Intracoronary near infrared autofluorescence signal calibration.

Near infrared autofluorescence (NIRAF) optical coherence tomography (OCT) is an intravascular imaging modality, based on a catheter which emits light at two different wavelengths through an optical fiber. Since OCT is becoming the method of choice in interventional cardiology and NIRAF is proven to be higher in plaque lesions having higher risk morphologic phenotypes, the NIRAF-OCT can become powerful and promising technology. However, there is NIRAF- distance dependence which has to be addressed before the technology can be applied in clinical practice. The present paper aims at presenting a method which calibrates the distance dependent NIRAF signal and ensures that similar NIRAF values are depicted when targeting the same lesion. Towards this purpose, autofluorescence phantoms were constructed, accurate distance measurements were conducted and the NIRAF-distance relationship was quantified. Finally, a calibration function was proposed which is able to accurately calibrate the NIRAF signal in any NIRAF-OCT pullback.

Volumetric assessment of lesion severity with optical coherence tomography: relationship with fractional flow.

AIMS: Frequency-domain optical coherence tomography (FD-OCT) provides a rapid tomographic scan of a coronary vessel, with an accurate reconstruction of its lumen profile. An FD-OCT-based metric that corresponds more closely with physiological significance of lesions may enable more precise guidance of interventional procedures. The aim of this feasibility study was to evaluate a new method for quantifying coronary lesion severity that estimates hyperaemic flow resistance of branched vessel segments imaged by FD-OCT. METHODS AND RESULTS: An analytical flow model was developed that relates fractional flow reserve (FFR) to the vascular resistance ratio (VRR), a measure of blood flow resistance derived from volumetric FD-OCT lumen profiles. The VRR-FFR relationship was evaluated in 21 patients on whom both pressure measurement and FD-OCT imaging were performed in a random order during maximal hyperaemia. Lesion severity assessed by VRR showed a stronger linear correlation with FFR measurements (before model optimisation [blinded]: r=0.81; p<0.001; root mean square error [RMSE]=0.095 FFR units; after model optimisation [unblinded]: r=0.91; p<0.001; RMSE=0.066 FFR units) than quantitative coronary angiography and FD-OCT-derived measurements of minimum lumen area (r=0.67; p=0.0012) and per cent area stenosis (r=-0.61; p=0.004). CONCLUSIONS: Accurate volumetric measurement of the lumen profile with FD-OCT correlates more closely with FFR than standard metrics derived from single image cross-sections. VRR shows promise as a method for evaluating lesion severity.