Normal Flow Pattern Research Articles

Ventricle wall movements and cerebrospinal fluid flow in hydrocephalus

The dynamics of fluid flow in normal pressure hydrocephalus (NPH) are poorly understood. Normally, CSF flows out of the brain through the ventricles. However, ventricular enlargement during NPH may be caused by CSF backflow into the brain through the ventricles. A previous study showed this reversal of flow; in the present study, the authors provide additional clinical data obtained in patients with NPH and supplement these data with computer simulations to better understand the CSF flow and ventricular wall displacement and emphasize its clinical implications. Three NPH patients and 1 patient with aqueductal stenosis underwent cine phase-contrast MR imaging (cine MR imaging) for measurement of CSF flow and ventricle wall movement during the cardiac cycle. These data were compared to data previously obtained in 8 healthy volunteers. The CSF flow measurements were obtained at the outlet of the aqueduct of Sylvius. Calculation of the ventricular wall movement was determined from the complete set of cine MR images obtained axially at the middle of the lateral ventricle. The data were obtained before and after CSF removal with a ventriculoperitoneal shunt with an adjustable valve. To supplement the clinical data, a computational model was used to predict the transmural pressure and flow. In healthy volunteers, net CSF aqueductal flow was 1.2 ml/minute in the craniocaudal direction. In patients with NPH, the net CSF flow was in the opposite direction--the caudocranial direction--before shunt placement. After shunting, the magnitude of the abnormal fluid flow decreased or reversed, with the flow resembling the normal flow patterns observed in healthy volunteers. The authors' MR imaging-based measurements of the CSF flow direction and lateral ventricle volume size change and the results of computer modeling of fluid dynamics lead them to conclude that the directional pattern and magnitude of CSF flow in patients with NPH may be an indication of the disease state. This has practical implications for shunt design and understanding the mechanisms that produce hydrocephalus.

Prognostic Significance of Left Ventricular Diastolic Dysfunction in Patients With Left Ventricular Hypertrophy and Systemic Hypertension (the LIFE Study)

Patients with hypertension and left ventricular (LV) hypertrophy commonly have impaired diastolic filling. However, it remains unknown whether changes in LV diastolic filling variables are associated with cardiovascular morbidity and mortality. In this study, 778 patients with hypertension with electrocardiographic LV hypertrophy who underwent echocardiography at baseline and annually thereafter during randomized losartan- or atenolol-based antihypertensive treatment were followed for a mean of 4.6 years. The composite cardiovascular end point was the first occurrence of fatal or nonfatal myocardial infarction, fatal or nonfatal stroke, and cardiovascular mortality. Antihypertensive therapy resulted in an increase in the prevalence of normal transmitral flow pattern from 28% to 46% of patients. Although antihypertensive treatment often resulted in a marked increase in the prevalence of normal mitral valve flow pattern, this was not associated with reduced cardiovascular morbidity and mortality when adjusting for blood pressure, left atrial diameter, LV mass index, and treatment in time-varying Cox analyses. In contrast, lower in-treatment E/A ratios and shorter mitral valve deceleration times were associated with less risk for heart failure. Similarly, normal in-treatment transmitral flow pattern was strongly associated with less risk for heart failure (hazard ratio 0.22, 95% confidence interval 0.05 to 0.98, p = 0.048), even when taking in-treatment left atrial diameter and blood pressure into account. In conclusion, antihypertensive treatment in patients with hypertension with electrocardiographic LV hypertrophy resulted in significant improvement in transmitral flow patterns; this was not associated with reduced cardiovascular morbidity and mortality. However, normal in-treatment LV filling was strongly associated with a reduced risk for hospitalization for heart failure.

Predischarge Angiographical Evaluation of Radial Artery Graft Harvested by Endoscopic Harvesting System

