Artifacts and Limitations
Magnetic resonance angiography (MRA) has emerged as a noninvasive technique for evaluating patients with different vascular diseases. However, with the standard two-dimensional (2D) time-of-flight (TOF) technique there are many difficulties in detecting s
- PDF / 2,949,063 Bytes
- 14 Pages / 547.08 x 765.36 pts Page_size
- 36 Downloads / 266 Views
CONTENTS 12.1 12.2 12.2.1 12.2.2 12.2.3 12.2.4 12.3 12.4 12.4.1 12.4.2 12.4.3 12.4.4 12.4.5 12.4.6 12.4.7 12.4.8 12.4.9 12.4.10 12.5
Introduction 167 General Artifacts 167 Motion, Breathing, Peristalsis, and Pulsation Hematoma 169 Slab Placement 169 Postprocessing 169 Artifacts of Non-Contrast-Enhanced MR Angiography 170 Artifacts of Contrast-Enhanced MR Angiography 174 Timing 174 Dose and Flow 174 Venous Enhancement 174 Maki Artifact 175 Pseudo disease 177 Image Filtering 177 Metallic Artifacts 177 Inflow Artifacts 177 Subtraction 179 Fat Suppression 179 Tips - Source Data, Overview MIP, and Targeted MIP 179 References 179
167
12.1
Introduction Magnetic resonance angiography (MRA) has emerged as a noninvasive technique for evaluating patients with different vascular diseases. However, with the standard two-dimensional (2D) time-of-flight (TOF) technique there are many difficulties in detecting stenoses and occlusions in diseased arteries because of a variety of flow-related artifacts (BRUNEREAU et al. 1998). Therefore, alternative strategies have been
MD Zentrum Radiologie der Universitat, R6ntgendiagnostik I, Robert-Koch-Strasse 40, 37083 G6ttingen, Germany PETER REIMER, MD Professor, Zentrale R6ntgendiagnostik, Stadtisches Klinikum, ROLF VOSS HENRICH,
Mo1tkestrasse 14,76133 Karlsruhe, Germany
I. P. Arlart et al. (eds.), Magnetic Resonance Angiography © Springer-Verlag Berlin Heidelberg 2002
studied to improve MRA (ATKINSON et al. 1997), including cardiac gating, segmented fast gradient-echo MRA, and the phase-contrast (PC) technique with variable velocity encoding. A few years ago, three-dimensional (3D) contrast-enhanced (CE) MRA was introduced as a method for vascular imaging with short acquisition times. A thorough understanding of the underlying mechanisms, proper techniques, and artifacts is essential to fully exploit the diagnostics potentials of these methods and to avoid misinterpretations (STRINGER 1997; TSURUDA et al. 1992). This chapter presents some of the artifacts, limitations, and pitfalls that may be encountered with MRA.
12.2 General Artifacts 12.2.1 Motion, Breathing, Peristalsis, and Pulsation A variety of artifacts are relatively independent of the chosen technique, always to a variable degree, depending on the imaged region present. Motion and breathing artifacts are predominantly encountered in MRA of the chest and abdomen (Figs. 12.1, 12.2). A short acquisition time, such as that used in CE-MRA, is an easy way of circumventing these artifacts. Alternatively, advanced gating techniques such as navigator techniques may solve these problems as well. Pulsation artifacts (Fig. 12.3) are visible throughout the body; however, they are most severe in the chest with highest flow velocities in normal arteries. Although ECG gating is helpful in minimizing pulsation artifacts, it extends acquisition times. Peristalsis in the abdomen is best minimized by short acquisition times, as with CE-MRA. Gross motion by uncooperative patients (Fig. 12.4) or patients unable to sustain a breath-held acqui
Data Loading...
