4D Flow Magnetic Resonance Imaging Research Articles

Emerging technologies and applications in multimodality imaging for ischemic heart disease: current state and future of artificial intelligence

Ischemic heart disease (IHD) is a major global health issue, frequently resulting in myocardial infarction and ischemic cardiomyopathy. Prompt and precise diagnosis is essential to avert complications such as heart failure and sudden cardiac death. Although invasive coronary angiography remains the gold standard for high-risk patients, noninvasive multimodality imaging is becoming more prevalent for those at low-to-intermediate risk. This review evaluated the current state of multimodality imaging in IHD, including echocardiography, nuclear cardiology, cardiac magnetic resonance imaging (MRI), computed tomography (CT) angiography, and invasive coronary angiography. Each modality has distinct strengths and limitations, and their complementary use provides a comprehensive assessment of cardiac health. Integrating artificial intelligence (AI) into imaging workflows holds promise for enhancing diagnostic accuracy and efficiency. AI algorithms can optimize image acquisition, processing, and interpretation of complex imaging data. Emerging technologies like 4D flow MRI, molecular imaging, and hybrid systems [e.g., positron emission tomography (PET)/MRI, PET/CT] integrate anatomical, functional, and molecular data, providing comprehensive insights into cardiac pathology and potentially revolutionizing the management of IHD. This review also explored the clinical applications and impact of multimodality imaging on patient outcomes, emphasizing its role in improving diagnostic precision and guiding therapeutic decisions. Future directions include AI-driven decision support systems and personalized medicine approaches. Addressing regulatory and ethical challenges, such as data privacy and algorithm transparency, is crucial for the broader adoption of these advanced technologies. This review highlighted the transformative potential of AI-enhanced multimodality imaging in improving the diagnosis and management of IHD.

Verification Study of in Silico Computed Intracardiac Blood Flow With 4D Flow MRI.

Major challenges for clinical applications of in silico medicine are limitations in time and computational resources. Computational approaches should therefore be tailored to specific applications with relatively low complexity and must be verified and validated against clinical gold standards. This study performed computational fluid dynamics simulations of left ventricular hemodynamics of different complexity based on shape reconstruction from steady state gradient echo magnetic resonance imaging (MRI) data. Computed flow results of a rigid wall model (RWM) and a prescribed motion fluid-structure interaction (PM-FSI) model were compared against phase-contrast MRI measurements for three healthy subjects. Extracted boundary conditions from the steady state MRI sequences as well as computed metrics, such as flow rate, valve velocities, and kinetic energy show good agreement with in vivo flow measurements. Regional flow analysis reveals larger differences. Basic flow structures are well captured with RWM and PM-FSI. For the computation of further biomarkers like washout or flow efficiency, usage of PM-FSI is required. Regarding boundary-near flow, more accurate anatomical models are inevitable. These results delineate areas of application of both methods and lay a foundation for larger validation studies and sensitivity analysis for healthy and diseased cases, being an essential step upon clinical translations.

A new method for scaling inlet flow waveform in hemodynamic analysis of aortic dissection.

Computational fluid dynamics (CFD) simulations have shown great potentials in cardiovascular disease diagnosis and postoperative assessment. Patient-specific and well-tuned boundary conditions are key to obtaining accurate and reliable hemodynamic results. However, CFD simulations are usually performed under non-patient-specific flow conditions due to the absence of in vivo flow and pressure measurements. This study proposes a new method to overcome this challenge by tuning inlet boundary conditions using data extracted from electrocardiogram (ECG). Five patient-specific geometric models of type B aortic dissection were reconstructed from computed tomography (CT) images. Other available data included stoke volume (SV), ECG, and 4D-flow magnetic resonance imaging (MRI). ECG waveforms were processed to extract patient-specific systole to diastole ratio (SDR). Inlet boundary conditions were defined based on a generic aortic flow waveform tuned using (1) SV only, and (2) with ECG and SV (ECG + SV). 4D-flow MRI derived inlet boundary conditions were also used in patient-specific simulations to provide the gold standard for comparison and validation. Simulations using inlet flow waveform tuned with ECG + SV not only successfully reproduced flow distributions in the descending aorta but also provided accurate prediction of time-averaged wall shear stress (TAWSS) in the primary entry tear (PET) and abdominal regions, as well as maximum pressure difference, ∆Pmax, from the aortic root to the distal false lumen. Compared with simulations with inlet waveform tuned with SV alone, using ECG + SV in the tuning method significantly reduced the error in false lumen ejection fraction at the PET (from 149.1% to 6.2%), reduced errors in TAWSS at the PET (from 54.1% to 5.7%) and in the abdominal region (from 61.3% to 11.1%), and improved ∆Pmax prediction (from 283.1% to 18.8%) However, neither of these inlet waveforms could be used for accurate prediction of TAWSS in the ascending aorta. This study demonstrates the importance of SDR in tailoring inlet flow waveforms for patient-specific hemodynamic simulations. A well-tuned flow waveform is essential for ensuring that the simulation results are patient-specific, thereby enhancing the confidence and fidelity of computational tools in future clinical applications.