Endoscopic radial artery harvesting (ERAH) has superior cosmetic advantages over conventional harvesting methods. With instrumental advancements, these techniques have become easier to adopt and require less time to learn. In most reported cases, the quality of harvested conduits is discussed based on macroscopic and histologic examinations and clinical outcomes. However, predischarge angiography gives a straightforward answer regarding quality of harvested conduit. The aim of this study is to assess the quality of endoscopically harvested radial artery by predischarge angiographic evaluation. Endoscopic procedure using VasoView 4 system was performed in 87 patients between September 2004 and December 2007, and 78 predischarge angiographical evaluations were completed and reviewed. Mean age of the patients was 66 ± 10 years and 18% were women. After ERAH was performed, accompanying veins were dissected by ultrasound scalpel. All conduits were as aortocoronary bypass under cardiopulmonary bypass. Mean arm ischemic time was 32 ± 13 minutes and length of harvested conduit was 17.8 ± 1.3 cm. Predischarge angiography demonstrated two occlusions at the proximal anastomosis in the 51st and 71st cases, although intraoperative flow study showed normal flow patterns in both cases. Stenosis in the conduits was observed in the first, sixth, and seventh cases. No further angiographical problems were found in the remaining conduits. Based on the angiographical results, problems with the harvested conduits occurred only in initial period. ERAH with VasoView system provides satisfactory angiographical quality after initial learning curve.

Aortic Pressures, Stiffness and Left Ventricular Function in Coronary Slow Flow Phenomenon

Background: Coronary slow flow (CSF) phenomenon is characterized by delayed opacification of coronary vessels in a normal coronary angiogram. Although clinical and pathological features have been previously described, the underlying pathophysiology has not been fully elucidated. In this study, we aimed to evaluate central aortic pressure, aortic stiffness and left ventricular (LV) function in patients with coronary slow flow. Method and Results: The study population consisted of 154 patients who underwent coronary angiography because of typical and quasi-typical symptoms of angina. 81 patients with angiographically proven CSF and 73 cases with normal coronary flow pattern with similar risk profiles were enrolled in the study. Aortic pressures and indexes of elastic properties were evaluated using invasive methods. Aortic pulse pressure (mm Hg) and pulsality index of patients with CSF were found to be significantly higher than those of controls (60.8 ± 13.8 vs. 53.7 ± 14.5, p = 0.002; 0.84 ± 0.22 vs. 0.67 ± 0.18, p = 0.0001, respectively). LV Doppler parameters were deteriorated in patients with CSF. Aortic fractional pulse pressure and pulsality index were significantly correlated with the mean TIMI frame count and LV diastolic parameters in correlation analysis. Conclusion: The present findings allow us to conclude that impaired aortic elasticity in patients with CSF may also be responsible for the impaired LV diastolic parameters.

Semi-automatic quantification of 4D left ventricular blood flow.

BackgroundThe beating heart is the generator of blood flow through the cardiovascular system. Within the heart's own chambers, normal complex blood flow patterns can be disturbed by diseases. Methods for the quantification of intra-cardiac blood flow, with its 4D (3D+time) nature, are lacking. We sought to develop and validate a novel semi-automatic analysis approach that integrates flow and morphological data.MethodIn six healthy subjects and three patients with dilated cardiomyopathy, three-directional, three-dimensional cine phase-contrast cardiovascular magnetic resonance (CMR) velocity data and balanced steady-state free-precession long- and short-axis images were acquired. The LV endocardium was segmented from the short-axis images at the times of isovolumetric contraction (IVC) and isovolumetric relaxation (IVR). At the time of IVC, pathlines were emitted from the IVC LV blood volume and traced forwards and backwards in time until IVR, thus including the entire cardiac cycle. The IVR volume was used to determine if and where the pathlines left the LV. This information was used to automatically separate the pathlines into four different components of flow: Direct Flow, Retained Inflow, Delayed Ejection Flow and Residual Volume. Blood volumes were calculated for every component by multiplying the number of pathlines with the blood volume represented by each pathline. The accuracy and inter- and intra-observer reproducibility of the approach were evaluated by analyzing volumes of LV inflow and outflow, the four flow components, and the end-diastolic volume.ResultsThe volume and distribution of the LV flow components were determined in all subjects. The calculated LV outflow volumes [ml] (67 ± 13) appeared to fall in between those obtained by through-plane phase-contrast CMR (77 ± 16) and Doppler ultrasound (58 ± 10), respectively. Calculated volumes of LV inflow (68 ± 11) and outflow (67 ± 13) were well matched (NS). Low inter- and intra-observer variability for the assessment of the volumes of the flow components was obtained.ConclusionsThis semi-automatic analysis approach for the quantification of 4D blood flow resulted in accurate LV inflow and outflow volumes and a high reproducibility for the assessment of LV flow components.

