Early detection of complete vascular occlusion in a pedicle flap model using quantitative [corrected] spectral imaging

Abstract

Background: Vascular occlusion after tissue transfer is a devastating complication that can lead to complete flap loss. Spatial frequency domain imaging is a new, noncontact, noninvasive, wide-field imaging technology capable of quantifying oxygenated and deoxygenated hemoglobin levels, total hemoglobin, and tissue saturation.

Methods: Pedicled fasciocutaneous flaps on Wistar rats (400 to 500 g) were created and underwent continuous imaging using spatial frequency domain imaging before and after selective vascular occlusion. Three flap groups (control, selective arterial occlusion, and selective venous occlusion) and a fourth group composed of native skin between the flaps were measured.

Results: There were no statistically significant differences between the control flap group and the experimental flap groups before selective vascular occlusion: oxyhemoglobin (p=0.2017), deoxyhemoglobin (p=0.3145), total hemoglobin (p=0.2718), and tissue saturation, (p=0.0777). In the selective arterial occlusion flap group, percentage change in total hemoglobin was statistically different from that of the control flap group (p=0.0218). The remaining parameters were not statistically different from those of the control flap: percentage change in oxyhemoglobin (p=0.0888), percentage change in deoxyhemoglobin (p=0.5198), and percentage change in tissue saturation (p=0.4220). The selective venous occlusion flap group demonstrated changes statistically different compared with the control flap group: percentage change in oxyhemoglobin (p=0.0029) and deoxyhemoglobin, total hemoglobin, and tissue saturation (p<0.0001).

Conclusions: Spatial frequency domain imaging provides two-dimensional, spatially resolved maps of tissue oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and tissue saturation. Results presented here indicate that this can be used to quantify and detect physiologic changes that occur after arterial and venous occlusion in a rodent tissue transfer flap model. This portable, noncontact, noninvasive device may have a high clinical applicability in monitoring postoperative patients.

Fig. 1

Diagram of typical orientation of the flaps on the animal and the region imaged by the prototype spatial frequency domain imaging device (Tissue OxImager). The illumined region out-lined by the golden box is the region imaged by the device. The blue box is the area outside of the surgical field used as the native skin group. The black boxes represent the area on either the control flap or experimental flaps (selective arterial or selective venous occlusion flaps). Note the incisions caudal to the flaps used to perform selective ligation of the vessels.

Fig. 2

Sample of digital photograph and the corresponding chromophore maps as generated by the Tissue OxImager for all four chromophores parameters (oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and tissue saturation). The flap on the left of each image represents a control flap, whereas the flap on the right is an experimental flap that underwent selective venous occlusion. The images at time 0 were obtained just before selective venous occlusion to the flap on the right side. Note the similar appearance between the control flap and the experimental flap at this time. The photographs and chromophore maps at time 5, 25, and 55 minutes illustrate the changes over time after selective venous occlusion of the flap on the right of each image. Note how the Tissue OxImager detects changes in oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and tissue saturation by 5 minutes after selective venous occlusion, whereas the clinical appearance of the flap as illustrated by digital photography is only subtly different in appearance even after 55 minutes.

Fig. 3

Comparison of measured chromophore values among all four groups (control flaps, selective venous occlusion flaps, selective arterial occlusion flaps, and native skin) during the baseline measurement period from −10 minutes to 0 minutes. The mean values are depicted as the center line and the error bars represent the range. The confidence interval of 2.5 to 97.5 percent is depicted by the colored boxes.

Fig. 4

Graphic illustration of the percentage changes from baseline for each parameter measured in the control flap group compared with the selective arterial occlusion flap group (note the scale differences on the y axis). Baseline measurements are from −10 minutes to 0 minutes. Selective arterial occlusion occurred at time 0 minutes. The p values reflect the differences over the entire time course between the curve representing the control flap group (gray) and the selective arterial occlusion flap group (color). Only percentage change in total hemoglobin was found to be statistically different between the control flap group and the selective arterial occlusion flap group over the entire postocclusion time course (time 0 to 55 minutes). A Bonferroni posttest analysis did not reveal statistically significant differences at any given individual time point in any of the four chromophore parameters (percentage change in oxyhemoglobin, deoxyhemoglobin, total hemoglobin, and tissue saturation).

Fig. 5

Graphic illustration of the percentage changes from baseline for each parameter measured in the control flap group compared with the selective venous occlusion flap group (note the scale differences on the y axis). Baseline measurements are from −10 minutes to 0 minutes. Selective venous occlusion occurred at 0 minutes. The p values reflect the differences over the entire time course between the curve representing the control flap group (gray) and the selective venous occlusion flap group (color). A Bonferroni posttest analysis found a statistically significant difference (p < 0.05) in percentage change in oxyhemoglobin at 8 minutes, percentage change in deoxy hemoglobin at 2 minutes, percentage change in total hemoglobin at 4 minutes, and percentage change in tissue saturation at 1 minute following selective venous ligation.