Mapping the future of cardiac MR imaging: case-based review of T1 and T2 mapping techniques

The Role of T2 Mapping in Cardiac Amyloidosis

Cardiac amyloidosis (CA) is an infiltrative cardiomyopathy divided into two types: light-chain (LA) and transthyretin (ATTR) CA. Cardiac magnetic resonance (CMR) has emerged as an important diagnostic tool in CA. While late gadolinium enhancement (LGE), T1 mapping and extracellular volume (ECV) have a consolidate role in the assessment of CA, T2 mapping has been less often evaluated. We aimed to test the value of T2 mapping in the evaluation of CA. This study recruited 70 patients with CA (51 ATTR, 19 AL). All the subjects underwent 1.5 T CMR with T1 and T2 mapping and cine and LGE imaging. Their QALE scores were evaluated. The myocardial T2 values were significantly (p < 0.001) increased in both types of CA compared to the controls. In the AL-CA group, increased T2 values were associated with a higher QALE score. The myocardial native T1 values and ECV were significantly (p < 0.001) higher in the CA patients than in the healthy subjects. Left ventricular (LV) mass, QALE score and ECV were higher in ATTR amyloidosis compared with AL amyloidosis, while the LV ejection fraction was lower (p < 0.001). These results support the concept of the presence of myocardial edema in CA. Therefore, a CMR evaluation including not only myocardial T1 imaging but also myocardial T2 imaging allows for more comprehensive tissue characterization in CA.

Inter- and intra-rater reproducibility of quantitative T1 measurement using semiautomatic region of interest placement in myometrium

PURPOSE

This study aimed to investigate the inter- and intraobserver reproducibility of quantitative T1 (qT1) measurements using manual and semiautomatic region of interest (ROI) placements. We hypothesized the usefulness of the semiautomatic method, which utilizes a three-dimensional (3D) anatomical relationship between the myometrium and other tissues, for minimizing ROI placement variation, thereby improving qT1 reproducibility compared to the manual approach. The semiautomatic approach, which considered anatomical relationships, was expected to enhance reproducibility by reducing ROI placement variabilities.

MATERIALS AND METHODS

This study recruited 23 healthy female volunteers. Data with variable flip angle (VFA) and inversion recovery were acquired using 3D-spoiled gradient echo and spin echo sequences, respectively. T1 maps were generated with VFA. Manual and semiautomatic ROI placements were independently conducted. Mean qT1 values were calculated from the T1 maps using the corresponding pixel values of the myometrial ROI. Inter- and intraobserver reproducibility of qT1 values was investigated. The inter- and intraobserver reproducibility of qT1 values was evaluated by calculating the coefficient of variation (CoV). Further, reproducibility was evaluated with inter- and intraobserver errors and intraclass correlation coefficients (ICCs). Bland-Altman analysis was utilized to compare the results, estimate bias, and determine the limits of agreement.

RESULTS

The mean inter- and intraobserver CoV of the qT1 values for semiautomatic ROI placement was significantly lower than those for manual ROI placement (p < 0.05 and p < 0.01, respectively). ICCs for semiautomatic ROI placement were greater than those for manual ROI placement. Further, the mean inter- and intraobserver errors for semiautomatic ROI placement were significantly lower than those for manual ROI placement (p < 0.05 and p < 0.01, respectively).

CONCLUSION

Semiautomatic ROI placement demonstrated high reproducibility of qT1 measurements compared with manual methods. Semiautomatic ROI placement may be useful for evaluating uterine qT1 with high reproducibility.

Inter-scanner comparability of Z-scores for native myocardial T1 and T2 mapping

BACKGROUND

Cardiovascular Magnetic Resonance (CMR) native T1 and T2 mapping serve as robust, contrast-agent-free diagnostic tools, but hardware- and software-specific sources of variability limit the generalizability of data across CMR platforms, consequently limiting the interpretability of patient-specific parametric data. Z-scores are used to describe the relationship of observed values to the mean results as obtained in a sufficiently large normal sample. They have been successfully used to describe the severity of quantifiable abnormalities in medicine, specifically in children and adolescents. The objective of this study was to observe whether z-scores can improve the comparability of T1 and T2 mapping values across CMR scanners, field strengths, and sequences from different vendors in the same participant rather than different participants (as seen in previous studies).

METHODS

Fifty-one healthy volunteers (26 men/25 women, mean age = 43 ± 13.51) underwent three CMR exams on three different scanners, using a Modified Look-Locker Inversion Recovery (MOLLI) 5-(3)- 3 sequence to quantify myocardial T1. For T2 mapping, a True Fast Imaging with steady-state free precession (TRUFI) sequence was used on a 3 T Skyra™ (Siemens), and a T2 Fast Spin Echo (FSE) sequence was used on 1.5 T Artist™ (GE) and 3.0 T Premier™ (GE) scanners. The averages of basal and mid-ventricular short axis slices were used to derive means and standard deviations of global mapping values. We used intra-class comparisons (ICC), repeated measures ANOVA, and paired Student's t-tests for statistical analyses.

RESULTS

There was a significant improvement in intra-subject comparability of T1 (ICC of 0.11 (95% CI= -0.018, -0.332) vs 0.78 (95% CI= 0.650, 0.866)) and T2 (ICC of 0.35 (95% CI= -0.053, 0.652) vs 0.83 (95% CI= 0.726, 0.898)) when using z-scores across all three scanners. While the absolute global T1 and T2 values showed a statistically significant difference between scanners (p < 0.001), no such differences were identified using z-scores (T1z: p = 0.771; T2z: p = 0.985). Furthermore, when images were not corrected for motion, T1 z-scores showed significant inter-scanner variability (p < 0.001), resolved by motion correction.

CONCLUSION

Employing z-scores for reporting myocardial T1 and T2 removes the variation of quantitative mapping results across different MRI systems and field strengths, improving the clinical utility of myocardial tissue characterization in patients with suspected myocardial disease.

Hypertrophic Cardiomyopathy-Advances in Imaging and Diagnostic Strategies

Hypertrophic cardiomyopathy (HCM) is the most important and prevalent cardiac disease in cats. Due to the highly variable nature of HCM, a multimodal approach including physical examination, genetic evaluation, cardiac biomarkers, and imaging are all essential elements to appropriate and timely diagnosis. These foundational elements are advancing rapidly in veterinary medicine. Newer biomarkers such as galectin-3 are currently being researched and advances in tissue speckle-tracking and contrast-enhanced echocardiography are readily available. Advanced imaging techniques, such as cardiac MRI, are providing previously unavailable information about myocardial fibrosis and paving the way for enhanced diagnostic capabilities and risk-stratification in cats with HCM.

Application of Artificial Intelligence in Image Processing of Neurodegenerative Disorders: A Review Study

: Neurodegenerative diseases can make life difficult and lead to death in many cases. They also can be difficult, time-consuming, and costly to diagnose with enough accuracy/certainty. Artificial intelligence (AI) has shown promise in tackling some of the challenges present in medical imaging and is anticipated to become a crucial tool in health care applications in the near future. In particular, deep learning methods have displayed great performance in various subfields of image processing, including but not limited to image segmentation, image synthesis, and image reconstruction. In this paper, many state-of-the-art applications of deep learning models in image processing were reviewed.

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.

