Magnetic Resonance Angiography Data Research Articles

Highly accelerated contrast-enhanced MR angiography: Improved reconstruction accuracy and reduced noise amplification with complex subtraction

Contrast-enhanced magnetic resonance angiography is routinely performed using parallel imaging to best capture the first pass of contrast material through the target vasculature, followed by digital subtraction to suppress the appearance of unwanted signal from background tissue. Both processes, however, amplify noise and can produce uninterpretable images when large acceleration factors are used. Using a phantom study of contrast-enhanced magnetic resonance angiography, we show that complex subtraction processing prior to partially parallel reconstruction improves reconstruction accuracy relative to magnitude subtraction processing for reduction factors as large as 12. Time-resolved contrast-enhanced magnetic resonance angiographic data obtained with complex subtraction in volunteers supported the results of the phantom study and when compared with magnitude subtraction processing demonstrated reduced geometry factors as well as improved image quality at large reduction factors.

Lenticulostriate Arteries in Chronic Stroke Patients Visualised by 7 T Magnetic Resonance Angiography

Noninvasive magnetic resonance angiography using ultra-high-field magnetic resonance imaging has recently provided us with the potential to image cerebral microvascular structures such as the lenticulostriate arteries. However, most studies using ultra-high-field magnetic resonance angiography have been limited to the visualisation of microvessels in healthy subjects, and the direct comparison of patients with microvascular disease has not been reported. The aim of this study was to investigate the lenticulostriate arteries of patients with lacunar strokes of the basal ganglia and surrounding areas using 7 T magnetic resonance angiography. Ten stroke patients who had infarctions in the basal ganglia and adjacent areas detected using T2(*)-weighted images obtained from a conventional 1·5 T magnetic resonance imaging and 10 age-matched healthy subjects were recruited for this study. The large main vessels in the patient group were inspected to identify abnormalities such as stenosis. The characteristics of the lenticulostriate arteries visualised by 7 T magnetic resonance angiography, such as the number of branches and stems, curvature and tortuosity were analysed and compared between the patient and the control groups. All patients had infarctions in the basal ganglia and adjacent regions, which were clearly determined by T2(*)-weighted images. However, there was no evidence of large-vessel abnormalities in the patient group. Analysis of 7 T magnetic resonance angiography data revealed that the overall number of lenticulostriate arteries branches in the patient group was significantly less than the control group (P=0·003). However, no statistical difference in the number of stems, curvature and tortuosity between the two groups was found (P=0·396, 0·258 and 0·888, respectively). This study demonstrates that noninvasive magnetic resonance angiography using 7 T magnetic resonance imaging can visualise abnormalities in the cerebral microvasculature of stroke patients, and that the number of lenticulostriate arteries supplying the region of the basal ganglia is less in these patients compared with age-matched controls.

Endovascular Procedures with CTA and MRA Roadmapping

Prior to interventional neuroradiology procedures, many patients undergo noninvasive studies such as computed tomography angiography (CTA) and magnetic resonance angiography (MRA). The ability to use these studies during invasive neuroangiographic procedures reduces additional contrast and radiation exposure, and allows for the integration of extravascular imaging. Navigation roadmaps were created by merging CTA or MRA studies with 3-dimensional volumes in the angiography suite. Roadmaps were created for 3 patients undergoing interventional procedures, one of which used a noncontrasted rotational volume. Coregistration of CTA or MRA data with real-time angiographic imaging was successful in all 3 patients. Coregistration persisted despite table movement. These roadmaps were used to successfully navigate catheters and wires between vessels in 2 patients. Offline CTA and MRA studies were successfully combined with real-time imaging at the time of angiography. This technique can reduce radiation and iodinated contrast exposure, and expands the application of angiographic technology in cerebrovascular and other neurosurgical diseases.

