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Introduction

Effects of Diffusion Times on Diffusion-Tensor-Imaging Contrast Govind Nair, Timothy Q Duong Center for Comparative NeuroImaging, Psychiatry University of Massachusetts Medical School, Worcester, MA 01655. Introduction. DTI is widely used to map fiber tracks

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Introduction

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  1. Effects of Diffusion Times on Diffusion-Tensor-Imaging ContrastGovind Nair, Timothy Q DuongCenter for Comparative NeuroImaging, PsychiatryUniversity of Massachusetts Medical School, Worcester, MA 01655

  2. Introduction • DTI is widely used to map fiber tracks • Most DTI studies used diffusion time (tdiff) of 30-40 ms • DTI contrast could be dependent on tdiff • On the order of cell size, ADC is a function of tdiff < 5 ms, highly dependent > 20 ms much slower variations • On the order of larger than cell size, • Horsfield (1994) observed a tdiff dependence (40-800 ms) of WM ADC in human brain

  3. Objective We hypothesize that • DTI contrast could be improved at longer tdiff These hypotheses were tested on • Normal mice and • Myelin-deficient shiverer mice

  4. Methods • Seven wild type (wt) mice (20-30g) • Eight Shiverer (shi)mice (20-30g) • 1% isoflurane • Spontaneously breathing • Head stereotaxic device • Respiratory rate: 100-150 bpm • Rectal temperature: 37.5 ± 0.25°C

  5. Methods • 9.4T/89mm vertical bore magnet • 100 G/cm gradient (ID = 45 mm) • STEAM sequence • TR/TE = 2500/14 ms, variable TM • 64 x 64, 15x15 mm2, 4 averages • b = 10, 1200 s/mm2 • DWI acquired at 6 directions • diffusion time = 30, 80,180, 280 ms • 10 mins per DTI axis per diffusion time

  6. Data analysis (Basser & Pierpaoli, 1998) (Le Bihan 2001)

  7. Phantom experiments • Cross-terms at different tdiff yielded different effective b-values • In principle, cross terms could be calculated • Instead we adjusted the diffusion gradients to yield identical effective b values at different tdiff on a phantom • Results were validated on two phantoms.

  8. Phantom: NAA in DMSO and water(in image mode, identical parameters as in vivo studies) NAA in DMSO Trace ADCl Average ADC NAA in DMSO across tdiff: 0.51 ± 0.02 x10-3 mm2/s Temp = 22o C Average ADCWater across tdiff: 1.98 ± 0.02 x 10-3 mm2/s Temp = 20o C 30 80 180 280 30 80 180 280 ms Diffusion time

  9. *** ** * *** P < 0.001 ** P < 0.01 * P < 0.05

  10. corpus callosum hippocampus

  11. Variation in l with tdiff corpus callosum hippocampus * *** * * *** l (x 10-3 mm2/s) • 80 180 280 30 80 180 280 ms • Diffusion time

  12. Variation in ADCtrace with tdiff corpus callosum hippocampus * ** ** ADCtrace (x 10-3 mm2/s) • 80 180 280 30 80 180 280 ms • Diffusion time

  13. Variation in FA with tdiff corpus callosum hippocampus * * * • 80 180 280 30 80 180 280 ms • Diffusion time

  14. Variation in VR with tdiff corpus callosum hippocampus * * ** • 80 180 280 30 80 180 280 ms • Diffusion time

  15. Conclusions • Scheme to correct for cross terms for different tdiff • In corpus callosum: • Wt:l showed tdiff dependence • Shi:l showed lesser tdiff dependence • l// in both wt and shi were independent of tdiff • Anisotropy of wt showed a greater dependence on tdiff than shi • In hippocampus, FA, VR, l, ADCtrace showed small tdiff dependence; there was no difference between wt and shi

  16. Grant supportsWhitaker Foundation, RG-02-0005 American Heart Association, SDG-0430020NIH, NEI R01 EY014211NIH, NINDS R01 NS45879Authors wish to thank Dr. Karl Helmer for his technical assistance

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