- Email: [email protected]
Clinical 3D-PRESTO FMRI compared to 2D-single-shot FMRI
NemoImage
11, Number
5, 2000, Part 2 of 2 Parts
1 D E al”
METHODS
- ACQUISITION
Clinical 3D-PRESTO FMRI compared to 2D-Single-Shot FMRI Lukas Scheep, Christiane *Dep.
K. Kuhl*, Juergen Gieseket, Paul FolkemS, H. H. Schild* of Radiology.
l-Philips $Philips
Medical Medical
University
of Bonn,
Systems, Hamburg,
Germany Germany
Systems, Best, Netherlands
Subject: Even though the feasibility of three-dimensional BOLD imaging techniques for functional MRI has already been shown years ago. very little work has been done so far to compare 3D techniques (1) with single shot sequences. The advantages of lower inflow effects and higher signal-tonoise-ratios might allow a more significant detection of brain activation compared to single shol sequences. We have tested both techniques on the same scanner in order to examine whether it is possible to detect brain function under clinical conditions using a 3D-PRESTO gradient echo EPI sequence with a higher or comparable statistical significance as compared to a single shot gradient echo EPI sequence. As an easy and well established task for assessing brain function, a linger tapping paradigm was chosen. This paradigm has been shown to be stable and the location of the cortical activation is easily identified morphologically using Tl weighted images. Methods: All experiments were performed on a 1.5 Tesla MR (Philips Gyroscan NT) equipped with the gradient system POWERTRAK 6000 (23mT/m, rise time 0.2ms). A quadrature head coil was used for all measurements. Scan parameters were as follows: 1. Single shot EPI: TR=2000ms, TE=50 ms, Flip angle 90”, EPI-factor 51, slice thickness 5mm, FOV 240 mm, 64x64 matrix size 2. 3D FFE (TE>TR) EPI : TR= 24.5 ms, TE=35.5 ms, Flip angle IO”,17 echoes per excitation, phase navigator prior to acquisition, slice thickness 3.5 mm. Nine healthy volunteers performed an unilateral selfpaced finger-tapping protocol. A single activation phase lasted for ten dynamic scans. The rest period was of equal length. In a single experiment the Pm** en~nn*rcata rest/activation cycle was repeated six times. To avoid misinterpretation due to habituation effects, we randomly started either with the 3D sequence or with the single shot sequence. In addition, after each functional scan Tl weighted images i; 10 were acquired with the same geometrical set up as the corresponding scan in order B i $ o,a i. to match the functional results more easily with the anatomical structures and to 2, { 36 t give the volunteers a rest between the functional scans. The two sequences were ; i 4 run two times altematingly. ” 12 The reconstructed images were preprocessed and analyzed using AFNI (2) and Stimulate (3). For each time series of images cross correlation (CC) maps were calculated using shifted box car reference functions. To compare the size and location of “above threshold” pixel for the sensorimotor cortex we applied a correlation coefficent threshold to the CC maps that corresponded to a Bonferronicorrected p-value of p < 0.01. Results: The right hand motor area was successfully detected in every 2D- and 3D-scan. Using the criteria described above we were able to detect motor activation highly significantly (p < 0.001). Regarding the number of activated pixels we found in av’erage a higher number of activated pixels using single shot sequences compared to the 3D sequence. High CC values projecting in sulci have been observed more frequently and with a higher cluster size for single shot sequences. SMA activation was found for coven volunteers. In four cases both sequences detected the identical SMA pattern. In two casts. SMA activation was showpn only by the single shot sequence. in one case only by the 3D technique. Our volunteer study indicates that there is no significant difference in reliability of both sequence, for semorimotor ctbrtex activation detection. The detected cluster size is. in average smaller for the 3D sequences. Smaller cluster sizes did not lead to a reduction in significance in terms of calculated p-values. The 3D technique proved to be at least as robust as the single shot counterpart. Venous How phenomena projecting into sulci. mimicking cortical activation are markedly reduced using the 3D sequence. Therefore this technique may provide a higher significant identification of activated cortex. References: 1. Van Gelderen, P; Ramesey, NF et al. Proc.Natl. AcadSci. USA, 1995, 92: 6906-6910 2. RW Cox; AFNI: Software for analysis and visualization of functional magnetic resonance neuroimages; Computers Biomedical Research, 29: 162-173, 1996 3. J.P. Strupp. “Stimulate: A GUI based fMRI Analysis Software Package.” NeuroImage, 3(3):S607, June 1996
s601
and
11, Number
5, 2000, Part 2 of 2 Parts
1 D E al”
METHODS
- ACQUISITION
Clinical 3D-PRESTO FMRI compared to 2D-Single-Shot FMRI Lukas Scheep, Christiane *Dep.
