Articles
Osteoporosis is a progressive disease that leads to thousands of fragility fractures each year, so the development of methods to diagnose bone problems at an early stage is a priority.
That’s why the findings of our team at Imperial College London, along with colleagues in the laser team at the Science and Technology Facilities Council, have caused quite a stir. Our research has led to the development of a new method of taking highly detailed X-ray images of bone using powerful laser beams, which could ultimately enable doctors to make an early diagnosis without needing a biopsy.
The X-rays are produced using a laser wakefield accelerator – a compact type of particle accelerator. For the first time, we have identified a medical application for this type of accelerator by demonstrating that X-rays produced as the electrons accelerate can be used to create high-resolution images of dense material such as bones. Our results show that it is possible to use this X-ray source to produce 3D images of bone samples at resolutions of around 50µm. These would allow clinicians to spot features within the bone at around 100µm thick.
In a laser wakefield accelerator, the laser is fired into a helium gas cell. Electrons in the gas are shaken free from their parent atoms to make a plasma of charged particles. The intense pressure of the high-power laser then generates a cavity in the plasma that can accelerate some of these electrons almost to the speed of light within 1cm or less. A focused beam of energetic electrons exits the plasma, which can then be used for physics experiments. Another consequence is that the electrons naturally oscillate in the cavity and emit a beam of high-energy X-ray particles. Since the cavity is also compact, the size of the X-ray source is small – about the order of 1µm. This effect enables high-resolution imaging, simply by propagating the X-rays through a sample.
We’ve shown that the laser technology can be adapted to create X-rays that reveal unprecedented detail and that would be useful for identifying conditions such as osteoporosis. Conventional X-ray scanning cannot get the full picture, as early-stage bone cracks can be too fine to be picked up.
We used this beam to produce pictures of a sample from the leg bone taken from an elderly patient who had had a hip replacement. By rotating the bone slightly after each picture, a full 3D reconstruction of the sample was produced, showing fine detail of the internal structure.
Producing this kind of study requires expensive equipment, and the technology is not yet sufficiently refined to detect microfractures, which can be an early indication of osteoporosis. Microfractures can be just 10µm thick, and can be detected currently only by taking a biopsy and sending the sample for analysis by microtomography machines.We expect that, with refinement, our system could provide a practical alternative to microtomography. It could match microtomography machines in terms of the resolution achieved – and could, eventually, become a viable technique for bone analysis in hospitals.
We are now working on refining our technique, and exploring how the technology could be adapted for use in a hospital. In particular, work is under way to miniaturise the laser system that underpins this work, so that the whole system can be made to fit into a hospital imaging department.