T1 and extracellular volume mapping in the heart: estimation of error maps and the influence of noise on precision

The influence of left bundle branch block on myocardial T1 mapping

Tissue characterisation using T1 mapping has become an established magnetic resonance imaging (MRI) technique to detect myocardial diseases. This retrospective study aimed to determine the influence of left bundle branch block (LBBB) on T1 mapping at 1.5 T. Datasets of 36 patients with LBBB and 27 healthy controls with T1 mapping (Modified Look-Locker inversion-recovery (MOLLI), 5(3)3 sampling) were included. T1 relaxation times were determined on mid-cavity short-axis images. R2 maps were generated as a pixel-wise indicator for the goodness of the fit of T1 maps. R2 values were significantly lower in patients with LBBB than in healthy controls (whole myocardium/septum, 0.997, IQR, 0.00 vs. 0.998, IQR, 0.00; p = 0.008/0.998, IQR, 0.00 vs. 0.999, IQR, 0.00; p = 0.027). Manual correction of semi-automated evaluation tended to improve R2 values but not significantly. Strain analysis was performed and the systolic dyssynchrony index (SDIglobal) was calculated as a measure for left ventricular dyssynchrony. While MRI is generally prone to artefacts, lower goodness of the fit in LBBB may be mainly attributable to asynchronous contraction. Therefore, careful checking of the source data and, if necessary, manual post-processing is important. New techniques might improve the goodness of the fit of T1 mapping by reducing sampling in the motion prone diastole of LBBB patients.

Automated assessment of cardiac pathologies on cardiac MRI using T1-mapping and late gadolinium phase sensitive inversion recovery sequences with deep learning

BACKGROUND

A deep learning (DL) model that automatically detects cardiac pathologies on cardiac MRI may help streamline the diagnostic workflow. To develop a DL model to detect cardiac pathologies on cardiac MRI T1-mapping and late gadolinium phase sensitive inversion recovery (PSIR) sequences were used.

METHODS

Subjects in this study were either diagnosed with cardiac pathology (n = 137) including acute and chronic myocardial infarction, myocarditis, dilated cardiomyopathy, and hypertrophic cardiomyopathy or classified as normal (n = 63). Cardiac MR imaging included T1-mapping and PSIR sequences. Subjects were split 65/15/20% for training, validation, and hold-out testing. The DL models were based on an ImageNet pretrained DenseNet-161 and implemented using PyTorch and fastai. Data augmentation with random rotation and mixup was applied. Categorical cross entropy was used as the loss function with a cyclic learning rate (1e-3). DL models for both sequences were developed separately using similar training parameters. The final model was chosen based on its performance on the validation set. Gradient-weighted class activation maps (Grad-CAMs) visualized the decision-making process of the DL model.

RESULTS

The DL model achieved a sensitivity, specificity, and accuracy of 100%, 38%, and 88% on PSIR images and 78%, 54%, and 70% on T1-mapping images. Grad-CAMs demonstrated that the DL model focused its attention on myocardium and cardiac pathology when evaluating MR images.

CONCLUSIONS

The developed DL models were able to reliably detect cardiac pathologies on cardiac MR images. The diagnostic performance of T1 mapping alone is particularly of note since it does not require a contrast agent and can be acquired quickly.

Cardiac Magnetic Resonance Imaging Findings and Clinical Features of COVID-19 Vaccine-Associated Myocarditis, Compared With Those of Other Types of Myocarditis

BACKGROUND

To compare the clinical and cardiac magnetic resonance (CMR) imaging findings of coronavirus disease 2019 (COVID-19) vaccine-associated myocarditis (VAM) with those of other types of myocarditis.

METHODS

From January 2020 to March 2022, a total of 39 patients diagnosed with myocarditis via CMR according to the Modified Lake Louise criteria were included in the present study. The patients were classified into two groups based on their vaccination status: COVID-19 VAM and other types of myocarditis not associated with COVID-19 vaccination. Clinical outcomes, including the development of clinically significant arrhythmias, sudden cardiac arrest, and death, and CMR imaging features were compared between COVID-19 VAM and other types of myocarditis.

RESULTS

Of the 39 included patients (mean age, 39 years ± 16.4 [standard deviation]; 23 men), 23 (59%) had COVID-19 VAM and 16 (41%) had other types of myocarditis. The occurrence of clinical adverse events did not differ significantly between the two groups. As per the CMR imaging findings, the presence and dominant pattern of late gadolinium enhancement did not differ significantly between the two groups. The presence of high native T1 or T2 values was not significantly different between the two groups. Although the native T1 and T2 values tended to be lower in COVID-19 VAM than in other types of myocarditis, there were no statistically significant differences between the native T1 and T2 values in the two groups.

CONCLUSION

The present study demonstrated that the CMR imaging findings and clinical outcomes of COVID-19 VAM did not differ significantly from those of other types of myocarditis during hospitalization.

The Impact of Long COVID-19 on the Cardiovascular System

Long coronavirus disease (COVID) is the development or persistence of symptoms after an acute SARS-CoV-2 (COVID-19) infection. Fewer patients are developing acute COVID-19 infections, but patients with long COVID continue to have alarming long-term sequelae. Many cardiac magnetic resonance imaging studies show significant changes in cardiac structure after a COVID-19 infection, suggestive of an increased burden of many cardiovascular diseases, notably myocarditis. The pathophysiology of COVID-19 requires viral binding to angiotensin-converting enzyme 2 protein receptors throughout the body, which are upregulated by inflammation. Consequently, the numerous preexisting conditions that worsen or prolong inflammation enhance this binding and have differing effects on patients based on their unique immune systems. These pathophysiological changes drive long COVID cardiac sequelae such as inappropriate sinus tachycardia, postural orthostatic tachycardia, and other types of orthostatic intolerance. Increased screening for long COVID and low-risk interventions such as exercise regimens could alleviate the suffering endured by patients with long COVID. Many studies such as the Researching COVID to Enhance Recovery Initiative (RECOVER) trials at the National Institutes of Health are exploring potential treatments for long COVID patients.

Normal values for native T1 at 1.5 T in the pericardial fluid of healthy volunteers

Aims

T1 mapping cardiovascular magnetic resonance (CMR) imaging has been used to characterize pericardial effusions. The aim of this study was to measure pericardial fluid native T1 values in healthy volunteers to establish normal values.

Methods and results

Prospectively recruited volunteers (n = 30) underwent CMR at 1.5 T, and native T1 maps were acquired using a modified look-locker inversion recovery 5s(3s)3s acquisition scheme. A volume of pericardial fluid was imaged in a short-axis slice and in a slice perpendicular to the short-axis orientation. A reliable measurement had a region of interest (ROI) size > 10 mm2, coefficient of variation < 10%, and a relative difference < 5% between the two slice orientations. In 26/30 (87%) of volunteers, there was a sufficient amount of pericardial fluid to enable reliable measurement. Native T1 of pericardial fluid was 3262 ± 163 (95% normal limits 2943-3581 ms) and did not differ in the perpendicular slice orientation (3267 ± 173 ms, P = 0.75), due to sex (female 3311 ± 177 vs. male 3220 ± 142 ms, P = 0.17), age (R 2 = 0.03, P = 0.44), heart rate (R 2 = 0.005, P = 0.7), or size of the ROI (0.06, P = 0.23).

Conclusion

This study shows that T1 values can be reliably measured in the pericardial fluid of healthy volunteers. It is the first to report normal reference ranges for T1 values at 1.5 T in the pericardial fluid of healthy volunteers.

Quantification of myocardial extracellular volume without blood sampling

Aims

Cardiac magnetic resonance (CMR) T1 relaxation time mapping is an established technique primarily used to identify diffuse interstitial fibrosis and oedema. The myocardial extracellular volume (ECV) can be calculated from pre- and post-contrast T1 relaxation times and is a reproducible parametric index of the proportion of volume occupied by non-cardiomyocyte components in myocardial tissue. The conventional calculation of the ECV requires blood sampling to measure the haematocrit (HCT). Given the high variability of the HCT, the blood collection is recommended within 24 h of the CMR scan, limiting its applicability and posing a barrier to the clinical routine use of ECV measurements. In recent years, several research groups have proposed a method to determine the ECV by CMR without blood sampling. This is based on the inverse relationship between the T1 relaxation rate (R1) of blood and the HCT. Consequently, a 'synthetic' HCT could be estimated from the native blood R1, avoiding blood sampling.

Methods and results

We performed a review and meta-analysis of published studies on synthetic ECV, as well as a secondary analysis of previously published data to examine the effect of the chosen regression modell on bias. While, overall, a good correlation and little bias between synthetic and conventional ECV were found in these studies, questions regarding its accuracy remain.

Conclusion

Synthetic HCT and ECV can provide a 'non-invasive' quantitative measurement of the myocardium's extracellular space when timely HCT measurements are not available and large alterations in ECV are expected, such as in cardiac amyloidosis. Due to the dependency of T1 relaxation times on the local setup, calculation of local formulas using linear regression is recommended, which can be easily performed using available data.

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.

Free-breathing pseudo-golden-angle bSSFP cine cardiac MRI for biventricular functional assessment in congenital heart disease

PURPOSE

To compare standard breath-hold (BH) cine imaging to a radial pseudo-golden-angle free-breathing (FB) technique in congenital heart disease (CHD).

METHODS

In this prospective study, short-axis and 4-chamber BH and FB cardiac MRI sequences of 25 participants with CHD acquired at 1.5 Tesla, were quantitatively compared regarding ventricular volumes, function, interventricular septum thickness (IVSD), apparent signal to noise ratio (aSNR), and estimated contrast to noise ratio (eCNR). For qualitative comparison, three image quality criteria (contrast, endocardial edge definition, and artefacts) were rated on a 5-point Likert scale (5: excellent, 1: non-diagnostic). Paired t-Test was used for group comparisons, Bland-Altman analysis for agreement between techniques. Inter-reader agreement was compared using intraclass correlation coefficient.

RESULTS

IVSD (BH 7.4 ± 2.1 mm vs FB 7.4 ± 1.9 mm, p =.71), biventricular ejection fraction (left ventricle [LV]: 56.4 ± 10.8% vs 56.1 ± 9.3%, p =.83; right ventricle [RV]: 49.5 ± 8.6% vs 49.7 ± 10.1%, p =.83), and biventricular end diastolic volume (LV: 176.3 ± 63.9 ml vs 173.9 ± 64.9 ml, p =.90; RV: 185.4 ± 63.8 ml vs 189.6 ± 66.6 ml, p =.34) were comparable. Mean measurement time for FB short-axis sequences was 8.1 ± 1.3 compared to 4.4 ± 1.3 min for BH (p <.001). Subjective image quality between sequences was deemed comparable, (4.6 ± 0.6 vs 4.5 ± 0.6, p =.26, for 4-chamber views) with a significant difference regarding short-axis views (4.9 ± 0.3 vs 4.5 ± 0.6, p =.008). aSNR was similar (BH 25.8 ± 11.2 vs FB 22.2 ± 9.5, p =.24), while eCNR was higher for BH (89.1 ± 36.1 vs 68.5 ± 32.1, p =.03).

