Chronic thromboembolic pulmonary hypertension (CTEPH) causes severe pulmonary hypertension. Right ventricular (RV) function has a significant impact on the prognosis of CTEPH, as it does on other forms of pulmonary arterial hypertension (PH).¹ Cine imaging has enabled accurate and reproducible assessment of RV function, but this procedure is time consuming and requires significant operator expertise due to the complex RV anatomy. Feature tracking imaging (FTI) is a novel MRI-based method for analysis of myocardial strain; it is fast, simple, and has potential for clinical use.² FTI can be tracked on routine steady-state free precession or gradient echo cine imaging, without the need for additional imaging such as tagging methods.In this study, we evaluated the potential of FTI for right ventricular functional assessment in patients with CTEPH.Twelve patients with CTEPH and 5 healthy control subjects underwent cardiac MRI with a 1.5 T clinical machine (MAGNETOM Sonata, Siemens AG Healthcare Sector, Erlangen, Germany). The CTEPH patients then underwent balloon pulmonary angioplasty (BPA) and follow-up cardiac MRI with the same protocol after BPA. Short and long axial cine images were obtained using segmented SSFP (True-FISP) cine sequences with a standardized clinical protocol (TE/TR=1.6/3.2msec, flip angle 55°, FOV 340mm, matrix 190×190, slice thickness 6 mm, and temporal resolution 45 msec). Myocardial strains were obtained with dedicated feature tracking software (Diogenes MRI, TomTec Imaging Systems, Germany). After semi-automated tracing of the endocardial and epicardial borders on cine images, the strain values were calculated. Global radial and circumferential strains (GRS and GCS) were derived from the short axis plane, and the global longitudinal strain (GLS) was derived from the 4-chamber long axis plane (Figure 1). The FTI-derived strains were compared with the RV function (RV ejection fraction: RVEF) analyzed using cine imaging and the mean pulmonary artery pressure (mPAP) measured by right heart catheterization.The mean GRS, GCS, and GLS in CTEPH patients showed a significant reduction when compared to the normal controls (p=0.04, p=0.01, and p=0.001, respectively). The mean GLS was significantly reduced even in preserved RVEF patients (>40%) with CTEPH when compared to the normal controls (p=0.01). Figure 2 and 3 show the strain correlation with RVEF and mPAP. Significant correlation with GCS and GLS were observed for RVEF and mPAP. Compared to GCS, GLS showed better correlation. The mean GRS, GCS, and GLS significantly increased after BPA. Table 1 shows the correlation between the change in each strain by FTI and the change in RVEF. The change in GLS had the best correlation with the change in RVEF (r=0.78 / p=0.02).Our results demonstrated that FTI allows the detailed assessment of RV strain from conventional cine images in CTEPH patients. Currently, Doppler echocardiography (cardiac US) is widely used for noninvasive strain measurement, but cardiac US has disadvantages of a limited acoustic window and observer dependency. FTI software delivers outputs of myocardial strain, segmental velocity, and displacement parameters that are relatively quick in terms of image acquisition and post processing. The technique avoids the additional time needed for either tissue phase mapping or tagging and raises the possibility of retrospective analysis of existing MRI datasets. In this study, when compared to the GRS and GCS, the GLS showed better correlation with the RVEF and mPAP. Furthermore, the GLS showed a significant reduction even in preserved EF patients. Previous studies of ventricular contraction have indicated a difference between LV and RV wall motion.³ The LV contraction is accomplished by circumferential shortening, whereas the RV function is mainly achieved by shortening of longitudinal direction in the free wall. The reduction in the peak longitudinal strain value in PH patients, even with preserved RVEF, suggested that the longitudinal strain is a potential sensitive marker for RV dysfunction before other recognized markers fall. Because RVEF has prognostic potential for PH patients, the longitudinal strain with high predictive value for RVEF might be useful in clinical practice. In this study, FTI enabled the quantification of the RV functional improvement after BPA. The change in GLS, in particular, has the best correlation with the change in RVEF. Non-invasive longitudinal strain measurements have the potential ability to monitor the RV function and follow PH patients in clinical settings.RV strain measurement with FTI is clinically feasible and could be clinically useful as a good detector of RV dysfunction and for repeatable monitoring after therapeutic intervention.