Real-time Cardiovascular Magnetic Resonance Research Articles

Radiofrequency ablation guided by real-time cardiovascular magnetic resonance.

Cardiovascular magnetic resonance (CMR) is gaining ground in guiding electrophysiology (EP)-based ablation procedures of typical atrial flutter and atrial fibrillation, allowing for the avoidance of radiation exposure for patients and operators and reducing the risk of occupational illnesses. CMR allows comprehensive assessment of cardiac anatomy and provides tissue characterization by identifying pathological substrates, such as myocardial scars and edema, identified with the implementation of late gadolinium enhancement and T2-weighted short-tau inversion recovery sequences. Intraprocedural imaging is useful for real-time catheter tracking during the ablation procedure while simultaneously providing visualization of cardiac anatomy. Additionally, CMR facilitates the evaluation of the ablation procedure accuracy by acquiring edema-sensitive sequences, thereby aiding in preventing early complications. This report serves as a primer for radiologists and illustrates the value of CMR in planning and performing the ablation procedure, as well as its role in post-procedural imaging.

Assessment of the cardiac output at rest and during exercise stress using real-time cardiovascular magnetic resonance imaging in HFpEF-patients

This methodological study aimed to validate the cardiac output (CO) measured by exercise-stress real-time phase-contrast cardiovascular magnetic resonance imaging (CMR) in patients with heart failure and preserved ejection fraction (HFpEF). 68 patients with dyspnea on exertion (NYHA ≥ II) and echocardiographic signs of diastolic dysfunction underwent rest and exercise stress right heart catheterization (RHC) and CMR within 24 h. Patients were diagnosed as overt HFpEF (pulmonary capillary wedge pressure (PCWP) ≥ 15mmHg at rest), masked HFpEF (PCWP ≥ 25mmHg during exercise stress but < 15mmHg at rest) and non-cardiac dyspnea. CO was calculated using RHC as the reference standard, and in CMR by the volumetric stroke volume, conventional phase-contrast and rest and stress real-time phase-contrast imaging. At rest, the CMR based CO showed good agreement with RHC with an ICC of 0.772 for conventional phase-contrast, and 0.872 for real-time phase-contrast measurements. During exercise stress, the agreement of real-time CMR and RHC was good with an ICC of 0.805. Real-time measurements underestimated the CO at rest (Bias:0.71 L/min) and during exercise stress (Bias:1.4 L/min). Patients with overt HFpEF had a significantly lower cardiac index compared to patients with masked HFpEF and with non-cardiac dyspnea during exercise stress, but not at rest. Real-time phase-contrast CO can be assessed with good agreement with the invasive reference standard at rest and during exercise stress. While moderate underestimation of the CO needs to be considered with non-invasive testing, the CO using real-time CMR provides useful clinical information and could help to avoid unnecessary invasive procedures in HFpEF patients.

Non-invasive pressure-volume loops using the elastance model and CMR: a porcine validation at transient pre-loads.

Pressure-volume (PV) loops have utility in the evaluation of cardiac pathophysiology but require invasive measurements. Recently, a time-varying elastance model to derive PV loops non-invasively was proposed, using left ventricular (LV) volume by cardiovascular magnetic resonance (CMR) and brachial cuff pressure as inputs. Validation was performed using CMR and pressure measurements acquired on the same day, but not simultaneously, and without varying pre-loads. This study validates the non-invasive elastance model used to estimate PV loops at varying pre-loads, compared with simultaneous measurements of invasive pressure and volume from real-time CMR, acquired concurrent to an inferior vena cava (IVC) occlusion. We performed dynamic PV loop experiments under CMR guidance in 15 pigs (n = 7 naïve, n = 8 with ischaemic cardiomyopathy). Pre-load was altered by IVC occlusion, while simultaneously acquiring invasive LV pressures and volumes from real-time CMR. Pairing pressure and volume signals yielded invasive PV loops, and model-based PV loops were derived using real-time LV volumes. Haemodynamic parameters derived from invasive and model-based PV loops were compared. Across 15 pigs, 297 PV loops were recorded. Intra-class correlation coefficient (ICC) agreement was excellent between model-based and invasive parameters: stroke work (bias = 0.007 ± 0.03 J, ICC = 0.98), potential energy (bias = 0.02 ± 0.03 J, ICC = 0.99), ventricular energy efficiency (bias = -0.7 ± 2.7%, ICC = 0.98), contractility (bias = 0.04 ± 0.1 mmHg/mL, ICC = 0.97), and ventriculoarterial coupling (bias = 0.07 ± 0.15, ICC = 0.99). All haemodynamic parameters differed between naïve and cardiomyopathy animals (P < 0.05). The invasive vs. model-based PV loop dice similarity coefficient was 0.88 ± 0.04. An elastance model-based estimation of PV loops and associated haemodynamic parameters provided accurate measurements at transient loading conditions compared with invasive PV loops.

