Guide wire shadow assessed by shading index is reduced in sparse spring coil wire in optical coherence tomography

One of the major problems of a Fourier-domain optical coherence tomography (FD-OCT) is the guide wire (GW) shadow which disturbs precise coronary assessment. If two or more GWs are used in a bifurcation PCI, the GW shadow becomes larger. In FD-OCT, GWs were usually observed as a crescent shape, but GWs with the sparse spring coil were observed as either round or crescent shape. The measured angle making GW shadow of GW without the sparse spring coil was similar to its theoretical angle (30.4 ± 1.7° vs. 30.1 ± 0.7°, p = 0.21); however, the measured angle of GW with the sparse spring coil was significantly smaller than its theoretical angle (16.8 ± 4.8° vs. 28.7 ± 1.5°, p < 0.01). For standardization of shading-effect of GW, a virtual diameter of GW which was calculated from a measured angle, an actual diameter of GW, and a distance between an imaging catheter and GW was defined as the shading index. The shading index of GW with the sparse spring coil was significantly smaller than that of GW without the sparse spring coil (0.008 ± 0.002 vs. 0.014 ± 0.001, p < 0.01). Shading indices of GWs with the sparse spring coil were smaller than their actual diameters. The sparse spring coil structure could contribute to the reduction of the GW shadow in FD-OCT. Also, we proposed the new and useful shading index to indicate the shading-effect of GW.