Three-dimensional Phase-contrast Magnetic Resonance Research Articles

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.

Laser Doppler velocimetry (LDV) and 3D phase‐contrast magnetic resonance angiography (PC‐MRA) velocity measurements: Validation in an anatomically accurate cerebral artery aneurysm model with steady flow

To verify the accuracy of velocity mapping with three-dimensional (3D) phase-contrast magnetic resonance angiography (PC-MRA) for steady flow in a realistic model of a cerebral artery aneurysm at a 3T scanner. Steady flow through an original geometry model of a cerebral aneurysm was mapped at characteristic positions by state-of-the-art laser Doppler velocimetry (LDV) as well as 3D PC-MRA at 3T. The spatial distributions and local values of two velocity components obtained with these two measurement methods were compared. The 3D PC-MRA velocity field distribution and mean velocity values exhibited only minor differences to compare to the LDV measurements in straight artery regions for both main and secondary velocities. The differences increased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the main flow direction. 3D PC-MRA can provide reliable measurements of velocity components of steady flow in small arteries. The accuracy of such measurements depends on the artery size and the measurement plane positioning.

The value of MR angiography techniques in the detection of head and neck paragangliomas

Objective: The objective of this study was to compare three-dimensional phase-contrast angiography (3D PCA), 2D time-of-flight (2D TOF), and 3D TOF magnetic resonance (MR) angiography and a proton density weighted technique in terms of their ability to detect head and neck paragangliomas. Materials and methods: 14 patients with 29 paragangliomas were examined at 1.5 T. Three MR angiography sequences (3D PCA, 2D TOF, and multi-slab 3D TOF) and a proton density (PD) weighted sequence were reviewed by four neuroradiologists. The gold standard was digital subtraction angiography. Presence of tumor was assessed in five grades of confidence. Sensitivity and specificity were calculated after dichotomizing the results. Data was analyzed using the logistic regression method. Results: Mean sensitivity and specificity for the four observers were for PD: 72%/97%, for 3D PCA: 75%/90%, for 2D TOF: 66%/93%, and for 3D TOF: 90%/92%. Sensitivity was significantly better for 3D TOF MRA ( P<0.001). No substantial between-observer variation for tumor detection was present. Conclusion: Our results demonstrate that, using 3D TOF MRA, paragangliomas in the head and neck region can be detected with high sensitivity and specificity. Further investigation is necessary to judge the value of 3D TOF MR angiography against fat suppressed contrast enhanced T1 weighted and fat suppressed T2 weighted MR sequences to find the optimal imaging sequence for paragangliomas.

Three-Dimensional Phase-Contrast Magnetic Resonance Angiography: A Useful Clinical Adjunct to Gadolinium-Enhanced Three-Dimensional Renal Magnetic Resonance Angiography?

To assess the value of three-dimensional (3D) phase-contrast (PC) magnetic resonance angiography (MRA) after gadolinium (Gd)-enhanced 3D MRA for renal artery imaging. Twenty-one patients with suspected renal artery hypertension were reviewed. All studies included Gd-enhanced 3D MRA and 3D PC MRA. Blinded interpretation of the images was performed for each technique independently and in combination. Conventional X-ray angiography was used for diagnostic correlation when available. Renal artery stenosis was present in 7 (16.3%) of 43 renal arteries, confirmed by X-ray angiography. MRA images demonstrated 100% sensitivity and 74% specificity for Gd-enhanced 3D MRA and 100% sensitivity and 94% specificity for 3D PC MRA. All vessels were diagnosed correctly when both image sets were viewed. 3D PC MRA can improve the specificity of renal MRA by decreasing the number of false-positive Gd-enhanced 3D MRA interpretations.

Three-Dimensional Phase-Contrast Magnetic Resonance Angiography: A Useful Clinical Adjunct to Gadolinium-Enhanced Three-Dimensional Renal Magnetic Resonance Angiography?

Three-Dimensional Phase-Contrast Magnetic Resonance Angiography: A Useful Clinical Adjunct to Gadolinium-Enhanced Three-Dimensional Renal Magnetic Resonance Angiography?

MR angiography of the intracranial venous system.