Real-time cardiovascular magnetic resonance imaging for non-invasive characterisation of heart failure with preserved ejection fraction: final outcomes of the HFpEF stress trial

BackgroundThe diagnosis of heart failure with preserved ejection fraction (HFpEF) remains challenging. Recently, the HFpEF Stress Trial demonstrated feasibility and accuracy of non-invasive cardiovascular magnetic resonance (CMR) real-time (RT) exercise-stress atrial function imaging for early identification of HFpEF. However, no outcome data have yet been presented.MethodsThe HFpEF Stress Trial (DZHK-17) prospectively recruited 75 patients with dyspnea on exertion and echocardiographic preserved EF and signs of diastolic dysfunction (E/eʹ > 8). 68 patients entered the final study cohort and were characterized as HFpEF (n = 34) or non-cardiac dyspnea (n = 34) according to pulmonary capillary wedge pressure (HFpEF: PCWP rest: ≥ 15 mmHg stress: ≥ 25 mmHg). These patients were contacted by telephone and hospital charts were reviewed. The clinical endpoint was cardiovascular events (CVE).ResultsFollow-up was performed after 48 months; 1 patient was lost to follow-up. HFpEF patients were more frequently compared to non-cardiac dyspnea (15 vs. 8, p = 0.059). Hospitalised patients during follow-up had higher H2FPEF scores (5 vs. 3, p < 0.001), and impaired left atrial (LA) function at rest (p ≤ 0.002) and stress (p ≤ 0.006). Impairment of CMR-derived atrial function parameters at rest and during exercise-stress (p ≤ 0.003) was associated with increased likelihood for CVE. CMR-Feature Tracking LA Es/Ee (p = 0.016/0.017) and RT-CMR derived LA long axis strain (p = 0.003) were predictors of CVE independent of the presence of atrial fibrillation.ConclusionsLeft atrial function emerged as the strongest predictor for 4-year outcome in the HFpEF Stress Trial. A combination of rest and exercise-stress LA function quantification allows accurate diagnostic and prognostic stratification in HFpEF.Clinicaltrials.gov: NCT03260621.Graphical abstract

Kiosk 4R-TA-06 - Assessment of the Cardiac Output at Rest and During Exercise Stress Using Real-time Cardiovascular Magnetic Resonance Imaging in Hfpef-patients

Kiosk 4R-TA-06 - Assessment of the Cardiac Output at Rest and During Exercise Stress Using Real-time Cardiovascular Magnetic Resonance Imaging in Hfpef-patients

Dynamic pressure–volume loop analysis by simultaneous real-time cardiovascular magnetic resonance and left heart catheterization

