Magnetic Resonance Phase Contrast Velocity Research Articles

Correlation mapping for visualizing propagation of pulsatile CSF motion in intracranial space based on magnetic resonance phase contrast velocity images: preliminary results.

Correlation time mapping based on magnetic resonance (MR) velocimetry has been applied to pulsatile cerebrospinal fluid (CSF) motion to visualize the pressure transmission between CSF at different locations and/or between CSF and arterial blood flow. Healthy volunteer experiments demonstrated that the technique exhibited transmitting pulsatile CSF motion from CSF space in the vicinity of blood vessels with short delay and relatively high correlation coefficients. Patient and healthy volunteer experiments indicated that the properties of CSF motion were different from the healthy volunteers. Resultant images in healthy volunteers implied that there were slight individual difference in the CSF driving source locations. Clinical interpretation for these preliminary results is required to apply the present technique for classifying status of hydrocephalus.

Accuracy of four-dimensional phase-contrast velocity mapping for blood flow visualizations: a phantom study

Time-resolved three-dimensional, three-directional phase-contrast magnetic resonance velocity mapping (4D PC-MRI) is a powerful technique to depict dynamic blood flow patterns in the human body. However, the impact of phase background effects on flow visualizations has not been thoroughly studied previously, and it has not yet been experimentally demonstrated to what degree phase offsets affect flow visualizations and create errors such as inaccurate particle traces. To quantify background phase offsets and their subsequent impact on particle trace visualizations in a 4D PC-MRI sequence. Additionally, we sought to investigate to what degree visualization errors are reduced by background phase correction. A rotating phantom with a known velocity field was used to quantify background phase of 4D PC-MRI sequences accelerated with SENSE as well as different k-t BLAST speed-up factors. The deviation in end positions between particle traces in the measured velocity fields were compared before and after the application of two different phase correction methods. Phantom measurements revealed background velocity offsets up to 7 cm/s (7% of velocity encoding sensitivity) in the central slice, increasing with distance from the center. Background offsets remained constant with increasing k-t BLAST speed-up factors. End deviations of up to 5.3 mm (1.8 voxels) in the direction perpendicular to the rotating disc were found between particle traces and the seeding plane of the traces. Phase correction by subtraction of the data from the stationary phantom reduced the average deviation by up to 56%, while correcting the data-set with a first-order polynomial fit to stationary regions decreased average deviation up to 78%. Pathline visualizations can be significantly affected by background phase errors, highlighting the importance of dedicated and robust phase correction methods. Our results show that pathline deviation can be substantial if adequate phase background errors are not minimized.

Integrated morphologic and functional assessment of the aortic root after different tissue valve root replacement procedures

This study was undertaken to explore aspects of the hemodynamic function of different biologic tissue aortic valve root replacements. We set out to image and display the spatiotemporal distributions of axially directed blood velocity through the aortic root. The flow velocities through a plane transecting the aortic root were measured by 2-dimensional cine phase-contrast magnetic resonance velocity mapping in 44 subjects: 29 patients who had undergone aortic root replacement approximately 10 years previously (13 autografts, 10 stentless xenografts, and 6 homografts) and 15 healthy control subjects. With cine as well as velocity images, aortic sinus dimensions, effective orifice area, and several velocity parameters were measured. Color-coded plots of velocity relative to the sinus cross sections and velocity-time plots were used to compare spatiotemporal distributions of velocity. Peak flow velocity was similar between the autografts (102 ± 28.0 cm/s) and control valves (119 ± 20.0 cm/s) but was higher in xenografts (167 ± 36.0 cm/s) and homografts (206 ± 91.0 cm/s). These measurements showed an inverse relationship with the effective orifice area (7.27 ± 0.20, 4.24 ± 0.81, 3.37 ± 0.32, and 3.28 ± 0.87 cm(2), respectively). Autograft peak flow velocity showed no significant difference from control valve peak flow velocity, despite larger root dimensions (P < .001). The graphic displays provided further spatiotemporal information. Peak velocities and spatiotemporal flow patterns depend on the type of valve substitute. In the parameters measured, autograft replacements differed least from normal aortic valves.

