Myocardial Tissue Phase Mapping with Cine Phase-Contrast MR Imaging: Regional Wall Motion Analysis in Healthy Volunteers

Texture analysis of native T1 images as a novel method for non-invasive assessment of heart failure with preserved ejection fraction in end-stage renal disease patients

OBJECTIVES

To explore the diagnostic potential of texture analysis applied to native T1 maps obtained from cardiac magnetic resonance (CMR) images for the assessment of heart failure with preserved ejection fraction (HFpEF) among patients with end-stage renal disease (ESRD).

METHODS

This study, conducted from June 2018 to November 2020, included 119 patients (35 on hemodialysis, 55 on peritoneal dialysis, and 29 with kidney transplants) in Renji Hospital. Native T1 maps were assessed with texture analysis, using a freely available software package, in participants who underwent cardiac MRI at 3.0 T. Four texture features, selected by dimension reduction specific to the diagnosis of HFpEF, were analyzed. Multivariate logistic regression was performed to examine the independent association between the selected features and HFpEF in ESRD patients.

RESULTS

Seventy-six of 119 patients were diagnosed with HFpEF. Demographic, laboratory, cardiac MRI, and echocardiogram characteristics were compared between HFpEF and non-HFpEF groups. The four texture features that were analyzed showed statistically significant differences between groups. In multivariate analysis, age, left atrial volume index (LAVI), and sum average 4 (SA4) turned out to be independent predictors for HFpEF in ESRD patients. Combining the texture feature, SA4, with typical predictive factors resulted in higher C-index (0.923 vs. 0.898, p = 0.045) and a sensitivity and specificity of 79.2% and 95.2%, respectively.

CONCLUSIONS

Texture analysis of T1 maps adds diagnostic value to typical clinical parameters for the assessment of heart failure with preserved ejection fraction in patients with end-stage renal disease.

KEY POINTS

• Non-invasive assessment of HFpEF can help predict prognosis in ESRD patients and help them take timely preventative measures. • Texture analysis of native T1 maps adds diagnostic value to the typical clinical parameters for the assessment of HFpEF in patients with ESRD.

Differential Adaptation of Biventricular Myocardial Kinetic Energy in Patients With Repaired Tetralogy of Fallot Assessed by MR Tissue Phase Mapping

BACKGROUND

The myocardial kinetic energy (KE) and its association with pulmonary regurgitation (PR) have yet to be investigated in repaired tetralogy of Fallot (rTOF) patients.

PURPOSE

To evaluate the adaptation of myocardial KE in rTOF patients by tissue phase mapping (TPM).

STUDY TYPE

Prospective.

POPULATION

A total of 49 rTOF patients (23 ± 5 years old; male = 32), 47 normal controls (22 ± 1 year old; male = 29).

FIELD STRENGTH/SEQUENCE

3-T/2D dark-blood three-directional velocity-encoded gradient-echo sequence.

ASSESSMENT

Left and right ventricle (LV, RV) myocardial KE in radial (KE_r ), circumferential (KE_ø ), longitudinal (KE_z ) directions. The proportions of KE in each direction to the sum of all KE (KE_røz ): %KE_r , %KE_ø , %KE_z . PR fraction.

STATISTICAL TEST

Student's t test, multivariable regression. Statistical significance: P < 0.05.

RESULTS

In rTOF group, LV KE_z remained normal in systole (P = 0.565) and diastole (P = 0.210), whereas diastolic LV %KE_z (62% ± 14% vs. 72% ± 7%) and systolic LV %KE_ø (9% ± 6% vs. 20% ± 7%) were significantly decreased. The KE_r and %KE_r of both ventricles significantly increased in the rTOF group (RV in diastole: 6 ± 3 vs. 3 ± 1 μJ and 54% ± 13% vs. 27% ± 7%). The rTOF group exhibited significantly higher RV/LV ratios of %KE_r (systole: 1.3 ± 0.3 vs. 1.0 ± 0.3) and %KE_ø (systole: 1.6 ± 0.8 vs. 1.0 ± 0.3) and significantly lower ratios of %KE_z in systole (0.7 ± 0.2 vs. 1.0 ± 0.1) and diastole (0.5 ± 0.2 vs. 0.9 ± 0.1). In multivariable regression analysis, the RV peak systolic KE_røz , RV systolic KE_z , and LV diastolic %KE_ø were independently associated with PR fraction in the rTOF group (adjusted R²  = 0.479).

DATA CONCLUSION

In rTOF patients, the adaptation of the KE proportion occurred earlier than that of the KE amplitude, and the biventricular balance of %KE was disrupted. PR may cause differential KE adaptation in RV and LV. TPM-derived KE may be useful in investigation of myocardial adaptation in rTOF patients.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 3.

The role of cardiac magnetic resonance imaging in the assessment of heart failure with preserved ejection fraction

Heart failure (HF) is a major cause of morbidity and mortality worldwide. Current classifications of HF categorize patients with a left ventricular ejection fraction of 50% or greater as HF with preserved ejection fraction or HFpEF. Echocardiography is the first line imaging modality in assessing diastolic function given its practicality, low cost and the utilization of Doppler imaging. However, the last decade has seen cardiac magnetic resonance (CMR) emerge as a valuable test for the sometimes challenging diagnosis of HFpEF. The unique ability of CMR for myocardial tissue characterization coupled with high resolution imaging provides additional information to echocardiography that may help in phenotyping HFpEF and provide prognostication for patients with HF. The precision and accuracy of CMR underlies its use in clinical trials for the assessment of novel and repurposed drugs in HFpEF. Importantly, CMR has powerful diagnostic utility in differentiating acquired and inherited heart muscle diseases presenting as HFpEF such as Fabry disease and amyloidosis with specific treatment options to reverse or halt disease progression. This state of the art review will outline established CMR techniques such as transmitral velocities and strain imaging of the left ventricle and left atrium in assessing diastolic function and their clinical application to HFpEF. Furthermore, it will include a discussion on novel methods and future developments such as stress CMR and MR spectroscopy to assess myocardial energetics, which show promise in unraveling the mechanisms behind HFpEF that may provide targets for much needed therapeutic interventions.

The Potential for Quantifying Regional Distributions of Radial and Shear Strain in the Thoracic and Abdominal Aortic Wall Using Spiral Cine DENSE Magnetic Resonance Imaging

Aortic displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) was recently developed to assess heterogeneities in aortic wall circumferential strain (CS). However, previous studies neglected potential radial and shear strain (RSS) distributions. Herein, we present an improved aortic DENSE MRI postprocessing method to assess the feasibility of quantifying all components of the two-dimensional (2D) strain tensor. 32 previously acquired 2D DENSE scans from three distinct aortic locations were re-analyzed. Contrasting previous studies, displacements of the inner and outer aortic wall layers were processed separately to preserve RSS. Differences in regional strain between the new and old postprocessing methods were evaluated, along with interobserver, intraobserver, and interscan repeatability for all strain components. The new postprocessing method revealed an overall mean absolute difference in regional CS of 0.01 ± 0.01 compared to the prior method, with minimal impact on CS repeatability. Mean absolute magnitudes of regional RSS increased significantly compared to changes in CS (radial 0.04 ± 0.05, p < 0.001; shear 0.04 ± 0.04, p = 0.02). Most repeatability metrics for RSS were significantly worse than for CS. The unique distributions of RSS for each axial location associated well with local periaortic structures and mean aortic displacement. The new postprocessing method captures heterogeneous distributions of nonzero RSS which may provide new information for improving clinical diagnostics and computational modeling of heterogeneous aortic wall mechanics. However, future studies are required to improve the repeatability of RSS and assess the influence of partial volume effects.

Left ventricular myocardial strain quantification with two- and three-dimensional cardiovascular magnetic resonance based tissue tracking

Background

Cardiovascular magnetic resonance based tissue tracking (CMR-TT) was reported to provide detailed insight into left ventricular (LV) contractile function and deformation with both of two- and three-dimensional (2/3D) algorithms. This study was designed to investigate the feasibility and reproducibility of these two techniques for measuring LV global and segmental strain, and establish gender- and age-related reference values of global multi-dimensional peak strains among large healthy population.