BackgroundLeft ventricular (LV) contractility and compliance are derived from pressure–volume (PV) loops during dynamic preload reduction, but reliable simultaneous measurements of pressure and volume are challenging with current technologies. We have developed a method to quantify contractility and compliance from PV loops during a dynamic preload reduction using simultaneous measurements of volume from real-time cardiovascular magnetic resonance (CMR) and invasive LV pressures with CMR-specific signal conditioning. MethodsDynamic PV loops were derived in 16 swine (n = 7 naïve, n = 6 with aortic banding to increase afterload, n = 3 with ischemic cardiomyopathy) while occluding the inferior vena cava (IVC). Occlusion was performed simultaneously with the acquisition of dynamic LV volume from long-axis real-time CMR at 0.55 T, and recordings of invasive LV and aortic pressures, electrocardiogram, and CMR gradient waveforms. PV loops were derived by synchronizing pressure and volume measurements. Linear regression of end-systolic- and end-diastolic- pressure–volume relationships enabled calculation of contractility. PV loops measurements in the CMR environment were compared to conductance PV loop catheter measurements in 5 animals. Long-axis 2D LV volumes were validated with short-axis-stack images. ResultsSimultaneous PV acquisition during IVC-occlusion was feasible. The cardiomyopathy model measured lower contractility (0.2 ± 0.1 mmHg/ml vs 0.6 ± 0.2 mmHg/ml) and increased compliance (12.0 ± 2.1 ml/mmHg vs 4.9 ± 1.1 ml/mmHg) compared to naïve animals. The pressure gradient across the aortic band was not clinically significant (10 ± 6 mmHg). Correspondingly, no differences were found between the naïve and banded pigs. Long-axis and short-axis LV volumes agreed well (difference 8.2 ± 14.5 ml at end-diastole, -2.8 ± 6.5 ml at end-systole). Agreement in contractility and compliance derived from conductance PV loop catheters and in the CMR environment was modest (intraclass correlation coefficient 0.56 and 0.44, respectively). ConclusionsDynamic PV loops during a real-time CMR-guided preload reduction can be used to derive quantitative metrics of contractility and compliance, and provided more reliable volumetric measurements than conductance PV loop catheters.

A deep learning approach to real-time volumetric measurements without image reconstruction for cardiovascular magnetic resonance

Objective. Cardiovascular magnetic resonance (CMR) can measure ventricular volumes for the quantitative assessment of cardiac function in clinical cardiology. Conventionally, CMR volumetric measurements require image reconstruction and segmentation. There are limited clinical applications of real-time CMR for volumetric measurements because real-time images cannot provide sufficient quality for accurate segmentation. The presented work aims to develop a new deep learning approach to measuring ventricular volumes without image reconstruction and demonstrate that this ‘imageless’ approach would improve volumetric measurements with real-time CMR. Approach. We have developed a deep learning model for measuring ventricular volumes directly from real-time CMR raw data without image reconstruction. This novel ‘imageless’ deep learning model, not being as sensitive to image quality, provided reliable volumetric measurements for real-time CMR. To demonstrate ‘imageless’ volumetric measurements, we conducted a real-time CMR study with healthy volunteers. Several performance metrics, including mean absolute error (MAE), the Pearson correlation coefficient, and Bland–Altman analysis, were used to evaluate the proposed ‘imageless’ deep learning model in reference to U-net and fully convolutional neural network (FCNN) models based on conventional image reconstruction and segmentation. Main results. With the same raw data, the ‘imageless’ deep learning model gave a lower MAE (‘imageless’ ≤9.6 ml; ‘image-based’ ≥12.1 ml), a higher correlation coefficient (‘imageless’ ≥0.75; ‘image-based’ ≤0.51) and smaller measurement difference ranges in Bland–Altman analysis (‘imageless’ ≤23.1 ml; ‘image-based’ ≥33.8 ml). To achieve comparable performance, the ‘imageless’ deep learning model needed 2/3 of the raw data used in image reconstruction for U-net and FCNN models, indicating there was a gain in imaging acceleration for real-time CMR. Significance. We have demonstrated a novel deep learning framework that can provide reliable volumetric measurements from real-time CMR raw data without image reconstruction. This ‘imageless’ approach to real-time volumetric measurements will improve the quantitative assessment of cardiac function in clinical cardiology.

