MyocardialT1rho mapping of patients with end-stage renal disease and its comparison withT1mapping andT2mapping: A feasibility and reproducibility study

Effect of spin-lock frequency on quantitative myocardial T1ρ mapping

OBJECTIVES

To use T1ρ mapping to assess myocardial fibrosis and to provide a reference for future clinical application, it is necessary to understand the factors influencing T1ρ values. This study explored the influence of different spin-locking frequencies on T1ρ values under a 3.0-T MR system.

METHODS

Fifty-seven healthy subjects were prospectively and consecutively included in this study, and T1ρ mapping was performed on them in 3 short-axis slices with three spin-lock frequencies at the amplitude of 300 Hz, 400 Hz, and 500 Hz, then nine T1ρ images were acquired per subject. Four T1ρ-weighted images were acquired using a spin-lock preparation pulse with varying durations (0 msec, 13.3 msec, 26.6 msec, 40 msec). T1ρ relaxation times were quantified for each slice and each myocardial segment. The results were analyzed using Student's t-test and one-way analysis of variance (ANOVA) methods.

RESULTS

Mean T1ρ relaxation times were 43.5 ± 2.8 msec at 300 Hz, 44.9 ± 3.6 msec at 400 Hz, and 46.2 ± 3.1 msec at 500 Hz, showing a significant progressive increase from low to high spin-lock frequency (300 Hz vs. 400 Hz, p = 0.046; 300 Hz vs. 500 Hz, p < 0.001; 400 Hz vs. 500 Hz, p = 0.043). In addition, The T1ρ values of females were significantly higher than those of males (300 Hz, p = 0.049; 400 Hz, p = 0.01; 500 Hz, p = 0.002).

CONCLUSION

In this prospective study, myocardial T1ρ values for the specific CMR setting are provided, and we found that gender and spin-lock frequency can affect the T1ρ values.

CRITICAL RELEVANCE STATEMENT

T1ρ mapping could supersede late gadolinium enhancement for detection of myocardial fibrosis. Establishing reference mean values that take key technical elements into account will facilitate interpretation of data in disease states.

KEY POINTS

This study established myocardial T1ρ reference values for different spin-lock frequencies. T1ρ values increased with spin-lock frequency, but numerical differences were minimal. Females had higher T1ρ values than males at all frequencies.

Advanced Myocardial MRI Tissue Characterization Combining Contrast Agent-Free T1-Rho Mapping With Fully Automated Analysis

BACKGROUND

Myocardial T1-rho (T1ρ) mapping is a promising method for identifying and quantifying myocardial injuries without contrast agents, but its clinical use is hindered by the lack of dedicated analysis tools.

PURPOSE

To explore the feasibility of clinically integrated artificial intelligence-driven analysis for efficient and automated myocardial T1ρ mapping.

STUDY TYPE

Retrospective.

POPULATION

Five hundred seventy-three patients divided into a training (N = 500) and a test set (N = 73) including ischemic and nonischemic cases.

FIELD STRENGTH/SEQUENCE

Single-shot bSSFP T1ρ mapping sequence at 1.5 T.

ASSESSMENT

The automated process included: left ventricular (LV) wall segmentation, right ventricular insertion point detection and creation of a 16-segment model for segmental T1ρ value analysis. Two radiologists (20 and 7 years of MRI experience) provided ground truth annotations. Interobserver variability and segmentation quality were assessed using the Dice coefficient with manual segmentation as reference standard. Global and segmental T1ρ values were compared. Processing times were measured.

STATISTICAL TESTS

Intraclass correlation coefficients (ICCs) and Bland-Altman analysis (bias ±2SD); Paired Student's t-tests and one-way ANOVA. A P value <0.05 was considered significant.

RESULTS

The automated approach significantly reduced processing time (3 seconds vs. 1 minute 51 seconds ± 22 seconds). In the test set, automated LV wall segmentation closely matched manual results (Dice 81.9% ± 9.0) and closely aligned with interobserver segmentation (Dice 82.2% ± 6.5). Excellent ICCs were achieved on a patient basis (0.94 [95% CI: 0.91 to 0.96]) with bias of -0.93 cm2 ± 6.60. There was no significant difference in global T1ρ values between manual (54.9 msec ± 4.6; 95% CI: 53.8 to 56.0 msec, range: 46.6-70.9 msec) and automated processing (55.4 msec ± 5.1; 95% CI: 54.2 to 56.6 msec; range: 46.4-75.1 msec; P = 0.099). The pipeline demonstrated a high level of agreement with manual-derived T1ρ values at the patient level (ICC = 0.85; bias +0.52 msec ± 5.18). No significant differences in myocardial T1ρ values were found between methods across the 16 segments (P = 0.75).

DATA CONCLUSION

Automated myocardial T1ρ mapping shows promise for the rapid and noninvasive assessment of heart disease.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 1.

Assessment of myocardial injuries in ischaemic and non-ischaemic cardiomyopathies using magnetic resonance T1-rho mapping

AIMS

To identify clinical correlates of myocardial T1ρ and to examine how myocardial T1ρ values change under various clinical scenarios.