FourFlow - open source code software for quantification and visualization of time-resolved three-directional phase contrast magnetic resonance velocity mapping

Summary We have developed an open source software for quantification and visualization of 4D PC-MR data that enables development of new quantitative analysis tools. Background Time-resolved three-directional phase contrast magnetic resonance velocity mapping (4D PC-MR) has the potential to be a powerful modality for studying normal physiology and pathophysiology. However, a wider application of 4D PC-MR is hampered by a lack of methods for quantitative analysis. Currently available software packages for visualization of 4D PC-MR do not allow for modifications or additions by users. This limits innovation of new quantification tools, and limits the possibilities to answer specific clinical and physiological questions. Therefore, the aim of this study was to develop ac omprehensive open source software for quantification and analysis of 4D PC-MR data that includes the possibility to develop and add new quantitative analysis methods. Methods

Diastolic vortex ring formation in the human left ventricle: quantitative analysis using Lagrangian coherent structures and 4D cardiovascular magnetic resonance velocity mapping

Summary We show that 4D magnetic resonance velocity mapping and Lagrangian Coherent Structures can be used to quantify vortex ring volume in the human left ventricle. Background The vortex ring formed in the left ventricle (LV) of the human heart during early diastolic inflow (corresponding to the Doppler E-wave) contains information about the normal and pathophysiologic aspects of diastole. Previous studies suggest that the volume of the vortex ring is an important characteristic of vortex ring formation. However, due to lack of quantitative methods, vortex ring volume has not previously been studied in the human left ventricle. The study of Lagrangian Coherent Structures (LCS) is a new flow analysis method, which for the first time enables a description of vortex ring shape and the quantification of vortex ring volume. LCS have not previously been used to quantify diastolic vortex volume in humans. Therefore, the purpose of this study was to investigate if LCS and three-dimensional, time-resolved, three-directional phase contrast magnetic resonance velocity mapping (4D PC-MR) can be used to describe vortex ring shape and quantify vortex ring volume in the human LV. Methods

Tridirectional phase-contrast magnetic resonance velocity mapping depicts severe hemodynamic alterations in a patient with aortic dissection type Stanford B

This report describes flow patterns derived by three-dimensional (3D) three-directional velocity-encoded cine (VEC) magnetic resonance imaging (MRI), in a patient with chronic Stanford type B aortic dissection. Acquired 3D VEC MRI data illustrated an acceleration of blood flow through the primary entry toward the vessel wall of the false lumen, leading to disturbed intraluminal flow. Furthermore, accelerated blood flow was observed in the partially compressed true lumen. 3D VEC MRI data may be helpful to guide physicians for a more comprehensive preoperative and postoperative assessment of complex aortic pathologies.

Using magnetic resonance phase-contrast velocity mapping for diagnosing pelvic congestion syndrome

To evaluate phase-contrast velocity mapping (PCVM) as a diagnostic tool for pelvic congestion syndrome and comparing this approach with direct venography. We prospectively include nine women with clinical suspicion of pelvic congestion syndrome during a six-month period. All patients underwent a magnetic resonance phase-contrast scan before a direct venography. We considered a case of pelvic congestion syndrome when the PCVM showed a retrograde or slow (less than 5 cm/second) flow in any gonadal vein. This criterion was compared with the standard diagnostic criterion observed from a direct venography. Using direct venography we found 14 abnormal veins and all of them were correctly identified by the PCVM. The other four veins were found to be normal by the direct venography. However, two of them (the same patient) were abnormal in the PCVM, even though this patient had the classical symptoms of pelvic congestion syndrome. PCVM is a useful tool for diagnosing pelvic contrast syndrome and can avoid invasive procedures such as direct venography.

Longitudinally and circumferentially directed movements of the left ventricle studied by cardiovascular magnetic resonance phase contrast velocity mapping.

ObjectiveUsing high resolution cardiovascular magnetic resonance (CMR), we aimed to detect new details of left ventricular (LV) systolic and diastolic function, to explain the twisting and longitudinal movements of the left ventricle.MethodsUsing CMR phase contrast velocity mapping (also called Tissue Phase Mapping) regional wall motion patterns and longitudinally and circumferentially directed movements of the left ventricle were studied using a high temporal resolution technique in healthy male subjects (n = 14, age 23 ± 3 years).ResultsPreviously undescribed systolic and diastolic motion patterns were obtained for left ventricular segments (based on the AHA segmental) and for basal, mid and apical segments. The summation of segmental motion results in a complex pattern of ventricular twisting and longitudinal motion in the normal human heart which underlies systolic and diastolic function. As viewed from the apex, the entire LV initially rotates in a counter-clockwise direction at the beginning of ventricular systole, followed by opposing clockwise rotation of the base and counter-clockwise rotation at the apex, resulting in ventricular torsion. Simultaneously, as the entire LV moves in an apical direction during systole, the base and apex move towards each other, with little net apical displacement. The reverse of these motion patterns occur in diastole.ConclusionLeft ventricular function may be a consequence of the relative orientations and moments of torque of the sub-epicardial relative to the sub-endocardial myocyte layers, with influence from tethering of the heart to adjacent structures and the directional forces associated with blood flow. Understanding the complex mechanics of the left ventricle is vital to enable these techniques to be used for the evaluation of cardiac pathology.

