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Yiping P. Du¹, Zhaoyang Jin², ³

¹University of Colorado Denver School of Medicine, Aurora, Colorado , USA; ²Hangzhou Dianzi University, Hangzhou, People's Republic of China; ³Zhejiang University, Hangzhou, People's Republic of China

A dual-echo pulse sequence has been developed for simultaneous acquisition of MR angiography and venography (MRAV). The acquisition of a second echo for susceptibility-weighted imaging (SWI) based MR venography (MRV) is added to the conventional 3D time-of-flight MR angiography (MRA) pulse sequence. Using this dual-echo acquisition approach, the MRV data can be acquired without increasing the TR and, therefore, scan time in routine MRA scans at 3 Tesla. Brain scans have been used to demonstrate the feasibility of simultaneous acquisition of MRAV.

Julia V. Velikina¹, Kevin Johnson, Yijing Wu, Patrick Turski, Charles Mistretta

¹University of Wisconsin - Madison, Madison, Wisconsin, USA

We propose a novel method, PC HYPR Flow, that combines the benefits of rapid three dimensional radial acquisition and HYPR reconstruction to obtain a time series of 3D images with isotropic submillimeter spatial resolution, subsecond temporal resolution, and high SNR. PC HYPR Flow consists of a contrast enhanced exam immediately followed by a phase contrast scan that is used to constrain the reconstruction of the time series and to provide additional physiological information about the hemodynamics. We explore the feasibility of the new technique in a series of in vivo exams in healthy subjects and patients with brain arterio-venous malformations. The temporal resolution of PC HYPR Flow is studied in phantom experiments.

Hyun Jeong¹, Timothy John Carroll¹, ², Christopher Getch¹, Christpher S. Eddleman¹, Mark A. Griswold³

¹Northwestern University, Chicago, Illinois, USA; ²Chicago , Illinois, USA; ³Case Western Reserve University, Cleveland, Ohio, USA

HYPR increases SNR of MRA images, but also introduces cross-talk and artifacts in the images.  Conjugate-gradient HYPR is an algorithm to iteratively correct the image errors resulting from HYPR.  Temporal profiles of HYPR, CG HYPR, and MRA without HYPR were studied.  The images were taken from angiographically confirmed AVM patients, which were correlated with XRA.

Tokunori Kimura¹, Masato Ikedo¹, Syuhei Takemoto²

¹Toshiba Medical Systems, Otawara, Japan; ²Toshiba Medical Systems, Tokyo, Japan

We proposed a novel MR angiography technique named Hybrid-MRA (HMRA) with 3D dual-echo gradient echo sequence combined Time-of-Flight (TOF) with Flow-Sensitive Black-Blood (FSBB) employed flow dephasing gradients. HMRA images were simply obtained with the maximum intensity projection (MIP) after weighted subtraction of original images of TOF and FSBB with or without high-pass filtering. We demonstrated that slower and narrower vessels such as collateral were visualized better by HMRA than the standard TOF-MRA with and without MTC pulses. HMRA technique will provide clinically additional information about slower vessels which is hard to be visualized by current TOF-MRA.

David Saloner¹, ², Loic Boussel¹, Vitaliy L. Rayz¹, Joseph R. Leach¹, Alastair J. Martin³, Gabriel Acevedo-Bolton¹, Randall T. Higashida³, Michael T. Lawton³, William L. Young³

¹VA Medical Center, San Francisco, USA; ²University of California San Francisco, San Francisco, USA; ³University of California San Francisco, USA

CE-MRA was used to monitor aneurysm growth over time in patients with untreated aneurysms.   Computational Fluid Dynamics models were constructed using the CE-MRA boundary conditions together with values of inlet and outlet flow as measured by PC-MRI. Serial studies were co-registered using internal fiducials. Areas of lumenal growth were correlated with hemodynamic descriptors extracted from the numerical simulations, and increased growth was noted at locations of low wall shear stress.  This study demonstrates the ability to base patient-specific determination of hemodynamic factors on MR methods, and to correlate those factors with volume changes as assessed by MRA.

Dariusch Reza Hadizadeh¹, Jürgen Gieseke¹, ², Guido Kukuk¹, Liesbeth Geerts², Gabriele Beck², Hans Heinz Schild¹, Winfried Albert Willinek¹

¹University of Bonn, Bonn, Germany; ²Philips Medical Systems, Best, Netherlands

Adequate diagnosis and treatment of cerebral arteriovenous malformations (cAVM) requires detailed characterization of both angioarchitecture and hemodynamics. In previous studies, a combination of CENTRA, Keyhole, parallel imaging (SENSE) and partial Fourier allowed for high temporal resolution 4D contrast-enhanced MRA at 3.0T. The addition of view sharing for further acceleration and increase of spatial resolution was evaluated in 11 subjects including 2 patients with cAVM and DSA correlation. 4D CEMRA with additional view sharing at 3.0T allowed for further increase in temporal and spatial resolution and clear depiction of arterial and venous phases without additional artefacts or decline in image quality.

