2D sodium MRI of the human calf using half-sinc excitation pulses and compressed sensing.

PURPOSE: Sodium MRI can be used to quantify tissue sodium concentration (TSC) in vivo; however, UTE sequences are required to capture the rapidly decaying signal. 2D MRI enables high in-plane resolution but typically has long TEs. Half-sinc excitation may enable UTE; however, twice as many readouts are necessary. Scan time can be minimized by reducing the number of signal averages (NSAs), but at a cost to SNR. We propose using compressed sensing (CS) to accelerate 2D half-sinc acquisitions while maintaining SNR and TSC. METHODS: Ex vivo and in vivo TSC were compared between 2D spiral sequences with full-sinc (TE = 0.73 ms, scan time ≈ 5 min) and half-sinc excitation (TE = 0.23 ms, scan time ≈ 10 min), with 150 NSAs. Ex vivo, these were compared to a reference 3D sequence (TE = 0.22 ms, scan time ≈ 24 min). To investigate shortening 2D scan times, half-sinc data was retrospectively reconstructed with fewer NSAs, comparing a nonuniform fast Fourier transform to CS. Resultant TSC and image quality were compared to reference 150 NSAs nonuniform fast Fourier transform images. RESULTS: TSC was significantly higher from half-sinc than from full-sinc acquisitions, ex vivo and in vivo. Ex vivo, half-sinc data more closely matched the reference 3D sequence, indicating improved accuracy. In silico modeling confirmed this was due to shorter TEs minimizing bias caused by relaxation differences between phantoms and tissue. CS was successfully applied to in vivo, half-sinc data, maintaining TSC and image quality (estimated SNR, edge sharpness, and qualitative metrics) with ≥50 NSAs. CONCLUSION: 2D sodium MRI with half-sinc excitation and CS was validated, enabling TSC quantification with 2.25 × 2.25 mm2 resolution and scan times of ≤5 mins.

Real-time deep artifact suppression using recurrent U-Nets for low-latency cardiac MRI.

PURPOSE: Real-time low latency MRI is performed to guide various cardiac interventions. Real-time acquisitions often require iterative image reconstruction strategies, which lead to long reconstruction times. In this study, we aim to reconstruct highly undersampled radial real-time data with low latency using deep learning. METHODS: A 2D U-Net with convolutional long short-term memory layers is proposed to exploit spatial and preceding temporal information to reconstruct highly accelerated tiny golden radial data with low latency. The network was trained using a dataset of breath-hold CINE data (including 770 time series from 7 different orientations). Synthetic paired data were created by retrospectively undersampling the magnitude images, and the network was trained to recover the target images. In the spirit of interventional imaging, the network was trained and tested for varying acceleration rates and orientations. Data were prospectively acquired and reconstructed in real time in 1 healthy subject interactively and in 3 patients who underwent catheterization. Images were visually compared to sliding window and compressed sensing reconstructions and a conventional Cartesian real-time sequence. RESULTS: The proposed network generalized well to different acceleration rates and unseen orientations for all considered metrics in simulated data (less than 4% reduction in structural similarity index compared to similar acceleration and orientation-specific networks). The proposed reconstruction was demonstrated interactively, successfully depicting catheters in vivo with low latency (39 ms, including 19 ms for deep artifact suppression) and an image quality comparing favorably to other reconstructions. CONCLUSION: Deep artifact suppression was successfully demonstrated in the time-critical application of non-Cartesian real-time interventional cardiac MR.

Reducing Contrast Agent Dose in Cardiovascular MR Angiography with Deep Learning.

