Comparison of Frequency Domain Optical System with Ultrasound Imaging in the Classification of Joints of Systemic Lupus Erythematosus Patients

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease which causes arthritis (joint inflammation) in up to 95% of patients. Data from one-hundred twenty-eight (128) interphalangeal joints from sixteen (16) SLE patients were collected using both a frequency-domain optical tomographic imaging system and a systematic multiplanar grey-scale (GS) and power doppler (PD) ultrasound (US). A combined PDGS score was calculated using the US OMERACT consensus definitions for joint pathologies. The optical instrumentation consists of one 8mW laser at 670nm, with a 1 mm diameter beam modulated at 300 MHz as light source. The laser beam scans the peripheral interphalangeal joint along its length in 10 points with a step of 2mm. The transmitted light was collected by an intensified charge-coupled device camera and the absorption and scattering distributions inside the finger are reconstructed using a radiative transfer equation model. The combined PDGS score showed 34 joints graded 0, 45 joints graded 1, 22 joints graded 2 and 27 joints graded 3. The absorption and scattering data were obtained from the reconstructed images. Both the mean scattering and absorption coefficients positively correlated with the ultrasound data (p-values < 0.01) when evaluating the healthiness of fingers in SLE patients. For not or only slightly affected joints (PDGS 0 or 1), the corresponding mean scattering coefficient is 8.3±0.6 cm-1, while, when considering heavily affected joints (PDGS 2 or 3), is 8.8±1.4 cm-1. The corresponding mean absorption coefficients are 0.18±0.1 cm-1 and 0.25±0.18 cm-1.