Advanced visualization of aortic dissection anatomy and hemodynamics

Aortic dissection is a life-threatening cardiovascular disease constituted by the delamination of the aortic wall. Due to the weakened structure of the false lumen, the aorta often dilates over time, which can – after certain diameter thresholds are reached – increase the risk of fatal aortic rupture. The identification of patients with a high risk of late adverse events is an ongoing clinical challenge, further complicated by the complex dissection anatomy and the wide variety among patients. Moreover, patient-specific risk stratification depends not only on morphological, but also on hemodynamic factors, which can be derived from computer simulations or 4D flow magnetic resonance imaging (MRI). However, comprehensible visualizations that depict the complex anatomical and functional information in a single view are yet to be developed. These visualization tools will assist clinical research and decision-making by facilitating a comprehensive understanding of the aortic state. For that purpose, we identified several visualization tasks and requirements in close collaboration with cardiovascular imaging scientists and radiologists. We displayed true and false lumen hemodynamics using pathlines as well as surface hemodynamics on the dissection flap and the inner vessel wall. Pathlines indicate antegrade and retrograde flow, blood flow through fenestrations, and branch vessel supply. Dissection-specific hemodynamic measures, such as interluminal pressure difference and flap compliance, provide further insight of the blood flow throughout the cardiac cycle. Finally, we evaluated our visualization techniques with cardiothoracic and vascular surgeons in two separate virtual sessions.

Fluid-structure interaction analysis of a healthy aortic valve and its surrounding haemodynamics.

The opening and closing dynamics of the aortic valve (AV) has a strong influence on haemodynamics in the aortic root, and both play a pivotal role in maintaining normal physiological functions of the valve. The aim of this study was to establish a subject-specific fluid-structure interaction (FSI) workflow capable of simulating the motion of a tricuspid healthy valve and the surrounding haemodynamics under physiologically realistic conditions. A subject-specific aortic root was reconstructed from magnetic resonance (MR) images acquired from a healthy volunteer, whilst the valve leaflets were built using a parametric model fitted to the subject-specific aortic root geometry. The material behaviour of the leaflets was described using the isotropic hyperelastic Ogden model, and subject-specific boundary conditions were derived from 4D-flow MR imaging (4D-MRI). Strongly coupled FSI simulations were performed using a finite volume-based boundary conforming method implemented in FlowVision. Our FSI model was able to simulate the opening and closing of the AV throughout the entire cardiac cycle. Comparisons of simulation results with 4D-MRI showed a good agreement in key haemodynamic parameters, with stroke volume differing by 7.5% and the maximum jet velocity differing by less than 1%. Detailed analysis of wall shear stress (WSS) on the leaflets revealed much higher WSS on the ventricular side than the aortic side and different spatial patterns amongst the three leaflets.

Combining 4D flow magnetic resonance imaging with cardiac catheterization for pre-operative blood flow assessment in an older child with complex congenital heart disease.

Combining 4D flow magnetic resonance imaging with cardiac catheterization for pre-operative blood flow assessment in an older child with complex congenital heart disease.