Methods

We retrospectively recruited 150 healthy volunteers (75 males/females) and divided them into three age groups (G_20-40, G_41-60 and G_61-80). LV global mean and peak strains as well as segmental strains in radial, circumferential and longitudinal directions were derived from post-hoc 2/3D CMR-TT analysis of standard steady-state free precession (SSFP) cine images acquired at 1.5T field strength.

Results

Both 2D and 3D CMR-TT modalities enable the tracking of LV myocardial tissues and generate global and segmental strain data. By comparison, 3D CMR-TT was more feasible in measuring segmental deformation since it could generate values at all segments. The amplitudes of LV 3D global peak strain were the smallest among those of 2/3D corresponding global mean or peak strains except in the radial direction, and was highly correlated with 2D global mean strains (correlation coefficient r=0.71-0.90), 2D global peak strains (r=0.75-0.89) and 3D global mean strains (all r=0.99). In healthy cohort, LV 3D global peak values were 44.4%±13.0% for radial, -17.0%±2.7% for circumferential and -15.4%±2.3% for longitudinal strain. Females showed significantly larger amplitude of strains than males, especially in G_61-80 (P<0.05). The subjects in G_61-80 showed larger amplitude of strains than the volunteers in younger groups. The intra- and inter-observer agreement of 2/3D CMR-TT analysis in evaluating LV myocardial global deformation was better than segmental measurement.

Conclusions

CMR-TT is a feasible and reproducible technique for assessing LV myocardial deformation, especially at the global level. The establishment of specific reference values of LV global and segmental systolic strains and the investigation of dimension-, gender- and age-related differences provide a fundamental insight into the features of LV contraction and works as an essential step in clinical routine.

Morphologies and prognostic significance of left ventricular volume/time curves with cardiac magnetic resonance in patients with non-ischaemic heart failure and left bundle branch block

Patients with non-ischaemic systolic heart failure (HF) and left bundle branch block (LBBB) can display a wide or narrow pattern (WP/NP) of the systolic phase of the left ventricular (LV) volume/time (V/t) curve in cardiac magnetic resonance (CMR). The clinical and prognostic significance of these patterns is unknown. Consecutive patients with non-ischaemic HF, LV ejection fraction < 50% and LBBB underwent 1.5 T CMR. Maximal dyssynchrony time (time between the earliest and latest end-systolic peaks), systolic dyssynchrony index (standard deviation of times to peak volume change), and contractility index (maximum rate of change of pressure-normalized stress) were calculated. The endpoint was a composite of cardiovascular death, HF hospitalization, and appropriate defibrillator shock. NP was found in 29 and WP in 72 patients. WP patients had higher volumes and NT-proBNP, and lower LVEF. WP patients had a longer maximal dyssynchrony time (absolute duration: 192 ± 80 vs. 143 ± 65 ms, p < 0.001; % of RR interval: 25 ± 11% vs. 8 ± 4%, p < 0.001), a higher systolic dyssynchrony index (13 ± 4 vs. 7 ± 3%, p < 0.001), and a lower contractility index (2.6 ± 1.2 vs 3.2 ± 1.7, p < 0.05). WP patients had a shorter survival free from the composite endpoint regardless of age, NT-proBNP or LVEF. Nonetheless, WP patients responded more often to cardiac resynchronization therapy (CRT) than those with NP (24/28 [86%] vs. 1/11 [9%] responders, respectively; p < 0.001). In patients with non-ischaemic systolic HF and LBBB, the WP of V/t curves identifies a subgroup of patients with greater LV dyssynchrony and worse outcome, but better response to CRT.

Cardiac MRI Myocardial Functional and Tissue Characterization Detects Early Cardiac Dysfunction in a Mouse Model of Chemotherapy-Induced Cardiotoxicity

BACKGROUND

Doxorubicin and doxorubicin-trastuzumab combination chemotherapy have been associated with cardiotoxicity that eventually leads to heart failure and may limit dose-effective cancer treatment. Current diagnostic strategies rely on decreased ejection fraction (EF) to diagnose cardiotoxicity.

PURPOSE

The aim of this study is to explore the potential of cardiac MR (CMR) imaging to identify imaging biomarkers in a mouse model of chemotherapy-induced cardiotoxicity.

METHODS

A cumulative dose of 25 mg/kg doxorubicin was administered over three weeks using subcutaneous pellets (n = 9, Dox). Another group (n = 9) received same dose of Dox and a total of 10 mg/kg trastuzumab (DT). Mice were imaged at baseline, 5/6 weeks and 10 weeks post-treatment on a 7T MRI system. The protocol included short-axis cine MRI covering the left ventricle (LV) and mid-ventricular short-axis tissue phase mapping (TPM), pre- and post-contrast T1 mapping, T2 mapping and Displacement Encoding with Stimulated Echoes (DENSE) strain encoded MRI. EF, peak myocardial velocities, native T1, T2, extracellular volume (ECV), and myocardial strain were quantified. N = 7 mice were sacrificed for histopathologic assessment of apoptosis at 5/6 weeks.

RESULTS

Global peak systolic longitudinal velocity was reduced at 5/6 weeks in Dox (0.6 ± 0.3 vs 0.9 ± 0.3, p = 0.02). In the Dox group, native T1 was reduced at 5/6 weeks (1.3 ± 0.2 ms vs 1.6 ± 0.2 ms, p = 0.02), and relatively normalized at week 10 (1.4 ± 0.1 ms vs 1.6 ± 0.2 ms, p > 0.99). There was no change in EF and other MRI parameters and histopathologic results demonstrated minimal apoptosis in all mice (~1-2 apoptotic cell/high power field), suggesting early-stage cardiotoxicity.

CONCLUSIONS

In a mouse model of chemotherapy-induced cardiotoxicity using doxorubicin and trastuzumab, advanced CMR shows promise in identifying treatment-related decrease in myocardial velocity and native T1 prior to the onset of cardiomyocyte apoptosis and reduction of EF.

Evaluating Biventricular Myocardial Velocity and Interventricular Dyssynchrony in Adult Patients During the First Year After Heart Transplantation

BACKGROUND

Magnetic resonance tissue phase mapping (TPM) measures three-directional myocardial velocities of the left and right ventricle (LV, RV). This noninvasive technique may supplement endomyocardial biopsy (EMB) in monitoring grafts post-heart transplantation (HTx).

PURPOSE

To assess biventricular myocardial velocity alterations in grafts and investigate the relationship between velocities and acute cellular rejection (ACR) episodes.

STUDY TYPE

Prospective.

SUBJECTS

Twenty-seven patients within 1 year post-HTx (49 ± 13 years, 19 M) and 18 age-matched controls (49 ± 15 years, 12 M).

FIELD STRENGTH/SEQUENCE

1.5T, 2D balanced steady-state free precession, and TPM.

ASSESSMENT

Ventricular function: end-diastolic and end-systolic volumes, stroke volumes, ejection fraction (EF), and myocardial mass. TPM velocities: peak-systolic and peak-diastolic velocities, cardiac twist, and interventricular dyssynchrony. ACR rejection episodes: International Society for Heart and Lung Transplantation grading of EMB specimens.

STATISTICAL TESTS

The Lilliefors test for normality, unpaired t-tests, and Wilcoxon rank-sum tests for normally and nonnormally distributed data, respectively, were used, as well as multivariate regression for confounding variables and Pearson's correlation for associations between TPM velocities and global function.

RESULTS

Compared to controls, HTx patients demonstrated reduced biventricular systolic longitudinal velocities (LV: 5.2 ± 2.1 vs. 4.0 ± 1.5 cm/s, P < 0.05; RV: 4.2 ± 1.3 vs. 3.1 ± 1.2 cm/s, P < 0.01). Correlation analysis revealed significant positive relationships for biventricular EF with radial peak velocities of the same ventricle in both systole and diastole (LV systole: r = 0.48, P < 0.01; LV diastole: r = 0.28, P < 0.05; RV systole: r = 0.35, P < 0.01; RV diastole: r = 0.36, P < 0.01). Segmentally, longitudinal velocities were impaired in 7/16 LV segments and 5/10 RV segments in systole and 7/10 RV segments in diastole. TPM analysis in studies with >4 preceding ACR episodes showed globally reduced RV and LV systolic radial velocity, and segmentally reduced radial and longitudinal systolic velocities.