Validation and quantification of left ventricular function during exercise and free breathing from real-time cardiac magnetic resonance images

Exercise cardiovascular magnetic resonance (CMR) can unmask cardiac pathology not evident at rest. Real-time CMR in free breathing can be used, but respiratory motion may compromise quantification of left ventricular (LV) function. We aimed to develop and validate a post-processing algorithm that semi-automatically sorts real-time CMR images according to breathing to facilitate quantification of LV function in free breathing exercise. A semi-automatic algorithm utilizing manifold learning (Laplacian Eigenmaps) was developed for respiratory sorting. Feasibility was tested in eight healthy volunteers and eight patients who underwent ECG-gated and real-time CMR at rest. Additionally, volunteers performed exercise CMR at 60% of maximum heart rate. The algorithm was validated for exercise by comparing LV mass during exercise to rest. Respiratory sorting to end expiration and end inspiration (processing time 20 to 40 min) succeeded in all research participants. Bias ± SD for LV mass was 0 ± 5 g when comparing real-time CMR at rest, and 0 ± 7 g when comparing real-time CMR during exercise to ECG-gated at rest. This study presents a semi-automatic algorithm to retrospectively perform respiratory sorting in free breathing real-time CMR. This can facilitate implementation of exercise CMR with non-ECG-gated free breathing real-time imaging, without any additional physiological input.

Cardiovascular Magnetic Resonance-Guided Radiofrequency Ablation: Where Are We Now?

The possibilities of cardiovascular magnetic resonance (CMR) imaging for myocardial tissue characterization and catheter ablation guidance are accompanied by some fictional concepts. In this review, we present the available facts about CMR-guided catheter ablation procedures as well as promising, however unproven, theoretical concepts. CMR promises to visualize the respective arrhythmogenic substrate and may thereby make it more localizable for electrophysiology (EP)-based ablation. Robust CMR imaging is challenged by motion of the heart resulting from cardiac and respiratory cycles. In contrast to conventional "passive" tracking of the catheter tip by real-time CMR, novel approaches based on "active" tracking are performed by integrating microcoils into the catheter tip that send a receiver signal. Several experimental and clinical studies were already performed based on real-time CMR for catheter ablation of atrial and ventricular arrhythmias. Importantly, successful ablation of the cavotricuspid isthmus was already performed in patients with typical atrial flutter. However, a complete EP procedure with real-time CMR-guided transseptal puncture and subsequent pulmonary vein isolation has not been shown so far in patients with atrial fibrillation. Moreover, real-time CMR-guided EP for ventricular tachycardia ablation was only performed in animal models using a transseptal, retrograde, or epicardial access-but not in humans. Essential improvements within the next few years regarding basic technical requirements, such as higher spatial and temporal resolution of real-time CMR imaging as well as clinically approved cardiac magnetic resonance-conditional defibrillators, are ultimately required-but can also be expected-and will move this field forward.

Real-time CMR guidance for intracardiac and great vessel pressure mapping in patients with congenital heart disease using an MR conditional guidewire-results of 25 patients.

The aim of this study was to test a CE-certified MR-conditional guidewire to facilitate blood pressure measurement in cardiovascular magnetic resonance (CMR) using fluid-filled catheters in patients with congenital heart disease (CHD). The main purpose was to determine procedural success in a post market clinical follow-up (PMCF) for routine procedure in a diagnostic and interventional workflow. Real-time CMR provides high quality imaging without the risk of exposing the patient to X-rays, especially for patients with irregular heart anatomy and patients who are susceptible to radiation and iodinated contrast media. To date, the assessment of blood pressure gradients is not a common feature of CMR, as these gradients cannot be accurately evaluated in routine CMR. Twenty-five CHD patients who were planned for combined clinical CMR and diagnostic and/or interventional catheterization were enrolled in the trial. Prior to inclusion, a specific procedure for catheterization in CMR was defined, encompassing the assessment of pressure and pressure gradients in the heart and great vessels. By the use of an MR-conditional guidewire we successfully measured specific pressure and pressure gradients in up to 92% of cases with liquid-filled catheters which were guided exclusively under CMR guidance. There were no guidewire-related adverse events, and guidewire guidance and manipulation of catheters were successful. Using a MR-conditional guidewire assists in easily reaching targets in the heart and great vessels and makes the catheter itself visible, so that invasive blood pressure assessment by CMR guidance with liquid-filled catheters can be improved. Cardiovascular magnetic resonance (CMR); congenital heart disease (CHD); cardiac catheterization; magnetic resonance; pressure; guidewire.

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

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. 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. 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). 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.

