Medical applications of synchrotron radiation

Energy response calibration of photon-counting detectors using x-ray fluorescence: a feasibility study

Accurate energy calibration is critical for the application of energy-resolved photon-counting detectors in spectral imaging. The aim of this study is to investigate the feasibility of energy response calibration and characterization of a photon-counting detector using x-ray fluorescence. A comprehensive Monte Carlo simulation study was performed using Geant4 Application for Tomographic Emission (GATE) to investigate the optimal technique for x-ray fluorescence calibration. Simulations were conducted using a 100 kVp tungsten-anode spectra with 2.7 mm Al filter for a single pixel cadmium telluride (CdTe) detector with 3 × 3 mm(2) in detection area. The angular dependence of x-ray fluorescence and scatter background was investigated by varying the detection angle from 20° to 170° with respect to the beam direction. The effects of the detector material, shape, and size on the recorded x-ray fluorescence were investigated. The fluorescent material size effect was considered with and without the container for the fluorescent material. In order to provide validation for the simulation result, the angular dependence of x-ray fluorescence from five fluorescent materials was experimentally measured using a spectrometer. Finally, eleven of the fluorescent materials were used for energy calibration of a CZT-based photon-counting detector. The optimal detection angle was determined to be approximately at 120° with respect to the beam direction, which showed the highest fluorescence to scatter ratio (FSR) with a weak dependence on the fluorescent material size. The feasibility of x-ray fluorescence for energy calibration of photon-counting detectors in the diagnostic x-ray energy range was verified by successfully calibrating the energy response of a CZT-based photon-counting detector. The results of this study can be used as a guideline to implement the x-ray fluorescence calibration method for photon-counting detectors in a typical imaging laboratory.

Radiation dose and image quality in K-edge subtraction computed tomography of lung in vivo

K-edge subtraction computed tomography (KES-CT) allows simultaneous imaging of both structural features and regional distribution of contrast elements inside an organ. Using this technique, regional lung ventilation and blood volume distributions can be measured experimentally in vivo. In order for this imaging technology to be applicable in humans, it is crucial to minimize exposure to ionizing radiation with little compromise in image quality. The goal of this study was to assess the changes in signal-to-noise ratio (SNR) of KES-CT lung images as a function of radiation dose. The experiments were performed in anesthetized and ventilated rabbits using inhaled xenon gas in O2 at two concentrations: 20% and 70%. Radiation dose, defined as air kerma (Ka), was measured free-in-air and in a 16 cm polymethyl methacrylate phantom with a cylindrical ionization chamber. The dose free-in-air was varied from 2.7 mGy to 8.0 Gy. SNR in the images of xenon in air spaces was above the Rose criterion (SNR > 5) when Ka was over 400 mGy with 20% xenon, and over 40 mGy with 70% xenon. Although in human thorax attenuation is higher, based on these findings it is estimated that, by optimizing the imaging sequence and reconstruction algorithms, the radiation dose could be further reduced to clinically acceptable levels.

Diffraction-enhanced Synchrotron Imaging of Bovine Ovaries Ex Vivo

OBJECTIVES

The objective of this study was to test the hypothesis that diffraction-enhanced imaging (DEI), a synchrotron x-ray imaging technique, would provide greater contrast for evaluating bovine ovaries compared with conventional diagnostic ultrasonography.

MATERIALS AND METHODS

Bovine ovaries were evaluated ex vivo as follows: fresh without radiographic arterial contrast (n = 2), fresh with contrast (n = 1), preserved in 10% formalin without contrast (n = 2), and preserved with contrast (n = 1). Each ovary was imaged with DEI and subsequently with ultrasonography and histology. The ability to visualize and differentiate preantral and antral follicles, corpora lutea (CL), and cumulus oocyte complexes (COCs) were compared using DEI, ultrasonography, and histology. The diameter of follicles and CL were measured and compared using ultrasonography, DEI, and histology. The diameter of the smallest follicle detected was reported using each of the three imaging methods. The number of antral follicles (antral follicle count ≥2 mm) was compared between ultrasonography and DEI.