4D flow magnetic resonance imaging evaluation after transcatheter closure of sinus venosus defects

4D flow magnetic resonance imaging evaluation after transcatheter closure of sinus venosus defects

A comprehensive MRI-based computational model of blood flow in compliant aorta using radial basis function interpolation

BackgroundProperly understanding the origin and progression of the thoracic aortic aneurysm (TAA) can help prevent its growth and rupture. For a better understanding of this pathogenesis, the aortic blood flow has to be studied and interpreted in great detail. We can obtain detailed aortic blood flow information using magnetic resonance imaging (MRI) based computational fluid dynamics (CFD) with a prescribed motion of the aortic wall.MethodsWe performed two different types of simulations—static (rigid wall) and dynamic (moving wall) for healthy control and a patient with a TAA. For the latter, we have developed a novel morphing approach based on the radial basis function (RBF) interpolation of the segmented 4D-flow MRI geometries at different time instants. Additionally, we have applied reconstructed 4D-flow MRI velocity profiles at the inlet with an automatic registration protocol.ResultsThe simulated RBF-based movement of the aorta matched well with the original 4D-flow MRI geometries. The wall movement was most dominant in the ascending aorta, accompanied by the highest variation of the blood flow patterns. The resulting data indicated significant differences between the dynamic and static simulations, with a relative difference for the patient of 7.47±14.18% in time-averaged wall shear stress and 15.97±43.32% in the oscillatory shear index (for the whole domain).ConclusionsIn conclusion, the RBF-based morphing approach proved to be numerically accurate and computationally efficient in capturing complex kinematics of the aorta, as validated by 4D-flow MRI. We recommend this approach for future use in MRI-based CFD simulations in broad population studies. Performing these would bring a better understanding of the onset and growth of TAA.

Assessment of 4D flow MRI for quantification of left-to-right shunt in pediatric patients with ventricular septal defect: comparison with right heart catheterization.

The percentage of shunt fraction significantly impacts the management of patients with congenital shunts, influencing strategic choices such as surgical or interventional procedures. This study compared the estimated shunt fraction (the ratio of pulmonary-to-systemic flow, Qp/Qs) for quantifying the left-to-right shunt in children with ventricular septal defect (VSD) using heart catheterization, four-dimensional (4D) flow, and two-dimensional (2D) flow magnetic resonance imaging (MRI). The goal was to establish a non-invasive and reliable measurement ratio between pulmonary and systemic blood flow in these patients. Between July 2022 and June 2023, patients scheduled to undergo invasive right heart catheterization were included in this study. MRI was performed one hour before the catheterization procedure. The correlation of shunt fraction was assessed between all methods after calculating the Qp/Qs ratio from 2D and 4D flow MRI and catheterization. A total of 24 patients (aged 3-15 years, eight females) were ultimately included in the study. The Qp/Qs ratios obtained from 4D flow had a robust correlation (correlation coefficient r = 0.962) compared to those obtained during catheterization. Cardiac catheterization recorded the mean shunt fraction at 1.499 ± 0.396, while 4D flow measured it at 1.403 ± 0.344, with no significant difference between the two techniques. Moreover, there was a reasonable correlation (r = 0.894) between 2D flow measurements of Qp/Qs and the results obtained from catheterization, with a mean shunt fraction of 1.326 ± 0.283. 4D flow MRI has the potential to be a non-invasive method for accurately measuring the left-to-right shunt in children with VSD.

Characterization of Maximum Wall Shear Stress Points in Unruptured Cerebral Aneurysms Using Four-dimensional Flow Magnetic Resonance Imaging.

