Handheld optical elastography probe spots breast cancer malignancies

A project led by the University of Western Australia (UWA) has developed a wireless handheld optical elastography probe to help clinicians distinguish between malignant and benign tissue in breast-conservation surgery, the primary surgical treatment for early-stage breast cancer.

Described in APL Bioengineering, the device would help clinicians assess the precise margins of malignancy when carrying out surgery, and so reduce the number of subsequent re-excisions necessary.

The probe employs elastography to differentiate tumors from healthy tissue, using the tumor's mechanical properties.

This exploits the fact that tumor tissue is stiffer than the normal surroundings, thanks to the changed proportion of rigid and soft cells within it; a difference that can be felt during surgery and used to inform the surgeon's decisions.

"Clinical palpation, the surgeon's sense of touch, remains an essential component of detection of tumor," wrote the project in its paper. "A range of biophotonics techniques have also been proposed, however these techniques have yet to demonstrate the clinical value required for widespread uptake. As a result, many surgeons still often rely on clinical palpation for intraoperative assessment."

The UWA hand-held probe is based on stereoscopic optical palpation (SOP), combining optical imaging with mechanical measurements of elasticity. Since the probe also provides surgeons with a visual of the tissue, users have another data point to differentiate the two tissue types. 

"The wireless probe is an extension of previous bench-top implementations of SOP," said Rhys Jones from UWA. "Our process began with establishing key requirements for the probe through consultation with surgeons: We decided that our targets were an ergonomic hand-held format, a field of view of at least 6 by 6 millimeters, wireless operation, a minimum one-hour battery life, and low material costs."

Mechanical contrast between tumor and benign tissue

According to the team's paper, its SOP implementation utilizes two parallel digital cameras to measure layer deformation, along with embedded phosphorescent microparticles that emit green light under UV illumination but are mostly transparent under visible light. Incorporating both visible and UV illumination in the device allows SOP to sequentially capture white light photographs and images of the UV illuminated particle plane, which are then used to calculate mechanical stress at the tissue surface.

In trials, the project validated its SOP probe on silicon phantoms and developed finite element analysis methods to visualize the stresses at the surface from optical data. It then applied the device to four freshly excised breast tissue specimens as proof of concept, which showed that "the probe can visualize the mechanical contrast between invasive tumor and benign tissue, with the computational method allowing distinction between different types of soft benign tissue."

The material cost of the prototype was around $1,200, which is less than similar bench-top SOP devices, but UWA believes this can be reduced further if it is mass-produced. Ultimately, Rhys Jones wants the device to be used in vivo during surgery, and perhaps for clinical applications other than tumor removal.

"Beyond breast-conserving surgery, we believe that the probe could be used in many clinical scenarios where palpation is currently used, including the assessment of skin lesions," said Jones.