Insight into the patterns of cerebrospinal fluid flow in the human ventricular system using MR velocity mapping

The patterns of cerebrospinal fluid (CSF) flow within the human ventricular system are still not fully understood in all their complexity. Knowledge is based on either the interpretation of CSF flow curves or computational simulations. Both approaches only provide an incomplete insight into the spatial and temporal dynamics of CSF flow. Time-resolved three-dimensional magnetic resonance velocity mapping has previously been used to investigate normal and pathologic blood flow patterns in the human vascular system. Here we used this technique to study the spatial and temporal dynamics of CSF flow in the ventricular system of 40 normal volunteers. Classification of the patterns of CSF flow based on calculation of three-dimensional particle path lines over the cardiac cycle revealed one uniform flow pattern for the lateral ventricles, three categories for the third and two categories for the fourth ventricle. We found no significant aging effects on either the presence of a specific CSF flow pattern or on CSF flow velocities. Our results provide the first detailed demonstration of the patterns of CSF flow within the human ventricular system.

Traces: Making Sense of Urodynamics Testing - Part 2: Uroflowmetry (Abstract Only): Special Series on Urodynamics

Uroflowmetry is an electronic recording of urinary flow. It is typically measured by one of two types of transducers. One type measures the weight of urine as it falls into a beaker or container placed on the transducer, and the other uses a spinning disc to measure urinary flow. Uroflowmetry is a non-invasive, comparatively inexpensive study often used to identify voiding abnormalities. Experienced clinicians can use uroflow tracings to differentiate a continuous (normal) flow pattern from abnormal patterns. While uroflowmetry has been found to reliably distinguish normal from abnormal flow patterns, uroflowmetry does not reliably distinguish the underlying cause of voiding abnormalities. Differential diagnosis of poor detrusor contraction strength from bladder outlet obstruction relies on a voiding pressure flow study that combines uroflowmetry with the various pressure studies used to generate a cystometrogram and pelvic floor muscle electromyography.

Do uroflowmetric findings change by treatment of urinary tract infection in girls with dysfunctional voiding?

The goal of the study was to evaluate the efficiency of repeated uroflowmetry study in girls who present with dysfunctional voiding with normal radiologic evaluation. Materials and methods: Twenty five children (25 girls with a mean age of 8.9 years) with recurrent urinary tract infection (UTI) and dysfunctional voiding who have normal radiologic evaluation were prospectively evaluated by uroflowmetry tests. Uroflowmetry study was repeated after the UTI treatment in asymptomatic period. Results: Mean urine volume was 254.31 ± 199.49 cc and the mean micturition time was 25.22 ± 15.43 s at the first uroflowmetry. Prolonged micturition time was noted in 8 (32%) patients. At the second uroflowmetry, mean urine volume was 370.77 ± 217.89 cc, and the mean micturition time was 29.63 ± 26.42 s. Prolonged micturition time was noted in 7 (28%) patients. Flow pattern curve was bell-shaped in 9 patients and abnormal in 16 patients (64%). In the second investigation a normal flow pattern curve was noted in 10 patients and an abnormal pattern in 15 patients. Conclusion: There was no difference between pre- and post-treatment uroflowmetry pattern in patients with dysfunctional voiding. Uroflowmetry investigation is not a very proper way for follow-up.

Successful treatment of spontaneous kidney graft decapsulation 18 years after renal transplantation: a case report.

