Real-time Cardiac Magnetic Resonance Imaging Research Articles

Temporospatial characterization of ventricular wall motion with real-time cardiac magnetic resonance imaging in health and disease

Cardiac magnetic resonance imaging (MRI) has been largely dependent on retrospective cine for data acquisition. Real-time imaging, although inferior in image quality to retrospective cine, is more informative about motion dynamics. We herein developed a real-time cardiac MRI approach to temporospatial characterization of left ventricle (LV) and right ventricle (RV) wall motion. This approach provided two temporospatial indices, temporal periodicity and spatial coherence, for quantitative assessment of ventricular function. In a cardiac MRI study, we prospectively investigated temporospatial characterization in reference to standard volumetric measurements with retrospective cine. The temporospatial indices were found to be effective for evaluating the difference of ventricular performance between the healthy volunteers and the heart failure (HF) patients (LV temporal periodicity 0.24 ± 0.037 vs. 0.14 ± 0.021; RV temporal periodicity 0.18 ± 0.030 vs. 0.10 ± 0.014; LV spatial coherence 0.52 ± 0.039 vs. 0.38 ± 0.040; RV spatial coherence 0.50 ± 0.036 vs. 0.35 ± 0.035; all in arbitrary unit). The HF patients and healthy volunteers were well differentiated in the scatter plots of spatial coherence and temporal periodicity while they were mixed in those of end-systolic volume (ESV) and ejection fraction (EF) from volumetric measurements. This study demonstrated the potential of real-time cardiac MRI for intricate analysis of ventricular function beyond retrospective cine.

Optical Flow Analysis of Left Ventricle Wall Motion with Real-Time Cardiac Magnetic Resonance Imaging in Healthy Subjects and Heart Failure Patients.

In cardiology, magnetic resonance imaging (MRI) provides a clinical standard for measuring ventricular volumes. Owing to their reliability, volumetric measurements with cardiac MRI have become an essential tool for quantitative assessment of ventricular function. However, as volumetric indices are indirectly related to myocardial motion that drives ventricular filling and ejection, cardiac MRI cannot provide comprehensive evaluation of ventricular performance. To overcome this limitation, the presented work sought to measure ventricular wall motion directly with optical flow analysis of real-time cardiac MRI. By modeling left ventricle (LV) walls in real-time images based on myocardial architecture, we developed an optical flow approach to analyzing LV radial and circumferential wall motion for improved quantitative assessment of ventricular function. For proof-of-concept, a cardiac MRI study was conducted with healthy volunteers and heart failure (HF) patients. It was found that, as real-time images provided sufficient temporal information for correlation analysis between different LV wall motion velocity components, optical flow assessment detected the difference of ventricular performance between the HF patients and the healthy volunteers more effectively than volumetric measurements. We expect that this model-based optical flow assessment with real-time cardiac MRI would offer intricate analysis of ventricular function beyond conventional volumetric measurements.

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

ObjectivesQuantitative 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. MethodsConsecutive 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. ResultsIn 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). ConclusionRT 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.

Exercise Stress Real-Time Cardiac Magnetic Resonance Imaging for Noninvasive Characterization of Heart Failure With Preserved Ejection Fraction: The HFpEF-Stress Trial.

