Detection and Monitoring of Acute Myocarditis Applying Quantitative Cardiovascular Magnetic Resonance.

BACKGROUND: Cardiovascular magnetic resonance based on the Lake Louise Criteria is used to make the diagnosis of acute myocarditis. Novel quantitative parametric mapping techniques promise to overcome some of its limitations. We aimed to evaluate quantitative cardiovascular magnetic resonance to detect and monitor acute myocarditis. METHODS AND RESULTS: Eighteen patients with clinical diagnosis of acute myocarditis (25 years [23-38 years]; 78% males) were prospectively enrolled and repeatedly underwent cardiovascular magnetic resonance at 1.5 T seven days (5-10 days) after symptom onset (FU0), after 5 weeks (FU1), and after 6 months (FU2). Eighteen age- and sex-matched healthy subjects served as controls. Cardiovascular magnetic resonance included imaging of edema, hyperemia, necrosis, and fibrosis using semiquantitative T2-weighted spin echo, T2 mapping, and T1 mapping before and 3 and 10 minutes after gadobutrol administration. Extracellular volume for diffuse and late gadolinium enhancement for focal fibrosis were assessed. Compared with controls, patients had significantly higher global T2 times at FU0 (55.1 ms [53.3-57.2 ms] versus 50.2 ms [49.2-52.0 ms]; P<0.001) and at FU1 (52.0 ms [52.0-53.2 ms]; P=0.007), which normalized at FU2 (50.9 ms [49.6-53.3 ms]; P=0.323). Global native T1 times in patients were elevated acutely (1004 ms [988-1048 ms] versus 975 ms [957-1004 ms]; P=0.002) and remained elevated throughout the follow-up (FU1: 998 ms [990-1027 ms]; P=0.014; FU2: 1000 ms [972-1027 ms]; P=0.044). Global extracellular volume fraction was statistically not different between patients and controls (P=0.057). 77.8% (14/18) of patients had focal late gadolinium enhancement. T2 ratio was significantly elevated in patients with myocarditis at FU0 (2.2 [2.0-2.3] versus 1.6 [1.5-1.7]; P<0.001). The difference decreased during follow-up (FU1: 1.9 [1.7-1.9]; P=0.001 and FU2: 1.7 [1.7-1.8]; P=0.053). The diagnostic accuracy to discriminate between patients with acute myocarditis and healthy controls was 86% for T2>52 ms, 78% for native T1>981 ms, 74% for extracellular volume fraction >0.24, and 100% for T2 ratio >1.9. CONCLUSIONS: Although both T2 and T1 mapping reliably detected acute myocarditis, only T2 mapping discriminated between acute and healed stages, underlining the incremental value of T2 mapping.

Effects of heart valve prostheses on phase contrast flow measurements in Cardiovascular Magnetic Resonance - a phantom study.

BACKGROUND: Cardiovascular Magnetic Resonance is often used to evaluate patients after heart valve replacement. This study systematically analyses the influence of heart valve prostheses on phase contrast measurements in a phantom trial. METHODS: Two biological and one mechanical aortic valve prostheses were integrated in a flow phantom. B0 maps and phase contrast measurements were acquired at a 1.5 T MR scanner using conventional gradient-echo sequences in predefined distances to the prostheses. Results were compared to measurements with a synthetic metal-free aortic valve. RESULTS: The flow results at the level of the prosthesis differed significantly from the reference flow acquired before the level of the prosthesis. The maximum flow miscalculation was 154 ml/s for one of the biological prostheses and 140 ml/s for the mechanical prosthesis. Measurements with the synthetic aortic valve did not show significant deviations. Flow values measured approximately 20 mm distal to the level of the prosthesis agreed with the reference flow for all tested all prostheses. CONCLUSIONS: The tested heart valve prostheses lead to a significant deviation of the measured flow rates compared to a reference. A distance of 20 mm was effective in our setting to avoid this influence.

Local Multi-Channel RF Surface Coil versus Body RF Coil Transmission for Cardiac Magnetic Resonance at 3 Tesla: Which Configuration Is Winning the Game?

