Assessment of deep learning segmentation for real-time free-breathing cardiac magnetic resonance imaging at rest and under exercise stress

In recent years, a variety of deep learning networks for cardiac MRI (CMR) segmentation have been developed and analyzed. However, nearly all of them are focused on cine CMR under breathold. In this work, accuracy of deep learning methods is assessed for volumetric analysis (via segmentation) of the left ventricle in real-time free-breathing CMR at rest and under exercise stress. Data from healthy volunteers (n = 15) for cine and real-time free-breathing CMR at rest and under exercise stress were analyzed retrospectively. Exercise stress was performed using an ergometer in the supine position. Segmentations of two deep learning methods, a commercially available technique (comDL) and an openly available network (nnU-Net), were compared to a reference model created via the manual correction of segmentations obtained with comDL. Segmentations of left ventricular endocardium (LV), left ventricular myocardium (MYO), and right ventricle (RV) are compared for both end-systolic and end-diastolic phases and analyzed with Dice's coefficient. The volumetric analysis includes the cardiac function parameters LV end-diastolic volume (EDV), LV end-systolic volume (ESV), and LV ejection fraction (EF), evaluated with respect to both absolute and relative differences. For cine CMR, nnU-Net and comDL achieve Dice's coefficients above 0.95 for LV and 0.9 for MYO, and RV. For real-time CMR, the accuracy of nnU-Net exceeds that of comDL overall. For real-time CMR at rest, nnU-Net achieves Dice's coefficients of 0.94 for LV, 0.89 for MYO, and 0.90 for RV and the mean absolute differences between nnU-Net and the reference are 2.9 mL for EDV, 3.5 mL for ESV, and 2.6% for EF. For real-time CMR under exercise stress, nnU-Net achieves Dice's coefficients of 0.92 for LV, 0.85 for MYO, and 0.83 for RV and the mean absolute differences between nnU-Net and reference are 11.4 mL for EDV, 2.9 mL for ESV, and 3.6% for EF. Deep learning methods designed or trained for cine CMR segmentation can perform well on real-time CMR. For real-time free-breathing CMR at rest, the performance of deep learning methods is comparable to inter-observer variability in cine CMR and is usable for fully automatic segmentation. For real-time CMR under exercise stress, the performance of nnU-Net could promise a higher degree of automation in the future.

Evaluation of MR-safe bioptomes for MR-guided endomyocardial biopsy in minipigs: a potential radiation-free clinical approach

BACKGROUND

Diagnostic accuracy of endomyocardial biopsy could improve if clinically safe magnetic resonance (MR)-compatible bioptomes were available. We explored two novel MR-compatible cardiac bioptomes for performance, safety, and clinical viability, employing in vivo minipig trials and phase-contrast synchrotron radiation computed microtomography (SRµCT).

METHODS

Analysis of ex vivo obtained pig endomyocardial biopsies was performed using phase-contrast SRµCT and conventional two-dimensional histology. The technical performance was evaluated by measuring volume, inner and outer integrities, compression, and histological diagnostic value in 3 sets (6 per set) of biopsies for each experimental bioptome. The bioptomes were tested in vivo in 3 healthy minipigs per bioptome. The clinical feasibility was evaluated by procedural and cutting success as well as histological diagnostic value.

RESULTS

The bioptome with the 'grind-grind' design achieved similar values to control in compression (p = 0.822), inner (p = 0.628), and outer (p = 0.507), integrities ex vivo. It showed a better performance in the in vivo real-time MRI setting demonstrating a higher cutting success (91.7%) than the 'grind-anvil' (86.2%) design. In both ex vivo and in vivo evaluations, the 'grind-grind' design displayed sufficient diagnostic value (83% and 95%). The 'grind-anvil' design showed adequate diagnostic value both ex vivo and in vivo (78% and 87.5%) but was not comparable to control according to the three-dimensional (3D) analysis.

CONCLUSION

A novel MR-compatible bioptome was identified as plausible in a clinical setting. Additionally, SRµCT and subsequent 3D structural analysis could be valuable in the label-free investigation of myocardial tissue at a micrometer level.

RELEVANCE STATEMENT

Implementation of MR-guided biopsy can improve animal studies on structural myocardial changes at any point in an experimental setup. With further improvements in guiding catheters, MR-guided biopsy, using the new bioptome, has a potential to increase quality and diagnostic accuracy in patients both with structural and inflammatory cardiomyopathies.

KEY POINTS

• Novel MR-compatible bioptomes show promise for a clinical application. • SRµCT enabled detailed analysis of endomyocardial biopsies. • The bioptomes showed adequate in vivo performance without major complications.

Comparison between cone-beam breast-CT and full-field digital mammography for microcalcification detection depending on breast density

The purpose of this study was to evaluate the impact of breast density on the diagnostic performance of cone-beam breast-CT (CBBCT) in comparison to full-field digital mammography (FFDM) for the detection of microcalcifications. This retrospective IRB-approved study was conducted between December 2015 and March 2017 and enrolled 171 women with Breast Imaging Reporting and Data System category 4 or 5 lesions on FFDM and additional CBBCT; 56 of which were ineligible. The inclusion was restricted to 83 women (90 breasts, 90 lesions) with microcalcifications. All lesions underwent histology or were monitored by FFDM and a clinical examination at least 2 years after enrollment. Two breast radiologists independently read each data set twice. Sensitivity, specificity and area under the curve were compared between the modalities. Thirty-two breasts (35.5%) were grouped as non-dense breasts (American College of Radiology types a/b) and 58 breasts (64.5%) as dense breasts (American College of Radiology types c/d). Histopathological assessment was performed in 61 of 90 breast lesions (32 malignant, 1 high-risk and 28 benign). Area under the curve was larger for FFDM than for CBBCT (P = .085). The sensitivity was significantly higher for FFDM compared to CBBCT (P = .009). The specificity showed no significant differences comparing FFDM (both readers: 0.62) versus CBBCT (reader 1: 0.76, reader 2: 0.60; P = .192). Inter-observer-reliability on BI-RADS readings was almost perfect for FFDM and moderate for CBBCT (κ = 0.84, κ = 0.54, respectively). Intra-observer agreement was substantial to almost perfect for both methods and readers. Compared with FFDM, CBBCT demonstrated non-comparable results for microcalcification detection in dense and non-dense breasts.