To compare the effectiveness of different imaging planes at time-of-flight (TOF) magnetic resonance (MR) angiography and phase-contrast MR angiography in the visualization of the normal intracranial venous system. In 12 healthy volunteers, two-dimensional (2D) TOF MR angiography and three-dimensional (3D) phase-contrast MR angiography were performed in transverse, sagittal, and coronal planes. All data were displayed as maximum intensity projection (MIP) images. Four neuroradiologists assessed the visibility of 28 intracranial venous structures on the MIP images. Statistical analysis was performed by using the Friedman two-way analysis of variance and the Cochran Q test. Visualization of the normal intracranial venous system was better with 3D phase-contrast and coronal 2D TOF MR angiography than with transverse or sagittal 2D TOF MR angiography (P < .05, Friedman test) for each observer and the group of observers. Differences were found between each of the 2D TOF and 3D phase-contrast MR angiographic sequences in the visualization of individual venous structures (Cochran Q test). The kappa values ranged from 0.36 to 0.71, which indicated a moderate to good agreement between observers. The normal intracranial venous system is adequately visualized with 3D phase-contrast and coronal 2D TOF MR angiography.

Three-dimensional phase contrast MR cerebral venography with zero filling interpolation in the slice encoding direction

The purpose of this study was to evaluate the magnetic resonance (MR) cerebral venography findings of a three-dimensional phase contrast MR sequence with zero filling interpolation of the data in the slice encoding direction. Fifty volunteers were enrolled in the study. Images were obtained on a 1.5 MR imaging system with acquisition time of 12 min. MIP images were reconstructed throughout the entire imaging volume. A grading scale system was used to assess dural venous sinuses, major deep veins, cortical, and cortical eponymic veins. Inferior group of dural venous sinuses, inferior sagittal sinus, and cortical eponymic veins were poorly demonstrated. Score of the superior sagittal sinus, the straight sinus, the confluence of the superior sinus group, the right transverse and sigmoid sinuses, the internal veins, and the vein of Galen was excellent. The score of the left transverse and sigmoid sinuses was good. In conclusion, when using zero filling interpolation of the data in a three-dimensional phase contrast MR cerebral venography sequence, the superior group of dural venous sinuses and main major deep veins are demonstrated with good conspicuity.

Application and Validation of Three‐Dimensional Data Sets From a Phase Contrast MR Angiography for Preoperative Computer Simulation of Brain Tumors

We applied a three-dimensional (3D) phase contrast magnetic resonance angiography as the source for generating integrated 3D images for surgical planning of brain tumors. In the 3D model, we defined the Cingulomarginal sulcus and subsequently the central sulcus in the interhemispheric plane. This method solved the misregistration problem caused by the combination of multi-sequence data sets and can be feasible for surgical planning.J. Magn. Reson. Imaging 1999;10:102–106. © 1999 Wiley-Liss, Inc.

Application and validation of three-dimensional data sets from a phase contrast MR angiography for preoperative computer simulation of brain tumors.

We applied a three-dimensional (3D) phase contrast magnetic resonance angiography as the source for generating integrated 3D images for surgical planning of brain tumors. In the 3D model, we defined the Cingulomarginal sulcus and subsequently the central sulcus in the interhemispheric plane. This method solved the misregistration problem caused by the combination of multi-sequence data sets and can be feasible for surgical planning.

GD-enhanced 3D phase-contrast MR angiography and dynamic perfusion imaging in the diagnosis of renal artery stenosis

