Why virtual micro-endoscopy?
Light-based methods are widely used for functional and structural medical imaging, as well as therapeutic interventions. However, scattering of light in biological tissue limits the application of such methods to only superficial layers. While optical implants enable access to deep tissue, their invasive nature belies the non-invasive promise of optical techniques and causes tissue damage. In this project, we demonstrate a novel non-invasive approach for micro-endoscopy using programmable ultrasonically sculpted virtual relay lenses in tissue.
In conventional microendoscopy, a cylindrical GRIN lens is inserted into the medium (e.g., tissue) to relay the image of the target to outside the medium. In the presented method, ultrasonic waves sculpt a virtual GRIN lens directly into the medium.
Non-invasive propagation of electromagnetic waves in different frequency bands (from X-rays to radio frequency waves and light waves in the visible and near-infrared spectrum) through biological tissue has been widely utilized to access different parts of the body. In particular, light-based methods are now widely used for functional and structural medical imaging as well as therapeutic interventions, such as photodynamic therapy (PDT) of malignant tumors and optogenetic stimulation of neurons. However, scattering of light within biological tissue limits the depth and the resolution of optical methods, especially in the visible and near-infrared range of the spectrum. we discuss a radical approach to use the target medium itself to sculpt and shape a virtual GRIN lens using ultrasonic waves that can propagate through the medium non-invasively, thus providing an alternative to implanting an invasive, bulky physical GRIN lens.
In contrast to physical GRIN lens implants that are limited to imaging from fixed positions in tissue, the ultrasonically sculpted optical relay lenses can be reconfigured dynamically to scan and image a 3D volume non-invasively, thus preventing an inflammatory tissue response that would happen when repositioning a physical GRIN lens in the tissue.
Ultrasonically sculpted virtual relay lens for micro-endoscopic imaging through scattering tissue
We show that a virtual optical graded-index (GRIN) lens can be sculpted in the medium using in situ reconfigurable ultrasonic interference patterns to relay images through the medium. Ultrasonic wave patterns change the local density of the medium to sculpt a graded refractive index pattern normal to the direction of light propagation, which modulates the phase front of light, causing it to focus within the medium and effectively creating a virtual relay lens. In addition, the virtual lenses can be reconfigured dynamically by changing the ultrasonic wave parameters, to scan and image a 3D volume non-invasively.
Matteo Giuseppe Scopelliti