Free-Breathing Liver Fat, R₂* and B₀ Field Mapping Using Multi-Echo Radial FLASH and Regularized Model-Based Reconstruction

This work introduced a stack-of-radial multi-echo asymmetric-echo MRI sequence for free-breathing liver volumetric acquisition. Regularized model-based reconstruction was implemented in Berkeley Advanced Reconstruction Toolbox (BART) to jointly estimate all physical parameter maps (water, fat, R2∗ , and B0 field inhomogeneity maps) and coil sensitivity maps from self-gated k -space data. Specifically, locally low rank and temporal total variation regularization were employed directly on physical parameter maps. The proposed free-breathing radial technique was tested on a water/fat & iron phantom, a young volunteer, and obesity/diabetes/hepatic steatosis patients. Quantitative fat fraction and R2∗ accuracy were confirmed by comparing our technique with the reference breath-hold Cartesian scan. The multi-echo radial sampling sequence achieves fast k -space coverage and is robust to motion. Moreover, the proposed motion-resolved model-based reconstruction allows for free-breathing liver fat and R2∗ quantification in multiple motion states. Overall, our proposed technique offers a convenient tool for non-invasive liver assessment with no breath holding requirement.

Free-breathing myocardial T1 mapping using inversion-recovery radial FLASH and motion-resolved model-based reconstruction

PURPOSE

To develop a free-breathing myocardialT 1 $$ {\mathrm{T}}_1 $$ mapping technique using inversion-recovery (IR) radial fast low-angle shot (FLASH) and calibrationless motion-resolved model-based reconstruction.

METHODS

Free-running (free-breathing, retrospective cardiac gating) IR radial FLASH is used for data acquisition at 3T. First, to reduce the waiting time between inversions, an analytical formula is derived that takes the incompleteT 1 $$ {\mathrm{T}}_1 $$ recovery into account for an accurateT 1 $$ {\mathrm{T}}_1 $$ calculation. Second, the respiratory motion signal is estimated from the k-space center of the contrast varying acquisition using an adapted singular spectrum analysis (SSA-FARY) technique. Third, a motion-resolved model-based reconstruction is used to estimate both parameter and coil sensitivity maps directly from the sorted k-space data. Thus, spatiotemporal total variation, in addition to the spatial sparsity constraints, can be directly applied to the parameter maps. Validations are performed on an experimental phantom, 11 human subjects, and a young landrace pig with myocardial infarction.

RESULTS

In comparison to an IR spin-echo reference, phantom results confirm goodT 1 $$ {\mathrm{T}}_1 $$ accuracy, when reducing the waiting time from 5 s to 1 s using the new correction. The motion-resolved model-based reconstruction further improvesT 1 $$ {\mathrm{T}}_1 $$ precision compared to the spatial regularization-only reconstruction. Aside from showing that a reliable respiratory motion signal can be estimated using modified SSA-FARY, in vivo studies demonstrate that dynamic myocardialT 1 $$ {\mathrm{T}}_1 $$ maps can be obtained within 2 min with good precision and repeatability.

CONCLUSION

Motion-resolved myocardialT 1 $$ {\mathrm{T}}_1 $$ mapping during free-breathing with good accuracy, precision and repeatability can be achieved by combining inversion-recovery radial FLASH, self-gating and a calibrationless motion-resolved model-based reconstruction.

Magnetic resonance imaging of organ iron before and after correction of iron deficiency in patients with heart failure

AIMS

Intravenous iron therapy (IVIT) is known to improve functional status in chronic heart failure (CHF) patients. The exact mechanism is not completely understood. We correlated magnetic resonance imaging (MRI) patterns of T2* iron signal in various organs to systemic iron and exercise capacity (EC) in CHF before and after IVIT.

METHODS AND RESULTS

We prospectively analysed 24 patients with systolic CHF for T2* MRI pattern of the left ventricle (LV), small and large intestines, spleen, liver, skeletal muscle, and brain for iron. In 12 patients with iron deficiency (ID), we restored iron deficit by IVIT using ferric carboxymaltose. The effects after 3 months were analysed by spiroergometry and MRI. Patients with vs. without ID showed lower blood ferritin, haemoglobin (76 ± 63 vs. 196 ± 82 μg/L and 12.3 ± 1.1 vs. 14.2 ± 1.1 g/dL, all P < 0.002), and in trend a lower transferrin saturation (TSAT) (19.1 [13.1; 28.2] vs. 25.1 [21.3; 29.1] %, P = 0.05). Spleen and liver iron was lower as expressed by higher T2* value (71.8 [66.4; 93.1] vs. 36.9 [32.9; 51.7] ms, P < 0.002 and 33.5 ± 5.9 vs. 28.8 ± 3.9 ms, and P < 0.03). There was a strong trend for a lower cardiac septal iron content in ID (40.6 [33.0; 57.3] vs. 33.7 [31.3; 40.2] ms, P = 0.07). After IVIT, ferritin, TSAT, and haemoglobin increased (54 [30; 104] vs. 235 [185; 339] μg/L, 19.1 [13.1; 28.2] vs. 25.0 [21.0; 33.7] %, 12.3 ± 1.1 vs. 13.3 ± 1.3 g/L, all P < 0.04). Peak VO₂ improved (18.2 ± 4.2 vs. 20.9 ± 3.8 mL/min/kg^-1 , P = 0.05). Higher peak VO₂ at anaerobic threshold was associated with higher blood ferritin, reflecting higher metabolic exercise capacity after therapy (r = 0.9, P = 0.0009). Increase in EC was associated with haemoglobin increase (r = 0.7, P = 0.034). LV iron increased by 25.4% (48.5 [36.2; 64.8] vs. 36.2 [32.9; 41.9] ms, P < 0.04). Spleen and liver iron increased by 46.4 and 18.2%, respectively (71.8 [66.4; 93.1] vs. 38.5 [22.4; 76.9] ms, P < 0.04 and 33.5 ± 5.9 vs. 27.4 ± 8.6 ms, P < 0.007). Iron in skeletal muscle, brain, intestine, and bone marrow remained unchanged (29.6 [28.6; 31.2] vs. 30.4 [29.7; 30.7] ms, P = 0.7, 81.0 ± 6.3 vs. 82.9 ± 9.9 ms, P = 0.6, 34.3 ± 21.4 vs. 25.3 ± 14.1 ms, P = 0.2, 9.4 [7.5; 21.8] vs. 10.3 [6.7; 15.7] ms, P = 0.5 and 9.8 ± 1.5 vs. 13.7 ± 8.9 ms, P = 0.1).