BACKGROUND: Contrast-enhanced magnetic resonance angiography (MRA) is used to assess various cardiovascular conditions. However, gadolinium-based contrast agents (GBCAs) carry a risk of dose-related adverse effects. PURPOSE: To develop a deep learning method to reduce GBCA dose by 80%. STUDY TYPE: Retrospective and prospective. POPULATION: A total of 1157 retrospective and 40 prospective congenital heart disease patients for training/validation and testing, respectively. FIELD STRENGTH/SEQUENCE: A 1.5 T, T1-weighted three-dimensional (3D) gradient echo. ASSESSMENT: A neural network was trained to enhance low-dose (LD) 3D MRA using retrospective synthetic data and tested with prospective LD data. Image quality for LD (LD-MRA), enhanced LD (ELD-MRA), and high-dose (HD-MRA) was assessed in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and a quantitative measure of edge sharpness and scored for perceptual sharpness and contrast on a 1-5 scale. Diagnostic confidence was assessed on a 1-3 scale. LD- and ELD-MRA were assessed against HD-MRA for sensitivity/specificity and agreement of vessel diameter measurements (aorta and pulmonary arteries). STATISTICAL TESTS: SNR, CNR, edge sharpness, and vessel diameters were compared between LD-, ELD-, and HD-MRA using one-way repeated measures analysis of variance with post-hoc t-tests. Perceptual quality and diagnostic confidence were compared using Friedman's test with post-hoc Wilcoxon signed-rank tests. Sensitivity/specificity was compared using McNemar's test. Agreement of vessel diameters was assessed using Bland-Altman analysis. RESULTS: SNR, CNR, edge sharpness, perceptual sharpness, and perceptual contrast were lower (P < 0.05) for LD-MRA compared to ELD-MRA and HD-MRA. SNR, CNR, edge sharpness, and perceptual contrast were comparable between ELD and HD-MRA, but perceptual sharpness was significantly lower. Sensitivity/specificity was 0.824/0.921 for LD-MRA and 0.882/0.960 for ELD-MRA. Diagnostic confidence was 2.72, 2.85, and 2.92 for LD, ELD, and HD-MRA, respectively (PLD-ELD , PLD-HD  < 0.05). Vessel diameter measurements were comparable, with biases of 0.238 (LD-MRA) and 0.278 mm (ELD-MRA). DATA CONCLUSION: Deep learning can improve contrast in LD cardiovascular MRA. LEVEL OF EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: Stage 2.

Reduced exercise capacity in patients with systemic sclerosis is associated with lower peak tissue oxygen extraction: a cardiovascular magnetic resonance-augmented cardiopulmonary exercise study.

BACKGROUND: Exercise intolerance in systemic sclerosis (SSc) is typically attributed to cardiopulmonary limitations. However, problems with skeletal muscle oxygen extraction have not been fully investigated. This study used cardiovascular magnetic resonance (CMR)-augmented cardiopulmonary exercise testing (CMR-CPET) to simultaneously measure oxygen consumption and cardiac output. This allowed calculation of arteriovenous oxygen content gradient, a recognized marker of oxygen extraction. We performed CMR-CPET in 4 groups: systemic sclerosis (SSc); systemic sclerosis-associated pulmonary arterial hypertension (SSc-PAH); non-connective tissue disease pulmonary hypertension (NC-PAH); and healthy controls. METHODS: We performed CMR-CPET in 60 subjects (15 in each group) using a supine ergometer following a ramped exercise protocol until exhaustion. Values for oxygen consumption, cardiac output and oxygen content gradient, as well as ventricular volumes, were obtained at rest and peak-exercise for all subjects. In addition, T1 and T2 maps were acquired at rest, and the most recent clinical measures (hemoglobin, lung function, 6-min walk, cardiac and catheterization) were collected. RESULTS: All patient groups had reduced peak oxygen consumption compared to healthy controls (p < 0.022). The SSc and SSc-PAH groups had reduced peak oxygen content gradient compared to healthy controls (p < 0.03). Conversely, the SSc-PAH and NC-PH patients had reduced peak cardiac output compared to healthy controls and SSc patients (p < 0.006). Higher hemoglobin was associated with higher peak oxygen content gradient (p = 0.025) and higher myocardial T1 was associated with lower peak stroke volume (p = 0.011). CONCLUSIONS: Reduced peak oxygen consumption in SSc patients is predominantly driven by reduced oxygen content gradient and in SSc-PAH patients this was amplified by reduced peak cardiac output. Trial registration The study is registered with ClinicalTrials.gov Protocol Registration and Results System (ClinicalTrials.gov ID: 100358).

Rapid whole-heart CMR with single volume super-resolution.