METHODS AND RESULTS

A total of 66 patients (26% female, median age 57 years [Q1-Q3, 44-65 years]) with known structural heart disease and 44 controls (50% female, median age 47 years [28-57 years]) underwent cardiac magnetic resonance imaging at 1.5 T, including T1ρ mapping, T2 mapping, native T1 mapping, late gadolinium enhancement, and extracellular volume (ECV) imaging. In controls, T1ρ positively related with T2 (P = 0.038) and increased from basal to apical levels (P < 0.001). As compared with controls and remote myocardium, T1ρ significantly increased in all patients' sub-groups and all types of myocardial injuries: acute and chronic injuries, focal and diffuse tissue abnormalities, as well as ischaemic and non-ischaemic aetiologies (P < 0.05). T1ρ was independently associated with T2 in patients with acute injuries (P = 0.004) and with native T1 and ECV in patients with chronic injuries (P < 0.05). Myocardial T1ρ mapping demonstrated good intra- and inter-observer reproducibility (intraclass correlation coefficient = 0.86 and 0.83, respectively).

CONCLUSION

Myocardial T1ρ mapping appears to be reproducible and equally sensitive to acute and chronic myocardial injuries, whether of ischaemic or non-ischaemic origins. It may thus be a contrast-agent-free biomarker for gaining new and quantitative insight into myocardial structural disorders. These findings highlight the need for further studies through prospective and randomized trials.

Early detection of myocardial involvement by non-contrast T1ρ mapping of cardiac magnetic resonance in type 2 diabetes mellitus

Objective

This study aims to determine the effectiveness of T1ρ in detecting myocardial fibrosis in type 2 diabetes mellitus (T2DM) patients by comparing with native T1 and extracellular volume (ECV) fraction.

Methods

T2DM patients (n = 35) and healthy controls (n = 30) underwent cardiac magnetic resonance. ECV, T1ρ, native T1, and global longitudinal strain (GLS) values were assessed. Diagnostic performance was analyzed using receiver operating curves.

Results

The global ECV and T1ρ of T2DM group (ECV = 32.1 ± 3.2%, T1ρ = 51.6 ± 3.8 msec) were significantly higher than those of controls (ECV = 26.2 ± 1.6%, T1ρ = 46.8 ± 2.0 msec) (all P < 0.001), whether there was no significant difference in native T1 between T2DM and controls (P = 0.264). The GLS decreased significantly in T2DM patients compared with controls (-16.5 ± 2.4% vs. -18.3 ± 2.6%, P = 0.015). The T1ρ and native T1 were associated with ECV (Pearson's r = 0.50 and 0.25, respectively, both P < 0.001); the native T1, T1ρ, and ECV were associated with hemoglobin A1c (Pearson's r = 0.41, 0.52, and 0.61, respectively, all P < 0.05); and the ECV was associated with diabetes duration (Pearson's r = 0.41, P = 0.016). The AUC of ECV, T1ρ, GLS, and native T1 were 0.869, 0.810, 0.659, and 0.524, respectively.

Conclusion

In T2DM patients, T1ρ may be a new non-contrast cardiac magnetic resonance technique for identifying myocardial diffuse fibrosis, and T1ρ may be more sensitive than native T1 in the detection of myocardial diffuse fibrosis.

Cardiac T1ρ Mapping Values Affected by Age and Sex in a Healthy Chinese Cohort

BACKGROUND

To facilitate the clinical use of cardiac T1ρ, it is important to understand the impact of age and sex on T1ρ values of the myocardium.

PURPOSE

To investigate the impact of age and gender on myocardial T1ρ values.

STUDY TYPE

Cross-sectional.

POPULATION

Two hundred ten healthy Han Chinese volunteers without cardiovascular risk factors (85 males, mean age 34.4 ± 12.5 years; 125 females, mean age 37.9 ± 14.8 years).

FIELD STRENGTH/SEQUENCE

1.5 T; T1ρ-prepared steady-state free precession (T1ρ mapping) sequence.

ASSESSMENT

Basal, mid, and apical short-axis left ventricular T1ρ maps were acquired. T1ρ maps acquired with spin-lock frequencies of 5 and 400 Hz were subtracted to create a myocardial fibrosis index (mFI) map. T1ρ and mFI values across different age decades, sex, and slice locations were compared.

STATISTICAL TESTS

Shapiro-Wilk test, Student's t test, Mann-Whitney U test, linear regression analysis, one-way analysis of variance and intraclass correlation coefficient.

SIGNIFICANCE

P value <0.05.

RESULTS

Women had significantly higher T1ρ and mFI values than men (50.3 ± 2.0 msec vs. 47.7 ± 2.4 msec and 4.7 ± 1.0 msec vs. 4.3 ± 1.1 msec, respectively). Additionally, in males and females combined, there was a significant positive but weak correlation between T1ρ values and age (r = 0.27), while no correlation was observed between the mFI values and age (P = 0.969).

DATA CONCLUSION

We report potential reference values for cardiac T1ρ by sex, age distribution, and slice location in a Chinese population. T1ρ was significantly correlated with age and sex, while mFI was only associated with sex.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 1.

Robust cardiac T 1 ρ $$ {\mathrm{T}}_{1_{\boldsymbol{\rho}}} $$ mapping at 3T using adiabatic spin-lock preparations

PURPOSE

The aim of this study is to develop and optimize an adiabaticT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ (T 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ ) mapping method for robust quantification of spin-lock (SL) relaxation in the myocardium at 3T.