Right heart catheterization using exercise stress is the reference standard for the diagnosis of heart failure with preserved ejection fraction (HFpEF) but carries the risk of the invasive procedure. We hypothesized that real-time cardiac magnetic resonance (RT-CMR) exercise imaging with pathophysiologic data at excellent temporal and spatial resolution may represent a contemporary noninvasive alternative for diagnosing HFpEF. The HFpEF-Stress trial (CMR Exercise Stress Testing in HFpEF; URL: https://www.clinicaltrials.gov; Unique identifier: NCT03260621. URL: https://dzhk.de/; Unique identifier: DZHK-17) prospectively recruited 75 patients with echocardiographic signs of diastolic dysfunction and dyspnea on exertion (E/e'>8, New York Heart Association class ≥II) to undergo echocardiography, right heart catheterization, and RT-CMR at rest and during exercise stress. HFpEF was defined according to pulmonary capillary wedge pressure (≥15 mm Hg at rest or ≥25 mm Hg during exercise stress). RT-CMR functional assessments included time-volume curves for total and early (1/3) diastolic left ventricular filling, left atrial (LA) emptying, and left ventricular/LA long axis strain. Patients with HFpEF (n=34; median pulmonary capillary wedge pressure at rest, 13 mm Hg; at stress, 27 mm Hg) had higher E/e' (12.5 versus 9.15), NT-proBNP (N-terminal pro-B-type natriuretic peptide; 255 versus 75 ng/L), and LA volume index (43.8 versus 36.2 mL/m2) compared with patients with noncardiac dyspnea (n=34; rest, 8 mm Hg; stress, 18 mm Hg; P≤0.001 for all). Seven patients were excluded because of the presence of non-HFpEF cardiac disease causing dyspnea on imaging. There were no differences in RT-CMR left ventricular total and early diastolic filling at rest and during exercise stress (P≥0.164) between patients with HFpEF and noncardiac dyspnea. RT-CMR revealed significantly impaired LA total and early (P<0.001) diastolic emptying in patients with HFpEF during exercise stress. RT-CMR exercise stress LA long axis strain was independently associated with HFpEF (adjusted odds ratio, 0.657 [95% CI, 0.516-0.838]; P=0.001) after adjustment for clinical and imaging measures and emerged as the best predictor for HFpEF (area under the curve at rest 0.82 versus exercise stress 0.93; P=0.029). RT-CMR allows highly accurate identification of HFpEF during physiologic exercise and qualifies as a suitable noninvasive diagnostic alternative. These results will need to be confirmed in multicenter prospective research studies to establish widespread routine clinical use. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03260621. URL: https://dzhk.de/; Unique identifier: DZHK-17.

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.

AUTOMATIC EXTRACTION AND SIGN DETERMINATION OF RESPIRATORY SIGNAL IN REAL-TIME CARDIAC MAGNETIC RESONANCE IMAGING.

In real-time (RT) cardiac cine imaging, a stack of 2D slices is collected sequentially under free-breathing conditions. A complete heartbeat from each slice is then used for cardiac function quantification. The inter-slice respiratory mismatch can compromise accurate quantification of cardiac function. Methods based on principal components analysis (PCA) have been proposed to extract the respiratory signal from RT cardiac cine, but these methods cannot resolve the inter-slice sign ambiguity of the respiratory signal. In this work, we propose a fully automatic sign correction procedure based on the similarity of neighboring slices and correlation to the center-of-mass curve. The proposed method is evaluated in eleven volunteers, with ten slices per volunteer. The motion in a manually selected region-of-interest (ROI) is used as a reference. The results show that the extracted respiratory signal has a high, positive correlation with the reference in all cases. The qualitative assessment of images also shows that the proposed approach can accurately identify heartbeats, one from each slice, belonging to the same respiratory phase. This approach can improve cardiac function quantification for RT cine without manual intervention.

MRI Catheterization: Ready for Broad Adoption.

In recent years, interventional cardiac magnetic resonance imaging (iCMR) has evolved from attractive theory to clinical routine at several centers. Real-time cardiac magnetic resonance imaging (CMR fluoroscopy) adds value by combining soft-tissue visualization, concurrent hemodynamic measurement, and freedom from radiation. Clinical iCMR applications are expanding because of advances in catheter devices and imaging. In the near future, iCMR promises novel procedures otherwise unsafe under standalone X-Ray guidance.

A Deep Learning Segmentation Approach in Free-Breathing Real-Time Cardiac Magnetic Resonance Imaging.

Objectives The purpose of this study was to segment the left ventricle (LV) blood pool, LV myocardium, and right ventricle (RV) blood pool of end-diastole and end-systole frames in free-breathing cardiac magnetic resonance (CMR) imaging. Automatic and accurate segmentation of cardiac structures could reduce the postprocessing time of cardiac function analysis. MethodWe proposed a novel deep learning network using a residual block for the segmentation of the heart and a random data augmentation strategy to reduce the training time and the problem of overfitting. Automated cardiac diagnosis challenge (ACDC) data were used for training, and the free-breathing CMR data were used for validation and testing. Results The average Dice was 0.919 (LV), 0.806 (myocardium), and 0.818 (RV). The average IoU was 0.860 (LV), 0.699 (myocardium), and 0.761 (RV). Conclusions The proposed method may aid in the segmentation of cardiac images and improves the postprocessing efficiency of cardiac function analysis.

Exercise cardiac MRI unmasks right ventricular dysfunction in acute hypoxia and chronic pulmonary arterial hypertension.

