Arterial transit time (ATT) prolongation causes an error of cerebral blood flow (CBF) measurement during arterial spin labeling (ASL). To improve the accuracy of ATT and CBF in patients with prolonged ATT, we propose a robust ATT and CBF estimation method for clinical practice. The proposed method consists of a three‐delay Hadamard‐encoded pseudo‐continuous ASL (H‐pCASL) with an additional‐encoding and single‐delay with long‐labeled long‐delay (1dLLLD) acquisition. The additional‐encoding allows for the reconstruction of a single‐delay image with long‐labeled short‐delay (1dLLSD) in addition to the normal Hadamard sub‐bolus images. Five different images (normal Hadamard 3 delay, 1dLLSD, 1dLLLD) were reconstructed to calculate ATT and CBF. A Monte Carlo simulation and an in vivo study were performed to access the accuracy of the proposed method in comparison to normal 7‐delay (7d) H‐pCASL with equally divided sub‐bolus labeling duration (LD). The simulation showed that the accuracy of CBF is strongly affected by ATT. It was also demonstrated that underestimation of ATT and CBF by 7d H‐pCASL was higher with longer ATT than with the proposed method. Consistent with the simulation, the 7d H‐pCASL significantly underestimated the ATT compared to that of the proposed method. This underestimation was evident in the distal anterior cerebral artery (ACA; P = 0.0394) and the distal posterior cerebral artery (PCA; 2 P = 0.0255). Similar to the ATT, the CBF was underestimated with 7d H‐pCASL in the distal ACA (P = 0.0099), distal middle cerebral artery (P = 0.0109), and distal PCA (P = 0.0319) compared to the proposed method. Improving the SNR of each delay image (even though the number of delays is small) is crucial for ATT estimation. This is opposed to acquiring many delays with short LD. The proposed method confers accurate ATT and CBF estimation within a practical acquisition time in a clinical setting.

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:565-571.

Background: An inherently poor signal-to-noise ratio (SNR) causes inaccuracy and less precision in cerebral blood flow (CBF) and arterial transit time (ATT) when using arterial spin labeling (ASL). Deep neural network (DNN)-based parameter estimation can solve these problems. Purpose: To reduce the effects of Rician noise on ASL parameter estimation and compute unbiased CBF and ATT using simulation-based supervised DNNs. Study Type: Retrospective. Population: One million simulation test data points, 17 healthy volunteers (five women and 12 men, 33.2 AE 14.6 years of age), and one patient with moyamoya disease. Field Strength/Sequence: 3.0 T/Hadamard-encoded pseudo-continuous ASL with a three-dimensional fast spin-echo stack of spirals. Assessment: Performances of DNN and conventional methods were compared. For test data, the normalized mean absolute error (NMAE) and normalized root mean squared error (NRMSE) between the ground truth and predicted values were evaluated. For in vivo data, baseline CBF and ATT and their relative changes with respect to SNR using artificial noiseadded images were assessed. Statistical Tests: One-way analysis of variance with post-hoc Tukey's multiple comparison test, paired t-test, and the Bland-Altman graphical analysis. Statistical significance was defined as P < 0.05. Results: For both CBF and ATT, NMAE and NRMSE were lower with DNN than with the conventional method. The baseline values were significantly smaller with DNN than with the conventional method (CBF in gray matter, 66 AE 10 vs. 71 AE 12 mL/100 g/min; white matter, 45 AE 6 vs. 46 AE 7 mL/100 g/min; ATT in gray matter, 1424 AE 201 vs. 1471 AE 154 msec). CBF and ATT increased with decreasing SNR; however, their change rates were smaller with DNN than were those with the conventional method. Higher CBF in the prolonged ATT region and clearer contrast in ATT were identified by DNN in a clinical case. Data Conclusion: DNN outperformed the conventional method in terms of accuracy, precision, and noise immunity.

We used magnetic resonance imaging (MRI) to assess how a patient's posture affects intraocular gas changes and whether the postoperative prone position is required after pars plana vitrectomy (ppV) with gas tamponade for rhegmatogenous retinal detachments (RRDs). eight patients with RRDs who underwent ppV combined with cataract surgery with gas tamponade were prospectively included. they underwent MRi examination both in the prone and supine positions. We separated the retina into four parts: superior-posterior, superior-anterior, inferior-posterior, and inferior-anterior. We then calculated the gas contact rate as (the length of the retina contacting the gas in each retinal part) divided by (the length of each retinal part) × 100% in both the prone and supine positions. The mean gas contact rate of the superior-anterior part of the retina was significantly higher (P = 0.006) in the supine position than in the prone position. the mean gas contact rate of the inferior-anterior part of the retina was also significantly higher (P = 0.0004) in the supine position than in the prone position. We believe that if all retinal breaks were located anterior to the equator, the supine position may provide better tamponade gas coverage for the breaks than the prone position. Although potential postoperative complications caused by the supine position require careful attention, our result may shorten the duration of postoperative prone position and may decrease the patients' discomfort after ppV with gas tamponade for RRDs.