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

Abstract

Background: Patient motion constitutes a limitation to ¹⁵O-water cardiac PET imaging. We examined the ability of image readers to detect and correct patient motion using simulated motion data and clinical patient scans.

Methods: Simulated data consisting of 16 motions applied to 10 motion-free scans were motion corrected using two approaches, pre-analysis and post-analysis for motion identification. Both approaches employed a manual frame-by-frame correction method. In addition, a clinical cohort was analyzed for assessment of prevalence and effect of motion and motion correction.

Results: Motion correction was performed on 94% (pre-analysis) and 64% (post-analysis) of the scans. Large motion artifacts were corrected in 91% (pre-analysis) and 74% (post-analysis) of scans. Artifacts in MBF were reduced in 56% (pre-analysis) and 58% (post-analysis) of the scans. The prevalence of motion in the clinical patient cohort (n = 762) was 10%. Motion correction altered exam interpretation in only 10 (1.3%) clinical patient exams.

Conclusion: Frame-by-frame motion correction after visual inspection is useful in reducing motion artifacts in cardiac ¹⁵O-water PET. Reviewing the initial results (parametric images and polar maps) as part of the motion correction process, reduced erroneous corrections in motion-free scans. In a large clinical cohort, the impact of motion correction was limited to few patients.

Keywords: PET; image analysis; myocardial blood flow; perfusion agents.

Figure 1

Frame-by-frame motion correction software. All 21 frames are displayed, showing an overlay of the left ventricular segmentation from the aQuant pre-correction analysis. Each frame can be manually shifted in the x-, y-, or z-direction

Figure 2

Heat maps of uncorrected (A, D, G) and motion corrected images using the pre-analysis (B, E, H) and post-analysis (C, F, I) approach. The X-axis represents each type of motion. The Y-axis represents the coronary territories (LAD, RCA, LCx, and global). Median relative deviation (%) in MBF from the original motion-free images in uncorrected (A) and motion-corrected (B) images. Maximum relative deviation (%) in MBF from the original motion-free images in uncorrected (D) and in motion-corrected images using the preanalysis approach (E) and post-analysis approach (F). Results of the Wilcoxon signed-rank test, showing level of significance (P > .05, P < .05 or P < .005) in MBF deviation from the original motion-free images in uncorrected (G) and in motion-corrected images using the pre-analysis approach (H) and post-analysis approach (I). Every cell in A, B, C, G, H and I contains results from all 10 patients. Every cell in D, E and F contains results from the one patient with the highest maximum deviation

Figure 3

Median residual motion calculated as the difference between the actual simulated motion and the motion corrected by the two motion correction approaches. Positive values indicate under-correction, while negative values indicate over-correction. The values represent the magnitude of the residual motion in millimeters

Figure 4

Polar plots from a patient scan comparing images pre-correction (A), post-correction (B), and original motion-free (C). The simulated linear slide motion (20 mm, 1 minute post-injection) increased MBF in the anterior part and reduced MBF in the inferior part with a large apical inferolateral defect (A). After motion correction, the artifact disappeared (B), aligning with the original motion-free image (C)

Figure 5

PET images representing a patient from the clinical cohort pre- (A, B) and post-motion (C, D) correction. In the polar plot in A, a motion artifact has caused a false positive defect (20.1 %) in the RCA territory. In the post-motion correction polar plot in C, the motion artifact is completely reduced (defect 0.0 %). Splash images of short axis, horizontal long axis, and vertical long axis in B demonstrate the effect of motion artifacts on the visual interpretation of the images. The inferior wall appears hypoperfused compared to the rest of the myocardium. The post-motion correction splash images in D, demonstrate a uniform tracer uptake, thereby eliminating any suspicions of defects in the inferior wall. MBF, myocardial blood flow (mL⋅min⁻¹⋅g⁻¹); PTF, perfusable tissue fraction (mL⋅mL⁻¹)

Figure 6

Scatter plots and Bland–Altman plots of regional MBFstress as well as global MBFstress for precorrection vs motion-corrected images in the clinical patient cohort. Dashed lines in the scatter plots indicate the threshold of normal values (MBF ≥ 2.3 mL⋅min⁻¹⋅g⁻¹). Red lines represent lines of identity. Dashed lines in the Bland–Altman plots represent limits of agreement