BACKGROUND: Three-dimensional, whole heart, balanced steady state free precession (WH-bSSFP) sequences provide delineation of intra-cardiac and vascular anatomy. However, they have long acquisition times. Here, we propose significant speed-ups using a deep-learning single volume super-resolution reconstruction, to recover high-resolution features from rapidly acquired low-resolution WH-bSSFP images. METHODS: A 3D residual U-Net was trained using synthetic data, created from a library of 500 high-resolution WH-bSSFP images by simulating 50% slice resolution and 50% phase resolution. The trained network was validated with 25 synthetic test data sets. Additionally, prospective low-resolution data and high-resolution data were acquired in 40 patients. In the prospective data, vessel diameters, quantitative and qualitative image quality, and diagnostic scoring was compared between the low-resolution, super-resolution and reference high-resolution WH-bSSFP data. RESULTS: The synthetic test data showed a significant increase in image quality of the low-resolution images after super-resolution reconstruction. Prospectively acquired low-resolution data was acquired ~× 3 faster than the prospective high-resolution data (173 s vs 488 s). Super-resolution reconstruction of the low-resolution data took < 1 s per volume. Qualitative image scores showed super-resolved images had better edge sharpness, fewer residual artefacts and less image distortion than low-resolution images, with similar scores to high-resolution data. Quantitative image scores showed super-resolved images had significantly better edge sharpness than low-resolution or high-resolution images, with significantly better signal-to-noise ratio than high-resolution data. Vessel diameters measurements showed over-estimation in the low-resolution measurements, compared to the high-resolution data. No significant differences and no bias was found in the super-resolution measurements in any of the great vessels. However, a small but significant for the underestimation was found in the proximal left coronary artery diameter measurement from super-resolution data. Diagnostic scoring showed that although super-resolution did not improve accuracy of diagnosis, it did improve diagnostic confidence compared to low-resolution imaging. CONCLUSION: This paper demonstrates the potential of using a residual U-Net for super-resolution reconstruction of rapidly acquired low-resolution whole heart bSSFP data within a clinical setting. We were able to train the network using synthetic training data from retrospective high-resolution whole heart data. The resulting network can be applied very quickly, making these techniques particularly appealing within busy clinical workflow. Thus, we believe that this technique may help speed up whole heart CMR in clinical practice.

Real-time cardiovascular MR with spatio-temporal artifact suppression using deep learning-proof of concept in congenital heart disease.

PURPOSE: Real-time assessment of ventricular volumes requires high acceleration factors. Residual convolutional neural networks (CNN) have shown potential for removing artifacts caused by data undersampling. In this study, we investigated the ability of CNNs to reconstruct highly accelerated radial real-time data in patients with congenital heart disease (CHD). METHODS: A 3D (2D plus time) CNN architecture was developed and trained using synthetic training data created from previously acquired breath hold cine images from 250 CHD patients. The trained CNN was then used to reconstruct actual real-time, tiny golden angle (tGA) radial SSFP data (13 × undersampled) acquired in 10 new patients with CHD. The same real-time data was also reconstructed with compressed sensing (CS) to compare image quality and reconstruction time. Ventricular volume measurements made using both the CNN and CS reconstructed images were compared to reference standard breath hold data. RESULTS: It was feasible to train a CNN to remove artifact from highly undersampled radial real-time data. The overall reconstruction time with the CNN (including creation of aliased images) was shown to be >5 × faster than the CS reconstruction. In addition, the image quality and accuracy of biventricular volumes measured from the CNN reconstructed images were superior to the CS reconstructions. CONCLUSION: This article has demonstrated the potential for the use of a CNN for reconstruction of real-time radial data within the clinical setting. Clinical measures of ventricular volumes using real-time data with CNN reconstruction are not statistically significantly different from gold-standard, cardiac-gated, breath-hold techniques.

The aorta after coarctation repair - effects of calibre and curvature on arterial haemodynamics.

