Near-Infrared Spectroscopy Enhances Intravascular Ultrasound Assessment of Vulnerable Coronary Plaque: A Combined Pathological and In Vivo Study.

OBJECTIVES: Pathological studies demonstrate the dual significance of plaque burden (PB) and lipid composition for mediating coronary plaque vulnerability. We evaluated relationships between intravascular ultrasound (IVUS)-derived PB and arterial remodeling with near-infrared spectroscopy (NIRS)-derived lipid content in ex vivo and in vivo human coronary arteries. APPROACH AND RESULTS: Ex vivo coronary NIRS and IVUS imaging was performed through blood in 116 coronary arteries of 51 autopsied hearts, followed by 2-mm block sectioning (n=2070) and histological grading according to modified American Heart Association criteria. Lesions were defined as the most heavily diseased 2-mm block per imaged artery on IVUS. IVUS-derived PB and NIRS-derived lipid core burden index (LCBI) of each block and lesion were analyzed. Block-level analysis demonstrated significant trends of increasing PB and LCBI across more complex atheroma (Ptrend <0.001 for both LCBI and PB). Lesion-based analyses demonstrated the highest LCBI and remodeling index within coronary fibroatheroma (Ptrend <0.001 and 0.02 versus all plaque groups, respectively). Prediction models demonstrated similar abilities of PB, LCBI, and remodeling index for discriminating fibroatheroma (c indices: 0.675, 0.712, and 0.672, respectively). A combined PB+LCBI analysis significantly improved fibroatheroma detection accuracy (c index 0.77, P=0.028 versus PB; net-reclassification index 43%, P=0.003), whereas further adding remodeling index did not (c index 0.80, P=0.27 versus PB+LCBI). In vivo comparisons of 43 age- and sex-matched patients (to the autopsy cohort) undergoing combined NIRS-IVUS coronary imaging yielded similar associations to those demonstrated ex vivo. CONCLUSIONS: Adding NIRS to conventional IVUS-derived PB imaging significantly improves the ability to detect more active, potentially vulnerable coronary atheroma.

Robust quantitative assessment of collagen fibers with picrosirius red stain and linearly polarized light as demonstrated on atherosclerotic plaque samples.

Collagen is an important component in maintaining structural integrity and functionality of tissues and is modulated in various biological processes. Its visualization and possible quantification using histopathological stains can be important for understanding disease progression or therapeutic response. Visualization of collagen fiber with the histological stain picrosirius red (PSR) is enhanced with polarized light and quantitative analysis is possible using circular polarizers. However, linear polarizers are more commonly available and easier to optically align. The objective of the present study is to demonstrate a novel image acquisition technique and analysis method using linearly polarized light. The proposed imaging technique is based on image acquisition at multiple slide rotation angles, which are co-registered to form a composite image used for quantitative analysis by pixel intensity or pixel counting. The technique was demonstrated on multiple human coronary samples with varying histopathologies and developed specifically to analyze cap collagen in atherosclerotic plaque. Pixel counting image analysis was found to be reproducible across serial tissue sections and across different users and sufficiently sensitive to detect differences in cap structural integrity that are likely relevant to prediction of rupture risk. The benefit of slide rotation angle under linear polarization to acquire images represents a feasible and practical implementation for expanding the general utility of PSR for quantitative analysis.

Intravascular ultrasound and near-infrared spectroscopic features of coronary lesions with intraplaque haemorrhage.

AIMS: Intraplaque haemorrhage is considered a major contributor to lesion progression. We assessed coronary lesions with intraplaque haemorrhage using intravascular ultrasound (IVUS) and near-infrared spectroscopy (NIRS). METHODS AND RESULTS: We evaluated coronary arteries from autopsy hearts using 40MHz IVUS and NIRS and compared the imaging findings to histopathology. A total of 2324 2-mm long histological segments from 101 coronary arteries from 56 autopsy hearts were included. Intraplaque haemorrhage was found pathologically in 0.8% (18/2324) of segments. Segments with intraplaque haemorrhage had more fibroatheromas (FAs) with a greater IVUS plaque burden, a greater prevalence of IVUS echolucent zones, and a higher NIRS-lipid core burden index (LCBI) compared to segments without intraplaque haemorrhage (FAs: 72.2% vs. 18.3%, P < 0.0001; plaque burden: 59.7% [95% confidence interval: 55.5, 64.0] vs. 48.6% [45.8, 51.3], P < 0.0001; echolucent zones: 88.9% vs. 2.8%, P < 0.0001; NIRS-LCBI: 176 [88, 264] vs. 72 [53, 91], P = 0.02). The 16 IVUS superficial echolucent zones with intraplaque haemorrhage had more late FAs but shorter echolucent zone lengths (0.9 mm [0.7, 1.1] vs. 1.7 mm [1.5, 1.9], P < 0.0001) compared to 65 IVUS superficial echolucent zones without intraplaque haemorrhage. CONCLUSIONS: Intracoronary imaging features consistent with intraplaque haemorrhage included a greater plaque burden, a higher NIRS-LCBI, and a greater prevalence of IVUS echolucent zones compared to lesions without intraplaque haemorrhage.