Rapid cardiovascular magnetic resonance protocol utilizing compressed sensing real-time imaging during the COVID-19 pandemic

Funding AcknowledgementsType of funding sources: None.BackgroundCoronavirus Disease 2019 (COVID-19) poses many workflow challenges for healthcare systems. Elective cardiovascular magnetic resonance (CMR) exams were postponed until safety protocols were instituted. Since reopening, imaging labs are managing COVID-19 safety triaging, exam backlog, and increased referrals, thus innovative solutions for process improvement are needed.PurposeAn accelerated compressed sensing (CS) real-time (RT) technique offers dynamic cardiac imaging with high spatial and temporal resolution without image degradation. We sought to evaluate the efficiency of a rapid RT CMR protocol with a goal to decrease scan time without compromising study quality and comprehensiveness.MethodsWe retrospectively evaluated 219 CMRs (Siemens Magnetom Sola 1.5T) performed 09/01/2020 - 10/15/2020. After excluding 81 exams due to heterogeneous protocols (Figure 1), we analyzed 138 CMR exams using standard cardiomyopathy or myocarditis protocols. CMR studies utilized either a rapid RT short axis (SAX) cine (spatial resolution of 2.5 mm2 or better and temporal resolution of 55 ms or better) or standard breath-held (BH) SAX cine protocol (Figure 2). Protocols were chosen by the interpreting physician. Previous internal quality control demonstrated similar volumetric quantification between RT and BH SAX cines. RT cines were reconstructed inline using a CS-based method. We analyzed the length of time needed to complete each protocol and the number of series performed. Statistical analysis included student t-test with p value <0.05 considered significant.ResultsOf 138 analyzed CMR exams, there were 23 rapid protocols and 115 standard protocols performed. The mean image acquisition time for the rapid protocol was significantly shorter at 26 ± 6 minutes (range 18-44 min) vs 33 ± 6 minutes (range 22-49 min) for the standard protocol, p < 0.001. This represents a mean relative reduction in scan time of 21%. More time was saved in rapid myocarditis (scan time 25 ± 6 min vs 34 ± 6 min, p = 0.01; relative time reduction 26%) vs rapid cardiomyopathy protocols (scan time 27 ± 6 min vs 31 ± 6 min, p = 0.04; relative time reduction 13%). There was no significant difference in the number of series performed (62 ± 14 series in rapid vs 67 ± 11 series in standard protocols, p = 0.09). T1 and T2 maps constituted the same percentage of acquired images regardless of protocol used (T1 maps 1.8% vs 1.7% for cardiomyopathy, 1.4% vs 1.4% for myocarditis in standard vs rapid protocols respectively; T2 maps 1.8% vs 1.7% for cardiomyopathy, 5.6% vs 5.8% for myocarditis in standard vs rapid protocols respectively).ConclusionsA rapid CMR protocol utilizing a CS-based RT imaging is significantly shorter as compared to the standard protocol with adequate diagnostic quality. Rapid CMR protocols are an effective tool for process improvement during the COVID-19 pandemic. Figure. Flow diagram of the analyzed studies. Figure. Rapid (top) and standard CMR (bottom).

Native contrast visualization and tissue characterization of myocardial radiofrequency ablation and acetic acid chemoablation lesions at 0.55\xa0T

