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Journal ArticleDOI

Hepatic vascular flow measurements by phase contrast MRI and doppler echography: A comparative and reproducibility study

01 Mar 2010-Journal of Magnetic Resonance Imaging (Wiley Subscription Services, Inc., A Wiley Company)-Vol. 31, Iss: 3, pp 579-588
TL;DR: To directly compare and study the variability of parameters related to hepatic blood flow measurements using 3 T phase‐contrast magnetic resonance imaging (PC‐MRI) and Doppler ultrasound (US).
Abstract: Purpose: To directly compare and study the variability of parameters related to hepatic blood flow measurements using 3 T phase-contrast magnetic resonance imaging (PC-MRI) and Doppler ultrasound (US). Materials and Methods: Nine healthy subjects were studied. Blood velocities and flow rate measurements were performed in the portal vein and the proper hepatic artery. MR studies were performed using a 3 T imager. Gradient-echo fast phase contrast sequences were used with both cardiac and respiratory gating. MR and Doppler flow parameters were extracted and compared. Two methods of calculation were used for Doppler flow rate analysis. Results: Compared to Doppler US, PC-MRI largely underestimated hepatic flow data with lower variability and higher reproducibility. This reproducibility was more pronounced in the portal vein than in the proper hepatic artery associated with poorer velocity correlations. Total hepatic flow values were 1239 ± 223 mL/min and 1595 ± 521 mL/min for PC-MRI and Doppler US, respectively. Conclusion: Free-breathing PC-MRI can provide reliable noninvasive measurement of hepatic flow parameters compared to Doppler US. The MR technique could help to improve Doppler flow calculations, thereby allowing standardization of protocols, particularly for applications in disease. J. Magn. Reson. Imaging 2010;31:579–588. © 2010 Wiley-Liss, Inc.
Citations
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Journal ArticleDOI
TL;DR: The purpose of this review is to describe the methods used for 4D flow MRI acquisition, post-processing and data analysis and provide an overview of the clinical applications of 4D Flow MRI, which includes a review of applications in the heart, thoracic aorta and hepatic system.
Abstract: Magnetic resonance imaging (MRI) has become an important tool for the clinical evaluation of patients with cardiovascular disease. Since its introduction in the late 1980s, 2-dimensional phase contrast MRI (2D PC-MRI) has become a routine part of standard-of-care cardiac MRI for the assessment of regional blood flow in the heart and great vessels. More recently, time-resolved PC-MRI with velocity encoding along all three flow directions and three-dimensional (3D) anatomic coverage (also termed ‘4D flow MRI’) has been developed and applied for the evaluation of cardiovascular hemodynamics in multiple regions of the human body. 4D flow MRI allows for the comprehensive evaluation of complex blood flow patterns by 3D blood flow visualization and flexible retrospective quantification of flow parameters. Recent technical developments, including the utilization of advanced parallel imaging techniques such as k-t GRAPPA, have resulted in reasonable overall scan times, e.g., 8-12 minutes for 4D flow MRI of the aorta and 10-20 minutes for whole heart coverage. As a result, the application of 4D flow MRI in a clinical setting has become more feasible, as documented by an increased number of recent reports on the utility of the technique for the assessment of cardiac and vascular hemodynamics in patient studies. A number of studies have demonstrated the potential of 4D flow MRI to provide an improved assessment of hemodynamics which might aid in the diagnosis and therapeutic management of cardiovascular diseases. The purpose of this review is to describe the methods used for 4D flow MRI acquisition, post-processing and data analysis. In addition, the article provides an overview of the clinical applications of 4D flow MRI and includes a review of applications in the heart, thoracic aorta and hepatic system.

294 citations


Cites background from "Hepatic vascular flow measurements ..."

  • ...All techniques, however, have specific limitations such as ionizing radiation and possible side effects of contrast application (112), limited anatomical coverage (113), poor observer variability (114) or invasiveness (115)....