Maximum wall shear stress (maxWSS) points of unruptured cerebral aneurysms (UCAs) may cause wall remodeling leading to rupture. We characterized maxWSS points and their inherent intra-aneurysmal flow structures in asizable cohort of saccular UCAs using four-dimensional (4D) flow magnetic resonance imaging (MRI). After contrast administration, 50saccular UCAs were subjected to 4D flow MRI using a1.5 T MRI scanner. Post-processing of obtained data was performed using commercially available software. The maxWSS points and maxWSS values were evaluated. The maxWSS values were statistically compared between aneurysm groups. The maxWSS point was located on the aneurysm apex in9 (18.0%), body in2 (4.0%), and neck in 39 (78.0%) UCAs. The inherent intra-aneurysmal flow structure of the maxWSS point was an inflow zone in 34 (68.0%) UCAs, an inflow jet in 8 (16.0%), and an impingement zone in 8 (16.0%). The maxWSS point on the neck had significantly higher maxWSS values than those points on the other wall areas (P = 0.008). The maxWSS values of the maxWSS points on the apex and on the impingement zone were not significantly different compared with those of the other maxWSS points. The maxWSS points existed preferentially on the aneurysmal neck adjacent to the inflow zone with higher maxWSS values. The maxWSS points existed occasionally on the aneurysmal apex adjacent to the impingement zone. 4D flow MRI may be helpful to discriminate saccular UCAs with higher-risk maxWSS points that can cause wall remodeling leading to rupture.

The hemodynamic and geometric characteristics of carotid artery atherosclerotic plaque formation.

Ischemic stroke, which has a high incidence, disability, and mortality rate, is mainly caused by carotid atherosclerotic plaque. The difference in the geometric structures of the carotid arteries inevitably leads to the variability in the local hemodynamics, which plays a key role in the formation of carotid atherosclerosis. At present, the combined mechanisms of hemodynamic and geometric in the formation of carotid atherosclerotic plaque are not clear. Thus, this study characterized the geometric and hemodynamic characteristics of carotid atherosclerotic plaque formation using four-dimensional (4D) flow magnetic resonance imaging (MRI). Ultimately, 122 carotid arteries from 61 patients were examined in this study. According to the presence of plaques at the bifurcation of the carotid artery on cervical vascular ultrasound (US), carotid arteries were placed into a plaque group (N=69) and nonplaque group (N=53). The ratio of the maximum internal carotid artery (ICA) inner diameter to the maximum common carotid artery (CCA) inner diameter (ICA-CCA diameter ratio), bifurcation angle, and tortuosity were measured using neck three-dimensional time-of-flight magnetic resonance angiography (3D TOF-MRA). Meanwhile, 4D flow MRI was used to obtain the following hemodynamic parameters of the carotid arteries: volume flow rate, velocity, wall shear stress (WSS), and pressure gradient (PG). Independent sample t-tests were used to compare carotid artery geometry and hemodynamic changes between the plaque group and nonplaque group. The ICA-CCA diameter ratio between the plaque group and the nonplaque group was not significantly different (P=0.124), while there were significant differences in the bifurcation angle (P=0.005) and tortuosity (P=0.032). The bifurcation angle of the plaque group was greater than that of the nonplaque group (60.70°±20.75° vs. 49.32°±22.90°), and the tortuosity was smaller than that of the nonplaque group (1.07±0.04 vs. 1.09±0.05). There were no significant differences between the two groups in terms of volume flow rate (P=0.351) and the maximum value of velocity (velocitymax) (P=0.388), but the axial, circumferential, and 3D WSS values were all significantly different, including their mean values (all P values <0.001) and the maximum value of 3D WSS (P<0.001), with the mean axial, circumferential, 3D WSS values, along with the maximum 3D WSS value, being lower in the plaque group. The two groups also differed significantly in terms of maximum PG value (P=0.030) and mean PG value (P=0.026), with these values being greater in the nonplaque group than in the plaque group. A large bifurcation angle and a low tortuosity of the carotid artery are geometric risk factors for plaque formation in this area. Low WSS and low PG values are associated with carotid atherosclerotic plaque formation.

Medical-Surgical Implications of Branching Variation of Human Aortic Arch Known as Bovine Aortic Arch (BAA).

