Purpose: To compare the image quality and acquisition time of thoracic great vessels using a novel, 3D isotropic non-contrast-enhanced MR angiography that combines respiratory compensation, electrocardiogram-triggering, compressed sensing, and Dixon water-fat separation at 3T (CS-MRA) to a conventional MRA employing parallel imaging and spectral attenuated inversion recovery (cMRA).

Methods: This study included 20 healthy volunteers and 19 patients with thoracic vascular diseases. All scans were performed on a 3T MRI scanner using a T2-prepared 3D fast low angle shot (FLASH) sequence. Visual image quality of thoracic great vessels was assessed using a 4-point scale. Quantitative parameters including SNR, contrast-to-noise ratio (CNR), contrast ratio (CR), and coefficient of variation (CV) were evaluated. Aortic diameters were measured, and reproducibility was assessed using Bland–Altman analysis and the intraclass correlation coefficient (ICC). Image acquisition times were also compared.

Results: Visual assessment demonstrated significantly higher scores with CS-MRA compared to cMRA across all evaluated thoracic vessels in both volunteers and patients (median score: 3 vs. 2, P < 0.05). Quantitative analysis showed that CS-MRA yielded significantly higher SNR, CNR, and CR (P < 0.05 for all), along with better signal homogeneity (lower CV). CS-MRA showed excellent intra- and inter-observer agreement for aortic diameter measurements, with ICCs ≥ 0.91 in volunteers and ≥ 0.95 in patients. CS-MRA also achieved significantly shorter acquisition times (volunteers: 5.3 ± 1.4 min vs. 6.0 ± 1.7 min, P < 0.01; patients: 5.1 [4.6–6.3] min vs. 6.9 [5.0–9.6] min, P < 0.01).

Conclusion: CS-MRA provides superior image quality, comparable measurement reproducibility, and significantly reduced acquisition times compared to cMRA. These findings support the clinical utility of CS-MRA as an efficient and reliable non-contrast technique for thoracic vascular evaluation.

Purpose: To evaluate hemodynamic changes associated with aortic stiffness after endovascular aneurysm repair (EVAR) for abdominal aortic aneurysm using 4-dimensional flow MRI (4D Flow MRI), with a focus on blood flow energy loss (EL).

Methods: Thirty-five patients underwent 4D Flow MRI before and after EVAR. Flow velocity, volume, and reflux ratio were measured at the juxtarenal aorta, aneurysmal orifice, and distal iliac landing zone. EL was assessed at the neck and treatment segments, and its relationship with pulse wave velocity (PWV) was analyzed.

Results: Post-EVAR velocity and volume increased across all segments, whereas reflux ratio decreased at the aneurysmal orifice. EL significantly increased at the neck (6.3 [4.0–9.7] vs 16.7 [5.4–29.9] mW, P < 0.001) and treatment segments (29.0 [21.8–45.2] vs 265.6 [182.7–443.6] mW, P < 0.001). Patients with increased PWV showed a greater EL rise at the neck (6.8 [4.2–11.5] vs 16.9 [7.9–30.4] mW, P = 0.001). When stratified by pre-EVAR brachial–ankle PWV, the high-risk group (≥ 1800 cm/s) had a higher post-/pre-EL ratio (6.7 [4.0–10.6] vs 10.4 [7.0–15.8], P = 0.018).

Conclusion: EVAR induces specific hemodynamic alterations. The post-operative rise in flow velocity, volume, and EL indicates increased aortic stiffness, suggesting elevated cardiac afterload in patients with advanced arterial stiffness.

Purpose: Airflow obstruction (AO) and coronary artery disease (CAD) share smoking as a risk factor. They may be associated with alterations in ventricular and atrial volumes and functions, and global coronary flow reserve (CFR), all of which can be assessed by cardiovascular MR (CMR). The purpose of this study was to evaluate the association between AO severity and CMR parameters in patients with known or suspected CAD.

Methods: Eighty patients with known or suspected CAD who underwent CMR, including cine, stress and rest perfusion, stress and rest coronary sinus flow measurements by phase-contrast cine, and late gadolinium enhancement; spirometry; and lung CT within 6 months were included in the study. Ventricular and atrial volumes and functions, and global CFR were evaluated by CMR. AO severity was evaluated by the ratio of the forced expiratory volume in the first second to the forced vital capacity (FEV1/FVC). Emphysema severity was determined by Goddard score.