CONCLUSION

FB sequences yielded comparable results to BH regarding image quality, biventricular volumetry, and function, though measurement times were longer. The FB sequence described might be clinically valuable when BHs are insufficiently performed.

A Left ventricle remodeling in patients with bicuspid aortic valve

PURPOSE

We assessed the impact of bicuspid aortic valve (BAV), aortic stenosis (AS), and regurgitation (AR) on the metrics of left ventricular (LV) remodeling, as measured by electrocardiogram (ECG), transthoracic echocardiography (TTE), and cardiac magnetic resonance (CMR).

METHODS

This retrospective CMR study included 11 patients with both AS and AR (BAV-ASR), 30 with AS (BAV-AS), 28 with AR (BAV-AR), 47 with neither AS nor AR (BAV-no_AS/AR), and 40 with trileaflet aortic valve (TAV-no_AS/AR). CMR analysis included the LV end-diastolic volume index (LVEDVi), mass index (LVMi), and extracellular volume fraction (ECV). The Sokolow-Lyon and Cornell products by ECG and TTE-derived E/e' were measured.

RESULTS

There were no differences in the ECG, TTE, and CMR parameters between BAV-no_AS/AR and TAV-no_AS/AR. However, the presence of aortic valve dysfunction resulted in an elevated Sokolow-Lyon product for BAV-ASR (p = 0.017) and BAV-AR (p = 0.001), as well as increased Cornell product (p = 0.04) and E/e' (p < 0.001) for BAV-AS compared with BAV-no_AS/AR. LVEDVi and LVMi were elevated in patients with BAV-ASR and BAV-AR compared with those with BAV-no_AS/AR (LVEDVi: 101 ± 29 ml/m² and 112 ± 32 ml/m² vs. 74 ± 15 ml/m², p = 0.005 and p < 0.001, LVMi: 75 ± 7 g/m² and 64 ± 14 g/m² vs. 47 ± 9 g/m², respectively; p < 0.001). There was no difference in ECV between the BAV and TAV-no_AS/AR subgroups.

CONCLUSION

Normally functioning BAV did not result in LV remodeling. However, concomitant AV dysfunction was associated with statistically significant morphological remodeling.

Non-LGE Cardiac Magnetic Resonance Imaging in Patients with Cardiac Amyloidosis

Cardiac involvement is the leading cause of death in patients with cardiac amyloidosis. Early recognition is crucial as it can significantly change the course of the disease. Until now, the imaging modality of choice for diagnosing cardiac amyloidosis has been cardiac magnetic resonance imaging (CMR) with late gadolinium enhancement (LGE). LGE-CMR in patients with cardiac amyloidosis reveals characteristic LGE patterns that lead to a diagnosis while also correlating well with disease prognosis. However, LGE-CMR has numerous drawbacks that the newer CMR modality, T1 mapping, aims to improve. T1 mapping can be further subdivided into native T1 mapping, which does not require the use of contrast, and ECV measurement, which requires the use of contrast. Numerous T1 mapping techniques have been developed, each one with its own advantages and disadvantages when it comes to procedure difficulty and image quality. A literature review to identify relevant published articles was performed by two authors. This review aimed to present the value of T1 mapping in diagnosing cardiac amyloidosis, quantifying the amyloid burden, and evaluating the prognosis of patients with amyloidosis with cardiac involvement.

T1 Mapping MOLLI 5(3)3 Acquisition Scheme Yields High Accuracy in 1.5 T Cardiac Magnetic Resonance

Objectives: To systematically compare two modified Look-Locker inversion recovery (MOLLI) T1 mapping sequences and their impact on (1) myocardial T1 values native, (2) post-contrast and (3) extracellular volume (ECV). Methods: 200 patients were prospectively included for 1.5 T CMR for work-up of ischemic or non-ischemic cardiomyopathies. To determine native and post-contrast T1 for ECV calculation, two different T1 mapping MOLLI acquisition schemes, 5(3)3 (designed for native scans with long T1) and 4(1)3(1)2 (designed for post-contrast scans with short T1), were acquired in identical mid-ventricular short-axis slices. Both schemes were acquired in native and post-contrast scans. Results: Datasets from 163 patients were evaluated (age 55 ± 17 years; 38% female). Myocardial T1 native for 5(3)3 was 1017 ± 42 ms vs. 956 ± 40 ms for 4(1)3(1)2, with mean intraindividual difference −61 ms (p < 0.0001). Post-contrast myocardial T1 in patients was similar for both acquisition schemes, with 494 ± 48 ms for 5(3)3 and 490 ± 45 ms for 4(1)3(1)2 and mean intraindividual difference −4 ms. Myocardial ECV for 5(3)3 was 27.6 ± 4% vs. 27 ± 4% for 4(1)3(1)2, with mean difference −0.6 percentage points (p < 0.0001). Conclusions: The T1 MOLLI 5(3)3 acquisition scheme provides a reliable estimation of myocardial T1 for the clinically relevant range of long and short T1 values native and post-contrast. In contrast, the T1 MOLLI 4(1)3(1)2 acquisition scheme may only be used for post-contrast scans according to its designed purpose.

Reference values of myocardial native T1 and T2 mapping values in normal Indian population at 1.5 Tesla scanner

T1 and T2 mapping techniques on cardiovascular magnetic resonance (CMR) provide insights into the myocardial tissue characterisation. We sought to establish the normal reference values of native T1 and T2 mapping in Indian population which can be used subsequently in clinical practice for addressing various cardiac pathologies. This prospective study included consecutive healthy volunteers (18-60 years) who underwent CMR on a 1.5 Tesla scanner using standard protocol. T1 mapping sequence was performed using MOLLI sequence with two different flip angles (FA) (35° and 50°). T2 mapping was performed using a hybrid gradient and spin-echo sequence sequence with two different FA (70° and 12°). Images were analysed with ROIs drawn in all the 16 AHA myocardial segments. 50 volunteers (average age-34 years, males-72%) were included. All the scans were normal. The mean T1 value at 35-degree FA was 946.86 + 14.16 ms and at 50-degree FA was 941.60 + 11.89 ms. The mean T2 mapping value at 70-degree FA was 45.67 + 1.39 ms and at 12-degree FA was 45.61 + 1.47 ms. The mapping values were not statistically different between males and females (all p > 0.2). The T1 and T2 mapping values did not show any significant correlation with LVEF, age, BMI or heart rate (all r < 0.33). The T1 mapping values significantly differ at 35- and 50-degree FAs (p = 0.002). The results establish the normal reference T1 and T2 mapping value for Indian population in institutes using the same protocol and parameters at 1.5 Tesla and may guide future research.

Improving accuracy of myocardial T1 estimation in MyoMapNet

PURPOSE

To improve the accuracy and robustness of T₁ estimation by MyoMapNet, a deep learning-based approach using 4 inversion-recovery T₁ -weighted images for cardiac T₁ mapping.

METHODS

MyoMapNet is a fully connected neural network for T₁ estimation of an accelerated cardiac T₁ mapping sequence, which collects 4 T₁ -weighted images by a single Look-Locker inversion-recovery experiment (LL4). MyoMapNet was originally trained using in vivo data from the modified Look-Locker inversion recovery sequence, which resulted in significant bias and sensitivity to various confounders. This study sought to train MyoMapNet using signals generated from numerical simulations and phantom MR data under multiple simulated confounders. The trained model was then evaluated by phantom data scanned using new phantom vials that differed from those used for training. The performance of the new model was compared with modified Look-Locker inversion recovery sequence and saturation-recovery single-shot acquisition for measuring native and postcontrast T₁ in 25 subjects.

RESULTS

In the phantom study, T₁ values measured by LL4 with MyoMapNet were highly correlated with reference values from the spin-echo sequence. Furthermore, the estimated T₁ had excellent robustness to changes in flip angle and off-resonance. Native and postcontrast myocardium T₁ at 3 Tesla measured by saturation-recovery single-shot acquisition, modified Look-Locker inversion recovery sequence, and MyoMapNet were 1483 ± 46.6 ms and 791 ± 45.8 ms, 1169 ± 49.0 ms and 612 ± 36.0 ms, and 1443 ± 57.5 ms and 700 ± 57.5 ms, respectively. The corresponding extracellular volumes were 22.90% ± 3.20%, 28.88% ± 3.48%, and 30.65% ± 3.60%, respectively.

CONCLUSION

Training MyoMapNet with numerical simulations and phantom data will improve the estimation of myocardial T₁ values and increase its robustness to confounders while also reducing the overall T₁ mapping estimation time to only 4 heartbeats.

Clinical Impact of Cardiac MRI T1 and T2 Parametric Mapping in Patients with Suspected Cardiomyopathy

Background There are limited data on the incremental value of parametric mapping compared with core cardiac MRI protocols for suspected cardiomyopathy in routine clinical practice. Purpose To evaluate the impact of cardiac MRI T1 and T2 mapping in routine clinical practice with respect to diagnostic accuracy, reader diagnostic confidence, and downstream cardiac imaging utilization. Materials and Methods In this retrospective single-center study, consecutive clinical cardiac MRI scans obtained with and without T1 and T2 mapping for evaluation of suspected cardiomyopathy between January 2017 and October 2019 were evaluated. Diagnostic accuracy and reader diagnostic confidence were evaluated in a random subset. Downstream cardiac imaging utilization was analyzed in patients with a minimum of 1 year of clinical follow-up ending before January 2020. Results A total of 1876 patients (mean age, 51 years ± 17 [SD]; 1113 men) were evaluated. Of these, 751 (40%) underwent cardiac MRI with the core protocol and 1125 (60%) with the core protocol plus T1 and T2 mapping. In the mapping group, T1 and T2 were high in 280 (25%) and 47 patients (4%), respectively. In the subset evaluated for diagnostic utility (n = 450), the addition of T1 and T2 maps to the core protocol resulted in an improvement in reader diagnostic confidence in 174 patients (39%). Diagnostic sensitivity was higher with the core protocol plus mapping compared with the core protocol alone for myocarditis (89% [31 of 35 patients] vs 69% [24 of 35]; P = .008), Fabry disease (93% [13 of 14 patients] vs 50% [seven of 14]; P = .01), and amyloidosis (100% [16 of 16 patients] vs 63% [10 of 16]; P = .01). In the subset evaluated for downstream imaging utilization (n = 903), 47% of patients with mapping had at least one subsequent cardiac imaging test compared with 55% of patients without mapping (P = .01). Conclusion In patients with suspected cardiomyopathy, cardiac MRI with T1 and T2 mapping had high diagnostic utility and was associated with lower downstream cardiac imaging utilization. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Jerosch-Herold and Coelho-Filho in this issue.