(1) Background: The aortic arch (AA) branching model is challenging, considering the multiple anatomical variations documented in existing research. The bovine aortic arch (BAA) is the most prevalent anatomical variation among these. This variant of AA branching has long been considered a nonsymptomatic malformation, having been discovered incidentally during imaging investigations for other causes. However, more recent studies have demonstrated that BAA shows a frequent association with coarctation of the aorta (CoA), thoracic aortic disease (TAD), and stroke. At the same time, given the current context of increasing activity in the fields of interventional and surgical procedures in the aorta and its branches, it is very important to know the medical-surgical implications of this anatomical variant. (2) Methods: We conducted a comprehensive review using PubMed and Embase, focusing specifically on randomized trials and cohort analyses that examined the medical-surgical implications of BAA. We assessed information related to studied groups, medical procedures, and study outcomes. Initially, we identified 8454 studies, and after rigorous evaluation, we narrowed down our review to 25 articles. (3) Discussions: The intervention consisted of assessing the risks associated with BAA through different imaging investigation methods such as computer tomographic angiography (CTA), magnetic resonance imaging (MRI), or ultrasonography (US). The following results were evaluated: the prevalence of the BAA, the importance of imaging investigations in establishing the diagnosis and the therapeutic management and monitoring the evolution of patients with the BAA, the association of the BAA with CoA, TAD, and stroke, and the potential risks of interventional treatment in patients with the BAA. (4) Conclusions: The prevalence of the BAA differs both between different ethnic groups and between genders. Advanced imaging methods such as CTA and 4D flow MRI allow detailed descriptions of supra-aortic vascular anatomy and information about blood flow velocities, direction, and turbulence in the AA. US remains an easy and valuable imaging investigation, with the potential to detect and correctly diagnose the BAA and its hemodynamic implications. Anatomical variations in the AA are associated with increased rates of TAD, CoA, and stroke, necessitating early diagnosis and increased supervision of patients with such incidentally observed abnormalities. In addition, there is a need to further develop and refine the surgical techniques used and personalize them to the individual characteristics of patients with the BAA.

Real-time quantification of in vivo cerebrospinal fluid velocity using the functional magnetic resonance imaging inflow effect.

In vivo estimation of cerebrospinal fluid (CSF) velocity is crucial for understanding the glymphatic system and its potential role in neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Current cardiac or respiratory-gated approaches, such as 4D flow magnetic resonance imaging (MRI), cannot capture CSF movement in real time because of limited temporal resolution and, in addition, deteriorate in accuracy at low fluid velocities. Other techniques like real-time phase-contrast-MRI or time-spatial labeling inversion pulse are not limited by temporal averaging but have limited availability, even in research settings. This study aims to quantify the inflow effect of dynamic CSF motion on functional MRI (fMRI) for in vivo, real-time measurement of CSF flow velocity. We considered linear and nonlinear models of velocity waveforms and empirically fit them to fMRI data from a controlled flow experiment. To assess the utility of this methodology in human data, CSF flow velocities were computed from fMRI data acquired in eight healthy volunteers. Breath-holding regimens were used to amplify CSF flow oscillations. Our experimental flow study revealed that CSF velocity is nonlinearly related to inflow effect-mediated signal increase and well estimated using an extension of a previous nonlinear framework. Using this relationship, we recovered velocity from in vivo fMRI signal, demonstrating the potential of our approach for estimating CSF flow velocity in the human brain. This novel method could serve as an alternative approach to quantifying slow flow velocities in real time, such as CSF flow in the ventricular system, thereby providing valuable insights into the glymphatic system's function and its implications for neurological disorders.

Modeling cerebrospinal fluid dynamics across the entire intracranial space through integration of four-dimensional flow and intravoxel incoherent motion magnetic resonance imaging