Results: Median FEV1/FVC for all patients was 74.8%. Compared with patients with FEV1/FVC above the median, those with FEV1/FVC below the median had more impaired left atrial (LA) reservoir strain (P = 0.010), LA conduit strain (P = 0.012), left ventricular global longitudinal strain (P = 0.025), right atrial reservoir strain (P = 0.028), and Goddard score (P < 0.001). There was no significant difference in global CFR between the groups. Multiple linear regression analysis revealed LA conduit strain and Goddard score as independently associated with FEV1/FVC (β = 0.318, P = 0.001 and β = −0.422, P < 0.001, respectively).

Conclusion: LA conduit function was independently associated with FEV1/FVC in patients with known or suspected CAD after adjusting for age, sex, smoking, and the CMR indices. This finding suggests that AO severity is associated primarily with impaired LA conduit function in patients with known or suspected CAD.

Purpose: To develop and evaluate short-TR acquisition time-of-flight (STRA-TOF) MR angiography (MRA), which combines an optimized STRA with deep learning–based reconstruction to achieve scan-time reduction while maintaining image quality in the visualization of intracranial arteries.

Methods: Ten healthy volunteers and 3 patients with moyamoya disease were examined using 3D TOF MRA with the clinical moyamoya protocol and 2 STRA-TOF protocols employing 4-slab (STRA4) and 9-slab (STRA9) configurations. STRA-TOF employed a TR of approximately 10 ms with variable-density Poisson-disc sampling and unrolled deep learning reconstruction. Bloch equation simulations validated the theoretical basis for STRA. Quantitative assessment included SNR and contrast-to-noise ratio measurements. Two radiologists independently evaluated image quality using a 3-point scale across 9 vascular territories and overall image quality, with blinded assessment. Statistical analysis was performed using the Friedman test with post hoc Wilcoxon signed-rank tests.

Results: STRA-TOF achieved approximately a 50% reduction in scan time compared with conventional protocols. Both STRA sequences demonstrated significantly higher SNR and contrast-to-noise ratio than conventional TOF (P < 0.001). Overall image quality scores were higher for STRA4 and STRA9 compared with conventional TOF in both readers. Across the 9 vascular territories, both readers consistently rated STRA sequences equal to or superior to conventional TOF, particularly for distal branches. In the small patient cohort with moyamoya disease (n = 3), STRA-TOF demonstrated feasibility for visualizing complex arterial pathology, including stenotic vessels, collateral circulation, and postsurgical vascular changes.

Conclusion: STRA-TOF achieved approximately a 50% reduction in scan time while maintaining or improving image quality compared with conventional 3D TOF MRA. This technique addresses the fundamental scan-time limitations of the conventional method, with potential for significant clinical benefits in terms of patient comfort, workflow efficiency, and improved access to intracranial artery evaluation.

This study aimed to clarify the accuracy and variability of heart rate variability effects on T1 relaxation time values acquired using different sampling schemes of the modified Look–Locker inversion recovery (MOLLI) method. Five MOLLI sampling schemes—5(3)3, 5s(3s)3s, 4(1)3(1)2, 4s(1s)3s(1s)2s, and 3(3)3(3)5—were compared using a simulated electrocardiogram signal in a phantom experiment. The 5(3)3 and 5s(3s)3s schemes demonstrated high accuracy across the range of native and contrast-enhanced T1 values, with correlation coefficients exceeding 0.95 compared with the reference T1. Regarding heart rate variability, the 5(3)3 scheme showed minimal variation in the measured value across different heart rates, regardless of the T1 value, with an error rate below 6% relative to the reference T1. Therefore, the 5(3)3 scheme can achieve highly accurate measurements over a wide T1 range and is robust against heart rate variability.

Purpose: To evaluate short T₂ components potentially reflecting calcification or other susceptibility-affected tissue components in atherosclerotic plaques, using multicomponent analysis with ultrashort TE (UTE) MRI.