INTRODUCTION: The purpose of this study was to demonstrate the feasibility and efficiency of cardiac MR at 3 Tesla using local four-channel RF coil transmission and benchmark it against large volume body RF coil excitation. METHODS: Electromagnetic field simulations are conducted to detail RF power deposition, transmission field uniformity and efficiency for local and body RF coil transmission. For both excitation regimes transmission field maps are acquired in a human torso phantom. For each transmission regime flip angle distributions and blood-myocardium contrast are examined in a volunteer study of 12 subjects. The feasibility of the local transceiver RF coil array for cardiac chamber quantification at 3 Tesla is demonstrated. RESULTS: Our simulations and experiments demonstrate that cardiac MR at 3 Tesla using four-channel surface RF coil transmission is competitive versus current clinical CMR practice of large volume body RF coil transmission. The efficiency advantage of the 4TX/4RX setup facilitates shorter repetition times governed by local SAR limits versus body RF coil transmission at whole-body SAR limit. No statistically significant difference was found for cardiac chamber quantification derived with body RF coil versus four-channel surface RF coil transmission. Our simulation also show that the body RF coil exceeds local SAR limits by a factor of ~2 when driven at maximum applicable input power to reach the whole-body SAR limit. CONCLUSION: Pursuing local surface RF coil arrays for transmission in cardiac MR is a conceptually appealing alternative to body RF coil transmission, especially for patients with implants.

Cardiac Involvement in Myotonic Dystrophy Type 2 Patients With Preserved Ejection Fraction: Detection by Cardiovascular Magnetic Resonance.

BACKGROUND: Myotonic dystrophy type 2 (DM2) is a genetic disorder characterized by skeletal muscle symptoms, metabolic changes, and cardiac involvement. Histopathologic alterations of the skeletal muscle include fibrosis and fatty infiltration. The aim of this study was to investigate whether subclinical cardiac involvement in DM2 is already detectable in preserved left ventricular function by cardiovascular magnetic resonance. METHODS AND RESULTS: Twenty-seven patients (mean age, 54±10 years; 20 females) with a genetically confirmed diagnosis of DM2 were compared with 17 healthy age- and sex-matched controls using a 1.5 T magnetic resonance imaging. For myocardial tissue differentiation, T1 and T2 mapping, fat/water-separated imaging, focal fibrosis imaging (late gadolinium enhancement [LGE]), and (1)H magnetic resonance spectroscopy were performed. Extracellular volume fraction was calculated. Conduction abnormalities were diagnosed based on Groh criteria. LGE located subepicardial basal inferolateral was detectable in 22% of the patients. Extracellular volume was increased in this region and in the adjacent medial inferolateral segment (P=0.03 compared with healthy controls). In 21% of patients with DM2, fat deposits were detectable (all women). The control group showed no abnormalities. Myocardial triglycerides were not different in LGE-positive and LGE-negative subjects (P=0.47). Six patients had indicators for conduction disease (60% of LGE-positive patients and 12.5% of LGE-negative patients). CONCLUSIONS: In DM2, subclinical myocardial injury was already detectable in preserved left ventricular ejection fraction. Extracellular volume was also increased in regions with no focal fibrosis. Myocardial fibrosis was related to conduction abnormalities.

Current T1 and T2 mapping techniques applied with simple thresholds cannot discriminate acute from chronic myocadial infarction on an individual patient basis: a pilot study.

BACKGROUND: Studying T1- and T2-mapping for discrimination of acute from chronic myocardial infarction (AMI, CMI). METHODS: Eight patients with AMI underwent CMR at 3 T acutely and after >3 months. Imaging techniques included: T2-weighted imaging, late enhancement (LGE), T2-mapping, native and post-contrast T1-mapping. Myocardial T2- and T1-relaxation times were determined for every voxel. Abnormal voxels as defined by having T2- and T1-values beyond a predefined threshold (T2 > 50 ms, native T1 > 1250 ms and post-contrast T1 < 350 ms) were highlighted and compared with LGE as the reference. RESULTS: Abnormal T2-relaxation times were present in the voxels with AMI (=> delete acute infarction; unfortunately this is not possible in your web interface) acute infarction only in half of the subjects. Abnormal T2-values were also present in subjects with CMI, thereby matching the chronically infarcted territory in some. Abnormal native T1 times were present in voxels with AMI in 5/8 subjects, but also remote from the infarcted territory in four. In CMI, abnormal native T1 values corresponded with infarcted voxels, but were also abnormal remote from the infarcted territory. Voxels with abnormal post-contrast T1-relaxation times agreed well with LGE in AMI and CMI. CONCLUSIONS: In this pilot-study, T2- and T1-mapping with simple thresholds did not facilitate the discrimination of AMI and CMI.