METHODS

Adiabatic SL (aSL) preparations were optimized for resilience againstB 0 $$ {\mathrm{B}}_0 $$ andB 1 + $$ {\mathrm{B}}_1^{+} $$ inhomogeneities using Bloch simulations. OptimizedB 0 $$ {\mathrm{B}}_0 $$ -aSL, Bal-aSL andB 1 $$ {\mathrm{B}}_1 $$ -aSL modules, each compensating for different inhomogeneities, were first validated in phantom and human calf. MyocardialT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ mapping was performed using a single breath-hold cardiac-triggered bSSFP-based sequence. Then, optimizedT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ preparations were compared to each other and to conventional SL-preparedT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ maps (RefSL) in phantoms to assess repeatability, and in 13 healthy subjects to investigate image quality, precision, reproducibility and intersubject variability. Finally, aSL and RefSL sequences were tested on six patients with known or suspected cardiovascular disease and compared with LGE,T 1 $$ {\mathrm{T}}_1 $$ , and ECV mapping.

RESULTS

The highestT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ preparation efficiency was obtained in simulations for modules comprising 2 HS pulses of 30 ms each. In vivoT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ maps yielded significantly higher quality than RefSL maps. Average myocardialT 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ values were 183.28± $$ \pm $$ 25.53 ms, compared with 38.21± $$ \pm $$ 14.37 ms RefSL-preparedT 1 ρ $$ {\mathrm{T}}_{1\uprho} $$ .T 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ maps showed a significant improvement in precision (avg. 14.47± $$ \pm $$ 3.71% aSL, 37.61± $$ \pm $$ 19.42% RefSL, p < 0.01) and reproducibility (avg. 4.64± $$ \pm $$ 2.18% aSL, 47.39± $$ \pm $$ 12.06% RefSL, p < 0.0001), with decreased inter-subject variability (avg. 8.76± $$ \pm $$ 3.65% aSL, 51.90± $$ \pm $$ 15.27% RefSL, p < 0.0001). Among aSL preparations,B 0 $$ {\mathrm{B}}_0 $$ -aSL achieved the better inter-subject variability. In patients,B 1 $$ {\mathrm{B}}_1 $$ -aSL preparations showed the best artifact resilience among the adiabatic preparations.T 1 ρ , adiab $$ {\mathrm{T}}_{1\uprho, \mathrm{adiab}} $$ times show focal alteration colocalized with areas of hyper-enhancement in the LGE images.

CONCLUSION

Adiabatic preparations enable robust in vivo quantification of myocardial SL relaxation times at 3T.

Magnetic resonance myocardial T1ρ mapping : Technical overview, challenges, emerging developments, and clinical applications

The potential of cardiac magnetic resonance to improve cardiovascular care and patient management is considerable. Myocardial T1-rho (T1ρ) mapping, in particular, has emerged as a promising biomarker for quantifying myocardial injuries without exogenous contrast agents. Its potential as a contrast-agent-free ("needle-free") and cost-effective diagnostic marker promises high impact both in terms of clinical outcomes and patient comfort. However, myocardial T1ρ mapping is still at a nascent stage of development and the evidence supporting its diagnostic performance and clinical effectiveness is scant, though likely to change with technological improvements. The present review aims at providing a primer on the essentials of myocardial T1ρ mapping, and to describe the current range of clinical applications of the technique to detect and quantify myocardial injuries. We also delineate the important limitations and challenges for clinical deployment, including the urgent need for standardization, the evaluation of bias, and the critical importance of clinical testing. We conclude by outlining technical developments to be expected in the future. If needle-free myocardial T1ρ mapping is shown to improve patient diagnosis and prognosis, and can be effectively integrated in cardiovascular practice, it will fulfill its potential as an essential component of a cardiac magnetic resonance examination.

A robust adiabatic constant amplitude spin-lock preparation module for myocardial T1ρ quantification at 3 T

T_1ρ quantification has the potential to assess myocardial fibrosis without contrast agent. However, its preparation spin-lock pulse is sensitive to B₁ and B₀ inhomogeneities, resulting in severe banding artifacts in the heart region, especially at high magnetic field such as 3 T. We aimed to design a robust spin-lock (SL) preparation module that can be used in myocardial T_1ρ quantification at 3 T. We used the tan/tanh pulse to tip up and tip down the magnetization in the spin-lock preparation module (tan/tanh-SL). Bloch simulation was used to optimize pulse shape parameters of the tan/tanh with a pulse duration (T_p ) of 8, 4, and 2 ms, respectively. The designed tan/tanh-SL modules were implemented on a 3-T MR scanner. They were evaluated in phantom studies under three different cases of B₀ and B₁ inhomogeneities, and tested in cardiac T_1ρ quantification of healthy volunteers. The performance of the tan/tanh-SL was compared with the composite SL preparation pulses and the commonly used hyperbolic secant pulse for spin-lock (HS-SL). Feasible pulse shape parameters were obtained using Bloch simulation. Compared with HS-SL, the quantification error of tan/tanh-SL was reduced by 27.7% for T_p  = 8 ms (mean ∆Q = 126.15 vs. 174.42) and 75.6% for T_p  = 4 ms (mean ∆Q = 136.65 vs. 559.53). In the phantom study, tan/tanh-SL was less sensitive to B₁ and B₀ inhomogeneity compared with composite SL pulses and HS-SL. In cardiac T_1ρ quantification, the T_1ρ maps using tan/tanh-SL showed fewer banding artifacts than using composite SL pulses and HS-SL. The proposed tan/tanh-SL preparation module greatly improves the robustness to B₀ and B₁ field inhomogeneities and can be used in cardiac T_1ρ quantification at 3 T.