Methods: A phantom experiment was conducted using a 4-echo UTE sequence, mimicking the sample as a small amount of calcification found intra-voxel. The phantom included 6 samples containing varying concentrations of hydroxyapatite (calcification) and mayonnaise (lipid–water emulsion). Data acquired from the UTE sequence were compared with those obtained using a conventional multi-echo gradient-echo (mGRE) method.

Results: Bi-exponential analysis of UTE data successfully separated short- and long-T₂* components, with ranges of 0.44–4.81 ms and 4.29–24.37 ms, respectively. Short T₂* values derived from UTE showed minor changes with increasing hydroxyapatite concentration. Using bi-exponential analysis of mGRE data, short and long T₂* values ranged from 0.17–0.77 ms and 6.16–39.20 ms, respectively. For mono-exponential fitting of mGRE data, T₂* values ranged from 4.84–38.32 ms. In all datasets, 1/T₂* increased with hydroxyapatite concentration. The signal fraction of short T₂* components in the UTE dataset decreased as hydroxyapatite concentration increased. A clinical scan of 1 patient with an atherosclerotic plaque yielded mean short and long T₂* values of 0.12 ± 0.35 ms and 33.22 ± 17.25 ms, respectively.

Conclusion: T₂* analysis using UTE data enabled the separation of mixed calcification and mayonnaise (lipid–water emulsion) within a sample into 2 components and detected short T₂* components that may reflect calcification-related susceptibility effects, without directly indicating calcification. Multicomponent T₂* analysis with UTE-MRI is a promising technique for evaluating calcification and other short T₂* components in atherosclerotic plaques.

Purpose: Aortopathy, characterized by aortic dilatation caused by cystic medial necrosis, typically develops in adulthood but has been observed at a young age in patients with tetralogy of Fallot. We hypothesized that some patients with tetralogy of Fallot or double-outlet right ventricle experience early-onset aortic disturbed flow. This study aimed to identify and analyze the causes of disturbed flow using 4D flow MRI.

Methods: This study included 24 patients who underwent 4D flow MRI at our institution between January 2022 and September 2024. MRI and cardiac catheterization were performed during follow-up. 4D flow MRI was used to detect disturbed flow and investigate its underlying causes.

Results: The mean age of patients with tetralogy of Fallot or double-outlet right ventricle was 12 years (range, 1 to 37 years). Of the 24 participants, 11 (46%) exhibited disturbed flow. Patients with disturbed flow had significantly higher Valsalva Z-scores (4.7 ± 3.1 vs. 2.4 ± 1.4, P = 0.013) and a significantly narrower left ventricular outflow tract-ascending aorta angle (113.5 ± 11.6 vs. 127.1 ±  6.7°, P = 0.002). Wall shear stress and energy loss were not significantly different between the 2 groups.

Conclusion: Aortic disturbed flow may occur in patients with tetralogy of Fallot or double-outlet right ventricle, regardless of age, suggesting an association with the left ventricular outflow tract-ascending aorta angle. The occurrence of disturbed flow at a young age should be noted as it may contribute to the future progression of aortopathy.

Purpose: To evaluate the effect of model-based deep-learning reconstruction (DLR) compared with that of compressed sensing–sensitivity encoding (CS) on cine cardiac magnetic resonance (CMR).

Methods: Cine CMR images of 10 healthy volunteers were obtained with reduction factors of 2, 4, 6, and 8 and reconstructed using CS and DLR. The visual image quality scores assessed sharpness, image noise, and artifacts. Left-ventricular (LV) end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) were manually measured. LV global circumferential strain (GCS) was automatically measured using the software. The precision of EDV, ESV, SV, EF, and GCS measurements was compared between CS and DLR using Bland–Altman analysis with full-sampling data as the gold standard.

Results: Compared with CS, DLR significantly improved image quality with reduction factors of 6 and 8. The precision of EDV and ESV with a reduction factor of 8, and GCS with reduction factors of 6 and 8 measurements improved with DLR compared with CS, whereas those of SV and EF measurements were not different between DLR and CS.

Conclusion: The effect of DLR on cine CMR’s image quality and precision in evaluating quantitative volume and strain was equal or superior to that of CS. DLR may replace CS for cine CMR.

Purpose: To investigate the potential of 4D flow MRI-derived pulmonary hemodynamic parameters as sensitive markers for chronic obstructive pulmonary disease (COPD) patients with right ventricular dysfunction (RVD).