Coupling of right ventricular (RV) contractility to afterload is maintained at rest in the early stages of pulmonary arterial hypertension (PAH), but exercise may unmask depleted contractile reserves. We assessed whether elevated afterload reduces RV contractile reserve despite compensated resting function using noninvasive exercise imaging. Fourteen patients with PAH (mean age: 39.1 yr, 10 women and 4 men) and 34 healthy control subjects (mean ageL 35.6 yr, 17 women and 17 men) completed real-time cardiac magnetic resonance imaging during submaximal exercise breathing room air. Control subjects were then also exercised during acute normobaric hypoxia (fraction of inspired O2: 12%). RV contractile reserve was assessed by the effect of exercise on ejection fraction. In control subjects, the increase in RV ejection fraction on exercise was less during hypoxia (P = 0.017), but the response of left ventricular ejection fraction to exercise did not change. Patients with PAH had an impaired RV reserve, with half demonstrating a fall in RV ejection fraction on exercise despite comparable resting function to controls (PAH: rest 53.6 ± 4.3% vs. exercise 51.4 ± 10.7%; controls: rest 57.1 ± 5.2% vs. exercise 69.6 ± 6.1%, P < 0.0001). In control subjects, the increase in stroke volume index on exercise was driven by reduced RV end-systolic volume, whereas patients with PAH did not augment the stroke volume index, with increases in both end-diastolic and end-systolic volumes. From baseline hemodynamic and exercise capacity variables, only the minute ventilation-to-CO2 output ratio was an independent predictor of RV functional reserve (P = 0.021). In conclusion, noninvasive cardiac imaging during exercise unmasks depleted RV contractile reserves in healthy adults under hypoxic conditions and patients with PAH under normoxic conditions despite preserved ejection fraction at rest.NEW & NOTEWORTHY Right ventricular (RV) reserve was assessed using real-time cardiac magnetic resonance imaging in patients with pulmonary arterial hypertension and in healthy control subjects under normobaric hypoxia, which has been previously associated with acute pulmonary hypertension. Hypoxia caused a mild reduction in RV reserve, whereas chronic pulmonary arterial hypertension was associated with a marked reduction in RV reserve.

Respiratory Effects on Fontan Circulation During Rest and Exercise Using Real-Time Cardiac Magnetic Resonance Imaging

It is known that respiration modulates cavopulmonary flows, but little data compare mean flows under breath-holding and free-breathing conditions to isolate the respiratory effects and effects of exercise on the respiratory modulation. Real-time phase-contrast magnetic resonance combined with a novel method to track respiration on the same image acquisition was used to investigate respiratory effects on Fontan caval and aortic flows under breath-holding, free-breathing, and exercise conditions. Respiratory phasicity indices that were based on beat-averaged flow were used to quantify the respiratory effect. Flow during inspiration was substantially higher than expiration under the free-breathing and exercise conditions for both inferior vena cava (inspiration/expiration: 1.6 ± 0.5 and 1.8 ± 0.5, respectively) and superior vena cava (inspiration/expiration: 1.9 ± 0.6 and 2.6 ± 2.0, respectively). Changes from rest to exercise in the respiratory phasicity index for these vessels further showed the impact of respiration. Total systemic venous flow showed no significant statistical difference between the breath-holding and free-breathing conditions. In addition, no substantial difference was found between the descending aorta and inferior vena cava mean flows under either resting or exercise conditions. This study demonstrated that inferior vena cava and superior vena cava flow time variance is dominated by respiratory effects, which can be detected by the respiratory phasicity index. However, the minimal respiration influence on net flow validates the routine use of breath-holding techniques to measure mean flows in Fontan patients. Moreover, the mean flows in the inferior vena cava and descending aorta are interchangeable.

Radiotherapy beyond cancer: target localization in real-time MRI and treatment planning for cardiac radiosurgery.