CONCLUSIONS

CHF patients with ID showed lower spleen, liver, and in trend lower cardiac septal iron. After IVIT, iron signal of the left ventricle as well as spleen and liver increased. Improvement in EC was associated with increase in haemoglobin after IVIT. In ID, liver, spleen, and brain but not heart iron were associated with markers of systemic ID.

Imaging of arrhythmia: Real-time cardiac magnetic resonance imaging in atrial fibrillation

Objectives

Quantitative evaluations of function, volume and mass are fundamental in the diagnostic workup of different cardiovascular diseases and can be exactly determined by CMRI in sinus rhythm. This does not hold true in arrhythmia as CMR is hampered by reconstruction artifacts caused by inconsistent data from multiple heartbeats. Real-time (RT) MRI at high temporal resolution might reduce these problems.

Methods

Consecutive patients with atrial fibrillation were prospectively included and underwent RT and conventional CINE CMR in randomized order. 29 patients were studied at 1.5 T and 30 patients at 3 T. At 3 T a group of 20 subjects in sinus rhythm served as controls. RT and CINE image quality was evaluated in different planes and for different wall sections using a Likert scale (from zero to four). Volumetric analysis was performed using two types of software and differences between RT and CINE CMR were evaluated.

Results

In patients with atrial fibrillation RT CMR short axis (SA) resulted in a significantly higher image quality compared to CINE imaging both at 1.5 T and 3 T (1.5 T: mid SA: 3.55 ± 0.5 RT vs 2.6 ± 0.9 CINE, p = 0.0001; 3 T: mid SA: 3.15 ± 0.9 RT vs 2.6 ±1.0 CINE, p = 0.03); This qualitative difference was more marked and significant for the long axis views (2CV and 4CV) at 1.5 T (1.5 T: 2CV: 3.2 ± 0.6 RT vs 2.65 ± 1.1 CINE; p = 0.011; 4CV: 2.9 ± 0.69 RT vs 2.4 ± 0.9 CINE; p = 0.0044). During sinus rhythm CINE images were superior concerning diagnostic quality (3 T mid SA: 3.35 ± 0.45 RT vs 3.8 ± 0.5 CINE, p = 0.008). Quantitative analysis was successful with both software packages and the results showed a good correlation (Pearson correlation between 0.679 and 0.921 for patients). RT CMR resulted in slightly lower functional volumes than CINE CMR (3 T: patients: EDVI 86 ± 29 ml/m² RT vs 93 29 ml/m²± 29 CINE, Pearson r = 0.902) but similar ejection fractions (3 T: patients: EF 47 ± 16% RT vs 45 ± 13% CINE, Pearson r = 0679; controls: EF 63 ± 6 RT vs 63 ± 3 CINE, Pearson r = 0.695).

Conclusion

RT CMR improves image quality in arrhythmic patients and renders studies more comfortable. Volumetric analysis is feasible with slightly lower values relative to CINE CMR, while ejection fractions are comparable.

•

Real time cardiac magnetic imaging is superior to conventional CINE in arrhythmias: concerning image quality. Volumetric and functional analysis of real time is comparable to CINE. Acquistion time is reduced in real time. Improvement of postprocessing software of real time imaging is mandatory.

Impaired Exercise Tolerance in Repaired Tetralogy of Fallot Is Associated With Impaired Biventricular Contractile Reserve: An Exercise-Stress Real-Time Cardiovascular Magnetic Resonance Study

BACKGROUND

Correction of tetralogy of Fallot (cTOF) often results in pulmonary valve pathology and right ventricular (RV) dysfunction. Reduced exercise capacity in cTOF patients cannot be explained by these findings alone. We aimed to explore why cTOF patients exhibit impaired exercise capacity with the aid of a comprehensive cardiopulmonary exercise testing (CPET) and real-time cardiovascular magnetic resonance exercise testing (CMR-ET) protocol.

METHODS

Thirty three cTOF patients and 35 matched healthy controls underwent CPET and CMR-ET in a prospective case-control study. Real-time steady-state free precession cine and phase-contrast sequences were obtained during incremental supine in-scanner cycling at 50, 70, and 90 W. RV and left ventricle (LV) volumes and pulmonary blood flow (Qp) were calculated. Differences of CPET and CMR-ET between cTOF versus controls and correlations between CPET and CMR-ET parameters in cTOF were evaluated statistically for all CMR exercise levels using Mann-Whitney U and Spearman rank-order correlation tests.

RESULTS

CPET capacity was significantly lower in cTOF than in controls. cTOF patients exhibited not only significantly reduced Qp and RV function but also lower LV function on CMR-ET. Higher CPET values in cTOF correlated with higher Qp (Qp 90 W versus carbon dioxide ventilatory equivalent %: R=-0.519, P<0.05), higher LV-end-diastolic volume indexed to body surface area (LV-end-diastolic volume indexed to body surface area at 50 W versus oxygen uptake in % at maximum exercise on CPET R=0.452, P<0.05), and change in LV ejection fraction (EF; LV-EF at 90 W versus Watt %: r=-0.463, P<0.05). No correlation was found with regard to RV-EF. Significant RV-LV interaction was observed during CMR-ET (RV-EF versus LV-EF at 50 W and 70 W: r=0.66, P<0.02 and r=0.52, P<0.05, respectively).

CONCLUSIONS

Impaired exercise capacity in cTOF resulted from a reduction in not only RV, but also LV function. cTOF with good exercise capacity on CPET demonstrated higher LV reserve and pulmonary blood flow during incremental CMR-ET. Apart from RV parameters, CMR-ET-derived LV function could be a valuable tool to stratify cTOF patients for pulmonary valve replacement.

Model-based myocardial T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH cardiovascular magnetic resonance

BACKGROUND

This study develops a model-based myocardial T1 mapping technique with sparsity constraints which employs a single-shot inversion-recovery (IR) radial fast low angle shot (FLASH) cardiovascular magnetic resonance (CMR) acquisition. The method should offer high resolution, accuracy, precision and reproducibility.

