If medical imaging had access to X-rays with synchrotron radiation intensity, it would be possible to discover tiny cancer tumors before they metastasize. But very expensive particle accelerators are required to generate synchrotron radiation. Consequently, it is not practical for X-ray imaging, which makes fine tissue structures visible.
Scientists at the Center for Advanced Laser Applications (CALA) at the Garching research campus near Munich are not prepared to accept this. They are working towards generating high-brilliance X-radiation using ultrashort pulse (USP) lasers in compact spaces to make it accessible for medical diagnostics.
The centerpieces of CALA are two laser systems: the advanced titanium-sapphire laser (AT-LAS) and the petawatt field synthesizer (PFS-pro). ATLAS delivers 20 femtosecond (fs) laser pulses that achieve power peaks of up to three petawatts (3 PW). An amplifier from Thales increases the energy content of the laser pulses from 2.5 to 60 joules. The researchers aim this extremely concentrated energy at hydrogen atoms to wrest electrons and accelerate them to almost the speed of light. If these speeding electrons encounter laser-induced strong plasma fields, they start oscillating—and emit the high-brilliance X-radiation. While light travels roughly just 6 µm in 20 fs, electrons can be released and excited in a very small space. Compact synchrotron radiation sources for clinical diagnosis are conceivable.
The Munich researchers have already carried out tomographies of mice, insects, and human bone samples. In addition to ATLAS, they also used the PFS-pro laser system, which provides intensive, ultrashort light pulses from three output channels. One of these is the X-ray source SPECTRE. A USP laser produces an electron package in a vacuum chamber. Scientists aim a second laser beam at this which causes the electrons to oscillate and emit the high intensity X-ray beams.
At CALA, researchers at Ludwig Maximilian University of Munich (LMU), the University of Technology (TU), and the Max Planck Institute of Quantum Optics have access to the Electron and Thomson Test Facility (ETTF). In this, they can accelerate the released electrons with the ATLAS laser in a range of several gigaelectron volts (GeV) and generate electron beams with a previously unattainable combination of electron charge and phase space density. These are precursors to the brilliant X-ray beams that will give physicians complete transparency in the future.
One key approach is phase-contrast X-ray imaging. Instead of using absorption of X-ray beams in the tissue, this uses the wave character of high frequency, extremely shortwave light: When tissue is X-rayed, there are minimal specific phase shifts. With the help of optical grating, the scientists in Munich can detect these interferences exactly and translate them into extremely detailed X-ray images, using imaging software that they developed.
But the Munich high-tech laser system can do even more: ATLAS and PFS-pro are also used as sources for “laser-driven ion acceleration” (LION), which will allow more effective radiation of malignant tissue mutations. To do this, the lasers release ions from carbon-based film and accelerate them to about a tenth of the speed of light. This enables the scientists to use ion radiation with USP Lasers. If laser-induced X-ray and ion radiation can be transferred to clinical practice, it could be combined with early cancer detection with direct radiation without having to move the patients in between times. Combined X-ray and ion radiation devices based on lasers could save patients torturous waiting times and the annoying trips between diagnosis and treatment.
It is not only the CALA researchers who believe in their technology. The French USP experts at Amplitude Laser are also convinced that laser-based X-ray sources will revolutionize medical imaging. How soon this will happen is still uncertain. Still, manufacturers like Agfa Healthcare, Canon and Philips are developing X-ray technology at a breathtaking pace. For example, surgeons with mobile C-arms can access high resolution X-ray images of the patient during operations. And wireless compact devices X-ray patients, who cannot be transported, in their hospital beds. Thanks to digital imaging and wireless data transfer, X-ray systems such as this can be integrated seamlessly into the fully networked data world of modern hospitals.