BACKGROUND: Aortic shape has been proposed as an important determinant of adverse haemodynamics following coarctation repair. However, previous studies have not demonstrated a consistent relationship between shape and vascular load. In this study, 3D aortic shape was evaluated using principal component analysis (PCA), allowing investigation of the relationship between 3D shape and haemodynamics. METHODS: Sixty subjects (38 male, 25.0 ± 7.8 years) with repaired coarctation were recruited. Central aortic haemodynamics including wave intensity analysis were measured noninvasively using a combination of blood pressure and phase contrast cardiovascular magnetic resonance (CMR). 3D curvature and radius data were derived from CMR angiograms. PCA was separately performed on 3D radius and curvature data to assess the role of arch geometry on haemodynamics. Clinical findings were corroborated using 1D vascular models. RESULTS: There were no independent associations between 3D curvature and any hemodynamic parameters. However, the magnitude of the backwards compression wave was related to the 1st (r = - 0.36, p = 0.005), 3rd (r = 0.27, p = 0.036) and 4th (r = - 0.31, p = 0.017) principle components of radius. The 4th principle componentof radius also correlated with central aortic systolic pressure. These aortas had larger aortic roots, more transverse arch hypoplasia and narrower aortic isthmuses. CONCLUSIONS: There are major modes of variation in 3D aortic shape after coarctation repair witha modest association between variation in aortic radius and pathological wave reflections, but not with 3D curvature. Taken together, these data suggest that shape is not the major determinant of vascular load following coarctation repair, and calibre is more important than curvature.

Correction to: The aorta after coarctation repair - effects of calibre and curvature on arterial haemodynamics.

In the original version of this article [1], published on 11 April 2019, there is 1 error in the 'Conclusion' paragraph of the abstract.

The cardiovascular phenotype of childhood hypertension: a cardiac magnetic resonance study.

BACKGROUND: The cardiovascular phenotype is poorly characterized in treated pediatric hypertension. Cardiovascular magnetic resonance imaging (MRI) can be used to better characterize both cardiac and vascular phenotype in children with hypertension. OBJECTIVE: To use MRI to determine the cardiac and vascular phenotypes of different forms of treated hypertension and compare the results with those of healthy children. MATERIALS AND METHODS: Sixty children (15 with chronic renal disease with hypertension, 15 with renovascular hypertension, 15 with essential hypertension and 15 healthy subjects) underwent MRI with noninvasive blood pressure measurements. Cardiovascular parameters measured include systemic vascular resistance, total arterial compliance, left ventricular mass and volumetric data, ejection fraction and myocardial velocity. Between-group comparisons were used to investigate differences in the hypertension types. RESULTS: Renal hypertension was associated with elevated vascular resistance (P≤0.007) and normal arterial compliance. Conversely, children with essential hypertension had normal resistance but increased compliance (P=0.001). Renovascular hypertension was associated with both increased resistance and compliance (P≤0.03). There was no difference in ventricular volumes, mass or cardiac output between groups. Children with renal hypertension also had lower systolic and diastolic myocardial velocities. CONCLUSION: Cardiovascular MRI may identify distinct vascular and cardiac phenotypes in different forms of treated childhood hypertension. Future studies are needed to investigate how this may inform further optimisation of blood pressure treatment in different types of hypertension.

Real-time assessment of right and left ventricular volumes and function in children using high spatiotemporal resolution spiral bSSFP with compressed sensing.

BACKGROUND: Real-time cardiovascular magnetic resonance (CMR) assessment of ventricular volumes and function enables data acquisition during free-breathing. The requirement for high spatiotemporal resolution in children necessitates the use of highly accelerated imaging techniques. METHODS: A novel real-time balanced steady state free precession (bSSFP) spiral sequence reconstructed using Compressed Sensing (CS) was prospectively validated against the breath-hold clinical standard for assessment of ventricular volumes in 60 children with congenital heart disease. Qualitative image scoring, quantitative image quality, as well as evaluation of biventricular volumes was performed. Standard BH and real-time measures were compared using the paired t-test and agreement for volumetric measures were evaluated using Bland Altman analysis. RESULTS: Acquisition time for the entire short axis stack (~ 13 slices) using the spiral real-time technique was ~ 20 s, compared to ~ 348 s for the standard breath hold technique. Qualitative scores reflected more residual aliasing artefact (p < 0.001) and lower edge definition (p < 0.001) in spiral real-time images than standard breath hold images, with lower quantitative edge sharpness and estimates of image contrast (p < 0.001). There was a small but statistically significant (p < 0.05) overestimation of left ventricular (LV) end-systolic volume (1.0 ± 3.5 mL), and underestimation of LV end-diastolic volume (- 1.7 ± 4.6 mL), LV stroke volume (- 2.6 ± 4.8 mL) and LV ejection fraction (- 1.5 ± 3.0%) using the real-time technique. We also observed a small underestimation of right ventricular stroke volume (- 1.8 ± 4.9 mL) and ejection fraction (- 1.4 ± 3.7%) using the real-time imaging technique. No difference in inter-observer or intra-observer variability were observed between the BH and real-time sequences. CONCLUSIONS: Real-time bSSFP imaging using spiral trajectories combined with a compressed sensing reconstruction showed good agreement for quantification of biventricular metrics in children with heart disease, despite slightly lower image quality. This technique holds the potential for free breathing data acquisition, with significantly shorter scan times in children.

