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Aim: Two‐dimensional phase‐contrast magnetic resonance imaging (2D flow MRI) and its multidimensional alternatives, 4D and 5D flow MRI, measure blood flow in the heart and great vessels. While 2D flow MRI is the standard technique, it has limitations regarding need for precise image plane prescribing and long scan time. In contrast, 4D and 5D flow MRI acquire 3D volumes, enabling retrospective assessment of all vessels. This review evaluates these three techniques for quantification of blood flow of the aortic and pulmonary valves in congenital heart disease. Methods: A systematic literature search was conducted in August 2024 using the PUBMED database, including articles comparing 2D, 4D, and 5D flow MRI. Results: Fifteen articles comparing 2D and 4D, one comparing 2D and 5D and three articles comparing 4D and 5D flow MRI were included. No study compared all three techniques. 2D, 4D and 5D flow MRI demonstrated a good agreement for flow quantification. 4D flow MRI, however, tends to present a better accuracy and internal consistency than 2D flow MRI for determination of peak velocities and flow in stenotic lesions, particularly when comparing velocities to echocardiography. 4D and 5D flow MRI are associated with shorter scan times than 2D flow MRI. Conclusions: 4D and 5D flow MRI appear to offer promising alternatives to 2D flow MRI with the advantage of reduced scan times. Larger and prospective studies including echocardiography are needed to evaluate the potential of 4D and 5D to replace 2D flow MRI for flow quantification and peak velocity determination. [ABSTRACT FROM AUTHOR]

Purpose: In this work, we integrated the pilot tone (PT) navigation system into a reconstruction framework for respiratory and cardiac motion‐resolved 5D flow. We tested the hypotheses that PT would provide equivalent respiratory curves, cardiac triggers, and corresponding flow measurements to a previously established self‐gating (SG) technique while being independent from changes to the acquisition parameters. Methods: Fifteen volunteers and 9 patients were scanned with a free‐running 5D flow sequence, with PT integrated. Respiratory curves and cardiac triggers from PT and SG were compared across all subjects. Flow measurements from 5D flow reconstructions using both PT and SG were compared to each other and to a reference electrocardiogram‐gated and respiratory triggered 4D flow acquisition. Radial trajectories with variable readouts per interleave were also tested in 1 subject to compare cardiac trigger quality between PT and SG. Results: The correlation between PT and SG respiratory curves were 0.95 ± 0.06 for volunteers and 0.95 ± 0.04 for patients. Heartbeat duration measurements in volunteers and patients showed a bias to electrocardiogram measurements of, respectively, 0.16 ± 64.94 ms and 0.01 ± 39.29 ms for PT versus electrocardiogram and of 0.24 ± 63.68 ms and 0.09 ± 32.79 ms for SG versus electrocardiogram. No significant differences were reported for the flow measurements between 5D flow PT and from 5D flow SG. A decrease in the cardiac triggering quality of SG was observed for increasing readouts per interleave, whereas PT quality remained constant. Conclusion: PT has been successfully integrated in 5D flow MRI and has shown equivalent results to the previously described 5D flow SG technique, while being completely acquisition‐independent. [ABSTRACT FROM AUTHOR]

Background: Current standard methods in monitoring glaucoma progression, like optical coherence tomography (OCT) and standard automated perimetry (SAP), have limitations in certain cases. Automated relative afferent pupillary defect (RAPD) and pupillary light reflex (PLR) testing may offer more objective alternatives. This pilot study aimed to evaluate whether RAPD could sufficiently distinguish between the two eyes in asymmetrical glaucoma, and thus could lay the foundation for using the PLR of a single eye to monitor progression longitudinally., Methods: Twenty-one patients underwent quantitative PLR measurements using a virtual reality headset. RAPD was calculated by subtracting the amplitude of PLRs between eyes. Both RAPD and relative SAP (measured using the mean defect or MD) results were correlated to the thickness of the peripapillary retinal nerve fiber layer (RNFL), as measured by OCT., Results: Data from 18 patients was analyzed after exclusions. RAPD significantly correlated with differences between the two eyes as measured by RNFL thickness (Pearson r = 0.79, p = 0.05). MD differences correlated slightly better with RNFL differences (Pearson r = 0.87, p < 0.05). RAPD and MD combined yielded an improved prediction of RNFL differences by 5% compared to using MD only., Conclusions: RAPD measurements reliably detected asymmetries in optic nerve damage in glaucoma patients. SAP measurements correlated better with OCT results than RAPD results. However, SAP and RAPD combined led to an improved prediction of RNFL thickness. This could possibly allow us to use PLR only over longer periods of time to monitor glaucomatous optic nerve damage in a single eye in the future., Competing Interests: Mathias Abegg, Avantika Naidu and Bruno Hauser are employees of the company machineMD. Mathias Abegg is a shareholder of the company machineMD. machineMD is the manufacturer of the medical device neos, which was used for the measurements in this study. The significance of pupils for glaucoma investigated in the study presented here does not play a role in either the current or planned future versions of neos., (Thieme. All rights reserved.)