Choice of In Vivo Versus Idealized Velocity Boundary Conditions Influences Physiologically Relevant Flow Patterns in a Subject-Specific Simulation of Flow in the Human Carotid Bifurcation

Accurate fluid mechanics models are important tools for predicting the flow field in the carotid artery bifurcation and for understanding the relationship between hemodynamics and the initiation and progression of atherosclerosis. Clinical imaging modalities can be used to obtain geometry and blood flow data for developing subject-specific human carotid artery bifurcation models. We developed subject-specific computational fluid dynamics models of the human carotid bifurcation from magnetic resonance (MR) geometry data and phase contrast MR velocity data measured in vivo. Two simulations were conducted with identical geometry, flow rates, and fluid parameters: (1) Simulation 1 used in vivo measured velocity distributions as time-varying boundary conditions and (2) Simulation 2 used idealized fully-developed velocity profiles as boundary conditions. The position and extent of negative axial velocity regions (NAVRs) vary between the two simulations at any given point in time, and these regions vary temporally within each simulation. The combination of inlet velocity boundary conditions, geometry, and flow waveforms influences NAVRs. In particular, the combination of flow division and the location of the velocity peak with respect to individual carotid geometry landmarks (bifurcation apex position and the departure angle of the internal carotid) influences the size and location of these reversed flow zones. Average axial wall shear stress (WSS) distributions are qualitatively similar for the two simulations; however, instantaneous WSS values vary with the choice of velocity boundary conditions. By developing subject-specific simulations from in vivo measured geometry and flow data and varying the velocity boundary conditions in otherwise identical models, we isolated the effects of measured versus idealized velocity distributions on blood flow patterns. Choice of velocity distributions at boundary conditions is shown to influence pathophysiologically relevant flow patterns in the human carotid bifurcation. Although mean WSS distributions are qualitatively similar for measured and idealized inlet boundary conditions, instantaneous NAVRs differ and warrant imposing in vivo velocity boundary conditions in computational simulations. A simulation based on in vivo measured velocity distributions is preferred for modeling hemodynamics in subject-specific carotid artery bifurcation models when studying atherosclerosis initiation and development.

Cross‐correlation delay to quantify myocardial dyssynchrony from phase contrast magnetic resonance (PCMR) velocity data

To apply cross-correlation delay (XCD) analysis to myocardial phase contrast magnetic resonance (PCMR) tissue velocity data and to compare XCD to three established "time-to-peak" dyssynchrony parameters. Myocardial tissue velocity was acquired using PCMR in 10 healthy volunteers (negative controls) and 10 heart failure patients who met criteria for cardiac resynchronization therapy (positive controls). All dyssynchrony parameters were computed from PCMR velocity curves. Sensitivity, specificity, and receiver operator curve (ROC) analysis for separating positive and negative controls were computed for each dyssynchrony parameter. XCD had higher sensitivity (90%) and specificity (100%) for discriminating between normal and patient groups than any of the time-to-peak dyssynchrony parameters. ROC analysis showed that XCD was the best parameter for separating the positive and negative control groups. XCD is superior to time-to-peak dyssynchrony parameters for discriminating between subjects with and without dyssynchrony and may aid in the selection of patients for cardiac resynchronization therapy.