Myocardial Approximate Spin-lock Dispersion Mapping using a Simultaneous T2 and TRAFF2 Mapping at 3T MRI

Ischemic heart disease (IHD) is one of the leading causes of death worldwide. Myocardial infarction (MI) represents a third of all IHD cases, and cardiac magnetic resonance imaging (MRI) is often used to assess its damage to myocardial viability. Late gadolinium enhancement (LGE) is the current gold standard, but the use of gadolinium-based agents limits the clinical applicability in some patients. Spin-lock (SL) dispersion has recently been proposed as a promising non-contrast biomarker for the assessment of MI. However, at 3T, the required range of SL preparations acquired at different amplitudes suffers from specific absorption rate (SAR) limitations and off-resonance artifacts. Relaxation Along a Fictitious Field (RAFF) is an alternative to SL preparations with lower SAR requirements, while still sampling relaxation in the rotating frame. In this study, a single breath-hold simultaneous TRAFF2 and T2 mapping sequence is proposed for SL dispersion mapping at 3T. Excellent reproducibility (coefficient of variations lower than 10%) was achieved in phantom experiments, indicating good intrascan repeatability. The average myocardial TRAFF2, T2, and SL dispersion obtained with the proposed sequence (68.0±10.7 ms, 44.0±4.0 ms, and 0.4±0.2 ×10-4 s2, respectively) were comparable to the reference methods (62.7±11.7 ms, 41.2±2.4 ms, and 0.3±0.2x 10-4s2, respectively). High visual map quality, free of B0 and B1+ related artifacts, for T2, TRAFF2, and SL dispersion maps were obtained in phantoms and in vivo, suggesting promise in clinical use at 3T. Clinical relevance - and imaging promises non-contrast assessment of scar and focal fibrosis in a single breath-hold using approximate spin-lock dispersion mapping.

Image resampling and discretization effect on the estimate of myocardial radiomic features from T1 and T2 mapping in hypertrophic cardiomyopathy

Radiomics is emerging as a promising and useful tool in cardiac magnetic resonance (CMR) imaging applications. Accordingly, the purpose of this study was to investigate, for the first time, the effect of image resampling/discretization and filtering on radiomic features estimation from quantitative CMR T1 and T2 mapping. Specifically, T1 and T2 maps of 26 patients with hypertrophic cardiomyopathy (HCM) were used to estimate 98 radiomic features for 7 different resampling voxel sizes (at fixed bin width), 9 different bin widths (at fixed resampling voxel size), and 7 different spatial filters (at fixed resampling voxel size/bin width). While we found a remarkable dependence of myocardial radiomic features from T1 and T2 mapping on image filters, many radiomic features showed a limited sensitivity to resampling voxel size/bin width, in terms of intraclass correlation coefficient (> 0.75) and coefficient of variation (< 30%). The estimate of most textural radiomic features showed a linear significant (p < 0.05) correlation with resampling voxel size/bin width. Overall, radiomic features from T2 maps have proven to be less sensitive to image preprocessing than those from T1 maps, especially when varying bin width. Our results might corroborate the potential of radiomics from T1/T2 mapping in HCM and hopefully in other myocardial diseases.

Study protocol: MyoFit46-the cardiac sub-study of the MRC National Survey of Health and Development

BACKGROUND

The life course accumulation of overt and subclinical myocardial dysfunction contributes to older age mortality, frailty, disability and loss of independence. The Medical Research Council National Survey of Health and Development (NSHD) is the world's longest running continued surveillance birth cohort providing a unique opportunity to understand life course determinants of myocardial dysfunction as part of MyoFit46-the cardiac sub-study of the NSHD.

METHODS

We aim to recruit 550 NSHD participants of approximately 75 years+ to undertake high-density surface electrocardiographic imaging (ECGI) and stress perfusion cardiovascular magnetic resonance (CMR). Through comprehensive myocardial tissue characterization and 4-dimensional flow we hope to better understand the burden of clinical and subclinical cardiovascular disease. Supercomputers will be used to combine the multi-scale ECGI and CMR datasets per participant. Rarely available, prospectively collected whole-of-life data on exposures, traditional risk factors and multimorbidity will be studied to identify risk trajectories, critical change periods, mediators and cumulative impacts on the myocardium.

DISCUSSION

By combining well curated, prospectively acquired longitudinal data of the NSHD with novel CMR-ECGI data and sharing these results and associated pipelines with the CMR community, MyoFit46 seeks to transform our understanding of how early, mid and later-life risk factor trajectories interact to determine the state of cardiovascular health in older age.

TRIAL REGISTRATION

Prospectively registered on ClinicalTrials.gov with trial ID: 19/LO/1774 Multimorbidity Life-Course Approach to Myocardial Health- A Cardiac Sub-Study of the MCRC National Survey of Health and Development (NSHD).

Myocardial Injury Pattern at MRI in COVID-19 Vaccine-associated Myocarditis

Background

There are limited data on the pattern and severity of myocardial injury in patients with COVID-19 vaccination–associated myocarditis.

Purpose

To describe myocardial injury following COVID-19 vaccination and to compare these findings to other causes of myocarditis.

Materials and Methods

In this retrospective cohort study, consecutive adult patients with myocarditis with at least one T1-based and at least one T2-based abnormality at cardiac MRI performed at a tertiary referral hospital from December 2019 to November 2021 were included. Patients were classified into one of three groups: myocarditis following COVID-19 vaccination, myocarditis following COVID-19 illness, and other myocarditis not associated with COVID-19 vaccination or illness.

Results

Of the 92 included patients, 21 (23%) had myocarditis following COVID-19 vaccination (mean age, 31 years ± 14 [SD]; 17 men; messenger RNA–1273 in 12 [57%] and BNT162b2 in nine [43%]). Ten of 92 (11%) patients had myocarditis following COVID-19 illness (mean age, 51 years ± 14; three men) and 61 of 92 (66%) patients had other myocarditis (mean age, 44 years ± 18; 36 men). MRI findings in the 21 patients with vaccine-associated myocarditis included late gadolinium enhancement (LGE) in 17 patients (81%) and left ventricular dysfunction in six (29%). Compared with other causes of myocarditis, patients with vaccine-associated myocarditis had a higher left ventricular ejection fraction and less extensive LGE, even after controlling for age, sex, and time from symptom onset to MRI. The most frequent location of LGE in all groups was subepicardial at the basal inferolateral wall, although septal involvement was less common in vaccine-associated myocarditis. At short-term follow-up (median, 22 days [IQR, 7–48 days]), all patients with vaccine-associated myocarditis were asymptomatic with no adverse events.

Conclusion

Cardiac MRI demonstrated a similar pattern of myocardial injury in vaccine-associated myocarditis compared with other causes, although abnormalities were less severe, with less frequent septal involvement and no adverse events over the short-term follow-up.

© RSNA, 2022

Online supplemental material is available for this article.

See also the editorial by Raman and Neubauer in this issue.

Improved cardiac T1 mapping accuracy and precision with a new hybrid MOLLI and SASHA technique: MOSHA

PURPOSE

To develop and validate a new myocardial T₁ mapping sequence (MOSHA) which is based on a combination of the modified Look-Locker inversion recovery (MOLLI) and the saturation recovery single-shot acquisition (SASHA) sequences.

METHODS

Prior studies have shown that myocardial T₁ mapping by SASHA is more accurate but less precise than MOLLI. A new myocardial T₁ mapping technique (MOSHA) based on single-shot acquisitions is developed by combining the MOLLI and SASHA sequences. Phantom and patient studies on 15 patients (9 males, median age 21 years) were performed to validate and compare MOSHA with the MOLLI and SASHA sequences in terms of accuracy and precision.

RESULTS

In the phantom study, MOSHA was as accurate as SASHA (P-value = 0.88) and as precise as MOLLI (P-value = 0.59). Similar trends were observed in the patient study. Compared to SASHA, MOSHA accuracy was comparable for blood pre-contrast (P-value≥0.10) and post-contrast (P-value≥0.70), and for myocardium pre-contrast (P-value = 0.70) and post-contrast (P-value = 0.09). Compared to MOLLI, MOSHA precision was lower for blood pre-contrast (P-value<0.01) and higher for blood post-contrast (P-value≤0.01), and comparable for myocardium pre-contrast (P-value = 0.24) and post-contrast (P-value = 0.07). Synthetic Extracellular volume fraction (ECV) calculated by MOSHA was more precise than those of SASHA and MOLLI (P-value ≤0.01).

CONCLUSION

In phantom studies and patients, MOSHA has comparable accuracy as SASHA and nearly similar precision as MOLLI for T₁ mapping. Precision of MOSHA was better than MOLLI and SASHA in synthetic ECV measurements. Therefore, it may be a superior choice in clinical practice for a precise and accurate calculation of T₁ and ECV.

Cartesian dictionary-based native T1 and T2 mapping of the myocardium

PURPOSE

To implement and evaluate a new dictionary-based technique for native myocardial T₁ and T₂ mapping using Cartesian sampling.

METHODS

The proposed technique (Multimapping) consisted of single-shot Cartesian image acquisitions in 10 consecutive cardiac cycles, with inversion pulses in cycle 1 and 5, and T₂ preparation (TE: 30 ms, 50 ms, and 70 ms) in cycles 8-10. Multimapping was simulated for different T₁ and T₂ , where entries corresponding to the k-space centers were matched to acquired data. Experiments were performed in a phantom, 16 healthy subjects, and 3 patients with cardiovascular disease.

RESULTS

Multimapping phantom measurements showed good agreement with reference values for both T₁ and T₂ , with no discernable heart-rate dependency for T₁ and T₂ within the range of myocardium. In vivo mean T₁ in healthy subjects was significantly higher using Multimapping (T₁ = 1114 ± 14 ms) compared to the reference (T₁ = 991 ± 26 ms) (p < 0.01). Mean Multimapping T₂ (47.1 ± 1.3 ms) and T₂ spatial variability (5.8 ± 1.0 ms) was significantly lower compared to the reference (T₂ = 54.7 ± 2.2 ms, p < 0.001; spatial variability = 8.4 ± 2.0 ms, p < 0.01). Increased T₁ and T₂ was detected in all patients using Multimapping.

CONCLUSIONS

Multimapping allows for simultaneous native myocardial T₁ and T₂ mapping with a conventional Cartesian trajectory, demonstrating promising in vivo image quality and parameter quantification results.