The objective of this study was to investigate the role of contrast enhancement using a three-dimensional (3D) phase-contrast (PC) magnetic resonance (MR) sequence (3D PC-MRA) and to assess the value of a dynamic MR perfusion study of the kidneys to determine the hemodynamic relevance of unilateral renal artery stenosis (RAS). Seventeen patients with unilateral RAS were examined on a standard 1.0 T imaging system using a phase shift and magnitude sensitive 3D PC sequence (TR = 160 ms, TE = 9 ms, venc. 30 cm/s). Following the initial pre-contrast 3D PC-MRA a dynamic first pass perfusion study was performed using a Turbo-FLASH 2D sequence (TR = 4.5 ms, TE = 2.2 ms, TI = 400 ms) after bolus injection of 0.15 mmol gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)/kg body weight. The 3D PC-MRA was then repeated during infusion of 0.15 mmol Gd-DTPA/kg body weight. Evaluation by three independent readers was based on maximum intensity projection images. Source images were rendered on request. Signal intensity (SI) over time curves of the renal cortex were obtained from the dynamic perfusion study and analyzed for maximum signal enhancement as well as temporal relationship to the aortic SI curve. Results from 3D PC-MRA revealed a sensitivity (pre-/post-contrast) of 100%/89%, specificity of 76%/63%, positive predictive value of 80%/69%, negative predictive value of 90%/78%, and accuracy of 85%/75% ( p = 0.07). Interobserver agreement was κ = 0.61/κ = 0.47 (pre/post Gd-DTPA), respectively. Increased signal-to-noise was present in all segments of the renal arteries post contrast ( p = 0.0003). This came along with image degradation due to aliasing and elevated SI of venous flow that partially obscured the renal arteries. Dynamic SI curves showed a significantly decreased maximum SI in RAS ( p = 0.01–0.001). A temporal delay of cortical signal intensity enhancement could not be confirmed in this setting. Gd-enhanced 3D PC-MRA did not yield a superior diagnostic value in the diagnosis of RAS compared to pre-contrast measurements. Dynamic perfusion imaging of the kidneys, in combination with 3D PC-MRA, can contribute additional information in suspected unilateral RAS.

Alterations in pulmonary artery flow patterns and shear stress determined with three-dimensional phase-contrast magnetic resonance imaging in fontan patients

Objective: This study compares in vivo pulmonary blood flow patterns and shear stresses in patients with either the direct atrium–pulmonary artery connection or the bicaval tunnel connection of the Fontan procedure to those in normal volunteers. Comparisons were made with the use of three-dimensional phase contrast magnetic resonance imaging. Methods: Three-dimensional velocities, flows, and pulmonary artery cross-sectional areas were measured in both pulmonary arteries of each subject. Axial, circumferential, and radial shear stresses were calculated with the use of velocities and estimates of viscosity. Results: The axial velocities were not significantly different between subject groups. However, the flows and cross-sectional areas were higher in the normal group than in the two patient groups in both pulmonary arteries. The group with the bicaval connection had circular swirling in the cross section of both pulmonary arteries, causing higher shear stresses than in the controls. The disorder caused by the connection of the atrium to the pulmonary artery caused an increase in some shear stresses over the controls, but not higher than those found in the group having a bicaval tunnel. Conclusions: We found that pulmonary flow was equally reduced compared with normal flow in both patient groups. This reduction in flow can be attributed in part to the reduced size of the pulmonary arteries in both patient groups without change in axial velocity. We also found higher shear stress acting on the wall of the vessels in the patients having a bicaval tunnel, which may alter endothelial function and affect the longevity of the repair. (J Thorac Cardiovasc Surg 1998;116:294-304)

Objective Stenosis Quantification From Post-Stenotic Signal Loss in Phase-Contrast Magnetic Resonance Angiographic Datasets of Flow Phantoms and Renal Arteries

In this study a semi-automated and observer-independent algorithm for quantifying post-stenotic signal loss (PSL) in three-dimensional phase-contrast (PC) magnetic resonance angiography (MRA) of patients with renal artery stenosis is presented. This algorithm was developed on MRA datasets of stenotic phantoms, included in a flow circuit with stationary flows. The length and the severity of the PSL (incorporating both the length and the degree of PSL) in the MRA datasets were proposed for quantifying the stenoses. The algorithm was tested in renal arteries; ten patients with renal artery stenosis and seven healthy volunteers were investigated. Digital subtraction angiography was performed in the patients and served as the gold standard. Stenosis severity showed better correlation with the severity of the PSL than with the length, both for in vitro and in vivo measurements. Spearman correlation coefficients (r s) showed statistically significant correlations between the severity of the PSL and parameters determined by digital subtraction angiography, i.e., percent diameter stenosis (r s = 0.90). The length of the PSL showed no correlation with the diameter stenosis (r s = 0.37). In conclusion, this study presents a semi-automated and observer-independent way of quantifying signal loss, and the severity of the PSL is proposed for quantifying stenoses, rather than the length of PSL.

