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Chapter 11 Lecture. Mark D. Herbst, M.D., Ph.D. Acquistion Time and Protocol Optimization. Time of scan = (# phase encoding steps xTR x NEX)/ETL. Ways to save time. Reduced matrix always done in phase direction (why do it if it doesn’t save time?) No change in frequency matrix
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Chapter 11 Lecture Mark D. Herbst, M.D., Ph.D.
Acquistion Time and Protocol Optimization • Time of scan = (# phase encoding steps xTR x NEX)/ETL
Ways to save time • Reduced matrix • always done in phase direction (why do it if it doesn’t save time?) • No change in frequency matrix • Reduces number of phase encoding steps
Ways to save time • Rectangular FOV • Done in phase enc direction, to match reduced matrix size to make square pixels
Ways to save time • Half acquistions • Half scan or half Fourier • Uses the phenomenon of Hermitian Symmetry to make up the empty part of k-space with known info • Equal to ½ NEX • Results in decreased S/N • Incorrect in book---says increases noise…not really, it decreases S
Signal Averaging • Decreases noise, but increases time (NEX)
Protocol Design • Usually all are optimized by manufacturer or techs that are working at that center • Consider contrast sensitivity • For example, uterus is shown well with T2WI, not so well with T1WI • Image detail – rule of thumb is to make the slices half the size of the thing you want to see, or less.
Protocol Design • Consider rectangular FOV and matrix • Don’t overdo detail, since small voxels will give you decreased S/N • Consider “3D” MR, which gives more signal • Artifact reduction (see ch 14) • Speed factor = turbo factor = ETL for Fast Spin Echo (FSE, TurboSE)