Reference Values of Native T1 at 3T Cardiac Magnetic Resonance-Standardization Considerations between Different Vendors

This study aimed at establishing native T1 reference values for a Canon Vantage Galan 3T system and comparing them with previously published values from different vendors. A total of 20 healthy volunteers (55% Women; 33.9 ± 11.1 years) underwent left ventricular T1 mapping at 3T MR. A MOLLI 5(3)3 sequence was used, acquiring three short-axis slices. Native T1 values are shown as means (±standard deviation) and Student’s independent samples t-test was used to test gender differences in T1 values. Pearson’s correlation coefficient analysis was used to compare two processes of T1 analysis. The results show a global native T1 mean value of 1124.9 ± 55.2 ms (exponential analysis), that of women being statistically higher than men (1163 ± 30.5 vs. 1077.9 ± 39.5 ms, respectively; p < 0.001). There were no specific tendencies for T1 times in different ventricular slices. We found a strong correlation (0.977, p < 0.001) with T1 times derived from parametric maps (1136.4 ± 60.2 ms). Native T1 reference values for a Canon 3T scanner were provided, and they are on par with those already reported from other vendors for a similar sequence. We also found a correlation between native T1 and gender, with higher values for women.

Cardiovascular Magnetic Resonance Parametric Mapping Techniques: Clinical Applications and Limitations

PURPOSE OF REVIEW

Parametric mapping represents a significant innovation in cardiovascular magnetic resonance (CMR) tissue characterisation, allowing the quantification of myocardial changes based on changes on T1, T2 and T2* relaxation times and extracellular volume (ECV). Its clinical use is rapidly expanding, but it requires availability of dedicated equipment as well as expertise in image acquisition and analysis. This review focuses on the principles of CMR parametric mapping, its current clinical applications, important limitations, as well as future directions of this technique in cardiovascular medicine.

RECENT FINDINGS

There is increasing evidence that CMR parametric mapping techniques provide accurate diagnostic and prognostic tools that can be applied to and support the clinical management of patients with a range of cardiovascular disease. The unique capability of CMR myocardial tissue characterisation in cardiovascular diseases has further expanded by the introduction of parametric mapping. Its use in clinical practice presents opportunities but has also limitations.

Prospective Case-Control Study of Cardiovascular Abnormalities 6 Months Following Mild COVID-19 in Healthcare Workers

OBJECTIVES

The purpose of this study was to detect cardiovascular changes after mild severe acute respiratory syndrome-coronavirus-2 infection.

BACKGROUND

Concern exists that mild coronavirus disease 2019 may cause myocardial and vascular disease.

METHODS

Participants were recruited from COVIDsortium, a 3-hospital prospective study of 731 health care workers who underwent first-wave weekly symptom, polymerase chain reaction, and serology assessment over 4 months, with seroconversion in 21.5% (n = 157). At 6 months post-infection, 74 seropositive and 75 age-, sex-, and ethnicity-matched seronegative control subjects were recruited for cardiovascular phenotyping (comprehensive phantom-calibrated cardiovascular magnetic resonance and blood biomarkers). Analysis was blinded, using objective artificial intelligence analytics where available.

RESULTS

A total of 149 subjects (mean age 37 years, range 18 to 63 years, 58% women) were recruited. Seropositive infections had been mild with case definition, noncase definition, and asymptomatic disease in 45 (61%), 18 (24%), and 11 (15%), respectively, with 1 person hospitalized (for 2 days). Between seropositive and seronegative groups, there were no differences in cardiac structure (left ventricular volumes, mass, atrial area), function (ejection fraction, global longitudinal shortening, aortic distensibility), tissue characterization (T1, T2, extracellular volume fraction mapping, late gadolinium enhancement) or biomarkers (troponin, N-terminal pro-B-type natriuretic peptide). With abnormal defined by the 75 seronegatives (2 SDs from mean, e.g., ejection fraction <54%, septal T1 >1,072 ms, septal T2 >52.4 ms), individuals had abnormalities including reduced ejection fraction (n = 2, minimum 50%), T1 elevation (n = 6), T2 elevation (n = 9), late gadolinium enhancement (n = 13, median 1%, max 5% of myocardium), biomarker elevation (borderline troponin elevation in 4; all N-terminal pro-B-type natriuretic peptide normal). These were distributed equally between seropositive and seronegative individuals.

CONCLUSIONS

Cardiovascular abnormalities are no more common in seropositive versus seronegative otherwise healthy, workforce representative individuals 6 months post-mild severe acute respiratory syndrome-coronavirus-2 infection.

Synthetic extracellular volume fraction without hematocrit sampling for hepatic applications

Purpose

Calculation of extracellular volume fraction (ECV) currently receives increasing interest as a potential biomarker for non-invasive assessment of liver fibrosis. ECV calculation requires hematocrit (Hct) sampling, which might be difficult to obtain in a high-throughput radiology department. The aim of this study was to generate synthetic ECV for hepatic applications without the need for Hct sampling.

Methods

In this prospective study participants underwent liver MRI. T1 mapping was performed before and after contrast administration. Blood Hct was obtained prior to MRI. We hypothesized that the relationship between Hct and longitudinal relaxation rate of blood (R1 = 1/T1_blood) could be calibrated and used to generate the equation for synthetic Htc and ECV calculation. Conventional and synthetic ECV were calculated. Pearson correlation, linear regression and Bland–Altman method were used for statistical analysis.

Results

180 consecutive patients were divided into derivation (n = 90) and validation (n = 90) cohorts. In the derivation cohort, native R1_blood and Hct showed a linear relationship (Hct_MOLLI = 98.04 × (1/T1_blood) − 33.17, R² = 0.75, P < 0.001), which was used to calculate synthetic ECV in the validation and whole study cohorts. Synthetic and conventional ECV showed significant correlations in the derivation, validation and in the whole study cohorts (r = 0.99, 0.97 and 0.99, respectively, P < 0.001, respectively) with minimal bias according to the Bland–Altman analysis.

Conclusion

Synthetic ECV seems to offer an alternative method for non-invasive quantification of the hepatic ECV. It may potentially overcome an important barrier to clinical implementation of ECV and thus, enable broader use of hepatic ECV in routine clinical practice.

Free-breathing simultaneous T1 , T2 , and T2∗ quantification in the myocardium

PURPOSE

To implement a free-breathing sequence for simultaneous quantification of T 1 , T 2 , and T 2 ∗ for comprehensive tissue characterization of the myocardium in a single scan using a multi-gradient-echo readout with saturation and T 2 preparation pulses.

METHODS

In the proposed Saturation And T 2 -prepared Relaxometry with Navigator-gating (SATURN) technique, a series of multi-gradient-echo (GRE) images with different magnetization preparations was acquired during free breathing. A total of 35 images were acquired in 26.5 ± 14.9 seconds using multiple saturation times and T 2 preparation durations and with imaging at 5 echo times. Bloch simulations and phantom experiments were used to validate a 5-parameter fit model for accurate relaxometry. Free-breathing simultaneous T 1 , T 2 , and T 2 ∗ measurements were performed in 10 healthy volunteers and 2 patients using SATURN at 3T and quantitatively compared to conventional single-parameter methods such as SASHA for T 1 , T 2 -prepared bSSFP, and multi-GRE for T 2 ∗ .

RESULTS

Simulations confirmed accurate fitting with the 5-parameter model. Phantom measurements showed good agreement with the reference methods in the relevant range for in vivo measurements. Compared to single-parameter methods comparable accuracy was achieved. SATURN produced in vivo parameter maps that were visually comparable to single-parameter methods. No significant difference between T 1 , T 2 , and T 2 ∗ times acquired with SATURN and single-parameter methods was shown in quantitative measurements (SATURN T 1 = 1573 ± 86 ms , T 2 = 33.2 ± 3.6 ms , T 2 ∗ = 25.3 ± 6.1 ms ; conventional methods: T 1 = 1544 ± 107 ms , T 2 = 33.2 ± 3.6 ms , T 2 ∗ = 23.8 ± 5.5 ms ; P > . 2 ) CONCLUSION: SATURN enables simultaneous quantification of T 1 , T 2 , and T 2 ∗ in the myocardium for comprehensive tissue characterization with co-registered maps, in a single scan with good agreement to single-parameter methods.

Single-source dual energy CT to assess myocardial extracellular volume fraction in aortic stenosis before transcatheter aortic valve implantation (TAVI)

PURPOSE

To assess myocardial extracellular volume fraction (ECV) measurement provided by a single-source dual-energy computed tomography (SSDE-CT) acquisition added at the end of a routine CT examination before transcatether aortic valve implantation (TAVI) compared to cardiac magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Twenty-one patients (10 men, 11 women; mean age, 86±4.9 years [SD]; age range: 71-92 years) with severe aortic stenosis underwent standard pre-TAVI CT with additional cardiac SSDE-CT acquisition 7minutes after intravenous administration of iodinated contrast material and myocardial MRI including pre- and post-contrast T1-maps. Myocardial ECV and standard deviation (σECV) were calculated in the 16-segments model. ECV provided by SSDE-CT was compared to ECV provided by MRI, which served as the reference. Analyses were performed on a per-segment basis and on a per-patient involving the mean value of the 16-segments.

RESULTS

ECV was slightly overestimated by SSDE-CT (29.9±4.6 [SD] %; range: 20.9%-48.3%) compared to MRI (29.1±3.9 [SD] %; range: 22.0%-50.7%) (P<0.0001) with a bias and limits of agreement of +2.3% (95%CI: -16.1%-+20.6%) and +2.5% (95%CI: -2.1%-+7.1%) for per-segment and per-patient-analyses, respectively. Good (r=0.81 for per-segment-analysis) to excellent (r=0.97 for per-patient-analysis) linear relationships (both P<0.0001) were obtained. The σECV was significantly higher at SSDE-CT (P<0.0001). Additional radiation dose from CT was 1.89±0.38 (SD) mSv (range: 1.48-2.47 mSv).

CONCLUSION

A single additional SSDE-CT acquisition added at the end of a standard pre-TAVI CT protocol can provide ECV measurement with good to excellent linear relationship with MRI.

Measurement of T1 Mapping in Patients With Cardiac Devices: Off-Resonance Error Extends Beyond Visual Artifact but Can Be Quantified and Corrected

Background: Measurement of myocardial T1 is increasingly incorporated into standard cardiovascular magnetic resonance (CMR) protocols, however accuracy may be reduced in patients with metallic cardiovascular implants. Measurement is feasible in segments free from visual artifact, but there may still be off-resonance induced error.

Aim: To quantify off-resonance induced T1 error in patients with metallic cardiovascular implants, and validate a method for error correction for a conventional MOLLI pulse sequence.

Methods: Twenty-four patients with cardiac implantable electronic devices (CIEDs: 46% permanent pacemakers, PPMs; 33% implantable loop recorders, ILRs; and 21% implantable cardioverter-defibrillators, ICDs); and 31 patients with aortic valve replacement (AVR) (45% metallic) were studied. Paired mid-myocardial short-axis MOLLI and single breath-hold off-resonance field maps were acquired at 1.5 T. T1 values were measured by AHA segment, and segments with visual artifact were excluded. T1 correction was applied using a published relationship between off-resonance and T1. The accuracy of the correction was assessed in 10 healthy volunteers by measuring T1 before and after external placement of an ICD generator next to the chest to generate off-resonance.

