WEEKDAY EDUCATIONAL COURSE Everything You Wanted to Know about Magnetic Susceptibility & Why It Is Important
نویسنده
چکیده
Gradient Recalled Echo (GRE) based MR imaging techniques have wide applications in MRI. Due to the absence of refocusing RF pulses GRE sequences are fast and since low flip angles are usually applied, GRE sequences have low specific absorption rate, hence are particularly well suited for high field MRI. While MR signal generated from GRE techniques is complex, most traditional applications rely only on magnitude information whereas the phase information from the data is usually discarded. However, certain newer applications also rely on phase data. Among these, Susceptibility Weighted Imaging (SWI) (1,2) uses a specific algorithm based on GRE T2* weighted magnitude and phase data to create images sensitive to variations in tissue magnetic susceptibility resulting from sources such as venous blood, calcification, hemorrhage, iron stores, etc. Other techniques, some of which rely exclusively on the phase data of the GRE signal have also been intensely explored for uniquely characterizing anatomical structures that are especially evident at high field MRI (3-6), and even for creating maps of tissue magnetic susceptibility – the so called Quantitative Susceptibility Mapping (QSM) (7-12). Another technique – Gradient Echo Plural Contrast Imaging (GEPCI) (13-15) combines information from phase and magnitude images obtained with multi-gradient-echo sequence to generate a variety of images. The information obtained from these techniques reveals image features complimentary to that obtained from traditional magnitude-based imaging and could improve our understanding of both normal tissue anatomy as well as changes in tissue in various pathological conditions.
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Weekday Educational Course Everything You Wanted to Know About Magnetic Susceptibility & Why It Is Important: Major Sources of Phase Contrast in the Brain Thursday 15 May 2014
Highlights Gradient-echo MRI phase contrast depends on the underlying tissue magnetic susceptibility but is orientation-dependent and non-local. Calculating tissue magnetic susceptibility maps overcomes the orientation-dependent and non-local nature of phase contrast. Phase and susceptibility are primarily affected by tissue composition. For example, tissues rich in ferritin (stored iron)...
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