RESULTS

DEI enabled the detection of 71% of follicles and 67% of CL that were detected ultrasonographically. However, DEI did not allow the detection of COCs and cell layers of the follicle wall that were visualized histologically. Luteal tissues were not easily distinguished using DEI, and DEI was inferior for differentiating follicles and CL compared with ultrasonography. The mean follicle diameter was similar between DEI (4.00 ± 0.35 mm, fresh with contrast; 9.62 ± 2.43 mm, fresh without contrast) and ultrasonography (3.85 ± 0.28 mm, fresh with contrast; 8.97 ± 2.60 mm, fresh without contrast) (P > .05). However, the mean follicle diameter was greater using both DEI (4.00 ± 0.35 mm) and ultrasonography (3.85 ± 0.28 mm) compared with histology (2.21 ± 0.38 mm; P = .01, fresh ovaries with contrast). The mean CL diameter was similar between DEI (11.64 ± 1.67 mm), ultrasonography (9.34 ± 0.35 mm), and histology (9.59 ± 0.36 mm) (P > .05). The mean diameter of the smallest follicle detected was similar between DEI (3.06 ± 0.45 mm) and ultrasonography (2.95 ± 0.74 mm); both DEI and ultrasonographic measurements were greater than histology (0.39 ± 0.04 mm, P < .0001). The mean antral follicle count was similar between ultrasonography (6.50 ± 0.71 mm, fresh with no contrast; 6.50 ± 2.50 mm, preserved with no contrast) and DEI (4.50 ± 0.50 mm, fresh with no contrast; 6.50 ± 0.50 mm, preserved with no contrast) (P > .05).

CONCLUSIONS

The contrast resolution of antral follicles, CL, and COCs in bovine ovaries was inferior using DEI compared with ultrasonography and histology. Alternative synchrotron techniques, such as phase-contrast computed tomography and DEI computed tomography, may prove more effective than DEI for imaging ovaries ex vivo.

Development of a bent Laue beam-expanding double-crystal monochromator for biomedical X-ray imaging

The Biomedical Imaging and Therapy (BMIT) beamline at the Canadian Light Source has produced some excellent biological imaging data. However, the disadvantage of a small vertical beam limits its usability in some applications. Micro-computed tomography (micro-CT) imaging requires multiple scans to produce a full projection, and certain dynamic imaging experiments are not possible. A larger vertical beam is desirable. It was cost-prohibitive to build a longer beamline that would have produced a large vertical beam. Instead, it was proposed to develop a beam expander that would create a beam appearing to originate at a source much farther away. This was accomplished using a bent Laue double-crystal monochromator in a non-dispersive divergent geometry. The design and implementation of this beam expander is presented along with results from the micro-CT and dynamic imaging tests conducted with this beam. Flux (photons per unit area per unit time) has been measured and found to be comparable with the existing flat Bragg double-crystal monochromator in use at BMIT. This increase in overall photon count is due to the enhanced bandwidth of the bent Laue configuration. Whilst the expanded beam quality is suitable for dynamic imaging and micro-CT, further work is required to improve its phase and coherence properties.

Roles of NAD (+) , PARP-1, and Sirtuins in Cell Death, Ischemic Brain Injury, and Synchrotron Radiation X-Ray-Induced Tissue Injury

NAD(+) plays crucial roles in a variety of biological processes including energy metabolism, aging, and calcium homeostasis. Multiple studies have also shown that NAD(+) administration can profoundly decrease oxidative cell death and ischemic brain injury. A number of recent studies have further indicated that NAD(+) administration can decrease ischemic brain damage, traumatic brain damage and synchrotron radiation X-ray-induced tissue injury by such mechanisms as inhibiting inflammation, decreasing autophagy, and reducing DNA damage. Our latest study that applies nano-particles as a NAD(+) carrier has also provided first direct evidence demonstrating a key role of NAD(+) depletion in oxidative stress-induced ATP depletion. Poly(ADP-ribose) polymerase-1 (PARP-1) and sirtuins are key NAD(+)-consuming enzymes that mediate multiple biological processes. Recent studies have provided new information regarding PARP-1 and sirtuins in cell death, ischemic brain damage and synchrotron radiation X-ray-induced tissue damage. These findings have collectively supported the hypothesis that NAD(+) metabolism, PARP-1 and sirtuins play fundamental roles in oxidative stress-induced cell death, ischemic brain injury, and radiation injury. The findings have also supported "the Central Regulatory Network Hypothesis", which proposes that a fundamental network that consists of ATP, NAD(+) and Ca(2+) as its key components is the essential network regulating various biological processes.