High Spatial Resolution Cardiovascular Magnetic Resonance at 7.0 Tesla in Patients with Hypertrophic Cardiomyopathy - First Experiences: Lesson Learned from 7.0 Tesla.

BACKGROUND: Cardiovascular Magnetic Resonance (CMR) provides valuable information in patients with hypertrophic cardiomyopathy (HCM) based on myocardial tissue differentiation and the detection of small morphological details. CMR at 7.0T improves spatial resolution versus today's clinical protocols. This capability is as yet untapped in HCM patients. We aimed to examine the feasibility of CMR at 7.0T in HCM patients and to demonstrate its capability for the visualization of subtle morphological details. METHODS: We screened 131 patients with HCM. 13 patients (9 males, 56 ±31 years) and 13 healthy age- and gender-matched subjects (9 males, 55 ±31years) underwent CMR at 7.0T and 3.0T (Siemens, Erlangen, Germany). For the assessment of cardiac function and morphology, 2D CINE imaging was performed (voxel size at 7.0T: (1.4x1.4x2.5) mm3 and (1.4x1.4x4.0) mm3; at 3.0T: (1.8x1.8x6.0) mm3). Late gadolinium enhancement (LGE) was performed at 3.0T for detection of fibrosis. RESULTS: All scans were successful and evaluable. At 3.0T, quantification of the left ventricle (LV) showed similar results in short axis view vs. the biplane approach (LVEDV, LVESV, LVMASS, LVEF) (p = 0.286; p = 0.534; p = 0.155; p = 0.131). The LV-parameters obtained at 7.0T where in accordance with the 3.0T data (pLVEDV = 0.110; pLVESV = 0.091; pLVMASS = 0.131; pLVEF = 0.182). LGE was detectable in 12/13 (92%) of the HCM patients. High spatial resolution CINE imaging at 7.0T revealed hyperintense regions, identifying myocardial crypts in 7/13 (54%) of the HCM patients. All crypts were located in the LGE-positive regions. The crypts were not detectable at 3.0T using a clinical protocol. CONCLUSIONS: CMR at 7.0T is feasible in patients with HCM. High spatial resolution gradient echo 2D CINE imaging at 7.0T allowed the detection of subtle morphological details in regions of extended hypertrophy and LGE.

Myocardial dysfunction in patients with aortic stenosis and hypertensive heart disease assessed by MR tissue phase mapping.

PURPOSE: To identify abnormalities of myocardial velocities in patients with left ventricular pressure overload using magnetic resonance tissue phase mapping (TPM). MATERIAL AND METHODS: Thirty-three patients (nine with hypertensive heart disease [HYP], 24 with aortic stenosis [AS]) and 41 healthy controls were enrolled. To assess left ventricular motion, a basal, midventricular, and apical slice were acquired using three-directional velocity-encoded phase-contrast MR with a 3T system. Target parameters were peak longitudinal (Vz ) and radial (Vr ) velocity in systole and diastole (Peaksys , Peakdias ). Analysis was done on each myocardial segment. In a subgroup (n = 7 HYP, n = 12 AS, n = 24 controls), measurement was repeated during handgrip exercise. RESULTS: AS had significantly lower Vz -Peaksys in the inferolateral and inferoseptal wall (P = 0.003-0.029) and Vr -Peaksys in the septum and anterior wall (P = 0.001-0.013) than controls. Vz -Peakdias and Vr -Peakdias were lower in AS than in controls in almost all segments (P < 0.001-0.028). HYP showed reduced Vz -Peakdias compared to controls in all basal segments as well as in the lateral midventricular wall (P < 0.001-0.045), and reduced Vr -Peakdias compared to controls predominantly in the midventricular and apical segments (P = 0.004-0.042). AS patients with focal fibrosis had significantly reduced myocardial velocities (P = 0.001-0.047) in segments without late enhancement. During exercise, Vz -Peaksys , Vr -Peaksys , and Vz -Peakdias remained unchanged in AS and HYP, but decreased in the lateral wall in controls (P < 0.001-0.043). CONCLUSION: Even with preserved left ventricle (LV) ejection fraction, peak longitudinal and radial velocities of the LV are reduced in AS and HYP, indicating early functional impairment. J. Magn. Reson. Imaging 2016;44:168-177.

