Three-dimensional sector-wise golden angle-improved k-space uniformity after electrocardiogram binning.

PURPOSE: To develop and evaluate a 3D sector-wise golden-angle (3D-SWIG) profile ordering scheme for cardiovascular MR cine imaging that maintains high k-space uniformity after electrocardiogram (ECG) binning. METHOD: Cardiovascular MR (CMR) was performed at 1.5 T. A balanced SSFP pulse sequence was implemented with a novel 3D-SWIG radial ordering, where k-space was divided into wedges, and each wedge was acquired in a separate heartbeat. The high uniformity of k-space coverage after physiological binning can be used to perform functional imaging using a very short acquisition. The 3D-SWIG was compared with two commonly used 3D radial trajectories for CMR (i.e., double golden angle and spiral phyllotaxis) in numerical simulations. Free-breathing 3D-SWIG and conventional breath-held 2D cine were compared in patients (n = 17) referred clinically for CMR. Quantitative comparison was performed based on left ventricular segmentation. RESULTS: Numerical simulations showed that 3D-SWIG both required smaller steps between successive readouts and achieved better k-space sampling uniformity after binning than either the double golden angle or spiral phyllotaxis trajectories. In vivo evaluation showed that measurements of left ventricular ejection fraction calculated from a 48 heart-beat free-breathing 3D-SWIG acquisition were highly reproducible and agreed with breath-held 2D-Cartesian cine (mean ± SD difference of -3.1 ± 3.5% points). CONCLUSIONS: The 3D-SWIG acquisition offers a simple solution for highly improved k-space uniformity after physiological binning. The feasibility of the 3D-SWIG method is demonstrated in this study through whole-heart cine imaging during free breathing with an acquisition time of less than 1 min.

Generalization of three-dimensional golden-angle radial acquisition to reduce eddy current artifacts in bSSFP CMR imaging.

PURPOSE: We propose a novel generalization of the three-dimensional double-golden-angle profile ordering, which allows for whole-heart volumetric imaging with retrospective binning and reduced eddy current artifacts. METHODS: A novel theory bridging the gap between the three-dimensional double golden-angle trajectory, and the two-dimensional tiny-golden-angle trajectory is presented. This enables a class of double golden-angle profile orderings with a smaller angular distance between successive k-space readouts. The novel profile orderings were evaluated through simulations, phantom experiments, and in vivo imaging. Comparisons were made to the original double-golden-angle trajectory. Image uniformity and off-resonance sensitivity were evaluated using phantom measurements, and qualitative image quality was assessed using in vivo images acquired in a healthy volunteer. RESULTS: The proposed theory successfully reduced the angular step while maintaining image uniformity after binning. Simulations revealed a slow degradation with decreasing angular steps and an increasing number of physiological bins. The phantom images showed a definite improvement in image uniformity and increased robustness to off-resonance, and in vivo imaging corroborated those findings. CONCLUSION: Reducing the angular step in cardio-respiratory-binned golden-angle imaging shows potential for overcoming eddy current-induced image artifacts associated with 3D golden-angle radial imaging.

Sector-wise golden-angle phase contrast with high temporal resolution for evaluation of left ventricular diastolic dysfunction.

PURPOSE: To develop a high temporal resolution phase-contrast pulse sequence for evaluation of diastolic filling patterns, and to evaluate it in comparison to transthoracic echocardiography. METHODS: A phase-contrast velocity-encoded gradient-echo pulse sequence was implemented with a sector-wise golden-angle radial ordering. Acquisitions were optimized for myocardial tissue (TE/TR: 4.4/6.8 ms, flip angle: 8º, velocity encoding: 30 cm/s) and transmitral flow (TE/TR: 4.0/6.6 ms, flip angle: 20º, velocity encoding: 150 cm/s). Shared velocity encoding was combined with a sliding-window reconstruction that enabled up to 250 frames per cardiac cycle. Transmitral and myocardial velocities were measured in 35 patients. Echocardiographic velocities were obtained with pulsed-wave Doppler using standard methods. RESULTS: Myocardial velocity showed a low difference and good correlation between MRI and Doppler (mean ± 95% limits of agreement 0.9 ± 3.7 cm/s, R2 = 0.63). Transmitral velocity was underestimated by MRI (P < .05) with a difference of -11 ± 28 cm/s (R2 = 0.45). The early-to-late ratio correlated well (R2 = 0.66) with a minimal difference (0.03 ± 0.6). Analysis of interobserver and intra-observer variability showed excellent agreement for all measurements. CONCLUSIONS: The proposed method enables the acquisition of phase-contrast images during a single breath-hold with a sufficiently high temporal resolution to match transthoracic echocardiography, which opens the possibility for many clinically relevant variables to be assessed by MRI.