Subtraction micro-computed tomography of angiogenesis and osteogenesis during bone repair using synchrotron radiation with a novel contrast agent

Quantitative three-dimensional (3D) imaging of angiogenesis during bone repair remains an experimental challenge. We developed a novel contrast agent containing 0.07- to 0.1-μm particles of zirconium dioxide (ZrCA) and established subtraction μCT using synchrotron radiation (sSRCT) for quantitative imaging of angiogenesis and bone repair. This method was applied to a rat model of tibial bone repair 3 days (DAY3; n = 2), 5 days (DAY5; n = 8), or 10 days (DAY10; n = 8) after drill-hole injury. Using the same drill-hole defect model, its potential use was illustrated by comparison of bone repair between hindlimbs subjected to mechanical unloading (n = 6) and normal weight bearing (n = 6) for 10 days. Following vascular casting with ZrCA, the defect site was scanned with 17.9- and 18.1-keV X-rays. In the latter, image contrast between ZrCA-filled vasculature and bone was enhanced owing to the sharp absorption jump of zirconium dioxide at 18.0 keV (k-edge). The two scan data sets were reconstructed with 2.74-μm voxel resolution, registered by mutual information, and digitally subtracted to extract the contrast-enhanced vascular image. K2HPO4 phantom solutions were scanned at 17.9 keV for quantitative evaluation of bone mineral. Angiogenesis had already started, but new bone formation was not found on DAY3. New bone emerged near the defect boundary on DAY5 and took the form of trabecular-like structure invaded by microvessels on DAY10. Vascular and bone volume fractions, blood vessel and bone thicknesses, and mineralization were higher on DAY10 than on DAY5. All these parameters were found to be decreased after 10 days of hindlimb unloading, indicating the possible involvement of angiogenesis in bone repair impairment caused by reduced mechanical stimuli. In conclusion, the combined technique of sSRCT and ZrCA vascular casting is suitable for quantitative 3D imaging of angiogenesis and its surrounding bone regeneration. This method will be useful for better understanding the linkage between angiogenesis and bone repair.

Prevention of cartilage dehydration in imaging studies with a customized humidity chamber

Quantitative three-dimensional imaging methods such as micro-computed tomography (μCT) allow for the rapid and comprehensive evaluation of cartilage and bone in animal models, which can be used for drug development and related research in arthritis. However, when imaging fresh cartilage tissue in air, a common problem is tissue dehydration which causes movement artifact in the resulting images. These artifacts distort scans and can render them unusable, leading to a considerable loss of time and effort with sample preparation and measurement. The sample itself is also irretrievably damaged by the dehydration, often unable to return to its full tissue thickness upon rehydration. Additionally, imaging with ionic contrast agents such as Hexabrix(TM) must be performed in air, otherwise the agent will be washed out if immersed in a liquid. The first goal of this study was to design a customized humidity chamber to maintain cartilage hydration without the need for immersion. Following this, the use of the humidity chamber during a synchrotron radiation-μCT scan was validated and its performance evaluated. Results showed that the loss of fluid film volume is associated with scanning at low humidity (87%), and can be avoided using the humidity chamber. Coupling this technology with advances in synchrotron imaging (e.g., phase contrast imaging) or contrast agents is promising.

Monochromatic x-rays for low-dose digital mammography: preliminary results

PURPOSE

The feasibility of using monochromatic x-ray imaging generated from an x-ray tube and a multilayer reflector for digital mammography with a low radiation dose was examined.

MATERIALS AND METHODS

A multilayer mirror was designed to select the x-ray peak with an energy of 21.5 keV generated from an x-ray tube with a tungsten target and was fabricated by the ion-beam sputtering deposition system. Monochromatic x-ray images were obtained from an experimental digital mammography setup with a scanning stage. The performance of the system was evaluated using a breast phantom, a spectrometer, and a radiation dosimeter. We measured the contrast-to-noise ratio and performed the 10% modulation function test to determine image quality and resolution.

RESULTS

The monochromatic beam from the multilayer reflector had a full-width-at-half-maximum of 0.9 keV at 21.5 keV, and the reflectivity was 0.70, which was 90% of the designed value. The polychromatic and monochromatic x-rays showed radiation doses of 0.497 and 0.0415 mGy, respectively. The monochromatic x-ray image shows fibers, calcifications, and masses more clearly than the polychromatic x-ray images do. The image contrast of the monochromatic x-rays was 1.85 times higher than that of the polychromatic x-rays. The experimental mammography setup had a spatial resolution of 7 lp/mm with both x-rays.

