Hyperspectral imaging and ankle: brachial indices in peripheral arterial disease

To evaluate the correlation between ankle:brachial indices (ABI) and visible light reflectance spectroscopy hyperspectral imaging (HSI) determinations of oxygenated and deoxygenated hemoglobin (oxyHgb and deoxyHgb) levels in the skin of the distal lower extremity. This is a prospective, open, comparator trial which took place at the Vascular laboratory of a Veterans Administration Hospital in Long Beach, USA. Fifty-eight patients (85 limbs) were referred for routine vascular laboratory studies including ABI had concomitant HSI. Limbs with noncompressible pedal signals were excluded from the analysis.

ABI was determined with continuous wave Doppler ultrasound and leg blood pressure cuffs. A commercial HSI system (Oxu-Vu(R), Hypermed, Inc.) was used to measure oxyHgb, deoxyHgb, and percent oxygenated hemoglobin (%oxyHgb) in the dorsum of the foot and ankle. HSI measurements of volar forearm skin were also obtained to normalize the lower extremity HSI measurements in a manner comparable with ABI.

For purposes of comparison, data sets were divided into 3 groups: ABI > 0.9 (n = 53), 0.45 < ABI < 0.9 (n = 22), and ABI < 0.45 (n = 10). There were no significant differences between oxgyHgb, %oxyHgb, normalized oxyHgb, and normalized %oxyHgb when means values for these parameters were compared between the three groups based on unpaired t test statistics.

The lack of a correlation between HSI measurements and ABI is consistent with previous observations that in moderate peripheral arterial disease skin perfusion is maintained at normal levels and in critical ischemia paradoxical increased flow may be present. Although the current study failed to show a clinically useful correlation between HSI measurements of oxyHgb levels, further evaluation of this novel technology is warranted.