Assessing spectral algorithms to predict atherosclerotic plaque composition with normalized and raw intravascular ultrasound data

Spectral analysis of backscattered intravascular ultrasound (IVUS) data has demonstrated the ability to characterize plaque. We compared the ability o f spectral parameters (e.g., slope, midband fit and y-intereept), computed via classic Fourier transform (CPSD), Welch power spectrum (WPSD) and autor egressive (MPSD) models, to classify plaque composition. Data were collecte d ex vivo from 32 human left anterior descending coronary arteries, Regions -of-interest (ROIs), selected from histology, comprised 64 collagen-rich, 2 4 fibrolipidic, 23 calcified and 37 calcified-necrotic regions. A novel qua ntitative method was used to correlate IVUS data with corresponding histolo gic sections. Periodograms of IVUS samples, identified for each ROI, were u sed to calculate spectral parameters. Statistical classification trees (CT) were computed with 75% of the data for plaque characterization. The remain ing data were used to assess the accuracy of the CTs. The overall accuracie s for normalized spectra with CPSD, WPSD and MPSD were, respectively, 84.7% , 85.6% and 81.1% (training data) and 54.1%, 64.9% and 37.8% (test data). T hese numbers were improved to 89.2%, 91.9% and 89.2% (training) and 62.2%, 73% and 59.5% (test) when the calcified and calcified-necrotic regions were combined for analysis. Most CTs misclassified a few fibrolipidic regions a s collagen, which is histologically acceptable, and the unnormalized and no rmalized spectra results were similar. (C) 2001 World Federation for Ultras ound in Medicine & Biology.