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Comparison of EPI ASE FLAIR and gradient echo imagings for fMRI studies of cortical motor areas
ABSTRACTS
Comparison of EPI ASE FLAIR and Gradient Echo imagings for fMRI studies of Cortical Motor Areas Zheng J, Ehrhardt JC, Zhu MW, *Cizadlo T
Dept. of Radiology, *Dept. of Psychiatry, The University of Iowa, Iowa City, IA Intrjuction Brain activation studies usually employ gradient echo(GE) sequences to detect a signal change by the BOLD (Blood-Oxygenation Level Dependent) effect. GE sequences are sensitive to large vein BOLD signals, whereas spin echo (SE)sequences are more sensitive to susceptibility signal change from the smaller vessels [1][2]. It has been reported that an EPI asymmetric spin echo (ASE) sequence may provide functional MR images at long TE[3]. One disadvantage of this ASE sequence, as well as GE fMRI sequences, is CSF pulsation, which may produce false activation signals. To suppress apparent CSF activation, we mixed ASE and FLAIR imaging methods md investigated this pulse sequence in a motor task fMRI study. GE images were also obtained for comparison.
26_g_hgAs The ASE-FLAIR sequence was implemented on a GE Signa MR imager retrofitted with Instascan EPI upgrade from Advanced NMR System,Inc. In practice, a EPI spin echo inversion recovery pulse sequence was modified by adding an operator controlled variable to offset the refocussing 180 ~ pulse relative to the center of echo. The imaging parameters of ASE-FLAIR used for motor cortex activation were: TR = 3000 ms, TI = 1200 ms, TE = 85 ms, 180 ~ offset = -30 ms, FOV = 20x40 cm 2, matrix = 128x256, 5 slices with 5 m m thickness and 1 m m interslice gap. The EPI GE had the same slice coverage as ASE-FLAIR and TR = 3000 ms, TE = 40 ms, flip angle = 75 ~ We also tested the ASE-FLAIR and GE sequences on a phantom and measured the signal-to-noise ratio (SNR) for each sequence. Five healthy right-handed volunteers were studied with a motor task paradigm consisting of a 3 minute series of alternating 30 second periods of rest and random tapping of the thumb and fingers of the right hand. In each series, a total 300 images with 5 slices covering the primary motor area (M1), supplementary motor area (SMA), premotor area (PMA), and sensorimotor area (S1) were acquired. This series was then repeated to obtain both ASEFLAIR and GE in varying order. All reconstructed images were registered in 2-dimensions to correct for brain motion. 19 slices that covered the above area were selected for further processing. Correlation images were used to identify activation regions.
Results Finger movement activation was observed on all subjects. Images from both sequences appeared to have comparable susceptibility artifacts. Phantom measurements showed that SNR for ASE-FLAIR was 27 and for GE 55. The functional distribution of activities was summarized in Table 1. The GE showed more activity in bilateral M1, contralateral $1, and bilateral SMA. The correlation coefficients were also higher for GE (r = 0.5 - 0.8) than ASE-FLAIR (r = 0.3 - 0.55). The latter, however, demonstrated different activation areas from the former. For example, the GE demonstrated activation regions in one subject in the contralateral M1, S1, ipsilateral PMA, and bilateral SMA. The ASE-FLAIR showed activated foci in the contralateral M1 and PMA. Signal from CSF was successfully suppressed and no functional activity was seen in CSF regions using ASE-FLAIR whereas 2/5 subjects showed artifactual activation within CSF areas using GE imaging. The activated pixel numbers for ASE-FLAIR decreased partially due to reduced SNR.
Conclusion ASE-FLAIR successfully suppressed the CSF signal which in turn limited the CSF artifacts in fMRI studies. Additionally, ASE-FLAIR demonstrated different activation regions from GE imaging and may provide another way to BOLD effects from small vessels in fMRI. Table 1. Total number of slices showing activation in motor area for ASE-FLAIR and GE images. Contra-PMA Ipsi-PMA ContraIpsi-M1 ContraIpsi-S1 ContraM1 S1 SMA ~ASE-FLAIR 8 2 13 4 8 4 6 GE 9 1 16 7 13 4 11
Referencg~ [1] Bandettini, P.A., Wong, E.C., and Hinks,R.S., 14th SMR Annual Meeting, 1995,1104. [2] Stables, L.S., Kennan,R.P., Gore,J.C., 14th SMR Annual Meeting, 1995, 243. [3] Lowe, M.J., Mock, B.J., and Sorenson, J.A.,14th SMR Annual Meeting, 1995, 778.