Atrial fibrillation (AFib) is the most common cardiac arrhythmia that affects millions of patients world-wide. AFib is usually treated with minimally invasive, time consuming catheter ablation techniques. While recently noninvasive radiosurgery to the pulmonary vein antrum (PVA) in the left atrium has been proposed for AFib treatment, precise target location during treatment is challenging due to complex respiratory and cardiac motion. A MRI linear accelerator (MRI-Linac) could solve the problems of motion tracking and compensation using real-time image guidance. In this study, the authors quantified target motion ranges on cardiac magnetic resonance imaging (MRI) and analyzed the dosimetric benefits of margin reduction assuming real-time motion compensation was applied. For the imaging study, six human subjects underwent real-time cardiac MRI under free breathing. The target motion was analyzed retrospectively using a template matching algorithm. The planning study was conducted on a CT of an AFib patient with a centrally located esophagus undergoing catheter ablation, representing an ideal case for cardiac radiosurgery. The target definition was similar to the ablation lesions at the PVA created during catheter treatment. Safety margins of 0 mm (perfect tracking) to 8 mm (untracked respiratory motion) were added to the target, defining the planning target volume (PTV). For each margin, a 30 Gy single fraction IMRT plan was generated. Additionally, the influence of 1 and 3 T magnetic fields on the treatment beam delivery was simulated using Monte Carlo calculations to determine the dosimetric impact of MRI guidance for two different Linac positions. Real-time cardiac MRI showed mean respiratory target motion of 10.2 mm (superior-inferior), 2.4 mm (anterior-posterior), and 2 mm (left-right). The planning study showed that increasing safety margins to encompass untracked respiratory motion leads to overlapping structures even in the ideal scenario, compromising either normal tissue dose constraints or PTV coverage. The magnetic field caused a slight increase in the PTV dose with the in-line MRI-Linac configuration. The authors' results indicate that real-time tracking and motion compensation are mandatory for cardiac radiosurgery and MRI-guidance is feasible, opening the possibility of treating cardiac arrhythmia patients completely noninvasively.

Right ventricular fatigue developing during endurance exercise: an exercise cardiac magnetic resonance study.

Prolonged intense exercise has often been associated with the impairment of right ventricular (RV) function after activity, whereas this is rare for the left ventricle (LV). The effect of prolonged exercise on the heart has not been adequately measured during exercise itself. We performed real-time cardiac magnetic resonance imaging at rest and during incremental exercise in 14 male endurance athletes (mean ± SD; age = 36 ± 6 yr, BMI = 23.1 ± 1.94 kg·m) 1-3 wk before (baseline) and immediately after a 150-km cycling event (end-of-race) to measure LV and RV end-diastolic and end-systolic volumes (EDV and ESV), ejection fraction (EF), and ventricular-arterial coupling (stroke volume [SV]/ESV). End-of-race RV EDV was unchanged from baseline at rest but was significantly increased during near-maximal exercise (235 ± 18 vs 217 ± 24 mL, P < 0.0001). Resting RV ESV was higher end-of-race (100 ± 16 vs 93 ± 15 mL, P = 0.009), which became more appreciable during near-maximal exercise (75 ± 15 vs 60 ± 14 mL, P < 0.0001). RV EF, although unchanged at rest, was significantly decreased during near-maximal exercise (68% ± 5% vs 73% ± 4%, P = 0.001). LV volume measures were similar at baseline and end-of-race. Therefore, the effect of endurance activity on the RV and LV was significantly different (P < 0.0001). Cardiac output increased to similar values at near-maximal exertion before and at the end of the race. However, whereas LV SV/ESV was unchanged, RV SV/ESV was attenuated end-of-race (P = 0.02 for interaction with race setting). Intense endurance exercise does not affect LV volume or function but results in RV dilatation and reduced RV EF, which becomes even more significant during exercise. Alterations in RV ventricular-arterial coupling suggest that this may be an expression of exercise-induced RV contractile impairment rather than changes in autonomic or loading conditions.

A Mechatronic System for Interactive Scan Plan Prescription during Real-Time Cardiac Magnetic Resonance Imaging

Real-time magnetic resonance imaging (MRI) has many advantages as compared to traditional MRI and can be used for the visualization of dynamic moving cardiac structures and functions without cardiac gating, as the fast data acquisition apparently freezes the motion resulting from heart beating and lung breathing. During the past decades, fast pulse sequences and image reconstruction algorithms had been developed to improve the temporal resolution with acceptable spatial resolution. However, the bottle neck of current real-time MRI systems is the availability of a user-friendly prescription tool to allow a MRI technician to prescribe the 6-Degree-of-freedom imaging plane of the MRI system. To meet the needs of real-time MRI, a 3D input tool is developed which facilitates user interactive specification of the center position and plane orientation of the MRI imaging plane. This paper reports such a custom designed 6 degree-of-freedom 3D input device, which allows the user to interactively and intuitively manipulate the scan plane to direct the real-time imaging capability to a target position based on the visual feedback provided on the MRI console in the form of real-time MRI images