Cardiac MRF using rosette trajectories for simultaneous myocardial T1, T2, and proton density fat fraction mapping

The goal of this work is to extend prior work on cardiac MR Fingerprinting (cMRF) using rosette k-space trajectories to enable simultaneous T₁, T₂, and proton density fat fraction (PDFF) mapping in the heart. A rosette trajectory designed for water-fat separation at 1.5T was used in a 2D ECG-triggered 15-heartbeat cMRF sequence. Water and fat specific T₁ and T₂ maps were generated from the cMRF data. A PDFF map was also retrieved using Hierarchical IDEAL by segmenting the rosette cMRF data into multiple echoes. The accuracy of rosette cMRF in T₁, T₂, and PDFF quantification was validated in the ISMRM/NIST phantom and an in-house built fat fraction phantom, respectively. The proposed method was also applied for myocardial tissue mapping of healthy subjects and cardiac patients at 1.5T. T₁, T₂, and PDFF values measured using rosette cMRF in the ISMRM/NIST phantom and the fat fraction phantom agreed well with the reference values. In 16 healthy subjects, rosette cMRF yielded T₁ values which were 80~90 ms higher than spiral cMRF and MOLLI. T₂ values obtained using rosette cMRF were ~3 ms higher than spiral cMRF and ~5 ms lower than conventional T₂-prep bSSFP method. Rosette cMRF was also able to detect abnormal T₁ and T₂ values in cardiomyopathy patients and may provide more accurate maps due to effective fat suppression. In conclusion, this study shows that rosette cMRF has the potential for efficient cardiac tissue characterization through simultaneous quantification of myocardial T₁, T₂, and PDFF.

Bi-ventricular assessment with cardiovascular magnetic resonance at 5 Tesla: A pilot study

Background

Cardiovascular magnetic resonance (CMR) imaging at ultra-high fields (UHF) such as 7T has encountered many challenges such as faster T2* relaxation, stronger B₀ and B₁₊ field inhomogeneities and additional safety concerns due to increased specific absorption rate (SAR) and peripheral nervous stimulation (PNS). Recently, a new line of 5T whole body MRI system has become available, and this study aims at evaluating the performance and benefits of this new UHF system for CMR imaging.

Methods

Gradient echo (GRE) CINE imaging was performed on healthy volunteers at both 5 and 3T, and was compared to balanced steady-state-free-procession (bSSFP) CINE imaging at 3T as reference. Higher spatial resolution GRE CINE scans were additionally performed at 5T. All scans at both fields were performed with ECG-gating and breath-holding. Image quality was blindly evaluated by two radiologists, and the cardiac functional parameters (e.g., EDV/ESV/mass/EF) of the left and right ventricles were measured for statistical analyses using the Wilcoxon signed-rank test and Bland-Altman analysis.

Results

Compared to 3T GRE CINE imaging, 5T GRE CINE imaging achieved comparable or improved image quality with significantly superior SNR and CNR, and it has also demonstrated excellent capability for high resolution (1.0 × 1.0 × 6.0 mm³) imaging. Functional assessments from 5T GRE CINE images were highly similar with the 3T bSSFP CINE reference.

Conclusions

This pilot study has presented the initial evaluation of CMR CINE imaging at 5T UHF, which yielded superior image quality and accurate functional quantification when compared to 3T counterparts. Along with reliable ECG gating, the new 5T UHF system has the potential to achieve well-balanced performance for CMR applications.

Multimodality Imaging in the Diagnosis and Assessment of Cardiac Amyloidosis

Amyloidosis is a rare disorder where abnormal protein aggregates are deposited in tissues forming amyloid fibrils, leading to progressive organ failure. Although any organ can be affected, cardiac involvement is the main cause of morbidity and mortality associated with amyloidosis as diagnosis is often delayed due to the indolent nature of the disease in some forms. An early diagnosis of disease and knowledge of the type/subtype of cardiac amyloidosis (CA) are essential for appropriate management and better outcome. Echocardiography is often the first line of investigation for patients suspected of CA and offers superior hemodynamic assessment. Although cardiovascular magnetic resonance (CMR) imaging is not diagnostic of CA, it provides vital clues to diagnosis and has a role in disease quantification and prognostication. Radiolabeled bone seeking tracers are the mainstay of diagnosis of CA and when combined with screening of monoclonal light chains, bone scintigraphy offers high sensitivity in diagnosing transthyretin type of CA. This review aims to describe the noninvasive imaging assessment and approach to diagnosis of patients with suspected CA. Imaging features of echocardiography, nuclear scintigraphy, and CMR are described with a brief mention on computed tomography.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

KEY POINTS

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

BUDA-MESMERISE: Rapid acquisition and unsupervised parameter estimation for T1 , T2 , M0 , B0 , and B1 maps

PURPOSE

Rapid acquisition scheme and parameter estimation method are proposed to acquire distortion-free spin- and stimulated-echo signals and combine the signals with a physics-driven unsupervised network to estimate T₁ , T₂ , and proton density (M₀ ) parameter maps, along with B₀ and B₁ information from the acquired signals.

THEORY AND METHODS

An imaging sequence with three 90° RF pulses is utilized to acquire spin- and stimulated-echo signals. We utilize blip-up/-down acquisition to eliminate geometric distortion incurred by the effects of B₀ inhomogeneity on rapid EPI acquisitions. For multislice imaging, echo-shifting is applied to utilize dead time between the second and third RF pulses to encode information from additional slice positions. To estimate parameter maps from the spin- and stimulated-echo signals with high fidelity, 2 estimation methods, analytic fitting and a novel unsupervised deep neural network method, are developed.

RESULTS

The proposed acquisition provided distortion-free T₁ , T₂ , relative proton density (M0), B₀ , and B₁ maps with high fidelity both in phantom and in vivo brain experiments. From the rapidly acquired spin- and stimulated-echo signals, analytic fitting and the network-based method were able to estimate T₁ , T₂ , M₀ , B₀ , and B₁ maps with high accuracy. Network estimates demonstrated noise robustness owing to the fact that the convolutional layers take information into account from spatially adjacent voxels.

CONCLUSION

The proposed acquisition/reconstruction technique enabled whole-brain acquisition of coregistered, distortion-free, T₁ , T₂ , M₀ , B₀ , and B₁ maps at 1 × 1 × 5 mm³ resolution in 50 s. The proposed unsupervised neural network provided noise-robust parameter estimates from this rapid acquisition.

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.

Respiratory Motion-Registered Isotropic Whole-Heart T2 Mapping in Patients With Acute Non-ischemic Myocardial Injury

Background: T₂ mapping is a magnetic resonance imaging technique that can be used to detect myocardial edema and inflammation. However, the focal nature of myocardial inflammation may render conventional 2D approaches suboptimal and make whole-heart isotropic 3D mapping desirable. While self-navigated 3D radial T₂ mapping has been demonstrated to work well at a magnetic field strength of 3T, it results in too noisy maps at 1.5T. We therefore implemented a novel respiratory motion-resolved compressed-sensing reconstruction in order to improve the 3D T₂ mapping precision and accuracy at 1.5T, and tested this in a heterogeneous patient cohort. Materials and Methods: Nine healthy volunteers and 25 consecutive patients with suspected acute non-ischemic myocardial injury (sarcoidosis, n = 19; systemic sclerosis, n = 2; acute graft rejection, n = 2, and myocarditis, n = 2) were included. The free-breathing T₂ maps were acquired as three ECG-triggered T₂-prepared 3D radial volumes. A respiratory motion-resolved reconstruction was followed by image registration of the respiratory states and pixel-wise T₂ mapping. The resulting 3D maps were compared to routine 2D T₂ maps. The T₂ values of segments with and without late gadolinium enhancement (LGE) were compared in patients. Results: In the healthy volunteers, the myocardial T₂ values obtained with the 2D and 3D techniques were similar (45.8 ± 1.8 vs. 46.8 ± 2.9 ms, respectively; P = 0.33). Conversely, in patients, T₂ values did differ between 2D (46.7 ± 3.6 ms) and 3D techniques (50.1 ± 4.2 ms, P = 0.004). Moreover, with the 2D technique, T₂ values of the LGE-positive segments were similar to those of the LGE-negative segments (T_2LGE-= 46.2 ± 3.7 vs. T_2LGE+ = 47.6 ± 4.1 ms; P = 0.49), whereas the 3D technique did show a significant difference (T_2LGE- = 49.3 ± 6.7 vs. T_2LGE+ = 52.6 ± 8.7 ms, P = 0.006). Conclusion: Respiratory motion-registered 3D radial imaging at 1.5T led to accurate isotropic 3D whole-heart T₂ maps, both in the healthy volunteers and in a small patient cohort with suspected non-ischemic myocardial injury. Significantly higher T₂ values were found in patients as compared to controls in 3D but not in 2D, suggestive of the technique's potential to increase the sensitivity of CMR at earlier stages of disease. Further study will be needed to demonstrate its accuracy.

