Effects of dorsal column (DC) fiber collaterals on kilohertz frequency spinal cord stimulation activation thresholds. (A) DC fiber activation threshold as a function of collateral diameter. A single collateral was added to a 11.5-μm diameter DC fiber. The collateral diameter (d_collateral) was varied at 0.0, 5.7, 7.3, and 11.5 μm. For each d_collateral, the DC fiber activation threshold was calculated as a function of the rostrocaudal position of the branching node relative to the cathode. The DC collateral was oriented perpendicular to the parent DC fiber and projected ventrally away from the spinal cord stimulation lead. (B and C) Reduction in activation thresholds for DC fibers due to collateral branching as a function of fiber diameter. In this analysis, d_collateral was assumed to equal the diameter of the parent DC fiber (d_fiber), and the branching node was centered at the rostrocaudal level of the cathode. (B) Shows the activation threshold for a range of fiber diameters with and without a collateral. (C) shows the relative ratio of activation threshold for a fiber with a collateral (I_{th,collateral}) to the activation threshold for the same fiber diameter with no collateral (I_{th,no collateral}).