Novel optical detection system for in vivo identification and localization of cervical intraepithelial neoplasia.

A noncontact optical detection system is developed for the in vivo identification and localization of high-grade cervical intraepithelial neoplasia (CIN 2,3). Diagnostic scans of the entire human cervix are performed following acetic acid application employing three integrated optical measurements: laser-induced fluorescence spectroscopy, white light diffuse reflectance spectroscopy, and video imaging. Full cervical scans comprising 499 interrogation locations at 1-mm spatial resolution are completed in 12 s. Diffuse reflectance and fluorescence spectra with signal-to-noise ratios of better than 100-to-1 are collected between 360 and 720 nm in increments of 1 nm, with an inherent spectral resolution of 8 nm. Glare reduction and optical vignetting are handled with a novel illumination scheme and subsequent spectral arbitration algorithms. The system is designed and found to be well below acceptable safe optical exposure levels. Typical reproducibility across multiple systems is approximately 5%, providing reliable and accurate detection of in vivo cervical neoplasia in normal clinical use.

Large lipid-rich coronary plaques detected by near-infrared spectroscopy at non-stented sites in the target artery identify patients likely to experience future major adverse cardiovascular events.

AIMS: A recent study demonstrated that intracoronary near-infrared spectroscopy (NIRS) findings in non-target vessels are associated with major adverse cardiovascular and cerebrovascular events (MACCE). It is unknown whether NIRS findings at non-stented sites in target vessels are similarly associated with future MACCE. This study evaluated the association between large lipid-rich plaques (LRP) detected by NIRS at non-stented sites in a target artery and subsequent MACCE. METHODS AND RESULTS: This study evaluated 121 consecutive registry patients undergoing NIRS imaging in a target artery. After excluding stented segments, target arteries were evaluated for a large LRP, defined as a maximum lipid core burden index in 4 mm (maxLCBI4 mm) ≥400. Excluding events in stented segments, Cox regression analysis was performed to evaluate for an association between a maxLCBI4 mm ≥400 and future MACCE, defined as all-cause mortality, non-fatal acute coronary syndrome, and cerebrovascular events. NIRS detected a maxLCBI4 mm ≥400 in a non-stented segment of the target artery in 17.4% of patients. The only baseline clinical variable marginally associated with MACCE was ejection fraction (HR 0.96, 95% CI 0.93-1.00, P = 0.054). A maxLCBI4 mm ≥400 in a non-stented segment at baseline was significantly associated with MACCE during follow-up (HR 10.2, 95% CI 3.4-30.6, P < 0.001). CONCLUSION: Detection of large LRP by NIRS at non-stented sites in a target artery was associated with an increased risk of future MACCE. These findings support ongoing prospective studies to further evaluate the ability of NIRS to identify vulnerable patients.

Combined IVUS and NIRS detection of fibroatheromas: histopathological validation in human coronary arteries.

