Blood flow in major cerebral arteries measured by phase-contrast cine MR.

PURPOSETo measure mean blood flow in individual cerebral arteries (carotid, basilar, anterior cerebral, middle cerebral, and posterior cerebral) using a cine phase contrast MR pulse sequence.METHODSTen healthy volunteers (22 to 38 years of age) were studied. The cine phase-contrast section was positioned perpendicular to the vessel of interest using oblique scanning planes. This pulse sequence used a velocity encoding range of 60 to 250 cm/sec. From the velocity and area measurements on the cine images, mean blood flow was calculated in milliliters per minute and milliliters per cardiac cycle. In the same subjects, transcranial Doppler measurements of blood velocity in these same vessels were also obtained.RESULTSThere was no difference in blood flow in the paired cerebral arteries. Carotid arteries had mean blood flow in the range of 4.8 +/- 0.4 ml/cycle, the basilar artery 2.4 +/- 0.2 ml/cycle, the middle cerebral artery 1.8 +/- 0.2 ml/cycle, the distal anterior cerebral artery 0.6 +/- 0.1 ml/cycle, and the posterior cerebral artery 0.8 +/- 0.1 ml/cycle. Overall, there was poor correlation between MR-measured and transcranial Doppler-measured peak velocity.CONCLUSIONAlthough careful attention to technical detail is required, mean blood flow measurements in individual cerebral vessels is feasible using a cine phase-contrast MR pulse sequence.     

Quantification of blood flow in the middle cerebral artery with phase-contrast MR imaging

The aim of this study was to assess blood flow in the middle cerebral artery (MCA) according to age, gender, and side. Eighty-eight subjects without carotid obstruction were measured for mean velocity, vessel area, and volume flow rates of both MCA with phase-contrast MR. A high-resolution sequence with a matrix of 300 × 512 and a double oblique localizing strategy was used for measurement. A mean velocity of 33 ± 6.8 cm/s, a mean vessel area of 6.2 ± 1.2 mm² and a mean flow rate of 121 ± 28 ml/min were measured in the MCA. Lower volume flow rates were seen in subjects aged over 50 years (p < 0.01). When comparing women with men, a lower vessel area (p < 0.05) of the MCA was counterbalanced by a higher velocity, resulting in no significant difference of the volume flow rate. No difference occurred between the right and the left side. Flow reduction occurs in the elderly. A lower vessel area of the MCA in women is compensated by a higher velocity. Received: 3 September 1999; Revised: 17 January 2000; Accepted: 23 February 2000     

Normal renal blood flow measurement using phase-contrast cine magnetic resonance imaging.

RATIONALE AND OBJECTIVES. This study assesses the ability of a cardiac-gated phase-contrast magnetic resonance imaging (MRI) technique to measure renal blood flow (RBF) noninvasively in humans. METHODS. In nine normal volunteers, total RBF in the renal arteries and in the left renal vein was estimated by MRI and correlated with RBF determined by the clearance of para-aminohippuric acid (CPAH) and the hematocrit level. RESULTS. Correlation of RBF estimated from left renal vein flow, with RBF by CPAH-hematocrit, yielded r = .86 (P less than .003). Repeated measurement of RBF by MRI demonstrated a high degree of reproducibility, with coefficients of variation ranging from 4.8% to 8.9%. However, the MRI measurements of arterial flow did not significantly correlate with the standard measurements. CONCLUSIONS. Reproducible noninvasive measurement of normal RBF is possible with the phase-contrast MRI technique used to measure renal venous blood flow.     

evaluation of communication between intracranial arachnoid cysts and cisterns with phase-contrast cine MR imaging

BACKGROUND AND PURPOSE: The demonstration of communication between arachnoid cysts (ACs) and the adjacent subarachnoid space is a prerequisite for their proper management. CT cisternography (CTC) is the conventional method for functional evaluation of ACs. The sensitivity of MR imaging to CSF flow has been demonstrated, but reports of the clinical usefulness of MR CSF flow techniques in this application are limited. The purpose of our study was to prospectively evaluate the accuracy of MR CSF flow study as an alternative to CTC in this setting. METHODS: MR CSF flow study with retrospective ECG-gated 2D, fast low-angle shot, phase-contrast (PC), cine gradient-echo sequence was performed in 39 patients with an intracranial AC. Results were compared with intraoperative and CTC findings. RESULTS: PC cine MR imaging results were compatible with operative or CTC findings in 36 (92.3%) of 39 patients. Twenty-four cysts were noncommunicating, and 15 were communicating. Three cysts were evaluated as being noncommunicating on PC cine MR imaging (false-negative) but demonstrated contrast enhancement on CTC. No false-positive diagnoses occurred. All cysts regarded as being communicating on PC cine MR imaging were also found to be communicating on both confirmation methods. CONCLUSION: MR CSF flow imaging with a PC cine sequence can be incorporated in the imaging work-up of ACs. This is a reliable alternative to invasive CTC for the functional evaluation of ACs.     