Determination of transmural, endocardial, and epicardial radial strain and strain rate from phase contrast MR velocity data

To develop a method for computing radial strain (epsilon) and strain rate (SR) from phase contrast magnetic resonance (PCMR) myocardial tissue velocity data. PCMR tissue velocity maps were acquired at basal and mid-short-axis slices in the myocardium in 10 healthy volunteers. An algorithm for computing radial strain and SR from PCMR tissue velocity data was developed. PCMR strain values were compared to values computed independently from contours drawn on cine steady-state free procession (SSFP) images. Peak endocardial and epicardial strain and SR values from PCMR data were compared. Excellent agreement was observed between peak strain values computed by PCMR and cine SSFP contours (38.1 +/- 5.4% vs. 38.1 +/- 6.2%; P = not significant [NS]). The presence of an endocardial-epicardial gradient was demonstrated in both strain and SR: peak endocardial values were larger than peak epicardial values in the basal and mid-short-axis slices (P < 0.05). This study presents a method for determining radial strain and SR values from PCMR velocity data. This technique illustrates a difference in strain and SR across the myocardium with peak endocardial values being greater than peak epicardial values.

Coronary artery flow measurement using navigator echo gated phase contrast magnetic resonance velocity mapping at 3.0 T

A validation study and early results for non-invasive, in vivo measurement of coronary artery blood flow using phase contrast magnetic resonance imaging (PC-MRI) at 3.0 T is presented. Accuracy of coronary artery blood flow measurements by phase contrast MRI is limited by heart and respiratory motion as well as the small size of the coronary arteries. In this study, a navigator echo gated, cine phase velocity mapping technique is described to obtain time-resolved velocity and flow waveforms of small diameter vessels at 3.0 T. Phantom experiments using steady, laminar flow are presented to validate the technique and show flow rates measured by 3.0 T phase contrast MRI to be accurate within 15% of true flow rates. Subsequently, in vivo scans on healthy volunteers yield velocity measurements for blood flow in the right, left anterior descending, and left circumflex arteries. Measurements of average, cross-sectional velocity were obtainable in 224/243 (92%) of the cardiac phases. Time-averaged, cross-sectional velocity of the blood flow was 6.8±4.3 cm/s in the LAD, 8.0±3.8 cm/s in the LCX, and 6.0±1.6 cm/s in the RCA.

Comparison of flow patterns in ascending aortic aneurysms and volunteers using four‐dimensional magnetic resonance velocity mapping

To determine the difference in flow patterns between healthy volunteers and ascending aortic aneurysm patients using time-resolved three-dimensional (3D) phase contrast magnetic resonance velocity (4D-flow) profiling. 4D-flow was performed on 19 healthy volunteers and 13 patients with ascending aortic aneurysms. Vector fields placed on 2D planes were visually graded to analyze helical and retrograde flow patterns along the aortic arch. Quantitative analysis of the pulsatile flow was carried out on manually segmented planes. In volunteers, flow progressed as follows: an initial jet of blood skewed toward the anterior right wall of the ascending aorta is reflected posterolaterally toward the inner curvature creating opposing helices, a right-handed helix along the left wall and a left-handed helix along the right wall; retrograde flow occurred in all volunteers along the inner curvature between the location of the two helices. In the aneurysm patients, the helices were larger; retrograde flow occurred earlier and lasted longer. The average velocity decreased between the ascending aorta and the transverse aorta in volunteers (47.9 mm/second decrease, P = 0.023), while in aneurysm patients the velocity increased (145 mm/second increase, P < 0.001). Dilation of the ascending aorta skews normal flow in the ascending aorta, changing retrograde and helical flow patterns.

Determination of Peak Velocity in Stenotic Areas: Echocardiography versus k-t SENSE Accelerated MR Fourier Velocity Encoding

The study was approved by the local ethical committees, and informed consent from each participant was obtained. The purpose of the study was to compare accelerated magnetic resonance (MR) Fourier velocity encoding (FVE), MR phase-contrast velocity mapping, and echocardiography with respect to peak velocity determination in vascular or valvular stenoses. FVE data collection was accelerated by using the k-space and time sensitivity encoding, or k-t SENSE, technique. Peak velocities were evaluated in five healthy volunteers (one woman, four men; mean age, 28 years; range, 23-34 years), three patients with stenotic aortic valves (two women, one man; mean age, 67 years; range, 39-82 years), two patients with pulmonary valvular stenosis (a 14-year-old girl and a 36-year-old man), and two patients with aortic stenosis (two women aged 18 and 27 years). In volunteers, peak velocity determined by the different methods agreed well. In patients, similar peak velocities were obtained by using accelerated MR FVE and echocardiography, while phase-contrast MR imaging results tended to underestimate these values.