A comprehensive characterization of myocardial and vascular phenotype in pediatric chronic kidney disease using cardiovascular magnetic resonance imaging.

BACKGROUND: Children with chronic kidney disease (CKD) have increased cardiovascular mortality. Identifying high-risk children who may benefit from further therapeutic intervention is difficult as cardiovascular abnormalities are subtle. Although transthoracic echocardiography may be used to detect sub-clinical abnormalities, it has well-known problems with reproducibility that limit its ability to accurately detect these changes. Cardiovascular magnetic resonance (CMR) is the reference standard method for assessing blood flow, cardiac structure and function. Furthermore, recent innovations enable the assessment of radial and longitudinal myocardial velocity, such that detection of sub-clinical changes is now possible. Thus, CMR may be ideal for cardiovascular assessment in pediatric CKD. This study aims to comprehensively assess cardiovascular function in pediatric CKD using CMR and determine its relationship with CKD severity. METHODS: A total of 120 children (40 mild, 40 moderate, 20 severe pre-dialysis CKD subjects and 20 healthy controls) underwent CMR with non-invasive blood pressure (BP) measurements. Cardiovascular parameters measured included systemic vascular resistance (SVR), total arterial compliance (TAC), left ventricular (LV) structure, ejection fraction (EF), cardiac timings, radial and longitudinal systolic and diastolic myocardial velocities. Between group comparisons and regression modelling were used to identify abnormalities in CKD and determine the effects of renal severity on myocardial function. RESULTS: The elevation in mean BP in CKD was accompanied by significantly increased afterload (SVR), without evidence of arterial stiffness (TAC) or increased fluid overload. Left ventricular volumes and global function were not abnormal in CKD. However, there was evidence of LV remodelling, prolongation of isovolumic relaxation time and reduced systolic and diastolic myocardial velocities. CONCLUSION: Abnormal cardiovascular function is evident in pre-dialysis pediatric CKD. Novel CMR biomarkers may be useful for the detection of subtle abnormalities in this population. Further studies are needed to determine to prognostic value of these biomarkers.

Physiological adaptations to chronic stress in healthy humans - why might the sexes have evolved different energy utilisation strategies?

KEY POINTS: The human stress response activates the autonomic nervous system and endocrine systems to increase performance during environmental challenges. This response is usually beneficial, improving the chance of overcoming environmental challenges, but costs resources such as energy. Humans and other animals are known to adapt their responses to acute stress when they are stimulated chronically, presumably to optimise resource utilisation. Characterisation of these adaptations has been limited. Using advanced imaging techniques, we show that cardiovascular and endocrine physiology, reflective of energy utilisation during acute stress, and energy storage (fat) differ between the sexes when they are exposed to chronic stress. We examine possible evolutionary explanations for these differences, related to energy use, and point out how these physiological differences could underpin known disparities between the sexes in their risk of important cardiometabolic disorders such as obesity and cardiovascular disease. ABSTRACT: Obesity and associated diseases, such as cardiovascular disease, are the dominant human health problems in the modern era. Humans develop these conditions partly because they consume excess energy and exercise too little. Stress might be one of the factors contributing to these disease-promoting behaviours. We postulate that sex-specific primordial energy optimisation strategies exist, which developed to help cope with chronic stress but have become maladaptive in modern societies, worsening health. To demonstrate the existence of these energy optimisation strategies, we recruited 88 healthy adults with varying adiposity and chronic stress exposure. Cardiovascular physiology at rest and during acute stress (Montreal Imaging Stress Task), and body fat distribution were measured using advanced magnetic resonance imaging methods, together with endocrine function, cardiovascular energy use and cognitive performance. Potential confounders such as lifestyle, social class and employment were accounted for. We found that women exposed to chronic stress had lower adiposity, greater acute stress cardiovascular responses and better cognitive performance. Conversely, chronic stress-exposed men had greater adiposity and lower cardiovascular responses to acute stress. These results provide initial support for our hypothesis that differing sex-specific energy conservation strategies exist. We propose that these strategies have initially evolved to benefit humans but are now maladaptive and increase the risk of disorders such as obesity, especially in men exposed to chronic stress.