Hybrid of Opposite-Contrast Magnetic Resonance Angiography of the Brain by Combining Time-of-Flight and Black Blood Sequences

We assessed the value of a new magnetic resonance angiography (MRA) technique named hybrid of opposite-contrast (HOP) MRA in the diagnosis of moyamoya disease. Using a dual-echo sequence, we obtained the first echo for time-of-flight (TOF) MRA followed by the second echo for black blood MRA. We then subtracted the black blood MRA data set from that of the TOF MRA followed by maximum-intensity projection. In 14 patients, we performed HOP MRA and compared the findings with those on 3-dimensional TOF MRA and MR images. The HOP MRA was also compared with a radionuclide perfusion study (7 patients). The HOP MRA technique improved the demonstration of distal arteries in 13 patients. The findings in HOP MRA correlated with MR images in 9 patients as well as with the perfusion study in 6 patients. The HOP MRA technique demonstrated the distal arterial branches in moyamoya disease well and facilitated the perfusion assessment with MR imaging.

Restoring three-dimensional magnetic resonance angiography images with mean curvature motion

Objective: The management of neurovascular disease requires precise information on the cerebral vascular anatomy. Digital subtraction angiography (DSA) is the gold standard against which other imaging modalities have to be measured. To improve the quality of three-dimensional (3D) magnetic resonance angiography (MRA) images, we present a novel concept in 3D image analysis.Methods: Five patients, harboring cerebral aneurysm, underwent DSA, computed tomography angiography (CTA) and MRA. MRA data were processed using a novel anisotropic curvature motion model. Three-dimensional reconstructions of CTA and MRA datasets were used for comparison.Results: The 3D-reconstructed images accurately displayed all aneurysms. The anatomy of the anterior part of the circle of Willis was visualized reliably. The smoothened vessel surfaces enhanced the readability of the images. Regarding visual representation of the posterior part of the circle of Willis, the post-processed MRA showed the arterial segments less accurate than the standard modalities.Conclusions: This new approach is a promising tool for planning of neurovascular interventions and preoperative evaluation.

BLOOD FLOW IMAGING

The objective of this study was to investigate the clinical applicability of navigated blood flow imaging (BFI) in neurovascular applications. BFI is a new 2-dimensional ultrasound modality that offers angle-independent visualization of flow. When integrated with 3-dimensional (3D) navigation technology, BFI can be considered as a first step toward the ideal tool for surgical needs: a real-time, high-resolution, 3D visualization that properly portrays both vessel geometry and flow direction. A 3D model of the vascular tree was extracted from preoperative magnetic resonance angiographic data and used as a reference for intraoperative any-plane guided ultrasound acquisitions. A high-end ultrasound scanner was interconnected, and synchronized recordings of BFI and 3D navigation scenes were acquired. The potential of BFI as an intraoperative tool for flow visualization was evaluated in 3 cerebral aneurysms and 3 arteriovenous malformations. The neurovascular flow direction was properly visualized in all cases using BFI. Navigation technology allowed for identification of the vessels of interest, despite the presence of brain shift. The surgeon found BFI to be very intuitive compared with conventional color Doppler methods. BFI allowed for quality control of sufficient flow in all distal arteries during aneurysm surgery and made it easier to discern between feeding arteries and draining veins during surgery for arteriovenous malformations. BFI seems to be a promising modality for neurovascular flow visualization that may provide the neurosurgeon with a valuable tool for safer surgical interventions. However, further work is needed to establish the clinical usefulness of the proposed imaging setup.

Effect of Curvature on Displacement Forces Acting on Aortic Endografts: A 3-Dimensional Computational Analysis

To determine the effect of curvature on the magnitude and direction of displacement forces acting on aortic endografts in 3-dimensional (3D) computational models. A 3D computer model was constructed based on magnetic resonance angiography data from a patient with an infrarenal aortic aneurysm. Computational fluid dynamics tools were used to simulate realistic flow and pressure conditions of the patient. An aortic endograft was deployed in the model, and the displacement forces acting on the endograft were calculated and expressed in Newtons (N). Additional models were created to determine the effects of reducing endograft curvature, neck angulation, and iliac angulation on displacement forces. The aortic endograft had a curved configuration as a result of the patient's anatomy, with curvature in the anterolateral direction. Total displacement force acting on the endograft was 5.0 N, with 28% of the force in a downward (caudal) direction and 72% of the force in a sideways (anterolateral) direction. Elimination of endograft curvature (planar graft configuration) reduced total displacement force to 0.8 N, with the largest component of force (70%) acting in the sideways direction. Straightening the aortic neck in the curved endograft configuration reduced the total force acting on the endograft to 4.2 N, with a reduction of the sideways component to 55% of the total force. Straightening the iliac limbs of the endograft reduced the total force acting on the endograft to 2.1 N but increased the sideways component to 91% of the total force. The largest component of the force acting on the aortic endograft is in the sideways direction, with respect to the blood flow, rather than in the downward (caudal) direction as is commonly assumed. Increased curvature of the aortic endograft increases the magnitude of the sideways displacement force. The degree of angulation of the proximal and distal ends of the endograft influence the magnitude and direction of displacement force. These factors may have a significant influence on the propensity of endografts to migrate in vivo.

