Characterisation of atherosclerotic plaque by spectral analysis of 30 MHz intravascular ultrasound radio frequency data

Accurate coronary plaque characterisation by ultrasound would have a major impact on the management of cardiac patients. The aim of this study has been to develop radio-frequency analysis techniques for this purpose. Postmortem coronary arteries (n=5) were imaged with 30 MHz intravascular ultrasound (IVUS) and the raw signals digitised (f=250 MHz) at 11 sites. Spectral parameters were compiled from regions of interest (ROIs=45) within areas of loose fibrotic tissue (DFT), moderate fibrotic tissue (MFT), dense fibrotic tissue (DFT) and calcium (CA), located using scan-converted representations of the data. Power spectra were normalised with respect to a perfect reflector and power- and frequency-related parameters were measured within the bandwidth 17-42 MHz. Significant discrimination between LFT/DFT and LFT/CA was given by maximum power and spectral slope (dB/MHz). The clearest discrimination was provided by the 0 Hz intercept of the spectral slope: LFT/DFT (p<.001); LFT/CA (p<.0001); DFT/CA (p<.1). In order to evaluate the predictive power of these measurements, parametric images were constructed to show the distribution of the plaque types as determined by each parameter