BackgroundBidirectional reciprocal motion of cerebrospinal fluid (CSF) was quantified using four-dimensional (4D) flow magnetic resonance imaging (MRI) and intravoxel incoherent motion (IVIM) MRI. To estimate various CSF motions in the entire intracranial region, we attempted to integrate the flow parameters calculated using the two MRI sequences. To elucidate how CSF dynamics deteriorate in Hakim’s disease, an age-dependent chronic hydrocephalus, flow parameters were estimated from the two MRI sequences to assess CSF motion in the entire intracranial region.MethodsThis study included 127 healthy volunteers aged ≥ 20 years and 44 patients with Hakim’s disease. On 4D flow MRI for measuring CSF motion, velocity encoding was set at 5 cm/s. For the IVIM MRI analysis, the diffusion-weighted sequence was set at six b-values (i.e., 0, 50, 100, 250, 500, and 1000 s/mm2), and the biexponential IVIM fitting method was adapted. The relationships between the fraction of incoherent perfusion (f) on IVIM MRI and 4D flow MRI parameters including velocity amplitude (VA), absolute maximum velocity, stroke volume, net flow volume, and reverse flow rate were comprehensively evaluated in seven locations in the ventricles and subarachnoid spaces. Furthermore, we developed a new parameter for fluid oscillation, the Fluid Oscillation Index (FOI), by integrating these two measurements. In addition, we investigated the relationship between the measurements and indices specific to Hakim’s disease and the FOIs in the entire intracranial space.ResultsThe VA on 4D flow MRI was significantly associated with the mean f-values on IVIM MRI. Therefore, we estimated VA that could not be directly measured on 4D flow MRI from the mean f-values on IVIM MRI in the intracranial CSF space, using the following formula; e0.2(f−85) + 0.25. To quantify fluid oscillation using one integrated parameter with weighting, FOI was calculated as VA × 10 + f × 0.02. In addition, the FOIs at the left foramen of Luschka had the strongest correlations with the Evans index (Pearson’s correlation coefficient: 0.78). The other indices related with Hakim’s disease were significantly associated with the FOIs at the cerebral aqueduct and bilateral foramina of Luschka. FOI at the cerebral aqueduct was also elevated in healthy controls aged ≥ 60 years.ConclusionsWe estimated pulsatile CSF movements in the entire intracranial CSF space in healthy individuals and patients with Hakim’s disease using FOI integrating VA from 4D flow MRI and f-values from IVIM MRI. FOI is useful for quantifying the CSF oscillation.

Eleven Years After Scimitar Syndrome Repair With the Lugones Technique: Usefulness of Four-Dimensional Flow Magnetic Resonance Imaging.

Anatomic and physiologic assessment of surgical repair of scimitar syndrome can be challenging. We evaluated the first patient who underwent the Lugones procedure in 2012 using 4D flow magnetic resonance imaging. With this technology, we demonstrate that the reconstructed right pulmonary venous return drains into the left atrium with laminar flow, just as normal pulmonary veins do.

4D flow MRI: value and clinical perspectives in patients with pathology of the heart and great vessels. A review

The study of blood flow is becoming a new trend in cardiology and cardiovascular surgery. Based on the literature and our own data, a review is presented on the use of 4D flow in diseases of the heart and blood vessels. The main state of the question about the features of the application of the technique in various pathologies of the cardiovascular system is described in detail, the priorities, limitations and promising directions of the technique application are considered taking into account the goals of practical medicine. The review consists of two parts. The first is devoted to general issues, limitations of the technique, and issues of 4D flow mapping in patients with lesions of the great vessels. In the second part, the emphasis is on the use of 4D flow magnetic resonance imaging in the study of intraventricular blood flow and the application of the technique in congenital heart and vascular diseases.

Repaired coarctation of the aorta does not affect four-dimensional flow metrics in bicuspid aortic valve disease.

The objective of this study was primarily to compare four-dimensional flow magnetic resonance imaging metrics in the ascending aorta (AA) of patients with right-left fusion type bicuspid aortic valve (RL-BAV) and repaired coarctation of the aorta (CoA) to RL-BAV without CoA. Metrics of patients with RL-BAV were also compared to the matched group of patients with common tricuspid aortic valve (TAV). Eleven patients with RL-BAV and CoA, 11 patients with RL-BAV without CoA and 22 controls with TAV were investigated. Peak velocity (cm/s), peak flow (ml/s) and flow displacement (%) were analysed at 5 pre-defined AA levels. In addition, regional wall shear stress (WSS, mN/m2), circumferential WSS (WSSc) and axial WSS (WSSa) at all levels were quantified in 6 sectors of the aortic circle. Averaged WSS values on each level (WSSavg, WSSc, avg and WSSa, avg) were calculated as well. Peak velocity at the proximal tubular AA was significantly lower in BAV and CoA group (P = 0.047) compared to BAV without CoA. In addition, the WSSa, avg was found to be higher for the BAV and CoA group at proximal AA respectively (P = 0.040). No other significant differences were found between these groups. BAV group's peak velocity was higher at every level (P < 0.001-0.004) compared to TAV group. Flow displacement was significantly higher for the BAV group at every level (P < 0.001) besides at the most distal level. All averaged WSS values were significantly higher in BAV patients in distal AA (P < 0.001-0.018). Repaired CoA does not relevantly alter four-dimensional flow metrics in the AA of patients with RL-BAV. However, RL-BAV majorly alters flow dynamics in the AA when compared to patients with TAV. https://www.clinicaltrials.gov/study/NCT05065996, Unique Protocol ID 5063566.