Myocardium Assessment by Relaxation along Fictitious Field, Extracellular Volume, Feature Tracking, and Myocardial Strain in Hypertensive Patients with Left Ventricular Hypertrophy

Background

Previous research has shown impaired global longitudinal strain (GLS) and slightly elevated extracellular volume fraction (ECV) in hypertensive patients with left ventricular hypertrophy (HTN LVH). Up to now, only little attention has been paid to interactions between macromolecules and free water in hypertrophied myocardium.

Purpose

To evaluate the feasibility of relaxation along a fictitious field with rank 2 (RAFF2) in HTN LVH patients. Study Type. Single institutional case control.

Subjects

9 HTN LVH (age, 69 ± 10 years) and 11 control subjects (age, 54 ± 12 years). Field Strength/Sequence. Relaxation time mapping (T 1, T 1ρ , and T RAFF2 with 11.8 μT maximum radio frequency field amplitude) was performed at 1.5 T using a Siemens Aera (Erlangen, Germany) scanner equipped with an 18-channel body array coil. Assessment. ECV was calculated using pre- and postcontrast T 1, and global strains parameters were assessed by Segment CMR (Medviso AB Co, Sweden). The parametric maps of T 1ρ and T RAFF2 were computed using a monoexponential model, while the Bloch-McConnell equations were solved numerically to model effect of the chemical exchange during radio frequency pulses. Statistical Tests. Parametric maps were averaged over myocardium for each subject to be used in statistical analysis. Kolmogorov-Smirnov was used as the normality test followed by Student's t-test and Pearson's correlation to determine the difference between the HTN LVH patients and controls along with Hedges' g effect size and the association between variables, respectively.

Results

T RAFF2 decreased statistically (83 ± 2 ms vs 88 ± 6 ms, P < 0.031), and global longitudinal strain was impaired (GLS, -14 ± 3 vs - 18 ± 2, P < 0.002) in HTN LVH patients compared to the controls, respectively. Also, significant negative correlation was found between T RAFF2 and GLS (r = -0.53, P < 0.05). Data Conclusion. Our results suggest that T RAFF2 decrease in HTN LVH patients may be explained by gradual collagen accumulation which can be reflected in GLS changes. Most likely, it increases the water proton interactions and consequently decreases T RAFF2 before myocardial scarring.

T2 mapping in myocardial disease: a comprehensive review

Cardiovascular magnetic resonance (CMR) is considered the gold standard imaging modality for myocardial tissue characterization. Elevated transverse relaxation time (T2) is specific for increased myocardial water content, increased free water, and is used as an index of myocardial edema. The strengths of quantitative T2 mapping lie in the accurate characterization of myocardial edema, and the early detection of reversible myocardial disease without the use of contrast agents or ionizing radiation. Quantitative T2 mapping overcomes the limitations of T2-weighted imaging for reliable assessment of diffuse myocardial edema and can be used to diagnose, stage, and monitor myocardial injury. Strong evidence supports the clinical use of T2 mapping in acute myocardial infarction, myocarditis, heart transplant rejection, and dilated cardiomyopathy. Accumulating data support the utility of T2 mapping for the assessment of other cardiomyopathies, rheumatologic conditions with cardiac involvement, and monitoring for cancer therapy-related cardiac injury. Importantly, elevated T2 relaxation time may be the first sign of myocardial injury in many diseases and oftentimes precedes symptoms, changes in ejection fraction, and irreversible myocardial remodeling. This comprehensive review discusses the technical considerations and clinical roles of myocardial T2 mapping with an emphasis on expanding the impact of this unique, noninvasive tissue parameter.

Value of native T1 mapping in the prediction of major adverse cardiovascular events in hemodialysis patients

OBJECTIVES

This study aimed to evaluate the association of myocardial characterization by native T1 mapping using cardiac MR (CMR) with the incidence of major adverse cardiovascular event (MACE) in end-stage renal dysfunction (ESRD) patients on hemodialysis.

METHODS

A total of 52 ESRD patients and 52 healthy individuals were prospectively recruited between June 2017 and June 2018. ESRD patients underwent CMR examinations post-hemodialysis for the evaluation of cardiac function and global native T1 mapping. Demographics, serum biomarkers, and coronary artery calcification were collected. MACE including all-caused death, and new onset of myocardial infarction, heart failure leading to hospitalization, fatal arrhythmia, and cardiac arrest was set as the endpoint.

RESULTS

During a median follow-up of 38.0 months, 13 patients (25.0%) reached the endpoints. Global native T1 mapping in patients on hemodialysis was significantly higher compared with that of healthy individuals (1280.3 ms ± 45.3 vs. 1238.2 ms ± 31.1, p < 0.001). In the univariate Cox regression analysis, global native T1 mapping (HR [hazard ratios]: 1.887, 95% CI [confidence interval]: 1.302-2.736, p = 0.001) was associated with the prediction of MACE. Multivariate Cox regression analysis demonstrated that global native T1 mapping (HR: 1.580, 95% CI: 1.112-2.244, p = 0.011) and age (HR: 1.088, 95% CI: 1.032-1.146, p = 0.002) were associated with the incidence of MACE after adjusting for other conventional risk factors.

