Purpose: To systematically assess the feasibility and performance of a highly accelerated compressed sensing (CS) 4D flow MRI framework at three different acceleration factors (R) for the quantification of aortic flow dynamics and wall shear stress (WSS) in patients with aortic disease. Methods: Twenty patients with aortic disease (58 ± 15 y old; 19 M) underwent four 4D flow scans: one conventional (GRAPPA, R = 2) and three CS 4D flows with R = 5.7, 7.7, and 10.2. All scans were acquired with otherwise equivalent imaging parameters on a 1.5T scanner. Peak-systolic velocity (V max), peak flow (Q max), and net flow (Q net) were quantified at the ascending aorta (AAo), arch, and descending aorta (DAo). WSS was calculated at six regions within the AAo and arch. Results: Mean scan times for the conventional and CS 4D flows with R =

Highly accelerated real-time cine MRI using compressed sensing (CS) is a promising approach to achieve high spatio-temporal resolution and clinically acceptable image quality in patients with arrhythmia and/or dyspnea. However, its lengthy image reconstruction time may hinder its clinical translation. The purpose of this study was to develop a neural network for reconstruction of non-Cartesian real-time cine MRI k-space data faster (<1 min per slice with 80 frames) than graphics processing unit (GPU)-accelerated CS reconstruction, without significant loss in image quality or accuracy in left ventricular (LV) functional parameters. We introduce a perceptual complex neural network (PCNN) that trains on complex-valued MRI signal and incorporates a perceptual loss term to suppress incoherent image details. This PCNN was trained and tested with multi-slice, multi-phase, cine images from 40 patients (20 for training, 20 for testing), where the zero-filled images were used as input and the corresponding CS reconstructed images were used as practical ground truth. The resulting images were compared using quantitative metrics (structural similarity index (SSIM) and normalized root mean square error (NRMSE)) and visual scores (conspicuity, temporal fidelity, artifacts, and noise scores), individually graded on a five-point scale (1, worst; 3, acceptable; 5, best), and LV ejection fraction (LVEF). The mean processing time per slice with 80 frames for PCNN was 23.7 ± 1.9 s for preprocessing (Step 1, same as CS) and 0.822 ± 0.004 s for dealiasing (Step 2, 166 times faster than CS). Our PCNN produced higher data fidelity metrics (SSIM = 0.88 ± 0.02, NRMSE = 0.014 ± 0.004) compared with CS. While all the visual scores were significantly different (P < 0.05), the median scores were all 4.0 or higher for both CS and PCNN. LVEFs measured from CS and PCNN were strongly correlated (R 2 = 0.92) and in good agreement (mean difference = −1.4% [2.3% of mean]; limit of agreement = 10.6% [17.6% of mean]). The proposed PCNN is capable of rapid reconstruction (25 s per slice with 80 frames) of non-Cartesian real-time cine MRI k-space data, without significant loss in image quality or accuracy in LV functional parameters.

Background Stroke etiology is undetermined in approximately one‐sixth to one‐third of patients. The presence of aortic flow reversal and plaques in the descending aorta (DAo) has been identified as a potential retrograde embolic mechanism. Purpose To assess the relationships between aortic stiffness, wall thickness, and flow reversal in patients with cryptogenic stroke and healthy controls. Study Type Prospective. Population Twenty one patients with cryptogenic stroke and proven DAo plaques (69 ± 9 years, 43% female), 18 age‐matched controls (age: 65 ± 8 years, 61% female), and 14 younger controls (36 ± 9 years, 57% female). Field Strength/Sequence 1.5T; 4D flow MRI and 3D dark blood T1‐weighted turbo spin echo MRI of the aorta. Assessment Noncontrast aortic 4D flow MRI to measure 3D flow dynamics and 3D dark blood aortic wall MRI to assess wall thickness. 4D flow MRI analysis included automated quantification of aortic stiffness by pulse wave velocity (PWV) and voxelwise mapping of the flow reversal fraction (FRF). Statistical Tests Analysis of variance (ANOVA) or Kruskal–Wallis tests, Student's unpaired t‐tests or Wilcoxon rank‐sum tests, regression analysis. Results Aortic PWV and FRF were statistically higher in patients (8.9 ± 1.7 m/s, 18.4 ± 7.7%) than younger controls (5.3 ± 0.8 m/s, P < 0.0167; 8.5 ± 2.9%, P < 0.0167), but not age‐matched controls (8.2 ± 1.6 m/s, P = 0.22; 15.6 ± 5.8%, P = 0.22). Maximum aortic wall thickness was higher in patients (3.1 ± 0.7 mm) than younger controls (2.2 ± 0.2 mm, P < 0.0167) and age‐matched controls (2.7 ± 0.5 mm) (P < 0.0167). For all subjects, positive relationships were found between PWV and age (R2 = 0.71, P < 0.05), aortic wall thickness (R2 = 0.20, P < 0.05), and FRF (R2 = 0.47, P < 0.05). Patients demonstrated relationships between PWV and FRF in the ascending aorta (R2 = 0.32, P < 0.05) and arch (R2 = 0.24, P < 0.05). Data Conclusion This study showed the utility of 4D flow MRI for evaluating aortic PWV and voxelwise flow reversal. Positive relationships between aortic PWV, wall thickness, and flow reversal support the hypothesis that aortic stiffness is involved in this retrograde embolic mechanism. Level of Evidence 2 Technical Efficacy Stage 1