Validation of volume flow measurements with cine phase-contrast MR imaging for peripheral arterial waveforms

A flow phantom was used to study MR volume flow measurements for monophasic and triphasic waveforms over the flow range expected in peripheral arteries at rest and with exercise (2–24 mL/sec, n = 50). The improvement in accuracy with phase-correction image processing to eliminate errors caused by eddy currents was measured. Volume flow estimates with Doppler sonography were also measured. MR volume flow measurements correlated with volume collection with r = 0.996 and mean error = 4.6%. Phase–correction processing decreased mean error from 12.6% to 4.6% (P <.001, paired t-test). Doppler sonography had a higher mean error of 10.3% (P <.001, unpaired t-test). Cine phase-contrast MR imaging provides accurate estimates of volume blood flow for waveforms and flow ranges expected in peripheral arteries.     

Normal flow patterns of intracranial and spinal cerebrospinal fluid defined with phase-contrast cine MR imaging

A phase-contrast cine magnetic resonance (MR) imaging technique was used to study normal dynamics of cerebrospinal fluid (CSF) in 10 healthy volunteers and four patients with normal MR images. This pulse sequence yielded 16 quantitative flow-encoded images per cardiac cycle (peripheral gating). Flow encoding depicted craniocaudal flow as high signal intensity and caudo-cranial flow as low signal intensity. Sagittal and axial images of the head, cervical spine, and lumbar spine were obtained, and strategic sites were analyzed for quantitative CSF flow. The onset of CSF systole in the subarachnoid space was synchronous with the onset of systole in the carotid artery. CSF systole and diastole at the foramen of Monro and aqueduct were essentially simultaneous. The systolic and diastolic components were different in the subarachnoid space, where systole occupied approximately 40% and diastole 60% of the cardiac cycle, compared with the ventricular system, where they were equal. This difference results in systole in the intracranial and spinal subarachnoid spaces preceding that in the ventricular system; the same is true for diastole. The fourth ventricle and cisterna magna serve as mixing chambers. The high-velocity flow in the cervical spine and essentially no flow in the distal lumbar sac indicate that a portion of the capacitance necessary in this essentially closed system resides in the distal spinal canal.     

Comparison of cerebral artery blood flow measurements with gated cine and ungated phase-contrast techniques

Cine phase-contrast (PC) magnetic resonance (MR) pulse sequences have been used to measure blood flow in a variety of vessels. Because the cine PC sequence is time-consuming, this prospective study was undertaken to compare it with an ungated PC technique for measuring average blood flow in individual cerebral arteries to potentially achieve substantial time savings. The following cerebral arteries were studied in 10 healthy volunteers: carotid, basilar, middle cerebral, anterior cerebral, and posterior cerebral. Imaging planes were placed perpendicular to the vessel of interest, and velocity encoding, ranging from 40 to 250 cm/sec, was matched to individual arteries. Good correlation between cine and ungated PC blood flow measurements was obtained for both high- and low-flow vessels, with an overall correlation coefficient of 978. The ungated PC sequence, because of its short imaging time, allows measurement of the blood volume flow rate in the circle of Willis in approximately 20 minutes, a clinically acceptable time.     

Cerebrospinal fluid pulsation amplitude and its quantitative relationship to cerebral blood flow pulsations: a phase-contrast MR flow imaging study

Our purpose in this investigation was to explain the heterogeneity in the cerebrospinal fluid (CSF) flow pulsation amplitudes. To this end, we determined the contributions of the cerebral arterial and jugular venous flow pulsations to the amplitude of the CSF pulsation. We examined 21 healthy subjects by cine phase-contrast MRI at the C2–3 disc level to demonstrate the CSF and vascular flows as waveforms. Multiple regression analysis was performed to calculate the contributions of (a) the arterial and venous waveform amplitudes and (b) the delay between the maximum systolic slopes of the arterial and venous waveforms (AV delay), in order to predict the amplitude of the CSF waveform. The contribution of the arterial waveform amplitude was positive (r = 0.61; p = 0.003) to the CSF waveform amplitude and that of the venous waveform amplitude was negative (r = −0.50; p = 0.006). Both in combination accounted for 56 % of the variance in predicting the CSF waveform amplitude (p < 0.0006). The contribution of AV delay was not significant. The results show that the variance in the CSF flow pulsation amplitudes can be explained by concurrent evaluation of the CSF and vascular flows. Improvement in the techniques, and controlled experiments, may allow use of CSF flow pulsation amplitudes for clinical applications in the non-invasive assessment of intracranial dynamics by MRI. Received: 3 January 1996 Accepted: 5 June 1996     

Visualization and quantification of flow and velocity fields in intracranial arteriovenous malformations using phase-contrast MR angiography

OBJECTIVE: The objective of this study was to describe postprocessing tools for MR phase-contrast flow quantification images and apply those tools to cerebral arteriovenous malformations (AVMs) to visualize blood flow dynamics noninvasively. CONCLUSION: Inflow and outflow zones were clearly depicted at different regions in the AVM. The processed images showed flow patterns including vortical flow and variations in velocity over the cardiac cycle. Particle tracking gave an impression of the overall flow state and of the venous drainage system in particular.     