Changes in biventricular volumes during respiration: assessment of the respiratory pump using real-time cardiac magnetic resonance imaging during exercise

Background: Real-time cardiac magnetic resonance (CMR) imaging has emerged as an accurate and reproducible tool for biventricular volume assessment during free-breathing and whilst exercising. The aim of this study was to examine the degree to which the respiratory pump influenced cardiac filling and performance at rest and during exercise. Methods: Nine healthy subjects (8 male, 1 female) underwent CMR during free-breathing using an ungated real-time CMR sequence. ECG and respiratory movements were retrospectively synchronized enabling compensation for cardiac cycle and respiratory phase and cardiac volumes were determined for the left and right ventricles (LV and RV) from stacks of bi-plane cine images using customized software. End-diastolic and end-systolic volumes (EDV and ESV) as well as diastolic and systolic eccentricity indexes were measured for the LV and RV during peak inspiration and peak expiration, both at rest (heart rate 58±10 bpm) and whilst cycling at low (110±17 bpm), moderate (138±18 bpm) and strenuous (153±20 bpm) workload intensities. Results: As compared with expiration, there was an increase in RV volumes during inspiration (RVEDV +11%, RVESV +12%, RVSV +10%, p<0.05) In contrast, LV EDV, LV ESV and LV SV reduced during inspiration (-6%, -6%, -6%, p<0.05). LVEF and RVEF did not change with respiration, at rest or during exercise. During inspiration, RV SV tended to be larger than LV SV (p=0.064), whilst LV SV was significantly larger than RV SV during expiration (p<0.0001). Mean SV, defined as the average of peak-inspiratory and peak expiratory SV, was slightly greater (5%, p=0.047) for the LV than for the RV, possibly reflecting the expected physiological excess due to the bronchial and thebesian circulation. The interventricular septum pushed toward the LV during inspiration as evidenced by a greater eccentricity index during inspiration than during expiration, which was greatest in diastole (+ 16%, p<0.0001) but also evident during systole (+ 6%, p=0.019). Conclusions: Ventricular volumes oscillate with respiratory phase such that RV volumes and LV volumes are maximal during inspiration and expiration, respectively. Thus, instantaneous measures of stroke volume should not be expected to be equal. Real-time CMR provides a novel means of quantifying the degree to which pulmonary disorders may impact on cardiac performance.

Right ventricular fatigue limits cardiac performance during intense endurance exercise: a novel Cardiac Magnetic Resonance (CMR) study during exercise

Background: Cardiac dysfunction following prolonged intense exercise has been shown to predominantly affect the right ventricle (RV). However, these changes have only been observed at rest and we do not know whether cardiac dysfunction is also present during exercise. Methods: Real-time CMR imaging was performed in 14 male endurance athletes at rest and then during 3 stages of incremental exercise to maximal exertion. CMR was performed 1-3 weeks before (baseline) and immediately after (post-race) a 150 km cycling event. Images obtained during exercise and free-breathing were analyzed using in-house developed software in which end-diastolic and end-systolic volumes (EDV,ESV) were obtained from endocardial tracings of bi-plane cine stacks after compensation for respiratory motion. Stroke volume (SV) was calculated as EDV – ESV, cardiac output (CO) as SV x heart rate (HR) and ejection fraction (EF) as SV/EDV %. Results: As compared with baseline, CO increased to similar values at maximal exertion in the post-race setting (24.1±2.4 vs. 24.7±2.1 l/min; P=0.448). However, RVEDV (P=0.021) and RVESV (P<0.0001) were significantly higher post-race than baseline, with greater discrepancy throughout exercise intensities, whereas LVEDV (P=0.163) and LVESV (P=0.127) were similar throughout exercise at baseline and post-race. At baseline and post-race LVEF augmented normally whereas both resting and exercise RVEF was attenuated after prolonged intense exercise as compared to baseline (figure). ![Figure][1] Attenuated RVEF after endurance exercise Conclusions: Whilst LV function is unchanged, intense endurance exercise results in RV dilation and reduced RV function, both at rest and during exercise. This indicates that cardiac performance during extreme exercise is limited by right ventriculo-arterial interaction. [1]: pending:yes