OBJECTIVES: This study assessed grayscale intravascular ultrasound (IVUS) and near-infrared spectroscopy (NIRS) detection of a histological fibroatheroma (FA). BACKGROUND: NIRS-detected, lipid-rich plaques (LRPs) and IVUS-detected attenuated plaques are considered to be vulnerable. METHODS: IVUS-attenuated plaque and NIRS-LRP (yellow or tan block chemogram) were compared with histopathology in 1,943 sections of 103 coronary arteries from 56 autopsied hearts. RESULTS: IVUS-superficial attenuation and NIRS-LRP showed a similar high specificity of approximately 95%, whereas IVUS-superficial attenuation alone had a poor sensitivity (vs. NIRS-LRP) in detecting FAs (36% vs. 47%; p = 0.001). Compared with FA sections with superficial attenuation, FA sections without superficial attenuation had a smaller plaque burden (57.1% vs. 67.7%), a larger arc of calcium (79.7° vs. 16.8°), and a lower prevalence of a ≥20% histological necrotic core (28% vs. 50%) or late FA (14% vs. 37%; all p < 0.05). Compared with FA sections with NIRS-LRP, FA sections without NIRS-LRP showed a smaller plaque burden (58.0% vs. 63.3%) and a lower prevalence of a ≥20% necrotic core (27% vs. 46%). Conversely, non-FAs with NIRS-LRP (vs. non-FAs without LRP) showed a larger plaque burden (55.1% vs. 46.3%), a greater prevalence of a ≥20% histological lipid pool (34% vs. 5%), and mostly pathological intimal thickening (50%) or fibrocalcific plaque (33%). When sections showed either IVUS attenuation or NIRS-LRP, the sensitivity for predicting a FA was significantly higher compared with IVUS attenuation alone (63% vs. 36%; p < 0.001) or NIRS-LRP alone (63% vs. 47%; p < 0.001). When sections showed both IVUS attenuation and NIRS-LRP, the positive predictive value improved compared with IVUS attenuation alone (84% vs. 66%; p < 0.001) or NIRS-LRP alone (84% vs. 65%; p < 0.001). CONCLUSIONS: NIRS-LRP was more accurate than IVUS for predicting plaque containing a necrotic core or a large lipid pool, and the combination was more accurate than either alone.

Application of multivariate curve resolution for analysis of FT-IR microspectroscopic images of in situ plant tissue.

The chemometric techniques of multivariate curve resolution (MCR) are aimed at extracting the spectra and concentrations of individual components present in mixtures using a minimum set of initial assumptions. We present results from the application of alternating least squares (ALS) based MCR to the analysis of hyperspectral images of in situ biological material. The spectra of individual pure components were mathematically extracted and then identified by searching the spectra against a commercial library. No prior information about the chemical composition of the material was used in the data analysis. The spectra recovered by ALS-MCR analysis of an FT-IR microspectroscopic image of an 8-micron-cornkernel section matched very well the spectra of the corn storage protein, zein, and starch. Through the application of MCR, we were able to show the presence of a second spectrally different protein, which could not be easily seen using univariate analysis. These results demonstrate the value of multivariate curve resolution techniques for the analysis of biological tissue. The value of principal components analysis (PCA) for hyperspectral image analysis is also discussed.

Insights into echo-attenuated plaques, echolucent plaques, and plaques with spotty calcification: novel findings from comparisons among intravascular ultrasound, near-infrared spectroscopy, and pathological histology in 2,294 human coronary artery segments.

OBJECTIVES: Three intravascular ultrasound (IVUS) signatures have been associated with coronary artery disease instability: echo attenuation, an intraplaque echolucent zone, and spotty calcification. The aim of this study was to investigate the substrates responsible for these IVUS signatures in a relatively large series of post-mortem human coronary samples. BACKGROUND: The exact mechanisms and pathological correlates underlying echo attenuation, an intraplaque echolucent zone, and spotty calcification remain poorly understood. METHODS: IVUS was compared with near-infrared spectroscopic detection of lipid core plaque and histopathology in 2,294 vessel segments from 151 coronary specimens from 62 patients at necropsy using the modified American Heart Association classification. RESULTS: IVUS detected echo-attenuated plaques in 18.3% of segments, echolucent plaques in 10.5% of segments, and spotty calcification in 14.4% of segments. Histopathologically, 91.4% of echo-attenuated plaques corresponded to either a fibroatheroma (FA) with a necrotic core (NC) or pathological intimal thickening with a lipid pool; almost all segments with superficial echo attenuation indicated the presence of an FA with an advanced NC. Echolucent plaques indicated the presence of a relatively smaller lipid or NC compared with echo-attenuated plaques (thickness: 0.51 mm [interquartile range (IQR): 0.35 to 0.64 mm] vs. 0.70 mm [IQR: 0.54 to 0.92 mm] [p < 0.001]; arc: 74.5° [IQR: 59.0° to 101.0°] vs. 90° [IQR: 70.0° to 112.0°] [p < 0.001]), although 82.8% of superficial echolucent zones indicated an NC-containing FA. IVUS spotty calcification, especially when superficial in location (72.6%), was often associated with an FA with calcium deposits and had smaller arcs of calcium in the setting of FA compared with fibrocalcific plaques (37.5° [IQR: 23.0° to 53.0°] vs. 59.0° [IQR: 46.0° to 69.0°]; p < 0.001). Comparisons between IVUS and near-infrared spectroscopy revealed that echo-attenuated plaques contained the highest probability of near-infrared spectroscopy-derived lipid core plaque, followed by echolucent plaques and spotty calcifications. CONCLUSIONS: This study demonstrated that echo-attenuated plaque, especially superficial echo attenuation, was the most reliable IVUS signature for identifying a high-risk plaque (i.e., an FA containing a large NC).