Real-time phase contrast magnetic resonance imaging for assessment of haemodynamics: from phantom to patients.

OBJECTIVES: Assessment of haemodynamics is crucial in many cardiac diseases. Phase contrast MRI (PC-MRI) can accurately access it. Arrhythmia is a major limitation in conventional segmented PC-MRI (SEG). A real-time PC-MRI sequence (RT) could overcome this. We validated RT by comparing to SEG. METHODS: A prototype RT using shared velocity encoding was tested against SEG at 1.5 T in a flow phantom and consecutively included patients with (n = 55) or without (n = 59) aortic valve disease. In patients with atrial fibrillation (Afib, n = 15), only RT was applied. Phantom: PC images were acquired in front of and behind an interchangeable aortic-stenosis-like inlay. Mean velocity and flow were quantified. PATIENTS: PC images were acquired in the ascending aorta, pulmonary trunk and superior caval vein. Peak velocity, stroke volume and regurgitant fraction were quantified. RESULTS: Phantom: Mean velocities (11 ± 1 to 207 ± 10 cm/s) and flow correlated closely between SEG and RT (r ≥ 0.99, ICC ≥ 0.98, p < 0.0005). Patients without AVD or with aortic regurgitation: Concordance of SEG and RT was excellent regarding peak velocities, stroke volumes (r ≥ 0.91, ICC ≥ 0.94, p < 0.0005) and regurgitant fractions (r = 0.95, ICC = 0.95, p < 0.0005). RT was feasible in all patients with Afib. CONCLUSIONS: The real-time sequence is accurate compared to conventional segmented PC-MRI. Its applicability in Afib was shown. Real-time PC-MRI might become a valuable tool in arrhythmia. KEY POINTS: • Assessment of haemodynamics is crucial in many cardiac diseases. • Arrhythmias are a major limitation of conventional techniques in cardiac magnetic resonance. • A real-time technique, which allows application in arrhythmia, was validated. • This real-time technique might become a valuable tool in arrhythmic patients.

Cardiac Fibrosis in Aortic Stenosis and Hypertensive Heart Disease Assessed by Magnetic Resonance T1 Mapping.

BACKGROUND: Continuous pressure overload may lead to subclinical myocardial tissue changes in patients with hypertensive heart disease (HHD) and aortic stenosis (AS). The study aim was to detect interstitial fibrosis using quantitative cardiovascular magnetic resonance. METHODS: Fifteen patients with HHD (arterial hypertension + septal wall thickness ≥13 mm), 33 with AS (eight mild, 15 moderate, 10 severe), and 60 healthy controls were enrolled. Native T1 maps (modified Look-Locker inversion recovery) were obtained in a basal, mid-ventricular, and apical shortaxis slice of the left ventricle to assess cardiac fibrosis. Focal fibrosis was assessed with late gadolinium enhancement (LGE). RESULTS: Patients with HHD and controls did not differ regarding the native myocardial T1 values, both per slice and per segment. In AS patients, apical native T1 values were lower than in controls, and there was a trend towards higher T1 values in the septum in severe AS (1172.6 ± 62.0 ms versus 1152.9 ± 43.9 ms). Five HHD patients and 11 AS patients had non-ischemic fibrosis in LGE images. Native T1 times did not differ between LGE-positive and LGEnegative groups (both with inclusion and exclusion of segments with LGE). CONCLUSIONS: T1 mapping did not reveal any evidence of abnormal interstitial fibrosis in HHD subjects with mild hypertrophy. In severe AS, a trend towards more interstitial fibrosis was present, but absolute differences were small for decision making.

Anchoring dipalmitoyl phosphoethanolamine to nanoparticles boosts cellular uptake and fluorine-19 magnetic resonance signal.

