04 Jul 2008
An image-guided femtosecond laser is allowing surgeons to remove individual cancer cells while adjacent cells remain intact.
Researchers from the universities of Texas and Stanford, US, have demonstrated a miniaturized probe that enables ablation of single cells and subcellular structures at high precision. The tool combines two-photon microscopy and femtosecond laser microsurgery in a 10 x 15 x 40 mm housing (Optics Express 16 9996).
In the approach, high-energy pulses sear the targeted cell so rapidly and accurately that the heat has no time to spread and damage nearby healthy cells. To fully realize the technique's clinical potential, however, this ablation process needs to be guided and monitored by an equally precise and penetrating 3D imaging technique, such as two-photon fluorescence microscopy.
The system uses a single photonic-crystal fibre to deliver the femtosecond laser pulses for both microsurgery and fluorescence excitation, thus providing visualization of the exact site of ablation. The imaging pulses have a wavelength of near 753 nm and a measured pulse duration of 152 fs, while pulses used for microsurgery are delivered near 780 nm with a pulse duration of 178 fs.
The probe focuses the light pulses to a spot size smaller than that of human cells. Its other key components include a microelectromechanical systems (MEMS)-based scanning mirror, a miniature relay lens system and a gradient index objective lens. All of these components are both compact in size and able to handle high-intensity infrared laser pulses.
The researchers tested the capabilities of the experimental probe using breast-cancer cells grown in a single layer and labelled with a fluorescent cell-viability dye. Following laser microsurgery with a single 280 nJ pulse, two-photon images of the target cell showed a loss of the fluorescence signal – indicating cell ablation. The researchers note that that the technique's high precision allowed disintegration of the target cell while adjacent cells remained intact.
"You can remove a cell with high precision in 3D without damaging the cells above and below it," explained Adela Ben-Yakar, assistant professor of mechanical engineering at the University of Texas. "And with the same precision, you can see what you are doing to guide your microsurgery."
Ben-Yakar's team also demonstrated imaging and ablation of cells within a 3D tissue phantom comprising breast-cancer cells embedded in a collagen matrix. She has since also studied laboratory-grown, layered cell structures that mimic skin and other tissues.
Within a few years, Ben-Yakar expects to shrink the probe's 15 mm diameter three-fold to match the size of endoscopes used for laparoscopic surgery. Future applications could include the accurate ablation of small vocal-cord tumours, cancer cells left behind after the removal of solid tumours, individual cancer cells scattered throughout brain or other tissue, and plaque in arteries. The probe could be made disposable for operating on people who have infectious diseases or destroying deadly viruses and other biomaterials.