Sir, The detection of a perirenal fluid collection causing graft dysfunctions is common in the early postoperative phase after renal transplantation. These are typically lymphoceles, urinomas, abscesses and haematomas, and treatment is well established. Perirenal fluid collection causing acute or sub-acute renal failure several years after engraftment is unusual. A rare, but potentially treatable condition is acute spontaneous decapsulation of the kidney graft. We hereby present a case of spontaneous decapsulation and rapid decline of renal function 18 years after engraftment. A 41-year-old Caucasian male with end-stage renal failure was diagnosed in 1989 with chronic glomerulonephritis (not biopsy verified) and received a renal transplant in 1990 at age 23, from his HLA-identical 21-year-old brother (CMV+ to +, PRA−). There were no rejections or other early complications. Graft function remained steady over the next 18 years with s-creatinine 100–120 μmol/L. Immunosuppression consisted of CsA (125 mg b.i.d., C0 target level 75–125), prednisolone (5 mg × 1/day) and azathioprine (75 mg/day, 6-TGN target 100). In 2003, an ultrasound of the renal graft and in 2005 a CT scan of the abdomen was done with normal findings regarding the graft. During a routine control at the local hospital s-creatinine had increased from a stable value (100–120 μmol/L) to 150 μmol/L. The development of chronic allograft nephropathy was suspected. Azathioprine was replaced by mycophenolate mofetil (MMF; 750 mg b.i.d.), and an ultrasound-guided renal biopsy was planned. The day after switch from azathioprine to MMF, the patient experienced a sudden onset of severe pain, and swelling in the graft was localized. S-creatinine at admission had further increased to 201 μmol/L. A CT scan of the abdomen revealed a large fluid collection (>1 L) encasing the renal graft (Figure 1). A pigtail catheter was placed within the cavity. On the first day, 800 ml of yellow-coloured fluid was drained out and analysis showed an albumin content of 9 g/L, creatinine level 102 μmol/L, WBC < 0.1 × 109/L and lactate dehydrogenase 68 U/L. Ultrasound/Doppler examination of the graft (after drainage) demonstrated normal parenchyma, renal pelvis and flow pattern. A renal biopsy was not performed. His symptoms resolved and s-creatinine normalized. Fig. 1 A CT Scan of the abdomen revealed a fluid collection (A) encasing the renal graft (B). However, fluid secretion through the pigtail catheter persisted, at the level of 100–200 mL/day. A laparoscopic exploration was therefore performed after 1 week. Perioperatively, a huge cyst encapsulating the kidney graft was noted. A fenestration to the peritoneal cavity was easily performed by making a 3-inch window in the anterior/cranial wall of the cyst. The kidney surface was described as intensely red and ‘bare’—well in conjunction with the CT finding of renal decapsulation. Three months after the procedure, the renal allograft was functioning remarkably well with s-creatinine 95 μmol/L.

Fetal Aortic-cerebral Doppler Resistance Index Ratio: An Indicator of Physiologic Blood Flow Distribution

Abstract Identical hemodynamic impedance and constant ratio of the fetal descending aorta and middle cerebral artery of uncomplicated pregnancies at term. Fetal aortic-cerebral Doppler resistance index ratio: An indicator of physiologic blood flow distribution. Objective To interpret the physiologic fetal arterial blood flow distribution by relating the vascular impedance of the fetal descending aorta (DA) and middle cerebral artery (MCA) and to establish the reference ranges for the aortic-cerebral Doppler resistance index ratio (ACRI). Study design Ninety-six patients with uncomplicated pregnancies were recruited for the cross-sectional assessment of the Doppler resistance index (RI) in the fetal DA and MCA between the 38rd and 40th weeks of gestation. The normal ranges of the ACRI were calculated. A cut-off value was designed to facilitate the clinical application of the ACRI. Results Between the 38th and 40th weeks of gestation in normal pregnancies the ACRI of healthy fetuses is constant, the overall mean is: 1.062 (+/– 0.087). A single cut-off value of 1.2 is recommended to assist separating normal and pathologic arterial blood flow patterns. Conclusion The normal ACRI reflects the identical vascular resistance of the descending aorta and the cerebral vessels, which maintains the physiologic fetal central arterial blood flow. Additional clinical studies are necessary to assess the diagnostic efficacy of the abnormal ACRI (&gt;1.2) as a potentially useful marker of the centralized arterial circulation indicating the early stage of fetal hypoxemic jeopardy.

TCD Systolic Spikes in a Malignant MCA Infarct

Malignant MCA infarction results in significant space occupying effect and intracranial pressure (ICP) increment. Due to the high mortality rate in such patients, the term malignant MCA infarction was coined. We studied a patient who developed a sudden onset of slurred speech, right hemiplegia, and decreased level of arousal. Two days later CT scan showed a massive cerebral infarct, involving the left MCA territory. A transcranial Doppler exam showed a normal flow pattern in the right hemisphere, but in the left hemisphere systolic spikes without diastolic flow were observed in internal carotid artery, anterior cerebral artery, as well as in the MCA. The pathophysiologic mechanisms leading to BD might asymmetrically begin in cerebral hemispheres in malignant MCA infarcts.