K. Kuhl*, Juergen Gieseket, Paul FolkemS, H. H. Schild* of Radiology.
l-Philips $Philips
Medical Medical
University
of Bonn,
Systems, Hamburg,
Germany Germany
Systems, Best, Netherlands
Subject: Even though the feasibility of three-dimensional BOLD imaging techniques for functional MRI has already been shown years ago. very little work has been done so far to compare 3D techniques (1) with single shot sequences. The advantages of lower inflow effects and higher signal-tonoise-ratios might allow a more significant detection of brain activation compared to single shol sequences. We have tested both techniques on the same scanner in order to examine whether it is possible to detect brain function under clinical conditions using a 3D-PRESTO gradient echo EPI sequence with a higher or comparable statistical significance as compared to a single shot gradient echo EPI sequence. As an easy and well established task for assessing brain function, a linger tapping paradigm was chosen. This paradigm has been shown to be stable and the location of the cortical activation is easily identified morphologically using Tl weighted images. Methods: All experiments were performed on a 1.5 Tesla MR (Philips Gyroscan NT) equipped with the gradient system POWERTRAK 6000 (23mT/m, rise time 0.2ms). A quadrature head coil was used for all measurements. Scan parameters were as follows: 1. Single shot EPI: TR=2000ms, TE=50 ms, Flip angle 90”, EPI-factor 51, slice thickness 5mm, FOV 240 mm, 64x64 matrix size 2. 3D FFE (TE>TR) EPI : TR= 24.5 ms, TE=35.5 ms, Flip angle IO”,17 echoes per excitation, phase navigator prior to acquisition, slice thickness 3.5 mm. Nine healthy volunteers performed an unilateral selfpaced finger-tapping protocol. A single activation phase lasted for ten dynamic scans. The rest period was of equal length. In a single experiment the Pm** en~nn*rcata rest/activation cycle was repeated six times. To avoid misinterpretation due to habituation effects, we randomly started either with the 3D sequence or with the single shot sequence. In addition, after each functional scan Tl weighted images i; 10 were acquired with the same geometrical set up as the corresponding scan in order B i $ o,a i. to match the functional results more easily with the anatomical structures and to 2, { 36 t give the volunteers a rest between the functional scans. The two sequences were ; i 4 run two times altematingly. ” 12 The reconstructed images were preprocessed and analyzed using AFNI (2) and Stimulate (3). For each time series of images cross correlation (CC) maps were calculated using shifted box car reference functions. To compare the size and location of “above threshold” pixel for the sensorimotor cortex we applied a correlation coefficent threshold to the CC maps that corresponded to a Bonferronicorrected p-value of p < 0.01. Results: The right hand motor area was successfully detected in every 2D- and 3D-scan. Using the criteria described above we were able to detect motor activation highly significantly (p < 0.001). Regarding the number of activated pixels we found in av’erage a higher number of activated pixels using single shot sequences compared to the 3D sequence. High CC values projecting in sulci have been observed more frequently and with a higher cluster size for single shot sequences. SMA activation was found for coven volunteers. In four cases both sequences detected the identical SMA pattern. In two casts. SMA activation was showpn only by the single shot sequence. in one case only by the 3D technique. Our volunteer study indicates that there is no significant difference in reliability of both sequence, for semorimotor ctbrtex activation detection. The detected cluster size is. in average smaller for the 3D sequences. Smaller cluster sizes did not lead to a reduction in significance in terms of calculated p-values. The 3D technique proved to be at least as robust as the single shot counterpart. Venous How phenomena projecting into sulci. mimicking cortical activation are markedly reduced using the 3D sequence. Therefore this technique may provide a higher significant identification of activated cortex. References: 1. Van Gelderen, P; Ramesey, NF et al. Proc.Natl. AcadSci. USA, 1995, 92: 6906-6910 2. RW Cox; AFNI: Software for analysis and visualization of functional magnetic resonance neuroimages; Computers Biomedical Research, 29: 162-173, 1996 3. J.P. Strupp. “Stimulate: A GUI based fMRI Analysis Software Package.” NeuroImage, 3(3):S607, June 1996
s601
and