Quantitative evaluation of pulmonary hypertension using 4D flow MRI: A retrospective study

BackgroundPulmonary hypertension (PH) is a severe vascular disorder that may affect 50 % of patients with heart failure. Currently, right-sided heart catheterization is required to definitively diagnose PH. However, this method is invasive and thus may not be appropriate for repeated, long-term monitoring of PH patients. This retrospective study's aim was to evaluate whether 4D flow magnetic resonance imaging (MRI) can be used to quantitively measure flow parameters to identify patients with PH. MethodsThe study cohort included 97 patients recruited from a single institution and divided into three groups based on echocardiographic estimate of pulmonary artery systolic pressure (PASP): normal group with PASP<36 mmHg, borderline PH group with PASP of 37–50 mmHg, and PH group with PASP>50 mmHg. 4D flow MRI was used to quantitively assess blood flow and velocity, regurgitation, wall shear stress (WSS) and kinetic energy in the pulmonary artery trunk, right main pulmonary artery, and left pulmonary artery. Two experienced radiologists independently analyzed the MR images, blinded to clinical details. ResultsWe found a significant difference in WSS in the pulmonary artery trunk, right main pulmonary artery and left main pulmonary artery among the three patient groups. We also found significant differences in the kinetic energy and average through velocity in the pulmonary artery trunk and right main pulmonary artery, and significant differences in the flow rate in the right main pulmonary artery. ConclusionThese data suggest that 4D flow MRI can quantitate pulmonary artery flow parameters and distinguish between patients with and without PH.

Biological sex alters the association between cerebral pulsatility and hippocampal volume in cognitively unimpaired adults

Cerebrovascular dysregulation with age contributes to cognitive decline. Age-related changes in intracranial blood flow and cerebral pulsatility are linked with adverse structural changes including white matter hyperintensities. The hippocampus represents a key area for cognition and demonstrates rapid deterioration in the early stages of Alzheimer’s disease. Yet the impact of intracranial blood flow and cerebral pulsatility on hippocampal deterioration in cognitively unimpaired adults remains unclear. Importantly, age-related changes in intracranial blood flow and cerebral pulsatility differ by sex. Therefore, this study tested the hypothesis that intracranial blood flow is positively associated with hippocampal volume, while cerebral pulsatility is negatively associated with hippocampal volume and that the associations would differ by sex. Cognitively unimpaired adults (388 total, 263 females, 64 ± 8 years of age) completed 3T magnetic resonance imaging (MRI). Hippocampal volume (mm3) was normalized to intracranial volume and evaluated from T1-weighted images. Intracranial blood flow (mL/min) and cerebral pulsatility (maximum flow − minimum flow/mean flow; a.u.) were evaluated in the internal carotid arteries (ICA), middle cerebral arteries (MCA), and basilar artery from 4D flow MRI. All data are reported for the left side of the brain. Age was negatively associated with hippocampal volume and similar relationships were observed in males (β = -16 ± 3, P &lt; 0.01) and females (β = -17 ± 2, P &lt; 0.01). As such, age was included as a covariate in all models. Blood flow in the ICA, MCA, and basilar artery was not associated with hippocampal volume (all P &gt; 0.37) and there were no flow-by-sex interactions (all P &gt; 0.19). In contrast, cerebral pulsatility was negatively associated with hippocampal volume in a sex and vessel specific manner. ICA pulsatility was associated with hippocampal volume (P = 0.03, β = -183 ± 83) and the relationship did not differ by sex (pulsatility-by-sex interaction: P = 0.19). Basilar artery pulsatility was associated with hippocampal volume in a sex-specific manner (pulsatility-by-sex interaction: P &lt; 0.01) such that there was an association in females (β = -346 ± 63, P &lt; 0.01) but not males (β = 60 ± 92, P = 0.51). A sex-specific relationship (pulsatility-by-sex interaction: P &lt; 0.01) was also observed between MCA pulsatility and hippocampal volume (females: β = -180 ± 54, P &lt; 0.01; males: β = 1 ± 136, P = 0.99). Therefore, elevated cerebral pulsatility is linked with hippocampal deterioration in a sex and vessel specific manner. These findings may provide insights into sex differences in cognitive decline with age and the development of Alzheimer’s disease. This research was funded by NIH grants (R03 AG070469-01 and R03 AG070469-S1; JNB), a Virginia Horne Henry Research Grant (JNB), and a Wisconsin Alzheimer's Disease Research Center Grant (P30-AG062715). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comparing two MRI methods to assess fundamental sex differences in resting cerebral blood flow