Breathhold time‐resolved three‐directional MR velocity mapping of aortic flow in patients after aortic valve‐sparing surgery

To evaluate the utility of breathhold time-resolved three-directional MR velocity mapping for quantifying the restoration of normal flow patterns in patients after aortic valve-sparing surgery. Breathhold time-resolved three-directional MR velocity mapping was performed on 13 patients with aortic valve-sparing surgery. Ten healthy volunteers and 12 patients with ascending aortic aneurysm underwent the same MR examination for comparison. Aortic laminar flow, turbulent flow, and the presence of vortical flow in the sinuses of Valsalva were semiquantitatively assessed and statistically compared between the three groups of subjects. The average score of laminar flow in the ascending aorta for patients with surgery was not significantly different from that of volunteers (P=0.210), but was significantly greater than that of patients with aneurysm (P<0.01). The average score of turbulent flow in patients with surgery was significantly smaller than that of patients with aneurysm (P<0.01). The presence of systolic vortical flow in the sinuses of Valsalva for patients with surgery was not significantly different from that of healthy volunteers (P=0.405) and patients with aneurysm (P=0.238). Breathhold time-resolved three-directional MR velocity mapping allows for quantifying flow patterns in the aortic root and ascending aorta. Normal laminar flow in the ascending aorta and vortical flow in the sinuses of Valsalva can be restored in patients after aortic valve-sparing surgery.

Invited Commentary

The advent of fetal echocardiography rapidly confirmed what cardiac morphologists had long hypothesized in that some developing hearts start out normal in early gestation, and due to an intrauterine event that results in changed blood flow patterns, develop severe and uncorrectable defects develop by the time the child is born. As evidence for this has accumulated, it has brought a new challenge for congenital heart surgeons to address the problem of restoring normal blood flow pattern and hopefully normal growth in the fetus.

Determination of diastolic dysfunction by conventional and Doppler tissue echocardiography in dogs

The aim of this study was to explore the feasibility and the diagnostic value of conventional Doppler parameters of transmitral inflows and Doppler tissue echocardiography parameters of septal annulus motion for the assessment of diastolic dysfunction in dogs with cardiac failure. The LV diastolic mitral flow patterns were divided into normal diastolic flow pattern (group 1), delayed relaxation pattern (group 2), pseudonormal flow pattern (group 3), and restrictive pattern (group 4). In our study population, 17 patients had normal mitral inflow variables (E/A ratio > 1 and Dt < 109 m). The other 7 patients were classified as having abnormal mitral inflow pattern (E' > 8 cm/s, E'/A' > 1). In conclusion, the combination of Doppler tissue echocardiography of the mitral septal annulus and mitral inflow patterns by conventional Doppler indices provides better estimates of diastolic dysfunction in dogs.

Imaging of the Thoracic Aorta with Time-Resolved Three-Dimensional Phase-Contrast MRI: A Review

Time-resolved three-dimensional (3D) phase-contrast (PC) magnetic resonance imaging (MRI), or four-dimensional (4D) flow, is able to provide robust 3D images with three-directional velocities. This review discusses the technique and application of 4D flow in the imaging of thoracic aortic pathologies. It has been instrumental in describing normal flow patterns throughout the cardiac cycle in the ascending and descending aorta and has shown the variety of flow patterns that exist in ascending aortic aneurysms.

Intraoperative coronary artery pulse Doppler patterns in patients with complete transposition of the great arteries undergoing the arterial switch operation

Arterial switch operation is standard repair for complete transposition of the great arteries (TGA). Coronary artery abnormalities are the most common cause of morbidity and mortality in the acute postoperative phase. This study was designed to determine whether coronary artery pulse Doppler flow patterns obtained by transesophageal echocardiography during the arterial switch operation are correlated with acute postoperative outcomes. A retrospective review of all patients with TGA undergoing the arterial switch operation between 2004 and 2006 was performed. Intraoperative coronary artery pulse Doppler flow patterns were analyzed by 2 blinded investigators. Associations of coronary artery pulse Doppler flow patterns with clinical outcomes were sought using multivariable linear and logistic regression analysis. Sixty-three patients (48 male, gestational age 38 +/- 2 weeks, birth weight 3,514 +/- 613 g) were analyzed. Three patients needed mechanical support (2 died), 19 had delayed sternal closure, 17 had arrhythmias, and 9 had ST changes. The most common coronary artery pulse Doppler flow pattern consisted of a late systolic peak followed by low-velocity flow throughout diastole. A left main coronary artery (LMCA) velocity time integral >0.14 (P = .01) and an LMCA peak systolic velocity >0.6 cm/s (P = .05) were associated with need for surgical revision. Abnormalities in LMCA flow were associated with the need for surgical revision in patients with TGA undergoing the arterial switch operation. Normal coronary artery pulse Doppler flow patterns after the arterial switch operation consisted of a late systolic peak followed by low-velocity flow throughout diastole.