Partial Anomalous Left Pulmonary Artery

A 4-year-old girl with Kabuki syndrome was evaluated and diagnosed with an atrial septal defect on the basis of an abnormal cardiac physical examination. A chest radiograph was performed, which demonstrated multiple skeletal abnormalities and mild prominence of the pulmonary vasculature consistent with an atrial septal defect (Figure 1). A complete echocardiogram was performed under sedation, which demonstrated the atrial septal defect as well as dual pulmonary arterial supply to the left lung with a partial anomalous left pulmonary artery (LPA) from the right pulmonary artery (RPA) (Figure 2). Cardiac magnetic resonance (MR) imaging was performed to further delineate pulmonary arterial anatomy as well as possible tracheal compression from the partial anomalous LPA. Figure 1. Chest radiograph in the anteroposterior projection demonstrates irregularity of the right clavicle with separation of the hypoplastic distal half (arrowhead), butterfly vertebrae of T11 (arrow), absence of the left twelfth rib (asterisk), mild prominence of the pulmonary vasculature, and a normal cardiac silhouette. Figure 2. High parasternal short-axis echocardiogram with color compare shows the partial anomalous LPA (ALPA) arising from the RPA. AAo indicates ascending aorta; MPA, main pulmonary artery; and DRPA, distal RPA. A complete cardiac MR study was performed including gadolinium-enhanced MR angiography. The 3-dimensional reconstructed MR angiography data set demonstrates that the left lung receives blood supply from 2 left pulmonary arteries. One of …

Limitation of Brachial-Ankle Pulse Wave Velocity in Assessing the Risk of Stroke: Importance of Instantaneous Blood Pressure

Background and Objective: The carotid-femoral pulse wave velocity is a well-established index of aortic stiffness, and the brachial-ankle pulse wave velocity (baPWV) has recently been developed as a new method for evaluating arterial stiffness. However, whether the baPWV is also useful in evaluating the risk of stroke is currently controversial. Moreover, it is also unknown which types of stroke and neuroradiological findings are associated with increased arterial stiffness. We investigated the association between the baPWV and risk of stroke using a case-control design. Methods: This study enrolled 223 stroke patients (aged 65.6 ± 10.3 years, mean ± SD) and the same number of age- and sex-matched controls. All of the subjects in this study underwent a structured interview and had their vascular risk factors assessed. We reviewed brain magnetic resonance imaging and magnetic resonance angiography data of stroke patients to assessthe severity of white-matter hyperintensity lesions, number of cerebral microbleeds, and the stenosis of both intracranial and extracranial arteries. The baPWV was measured noninvasively by an oscillometric method. Results: The baPWV was most affected by the instantaneous systolic blood pressure, and was significantly higher in stroke patients than control subjects (1,721 ± 395 cm/s vs. 1,657 ± 366 cm/s, p = 0.03). However, the baPWV did not differ significantly with a specific type of stroke or subtype of ischemic stroke. Multiple regression analysis revealed that the baPWV was not independently associated with increased risk of stroke, or the severity of white-matter hyperintensity lesions or cerebral microbleeds. Conclusion: Although the baPWV was significantly higher in stroke patients than control subjects, it was not independently associated with increased risk of stroke or specific subtypes of ischemic stroke or neuroradiological findings.