DATA CONCLUSION

Biventricular global and segmental velocities were reduced in HTx patients. Patients with >4 rejection episodes showed reduced myocardial velocities. The TPM sequence may add functional information for monitoring graft dysfunction.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 2 J. Magn. Reson. Imaging 2020;52:920-929.

Altered regional myocardial velocities by tissue phase mapping and feature tracking in pediatric patients with hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is associated with heart failure, atrial fibrillation and sudden death. Reduced myocardial function has been reported in HCM despite normal left ventricular (LV) ejection fraction. Additionally, LV fibrosis is associated with elevated T1 and might be an outcome predictor.

OBJECTIVE

To systematically compare tissue phase mapping and feature tracking for assessing regional LV function in children and young adults with HCM and pediatric controls, and to evaluate structure-function relationships among myocardial velocities, LV wall thickness and myocardial T1.

MATERIALS AND METHODS

Seventeen pediatric patients with HCM and 21 age-matched controls underwent cardiac MRI including standard cine imaging, tissue phase mapping (two-dimensional cine phase contrast with three-directional velocity encoding), and modified Look-Locker inversion recovery to calculate native global LV T1. Maximum LV wall thickness was measured on cine images. LV radial, circumferential and long-axis myocardial velocity time courses, as well as global and segmental systolic and diastolic peak velocities, were quantified from tissue phase mapping and feature tracking.

RESULTS

Both tissue phase mapping and feature tracking detected significantly decreased global and segmental diastolic radial and long-axis peak velocities (by 12-51%, P<0.001-0.05) in pediatric patients with HCM vs. controls. Feature tracking peak velocities were lower than directly measured tissue phase mapping velocities (mean bias = 0.3-2.9 cm/s). Diastolic global peak velocities correlated moderately with global T1 (r = -0.57 to -0.72, P<0.01) and maximum wall thickness (r = -0.37 to -0.61, P<0.05).

CONCLUSION

Both tissue phase mapping and feature tracking detected myocardial velocity changes in children and young adults with HCM vs. controls. Associations between impaired diastolic LV velocities and elevated T1 indicate structure-function relationships in HCM.

Optimal Dual-VENC Unwrapping in Phase-Contrast MRI

Dual-VENC strategies have been proposed to improve the velocity-to-noise ratio in phase-contrast MRI. However, they are based on aliasing-free high-VENC data. The aim of this paper is to propose a dual-VENC velocity estimation method allowing high-VENC aliased data. For this purpose, we reformulate the phase-contrast velocity as a least squares estimator, providing a natural framework for including multiple encoding gradient measurements. By analyzing the mathematical properties of both single- and dual-VENC problems, we can justify theoretically high/low-VENC ratios such that the aliasing velocity can be minimized. The resulting reconstruction algorithm was assessed using three types of data: numerical, experimental, and volunteers. In clinical practice, this method would allow shorter examination times by avoiding tedious adaptation of VENC values by repeated scans.

Impact of age and cardiac disease on regional left and right ventricular myocardial motion in healthy controls and patients with repaired tetralogy of fallot

The assessment of both left (LV) and right ventricular (RV) motion is important to understand the impact of heart disease on cardiac function. The MRI technique of tissue phase mapping (TPM) allows for the quantification of regional biventricular three-directional myocardial velocities. The goal of this study was to establish normal LV and RV velocity parameters across a wide range of pediatric to adult ages and to investigate the feasibility of TPM for detecting impaired regional biventricular function in patients with repaired tetralogy of Fallot (TOF). Thirty-six healthy controls (age = 1-75 years) and 12 TOF patients (age = 5-23 years) underwent cardiac MRI including TPM in short-axis locations (base, mid, apex). For ten adults, a second TPM scan was used to assess test-retest reproducibility. Data analysis included the calculation of biventricular radial, circumferential, and long-axis velocity components, quantification of systolic and diastolic peak velocities in an extended 16 + 10 LV + RV segment model, and assessment of inter-ventricular dyssynchrony. Biventricular velocities showed good test-retest reproducibility (mean bias ≤ 0.23 cm/s). Diastolic radial and long-axis peak velocities for LV and RV were significantly reduced in adults compared to children (19-61%, p < 0.001-0.02). In TOF patients, TPM identified significantly reduced systolic and diastolic LV and RV long-axis peak velocities (20-50%, p < 0.001-0.05) compared to age-matched controls. In conclusion, tissue phase mapping enables comprehensive analysis of global and regional biventricular myocardial motion. Changes in myocardial velocities associated with age underline the importance of age-matched controls. This pilot study in TOF patients shows the feasibility to detect regionally abnormal LV and RV motion.

Modeling left ventricular dynamics using a switched system approach based on a modified atrioventricular piston unit

The contribution of the longitudinal atrioventricular plane displacement to ventricular pumping has drawn more and more attentions. In this paper, differential equations of the left ventricle (LV) are derived via the atrioventricular piston concept. The contribution of left ventricular radial function to blood flow was converted to an equivalent coefficient. A systemic circulatory model incorporating the modified atrioventricular piston unit was developed on a switched system form by adding some state-dependent switching planes. Simulation results prove that the end-systolic pressure volume relationship of the model with a changing systemic arterial resistance is approximately linear and insensitive to perturbations in afterload. Then the LV model was validated using a data fitting method. A pressure-volume loop from a patient undergoing routine diagnostic cardiac catheterization with LV angiography was used as measurements. Model parameters and the trapezoidal profile of contraction forces were adjusted by a trial method. The root mean squared error between the measured and estimated LV pressure is 2.99 mmHg. The LV compliance is 0.34 ml/mmHg. The ratio between left ventricular and left atrial cross-section is 1.8. Therefore, parameter values used in the modified LV model match physiological data. The model can reproduce the realistic pressure-flow relationship in the LV chamber.

Strain imaging using cardiac magnetic resonance

The objective assessments of left ventricular (LV) and right ventricular (RV) ejection fractions (EFs) are the main important tasks of routine cardiovascular magnetic resonance (CMR). Over the years, CMR has emerged as the reference standard for the evaluation of biventricular morphology and function. However, changes in EF may occur in the late stages of the majority of cardiac diseases, and being a measure of global function, it has limited sensitivity for identifying regional myocardial impairment. On the other hand, current wall motion evaluation is done on a subjective basis and subjective, qualitative analysis has a substantial error rate. In an attempt to better quantify global and regional LV function; several techniques, to assess myocardial deformation, have been developed, over the past years. The aim of this review is to provide a comprehensive compendium of all the CMR techniques to assess myocardial deformation parameters as well as the application in different clinical scenarios.

Myocardial motion analysis based on an optical flow method using tagged MR images

We developed a method of velocimetry based on an optical flow method using quantitative analyses of tagged magnetic resonance (MR) images (tagged MR-optical flow velocimetry, tMR-O velocimetry). The purpose of our study was to examine the accuracy of measurement of the proposed tMR-O velocimetry. We performed retrospective pseudo-electrocardiogram (ECG) gating tagged cine MR imaging on a rotating phantom. We optimized imaging parameters for tagged MR imaging, and validated the accuracy of tMR-O velocimetry. Our results indicated that the difference between the reference velocities and the computed velocities measured using optimal imaging parameters was less than 1%. In addition, we performed tMR-O velocimetry and echocardiography on 10 healthy volunteers, for four sections of the heart (apical, midventricular, and basal sections aligned with the short-axis, and a four-chamber section aligned with the long-axis), and obtained radial and longitudinal myocardial velocities in these sections. We compared the myocardial velocities obtained using tMR-O velocimetry with those obtained using echocardiography. Our results showed good agreement between tMR-O velocimetry and echocardiography in the radial myocardial velocities in three short-axial sections and longitudinal myocardial velocities on the midventricular portion of the four-chamber section in the long-axis. In the study conducted on the rotating phantom, tMR-O velocimetry showed high accuracy; moreover, in the healthy volunteers, the myocardial velocities obtained using tMR-O velocimetry were relatively similar to those obtained using echocardiography. In conclusion, tMR-O velocimetry is a potentially feasible method for analyzing myocardial motion in the human heart.