Background: Cerebral blood flow (CBF) is a critical measurement for understanding healthy brain physiology prior to aging or neurologic diseases. Patterns of stroke and neurologic pathologies are often sex-specific. Therefore, it is important to understand basic sex differences in CBF, which are often associated with poor brain outcomes. Furthermore, prior literature examining sex differences in CBF is confounded by age, comorbidities, medications, lack of control of menstrual cycle and/or hormonal contraceptive use, and methodological discrepancies. The objective of this study was to compare two different magnetic resonance imaging (MRI) methods of quantifying CBF in young adults while controlling for the aforementioned confounding factors. We hypothesized that females would display higher CBF than males, and that there would be a high reliability between Arterial Spin Labeling (ASL) and 4D Flow MRI. Methods: 30 males and 26 females (23 ± 4yr) were studied on a single MRI (3T) visit. Subjects were fasted 8 hours and withheld caffeine, exercise, and NSAIDs for at least 24 hours. Females were not taking hormonal contraception and were studied on days 1-7 of the menstrual cycle. Microvascular CBF (mL/100g/min) was assessed via pseudo-continuous ASL (pcASL) while 4D Flow MRI acquired with Phase Contrast Vastly undersampled Isotropic Projection Reconstruction (PC VIPR) yielded macrovascular flow via the larger cerebral arteries, summing the internal carotid arteries and basilar artery for total CBF (mL/min). A T1-weighted MRI scan was used to provide brain volumes, allowing CBF from PC VIPR to be normalized and compared to ASL (mL/100g/min). The scans were taken consecutively, with subjects breathing normoxic gas while hemodynamics and end tidal CO2 were monitored. Regression analysis was used to determine reliability of two measures to test a sex difference in CBF. Results: Linear regression analysis demonstrated reliability between measurements of resting CBF via ASL and PC VIPR (p&lt;0.001, R2=0.621). However, ASL measured significantly higher blood flows than PC VIPR in females (63.40 ± 8.55 vs. 56.47 ± 8.48 mL/100g/min, p&lt;0.001) while male subjects had similar flows measured by both methods (45.75 ± 9.39 vs. 46.69 ± 8.19 mL/100g/min, p=0.464). Females displayed an increase in resting CBF compared to males, being 27.8% and 17.3% higher in the ASL and PC VIPR flow measurements (both p&lt;0.001), respectively. Conclusions: These results demonstrate that ASL and PC VIPR CBF display a strong correlation, and that females have greater resting CBF compared to males that is detected by both MRI methods of quantification. However, ASL resulted in greater flow measurements in females, resulting in larger differences being observed (27.8% versus 17.3%). This discrepancy in CBF quantification warrants further investigation to determine the optimal mode of CBF measurement and comparison. Funding by NIH (HL150361). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.