Results: T1 values in healthy volunteers with an ICD were underestimated compared to without (967 ± 52 vs. 997 ± 26 ms respectively, p = 0.0001), but were similar after correction (p = 0.57, residual difference 2 ± 27 ms). Artifact was visible in 4 ± 12, 42 ± 31, and 53 ± 27% of AHA segments in patients with ILRs, PPMs, and ICDs, respectively. In segments without artifact, T1 was underestimated by 63 ms (interquartile range: 7–143) per patient. The greatest error for patients with ILRs, PPMs and ICDs were 79, 146, and 191 ms, respectively. The presence of an AVR did not generate T1 error.

Conclusion: Even when there is no visual artifact, there is error in T1 in patients with CIEDs, but not AVRs. Off-resonance field map acquisition can detect error in measured T1, and a correction can be applied to quantify T1 MOLLI accurately.

Myocardial Substrate Characterization by CMR T1 Mapping in Patients With NICM and No LGE Undergoing Catheter Ablation of VT

OBJECTIVES

The goal of this study was to characterize the relationship between DF, the electroanatomic mapping (EAM) substrate, and outcomes of catheter ablation of VT in NICM.

BACKGROUND

A substantial proportion of patients with nonischemic dilated cardiomyopathy (NICM) and ventricular tachycardia (VT) do not have scar detectable by cardiac magnetic resonance late gadolinium enhancement (LGE) imaging. In these patients, the significance of diffuse fibrosis (DF) detected with T₁ mapping has not been previously investigated.

METHODS

This study included 51 patients with NICM and VT undergoing catheter ablation (median age 55 years; 77% male subjects) who had no evidence of LGE on pre-procedural cardiac magnetic resonance. Post-contrast T₁ relaxation time determined on the septum was assessed as a surrogate of DF burden. The extent of endocardial low-voltage areas (LVAs) at EAM was correlated with T₁ mapping data.

RESULTS

Bipolar LVAs were present in 22 (43%) patients (median extent 15 cm² [8 to 29 cm²]) and unipolar LVA in all patients (median extent 48 cm² [26 to 120 cm²]). A significant inverse correlation was found between T₁ values and both unipolar-LVA (R² = 0.64; β = -0.85; p < 0.01) and bipolar-LVA (R² = 0.16; β = -1.63; p < 0.01). After a median follow-up of 45 months (22 to 57 months), 2 (4%) patients died, 3 (6%) underwent heart transplantation, and 8 (16%) experienced VT recurrence. Shorter post-contrast T₁ time was associated with an increased risk of VT recurrence (hazard ratio: 1.16; 95% confidence interval: 1.03 to 1.33 per 10 ms decrease; p = 0.02).

CONCLUSIONS

In patients with NICM and no evidence of LGE undergoing catheter ablation of VT, DF estimated by using post-contrast T₁ mapping correlates with the voltage abnormality at EAM and seems to affect post-ablation outcomes.

Cardiac MRI Assessment of Mouse Myocardial Infarction and Regeneration

Small animal models are indispensable for cardiac regeneration research. Studies in mouse and rat models have provided important insights into the etiology and mechanisms of cardiovascular diseases and accelerated the development of therapeutic strategies. It is vitally important to be able to evaluate the therapeutic efficacy and have reliable surrogate markers for therapeutic development for cardiac regeneration research. Magnetic resonance imaging (MRI), a versatile and noninvasive imaging modality with excellent penetration depth, tissue coverage, and soft-tissue contrast, is becoming a more important tool in both clinical settings and research arenas. Cardiac MRI (CMR) is versatile, noninvasive, and capable of measuring many different aspects of cardiac functions, and, thus, is ideally suited to evaluate therapeutic efficacy for cardiac regeneration. CMR applications include assessment of cardiac anatomy, regional wall motion, myocardial perfusion, myocardial viability, cardiac function assessment, assessment of myocardial infarction, and myocardial injury. Myocardial infarction models in mice are commonly used model systems for cardiac regeneration research. In this chapter, we discuss various CMR applications to evaluate cardiac functions and inflammation after myocardial infarction.

Is a timely assessment of the hematocrit necessary for cardiovascular magnetic resonance-derived extracellular volume measurements?

BACKGROUND

Cardiovascular magnetic resonance (CMR)-derived extracellular volume (ECV) requires a hematocrit (Hct) to correct contrast volume distributions in blood. However, the timely assessment of Hct can be challenging and has limited the routine clinical application of ECV. The goal of the present study was to evaluate whether ECV measurements lead to significant error if a venous Hct was unavailable on the day of CMR.

METHODS

109 patients with CMR T1 mapping and two venous Hcts (Hct0: a Hct from the day of CMR, and Hct1: a Hct from a different day) were retrospectively identified. A synthetic Hct (Hctsyn) derived from native blood T1 was also assessed. The study used two different ECV methods, (1) a conventional method in which ECV was estimated from native and postcontrast T1 maps using a region-based method, and (2) an inline method in which ECV was directly measured from inline ECV mapping. ECVs measured with Hct0, Hct1, and Hctsyn were compared for each method, and the reference ECV (ECV0) was defined using the Hct0. The error between synthetic (ECVsyn) and ECV0was analyzed for the two ECV methods.

RESULTS

ECV measured using Hct1 and Hctsyn were significantly correlated with ECV0 for each method. No significant differences were observed between ECV0 and ECV measured with Hct1 (ECV1; 28.4 ± 6.6% vs. 28.3 ± 6.1%, p = 0.789) and between ECV0 and ECV calculated with Hctsyn (ECVsyn; 28.4 ± 6.6% vs. 28.2 ± 6.2%, p = 0.45) using the conventional method. Similarly, ECV0 was not significantly different from ECV1 (28.5 ± 6.7% vs. 28.5 ± 6.2, p = 0.801) and ECVsyn (28.5 ± 6.7% vs. 28.4 ± 6.0, p = 0.974) using inline method. ECVsyn values revealed relatively large discrepancies in patients with lower Hcts compared with those with higher Hcts.

CONCLUSIONS

Venous Hcts measured on a different day from that of the CMR examination can still be used to measure ECV. ECVsyn can provide an alternative method to quantify ECV without needing a blood sample, but significant ECV errors occur in patients with severe anemia.

Systolic modified Look-Locker inversion recovery myocardial T1 mapping improves the accuracy of T1 and extracellular volume fraction measurements of patients with high heart rate or atrial fibrillation

Image data for T1 mapping are generally acquired during mid-diastole period. However, T1 mapping tends to fail for patients with high heart rate or atrial fibrillation because of short or irregular R-R interval. Focusing on the evidence that the timing of systole is more stable than that of diastole from the R wave, we compared systolic T1 mapping with conventional diastolic T1 mapping for all participants (n = 58) by visual scoring of T1 calculation error. The systolic scores were significantly better than the diastolic scores (p < 0.05). This advantage of the systolic scores was confirmed selectively for patients with atrial fibrillation (p < 0.05, n = 19). The successful number of nonrigid image registration alignment for extracellular volume fraction (ECV) analysis also increased significantly for systolic images compared with diastolic images (p < 0.05). Thus, systolic T1 mapping improves the accuracy of T1 values and ECV analysis.

T1, T2, and Fat Fraction Cardiac MR Fingerprinting: Preliminary Clinical Evaluation

BACKGROUND

Dixon cardiac magnetic resonance fingerprinting (MRF) has been recently introduced to simultaneously provide water T₁ , water T₂ , and fat fraction (FF) maps.

PURPOSE

To assess Dixon cardiac MRF repeatability in healthy subjects and its clinical feasibility in a cohort of patients with cardiovascular disease.

POPULATION

T1MES phantom, water-fat phantom, 11 healthy subjects and 19 patients with suspected cardiovascular disease.

STUDY TYPE

Prospective.

FIELD STRENGTH/SEQUENCE

1.5T, inversion recovery spin echo (IRSE), multiecho spin echo (MESE), modified Look-Locker inversion recovery (MOLLI), T₂ gradient spin echo (T₂ -GRASE), 6-echo gradient rewound echo (GRE), and Dixon cardiac MRF.

ASSESSMENT

Dixon cardiac MRF precision was assessed through repeated scans against conventional MOLLI, T₂ -GRASE, and PDFF in phantom and 11 healthy subjects. Dixon cardiac MRF native T₁ , T₂ , FF, postcontrast T₁ and synthetic extracellular volume (ECV) maps were assessed in 19 patients in comparison to conventional sequences. Measurements in patients were performed in the septum and in late gadolinium enhanced (LGE) areas and assessed using mean value distributions, correlation, and Bland-Altman plots. Image quality and diagnostic confidence were assessed by three experts using 5-point scoring scales.

STATISTICAL TESTS

Paired Wilcoxon rank signed test and paired t-tests were applied. Statistical significance was indicated by *(P < 0.05).

RESULTS

Dixon cardiac MRF showed good overall precision in phantom and in vivo. Septal average repeatability was ~23 msec for T₁ , ~2.2 msec for T₂ , and ~1% for FF. Biases in healthy subjects/patients were measured at +37 msec*/+60 msec* and -8.8 msec*/-8 msec* when compared to MOLLI and T₂ -GRASE, respectively. No statistically significant differences in postcontrast T₁ (P = 0.17) and synthetic ECV (P = 0.19) measurements were observed in patients.

DATA CONCLUSION

Dixon cardiac MRF attained good overall precision in phantom and healthy subjects, while providing coregistered T₁ , T₂ , and fat fraction maps in a single breath-hold scan with similar or better image quality than conventional methods in patients.

LEVEL OF EVIDENCE

2.

TECHNICAL EFFICACY STAGE

2.

Precision-optimized single protocol pre-/post-contrast modified-look locker inversion T1 mapping using composite inversion group fitting

BACKGROUND

Investigation of a simple, precision optimized, identical pre-/post-contrast modified look locker inversion recovery (MOLLI) protocol employing Composite inversion group (IG) fitting in a clinical cardiomyopathy population.

METHODS

Cardiac magnetic resonance imaging (MRI) was performed at 3 Tesla in 36 patients (48.0 years [IQR: 35.7, 58.2 years]) with known/suspicion of hypertrophic cardiomyopathy. T1 mapping was performed pre-/post-contrast (0.15 mmol/kg Gadobutrol) using a standard 3-parameter fit (STANDARD) and an optimized (OPTIMAL) single-protocol Composite-IG fitting MOLLI approach. The OPTIMAL protocol was based on a simulation study (for 11hb acquisitions) with cost metric analysis across the range of expected T1 values (300-1400 ms) and heart rates (50-80 bpm). All maps were generated offline based on motion corrected source images. Based on region of interest analysis, the precision of both approaches was assessed using a previously validated propagation of errors technique for pre-/post-contrast T1 mapping as well as calculated ECV (based on point-of care hematocrit measurements. Furthermore, respective T1 and ECV values were calculated. Statistical methods included Wilcoxon Signed-Rank tests and Student's paired t-test.

