SFDI and HFUS noninvasively map contrast in human skin tumors

Spatial frequency domain imaging (SFDI) and high frequency ultrasound (HFUS) are capable of noninvasively mapping optical, physiological, and ultrasound contrasts in human skin tumors for surgery guidance and therapy planning, according to a study published in the February 2014 issue of Academic Radiology.

While the standard of care for nonmelanoma skin cancers (NMSCs) is typically surgical excision, Mohs microscopic surgery, or photodynamic therapy (PDT), information about the depth and size of the tumor is especially helpful for more accurate lesion removal and therapy decision-making.

“SFDI can quantify both optical absorption and scattering during reflectance imaging mode,” wrote lead author Daniel J. Rohrbach, of the Roswell Park Cancer Institute in Buffalo, N.Y., and colleagues. “HFUS can provide information regarding skin structure (thickness of epidermis, dermis, etc.) and lesion thickness, which can guide optical imaging for improved accuracy, as demonstrated recently for guiding fluorescence imaging.”

Rohrbach and colleagues analyzed two clinical cases from their ongoing clinical trial in which SFDI and HFUS were utilized for quantifying optical, vascular, and tissue structure parameters in patients with NMSCs. The researchers created a custom system that used HFUS imaging to complement the SFDI measurements. This system was then used on participants with biopsy-proven nonmelanoma cancer lesions slated to be removed with Mohs microscopic surgery.

Optical and physiological parameters were imaged and quantified in two patients. In one image scanned by HFUS, the lesion was determined to be 1.79 mm and 1.76 mm with H&E staining, proving HFUS was highly accurate in the quantification of tumor structure.

Results revealed that the custom SFDI system was able to reconstruct absorption and scattering parameters with high precision. The correlation coefficients for extracted and actual values were 0.991 and 0.992 for optical absorption and scattering parameters, respectively.

Image analysis between two tumors indicated that tumor region of interest portrayed a higher mean absorption parameter but lower mean scattering parameter. The blood oxygen saturation (StO₂) and total hemoglobin concentration (THC) were higher in the tumor for patient one. However, StO₂ was lower in the tumor and THC did not show contrast for patient two. There were also differences in contrast between the two tumors. Patient two had approximately 33.5 percent higher absorption and approximately 8.7 percent lower scattering than patient one. The StO₂ for both tumors were comparable but the THC was 40 percent higher in patient two. This finding reinforces the fact that squamous cell carcinomas are usually well vascularized compared to basal cell carcinomas.

“The proposed approach is significant not only for PDT but also for surgery because these noninvasive parameters can provide additional information about the tumor structure and contrast for surgical guidance,” concluded the authors.