Renal artery stenosis: value of screening with three-dimensional phase-contrast MR angiography with a phased-array multicoil.

To evaluate screening with three-dimensional (3D) phase-contrast magnetic resonance (MR) angiography with a phased-array multicoil to detect renal artery stenosis. Fifty consecutive patients suspected of having renovascular disease were prospectively examined with 3D phase-contrast MR imaging with a phased-array multicoil. Findings were correlated with those at intra-arterial digital subtraction angiography (DSA) as the standard of reference for grade of stenosis. MR angiography depicted 101 of 103 renal arteries depicted at intraarterial DSA; the two missed arteries were an accessory artery outside the imaging volume and an artery with a stent. At intraarterial DSA, a stenosis was found in 31 of 101 arteries. On the basis of findings at 3D phase-contrast MR angiography, the presence of any degree of stenosis was correctly depicted in 29 of 31 cases and the absence of stenosis was correctly depicted in 66 of 70 cases (accuracy, 94%; sensitivity, 94%; negative predictive value, 97%). Overall accuracy was 97% for correct depiction of severe renal artery stenosis (> 50%). 3D phase-contrast MR angiography with a phased-array multicoil was an accurate noninvasive screening technique in patients with suspected renal artery stenosis.

Role of 3D Display MR Angiography in the Study of Intracranial Aneurysms

This paper determines the usefulness of threedimensional (3D) phase-contrast (PC) magnetic resonance (MR) angiography with 3D display in characterizing large intracranial saccular aneurysms. Eight patients referred for non invasive confirmation of unruptured aneurysm (n=9) detected by conventional CT and/or MR imaging were studied by 3D PC (VENC of 20 cm/s, 3 axes) in axial acquisition localised on the circle of Willis using a 0.5 T unit (Vectra, GE). We used 3D display images to assess the feasibility of selective treatment. Results were correlated with catheter angiograms in 3 patients. In two thirds of the cases, location and size of the orifice, size of the sac, and clarification of parent artery were clearly provided allowing prediction of therapeutic management. In the remaining cases results remained doubful because of lack of spatial resolution. The benefit of the method was coupled with the clinical status of the patients to influence the final decision. 3D PC MR angiography with 3D display has emerged as an improvement in predicting therapeutic management, and is especially useful in large unruptured aneurysms in elderly or ill patients.

5309100 Flow measurement of incompressible fluid using divergence-free constraint

A method and apparatus to reduce the noise in three-dimensional phase contrast magnetic resonance velocity measurements exploits the property that blood is incompressible and therefore the velocity field describing its flow must be divergence-free. The divergence-free condition can be incorporated by the projection operation on Hilbert space where the velocity measurements are projected onto the space of divergence-free velocity fields. The reduction of noise is achieved since the projection operation eliminates the noise component that is not divergence-free. Higher quality angiograms are produced due to the noise reduction in the velocity measurement signals.

Comparison of three-dimensional phase-contrast magnetic resonance angiography with three-dimensional time-of-flight magnetic resonance angiography in cerebral aneurysms

Magnetic resonance angiography (MRA) can be divided into two types: namely, the phase-contrast (PC) method and the time-of-flight (TOF) method. The purpose of this study is to determine which method is better suited to demonstrate cerebral aneurysms. In a total of 27 cerebral aneurysms confirmed by cerebral angiography, both three-dimensional (3-D) PC and 3-D TOF methods were performed, and the corresponding findings were compared with conventional cerebral angiographic findings. Aneurysm visualization was grouped into three categories: “good” when clearly distinguishable, “fair” if distinguishable when reconstructed, and “poor” if completely undistinguishable. All MRAs were independently interpreted by two neurosurgeons in our institute. Sensitivity was 92.6% when MRA was performed with the TOF method, whereas it was 70.4% when performed with the PC method. In conclusion, the TOF method was more useful for demonstrating the aneurysms than the PC method due to its higher spatial resolution and shorter imaging time.