Response to Letter Regarding Article, “Cardiac Magnetic Resonance Imaging: A New Gold Standard for Ventricular Volume Quantification During High-Intensity Exercise”

HomeCirculation: Cardiovascular ImagingVol. 6, No. 3Response to Letter Regarding Article, “Cardiac Magnetic Resonance Imaging: A New Gold Standard for Ventricular Volume Quantification During High-Intensity Exercise” Free AccessResearch ArticlePDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessResearch ArticlePDF/EPUBResponse to Letter Regarding Article, “Cardiac Magnetic Resonance Imaging: A New Gold Standard for Ventricular Volume Quantification During High-Intensity Exercise” Andre La Gerche, MD, PhD, Guido Claessen, MD, Alexander Van de Bruaene, MD, Nele Pattyn, MSc, Johan Van Cleemput, MD, PhD, Marc Gewillig, MD, PhD, Jan Bogaert, MD, PhD, Steven Dymarkowski, MD, PhD, Piet Claus, PhD and Hein Heidbuchel, MD, PhD Andre La GercheAndre La Gerche University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Guido ClaessenGuido Claessen University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Alexander Van de BruaeneAlexander Van de Bruaene University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Nele PattynNele Pattyn University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Johan Van CleemputJohan Van Cleemput University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Marc GewilligMarc Gewillig University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Jan BogaertJan Bogaert University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Steven DymarkowskiSteven Dymarkowski University Hospital of LeuvenLeuven, Belgium Search for more papers by this author , Piet ClausPiet Claus University Hospital of LeuvenLeuven, Belgium Search for more papers by this author and Hein HeidbuchelHein Heidbuchel University Hospital of LeuvenLeuven, Belgium Search for more papers by this author Originally published1 May 2013https://doi.org/10.1161/CIRCIMAGING.113.000389Circulation: Cardiovascular Imaging. 2013;6:e20We thank Drs Yoneyama and Akashi for their important reference to the confounding influence of respiration on biventricular volume assessment by real-time cardiac magnetic resonance imaging. As we noted in the Discussion, changes in biventricular volumes “may be caused by physiological differences in preload attributable to the fall in intrathoracic pressures during inspiration and cardiac translation through the imaging plane.”1 Real-time cardiac magnetic resonance imaging provides a novel means of expanding on the eloquent work of Natarajan et al2 on assessing the influence of the respiratory pump on cardiac filling and function. This interaction between breathing and cardiac function has received limited attention, but now we have an excellent noninvasive tool for very accurately detailing changes in both right and left ventricular volumes with various respiratory maneuvers. We hope to provide novel data in the peer-reviewed literature soon that will detail the importance of this respiratory pump in enhancing cardiac filling. We slightly disagree with the assertion that breath-hold imaging should be considered a gold standard. Breath-holding is a nonphysiological surrogate that has previously been necessary to enable gating of cardiac magnetic resonance images. Real-time imaging enables the investigator to apply the accuracy of cardiac magnetic resonance to real physiological settings. We can neither ignore the fact that our patients breathe nor ignore the fact that most of our patients develop symptoms with exertion. This new methodology finally enables us to accurately measure cardiac function when it really matters.Andre La Gerche, MD, PhDGuido Claessen, MDAlexander Van de Bruaene, MDNele Pattyn, MScJohan Van Cleemput, MD, PhDMarc Gewillig, MD, PhDJan Bogaert, MD, PhDSteven Dymarkowski, MD, PhDPiet Claus, PhDHein Heidbuchel, MD, PhDUniversity Hospital of LeuvenLeuven, BelgiumDisclosuresNone.

Detailed assessment of the hemodynamic response to psychosocial stress using real‐time MRI

To demonstrate that combining the Montreal Imaging Stress Task (MIST) with real-time cardiac magnetic resonance imaging (MRI) allows detailed assessment of the cardiovascular mental stress response. 22 healthy volunteers (1:1 M:F, 26-64 years) underwent MRI during rest and the MIST. Real-time spiral phase contrast MR, accelerated with sensitivity encoding (SENSE) was used to assess stroke volume (SV), and radial k-t SENSE was used to assess ventricular volumes. Simultaneous heart rate (HR) and blood pressure (BP) measures allowed calculation of cardiac output (CO), systemic vascular resistance (SVR), and arterial compliance (TAC). Endocrine responses were assessed using salivary cortisol. In response to stress, BP increased due to increased CO and reduced TAC but not increased SVR, which fell. HR, not SV, determined CO increases. Greater BP responses occurred in men due to greater CO increases and relatively higher SVR. Older participants had greater BP responses due to greater falls in TAC. Greater cortisol response was correlated with greater falls in TAC but resting cortisol and TAC were not related. This new approach allows detailed, accurate assessment of stress physiology. Preliminary findings suggest stress exposes relationships, not seen at rest, of cardiovascular function with age, sex, and endocrine function.