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Journal ArticleDOI
TL;DR: The collected data presented in this paper provide a potentially useful singular resource for key parameters needed for PBPK modelling in pregnancy, which facilitates the risk assessment of environmental chemicals and therapeutic drug dose adjustments in the pregnant population.
Abstract: Background: Pregnancy is associated with considerable changes in the physiological, anatomical and biochemical attributes in women. These may alter the exposure to xenobiotics between pregnant and non-pregnant women who receive similar doses, with implications for different susceptibility to environmental pollutants or therapeutic agents. Physiologically based pharmacokinetic (PBPK) models together with in vitro in vivo extrapolation (IVIVE) of absorption, distribution, metabolism and excretion (ADME) characteristics may capture the likely changes. However, such models require comprehensive information on the longitudinal variations of PBPK parameter values; a set of data that are as yet not available from a singular source. Aim: The aim of this article was to collect, integrate and analyse the available time-variant parameters that are needed for the PBPK modelling of xenobiotic kinetics in a healthy pregnant population. Methods: A structured literature search was carried out on anatomical, physiological and biochemical parameters likely to change in pregnancy and alter the kinetics of xenobiotics. Collated data were carefully assessed, integrated and analysed for trends with gestational age. Algorithms were generated to describe the changes in parameter values with gestational age. These included changes in maternal weight, the individual organ volumes and blood flows, glomerular filtration rates, and some drug-metabolising enzyme activities. Results: Articles were identified using relevant keywords, quality appraised and data were extracted by two investigators. Some parameters showed no change with gestational age and for others robust data were not available. However, for many parameters significant changes were reported during the course of pregnancy, e.g. cardiac output, protein binding and expression/activity of metabolizing enzymes. The trend for time-variant parameters was not consistent (with respect to direction and mono-tonicity). Hence, various mathematical algorithms were needed to describe individual parameter values. Conclusion: Despite the limitations identified in the availability of some values, the collected data presented in this paper provide a potentially useful singular resource for key parameters needed for PBPK modelling in pregnancy. This facilitates the risk assessment of environmental chemicals and therapeutic drug dose adjustments in the pregnant population.

289 citations


Cites background from "Hepatic vascular flow measurements ..."

  • ...Based on the available information, and the knowledge thatDoppler flow studies are subject to high variationbetween and within individuals,([247,248]) it is difficult, at this stage, to describe the magnitude and significant of changes in maternal hepatic blood flow....

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Journal ArticleDOI
TL;DR: This article focuses on probe drugs lacking significant metabolism to highlight mechanisms of interactions of selected intestinal, hepatic and renal drug transporters and Genotype-dependent drug-drug interactions are discussed.
Abstract: Drug–drug interactions are a serious clinical issue. An important mechanism underlying drug–drug interactions is induction or inhibition of drug transporters that mediate the cellular uptake and efflux of xenobiotics. Especially drug transporters of the small intestine, liver and kidney are major determinants of the pharmacokinetic profile of drugs. Transporter-mediated drug–drug interactions in these three organs can considerably influence the pharmacokinetics and clinical effects of drugs. In this article, we focus on probe drugs lacking significant metabolism to highlight mechanisms of interactions of selected intestinal, hepatic and renal drug transporters (e.g., organic anion transporting polypeptide [OATP] 1A2, OATP2B1, OATP1B1, OATP1B3, P-gp, organic anion transporter [OAT] 1, OAT3, breast cancer resistance protein [BCRP], organic cation transporter [OCT] 2 and multidrug and toxin extrusion protein [MATE] 1). Genotype-dependent drug–drug interactions are also discussed.

152 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the use of non-contrast quantitative magnetic resonance imaging (MRI) as a surrogate measure of portal pressure, and the correlation of all non-invasive parameters with HVPG was evaluated.

84 citations


Cites background from "Hepatic vascular flow measurements ..."

  • ...Yzet and colleagues reported that PC-MR was a more reliable measure of hepatic blood flow compared to Doppler ultrasound with lower variability and higher reproducibility [18]....

