Intracoronary near-infrared spectroscopy (NIRS) can identify lipid in the coronary arteries, but lacks depth resolution. A
novel catheter is currently in clinical use that combines NIRS with intravascular ultrasound (IVUS), which provides
depth-resolved structural information via the IVUS modality. A measure designated as lipid-rich plaque burden (LRPB)
has been proposed as a means to interpret the combined acoustic and optical information of NIRS-IVUS. LRPB is
defined as the area created by the intersection of the NIRS lipid-rich arc with the corresponding IVUS-measured plaque
burden. We determined the correlation in human coronary autopsy specimens between LRPB, a measure of lipid
presence and extent available via intravascular imaging in patients, and the area of lipid-rich plaque as determined by the
gold-standard of histology.
Fifteen artery segments from 8 human autopsy hearts were imaged with the NIRS-IVUS system (TVC Imaging System,
Infraredx Inc., Burlington, MA). Arteries were imaged in a specialty fixture that assured accurate co-registration
between imaging and histology. The arteries were then fixed and divided into 2 mm blocks for histological staining.
Pathological contouring of lipid-rich areas was performed on the stained thin sections for 54 lipid-rich blocks.
Computation of LRPB was performed on transverse NIRS-IVUS frames corresponding to the histologic sections. The
quantified LRPB was frequently higher than the lipid-rich plaque area determined by histology, because the region
denoted by the EEL and lumen within the NIRS lipid-rich arc is not entirely comprised of lipid. Overall, a moderate to
strong correlation (R = 0.73) was found between LRPB determined by NIRS-IVUS imaging and the lipid-rich plaque
area determined by histology. LRPB, which can be measured in patients with NIRS-IVUS imaging, corresponds to the
amount of lipid-rich plaque in a coronary artery. LRPB should be evaluated in prospective clinical trials for its ability to
identify vulnerable plaques.