Cerebral blood flow evaluation of arteriovenous malformations with stable xenon CT

Twenty patients with supratentorial arteriovenous malformations (AVMs) were evaluated with angiography, conventional CT, and stable xenon CT to determine cerebral blood flow. Contralateral and ipsilateral regions of interest relative to the AVM were evaluated from cerebral blood flow maps and correlated with angiography. A significant decrease in cerebral blood flow was observed in the ipsilateral cortical gray matter adjacent to the AVM relative to the corresponding contralateral cortex (mean difference = 9.52 ml/100 g/min, p less than .01). The larger AVMs (greater than 8 cm3) were associated with a more marked decrease with a mean difference of 12.22 ml/100 g/min (p less than .02). Regions of interest were also chosen on the basis of angiographic findings, which suggested areas of decreased flow. Comparison of these areas with analogous contralateral areas also showed a significant decline in cerebral blood flow (mean difference = 8.86 ml/100 g/min); this decline was greater with larger AVMs (volume greater than 8 cm3), which had a mean difference of 11.38 ml/100 g/min (p less than .01). Our correlative study enabled us to pinpoint the regions most likely to have reduced flow from an AVM.     

Renal artery blood flow: quantification with breath-hold or respiratory triggered phase-contrast MR imaging

The aim of this study was to evaluate the validity and reproducibility of breath-hold and respiratory triggered phase-contrast (PC) MR imaging techniques in the measurement of renal artery blood flow. In 12 healthy subjects cardiac-gated PC flow measurements were obtained in the renal arteries using a breath-hold and a respiratory-triggered technique. The flow measurements were repeated in each renal artery separately. Comparison between the sum of flow measurements in the renal arteries and the difference in aortic flow measurements above and below the renal arteries served as an internal control. The flow measurements showed a good reproducibility both with the breath-hold (r = 0.92, p < 0.0001) and with the respiratory-triggered (r = 0.91, p < 0.0001) technique. The validity of both methods was good and there was no statistically significant difference. Reproducible quantitative measurements of renal artery blood flow are possible with respiratory controlled, cardiac-gated, PC MR imaging. Received: 12 February 1999; Revised: 8 February 2000; Accepted: 9 February 2000     

Persistent nidus blood flow in cerebral arteriovenous malformation after stereotactic radiosurgery: MR imaging assessment

Stereotactic radiosurgery has become a major force in the treatment of arteriovenous malformations (AVMs) of the brain. After treatment, obliteration of flow through the malformation occurs in 75%-85% of cases within 2 years, assuming the entire AVM nidus can be encompassed by the radiation field. Because the follow-up period is relatively long, a noninvasive means to assess residual transnidus blood flow is desirable. The authors report favorable findings after a comparative analysis of 85 posttreatment magnetic resonance images and 27 follow-up cerebral arteriograms in 34 patients treated with stereotactic radiosurgery. The authors found that transnidus flow can be determined from apparent signal intensity differences between tandem two-dimensional gradient-recalled echo images obtained first without and then with gradient moment nulling (flow compensation), with empirically derived pulse parameters. This method provides a means to monitor the reduction in AVM matrix size and to assess the extent of persistent arteriovenous shunting (ie, blood flow) across the nidus.     

Dark flow artifacts with steady-state free precession cine MR technique: causes and implications for cardiac MR imaging

Steady-state free precession cine images from cardiac magnetic resonance imaging studies of 24 patients were reviewed retrospectively to identify dark flow artifacts. The cause and features of the artifacts were studied in flow phantom experiments. Dark flow artifacts were recognized in eight of the 24 cases and were characterized by low or inhomogeneous signal intensity in blood pools with little change in adjacent tissues. The artifacts could be mimicked in flow phantom experiments by deliberately deshimming the gradients and appeared periodically during imaging with off-centered frequencies. These artifacts appeared to be caused by spins moving within an inhomogeneous magnetic field.     

Spontaneous ventriculostomy: report of three cases revealed by flow-sensitive phase-contrast cine MR imaging.

Spontaneous ventriculostomy is a rare condition that occurs with the spontaneous rupture of a ventricle, resulting in a communication between the ventricular system and the subarachnoid space. Three cases of spontaneous ventriculostomy through the floor of the third ventricle that occurred in cases of chronic obstructive hydrocephalus are presented. The communication was identified via flow-sensitive phase-contrast cine MR imaging. Spontaneous ventriculostomy is probably a result of a rupture of the normally thin membrane that forms the floor of the third ventricle and, with long-standing obstructive hydrocephalus, creates an internal drainage pathway that spontaneously compensates for the hydrocephalus.