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Time-resolved functional near-infrared spectroscopy

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Presentation on theme: "Time-resolved functional near-infrared spectroscopy"— Presentation transcript:

1 Time-resolved functional near-infrared spectroscopy
A.Torricelli, D.Contini, A.Pifferi, L.Spinelli and R.Cubeddu ULTRAS-CNR-INFM and IFN-CNR, Politecnico di Milano, Dipartimento di Fisica L.Craighero, L.Fadiga Faculty of Medicine – DBSTA, Section of Human Physiology, Università di Ferrara Trieste Workshop - “Tools to study language acquisition in early infancy”, May 5-8, 2006

2 Principles of functional NIRS (fNIRS)
O2Hb HHb l1 l2 wavelength (nm) e (cm-1 M-1)

3 Lambert-Beer law Light attenuation in a clear medium L ma = e C I(0)
I(L) z dz I = light intensity [W cm-2] ma = absorption coefficient [cm-1] L = source-detector distance = pathlength [cm]

4 Light Propagation in Diffusive Media
clear medium turbid medium Light scattering is greater than absorption  Photons pathlength is not the geometrical source-detector distance  Attenuation is dependent also on scattering

5 Modified Lambert-Beer Law
B = Differential Pathlength Factor (DPF) [-] G = Signal loss due to scattering [-] L = source-detector distance [cm] L* = L B = effective pathlength [cm] Main problem: B (DPF) and G depend on wavelength, geometry, subject, ... Partial solution:  Monitor changes, not absolute values

6 Principles of Time-Resolved fNIRS
Intensity r m’s , ma

7 Time-resolved fNIRS Effect of scattering Effect of absorption log10I
Slope changes m’s ma Slope do not change! time time Time position do not change! Time position changes

8 Motor task on human subject: - Time-gate analysis
Head is not homogeneous! r m’s1 , ma1 m’s2 , ma2 m’s0 , ma0 S0 S1 S2 Dma2 Martelli et al. Perturbation model for light propagation through diffusive layered media Phys. Med. Biol (2005) scalp/skull csf brain r I time Steinbrink et al. Phys Med Biol 46: (2001) Del Bianco et al. Phys Med Biol 47: (2002) Semi-empirical approach: time-gate analysis

9 Motor task on human subject: - Time-gate & microscopic Lambert-Beer law
baseline task recovery baseline task recovery [ Nomura et al., Phys Med Biol 42: (1997) ]

10 PoliMi multi-channel time-resolved fNIRS system - new set-up: S16-D64
PicoQuant PDL800 Piezojena F-SM19 OZOptics VISNIR5050 Microchip Technology dsPIC30F6014 Hamamatsu R M4 Becker & Hickl, SPC-134, HRT-41, HAFC-26

11 System characterization: - detection section
4 anode PMT + high sensitivity: SS20 0.6%, SS25 nm + large area (9x9 mm2 each quadrant) — temporal resolution (TTS 300 ps) 18 mm Fiber bundle + large NA (0.5) + home-made, low cost — seven 1-mm plastic fibers: not so flexible! — modal dispersion limits length to 1.5 m 3 mm  4 fiber bundles in each quadrant  total number of fiber bundles 64 … now limited to 16!!  See poster ME21 Contini et al. for details

12 System characterization: - Instrument response function (IRF)
510 ps FWHM 520 ps FWHM FWHM  500 ps 5 ms minimum acquisition time per single channel max injected power < 0.5 mW 8 MHz (2MHz/board)  106 ph/s per wavelength  See poster ME21 Contini et al. for details

13 System characterization: - Linearity for absorption
Results for 690 nm, no major differences at 820 nm Inter-channel dispersion (CV) < 9% Integral non-linearity < 3% Negligible coupling between ma and ms’  See poster ME21 Contini et al. for details

14 System characterization: - Noise
@ 200K counts CV abs:  2% CV abs:  0.4% CV late gate:  0.1% Pifferi et al., “ ...The Medphot Protocol”, Applied Optics 44: (2005)

15 Motor task on human subject: - protocol
Motor area for right hand identified by Transcranial Magnetic Stimulation (TMS) 2 cm S2 D2 2 cm S1 D1 volounteer solid phantom Protocol: 20 s baseline, 20 s task (finger tapping with right hand at 2Hz), 40 s recovery 9 repetitions, acquisition time 1s

16 Motor task on human subject: - DHHb and DO2Hb
baseline task recovery chan 1 baseline task recovery solid phantom 9 repetitions

17 Motor task on human subject: - DHHb and DO2Hb (single trials)
15s task: 1 repetition 10s task : 1 repetition 5s task : 1 repetition

18 Motor task on human subject: - mapping DHHb and DO2Hb
2 cm Protocol: 20 s baseline, 20 s task (finger tapping with right hand at 2Hz), 40 s recovery 4 repetitions, acquisition time 250 ms

19 Time-resolved fNIRS of primate brain: - first results
task rest S1 D1 1 mm fiber 1 cm Optodes in direct contact with the dura Task: grasp food

20 Future Perspectives Source: whitelight fiber laser
Leon-Saval et al., “Multimode fiber devices with single-mode performance”, Optics Letters 30: (2005) Optics: photonic crystal devices Zappa et al., “Complete single-photon counting and timing module in a microchip” Optics Letters 30: (2005) Detection & Acquisition: IC SPAD

21 Time-Resolved fNIRS at Null Source-Detector Separation
Improved contrast and resolution Torricelli et al. Phys Rev Lett 95, (2005)

22 “Future” Perspectives?
"Pre-Crime" Image Thoughts of PreCogs (2054) Philip K. Dick, ”The Minority Report” (1956) Steven Spielberg, "Minority Report” (2002) Thanks to Turgut Durduran, Upenn

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