Handbook of MRI Technique. Catherine Westbrook

Balanced GRE Balanced GRE Short TE Minimum Short TE Minimum Short TR Minimum Short TR Minimum Flip angle >35° Flip angle >35° Reverse echo GRE Reverse echo GRE TE (effective) Minimum TE (effective) Minimum Short TR <50 ms Short TR <50 ms Flip angle 30° to 45° Flip angle 30° to 45° 1.5T and 3T Slice thickness 2D Slice thickness 3D Thin <1 mm/1 mm Thin <1 mm/1 mm Medium 2 –4 mm Thick 2–4 mm Thick 5 mm+ FOV Matrix Small <160 mm Coarse <256 × 128 Medium 160–300 mm Medium 256/512 × 256 Large 300 mm+ Fine 512 ×512 Very fine >1024 × 1024 NEX/NSA Slice number 3D Low 1 or less Small <32 Medium 2–3 Medium 64 High/multiple 4+ Large >128 PC‐MRA 2D and 3D TOF‐MRA 2D TE Minimum TE Minimum TR 25–33 ms TR 28–45 ms Flip angle 30° Flip angle 40°–60° VENC venous 20–40 cm/s VENC arterial 60 cm/s TOF‐MRA 3D TE Minimum TR 25–50 ms Flip angle 20°–30°

SIGNAL‐TO‐NOISE RATIO (SNR)

      SNR is defined as the ratio of the amplitude of signal received by the receiver coil to the average amplitude of the noise. The signal is the voltage induced in the receiver coil, and the noise is a constant value depending on the area under examination and the background electrical noise of the system. SNR may be increased by using:

       conventional spin echo (CSE) and fast or turbo spin echo (FSE/TSE) pulse sequences

       a long repetition time (TR) and a short echo time (TE)

       a flip angle of 90° in all spin echo type pulse sequences or the Ernst angle in gradient echo (GRE) pulse sequences

       a well‐tuned and correctly sized receiver coil

       a coarse matrix

       a large FOV

       thick slices

       a narrow receiver bandwidth

       high‐order signal averages (number