Poster abstracts

Poster number 35 submitted by Wenbo Wei

Amide Proton Transfer (APT) MRI: A 3T vs. 7T Comparison

Wenbo Wei (Radiology department, OSU), G. Jia (Radiology department, OSU), J. Zhou (Radiology department, OSU), S. Choi (Radiology department, OSU), S. Sammet (Radiology department, OSU), M. V. Knopp (Radiology department, OSU)

Abstract:
Introduction: Amide-proton-transfer (APT) MRI has been developed to detect the over-expressed proteins and peptides in brain tumors for evaluating tumor malignancy and inhomogeneity and to detect cartilage glycosaminoglycan concentration. This study is to demonstrate that clinical whole-body 7T MRI can better facilitate the detection of APT effect than clinical 3T using egg phantom. Material and Methods: By scanning the phantom consisted of an egg submerged in oil-filled container with an 8-channel knee coil in a 3 Tesla MR system (Achieva, Philips), and in a Nova knee coil at whole body 7T MR system (Philips), we acquired APT images on a single slice covering the mid-section of the egg. S0 was acquired by TSE image with maximum saturation frequency offset (100,000 Hz) allowed in the scanners. The pre-saturation pulse was composed of a train of sixteen 1400º block pulses with pulse length of 30 ms and saturation power of 130 Hz (~2.8 T). MTRasym at 3.5 ppm without B0 correction was calculated by directly subtracting TSE images at 3.5 ppm from the images at -3.5 ppm. MTRasym at 3.5 ppm with B0 correction was calculated by finding each pixel’s B0 and subtracting the data points at -3.5 ppm and 3.5 ppm with respect to B0. Results: There are a better separation between amide proton saturation and free water saturation profiles and a clearer dip that reflects the APT effect in the MT-spectrum of egg white at 7T than that at 3T. APTR derived using the new algorithm showed the peak at 3.5 ppm. APTR in egg white ROI was 9.0% ± 1.2%, more homogeneous than MTRasym(3.5ppm) without B0 correction (6.8% ± 1.5%). APTR in egg latebra was 5.7% ± 0.7% and MTRasym(3.5ppm) was negative due to the artifact caused by larger fat saturation at -3.5 ppm. Conclusions: It is demonstrated that APT-MRI at 7T shows the better separation of amide proton, free water, and fat in MT-spectrum and the clearer APT effect than APT at 3T under the same saturation condition.

References:
1. Zhou J, et al. Magn Reson Med. 2003 Dec;50(6):1120-6.
2. Jones CK, et al. Magn Reson Med. 2006 Sep;56(3):585-92.
3. Ling W, et al. Proc Natl Acad Sci U S A. 2008 Feb 19;105(7):2266-70.
4. http://www.physics.wisc.edu/~craigm/idl/fitting.html

Keywords: MRI, Amide Proton Transfer (APT)