Methods: We enrolled 15 COPD patients combined with RVD and 43 non-RVD participants, all of them underwent pulmonary function tests, thoracic CT and cardiac MR examinations, and the image post-processing analysis was completed. After comparing the 2 groups, the average flow velocity of the main pulmonary artery (Vavg-MPA) and the right pulmonary artery (Vavg-RPA) were identified as statistically significant confounding factors, propensity score matching was used to pair patients controlling for these 2 parameters. Univariate and multivariate logistic regression analyses were performed to assess the pulmonary hemodynamic parameters obtained from 4D flow MRI that could serve as sensitive markers for identifying COPD patients with RVD based on the matched participants dataset.

Results: Fourteen COPD patients combined with RVD and 29 non-RVD participants were successfully matched. Logistic regression analysis showed that the decreased systolic pressure drop along the MRA-RPA tract (odds ratio [OR]: 0.31; 95% confidence interval [CI]: 0.12–0.78; P =0.013) and the presence of vortex (OR: 8.82; 95% CI: 1.11–70.36; P =0.040) were identified as independent risk factors for RVD in COPD patients.

Conclusion: Pulmonary hemodynamic parameters derived from 4D flow MRI, specifically the systolic pressure drop along the MPA-RPA tract and the presence of vortex in the main pulmonary artery, can serve as sensitive indicators for predicting right ventricular dysfunction in COPD patients.

Purpose: To assess right heart diastolic energy loss (EL) as a cardiac workload and evaluate its association with major cardiac events (MACE) in adult patients with pulmonary atresia with an intact ventricular septum (PAIVS).

Methods: We retrospectively enrolled and compared 30 consecutive adult patients (18 with PAIVS and 12 with pulmonary stenosis [PS] as controls) who underwent right ventricular (RV) outflow tract reconstruction and 4D flow MRI. EL, conventional parameters on MRI, and the severity of tricuspid regurgitation (TR) on echocardiography were assessed. We also evaluated the association between MACE including arrhythmias, heart failure, surgical intervention, and imaging parameters in adults with PAIVS.

Results: Patients with PAIVS were younger, had a higher diastolic EL/cardiac output (CO) ratio, and had a more significant TR than those with PS (controls). However, RV volume, ejection fraction (EF), and pulmonary regurgitation (PR) severity did not differ between the two groups. Higher RV end-diastolic pressure (EDP) and lower cardiac index (CI) correlated with the diastolic EL/CO in patients with PAIVS. Univariate logistic analysis demonstrated that older age and a higher diastolic EL/CO ratio were important factors for MACE in adults with PAIVS (P = 0.048, 0.049).

Conclusion: A higher diastolic EL/CO ratio was associated with a higher RV EDP and lower CI. A high diastolic EL/CO ratio is also associated with MACE in adults with PAIVS. Even in adults with normal RV volume and EF, the right heart EL was elevated, suggesting an excessive right-sided cardiac workload that integrated both afterload and preload beyond the RV size in adult patients with PAIVS.

Purpose: Fresh blood imaging (FBI) utilizes physiological blood signal differences between diastole and systole, causing a long acquisition time. The purpose of this study is to develop a fast FBI technique using a centric k_y – k_z k-space trajectory (cFBI) and an exponential refocusing flip angle (eFA) scheme with fast longitudinal restoration.

Methods: This study was performed on 8 healthy subjects and 2 patients (peripheral artery disease and vascular disease) with informed consent, using a clinical 3-Tesla MRI scanner. A numeric simulation using extended phase graph (EPG) and phantom studies of eFA were carried out to investigate the restoration of longitudinal signal by lowering refocusing flip angles in later echoes. cFBI was then acquired on healthy subjects at the popliteal artery station to assess the effect of varying high/low flip ratios on the longitudinal restoration effects. In addition, trigger-delays of cFBI were optimized owing to the long acquisition window in zigzag centric k_y – k_z k-space trajectory. After optimizations, cFBI images were compared against standard FBI (sFBI) images in terms of scan time, motion artifacts, Nyquist N/2 artifacts, blurring, and overall image quality. We also performed two-way repeated measures analysis of variance.