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.

Cardiac extracellular volume fraction in cats with preclinical hypertrophic cardiomyopathy

Background

Cardiac magnetic resonance imaging (CMR) allows for detection of fibrosis in hypertrophic cardiomyopathy (HCM) by quantification of the extracellular volume fraction (ECV).

Hypothesis/Objectives

To quantify native T1 mapping and ECV in cats. We hypothesize that native T1 mapping and ECV will be significantly increased in HCM cats compared with healthy cats.

Animals

Seventeen healthy and 12 preclinical HCM, age‐matched, client‐owned cats.

Methods

Prospective observational study. Tests performed included indirect blood pressure, CBC, biochemical analysis including total thyroid, urinalysis, transthoracic echocardiogram, and CMR. Cats were considered healthy if all tests were within normal limits and a diagnosis of HCM was determined by the presence of left ventricular concentric hypertrophy ≥6 mm on echocardiography.

Results

There were statistically significant differences in LV mass (healthy = 5.87 g, HCM = 10.3 g, P < .0001), native T1 mapping (healthy = 1122 ms, HCM = 1209 ms, P = .004), and ECV (healthy = 26.0%, HCM = 32.6%, P < .0001). Variables of diastolic function including deceleration time of early diastolic transmitral flow (DTE), ratio between peak velocity of early diastolic transmitral flow and peak velocity of late diastolic transmitral flow (E : A), and peak velocity of late diastolic transmitral flow (A wave) were significantly correlated with ECV (DTE; r = 0.73 P = .007, E : A; r = −0.75 P = .004, A wave; r = 0.76 P = .004).

Conclusions and Clinical Importance

Quantitative assessment of cardiac ECV is feasible and can provide additional information not available using echocardiography.

Multiparametric cardiac magnetic resonance imaging in pediatric and adolescent patients with acute myocarditis

BACKGROUND

The diagnostic value of cardiac magnetic resonance imaging (MRI) employing the 2018 Lake Louise criteria in pediatric and adolescent patients with acute myocarditis is undefined.

OBJECTIVE

To evaluate the diagnostic value of the Lake Louise criteria in pediatric and adolescent patients with suspected acute myocarditis and to show the utility of cardiac MRI for follow-up in this patient cohort.

MATERIALS AND METHODS

Forty-three patients (age range: 8-21 years) with suspected acute myocarditis and 13 control patients who underwent cardiac MRI were retrospectively analyzed. T2-weighted and late gadolinium enhancement imaging were performed in all patients. T1 and T2 mapping were available in 26/43 patients (60%). The Lake Louise criteria were assessed. In 27/43 patients (63%), cardiac MRI follow-up was available. Receiver operating characteristic analysis, Pearson's correlation coefficient and paired Student's t-test were used for statistical analysis.

RESULTS

In the total cohort, the Lake Louise criteria achieved a sensitivity of 86% (95% confidence interval [CI]: 72-95%) and a specificity of 100% (95% CI: 79-100%) for the diagnosis of acute myocarditis. In the subgroup of patients with available mapping parameters, the diagnostic performance of the Lake Louise criteria was higher when mapping parameters were implemented into the score (area under the receiver operating characteristic curve: 0.944 vs. 0.870; P=0.033). T2 relaxation times were higher in patients with admission to the intermediate care unit and were associated with the length of intermediate care unit stay (r=0.879, P=0.049). Cardiac MRI markers of active inflammation decreased on follow-up examinations (e.g., T1 relaxation times: 1,032±39 ms vs. 975±33 ms, P<0.001; T2 relaxation times: 58±5 ms vs. 54±5 ms, P=0.003).

CONCLUSION

The Lake Louise criteria have a high diagnostic performance for the diagnosis of acute myocarditis and are a valuable tool for follow-up in pediatric and adolescent patients. The mapping techniques enhance the diagnostic performance of the 2018 Lake Louise criteria.

Multi-parametric MRI of kidney disease progression for autosomal recessive polycystic kidney disease: mouse model and initial patient results

BACKGROUND

Autosomal recessive polycystic kidney disease (ARPKD) is a rare but potentially lethal genetic disorder typically characterized by diffuse renal microcysts. Clinical trials for patients with ARPKD are not currently possible due to the absence of sensitive measures of ARPKD kidney disease progression and/or therapeutic efficacy.

METHODS

In this study, animal and human magnetic resonance imaging (MRI) scanners were used to obtain quantitative kidney T1 and T2 relaxation time maps for both excised kidneys from bpk and wild-type (WT) mice as well as for a pediatric patient with ARPKD and a healthy adult volunteer.

RESULTS

Mean kidney T1 and T2 relaxation times showed significant increases with age (p < 0.05) as well as significant increases in comparison to WT mice (p < 2 × 10-10). Significant or nearly significant linear correlations were observed for mean kidney T1 (p = 0.030) and T2 (p = 0.054) as a function of total kidney volume, respectively. Initial magnetic resonance fingerprinting assessments in a patient with ARPKD showed visible increases in both kidney T1 and T2 in comparison to the healthy volunteer.

CONCLUSIONS

These preclinical and initial clinical MRI studies suggest that renal T1 and T2 relaxometry may provide an additional outcome measure to assess cystic kidney disease progression in patients with ARPKD.

IMPACT

A major roadblock for implementing clinical trials in patients with ARPKD is the absence of sensitive measures of ARPKD kidney disease progression and/or therapeutic efficacy. A clinical need exists to develop a safe and sensitive measure for kidney disease progression, and eventually therapeutic efficacy, for patients with ARPKD. Mean kidney T1 and T2 MRI relaxation times showed significant increases with age (p < 0.05) as well as significant increases in comparison to WT mice (p < 2 ×10-10), indicating that T1 and T2 may provide sensitive assessments of cystic changes associated with progressive ARPKD kidney disease. This preclinical and initial clinical study suggests that MRI-based kidney T1 and T2 mapping could be used as a non-invasive assessment of ARPKD kidney disease progression. These non-invasive, quantitative MRI techniques could eventually be used as an outcome measure for clinical trials evaluating novel therapeutics aimed at limiting or preventing ARPKD kidney disease progression.

Magnetic Resonance Kidney Parenchyma-T2 as a Novel Imaging Biomarker for Autosomal Dominant Polycystic Kidney Disease

OBJECTIVE

Autosomal dominant polycystic kidney disease (ADPKD) is a chronic progressive disorder with a significant disease burden leading to end-stage renal disease in more than 75% of the affected individuals. Although prediction of disease progression is highly important, all currently available biomarkers-including height-adjusted total kidney volume (htTKV)-have important drawbacks in the everyday clinical setting. Thus, the purpose of this study was to evaluate T2 mapping as a source of easily obtainable and accurate biomarkers, which are needed for improved patient counseling and selection of targeted treatment options.

