Multivendor comparison of global and regional 2D cardiovascular magnetic resonance feature tracking strains vs tissue tagging at 3T

Background Cardiovascular magnetic resonance (CMR) 2D feature tracking (FT) left ventricular (LV) myocardial strain has seen widespread use to characterize myocardial deformation. Yet, validation of CMR FT measurements remains scarce, particularly for regional strain. Therefore, we aimed to perform intervendor comparison of 3 different FT software against tagging. Methods In 61 subjects (18 healthy subjects, 18 patients with chronic myocardial infarction, 15 with dilated cardiomyopathy, and 10 with LV hypertrophy due to hypertrophic cardiomyopathy or aortic stenosis) were prospectively compared global (G) and regional transmural peak-systolic Lagrangian longitudinal (LS), circumferential (CS) and radial strains (RS) by 3 FT software (cvi42, Segment, and Tomtec) among each other and with tagging at 3T. We also evaluated the ability of regional LS, CS, and RS by different FT software vs tagging to identify late gadolinium enhancement (LGE) in the 18 infarct patients. Results GLS and GCS by all 3 software had an excellent agreement among each other (ICC = 0.94–0.98 for GLS and ICC = 0.96–0.98 for GCS respectively) and against tagging (ICC = 0.92–0.94 for GLS and ICC = 0.88–0.91 for GCS respectively), while GRS showed inconsistent agreement between vendors (ICC 0.10–0.81). For regional LS, the agreement was good (ICC = 0.68) between 2 vendors but less vs the 3rd (ICC 0.50–0.59) and moderate to poor (ICC 0.44–0.47) between all three FT software and tagging. Also, for regional CS agreement between 2 software was higher (ICC = 0.80) than against the 3rd (ICC = 0.58–0.60), and both better agreed with tagging (ICC = 0.70–0.72) than the 3rd (ICC = 0.57). Regional RS had more variation in the agreement between methods ranging from good (ICC = 0.75) to poor (ICC = 0.05). Finally, the accuracy of scar detection by regional strains differed among the 3 FT software. While the accuracy of regional LS was similar, CS by one software was less accurate (AUC 0.68) than tagging (AUC 0.80, p < 0.006) and RS less accurate (AUC 0.578) than the other two (AUC 0.76 and 0.73, p < 0.02) to discriminate segments with LGE. Conclusions We confirm good agreement of CMR FT and little intervendor difference for GLS and GCS evaluation, with variable agreement for GRS. For regional strain evaluation, intervendor difference was larger, especially for RS, and the diagnostic performance varied more substantially among different vendors for regional strain analysis.

Regional myocardial function at preclinical disease stage of hypertrophic cardiomyopathy in female gene variant carriers

We recently showed more severe diastolic dysfunction at the time of myectomy in female compared to male patients with obstructive hypertrophic cardiomyopathy. Early recognition of aberrant cardiac contracility using cardiovascular magnetic resonance (CMR) imaging may identify women at risk of cardiac dysfunction. To define myocardial function at an early disease stage, we studied regional cardiac function using CMR imaging with tissue tagging in asymptomatic female gene variant carriers. CMR imaging with tissue tagging was done in 13 MYBPC3, 11 MYH7 and 6 TNNT2 gene carriers and 16 age-matched controls. Regional peak circumferential strain was derived from tissue tagging images of the basal and midventricular segments of the septum and lateral wall. Left ventricular wall thickness and global function were comparable between MYBPC3, MYH7, TNNT2 carriers and controls. MYH7 gene variant carriers showed a different strain pattern as compared to the other groups, with higher septal peak circumferential strain at the basal segments compared to the lateral wall, whereas MYBPC3, TNNT2 carriers and controls showed higher strain at the lateral wall compared to the septum. Only subtle gene-specific changes in strain pattern occur in the myocardium preceding development of cardiac hypertrophy. Overall, our study shows that there are no major contractile deficits in asymptomatic females carrying a pathogenic gene variant, which would justify the use of CMR imaging for earlier diagnosis.

Global and regional cardiac function

Cardiovascular magnetic resonance is currently the most accurate and reproducible method for the measurement of biventricular global and regional systolic function, as well as diastolic and atrial function. Regional wall motion can be visually evaluated and quantified with tissue tagging or feature tracking analysis techniques. Wall motion analysis is usually performed at rest but can also be done with low-dose and high-dose dobutamine. Segmental strain is best measured with tissue tagging or displacement-encoded phase contrast imaging. Current analysis software enables the measurement of ventricular volumes throughout the cardiac cycle, and assessment of left and right ventricular diastolic function can be done by evaluating the time–flow curve, derived from the volume–time curve obtained in the volumetric analysis. Although contrast between flowing blood and the myocardium in cardiac cine images is typically excellent, the precise placement of the contours is reader-dependent and training is highly recommended due to the subjective nature of contour placement.

A Nearest Neighbor Finite Element Method (NNFEM) for Validating Left-Ventricular Regional Strain from Displacement Encoding with Stimulated Echoes (DENSE) MRI, Compared to Tagged MRI

Cardiovascular magnetic resonance (CMR) is a magnetic resonance imaging (MRI) technique that is considered the most viable noninvasive technology for quantifying and visualizing regional myocardial function. CMR is expensive but characterized by higher spatial resolution and functional observations. The attribute of high spatial resolution allows quantitative assessment of cardiac wall motion and computation of transmural strains, allowing phenotyping cardiovascular physiopathologies [1-9]. Currently two CMR techniques are accepted as standard research practice which are 1. MRI tissue tagging (TMRI) [1-3] and 2. Stimulated echoes [6-9]. The first of the two, TMRI, is a method for tracking myocardial motion which places noninvasive markers (tags) within the tissue by locally induced perturbations of the magnetization. The altered magnetization shows as dark lines in the tagged region in successive images and myocardial deformation during the cardiac cycle is tracked [2,3]. However the intrinsic problem with tag lines is their fading after several cardiac phases. Hence, in addition to improvements toward longer tag persistence, parallel advancements in non-TMRI quantitative gradient technologies have also been made. One such technique is displacement encoding with stimulated echoes (DENSE) which directly encodes displacements into MRI phase data in three orthogonal phase encoding directions and facilitates rapid quantification of myocardial displacement through the cardiac cycle [6-9]. It is noted that while DENSE uses high displacement encoding frequencies resulting in phase wrapping, accurate measurements of displacements can be obtained using quality-guided spatio-temporal phase unwrapping algorithms [9].

Left Ventricular Pressure Gating in Ovine Cardiac Studies: A Software-Based Method

Cardiac imaging using magnetic resonance requires a gating signal in order to compensate for motion. Human patients are routinely scanned using an electrocardiogram (ECG) as a gating signal during imaging. However, we found that in sheep the ECG is not a reliable method for gating. We developed a software based method that allowed us to use the left ventricular pressure (LVP) as a reliable gating signal. By taking the time derivative of the LVP (dP/dt), we were able to start imaging at both end-diastole for systolic phase images, and end-systole for diastolic phase images. We also used MR tissue tagging to calculate 3D strain information during diastole. Using the LVP in combination with our digital circuit provided a reliable and time efficient method for ovine cardiac imaging. Unlike the ECG signal the left ventricular pressure was a clean signal and allowed for accurate, nondelay based triggering during systole and diastole.