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G. Tamer Jr. 1 , T.M. Talavage 1,2 , J.L. Ulmer 3

Characterizing the Attenuation and/or Saturation Effect of the Acoustic Scanner Noise In Auditory Event-Related Functional Magnetic Resonance Imaging. G. Tamer Jr. 1 , T.M. Talavage 1,2 , J.L. Ulmer 3 1 School of Electrical & Computer Engineering, Purdue University

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G. Tamer Jr. 1 , T.M. Talavage 1,2 , J.L. Ulmer 3

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  1. Characterizing the Attenuation and/or Saturation Effect of the Acoustic Scanner Noise In Auditory Event-Related Functional Magnetic Resonance Imaging G. Tamer Jr.1, T.M. Talavage1,2, J.L. Ulmer3 1School of Electrical & Computer Engineering, Purdue University 2Department of Biomedical Engineering, Purdue University 3Department of Radiology, Medical College of Wisconsin

  2. Motivation • Goal: study auditory cortex, language areas • Method: functional MRI • Problem: acoustic scanner noise (ASN) • Loud, distinct “ping” – 115 dB SPL • When: acquisition of an image • Response interaction*; masking; distraction • Objective: characterize and account for ASN interaction with response to a desired stimulus * - Bandettini et al., 1998 and Talavage et al., 1999

  3. Auditory Cortex Figure 1: diagram of the brain in left lateral view Illustration is from Sylvius 2.0 (CD-ROM) by SM Williams.

  4. fMRI • MRI foundation • Blood oxygenation level dependent (BOLD)* • Applied stimulus - cortical activity • Small, time-dependent signal changes Figure 2: MRI gantry at the Medical College of Wisconsin (MCW) (picture by Brosch, Purdue University) * - Ogawa et al., 1990, 1992

  5. Hemodynamic Response Model (Dale and Buckner, 1997) Figure 3: hemodynamic response model

  6. Typical fMRI Event-Related Design Stimulus # slices TR Inter-stimulus interval (ISI) Figure 4: event-related paradigm and hemodynamic response

  7. Acoustic History • ASN History: # slices, TR, volume acquisition • Stimulus History: ISI, duration • Objective: estimate the dependence of response to acoustic stimulus on the acoustic history through controlled variation of these parameters.

  8. fMRI Experiment Parameters • 5 normal-hearing subjects @ MCW • Auditory surface coils* • Clustered volume acquisition (CVA)** • Blipped echo-planar imaging sequence • 1.5 T field strength, 64x64, 20x20 cm FOV • 5 slices (5 mm thickness) • Voxel resolution – 3.125 x 3.125 x 5 mm * - Talavage et al., 2000 ; ** - Edmister et al., 1999,

  9. fMRI Experiment Parameters • Stimulus – 1-s instrumental jazz music snippet • Event-Related paradigm • TR: 1.5, 2.0, 3.0, and 6.0 s • ISI: 12 and 18 s • 16 event-related runs – two runs for each set of parameters • 20 trials/run * 2 runs/set = 40 trials/set

  10. Varying ISI Figure 6: ISI - 12 s vs. 18 s

  11. Varying TR Figure 5: TR - 3 s vs. 6 s

  12. Image Processing Stream • Reconstruction • Motion correction • Alignment with 3d SPGR anatomicals • Registration • Normalization and drift correction • Select and isolate Region of Interest (ROI) • ROI averaging and normalization of HDR estimates • Inter-subject averaging • Plotting estimates of HDR

  13. Experiment Results 12-s ISI 18-s ISI Figure 12: left auditory cortex, 5-subject average

  14. Experiment Results 12-s ISI 18-s ISI Figure 12: right auditory cortex, 5-subject average

  15. Experiment Results Table 1 – Student’s t-test paired two samples for mean, P(T<=t) one-tail, L = left auditory cortex, R = right. Comparison between TR/ISI parameter pairs. Five-subject average.

  16. Attenuation model of HDR • Gamma-variate model: • Incorporate ASN accounting factor into HDR model: ; • Regression: Alliney and Ruzinsky, 1994

  17. Conclusions • TR value affects estimate of HDR in both cortices • Chosen ISI parameters have no significant difference Future Investigations • 8-s vs. 12-s ISI • Vary # slices and stimulus duration • Pulse sequences, field strengths

  18. References Alliney, S, Ruzinsky, SA, “An algorithm for the minimization of mixed L1 and L2 norms with application to Bayesian estimation,” IEEE Trans Sig Proc 42:618­–627, 1994. Bandettini PA, Jesmanowicz A, Van Kylen J, Birn RM, Hyde JS, “Functional MRI of brain activation induced by scanner acoustic noise,” Magn Reson Med 39:410-6, 1998. Dale, AM, Buckner, RL, “Selective Averaging of Rapidly Presented Individual Trials Using fMRI,” Hum Brain Map 5:329-340, 1997. Edmister, WB, Talavage, TM, Ledden, PJ, Weisskoff, RM, “Improved Auditory Cortex Imaging Using Clustered Volume Acquisitions,” Hum Brain Map 7:89-97, 1999. Ogawa S, Lee TM, Kay AR, Tank DW, “Brain magnetic resonance imaging with contrast dependent on blood oxygenation,” Proc Natl Acad Sci U S A, 87:9868-72, 1990. Ogawa, S, Tank, DW, Menon, R, Ellermann, JM, Kim, SG, Merkle, H, Ugurbil, K, “Intrinsic signal changes accompanying sensory stimulation: functional brain mapping using MRI,” Proc Natl Acad Sci USA 89:5951-5955, 1992. Talavage, TM, Edmister, WB, Ledden, PJ, Weisskoff, RM, “Quantitative Assesment of Auditory Cortex Responses Induced by Imager Acoustic Noise,” Hum Brain Map 7:79-88, 1999. Talavage, TM, Ledden, PJ, Benson, RR, Rosen, BR, Melcher, JR, “Frequency-dependent responses exhibited by multiple regions in human auditory cortex,” Hearing Research 150:225-244, 2000

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