Comprehensive assessment of the global and regional vascular responses to food ingestion in humans using novel rapid MRI.

Ingestion of food is known to increase mesenteric blood flow. It is not clear whether this increased flow demand is compensated by a rise in cardiac output (CO) alone or by redistribution of blood flow from other organs. We used a new comprehensive imaging method to assess the human cardiovascular response to food ingestion. Following a 12-h fast, blood flow in segments of the aorta and in organ-specific arteries, and ventricular volumes were assessed in 20 healthy adults using MRI at rest and following ingestion of a high-energy liquid meal. Systemic vascular resistance (SVR) fell substantially and CO rose significantly. Blood pressure remained stable. These changes were predominantly driven by a rapid fall in mesenteric vascular resistance, resulting in over four times more intestinal blood flow. Renal vascular resistance also declined but less dramatically. No changes in blood flow to the celiac territory, the brain, or the limbs were observed. In conclusion, this is the first study to fully characterize systemic and regional changes in vascular resistance after food ingestion in humans. Our findings show that the postprandial drop in SVR is fully compensated for by increased CO and not by redistribution of blood from other organs. With the exception of a modest increase in renal blood flow, there was no evidence of altered blood flow to nondigestive organs. The proposed oral food challenge protocol can be applied safely in an MRI environment and may be useful for studying the involvement of the gut in systemic or cardiovascular disease.

Rapid breath-hold assessment of myocardial velocities using spiral UNFOLD-ed SENSE tissue phase mapping.

PURPOSE: To develop and validate a rapid breath-hold tissue phase mapping (TPM) sequence. MATERIALS AND METHODS: The sequence was based on an efficient uniform density spiral acquisition, combined with data acceleration. A novel acquisition and reconstruction strategy enabled combination of UNFOLD (2×) and SENSE (3×): UNFOLD-ed SENSE. The sequence was retrospectively cardiac-gated, and a graphics processing unit (GPU) was used for rapid "online" reconstruction. The optimal UNFOLD parameters for the data were calculated using an in silico model. The technique was validated on a 1.5T MR scanner in 15 patients with known aortic valve disease, against a respiratory self-navigated free-breathing TPM technique. Quantitative image quality measures (velocity-to-noise and edge sharpness) were made as well as calculation of longitudinal, radial, and tangential myocardial velocities in the left ventricle. RESULTS: The proposed breath-hold TPM data took eight heartbeats to acquire. The breath-hold TPM images had significantly higher edge sharpness (P = 0.0014) than the self-navigated TPM images, but with significantly lower velocity-to-noise ratio (P < 0.0001). There was excellent agreement (r > 0.94) in the longitudinal, radial, and tangential velocities between the self-navigated data and the proposed breath-hold TPM sequence. CONCLUSION: We demonstrate the feasibility of using spiral UNFOLD-ed SENSE to measure myocardial velocities using a rapid breath-hold spiral TPM sequence. This novel technique might enable accurate measurement of myocardial velocities, in a short scan time, which is especially important in a busy clinical workflow. J. MAGN. RESON. IMAGING 2016;44:1003-1009.

Isometric stress in cardiovascular magnetic resonance-a simple and easily replicable method of assessing cardiovascular differences not apparent at rest.