Segmental biventricular analysis of myocardial function using high temporal and spatial resolution tissue phase mapping

OBJECTIVE

Myocardial dysfunction of the right ventricle (RV) is an important indicator of RV diseases, e.g. RV infarction or pulmonary hypertension. Tissue phase mapping (TPM) has been widely used to determine function of the left ventricle (LV) by analyzing myocardial velocities. The analysis of RV motion is more complicated due to the different geometry and smaller wall thickness. The aim of this work was to adapt and optimize TPM to the demands of the RV.

MATERIALS AND METHODS

TPM measurements were acquired in 25 healthy volunteers using a velocity-encoded phase-contrast sequence and kt-accelerated parallel imaging in combination with optimized navigator strategy and blood saturation. Post processing was extended by a 10-segment RV model and a detailed biventricular analysis of myocardial velocities was performed.

RESULTS

High spatio-temporal resolution (1.0 × 1.0 × 6 mm³, 21.3 ms) and the optimized blood saturation enabled good delineation of the RV and its velocities. Global and segmental velocities, as well as time to peak velocities showed significant differences between the LV and RV. Furthermore, complex timing of the RV could be demonstrated by segmental time to peak analysis.

CONCLUSION

High spatio-temporal resolution TPM enables a detailed biventricular analysis of myocardial motion and might provide a reliable tool for description and detection of diseases affecting left and right ventricular function.

Automated Description of Regional Left Ventricular Motion in Patients With Cardiac Amyloidosis: A Quantitative Study Using Heart Deformation Analysis

OBJECTIVE

The purpose of this article is to test the hypothesis that heart deformation analysis can automatically quantify regional myocardial motion patterns in patients with cardiac amyloidosis.

SUBJECTS AND METHODS

Eleven patients with cardiac amyloidosis and 11 healthy control subjects were recruited to undergo cardiac MRI. Cine images were analyzed using heart deformation analysis and feature tracking. Heart deformation analysis-derived myocardial motion indexes in radial and circumferential directions, including radial and circumferential displacement, radial and circumferential velocity, radial and circumferential strain, and radial and circumferential strain rate, were compared between the two groups.

RESULTS

) than did healthy control subjects. Heart deformation analysis-derived indexes correlated with feature tracking-derived indexes (r = 0.411 and 0.552).

CONCLUSION

Heart deformation analysis is able to automatically quantify regional myocardial motion in patients with cardiac amyloidosis without the need for operator interaction.

Magnetic resonance tissue phase mapping demonstrates altered left ventricular diastolic function in children with chronic kidney disease

BACKGROUND

Echocardiographic examinations have revealed functional cardiac abnormalities in children with chronic kidney disease.

OBJECTIVE

To assess the feasibility of MRI tissue phase mapping in children and to assess regional left ventricular wall movements in children with chronic kidney disease.

MATERIALS AND METHODS

Twenty pediatric patients with chronic kidney disease (before or after renal transplantation) and 12 healthy controls underwent tissue phase mapping (TPM) to quantify regional left ventricular function through myocardial long (Vz) and short-axis (Vr) velocities at all 3 levels of the left ventricle.

RESULTS

Patients and controls (age: 8 years-20 years) were matched for age, height, weight, gender and heart rate. Patients had higher systolic blood pressure. No patient had left ventricular hypertrophy on MRI or diastolic dysfunction on echocardiography. Fifteen patients underwent tissue Doppler echocardiography, with normal z-scores for mitral early diastolic (V_E), late diastolic (V_A) and peak systolic (V_S) velocities. Throughout all left ventricular levels, peak diastolic Vz and Vr (cm/s) were reduced in patients: Vz_base -10.6 ± 1.9 vs. -13.4 ± 2.0 (P < 0.0003), Vz_mid -7.8 ± 1.6 vs. -11 ± 1.5 (P < 0.0001), Vz_apex -3.8 ± 1.6 vs. -5.3 ± 1.6 (P = 0.01), Vr_base -4.2 ± 0.8 vs. -4.9 ± 0.7 (P = 0.01), Vr_mid -4.7 ± 0.7 vs. -5.4 ± 0.7 (P = 0.01), Vr_apex -4.7 ± 1.4 vs. -5.6 ± 1.1 (P = 0.05).

CONCLUSION

Tissue phase mapping is feasible in children and adolescents. Children with chronic kidney disease show significantly reduced peak diastolic long- and short-axis left ventricular wall velocities, reflecting impaired early diastolic filling. Thus, tissue phase mapping detects chronic kidney disease-related functional myocardial changes before overt left ventricular hypertrophy or echocardiographic diastolic dysfunction occurs.

Heart deformation analysis for automated quantification of cardiac function and regional myocardial motion patterns: A proof of concept study in patients with cardiomyopathy and healthy subjects

OBJECTIVE

To test the performance of HDA in characterizing left ventricular (LV) function and regional myocardial motion patterns in the context of cardiomyopathy based on cine cardiovascular magnetic resonance (CMR).

MATERIALS AND METHODS

Following the approval of the institutional review board (IRB), standard cine images of 45 subjects, including 15 healthy volunteers, 15 patients with hypertrophic cardiomyopathy (HCM) and 15 patients with dilated cardiomyopathy (DCM) were retrospectively analyzed using HDA. The variations of LV ejection fraction (LVEF), LV mass (LVM), and regional myocardial motion indices, including radial (Drr), circumferential (Dcc) displacement, radial (Vrr) and circumferential (Vcc) velocity, radial (Err), circumferential (Ecc) and shear (Ess) strain and radial (SRr) and circumferential (SRc) strain rate, were calculated and compared among subject groups. Inter-study reproducibility of HDA-derived myocardial motion indices were tested on 15 volunteers by using intra-class correlation coefficient (ICC) and coefficient of variation (CoV).

RESULTS

HDA identified significant differences in cardiac function and motion indices between subject groups. DCM patients had significantly lower LVEF (33.5±9.65%), LVM (105.88±21.93g), peak Drr (0.29±0.11cm), Vrr-sys (2.14±0.72cm/s), Err (0.17±0.08), Ecc (-0.08±0.03), SRr-sys (0.91±0.44s(-1)) and SRc-sys (-0.64±0.27s(-1)) compared to the other two groups. HCM patients demonstrated increased LVM (171.69±34.19) and lower peak Vcc-dia (0.78±0.30cm/s) than other subjects. Good inter-study reproducibility was found for all HDA-derived myocardial indices in healthy volunteers (ICC=0.664-0.942, CoV=15.1%-37.1%).

CONCLUSION

Without the need for operator interaction, HDA is a reproducible method for the automated characterization of global and regional LV function in the context of cardiomyopathy.

Reproducibility and observer variability of tissue phase mapping for the quantification of regional myocardial velocities

To systematically investigate the reproducibility of global and segmental left ventricular (LV) velocities derived from tissue phase mapping (TPM). Breath held and ECG synchronized TPM data (spatial/temporal resolution = 2 × 2 mm(2)/20.8 ms) were acquired in 18 healthy volunteers. To analyze scan-rescan variability, TPM was repeated in all subjects during a second visit separated by 16 ± 5 days. Data analysis included LV segmentation, and quantification of global and regional (AHA 16-segment modal) metrics of LV function [velocity-time curves, systolic and diastolic peak and time-to-peak (TTP) velocities] for radial (Vr), long-axis (Vz) and circumferential (VΦ) LV velocities. Mean velocity time curves in basal, mid-ventricular, and apical locations showed highly similar LV motion patterns for all three velocity components (Vr, VΦ, Vz) for scan and rescan. No significant differences for both systolic and diastolic peak and TTP myocardial velocities were observed. Segmental analysis revealed similar regional peak Vr and Vz during both systole and diastole except for three LV segments (p = 0.045, p = 0.033, and p = 0.009). Excellent (p < 0.001) correlations between scans and rescan for peak Vr (R(2) = 0.92), peak Vz (R(2) = 0.90), radial TTP (R(2) = 0.91) and long-axis TTP (R(2) = 0.88) confirmed good agreement. Bland-Altman analysis demonstrated excellent intra-observer and good inter-observer analysis agreement but increased variability for long axis peak velocities. TPM based analysis of global and regional myocardial velocities can be performed with good reproducibility. Robustness of regional quantification of long-axis velocities was limited but spatial velocity distributions across the LV could reliably be replicated.