CONCLUSION

Monochromatic x-rays generated using a multilayer mirror may be a useful diagnostic tool for breast examination by providing high contrast imaging with a low radiation dose.

Synchrotron radiation imaging for advancing our understanding of cardiovascular function

Synchrotron radiation (SR) is increasingly being used for micro-level and nano-level functional imaging in in vivo animal experiments. This review focuses on the methodology that enables repeated and regional assessment of vessel internal diameter and flow in the resistance vessels of different organ systems. In particular, SR absorption microangiography approaches offer unique opportunities for real-time in vivo vascular imaging in small animals, even during dynamic motion of the heart and lungs. We also describe recent progress in the translation of multiple phase-contrast imaging techniques from ex vivo to in vivo small-animal studies. Furthermore, we also review the utility of SR for multiple pinpoint (dimensions 0.2×0.2 mm) assessments of myocardial function at the cross-bridge level in different regions of the heart using small-angle X-ray scattering, resulting from increases in SR flux at modern facilities. Finally, we present cases for the use of complementary SR approaches to study cardiovascular function, particularly the pathological changes associated with disease using small-animal models.

X-ray phase-contrast imaging: from pre-clinical applications towards clinics

Phase-contrast x-ray imaging (PCI) is an innovative method that is sensitive to the refraction of the x-rays in matter. PCI is particularly adapted to visualize weakly absorbing details like those often encountered in biology and medicine. In past years, PCI has become one of the most used imaging methods in laboratory and preclinical studies: its unique characteristics allow high contrast 3D visualization of thick and complex samples even at high spatial resolution. Applications have covered a wide range of pathologies and organs, and are more and more often performed in vivo. Several techniques are now available to exploit and visualize the phase-contrast: propagation- and analyzer-based, crystal and grating interferometry and non-interferometric methods like the coded aperture. In this review, covering the last five years, we will give an overview of the main theoretical and experimental developments and of the important steps performed towards the clinical implementation of PCI.

Synchrotron radiation in cancer treatments and diagnostics: an overview

During the last 30 years many groups have carried out experiments and trials to develop new imaging and radiotherapy techniques in oncology, based on the use of synchrotron X-rays. There are several synchrotron biomedical stations around the world, which offer an excellent platform to improve either the imaging diagnosis or radiotherapy treatment for different tumour types. In the coming months the first radiotherapy clinical trials will be seen at the Biomedical Beamline at the ESRF synchrotron in Grenoble (France). In this article we highlight the results of some of the techniques and strategies that have been developed at different biomedical synchrotron stations.

Real time observation of mouse fetal skeleton using a high resolution X-ray synchrotron

The X-ray synchrotron is quite different from conventional radiation sources. This technique may expand the capabilities of conventional radiology and be applied in novel manners for special cases. To evaluate the usefulness of X-ray synchrotron radiation systems for real time observations, mouse fetal skeleton development was monitored with a high resolution X-ray synchrotron. A non-monochromatized X-ray synchrotron (white beam, 5C1 beamline) was employed to observe the skeleton of mice under anesthesia at embryonic day (E)12, E14, E15, and E18. At the same time, conventional radiography and mammography were used to compare with X-ray synchrotron. After synchrotron radiation, each mouse was sacrificed and stained with Alizarin red S and Alcian blue to observe bony structures. Synchrotron radiation enabled us to view the mouse fetal skeleton beginning at gestation. Synchrotron radiation systems facilitate real time observations of the fetal skeleton with greater accuracy and magnification compared to mammography and conventional radiography. Our results show that X-ray synchrotron systems can be used to observe the fine structures of internal organs at high magnification.

In vivo CT quantification of trabecular bone dynamics in mice after sciatic neurectomy using monochromatic synchrotron radiation

