Figure 3. Images of basal cell carcinoma (BCC) subtypes . FF-OCT images: (A) superficial BCC with grayish tumor nodules (yellow arrow). Epidermal attachment is not visible due to the lack of epidermis caused by inadequate tissue flattening. (B) micronodular BCC with small grayish tumor nodules, and (C) infiltrative BCC with grayish tumor strands (yellow arrows). BCC nodules are surrounded by a collagenous matrix. (D-F) Corresponding histopathology sections with Toluidine blue. Magnifications: (A-C) = 2 x 1.5 mm; (D-F) = 10x.
3) Squamous cell carcinoma: SCC was seen as sheets of polygonal cells with abundant grayish cytoplasm and enlarged irregular dark nuclei. Within the nucleus, a bright dot was often identified, which could be the nucleolus (Supplemental Figure 4) .
4) Other tumors: Cylindroma (Supplemental Figure 5)appeared as well circumscribed large multi-lobated grayish structure within the dermis. Some of the lobules were surrounded by a bright thickened band of collagen. Each lobule is composed of monomorphic cells with a dark round nucleus and a rim of scant grayish cytoplasm. No clefting around the nodule was seen.
Blinded analysis: Diagnostic accuracy of FF-OCT device in detecting residual tumors in the surgically excised fresh tissue : Readers 1 (CSJC) and 2 (MJ) each demonstrated high sensitivity (91.6% and 95.8%) and moderate specificity (55.6% and 61.1%), respectively, for detecting the presence of any malignant tumor in the margin(Table 1) .