METHODS

The proposed reconstruction estimates myocardial parameter maps directly from undersampled k-space which is continuously measured by IR radial FLASH with a 4 s breathhold and retrospectively sorted based on a cardiac trigger signal. Joint sparsity constraints are imposed on the parameter maps to further improve T1 precision. Validations involved studies of an experimental phantom and 8 healthy adult subjects.

RESULTS

In comparison to an IR spin-echo reference method, phantom experiments with T1 values ranging from 300 to 1500 ms revealed good accuracy and precision at simulated heart rates between 40 and 100 bpm. In vivo T1 maps achieved better precision and qualitatively better preservation of image features for the proposed method than a real-time CMR approach followed by pixelwise fitting. Apart from good inter-observer reproducibility (0.6% of the mean), in vivo results confirmed good intra-subject reproducibility (1.05% of the mean for intra-scan and 1.17, 1.51% of the means for the two inter-scans, respectively) of the proposed method.

CONCLUSION

Model-based reconstructions with sparsity constraints allow for single-shot myocardial T1 maps with high spatial resolution, accuracy, precision and reproducibility within a 4 s breathhold. Clinical trials are warranted.

Artifacts Caused by Breast Tissue Markers in a Dedicated Cone-beam Breast CT in Comparison to Full-field Digital Mammography

RATIONALE AND OBJECTIVES

The purpose of this ex vivo study was to investigate artifacts in a cone-beam breast computed tomography (CBBCT) caused by breast tissue markers.

MATERIALS AND METHODS

Breast phantoms with self-made tissue pork mincemeat were created. Twenty-nine different, commercially available markers with varying marker size, composition, and shape were evaluated. A dedicated CBBCT evaluation of all phantoms was performed with 49 kVp, 50 and 100 mA, and marker orientation parallel and orthogonal to the scan direction. The resultant images were evaluated in sagittal, axial, and coronal view with a slice thickness of 0.5 mm. Additionally, measurements of all markers in the same directions were done with full-field digital mammography.

RESULTS

All markers were visible in full-field digital mammography without any artifacts. However, all markers caused artifacts on a CBBCT. Artifacts were measured as the length of the resulting streakings. Median length of artifacts was 7.2 mm with a wide range from 0 to 48.3 mm (interquartile range 4.3-11.4 mm) dependent on composition, size, shape, weight, and orientation of the markers. The largest artifacts occurred in axial view with a median size of 12.6 mm, with a range from 0 to 48.3 mm, resulting in a relative artifact length (quotient artifact in mm/real physical length of the marker itself) of 4.1 (interquartile range 2.3-6.1, range 0-8.7).

CONCLUSIONS

Artifacts caused by markers can significantly influence image quality in a CBBCT, thus limiting primary diagnostics and follow-up in breast cancer. The size of the artifacts depends on the marker characteristics, orientation, and the image plane of reconstruction.

Quantification of left atrial volume and phasic function using cardiovascular magnetic resonance imaging-comparison of biplane area-length method and Simpson's method

Left atrial (LA) enlargement and dysfunction are markers of chronic diastolic dysfunction and an important predictor of adverse cardiovascular and cerebrovascular outcomes. Accordingly, accurate quantification of left atrial volume (LAV) and function is needed. In routine clinical cardiovascular magnetic resonance (CMR) imaging the biplane area-length method (Bi-ALM) is frequently applied due to time-saving image acquisition and analysis. However, given the varying anatomy of the LA we hypothesized that the diagnostic accuracy of the Bi-ALM is not sufficient and that results would be different from a precise volumetric assessment of transversal multi-slice cine images using Simpson's method. Thirty one patients of the FIND-AF_RANDOMISED-study with status post acute cerebral ischemia (mean age 70.5 ± 6.2 years) received CMR imaging at 3T. The study protocol included cine SSFP sequences in standard 2- and 4 CV and a stack of contiguous slices in transversal orientation. Total, passive and active LA emptying fractions were calculated from LA maximal volume, minimal volume and volume prior to atrial contraction. Intra- and inter-observer variability was assessed in ten patients. Significant differences were found for LA volume and phasic function. The Bi-ALM significantly underestimated LA volume and overestimated LA function in comparison to Simpson's method (Bi-ALM vs. Simpson's method: LAV_max: 80.18 vs. 98.80 ml; LAV_pre-ac: 61.09 vs. 80.41 ml; LAV_min: 36.85 vs. 52.66 ml; LAEF_Total: 55.17 vs. 47.85%; LAEF_Passive: 23.96 vs. 19.15%; LAEF_Booster: 40.87 vs. 35.64%). LA volumetric and functional parameters were reproducible on an intra- and inter-observer levels for both methods. Intra-observer agreement for LA function was better for Simpson's method (Bi-ALM vs. Simpson's method; ICC LAEF_Total: 0.84 vs. 0.96; ICC LAEF_Passive: 0.74 vs. 0.92; ICC LAEF_Booster: 0.86 vs. 0.89). The Bi-ALM is based on geometric assumptions that do not reflect the complex individual LA geometry. The assessment of transversal slices covering the left atrium with Simpson's method is feasible and might be more suitable for an accurate quantification of LA volume and phasic function.

Targeted endomyocardial biopsy guided by real-time cardiovascular magnetic resonance

BACKGROUND

Endomyocardial biopsies (EMB) are an important diagnostic tool for myocarditis and other infiltrative cardiac diseases. Routinely, biopsies are obtained under fluoroscopic guidance with a substantial radiation burden. Despite procedural success, there is a large sampling error caused by missing the affected myocardium. Therefore, multiple (>6) biopsies are taken in the clinical setting. In cardiovascular magnetic resonance (CMR), late gadolinium enhancement (LGE) depicts areas of affected myocardium in myocarditis or in other infiltrative cardiomyopathies. Thus, targeted biopsy under real-time CMR image guidance might reduce the problem of sampling error.

METHODS

Seven minipigs of the Goettingen strain underwent radiofrequency ablation in the left ventricle. At least two focal lesions were induced on the lateral wall in five and the apex in two animals. Each ablation lesion was created by two consecutive 30 sec ablations (max. 30 W, temperature 60-64 °C). Biopsies were taken immediately after lesion induction using a commercially available 7 F conventional bioptome under fluoroscopic guidance at the ablation site. Afterwards the animals underwent CMR and lesion visualization by LGE at 3T. The lesions were then targeted and biopsied under CMR-guidance using a MR-conditional bioptome guided by a steerable catheter. Interactive real-time (RT) visualization of the intervention on an in-room monitor was based on radial FLASH with nonlinear inverse reconstruction (NLINV) at a temporal resolution of 42 ms. All samples underwent a standard histological evaluation.