PurposeLow-field (0.55 T) high-performance cardiovascular magnetic resonance (CMR) is an attractive platform for CMR-guided intervention as device heating is reduced around 7.5-fold compared to 1.5 T. This work determines the feasibility of visualizing cardiac radiofrequency (RF) ablation lesions at low field CMR and explores a novel alternative method for targeted tissue destruction: acetic acid chemoablation.MethodsN = 10 swine underwent X-ray fluoroscopy-guided RF ablation (6–7 lesions) and acetic acid chemoablation (2–3 lesions) of the left ventricle. Animals were imaged at 0.55 T with native contrast 3D-navigator gated T1-weighted T1w) CMR for lesion visualization, gated single-shot imaging to determine potential for real-time visualization of lesion formation, and T1 mapping to measure change in T1 in response to ablation. Seven animals were euthanized on ablation day and hearts imaged ex vivo. The remaining animals were imaged again in vivo at 21 days post ablation to observe lesion evolution.ResultsChemoablation lesions could be visualized and displayed much higher contrast than necrotic RF ablation lesions with T1w imaging. On the day of ablation, in vivo myocardial T1 dropped by 19 ± 7% in RF ablation lesion cores, and by 40 ± 7% in chemoablation lesion cores (p < 4e−5). In high resolution ex vivo imaging, with reduced partial volume effects, lesion core T1 dropped by 18 ± 3% and 42 ± 6% for RF and chemoablation, respectively. Mean, median, and peak lesion signal-to-noise ratio (SNR) were all at least 75% higher with chemoablation. Lesion core to myocardium contrast-to-noise (CNR) was 3.8 × higher for chemoablation. Correlation between in vivo and ex vivo CMR and histology indicated that the periphery of RF ablation lesions do not exhibit changes in T1 while the entire extent of chemoablation exhibits T1 changes. Correlation of T1w enhancing lesion volumes indicated in vivo estimates of lesion volume are accurate for chemoablation but underestimate extent of necrosis for RF ablation.ConclusionThe visualization of coagulation necrosis from cardiac ablation is feasible using low-field high-performance CMR. Chemoablation produced a more pronounced change in lesion T1 than RF ablation, increasing SNR and CNR and thereby making it easier to visualize in both 3D navigator-gated and real-time CMR and more suitable for low-field imaging.

Real-time cardiovascular magnetic resonance tissue characterisation in patients undergoing transcatheter aortic valve replacement

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): German Research Foundation (DFG, CRC 1002, D1) Background Myocardial fibrosis is a major determinant of outcome in aortic stenosis (AS). Novel fast real-time (RT) cardiac magnetic resonance (CMR) mapping techniques allow comprehensive quantification of fibrosis but have not yet been compared against standard techniques and histology. Methods Patients with severe AS underwent CMR before (n = 110) and left ventricular (LV) endomyocardial biopsy (n = 46) at transcatheter aortic valve replacement (TAVR). Midventricular short axis (SAX) native, post-contrast T1 and extracellular volume fraction (ECV) maps were generated using commercially available MOLLI (native: 5(3)3, post-contrast: 4(1)3(1)2) and RT single-shot inversion recovery fast low-angle shot (FLASH) with radial undersampling. Focal late gadolinium enhancement was excluded from T1 and ECV regions of interest. ECV and LV mass were used to calculate LV matrix volumes. Variability and agreements were assessed between RT, MOLLI and histology using intraclass correlation coefficients, coefficients of variation and Bland Altman analyses. Results RT and MOLLI derived ECV were similar for midventricular SAX slice coverage (26.2 vs. 26.5, p = 0.073) and septal region of interest (26.2 vs. 26.5, p = 0.216). MOLLI native T1 time was in median 20 ms longer compared to RT (p &amp;lt; 0.001). Agreement between RT and MOLLI was best for ECV (ICC &amp;gt;0.91), excellent for post-contrast T1 times (ICC &amp;gt;0.81) and good for native T1 times (ICC &amp;gt;0.62). Diffuse collagen volume fraction by biopsies was in median 7.8%. ECV (RT r = 0.345, p = 0.039; MOLLI r = 0.40, p = 0.010) and LV matrix volumes (RT r = 0.45, p = 0.005; MOLLI r = 0.43, p = 0.007) were the only parameters associated with histology. Conclusions RT mapping offers fast and sufficient ECV and LV matrix volume calculation in AS. ECV and LV matrix volume represent robust and universally comparable parameters with associations to histologically assessed fibrosis and may emerge as potential targets for clinical decision making.

