Terahertz tomographic imaging of transdermal drug delivery

In vivo imaging methods to trace topical drugs within the skin are in high demand with recent advances in transdermal drug delivery technology. With imaging and chemical identification capabilities, terahertz (THz) spectroscopy can be a good modality for visualizing and quantifying transdermal drug delivery. In this study, we evaluated the feasibility of THz reflection tomographic imaging for visualizing the distribution and penetration of a topical agent, ketoprofen dissolved in DMSO, using ex vivo and in vivo mouse skins. THz reflection imaging of ex vivo and in vivo skins demonstrated greater contrast between the drug-applied sites and unapplied skin than that of visual images. The reflectance signal of drug-applied sites was determined by mixed THz response of skin tissue, diffused ketoprofen, and DMSO content. Interestingly, serial B-scan images revealed that a new dark layer appeared at the drug-applied sites 1 h after drug application, which might be related with permeated ketoprofen. This study demonstrates that THz imaging technique can be utilized for imaging the distribution of topically applied drugs.