MATERIALS AND METHODS

A total of 139 ADPKD patients from The German ADPKD Tolvaptan Treatment Registry and 10 healthy controls underwent magnetic resonance imaging on a clinical 1.5-T system including acquisition of a Gradient-Echo-Spin-Echo T2 mapping sequence. The ADPKD patients were divided into 3 groups according to kidney cyst fraction (0%-35%, 36%-70%, >70%) as a surrogate marker for disease severity. The htTKV was calculated based on standard T2-weighted imaging. Mean T2 relaxation times of both kidneys (kidney-T2) as well as T2 relaxation times of the residual kidney parenchyma (parenchyma-T2) were measured on the T2 maps.

RESULTS

Calculation of parenchyma-T2 was 6- to 10-fold faster than determination of htTKV and kidney-T2 (0.78 ± 0.14 vs 4.78 ± 1.17 minutes, P < 0.001; 0.78 ± 0.14 vs 7.59 ± 1.57 minutes, P < 0.001). Parenchyma-T2 showed a similarly strong correlation to cyst fraction (r = 0.77, P < 0.001) as kidney-T2 (r = 0.76, P < 0.001), the strongest correlation to the serum-derived biomarker copeptin (r = 0.37, P < 0.001), and allowed for the most distinct separation of patient groups divided according to cyst fraction. In contrast, htTKV showed an only moderate correlation to cyst fraction (r = 0.48, P < 0.001). These observations were even more evident when considering only patients with preserved kidney function.

CONCLUSIONS

The rapidly assessable parenchyma-T2 shows a strong association with disease severity early in disease and is superior to htTKV when it comes to correlation with renal cyst fraction.

Identifying myocardial injuries in "normal-appearing" myocardium in pediatric patients with clinically suspected myocarditis using mapping techniques

Background

Mapping techniques using cardiac magnetic resonance imaging have significantly improved the diagnostic accuracy for myocarditis with focal myocardial injuries. The aim of our study was to determine whether T1 and T2 mapping techniques could identify diffuse myocardial injuries in "normal-appearing" myocardium in pediatric patients with clinically suspected myocarditis and to evaluate the associations between diffuse myocardial injuries and cardiac function parameters.

Methods

Forty-six subjects were included in this study: 20 acute myocarditis patients, 11 subacute/chronic myocarditis patients and 15 control children. T2 values, native T1 values and the extracellular volume (ECV) of "normal-appearing" myocardium were compared among the three groups of patients. Associations between diffuse myocardial injuries and cardiac function parameters were also evaluated.

Results

The ECV of "normal-appearing" myocardium was significantly higher in the subacute/chronic myocarditis group than in the control group (30.1 ± 0.9 vs 27.0 ± 0.6, P =0.004). No significant differences in T1 and T2 values between the acute myocarditis and control groups were found. In the subacute/chronic myocarditis group, a significant association between ECV and left ventricle ejection fraction was found (P=0.03).

Conclusions

Diffuse myocardial injuries are likely to occur in subacute/chronic myocarditis patients with prolonged inflammatory responses. Mapping techniques have great value for the diagnosis and monitoring of myocarditis.

Cardiovascular magnetic resonance techniques for tissue characterization after acute myocardial injury

The annual incidence of hospital admission for acute myocardial infarction lies between 90 and 312 per 100 000 inhabitants in Europe. Despite advances in patient care 1 year mortality after ST-segment elevation myocardial infarction (STEMI) remains around 10%. Cardiovascular magnetic resonance imaging (CMR) has emerged as a robust imaging modality for assessing patients after acute myocardial injury. In addition to accurate assessment of left ventricular ejection fraction and volumes, CMR offers the unique ability of visualization of myocardial injury through a variety of imaging techniques such as late gadolinium enhancement and T2-weighted imaging. Furthermore, new parametric mapping techniques allow accurate quantification of myocardial injury and are currently being exploited in large trials aiming to augment risk management and treatment of STEMI patients. Of interest, CMR enables the detection of microvascular injury (MVI) which occurs in approximately 40% of STEMI patients and is a major independent predictor of mortality and heart failure. In this article, we review traditional and novel CMR techniques used for myocardial tissue characterization after acute myocardial injury, including the detection and quantification of MVI. Moreover, we discuss clinical scenarios of acute myocardial injury in which the tissue characterization techniques can be applied and we provide proposed imaging protocols tailored to each scenario.

Artificial intelligence in cardiac radiology

Artificial intelligence (AI) is entering the clinical arena, and in the early stage, its implementation will be focused on the automatization tasks, improving diagnostic accuracy and reducing reading time. Many studies investigate the potential role of AI to support cardiac radiologist in their day-to-day tasks, assisting in segmentation, quantification, and reporting tasks. In addition, AI algorithms can be also utilized to optimize image reconstruction and image quality. Since these algorithms will play an important role in the field of cardiac radiology, it is increasingly important for radiologists to be familiar with the potential applications of AI. The main focus of this article is to provide an overview of cardiac-related AI applications for CT and MRI studies, as well as non-imaging-based applications for reporting and image optimization.

Myocardial T1 and T2 quantification and water-fat separation using cardiac MR fingerprinting with rosette trajectories at 3T and 1.5T

PURPOSE

This work aims to develop an approach for simultaneous water-fat separation and myocardial T₁ and T₂ quantification based on the cardiac MR fingerprinting (cMRF) framework with rosette trajectories at 3T and 1.5T.

METHODS

Two 15-heartbeat cMRF sequences with different rosette trajectories designed for water-fat separation at 3T and 1.5T were implemented. Water T₁ and T₂ maps, water image, and fat image were generated with B₀ inhomogeneity correction using a B₀ map derived from the cMRF data themselves. The proposed water-fat separation rosette cMRF approach was validated in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology MRI system phantom and water/oil phantoms. It was also applied for myocardial tissue mapping of healthy subjects at both 3T and 1.5T.

RESULTS

Water T₁ and T₂ values measured using rosette cMRF in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom agreed well with the reference values. In the water/oil phantom, oil was well suppressed in the water images and vice versa. Rosette cMRF yielded comparable T₁ but 2~3 ms higher T₂ values in the myocardium of healthy subjects than the original spiral cMRF method. Epicardial fat deposition was also clearly shown in the fat images.

CONCLUSION

Rosette cMRF provides fat images along with myocardial T₁ and T₂ maps with significant fat suppression. This technique may improve visualization of the anatomical structure of the heart by separating water and fat and could provide value in diagnosing cardiac diseases associated with fibrofatty infiltration or epicardial fat accumulation. It also paves the way toward comprehensive myocardial tissue characterization in a single scan.

Diffusion-weighted imaging in hypertrophic cardiomyopathy: association with high T2-weighted signal intensity in addition to late gadolinium enhancement

Diffusion-weighted imaging (DWI) has been confirmed to be associated with late gadolinium enhancement (LGE) in hypertrophic cardiomyopathy (HCM). In this context, we aimed to study whether DWI could reflect the active tissue injury and edema information of HCM which were usually indicated by T2 weighted images. Forty HCM patients were examined using a 3.0 T magnetic resonance scanner. Cine, T2-weighted short tau inversion recovery (T2-STIR), DWI and LGE sequences were acquired. T1 mapping was also included to quantify the focal and diffuse fibrosis. Cardiac troponin I (cTnI) was tested to assess the recently myocardial injury. Student's t-test, Mann-Whitney U test, One-way analysis, Kruskal-Wallis analysis, the Spearman correlation analysis, and multivariable regression were used in this study. The apparent diffusion coefficient (ADC) was significantly elevated in the cTnI positive group (P = 0.01) and correlated with LGE (ρ = 0.312, P = 0.049) and HighT2 extent (ρ = 0.443, P = 0.004) in the global level. In the segmental analysis, the ADC significantly differentiated the segments with and without HighT2/LGE presence (P = 0.00). The average ADC values were higher in segments with HighT2 and LGE coexistence than in those with only LGE presence (P < 0.05). Multivariable regression indicated that segmental HighT2 and LGE were both contributing factors to the ADC values. In this study of HCM, we confirmed that ADC as a molecular diffusion parameter reflects the replacement fibrosis of myocardium. Moreover, it also reveals edema extent and its association with serum cTnI.