RESULTS

Radiofrequency ablation was successful in all animals. Fluoroscopy-guided biopsies were performed with a success rate of 6/6 minipigs - resulting in a nonlethal pericardial effusion in one animal. Visualization of radiofrequency lesions by CMR was successful in 7/7 minipig, i.e. at least one lesion was clearly visible. Localization and tracking of the catheters and the bioptome using interactive control of the imaging plane was achieved in 6/6 MP; however in the animal with a large pericardial effusion after EMB under fluoroscopy no further EMB was attempted for safety reasons. Biopsies under interactive RT-CMR guidance were successfully performed in 5/6 animals, in one animal the bioptome reached the lesion, however the forceps did not cut out a sample. Specimens obtained under CMR guidance contained part of the lesion in 6/15 (40%) myocardial specimens and in 4/5 (80%) animals in which samples were achieved. Conventional biopsies revealed ablation lesions in 4/17 (23.5%) specimens in 3/6 minipigs (50%).

CONCLUSION

Focal lesions induced by radiofrequency ablation in a minipig model are a useful tool for CMR-guided biopsy studies. In contrast to fluoroscopy, CMR provides excellent visualization of lesions. Interactive real-time CMR allows excellent passive tracking of the instruments and EMB provides significantly superior sampling accuracy compared to fluoroscopy-guided biopsies. Nonetheless, further improvements of MR-compatible bioptomes and guiding catheters are essential before applying this method in a clinical setting.

Peak flow velocities in the ascending aorta-real-time phase-contrast magnetic resonance imaging vs. cine magnetic resonance imaging and echocardiography

This prospective study of eight healthy volunteers evaluates peak flow velocities (PFV) in the ascending aorta using real-time phase-contrast magnetic resonance imaging (MRI) in comparison to cine phase-contrast MRI and echocardiography. Flow measurements by echocardiography and cine phase-contrast MRI with breath-holding were performed according to clinical standards. Real-time phase-contrast MRI at 40 ms temporal resolution and 1.3 mm in-plane resolution was based on highly undersampled radial fast low-angle shot (FLASH) sequences with image reconstruction by regularized nonlinear inversion (NLINV). Evaluations focused on the determination of PFV. Linear regressions and Bland-Altman plots were used for comparisons of methods. When averaged across subjects, real-time phase-contrast MRI resulted in PFV of 120±20 cm s(-1) (mean ± SD) in comparison to 122±16 cm s(-1) for cine MRI and 124±20 cm s(-1) for echocardiography. The maximum deviations between real-time phase-contrast MRI and echocardiography ranged from -20 to +14 cm s(-1) (cine MRI: -10 to +12 cm s(-1)). Thus, in general, real-time phase-contrast MRI of cardiac outflow revealed quantitative agreement with cine MRI and echocardiography. The advantages of real-time MRI are measurements during free breathing and access to individual cardiac cycles.

Non-invasive estimation of pulmonary outflow tract obstruction: A comparative study of cardiovascular phase contrast magnetic resonance and Doppler echocardiography versus cardiac catheterization

AIM

To compare estimated pressure gradients from routine follow-up cardiovascular phase-contrast magnetic resonance (PC-MR) with those from Doppler echocardiography and invasive catheterization in patients with congenital heart disease (CHD) and pulmonary outflow tract obstruction.

METHODS

In 75 patients with pulmonary outflow tract obstruction maximal and mean PC-MR gradients were compared to maximal and mean Doppler gradients. Additionally, in a subgroup of 31 patients maximal and mean PC-MR and Doppler pressure gradients were compared to catheter peak-to-peak pressure gradients (PPG).

RESULTS

Maximal and mean PC-MR gradients underestimated pulmonary outflow tract obstruction as compared to Doppler (max gradient: bias = + 8.4 mm Hg (+ 47.6%), r = 0.89, p < 0.001; mean gradient: + 4.3 mm Hg (+ 49.0%), r = 0.88, p < 0.001). However, in comparison to catheter PPG, maximal PC-MR gradients (bias = + 1.8 mm Hg (+ 8.8%), r = 0.90, p = 0.14) and mean Doppler gradients (bias = - 2.3 mm Hg (- 11.2%), r = 0.87, p = 0.17) revealed best agreement. Mean PC-MR gradients underestimated (bias = - 7.7 mm Hg (- 55.6%), r = 0.90, p < 0.001) while maximal Doppler gradients systematically overestimated catheter PPG (bias = + 13.9 mm Hg (+ 56.5%), r = 0.88, p < 0.001).

CONCLUSIONS

Estimated maximal PC-MR pressure gradients from routine CHD follow-up agree well with invasively assessed peak-to-peak pressure gradients. Estimated maximal Doppler pressure gradients tend to overestimate, while Doppler mean gradients agree better with catheter PPG. Therefore, our data provide reasonable arguments to either apply maximal PC-MR gradients or mean Doppler gradients to non-invasively evaluate the severity of pulmonary outflow tract obstruction in the follow-up of CHD.

Cardiovascular magnetic resonance feature-tracking assessment of myocardial mechanics: Intervendor agreement and considerations regarding reproducibility

Aim

To assess intervendor agreement of cardiovascular magnetic resonance feature tracking (CMR-FT) and to study the impact of repeated measures on reproducibility.

Materials and methods

Ten healthy volunteers underwent cine imaging in short-axis orientation at rest and with dobutamine stimulation (10 and 20 μg/kg/min). All images were analysed three times using two types of software (TomTec, Unterschleissheim, Germany and Circle, cvi⁴², Calgary, Canada) to assess global left ventricular circumferential (Ecc) and radial (Err) strains and torsion. Differences in intra- and interobserver variability within and between software types were assessed based on single and averaged measurements (two and three repetitions with subsequent averaging of results, respectively) as determined by Bland–Altman analysis, intraclass correlation coefficients (ICC), and coefficient of variation (CoV).