Clinical validation of three cardiovascular magnetic resonance techniques to measure strain and torsion in patients with suspected coronary artery disease.

BACKGROUND: Several cardiovascular magnetic resonance (CMR) techniques can measure myocardial strain and torsion with high accuracy. The purpose of this study was to compare displacement encoding with stimulated echoes (DENSE), tagging and feature tracking (FT) for measuring circumferential and radial myocardial strain and myocardial torsion in order to assess myocardial function and infarct scar burden both at a global and at a segmental level. METHOD: 116 patients with a high likelihood of coronary artery disease (European SCORE > 15%) underwent CMR examination including cine images, tagging, DENSE and late gadolinium enhancement (LGE) in the short axis direction. In total, 97 patients had signs of myocardial disease and 19 had no abnormalities in terms of left ventricular (LV) wall mass index, LV ejection fraction, wall motion, LGE or a history of myocardial infarction. Thirty-four patients had myocardial infarct scar with a transmural LGE extent (transmurality) that exceeded 50% of the wall thickness in at least one segment. Global circumferential strain (GCS) and global radial strain (GRS) was analyzed using FT of cine loops, deformation of tag lines or DENSE displacement. RESULTS: DENSE and tagging both showed high sensitivity (82% and 71%) at a specificity of 80% for the detection of segments with > 50% LGE transmurality, and receiver operating characteristics (ROC) analysis showed significantly higher area under the curve-values (AUC) for DENSE (0.87) than for tagging (0.83, p < 0.001) and FT (0.66, p = 0.003). GCS correlated with global LGE when determined with DENSE (r = 0.41), tagging (r = 0.37) and FT (r = 0.15). GRS had a low but significant negative correlation with LGE; DENSE r = - 0.10, FT r = - 0.07 and tagging r = - 0.16. Torsion from DENSE and tagging had a weak correlation (- 0.20 and - 0.22 respectively) with global LGE. CONCLUSION: Circumferential strain from DENSE detected segments with > 50% scar with a higher AUC than strain determined from tagging and FT at a segmental level. GCS and torsion computed from DENSE and tagging showed similar correlation with global scar size, while when computed from FT, the correlation was lower.

Cardiovascular magnetic resonance 4D flow analysis has a higher diagnostic yield than Doppler echocardiography for detecting increased pulmonary artery pressure.

BACKGROUND: Pulmonary hypertension is definitively diagnosed by the measurement of mean pulmonary artery (PA) pressure (mPAP) using right heart catheterization. Cardiovascular magnetic resonance (CMR) four-dimensional (4D) flow analysis can estimate mPAP from blood flow vortex duration in the PA, with excellent results. Moreover, the peak systolic tricuspid regurgitation (TR) pressure gradient (TRPG) measured by Doppler echocardiography is commonly used in clinical routine to estimate systolic PA pressure. This study aimed to compare CMR and echocardiography with regards to quantitative and categorical agreement, and diagnostic yield for detecting increased PA pressure. METHODS: Consecutive clinically referred patients (n = 60, median [interquartile range] age 60 [48-68] years, 33% female) underwent echocardiography and CMR at 1.5 T (n = 43) or 3 T (n = 17). PA vortex duration was used to estimate mPAP using a commercially available time-resolved multiple 2D slice phase contrast three-directional velocity encoded sequence covering the main PA. Transthoracic Doppler echocardiography was performed to measure TR and derive TRPG. Diagnostic yield was defined as the fraction of cases in which CMR or echocardiography detected an increased PA pressure, defined as vortex duration ≥15% of the cardiac cycle (mPAP ≥25 mmHg) or TR velocity > 2.8 m/s (TRPG > 31 mmHg). RESULTS: Both CMR and echocardiography showed normal PA pressure in 39/60 (65%) patients and increased PA pressure in 9/60 (15%) patients, overall agreement in 48/60 (80%) patients, kappa 0.49 (95% confidence interval 0.27-0.71). CMR had a higher diagnostic yield for detecting increased PA pressure compared to echocardiography (21/60 (35%) vs 9/60 (15%), p < 0.001). In cases with both an observable PA vortex and measurable TR velocity (34/60, 56%), TRPG was correlated with mPAP (R2 = 0.65, p < 0.001). CONCLUSIONS: There is good quantitative and fair categorical agreement between estimated mPAP from CMR and TRPG from echocardiography. CMR has higher diagnostic yield for detecting increased PA pressure compared to echocardiography, potentially due to a lower sensitivity of echocardiography in detecting increased PA pressure compared to CMR, related to limitations in the ability to adequately visualize and measure the TR jet by echocardiography. Future comparison between echocardiography, CMR and invasive measurements are justified to definitively confirm these findings.