Myocardial Infarction With Nonobstructive Coronary Arteries (MINOCA): Potential Etiologies, Mimics and Imaging Findings

Myocardial infarction with nonobstructive coronary arteries (MINOCA) occurs when a patient presents with positive cardiac enzymes in the absence of obstructive atherosclerosis on coronary angiography. Several hypotheses for the pathogenesis of MINOCA have been suggested and multiple potential underlying etiologies have been reported. This review will outline the reported causes of MINOCA and associated major imaging features. In doing so, it will increase awareness of this entity and equip cardiac imagers with the knowledge to appropriately tailor imaging to make a prompt and accurate diagnosis.

Cardiovascular magnetic resonance native T2 and T2* quantitative values for cardiomyopathies and heart transplantations: a systematic review and meta-analysis

BACKGROUND

The clinical application of cardiovascular magnetic resonance (CMR) T2 and T2* mapping is currently limited as ranges for healthy and cardiac diseases are poorly defined. In this meta-analysis we aimed to determine the weighted mean of T2 and T2* mapping values in patients with myocardial infarction (MI), heart transplantation, non-ischemic cardiomyopathies (NICM) and hypertension, and the standardized mean difference (SMD) of each population with healthy controls. Additionally, the variation of mapping outcomes between studies was investigated.

METHODS

The PRISMA guidelines were followed after literature searches on PubMed and Embase. Studies reporting CMR T2 or T2* values measured in patients were included. The SMD was calculated using a random effects model and a meta-regression analysis was performed for populations with sufficient published data.

RESULTS

One hundred fifty-four studies, including 13,804 patient and 4392 control measurements, were included. T2 values were higher in patients with MI, heart transplantation, sarcoidosis, systemic lupus erythematosus, amyloidosis, hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM) and myocarditis (SMD of 2.17, 1.05, 0.87, 1.39, 1.62, 1.95, 1.90 and 1.33, respectively, P <  0.01) compared with controls. T2 values in iron overload patients (SMD = - 0.54, P = 0.30) and Anderson-Fabry disease patients (SMD = 0.52, P = 0.17) did both not differ from controls. T2* values were lower in patients with MI and iron overload (SMD of - 1.99 and - 2.39, respectively, P <  0.01) compared with controls. T2* values in HCM patients (SMD = - 0.61, P = 0.22), DCM patients (SMD = - 0.54, P = 0.06) and hypertension patients (SMD = - 1.46, P = 0.10) did not differ from controls. Multiple CMR acquisition and patient demographic factors were assessed as significant covariates, thereby influencing the mapping outcomes and causing variation between studies.

CONCLUSIONS

The clinical utility of T2 and T2* mapping to distinguish affected myocardium in patients with cardiomyopathies or heart transplantation from healthy myocardium seemed to be confirmed based on this meta-analysis. Nevertheless, variation of mapping values between studies complicates comparison with external values and therefore require local healthy reference values to clinically interpret quantitative values. Furthermore, disease differentiation seems limited, since changes in T2 and T2* values of most cardiomyopathies are similar.

Towards measuring the effect of flow in blood T 1 assessed in a flow phantom and in vivo

Measurement of the blood T ₁ time using conventional myocardial T ₁ mapping methods has gained clinical significance in the context of extracellular volume (ECV) mapping and synthetic hematocrit (Hct). However, its accuracy is potentially compromised by in-flow of non-inverted/non-saturated spins and in-flow of spins which are not partially saturated from previous imaging pulses. Bloch simulations were used to analyze various flow effects separately. T ₁ measurements of gadolinium doped water were performed using a flow phantom with adjustable flow velocities at 3 T. Additionally, in vivo blood T ₁ measurements were performed in 6 healthy subjects (26 ± 5 years, 2 female). To study the T ₁ time as a function of the instantaneous flow velocity, T ₁ times were evaluated in an axial imaging slice of the descending aorta. Velocity encoded cine measurements were performed to quantify the flow velocity throughout the cardiac cycle. Simulation results show more than 30% loss in accuracy for 10% non-prepared in-flowing spins. However, in- and out-flow to the imaging plane only demonstrated minor impact on the T ₁ time. Phantom T ₁ times were decreased by up to 200 ms in the flow phantom, due to in-flow of non-prepared spins. High flow velocities cause in-flow of spins that lack partial saturation from the imaging pulses but only lead to negligible T ₁ time deviation (less than 30 ms). In vivo measurements confirm a substantial variation of the T ₁ time depending on the flow velocity. The highest aortic T ₁ times are observed at the time point of minimal flow with increased flow velocity leading to reduction of the measured T ₁ time by up to [Formula: see text] at peak velocity. In this work we attempt to dissect the effects of flow on T ₁ times, by using simulations, well-controlled, simplified phantom setup and the linear flow pattern in the descending aorta in vivo.

Practical Guide to Evaluating Myocardial Disease by Cardiac MRI

OBJECTIVE. A spectrum of pathophysiologic mechanisms can lead to the development of myocardial disorders including ischemia, genetic abnormalities, and systemic disorders. Cardiac MRI identifies different myocardial disorders, provides prognostic information, and directs therapy. In comparison with other imaging modalities, cardiac MRI has the advantage of allowing both functional assessment and tissues characterization in a single examination without the use of ionizing radiation. Newer cardiac MRI techniques including mapping can provide additional information about myocardial disease that may not be detected using conventional techniques. Emerging techniques including MR spectroscopy and finger printing will likely change the way we understand the pathophysiology mechanisms of the wide array of myocardial disorders. CONCLUSION. Imaging of myocardial disorders encompasses a large variety of conditions including both ischemic and nonischemic diseases. Cardiac MRI sequences, such as balanced steady-state free precession and late gadolinium enhancement, play a critical role in establishing diagnosis, determining prognosis, and guiding therapeutic management. Additional sequences-including perfusion imaging, T2*, real-time cine, and T2-weighted sequences-should be performed in specific clinical scenarios. There is emerging evidence for the use of mapping in imaging of myocardial disease. Multiple other new techniques are currently being studied. These novel techniques will likely change the way myocardial disorders are understood and diagnosed in the near future.

Cardiovascular magnetic resonance: contribution to the exploration of cardiomyopathies

Background and aims

Magnetic resonance imaging is a non-invasive and non-irradiating imaging method, complementary to cardiac ultrasound in the assessment of cardiovascular disease and implicitly of cardiomyopathies. Although it is not a first intention imaging method, it is superior in the assessment of cardiac volumes, left ventricular ejection fraction, in the analysis of cardiac wall dyskinesia and myocardial tissue characteristics with and without using a contrast agent. The purpose of this paper is to review the current knowledge regarding cardiovascular magnetic resonance imaging (CMR) and its applications in cardiomyopathy analysis.

Methods

In order to create this review, relevant articles were searched and analyzed by using MeSH terms such as: “cardiac magnetic resonance imaging”, “cardiomyopathy”, “myocardial fibrosis”. Three main international databases PubMed, Web of Science and Medscape were searched. We carried out a narrative review focused on the current indications of cardiovascular magnetic resonance imaging in cardiomyopathies, both common and raret, of ischemic and nonischemic types.

