ABSTRACT
Objective To evaluate the advantages of MR LAVA multi-phase dynamic contrast enhancement in abdominal MRI.Methods 42 cases which clinically suspected liver lesions and 15 normal volunteers underwent MRI examination,including routine T_1WI and T_2WI scan,T_1W 2D and 3D FSPGR,LAV A multi-phase contrast enhancement.The detecting rates of 2D,3D and LAVA images were analysed and the signal noise ratio(SNR)of the liver and spleen was observed.Results 68 lesions were detected by LAVA sequence,the detecting rate was 100%,the accurate rate of diagnosis was 95.6%(65/68),while the detecting rates of the lesions were 91.2%(62/68)and 89.7%(61/68)with 3D T1W FSPGR and 2D T1W FSPGR,respectively,the accurate rates in diagnosing the lesions were 76.5%(52/68)and 70.6%(48/68)with 3D and 2D sequences,respectively.The SNR of liver,spleen of 15 normal volunteers were:29.68±2.31 in liver,36.21 ±3.67 in spleen at LAVA plain scan,46.21 ±5.32 in liver,58.75±4.68 in spleen at 2D T_1W FSPGR,19.79±2.23 in liver,23.63±2.14 in spleen at 3D T_1W FSPGR,41.75±5.13 in liver,57.96±6.13 in spleen at LAVA contrast enhancement,56.33±5.63 in liver,63.21±5.32 in spleen at 2D contrast enhancement,29.05±4.68 in liver,46.37±5.17 in spleen at 3D contrast enhancement sequence.Conclusion LAVA multi-phase dynamic contrast enhancement is more predominant than T1W 2D and 3D and 3D FSPGR in displaying the lesions and blood vessels of liver.
ABSTRACT
Objective To observe the effect of full width half max (FWHM) on spectra signal-to-noise ratio (SNR), NAA/Cr, Cho/Cr and water suppression at 3.0T MR. Methods GE Signa Excite HD 3.0T MR scanner with 8 channel phrased-array head and neck coil was used. The respective study of liver 1H-MRS was performed using PRESS sequence. A total of 49 spectrums were obtained with parameters of TR 1500 ms, TE 30 ms, NSA 128. FWHM and water suppression were recorded automatically and the subjects were divided into better shimming group (FWHM<10 Hz) and worse shimming group (FWHM≥10 Hz). Independent t test was used to analyze the Cr_SNR, NAA/Cr, Cho/Cr, water suppression and volume of interest (VOI). Results Compared with worse shimming group, better shimming group could provide better Cr_SNR (t=5.976, P<0.001), higher NAA/Cr (t=2.469, P=0.017), lower Cho/Cr (t=-4.460, P<0.001) and smaller VOI (t=3.862, P<0.001). Conclusion When single voxel proton spectroscopy of head is adopted with 3.0T MR, small VOI is easy to achieve effective shimming, and better shimming is helpful to improve SNR, the ratio of main metabolites as well as water suppression.
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Objective To evaluate the effect of intravenous Gd-DTPA on 3.0T proton MR spectroscopy (MRS) water suppression and shimming. Methods Prospective study of proton MRS was performed with GE Signa Excite HD 3.0T system and eight-channel phased-array coils with PRESS sequence (head, liver and kidney, respectively). Routine auto prescan program was operated to record full width half maximum (FWHM) and water suppression (WS%). Routine scan was performed after injection of Gd-DTPA, then prescan program was reoperated to record FWHM and WS%. The data of FWHM and WS% in head, liver and kidney were compared between before and after injection of Gd-DTPA with the Wilcoxon matched pairs signed test. Results WS% of spectroscopy of head and liver after administration of Gd-DTPA decreased significantly (T_+=12, T_-=66, P=0.02; T_+=0, T_-=45, P=0.007). The effect of shimming of kidney after administration of Gd-DTPA was poor (T_+=0, T_-=435, P<0.001) and WS% of spectroscopy of kidney after administration of Gd-DTPA decreased significantly (T_+=0, T_-=435, P<0.001). Conclusion WS% of spectroscopy in head, liver and kidney can be impacted negatively by Gd-DTPA. Gd-DTPA has great influence on shimming of spectroscopy of kidney, but has little influence on shimming of spectroscopy of head and liver. It is better to acquire MRS data before administration of contrast medium in kidney.
ABSTRACT
Objective To characterize the effect of the ~1H-MRS scan parametem, 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-resolred 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×2 cm×2 cm and NSA of 64 times was acquired using eight-channel torso phased-array coils.(The first PRESS sequence parametem 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 autoshimming 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×2 cm×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 ×2 cm × 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 builtin body coli.The sequence with VOI of 2 cm ×2 cm ×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.