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Fusion imaging of magnetic resonance angiography (MRA) and MR imaging (MRI) is valuable to assess the location of the horizontal portion of the middle cerebral artery (MCA), MC bifurcation aneurysm (AN) and limen insulae. In this study, we evaluated the usefulness of fusion imaging in MC bifurcation aneurysm surgery. Between October 2007 and February 2008, 18 patients underwent clipping for unruptured MC bifurcation ANs at the authors’ institution. Preoperatively, 3DFSPGR MRI and 3DSPGR MRA data were fused. The distance of limen insulae and distal end of the horizontal portion of MCA were calculated. The mean distance in 9 distal approaches was ＋4.3±1.8 mm and －7.2±6.3 mm in 9 superior approaches, respectively. Preoperative simulation images were coincident with operative findings in all cases. Fusion images of MRA and MRI are useful for planning the treatment of unruptured MCA ANs.

Numerical Simulations of Flow in Cerebral Aneurysms: Comparison of CFD Results and In Vivo MRI Measurements

Computational fluid dynamics (CFD) methods can be used to compute the velocity field in patient-specific vascular geometries for pulsatile physiological flow. Those simulations require geometric and hemodynamic boundary values. The purpose of this study is to demonstrate that CFD models constructed from patient-specific magnetic resonance (MR) angiography and velocimetry data predict flow fields that are in good agreement with in vivo measurements and therefore can provide valuable information for clinicians. The effect of the inlet flow rate conditions on calculated velocity fields was investigated. We assessed the internal consistency of our approach by comparing CFD predictions of the in-plane velocity field to the corresponding in vivo MR velocimetry measurements. Patient-specific surface models of four basilar artery aneurysms were constructed from contrast-enhanced MR angiography data. CFD simulations were carried out in those models using patient-specific flow conditions extracted from MR velocity measurements of flow in the inlet vessels. The simulation results computed for slices through the vasculature of interest were compared with in-plane velocity measurements acquired with phase-contrast MR imaging in vivo. The sensitivity of the flow fields to inlet flow ratio variations was assessed by simulating five different inlet flow scenarios for each of the basilar aneurysm models. In the majority of cases, altering the inlet flow ratio caused major changes in the flow fields predicted in the aneurysm. A good agreement was found between the flow fields measured in vivo using the in-plane MR velocimetry technique and those predicted with CFD simulations. The study serves to demonstrate the consistency and reliability of both MR imaging and numerical modeling methods. The results demonstrate the clinical relevance of computational models and suggest that realistic patient-specific flow conditions are required for numerical simulations of the flow in aneurysmal blood vessels.

“TARGET BYPASS”

To introduce a method for preoperative targeting of a proper recipient artery in superficial temporal artery-to-middle cerebral artery anastomosis. Six operations for superficial temporal artery-to-middle cerebral artery anastomosis in four patients with moyamoya disease or moyamoya-like disease and two operations in two patients with atherosclerotic cerebrovascular occlusive disease accompanied by coronary artery stenosis were performed using our method. Before surgery, a 3-Tesla magnetic resonance imaging study was performed with axial T1-weighted three-dimensional magnetization-prepared rapid acquisition gradient-echo sequences and three-dimensional time-of-flight magnetic resonance angiography. Data on quantitative regional cerebral blood flow were obtained by iodine-123-labeled N-isopropyl-iodoamphetamine single-photon emission computed tomography or positron emission computed tomography. The magnetic resonance angiography and regional cerebral blood flow data sets were registered with the magnetization-prepared rapid acquisition gradient-echo data set by means of the coregistration function of the SPM2 software. We examined the arteries located on or near the cortex where the regional cerebral blood flow had significantly decreased and used the coregistered data set and MRIcro software to select the cortical artery with the largest diameter as the target recipient artery. At the surgery, the data sets were applied to the neuronavigation system and the actual site of the target was confirmed in the operation before scalp incision. The superficial temporal artery was anastomosed with the target through a small craniotomy. Successful bypass surgery to the target was confirmed in all cases. The "target bypass" method might be effective for cases with moyamoya disease or for cases requiring surgery through a small craniotomy.

Vasculature Segmentation in MRA Images Using Gradient Compensated Geodesic Active Contours

Precise segmentation of vasculature from three-dimensional (3D) magnetic resonance angiography (MRA) images is playing an important role in image-guided neurosurgery, pre-operation planning and clinical analysis. Active Contour based evolution algorithms are being widely applied to MRA data sets, however existing approaches exhibit some difficulties in extracting tiny parts of the vessels. Our objective is to develop an automated segmentation scheme to accurately extract vasculature of the brain, especially tiny vessels. Inspired by the intrinsic properties of MRA, we have proposed a scheme called the gradient compensated geodesic active contours (GCGAC), which compensates for low gradients near edges of thin vessels. The GCGAC, which is implemented based on level set, has been tested on both synthetic volumetric image and real 3D MRA images. Our experiments show that the introduced gradient compensation can facilitate more accurate segmentation of tiny blood vessels.

