GE 3.0T NPW,TRF,FAST,F R NPW,TRF,FAST,F R

Transcription

1 GE 3.0T 3.0T WRIST Invivo 8CH Wrist Coil Sequence Ax T2 Cor PD Cor PDFS Cor T1 Cor PD (Small FOV) FOV (mm) Matrix 384x x x x x192 Phase Direction RL RL RL RL RL # of Slices TR/TE (msec) 3000/ / /30 800/ /42 Echo Train (ETL/TF) WFS (BW) Parallel Imaging No No No No No Options TRF,FAST,FR NPW,TRF,FAST,F R NPW,TRF,FAST,F R NPW,TRF,FAST,F R NPW,FAST Sequence Type FRFSE-XL FRFSE-XL FRFSE-XL FRFSE-XL FSE-XL Fat Sat No No Yes No No NEX Scan Time 3:18 4:41 5:00 4:18 5:40 Abbreviations ETL/TF: Echo Train Length or Turbo Factor, the number of k-space lines after an excitation pulse FOV: Field of View GRE: Gradient Echo NEX: Number of Signal Averages or Number of Excitations NPW: No Phase Wrap, conventional oversampling method to prevent image fold-over PD: Proton Density, weighting for short TE, long TR spin-echo scans SAR: Specific Absorption Rate; tissue heating measure limited by the FDA SNR: Signal to Noise Ratio, measure of image quality WFS: Water-Fat Shift (see over), a measure of receiver bandwidth (BW)

2 AX T2

3 COR PD

4 COR PD FS

5 COR T1

6 COR PD Sml FOV

7 GE Healthcare Pulse Sequence Guide SE Pulse Sequence Characteristics 90-degree RF pulse followed by a 180-degree refocusing pulse. Utility Produces T1, PD and T2 weighted images. Differences in contrast are determined by TR/TE. Suggestions 1.5T 3.0T Consider reducing the flip angle for improved contrast (T2 MEMP). Reduce flip angle to 70 (increased contrast, reduced SAR). FSE-XL 90-degree RF pulse followed by multiple "trains" of refocusing 180-degree pulses. Increased blurring compared to SE. Produces T1, PD and T2 weighted images. Differences in contrast are determined by TR/TE. Due to larger B0, consider reduced ETL (reduced blurring) and increased RBW (faster sampling and reduced echo spacing). FRFSE-XL GRE/SPGR FLAIR T1 FLAIR 90-degree RF pulse followed by mutiple "trains" of revocusing 180-degree pulses. A -90- degree pulse is applied at the end of the Echo train to increase T2 weighting. Reduced flip angle for the itinal RF pulse. Gradient reversal is used to refocus the echo. 180-degree inversion pulse applied prior to a conventional FSE based sequence. A T1 (time to invert) determines signal suppression. Same pulse sequence as FLAIR, but the T1 time is based on the desired contrast. Produces T1, PD and T2 weighted images. Differences in contrast are determined by TR/TE. Due to the -90-degree pulse, an increased T2 weighting will be seen as compared to FSE-SL. Reduce TR vs. FSE-XL, T2: <2800 ETL, T1: 3-4, PD: T2:16-24 Produces T1, PD and T2*weighted images. GRE-Reverses gradient polarity. Differences in contrast are determined by TR/TE SPGR - Continuous phase shifting of the RF and flip angle. This sequence is more susceptible to pulse to spoil residual transverse metal inhomogenaity. magnetization. Reduction in signal from fluids that corresponds to T1 time (time to invert). T1 FLAIR is designed to scan the same number of slices as SE, but in an equivalent or shorter scan time. Compared to SE, better CNR and SNR ratios. Reduce TR vs. FSE-XL, T2: <3500 ETL, T1: 2-3, PD:6-8, T2:12-16 Increased susceptibility and flow artifacts. Increase frequency matrix to reduce this effect. Reduce flip angle compared to 1.5T for increased contrast. T2 FLAIR CartiGram (T2 Mapping) TRICKS COSMIC Same pulse sequence as FLAIR, but the T1 time is based on the desired contrast. CartiGram(T2 Mapping) is used to noninvasively detect changes in the collagen component of the extracellular matrix of cartilage. Time Resolved Imaging of Contrast Kinetics (TRICKS). Coherent Oscillatroy State Acquistion for the Manipulation of Imaging Contrast (COSMIC). Fully balanced coherent imaging sequence, with segmented multi-chop centric acquisition. T2 FLAIR is based on the null point of CSF. TR: 3000, TE: 50, T1: 150, RBW 31kHz TR:4000, TE:40, T1:180, RBW:50kHz This application acquires multiple scans at each slice location;each set of scans has a unique TE resulting in a set of gray scal images that represent different T2 weighting. This angio-based technique allows robust, accelerated imaging of dynamic processes in significantly reduced scan times. High SNR and CNR among bone, muscle, cartilage and fluid. Provides mixed T2/T1 and T2 contrast. TR: 800, 256 (freq) x 256 (phase), RBW:31kHz RTR:1000, 384(freq) x 256(phase), RBW: 62 khz