Results

Cardiac magnetic resonance imaging has a very important role in the diagnosis, assessment and prognosis of common cardiomyopathies (the dilated, hypertrophic and inflammatory types) or other more rare ones such as (amyloidosis, arrhythmogenic right ventricular, non-compaction or Takotsubo cardiomyopathy), as it represents the gold standard for evaluating the ejection fraction, ventricular volumes and mass. CMR techniques, such as late gadolinium enhancement, T1 and T2 mapping have proven their usefulness, helping differentiate between ischemic (subendocardial enhancement) and nonischemic cardiomyopathy (varied pattern) or also establish the etiology. Another important feature of this imaging technique is that it can establish the myocardial viability, thus the chance of contractile recovery after revascularization. This feature is based on the transmural extent of LGE, left ventricle wall thickness and the assessment of the contractile reserve after administration of low dose dobutamine.

Conclusions

Cardiovascular magnetic resonance imaging is an indispensable tool, with proven efficiency, capable of providing the differential diagnosis between ischemic and nonischemic cardiomyopathy or establishing the etiology in the nonischemic type. In addition, these findings have a prognostic value, they may guide the patient management plan and, if necessary, can evaluate treatment response. Therefore, this technique should be part of any routine investigation of various cardiomyopathies.

Free-running 3D whole heart myocardial T1 mapping with isotropic spatial resolution

PURPOSE

To develop a free-running (free-breathing, retrospective cardiac gating) 3D myocardial T1 mapping with isotropic spatial resolution.

METHODS

The free-running sequence is inversion recovery (IR)-prepared followed by continuous 3D golden angle radial data acquisition. 1D respiratory motion signal is extracted from the k-space center of all spokes and used to bin the k-space data into different respiratory states, enabling estimation and correction of 3D translational respiratory motion, whereas cardiac motion is recorded using electrocardiography and synchronized with data acquisition. 3D translational respiratory motion compensated T1 maps at diastole and systole were generated with 1.5 mm isotropic spatial resolution with low-rank inversion and high-dimensionality patch-based undersampled reconstruction. The technique was validated against conventional methods in phantom and 9 healthy subjects.

RESULTS

Phantom results demonstrated good agreement (R2 = 0.99) of T1 estimation with reference method. Homogeneous systolic and diastolic 3D T1 maps were reconstructed from the proposed technique. Diastolic septal T1 estimated with the proposed method (1140 ± 36 ms) was comparable to the saturation recovery single-shot acquisition (SASHA) sequence (1153 ± 49 ms), but was higher than the modified Look-Locker inversion recovery (MOLLI) sequence (1037 ± 33 ms). Precision of the proposed method (42 ± 8 ms) was comparable to MOLLI (41 ± 7 ms) and improved with respect to SASHA (87 ± 19 ms).

CONCLUSIONS

The proposed free-running whole heart T1 mapping method allows for reconstruction of isotropic resolution 3D T1 maps at different cardiac phases, serving as a promising tool for whole heart myocardial tissue characterization.

Diagnostic performance of cardiovascular magnetic resonance native T1 and T2 mapping in pediatric patients with acute myocarditis

BACKGROUND

Multiple studies in adult patients suggest that tissue mapping performed by cardiovascular magnetic resonance (CMR) has excellent diagnostic accuracy in acute myocarditis, however, these techniques have not been studied in depth in children.

METHODS

CMR data on 23 consecutive pediatric patients from 2014 to 2017 with a clinical diagnosis of acute myocarditis were retrospectively analyzed and compared to 39 healthy controls. The CMR protocol included native T1, T2, and extracellular volume fraction (ECV) in addition to standard Lake Louise Criteria (LLC) parameters on a 1.5 T scanner.

RESULTS

Mean global values for novel mapping parameters were significantly elevated in patients with clinically suspected acute myocarditis compared to controls, with native T1 1098 ± 77 vs 990 ± 34 ms, T2 52.8 ± 4.6 ms vs 46.7 ± 2.6 ms, and ECV 29.8 ± 5.1% vs 23.3 ± 2.6% (all p-values < 0.001). Ideal cutoff values were generated using corresponding ROC curves and were for global T1 1015 ms (AUC 0.936, sensitivity 91%, specificity 86%), for global T2 48.5 ms (AUC 0.908, sensitivity 91%, specificity 74%); and for ECV 25.9% (AUC 0.918, sensitivity 86%, specificity 89%). While the diagnostic yield of the LLC was 57% (13/23) in our patient cohort, 70% (7/10) of patients missed by the LLC demonstrated abnormalities across all three global mapping parameters (native T1, T2, and ECV) and another 20% (2/10) of patients demonstrated at least one abnormal mapping value.

CONCLUSIONS

Similar to findings in adults, pediatric patients with acute myocarditis demonstrate abnormal CMR tissue mapping values compared to controls. Furthermore, we found CMR parametric mapping techniques measurably increased CMR diagnostic yield when compared with conventional LLC alone, providing additional sensitivity and specificity compared to historical references. Routine integration of these techniques into imaging protocols may aid diagnosis in children.

Comparison of native myocardial T1 and T2 mapping at 1.5T and 3T in healthy volunteers : Reference values and clinical implications

Background

Myocardial native T1 and T2 mapping are promising techniques for quantitative assessment of diffuse myocardial pathologies; however, due to conflicting data regarding normal values, routine clinical implementation of this method is still challenging.

Methods

To evaluate this situation during daily clinical practice the characteristics of normal values obtained in 60 healthy volunteers who underwent magnetic resonance imaging (MRI) scans on 1.5T and 3T scanners were studied. The T1 modified look-locker inversion recovery (MOLLI; 5(3)3; modified for higher heart rates) and T2 navigator gated black-blood prepared gradient-spin-echo (GraSE) sequences were used.

Results

While age and body mass index did not affect relaxation times, a gender and heart rate dependency was found showing higher T1 and T2 values in females, whereas at higher heart rates a prolongation of T1 and a shortening of T2 relaxation times was found. Particularly prone to artifacts were T2 measurements at 3T and the inferolateral wall. In the individual setting mean relaxation times for T1 were 995.8 ± 30.9 ms at 1.5T and 1183.8 ± 37.5 ms at 3T and 55.8 ± 2.8 ms at 1.5T and 51.6 ± 3 ms at 3T for T2 indicating a high dependency of reference values on MRI protocol when compared to the literature. Furthermore, as presumed mean T1 and T2 values correlated in the same individual.

Conclusions

The T1 and T2 relaxation times depend on physiological factors and especially on MRI protocols. Therefore, reference values should be validated individually in every radiological institution before implementing mapping protocols in daily clinical practice. Correlation of mean T1 and T2 values in the same proband at both field strengths indicates intraindividual reproducibility.

Cardiac Magnetic Resonance Fingerprinting: Technical Overview and Initial Results

Cardiovascular magnetic resonance is a versatile tool that enables noninvasive characterization of cardiac tissue structure and function. Parametric mapping techniques have allowed unparalleled differentiation of pathophysiological differences in the myocardium such as the delineation of myocardial fibrosis, hemorrhage, and edema. These methods are increasingly used as part of a tool kit to characterize disease states such as cardiomyopathies and coronary artery disease more accurately. Currently conventional mapping techniques require separate acquisitions for T1 and T2 mapping, the values of which may depend on specifics of the magnetic resonance imaging system hardware, pulse sequence implementation, and physiological variables including blood pressure and heart rate. The cardiac magnetic resonance fingerprinting (cMRF) technique has recently been introduced for simultaneous and reproducible measurement of T1 and T2 maps in a single scan. The potential for this technique to provide consistent tissue property values independent of variables including scanner, pulse sequence, and physiology could allow an unbiased framework for the assessment of intrinsic properties of cardiac tissue including structure, perfusion, and parameters such as extracellular volume without the administration of exogenous contrast agents. This review seeks to introduce the basics of the cMRF technique, including pulse sequence design, dictionary generation, and pattern matching. The potential applications of cMRF in assessing diseases such as nonischemic cardiomyopathy are also briefly discussed, and ongoing areas of research are described.

