Optimization of scan parameters for proton MR spectroscopy on liver in vivo at 3.0 T

Objective: To characterize the effect of the 1H-MRS scan parameters, including the type of coil, TE, NSA and VOI, on shimming, water suppression, spectral signal to noise ratio (SNR) and the stability of the baseline of liver in vivo. Methods: 1H-MRS of liver in vivo was performed prospectively on GE Signa Excite HD 3.0 T system in 46 volunteers. Point-resolved spectroscopy (PRESS) sequence with built-in body coil and eight-channel torso phased-array coils was applied. After the localized scan, the first PRESS sequence with a TR of 1500 ms ,TE of 30 ms, VOI of 2 cm x 2 cm x 2 cm and NSA of 64 times was acquired using eight-channel torso phased-array coils. (The first PRESS sequence parameters was deemed as A). Then, the sequence was repeated with alteration of the three parameters including the type of coil, TE and size of VOI. (Changed parameters deem as B). The data were analyzed with the Wilcoxon matched pairs signed test. 0 mark: A is similar to B, 1 mark: A better than B, -1 mark: A worse than B. Results: SNR(-1 mark 0 pair, 0 mark 1 pair,1 mark 10 pair, Z= -3.162, P=0.002) was better in data (n=11) with eight-channel torso phased-array coils (A) than that with the built-in body coil (B), but the auto- shimming line width with eight-channel torso phased-array coils were inferior to those with built-in body coil (-1 mark 8 pair, 0 mark 2 pair, 1 mark 1 pair, Z=-2.511, P=0.012). SNR was better in data (n=13) with TE of 30 ms(A) than that at the sequence with TE of 90 ms(B) (-1 mark 2 pair, 0 mark 0 pair, 1 mark 11 pair, Z=-2.496, P=0.013), whereas baseline stability was poorer in the former (-1 mark 10 pair, 0 mark 2 pair, 1 mark 1 pair, Z=-2.333, P=0.020). SNR at the sequence (n=10) with VOI of 2 cm x 2 cm x 3 cm(B) was better (-1 mark 6 pair, 0 mark 4 pair, 1 mark 0 pair, Z=-2.449, P= 0.014) than that at the sequence (n=29) with VOI of 2 cm x 2 cm x 2 cm (A), but poorer (-1 mark 0 pair, 0 mark 5 pair, 1 mark 5 pair, Z=-2.041, P=0.041) auto-shimming line width was shown. By comparison the sequences with NSA of 128 times(B) and NSA of 64 times (A), the former could provide better spectrum SNR(-1 mark 21 pair, 0 mark 7 pair, 1 mark 1 pair, Z=-4.264, P=0.000). Conclusion: It is more easy to achieve a homogeneous bo magnetic field using a small size of VOI and built- in body coli. The sequence with VOI of 2 cm x 2 cm x 3 cm, NSA of 128 times is recommended for clinical use. Increase VOI and NSA are helpful to improve SNR. Longer TE is helpful to improve baseline stability. (authors)