Heart deformation analysis: measuring regional myocardial velocity with MR imaging

The aim of the present study was to test the hypothesis that heart deformation analysis (HDA) may serve as an alternative for the quantification of regional myocardial velocity. Nineteen healthy volunteers (14 male and 5 female) without documented cardiovascular diseases were recruited following the approval of the institutional review board (IRB). For each participant, cine images (at base, mid and apex levels of the left ventricle [LV]) and tissue phase mapping (TPM, at same short-axis slices of the LV) were acquired within a single magnetic resonance (MR) scan. Regional myocardial velocities in radial and circumferential directions acquired with HDA (Vrr and Vcc) and TPM (Vr and VФ) were measured during the cardiac cycle. HDA required shorter processing time compared to TPM (2.3 ± 1.1 min/case vs. 9.5 ± 3.7 min/case, p < 0.001). Moderate to good correlations between velocity components measured with HDA and TPM could be found on multiple myocardial segments (r = 0.460-0.774) and slices (r = 0.409-0.814) with statistical significance (p < 0.05). However, significant biases of velocity measures at regional myocardial areas between HDA and TPM were also noticed. By providing comparable velocity measures as TPM does, HDA may serve as an alternative for measuring regional myocardial velocity with a faster image processing procedure.

Rapid breath-hold assessment of myocardial velocities using spiral UNFOLD-ed SENSE tissue phase mapping

PURPOSE

To develop and validate a rapid breath-hold tissue phase mapping (TPM) sequence.

MATERIALS AND METHODS

The sequence was based on an efficient uniform density spiral acquisition, combined with data acceleration. A novel acquisition and reconstruction strategy enabled combination of UNFOLD (2×) and SENSE (3×): UNFOLD-ed SENSE. The sequence was retrospectively cardiac-gated, and a graphics processing unit (GPU) was used for rapid "online" reconstruction. The optimal UNFOLD parameters for the data were calculated using an in silico model. The technique was validated on a 1.5T MR scanner in 15 patients with known aortic valve disease, against a respiratory self-navigated free-breathing TPM technique. Quantitative image quality measures (velocity-to-noise and edge sharpness) were made as well as calculation of longitudinal, radial, and tangential myocardial velocities in the left ventricle.

RESULTS

The proposed breath-hold TPM data took eight heartbeats to acquire. The breath-hold TPM images had significantly higher edge sharpness (P = 0.0014) than the self-navigated TPM images, but with significantly lower velocity-to-noise ratio (P < 0.0001). There was excellent agreement (r > 0.94) in the longitudinal, radial, and tangential velocities between the self-navigated data and the proposed breath-hold TPM sequence.

CONCLUSION

We demonstrate the feasibility of using spiral UNFOLD-ed SENSE to measure myocardial velocities using a rapid breath-hold spiral TPM sequence. This novel technique might enable accurate measurement of myocardial velocities, in a short scan time, which is especially important in a busy clinical workflow. J. MAGN. RESON. IMAGING 2016;44:1003-1009.

Myocardial dysfunction in patients with aortic stenosis and hypertensive heart disease assessed by MR tissue phase mapping

PURPOSE

To identify abnormalities of myocardial velocities in patients with left ventricular pressure overload using magnetic resonance tissue phase mapping (TPM).

MATERIAL AND METHODS

Thirty-three patients (nine with hypertensive heart disease [HYP], 24 with aortic stenosis [AS]) and 41 healthy controls were enrolled. To assess left ventricular motion, a basal, midventricular, and apical slice were acquired using three-directional velocity-encoded phase-contrast MR with a 3T system. Target parameters were peak longitudinal (Vz ) and radial (Vr ) velocity in systole and diastole (Peaksys , Peakdias ). Analysis was done on each myocardial segment. In a subgroup (n = 7 HYP, n = 12 AS, n = 24 controls), measurement was repeated during handgrip exercise.

RESULTS

AS had significantly lower Vz -Peaksys in the inferolateral and inferoseptal wall (P = 0.003-0.029) and Vr -Peaksys in the septum and anterior wall (P = 0.001-0.013) than controls. Vz -Peakdias and Vr -Peakdias were lower in AS than in controls in almost all segments (P < 0.001-0.028). HYP showed reduced Vz -Peakdias compared to controls in all basal segments as well as in the lateral midventricular wall (P < 0.001-0.045), and reduced Vr -Peakdias compared to controls predominantly in the midventricular and apical segments (P = 0.004-0.042). AS patients with focal fibrosis had significantly reduced myocardial velocities (P = 0.001-0.047) in segments without late enhancement. During exercise, Vz -Peaksys , Vr -Peaksys , and Vz -Peakdias remained unchanged in AS and HYP, but decreased in the lateral wall in controls (P < 0.001-0.043).

CONCLUSION

Even with preserved left ventricle (LV) ejection fraction, peak longitudinal and radial velocities of the LV are reduced in AS and HYP, indicating early functional impairment. J. Magn. Reson. Imaging 2016;44:168-177.

Cardiovascular magnetic resonance phase contrast imaging

Cardiovascular magnetic resonance (CMR) phase contrast imaging has undergone a wide range of changes with the development and availability of improved calibration procedures, visualization tools, and analysis methods. This article provides a comprehensive review of the current state-of-the-art in CMR phase contrast imaging methodology, clinical applications including summaries of past clinical performance, and emerging research and clinical applications that utilize today's latest technology.

Extracellular volume fraction is more closely associated with altered regional left ventricular velocities than left ventricular ejection fraction in nonischemic cardiomyopathy

BACKGROUND

Nonischemic cardiomyopathy is a common cause of left ventricular (LV) dysfunction and myocardial fibrosis. The purpose of this study was to noninvasively evaluate changes in segmental LV extracellular volume (ECV) fraction, LV velocities, myocardial scar, and wall motion in nonischemic cardiomyopathy patients.

METHODS AND RESULTS

Cardiac MRI including pre- and postcontrast myocardial T1 mapping and velocity quantification (tissue phase mapping) of the LV (basal, midventricular, and apical short axis) was applied in 31 patients with nonischemic cardiomyopathy (50±18 years). Analysis based on the 16-segment American Heart Association model was used to evaluate the segmental distribution of ECV, peak systolic and diastolic myocardial velocities, scar determined by late gadolinium enhancement, and wall motion abnormalities. LV segments with scar or impaired wall motion were significantly associated with elevated ECV (rs =0.26; P<0.001) and reduced peak systolic radial velocities (r=-0.43; P<0.001). Regional myocardial velocities and ECV were similar for patients with reduced (n=12; ECV=0.28±0.06) and preserved left ventricular ejection fraction (n=19; ECV=0.30±0.09). Patients with preserved left ventricular ejection fraction showed significant relationships between increasing ECV and reduced systolic (r=-0.19; r=-0.30) and diastolic (r=0.34; r=0.26) radial and long-axis peak velocities (P<0.001). Even after excluding myocardial segments with late gadolinium enhancement, significant relationships between ECV and segmental LV velocities were maintained indicating the potential of elevated ECV to identify regional diffuse fibrosis not visible by late gadolinium enhancement, which was associated with impaired regional LV function.

CONCLUSIONS

Regionally elevated ECV negatively affected myocardial velocities. The association of elevated regional ECV with reduced myocardial velocities independent of left ventricular ejection fraction suggests a structure-function relationship between altered ECV and segmental myocardial function in nonischemic cardiomyopathy.

Spiral tissue phase velocity mapping in a breath-hold with non-cartesian SENSE

PURPOSE

Tissue phase velocity mapping (TPVM) is capable of reproducibly measuring regional myocardial velocities. However acquisition durations of navigator gated techniques are long and unpredictable while current breath-hold techniques have low temporal resolution. This study presents a spiral TPVM technique which acquires high resolution data within a clinically acceptable breath-hold duration.