The anatomy of the posterior communicating artery as a risk factor for ischemic cerebral infarction.

After the occlusion of an internal carotid artery the principal source of collateral flow is through the arteries of the circle of Willis, but the size and patency of these arteries are quite variable. Study of the anatomy of the collateral pathways in patients with internal-carotid-artery occlusion with or without infarction in the watershed area of the deep white matter may identify patterns that afford protection from ischemic infarction. Using conventional magnetic resonance imaging and three-dimensional phase-contrast magnetic resonance angiography, we evaluated 29 consecutive patients (32 hemispheres at risk) with angiographically proved occlusion of the internal carotid artery. Four collateral pathways to the occluded vessel were evaluated: the proximal segment of the anterior cerebral artery, the posterior communicating artery, the ophthalmic artery, and leptomeningeal collateral vessels from the posterior cerebral artery. Only features of the ipsilateral posterior communicating artery were related to the risk of watershed infarction. The presence of posterior communicating arteries measuring at least 1 mm in diameter was associated with the absence of watershed infarction (13 hemispheres, no infarcts; P < 0.001). Conversely, there were 4 watershed infarcts in the 6 hemispheres with posterior communicating arteries measuring less than 1 mm in diameter and 10 infarcts in the 13 hemispheres with no detectable flow in the ipsilateral posterior communicating artery. A small (< 1 mm in diameter) or absent ipsilateral posterior communicating artery is a risk factor for ischemic cerebral infarction in patients with internal-carotid-artery occlusion.

Multichannel magnetoencephalographic mapping of sensorimotor cortex for epilepsy surgery.

Preliminary reports have shown a close correlation between the anatomic location of evoked magnetic somatosensory fields and intraoperative evoked somatosensory potentials in patients with mass lesions. We have performed magnetic source imaging (MSI) of sensory and motor (MER) evoked responses or fields on 4 patients with frontal convexity epileptic foci. The method involves (1) graphic overlaying of magnetoencephalography evoked field data and three-dimensional (3D) phase contrast magnetic resonance angiographic data on 3D MRI surface cortical renderings, and (2) correlating these data with intraoperative stimulation-mapped sensory and/or motor responses and local cortical venous anatomy. Our initial results indicate that the location of MSI evoked sensory data correlates closely with the results of intraoperative stimulation mapping. MSI MERs have tended to show a less discrete spatial topography, involving areas of cortex extending beyond the motor strip.

Assessment of renal artery stenosis by phase-contrast magnetic resonance angiography

Three-dimensional (3D) phase-contrast magnetic resonance angiography (MRA) and velocity-encoded cine magnetic resonance (VEC-MR) imaging were performed in 23 subjects to assess the severity of renal artery stenosis. MRA was used for detection of stenosis, demonstrating a sensitivity of 100% and a specificity of 80%; the severity of stenosis was overestimated in 33%. VEC-MR was used to quantify the renal flow oattern and was successful in 11 subjects. Mean blood flow of normal renal arteries (420 +- 107 ml/min) was significantly higher (P < 0.01) than mean blood flow of stenotic arteries (131 +- 46ml/min). The flow profile displayed both systolic and diastolic peaks in 75% of the normal arteries, while the flow in stenotic arteries showed only a single systolic peak in all cases. The systolic peak in stenotic arteries occurred significantly later (32 +- 3% of the period of one cardiac cycle) than in normal subjects (21 +- 7%) (P < 0.05). Phase-contrast MR is likely to gain considerable importance in the noninvasive aetection and quantification of renal artery stenosis.

Surgical clip artefact mimicking arterial stenosis: A problem with magnetic resonance angiography

In three patients undergoing three-dimensional phase contrast magnetic resonance angiography (MRA) for evaluation of renal transplant arteries, a convincing stenosis was demonstrated that was not present on conventional angiograms. In each patient there was a stainless steel surgical clip in the soft tissues adjacent to the renal artery. Although the clip artefact was easily recognized on the acquired tomographic magnetic resonance slices, it was completely indistinguishable from a true stenosis on the final projection images. This may limit the use of MRA in post-surgical vascular evaluation unless review is made of the phase contrast images.