Abstract 15545: Exercise-stress Real-time Cardiac Magnetic Resonance Imaging for Non-invasive Characterisation of Heart Failure With Preserved Ejection Fraction: The Hfpef Stress Trial

Introduction: Invasive right heart catherization (RHC) using exercise-stress is the reference-standard for the diagnosis of heart failure with preserved ejection fraction (HFpEF) but carries the risk of the procedure. Real-time cardiovascular magnetic resonance (RT-CMR) imaging allows bicycle exercise CMR with unprecedented temporal and spatial resolution and may represent a novel non-invasive alternative. Methods: The HFpEF stress trial (NCT03260621) prospectively included 75 patients with echocardiographic signs of diastolic dysfunction and dyspnoea on exertion (E/E’&gt;8, NYHA≥II) who underwent echocardiography, RHC and RT-CMR at rest and exercise-stress. HFpEF was defined according to pulmonary capillary wedge pressure (PCWP ≥15mmHg at rest or ≥25mmHg during exercise stress). RT-CMR functional assessments included time-volume-curves for total and early (1/3) diastolic left ventricular (LV) filling or left atrial (LA) emptying and LV/LA long axis strain (LAS). Results: HFpEF patients (n=34, mean PCWP rest 13mmHg, stress 27mmHg) had higher E/e’ (12.5 vs 9.15), NT-proBNP (255 vs 75ng/l) and LA volume index (43.8 vs 36.2ml/m 2 ) compared to non-HFpEF patients (n=34, rest 8mmHg, stress 18mmHg, p≤0.001 for all). There were no differences in RT-CMR LV total and early diastolic filling at rest and during exercise-stress (p≥0.164). In contrast, RT-CMR revealed impaired stress LA total (p=0.033) and early (p&lt;0.001) diastolic emptying in HFpEF. LA LAS was the only impaired parameter at rest (p&lt;0.001) and emerged as the best predictor for the presence of HFpEF during exercise-stress testing (AUC rest 0.82 vs stress 0.93, p=0.029). Conclusions: RT-CMR allows highly accurate identification of HFpEF during physiological exercise and may establish itself as a novel non-invasive diagnostic alternative for routine clinical use.

Real-time cardiovascular magnetic resonance T1 and extracellular volume fraction mapping for tissue characterisation in aortic stenosis

BackgroundMyocardial fibrosis is a major determinant of outcome in aortic stenosis (AS). Novel fast real-time (RT) cardiovascular magnetic resonance (CMR) mapping techniques allow comprehensive quantification of fibrosis but have not yet been compared against standard techniques and histology.MethodsPatients with severe AS underwent CMR before (n = 110) and left ventricular (LV) endomyocardial biopsy (n = 46) at transcatheter aortic valve replacement (TAVR). Midventricular short axis (SAX) native, post-contrast T1 and extracellular volume fraction (ECV) maps were generated using commercially available modified Look-Locker Inversion recovery (MOLLI) (native: 5(3)3, post-contrast: 4(1)3(1)2) and RT single-shot inversion recovery Fast Low-Angle Shot (FLASH) with radial undersampling. Focal late gadolinium enhancement was excluded from T1 and ECV regions of interest. ECV and LV mass were used to calculate LV matrix volumes. Variability and agreements were assessed between RT, MOLLI and histology using intraclass correlation coefficients, coefficients of variation and Bland Altman analyses.ResultsRT and MOLLI derived ECV were similar for midventricular SAX slice coverage (26.2 vs. 26.5, p = 0.073) and septal region of interest (26.2 vs. 26.5, p = 0.216). MOLLI native T1 time was in median 20 ms longer compared to RT (p < 0.001). Agreement between RT and MOLLI was best for ECV (ICC > 0.91), excellent for post-contrast T1 times (ICC > 0.81) and good for native T1 times (ICC > 0.62). Diffuse collagen volume fraction by biopsies was in median 7.8%. ECV (RT r = 0.345, p = 0.039; MOLLI r = 0.40, p = 0.010) and LV matrix volumes (RT r = 0.45, p = 0.005; MOLLI r = 0.43, p = 0.007) were the only parameters associated with histology.ConclusionsRT mapping offers fast and sufficient ECV and LV matrix volume calculation in AS patients. ECV and LV matrix volume represent robust and universally comparable parameters with associations to histologically assessed fibrosis and may emerge as potential targets for clinical decision making.