CONCLUSIONS

Global native T1 mapping by CMR can potentially become a novel predictor of MACE in ESRD patients on hemodialysis, providing additional prognostic values over conventional risk factors. However, this conclusion should be validated in a larger sample size of hemodialysis patients.

KEY POINTS

• Global native T1 mapping was significantly higher in ESRD patients on hemodialysis compared with that of normal controls. • Global native T1 mapping was associated with myocardial enzymes, myocardial hypertrophy, coronary calcification, and cardiac function. • Global native T1 mapping value was independently predictive of MACE in hemodialysis patients, providing additional prognostic values over conventional risk factors.

The Road Toward Reproducibility of Parametric Mapping of the Heart: A Technical Review

Parametric mapping of the heart has become an essential part of many cardiovascular magnetic resonance imaging exams, and is used for tissue characterization and diagnosis in a broad range of cardiovascular diseases. These pulse sequences are used to quantify the myocardial T₁, T₂, T2*, and T_1ρ relaxation times, which are unique surrogate indices of fibrosis, edema and iron deposition that can be used to monitor a disease over time or to compare patients to one another. Parametric mapping is now well-accepted in the clinical setting, but its wider dissemination is hindered by limited inter-center reproducibility and relatively long acquisition times. Recently, several new parametric mapping techniques have appeared that address both of these problems, but substantial hurdles remain for widespread clinical adoption. This review serves both as a primer for newcomers to the field of parametric mapping and as a technical update for those already well at home in it. It aims to establish what is currently needed to improve the reproducibility of parametric mapping of the heart. To this end, we first give an overview of the metrics by which a mapping technique can be assessed, such as bias and variability, as well as the basic physics behind the relaxation times themselves and what their relevance is in the prospect of myocardial tissue characterization. This is followed by a summary of routine mapping techniques and their variations. The problems in reproducibility and the sources of bias and variability of these techniques are reviewed. Subsequently, novel fast, whole-heart, and multi-parametric techniques and their merits are treated in the light of their reproducibility. This includes state of the art segmentation techniques applied to parametric maps, and how artificial intelligence is being harnessed to solve this long-standing conundrum. We finish up by sketching an outlook on the road toward inter-center reproducibility, and what to expect in the future.

Current insights of applying MRI in Graves' ophthalmopathy

Graves' ophthalmopathy (GO) is an autoimmune disease related to Grave's disease (GD). The therapeutic strategies for GO patients are based on precise assessment of the activity and severity of the disease. However, the current assessment systems require development to accommodate updates in treatment protocols. As an important adjunct examination, magnetic resonance imaging (MRI) can help physicians evaluate GO more accurately. With the continuous updating of MRI technology and the deepening understanding of GO, the assessment of this disease by MRI has gone through a stage from qualitative to precise quantification, making it possible for clinicians to monitor the microstructural changes behind the eyeball and better integrate clinical manifestations with pathology. In this review, we use orbital structures as a classification to combine pathological changes with MRI features. We also review some MRI techniques applied to GO clinical practice, such as disease classification and regions of interest selection.

Endogenous assessment of myocardial injury with single-shot model-based non-rigid motion-corrected T1 rho mapping

BACKGROUND

Cardiovascular magnetic resonance T1ρ mapping may detect myocardial injuries without exogenous contrast agent. However, multiple co-registered acquisitions are required, and the lack of robust motion correction limits its clinical translation. We introduce a single breath-hold myocardial T1ρ mapping method that includes model-based non-rigid motion correction.

METHODS

A single-shot electrocardiogram (ECG)-triggered balanced steady state free precession (bSSFP) 2D adiabatic T1ρ mapping sequence that collects five T1ρ-weighted (T1ρw) images with different spin lock times within a single breath-hold is proposed. To address the problem of residual respiratory motion, a unified optimization framework consisting of a joint T1ρ fitting and model-based non-rigid motion correction algorithm, insensitive to contrast change, was implemented inline for fast (~ 30 s) and direct visualization of T1ρ maps. The proposed reconstruction was optimized on an ex vivo human heart placed on a motion-controlled platform. The technique was then tested in 8 healthy subjects and validated in 30 patients with suspected myocardial injury on a 1.5T CMR scanner. The Dice similarity coefficient (DSC) and maximum perpendicular distance (MPD) were used to quantify motion and evaluate motion correction. The quality of T1ρ maps was scored. In patients, T1ρ mapping was compared to cine imaging, T2 mapping and conventional post-contrast 2D late gadolinium enhancement (LGE). T1ρ values were assessed in remote and injured areas, using LGE as reference.

RESULTS

Despite breath holds, respiratory motion throughout T1ρw images was much larger in patients than in healthy subjects (5.1 ± 2.7 mm vs. 0.5 ± 0.4 mm, P < 0.01). In patients, the model-based non-rigid motion correction improved the alignment of T1ρw images, with higher DSC (87.7 ± 5.3% vs. 82.2 ± 7.5%, P < 0.01), and lower MPD (3.5 ± 1.9 mm vs. 5.1 ± 2.7 mm, P < 0.01). This resulted in significantly improved quality of the T1ρ maps (3.6 ± 0.6 vs. 2.1 ± 0.9, P < 0.01). Using this approach, T1ρ mapping could be used to identify LGE in patients with 93% sensitivity and 89% specificity. T1ρ values in injured (LGE positive) areas were significantly higher than in the remote myocardium (68.4 ± 7.9 ms vs. 48.8 ± 6.5 ms, P < 0.01).

