1. Biomedical Optics: Multichannel Spectroscopy
Andrew Berger
The Institute of Optics
University of Rochester
Quantum-Limited Imaging Detectors Symposium
Rochester Institute of Technology
March 2, 2009
3 biomedical spectroscopy arenas detectors used daring to dream

2. Biomedical Optics: Application Areas
diffuse photon propagation
fluorescence lifetime spectroscopy
Raman spectroscopy
barely imaging!!!

3. Area #1: Diffuse photon propagation

4. Where biomedical optics lives….
DNA
biological window
Melanin may not really be "asborbing". Also, remember its small physical distance.
Some additional points: in biological window, fat (lipid) is another important absorber, at its body concentration. Also, in vibrational regime, if you dry out the sample you can get a lot of analytes to contribute.
courtesy V. Venugopalan,

5. Important near-IR absorbers
water
32 mM HbO2
11mM Hb
0.3 g/cm3
fat

6. Near-infrared cerebral blood monitoring
light in (690, 830 nm)
light out

7. discuss motivation here: infants are small, uncommunicative, lots of good questions, can’t hold still…

8. Seeing functional responses: visual stimulation

9. Brain monitoring system layout
1-10 kHz modulation for wavelength encoding
Analog Out
DAQ Card
830 nm
Source 1
High Speed DAQ Card for demultiplexing
690 nm
830 nm
Avalanche photodiodes
Source 2
near
690 nm
near
far
l690
l830
Decoded Wavelength Data
far
far
far
far
far
Sample

10. Typical detector for NIRS work
Hamamatsu silicon avalanche photodiode modules
Frequency rolloff in low MHz to GHz
Spectral response out to 1000 nm

11. Time-resolved measurements
pulse at t=0
remitted light at t > 0 r
absorption and scattering

12. Hand-Held Optical Breast Scanner

13. Hand-Held Optical Breast Scanner
Pham, TH., et al. Review of Scientific Instruments, 71 , 1 – 14, (2000).
Bevilacqua, F., et al. Applied Optics, 39, , (2000).
Jakobowski et al., J. Biomed. Opt., 9(1), (2004).
(courtesy F. Bevilacqua)

14. Heavily multiplexed systems!
B. W. Pogueet al, Opt. Express 1, (1997),

15. Diffuse propagation: goals, requirements
Distinguish benign from malignant tumor tissue
Map blood activity (hemodynamics) within brain
Sense deep within tissue (cm)
Record at many locations
Record at many wavelengths
Time resolution to few psec

16. Area #2: Fluorescence lifetime spectroscopy
Once again, psec-nsec timescale!

17. Fluorescence lifetime spectroscopy
brain tissue
Butte et al., “Diagnosis of meningioma by time-resolved fluorescence spectroscopy,” Journal of Biomedical Optics 10(6), (November/December 2005).

18. Instrumentation for temporal fluorescence
Fang et al.

19. Same idea, different group!

20. Fluorescence lifetime: goals, requirements
Distinguish benign from malignant tumor tissue
Record at many wavelengths
Time resolution required to few psec
Desirable to record at many locations (imaging)

21. Area #3: Raman spectroscopy
incident photon with energy E
molecule

22. Raman spectroscopy to detector incident photon with energy E
molecule gains energy DE
scattered photon has energy E -DE
to detector

23. Raman spectrum of immune cell
aromatic amino acids
1340
RNA bases
1092
1259
720
phenylalanine
902
intensity (arb. units)
667
853
813
1580
1005
1651
619
1127
1457
783
1211
amide III
this should probably be a spectrum of a single lymphocyte
adenine
guanine
tyrosine
phenylalanine
C-H 2 def.
amide I
cytosine, uracil
C-N, C-C str.
Raman shift (cm-1)

24. Detectors for Raman spectroscopy
Thermoelectrically-cooled CCD array detectors
Sensitive out to ~1150 nm, limited by Si bandgap
25 micron square pixels
typical dimensions, 256 x 1024 pixels
Princeton Instruments PIXIS CCD

25. Raman spectroscopy: goals, requirements
Distinguish one cell type/state from another
Quantify chemical levels in biofluids (e.g. blood)
Yes, distinguish cancer from non-cancer
Record at many wavelengths
Long acquisition times (sec-minutes)
Necessary to wavelength-tune down the fluorescence
Desirable to time-gate away the fluorescence (intensified CCD or more exotic gating)

26. Benefits of QLIDs for biomedical optics
Diffuse photons
Fluorescence lifetime
psec temporal resolution
Raman
spectral resolution
spectral range
thousands of pixels
[noise...]

27. Summary biomedical spectroscopy: characterize tissue, biofluids, cells
frequently in near-IR
multiple factors driving sub-nsec time resolution
many-many-channel sensing: a game-changer
get past the Si bandgap cutoff
spectral resolution at each pixel: good for diffuse spectroscopy
Questions?