Results

Myocardial strains and torsion significantly increased on dobutamine stimulation with both types of software (p<0.05). Resting Ecc and torsion as well as Ecc values during dobutamine stimulation were lower measured with Circle (p<0.05). Intra- and interobserver variability between software types was lowest for Ecc (ICC 0.81 [0.63–0.91], 0.87 [0.72–0.94] and CoV 12.47% and 14.3%, respectively) irrespective of the number of analysis repetitions. Err and torsion showed higher variability that markedly improved for torsion with repeated analyses and to a lesser extent for Err. On an intravendor level TomTec showed better reproducibility for Ecc and torsion and Circle for Err.

Conclusions

CMR-FT strain and torsion measurements are subject to considerable intervendor variability, which can be reduced using three analysis repetitions. For both vendors, Ecc qualifies as the most robust parameter with the best agreement, albeit lower Ecc values obtained using Circle, and warrants further investigation of incremental clinical merit.

•

This is the first comparison of two types of CMR-FT software resulting in clinically valuable inter-vendor agreement data.

•

Assessment of myocardial strain and torsion is feasible with both types of software at rest and with dobutamine stimulation.

•

For both vendors, Ecc qualifies as the most robust parameter with the lowest variability.

BNP and haematological parameters are markers of severity of Ebstein's anomaly: correlation with CMR and cardiopulmonary exercise testing

AIMS

Ebstein's anomaly (EA) involves a displaced and dysplastic tricuspid valve resulting in an atrialized portion of the right ventricle and an enlargement of the functional right ventricle and right atrium. Biomarkers targeting heart failure such as brain natriuretic peptide (BNP) or haematological parameters [haemoglobin (Hb) and haematocrit (Hct)] are upregulated in states of pulmonary hypoperfusion. We hypothesized that decreased pulmonary perfusion dependent on the stage of right heart failure is a possible mechanism in EA, and that it can be correlated with cardiac magnetic resonance (CMR) parameters. The aim of this study was to investigate the relationship between BNP and haematological parameters with functional parameters from CMR and exercise testing in patients with EA.

METHODS AND RESULTS

Twenty-five patients with non-corrected EA were studied prospectively (mean age 26 ± 14 years). BNP level was increased (74 ± 127 ng/L), and in 16% markedly above the heart failure cut-off level of 100 ng/L. Hb and Hct were increased above normal levels in 20 and 24% of patients, respectively. BNP and Hct/Hb correlated with CMR [total right/left (R/L)-Volume-Index, right atrium-end-diastolic volume index (EDVi), functional right ventricle (fRV)-EDVi, fRV-ejection fraction (EF), tricuspid regurgitation, pulmonary artery flow, and left ventricular EF] and exercise testing [workload/kg, oxygen uptake (VO2), ventilatory response to carbon dioxide production (VE/VCO2), oxygen (O2) pulse, and heart rate reserve]. The higher BNP and haematological parameters, the higher was the disease severity and the more limited was the physical exercise capacity.

CONCLUSION

In this EA cohort, BNP levels and haematological parameters correlated well with functional data from CMR and exercise testing. The total R/L-Volume-Index and BNP, and to some extent hematological parameters, may be useful as prognostic markers in patients with EA.

Real-time magnetic resonance imaging of cardiac function and flow-recent progress

Cardiac structure, function and flow are most commonly studied by ultrasound, X-ray and magnetic resonance imaging (MRI) techniques. However, cardiovascular MRI is hitherto limited to electrocardiogram (ECG)-synchronized acquisitions and therefore often results in compromised quality for patients with arrhythmias or inabilities to comply with requested protocols-especially with breath-holding. Recent advances in the development of novel real-time MRI techniques now offer dynamic imaging of the heart and major vessels with high spatial and temporal resolution, so that examinations may be performed without the need for ECG synchronization and during free breathing. This article provides an overview of technical achievements, physiological validations, preliminary patient studies and translational aspects for a future clinical scenario of cardiovascular MRI in real time.

Situs inversus totalis with congenitally corrected transposition of the great arteries: insights from cardiac MRI

INTRODUCTION

Situs inversus totalis with congenitally corrected transposition of the great arteries represents a relatively rare congenital condition.

CASE DESCRIPTION

The current report describes the case of a 56 year old patient with an atrio-ventricular and ventricular-arterial discordance of the heart chambers without surgical correction, incidentally detected during hepatocellular carcinoma evaluation. The systemic venous blood arrived via the right atrium and a mitral valve in the morphologically left but pulmonary arterial ventricle that gave rise to a pulmonary trunk. The pulmonary venous blood passed the left atrium and the tricuspid valve into a morphologically right but systemic ventricle that gave rise to the aorta.

DISCUSSION AND EVALUATION

The switched anatomy was incidentally detected on echocardiography. The patient was referred to cardiac magnetic resonance imaging (CMR) including flow measurements, volumetry and late enhancement. CMR results showed a mildly impaired function and the switched anatomy. During a follow-up period of 2 years the patient was suffering from only mild heart failure and dyspnea.

CONCLUSIONS

Heart failure symptoms and arrhythmias can appear with increasing age in patients with congenitally corrected transposition. Early CMR allows accurate diagnosis and timely introduction of adequate therapy thereby avoiding disease progression.

Quantification of left ventricular torsion and diastolic recoil using cardiovascular magnetic resonance myocardial feature tracking

OBJECTIVES

Cardiovascular magnetic resonance feature tracking (CMR-FT) offers quantification of myocardial deformation from routine cine images. However, data using CMR-FT to quantify left ventricular (LV) torsion and diastolic recoil are not yet available. We therefore sought to evaluate the feasibility and reproducibility of CMR-FT to quantify LV torsion and peak recoil rate using an optimal anatomical approach.

METHODS

Short-axis cine stacks were acquired at rest and during dobutamine stimulation (10 and 20 µg · kg(-1) · min(-1)) in 10 healthy volunteers. Rotational displacement was analysed for all slices. A complete 3D-LV rotational model was developed using linear interpolation between adjacent slices. Torsion was defined as the difference between apical and basal rotation, divided by slice distance. Depending on the distance between the most apical (defined as 0% LV distance) and basal (defined as 100% LV distance) slices, four different models for the calculation of torsion were examined: Model-1 (25-75%), Model-2 (0-100%), Model-3 (25-100%) and Model-4 (0-75%). Analysis included subendocardial, subepicardial and global torsion and recoil rate (mean of subendocardial and subepicardial values).