Transit of Blood Flow Through the Human Left Ventricle Mapped by Cardiovascular Magnetic Resonance

The transit of blood through the beating heart is a basic aspect of cardiovascular physiology which remains incompletely studied. Quantification of the components of multidirectional flow in the normal left ventricle (LV) is lacking, making it difficult to put the changes observed with LV dysfunction and cardiac surgery into context. Three dimensional, three directional, time resolved magnetic resonance phase-contrast velocity mapping was performed at 1.5 Tesla in 17 normal subjects, 6 female, aged 44+/-14 years (mean+/-SD). We visualized and measured the relative volumes of LV flow components and the diastolic changes in inflowing kinetic energy (KE). Of total diastolic inflow volume, 44+/-11% followed a direct, albeit curved route to systolic ejection (videos 1 and 2), in contrast to 11% in a subject with mildly dilated cardiomyopathy (DCM), who was included for preliminary comparison (video 3). In normals, 16+/-8% of the KE of inflow was conserved to the end of diastole, compared with 5% in the DCM patient. Blood following the direct route lost or transferred less of its KE during diastole than blood that was retained until the next beat (1.6+/-1.0 millijoules vs 8.2+/-1.9 millijoules, p<0.05); whereas, in the DCM patient, the reduction in KE of retained inflow was 18-fold greater than that of the blood tracing the direct route. Multidimensional flow mapping can measure the paths, compartmentalization and kinetic energy changes of blood flowing into the LV, demonstrating differences of KE loss between compartments, and potentially between the flows in normal and dilated left ventricles.

Pulmonary and caval blood flow patterns in patients with intracardiac and extracardiac Fontan: a magnetic resonance study

We compared in vivo blood flow and pulsatility after different types of Fontan operation using magnetic resonance imaging. A total of 37 consecutive patients (mean age 19+/-7.9 years, 7.3+/-3.2 years after Fontan operation), 7 with atriopulmonary anastomosis (APC), 18 with intra-atrial lateral tunnel (LTFO) and 12 with extracardiac Fontan (ECFO) were studied using magnetic resonance phase-contrast velocity mapping. Blood flow (volume flow) in the superior vena cava (SVC), inferior vena cava (IVC) and both pulmonary arteries were measured and a pulsatility index was calculated for each vessel. For all modifications, the blood flow distribution between the SVC and IVC was normal (1:2). Patients with APC had a normal pulsatility, a dilated right atrium, partial backward flow in the IVC and physiological blood flow distribution between the pulmonary arteries. LTFO and ECFO patients had no retrograde flow in the IVC, equal blood flow distribution between the pulmonary arteries and very low or absent pulsatility. MRI allows hemodynamic quantification and characterization of various types of Fontan modifications and may be a valuable tool to predict Fontan failure. Despite showing normal pulsatility, patients with APC have right atrial dilatation and partial backward flow in the IVC, demonstrating suboptimal Fontan circulation. LTFO and ECFO both produce unidirectional antegrade flow in the IVC but pulsatility is very low or absent, which may promote poor pulmonary artery growth and increase of pulmonary vascular resistance contributing to late Fontan failure.

Haemodynamic Properties of PTFE Femoropopliteal Bypass Grafts as Determined by a New Magnetic Resonance Technique

Objectives. To apply the automatic three dimensional paraboloid (3DP) method for measurement of wall shear stress (WSS), blood flow, blood velocity, and cross sectional graft lumen area to magnetic resonance phase contrast velocity mapping data acquired from polytetrafluoroethylene (PTFE) suprageniculate 6 mm femoropopliteal bypass grafts to determine the biomechanical and haemodynamic properties immediately and three years after implantation. Materials and methods. Two patient cohorts, each of ten patients, with intermittent claudication were investigated by the 3DP method, one group (A) within 36 h after implantation of a femoropopliteal graft and the other group (B) 35 months after implantation. Results. The mean blood flow was 5.9 ml/s (SD: 1.6), and WSS at peak systole was 2.2 N/m 2 (SD: 0.6) 5 cm upstream to the distal anastomosis for group A, and 3.7 ml/s (SD: 1.9) and 1.9 N/m 2 (SD: 0.4) for Group B. The WSS varied according to the angular position of the graft circumference. The implanted grafts were not circular but had a slightly elliptical circumference with a greater anterior/posterior diameter. Conclusion. The 3DP method is a precise tool with subpixel resolution for determining the biomechanical and haemodynamic properties of implanted PTFE grafts, and it can be used to assess graft function immediately after implantation. It is potentially applicable for routine graft surveillance.