Transstenotic Pressure Gradients: Measurement in Swine—Retrospectively ECG-gated 3D Phase-Contrast MR Angiography versus Endovascular Pressure-sensing Guidewires

To prospectively evaluate the hypothesis that retrospectively electrocardiographically gated phase contrast with vastly undersampled isotropic projection reconstruction (VIPR) magnetic resonance (MR) angiography data sets can be used to measure transstenotic pressure gradients (TSPGs) in vivo. TSPGs were calculated by using phase-contrast VIPR MR angiography data sets; measurements obtained with a pair of endovascular pressure-sensing guidewires served as a reference standard. With institutional animal care and use committee approval, 12 swine underwent surgical creation of stenoses at the left common carotid, right renal, and left external iliac arteries. The percentage stenosis and reference diameter of the lesions were calculated from conventional digital subtraction angiograms. A pair of 0.014-inch pressure-sensing guidewires was placed in tandem; sensors 1 cm distal and 1 cm proximal to the lesions measured the mean TSPG. Phase-contrast VIPR phase difference images were analyzed with an iterative technique based on the Navier-Stokes equations to determine the mean TSPG. Pearson product correlation was calculated, and Bland-Altman plots were generated to determine the degree of agreement between the two methods. Twenty-one lesions (12 carotid, nine iliac; mean percentage stenosis, 52.4%; range, 29.8%-64.9%; mean reference diameter, 3.4 mm; range, 2.4-5.6 mm) were analyzed. For carotid and iliac lesions, phase-contrast VIPR and guidewire TSPG measurements were highly correlated (r = 0.952, P < .001). Bland-Altman plots (bias, 0.86 mm Hg; limits of agreement: -6.17 to 7.88 mm Hg) showed good agreement. Measurements in renal lesions (n = 9) were poorly correlated (r = -0.081, P = .835) and were excluded because of image degradation secondary to respiratory motion. Phase-contrast MR angiography with VIPR enables reliable measurements of TSPG in carotid and iliac lesions that are comparable to those obtained with endovascular pressure-sensing guidewires. However, further work to compensate for respiratory motion is required to extend this technique to the renal arteries.

Preoperative Evaluation of Potential Living Related Kidney Donors with High-Spatial-Resolution Magnetic Resonance (MR) Angiography at 3 Tesla

The purpose of this prospective study was to determine the feasibility and accuracy of high-spatial-resolution MR imaging at 3 Tesla (T) in the preoperative evaluation of potential living related kidney donors. Eighteen potential donors (8 men, 10 women; mean age, 50.1 +/- 14.2 years) for renal transplantation were evaluated with 3 T MR imaging. A high-spatial-resolution 3-dimensional (3D) gradient-echo MR angiography (repetition time/echo time, 3.0/1.14 ms; flip, 19-23 degrees; matrix, 512; slice thickness, 1.0 mm) using parallel acquisition technique (GRAPPA) with an acceleration factor of 3 was performed on a whole body scanner. Images were evaluated in a prospective and blinded fashion by 2 MR radiologists. The number of renal arteries, presence of early branches (defined as a branch arising within 2 cm of the main renal ostium), and renal artery stenosis were analyzed. The renal parenchyma, collecting system and ureters, were evaluated on the MR urograms. Interpretation of MR images were compared with surgical findings. Based on MR angiography data sets, a total of 36 main and 9 accessory renal arteries was found. There were 5 renal arteries presenting an early branching (<or=2 cm). The correct venous anatomy was identified in 13 of 14 patients (93%), including a single left renal vein anterior to the aorta (n = 3), retroaortic left renal vein (n = 2), and single right renal vein (n = 9). A single collecting system in all harvested kidneys was identified correctly with MR imaging. Overall, the sensitivity and positive predictive value of MRI in correctly determining the vascular and parenchymal anatomy in the harvested kidney was 85% and 93%, respectively. High-spatial-resolution contrast-enhanced MR angiography at 3 T can predict successful donor nephrectomy in potential living related kidney donors.

