Assessment of left atrial (LA) fibrosis from late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) adds to the management of patients with atrial fibrillation (AF). However, accurate assessment of fibrosis in the LA wall remains challenging. Excluding anatomical structures in the LA proximity using clipping techniques can reduce misclassification of LA fibrosis. A novel FK-means approach for combined automatic clipping and automatic fibrosis segmentation was developed. This approach combines a feature-based Voronoi diagram with a hierarchical 3D K-means fractal-based method. The proposed automatic Voronoi clipping method was applied on LGE MRI data and achieved a Dice score of 0.75, similar as the score obtained by a deep learning method (3D UNet) for clipping (0.74). The automatic fibrosis segmentation method, which utilizes the Voronoi clipping method, achieved a Dice score of 0.76. This outperformed a 3D U-Net method for clipping and fibrosis classification, which had a Dice score of 0.69. Moreover, the proposed automatic fibrosis segmentation method achieved a Dice score of 0.90, using manual clipping of anatomical structures. The findings suggest that the automatic FK-means analysis approach enables reliable LA fibrosis segmentation and that clipping of anatomical structures in the atrial proximity can add to the assessment of atrial fibrosis. 

Assessment of left atrial (LA) fibrosis from late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) adds to the management of patients with atrial fibrillation. However, accurate assessment of fibrosis in the LA wall remains challenging. Excluding anatomical structures in the LA proximity using clipping techniques can reduce misclassification of LA fibrosis. A novel FK-means approach for combined automatic clipping and automatic fibrosis segmentation was developed. This approach combines a feature-based Voronoi diagram with a hierarchical 3D K-means fractal-based method. The proposed automatic Voronoi clipping method was applied on LGE-MRI data and achieved a Dice score of 0.75, similar to the score obtained by a deep learning method (3D UNet) for clipping (0.74). The automatic fibrosis segmentation method, which uses the Voronoi clipping method, achieved a Dice score of 0.76. This outperformed a 3D UNet method for clipping and fibrosis classification, which had a Dice score of 0.69. Moreover, the proposed automatic fibrosis segmentation method achieved a Dice score of 0.90, using manual clipping of anatomical structures. The findings suggest that the automatic FK-means analysis approach enables reliable LA fibrosis segmentation and that clipping of anatomical structures in the atrial proximity can add to the assessment of atrial fibrosis.

Purpose To implement and evaluate a new dictionary-based technique for native myocardial T-1 and T-2 mapping using Cartesian sampling. Methods The proposed technique (Multimapping) consisted of single-shot Cartesian image acquisitions in 10 consecutive cardiac cycles, with inversion pulses in cycle 1 and 5, and T-2 preparation (TE: 30 ms, 50 ms, and 70 ms) in cycles 8-10. Multimapping was simulated for different T-1 and T-2, where entries corresponding to the k-space centers were matched to acquired data. Experiments were performed in a phantom, 16 healthy subjects, and 3 patients with cardiovascular disease. Results Multimapping phantom measurements showed good agreement with reference values for both T-1 and T-2, with no discernable heart-rate dependency for T-1 and T-2 within the range of myocardium. In vivo mean T-1 in healthy subjects was significantly higher using Multimapping (T-1 = 1114 +/- 14 ms) compared to the reference (T-1 = 991 +/- 26 ms) (p < 0.01). Mean Multimapping T-2 (47.1 +/- 1.3 ms) and T-2 spatial variability (5.8 +/- 1.0 ms) was significantly lower compared to the reference (T-2 = 54.7 +/- 2.2 ms, p < 0.001; spatial variability = 8.4 +/- 2.0 ms, p < 0.01). Increased T-1 and T-2 was detected in all patients using Multimapping. Conclusions Multimapping allows for simultaneous native myocardial T-1 and T-2 mapping with a conventional Cartesian trajectory, demonstrating promising in vivo image quality and parameter quantification results.

Objective To evaluate systolic flow-sensitive alternating inversion recovery (FAIR) during rest and exercise stress using 2RR (two cardiac cycles) or 1RR intervals between inversion pulse and imaging. Materials and methods 1RR and 2RR FAIR was implemented on a 3T scanner. Ten healthy subjects were scanned during rest and stress. Stress was performed using an in-bore ergometer. Heart rate, mean myocardial blood flow (MBF) and temporal signal-to-noise ratio (TSNR) were compared using paired t tests. Results Mean heart rate during stress was higher than rest for 1RR FAIR (85.8 +/- 13.7 bpm vs 63.3 +/- 11.1 bpm; p < 0.01) and 2RR FAIR (83.8 +/- 14.2 bpm vs 63.1 +/- 10.6 bpm; p < 0.01). Mean stress MBF was higher than rest for 1RR FAIR (2.97 +/- 0.76 ml/g/min vs 1.43 +/- 0.6 ml/g/min; p < 0.01) and 2RR FAIR (2.8 +/- 0.96 ml/g/min vs 1.22 +/- 0.59 ml/g/min; p < 0.01). Resting mean MBF was higher for 1RR FAIR than 2RR FAIR (p < 0.05), but not during stress. TSNR was lower for stress compared to rest for 1RR FAIR (4.52 +/- 2.54 vs 10.12 +/- 3.69; p < 0.01) and 2RR FAIR (7.36 +/- 3.78 vs 12.41 +/- 5.12; p < 0.01). 2RR FAIR TSNR was higher than 1RR FAIR for rest (p < 0.05) and stress (p < 0.001). Discussion We have demonstrated feasibility of systolic FAIR in rest and exercise stress. 2RR delay systolic FAIR enables non-contrast perfusion assessment during stress with relatively high TSNR.