Three-dimensional free breathing whole heart cardiovascular magnetic resonance T1 mapping at 3 T

BACKGROUND

This study demonstrates a three-dimensional (3D) free-breathing native myocardial T1 mapping sequence at 3 T.

METHODS

The proposed sequence acquires three differently T1-weighted volumes. The first two volumes receive a saturation pre-pulse with different recovery time. The third volume is acquired without magnetization preparation and after a significant recovery time. Respiratory navigator gating and volume-interleaved acquisition are adopted to mitigate misregistration. The proposed sequence was validated through simulation, phantom experiments and in vivo experiments in 12 healthy adult subjects.

RESULTS

In phantoms, good agreement on T1 measurement was achieved between the proposed sequence and the reference inversion recovery spin echo sequence (R2 = 0.99). Homogeneous 3D T1 maps were obtained from healthy adult subjects, with a T1 value of 1476 ± 53 ms and a coefficient of variation (CV) of 6.1 ± 1.4% over the whole left-ventricular myocardium. The averaged septal T1 was 1512 ± 60 ms with a CV of 2.1 ± 0.5%.

CONCLUSION

Free-breathing 3D native T1 mapping at 3 T is feasible and may be applicable in myocardial assessment. The proposed 3D T1 mapping sequence is suitable for applications in which larger coverage is desired beyond that available with single-shot parametric mapping, or breath-holding is unfeasible.

Cardiac magnetic resonance in patients with mitral valve prolapse: Focus on late gadolinium enhancement and T1 mapping

OBJECTIVES

To evaluate the incidence of late-gadolinium-enhancement (LGE) in mitral valve prolapse (MVP) (in the absence of other heart/valvular diseases), and its association with the degree of mitral regurgitation (MR) and/or with complex ventricular arrhythmia (ComVA), and to analyse the role of T1 mapping in the evaluation of MVP patients.

METHODS

We included all consecutive patients with MVP who underwent during 2015-2016 a comprehensive cardiac magnetic resonance (CMR) examination at 1.5 T. We evaluated the association of LGE with the MR fraction and the presence of ComVA. We compared myocardial T1-native and post-contrast times and extracellular volume (ECV)-values between MVP patients, both with and without LGE, and the control group.

RESULTS

Thirty-four patients with MVP were selected (56 ± 14 years old, 59% male). All patients had MR; LGE and ComVA were present in 15 (44%) and 11 (34%) patients, respectively. Significant associations of LGE with both MR severity and ComVA were not found (p=0.72 and 0.79, respectively). T1 mapping confirmed the presence of LGE in all cases. In one patient a thin signal alteration resulted in more evident T1 mapping than LGE. Patients with MVP had higher native T1-values, lower post-contrast T1-values and increased ECV-values compared with controls (p=0.01, 0.01 and 0.00, respectively).

CONCLUSION

Focal fibrosis with LGE was found in about half the MVP patients and it was independent of the degree of the valve dysfunction and the presence of ComVA. T1 mapping allows diffuse myocardial wall alterations to be identified, but no significant associations between the MR severity and ComVA and T1/ECV values were found.

KEY POINTS

• MVP is a common valvulopathy affecting 2-3% of the general population. • MVP has been associated with an increased risk of arrhythmic complications and sudden cardiac death. • CMR is a non-invasive imaging method that provides a precise and more accurate assessment of patients with MVP.

Parametric Imaging for the Assessment of Cardiac Motion: A Review

The assessment of wall motion abnormalities such as hypokinesia or dyskinesia and the identification of their extent as well as their degree of severity allow an accurate evaluation of several ischemic heart diseases and an early diagnosis of heart failure. These dysfunctions are usually revealed by a drop of contraction indicating a regional hypokinesia or a total absence of the wall motion in case of akinesia. The discrimination between these contraction abnormalities plays also a significant role in the therapeutic decision through the differentiation between the infarcted zones, which have lost their contractile function, and the stunned areas that still retain viable myocardial tissues. The lack of a reliable method for the evaluation of wall motion abnormalities in cardiac imaging presents a major limitation for a regional assessment of the left ventricular function. In the past years, several techniques were proposed as additional tools for the local detection of wall motion deformation. Among these approaches, the parametric imaging is likely to represent a promising technique for the analysis of a local contractile function. The aim of this paper is to review the most recent techniques of parametric imaging computation developed in cardiac imaging and their potential contributions in clinical practice.

Diagnostic performance of semi-quantitative and quantitative stress CMR perfusion analysis: a meta-analysis

BACKGROUND

Stress cardiovascular magnetic resonance (CMR) perfusion imaging is a promising modality for the evaluation of coronary artery disease (CAD) due to high spatial resolution and absence of radiation. Semi-quantitative and quantitative analysis of CMR perfusion are based on signal-intensity curves produced during the first-pass of gadolinium contrast. Multiple semi-quantitative and quantitative parameters have been introduced. Diagnostic performance of these parameters varies extensively among studies and standardized protocols are lacking. This study aims to determine the diagnostic accuracy of semi- quantitative and quantitative CMR perfusion parameters, compared to multiple reference standards.

METHOD

Pubmed, WebOfScience, and Embase were systematically searched using predefined criteria (3272 articles). A check for duplicates was performed (1967 articles). Eligibility and relevance of the articles was determined by two reviewers using pre-defined criteria. The primary data extraction was performed independently by two researchers with the use of a predefined template. Differences in extracted data were resolved by discussion between the two researchers. The quality of the included studies was assessed using the 'Quality Assessment of Diagnostic Accuracy Studies Tool' (QUADAS-2). True positives, false positives, true negatives, and false negatives were subtracted/calculated from the articles. The principal summary measures used to assess diagnostic accuracy were sensitivity, specificity, andarea under the receiver operating curve (AUC). Data was pooled according to analysis territory, reference standard and perfusion parameter.

RESULTS

Twenty-two articles were eligible based on the predefined study eligibility criteria. The pooled diagnostic accuracy for segment-, territory- and patient-based analyses showed good diagnostic performance with sensitivity of 0.88, 0.82, and 0.83, specificity of 0.72, 0.83, and 0.76 and AUC of 0.90, 0.84, and 0.87, respectively. In per territory analysis our results show similar diagnostic accuracy comparing anatomical (AUC 0.86(0.83-0.89)) and functional reference standards (AUC 0.88(0.84-0.90)). Only the per territory analysis sensitivity did not show significant heterogeneity. None of the groups showed signs of publication bias.

CONCLUSIONS

The clinical value of semi-quantitative and quantitative CMR perfusion analysis remains uncertain due to extensive inter-study heterogeneity and large differences in CMR perfusion acquisition protocols, reference standards, and methods of assessment of myocardial perfusion parameters. For wide spread implementation, standardization of CMR perfusion techniques is essential.

TRIAL REGISTRATION

CRD42016040176 .

T2 relaxometry mapping in demonstrating layered uterine architecture: parameter optimization and utility in endometrial carcinoma and adenomyosis: a feasibility study

OBJECTIVE

We evaluate the feasibility of T₂ relaxometry mapping of the uterus and demonstrate its diagnostic utility in endometrial carcinoma and adenomyosis and discuss the optimum imaging parameters as used in our institute.

METHODS

Institute review board approval was obtained and multispin echo (MSE) imaging of the pelvis was done with variable time to echo in three patients, two with endometrial carcinoma and one with adenomyosis. T₂ parametric maps and curves were plotted and the T₂ times of the diseased endometrium, superficial and deep myometrium were established.

RESULTS

T2 mapping of the uterus is feasible and demonstrated the four-layered uterine architecture with T₂ times of the diseased endometrium, inner myometrium and the outer myometrium being determined. The fourth myometrial layer was demonstrated in all the three cases on the parametric maps. The two cases with endometrial carcinoma had thinning and irregularity of the myometrial fourth layer which helped in predicting superficial myometrium invasion. Thickening of the fourth myometrial layer was demonstrated in the case with adenomyosis, which we believe might be a new imaging finding of adenomyosis.