We demonstrated the capability of in vivo synchrotron radiation CT (SRCT) in analyzing short-term changes in trabecular bone architecture (TBA) and the degree of bone mineralization (DBM) in small animals. Mice underwent unilateral sciatic neurectomy (SN) and sham operation on the contralateral side (SO) at 13 weeks of age. In vivo SRCT scans (11.7-μm cubic voxel) were made of both knees 7 and 17 days (group 1, n = 7) or only 17 days (group 2, n = 6) after surgery. In three mice in group 2, one knee was scanned twice on the same day in different orientations for reproducibility testing. Two scan data sets of the tibial proximal metaphysis acquired at different time points (group 1) or at the same time point (group 2) were registered for detecting differences in volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), connectivity density (Conn.D), and mean DBM (mDBM). The reproducibility test showed small errors of <2.5% in the TBA indexes and <3.0% in mDBM, while mismatched bone regions amounted to >25%. In group 1, Tb.Th increased but Tb.N and Conn.D decreased in both SN and SO; BV/TV and mDBM increased only in SO; accordingly, BV/TV, Tb.Th, and mDBM became lower in SN than in SO. No significant interaction between SN and irradiation was found; the SN effects on TBA and DBM were similar between groups 1 and 2, although synchrotron irradiation led to higher Tb.Th and lower Tb.N in group 1. In conclusion, in vivo SRCT has potential use for detecting short-term bone dynamics of small animals.

Energy filtering with X-ray lenses: optimization for photon-counting mammography

Chromatic properties of the multi-prism and prism-array X-ray lenses (MPL and PAL) can potentially be utilized for efficient energy filtering and dose reduction in mammography. The line-shaped foci of the lenses are optimal for coupling to photon-counting silicon strip detectors in a scanning system. A theoretical model was developed and used to investigate the benefit of two lenses compared with an absorption-filtered reference system. The dose reduction of the MPL filter was approximately 15% compared with the reference system at matching scan time, and the spatial resolution was higher. The dose of the PAL-filtered system was found to be approximately 20% lower than for the reference system at equal scan time and resolution, and only approximately 20% higher than for a monochromatic beam. An investigation of some practical issues remains, including the feasibility of brilliant-enough X-ray sources and manufacturing of a polymer PAL.

Polarization induced instabilities in external four-mirror Fabry-Perot cavities

Various four-mirror optical resonators are studied from the perspective of realizing passive stacking cavities. A comparative study of the mechanical stability is provided. The polarization properties of the cavity eigenmodes are described, and it is shown that the effect of mirror misalignments (or motions) induces polarization and stacking power instabilities. These instabilities increase with the finesse of the Fabry-Perot cavity. A tetrahedral configuration of the four mirrors is found to minimize the consequences of the mirrors' motion and misalignment by reducing the instability parameter by at least 2 orders of magnitude.

Curved crystal x-ray optics for monochromatic imaging with a clinical source

Monochromatic x-ray imaging has been shown to increase contrast and reduce dose relative to conventional broadband imaging. However, clinical sources with very narrow energy bandwidth tend to have limited intensity and field of view. In this study, focused fan beam monochromatic radiation was obtained using doubly curved monochromator crystals. While these optics have been in use for microanalysis at synchrotron facilities for some time, this work is the first investigation of the potential application of curved crystal optics to clinical sources for medical imaging. The optics could be used with a variety of clinical sources for monochromatic slot scan imaging. The intensity was assessed and the resolution of the focused beam was measured using a knife-edge technique. A simulation model was developed and comparisons to the measured resolution were performed to verify the accuracy of the simulation to predict resolution for different conventional sources. A simple geometrical calculation was also developed. The measured, simulated, and calculated resolutions agreed well. Adequate resolution and intensity for mammography were predicted for appropriate source/optic combinations.

Advances in biological structure, function, and physiology using synchrotron X-ray imaging*

Studies of the physiology and biomechanics of small ( approximately 1 cm) organisms are often limited by the inability to see inside the animal during a behavior or process of interest and by a lack of three-dimensional morphology at the submillimeter scale. These constraints can be overcome by an imaging probe that has sensitivity to soft tissue, the ability to penetrate opaque surfaces, and high spatial and temporal resolution. Synchrotron X-ray imaging has been successfully used to visualize millimeter-centimeter-sized organisms with micrometer-range spatial resolutions in fixed and living specimens. Synchrotron imaging of small organisms has been the key to recent novel insights into structure and function, particularly in the area of respiratory physiology and function of insects. X-ray imaging has been effectively used to examine the morphology of tracheal systems, the mechanisms of tracheal and air sac compression in insects, and the function of both chewing and sucking mouthparts in insects. Synchrotron X-ray imaging provides an exciting new window into the internal workings of small animals, with future promise to contribute to a range of physiological and biomechanical questions in comparative biology.