Detection by near-infrared spectroscopy of large lipid core plaques at culprit sites in patients with acute ST-segment elevation myocardial infarction.

OBJECTIVES: This study sought to describe near-infrared spectroscopy (NIRS) findings of culprit lesions in ST-segment elevation myocardial infarction (STEMI). BACKGROUND: Although autopsy studies demonstrate that most STEMI are caused by rupture of pre-existing lipid core plaque (LCP), it has not been possible to identify LCP in vivo. A novel intracoronary NIRS catheter has made it possible to detect LCP in patients. METHODS: We performed NIRS within the culprit vessels of 20 patients with acute STEMI and compared the STEMI culprit findings to findings in nonculprit segments of the artery and to findings in autopsy control segments. Culprit and control segments were analyzed for the maximum lipid core burden index in a 4-mm length of artery (maxLCBI(4mm)). RESULTS: MaxLCBI(4mm) was 5.8-fold higher in STEMI culprit segments than in 87 nonculprit segments of the STEMI culprit vessel (median [interquartile range (IQR)]: 523 [445 to 821] vs. 90 [6 to 265]; p < 0.001) and 87-fold higher than in 279 coronary autopsy segments free of large LCP by histology (median [IQR]: 523 [445 to 821] vs. 6 [0 to 88]; p < 0.001).Within the STEMI culprit artery, NIRS accurately distinguished culprit from nonculprit segments (receiver-operating characteristic analysis area under the curve = 0.90). A threshold of maxLCBI(4mm) >400 distinguished STEMI culprit segments from specimens free of large LCP by histology (sensitivity: 85%, specificity: 98%). CONCLUSIONS: The present study has demonstrated in vivo that a maxLCBI(4mm) >400, as detected by NIRS, is a signature of plaques causing STEMI.

Histopathologic validation of the intravascular ultrasound diagnosis of calcified coronary artery nodules.

A calcified nodule is a type of potentially vulnerable plaque accounting for approximately 2% to 7% of coronary events. Because its intravascular ultrasound (IVUS) features have never been validated, the aim of this study was to assess the IVUS characteristics of calcified nodules in comparison to histopathology. IVUS was performed in 856 pathologic slices in 29 coronary arteries (11 left anterior descending, 5 left circumflex, and 13 right coronary arteries) in 18 autopsy hearts. Pathologic sections were analyzed every 2 mm; qualitative and quantitative findings of matched IVUS were analyzed. IVUS detected calcification in 285 frames; 17 (6.0%) were calcified nodules, and 268 (94.0%) were non-nodular calcium by histopathology. Two calcified nodules (11.8%) were solitary, and 15 (88.2%) were adjacent to non-nodular calcium. IVUS characteristics of calcified nodules were (1) a convex shape of the luminal surface (94.1% in calcified nodules vs 9.7% in non-nodular calcium, p <0.001), (2) a convex shape of the luminal side of calcium (100% vs 16.0%, p <0.001), (3) an irregular luminal surface (64.7% vs 11.6%, p <0.001), and (4) an irregular leading edge of calcium (88.2% vs 19.0%, p <0.001). Luminal area at the calcified nodule site was larger (6.2 ± 2.4 vs 4.3 ± 1.6 mm(2), p <0.001) and plaque burden less (57 ± 6% vs 68 ± 5%, p <0.001) than at the minimum luminal area site. In conclusion, calcified nodules have distinct IVUS features (irregular and convex luminal surface) permitting their prospective identification in vivo.

In vivo validation of a catheter-based near-infrared spectroscopy system for detection of lipid core coronary plaques: initial results of the SPECTACL study.