METHODS

Ten healthy volunteers are scanned using a spiral sequence with temporal resolution of 24 ms and spatial resolution of 1.7 × 1.7 mm. Retrospective cardiac gating is used to acquire data over the entire cardiac cycle. The acquisition is accelerated by factors of 2 and 3 by use of non-Cartesian SENSE implemented on the Gadgetron GPU system resulting in breath-holds of 17 and 13 heartbeats, respectively. Systolic, early diastolic, and atrial systolic global and regional longitudinal, circumferential, and radial velocities are determined.

RESULTS

Global and regional velocities agree well with those previously reported. The two acceleration factors show no significant differences for any quantitative parameter and the results also closely match previously acquired higher spatial resolution navigator-gated data in the same subjects.

CONCLUSION

By using spiral trajectories and non-Cartesian SENSE high resolution, TPVM data can be acquired within a clinically acceptable breath-hold.

Novel insight into the detailed myocardial motion and deformation of the rodent heart using high-resolution phase contrast cardiovascular magnetic resonance

BACKGROUND

Phase contrast velocimetry cardiovascular magnetic resonance (PC-CMR) is a powerful and versatile tool allowing assessment of in vivo motion of the myocardium. However, PC-CMR is sensitive to motion related artifacts causing errors that are geometrically systematic, rendering regional analysis of myocardial function challenging. The objective of this study was to establish an optimized PC-CMR method able to provide novel insight in the complex regional motion and strain of the rodent myocardium, and provide a proof-of-concept in normal and diseased rat hearts with higher temporal and spatial resolution than previously reported.

METHODS

A PC-CMR protocol optimized for assessing the motion and deformation of the myocardium in rats with high spatiotemporal resolution was established, and ten animals with different degree of cardiac dysfunction underwent examination and served as proof-of-concept. Global and regional myocardial velocities and circumferential strain were calculated, and the results were compared to five control animals. Furthermore, the global strain measurements were validated against speckle-tracking echocardiography, and inter- and intrastudy variability of the protocol were evaluated.

RESULTS

The presented method allows assessment of regional myocardial function in rats with high level of detail; temporal resolution was 3.2 ms, and analysis was done using 32 circumferential segments. In the dysfunctional hearts, global and regional function were distinctly altered, including reduced global peak values, increased regional heterogeneity and increased index of dyssynchrony. Strain derived from the PC-CMR data was in excellent agreement with echocardiography (r = 0.95, p < 0.001; limits-of-agreement -0.02 ± 3.92%strain), and intra- and interstudy variability were low for both velocity and strain (limits-of-agreement, radial motion: 0.01 ± 0.32 cm/s and -0.06 ± 0.75 cm/s; circumferential strain: -0.16 ± 0.89%strain and -0.71 ± 1.67%strain, for intra- and interstudy, respectively).

CONCLUSION

We demonstrate, for the first time, that PC-CMR enables high-resolution evaluation of in vivo circumferential strain in addition to myocardial motion of the rat heart. In combination with the superior geometric robustness of CMR, this ultimately provides a tool for longitudinal studies of regional function in rodents with high level of detail.

Cold ischaemic time and time after transplantation alter segmental myocardial velocities after heart transplantation

OBJECTIVES

The aim of this study was to investigate changes in segmental, three-directional left ventricular (LV) velocities in patients after heart transplantation (Tx).

METHODS

Magnetic resonance tissue phase mapping was used to assess myocardial velocities in patients after Tx (n = 27) with normal LV ejection fraction (63 ± 5%) and those without signs of rejection. Regional wall motion and dyssynchrony were analysed in relation to cold ischaemic time (150 ± 57 min, median = 154 min), age of the donor heart (35 ± 13 years, median = 29 years), time after transplantation (32 ± 26 months, median = 31 months) and global LV morphology and function.

RESULTS

Segmental myocardial velocities were significantly altered in patients with cold ischaemic times >155 min resulting in an increase in peak systolic radial velocities (2 of 16 segments, P = 0.03-0.04) and reduced segmental diastolic long-axis velocities (5 of 16 segments, P = 0.01-0.04). Time after transplantation (n = 8 patients <12 months after Tx vs n = 19 >12 months) had a significant influence on systolic radial velocities (increased in 2 of 16 segments, P = 0.01-0.04) and diastolic long-axis velocities (reduced in 5 of 16 segments, P = 0.02-0.04). Correlation analysis and multiple regression revealed significant relationships of cold ischaemic time (R = -0.384, P = 0.048), the donor heart's age (β= 0.9, P = 0.01) and time from transplantation (β= -0.36, P = 0.03) with long-axis diastolic dyssynchrony.

CONCLUSIONS

Time after transplantation and cold ischaemic time strongly affect segmental systolic and diastolic motion in patients after Tx. The understanding of alterations in regional LV motion in the transplanted heart under stable conditions is essential in order to utilize this methodology in the future as a potentially non-invasive means of diagnosing transplant rejection.

Longitudinal myocardial peak velocities using high temporal resolution phase-contrast and simple averaging are comparable to tissue Doppler echocardiography

OBJECT

Phase contrast imaging is widely used to measure blood velocity. However tissue Doppler imaging (TDI) echocardiography is the reference for myocardial velocity assessment. This study aims at validating the ability of phase contrast (PC) sequences to correctly assess myocardial velocities and to compare these velocities to TDI. The phase contrast sequence was performed with breath-hold parameters and with parameters tuned to increase temporal resolution in free breathing.

MATERIALS AND METHODS

Left and Right auriculo-ventricular annuluses longitudinal velocities were recorded on six healthy volunteers with different temporal resolutions (TDI: 5 ms, breath-hold PC: 94 ms and free-breathing PC: 19 ms). Free-breathing PC was obtained by averaging of three excitations. Amplitudes of four standard echocardiographic and clinically relevant myocardial longitudinal velocity waves were compared: Early filling and auricular, systolic and isovolumic contractions.

RESULTS

Isovolumic contraction waves were only visible with free-breathing PC and TDI. The differences with the reference TDI wave velocities were lower (p = 0.02) for free-breathing PC (19.2 ± 2.6%) than for breath-hold PC (28.1 ± 2.9%). These differences for free-breathing PC were close to (p = 0.21) the coefficient of variation of the measurements provided by TDI (14.8 ± 1.2%).

CONCLUSION

Myocardial longitudinal peak velocities can be assessed with a PC sequence tuned to optimize temporal resolution.

Comparison of the right and left ventricular performance during the fetal development using velocity vector imaging

BACKGROUND

Studies on myocardial characteristics examined by speckle-tracking echocardiography are limited.

AIMS

To compare myocardial performance between the right and left ventricles during the fetal development using velocity vector imaging (VVI).

SUBJECTS AND STUDY DESIGN

Echocardiograms of 95 uncomplicated singleton fetuses (19-36 weeks pregnancy) were retrospectively analyzed by VVI to measure global longitudinal peak velocity, strain, and strain rate of both the right ventricle (RV) and left ventricle (LV). The regional values were calculated for three segments (base, mid, and apex) of the ventricular free wall and segment.

OUTCOME MEASURES

The VVI-derived measurements were examined for gestational age and compared between ventricles.

RESULTS

The global peak systolic and diastolic velocity values of both ventricles significantly increased over gestation examined, whereas the global systolic strain and strain rate were stable (RV: strain -22.6 ± 5.0%, strain rate -2.6 ± 0.7/s; LV: strain -21.5 ± 5.6%, strain rate -2.5 ± 0.7/s). Compared to the LV, the RV showed significantly higher global velocity in systole and diastole (P = 0.001 for systole, P < 0.001 for diastole). The global systolic velocity of the LV increased close to the RV toward term, whereas the RV was dominant in diastole throughout the examined gestation. Basal strain and strain rate in the RV were significantly greater than that of the LV, although there were no significant differences in the middle and apical values between ventricles.

CONCLUSION

Our findings suggest the RV predominance of longitudinal contraction and dilatation, compared to the LV in uncomplicated fetuses.

