Virtual Histology Intravascular Ultrasound (VH-IVUS)

 

Introduction

  • 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.

Introduction

  • 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 This wire-based probe can be placed over a coronary guidewire into the artery and withdrawn at a set rate (0.5 mm/sec) to provide segmental tomographic images of the vessel.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. 

advanced radiofrequency

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.