Results: cFBI with eFA achieved nearly a 50% scan time reduction compared to sFBI. The high/low flip angle of 180/2 degrees with lower refocusing pulses shows fast longitudinal restoration with the highest blood signals, yet also more sensitive to the background signals. Overall, 180/30 degrees images show reasonable blood signal recovery while minimizing the background signal artifacts. After the trigger delay optimization, maximum intensity projection image of cFBI after systole-diastole subtraction demonstrates less motion and N/2 artifacts than that of sFBI.

Conclusion: Together with eFA for fast longitudinal signal restoration, the proposed cFBI technique achieved a 2-fold reduction in scan time and improved image quality without major artifacts.

Purpose: Prolonged scanning of time-resolved 3D phase-contrast MRI (4D flow MRI) limits its routine use in clinical practice. An echo-planar imaging (EPI)-based sequence and compressed sensing can reduce the scan duration. We aimed to determine the impact of EPI for 4D flow MRI on the scan duration, image quality, and quantitative flow metrics.

Methods: This was a prospective study of 15 healthy volunteers (all male, mean age 33 ± 5 years). Conventional sensitivity encoding (SENSE), EPI with SENSE (EPI), and compressed SENSE (CS) (reduction factors: 6 and 12, respectively) were scanned.

Scan duration, qualitative indexes of image quality, and quantitative flow parameters of net flow volume, maximum flow velocity, wall shear stress (WSS), and energy loss (EL) in the ascending aorta were assessed. Two-dimensional phase-contrast cine MRI (2D-PC) was considered the gold standard of net flow volume and maximum flow velocity.

Results: Compared to SENSE, EPI and CS12 shortened scan durations by 71% and 73% (EPI, 4 min 39 sec; CS6, 7 min 29 sec; CS12, 4 min 14 sec; and SENSE, 15 min 51 sec). Visual image quality was significantly better for EPI than for SENSE and CS (P < 0.001). The net flow volumes obtained with SENSE, EPI, and CS12 and those obtained with 2D-PC were correlated well (r = 0.950, 0.871, and 0.850, respectively). However, the maximum velocity obtained with EPI was significantly underestimated (P < 0.010). The average WSS was significantly higher with EPI than with SENSE, CS6, and CS12 (P < 0.001, P = 0.040, and P = 0.012, respectively). The EL was significantly lower with EPI than with CS6 and CS12 (P = 0.002 and P = 0.007, respectively).

Conclusion: EPI reduced the scan duration, improved visual image quality, and was associated with more accurate net flow volume than CS. However, the flow velocity, WSS, and EL values obtained with EPI and other sequences may not be directly comparable.

Purpose: Polarity-corrected inversion time preparation (PCTIP), a myocardial T1 mapping technique, is expected to reduce measurement underestimation in the modified Look-Locker inversion recover method. However, measurement precision is reduced, especially for heart rate variability. We devised an analysis using a recurrence formula to overcome this problem and showed that it improved the measurement accuracy, especially at high heart rates. Therefore, this study aimed to determine the effect of this analysis on the accuracy and precision of T1 measurements for irregular heart rate variability.

Methods: A PCTIP scan using a 3T MRI scanner was performed in phantom experiment. We generated the simulated R-waves required for electrocardiogram (ECG)-gated acquisition using a signal generator set to 30 combinations. T1 map was generated using the signal train of the PCTIP images by nonlinear curve fitting using conventional and recurrence formulas. Accuracy against reference T1 and precision of heart rate variability were evaluated. To evaluate the fitting accuracy of both analyses, the relative fitting error was calculated.

Results: For the longer T1, the fitting error was larger than the short T1, with the conventional analysis showing 10.1±2.0%. The recurrence formula analysis showed a small fitting error less than 1%, which was consistent for all heart rate variability patterns. In the conventional analysis, the accuracy, especially for longer T1, showed a large underestimation of the measurements and poor linearity. However, in the recurrence formula analysis, the accuracy improved at a long T1, and linearity also improved. The Bland–Altman plot showed that it varied greatly depending on the heart rate variability pattern for the longer T1 in the conventional analysis, whereas the recurrence formula analysis suppressed this variation.

Conclusion: T1 analysis of PCTIP using the recurrence formula analysis achieved accurate and precise T1 measurements, even for irregular heart rate variability.

