Spatial Vascular Volume Fraction Imaging for Quantitative Assessment of Angiogenesis

Abstract

The purpose of this study is to set up a quantitative imaging strategy for therapeutic angiogenesis and monitoring the spatial distribution and survival of the transplanted mesenchymal stem cells (MSCs) in vivo simultaneously. Mouse adipose-derived MSCs (AD-MSCs) were isolated from firefly luciferase and enhanced green fluorescent protein positive transgenic mice, and implanted intramuscularly into hindlimbs of C57BL/6 mice. Serial spatial vascular volume fraction (SVVF) imaging was performed to quantitatively assess angiogenesis by calculating the spatially explicit vascular volume. The hybrid microcomputed tomography angiography/bioluminescence tomography (micro-CTA/BLT) was used to track the fate of AD-MSCs in vivo. Laser Doppler perfusion imaging (LDPI) was used to evaluate blood perfusion. Ex vivo conventional methods were performed to cross-validate the therapeutic angiogenesis. There was a linear correlation relation between the cell number and Fluc/Fluc protein signal intensity in AD-MSCs via BLT. LDPI showed improved perfusion rate in mice treated with cytotherapy, compared to control mice. Furthermore, angiogenesis assessed by SVVF was 10.67 ± 0.41 %, 13.99 ± 0.28 %, and 23.50 ± 1.23 % on days 7, 14, and 28 post-transplantation of AD-MSCs, respectively. Vascular densities of the longitudinally monitored ischemic hindlimbs were significantly higher than those at early time points and controls, which was also confirmed by vascular corrosion casting, scanning electron microscopic imaging, and histological analysis. Hybrid high-resolution micro-CTA/BLT enabled monitoring and quantitative assessment of cytotherapeutically induced angiogenesis in vivo.