This document discusses the use of near-infrared (NIR) spectroscopy to analyze atherosclerotic plaques. It provides definitions of NIR spectroscopy and describes how it allows chemical analysis of plaques. Studies are cited that have used NIR spectroscopy to detect plaque components like lipid pools, thin fibrous caps, and inflammatory cells. The document discusses both advantages and disadvantages of using NIR spectroscopy for in vivo chemical analysis of plaques. It concludes that NIR spectroscopy shows potential for identifying vulnerable plaques but questions remain about its ability to distinguish plaque types in living patients.

1. Editorial Slides
VP Watch, February 27, 2002, Volume 2, Issue 8
NIR Spectroscopy: Near or Far from Our
Expectations?

2.  NIR Spectroscopy definition:
• The use of the absorption, emission, or
scattering of light in the near infrared portion of
the electromagnetic spectrum by atoms or
molecules.
• The diffuse reflectance spectra from
wavelengths between 400 and 2400 nm allow
detailed analysis of chemical composition. 9

3.  Multiple techniques are being tested to identify
vulnerable plaques before they disrupt and cause
thrombosis. 1-8
 The first application of NIR in atheroma studies
dates back to 1993 when Cassis and Lodder
described the ability of NIR imaging in vitro. 12
 A near-IR imaging system and parallel vector
supercomputer were used with a fiber-optic probe
to produce chemical maps of the intimal surface of
living arteries. 10,12

4.  Romer et al. using NIR Raman spectroscopy have
shown the capability of detection of atherosclerotic
plaque. 8
However, Raman spectroscopy while more
sophisticated is also more challenging in clinical
applications.
 Naghavi, Soller, and colleagues have used NIR
spectroscopy for measuring plaque activity and
inflammation parameters such as pH and lactate. 13

5.  As highlighted in VP Watch of this week,
Moreno, Muller, and colleagues showed that NIR
spectroscopy identifies components of vulnerable
plaque (thin cap, lipid pool, and macrophage
presence) in postmortem plaques specimens. 9
 They determined that NIR spectroscopy sensitivity
and specificity are 90% and 93% for lipid pool,
77% and 93% for thin cap, and 84% and 89% for
inflammatory cells, respectively. 9

6.  Near infrared spectroscopy (NIRS) advantages
for in vivo chemical analysis of plaque
composition: 11
i. Non-ionizing radiation does not damage tissue.
ii. Good depth of penetration (2-3mm).
iii. Using advanced statistical methods, differentiation of
a single chemical compound among a great number
of other substances is possible, such as different
types of lipids and proteins.
iv. Can measure physiological factors within plaques,
such as pH concentration.

7.  Disadvantages:
I. Challenging training (calibration) set followed by
multiple testing sets are required to develop the
technique for new application.
II. Complex statistical analysis is required for
accurate determination of different constituents in
plaque.
III. Water in the blood and tissue may affect light
absorption and signal to noise ratio, in vivo.
IV. Cannot accurately identify detailed components of
plaque inflammation, for example monocyte
recruitment rate.

8. Conclusion:
I. Diffuse reflectance near infrared spectroscopy is
emerging as a novel technique for characterization of
vulnerable plaque.
II. Based on the evidence collected to date, catheter
near infrared spectroscopy is a new and exciting
development for vulnerable detection.

9. Questions:
I. Knowing the significant tissue changes in autopsy
specimens, the question is can NIR spectroscopy
distinguish vulnerable plaque from stable plaque in
vivo?
II. Knowing the noise effect of intravascular factors that
are present in vivo, the question is can NIR
spectroscopy catheter system provide sufficient signal
to noise ratio for reproducible/reliable clinical
measurements?

10. Questions:
I. Given equal feasibility, can NIR Raman spectroscopy
out perform NIR diffuse reflectance spectroscopy?
II. If NIRS measurement of plaque pH and lactate prove
to identify plaque activity and inflammation
(macrophage infiltration), would a combination of the
current technique (identifying fibrous cap and lipid
pool) and pH/lactate measurement be more valuable
for identification of vulnerable plaque?

11. Suggestion:
VP.org Editorial Suggestion:
- Please email your thoughts to:
Discussion-Group@VP.org or DG@VP.org

12. 1. Naghavi M, Madjid M, Khan MR, et al. New developments in the detection of vulnerable plaque. Curr
Atheroscler Rep. 2001; 3: 125–135.[Medline]
2. Pasterkamp G, Falk E, Woutman H, et al. Techniques characterizing the coronary atherosclerotic
plaque: influence on clinical decision making? J Am Coll Cardiol. 2000; 36: 13–21.[Medline]
3. Fayad ZA, Fuster V. Characterization of atherosclerotic plaques by magnetic resonance imaging. Ann N
Y Acad Sci. 2000; 902: 173–186.[Medline]
4. Brezinski ME, Tearney GJ, Weissman NJ, et al. Assessing atherosclerotic plaque morphology:
comparison of optical coherence tomography and high frequency intravascular ultrasound. Heart. 1997;
77: 397–403.[Abstract]
5. Uchida Y, Nakamura F, Tomaru T, et al. Prediction of acute coronary syndromes by percutaneous
coronary angioscopy in patients with stable angina. Am Heart J. 1995; 130: 195–203.[Medline]
6. Casscells W, Hathorn B, David M, et al. Thermal detection of cellular infiltrates in living atherosclerotic
plaques: possible implications for plaque rupture and thrombosis. Lancet. 1996; 347: 1447–1451.
[Medline]
7. Stefanadis C, Diamantopoulos L, Vlachopoulos C, et al. Thermal heterogeneity within human
atherosclerotic coronary arteries detected in vivo: a new method of detection by application of a special
thermography catheter. Circulation. 1999; 99: 1965–1971.[Abstract/Full Text]
8. Romer TJ, Brennan JFIII, Puppels GJ, et al. Intravascular ultrasound combined with Raman
spectroscopy to localize and quantify cholesterol and calcium salts in atherosclerotic coronary arteries.
Arterioscler Thromb Vasc Biol. 2000; 20: 478–483.
9. Detection of Lipid Pool, Thin Fibrous Cap, and Inflammatory Cells in Human Aortic Atherosclerotic
Plaques by Near-Infrared Spectroscopy; Pedro R. Moreno, Robert A. Lodder, K. Raman
Purushothaman, William E. Charash, William N. O’Connor, and James E. Muller ; Circulation 2002 105:
923 - 927; published online before print February 4 2002, 10.1161/hc0802.104291.
References

13. 10. Cassis LA, Lodder RA. Near-IR imaging of atheromas in living arterial tissue. Anal Chem. 1993; 65:
1247–1256.[Medline]
11. Jaross W, Neumeister V, Lattke P, Schuh D; Determination of cholesterol in atherosclerotic plaques
using near infrared diffuse reflection spectroscopy.; Atherosclerosis. 1999 Dec;147(2):327-37.
12. Cassis L., Lodder R; Near infrared imaging of atheromas in living tissue; Analytical Chemistry, 1993 Vol
65 1247-1256
13. Progress with calibration of 3f near infrared spectroscopy fiber optic catheter for monitoring the pH of
atherosclerosis plaque: introducing a novel approach for detection of vulnerable plaque ; Khan T, Soller
B, Madjid M, Willerson JT, Casscells SW, Naghavi M; Abstract Oral Presentation, AHA Scientific
Session 2001, Anaheim, CA, USA.
References