Image Acquisition Technique and Sequences Contrast-Enhanced MRA
Although MR angiography (MRA) can be performed using either black-blood or bright blood, wich have the disvantage of high sensitive to flow related-artifacts, in-plane saturation, and field inhomogeneity, and are also limited by the long acquisition times
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CONTENTS
ABSTRACT 3.1
Introduction
3.2
Basic Principle of CE-MRA
3.3
Contrast Administration Strategy
3.4 3.4.1 3.4.2 3.4.3 3.4.4
Imaging and Acquisition Technique Fast 3D Gradient Echo Sequences and Acquisition Technique 19 Parallel Imaging 21 Time-Resolved CE-MRA 21 Steady-State Imaging 21
3.5
k-Space Filling Strategies
3.6
Conclusions 25
References
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Marco Francone, MD, PhD Michele Anzidei, MD Ilaria Iacucci, MD Francesco Vullo, MD Carlo Catalano, MD Department of Radiology, University of Rome “La Sapienza,” Policlinico Umberto I, viale Regina Elena 324, 00161 Roma, Italy
Although MR angiography (MRA) can be performed using either black-blood or bright blood, wich have the disvantage of high sensitive to flow related-artifacts, in-plane saturation, and field inhomogeneity, and are also limited by the long acquisition times. Currently, the use of contrast medium for imaging of most vascular districts, agrees to obtain images of high diagnostic accuracy, that can be acquired in seconds rather than minutes with few flow-related artifacts. Such introduction explains the reason, Currently, MR angiography has proven to be the best approach for imaging of most vascular districts is the use of contrast-enhanced (CE-MRA), offering the opportunity to detect vascular disease rapidly and early in the course of the disease. CE-MRA is based on the principle of shortening the T1 relaxation of blood by intravenously injecting Gd-chelate contrast agents, wich results in a significant difference in signal intensity between flowing blood and stationary tissue, in T1 arterial or venous phase. Further advantage is shorter scan duration. Contrast administration should be optimized in order to concentrate the highest amount of gadolinium in the acquisition temporal window within district of interest, and imaging should be ideally performed at the peak of vascular enhancement, when a maximum difference exists between signal intensity of the target vessel and the surrounding overlapping structures. Three different techniques are currently available for this purpose: the test bolus scan, the automated bolus detection, and the MR fluoroscopic trigger.
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M. Francone, M. Anzidei, I. Iacucci et al.
Obviously, to deliver the best contrast, k-space center-filling must correspond to the moment of peak intravascular contrast; for this purpose, the acquisition of central k-space data is timed to the contrast bolus arrival within the target vessels The sequences best suited to CE-MRA imaging are: ● Fast 3D-GRE sequences (e.g., spoiled gradient echo SPGR-General Electric Medical Systems, Waukesha, WI); fast low-angle shot FLASH-Siemens Medical), used to obtain high spatial resolution and a good signal-to-noise. ● Parallel imaging that results in accelerated image acquisition while maintainingfull spatial resolution and image contrast. ● Time-resolved CE-MRA acquisition techniques, providing dynamic information along with highresolution, extended anatomical coverage, and without contamination by the venous signal.
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