CONCLUSIONS

The proposed motion-corrected T1ρ mapping framework enables a quantitative characterization of myocardial injuries with relatively low sensitivity to respiratory motion. This technique may be a robust and contrast-free adjunct to LGE for gaining new insight into myocardial structural disorders.

Cardiorenal Syndrome: Emerging Role of Medical Imaging for Clinical Diagnosis and Management

Cardiorenal syndrome (CRS) concerns the interconnection between heart and kidneys in which the dysfunction of one organ leads to abnormalities of the other. The main clinical challenges associated with cardiorenal syndrome are the lack of tools for early diagnosis, prognosis, and evaluation of therapeutic effects. Ultrasound, computed tomography, nuclear medicine, and magnetic resonance imaging are increasingly used for clinical management of cardiovascular and renal diseases. In the last decade, rapid development of imaging techniques provides a number of promising biomarkers for functional evaluation and tissue characterization. This review summarizes the applicability as well as the future technological potential of each imaging modality in the assessment of CRS. Furthermore, opportunities for a comprehensive imaging approach for the evaluation of CRS are defined.

Identification of cardiovascular abnormalities by multiparametric magnetic resonance imaging in end-stage renal disease patients with preserved left ventricular ejection fraction

OBJECTIVES

Our study aimed to evaluate myocardial strain and tissue characteristics by multiparametric cardiovascular magnetic resonance (CMR) imaging in end-stage renal disease (ESRD) patients on peritoneal dialysis with preserved left ventricular ejection fraction (LVEF).

METHODS

ESRD patients on peritoneal dialysis with echocardiographic LVEF > 50% and age- and sex-matched healthy volunteers underwent multiparametric CMR at 3 T. LV function, LV myocardial native T1 and T2, and biventricular strain were measured and compared between the patients and controls. Associations of LV myocardial mass index (LVMI) with tissue characterization and strain were evaluated by multiple linear regression.

RESULTS

A total of 65 subjects (42 healthy volunteers and 23 ESRD patients) were enrolled. ESRD group demonstrated larger LVMI, higher native T1 and T2 (1301.9 ± 30.6 ms, 44.6 ± 2.6 ms) than those of the control group (1255.8 ± 45.2 ms, 40.5 ± 1.6 ms; both p < 0.001). Decreased LV strain and increased right ventricular circumferential strain were observed in the ESRD group. In ESRD patients with normal diastolic function on echocardiography, native T1 and T2 values were higher than those of the control group (p = 0.006, p = 0.001). Increased LVMI was associated with increased native T1 (p = 0.001) and T2 value (p < 0.001) after adjusting for age and sex. Increased myocardial native T1 value was associated with reduced LV strain after adjusting age, sex, and LVMI.

CONCLUSIONS

ESRD patients on peritoneal dialysis with preserved LVEF demonstrated higher myocardial mass, higher native T1 and T2 values, decreased LV strain, and increased RVGCS compared with healthy controls. Increased myocardial T1 and T2 were found in ESRD even when no systolic or diastolic dysfunction was detected by routine echocardiography.

KEY POINTS

• Even with preserved LVEF and no known cardiovascular diseases, ESRD patients on peritoneal dialysis demonstrated elevated myocardial T1 and T2 values and decreased left ventricular strain. • Subclinical changes in myocardial tissue composition may exist in ESRD patients on peritoneal dialysis even when no systolic or diastolic dysfunction was detected by routine echocardiography based on ejection fraction, left atrium size, and tissue Doppler. • Right ventricular free wall strain could be enhanced in response to subclinical LV systolic dysfunction in ESRD patients on peritoneal dialysis with preserved LVEF at an early stage.

Texture Analysis of Native T1 Images as a Novel Method for Noninvasive Assessment of Uremic Cardiomyopathy

BACKGROUND

Noncontrast cardiac T₁ times are increased in dialysis patients which might indicate fibrotic alterations in uremic cardiomyopathy.

PURPOSE

To explore the application of the texture analysis (TA) of T₁ images in the assessment of myocardial alterations in dialysis patients.

STUDY TYPE

Case-control study.

POPULATION

A total of 117 subjects, including 22 on hemodialysis, 44 on peritoneal dialysis, and 51 healthy controls.

FIELD STRENGTH

A 3 T, steady-state free precession (SSFP) sequence, modified Look-Locker imaging (MOLLI).

ASSESSMENT

Two independent, blinded researchers manually delineated endocardial and epicardial borders of the left ventricle (LV) on midventricular T₁ maps for TA.

STATISTICAL TESTS

Texture feature selection was performed, incorporating reproducibility verification, machine learning, and collinearity analysis. Multivariate linear regressions were performed to examine the independent associations between the selected texture features and left ventricular function in dialysis patients. Texture features' performance in discrimination was evaluated by sensitivity and specificity. Reproducibility was estimated by the intraclass correlation coefficient (ICC).