Magnetic resonance (MR) methods to detect and quantify fluorine ((19)F) nuclei provide the opportunity to study the fate of cellular transplants in vivo. Cells are typically labeled with (19)F nanoparticles, introduced into living organisms and tracked by (19)F MR methods. Background-free imaging and quantification of cell numbers are amongst the strengths of (19)F MR-based cell tracking but challenges pertaining to signal sensitivity and cell detection exist. In this study we aimed to overcome these limitations by manipulating the aminophospholipid composition of (19)F nanoparticles in order to promote their uptake by dendritic cells (DCs). As critical components of biological membranes, phosphatidylethanolamines (PE) were studied. Both microscopy and MR spectroscopy methods revealed a striking (at least one order of magnitude) increase in cytoplasmic uptake of (19)F nanoparticles in DCs following enrichment with 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE). The impact of enriching (19)F nanoparticles with PE on DC migration was also investigated. By manipulating the nanoparticle composition and as a result the cellular uptake we provide here one way of boosting (19)F signal per cell in order to overcome some of the limitations related to (19)F MR signal sensitivity. The boost in signal is ultimately necessary to detect and track cells in vivo.

Accelerated fast spin-echo magnetic resonance imaging of the heart using a self-calibrated split-echo approach.

PURPOSE: Design, validation and application of an accelerated fast spin-echo (FSE) variant that uses a split-echo approach for self-calibrated parallel imaging. METHODS: For self-calibrated, split-echo FSE (SCSE-FSE), extra displacement gradients were incorporated into FSE to decompose odd and even echo groups which were independently phase encoded to derive coil sensitivity maps, and to generate undersampled data (reduction factor up to R = 3). Reference and undersampled data were acquired simultaneously. SENSE reconstruction was employed. RESULTS: The feasibility of SCSE-FSE was demonstrated in phantom studies. Point spread function performance of SCSE-FSE was found to be competitive with traditional FSE variants. The immunity of SCSE-FSE for motion induced mis-registration between reference and undersampled data was shown using a dynamic left ventricular model and cardiac imaging. The applicability of black blood prepared SCSE-FSE for cardiac imaging was demonstrated in healthy volunteers including accelerated multi-slice per breath-hold imaging and accelerated high spatial resolution imaging. CONCLUSION: SCSE-FSE obviates the need of external reference scans for SENSE reconstructed parallel imaging with FSE. SCSE-FSE reduces the risk for mis-registration between reference scans and accelerated acquisitions. SCSE-FSE is feasible for imaging of the heart and of large cardiac vessels but also meets the needs of brain, abdominal and liver imaging.

Rapid parametric mapping of the longitudinal relaxation time T1 using two-dimensional variable flip angle magnetic resonance imaging at 1.5 Tesla, 3 Tesla, and 7 Tesla.

INTRODUCTION: Visual but subjective reading of longitudinal relaxation time (T1) weighted magnetic resonance images is commonly used for the detection of brain pathologies. For this non-quantitative measure, diagnostic quality depends on hardware configuration, imaging parameters, radio frequency transmission field (B1+) uniformity, as well as observer experience. Parametric quantification of the tissue T1 relaxation parameter offsets the propensity for these effects, but is typically time consuming. For this reason, this study examines the feasibility of rapid 2D T1 quantification using a variable flip angles (VFA) approach at magnetic field strengths of 1.5 Tesla, 3 Tesla, and 7 Tesla. These efforts include validation in phantom experiments and application for brain T1 mapping. METHODS: T1 quantification included simulations of the Bloch equations to correct for slice profile imperfections, and a correction for B1+. Fast gradient echo acquisitions were conducted using three adjusted flip angles for the proposed T1 quantification approach that was benchmarked against slice profile uncorrected 2D VFA and an inversion-recovery spin-echo based reference method. Brain T1 mapping was performed in six healthy subjects, one multiple sclerosis patient, and one stroke patient. RESULTS: Phantom experiments showed a mean T1 estimation error of (-63±1.5)% for slice profile uncorrected 2D VFA and (0.2±1.4)% for the proposed approach compared to the reference method. Scan time for single slice T1 mapping including B1+ mapping could be reduced to 5 seconds using an in-plane resolution of (2×2) mm2, which equals a scan time reduction of more than 99% compared to the reference method. CONCLUSION: Our results demonstrate that rapid 2D T1 quantification using a variable flip angle approach is feasible at 1.5T/3T/7T. It represents a valuable alternative for rapid T1 mapping due to the gain in speed versus conventional approaches. This progress may serve to enhance the capabilities of parametric MR based lesion detection and brain tissue characterization.

Modular 32-channel transceiver coil array for cardiac MRI at 7.0T.

