SHAPE Society

1. Diffuse Reflectance Near
Infrared Spectroscopy of
Atherosclerotic Plaque,
Progress With an
Intracoronary Device
(Part Two)
Vulnerable Plaque Research Program,
University of Texas Houston and
Texas Heart Institute

2. TOC:
♦ Electromagnetic Spectrum and
Spectroscopy
♦ Emission Spectroscopy (Thermography)
♦ Diffuse Reflectance Spectroscopy
♦ Raman, and fluorescence Spectroscopy
♦ Structural/chemical Imaging vs.
Functional Imaging (pH, lactate, free
radicals…)
♦ The goal of combined
“Photonic Catheter”

3. What is electromagnetic radiation?
Electromagnetic radiation is a form of energy,
sometimes called optical energy. The most
familiar form of electromagnetic radiation is
visible light. However, there are many other
forms of electromagnetic radiation including:
•Gama rays
•X-rays
•Ultraviolet Light
•Infrared Light
•Microwaves
•Radio Waves

4. Spectroscopy Basics
In general, spectroscopy is the use of the electromagnetic
spectrum to perform physical or chemical analysis
E=hc/λ

5. Spectroscopy =
The interaction
of light with
various materials

6. Energy is either absorbed,
transmitted, or reflected by
molecules present in sample

7. 1) Non-ionizing radiation (light) is used to
interrogate sample. Example
wavelengths:
♦ Visible 0.4 – 0.7 microns
♦ Near-Infrared 0.7 – 2.5 microns
♦ Mid-Infrared 2.5 – 10 microns
2) Wavelengths are separated for detection
3) Detector converts intensity to voltage
signal as a function of wavelength

8. The human eye is a crude
reflectance spectrometer
A modern spectrometer, however, can measure finer
details over a broader wavelength range and with greater
precision. Thus, a spectrometer can measure absorptions
due to more processes than can be seen with the eye.

10. Light can reveal much about tissue without
ever damaging or changing it’s structure.
Light can be delivered/collected via optical fibers
which can access remote sites within the body via
endoscopic catheters.
Visible light penetrates only a few mm through
tissues. Near infrared light penetrates only a few
cm through tissues.

11. This is both a strength and a weakness. It is a
weakness because light can only interrogate
limited volumes of tissues.
It is a strength because much of the body
consists of thin tissue layers, therefore optical
techniques are well-suited for localized
interrogation of tissue layers.
In our case, studying arterial wall and
atherosclerotic plaque which are well within
millimeters, it works perfectly.

12. Near Infrared Spectroscopy has
come to be widely used to determine
the composition of a variety of
materials ranging from human and
animal feeds to foods.
Quality control of products, e.g. lean
from fat, fake arts and antiques from
originals and so many other
industrial applications…

13. Old Technique New Application

14. •Oximetry to assess blood oxygenation.
•Monitoring hyperbilirubinemia in jaundiced
neonates using reflectance.
•Locating early cancer in the lung, colon,
cervix, and other tissues using fluorescence.
•Assessing blood perfusion and oxygenation
of the brain during child birth.
•Measuring glucose by optical measurements
of skin.
•Detecting a pneomothorax in neonates.
•Detecting atheromatous plaque in blood
vessels using NIR, fluorescence, and IR
Raman.

15. Combining spectroscopy with
imaging yields a spectrally
weighted image that is used or
functional mappings:
•Mapping blood perfusion
•Mapping brain hemorrhage
•Mapping tissue oxygenation
•Mapping the redox potential of
tissues

16. Hyperspectral
Imaging
California Institute of Technology

17. Pioneering works:
Focus on lipid, calcium, and collagen analysis:
♦ Feld et.al. (MIT)
– Raman spectroscopy: currently working on
building Raman fiber optical catheter
– FTIR spectroscopy: only ex-vivo pathological
identification
♦ Lodder et al. (Univ. of Kentucky)
– NIR Catheter to study in-vivo rabbits
cholesterol contents;

18. In vivo determination of the molecular composition
of artery wall by intravascular Raman spectroscopy.
Buschman et al. The Netherlands
Intravascular
ultrasound combined
with Raman
spectroscopy to localize
and quantify
cholesterol and calcium
salts in atherosclerotic
coronary arteries.
Romer et al, The
Netherlands

19. Optical detection of triggered atherosclerotic
plaque disruption by fluorescence emission
analysis.
Christov et al Ontario, Canada.
Time-resolved Fluorescence reflectance
spectroscopy
Grundfest et al, UCLA
NIR spectroscopy and Partial Least Squares for total
cholesterol
Jaross et.al., Germany
Photo Dynamic Therapy “Photo-Angioplasty”!
Pharmacyclics Inc.
Others:

20. Fluorescence spectrum analysis of
atherosclerotic plaque using doxycycline.
Miyagi M et al. Japan
Small branch starches –
dextran and other photonic dies
yet to come
What about photonic
contrast media?

