Benchtop phase-contrast X-ray imaging
Introduction
To date, in clinical practice, X-ray imaging has been based on detection of differences in absorption of X-rays passing through the tissues being imaged. However, absorption imaging only provides low contrast for low Z elements. During the last decade, a number of novel methods have been developed, taking into account the phase shift the X-rays experience as a result of coherent X-ray scattering. This allows an increase in image contrast, especially in imaging weakly absorbing samples.
Some of the existing X-ray phase-contrast imaging methods require highly monochromatic plane wave radiation and sophisticated X-ray optics (Wilkins et al., 1996). However, the method adapted herein, known as propagation-based phase-contrast imaging but also as refraction-enhanced imaging, is a relatively simple method to implement, essentially requiring only a small focus X-ray tube and electronic detection. The three main methods used as phase-contrast techniques are illustrated in Fig. 1 (Wilkins et al., 1996; Lewis et al., 2005).
In biomedical research, attempts are being made to apply phase-contrast imaging techniques to a number of challenging clinical situations, including mammography, radiographic investigation of degenerative joint disease (bone is clearly visualised in conventional radiography, while cartilage is not) and lung imaging (Lewis, 2004). In the latter case, because of the difference in X-ray phase shift caused by blood and soft tissue, blood vessels can be revealed with phase-contrast image without the use of any contrast agent. In addition, and in regard to tumour imaging, because of the fact that more blood vessels are created near the cancerous cells for nutrition, phase contrast might also contribute to diagnosis of cancer. Even functional imaging might be possible if a material that modulates X-ray phase tends to concentrate to a particular location or condition (Momose et al., 2000).
Section snippets
Theory
Three different methods of phase imaging can be identified: the interferometric method, diffraction-enhanced imaging and in-line propagation. In the latter case, the simplicity of the experimental set-up encourages investigation of its possible implementation in clinical practice.
Review of some studies
Experiments employing synchrotron radiation have demonstrated propagation-enhanced contrast to be a valuable analytical tool in X-ray imaging. As an example, phase-contrast images of in vitro breast tissue specimens have been reported to provide superior quality to conventional mammographic images (Arfelli et al., 2000). Momose and Fukuda (1995) utilised an X-ray interferometer to image rat cerebellar slices that were not stained with contrast agent. While in the absorption-contrast image no
Present studies
At Surrey, use has been made of the experimental set-up illustrated in Fig. 2, comprising an X-ray tube, a 12 bit position-sensitive charged couple device (CCD) detector and an external fan. The system is mounted on an optical rail that enables separations of up to 1.5 m.
As previously noted, it is necessary for the radiation to enjoy high spatial or lateral coherence; for this reason, a small focal size tube is optimal. The Mo anode X-ray tube used was an Oxford Instruments Series 5000 Model
Results and discussion
As previously mentioned, blurring in the image increases with increase in the distance between the object and detector. The geometrical unsharpness for the particular X-ray tube is shown in the plot of Fig. 3. Beyond 0.7 m, blurring in the image is significant to cause loss of edge enhancement.
The first object imaged was a plastic cylinder of 0.8 mm wall thickness as shown in Fig. 4a. The images were obtained at 28 keV and 1 mA for 1 min using the Oxford tube with a focal spot size of 110 μm. The
Conclusions
Most of the experiments conducted for phase-contrast exploration employ synchrotron radiation because of its intensity and its spatial and temporal coherence. These experiments have shown that refraction-induced contrast is a very valuable analytical tool in X-ray imaging. Although it is possible to use such a source for clinical research, it would not be possible to use it for routine clinical applications because of the size, cost and availability of synchrotron facilities. Probably, in the
References (17)
- et al.
Low-dose phase contrast X-ray medical imaging
Phys. Med. Biol.
(1998) - et al.
Mammography with synchrotron radiation: phase-detection techniques
Radiology
(2000) - et al.
X-ray Tomography in Material Science
(2000) - et al.
Quantification of the effect of kVp on edge-enhancement index in phase-contrast radiography
Med. Phys.
(2002) - Fitzgerald, R., 2000. Phase-sensitive X-ray imaging. Available from:...
- et al.
Phase contrast enhancement of X-ray mammography: a design study
Phys. Med. Biol.
(1999) Medical phase contrast X-ray imaging: current status and future prospects
Phys. Med. Biol.
(2004)- et al.
X-ray refraction effects: application to the imaging of biological tissues
Br. J. Radiol.
(2003)
Cited by (19)
A review of X-ray explosives detection techniques for checked baggage
2012, Applied Radiation and IsotopesA digital approach to neutron-γ imaging with a narrow tungsten collimator aperture and a fast organic liquid scintillator detector
2012, Applied Radiation and IsotopesX-ray phase contrast imaging of the bone-cartilage interface
2010, Applied Radiation and IsotopesTransport and reaction in reconstructed porous polypropylene particles: Model validation
2010, Chemical Engineering ScienceCitation Excerpt :The previous generation of synchrotron-facilitated X-ray microscopy and tomography has been employed by Conner et al. (1990) and Ferrero et al. (1993) to visualize fragmentation of silica or MgCl2 carriers in polyolefin particles. The use of X-ray micro-tomography in the area of chemical engineering was demonstrated in recent years on examples of imaging the micro-structure evolution during sintering (Gundogdu et al., 2006), the morphology of cold-pressed pharmaceutical pills (Jenneson et al., 2004) and the improved phase contrast of biological samples (Gundogdu et al., 2007a). In situ observations of morphological changes taking place during fluidization of powder samples carried out with a high spatial (down to 400 nm) and temporal resolution (down to 1 ms) represent current state-of-the-art in micro-tomography imaging (Gundogdu et al., 2007b).
Processing of projections containing phase contrast in laboratory micro-computerized tomography imaging
2013, Journal of Applied Crystallography