The dynamics of extracellular gadolinium-based contrast agent excretion into pleural and pericardial effusions quantified by T1 mapping cardiovascular magnetic resonance.

INTRODUCTION: Excretion of cardiovascular magnetic resonance (CMR) extracellular gadolinium-based contrast agents (GBCA) into pleural and pericardial effusions, sometimes referred to as vicarious excretion, has been described as a rare occurrence using T1-weighted imaging. However, the T1 mapping characteristics as well as presence, magnitude and dynamics of contrast excretion into these effusions is not known. AIMS: To investigate and compare the differences in T1 mapping characteristics and extracellular GBCA excretion dynamics in pleural and pericardial effusions. METHODS: Clinically referred patients with a pericardial and/or pleural effusion underwent CMR T1 mapping at 1.5 T before, and at 3 (early) and at 27 (late) minutes after administration of an extracellular GBCA (0.2 mmol/kg, gadoteric acid). Analyzed effusion characteristics were native T1, ΔR1 early and late after contrast injection, and the effusion-volume-independent early-to-late contrast concentration ratio ΔR1early/ΔR1late, where ΔR1 = 1/T1post-contrast - 1/T1native. RESULTS: Native T1 was lower in pericardial effusions (n = 69) than in pleural effusions (n = 54) (median [interquartile range], 2912 [2567-3152] vs 3148 [2692-3494] ms, p = 0.005). Pericardial and pleural effusions did not differ with regards to ΔR1early (0.05 [0.03-0.10] vs 0.07 [0.03-0.12] s- 1, p = 0.38). Compared to pleural effusions, pericardial effusions had a higher ΔR1late (0.8 [0.6-1.2] vs 0.4 [0.2-0.6] s- 1, p < 0.001) and ΔR1early/ΔR1late (0.19 [0.08-0.30] vs 0.12 [0.04-0.19], p < 0.001). CONCLUSIONS: T1 mapping shows that extracellular GBCA is excreted into pericardial and pleural effusions. Consequently, the previously used term vicarious excretion is misleading. Compared to pleural effusions, pericardial effusions had both a lower native T1, consistent with lesser relative fluid content in relation to other components such as proteins, and more prominent early excretion dynamics, which could be related to inflammation. The clinical diagnostic utility of T1 mapping to determine quantitative contrast dynamics in pericardial and pleural effusions merits further investigation.

The relative contributions of myocardial perfusion, blood volume and extracellular volume to native T1 and native T2 at rest and during adenosine stress in normal physiology.

BACKGROUND: Both ischemic and non-ischemic heart disease can cause disturbances in the myocardial blood volume (MBV), myocardial perfusion and the myocardial extracellular volume fraction (ECV). Recent studies suggest that native myocardial T1 mapping can detect changes in MBV during adenosine stress without the use of contrast agents. Furthermore, native T2 mapping could also potentially be used to quantify changes in myocardial perfusion and/or MBV. Therefore, the aim of this study was to explore the relative contributions of myocardial perfusion, MBV and ECV to native T1 and native T2 at rest and during adenosine stress in normal physiology. METHODS: Healthy subjects (n = 41, 26 ± 5 years, 51% females) underwent 1.5 T cardiovascular magnetic resonance (CMR) scanning. Quantitative myocardial perfusion [ml/min/g] and MBV [%] maps were computed from first pass perfusion imaging at adenosine stress (140 microg/kg/min infusion) and rest following an intravenous contrast bolus (0.05 mmol/kg, gadobutrol). Native T1 and T2 maps were acquired before and during adenosine stress. T1 maps at rest and stress were also acquired following a 0.2 mmol/kg cumulative intravenous contrast dose, rendering rest and stress ECV maps [%]. Myocardial T1, T2, perfusion, MBV and ECV values were measured by delineating a region of interest in the midmural third of the myocardium. RESULTS: During adenosine stress, there was an increase in myocardial native T1, native T2, perfusion, MBV, and ECV (p ≤ 0.001 for all). Myocardial perfusion, MBV and ECV all correlated with both native T1 and native T2, respectively (R2 = 0.35 to 0.61, p < 0.001 for all). Multivariate linear regression revealed that ECV and perfusion together best explained the change in native T2 (ECV beta 0.21, p = 0.02, perfusion beta 0.66, p < 0.001, model R2 = 0.64, p < 0.001), and native T1 (ECV beta 0.50, p < 0.001, perfusion beta 0.43, p < 0.001, model R2 = 0.69, p < 0.001). CONCLUSIONS: Myocardial native T1, native T2, perfusion, MBV, and ECV all increase during adenosine stress. Changes in myocardial native T1 and T2 during adenosine stress in normal physiology can largely be explained by the combined changes in myocardial perfusion and ECV. TRIAL REGISTRATION: Clinicaltrials.gov identifier NCT02723747. Registered March 16, 2016.

