A formula to calculate the contrast volume required for optimal imaging quality in optical coherence tomography with non-occlusive technique

Background: Non-occlusive technique is universally accepted for acquisition of coronary optical coherence tomography (OCT), but the amount of contrast infused is still inconsistently calculated. Proposed herein, is an empirical formula for accurate contrast volume calculation. Methods: In an observational prospective study, contrast volume of consecutive patients undergoing OCT was either calculated with formula, or eyeballed based on manufacturer recommendations. The quality of pullback, defined as % of high quality cross-sections (CS) in the segment of interest (SOI), was analyzed by two independent operators and compared between groups, together with the amount of contrast per pullback. Results: Sixty patients (115 pullbacks, 4252 CS) were imaged using the formula, vs. 18 patients (22 pullbacks, 777 CS) eyeballing the contrast volume. The formula group used 18 mm/s as pullback speed more often (82.6% vs. 40.9%, p = 0.0001), but there were no significant differences between groups in SOI length or vessel imaged. The formula resulted in higher pullback quality than eyeballing (96.55% vs. 63.55%, p < 0.0001), interobserver agreement Kappa 0.903 (p < 0.0001), and tended to use less contrast per pullback than the eyeball group (13.03 mL vs. 14.55 mL, p = 0.057). After adjusting for pullback speed, SOI length and vessel in multivariate linear regression, the use of the formula significantly reduced the amount of contrast in 4.50 mL on average. Conclusions: Optical coherence tomography acquisition with the non-occlusive technique can be substantially eased with the use of a novel formula to calculate the contrast volume required. This method optimises the quality of the images whilst reducing the amount of contrast per pullback

Macrophagic enhancement in optical coherence tomography imaging by means of superparamagnetic iron oxide nanoparticles

Background: The ability of optical coherence tomography (OCT) to visualise macrophages in vivo in coronary arteries is still controversial. We hypothesise that imaging of macrophages in OCT could be enhanced by means of superparamagnetic nanoparticles. Methods: We compared the optical backscattering and attenuation of cell pellets containing RAW 264.7 macrophages with those of macrophagic cell pellets labelled with very small superparamagnetic oxydised nanoparticles (VSOP) by means of light intensity analysis in OCT. The labelled macrophages were incubated with VSOP at a concentration of 1 mM Fe, corresponding to intracellular iron concentrations of 8.8 pg/cell. To study the effect of intracellular accumulation on the backscattering, VSOP dilutions without cells were also compared. OCT pullbacks of the PCR tubes containing the cell pellets were obtained and light intensity analysis was performed on raw OCT images in polar view, after normalisation by the backscattering of the PCR tube. The backscattering was estimated by the peak normalised intensity, whilst the attenuation was estimated by the number of pixels between the peak and the normalised intensity 1 (peak-to-one). Results: VSOP-loaded macrophages have higher backscattering than the corresponding unlabelled macrophages (peak normalised intensity 6.30 vs. 3.15) with also slightly higher attenuation (peak-toone 61 vs. 66 pixels). The backscattering of the nanoparticles in suspension was negligible in the light intensity analysis. Conclusions: VSOP increase significantly the optical backscattering of macrophages in the nearinfrared region, with minimal increase in signal attenuation. This finding enables the enhancement of macrophages in conventional OCT imaging with an easily implementable methodology