Researchers at UCL Medical Physics & Biomedical Engineering and the University of Western Australia have developed a novel method to obtain highly detailed 3D x-ray images with low doses of radiation. In the future, the method could be applied to a wide range of biological and medical applications, such as for example small-animal preclinical imaging. The results, published in the July edition of Medical Physics (“Low-dose phase contrast tomography with conventional x-ray sources” by Charlotte Hagen and co-workers), were selected to feature on the front cover of the journal.
The novel method is based on a new contrast mechanism in x-ray imaging, known as phase contrast (PC). Conventional radiographic methods measure the absorption of x-rays while they travel through a sample, which can lead to poor contrast for weakly absorbing materials (for example, biological soft tissue). PC imaging, on the contrary, exploits the minimal (micro-radian) directional changes that x-rays suffer while they travel through matter, a phenomenon known as refraction. For biological soft tissues, x-ray refraction can be much stronger than absorption; therefore, PC imaging can overcome the problem of poor image quality and reveal more detailed information on the inside of a sample.
PC imaging has been investigated at UCL for almost a decade by the UCL Phase Contrast Group, currently nine-strong, led by Prof. Alessandro Olivo. The group’s main activity is the development of Edge Illumination PC, an approach compatible with x-ray sources ranging from highly specialised to commercially available.
Charlotte Hagen, first author on the Medical Physics paper, said: “It is very important to make sure that PC imaging can also be carried out with commercial x-ray equipment, which can already be found in many standard research labs, as this makes the benefits of PC imaging available to researchers from a wide range of disciplines.”
The publication in Medical Physics describes how Charlotte Hagen and co-workers have combined Edge Illumination PC with the principles of computed tomography. In this way, highly detailed 3D images of the inside of the sample can be reconstructed, revealing structures on the micrometre scale. Most importantly, these images can be obtained with commercially available x-ray sources and require a low radiation exposure, about a tenth of the recommended limit for small animal studies.