PURPOSE: To design and evaluate a modular transceiver coil array with 32 independent channels for cardiac MRI at 7.0T. METHODS: The modular coil array comprises eight independent building blocks, each containing four transceiver loop elements. Numerical simulations were used for B1 (+) field homogenization and radiofrequency (RF) safety validation. RF characteristics were examined in a phantom study. The array's suitability for accelerated high spatial resolution two-dimensional (2D) FLASH CINE imaging of the heart was examined in a volunteer study. RESULTS: Transmission field adjustments and RF characteristics were found to be suitable for the volunteer study. The signal-to-noise intrinsic to 7.0T together with the coil performance afforded a spatial resolution of 1.1 × 1.1 × 2.5 mm(3) for 2D CINE FLASH MRI, which is by a factor of 6 superior to standardized CINE protocols used in clinical practice at 1.5T. The 32-channel transceiver array supports one-dimensional acceleration factors of up to R = 4 without impairing image quality significantly. CONCLUSION: The modular 32-channel transceiver cardiac array supports accelerated and high spatial resolution cardiac MRI. The array is compatible with multichannel transmission and provides a technological basis for future clinical assessment of parallel transmission techniques at 7.0T.

Myocardial T1 and T2 mapping at 3 T: reference values, influencing factors and implications.

BACKGROUND: Myocardial T1 and T2 mapping using cardiovascular magnetic resonance (CMR) are promising to improve tissue characterization and early disease detection. This study aimed at analyzing the feasibility of T1 and T2 mapping at 3 T and providing reference values. METHODS: Sixty healthy volunteers (30 males/females, each 20 from 20-39 years, 40-59 years, 60-80 years) underwent left-ventricular T1 and T2 mapping in 3 short-axis slices at 3 T. For T2 mapping, 3 single-shot steady-state free precession (SSFP) images with different T2 preparation times were acquired. For T1 mapping, modified Look-Locker inversion recovery technique with 11 single shot SSFP images was used before and after injection of gadolinium contrast. T1 and T2 relaxation times were quantified for each slice and each myocardial segment. RESULTS: Mean T2 and T1 (pre-/post-contrast) times were: 44.1 ms/1157.1 ms/427.3 ms (base), 45.1 ms/1158.7 ms/411.2 ms (middle), 46.9 ms/1180.6 ms/399.7 ms (apex). T2 and pre-contrast T1 increased from base to apex, post-contrast T1 decreased. Relevant inter-subject variability was apparent (scatter factor 1.08/1.05/1.11 for T2/pre-contrast T1/post-contrast T1). T2 and post-contrast T1 were influenced by heart rate (p < 0.0001, p = 0.0020), pre-contrast T1 by age (p < 0.0001). Inter- and intra-observer agreement of T2 (r = 0.95; r = 0.95) and T1 (r = 0.91; r = 0.93) were high. T2 maps: 97.7% of all segments were diagnostic and 2.3% were excluded (susceptibility artifact). T1 maps (pre-/post-contrast): 91.6%/93.9% were diagnostic, 8.4%/6.1% were excluded (predominantly susceptibility artifact 7.7%/3.2%). CONCLUSIONS: Myocardial T2 and T1 reference values for the specific CMR setting are provided. The diagnostic impact of the high inter-subject variability of T2 and T1 relaxation times requires further investigation.

Assessment of the right ventricle with cardiovascular magnetic resonance at 7 Tesla.