RESULTS

Quantification of torsion and recoil rate was feasible in all subjects. There was no significant difference between the different models at rest. However, only Model-1 (25-75%) discriminated between rest and stress (Global Torsion: 2.7 ± 1.5° cm(-1), 3.6 ± 2.0° cm(-1), 5.1 ± 2.2° cm(-1), p<0.01; Global Recoil Rate: -30.1 ± 11.1° cm(-1) s(-1),-46.9 ± 15.0° cm(-1) s(-1),-68.9 ± 32.3° cm(-1) s(-1), p<0.01; for rest, 10 and 20 µg · kg(-)1 · min(-1) of dobutamine, respectively). Reproducibility was sufficient for all parameters as determined by Bland-Altman analysis, intraclass correlation coefficients and coefficient of variation.

CONCLUSIONS

CMR-FT based derivation of myocardial torsion and recoil rate is feasible and reproducible at rest and with dobutamine stress. Using an optimal anatomical approach measuring rotation at 25% and 75% apical and basal LV locations allows effective quantification of torsion and recoil dynamics. Application of these new measures of deformation by CMR-FT should next be explored in disease states.

Giant bypass aneurysm, a cause of suspected cardiac mass

Introduction

A 66-years old man suffering from coronary artery disease appeared without symptoms for routine follow-up in our clinic.

Case description

The echocardiogram revealed a tumorous mass of the right atrium and right ventricle. In the past, coronary revascularization with venous grafts of the right coronary artery and circumflex artery as well as internal mammaria graft to the left anterior descending artery was performed 20 years before. The general clinicians presented the case to the surgeons and it was decided to perform cardiac MRI as a preoperative diagnostic modality.

Discussion and evaluation

Following cardiac magnetic resonance imaging (MRI) showed a mass in the pericardium in the right atrioventricular groove with thrombotic material. Due to the MRI the patient underwent coronary angiography to confirm an aneurysm.

Conclusions

The learning points from this case are that cardiac MRI is a very useful tool for further evaluation of suspected cardiac masses and should be performed for further characterization.

Persistent left superior vena cava detected after central venous catheter insertion

Introduction

Persistent left superior vena cava is a rare case with an appearance of 0.3% to 0.5% of individuals in general population. Indication for jugular venous intervention could be different, such as implantable venous catheters for oncological therapy. The present report describes a case of a patient with a persistent left superior vena cava detected after central venous catheter (CVC) installation using computer-assisted tomography (CT).

Case description

In a control chest X-ray the CVC was not in the right superior vena cava as expected to be. A following blood gas analysis revealed venous concentration. The consultation of additional CT diagnostics yielded a persistent left superior vena cava with an outlet to dilated coronary sinus.

Discussion and evaluation

The patient was followed over 1 year with the underlying disease of chronic obstructive pulmonary disease. Cardiac insufficiency, sinus aneurysm and arryhtmias could appear with growing age in patients with persistence left superior vena cava, but most of them are asymptomatic. Knowing the venous anatomy is important for correct position and function of e.g. totally implantable venous catheters, central lines or pacemakers.

Conclusion

The importance of early imaging diagnosis of this anatomical variation could optimize adequate therapy and finally improve living conditions. CT can help adapting correct therapy with correct diagnostics.

Quantification of left atrial strain and strain rate using Cardiovascular Magnetic Resonance myocardial feature tracking: a feasibility study

BACKGROUND

Cardiovascular Magnetic Resonance myocardial feature tracking (CMR-FT) is a quantitative technique tracking tissue voxel motion on standard steady-state free precession (SSFP) cine images to assess ventricular myocardial deformation. The importance of left atrial (LA) deformation assessment is increasingly recognized and can be assessed with echocardiographic speckle tracking. However atrial deformation quantification has never previously been demonstrated with CMR. We sought to determine the feasibility and reproducibility of CMR-FT for quantitative derivation of LA strain and strain rate (SR) myocardial mechanics.

METHODS

10 healthy volunteers, 10 patients with hypertrophic cardiomyopathy (HCM) and 10 patients with heart failure and preserved ejection fraction (HFpEF) were studied at 1.5 Tesla. LA longitudinal strain and SR parameters were derived from SSFP cine images using dedicated CMR-FT software (2D CPA MR, TomTec, Germany). LA performance was analyzed using 4- and 2-chamber views including LA reservoir function (total strain [εs], peak positive SR [SRs]), LA conduit function (passive strain [εe], peak early negative SR [SRe]) and LA booster pump function (active strain [εa], late peak negative SR [SRa]).

RESULTS

In all subjects LA strain and SR parameters could be derived from SSFP images. There was impaired LA reservoir function in HCM and HFpEF (εs [%]: HCM 22.1 ± 5.5, HFpEF 16.3 ± 5.8, Controls 29.1 ± 5.3, p < 0.01; SRs [s⁻¹]: HCM 0.9 ± 0.2, HFpEF 0.8 ± 0.3, Controls 1.1 ± 0.2, p < 0.05) and impaired LA conduit function as compared to healthy controls (εe [%]: HCM 10.4 ± 3.9, HFpEF 11.9 ± 4.0, Controls 21.3 ± 5.1, p < 0.001; SRe [s]⁻¹: HCM -0.5 ± 0.2, HFpEF -0.6 ± 0.1, Controls -1.0 ± 0.3, p < 0.01). LA booster pump function was increased in HCM while decreased in HFpEF (εa [%]: HCM 11.7 ± 4.0, HFpEF 4.5 ± 2.9, Controls 7.8 ± 2.5, p < 0.01; SRa [s⁻¹]: HCM -1.2 ± 0.4, HFpEF -0.5 ± 0.2, Controls -0.9 ± 0.3, p < 0.01). Observer variability was excellent for all strain and SR parameters on an intra- and inter-observer level as determined by Bland-Altman, coefficient of variation and intraclass correlation coefficient analyses.

CONCLUSIONS

CMR-FT based atrial performance analysis reliably quantifies LA longitudinal strain and SR from standard SSFP cine images and discriminates between patients with impaired left ventricular relaxation and healthy controls. CMR-FT derived atrial deformation quantification seems a promising novel approach for the study of atrial performance and physiology in health and disease states.