The Multimapping technique was recently proposed for simultaneous myocardial T-1 and T-2 mapping. In this study, we evaluate its correlation with clinical reference mapping techniques in patients with a range of cardiovascular diseases (CVDs) and compare image quality and inter- and intra-observer repeatability. Multimapping consists of an ECG-triggered, 2D single-shot bSSFP readout with inversion recovery and T-2 preparation modules, acquired across 10 cardiac cycles. The sequence was implemented at 1.5T and compared to clinical reference mapping techniques, modified Look-Locker inversion recovery (MOLLI) and T-2 prepared bSSFP with four echo times (T(2)bSSFP), and compared in 47 patients with CVD (of which 44 were analyzed). In diseased myocardial segments (defined as the presence of late gadolinium enhancement), there was a high correlation between Multimapping and MOLLI for native myocardium T-1 (r(2) = 0.73), ECV (r(2) = 0.91), and blood T-1 (r(2) = 0.88), and Multimapping and T(2)bSSFP for native myocardial T-2 (r(2) = 0.80). In healthy myocardial segments, a bias for native T-1 (Multimapping = 1,116 +/- 21 ms, MOLLI = 1,002 +/- 21, P < 0.001), post-contrast T-1 (Multimapping = 479 +/- 31 ms, MOLLI = 426 +/- 27 ms, 0.001), ECV (Multimapping = 21.5 +/- 1.9%, MOLLI = 23.7 +/- 2.3%, P = 0.001), and native T-2 (Multimapping = 48.0 +/- 3.0 ms, T(2)bSSFP = 53.9 +/- 3.5 ms, P < 0.001) was observed. The image quality for Multimapping was scored as higher for all mapping techniques (native T-1, post-contrast T-1, ECV, and T(2)bSSFP) compared to the clinical reference techniques. The inter- and intra-observer agreements were excellent (intraclass correlation coefficient, ICC > 0.9) for most measurements, except for inter-observer repeatability of Multimapping native T-1 (ICC = 0.87), post-contrast T-1 (ICC = 0.73), and T(2)bSSFP native T-2 (ICC = 0.88). Multimapping shows high correlations with clinical reference mapping techniques for T-1, T-2, and ECV in a diverse cohort of patients with different cardiovascular diseases. Multimapping enables simultaneous T-1 and T-2 mapping and can be performed in a short breath-hold, with image quality superior to that of the clinical reference techniques.

Purpose: To develop and evaluate a robust cardiac B(1)(+)mapping sequence at 3 T, using Bloch-Siegert shift (BSS)-based preparations. Methods: A longitudinal magnetization preparation module was designed toencode |B-1(+)|. After magnetization tip-down, off-resonant Fermi pulses, placed sym-metrically around two refocusing pulses, induced BSS, followed by tipping backof the magnetization. Bloch simulations were used to optimize refocusing pulseparameters and to assess the mapping sensitivity. Relaxation-induced B-1(+) errorwas simulated for various T-1/T-2 times. The effective mapping range was determined in phantom experiments, and |B-1(+)| maps were compared to the conventionalBSS method and subadiabatic hyperbolic-secant 8 (HS8) pulse-sensitized method.Cardiac B-1(+) maps were acquired in healthy subjects, and evaluated for repeatability and imaging plane intersection consistency. The technique was modified forthree-dimensional (3D) acquisition of the whole heart in a single breath-hold, andcompared to two-dimensional (2D) acquisition. Results: Simulations indicate that the proposed preparation can be tailored toachieve high mapping sensitivity across various B-1(+) ranges, with maximum sensitivity at the upper B-1(+) range. T-1/T-2 -induced bias did not exceed 5.2%. Experimentallyreproduced B-1(+) sensitization closely matched simulations for B-1(+)>= 0.3B(1,max)(+)(mean difference 0.031 +/- 0.022, compared to 0.018 +/- 0.025 in the HS8-sensitized method),and showed 20-fold reduction in the standard deviation of repeated scans, comparedwith conventional BSS B(1 )(+)mapping, and an equivalent 2-fold reduction comparedwith HS8-sensitization. Robust cardiac B-1(+) map quality was obtained, with an average test-retest variability of 0.027 +/- 0.043 relative to normalized B(1 )(+)magnitude, and plane intersection bias of 0.052 +/- 0.031. 3D acquisitions showed good agreement with 2D scans (mean absolute deviation 0.055 +/- 0.061). Conclusion: BSS-based preparations enable robust and tailorable 2D/3D cardiac B(1)(+)mapping at 3 T in a single breath-hold.

