Perfused vascular volume before and after transplantation. ECFC/MPC/Matrigel suspensions were injected into a SCID mouse to form vascular networks in vivo, and the degree of perfusion in each implant was monitored at days 3 and 5 before transplantation, and days 3, 5, and 7 after transplantation. The 2D images were recorded as video (supplemental Videos 1 and 2) and analyzed. (A) Representative captured 2D image from low-perfused implant (posttransplantation day 3). (B) The plot of nonlinear ultrasound signal intensity (expressed in arbitrary units) integrated over the region of interest of the image plane of Figure 2A (contrast agent was injected at ∼ 10 seconds). (C) Representative captured 2D image from high-perfused implants (posttransplantation day 7). (D) Nonlinear ultrasound signal intensity as described in panel B, integrated over the region of interest of image plane of Figure 2C. (E) Perfused vascular volume was measured by collecting a stack of 2D images from the anterior to posterior ends of the implant (supplemental Videos 3 and 4). The difference in the percentage of voxels returning an ultrasound signal before and after contrast agent injection is perfused vascular volume (percentage), the proportion of implant volume occupied by functional, perfused vessels. *Significant difference (P ≤ .05) between groups (n = 8 for each time point; n = 5 for Matrigel control).