Efficient and reproducible high resolution spiral myocardial phase velocity mapping of the entire cardiac cycle

BACKGROUND

Three-directional phase velocity mapping (PVM) is capable of measuring longitudinal, radial and circumferential regional myocardial velocities. Current techniques use Cartesian k-space coverage and navigator-gated high spatial and high temporal resolution acquisitions are long. In addition, prospective ECG-gating means that analysis of the full cardiac cycle is not possible. The aim of this study is to develop a high temporal and high spatial resolution PVM technique using efficient spiral k-space coverage and retrospective ECG-gating. Detailed analysis of regional motion over the entire cardiac cycle, including atrial systole for the first time using MR, is presented in 10 healthy volunteers together with a comprehensive assessment of reproducibility.

METHODS

A navigator-gated high temporal (21 ms) and spatial (1.4 × 1.4 mm) resolution spiral PVM sequence was developed, acquiring three-directional velocities in 53 heartbeats (100% respiratory-gating efficiency). Basal, mid and apical short-axis slices were acquired in 10 healthy volunteers on two occasions. Regional and transmural early systolic, early diastolic and atrial systolic peak longitudinal, radial and circumferential velocities were measured, together with the times to those peaks (TTPs). Reproducibilities were determined as mean ± SD of the signed differences between measurements made from acquisitions performed on the two days.

RESULTS

All slices were acquired in all volunteers on both occasions with good image quality. The high temporal resolution allowed consistent detection of fine features of motion, while the high spatial resolution allowed the detection of statistically significant regional and transmural differences in motion. Colour plots showing the regional variations in velocity over the entire cardiac cycle enable rapid interpretation of the regional motion within any given slice. The reproducibility of peak velocities was high with the reproducibility of early systolic, early diastolic and atrial systolic peak radial velocities in the mid slice (for example) being -0.01 ± 0.36, 0.20 ± 0.56 and 0.14 ± 0.42 cm/s respectively. Reproducibility of the corresponding TTP values, when normalised to a fixed systolic and diastolic length, was also high (-13.8 ± 27.4, 1.3 ± 21.3 and 3.0 ± 10.9 ms for early systolic, early diastolic and atrial systolic respectively).

CONCLUSIONS

Retrospectively gated spiral PVM is an efficient and reproducible method of acquiring 3-directional, high resolution velocity data throughout the entire cardiac cycle, including atrial systole.

Self-navigated tissue phase mapping using a golden-angle spiral acquisition-proof of concept in patients with pulmonary hypertension

PURPOSE

To create a high temporal- and spatial-resolution retrospectively cardiac-gated, tissue phase mapping (TPM) sequence, using an image-based respiratory navigator calculated from the data itself.

METHODS

The sequence was based on a golden-angle spiral acquisition. Reconstruction of real-time images allowed creation of an image-based navigator. The expiratory spiral interleaves were then retrospectively cardiac-gated using data binning. TPM data were acquired in 20 healthy volunteers and 10 patients with pulmonary hypertension. Longitudinal and radial myocardial velocities were calculated in the left ventricle and right ventricle.

RESULTS

The image-based navigator was shown to correlate well with simultaneously acquired airflow data in 10 volunteers(r=0.93±0.04). The TPM navigated images had a significantly higher subjective image quality and edge sharpness (P<0.0001) than averaged spiral TPM. No significant differences in myocardial velocities were seen between conventional Cartesian TPM with navigator respiratory-gating and the proposed self-navigated TPM technique, in 10 volunteers. Significant differences in the velocities were seen between the volunteers and patients in the left ventricle at systole and end diastole and in the right ventricle at end diastole.

CONCLUSION

The feasibility of measuring myocardial motion using a golden-angle spiral TPM sequence was demonstrated, with an image-based respiratory navigator calculated from the TPM data itself.

Volumetric motion quantification by 3D tissue phase mapped CMR

BACKGROUND

The objective of this study was the quantification of myocardial motion from 3D tissue phase mapped (TPM) CMR. Recent work on myocardial motion quantification by TPM has been focussed on multi-slice 2D acquisitions thus excluding motion information from large regions of the left ventricle. Volumetric motion assessment appears an important next step towards the understanding of the volumetric myocardial motion and hence may further improve diagnosis and treatments in patients with myocardial motion abnormalities.

METHODS

Volumetric motion quantification of the complete left ventricle was performed in 12 healthy volunteers and two patients applying a black-blood 3D TPM sequence. The resulting motion field was analysed regarding motion pattern differences between apical and basal locations as well as for asynchronous motion pattern between different myocardial segments in one or more slices. Motion quantification included velocity, torsion, rotation angle and strain derived parameters.

RESULTS

All investigated motion quantification parameters could be calculated from the 3D-TPM data. Parameters quantifying hypokinetic or asynchronous motion demonstrated differences between motion impaired and healthy myocardium.

CONCLUSIONS

3D-TPM enables the gapless volumetric quantification of motion abnormalities of the left ventricle, which can be applied in future application as additional information to provide a more detailed analysis of the left ventricular function.

A novel surface electrocardiogram-based marker of ventricular arrhythmia risk in patients with ischemic cardiomyopathy

Background

Better sudden cardiac death risk markers are needed in ischemic cardiomyopathy (ICM). Increased heterogeneity of electrical restitution is an important mechanism underlying the risk of ventricular arrhythmia (VA). Our aim was to develop and test a novel quantitative surface electrocardiogram–based measure of VA risk in patients with ICM: the Regional Restitution Instability Index (R2I2).

Methods and Results

R2I2, the mean of the standard deviation of residuals from the mean gradient for each ECG lead at a range of diastolic intervals, was measured retrospectively from high-resolution 12-lead ECGs recorded during an electrophysiology study. Patient groups were as follows: Study group, 26 patients with ICM being assessed for implantable defibrillator; Control group, 29 patients with supraventricular tachycardia undergoing electrophysiology study; and Replication group, 40 further patients with ICM. R2I2 was significantly higher in the Study patients than in Controls (mean ± standard error of the mean: 1.09±0.06 versus 0.63±0.04, P<0.001). Over a median follow-up period of 23 months, 6 of 26 Study group patients had VA or death. R2I2 predicted VA or death independently of demographic factors, electrophysiology study result, left ventricular ejection fraction, or QRS duration (Cox model, P=0.029). R2I2 correlated with peri-infarct zone as assessed by cardiac magnetic resonance imaging (r=0.51, P=0.024). The findings were replicated in the Replication group: R2I2 was significantly higher in 11 of 40 Replication patients experiencing VA (1.18±0.10 versus 0.92±0.05, P=0.019). In combined analysis of ICM cohorts, R2I2 ≥1.03 identified subjects with significantly higher risk of VA or death (43%) compared with R2I2 <1.03 (11%) (P=0.004).

Conclusions

In this pilot study, we have developed a novel VA risk marker, R2I2, and have shown that it correlated with a structural measure of arrhythmic risk and predicted risk of VA or death in patients with ICM. R2I2 may improve risk stratification and merits further evaluation. (J Am Heart Assoc. 2012;1:e001552 doi: 10.1161/JAHA.112.001552.)

MR assessment of regional myocardial mechanics

Regional myocardial function can be measured by several MR techniques including tissue tagging, phase velocity mapping, and more recently, displacement encoding with stimulated echoes (DENSE) and strain encoding (SENC). Each of these techniques was developed separately and has undergone significant change since its original implementation. As a result, in the current literature, the common features and the differences between the techniques and what they measure are often unclear and confusing. This review article delivers an extensively referenced introductory text which clarifies the current methodology from the starting point of the Bloch equations. By doing this in a consistent way for each method, the similarities and differences between them are highlighted. In addition, their capabilities and limitations are discussed, together with their relative advantages and disadvantages. While the focus is on sequence design and development, the principal parameters measured by each technique are also summarized, together with brief results, with the reader being directed to the extensive literature on data processing and clinical applications for more detail.