Gamma knife surgery for arteriovenous malformations in the brain: integration of time-resolved contrast-enhanced magnetic resonance angiography into dosimetry planning

Object The aim of this study was to develop an algorithm for the integration of time-resolved contrast-enhanced magnetic resonance (MR) angiography into dosimetry planning for Gamma Knife surgery (GKS) of arteriovenous malformations (AVMs) in the brain. Methods Twelve patients harboring brain AVMs referred for GKS underwent intraarterial digital subtraction (DS) angiography and time-resolved MR angiography while wearing an externally applied cranial stereotactic frame. Time-resolved MR angiography was performed on a 1.5-tesla MR unit (Achieva, Philips Medical Systems) using contrast-enhanced 3D fast field echo sequencing with stochastic central k-space ordering. Postprocessing with interactive data language (Research Systems, Inc.) produced hybrid data sets containing dynamic angiographic information and the MR markers necessary for stereotactic transformation. Image files were sent to the Leksell GammaPlan system (Elekta) for dosimetry planning. Results Stereotactic transformation of the hybrid data sets containing the time-resolved MR angiography information with automatic detection of the MR markers was possible in all 12 cases. The stereotactic coordinates of vascular structures predefined from time-resolved MR angiography matched with DS angiography data in all cases. In 10 patients dosimetry planning could be performed based on time-resolved MR angiography data. In two patients, time-resolved MR angiography data alone were considered insufficient. The target volumes showed a notable shift of centers between modalities. Conclusions Integration of time-resolved MR angiography data into the Leksell GammaPlan system for patients with brain AVMs is feasible. The proposed algorithm seems concise and sufficiently robust for clinical application. The quality of the time-resolved MR angiography sequencing needs further improvement.

Gamma knife surgery for arteriovenous malformations in the brain: integration of time-resolved contrast-enhanced magnetic resonance angiography into dosimetry planning

The aim of this study was to develop an algorithm for the integration of time-resolved contrast-enhanced magnetic resonance (MR) angiography into dosimetry planning for Gamma Knife surgery (GKS) of arteriovenous malformations (AVMs) in the brain. Twelve patients harboring brain AVMs referred for GKS underwent intraarterial digital subtraction (DS) angiography and time-resolved MR angiography while wearing an externally applied cranial stereotactic frame. Time-resolved MR angiography was performed on a 1.5-tesla MR unit (Achieva, Philips Medical Systems) using contrast-enhanced 3D fast field echo sequencing with stochastic central k-space ordering. Postprocessing with interactive data language (Research Systems, Inc.) produced hybrid data sets containing dynamic angiographic information and the MR markers necessary for stereotactic transformation. Image files were sent to the Leksell GammaPlan system (Elekta) for dosimetry planning. Stereotactic transformation of the hybrid data sets containing the time-resolved MR angiography information with automatic detection of the MR markers was possible in all 12 cases. The stereotactic coordinates of vascular structures predefined from time-resolved MR angiography matched with DS angiography data in all cases. In 10 patients dosimetry planning could be performed based on time-resolved MR angiography data. In two patients, time-resolved MR angiography data alone were considered insufficient. The target volumes showed a notable shift of centers between modalities. Integration of time-resolved MR angiography data into the Leksell GammaPlan system for patients with brain AVMs is feasible. The proposed algorithm seems concise and sufficiently robust for clinical application. The quality of the time-resolved MR angiography sequencing needs further improvement.

Juvenile and Adult Congenital Heart Disease: Time-resolved 3D Contrast-enhanced MR Angiography