S45
Ipsi-SMA
11
Comparison of EPI ASE FLAIR and Gradient Echo imagings for fMRI studies of Cortical Motor Areas Zheng J, Ehrhardt JC, Zhu MW, *Cizadlo T
Dept. of Radiology, *Dept. of Psychiatry, The University of Iowa, Iowa City, IA Intrjuction Brain activation studies usually employ gradient echo(GE) sequences to detect a signal change by the BOLD (Blood-Oxygenation Level Dependent) effect. GE sequences are sensitive to large vein BOLD signals, whereas spin echo (SE)sequences are more sensitive to susceptibility signal change from the smaller vessels [1][2]. It has been reported that an EPI asymmetric spin echo (ASE) sequence may provide functional MR images at long TE[3]. One disadvantage of this ASE sequence, as well as GE fMRI sequences, is CSF pulsation, which may produce false activation signals. To suppress apparent CSF activation, we mixed ASE and FLAIR imaging methods md investigated this pulse sequence in a motor task fMRI study. GE images were also obtained for comparison.
26_g_hgAs The ASE-FLAIR sequence was implemented on a GE Signa MR imager retrofitted with Instascan EPI upgrade from Advanced NMR System,Inc. In practice, a EPI spin echo inversion recovery pulse sequence was modified by adding an operator controlled variable to offset the refocussing 180 ~ pulse relative to the center of echo. The imaging parameters of ASE-FLAIR used for motor cortex activation were: TR = 3000 ms, TI = 1200 ms, TE = 85 ms, 180 ~ offset = -30 ms, FOV = 20x40 cm 2, matrix = 128x256, 5 slices with 5 m m thickness and 1 m m interslice gap. The EPI GE had the same slice coverage as ASE-FLAIR and TR = 3000 ms, TE = 40 ms, flip angle = 75 ~ We also tested the ASE-FLAIR and GE sequences on a phantom and measured the signal-to-noise ratio (SNR) for each sequence. Five healthy right-handed volunteers were studied with a motor task paradigm consisting of a 3 minute series of alternating 30 second periods of rest and random tapping of the thumb and fingers of the right hand. In each series, a total 300 images with 5 slices covering the primary motor area (M1), supplementary motor area (SMA), premotor area (PMA), and sensorimotor area (S1) were acquired. This series was then repeated to obtain both ASEFLAIR and GE in varying order. All reconstructed images were registered in 2-dimensions to correct for brain motion. 19 slices that covered the above area were selected for further processing. Correlation images were used to identify activation regions.
Results Finger movement activation was observed on all subjects. Images from both sequences appeared to have comparable susceptibility artifacts. Phantom measurements showed that SNR for ASE-FLAIR was 27 and for GE 55. The functional distribution of activities was summarized in Table 1. The GE showed more activity in bilateral M1, contralateral $1, and bilateral SMA. The correlation coefficients were also higher for GE (r = 0.5 - 0.8) than ASE-FLAIR (r = 0.3 - 0.55). The latter, however, demonstrated different activation areas from the former. For example, the GE demonstrated activation regions in one subject in the contralateral M1, S1, ipsilateral PMA, and bilateral SMA. The ASE-FLAIR showed activated foci in the contralateral M1 and PMA. Signal from CSF was successfully suppressed and no functional activity was seen in CSF regions using ASE-FLAIR whereas 2/5 subjects showed artifactual activation within CSF areas using GE imaging. The activated pixel numbers for ASE-FLAIR decreased partially due to reduced SNR.
Conclusion ASE-FLAIR successfully suppressed the CSF signal which in turn limited the CSF artifacts in fMRI studies. Additionally, ASE-FLAIR demonstrated different activation regions from GE imaging and may provide another way to BOLD effects from small vessels in fMRI. Table 1. Total number of slices showing activation in motor area for ASE-FLAIR and GE images. Contra-PMA Ipsi-PMA ContraIpsi-M1 ContraIpsi-S1 ContraM1 S1 SMA ~ASE-FLAIR 8 2 13 4 8 4 6 GE 9 1 16 7 13 4 11
Referencg~ [1] Bandettini, P.A., Wong, E.C., and Hinks,R.S., 14th SMR Annual Meeting, 1995,1104. [2] Stables, L.S., Kennan,R.P., Gore,J.C., 14th SMR Annual Meeting, 1995, 243. [3] Lowe, M.J., Mock, B.J., and Sorenson, J.A.,14th SMR Annual Meeting, 1995, 778.
S45
Ipsi-SMA
11