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A Novel Pilot Study using Spatial Frequency Domain Imaging and Gradient Mapping to Assess Oxygenation of Perforator Flaps during Breast Reconstructive Surgery
John T. Nguyen, MD1, Samuel J. Lin, MD1, Adam M. Tobias, MD1, Sylvain Gioux, PhD1, Amaan Mazhar, PhD2, David K. Cuccia, PhD2, Yoshitomo Ashitate, MD1, Alan Stockdale, MEd1, Rafiou Oketoun, MEng1, Nicholas J. Durr, PhD1, Lorissa A. Moffitt, MS1, Anthony J. Durkin, PhD2, Bruce J. Tromberg, PhD2, John V. Frangioni, MD PhD1, Bernard T. Lee1.
1Beth Israel Deaconess Medical Center/ Harvard Medical School, Boston, MA, USA, 2University of California Irvine, Irvine, CA, USA.

Background:
There currently exists no reliable method for passively monitoring tissue oxygenation and perfusion during reconstructive surgery. It has been shown that early detection of vascular complications improves the rate of flap salvage. Our team has developed a novel imaging system using spatial frequency domain imaging (SFDI) to measure oxygenation over a large field of view (18 x 14 cm) without injection of a contrast agent. Skin flap, bowel, and liver vascular occlusion experiments were performed on large animals and demonstrated that over the course of the experiment, relative changes in oxygen saturation measured using SFDI had an accuracy within 10% of those made using the FDA-approved device. Our SFDI system was translated to the clinic in a first in-human pilot study that imaged skin flap oxygenation during reconstructive breast surgery intra-operatively.
Methods:
Three women undergoing breast reconstruction after mastectomy were enrolled for our study. Unilateral DIEP free flaps were performed on three patients, two of the patients having immediate reconstruction. The SFDI system was deployed into the operating room, draped and operated by trained personnel. Images were acquired and four SFDI measurements were taken over the course of the study. Time points included images of each hemi abdominal skin flap prior to elevation, image of the selected flap after perforator dissection, and after microsurgical transfer.
Results:
SFDI was able to measure oxyhemoglobin concentration (ctO2Hb), deoxyhemoglobin concentration (ctHHb) and O2 saturation (StO2). Gradient maps were created for each metric that can be displayed as images to the surgeon to monitor the flap status. All flaps showed a consistent ctO2Hb, ctHHb and StO2 gradient over time throughout our study. In one patient with postoperative fat necrosis, evaluation of the intraoperative images after flap elevation showed measurable increases in the ctO2Hb and ctHHb gradient that corresponded to the area of fat necrosis. The StO2 gradient map did not show any change in this area. From our preclinical studies this increase in ctO2Hb and ctHHb could indicate the presence of a venous congestion.
Conclusions:
The results of our initial human pilot study suggest that SFDI has the potential to provide intra-operative oxygenation images in real-time during surgery. In addition, our preclinical results suggest that variations in SFDI measurement metrics could predict the vascular origin of tissue ischemia (arterial, venous, or both). These measurements are potentially more accurate than currently available tissue oximetry systems that only provide point measurements of StO2. With the use of this technology, surgeons can obtain gradient maps to assist in intra-operative planning; this can potentially prevent complications and improve clinical outcomes.


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