Projection-based respiratory-resolved left ventricular volume measurements in patients using free-breathing double golden-angle 3D radial acquisition.

OBJECTIVE: To refine a new technique to measure respiratory-resolved left ventricular end-diastolic volume (LVEDV) in mid-inspiration and mid-expiration using a respiratory self-gating technique and demonstrate clinical feasibility in patients. MATERIALS AND METHODS: Ten consecutive patients were imaged at 1.5 T during 10 min of free breathing using a 3D golden-angle radial trajectory. Two respiratory self-gating signals were extracted and compared: from the k-space center of all acquired spokes, and from a superior-inferior projection spoke repeated every 64 ms. Data were binned into end-diastole and two respiratory phases of 15% respiratory cycle duration in mid-inspiration and mid-expiration. LVED volume and septal-lateral diameter were measured from manual segmentation of the endocardial border. RESULTS: Respiratory-induced variation in LVED size expressed as mid-inspiration relative to mid-expiration was, for volume, 1 ± 8% with k-space-based self-gating and 8 ± 2% with projection-based self-gating (P = 0.04), and for septal-lateral diameter, 2 ± 2% with k-space-based self-gating and 10 ± 1% with projection-based self-gating (P = 0.002). DISCUSSION: Measuring respiratory variation in LVED size was possible in clinical patients with projection-based respiratory self-gating, and the measured respiratory variation was consistent with previous studies on healthy volunteers. Projection-based self-gating detected a higher variation in LVED volume and diameter during respiration, compared to k-space-based self-gating.

Respiratory variation in left ventricular cardiac function with 3D double golden-angle whole-heart cine imaging.

PURPOSE: To develop a 3-dimensional free-breathing cardiovascular MR technique for quantifying the variation in left ventricular end-diastolic volume (LVEDV) during the respiratory cycle. METHODS: A 3-dimensional radial trajectory with double golden-angle ordering was used for free-running data acquisition during free breathing in healthy volunteers (N = 8). A respiratory self-gating signal was extracted from the center of k-space, and data were retrospectively binned into eight respiratory phases in end-diastole. Three-dimensional image volumes with 2-mm isotropic spatial resolution were reconstructed with conjugate-gradient sensitivity encoding for acquisition durations of 4.5, 9, and 25 min. The LVEDV was manually segmented for each respiratory phase and acquisition duration. RESULTS: Respiratory-induced variation expressed as minimum LVEDV (during mid-inspiration) relative to maximum LVEDV (during mid-expiration) was 5.9 ± 0.3% for 4.5 min, 5.3 ± 0.4% for 9 min (P = 0.64 versus 4.5 min), and 5.0 ± 0.4% for 25 min (P = 0.25 versus 4.5 min, and P = 1.00 versus 9 min). CONCLUSIONS: The proposed technique enables high spatial-resolution quantification of the respiratory variation in LVEDV during free breathing in under 5 min, and was found to be 5 to 6% for healthy volunteers. Magn Reson Med 79:2693-2701, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Pulmonary artery imaging under free-breathing using golden-angle radial bSSFP MRI: a proof of concept.

