Dark Blood
Dark blood images null the signal from blood using the double inversion recovery (DIR) technique, which is not discussed further here. DIR sequences can be fast spin echo, in which case each image is acquired in a separate breath hold, or single shot, in which case multiple images are acquired in one breath hold. DIR images are always gated to the EKG so that cardiac motion is removed from the images. These sequences are used to determine anatomy.
Bright Blood
Bright blood technique is either a balanced steady state (TRUE FISP or FIESTA) or a more conventional gradient echo (GRE) sequence. TRUE FISP is faster and has better signal to noise and contrast to noise ratios, but is more susceptible to metal artifact and magnetic field inhomogenieties. This is the sequence we use most often to watch the heart beat. GRE is more sensitive for detecting turbulent jets but has lower contrast and the images take longer to acquire. You might use GRE if you are looking to see the subtle jet of an ASD or VSD. Both techniques are gated to the EKG to produce movies of the beating heart. Generally, 1 slice is obtained per breath hold. These images are used to assess cardiac function by watching the heart beat.
No comments:
Post a Comment