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  • ...Recent advances in magnetic resonance imaging (MRI) have made it possible to measure multiple parameters associated with structural [17], blood flow [18] and perfusion [19] changes in the liver in a single scan session....

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Journal ArticleDOI
TL;DR: Flow-sensitive 4D MR imaging may constitute a promising, alternative technique to Doppler US for evaluating hemodynamics in the portal venous system of patients with liver cirrhosis and may be a means of assessing pathologic changes in flow characteristics.
Abstract: Flow-sensitive four-dimensional MR may be an alternative to Doppler US as a noninvasive and standardized technique, supplying information about portal venous hemodynamics and pathologic changes in flow characteristics in patients with liver cirrhosis.

74 citations

References
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Journal ArticleDOI
TL;DR: The Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less; there are, however, considerable random errors.
Abstract: Doppler ultrasound has now developed to the point where the rate of flow of blood in a given vessel can be measured with appropriate instrumentation. The theoretical basis of Doppler flow measurement is reviewed in this paper, with particular emphasis on the potential and actual sources of error. Three distinct approaches are identified, and the strengths and weaknesses of each discussed. The separate errors involved in estimating the vessel cross-sectional area, the angle of approach, and the Doppler shift are analyzed, together with the question of the uniformity of scattering from the blood. In vivo and in vitro tests of the accuracy obtained using a number of Doppler flow measuring instruments are then reviewed. It is concluded that the Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less. There are, however, considerable random errors, attributable primarily to errors in measuring the cross-sectional area and the angle of approach. Repeating the measurement of flow several times and averaging the results can reduce these random errors to an acceptable level.

768 citations

Journal ArticleDOI
TL;DR: With phase-contrast imaging, the overall error in flow measurement can be reduced to less than 10%, an acceptable level of error for routine clinical use.
Abstract: Phase-contrast magnetic resonance (MR) imaging is a well-known but undervalued method of obtaining quantitative information on blood flow. Applications of this technique in cardiovascular MR imaging are expanding. According to the sequences available, phase-contrast measurement can be performed in a breath hold or during normal respiration. Prospective as well as retrospective gating techniques can be used. Common errors in phase-contrast imaging include mismatched encoding velocity, deviation of the imaging plane, inadequate temporal resolution, inadequate spatial resolution, accelerated flow and spatial misregistration, and phase offset errors. Flow measurements are most precise if the imaging plane is perpendicular to the vessel of interest and flow encoding is set to through-plane flow. The sequence should be repeated at least once, with a high encoding velocity used initially. If peak velocity has to be estimated, flow measurement is repeated with an adapted encoding velocity. The overall error of a ...

624 citations


"Hepatic vascular flow measurements ..." refers background in this paper

  • ...It has been reported earlier that the Doppler technique tends to overestimate peak velocities (17,18)....

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Journal ArticleDOI
TL;DR: Hepatic parenchymal cell metabolic status does not control the hepatic arterial blood flow, and the mechanism of the arterial buffer response seems to depend on portal blood flow washing away local concentrations of adenosine from the area of thearterial resistance site.
Abstract: Hepatic parenchymal cell metabolic status does not control the hepatic arterial blood flow. Portal blood flow is a major intrinsic regulator of hepatic arterial tone. Hepatic arterial blood flow changes so as to buffer the impact of portal flow alterations on total hepatic blood flow, thus tending to regulate total hepatic flow at a constant level. This response is called the "hepatic arterial buffer response." The mechanism of the arterial buffer response seems to depend on portal blood flow washing away local concentrations of adenosine (production may be constant) from the area of the arterial resistance site. If portal flow decreases, less adenosine is washed away and the local concentration rises resulting in arterial dilation. Putative roles. Hepatic clearance of many hormones and endogenous compounds is blood flow limited. Constancy of total hepatic blood flow is crucial to homeostasis, and severe changes in the magnitude of flow can rapidly alter plasma concentrations of such compounds. The buffer may also prevent portal flow changes from severely altering intrahepatic blood pressures and liver blood volume. Pathological implications. If the O2 supply-to-demand ratio becomes too low, as in the case of a hypermetabolic liver (chronic alcohol exposure), a state of tissue hypoxia can exist without producing hepatic arterial dilation. Therapeutic implications. Livers show protection and improved recovery from several toxic agents, including alcohol, if the O2 supply-to-demand ratio can be increased. Arterial dilation by means of intra-arterial or intra-portal adenosine may prove useful.