RESULTS

Dialysis patients had greater T₁ values than normal (P < 0.05). Five texture features were filtered out through feature selection, and four showed a statistically significant difference between dialysis patients and healthy controls. Among the four features, vertical run-length nonuniformity (VRLN) had the most remarkable difference among the control and dialysis groups (144 ± 40 vs. 257 ± 74, P < 0.05), which overlap was much smaller than Global T₁ times (1268 ± 38 vs. 1308 ± 46 msec, P < 0.05). The VRLN values were notably elevated (cutoff = 170) in dialysis patients, with a specificity of 97% and a sensitivity of 88%, compared with T₁ times (specificity = 76%, sensitivity = 60%). In dialysis patients, VRLN was significantly and independently associated with left ventricular ejection fraction (P < 0.05), global longitudinal strain (P < 0.05), radial strain (P < 0.05), and circumferential strain (P < 0.05); however, T₁ was not.

DATA CONCLUSION

The texture features obtained by TA of T₁ images and VRLN may be a better parameter for assessing myocardial alterations than T₁ times.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY: Stage 3.

Respiratory motion-compensated high-resolution 3D whole-heart T1ρ mapping

BACKGROUND

Cardiovascular magnetic resonance (CMR) T1ρ mapping can be used to detect ischemic or non-ischemic cardiomyopathy without the need of exogenous contrast agents. Current 2D myocardial T1ρ mapping requires multiple breath-holds and provides limited coverage. Respiratory gating by diaphragmatic navigation has recently been exploited to enable free-breathing 3D T1ρ mapping, which, however, has low acquisition efficiency and may result in unpredictable and long scan times. This study aims to develop a fast respiratory motion-compensated 3D whole-heart myocardial T1ρ mapping technique with high spatial resolution and predictable scan time.

METHODS

The proposed electrocardiogram (ECG)-triggered T1ρ mapping sequence is performed under free-breathing using an undersampled variable-density 3D Cartesian sampling with spiral-like order. Preparation pulses with different T1ρ spin-lock times are employed to acquire multiple T1ρ-weighted images. A saturation prepulse is played at the start of each heartbeat to reset the magnetization before T1ρ preparation. Image navigators are employed to enable beat-to-beat 2D translational respiratory motion correction of the heart for each T1ρ-weighted dataset, after which, 3D translational registration is performed to align all T1ρ-weighted volumes. Undersampled reconstruction is performed using a multi-contrast 3D patch-based low-rank algorithm. The accuracy of the proposed technique was tested in phantoms and in vivo in 11 healthy subjects in comparison with 2D T1ρ mapping. The feasibility of the proposed technique was further investigated in 3 patients with suspected cardiovascular disease. Breath-hold late-gadolinium enhanced (LGE) images were acquired in patients as reference for scar detection.

RESULTS

Phantoms results revealed that the proposed technique provided accurate T1ρ values over a wide range of simulated heart rates in comparison to a 2D T1ρ mapping reference. Homogeneous 3D T1ρ maps were obtained for healthy subjects, with septal T1ρ of 58.0 ± 4.1 ms which was comparable to 2D breath-hold measurements (57.6 ± 4.7 ms, P = 0.83). Myocardial scar was detected in 1 of the 3 patients, and increased T1ρ values (87.4 ± 5.7 ms) were observed in the infarcted region.

CONCLUSIONS

An accelerated free-breathing 3D whole-heart T1ρ mapping technique was developed with high respiratory scan efficiency and near-isotropic spatial resolution (1.7 × 1.7 × 2 mm3) in a clinically feasible scan time of ~ 6 mins. Preliminary patient results suggest that the proposed technique may find applications in non-contrast myocardial tissue characterization.

Bio-SCOPE: fast biexponential T1ρ mapping of the brain using signal-compensated low-rank plus sparse matrix decomposition

PURPOSE

To develop and evaluate a fast imaging method based on signal-compensated low-rank plus sparse matrix decomposition to accelerate data acquisition for biexponential brain T_1ρ mapping (Bio-SCOPE).

METHODS

Two novel strategies were proposed to improve reconstruction performance. A variable-rate undersampling scheme was used with a varied acceleration factor for each k-space along the spin-lock time direction, and a modified nonlinear thresholding scheme combined with a feature descriptor was used for Bio-SCOPE reconstruction. In vivo brain T_1ρ mappings were acquired from 4 volunteers. The fully sampled k-space data acquired from 3 volunteers were retrospectively undersampled by net acceleration rates (R) of 4.6 and 6.1. Reference values were obtained from the fully sampled data. The agreement between the accelerated T_1ρ measurements and reference values was assessed with Bland-Altman analyses. Prospectively undersampled data with R = 4.6 and R = 6.1 were acquired from 1 volunteer.

RESULTS

T_1ρ -weighted images were successfully reconstructed using Bio-SCOPE for R = 4.6 and 6.1 with signal-to-noise ratio variations <1 dB and normalized root mean square errors <4%. Accelerated and reference T_1ρ measurements were in good agreement for R = 4.6 (T_{1ρ s} : 18.6651 ± 1.7786 ms; T_{1ρ l} : 88.9603 ± 1.7331 ms) and R = 6.1 (T_{1ρ s} : 17.8403 ± 3.3302 ms; T_{1ρ l} : 88.0275 ± 4.9606 ms) in the Bland-Altman analyses. T_1ρ parameter maps from prospectively undersampled data also show reasonable image quality using the Bio-SCOPE method.

CONCLUSION

Bio-SCOPE achieves a high net acceleration rate for biexponential T_1ρ mapping and improves reconstruction quality by using a variable-rate undersampling data acquisition scheme and a modified soft-thresholding algorithm in image reconstruction.

