The spatial resolution of 1.5T MRI has been improved by parallel imaging and 3D gradient- echo sequences. Thin-slice images can also be obtained using 3D gradient-echo imaging. Both of these advances are relevant to dynamic imaging investigations of hepatobiliary and pancreatic disease using gadoliniumbased contrast media.
Three-D gradient-echo sequences include LAVA (liver acquisition with volume acceleration, GE Healthcare), VIBE (volumetric interpolated breath - hold examination, Siemens Medical Solutions), and THRIVE (T1 high - resolution isotropic volume examination, Philips Medical Systems).
Three-T MRI has been used clinically in Japan since 2005, and its features have been studied widely. Moving to 3T doubles the signal-to-noise ratio compared with 1.5T MRI. This SNR gain can be kept or traded for speed, spatial resolution, or both.1 Thin-slice images obtained at 3T using 3D gradient-echo sequences are consequently superior to those obtained at 1.5T.
We now conduct all of our MRI investigations of hepatobiliary and pancreatic disease on a 3T system (Signa H Dx, GE). Our routine protocol be gins with T1-, T2-, and diffusion - weighted MRI. Dynamic imaging is then carried out with a fat- suppressed 3D T1-weighted gradient-echo sequence using parallel imaging (LAVA) with the following parameters:
• repetition time (TR): 3.4 to 3.5 msec
• effective echo time (TE): 1.4 to 1.6 msec
• flip angle: 12°
• bandwidth: 80 to 125 Hz/pixel
• field-of-view: 350 mm2
• matrix: 320 x 192
• slice thickness: 1.4 mm
• reconstruction: 0.7 mm
• partitions: 220 to 240
• parallel acquisition: 2 to 2.5
All studies are conducted during breath - holding.
