical scans, yielding 160 simulated scans.…”

“… 4 , 5 Previous studies on patient motion have reported a high occurrence of motion, with 30-68% of image acquisitions affected. 6 – 10 Motion can be random with independent patterns of motion magnitude and direction or due to coughing. 11 , 12 However, the most common causes of patient motion are related to discomfort from pharmacological stress agents, and the associated changes in respiratory pattern, which may result in a continuous displacement of the mean position of the heart, 13 or even rapid displacements which may appear like random motion.…”

“… 11 , 12 However, the most common causes of patient motion are related to discomfort from pharmacological stress agents, and the associated changes in respiratory pattern, which may result in a continuous displacement of the mean position of the heart, 13 or even rapid displacements which may appear like random motion. 6 , 8 In dynamic imaging, cardiac creep and motion in the early blood phase, has a significant impact on quantification, particularly in the right coronary artery (RCA) territory, and can cause severe errors in the estimation of MBF up to 500%. 7 , 8 , 14 …”

“… 22 Similarly, they found typical effects on MBF from different types of dynamic patient motion during the PET scan to be only slightly larger than the inter-observer variability. 6 Nevertheless, some types of motion lead to large errors in the LAD and RCA territories, potentially affecting patient management.…”

“…In the present study, we present a tool for manual frame-by-frame motion correction of 15 O-water MPI, and, using previously published simulated motion data, 6 we evaluated the ability of image readers to visually identify and correct patient motion using two different approaches. In addition, a large cohort (n = 762) of clinical 15 O-water scans were included for investigation of prevalence and effect of motion and motion correction.…”