RESULTS

A total of ~9000 11hb inversion groupings were simulated with a 4(0)2(0)2(0)2(0)1 grouping providing the optimal precision across the specified T1/heart rate range. In comparison to standard pre-contrast 5(3)3 MOLLI, this OPTIMAL protocol demonstrated a significantly improved pre-contrast precision (9.1 [6.2, 9.9]ms vs. 9.4 [7.3, 10.8]ms; P < 0.001) while no significant differences were found for post-contrast T1 mapping (4.5 [2.6, 5.3]ms vs. 4.2 [2.8, 5.1]ms; P = 0.25) and EVC mapping (0.38 [0.28, 0.45]ms vs. 0.35 [0.25, 0.44]ms; P = 0.07) or reproducibility (0.16 [0.14, 0.19] vs. 0.19 [0.13, 0.23]P = 0.53). Direct comparison of resulting T1/ECV values demonstrated no significant differences between STANDARD and OPTIMAL techniques for pre-contrast T1 (1178 [1158, 1199]ms vs. 1173 [1143, 1195]ms; P = 0.46) and significant differences for post-contrast T1 (466 [446, 506]ms vs. 456 [433, 503]ms; P = 0.04) and ECV (23.1 [20.8, 25.1]% vs. 23.9 [22.3, 26.4]%; P = 0.001).

CONCLUSIONS

A single optimized Composite-IG fitting protocol for pre-/post-contrast T1 mapping demonstrated improved precision over standard MOLLI techniques. It enables a simplified workflow with reduction of potential sources of error especially with respect to image data co-registration easing advanced post-processing for generation of patient specific ECV maps.

Role of CMR Mapping Techniques in Cardiac Hypertrophic Phenotype

Non-ischemic cardiomyopathies represent a heterogeneous group of myocardial diseases potentially leading to heart failure, life-threatening arrhythmias, and eventually death. Myocardial dysfunction is associated with different underlying pathological processes, ultimately inducing changes in morphological appearance. Thus, classification based on presenting morphological phenotypes has been proposed, i.e., dilated, hypertrophic, restrictive, and right ventricular cardiomyopathies. In light of the key diagnostic and prognostic role of morphological and functional features, cardiovascular imaging has emerged as key element in the clinical workflow of suspected cardiomyopathies, and above all, cardiovascular magnetic resonance (CMR) represents the ideal technique to be used: thanks to its physical principles, besides optimal spatial and temporal resolutions, incomparable contrast resolution allows to assess myocardial tissue abnormalities in detail. Traditionally, weighted images and late enhancement images after gadolinium-based contrast agent administration have been used to perform tissue characterization, but in the last decade quantitative assessment of pre-contrast longitudinal relaxation time (native T1), post-contrast longitudinal relaxation time (post-contrast T1) and transversal relaxation time (T2), all displayed with dedicated pixel-wise color-coded maps (mapping), has contributed to give precious knowledge insight, with positive influence of diagnostic accuracy and prognosis assessment, mostly in the setting of the hypertrophic phenotype. This review aims to describe the available evidence of the role of mapping techniques in the assessment of hypertrophic phenotype, and to suggest their integration in the routine CMR evaluation of newly diagnosed cardiomyopathies with increased wall thickness.

Free-breathing whole-heart multi-slice myocardial T1 mapping in 2 minutes

PURPOSE

To develop and validate a saturation-delay-inversion recovery preparation, slice tracking and multi-slice based sequence for measuring whole-heart native T₁ .

METHOD

The proposed free-breathing sequence performs T₁ mapping of multiple left-ventricular slices by slice-interleaved acquisition to collect 10 electrocardiogram-triggered single-shot slice-selective images for each slice. A saturation-delay-inversion recovery pulse is used for T₁ preparation. Prospective slice tracking by the diaphragm navigator and retrospective registration are used to reduce through-plane and in-plane motion, respectively. The proposed sequence was validated in both phantom and human subjects (12 healthy subjects and 15 patients who were referred for a clinical cardiac MR exam) and compared with saturation recovery single-shot acquisition (SASHA) and modified Look-Locker inversion recovery (MOLLI).

RESULTS

Phantom T₁ measured by the proposed sequence had excellent agreement (R²  = 0.99) with the ground-truth T₁ and was insensitive to heart rate. In both healthy subjects and patients, the proposed sequence yielded nine left-ventricular T₁ maps per volume in less than 2 minutes (healthy volunteers: 1.8 ± 0.4 minutes; patients: 1.9 ± 0.2 minutes). The average T₁ of whole left ventricle for all healthy subjects and patients were 1560 ± 61 and 1535 ± 49 ms by SASHA, 1208 ± 42 and 1233 ± 56 ms by MOLLI5(3)3, and 1397 ± 34 and 1433 ± 56 ms by the proposed sequence, respectively. The corresponding coefficient of variation of T₁ were 6.2 ± 1.4% and 5.8 ± 1.6%, 5.3 ± 1.1% and 5.1 ± 0.8%, and 4.9 ± 0.8% and 4.5 ± 0.8%, respectively.

CONCLUSION

The proposed sequence enables quantification of whole heart T₁ with good accuracy and precision in less than 2 minutes during free breathing.

Arrhythmia insensitive rapid cardiac T1 mapping: comparison to modified look locker inversion recovery T1 mapping in mitral valve prolapse patients

We compare a saturation recovery arrhythmia insensitive rapid (AIR) T1 mapping technique which is less sensitive to heart rate and requires shorter breath-holds to modified Look-Locker inversion recovery (MOLLI) T1 mapping in patients with mitral valve prolapse. 55 patients underwent AIR and MOLLI at 1.5 T. AIR and MOLLI-derived blood and myocardial T1 values and extracellular volume (ECV) were measured by two independent readers. T1 values and ECV from both techniques and inter-reader agreement were compared with Lin's concordance correlation coefficient (LCC) and reduced major axis regression. T1 values were consistently overestimated for AIR compared to MOLLI and vice versa for ECV. In the mitral valve prolapse population, mean native and post contrast myocardial T1 value for MOLLI were 1000 ± 40 ms and 411.9 ± 44.2 ms respectively and 1090.6 ± 58.7 ms and 488.2 ± 45.7 ms for AIR. Mean native and post contrast blood T1 values for MOLLI were 1566.6 ± 72.3 ms and 276.6 ± 34.1 ms respectively versus 1657.2 ± 180.9 ms and 294.9 ± 35.6 ms for AIR. AIR underestimated ECV relative to MOLLI (23.5 ± 0.4% vs 27.7 ± 0.4%). We found excellent inter-reader agreement (LCC all > 0.94, p < 0.0001) for both AIR and MOLLI techniques as well as intra-reader reliability (LCC all > 0.97, p < 0.0001). AIR can be performed in patients with mitral valve prolapse with excellent inter and intra-reader agreement, with higher T1 values compared to MOLLI, in line with other saturation recovery techniques. A consistent T1 mapping technique should be used when performing serial imaging.

MRI of tumor T cell infiltration in response to checkpoint inhibitor therapy

BACKGROUND

Immune checkpoint inhibitors, the most widespread class of immunotherapies, have demonstrated unique response patterns that are not always adequately captured by traditional response criteria such as the Response Evaluation Criteria in Solid Tumors or even immune-specific response criteria. These response metrics rely on monitoring tumor growth, but an increase in tumor size and/or appearance after starting immunotherapy does not always represent tumor progression, but also can be a result of T cell infiltration and thus positive treatment response. Therefore, non-invasive and longitudinal monitoring of T cell infiltration are needed to assess the effects of immunotherapies such as checkpoint inhibitors. Here, we proposed an innovative concept that a sufficiently large influx of tumor infiltrating T cells, which have a smaller diameter than cancer cells, will change the diameter distribution and decrease the average size of cells within a volume to a degree that can be quantified by non-invasive MRI.

METHODS

We validated our hypothesis by studying tumor response to combination immune-checkpoint blockade (ICB) of anti-PD-1 and anti-CTLA4 in a mouse model of colon adenocarcinoma (MC38). The response was monitored longitudinally using Imaging Microstructural Parameters Using Limited Spectrally Edited Diffusion (IMPULSED), a diffusion MRI-based method which has been previously shown to non-invasively map changes in intracellular structure and cell sizes with the spatial resolution of MRI, in cell cultures and in animal models. Tumors were collected for immunohistochemical and flow cytometry analyzes immediately after the last imaging session.

RESULTS

Immunohistochemical analysis revealed that increased T cell infiltration of the tumors results in a decrease in mean cell size (eg, a 10% increase of CD3+ T cell fraction results a ~1 µm decrease in the mean cell size). IMPULSED showed that the ICB responders, mice with tumor volumes were less than 250 mm3 or had tumors with stable or decreased volumes, had significantly smaller mean cell sizes than both Control IgG-treated tumors and ICB non-responder tumors.

CONCLUSIONS

IMPULSED-derived cell size could potentially serve as an imaging marker for differentiating responsive and non-responsive tumors after checkpoint inhibitor therapies, a current clinical challenge that is not solved by simply monitoring tumor growth.

Lung T1 mapping magnetic resonance imaging in the assessment of pulmonary disease in children with cystic fibrosis: a pilot study

BACKGROUND

Assessment tools for early cystic fibrosis (CF) lung disease are limited. Detecting early pulmonary disease is crucial to increasing life expectancy by starting interventions to slow the progression of the pulmonary disease with the many treatment options available.

OBJECTIVE

To compare the utility of lung T1-mapping MRI with ultrashort echo time (UTE) MRI in children with cystic fibrosis in detecting early stage lung disease and monitoring pulmonary exacerbations.

MATERIALS AND METHODS

We performed a prospective study in 16 children between September 2017 and January 2018. In Phase 1, we compared five CF patients with normal spirometry (mean 11.2 years) to five age- and gender-matched healthy volunteers. In Phase 2, we longitudinally evaluated six CF patients (median 11 years) in acute pulmonary exacerbation. All children had non-contrast lung T1-mapping and UTE MRI and spirometry testing. We compared the mean normalized T1 value and percentage lung volume without T1 value in CF patients and healthy subjects in Phase 1 and during treatment in Phase 2. We also performed cystic fibrosis MRI scoring. We evaluated differences in continuous variables using standard statistical tests.

RESULTS

In Phase 1, mean normalized T1 values of the lung were significantly lower in CF patients in comparison to healthy controls (P=0.02) except in the right lower lobe (P=0.29). The percentage lung volume without T1 value was also significantly higher in CF patients (P=0.006). UTE MRI showed no significant differences between CF patients and healthy volunteers (P=0.11). In Phase 2, excluding one outlier case who developed systemic disease in the course of treatment, the whole-lung T1 value increased (P=0.001) and perfusion scoring improved (P=0.02) following therapy. We observed no other significant changes in the MRI scoring.