Background: This study aimed to validate respiratory-resolved five-dimensional (5D) flow cardiovascular magnetic resonance (CMR) against real-time two-dimensional (2D) phase-contrast MRI, assess the impact of number of respiratory states, and measure the impact of respiration on hemodynamics in congenital heart disease (CHD) patients., Methods: Respiratory-resolved 5D flow MRI-derived net and peak flow measurements were compared to real-time 2D phase-contrast MRI-derived measurements in 10 healthy volunteers. Pulmonary-to-systemic flow ratios (Qp:Qs) were measured in 19 CHD patients and aortopulmonary collateral burden was measured in 5 Fontan patients. Additionally, the impact of number of respiratory states on measured respiratory-driven net flow changes was investigated in 10 healthy volunteers and 19 CHD patients (shunt physiology, n = 11, single ventricle disease [SVD], n = 8)., Results: There was good agreement between 5D flow MRI and real-time 2D phase-contrast-derived net and peak flow. Respiratory-driven changes had a good correlation (rho = 0.64, p < 0.001). In healthy volunteers, fewer than four respiratory states reduced measured respiratory-driven flow changes in veins (5.2 mL/cycle, p < 0.001) and arteries (1.7 mL/cycle, p = 0.05). Respiration drove substantial venous net flow changes in SVD (64% change) and shunt patients (57% change). Respiration had significantly greater impact in SVD patients compared to shunt patients in the right and left pulmonary arteries (46% vs 15%, p = 0.003 and 59% vs 20%, p = 0.002). Qp:Qs varied by 37 ± 24% over respiration in SVD patients and 12 ± 20% in shunt patients. Aortopulmonary collateral burden varied by 118 ± 84% over respiration in Fontan patients. The smallest collateral burden was measured during active inspiration in all patients and the greatest burden was during active expiration in four of five patients. Reduced respiratory resolution blunted measured flow changes in the caval veins of shunt and SVD patients (p < 0.005)., Conclusions: Respiratory-resolved 5D flow MRI measurements agree with real-time 2D phase contrast. Venous measurements are sensitive to number of respiratory states, whereas arterial measurements are more robust. Respiration has a substantial impact on caval vein flow, Qp:Qs, and collateral burden in CHD patients., Competing Interests: Declaration of competing interests Elizabeth Weiss, Justin Baraboo, and Michael Markl report financial support was provided by the National Heart Lung and Blood Institute. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: Four-dimensional (4D) flow magnetic resonance imaging (MRI) often relies on the injection of gadolinium- or iron-oxide-based contrast agents to improve vessel delineation. In this work, a novel technique is developed to acquire and reconstruct 4D flow data with excellent dynamic visualization of blood vessels but without the need for contrast injection. Synchronization of Neighboring Acquisitions by Physiological Signals (SyNAPS) uses pilot tone (PT) navigation to retrospectively synchronize the reconstruction of two free-running three-dimensional radial acquisitions, to create co-registered anatomy and flow images., Methods: Thirteen volunteers and two Marfan syndrome patients were scanned without contrast agent using one free-running fast interrupted steady-state (FISS) sequence and one free-running phase-contrast MRI (PC-MRI) sequence. PT signals spanning the two sequences were recorded for retrospective respiratory motion correction and cardiac binning. The magnitude and phase images reconstructed, respectively, from FISS and PC-MRI, were synchronized to create SyNAPS 4D flow datasets. Conventional two-dimensional (2D) flow data were acquired for reference in ascending (AAo) and descending aorta (DAo). The blood-to-myocardium contrast ratio, dynamic vessel area, net volume, and peak flow were used to compare SyNAPS 4D flow with Native 4D flow (without FISS information) and 2D flow. A score of 0-4 was given to each dataset by two blinded experts regarding the feasibility of performing vessel delineation., Results: Blood-to-myocardium contrast ratio for SyNAPS 4D flow magnitude images (1.5 ± 0.3) was significantly higher than for Native 4D flow (0.7 ± 0.1, p < 0.01) and was comparable to 2D flow (2.3 ± 0.9, p = 0.02). Image quality scores of SyNAPS 4D flow from the experts (M.P.: 1.9 ± 0.3, E.T.: 2.5 ± 0.5) were overall significantly higher than the scores from Native 4D flow (M.P.: 1.6 ± 0.6, p = 0.03, E.T.: 0.8 ± 0.4, p < 0.01) but still significantly lower than the scores from the reference 2D flow datasets (M.P.: 2.8 ± 0.4, p < 0.01, E.T.: 3.5 ± 0.7, p < 0.01). The Pearson correlation coefficient between the dynamic vessel area measured on SyNAPS 4D flow and that from 2D flow was 0.69 ± 0.24 for the AAo and 0.83 ± 0.10 for the DAo, whereas the Pearson correlation between Native 4D flow and 2D flow measurements was 0.12 ± 0.48 for the AAo and 0.08 ± 0.39 for the DAo. Linear correlations between SyNAPS 4D flow and 2D flow measurements of net volume (r 2 = 0.83) and peak flow (r 2 = 0.87) were larger than the correlations between Native 4D flow and 2D flow measurements of net volume (r 2 = 0.79) and peak flow (r 2 = 0.76)., Conclusion: The feasibility and utility of SyNAPS were demonstrated for joint whole-heart anatomical and flow MRI without requiring electrocardiography gating, respiratory navigators, or contrast agents. Using SyNAPS, a high-contrast anatomical imaging sequence can be used to improve 4D flow measurements that often suffer from poor delineation of vessel boundaries in the absence of contrast agents., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests. Peter Speier reports a relationship with Siemens Healthineers that includes employment. Mario Bacher reports a relationship with Siemens Healthineers that includes employment. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)