8 In-homogeneous fat saturation Fat saturation can be challenging in areas that are off-center,irregular in size, or very large Additional Topics of Interest Optimiazation of Fat Sat can be performed in several ways: Placing a shim colume over the area to increase homogeneity, choosing between regular or classic fat sat, or using routine fat sat efficiency techniques. Fat Sat efficiency - User CV 19. This al Magnetic susceptibility Signal drop-off, distroted images Increase frequency matrix, reduce slice thickness and increase reception bandwidth. Use FSE-XL, as Gradient Echo does not use refocusing pulses. TR: TE:34(EF), RBW: khz, 512 (f) x (p), NEX:3-4, ETL: increase as high as possible. Popliteal flow artifact (sagittal & coronal) Chemical Shift Fine Line Artifact Occurs in the phase direction only, with mismapping of the popliteal artery across the image Lines or streak-like artifacts Sawp phase and frequency direction. Phase should run S/I, frequence A/P. Add no phase wrap to eliminate phase wrap (alaising) Ensure voxel size is as low as possible. This can be achieved several ways, including: increased reception bandwidth, decreased frequency matrix. (See example) 223Hz x 256 (f) [2x50(RBW)] x 1000Hz=0.57 pixels 447Hz x 256 (f) [2x100(RBW)] x 1000Hz=0.57pixels User VS 21-Enchanced Fine Line Suppression: Widens the "crushers" to reduce the artifact, a slight increase in TE may occur. General 3.0T Guidelines Imaging at 3.0T offers clear benefits of increased SNR and uniform fat saturation. These changes allow increased spatial resolution, reduced NEX (NSA) and reduced scan times to maximize imaging capability. However, T1 recovery can be up to 30% longer an Pulse Sequence Suggestions 1.5T 3.0T T1 FSE TR: , RBW:15-20kHz, ETL:3-4, ST:4mm, 256 (f) x 192 (p), 2 NEX(NSA) TR: , RBW:25-31 khz, ST:3mm, 384(f) x 256(p), 1 NEX(NSA) PD FSE (Routine or Fat Sat) Fat Sat: Use Fat or Fat Classic, User CV 19 to optimize at various Fat Sat levels T2 FSE TR: , RBW:25-31 khz, ETL:8-10, ST: 4mm, 256(f) x 192 (p), 2 NEX(NSA) TR: , RBW:31-50kHz, ETL:16-24, ST:4mm, 256 (f) x 192(p), 2 NEX(NSA) TR: , RBW:42-50kHz, ETL:6-8, ST:3mm, 284(f) x 256(p), 1 NEX(NSA) TR: , RBW:42-50kHz, ETL:12-16, ST:3mm, 384(f) x 256(p), 1 NEX(NSA)