PURPOSE: To evaluate the feasibility of an improved motion and flow robust methodology for imaging the pulmonary vasculature using non-contrast-enhanced, free-breathing, golden-angle radial MRI. METHODS: Healthy volunteers (n = 10, age 46 ± 11 years, 50% female) and patients (n = 2, ages 27 and 84, both female) were imaged at 1.5 T using a Cartesian and golden-angle radial 2D balanced SSFP pulse sequence. The acquisitions were made under free breathing without contrast agent enhancement. The radial acquisitions were reconstructed at 3 temporal footprints. All series were scored from 1 to 5 for perceived diagnostic quality, artifact level, and vessel sharpness in multiple anatomical locations. In addition, vessel sharpness and blood-to-blood clot contrast were measured. RESULTS: Quantitative measurements showed higher vessel sharpness for golden-angle radial (n = 76, 0.79 ± 0.11 versus 0.71 ± 0.16, p < .05). Blood-to-blood clot contrast was found to be 23% higher in golden-angle radial in the 2 patients. At comparable temporal footprints, golden-angle radial was scored higher for diagnostic quality (mean ± SD, 2.3 ± 0.7 versus 2.2 ± 0.6, p < .01) and vessel sharpness (2.2 ± 0.8 versus 2.1 ± 0.5, p < .01), whereas the artifact level did not differ (3.0 ± 0.9 versus 3.0 ± 1.0, p = .80). The ability to retrospectively choose a temporal resolution and perform sliding-window reconstructions was demonstrated in patients. CONCLUSION: In pulmonary artery imaging, the motion and flow robustness of a radial trajectory does both improve image quality over Cartesian trajectory in healthy volunteers, and allows for flexible selection of temporal footprints and the ability to perform real-time sliding window reconstructions, which could potentially provide further diagnostic insight.

Synthetic late gadolinium enhancement cardiac magnetic resonance for diagnosing myocardial scar.

OBJECTIVES: Late gadolinium enhancement (LGE) is the in vivo reference standard for assessing focal myocardial fibrosis. Post-contrast T1-mapping by Modified Look-Locker Inversion recovery (MOLLI) can be used to generate synthetic late gadolinium enhancement (SynLGE) images with an image contrast similar to conventional LGE images. We hypothesized that SynLGE has an accuracy that approaches conventional LGE for diagnosing focal myocardial fibrosis. METHODS: Consecutive patients (n = 109, mean ± SD age 50 ± 16 years, 63% male) referred for clinical cardiac magnetic resonance imaging underwent LGE and post-contrast MOLLI starting 10-15 and 20-25 minutes post contrast, respectively. A cardiac short-axis stack and three long-axis views were acquired for SynLGE and LGE. SynLGE were generated from post-contrast T1-maps. Only LGE and SynLGE images were analyzed by two blinded observers for agreement regarding localization and origin of focal myocardial fibrosis on a per-patient basis. RESULTS: Consensus identified focal fibrosis by LGE in 44/109 (40%) patients. Compared to LGE, SynLGE yielded a diagnostic sensitivity of 34/44 (77%), specificity of 64/65 (98%), positive predictive value of 34/35 (97%), negative predictive value of 64/74 (86%), and an overall accuracy of 98/109 (90%). In cases where SynLGE missed focal fibrosis (n = 10), these were either small non-ischemic focal fibrosis (n = 8) or infarction in a thin myocardial wall (n = 2). In one case, SynLGE identified midmural non-ischemic focal fibrosis not identified by LGE. DISCUSSION: Overall, SynLGE showed good agreement with LGE. SynLGE derived from post-contrast T1-maps may provide the complementary ability to increase confidence in assessment of LGE images for focal myocardial fibrosis.

The ability of the electrocardiogram in left bundle branch block to detect myocardial scar determined by cardiovascular magnetic resonance.

AIMS: We aimed to improve the electrocardiographic 2009 left bundle branch block (LBBB) Selvester QRS score (2009 LBSS) for scar assessment. METHODS: We retrospectively identified 325 LBBB patients with available ECG and cardiovascular magnetic resonance imaging (CMR) with late gadolinium enhancement from four centers (142 [44%] with CMR scar). Forty-four semi-automatically measured ECG variables pre-selected based on the 2009 LBSS yielded one multivariable model for scar detection and another for scar quantification. RESULTS: The 2009 LBSS achieved an area under the curve (AUC) of 0.60 (95% confidence interval 0.54-0.66) for scar detection, and R2 = 0.04, p < 0.001, for scar quantification. Multivariable modeling improved scar detection to AUC 0.72 (0.66-0.77) and scar quantification to R2 = 0.21, p < 0.001. CONCLUSIONS: The 2009 LBSS detects and quantifies myocardial scar with poor accuracy. Improved models with extensive comparison of ECG and CMR had modest performance, indicating limited room for improvement of the 2009 LBSS.

Ejection fraction in left bundle branch block is disproportionately reduced in relation to amount of myocardial scar.