Real-time phase-contrast flow MRI of the ascending aorta and superior vena cava as a function of intrathoracic pressure (Valsalva manoeuvre)

OBJECTIVE

Real-time phase-contrast flow MRI at high spatiotemporal resolution was applied to simultaneously evaluate haemodynamic functions in the ascending aorta (AA) and superior vena cava (SVC) during elevated intrathoracic pressure (Valsalva manoeuvre).

METHODS

Real-time phase-contrast flow MRI at 3 T was based on highly undersampled radial gradient-echo acquisitions and phase-sensitive image reconstructions by regularized non-linear inversion. Dynamic alterations of flow parameters were obtained for 19 subjects at 40-ms temporal resolution, 1.33-mm in-plane resolution and 6-mm section thickness. Real-time measurements were performed during normal breathing (10 s), increased intrathoracic pressure (10 s) and recovery (20 s).

RESULTS

Real-time measurements were technically successful in all volunteers. During the Valsalva manoeuvre (late strain) and relative to values during normal breathing, the mean peak flow velocity and flow volume decreased significantly in both vessels (p < 0.001) followed by a return to normal parameters within the first 10 s of recovery in the AA. By contrast, flow in the SVC presented with a brief (1-2 heartbeats) but strong overshoot of both the peak velocity and blood volume immediately after pressure release followed by rapid normalization.

CONCLUSION

Real-time phase-contrast flow MRI may assess cardiac haemodynamics non-invasively, in multiple vessels, across the entire luminal area and at high temporal and spatial resolution.

ADVANCES IN KNOWLEDGE

Future clinical applications of this technique promise new insights into haemodynamic alterations associated with pre-clinical congestive heart failure or diastolic dysfunction, especially in cases where echocardiography is technically compromised.

Real-time phase-contrast flow MRI of haemodynamic changes in the ascending aorta and superior vena cava during Mueller manoeuvre

AIM

To evaluate the potential of real-time phase-contrast flow magnetic resonance imaging (MRI) at 40 ms resolution for the simultaneous determination of blood flow in the ascending aorta (AA) and superior vena cava (SVC) in response to reduced intrathoracic pressure (Mueller manoeuvre).

MATERIALS AND METHODS

Through-plane flow was assessed in 20 healthy young subjects using real-time phase-contrast MRI based on highly undersampled radial fast low-angle shot (FLASH) with image reconstruction by regularized non-linear inversion. Haemodynamic alterations (three repetitions per subject = 60 events) were evaluated during normal breathing (10 s), inhalation with nearly closed epiglottis (10 s), and recovery (20 s).

RESULTS

Relative to normal breathing and despite interindividual differences, reduced intrathoracic pressure by at least 30 mmHg significantly decreased the initial peak mean velocity (averaged across the lumen) in the AA by -24 ± 9% and increased the velocity in the SVC by +28 ± 25% (p < 0.0001, n = 23 successful events). Respective changes in flow volume per heartbeat were -25 ± 9% in the AA and +49 ± 44% in the SVC (p < 0.0001, n = 23). Flow parameters returned to baseline during sustained pressure reduction, while the heart rate was elevated by 10% (p < 0.0001) after the start (n = 24) and end (n = 17) of the manoeuvre.

CONCLUSIONS

Real-time flow MRI during low intrathoracic pressure non-invasively revealed quantitative haemodynamic adjustments in both the AA and SVC.

Current role of cardiac and extra-cardiac pathologies in clinically indicated cardiac computed tomography with emphasis on status before pulmonary vein isolation

PURPOSE

The aim of this study was to assess the incidence of cardiac and significant extra-cardiac findings in clinical computed tomography of the heart in patients with atrial fibrillation before pulmonary vein isolation (PVI).

MATERIALS AND METHODS

224 patients (64 ± 10 years; male 63 %) with atrial fibrillation were examined by cardiac 64-slice multidetector CT before PVI. Extra-cardiac findings were classified as "significant" if they were recommended to additional diagnostics or therapy, and otherwise as "non-significant". Additionally, cardiac findings were documented in detail.

RESULTS

A total of 724 cardiac findings were identified in 203 patients (91 % of patients). Additionally, a total of 619 extra-cardiac findings were identified in 179 patients (80 % of patients). Among these extra-cardiac findings 196 (32 %) were "significant", and 423 (68 %) were "non-significant". In 2 patients (1 %) a previously unknown malignancy was detected (esophageal cancer and lung cancer, local stage, no metastasis). 203 additional imaging diagnostics followed to clarify the "significant" findings (124 additional CT, costs 38 314.69 US dollars). Overall, there were 3.2 cardiac and 2.8 extra-cardiac findings per patient. Extra-cardiac findings appear significantly more frequently in patients over 60 years old, in smokers and in patients with a history of cardiac findings (p <0.05).

CONCLUSION

Cardiac CT scans before PVI should be screened for extracardiac incidental findings that could have important clinical implications for each patient.

Real-time cardiovascular magnetic resonance at 1.5 T using balanced SSFP and 40 ms resolution

BACKGROUND

While cardiovascular magnetic resonance (CMR) commonly employs ECG-synchronized cine acquisitions with balanced steady-state free precession (SSFP) contrast at 1.5 T, recent developments at 3 T demonstrate significant potential for T1-weighted real-time imaging at high spatiotemporal resolution using undersampled radial FLASH. The purpose of this work was to combine both ideas and to evaluate a corresponding real-time CMR method at 1.5 T with SSFP contrast.

METHODS

Radial gradient-echo sequences with fully balanced gradients and at least 15-fold undersampling were implemented on two CMR systems with different gradient performance. Image reconstruction by regularized nonlinear inversion (NLINV) was performed offline and resulted in real-time SSFP CMR images at a nominal resolution of 1.8 mm and with acquisition times of 40 ms.

RESULTS

Studies of healthy subjects demonstrated technical feasibility in terms of robustness and general image quality. Clinical applicability with access to quantitative evaluations (e.g., ejection fraction) was confirmed by preliminary applications to 27 patients with typical indications for CMR including arrhythmias and abnormal wall motion. Real-time image quality was slightly lower than for cine SSFP recordings, but considered diagnostic in all cases.

CONCLUSIONS

Extending conventional cine approaches, real-time radial SSFP CMR with NLINV reconstruction provides access to individual cardiac cycles and allows for studies of patients with irregular heartbeat.