CONCLUSION

Thinning and irregularity of the myometrial fourth layer in cases of endometrial malignancy might help in identification of superficial myoinvasion-this might be a new imaging armamentarium in nulliparous females where uterine preservation might be a consideration. The T₂ relaxation times of the myometrium and endometrium described here will help optimize the time to echo for the acquisition of MSE for relaxometry of the female pelvis. Advances in knowledge: Thinning and irregularity of the fourth myometrial layer helps in the identification of superficial myometrial invasion with a greater confidence and helps triage patients for uterine preservation when necessary. T₂ relaxometry might be undertaken in those nulliparous women with endometrial carcinoma in whom demonstration of no myometrial invasion will make them candidates for uterine preservation. Thickening of the fourth myometrial layer in adenomyosis requires further evaluation in a larger cohort of patients as an additional imaging finding. T₂ relaxation times of endometrial carcinoma is different from the normal endometrium in the three cases imaged, thus, further studies evaluating the T₂ values in a larger cohort might help in differentiating diseased from the healthy endometrium. T₂ time of the pelvic tissue described in the study will help select the time to echoes for MSE imaging of the female pelvis in further studies.

Motion-robust cardiac B1+ mapping at 3T using interleaved bloch-siegert shifts

PURPOSE

To develop and evaluate a robust motion-insensitive Bloch-Siegert shift based B1+ mapping method in the heart.

METHODS

Cardiac Bloch-Siegert B1+ mapping was performed with interleaved positive and negative off-resonance shifts and diastolic spoiled gradient echo imaging in 12 heartbeats. Numerical simulations were performed to study the impact of respiratory motion. The method was compared with three-dimensional (3D) actual flip angle imaging (AFI) and two-dimensional (2D) saturated double angle method (SDAM) in phantom scans. Cardiac B1+ maps of three different views were acquired in six healthy volunteers using Bloch-Siegert and SDAM during breath-hold and free breathing. In vivo maps were evaluated for inter-view consistency using the correlation coefficients of the B1+ profiles along the lines of intersection between the views.

RESULTS

For the Bloch-Siegert sequence, numerical simulations indicated high similarity between breath-hold and free breathing scans, and phantom results indicated low deviation from the 3D AFI reference (normalized root mean square error [NRMSE] = 2.0%). Increased deviation was observed with 2D SDAM (NRMSE = 5.0%) due to underestimation caused by imperfect excitation slice profiles. Breath-hold and free breathing Bloch-Siegert in vivo B1+ maps were visually comparable with no significant difference in the inter-view consistency (P > 0.36). SDAM showed strongly impaired B1+ map quality during free breathing. Inter-view consistency was significantly lower than with the Bloch-Siegert method (breath-hold: P = 0.014, free breathing: P < 0.0001).

CONCLUSION

The proposed interleaved Bloch-Siegert sequence enables cardiac B1+ mapping with improved inter-view consistency and high resilience to respiratory motion. Magn Reson Med 78:670-677, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Simultaneous multislice imaging for native myocardial T1 mapping: Improved spatial coverage in a single breath-hold

PURPOSE

To develop a saturation recovery myocardial T1 mapping method for the simultaneous multislice acquisition of three slices.

METHODS

Saturation pulse-prepared heart rate independent inversion recovery (SAPPHIRE) T1 mapping was implemented with simultaneous multislice imaging using FLASH readouts for faster coverage of the myocardium. Controlled aliasing in parallel imaging (CAIPI) was used to achieve minimal noise amplification in three slices. Multiband reconstruction was performed using three linear reconstruction methods: Slice- and in-plane GRAPPA, CG-SENSE, and Tikhonov-regularized CG-SENSE. Accuracy, spatial variability, and interslice leakage were compared with single-band T1 mapping in a phantom and in six healthy subjects.

RESULTS

Multiband phantom T1 times showed good agreement with single-band T1 mapping for all three reconstruction methods (normalized root mean square error <1.0%). The increase in spatial variability compared with single-band imaging was lowest for GRAPPA (1.29-fold), with higher penalties for Tikhonov-regularized CG-SENSE (1.47-fold) and CG-SENSE (1.52-fold). In vivo multiband T1 times showed no significant difference compared with single-band (T1 time ± intersegmental variability: single-band, 1580 ± 119 ms; GRAPPA, 1572 ± 145 ms; CG-SENSE, 1579 ± 159 ms; Tikhonov, 1586 ± 150 ms [analysis of variance; P = 0.86]). Interslice leakage was smallest for GRAPPA (5.4%) and higher for CG-SENSE (6.2%) and Tikhonov-regularized CG-SENSE (7.9%).

CONCLUSION

Multiband accelerated myocardial T1 mapping demonstrated the potential for single-breath-hold T1 quantification in 16 American Heart Association segments over three slices. A 1.2- to 1.4-fold higher in vivo spatial variability was observed, where GRAPPA-based reconstruction showed the highest homogeneity and the least interslice leakage. Magn Reson Med 78:462-471, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

Myocardial T2 Mapping in Patients With Hypertrophic Cardiomyopathy

OBJECTIVE

The aim of this study was to evaluate the usefulness of T2 mapping for detecting myocardial injuries in patients with hypertrophic cardiomyopathy (HCM).

METHODS

Twenty-one HCM patients and 7 healthy volunteers were examined. The T2 values were measured at hyperintense areas (high-T2 areas) identified with T2 mapping, at late gadolinium enhancement (LGE) areas, and in nullified myocardium of the HCM patients. The associations between T2 values and laboratory data or LGE areas were assessed.

RESULTS

High-T2 areas had significantly greater T2 values than LGE areas (P < 0.05) and nullified areas (P < 0.01) of HCM and normal myocardium (P < 0.01). The presence of high-T2 areas was associated with an increase in troponin T levels (P = 0.02), and T2 values correlated with the levels of brain natriuretic peptide (P = 0.036, r = 0.86).

CONCLUSIONS

T2 mapping identified myocardial injuries suggested by the laboratory data in HCM.

Saturation Recovery Myocardial T1 Mapping with a Composite Radiofrequency Pulse on a 3T MR Imaging System

PURPOSE

To evaluate the effect of a composite radiofrequency (RF) pulse on saturation recovery (SR) myocardial T₁ mapping using a 3T MR system.

MATERIALS AND METHODS

Phantom and in vivo studies were performed with a clinical 3T MR scanner. Accuracy and reproducibility of the SR T₁ mapping using conventional and composite RF pulses were first compared in phantom experiments. An in vivo study was performed of 10 healthy volunteers who were imaged with conventional and composite RF pulse methods twice each. In vivo reproducibility of myocardial T₁ value and the inter-segment variability were assessed.

RESULTS

The phantom study revealed significant differences in the mean T₁ values between the two methods, and the reproducibility for the composite RF pulse was significantly smaller than that for the conventional RF pulse. For both methods, the correlations of the reference and measured T₁ values were excellent (r² = 0.97 and 0.98 for conventional and composite RF pulses, respectively). The in vivo study showed that the mean T₁ value for composite RF pulse was slightly lower than that for conventional RF pulse, but this difference was not significant (P = 0.06). The inter-segment variability for the composite RF pulse was significantly smaller than that for conventional RF pulse (P < 0.01). Inter-scan correlations of T₁ measurements of the first and second scans were highly and weakly correlated to composite RF pulses (r = 0.83 and 0.29, respectively).

CONCLUSION

SR T₁ mapping using composite RF pulse provides accurate quantification of T₁ values and can lessen measurement variability and enable reproducible T₁ measurements.