449 citations


"Hepatic vascular flow measurements ..." refers background in this paper

  • ...These parameters could have a prognostic role in patients with cancer or cirrhosis (1,2)....

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Journal ArticleDOI
TL;DR: It is shown that limited resolution (partial‐volume effect) is the major obstacle to accurate flow measurement for both laminar and plug flow and at least 16 voxels must cover the cross section of the vessel lumen to obtain a measurement accuracy to within 10%.
Abstract: The accuracy of volume flow rate measurements obtained with phase-contrast methods was assessed by means of computer simulation and in vitro experiments. Factors studied include (a) the partial-volume effect due to voxel dimensions relative to vessel dimensions and orientation and (b) intravoxel phase dispersion. It is shown that limited resolution (partial-volume effect) is the major obstacle to accurate flow measurement for both laminar and plug flow. The results show that at least 16 voxels must cover the cross section of the vessel lumen to obtain a measurement accuracy to within 10%. Measurement accuracy also greatly depends on the relative signal intensity of stationary tissue and is better for laminar flow than plug flow.

295 citations


"Hepatic vascular flow measurements ..." refers background in this paper

  • ...Several explanations can be proposed for this difference: the size of the hepatic artery induces velocity undersampling in the whole vessel, the partial volume effects at the vascular wall caused by the lack of spatial resolution (24,25), artery motions, and the encoding velocity ideally selected at best to 25% above the maximum velocity value (26)....

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Journal ArticleDOI
TL;DR: Hepatic flow parameters measured with MR imaging correlate with the severity of cirrhosis and portal hypertension and Doppler US parameters are only weakly correlated with portal pressure.
Abstract: PURPOSE: To determine the correlations between hemodynamic parameters of hepatic flow measured with magnetic resonance (MR) imaging and Doppler ultrasonography (US) and the severity of cirrhosis and portal hypertension. MATERIALS AND METHODS: Forty-six patients referred for measurements of portal venous pressure (three with normal liver, 12 with chronic hepatitis, and 31 with cirrhosis [10 with Child-Pugh class A cirrhosis; 13 with class B cirrhosis; and eight with class C cirrhosis]) were included in the study. Apparent liver perfusion, apparent arterial and portal perfusion, portal fraction, distribution volume, and mean transit time were measured with dynamic contrast material–enhanced MR imaging. Portal velocity, portal flow, congestion index, right hepatic artery resistance index, and modified hepatic index were measured with Doppler US. Results in patients with cirrhosis and those without cirrhosis were compared with the Wilcoxon rank sum test. Correlations were assessed with Spearman rank correlati...

276 citations


"Hepatic vascular flow measurements ..." refers background or methods in this paper

  • ...Haag et al (15), followed by Annet et al (11), then calculated mean blood flow velocity by multiplying the time average velocity by a factor of 0.5 in patients, especially with cirrhosis, with no detailed discussion of the underlying assumptions....

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  • ...A second estimate (QD2) of portal blood flow was extracted from Haag et al (15) and Annet et al (11): QD2 1⁄4 0....

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  • ...In the present study, the method of Moriyasu et al (6) and its alternative were used to calculate QD1 and the formula used by Haag et al (15) and Annet et al (11) was used to calculate QD2 in the portal vein and hepatic artery....

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  • ...Finally, Annet et al (11) established a correlation between portal venous pressure and parameters measured by perfusion MRI, which was not the case with Doppler parameters....

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  • ...Haag et al (15), followed by Annet et al (11), then calculated mean blood flow velocity by multiplying the time average velocity by a factor of 0....

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