Stephan Meckel¹, Aurélien F. Stalder², Francesco Santini¹, Ernst-Wilhelm Radü¹, Klaus Scheffler¹, Michael Markl², Stephan G. Wetzel¹

¹University Hospital Basel, Basel, Switzerland; ²University Hospital Freiburg, Freiburg, Germany

Blood-flow patterns and wall shear stress (WSS) are assumed to play a major role in development and rupture of cerebral aneurysms. To date, these hemodynamic aspects have been extensively studied in-vitro using geometric realistic aneurysm models. The purpose of this study was to evaluate the feasibility of in-vivo flow-sensitized 4D MR imaging for the visualization and quantification of intra-aneurismal hemodynamics. 5 cerebral aneurysms, differing in size, shape and location, were examined using flow-sensitized 4D MR imaging at 3T in 3 patients. 3D postprocessing was performed with a dedicated, commercially available, software package combined with an in-house software tool. This included quantification of flow-velocities, visualization of time-resolved 2D vector graphs and 3D particle traces, vortex core localization, and WSS estimations from 3D velocity fields. Flow patterns were analyzed in relation to aneurysm geometry and aspect ratio (aneurysm depth/neck width). Strength, spatial and temporal evolution of vortical flow patterns differed markedly among all aneurysms. Particularly unstable vortical flow was demonstrated in a wide-necked parophthalmic ICA aneurysm (high aspect ratio). Relatively stable vortical flow was observed in aneurysms with lower aspect ratio. Except for a wide-necked cavernous ICA aneurysm (low aspect ratio), WSS was reduced in all aneurysms relative to the parent artery and showed a high spatial variation. In conclusion, in-vivo flow-sensitized 4D MR imaging can be applied to visualize and quantify blood flow patterns and to estimate WSS inside cerebral aneurysms. Flow patterns, distribution of flow velocities, and WSS seem to be determined by the vascular geometry of the aneurysm.

Christoph Moenninghoff¹, ², Stefan Maderwald¹, ², Jens M. Theysohn¹, ², Susanne C. Ladd¹, ², Oliver Kraff¹, ², Mark E. Ladd¹, ², Elke R. Gizewski¹, ², Michael Forsting¹, ², Isabel Wanke¹, ²

¹University Hospital Essen, Essen, Germany; ²University Duisburg-Essen, Essen, Germany

Time-of-Flight (TOF) MR angiography is the most frequently used MR technique for assessment of intracranial aneurysms. Highfield MRI is known to improve vessel-to-tissue contrast of TOF MRA. This is the first prospective study including ten patients with twelve unruptured intracranial aneurysms examined by 7T, 1.5T TOF MRA and conventional angiography. Two blinded neuroradiologists rated the image quality of aneurysms. 7T TOF MRA superiorly depicted the aneurysm dome in 58% and the aneurysm neck in 50% of twelve aneurysms in comparison to 1.5T MRA. New head coils and parallel imaging techniques are expected to further improve image quality of TOF MRA.

Jaco J.M. Zwanenburg¹, Fredy Visser², Taro Takahara¹, Jeroen Hendrikse¹, Peter Luijten¹

¹University Medical Center Utrecht, Utrecht, Netherlands; ²Philips Medical Systems, Best, Netherlands

This work shows that it is possible to visualize the lenticulostriate arteries (diameters 0.3 - 0.7 mm) using MRI at 7 Tesla, without a contrast agent. A straightforward time-of-flight sequence was used, with optimized planning to maximize the inflow effect and decrease the saturation of the blood in the distal internal carotid artery.

Cornelius von Morze¹, ², Derk D. Purcell¹, Suchandrima Banerjee¹, ², Duan Xu¹, Douglas AC Kelley, Pratik Mukherjee¹, ², Sharmila Majumdar¹, ², Daniel B. Vigneron¹, ²

¹UCSF, San Francisco, USA; ²UCSF/UCB Joint Graduate Group in Bioengineering, San Francisco, USA

Higher spatial resolution intracranial 3D TOF MRA is possible at higher field strengths, due to the increased CNR. However, at very high fields, spatial resolution is limited by the acquisition time required for sequential phase encoding. We applied a custom autocalibrating GRAPPA-based reconstruction to 7T TOF MRA studies of normal volunteers and patients with vascular disease, in order to obtain very high resolution (0.146mm3) images within a reasonable scan time. This technique produced high resolution MRA studies free from artifacts in all subjects, and correctly identified vascular pathology in patients.