MR成像要素.ppt

Artifact Motion : ( Physiologic active ) Chemical Shift and Magnetic Susceptibily effects Aliasing ( Phase Encoding and Frequency Encoding ) Truncation System Performance Artifact Artifact Motion : ( Physiologic active ) Cardiac Motion EKG / PG Respiratory Resp Comp / Resp trigger / Breath Hold Blood Flow FC / Spacial Sat CSF Pulsation PG / FC Aperiodic Motion ? Cooperation / Suitable Education In Phase Direction Truncation artifact: low intensity lines appearing near the boundaries of the brain / skull interface, are characteristic of a 128 encoding acquisition (A). This artifact is not present if 256 views are collected (B). MRI Pulse Sequences TE TR RF Pulse RF Pulse RF Received ... Gradient Pulse (Slice Selection) Gradient Pulse (Signal Readout) Gradient Pulse (Slice Selection) Spin Echo Gradient Echo SE IR FSE (FSE-XL FRFSE… ) FSE-IR SSFSE GRE SPGR FGRE FSPGR TOF PC SSFP FIESTA … … 2D 3D 3 Plane CINE Fast EPI Spiral Scan Mode Acquisition Mode Spin Echo (SE), Inversion Recovery (IR) 90° 180° refocus inhomogeneity - TE, TR, scan time PD, T1, T2 180 90 echo TR RF TE Gradient Echo (GRE), SPGR 90° Gradient Refocus Inhomogeneity sensitive ˉ TE, TR, scan time PD, T2* (GRE), T1 (SPGR) RF GZ GY GX echo TR TE 180 TI e GE Medical System China MR Applications Imaging Quality SNR Scan Time Contrast Artifact Resolution SNR Almost every thing have effective to SNR From application’s point: Magnetic Field Strength Pulse Sequence Parameter choosing ( TR ; VB ; Voxel NEX ; …. Contrast ------CNR Intrinsic Contrast Pulse Sequences Parameter Choosing Intrinsic Tissue Contrast Proton Density T2 (Decay (T2*)) T1 (Relaxation) Flow Diffusion Others ( MTC, ... H1 Proton Density (PD) The most straightforward contrast mechanism Intensity depends on how many prot