Chromatic distortion during angioscopy: assessment and correction by quantitative colorimetric angioscopic analysis

High yellow color intensity by angioscopy with quantitative colorimetry to identify high-risk features in culprit lesions of patients with acute coronary syndromes

High yellow color intensity (HYCI) regions of atherosclerotic plaque, determined by angioscopy with quantitative colorimetry, are associated with lipid cores underneath thin fibrous caps in ex vivo tissue samples. To determine whether HYCI regions of coronary plaque are associated with disruption or thrombus in living patients, quantitative colorimetry was applied to angioscopy, and the color of culprit lesions was measured in patients with acute coronary syndromes. In 46 patients with acute coronary syndromes (acute myocardial infarction, n = 14; unstable angina pectoris [UAP] with culprit thrombus, n = 16; and UAP without culprit thrombus, n = 16), the recorded angioscopic images of culprit lesions were analyzed using a quantitative colorimetric method based on the L*a*b* color space applied to angioscopy (positive b* = yellow color intensity). HYCI was defined as b* value >23. Plaque disruption was significantly more prevalent in 19 of 24 HYCI regions (79%) than in 9 of 22 non-HYCI regions (41%) (p = 0.007). Culprit HYCI regions were prevalent in patients with myocardial infarction (11 of 14 [79%]), followed by those with UAP with thrombus (9 of 16 [56%]) and UAP without thrombus (4 of 16 [25%]) (p = 0.01 for trend), and were significantly more prevalent in 66% of patients with myocardial infarction and UAP with thrombus compared with 25% of those with UAP without thrombus (p = 0.007). In conclusion, HYCI regions of coronary plaque may be indicative of high-risk lesions vulnerable to thrombosis. Coronary angioscopy with quantitative colorimetry could be used to study the association between high-risk coronary lesions and future cardiovascular events.

Plaque Color Analysis by the Conventional Yellow-Color Grading System and Quantitative Measurement Using LCH Color Space

BACKGROUND

Yellow plaques of higher color grades are regarded as more vulnerable. We tried to elucidate the characteristics of yellow color that are regarded as the sign of vulnerable plaques by an objective and quantitative plaque color analysis.

METHODS

The color of yellow plaques was quantitatively analyzed using LCH color space and was presented by the maximum values of lightness (Lmax), chroma (Cmax), and hue (Hmax). Effect of light intensity on these parameters was experimentally examined (five plaque models, six light intensities). Relation between conventional yellow-color grade and LCH parameters was examined (31 plaques). Color analysis with LCH color space was applied (1) to compare the culprit lesions of unstable angina (eight patients) and of stable effort angina (nine patients) and (2) to evaluate the regression of yellow plaque by 80-week statin treatment (four patients, 19 plaques).

RESULTS

Cmax and Hmax were not influenced by light intensity so far as it was within appropriate range. Cmax (13 +/- 3, 25 +/- 5, and 28 +/- 4) became higher and Hmax (178 +/- 26, 134 +/- 10, and 91 +/- 16) became lower as the grade became higher (P < 0.0001). Culprit lesions of unstable angina had higher Cmax (22.8 +/- 7.9 vs 14.8 +/- 7.5, P = 0.04) and lower Hmax (73.3 +/- 19.7 vs 168.0 +/- 71.5, P = 0.002) than stable effort angina. Statin treatment reduced Cmax (21.3 +/- 9.6 vs 14.6 +/- 3.1, P = 0.004) and increased Hmax (82.6 +/- 25.8 vs 142.3 +/- 54.1, P = 0.0005).

CONCLUSIONS

Plaque color was consistently and quantitatively measurable using LCH color space uninfluenced by light intensity of appropriate range. Vulnerable yellow color had high chroma and low hue, indicating vivid and reddish-yellow color.

Quantitative colorimetry of atherosclerotic plaque using the L*a*b* color space during angioscopy for the detection of lipid cores underneath thin fibrous caps

OBJECTIVES

Yellow plaques seen during angioscopy are thought to represent lipid cores underneath thin fibrous caps (LCTCs) and may be indicative of vulnerable sites. However, plaque color assessment during angioscopy has been criticized because of its qualitative nature. The purpose of the present study was to test the ability of a quantitative colorimetric system to measure yellow color intensity of atherosclerotic plaques during angioscopy and to characterize the color of LCTCs.

METHODS

Using angioscopy and a quantitative colorimetry system based on the L*a*b* color space [L* describes brightness (-100 to +100), b* describes blue to yellow (-100 to +100)], the optimal conditions for measuring plaque color were determined in three flat standard color samples and five artificial plaque models in cylinder porcine carotid arteries. In 88 human tissue samples, the colorimetric characteristics of LCTCs were then evaluated.

RESULTS

In in-vitro samples and ex-vivo plaque models, brightness L* between 40 and 80 was determined to be optimal for acquiring b* values, and the variables unique to angioscopy in color perception did not impact b* values after adjusting for brightness L* by manipulating light or distance. In ex-vivo human tissue samples, b* value >/=23 (35.91 +/- 8.13) with L* between 40 and 80 was associated with LCTCs (fibrous caps <100 mum).

CONCLUSIONS

Atherosclerotic plaque color can be consistently measured during angioscopy with quantitative colorimetry. High yellow color intensity, determined by this system, was associated with LCTCs. Quantitative colorimetry during angioscopy may be used for detection of LCTCs, which may be markers of vulnerability.