Near Infrared Spectroscopy

The pursuit to identify vulnerable plaque has been relentless, as it is responsible for major healthcare problems, such as sudden cardiac death and acute coronary syndromes, including acute myocardial infarction (AMI). Per definition, vulnerable plaque is plaque that is prone to rupture but has not yet ruptured.1 The features associated with vulnerable plaque include a large lipid core, thin fibrous cap overlying the lipid core, increased macrophage activity, positive remodeling, and increased vasa vasorum.2 Among these 5 components, the 2 most important ones are probably the large lipid core and thin fibrous cap.Article see p 55Since 95% of ruptured fibrous caps are thinner than 65 μm, noninvasive diagnostic tests such as computed tomography and magnetic resonance do not have sufficient resolution to accurately measure this thin structure. Therefore, a number of intravascular diagnostic modalities have been extensively tested over the last decade3 (Table). Among those most widely tested are radiofrequency intravascular ultrasound, angioscopy, and optical coherence tomography. Recently, near infrared spectroscopy (NIRS) received US Food and Drug Administration approval. It is now being actively investigated.View this table:Table. Comparison of Invasive Diagnostic Modalities for Detection of Vulnerable PlaqueRadiofrequency intravascular ultrasound was used in the PROSPECT trial4 and showed that plaque burden >70%, virtual histology-thin–cap fibroatheroma, and minimal luminal area ≤4.0 mm2 are factors for composite major adverse cardiac events during the 3-year follow-up period. Although the factors for future cardiac events were identified, all 3 predictors are related to plaque burden, …