Diffraction-enhanced imaging of a porcine eye

BACKGROUND

Diffraction-enhanced imaging (DEI) is a synchrotron-based x-ray imaging technique that has dramatically improved contrast over standard x-ray imaging techniques. It is possible to acquire images that analyze the x-ray refraction and the apparent absorption (elimination of small-angle scattering) of the object.

METHODS

Three formalin-fixed porcine eyes were studied at the National Synchrotron Light Source using DEI. Conventional absorption-type radiography was conducted for comparison.

RESULTS

Conventional absorption radiography did not yield significant detail of the eye anatomy. DEI showed excellent characterization of many ocular structures. The cornea, iris, lens, retina, optic nerve, as well as choroidal vasculature and the ampullae of the vortex veins could all be visualized.

INTERPRETATION

DEI represents a novel, high-resolution imaging technique that has excellent characterization of ocular anatomy. Further application of this imaging modality will be undertaken to study cataract and choroidal tumors and to examine ocular surface structures, such as the extraocular muscle insertions, more closely.

Imaging applications of synchrotron X-ray phase-contrast microtomography in biological morphology and biomaterials science. I. General aspects of the technique and its advantages in the analysis of millimetre-sized arthropod structure

Synchrotron-generated X-rays provide scientists with a multitude of investigative techniques well suited for the analysis of the composition and structure of all types of materials and specimens. Here, we describe the properties of synchrotron-generated X-rays and the advantages that they provide for qualitative morphological research of millimetre-sized biological organisms and biomaterials. Case studies of the anatomy of insect heads, of whole microarthropods and of the three-dimensional reconstruction of the cuticular tendons of jumping beetles, all performed at the beamline ID19 of the European Synchrotron Radiation Facility (ESRF), are presented to illustrate the techniques of phase-contrast tomography available for anatomical and structural investigations. Various sample preparation techniques are described and compared and experimental settings that we have found to be particularly successful are given. On comparing the strengths and weaknesses of the technique with traditional histological thin sectioning, we conclude that synchrotron radiation microtomography has a great potential in biological microanatomy.

Analyser-based phase contrast image reconstruction using geometrical optics

Analyser-based phase contrast imaging can provide radiographs of exceptional contrast at high resolution (<100 microm), whilst quantitative phase and attenuation information can be extracted using just two images when the approximations of geometrical optics are satisfied. Analytical phase retrieval can be performed by fitting the analyser rocking curve with a symmetric Pearson type VII function. The Pearson VII function provided at least a 10% better fit to experimentally measured rocking curves than linear or Gaussian functions. A test phantom, a hollow nylon cylinder, was imaged at 20 keV using a Si(1 1 1) analyser at the ELETTRA synchrotron radiation facility. Our phase retrieval method yielded a more accurate object reconstruction than methods based on a linear fit to the rocking curve. Where reconstructions failed to map expected values, calculations of the Takagi number permitted distinction between the violation of the geometrical optics conditions and the failure of curve fitting procedures. The need for synchronized object/detector translation stages was removed by using a large, divergent beam and imaging the object in segments. Our image acquisition and reconstruction procedure enables quantitative phase retrieval for systems with a divergent source and accounts for imperfections in the analyser.

High-resolution CT by diffraction-enhanced x-ray imaging: mapping of breast tissue samples and comparison with their histo-pathology

The aim of this study was to introduce high-resolution computed tomography (CT) of breast tumours using the diffraction-enhanced x-ray imaging (DEI) technique and to compare results with radiological and histo-pathological examinations. X-ray CT images of tumour-bearing breast tissue samples were acquired by monochromatic synchrotron radiation (SR). Due to the narrow beam and a large sample-to-detector distance scattering is rejected in the absorption contrast images (SR-CT). Large contrast enhancement is achieved by the use of the DEI-CT method, where the effects of refraction and scatter rejection are analysed by crystal optics. Clinical mammograms and CT images were recorded as reference material for a radiological examination. Three malignant and benign samples were studied in detail. Their radiographs were compared with optical images of stained histological sections. The DEI-CT images map accurately the morphology of the samples, including collagen strands and micro-calcifications of dimensions less than 0.1 mm. Histo-pathological examination and reading of the radiographs were done independently, and the conclusions were in general agreement. High-resolution DEI-CT images show strong contrast and permit visualization of details invisible in clinical radiographs. The radiation dose may be reduced by an order of magnitude without compromising image quality, which would make possible clinical in vivo DEI-CT with future compact SR sources.