BACKGROUND: Functional and morphologic assessment of the right ventricle (RV) is of clinical importance. Cardiovascular magnetic resonance (CMR) at 1.5T has become gold standard for RV chamber quantification and assessment of even small wall motion abnormalities, but tissue analysis is still hampered by limited spatial resolution. CMR at 7T promises increased resolution, but is technically challenging. We examined the feasibility of cine imaging at 7T to assess the RV. METHODS: Nine healthy volunteers underwent CMR at 7T using a 16-element TX/RX coil and acoustic cardiac gating. 1.5T served as gold standard. At 1.5T, steady-state free-precession (SSFP) cine imaging with voxel size (1.2 x 1.2 x 6) mm3 was used; at 7T, fast gradient echo (FGRE) with voxel size (1.2 x 1.2 x 6) mm3 and (1.3 x 1.3 x 4) mm3 were applied. RV dimensions (RVEDV, RVESV), RV mass (RVM) and RV function (RVEF) were quantified in transverse slices. Overall image quality, image contrast and image homogeneity were assessed in transverse and sagittal views. RESULTS: All scans provided diagnostic image quality. Overall image quality and image contrast of transverse RV views were rated equally for SSFP at 1.5T and FGRE at 7T with voxel size (1.3 x 1.3 x 4)mm3. FGRE at 7T provided significantly lower image homogeneity compared to SSFP at 1.5T. RVEDV, RVESV, RVEF and RVM did not differ significantly and agreed close between SSFP at 1.5T and FGRE at 7T (p=0.5850; p=0.5462; p=0.2789; p=0.0743). FGRE at 7T with voxel size (1.3 x 1.3 x 4) mm3 tended to overestimate RV volumes compared to SSFP at 1.5T (mean difference of RVEDV 8.2 ± 9.3 ml) and to FGRE at 7T with voxel size (1.2 x 1.2 x 6) mm3 (mean difference of RVEDV 9.3 ± 8.6 ml). CONCLUSIONS: FGRE cine imaging of the RV at 7T was feasible and provided good image quality. RV dimensions and function were comparable to SSFP at 1.5T as gold standard.

Isometric handgrip exercise during cardiovascular magnetic resonance imaging: set-up and cardiovascular effects.

PURPOSE: To establish a suitable setup for combining isometric handgrip exercise with cardiovascular magnetic resonance (CMR) imaging and to assess cardiovascular effects. MATERIALS AND METHODS: Fifty-three healthy volunteers (31 males, mean age 45 ± 17 years) underwent handgrip exercise in a 3T scanner using a prototype handgrip system and a custom-made feedback system that displayed the force. Handgrip was sustained at 30% of the maximal contraction for 6-8 minutes. Heart rate, blood pressure (BP), and double product were determined sequentially. Stroke volume was quantified in a subgroup (n = 21) at rest and stress using phase contrast acquisitions. RESULTS: Heart rate increased significantly between rest and stress by 20 ± 13%, systolic / diastolic / mean BP by 15 ± 11% / 20 ± 18% / 17 ± 13%, double product by 37 ± 21%, and cardiac output by 27 ± 16% (each P < 0.001). Stroke volume did not significantly increase (3 ± 9%; P = 0.215). Higher age was associated with reduced increase of stroke volume (P = 0.022) and cardiac output (P < 0.001). Overweight subjects showed less increases in heart rate (P = 0.021) and cardiac output (P = 0.002). CONCLUSION: The handgrip exercise during CMR with the presented set-up leads to considerable hemodynamic changes in healthy volunteers.

Progress and promises of human cardiac magnetic resonance at ultrahigh fields: a physics perspective.

A growing number of reports eloquently speak about explorations into cardiac magnetic resonance (CMR) at ultrahigh magnetic fields (B0≥7.0 T). Realizing the progress, promises and challenges of ultrahigh field (UHF) CMR this perspective outlines current trends in enabling MR technology tailored for cardiac MR in the short wavelength regime. For this purpose many channel radiofrequency (RF) technology concepts are outlined. Basic principles of mapping and shimming of transmission fields including RF power deposition considerations are presented. Explorations motivated by the safe operation of UHF-CMR even in the presence of conductive implants are described together with the physics, numerical simulations and experiments, all of which detailing antenna effects and RF heating induced by intracoronary stents at 7.0 T. Early applications of CMR at 7.0 T and their clinical implications for explorations into cardiovascular diseases are explored including assessment of cardiac function, myocardial tissue characterization, MR angiography of large and small vessels as well as heteronuclear MR of the heart and the skin. A concluding section ventures a glance beyond the horizon and explores future directions. The goal here is not to be comprehensive but to inspire the biomedical and diagnostic imaging communities to throw further weight behind the solution of the many remaining unsolved problems and technical obstacles of UHF-CMR with the goal to transfer MR physics driven methodological advancements into extra clinical value.

Design, construction, and evaluation of a dynamic MR compatible cardiac left ventricle model.

