FLASH/SPGR/T1-FFE/RF Spoiled SARGE/RSSG/FAstFE/T1-FAST
Fast Low Angle Shot (FLASH) is the most commonly used gradient-spoiled gradient-echo MRI sequence in abdominal imaging. FLASH employs radiofrequency excitation pulses with a low flip angle (less than 90 degrees) and subsequent reading gradient reversal to produce a gradient-echo signal. The small flip-angle pulses establish equilibrium of longitudinal magnetization. Transverse magnetization is eliminated by a strong gradient (spoiler gradient). T1-weighted and T2*-weighted contrasts can be achieved using the FLASH sequence.
MRI image appearance in FLASH
The easiest way to identify FLASH images is by looking for fluid-filled spaces in the body. These spaces include cerebrospinal fluid in the brain ventricles and spinal canal, free fluid in the abdomen, fluid in the gall bladder and common bile duct, synovial fluid in joints, fluid in the urinary tract and urinary bladder, as well as edema or any other pathological fluid collections in the body. Fluids typically appear dark in FLASH images. While VIBE and FLASH sequences look similar, the primary noticeable difference is that FLASH sequences have lower signal-to-noise ratio (SNR) compared to VIBE sequences (i.e. VIBE images are brighter than FLASH images).
Tissues and their T1 FLASH appearance
Bone marrow : – equal to or higher than that of muscle (fatty marrow is usually bright)
Moving blood : – normally gray (flow related artefacts will appear as bright )
Spleen : gray( darker than liver)
Muscles :- gray
White matter : – whiter
Liver : brighter than gray
Gray matter : – gray
Fluids : – dark
Bone : – dark
Fat : – bright
Air : – dark