Application of the Karhunen–Loeve transform temporal image filter to reduce noise in real-time cardiac cine MRI

Real-time dynamic magnetic resonance imaging (MRI) typically sacrifices the signal-to-noise ratio (SNR) to achieve higher spatial and temporal resolution. Spatial and/or temporal filtering (e.g., low-pass filtering or averaging) of dynamic images improves the SNR at the expense of edge sharpness. We describe the application of a temporal filter for dynamic MR image series based on the Karhunen–Loeve transform (KLT) to remove random noise without blurring stationary or moving edges and requiring no training data. In this paper, we present several properties of this filter and their effects on filter performance, and propose an automatic way to find the filter cutoff based on the autocorrelation of the eigenimages. Numerical simulation and in vivo real-time cardiac cine MR image series spanning multiple cardiac cycles acquired using multi-channel sensitivity-encoded MRI, i.e., parallel imaging, are used to validate and demonstrate these properties. We found that in this application, the noise standard deviation was reduced to 42% of the original with no apparent image blurring by using the proposed filter cutoff. Greater noise reduction can be achieved by increasing the length of the image series. This advantage of KLT filtering provides flexibility in the form of another scan parameter to trade for SNR.

The future of real-time cardiac magnetic resonance imaging

Dynamic changes in cardiac structure and function are usually examined by real-time imaging techniques such as angiography or echocardiography. MRI has many advantages compared with these established cardiac imaging modalities. However, system hardware and software limitations have limited cardiac MRI to gated acquisitions that are lengthy and often result in failed acquisitions and examinations. Recently, MRI has evolved into a technique capable of imaging dynamic processes in real time. Improvements in hardware, pulse sequences, and image reconstruction algorithms have enabled real-time cardiac MRI with high spatial resolution, high temporal resolution, and various types of image contrast without requiring cardiac gating or breath-holding. This article provides an overview of current capability and highlights key technical and clinical advances. The future prospects of real-time cardiac MRI will depend on 1) the development of techniques that further improve signal to noise ratio, contrast, spatial resolution, and temporal resolution, without introducing artifacts; 2) the development of software infrastructure that facilitates rapid interactive examination; and 3) the development and validation of several new clinical assessments.

Rapid evaluation of left ventricular volume and mass without breath-holding using real-time interactive cardiac magnetic resonance imaging system

OBJECTIVES The purpose of this study was to validate cardiac measurements derived from real-time cardiac magnetic resonance imaging (MRI) as compared with well-validated conventional cine MRI. BACKGROUND Although cardiac MRI provides accurate assessment of left ventricular (LV) volume and mass, most techniques have been relatively slow and required electrocardiogram (ECG) gating over many heart beats. A newly developed real-time MRI system allows continuous real-time dynamic acquisition and display without cardiac gating or breath-holding. METHODS Fourteen healthy volunteers and nine patients with heart failure underwent real-time and cine MRI in the standard short-axis orientation with a 1.5T MRI scanner. Nonbreath-holding cine MRI was performed with ECG gating and respiratory compensation. Left ventricular end-diastolic volume (LVEDV), left ventricular endsystolic volume (LVESV), ejection fraction (EF) and LV mass calculated from the images obtained by real-time MRI were compared to those obtained by cine MRI. RESULTS The total study time including localization for real-time MRI was significantly shorter than cine MRI (8.6 ± 2.3 vs. 24.7 ± 3.5 min, p < 0.001). Both imaging techniques yielded good quality images allowing cardiac measurements. The measurements of LVEDV, LVESV, EF and LV mass obtained with real-time MRI showed close correlation with those obtained with cine MRI (LVEDV: r = 0.985, p < 0.001; LVESV: r = 0.994, p < 0.001; EF: r = 0.975, p < 0.001; LV mass: r = 0.977, p < 0.001). CONCLUSIONS Real-time MRI provides accurate measurements of LV volume and mass in a time-efficient manner with respect to image acquisition.