Accelerated free-breathing 3D T1ρ cardiovascular magnetic resonance using multicoil compressed sensing

BACKGROUND

Endogenous contrast T1ρ cardiovascular magnetic resonance (CMR) can detect scar or infiltrative fibrosis in patients with ischemic or non-ischemic cardiomyopathy. Existing 2D T1ρ techniques have limited spatial coverage or require multiple breath-holds. The purpose of this project was to develop an accelerated, free-breathing 3D T1ρ mapping sequence with whole left ventricle coverage using a multicoil, compressed sensing (CS) reconstruction technique for rapid reconstruction of undersampled k-space data.

METHODS

We developed a cardiac- and respiratory-gated, free-breathing 3D T1ρ sequence and acquired data using a variable-density k-space sampling pattern (A = 3). The effect of the transient magnetization trajectory, incomplete recovery of magnetization between T1ρ-preparations (heart rate dependence), and k-space sampling pattern on T1ρ relaxation time error and edge blurring was analyzed using Bloch simulations for normal and chronically infarcted myocardium. Sequence accuracy and repeatability was evaluated using MnCl2 phantoms with different T1ρ relaxation times and compared to 2D measurements. We further assessed accuracy and repeatability in healthy subjects and compared these results to 2D breath-held measurements.

RESULTS

The error in T1ρ due to incomplete recovery of magnetization between T1ρ-preparations was T1ρhealthy = 6.1% and T1ρinfarct = 10.8% at 60 bpm and T1ρhealthy = 13.2% and T1ρinfarct = 19.6% at 90 bpm. At a heart rate of 60 bpm, error from the combined effects of readout-dependent magnetization transients, k-space undersampling and reordering was T1ρhealthy = 12.6% and T1ρinfarct = 5.8%. CS reconstructions had improved edge sharpness (blur metric = 0.15) compared to inverse Fourier transform reconstructions (blur metric = 0.48). There was strong agreement between the mean T1ρ estimated from the 2D and accelerated 3D data (R2 = 0.99; P < 0.05) acquired on the MnCl2 phantoms. The mean R1ρ estimated from the accelerated 3D sequence was highly correlated with MnCl2 concentration (R2 = 0.99; P < 0.05). 3D T1ρ acquisitions were successful in all human subjects. There was no significant bias between undersampled 3D T1ρ and breath-held 2D T1ρ (mean bias = 0.87) and the measurements had good repeatability (COV2D = 6.4% and COV3D = 7.1%).

CONCLUSIONS

This is the first report of an accelerated, free-breathing 3D T1ρ mapping of the left ventricle. This technique may improve non-contrast myocardial tissue characterization in patients with heart disease in a scan time appropriate for patients.

Novel cardiac nuclear magnetic resonance method for noninvasive assessment of myocardial fibrosis in hemodialysis patients

Left ventricular hypertrophy and myocardial fibrosis frequently occur in patients with end-stage renal disease receiving hemodialysis therapy and are associated with poor prognosis. Native T1 mapping is a novel cardiac magnetic resonance imaging technique that measures native myocardial T1 relaxation, a surrogate of myocardial fibrosis. Here we compared global and segmental native myocardial T1 time and global longitudinal, circumferential and segmental strain, and cardiac function of 35 hemodialysis patients and 22 control individuals. The median native global T1 time was significantly higher in the hemodialysis than the control group (1270 vs. 1085 ms), with the septal regions of hemodialysis patients having significantly higher median T1 times than nonseptal regions (1293 vs. 1252 ms). The mean peak global circumferential strain and global longitudinal strain were both significantly reduced in hemodialysis patients compared with controls (-18.3 vs. -21.7 and -16.1 vs. -20.4, respectively). Systolic strain was also significantly reduced in the septum compared with the nonseptal myocardium in hemodialysis patients (-16.2 vs. -21.9) but not in control subjects. Global circumferential strain and longitudinal strain significantly correlated with global native T1 values (r = 0.41 and 0.55, respectively), and the septal native T1 significantly correlated with the septal systolic strain (r = 0.46). Thus, myocardial fibrosis may be assessed noninvasively with native T1 mapping; the interventricular septum appears to be particularly prone to the development of fibrosis in hemodialysis patients.

Imaging of Myocardial Fibrosis in Patients with End-Stage Renal Disease: Current Limitations and Future Possibilities

Cardiovascular disease in patients with end-stage renal disease (ESRD) is driven by a different set of processes than in the general population. These processes lead to pathological changes in cardiac structure and function that include the development of left ventricular hypertrophy and left ventricular dilatation and the development of myocardial fibrosis. Reduction in left ventricular hypertrophy has been the established goal of many interventional trials in patients with chronic kidney disease, but a recent systematic review has questioned whether reduction of left ventricular hypertrophy improves cardiovascular mortality as previously thought. The development of novel imaging biomarkers that link to cardiovascular outcomes and that are specific to the disease processes in ESRD is therefore required. Postmortem studies of patients with ESRD on hemodialysis have shown that the extent of myocardial fibrosis is strongly linked to cardiovascular death and accurate imaging of myocardial fibrosis would be an attractive target as an imaging biomarker. In this article we will discuss the current imaging methods available to measure myocardial fibrosis in patients with ESRD, the reliability of the techniques, specific challenges and important limitations in patients with ESRD, and how to further develop the techniques we have so they are sufficiently robust for use in future clinical trials.