INTRODUCTION: The relationship between left ventricular (LV) ejection fraction (EF) and LV myocardial scar can identify potentially reversible causes of LV dysfunction. Left bundle branch block (LBBB) alters the electrical and mechanical activation of the LV. We hypothesized that the relationship between LVEF and scar extent is different in LBBB compared to controls. METHODS: We compared the relationship between LVEF and scar burden between patients with LBBB and scar (n = 83), and patients with chronic ischemic heart disease and scar but no electrocardiographic conduction abnormality (controls, n = 90), who had undergone cardiovascular magnetic resonance (CMR) imaging at one of three centers. LVEF (%) was measured in CMR cine images. Scar burden was quantified by CMR late gadolinium enhancement (LGE) and expressed as % of LV mass (%LVM). Maximum possible LVEF (LVEFmax) was defined as the function describing the hypotenuse in the LVEF versus myocardial scar extent scatter plot. Dysfunction index was defined as LVEFmax derived from the control cohort minus the measured LVEF. RESULTS: Compared to controls with scar, LBBB with scar had a lower LVEF (median [interquartile range] 27 [19-38] vs 36 [25-50] %, p < 0.001), smaller scar (4 [1-9] vs 11 [6-20] %LVM, p < 0.001), and greater dysfunction index (39 [30-52] vs 21 [12-35] % points, p < 0.001). CONCLUSIONS: Among LBBB patients referred for CMR, LVEF is disproportionately reduced in relation to the amount of scar. Dyssynchrony in LBBB may thus impair compensation for loss of contractile myocardium.

Blood correction reduces variability and gender differences in native myocardial T1 values at 1.5 T cardiovascular magnetic resonance - a derivation/validation approach.

BACKGROUND: Myocardial native T1 measurements are likely influenced by intramyocardial blood. Since blood T1 is both variable and longer compared to myocardial T1, this will degrade the precision of myocardial T1 measurements. Precision could be improved by correction, but the amount of correction and the optimal blood T1 variables to correct with are unknown. We hypothesized that an appropriate correction would reduce the standard deviation (SD) of native myocardial T1. METHODS: Consecutive patients (n = 400) referred for CMR with known or suspected heart disease were split into a derivation cohort for model construction (n = 200, age 51 ± 18 years, 50% male) and a validation cohort for assessing model performance (n = 200, age 48 ± 17 years, 50% male). Exclusion criteria included focal septal abnormalities. A Modified Look-Locker inversion recovery sequence (MOLLI, 1.5 T Siemens Aera) was used to acquire T1 and T1* maps. T1 and T1* maps were used to measure native myocardial T1, and blood T1 and T1*. A multivariate linear regression correction model was implemented using blood measurement of R1 (1/T1), R1* (1/T1*) or hematocrit. The correction model from the derivation cohort was applied to the validation cohort, and assessed for reduction in variability with the F-test. RESULTS: Blood [LV + RV] mean R1, mean R1* and hematocrit correlated with myocardial T1 (Pearson's r, range 0.37 to 0.45, p < 0.05 for all) in both the derivation and validation cohorts respectively, suggesting that myocardial T1 measurements are influenced by intramyocardial blood. Mean myocardial native T1 did not differ between the derivation and validation cohorts (1030 ± 42.6 ms and 1023 ± 45.2 ms respectively, p = 0.07). In the derivation cohort, correction using blood mean R1 and mean R1* yielded a decrease in myocardial T1 SD (45.2 ms to 36.6 ms, p = 0.03). When the model from the derivation cohort was applied to the validation cohort, the SD reduction was maintained (39.3 ms, p = 0.049). This 13% reduction in measurement variability leads to a 23% reduction in sample size to detect a 50 ms difference in native myocardial T1. CONCLUSIONS: Correcting native myocardial T1 for R1 and R1* of blood improves the precision of myocardial T1 measurement by ~13%, and could consequently improve disease detection and reduce sample size needs for clinical research.

Hyperpolarized Metabolic MR Imaging of Acute Myocardial Changes and Recovery after Ischemia-Reperfusion in a Small-Animal Model.

