December 12, 2008

Noninvasive Assessment of Heterogeneous Lower Extremity Perfusion Deficits Using an Emerging Spectroscopic Imaging Technology Before and After Successful Revascularization

Owen N. Johnson, III, M.D., Anton N. Sidawy, MD, MPH, Mark Slidell, MD, MPH, Peter Kreishman, MD, Roger Walcott, MD, Robyn A. Macsata, MD.
Veterans Affairs Medical Center, Washington, DC, USA.

BACKGROUND: Imaging spectroscopy has been shown to detect decreases in cutaneous oxygenation during hemorrhagic shock. We hypothesized this technology could be applied when evaluating patients with lower extremity peripheral arterial disease (PAD) to map hetereogenous zones of distal perfusion and detect changes after revascularization.
METHODS: This is a prospective validation study of a prototype hyperspectral imaging (HSI) camera. Patients evaluated by a vascular surgeon for PAD were included. In addition to other noninvasive tests and arteriography, preoperative dorsal and plantar foot images were obtained across various wavelengths of light. Spectroscopic data were used to calculate capillary oxyhemoglobin (Hb-Oxy), deoxyhemoglobin (Hb-Deoxy), and oxygen saturation (O₂-Sat) values. An infrared thermometer measured surface temperature. Patients were re-imaged postoperatively. Results are digitally mapped (resolution of 100 microns) which allows morphologic and quantitative comparisons for any user-defined region of interest.
RESULTS: Sixty-two limbs in 31 male patients (median age 65) were studied, of which 34 limbs were ischemic. There were 33 revascularizations and one amputation. HSI demonstrated non-uniform cutaneous oxygen distribution, which was significantly different in ischemic versus non-ischemic limbs. Surprisingly, differences in Hb-Oxy were not observed (P=.305), but ischemic limbs had higher Hb-Deoxy (P<.0001) and lower O₂-Sat (P=.001). After revascularization, Hb-Oxy showed no changes (P=.799), but Hb-Deoxy decreased 40% (P=.009) and O₂-Sat increased 55% (P=.01). Surface temperature was, on average, 8.1 +/- 1.2^o F cooler in ischemic feet (P<.0001), which was no longer true after successful revascularization. Non-ischemic limbs, used as internal controls, showed no perioperative changes in Hb-Oxy (P=.425), Hb-Deoxy (P=.359), or O₂-Sat (P=.568). In all 62 limbs, HSI profiles correlated with clinical course and arteriography findings.
CONCLUSIONS: HSI is a novel, noninvasive method to qualitatively and quantitatively measure peripheral perfusion deficits over a heterogeneous spatial distribution. It is of interest to find that patients with peripheral PAD do not have homogeneous foot skin envelope oxygenation even after successful revascularization.

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