OBJECTIVES: To determine whether catheter-based near-infrared spectroscopy (NIRS) signals obtained with a novel catheter-based system from coronaries of patients are similar to those from autopsy specimens and to assess initial safety of NIRS device. BACKGROUND: An intravascular NIRS system for detection of lipid core-containing plaques (LCP) has been validated in human coronary autopsy specimens. The SPECTACL (SPECTroscopic Assessment of Coronary Lipid) trial was a parallel first-in-human multicenter study designed to demonstrate the applicability of the LCP detection algorithm in living patients. METHODS: Intracoronary NIRS was performed in patients undergoing percutaneous coronary intervention. Acquired spectra were blindly compared with autopsy NIRS signals with multivariate statistics. To meet the end point of spectral similarity, at least two-thirds of the scans were required to have >80% of spectra similar to the autopsy spectra. RESULTS: A total of 106 patients were enrolled; there were no serious adverse events attributed to NIRS. Spectroscopic data could not be obtained in 17 (16%) patients due to technical limitations, leaving 89 patients for analysis. Spectra from 30 patients were unblinded to test the calibration of the LCP detection algorithm. Of the remaining 59 blinded cases, after excluding 11 due to inadequate data, spectral similarity was demonstrated in 40 of 48 spectrally adequate scans (83% success rate, 95% confidence interval: 70% to 93%, median spectral similarity/pullback: 96%, interquartile range 10%). The LCP was detected in 58% of 60 spectrally similar scans from both cohorts. CONCLUSIONS: This intravascular NIRS system safely obtained spectral data in patients that were similar to those from autopsy specimens. These results demonstrate the feasibility of invasive detection of coronary LCP with this novel system. (SPECTACL: SPECTroscopic Assessment of Coronary Lipid; NCT00330928).

Detection of lipid core coronary plaques in autopsy specimens with a novel catheter-based near-infrared spectroscopy system.

OBJECTIVES: This study sought to assess agreement between an intravascular near-infrared spectroscopy (NIRS) system and histology in coronary autopsy specimens. BACKGROUND: Lipid core plaques cannot be detected by conventional tests, yet are suspected to be the cause of most acute coronary syndromes. Near-infrared spectroscopy is widely used to determine the chemical content of substances. A NIRS system has been developed and used successfully in 99 patients. METHODS: Scanning NIRS was performed through blood in 212 coronary segments from 84 autopsy hearts. One histologic section was analyzed for every 2 mm of artery. Lipid core plaque of interest (LCP) was defined as a lipid core >60 degrees in circumferential extent, >200-microm thick, with a mean fibrous cap thickness <450 microm. The first 33 hearts were used to develop the algorithm; the subsequent 51 validation hearts were used in a prospective, double-blind manner to evaluate the accuracy of NIRS in detecting LCP. A NIRS-derived lipid core burden index for an entire artery was also validated by comparison to histologic findings. RESULTS: The LCPs were present in 115 of 2,649 (4.3%) sections from the 51 validation hearts. The algorithm prospectively identified LCP with a receiver-operator characteristic area of 0.80 (95% confidence interval [CI]: 0.76 to 0.85). The lipid core burden index detected the presence or absence of any fibroatheroma with an area under the curve of 0.86 (95% CI: 0.81 to 0.91). A retrospective analysis of lipid core burden index conducted in extreme artery segments with either no or extensive fibroatheroma yielded an area under the curve of 0.96 (95% CI: 0.92 to 1.00), confirming the accuracy of spectroscopy in identifying plaques with markedly different lipid content under ideal circumstances. CONCLUSIONS: This novel catheter-based NIRS system accurately identified lipid core plaques through blood in a prospective study in coronary autopsy specimens. It is expected that this novel capability will be of assistance in the management of patients with coronary artery disease.

Optical detection of high-grade cervical intraepithelial neoplasia in vivo: results of a 604-patient study.

OBJECTIVE: The purpose of this study was to assess the in vivo optical detection of high-grade cervical intraepithelial neoplasia (2/3+) on the whole cervix with a noncontact, spectroscopic device. STUDY DESIGN: Cervical scanning devices collected intrinsic fluorescence and broadband white light spectra and video images from 604 women during routine colposcopy examinations at 6 clinical centers. A statistically significant dataset was developed of intrinsic fluorescence and white light-induced cervical tissue spectra that was correlated to expert histopathologic determination. On the basis of a retrospective analysis of the acquired data, a classification algorithm was developed, validated, and optimized. RESULTS: Intrinsic fluorescence, backscattered white light, and video imaging each contribute complementary information to diagnostic algorithms for high-grade cervical neoplasia. More than 10000 measurements that were made on colposcopically identified tissue from >500 subjects were the basis for algorithm training and testing. Algorithm performance demonstrated a sensitivity of approximately 90%. This performance was confirmed by various training methods. With the use of a multivariate classification algorithm, optical detection is predicted to detect 33% more high-grade cervical intraepithelial neoplasia (2/3+) than colposcopy alone. CONCLUSION: Full cervix optical interrogation for the detection of high-grade cervical intraepithelial neoplasia is feasible and appears capable of detecting more high-grade cervical intraepithelial neoplasia than colposcopy alone. With the use of this classification algorithm, a multisite, randomized controlled trial is underway that compares the combination of optical detection and colposcopy versus colposcopy alone.