Synchrotron-based intravenous cerebral angiography in a small animal model

K-edge digital subtraction angiography (KEDSA), a recently developed synchrotron-based technique, utilizes monochromatic radiation and allows acquisition of high-quality angiography images after intravenous administration of contrast agent. We tested KEDSA for its suitability for intravenous cerebral angiography in an animal model. Adult male New Zealand rabbits were subjected to either angiography with conventional x-ray equipment or synchrotron-based intravenous KEDSA, using an iodine-based contrast agent. Angiography with conventional x-ray equipment after intra-arterial administration of contrast agent demonstrated the major intracranial vessels but no smaller branches. KEDSA was able to visualize the major intracranial vessels as well as smaller branches in both radiography mode (planar images) and tomography mode. Visualization was achieved with as little as 0.5 ml kg-1 of iodinated contrast material. We were able to obtain excellent visualization of the cerebral vasculature in an animal model using intravenous injection of contrast material, using synchrotron-based KEDSA.

Evaluation of x-ray diffraction enhanced imaging in the diagnosis of breast cancer

The significance of the x-ray diffraction enhanced imaging (DEI) technique in the diagnosis of breast cancer and its feasibility in clinical medical imaging are evaluated. Different massive specimens including normal breast tissues, benign breast tumour tissues and malignant breast tumour tissues are imaged with the DEI method. The images are recorded respectively by CCD or x-ray film at different positions of the rocking curve and processed with a pixel-by-pixel algorithm. The characteristics of the DEI images about the normal and diseased tissues are compared. The rocking curves of a double-crystal diffractometer with various tissues are also studied. The differences in DEI images and their rocking curves are evaluated for early diagnosis of breast cancers.

Qualitative evaluation of titanium implant integration into bone by diffraction enhanced imaging

Diffraction enhanced imaging (DEI) uses refraction of x-rays at edges, which allows pronounced visualization of material borders and rejects scattering which often obscures edges and blurs images. Here, the first evidence is presented that, using DEI, a destruction-free evaluation of the quality of integration of metal implants into bone is possible. Experiments were performed in rabbits and sheep with model implants to investigate the option for DEI as a tool in implant research. The results obtained from DEI were compared to conventional histology obtained from the specimens. DE images allow the identification of the quality of ingrowth of bone into the hydroxyapatite layer of the implant. Incomplete integration of the implant with a remaining gap of less than 0.3 mm caused the presence of a highly refractive edge at the implant/bone border. In contrast, implants with bone fully grown onto the surface did not display a refractive signal. Therefore, the refractive signal could be utilized to diagnose implant healing and/or loosening.

Irradiation in presence of iodinated contrast agent results in radiosensitization of endothelial cells: Consequences for computed tomography therapy

PURPOSE

To date, iodinated contrast agents (ICA) are commonly used in medical imaging to improve tumor visualization by attenuating scanners X-rays. However, some adverse reactions to ICAs are still reported, and their molecular origin remains unclear. In 1983, it was proposed to visualize and treat ICA-loaded tumors by using scanners as therapy machines to enhance X-rays absorption at the iodine atoms. Theoretically, such physical conditions are optimized at 50 keV and can be easily obtained with synchrotrons.

METHODS AND MATERIALS

Here, we examined the molecular and cellular responses of mammalian endothelial cells to radiation in the presence of iomeprol, one of the most extensively used ICAs.

RESULTS

Irradiation with X-rays at 50 keV in the presence of iomeprol produced a strong radiosensitization effect. The same conclusion was reached with a standard medical irradiator but to a lesser extent. While such treatment did not produce additional DNA double-strand breaks, we observed a dose-dependent production of iodides due to the iomeprol radiolysis that inhibit double-strand break repair rate by decreasing DNA-PK kinase activity.

CONCLUSIONS

Our data suggest that the concomitant use of ICA and radiation may be toxic when radiation-produced iodide concentrations and double-strand break yields are sufficient. The potential toxicity of ICAs during X-rays for diagnosis and therapy is discussed.

