Image: A CT slice reconstruction of rabbit kitten lungs with absorption contrast CT at 0.16 m (a), Phase contrast CT at 2 m (b), and algorithm phase retrieval at 2 m (Photo courtesy of Monash University).
X-ray phase-contrast imaging (PCI) can improve the visibility of soft tissues by an order of magnitude or more compared to conventional radiographs, according to a new study.
Researchers at Monash University (Melbourne, Australia), the Japan Synchrotron Radiation Research Institute (JASRI; Sayo, Japan), and other institutions attempted to enhance image contrast by using phase shifts (refraction) of X-rays to increase signal-to-noise ratio (SNR) by up to two orders of magnitude--compared to conventional computerized tomography (CT) at the same radiation dose--and without loss of image quality. The results revealed that as radiation dose decreases, the relative improvement in SNR increases.
The researchers found that the enhancement can be traded for a reduction in dose greater than the square of the gain in SNR. Thus, reducing the dose by 300 fold resulted in the phase-retrieved SNR that was still almost 10 times larger than the absorption contrast data. According to the researchers, the potential for dose reduction factors in the tens of thousands without loss in image quality is possible, which would have a profound impact on medical and industrial imaging applications. The study was published on November 21, 2017, in Nature Scientific Reports.
“CT with high SNR and spatial resolution can potentially be achieved with less dose than a single projection-absorption based image. We therefore recommend using a large number of very low dose projections, coupled with phase retrieval before CT slice reconstruction,” concluded lead author Marcus Kitchen, PhD, of Monash University, and colleagues. “This will result in images with high SNR, retaining high spatial resolution, and minimizing any reconstruction artefacts due to insufficient CT projection angles.”
PCI is a general term for technical methods that use information concerning changes in the phase of an X-ray beam that passes through an object in order to create its images. While standard X-ray imaging techniques such as CT rely on a decrease of the beam's intensity, in PCI the x-ray beam's phase shift is not measured directly, but is transformed into variations in intensity, which then can be recorded. When applied to samples that consist of elements with low atomic numbers, PCI is more sensitive to density variations than conventional transmission-based X-ray imaging, which leads to improved soft tissue contrast.
Japan Synchrotron Radiation Research Institute