This study evaluated the impact of correcting for myocardial creep and cardiorespiratory (cardiac and respiratory) motion in two cohorts, one comprising young, healthy volunteers with repeat
82Rb MPI sessions within 2 weeks and the other patients considered for coronary intervention. The main finding of this study was improved test-retest repeatability in the volunteer cohort and improved AUC for the detection of adenosine-induced myocardial ischemia by FFR in the patient cohort (iTPD:
P = .039) when employing the 3xMC. Likewise, a correlation trend was observed between motion during the MPI sessions and the relative change in the sTPD/iTPD assessments (Figure
3). Therefore, our results suggest that myocardial creep and cardiorespiratory motion correction significantly improve the accuracy of
82Rb MPI sessions and should be applied routinely.
In previous studies, cardiorespiratory and repositioning/myocardial creep events have been reported to have a detrimental impact on the assessment of both coronary plaques and myocardial perfusion.
3‐6 Despite the translatory impact of respiratory motion and myocardial creep, the clinical routine has a mainstay of motion-limiting ECG-gated reconstructions, which are used for assessments of the left ventricular ejection fraction.
16,17 However, studies employing dual-correction protocols (cardiorespiratory) have been proposed with great success.
12,18 In terms of myocardial creep corrections during MPI sessions, the primary solutions revolve around passive detections of myocardial creep during assessments of dynamic frames employed for myocardial blood flow analysis. Here, the passive correction only permits inter-frame motion correction and does not consider within-frame myocardial creep events, which might limit the effect of the myocardial creep correction technique.
3‐5 Further, this correction technique does not permit myocardial creep correction of perfusion assessments which often endures several minutes' data. Finally, this technique does not permit corrections for cardiorespiratory motion, which is known to affect quantitative accuracy.
12,18 The proposed myocardial creep detection technique permits the detection of myocardial creep events dynamically during the acquisition and, at the same time, extracts information on the respiratory motion, which can be used for 3xMC corrections. The myocardial creep detection employed in this study expands on previous attempts at detecting patient repositioning events as tracer-kinetics influence the count rate-based assessments during the scans. In brief, the influence of tracer-kinetic on the count rate-based assessment was corrected by evaluating how the uptake pattern in the myocardium changed compared to the count rates observed in the surrounding lung tissues. This analysis permitted detection of the myocardial creep events, that occurs frequently (up to seven times) during the scans (Table
2). The myocardial creep and cardiorespiratory motion-induced myocardial translations of up 33.9 mm during the scan, with consequential changes in the sTPD and iTPD assessment of up to 10% to 12% (Figure
2). Of note, the improvements in the TPD assessments following 3xMC exceed the 2% improvement observed with the introduction of CT-attenuation correction in SPECT images; thus, indicating that the 3xMC has the potential to significantly better the prognostic and diagnostic assessments when evaluating
82Rb MPI.
19 In general, the magnitude of motion observed during the scans reflected the change in sTPD and iTPD for patients who underwent revascularization following MPI (Figure
3).
In this study, the impact of myocardial creep was evaluated using two metrics, the test-retest repeatability of the sTPD and iTPD, obtained for the volunteers, and the AUC analyses obtained for the patients. Test-retest repeatability of the motion detection and correction technique is key for the clinical implementation; in this study, we tested the repeatability using SEM in the volunteer cohort in which no underlying perfusion deficits were expected. A more heterogeneous test-retest assessment of both sTPD and iTPD was observed when using Standard
Recon in comparison to the 3xMC technique, which in combination with an increased bias observed for the Standard
Recon highlights the detrimental impact of motion during rest/stress MPI sessions. The AUC assessments obtained for the elderly patient cohort with comorbidities support the finding in the healthy volunteer cohort. For the AUC assessments, the 3xMC provided significantly improved assessments of the ischemic burden (iTPD), highlighting the detrimental effect of motion during the MPI acquisitions (Figure
2). Further, the improved iTPD assessments obtained from 3xMC underline the importance of incorporating sophisticated motion correction protocols into routine assessments as the patients, on average, exert creep events 2.5 times during the 3.5 minutes reconstruction window considered in this study.