CONCLUSION

Lung T1-mapping MRI can detect early regional pulmonary CF disease in children and might be helpful in the assessment of acute pulmonary exacerbations.

Associations between Cardiac Magnetic Resonance T1 Mapping Parameters and Ventricular Arrhythmia in Patients with Chagas Disease

Chronic Chagas disease can progress to myocardial involvement with intense fibrosis, which may predispose patients to sudden cardiac death through ventricular arrhythmia. The associations of myocardial fibrosis detected by cardiac magnetic resonance (CMR) parameters with non-sustained ventricular tachycardia (NSVT) were evaluated. This cross-sectional study included patients in early stages of Chagas disease (n = 47) and a control group (n = 15). Patients underwent cardiac evaluation, including CMR examination. Myocardial fibrosis assessment by CMR with measurement of late gadolinium enhancement (LGE), native T1, and extracellular volume (ECV) was performed. There was an increase in myocardial fibrosis CMR parameters and ventricular arrhythmias among different stages of Chagas disease, combined with a decrease in the left ventricular ejection fraction (LVEF) by CMR and also in the right ventricular systolic function by S' wave on tissue Doppler. Fibrosis mass and ECV were associated with the Rassi score, ventricular extrasystole, and E/e' ratio in a logistic regression model adjusted for age and gender. The ECV maintained an association with the presence of NSVT, even after adjustments for fibrosis mass and LVEF assessed by CMR. The receiver-operating characteristic area under the curve for global ECV (0.85; 95% CI: 0.71-0.99) and NSVT was greater than that for fibrosis mass (0.75; 95% CI: 0.54-0.96), although this difference was not statistically significant. Extracellular volume could be an early marker of increased risk of ventricular arrhythmia in Chagas disease, presenting an independent association with NSVT in the initial stages of chronic Chagas cardiomyopathy, even after adjustment for fibrosis mass and LVEF.

Estimation of total collagen volume: a T1 mapping versus histological comparison study in healthy Landrace pigs

Right ventricular biopsy represents the gold standard for the assessment of myocardial fibrosis and collagen content. This invasive technique, however, is accompanied by perioperative complications and poor reproducibility. Extracellular volume (ECV) measured through cardiovascular magnetic resonance (CMR) has emerged as a valid surrogate method to assess fibrosis non-invasively. Nonetheless, ECV provides an overestimation of collagen concentration since it also considers interstitial space. Our study aims to investigate the feasibility of estimating total collagen volume (TCV) through CMR by comparing it with the TCV measured at histology. Seven healthy Landrace pigs were acutely instrumented closed-chest and transported to the MRI facility for measurements. For each protocol, CMR imaging at 3T was acquired. MEDIS software was used to analyze T1 mapping and ECV for both the left ventricular myocardium (LV_myo) and left ventricular septum (LV_septum). ECV was then used to estimate TCV_CMR at LV_myo and LV_septum following previously published formulas. Tissues were prepared following an established protocol and stained with picrosirius red to analyze the TCV_histo in LV_myo and LV_septum. TCV measured at LV_myo and LV_septum with both histology (8 ± 5 ml and 7 ± 3 ml, respectively) and T1-Mapping (9 ± 5 ml and 8 ± 6 ml, respectively) did not show any regional differences. TCV_histo and TCV_CMR showed a good level of data agreement by Bland–Altman analysis. Estimation of TCV through CMR may be a promising way to non-invasively assess myocardial collagen content and may be useful to track disease progression or treatment response.

Mapping hepatocyte size in vivo using temporal diffusion spectroscopy MRI

PURPOSE

The goal of this study is to implement a noninvasive method for in vivo mapping of hepatocyte size. This method will have a broad range of clinical and preclinical applications, as pathological changes in hepatocyte sizes are relevant for the accurate diagnosis and assessments of treatment response of liver diseases.

METHODS

Building on the concepts of temporal diffusion spectroscopy in MRI, a clinically feasible imaging protocol named IMPULSED (Imaging Microstructural Parameters Using Limited Spectrally Edited Diffusion) has been developed, which is able to report measurements of cell sizes noninvasively. This protocol acquires a selected set of diffusion imaging data and fits them to a model of water compartments in tissues to derive robust estimates of the cellular structures that restrict free diffusion. Here, we adapt and further develop this approach to measure hepatocyte sizes in vivo. We validated IMPULSED in livers of mice and rats and implemented it to image healthy human subjects using a clinical 3T MRI scanner.

RESULTS

The IMPULSED-derived mean hepatocyte sizes for rats and mice are about 15-20 µm and agree well with histological findings. Maps of mean hepatocyte size for humans can be achieved in less than 15 minutes, a clinically feasible scan time.

CONCLUSION

Our results suggest that this method has potential to overcome major limitations of liver biopsy and provide noninvasive mapping of hepatocyte sizes in clinical applications.

Relationship between Measurement Errors in Myocardial T1 Mapping and Heart Rate

PURPOSE

Modified Look-Locker inversion recovery (MOLLI) using a 5s(3s)3s scheme is robust to tachycardia, but some errors are occasionally observed in myocardial T₁ mapping. We sought to evaluate the relationship between measurement errors in T₁ mapping and heart rate (HR) using a confidence map.

METHODS

We enrolled 69 male patients with normal native T₁ values of the septal myocardium measured by a 5s(3s)3s MOLLI. The degree of measurement errors in the septal myocardium was assessed by two independent observers on a confidence map using a 4-point scale: 0, no errors; 1, errors located on the myocardial contour; 2, errors extended into the myocardial contour; and 3, errors extended into the midwall. We compared the scores of measurement errors and the average, maximum, minimum or variability of the HR indicated during the MOLLI scan (iHR), image phases of MOLLI or left ventricular ejection fraction (LVEF).

RESULTS

Patients with score >1 for the septal myocardium had significantly lower minimum iHR than those with a score ≤1 (P < 0.01; 49.8 ± 10.1 vs. 59.6 ± 9.7 beat per min).

CONCLUSION

The confidence map shows more measurement errors in patients with lower minimum iHR. The myocardial T₁ values should be measured carefully in patients with bradycardia during MOLLI scanning.

Temporal registration: a new approach to manage the incomplete recovery of the longitudinal magnetization in the Modified Look-Locker Inversion Recovery sequence (MOLLI) for T1 mapping of the heart

PURPOSE

To correct with post-processing effects of incomplete recovery of the longitudinal magnetization before a new inversion pulse in the Modified Look-Locker Inversion recovery sequence (MOLLI) sequence.

THEORY AND METHODS

We model such effects as a temporal shift ([Formula: see text]) of the signal of the Look-Locker block following next inversion pulses. After using the following equation [Formula: see text], a temporal registration of [Formula: see text] is applied to the signal of the affected block to adjust the sampling time of the recovery signal and correct the underlying effect on quantitative T1. To test our approach, simulations, phantoms, and five volunteers' data were used while applying different MOLLI sampling schemes at different heart rates and compared to the reference three-parameter fit.

RESULTS

The temporal registration of the affected signals allows to reach higher accuracy on long T1 when compared to the reference three parameters fit (10.15 vs 22.12% for T1 = 1785 ms; 8.22 vs 14.65% for T1 = 1278 ms), and lower average variation in case of rest-period deletion (62 vs 231 ms).

CONCLUSION

The proposed approach leads to more accurate T1 in case of incomplete recovery. It is less sensitive to parameters affecting the recovery such as the rest period or the sampling scheme; and, therefore, supports multi-center studies with different MOLLI protocols.

Reappraising myocardial fibrosis in severe aortic stenosis: an invasive and non-invasive study in 133 patients

Aims

To investigate myocardial fibrosis (MF) in a large series of severe aortic stenosis (AS) patients using invasive biopsy and non-invasive imaging.

Methods and results

One hundred thirty-three patients with severe, symptomatic AS accepted for surgical aortic valve replacement underwent cardiovascular magnetic resonance (CMR) with late gadolinium enhancement (LGE) and extracellular volume fraction (ECV) quantification. Intra-operative left ventricular (LV) biopsies were performed by needle or scalpel, yielding tissue with (n = 53) and without endocardium (n = 80), and compared with 10 controls. Myocardial fibrosis occurred in three patterns: (i) thickened endocardium with a fibrotic layer; (ii) microscopic scars, with a subendomyocardial predominance; and (iii) diffuse interstitial fibrosis. Collagen volume fraction (CVF) was elevated (P < 0.001) compared with controls, and higher (P < 0.001) in endocardium-containing samples with a decreasing CVF gradient from the subendocardium (P = 0.001). Late gadolinium enhancement correlated with CVF (P < 0.001) but not ECV. Both LGE and ECV correlated independently (P < 0.001) with N-terminal pro-brain natriuretic peptide and high-sensitivity-troponin T. High ECV was also associated with worse LV remodelling, left ventricular ejection fraction and functional capacity. Combining high ECV and LGE better identified patients with more adverse LV remodelling, blood biomarkers and histological parameters, and worse functional capacity than each parameter alone.

Conclusion

Myocardial fibrosis in severe AS is complex, but three main patterns exist: endocardial fibrosis, microscars (mainly in the subendomyocardium), and diffuse interstitial fibrosis. Neither histological CVF nor the CMR parameters ECV and LGE capture fibrosis in its totality. A combined, multi-parametric approach with ECV and LGE allows best stratification of AS patients according to the response of the myocardial collagen matrix.

The relative contributions of myocardial perfusion, blood volume and extracellular volume to native T1 and native T2 at rest and during adenosine stress in normal physiology

BACKGROUND

Both ischemic and non-ischemic heart disease can cause disturbances in the myocardial blood volume (MBV), myocardial perfusion and the myocardial extracellular volume fraction (ECV). Recent studies suggest that native myocardial T1 mapping can detect changes in MBV during adenosine stress without the use of contrast agents. Furthermore, native T2 mapping could also potentially be used to quantify changes in myocardial perfusion and/or MBV. Therefore, the aim of this study was to explore the relative contributions of myocardial perfusion, MBV and ECV to native T1 and native T2 at rest and during adenosine stress in normal physiology.

METHODS

Healthy subjects (n = 41, 26 ± 5 years, 51% females) underwent 1.5 T cardiovascular magnetic resonance (CMR) scanning. Quantitative myocardial perfusion [ml/min/g] and MBV [%] maps were computed from first pass perfusion imaging at adenosine stress (140 microg/kg/min infusion) and rest following an intravenous contrast bolus (0.05 mmol/kg, gadobutrol). Native T1 and T2 maps were acquired before and during adenosine stress. T1 maps at rest and stress were also acquired following a 0.2 mmol/kg cumulative intravenous contrast dose, rendering rest and stress ECV maps [%]. Myocardial T1, T2, perfusion, MBV and ECV values were measured by delineating a region of interest in the midmural third of the myocardium.

