While grayscale IVUS has the limited ability to analyze components within atherosclerotic lesions, VH-IVUS enables a detailed analysis of plaque composition.
VH-IVUS can distinguish between areas with low echo reflections, which can be beneficial in addition to IVUS imaging.
VH technique is based on backscatter analysis and mathematical modeling of the radiofrequency signals produced by the intravascular ultrasound unit.
It provides a color-coded tissue map of plaque composition superimposed on cross-sectional images of the coronary artery obtained by IVUS.
VH-IVUS is performed at the time of coronary angiography and involves a tiny ultrasound probe that emits high frequency signals (20–40 mHz). This wire-based probe can be placed over a coronary guidewire into the artery and withdrawn at a set rate (0.5 mm/sec) to provide segmental tomographic images of the vessel.
An advanced radiofrequency (RF) analysis of reflected ultrasound signals in a frequency domain analysis is used to visualize a reconstructed color-coded tissue map of plaque composition including fibrous, fibrofatty, necrotic core and dense calcium.
Limitations of VH-IVUS
Identification of intraluminal organizing thrombus is currently not possible by RF analysis.
The acquisition of VH-IVUS images is gated at the R-wave of the electrocardiography signal, which fails to allow to evaluate corresponding images in serial VH-IVUS imaging.
Recent study raises questions about the accuracy of VH-IVUS to identify necrotic core. VH-IVUS-identified necrotic core was not correlated to histology in a swine atherosclerosis model. However, it is important to note that swine necrotic core is inherently different from human ones.
Limited axial resolution.
Inability in the assessment of plaque composition behind calcium.