A Dual Echo Steady State Pulse Sequence in Evaluation of Brain Cerebrospinal Fluid Flow

This paper summarizes our experience of exploiting a Dual Echo Steady State (DESS) pulse sequence for the fast qualitative assessment of cerebrospinal fluid (CSF) flow dynamics at the aqueduct of Sylvius and Monro's foramina levels of the brain liquor pathways using a low-field magnetic resonance imager. Normal and pathologic CSF flow patterns are discussed. The capabilities of the described method as an effective extra tool for deriving the additional diagnostic information via visualization of flow voids in the brain CSF pathways are shown.

Inferring origin of vascular supply from tracer arrival timing patterns using bolus tracking MRI

To investigate the potential of novel postprocessing and visualization techniques to distinguish presence of collateral flow using Bolus Tracking MRI. Collateral blood supply is believed to be of paramount importance in acute stroke, yet clinical evaluation is challenging as the gold standard digital subtraction angiography is often not feasible in the acute scenario. In principle, bolus arrival delay data contains information about the route of blood supply into tissue and hereby presence of collateral flow patterns. We first examined the potential of current clinical bolus tracking protocols to accurately characterize bolus arrival delay. Using the simulation results, we analyzed bolus tracking data from one normal volunteer and one acute stroke patient. The bolus arrival patterns in the volunteer and in the normal hemisphere of the patient were found to be qualitatively similar and in good agreement with physiology. The bolus was seen to spread from the larger arteries toward the periphery. The stroke hemisphere in the patient indicated a retrograde direction of flow on the cortical mantle consistent with leptomeningeal vessels. Bolus tracking MRI can likely be used to distinguish collateral flow patterns from normal flow patterns.

Normal Doppler Spectral Waveforms of Major Pediatric Vessels: Specific Patterns

Every major vessel in the human body has a characteristic flow pattern that is visible in spectral waveforms obtained in that vessel with Doppler ultrasonography (US). Spectral waveforms reflect the physiologic status of the organ supplied by the vessel, as well as the anatomic location of the vessel in relation to the heart. In addition, the waveforms may be affected by age- and development-related hemodynamic differences. For example, adults tend to have higher flow velocities, whereas neonates, particularly those born prematurely, have higher resistance to flow, especially in the cerebral and renal vascular beds. As Doppler US is performed with increasing frequency for vascular evaluation in children, the recognition of normal flow patterns has become imperative. Familiarity with the waveforms characteristic of specific veins and arteries in children is important. In addition, an understanding of the hemodynamic factors involved provides a useful basis for interpreting waveform abnormalities.

A Doppler waveform index to characterize hepatic vein velocity pattern and evaluate hepatic fibrosis

To describe a Doppler waveform index representing the hepatic vein flow velocity pattern and to examine its relationship to the degree of hepatic fibrosis. Doppler waveforms were obtained in 66 patients scheduled for percutaneous liver needle biopsy and categorized as normal (with a retrograde flow phase) or abnormal (without retrograde flow). Waveforms were also characterized using a hepatic vein waveform index (HVWI): (maximum - minimum velocity)/(maximum velocity). Biopsy specimens were graded for fibrosis. There was a highly significant decrease in HVWI with increasing fibrosis score in the biopsy (p < 0.001, Jonckheere trend test). The biopsy showed cirrhosis in 14 of 29 patients (48%) with absent retrograde flow and 5 of 37 patients (14%) with a normal flow pattern. Using HVWI as the criterion, cirrhosis was present in 13 of 21 (62%) patients with HVWI < 0.75, in 6 of 31 (19%) patients with 0.75 < HVWI < 1.50, and in none of 14 (0%) patients with HVWI > 1.50. HVWI is inversely correlated to the degree of liver fibrosis and may be more efficient than the presence or absence of retrograde flow in diagnosing and grading hepatic fibrosis.