PURPOSE: To implement hyperpolarized magnetic resonance (MR) imaging in an animal model of ischemia-reperfusion and to assess in vivo the regional changes in pyruvate metabolism within the 1st hour and at 1 week after a brief episode of coronary occlusion and reperfusion. MATERIALS AND METHODS: All animal experiments were performed with adherence to the Swiss Animal Protection law and were approved by the regional veterinary office. A closed-chest rat model was implemented by using an inflatable balloon secured around the left coronary artery. Animals were placed in an MR system 5-7 days after surgery. [1-(13)C]pyruvate was polarized by using a home-built multisample hyperpolarizer. Hyperpolarized pyruvate was injected at five stages: at baseline; at reperfusion after 15 minutes of coronary occlusion; and at 30 minutes, 60 minutes, and 1 week after ischemia reperfusion. The conversion of pyruvate into lactate and bicarbonate was imaged by using dedicated MR sequences alongside wall motion and delayed enhancement imaging. After imaging, the heart was removed and stained to delineate the area at risk (AAR). Differences between AAR and remote myocardium were assessed by using a repeated measures analysis of variance and a post hoc Bonferroni multiple comparison test. RESULTS: Data were collected in 12 animals. Occlusion led to hypokinesia of the anterior or anterolateral segments of the myocardium. At reperfusion, the average lactate-to-bicarbonate ratio increased in the AAR relative to that at baseline (from 1.93 ± 0.48 to 3.01 ± 0.74, P < .001) and was significantly higher when compared with that in the remote area (1.91 ± 0.38, P < .001). In the 60 minutes after occlusion, the lactate-to-bicarbonate ratio in the AAR recovered but was still elevated relative to that in the remote area. One week after ischemia-reperfusion, no difference between AAR and remote area could be detected. CONCLUSION: Hyperpolarized metabolic MR imaging can be used to successfully detect acute changes in [1-(13)C]pyruvate metabolism after ischemia-reperfusion, thereby enabling in vivo monitoring of the metabolic effects of reperfusion strategies.

Quantification of turbulence and velocity in stenotic flow using spiral three-dimensional phase-contrast MRI.

PURPOSE: Evaluate spiral three-dimensional (3D) phase contrast MRI for the assessment of turbulence and velocity in stenotic flow. METHODS: A-stack-of-spirals 3D phase contrast MRI sequence was evaluated in vitro against a conventional Cartesian sequence. Measurements were made in a flow phantom with a 75% stenosis. Both spiral and Cartesian imaging were performed using different scan orientations and flow rates. Volume flow rate, maximum velocity and turbulent kinetic energy (TKE) were computed for both methods. Moreover, the estimated TKE was compared with computational fluid dynamics (CFD) data. RESULTS: There was good agreement between the turbulent kinetic energy from the spiral, Cartesian and CFD data. Flow rate and maximum velocity from the spiral data agreed well with Cartesian data. As expected, the short echo time of the spiral sequence resulted in less prominent displacement artifacts compared with the Cartesian sequence. However, both spiral and Cartesian flow rate estimates were sensitive to displacement when the flow was oblique to the encoding directions. CONCLUSION: Spiral 3D phase contrast MRI appears favorable for the assessment of stenotic flow. The spiral sequence was more than three times faster and less sensitive to displacement artifacts when compared with a conventional Cartesian sequence.

Retrospectively gated intracardiac 4D flow MRI using spiral trajectories.

PURPOSE: To develop and evaluate retrospectively gated spiral readout four-dimensional (4D) flow MRI for intracardiac flow analysis. METHODS: Retrospectively gated spiral 4D flow MRI was implemented on a 1.5-tesla scanner. The spiral sequence was compared against conventional Cartesian 4D flow (SENSE [sensitivity encoding] 2) in seven healthy volunteers and three patients (only spiral). In addition to comparing flow values, linear regression was used to assess internal consistency of aortic versus pulmonary net volume flows and left ventricular inflow versus outflow using quantitative pathlines analysis. RESULTS: Total scan time with spiral 4D flow was 44% ± 6% of the Cartesian counterpart (13 ± 3 vs. 31 ± 7 min). Aortic versus pulmonary flow correlated strongly for the spiral sequence (P < 0.05, slope = 1.03, R(2) = 0.88, N = 10), whereas the linear relationship for the Cartesian sequence was not significant (P = 0.06, N = 7). Pathlines analysis indicated good data quality for the spiral (P < 0.05, slope = 1.02, R(2) = 0.90, N = 10) and Cartesian sequence (P < 0.05, slope = 1.10, R(2) = 0.93, N = 7). Spiral and Cartesian peak flow rate (P < 0.05, slope = 0.96, R(2) = 0.72, N = 14), peak velocity (P < 0.05, slope = 1.00, R(2) = 0.81, N = 14), and pathlines flow components (P < 0.05, slope = 1.04, R(2) = 0.87, N = 28) correlated well. CONCLUSION: Retrospectively gated spiral 4D flow MRI permits more than two-fold reduction in scan time compared to conventional Cartesian 4D flow MRI, while maintaining similar data quality.