A cardiovascular magnetic resonance (CMR) safe metal braided catheter design for interventional CMR at 1.5\u2009T: freedom from radiofrequency induced heating and preserved mechanical performance

BackgroundCatheter designs incorporating metallic braiding have high torque control and kink resistance compared with unbraided alternatives. However, metallic segments longer than a quarter wavelength (~ 12 cm for 1.5 T scanner) are prone to radiofrequency (RF) induced heating during cardiovascular magnetic resonance (CMR) catheterization. We designed a braid-reinforced catheter with interrupted metallic segments to mitigate RF-induced heating yet retain expected mechanical properties for CMR catheterization.MethodsWe constructed metal wire braided 6 Fr catheter shaft subassemblies using electrically insulated stainless-steel wires and off-the-shelf biocompatible polymers. The braiding was segmented, in-situ, using lasers to create non-resonant wire lengths. We compared the heating and mechanical performance of segmented- with un-segmented- metal braided catheter shaft subassemblies.ResultsThe braiding segmentation procedure did not significantly alter the structural integrity of catheter subassemblies, torque response, push-ability, or kink resistance compared with non-segmented controls. Segmentation shortened the electrical length of individually insulated metallic braids, and therefore inhibited resonance during CMR RF excitation. RF-induced heating was reduced below 2 °C under expected use conditions in vitro.ConclusionWe describe a simple modification to the manufacture of metallic braided catheters that will allow CMR catheterization without RF-induced heating under contemporary scanning conditions at 1.5 T. The proposed segmentation pattern largely preserves braid structure and mechanical integrity while interrupting electrical resonance. This inexpensive design may be applicable to both diagnostic and interventional catheters and will help to enable a range of interventional procedures using real time CMR.

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

BackgroundThis 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.MethodsThe 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.ResultsIn 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.ConclusionModel-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.

Targeted endomyocardial biopsy guided by real-time cardiovascular magnetic resonance

BackgroundEndomyocardial 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.MethodsSeven 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.ResultsRadiofrequency 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%).ConclusionFocal 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.

Assessing exercise cardiac reserve using real-time cardiovascular magnetic resonance

BackgroundExercise cardiovascular magnetic resonance (ExCMR) has great potential for clinical use but its development has been limited by a lack of compatible equipment and robust real-time imaging techniques. We developed an exCMR protocol using an in-scanner cycle ergometer and assessed its performance in differentiating athletes from non-athletes.MethodsFree-breathing real-time CMR (1.5T Aera, Siemens) was performed in 11 athletes (5 males; median age 29 [IQR: 28–39] years) and 16 age- and sex-matched healthy volunteers (7 males; median age 26 [interquartile range (IQR): 25–33] years). All participants underwent an in-scanner exercise protocol on a CMR compatible cycle ergometer (Lode BV, the Netherlands), with an initial workload of 25W followed by 25W-increment every minute. In 20 individuals, exercise capacity was also evaluated by cardiopulmonary exercise test (CPET). Scan-rescan reproducibility was assessed in 10 individuals, at least 7 days apart.ResultsThe exCMR protocol demonstrated excellent scan-rescan (cardiac index (CI): 0.2 ± 0.5L/min/m2) and inter-observer (ventricular volumes: 1.2 ± 5.3mL) reproducibility. CI derived from exCMR and CPET had excellent correlation (r = 0.83, p < 0.001) and agreement (1.7 ± 1.8L/min/m2). Despite similar values at rest (P = 0.87), athletes had increased exercise CI compared to healthy individuals (at peak exercise: 12.2 [IQR: 10.2–13.5] L/min/m2 versus 8.9 [IQR: 7.5–10.1] L/min/m2, respectively; P < 0.001). Peak exercise CI, where image acquisition lasted 13–17 s, outperformed that at rest (c-statistics = 0.95 [95% confidence interval: 0.87–1.00] versus 0.48 [95% confidence interval: 0.23–0.72], respectively; P < 0.0001 for comparison) in differentiating athletes from healthy volunteers; and had similar performance as VO2max (c-statistics = 0.84 [95% confidence interval = 0.62–1.00]; P = 0.29 for comparison).ConclusionsWe have developed a novel in-scanner exCMR protocol using real-time CMR that is highly reproducible. It may now be developed for clinical use for physiological studies of the heart and circulation.