Purpose: The purposes of this study were to compare global coronary flow reserve (CFR) between patients with idiopathic dilated cardiomyopathy (DCM) and risk-matched controls using cardiac MRI (CMR), and to evaluate the relationship between global CFR and CMR left ventricular (LV) parameters.

Methods: Twenty-six patients with DCM and 26 risk-matched controls who underwent comprehensive CMR examination, including stress-rest coronary sinus flow measurement by phase contrast (PC) cine CMR were retrospectively studied. LV peak global longitudinal, radial, and circumferential strains (GLS, GRS, and GCS) were determined by feature tracking.

Results: Patients with DCM had significantly lower global CFR compared with the risk-matched controls (2.87 ± 0.86 vs. 4.03 ± 1.47, P = 0.001). Among the parameters, univariate linear regression analyses revealed significant correlation of global CFR with LV end-diastolic volume index (r = –0.396, P = 0.045), LV mass index (r = –0.461, P = 0.018), GLS (r = –0.558, P = 0.003), and GRS (r = 0.392, P = 0.047). Multiple linear regression analysis revealed GLS as the only independent predictor of global CFR (standardized β = –0.558, P = 0.003).

Conclusion: Global CFR was significantly impaired in patients with idiopathic DCM and independently associated with LV GLS, suggesting that microvascular dysfunction may contribute to deterioration of LV function in patients with idiopathic DCM.

Since thoracic MR imaging was first used in a clinical setting, it has been suggested that MR imaging has limited clinical utility for thoracic diseases, especially lung diseases, in comparison with x-ray CT and positron emission tomography (PET)/CT. However, in many countries and states and for specific indications, MR imaging has recently become practicable. In addition, recently developed pulmonary MR imaging with ultra-short TE (UTE) and zero TE (ZTE) has enhanced the utility of MR imaging for thoracic diseases in routine clinical practice. Furthermore, MR imaging has been introduced as being capable of assessing pulmonary function. It should be borne in mind, however, that these applications have so far been academically and clinically used only for healthy volunteers, but not for patients with various pulmonary diseases in Japan or other countries. In 2020, the Fleischner Society published a new report, which provides consensus expert opinions regarding appropriate clinical indications of pulmonary MR imaging for not only oncologic but also pulmonary diseases. This review article presents a brief history of MR imaging for thoracic diseases regarding its technical aspects and major clinical indications in Japan 1) in terms of what is currently available, 2) promising but requiring further validation or evaluation, and 3) developments warranting research investigations in preclinical or patient studies. State-of-the-art MR imaging can non-invasively visualize lung structural and functional abnormalities without ionizing radiation and thus provide an alternative to CT. MR imaging is considered as a tool for providing unique information. Moreover, prospective, randomized, and multi-center trials should be conducted to directly compare MR imaging with conventional methods to determine whether the former has equal or superior clinical relevance. The results of these trials together with continued improvements are expected to update or modify recommendations for the use of MRI in near future.

Cells in the tissues and organs of a living body are subjected to mechanical forces, such as pressure, friction, and tension from their surrounding environment. Cells are equipped with a mechanotransduction mechanism by which they perceive mechanical forces and transmit information into the cell interior, thereby causing physiological or pathogenetic mechano-responses. Endothelial cells (ECs) lining the inner surface of blood vessels are constantly exposed to shear stress caused by blood flow and a cyclic strain caused by intravascular pressure. A number of studies have shown that ECs are sensitive to changes in these hemodynamic forces and alter their morphology and function, sometimes by modifying gene expression. The mechanism of endothelial mechanotransduction has been elucidated, and the plasma membrane has recently been shown to act as a mechanosensor. The lipid order and cholesterol content of plasma membranes change immediately upon the exposure of ECs to hemodynamic forces, resulting in a change in membrane fluidity. These changes in a plasma membrane’s physical properties affect the conformation and function of various ion channels, receptors, and microdomains (such as caveolae and primary cilia), thereby activating a wide variety of downstream signaling pathways. Such endothelial mechanotransduction works to maintain circulatory homeostasis; however, errors in endothelial mechanotransduction can cause abnormalities in vascular physiological function, leading to the initiation and progression of various vascular diseases, such as hypertension, thrombosis, aneurysms, and atherosclerosis. Recent advances in detailed imaging technology and computational fluid dynamics analysis have enabled us to evaluate the hemodynamic forces acting on vascular tissue accurately, contributing greatly to our understanding of vascular mechanotransduction and the pathogenesis of vascular diseases, as well as the development of new therapies for vascular diseases.