Hybrid multiband excitation multiecho acquisition for hyperpolarized (13) C spectroscopic imaging.

PURPOSE: Fast dynamic imaging of hyperpolarized (13) C-labeled pyruvate and its downstream metabolites shows great potential for probing metabolic changes in the heart. Sequences that allow for fast encoding of the spectral and spatial information of the myocardial metabolism and optimal signal excitation are usually limited by gradient performance, especially at high magnetic fields. Here we propose a combination of a spectral-spatial multiband excitation and multiecho readout to overcome these limitations. METHODS: By using a low-bandwidth, two-pulse excitation, a thinner slice compared with conventional spectral-spatial excitation is achieved, while at the same time allowing for low flip angle excitation on pyruvate and high flip angle excitation on bicarbonate and lactate, which optimizes signal-to-noise ratio (SNR) in cardiac metabolic imaging. The implementation was evaluated in 13 healthy female Sprague-Dawley rats at 9.4T. RESULTS: Using a slice thickness of 4 mm, a mean (± standard deviation) peak SNR of 18.3 (±8.4), 15.2 (±6.6), and 8.6 (±2.0) was observed for pyruvate, lactate, and bicarbonate, respectively. CONCLUSION: This approach provides high SNR in metabolic images while at the same time allowing for a thin slice selection even at high magnetic fields. This is crucial in metabolic imaging in small animal models.

Clinical experience of strain imaging using DENSE for detecting infarcted cardiac segments.

BACKGROUND: We hypothesised that myocardial deformation determined with magnetic resonance imaging (MRI) will detect myocardial scar. METHODS: Displacement Encoding with Stimulated Echoes (DENSE) was used to calculate left ventricular strain in 125 patients (29 women and 96 men) with suspected coronary artery disease. The patients also underwent cine imaging and late gadolinium enhancement. 57 patients had a scar area >1% in at least one segment, 23 were considered free from coronary artery disease (control group) and 45 had pathological findings but no scar (mixed group). Peak strain was calculated in eight combinations: radial and circumferential strain in transmural, subendocardial and epicardial layers derived from short axis acquisition, and transmural longitudinal and radial strain derived from long axis acquisitions. In addition, the difference between strain in affected segments and reference segments, "differential strain", from the control group was analysed. RESULTS: In receiver-operator-characteristic analysis for the detection of 50% transmurality, circumferential strain performed best with area-under-curve (AUC) of 0.94. Using a cut-off value of -17%, sensitivity was 95% at a specificity of 80%. AUC did not further improve with differential strain. There were significant differences between the control group and global strain circumferential direction (-17% versus -12%) and in the longitudinal direction (-13% versus -10%). Interobserver and scan-rescan reproducibility was high with an intraclass correlation coefficient (ICC) >0.93. CONCLUSIONS: DENSE-derived circumferential strain may be used for the detection of myocardial segments with >50 % scar area. The repeatability of strain is satisfactory. DENSE-derived global strain agrees with other global measures of left ventricular ejection fraction.

Mapping mean and fluctuating velocities by Bayesian multipoint MR velocity encoding-validation against 3D particle tracking velocimetry.

PURPOSE: To validate Bayesian multipoint MR velocity encoding against particle tracking velocimetry for measuring velocity vector fields and fluctuating velocities in a realistic aortic model. METHODS: An elastic cast of a human aortic arch equipped with an 80 or 64% stenotic section was driven by a pulsatile pump. Peak velocities and peak turbulent kinetic energies of more than 3 m/s and 1000 J/m(3) could be generated. Velocity vector fields and fluctuating velocities were assessed using Bayesian multipoint MR velocity encoding with varying numbers of velocity encoding points and particle tracking velocimetry in the ascending aorta. RESULTS: Velocities and turbulent kinetic energies measured with 5-fold k-t undersampled 10-point MR velocity encoding and particle tracking velocimetry were found to reveal good correlation with mean differences of -4.8 ± 13.3 cm/s and r(2) = 0.98 for velocities and -21.8 ± 53.9 J/m(3) and r(2) = 0.98 for turbulent kinetic energies, respectively. Three-dimensional velocity patterns of fast flow downstream of the stenoses and regions of elevated velocity fluctuations were found to agree well. CONCLUSION: Accelerated Bayesian multipoint MR velocity encoding has been demonstrated to be accurate for assessing mean and fluctuating velocities against the reference standard particle tracking velocimetry. The MR method holds considerable potential to map velocity vector fields and turbulent kinetic energies in clinically feasible exam times of <15 min.