X-Ray Phase Tomography with Synchrotron Radiation Offers Better Contrast Than CT Imaging

X-ray phase tomography is an imaging technique that uses penetrating X-rays to create volumetric views through slices of soft biologic tissues, such as tumors, and it offers strongly enhanced contrast in comparison to conventional computed tomography (CT) scans. However, scientists still do not know which X-ray phase tomography methods are best suited to yield optimized results for a wide variety of conditions.

To answer this question, a large group of researchers in Europe set out to compare three different X-ray phase tomography methods at the European Synchrotron Radiation Facility’s (ESRF; Grenoble, France) beamline ID19—X-ray grating interferometry, propagation-based phase tomography with single-distance phase reconstruction, and holotomography.

Led by Dr. Irene Zanette, a scientist affiliated with both ESRF and the Technische Universität München (TUM; Germany), the researchers put these three techniques to the test by examining cancerous tissue from a mouse model and an entire rat’s heart, which they reported in October 2014 in the Journal of Applied Physics.

Along with colleagues Bert Müller, group leader of the Biomaterials Science Center (Basel, Switzerland) and Timm Weitkamp, a scientist from the Synchrotron SOLEIL (Saint-Aubin, France), the team explored which technology performs best in terms of spatial resolution and visualization/quantification of pertinent features in the samples. They also examined other related factors such as the simplicity of the setup, and the data acquisition and analysis involved in each method. To accomplish this, the researchers chose standard synchrotron radiation, which produces substantially higher-quality X-rays than standard X-ray generators, such as those found in hospitals.

“Think of synchrotron radiation as being analogous to the sort of monochromatic, collimated and intense light produced by lasers, while conventional X-ray generators in hospitals are more analogous to light bulbs we use within our homes,” explained Dr. Zanette, currently a postdoctoral scientist in biomedical physics at TUM.

Significantly, she pointed out, while their study was performed using synchrotron radiation, the same techniques are amenable to both polychromatic and divergent beams and can also be implemented at conventional X-ray sources. The researchers used an advanced X-ray technique known as phase-contrast imaging. This type of imaging works by making the X-ray beam interfere while it propagates from sample to detector, according to Dr. Zanette. “This interference is fundamental because it encodes precious information on the phase of the X-ray waves.”

By comparison, conventional X-ray imaging, of the sort performed at hospitals and airports, doesn't use phase information. Rather, it relies only on the attenuation of the amplitude (reduction in intensity) of the X-ray waves by the object under study to generate image contrast. “More detailed information is contained in the phase than the amplitude, so it enables us to obtain images with much greater contrast and clearly differentiates cancerous tissue from healthy tissue,” Dr. Zanette said.

By comparing these methods, the group was able to show that for each specimen, the spatial resolution derived from the characteristic morphologic features is about twice as good for holotomography and single-distance phase reconstruction compared to X-ray grating interferometry. They also found that X-ray grating interferometry data generally provide much better contrast-to-noise ratios for anatomic features, excel in fidelity of the density measurements, and are more robust against low-frequency artifacts than holotomography.

The group regards all three of the phase tomography methods as being complementary. “The application determines which spatial and density resolutions are desired for the imaging task and dose requirements, so it really comes down to a choice between the complexity of the experimental setup and the data processing,” noted Dr. Müller. “It’s important to choose the ideal technique for your specific purposes.”

Since synchrotron radiation is of higher quality than the radiation at conventional sources, measurements at synchrotrons represent benchmarking experiments when translating these tomography techniques to clinical practice-especially X-ray grating interferometry, which is gaining popularity for use in hospitals.

“Our research should help provide guidance for other researchers in developing an ideal phase-contrast imaging method, which will be adopted by hospitals in the future,” Dr. Zanette concluded.

Related Links:
European Synchrotron Radiation Facility
Technische Universität München