各校計畫成果

活動簡介

使用非侵入性影像技術研究皮膚結構和水合動態 

Towards studying skin structure and hydration dynamics with non-invasive imaging techniques

Establishing an optical laboratory that uses femtosecond lasers to generate terahertz radiation, which will then used to study skin with non-invasive imaging techniques. Future work will involve combining the terahertz beam with an optical coherence tomography.

Currently skin diseases are diagnosed by performing excisions and then sending the samples to laboratories for evaluation, whereas non-invasive in vivo diagnosis is currently done by the naked eye. The  ultimate aim of this project is to provide a technology, or demonstrate a technique, that gives clinicians an easy to use tool that allows them to better diagnose skin abnormalities without performing an excision and waiting for the results.

In order to address the challenge of early diagnosis – our approach must greatly enhance the insight into different types of skin cancer, without performing a biopsy and needing to wait for histology results (the current goldstandard). Two techniques with the potential to be used for skin cancer diagnosis without needing to perform an excision are Terahertz (THz) imaging and Opticalcoherence tomography (OCT), with wavelengths 100-3000μm and 1200-1400nm respectively. Known limitations of these techniques include the penetration depth into skin, and to overcome this, we will employ a reflection imaging geometry. Another issue when using THz to characterise skin is that THz imaging measures the amplitude and phase of the electric field but it relies on minimization algorithms to extract the refractive index and water content, and the exact thicknesses of the layers in the skin being unknown causes errors. However OCT uses the intensity of the back scattered wave to reveal structural information about the sample and can accurately determine the skin thickness. Combining the two techniques to probe the skin simultaneously will therefore combine their strengths and reduce their shortcomings. In particular, the structural information from the OCT scan will be used as an input into the minimization algorithms to extract the THz optical properties. In this way, the water content and the complex THz refractive index of the structure obtained from the OCT data will be determined accurately enabling them to be harnessed for cancer diagnosis.

The originality in this project comes the techniques to combine OCT and THz imaging for simultaneous measurement; for this single-pixel imaging technology will be employed, which works by imaging using a camera where its detector is a single-pixel. Because the singlepixel detector has no spatial resolution, the incident light beam is spatially patterned with a spatial light modulator, for example by a digital micromirror device or a micromachined deformable mirror array, and the detected signal is post-processed to obtain an image of the object. Such as camera is slower than the usual megapixel CCD arrays employed in visible light cameras, however a detector of a single-pixel is simpler to manufacture and much more robust. In fact, for THz radiation a multi-pixel detector array that has the detection capabilities needed for accurate medical diagnosis that is affordable and does not need an large optical bench is impossible. Whereas my previous research [1, 2, 3] has shown that single-pixel THz cameras can have good acquisition rates without sacrificing full detection capabilities (measurement of amplitude and phase over multiple frequencies) and using relatively cheap imaging components (below 4000 USD).

References

1. Stantchev, R. I., Yu, X., Blu, T. & Pickwell-macpherson, E. Realtime terahertz imaging with a single-pixel detector. Nature Communications 11, 1–8, https://doi.org/10.1038/ s41467-020-16370-x (2020).

2. Stantchev, R. I., Li, K. & Pickwell-MacPherson, E. Rapid Imaging of Pulsed Terahertz Radiation with Spatial Light Modulators and Neural Networks. ACS Photonics 8, 3150–3155, https://doi.org/10.1021/acsphotonics.1c00634 (2021).

3. Stantchev, R. I. et al. Noninvasive, near-field terahertz imaging of hidden objects using a single-pixel detector. Science Advances 2, e1600190, https://doi.org/10.1126/sciadv.1600190 (2016).

4. Wang, J. et al. THz in vivo measurements: the effects of pressure on skin reflectivity. Biomedical Optics Express 9, 6467, https://doi.org/10.1364/BOE.9.006467 (2018).