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Editorial Slides VP Watch, February 27, 2002, Volume 2, Issue 8
NIR Spectroscopy: Near or Far from Our Expectations?
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
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
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
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
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.
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.
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.
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?
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?
Suggestion:
VP.org Editorial Suggestion:
- Please email your thoughts to:
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
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.
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