1. A method for characterizing plaque tissue in accordance with received intravascular ultrasound echo segments, the method comprising: collecting analog ultrasound echo signals from a region of interest in a portion of an imaged body; computing, from RF-domain ultrasound echo signal segment data derived from the analog ultrasound echo signals, spectrally resolved information over an operating frequency range including: a power spectrum by performing spectral analysis, and a system transfer function; determining, in each of at least a first sub-band and a second sub-band within the operating frequency range, an integrated backscatter parameter from the power spectrum and system transfer function; comparing integrated backscatter values from at least the first sub-band and the second sub-band to obtain at least one integrated backscatter comparison parameter value; and applying the at least one integrated backscatter comparison parameter value to at least one tissue characterization criterion for rendering a plaque tissue characterization.