To assess the incremental diagnostic value of time-resolved three-dimensional (3D) magnetic resonance (MR) angiography over single-phase 3D MR angiography and cine MR imaging in juvenile and adult patients with congenital heart disease (CHD). The study was HIPAA compliant and was approved by the institutional review board. Written informed consent was obtained from each patient. Eighty-one consecutive patients (46 male and 35 female patients; mean age, 31.1 years +/- 13.5 [standard deviation]) with CHD were examined with a 1.5-T MR imaging unit. The imaging protocol comprised time-resolved MR angiography (repetition time msec/echo time msec, 2.01/0.81) after injection of 0.03 mmol gadodiamide per kilogram of body weight at 4 mL/sec and single-phase high-spatial-resolution MR angiography (2.87/0.97) after injection of 0.15 mmol/kg gadodiamide at 1.5 mL/sec. After review of the time-resolved and conventional MR angiographic data sets, each of two independent observers listed the additional clinical information gained from time-resolved MR angiographic data. A Wilcoxon signed rank test was used to test for statistical differences between the image quality ratings of the two observers. Time-resolved and single-phase high-spatial-resolution MR angiography yielded diagnostic image data in all patients. Observers 1 and 2 found functional information in time-resolved MR angiographic series in 52 and 51 patients, respectively, that was not seen at high-spatial-resolution MR angiography. Intra- and extracardiac shunts, respectively, were exclusively depicted by time-resolved MR angiography for observer 1 in 18 and two patients and for observer 2 in 15 and two patients. However, both observers reported higher confidence in the assessment of such smaller vascular structures as supraaortic vessels (in 12 patients for observer 1 and 11 patients for observer 2) and major aortopulmonary collateral arteries (in eight patients for observer 1 and 10 patients for observer 2) at high-spatial-resolution MR angiography. No significant difference was evident in image quality scoring between the two observers (P = .32 for time-resolved and P = .47 for conventional MR angiography). Compared with conventional MR angiography, time-resolved MR angiography yields clinically relevant information in a substantial number of patients; hence, the two techniques should be regarded as complementary.

Simplified skipped phase encoding and edge deghosting (SPEED) for imaging sparse objects with applications to MRA

The fast imaging method named skipped phase encoding and edge deghosting (SPEED) has been demonstrated to reduce scan time considerably with typical magnetic resonance imaging data. In this work, SPEED is simplified with improved efficiency to accelerate the scan of sparse objects; we refer to this method as S-SPEED. S-SPEED partially samples k-space into two interleaved data sets, each with the same skip size of N but a different relative shift in phase encoding. The sampled data are then Fourier transformed into two ghosted images with N aliasing ghosts. Given the sparseness of signal distribution, the ghosted images are simply modeled with a single-layer structure, analogous to that used in maximum-intensity projection. With an algorithm based on a least-square-error solution, a deghosted image is solved, and a residual map is output for quality control. S-SPEED can be generalized to include more layers with additional acquisitions for refined results. Without differential filtering and full central k-space sampling, S-SPEED reduces scan time further and achieves more straightforward reconstruction, as compared with SPEED. In this work, S-SPEED is applied to accelerate magnetic resonance angiography (MRA) by taking advantage of the sparse nature of MRA data. With sparse phantom data and in vivo phase contrast MRA data, S-SPEED is demonstrated to achieve satisfactory results with an acceleration factor of 5.5 using a single coil.

Methods for Three-Dimensional Geometric Characterization of the Arterial Vasculature

Complex vascular anatomy often affects endovascular procedural outcome. Accurate quantitative assessment of three-dimensional (3D) in-vivo arterial morphology is therefore vital for endovascular device design, and preoperative planning of percutaneous interventions. The aim of this work was to establish geometric parameters describing arterial branch origin, trajectory, and vessel curvature in 3D space that eliminate the errors implicit in planar measurements. 3D branching parameters at visceral and aortic bifurcation sites, as well as arterial tortuosity were determined from vessel centerlines derived from magnetic resonance angiography data for three subjects. Errors in coronal measurements of 3D branching angles for the right and left renal arteries were 3.1 +/- 3.4 degrees and 7.5 +/- 3.7 degrees , respectively. Distortion of the anterior visceral branching angles from sagittal measurements was less pronounced. Asymmetry in branching and planarity of the common iliac arteries was observed at aortic bifurcations. The renal arteries possessed considerably greater 3D curvature than the abdominal aorta and common iliac vessels with mean average values of 0.114 +/- 0.015 and 0.070 +/- 0.019 mm(-1) for the left and right, respectively. In conclusion, planar projections misrepresented branch trajectory, vessel length, and tortuosity proving the importance of 3D geometric characterization for possible applications in planning of endovascular interventional procedures and providing parameters for endovascular device design.