INTRODUCTION: Isometric exercise may unmask cardiovascular disease not evident at rest, and cardiovascular magnetic resonance (CMR) imaging is proven for comprehensive resting assessment. This study devised a simple isometric exercise CMR methodology and assessed the hemodynamic response evoked by isometric exercise. METHODS: A biceps isometric exercise technique was devised for CMR, and 75 healthy volunteers were assessed at rest, after 3-minute biceps exercise, and 5-minute of recovery using: 1) blood pressure (BP) and 2) CMR measured aortic flow and left ventricular function. Total peripheral resistance (SVR) and arterial compliance (TAC), cardiac output (CO), left ventricular volumes and function (ejection fraction, stroke volume, power output), blood pressure (BP), heart rate (HR), and rate pressure product were assessed at all time points. RESULTS: Image quality was preserved during stress. During exercise there were increases in CO (+14.9 %), HR (+17.0 %), SVR (+9.8 %), systolic BP (+22.4 %), diastolic BP (+25.4 %) and mean BP (+23.2 %). In addition, there were decreases in TAC (-22.0 %) and left ventricular ejection fraction (-6.3 %). Age and body mass index modified the evoked response, even when resting measures were similar. CONCLUSIONS: Isometric exercise technique evokes a significant cardiovascular response in CMR, unmasking physiological differences that are not apparent at rest. KEY POINTS: • Isometric exercise unmasks cardiovascular differences not evident at rest. • CMR is the reference standard for non-invasive cardiovascular assessment at rest. • A new easily replicable method combines isometric exercise with CMR. • Significant haemodynamic changes occur and differences are unmasked. • The physiological, isometric CMR stressor can be easily replicated.

Noninvasive pulmonary artery wave intensity analysis in pulmonary hypertension.

Pulmonary wave reflections are a potential hemodynamic biomarker for pulmonary hypertension (PH) and can be analyzed using wave intensity analysis (WIA). In this study we used pulmonary vessel area and flow obtained using cardiac magnetic resonance (CMR) to implement WIA noninvasively. We hypothesized that this method could detect differences in reflections in PH patients compared with healthy controls and could also differentiate certain PH subtypes. Twenty patients with PH (35% CTEPH and 75% female) and 10 healthy controls (60% female) were recruited. Right and left pulmonary artery (LPA and RPA) flow and area curves were acquired using self-gated golden-angle, spiral, phase-contrast CMR with a 10.5-ms temporal resolution. These data were used to perform WIA on patients and controls. The presence of a proximal clot in CTEPH patients was determined from contemporaneous computed tomography/angiographic data. A backwards-traveling compression wave (BCW) was present in both LPA and RPA of all PH patients but was absent in all controls (P = 6e(-8)). The area under the BCW was associated with a sensitivity of 100% [95% confidence interval (CI) 63-100%] and specificity of 91% (95% CI 75-98%) for the presence of a clot in the proximal PAs of patients with CTEPH. In conclusion, WIA metrics were significantly different between patients and controls; in particular, the presence of an early BCW was specifically associated with PH. The magnitude of the area under the BCW showed discriminatory capacity for the presence of proximal PA clot in patients with CTEPH. We believe that these results demonstrate that WIA could be used in the noninvasive assessment of PH.

Assessment of cardiac time intervals using high temporal resolution real-time spiral phase contrast with UNFOLDed-SENSE.

PURPOSE: To develop a real-time phase contrast MR sequence with high enough temporal resolution to assess cardiac time intervals. METHODS: The sequence utilized spiral trajectories with an acquisition strategy that allowed a combination of temporal encoding (Unaliasing by fourier-encoding the overlaps using the temporal dimension; UNFOLD) and parallel imaging (Sensitivity encoding; SENSE) to be used (UNFOLDed-SENSE). An in silico experiment was performed to determine the optimum UNFOLD filter. In vitro experiments were carried out to validate the accuracy of time intervals calculation and peak mean velocity quantification. In addition, 15 healthy volunteers were imaged with the new sequence, and cardiac time intervals were compared to reference standard Doppler echocardiography measures. For comparison, in silico, in vitro, and in vivo experiments were also carried out using sliding window reconstructions. RESULTS: The in vitro experiments demonstrated good agreement between real-time spiral UNFOLDed-SENSE phase contrast MR and the reference standard measurements of velocity and time intervals. The protocol was successfully performed in all volunteers. Subsequent measurement of time intervals produced values in keeping with literature values and good agreement with the gold standard echocardiography. Importantly, the proposed UNFOLDed-SENSE sequence outperformed the sliding window reconstructions. CONCLUSION: Cardiac time intervals can be successfully assessed with UNFOLDed-SENSE real-time spiral phase contrast. Real-time MR assessment of cardiac time intervals may be beneficial in assessment of patients with cardiac conditions such as diastolic dysfunction.