Does the application of gadolinium-DTPA have an impact on magnetic resonance phase contrast velocity measurements? Results from an in vitro study

Introduction/objective: To evaluate the potential influence of various concentrations of gadolinium (Gd)-DTPA on magnetic resonance phase contrast (MR PC) velocimetry. Material and methods: Imaging was done with a 1.0 T scanner using a standard Flash 2D sequence and a circular polarized extremity coil. In a validated flow phantom with a defined 75% area stenosis different concentrations of Gd-DTPA, diluted in a 10:1 water–yogurt mixture, MR PC measurements were correlated with a Doppler guide wire as gold standard. Results: MR PC measurements correlated well with the Doppler derived data ( r=0.99; P<0.01; maximum pre-stenotic velocity: 21.6±0.5 cm/s; maximum intra-stenotic velocity: 81.7±0.6 cm/s). Following Gd-DTPA administration no significant ( P>0.05; Student's t-test) flow measurement changes were noted (maximum pre-stenotic velocity: 21.3±1.3 cm/s; maximum intra-stenotic velocity: 84.0±3.6 cm/s). However, delineation of the perfused lumen was enhanced after the application of Gd-DTPA. Discussions and conclusion: The application of Gd-DTPA does not affect MR PC velocimetry. However, the application of contrast media allowed a more accurate vessel segmentation. MR PC measurements can be reliably carried out after application of Gd-DTPA.

MR validation of soft tissue mimicing phantom deformation as modeled by nonlinear finite element analysis.

A study of the applicability of nonlinear finite element analysis (FEA) to predict soft tissue deformation was validated with phase contrast magnetic resonance velocity imaging. A phantom of varying stiffness was placed in a special purpose, computer controlled MR compatible compression apparatus which provided precise, time varying compression with surface deformations on the order of 11%. The resulting motion was measured with MR velocity images acquired throughout the cycle of compression. The phantom geometry was modeled with a finite element mesh and the mechanical properties of the phantom material were measured and incorporated in the FEA model. The motion as calculated by the FEA model was compared to the motion measured with MRI and the results were found to vary with the material's Poisson's ratio and the coefficient of friction. A minimum difference was reached when the Poisson's ratio and coefficient of friction were set to 0.485 and 0.3, respectively. Under these conditions, the root mean square difference was found to be 14.4%.

Portal venous blood flow while breath-holding after inspiration or expiration and during normal respiration in controls and cirrhotics.

In this study, we used magnetic resonance (MR) imaging to measure portal blood flow in 12 healthy controls and 17 cirrhotics while they were breath-holding after inspiration and after expiration. We then compared the results with measurements made during normal respiration in the healthy controls and cirrhotics. Blood flow in the main portal vein under basal fasting conditions was quantitated using the cine phase-contrast MR velocity mapping method. Three measurements were made on one occasion, as follows: (1) throughout the cardiac cycle during normal respiration, (2) with the subject breath-holding after maximal inspiration, and (3) with the subject breath-holding after maximal expiration. During normal respiration, portal blood flow was 1.3 +/- 0.21/min in controls vs 1.0 +/- 0.11/min in cirrhotics (P < 0.0001); while subjects were breath-holding after inspiration, portal blood flow was 1.0 +/- 0.21/min in controls vs 0.9 +/- 0.11/min in cirrhotics; and while subjects were breath-holding after expiration, portal blood flow was 1.5 +/- 0.21/min in controls vs 1.1 +/- 0.21/min in cirrhotics (P < 0.0001). The differences were primarily due to changes in flow velocity. When the magnitude of these hemodynamic changes in the three respiratory conditions was compared in controls and cirrhotics, analysis of variance (ANOVA) showed a significant difference (P < 0.0001). In controls, portal blood flow decreased during maximal inspiration relative to flow during normal respiration (-24.6 +/- 8.3%). Changes in portal blood flow in controls were greater than in cirrhotics (-13.5 +/- 4.5%) (P < 0.0001); however, the difference in blood flow increase associated with maximal expiration between the two groups (+11.8 +/- 9.4% vs +5.9 +/- 11.5%) was not significant. We found that the respiration-induced hemodynamic variation in portal blood flow was less in cirrhotics than in the healthy controls. Portal blood flow measurements made during normal respiration using MR imaging closely reflect nearly physiologic conditions.