Quantitative analysis of synchrotron radiation intravenous angiographic images

A medical research protocol on clinical intravenous coronary angiography has been completed at the European Synchrotron Radiation Facility (ESRF) biomedical beamline. The aim was to investigate the accuracy of intravenous coronary angiography based on the K-edge digital subtraction technique for the detection of in-stent restenosis. For each patient, diagnosis has been performed on the synchrotron radiation images and monitored with the conventional selective coronary angiography method taken as the golden standard. In this paper, the methods of image processing and the results of the quantitative analysis are described. Image processing includes beam harmonic contamination correction, spatial deconvolution and the extraction of a 'contrast' and a 'tissue' image from each couple of radiograms simultaneously acquired at energies bracketing the K-edge of iodine. Quantitative analysis includes the estimation of the vessel diameter, the calculation of the absolute iodine concentration profiles along the coronary arteries and the stenosis degree measurement.

Improved image contrast of calcifications in breast tissue specimens using diffraction enhanced imaging

The contrast of calcifications in images of breast tissue specimens using a synchrotron-based diffraction enhanced imaging (DEI) apparatus has been measured and is compared to the contrast in images acquired using a conventional synchrotron-based radiographic imaging modality. DEI is an imaging modality which derives image contrast from x-ray absorption, refraction and small-angle scatter-rejection (extinction), unlike conventional radiographic techniques, which can only derive contrast from absorption. DEI is accomplished by inserting an analyser crystal in the beam path between the sample and the detector. Two of the three breast tissue specimens contained calcifications associated with cancer, while a third contained benign calcifications. Results of the image analysis indicate that the DEI contrast of images taken with the analyser crystal tuned to the peak of its rocking curve, was as much as 19 times that of the conventional radiograph, with an average of 5.5 for all calcifications. This improved image contrast for even near-pixel-size calcifications suggests potential utility for DEI in breast imaging.

Dose comparison between conventional and quasi-monochromatic systems for diagnostic radiology

Several techniques have been introduced in the last year to reduce the dose to the patient by minimizing the risk of tumour induced by radiation. In this work the radiological potential of dose reduction in quasi-monochromatic spectra produced via mosaic crystal Bragg diffraction has been evaluated, and a comparison with conventional spectra has been performed for four standard examinations: head, chest, abdomen and lumbar sacral spine. We have simulated quasi-monochromatic x-rays with the Shadow code, and conventional spectra with the Spectrum Processor. By means of the PCXMC software, we have simulated four examinations according to parameters established by the European Guidelines, and calculated absorbed dose for principal organs and the effective dose. Simulations of quasi-monochromatic laminar beams have been performed without anti-scatter grid, because of their inherent scatter geometry, and compared with simulations with conventional beams with anti-scatter grids. Results have shown that the dose reduction due to the introduction of quasi-monochromatic x-rays depends on different parameters related to the quality of the beam, the organ composition and the anti-scatter grid. With parameters chosen in this study a significant dose reduction can be achieved for two out of four kinds of examination.

Cure of Fisher Rats Bearing Radioresistant F98 Glioma Treated with cis-Platinum and Irradiated with Monochromatic Synchrotron X-Rays

High-grade gliomas are usually of poor prognosis, and conventional radiotherapy, even combined with chemotherapy, still fails to improve the survival of patients. Here, we propose an innovative therapeutic approach combining synchrotron radiation with cis-diamminedichloroplatinum (II) (CDDP). As suggested previously, monochromatic synchrotron irradiation of CDDP at 78.8 keV, just above the 78.4 keV platinum absorption K-edge, leads to an enhanced photoelectric effect and an increased local toxicity. To select a particular radiation energy that could provide supra-additive effect, we used pulsed-field gel electrophoresis to assess yields of DNA double-strand breaks induced in rat F98 glioma cells after CDDP treatment combined with synchrotron X-rays. Thereafter, intracerebral CDDP injection combined with synchrotron X-rays was applied to Fisher rats bearing F98 glioma. CDDP concentrations were mapped by synchrotron X-ray microfluorescence. An extra number of more slowly repaired double strand breaks were observed when irradiating CDDP-treated F98 cells at 78.8 keV. In vivo treatments were then performed with different radiation doses and CDDP concentrations. All cell inoculations in rat brain resulted in tumor development, and tumor presence was controlled by computed tomography. Among all of the conditions tested, the combination of 3 micro g of CDDP with 15 Gy resulted in the largest median survival time (206 days). After 1 year, about 34% of treated rats were still alive. This preclinical finding, validated by molecular analysis, represents the most protracted survival reported with this radioresistant glioma model and demonstrates the interest in powerful monochromatic X-ray sources as new tools for cancer treatments.