Investigating the limitations of single breath-hold renal artery blood flow measurements using spiral phase contrast MR with R-R interval averaging.

PURPOSE: 1) To validate an R-R interval averaged golden angle spiral phase contrast magnetic resonance (RAGS PCMR) sequence against conventional cine PCMR for assessment of renal blood flow (RBF) in normal volunteers; and 2) To investigate the effects of motion and heart rate on the accuracy of flow measurements using an in silico simulation. MATERIALS AND METHODS: In 20 healthy volunteers RAGS (∼6 sec breath-hold) and respiratory-navigated cine (∼5 min) PCMR were performed in both renal arteries to assess RBF. A simulation of RAGS PCMR was used to assess the effect of heart rate (30-105 bpm), vessel expandability (0-150%) and translational motion (x1.0-4.0) on the accuracy of RBF measurements. RESULTS: There was good agreement between RAGS and cine PCMR in the volunteer study (bias: 0.01 L/min, limits of agreement: -0.04 to +0.06 L/min, P = 0.0001). The simulation demonstrated a positive linear relationship between heart rate and error (r = 0.9894, P < 0.0001), a negative linear relationship between vessel expansion and error (r = -0.9484, P < 0.0001), and a nonlinear, heart rate-dependent relationship between vessel translation and error. CONCLUSION: We have demonstrated that RAGS PCMR accurately measures RBF in vivo. However, the simulation reveals limitations in this technique at extreme heart rates (<40 bpm, >100 bpm), or when there is significant motion (vessel expandability: >80%, vessel translation: >x2.2).

Free breathing contrast-enhanced time-resolved magnetic resonance angiography in pediatric and adult congenital heart disease.

BACKGROUND: Contrast enhanced magnetic resonance angiography (MRA) is generally performed during a long breath-hold (BH), limiting its utility in infants and small children. This study proposes a free-breathing (FB) time resolved MRA (TRA) technique for use in pediatric and adult congenital heart disease (CHD). METHODS: A TRA sequence was developed by combining spiral trajectories with sensitivity encoding (SENSE, x4 kx-ky and x2 kz) and partial Fourier (75% in kz). As no temporal data sharing is used, an independent 3D data set was acquired every ~1.3s, with acceptable spatial resolution (~2.3x2.3x2.3 mm). The technique was tested during FB over 50 consecutive volumes. Conventional BH-MRA and FB-TRA data was acquired in 45 adults and children with CHD. We calculated quantitative image quality for both sequences. Diagnostic accuracy was assessed in all patients from both sequences. Additionally, vessel measurements were made at the sinotubular junction (N = 43), proximal descending aorta (N = 43), descending aorta at the level of the diaphragm (N = 43), main pulmonary artery (N = 35), left pulmonary artery (N = 35) and the right pulmonary artery (N = 35). Intra and inter observer variability was assessed in a subset of 10 patients. RESULTS: BH-MRA had significantly higher homogeneity in non-contrast enhancing tissue (coefficient of variance, P <0.0001), signal-to-noise ratio (P <0.0001), contrast-to-noise ratio (P <0.0001) and relative contrast (P = 0.02) compared to the FB-TRA images. However, homogeneity in the vessels was similar in both techniques (P = 0.52) and edge sharpness was significantly (P <0.0001) higher in FB-TRA compared to BH-MRA. BH-MRA provided overall diagnostic accuracy of 82%, and FB-TRA of 87%, with no statistical difference between the two sequences (P = 0.77). Vessel diameter measurements showed excellent agreement between the two techniques (r = 0.98, P <0.05), with no bias (0.0 mm, P = 0.71), and clinically acceptable limits of agreement (-2.7 to +2.8 mm). Inter and intra observer reproducibility showed good agreement of vessel diameters (r>0.988, P<0.0001), with negligible biases (between -0.2 and +0.1mm) and small limits of agreement (between -2.4 and +2.5mm). CONCLUSIONS: We have described a FB-TRA technique that is shown to enable accurate diagnosis and vessel measures compared to conventional BH-MRA. This simplifies the MRA technique and will enable angiography to be performed in children and adults whom find breath-holding difficult.