Rapid pediatric cardiac assessment of flow and ventricular volume with compressed sensing parallel imaging volumetric cine phase-contrast MRI

OBJECTIVE

The quantification of cardiac flow and ventricular volumes is an essential goal of many congenital heart MRI examinations, often requiring acquisition of multiple 2D phase-contrast and bright-blood cine steady-state free precession (SSFP) planes. Scan acquisition, however, is lengthy and highly reliant on an imager who is well-versed in structural heart disease. Although it can also be lengthy, 3D time-resolved (4D) phase-contrast MRI yields global flow patterns and is simpler to perform. We therefore sought to accelerate 4D phase contrast and to determine whether equivalent flow and volume measurements could be extracted.

MATERIALS AND METHODS

Four-dimensional phase contrast was modified for higher acceleration with compressed sensing. Custom software was developed to process 4D phase-contrast images. We studied 29 patients referred for congenital cardiac MRI who underwent a routine clinical protocol, including cine short-axis stack SSFP and 2D phase contrast, followed by contrast-enhanced 4D phase contrast. To compare quantitative measurements, Bland-Altman analysis, paired Student t tests, and F tests were used.

RESULTS

Ventricular end-diastolic, end-systolic, and stroke volumes obtained from 4D phase contrast and SSFP were well correlated (ρ = 0.91-0.95; r(2) = 0.83-0.90), with no statistically significant difference. Ejection fractions were well correlated in a subpopulation that underwent higher-resolution compressed-sensing 4D phase contrast (ρ = 0.88; r(2) = 0.77). Four-dimensional phase contrast and 2D phase contrast flow rates were also well correlated (ρ = 0.90; r(2) = 0.82). Excluding ventricles with valvular insufficiency, cardiac outputs derived from outlet valve flow and stroke volumes were more consistent by 4D phase contrast than by 2D phase contrast and SSFP.

CONCLUSION

Combined parallel imaging and compressed sensing can be applied to 4D phase contrast. With custom software, flow and ventricular volumes may be extracted with comparable accuracy to SSFP and 2D phase contrast. Furthermore, cardiac outputs were more consistent by 4D phase contrast.

Acceleration of tissue phase mapping with sensitivity encoding at 3T

BACKGROUND

The objective of this study was to investigate the impact of sensitivity encoding on the quantitative assessment of cardiac motion in black blood cine tissue phase mapping (TPM) sequences. Up to now whole volume coverage of the heart is still limited by the long acquisition times. Therefore, a significant increase in imaging speed without deterioration of quantitative motion information is indispensable.

METHODS

20 volunteers were enrolled in this study. Each volunteer underwent myocardial short-axis TPM scans with different SENSE acceleration factors. The influence of SENSE acceleration on the measured motion curves was investigated.

RESULTS

It is demonstrated that all TPM sequences with SENSE acceleration have only minimum influence on the motion curves. Even with a SENSE factor of four, the decrease in the amplitude of the motion curve was less than 3%. No significant difference was observed for the global correlation coefficient and deviation between the motion curves obtained by the reproducibility and the SENSE accelerated measurements.

CONCLUSIONS

It is feasible to accelerate myocardial TPM measurements with SENSE factors up to 4 without losing substantial information of the motion pattern.

Ischemic heart disease: comprehensive evaluation by cardiovascular magnetic resonance

Considerable technical advances over the past decade have increased the clinical application of cardiovascular magnetic resonance (CMR) imaging. A comprehensive CMR examination can accurately measure left and right ventricular size and function, identify the presence and extent of reversible versus irreversible myocardial injury, and detect inducible ischemia. Streamlined protocols allow such a CMR examination to be a time-efficient diagnostic tool in patients with coronary artery disease. Moreover, edema imaging with T2-weighted CMR allows the detection of acute coronary syndromes. In this review, we present the relevant CMR methods and discuss practical uses of CMR in acute and chronic ischemic heart disease.

MR-based analysis of regional cardiac function in relation to cellular integrity in Fabry disease

BACKGROUND

Fabry cardiomyopathy is characterized by left ventricular (LV) hypertrophy and regional fibrosis. Recent high-end echocardiography studies of selected LV sections suggest an interrelation between regional fibrosis, impaired function, and hypertrophy possibly changing under specific enzyme replacement therapy (ERT).

METHODS

Magnetic resonance imaging (MRI) was used for a region dependent study of cardiac function, morphology and late enhancement (LE) in 25 Fabry patients before and after 12 months of ERT in comparison to 43 healthy volunteers.

RESULTS

Fabry patients presented with LV increased wall thickness (EDWT) and reduced wall thickening (WT) with a focus on basal and midventricular regions corresponding to areas of LE. The degree of hypertrophy and hypokinesia were the highest if LE was detectable. A significant decrease of the EDWT under ERT was observed in LE negative patients accompanied by a decline of hypokinesia with regional differences.

CONCLUSIONS

Regional differences of LV hypertrophy and wall motion were detected corresponding to the distribution of myocardial fibrosis (LE). Functional impairment was closely restricted to fibrotic regions while morphologic changes slightly exceeded the areas of fibrosis. ERT resulted in regional improvements whereby absence of fibrosis was connected to a better outcome.

A high-fat diet impairs cardiac high-energy phosphate metabolism and cognitive function in healthy human subjects

BACKGROUND

High-fat, low-carbohydrate diets are widely used for weight reduction, but they may also have detrimental effects via increased circulating free fatty acid concentrations.

OBJECTIVE

We tested whether raising plasma free fatty acids by using a high-fat, low-carbohydrate diet results in alterations in heart and brain in healthy subjects.

DESIGN

Men (n = 16) aged 22 ± 1 y (mean ± SE) were randomly assigned to 5 d of a high-fat, low-carbohydrate diet containing 75 ± 1% of calorie intake through fat consumption or to an isocaloric standard diet providing 23 ± 1% of calorie intake as fat. In a crossover design, subjects undertook the alternate diet after a 2-wk washout period, with results compared after the diet periods. Cardiac (31)P magnetic resonance (MR) spectroscopy and MR imaging, echocardiography, and computerized cognitive tests were used to assess cardiac phosphocreatine (PCr)/ATP, cardiac function, and cognitive function, respectively.

RESULTS

Compared with the standard diet, subjects who consumed the high-fat, low-carbohydrate diet had 44% higher plasma free fatty acids (P < 0.05), 9% lower cardiac PCr/ATP (P < 0.01), and no change in cardiac function. Cognitive tests showed impaired attention (P < 0.01), speed (P < 0.001), and mood (P < 0.01) after the high-fat, low-carbohydrate diet.

CONCLUSION

Raising plasma free fatty acids decreased myocardial PCr/ATP and reduced cognition, which suggests that a high-fat diet is detrimental to heart and brain in healthy subjects.

Four-dimensional phase contrast magnetic resonance angiography: potential clinical applications

Unlike other magnetic resonance angiographic techniques, phase contrast imaging (PC-MRI) offers co-registered morphologic images and velocity data within a single acquisition. While the basic principle of PC-MRI dates back almost 3 decades, novel time-resolved three-dimensional PC-MRI (4D PC-MRI) approaches have become increasingly researched over the past years. So-called 4D PC-MRI includes three-directional velocity encoding in a three-dimensional imaging volume over time, thereby providing the opportunity to comprehensively analyze human hemodynamics in vivo. Moreover, its large volume coverage offers the option to study systemic hemodynamic effects. Additionally, this offers the possibility to re-visit flow in any location of interest without being limited to predetermined two-dimensional slices. The attention received for hemodynamic research is partially based on flow-based theories of atherogenesis and arterial remodeling. 4D PC-MRI can be used to calculate flow-related vessel wall parameters and may hence serve as a diagnostic tool in preemptive medicine. Furthermore, technical improvements including the availability of sufficient computing power, data storage capabilities, and optimized acceleration schemes for data acquisition as well as comprehensive image processing algorithms have largely facilitated recent research progresses. We will present an overview of the potential of this relatively young imaging paradigm. After acquisition and processing the data in morphological and phase difference images, various visualization strategies permit the qualitative analysis of hemodynamics. A multitude of quantitative parameters such as pulse wave velocities and estimates of wall shear stress which might serve as future biomarkers can be extracted. Thereby, exciting new opportunities for vascular imaging and diagnosis are available.