RESULTS

During adenosine stress, there was an increase in myocardial native T1, native T2, perfusion, MBV, and ECV (p ≤ 0.001 for all). Myocardial perfusion, MBV and ECV all correlated with both native T1 and native T2, respectively (R2 = 0.35 to 0.61, p < 0.001 for all). Multivariate linear regression revealed that ECV and perfusion together best explained the change in native T2 (ECV beta 0.21, p = 0.02, perfusion beta 0.66, p < 0.001, model R2 = 0.64, p < 0.001), and native T1 (ECV beta 0.50, p < 0.001, perfusion beta 0.43, p < 0.001, model R2 = 0.69, p < 0.001).

CONCLUSIONS

Myocardial native T1, native T2, perfusion, MBV, and ECV all increase during adenosine stress. Changes in myocardial native T1 and T2 during adenosine stress in normal physiology can largely be explained by the combined changes in myocardial perfusion and ECV.

TRIAL REGISTRATION

Clinicaltrials.gov identifier NCT02723747. Registered March 16, 2016.

Accurate, precise, simultaneous myocardial T1 and T2 mapping using a radial sequence with inversion recovery and T2 preparation

We propose a simultaneous myocardial T1 and T2 mapping technique using a radial sequence with inversion recovery and T2 preparation, which achieves high accuracy and precision, with T1 and T2 reproducibility similar to the Modified Look-Locker Inversion recovery (MOLLI) sequence and the conventional bright blood T2 mapping technique, respectively. The sequence was developed by incorporating gold angle radial fast low angle shot (FLASH) readout combined with an inversion pulse and T2prep pulses. The extended Bloch equation simulation with slice profile correction (BLESSPC) algorithm was proposed to reconstruct T1 and T2 maps at the same time in a few seconds, while maintaining good T1 and T2 estimation accuracy. Accuracy and precision were compared among the proposed technique, MOLLI and conventional T2 mapping techniques using phantom studies, 10 healthy volunteers and three patients. In phantom studies, the proposed technique was more accurate than MOLLI (P < 0.05) while achieving similar precision (P = 0.3) in T1 estimation, and was more accurate (P < 0.05) and precise (P < 0.001) than conventional T2 mapping (two-parameter fitting) in T2 estimation. In vivo, the proposed technique achieved significantly higher T1 values (P < 0.001) and similar reproducibility (P = 0.3) compared with MOLLI, with significantly lower T2 values (P < 0.001) and similar reproducibility (P = 0.6) compared with the conventional T2 mapping technique. Thus, the proposed radial T1-T2 mapping technique allows for accurate, precise, simultaneous myocardial T1 and T2 mapping in an 11-heartbeat single breath-hold acquisition.

Differentiation between Fabry disease and hypertrophic cardiomyopathy with cardiac T1 mapping

PURPOSE

To evaluate the potential of non-contrast myocardial T1 mapping on cardiovascular magnetic resonance examination (CMR) in differentiating patients with Fabry disease (FD) from those with hypertrophic cardiomyopathy (HCM) and healthy control subjects.

MATERIALS AND METHODS

Seventeen patients with FD (8 men, 9 women; mean age, 48 ±18 [SD] years; [range: 19-73 years]; 53% with left ventricular hypertrophy [LVH]) were matched with 36 patients with hypertrophic cardiomyopathy (HCM) (22 men, 14 women; mean age, 57±16 [SD] years; [range: 22-85 years]) and 70 healthy control subjects (34 men, 36 women; mean age, 38 ±15 [SD] years; [range: 18-65 years]). Cardiac T1 mapping was performed using the modified Look-Locker inversion (MOLLI®) sequence on a 1.5-T magnet. T1 values were calculated, on midventricular section, for septal left ventricular segments (S8-S9) and all mid-ventricular ones (global T1 values; S7-S12). Statistical analysis included unpaired Mann-Whitney test, receiver operating characteristic curve and likelihood ratios.

RESULTS

Septal native T1 values were significantly decreased in patients with FD (889±61 [SD] ms; range: 784-980ms) compared to those with HCM (995±48 [SD] ms; range: 935-1125ms) (P<0.001) and versus healthy controls (965±29 [SD] ms; range: 910-1028ms) (P<0.001). Global native T1 values were also significantly decreased in patients with FD (891±49 [SD] ms; range 794-970ms) compared to those with HCM (995±34 [SD] ms; range: 952-1086ms) (P<0.001) and versus healthy controls (966±27 [SD] ms; range: 920-1042ms) (P<0.001). A septal left ventricular native T1 cutoff value of 940ms could distinguish FD from HCM with 88% sensitivity (95% CI: 73-100%) and 92% specificity (95% CI: 83-100%). Positive likelihood ratio was 11, negative likelihood ratio was 0.12. Compared to controls, the same threshold could distinguish FD with 88% sensitivity (95% CI: 73-100%) and 86% specificity (95% CI: 78-94%). Positive likelihood ratio was 6.3, negative likelihood ratio was 0.14. T1 value was abnormal in 4 of 8 (50%) of FD patients who did not have LVH.

CONCLUSION

Native T1 values are significantly lower in patients with FD by comparison with those with HCM and healthy volunteers.

Measuring extracellular volume fraction by MRI: First verification of values given by clinical sequences

Purpose

To verify MR measurements of myocardial extracellular volume fraction (ECV) based on clinically applicable T1‐mapping sequences against ECV measurements by radioisotope tracer in pigs and to relate the results to those obtained in volunteers.

Methods

Between May 2016 and March 2017, 8 volunteers (25 ± 4 years, 3 female) and 8 pigs (4 female) underwent ECV assessment with SASHA, MOLLI5(3b)3, MOLLI5(3s)3, and MOLLI5s(3s)3s. Myocardial ECV was measured independently in pigs using a radioisotope tracer method.

Results

In pigs, ECV in normal myocardium was not different between radioisotope (average ± standard deviation; 19 ± 2%) and SASHA (21 ± 2%; P = 0.086). ECV was higher by MOLLI5(3b)3 (26 ± 2%), MOLLI5(3s)3 (25 ± 2%), and MOLLI5s(3s)3s (25 ± 2%) compared with SASHA or radioisotope (P ≤ 0.001 for all). ECV in volunteers was higher by MOLLI5(3b)3 (26 ± 3%) and MOLLI5(3s)3 (26 ± 3%) than by SASHA (22 ± 3%; P = 0.022 and P = 0.033). No difference was found between MOLLI5s(3s)3s (25 ± 3%) and SASHA (P = 0.225). Native T1 of blood and myocardium as well as postcontrast T1 of myocardium was consistently lower using MOLLI compared with SASHA. ECV increased over time as measured by MOLLI5(3b)3 and MOLLI5(3s)3 for pigs (0.08% and 0.07%/min; P = 0.004 and P = 0.013) and by MOLLI5s(3s)3s for volunteers (0.07%/min; P = 0.032) but did not increase as measured by SASHA.

Conclusion

Clinically available MOLLI and SASHA techniques can be used to accurately estimate ECV in normal myocardium where MOLLI‐sequences show minor overestimation driven by underestimation of postcontrast T1 when compared with SASHA. The timing of imaging after contrast administration affected the measurement of ECV using some variants of the MOLLI sequence.

Early detection of heart function abnormality by native T1: a comparison of two T1 quantification methods

Objective

To compare the robustness of native T1 mapping using mean and median pixel-wise quantification methods.

Methods

Fifty-seven consecutive patients without overt signs of heart failure were examined in clinical routine for suspicion of cardiomyopathy. MRI included the acquisition of native T1 maps by a motion-corrected modified Look-Locker inversion recovery sequence at 1.5 T. Heart function status according to four established volumetric left ventricular (LV) cardio MRI parameter thresholds was used for retrospective separation into subgroups of normal (n = 26) or abnormal heart function (n = 31). Statistical normality of pixel-wise T1 was tested on each myocardial segment and mean and median segmental T1 values were assessed.

Results

Segments with normally distributed pixel-wise T1 (57/58%) showed no difference between mean and median quantification in either patient group, while differences were highly significant (p < 0.001) for the respective 43/42% non-normally distributed segments. Heart function differentiation between two patient groups was significant in 14 myocardial segments (p < 0.001–0.040) by median quantification compared with six (p < 0.001–0.042) by using the mean. The differences by median quantification were observed between the native T1 values of the three coronary artery territories of normal heart function patients (p = 0.023) and insignificantly in the abnormal patients (p = 0.053).

Conclusion

Median quantification increases the robustness of myocardial native T1 definition, regardless of statistical normality of the data. Compared with the currently prevailing method of mean quantification, differentiation between LV segments and coronary artery territories is better and allows for earlier detection of heart function impairment.

Key Points

• Median pixel-wise quantification of native T1 maps is robust and can be applied regardless of the statistical distribution of data points.

• Median quantification is more sensitive to early heart function abnormality compared with mean quantification.

• The new method yields significant native T1 value differentiation between the three coronary artery territories.

Electronic supplementary material

The online version of this article (10.1007/s00330-019-06364-9) contains supplementary material, which is available to authorized users.

Mapping versus source methods for quantifying myocardial T1 in controls and in repaired tetralogy of Fallot: interchangeability and reproducibility in children

BACKGROUND

Myocardial T1 relaxometry can be performed by contouring on individual T1-weighted source images (source method) or on a single T1 map (mapping method).

OBJECTIVE

This study compares (a) agreement between native T1 and extracellular volume results of the two methods and (b) interobserver reproducibility of the two methods in children without heart disease and those with tetralogy of Fallot (TOF).

MATERIALS AND METHODS

We retrospectively analyzed pediatric patients (controls and those with repaired TOF) with cardiac magnetic resonance examinations including extracellular volume quantification using the modified Look-Locker inversion recovery (MOLLI) sequence. We compared native T1 and extracellular volume of the entire left ventricle and interventricular septum derived using the source and the mapping approaches.

RESULTS

In the control group (n=25, median age 14.0 years, interquartile range [IQR] 11.5-16.5 years), the mapping method produced lower native T1 values than the source method in the interventricular septum (mean difference ± standard deviation [SD] = 12±15 ms, P<0.001). In the TOF group (n=50, median age 13.3 years, IQR 9.9-15.0 years), the mapping method produced lower values for native T1 and extracellular volume in the interventricular septum (mean difference 9±14 ms and 0.6±1.1%, P<0.001). In 6-12% of the children, differences were >3 standard deviations from the mean difference. Interobserver reproducibility between the two methods by intraclass correlation coefficients were clinically equivalent.

CONCLUSION

T1 and extracellular volume values generated by the source and mapping methods show systematic differences and can vary significantly in an individual child, and thus cannot be used interchangeably in clinical practice. The source method might allow for easier detection and, in some cases, mitigation of artifacts that are not infrequent in children and can be difficult to appreciate on the T1 map.