The purpose of using dual-phase chemical-shift imaging is to detect lipid either in hepatic parenchyma or within hepatocellular neoplasms. This is a non-enhanced breath-hold T1-weighted spoiled gradient-echo (SPGR) sequence in which periodic chemically selective fat-saturation pulses have been incorporated. Short TRs and short TEs are used. When TE is in phase (4.2 ms at 1.5 T), fat and water signals combine (in-phase imaging). Out-of-phase imaging is performed with a TE of 2.1 ms at 1.5 T. Fat will lose signal intensity on out-of phase images, because the signals from fat and water protons cancel each other. This sequence is also helpful to look for iron deposition in liver parenchyma. In patients with iron accumulation, parenchymal signal is lower on the longer TE in-phase images.
- Select 2 echoes, system automatically acquires in and out-of-phase images.
- User CV: Select turbo mode before entering the matrix values. Turbo mode reduces the RF pulse width and therefore shortens the TR. As the turbo mode gets faster, tissue contrast decreases but vessel-background contrast increases.
- Scan from top of liver to bottom of liver. Breath-holding is critical. Repeat as necessary for optimum image quality.