Most cardiac diseases cause a non-physiological blood flow pattern known as turbulence around the heart and great vessels, which further worsen the disease itself. However, there is no consensus on how blood flow can be defined in disease conditions. Especially, in the left atrium, the fact that vortex flow already exists makes this debate more complicated. 3D time-resolved phase-contrast (4D flow) MRI is expected to be able to capture blood flow patterns from multiple aspects, such as blood flow velocity, stasis, and vortex quantification. Previous studies have confirmed that physiological vortex flow is predominantly induced by the higher-volume flow from the superior left pulmonary vein. In atrial fibrillation, 4D flow MRI reveals a non-physiological blood flow pattern, which information may add value to well-established clinical risk factors. Currently, the research target of LA analysis has also widened to lung surgeons, pulmonary vein stump thrombosis after left upper lobectomy. 4D flow MRI is expected to be utilized for many more variable diseases that are currently unimaginable.

Pulmonary hypertension (PH) is characterized by elevated pulmonary arterial pressure (PAP). Although right-heart catheterization is the gold standard method for the diagnosis of PH by definition, various less-invasive imaging tests have been used for screening, detection of underlying diseases-causing PH, and monitoring of diseases. Among them, 4D flow MRI is an emerging and unique imaging test that allows for comprehensive visualization of blood flow in the right heart and proximal pulmonary arteries. The characteristic blood flow pattern observed in patients with PH is vortical flow formation in the main pulmonary artery. Recent studies have proposed the use of these findings to determine not only the presence of PH but also estimate the mean PAP. Other applications of 4D flow MRI for PH include measurement of wall shear stress, helicity, and 3D flow balance in the pulmonary arteries. It is worth noting that 4D flow has also the potential for longitudinal follow-ups. In this review, the clinical definition of PH, summary of conventional imaging tests, characteristics of pulmonary arterial flow as shown by 4D flow MRI, and clinical application of 4D flow MRI in the management of patients with PH will be discussed.

4D flow MRI allows time-resolved 3D velocity-encoded phase-contrast imaging for 3D visualization and quantification of aortic and intracardiac flow. Radiologists should be familiar with the principles of 4D flow MRI and methods for evaluating blood flow qualitatively and quantitatively. The most substantial benefits of 4D flow MRI are that it enables the simultaneous comprehensive assessment of different vessels, and that retrospective analysis can be achieved in all vessels in any direction in the field of view, which is especially beneficial for patients with complicated congenital heart disease (CHD). For aortic valvular diseases, new parameters such as wall shear stress and energy loss may provide new prognostic values for 4D flow MRI. In this review, we introduce the clinical applications of 4D flow MRI for the visualization of blood flow and quantification of hemodynamic metrics in the setting of aortic valvular disease and CHD, including intracardiac shunt and coronary artery anomaly.

Despite the recent technical developments, surgery on the thoracic aorta remains challenging and is associated with significant mortality and morbidity. Decisions about when and if to operate are based on a balance between surgical risk and the hazard of aortic rupture. These decisions are sometimes difficult in elective cases of thoracic aortic diseases, including aneurysms and dissections. Abnormal wall stress derived from flow alterations influences disease progression. Therefore, a better understanding of the complex hemodynamic environment inside the aortic lumen will facilitate patient-specific risk assessments of complications, which enable clinicians to provide timely prophylactic interventions. Time-resolved 3D phase-contrast (4D flow) MRI has many advantages for the in vivo assessment of flow dynamics. Recent developments in 4D flow imaging techniques has led to significant advances in our understanding of physiological flow dynamics in healthy subjects and patients with thoracic aortic diseases. In this clinically focused review of thoracic aortic diseases, we demonstrate the clinical advances acquired with 4D flow MRI from published studies. We provide a systematic overview of key evidences and considerations regarding normal thoracic aortas, thoracic aortic aneurysms, aortic dissections, and thoracic aortas with prosthetic graft replacement.