Background Cardiac magnetic resonance imaging (MRI) is becoming an alternative to right heart catheterization (RHC) for evaluating pulmonary hypertension (PH). A need exists to further evaluate cardiac MRI's ability to characterize PH. Purpose To evaluate the potential for four‐dimensional (4D) flow MRI‐derived pulmonary artery velocities to characterize PH. Study Type Prospective case–control. Population Fifty‐four PH patients (56% female); 25 controls (36% female). Field Strength/Sequence 1.5 T; gradient recalled echo 4D flow and balanced steady‐state free precession cardiac cine. Assessment RHC was used to derive patients' pulmonary vascular resistance (PVR). 4D flow measured blood velocities at the main, left, and right pulmonary arteries (MPA, LPA, and RPA); cine measured ejection fraction, end diastolic, and end systolic volumes (EF, EDV, and ESV). EDV and ESV were normalized (indexed) to body surface area (ESVI and EDVI). Parameters were evaluated between, and within, PH subgroups: pulmonary arterial hypertension (PAH); PH due to left heart disease (PH‐LHD)/chronic lung disease (PH‐CLD)/or chronic thrombo‐emboli (CTE‐PH). Statistical Tests Analysis of variance and Kruskal–Wallis tests compared parameters between subgroups. Pearson's r assessed velocity, PVR, and volume correlations. Significance definition: P < 0.05. Results PAH peak and mean velocities were significantly lower than in controls at the LPA (36 ± 12 cm/second and 20 ± 4 cm/second vs. 59 ± 15 cm/second and 32 ± 9 cm/second). At the RPA, mean velocities were significantly lower in PAH vs. controls (27 ± 6 cm/second vs. 40 ± 9 cm/second). Peak velocities significantly correlated with right ventricular EF at the MPA (r = 0.286), RPA (r = 0.400), and LPA (r = 0.401). Peak velocity significantly correlated with right ventricular ESVI at the RPA (r = −0.355) and LPA (r = −0.316). Significant correlations between peak velocities and PVR were moderate at the LPA in PAH (r = −0.641) and in PH‐LHD (r = −0.606) patients, and at the MPA in PH‐CLD (r = −0.728). CTE‐PH showed non‐significant correlations between peak velocity and PVR at all locations. Data Conclusion Preliminary findings suggest 4D flow can identify PAH and track PVR changes. Level of Evidence 1 Technical Efficacy Stage 5

Background: Gadobutrol (GB) and gadoterate meglumine (GM) are contrast agents used for contrast-enhanced magnetic resonance angiography (CEMRA). Supraaortic vasculature (SAV) CEMRAs are used to evaluate stroke risk and neurologic symptoms. There is a need to compare the SAV CEMRA image quality obtained with GB and GM. Purpose: To intra-individually compare MRA images obtained with equimolar GB and GM at 1.5 T in the SAV. Study Type: Prospective, crossover. Population: Twenty-eight subjects (54 AE 13 years; 17 female). Field Strength/Sequence: 1.5 T; three-dimensional (3D) gradient recalled echo. Assessment: Quantitative image quality was measured by normalized signal intensity (SI n ) [SI n = SI blood/SD blood] and contrast ratio (CR) [CR = SI blood/SI muscle], determined by an observer (JWC) with 1 year of vascular imaging experience. Three radiologists (AS, PA, and MU) with (5, 5, and 6 years of) vascular imaging experience evaluated image quality by Likert-scale ratings (of image impression, wall conspicuity, and artifact absence). Statistical Tests: SI n and CR were compared with paired t-tests or Wilcoxon signed-rank tests and Bland-Altman plots. Qualitative ratings were compared with Wilcoxon signed-rank test. Results: No significant difference in SI n was found between GB and GM. CRs with GB were significantly higher than GM at the right common carotid (6.9 AE 2.5 vs. 4.8 AE 1), left internal carotid (7.3 AE 2 vs. 4.4 AE 1.2), right internal carotid (7.7 AE 2.2 vs. 5 AE 1.1), and left vertebral (6.6 AE 2.2 vs. 4.5 AE 1.1) arteries. Bland-Altman plots showed relatively greater differences between GB and GM at higher CRs and SI n s. GM showed significantly higher artifact than GB (3.56 AE 0.52 vs. 3.36 AE 0.46) and significantly lower overall image quality (10.73 AE 1.45 vs. 11.26 AE 1.58) at the left vertebral artery. Data Conclusion: At 1.5 T and equimolar demonstration, GB (0.1 mL/kg, i.e., 0.1 mmol/kg) showed higher CRs in the SAV compared to GM (0.2 mL/kg, i.e., 0.1 mmol/kg) at most vessels. Subjective image quality was not significantly different between the two agents for most vessels. Level of Evidence: 2 Technical Efficacy: Stage 2