Background Epicardial adipose tissue (EAT) may induce left atrium (LA) wall inflammation and promote LA fibrosis. Therefore, simultaneous assessment of these two important atrial fibrillation (AF) risk factors would be desirable. Purpose To perform a comprehensive evaluation of 3D Dixon water-fat separated late gadolinium enhancement (LGE-Dixon) MRI by analysis of repeatability and systematic comparison with reference methods for assessment of fibrosis and fat. Study Type Prospective. Population Twenty-eight, 10, and 7 patients, respectively, with clinical indications for cardiac MRI. Field Strength/Sequence A 1.5-T scanner, inversion recovery multiecho spoiled gradient echo. Assessment Twenty-eight patients (age 58 +/- 19 years, 15 males) were scanned using LGE-Dixon. A 5-point Likert-type scale was used to grade the image quality. Another 10 patients (age 46 +/- 19 years, 9 males) were scanned using LGE-Dixon and 3D proton density Dixon (PD-Dixon). Finally, seven patients (age 62 +/- 14 years, 4 males) were scanned using LGE-Dixon and conventional LGE. The scan time, intraobserver and interobserver variability, and levels of agreement were assessed. Statistical Tests Students t-test, one-way ANOVA, and Mann-Whitney U-test were used; P < 0.05 was considered significant, intraclass correlation coefficient (ICC). Results The scan time (minutes:seconds) for LGE-Dixon (n = 28) was 5:01 +/- 1:40. ICC values for intraobserver and interobserver measurements of LA wall fibrosis percentage were 0.98 (95% CI, 0.97-0.99) and 0.97 (95% CI, 0.94-0.99) while of EAT were 0.92 (95% CI, 0.82-0.97) and 0.90 (95% CI, 0.80-0.95). The agreement for LA fibrosis percentage between the LGE-Dixon and the conventional LGE was 0.92 (95% CI, 0.66-0.99) and for EAT volume between the LGE-Dixon and the PD-Dixon was 0.93 (95% CI, 0.72-0.98). Conclusion LA fibrosis and EAT can be assessed simultaneously using LGE-Dixon. This method allows a high level of intraobserver and interobserver repeatability as well as agreement with reference methods and can be performed in a clinically feasible scan time. Evidence Level 2 Technical Efficacy Stage 3

Introduction: To develop and test the feasibility of free-breathing (FB), high-resolution quantitative first-pass perfusion cardiac MR (FPP-CMR) using dual-echo Dixon (FOSTERS; Fat-water separation for mOtion-corrected Spatio-TEmporally accelerated myocardial peRfuSion).

Materials and Methods: FOSTERS was performed in FB using a dual-saturation single-bolus acquisition with dual-echo Dixon and a dynamically variable Cartesian k-t undersampling (8-fold) approach, with low-rank and sparsity constrained reconstruction, to achieve high-resolution FPP-CMR images. FOSTERS also included automatic in-plane motion estimation and T∗22* correction to obtain quantitative myocardial blood flow (MBF) maps. High-resolution (1.6 x 1.6 mm2) FB FOSTERS was evaluated in eleven patients, during rest, against standard-resolution (2.6 x 2.6 mm2) 2-fold SENSE-accelerated breath-hold (BH) FPP-CMR. In addition, MBF was computed for FOSTERS and spatial wavelet-based compressed sensing (CS) reconstruction. Two cardiologists scored the image quality (IQ) of FOSTERS, CS, and standard BH FPP-CMR images using a 4-point scale (1–4, non-diagnostic – fully diagnostic).

Results: FOSTERS produced high-quality images without dark-rim and with reduced motion-related artifacts, using an 8x accelerated FB acquisition. FOSTERS and standard BH FPP-CMR exhibited excellent IQ with an average score of 3.5 ± 0.6 and 3.4 ± 0.6 (no statistical difference, p > 0.05), respectively. CS images exhibited severe artifacts and high levels of noise, resulting in an average IQ score of 2.9 ± 0.5. MBF values obtained with FOSTERS presented a lower variance than those obtained with CS.

Discussion: FOSTERS enabled high-resolution FB FPP-CMR with MBF quantification. Combining motion correction with a low-rank and sparsity-constrained reconstruction results in excellent image quality.