1 / 16

Introduction

cissy
Download Presentation

Introduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Echo-Planar Imaging BOLD fMRI in Mice on a 9.4T Vertical Bore MicroimagerGovind Nair, Timothy Q DuongCenter for Comparative NeuroImaging, PsychiatryUniversity of Massachusetts Medical School, Worcester, MA 01655Grant supportsWhitaker Foundation, RG-02-0005 American Heart Association, SDG-0430020NIH, NEI R01 EY014211NIH, NINDS R01 NS45879

  2. Introduction • Longitudinal imaging of transgenic mice and mouse disease models allows studies to be performed over their entire life span. • Narrow-vertical bore magnets (microimagers) are well suited for imaging mice • low cost • availability at high fields • availability of high-performance gradients • While anatomical imaging is readily available, fMRI in mice on microimagers remains a major challenge

  3. Introduction • Mice fMRI on microimager had been reported using conventional gradient-echo sequence (Arhens 2001; Huang 1996) and fast spin-echo with exogenous contrast agent sequence (Mueggler 2003) • These sequences generally yield • Reduced temporal resolution • Reduced SNR per unit time • Reduced sensitivity to BOLD contrast • Increased physiological noises • Echo-planar imaging overcomes these problems albeit • Increased susceptibility artifact • Harder to implement due to larger eddy current (small bore) • Poor shimming capability on small-bore magnets

  4. Introduction • Other challenges include • Limited spaces for physiological monitoring • More difficult to use mechanical ventilation • Increased susceptibility-induced signal loss due to small brain size and larger air-tissue interfaces • The goal of this study was • To develop a sensory-stimulation mouse model for fMRI studies • Explore echo-planar imaging for fMRI on a 9.4 T microimager

  5. Methods • Mouse head immobilized with ear, tooth and shoulder bars • Anesthetized with isoflurane • Spontaneously breathing mice • Monitored respiration via a transducer • Maintained body temperature at 37 ± 0.5 C

  6. Methods • Three sets of experiments were performed: • Graded isoflurane (0.25, 0.50, 0.75, 1.0, 1.25%) were explored using 10% CO2 to determine the optimal BOLD CNR (n = 9) • Hindpaw electrical stimulation (1-7 mA) on mice anesthetized under the optimal isoflurane level (n = 6) • Stimulation were explored in details with 4 and 6 mA and under 0.75% and 1.0% isoflurane (n = 5) • Relatively high currents were used because isoflurane is a potent anesthetic, relative to the widely used a-chloralose • Bench top observations were also observed in some of the hindpaw-stimulation animal and four additional animals

  7. Imaging Parameters • 9.4 T / 89 mm vertical magnet, 100 G/cm gradient (45 mm ID) • Surface coil (1.2-1.5 cm ID) – remote tuning and matching from top • Shimming over an 8-mm thick slab; linewidth of 30-45 Hz • Single-shot, spin-echo EPI • TR / TE = 2500 ms / 38 ms (TE ~ T2 at 9.4T) • FOV = 2 x 1 cm, matrix = 64x32 (312x312x600 mm) • Nine 0.6-mm slices (0.15 mm gap) • Paradigms • 2 mins baseline, 2 mins CO2 • 2 mins baseline, 1 mins stimulation, 2 mins baseline • Anatomy obtained with similar parameters but at higher resolution

  8. Data analysis • Hypercapnia • BOLD percent changes were calculated from a whole-brain ROI • BOLD contrast-to-noise ratio (CNR) was computed • Hindpaw stimulation • Cross-correlation maps were calculated • ROI’s of the hindpaw primary sensory cortex was drawn with reference to the average of all activation maps and anatomy • Time courses of different conditions were obtained from the same ROI’s without using an activation-map mask • Percent changes were computed

  9. Hypercapnic Challenge

  10. SE EPI and BOLD maps due to CO2 challenge Single-shot No average 15% 0%

  11. Hypercapnic Stimulation Hypercapnic challenge (N = 9) (N = 1)

  12. Hindpaw stimulation (Group II, n = 4) 0.9 CC 0.3 Stimulation

  13. Hindpaw stimulation (Group III, n = 5)

  14. Work in progress: GE EPI and segmented EPI Gradient-echo EPI Gradient-echo BOLD responses to 10% CO2 Multi-segment EPI (78x78x500 mm2, no signal average)

  15. Conclusions • Implemented spin-echo EPI for fMRI study • Developed a mouse model for sensory stimulation fMRI study • Optimized isoflurane concentration • Stimulation currents • These optimal parameters are in good agreement with an isoflurane-anesthetized sensory-stimulation model in rats where MABP, HR and RR and blood-gas measurements were carefully monitored. • Improvement in spatial resolution and BOLD contrast are under investigation.

  16. 4mA 6mA 8mA 20 mmHg 10 s RAT DATA: MABP traces and physiology under 1.15-1.25% isoflurane (n = 6, SD) * P = 0.01, ** P  0.008 (Liu, Schmidt et al., in press 2004)

More Related