21. NIR Spectroscopic Survey of
30 Human Carotid
Endartherectomized Plaques

25. Near Infrared Spectroscopy
Sensitivity 0.002 and Accuracy 0.016 pH unit
J Clin Monit 1996 Sep;12(5):387-95
Non-invasive measurement of tissue pH using
near-infrared reflectance spectroscopy.
Soller et al.
University of Massachusetts Medical Center,
Worcester 01655, USA.
Optical measurement of tissue pH: Patent #5,813,403

26. NIR Spectrum of Lactate
0.15
0.2
0.25
0.3
0.35
0.4
0.45
1700 1800 1900 2000 2100 2200 2300 2400 2500
wavelength (nm)
arbitraryunits(absorbance)

27. Diffuse Reflectance
NIR Spectroscopy
♦ Absorption is due to
combinations and overtones
of fundamental vibrations
♦ Reflectance Mode: path
length varies for different
tissues and wavelengths
♦ Catheter geometry and
optical coupling important
♦ Small source-detector
separations: light penetrates
tissue while restricting
volume interrogated
plaque
interface
to
spectrometer
~3 mm

28. Tissue Penetration Study
♦ NIR reflectance off mirror 100% signal
♦ Tissue stacks placed on probe end
♦ Incremental increase in signal with mirror
~50 um slices
Aortic tissue
Mirror-Enhanced
Reflectance
Tissue Absorption
& Scattering
Mirror
Fiber
Probe

29. Plaque Measurements
♦ Full spectrum absorbance data (400-2500 nm, FOSS NIRSystems)
♦ 24 gauge needle thermistors (Cole-Parmer model 8402-20)
♦ 750 µm diameter pH electrodes (Microelectrodes, MA)
♦ Punch needle biopsy 1 – 5 mg pieces for lactate assay
♦ Measurements on plaque in 37° incubator
♦ Histology on the rest of the plaque
°C
pH
spectrometer
10-20
m
m
~2 mm

30. Size ~3F
Length 1.5m
Fiber Material Low OH polyimide
coated
silica fibers
Fiber Diameter 100-140 x 10^-6 m
Total Number of Fibers 39
Illumination Fibers 13
Receiving Fibers 26
Side Looking Tip 0.5 mm width
Near Infrared Spectroscopy
Catheter (Prototype I)

32. Catheter Tipped with a Side Looking Silvered Conical
0.5 mm Mirror
cm0.5mm

34. Small Diameter Probe
♦ Preliminary visible/NIR
spectra (UMass Worcester)
Visible Spectra
0.1
0.15
0.2
0.25
0.3
0.35
0.4
400 500 600 700 800 900 1000 1100
Wavelengt h
Fibrofatty Ulcerated FTNIR Plaque
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900
w avelength
A.U.
fibrofatty ulcerated area

35. Large Diameter Probe: Full Spectrum of
Rabbit Aortic Arch
Aortic Arch
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
400 550 700 850 1000 1150 1300 1450 1600 1750 1900 2050 2200 2350 2500
wavelength
absorbance
aortic arch WHHL 0.9 mm NZ aortic arch
WHHL
New
Zealand

36. Area 2: Fibrous
Area 1: Thrombus
Area 3: Calcified/Mixed

39. Spectral ClassificationSpectral Classification
 Full range spectra: 400-2500 nm classification of spectralFull range spectra: 400-2500 nm classification of spectral
signaturesignature
 Cluster analysisCluster analysis
 Principal components analysis for data and noisePrincipal components analysis for data and noise
reductionreduction
 K-means algorithmK-means algorithm
 KK clusters,clusters, mm objects,objects, nn variablesvariables
 Mahalanobis distance metric (co-variance taken intoMahalanobis distance metric (co-variance taken into
account)account)
PC1
PC2
x
[ ] 211
b)(ab)(a −•−= −
CovD T

40. Yesterday’s Dream, Today’s Plan,
Tomorrow’s Catheter!
“Infrared Catheter” providing the following critical
information about plaque:
♦ 1- Temperature (IR)
♦ 2- physio-chemical properties (pH, lactate,
free radicals, oxidized lipids, oxidized
collagen… with NIR)
♦ 3- physio-pathological features (with photonic
contrast media and tracers)

41. Log on:
www.HotPlaque.com

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Research @ the Speed of Thought