PURPOSE: Development of magnetic resonance (MR) sequences is important to answer clinical questions and to overcome current limitations. To meet the challenges of cardiac MR, dynamic and reproducible testing conditions are required. We aimed at developing a dynamic MR-compatible cardiac left ventricle model that imitates myocardial tissue properties and simulates dynamic motion. METHODS: A dynamic left ventricle silicone model was designed to match myocardial T(1) and T(2) relaxation times. Silicone mixtures were explored to replicate T(2) values of myocardial edema. A controllable piston pump was constructed to produce pulsatile flow paradigms. They were validated against flow sensors and MR data, including SSFP-based and phase-contrast-based sequences. A dedicated software interface was developed for the control. RESULTS: Model dimensions represented cardiac left ventricle dimensions of healthy men. The range of end diastolic volumes was 85-175 ml, depending on the driven stroke volume. Stroke volume quantification for flow paradigms of 30∕60∕90∕120 ml resulted in 29.2∕57.6∕88.8∕118.4 ml by MR volumetry, 29.6∕59.9∕89.4∕119.0 ml by phase contrast measurements, and 29.9∕60.4∕91.1∕120.9 ml by flow meter revealing consistency. The system accurately replicated physiological and pathophysiological flow paradigms. The silicon model exhibited T(1) of 1002 ± 8 ms, T(2) of 58 ± 1 ms. Signal intensities (a.u.) of the ventricle model were 128 ± 23 for FGRE (vs 138 ± 17 in vivo) and 1156 ± 37 for b-SSFP (vs 991 ± 96 in vivo). T(2) of 75 ± 2 ms was achieved for the myocardial pathology. CONCLUSIONS: We developed a controllable left ventricle model resembling MR signal characteristics of human myocardium, including pathological conditions, and allowing for the replication of contraction and flow paradigms.

Detailing the use of magnetohydrodynamic effects for synchronization of MRI with the cardiac cycle: a feasibility study.

PURPOSE: To investigate the feasibility of using magnetohydrodynamic (MHD) effects for synchronization of magnetic resonance imaging (MRI) with the cardiac cycle. MATERIALS AND METHODS: The MHD effect was scrutinized using a pulsatile flow phantom at B(0) = 7.0 T. MHD effects were examined in vivo in healthy volunteers (n = 10) for B(0) ranging from 0.05-7.0 T. Noncontrast-enhanced MR angiography (MRA) of the carotids was performed using a gated steady-state free-precession (SSFP) imaging technique in conjunction with electrocardiogram (ECG) and MHD synchronization. RESULTS: The MHD potential correlates with flow velocities derived from phase contrast MRI. MHD voltages depend on the orientation between B(0) and the flow of a conductive fluid. An increase in the interelectrode spacing along the flow increases the MHD potential. In vivo measurement of the MHD effect provides peak voltages of 1.5 mV for surface areas close to the common carotid artery at B(0) = 7.0 T. Synchronization of MRI with the cardiac cycle using MHD triggering is feasible. MHD triggered MRA of the carotids at 3.0 T showed an overall image quality and richness of anatomic detail, which is comparable to ECG-triggered MRAs. CONCLUSION: This feasibility study demonstrates the use of MHD effects for synchronization of MR acquisitions with the cardiac cycle.

Design and application of a four-channel transmit/receive surface coil for functional cardiac imaging at 7T.

PURPOSE: To design and evaluate a four-channel cardiac transceiver coil array for functional cardiac imaging at 7T. MATERIALS AND METHODS: A four-element cardiac transceiver surface coil array was developed with two rectangular loops mounted on an anterior former and two rectangular loops on a posterior former. specific absorption rate (SAR) simulations were performed and a B 1+ calibration method was applied prior to obtain 2D FLASH CINE (mSENSE, R = 2) images from nine healthy volunteers with a spatial resolution of up to 1 × 1 × 2.5 mm(3). RESULTS: Tuning and matching was found to be better than 10 dB for all subjects. The decoupling (S(21)) was measured to be >18 dB between neighboring loops, >20 dB for opposite loops, and >30 dB for other loop combinations. SAR values were well within the limits provided by the IEC. Imaging provided clinically acceptable signal homogeneity with an excellent blood-myocardium contrast applying the B 1+ calibration approach. CONCLUSION: A four-channel cardiac transceiver coil array for 7T was built, allowing for cardiac imaging with clinically acceptable signal homogeneity and an excellent blood-myocardium contrast. Minor anatomic structures, such as pericardium, mitral, and tricuspid valves and their apparatus, as well as trabeculae, were accurately delineated.