Feasibility of synchrotron radiation computed tomography on rats bearing glioma after iodine or gadolinium injection. Jeune Equipe RSRM-UJF

K-edge Subtraction Computed Tomography with a Compact Synchrotron X-ray Source

In clinical diagnosis, X-ray computed tomography (CT) is one of the most important imaging techniques. Yet, this method lacks the ability to differentiate similarly absorbing substances like commonly used iodine contrast agent and calcium which is typically seen in calcifications, kidney stones and bones. K-edge subtraction (KES) imaging can help distinguish these materials by subtracting two CT scans recorded at different X-ray energies. So far, this method mostly relies on monochromatic X-rays produced at large synchrotron facilities. Here, we present the first proof-of-principle experiment of a filter-based KES CT method performed at a compact synchrotron X-ray source based on inverse-Compton scattering, the Munich Compact Light Source (MuCLS). It is shown that iodine contrast agent and calcium can be clearly separated to provide CT volumes only showing one of the two materials. These results demonstrate that KES CT at a compact synchrotron source can become an important tool in pre-clinical research.

Prolonged Blood-Brain Barrier Injury Occurs After Experimental Intracerebral Hemorrhage and Is Not Acutely Associated with Additional Bleeding

Intracerebral hemorrhage (ICH) causes blood-brain barrier (BBB) damage along with altered element levels in the brain. BBB permeability was quantified at 3, 7, and 14 days with Evans Blue dye after collagenase-induced ICH in rat. At peak permeability (day 3), a gadolinium (Gd)-based contrast agent was injected to further characterize BBB disruption, and X-ray fluorescence imaging (XFI) was used to map Gd, Fe, Cl, and other elements. XFI revealed that Ca, Cl, Gd, and Fe concentrations were significantly elevated, whereas K was significantly decreased. Therefore, using Gd-XFI, we co-determined BBB dysfunction with alterations in the metallome, including those that contribute to cell death and functional outcome. Warfarin was administered 3 days post-ICH to investigate whether additional or new bleeding occurs during peak BBB dysfunction, and hematoma volume was assessed on day 4. Warfarin administration prolonged bleeding time after a peripheral cut-induced bleed, but warfarin did not worsen hematoma volume. Accordingly, extensive BBB leakage occurred after ICH, but did not appear to affect total hematoma size.

γ-H2AX as a marker for dose deposition in the brain of wistar rats after synchrotron microbeam radiation

Objective

Synchrotron radiation has shown high therapeutic potential in small animal models of malignant brain tumours. However, more studies are needed to understand the radiobiological effects caused by the delivery of high doses of spatially fractionated x-rays in tissue. The purpose of this study was to explore the use of the γ-H2AX antibody as a marker for dose deposition in the brain of rats after synchrotron microbeam radiation therapy (MRT).

Methods

Normal and tumour-bearing Wistar rats were exposed to 35, 70 or 350 Gy of MRT to their right cerebral hemisphere. The brains were extracted either at 4 or 8 hours after irradiation and immediately placed in formalin. Sections of paraffin-embedded tissue were incubated with anti γ-H2AX primary antibody.

Results

While the presence of the C6 glioma does not seem to modulate the formation of γ-H2AX in normal tissue, the irradiation dose and the recovery versus time are the most important factors affecting the development of γ-H2AX foci. Our results also suggest that doses of 350 Gy can trigger the release of bystander signals that significantly amplify the DNA damage caused by radiation and that the γ-H2AX biomarker does not only represent DNA damage produced by radiation, but also damage caused by bystander effects.

Conclusion

In conclusion, we suggest that the γ-H2AX foci should be used as biomarker for targeted and non-targeted DNA damage after synchrotron radiation rather than a tool to measure the actual physical doses.

In vivo pink-beam imaging and fast alignment procedure for rat brain lesion microbeam radiation therapy

A fast 50 microm-accuracy alignment procedure has been developed for the radiosurgery of brain lesions in rats, using microbeam radiation therapy. In vivo imaging was performed using the pink beam (35-60 keV) produced by the ID17 wiggler at the ESRF opened at 120 mm and filtered. A graphical user interface has been developed in order to define the irradiation field size and to position the target with respect to the skull structures observed in X-ray images. The method proposed here allows tremendous time saving by skipping the swap from white beam to monochromatic beam and vice versa. To validate the concept, the somatosensory cortex or thalamus of GAERS rats were irradiated under several ports using this alignment procedure. The magnetic resonance images acquired after contrast agent injection showed that the irradiations were selectively performed in these two expected brain regions. Image-guided microbeam irradiations have therefore been realised for the first time ever, and, thanks to this new development, the ID17 biomedical beamline provides a major tool allowing brain radiosurgery trials on animal patients.

Imaging performance of the hybrid pixel detectors XPAD3-S

Hybrid pixel detectors, originally developed for tracking particles in high-energy physics experiments, have recently been used in material sciences and macromolecular crystallography. Their capability to count single photons and to apply a threshold on the photon energy suggests that they could be optimal digital x-ray detectors in low energy beams such as for small animal computed tomography (CT). To investigate this issue, we have studied the imaging performance of photon counting hybrid pixel detectors based on the XPAD3-S chip. Two detectors are considered, connected either to a Si or to a CdTe sensor, the latter being of interest for its higher efficiency. Both a standard 'International Electrotechnical Commission' (IEC) mammography beam and a beam used for mouse CT results published in the literature are employed. The detector stability, linearity and noise are investigated as a function of the dose for several imaging exposures ( approximately 0.1-400 microGy). The perfect linearity of both detectors is confirmed, but an increase in internal noise for counting statistics higher than approximately 5000 photons has been found, corresponding to exposures above approximately 110 microGy and approximately 50 microGy for the Si and CdTe sensors, respectively. The noise power spectrum (NPS), the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are then measured for two energy threshold configurations (5 keV and 18 keV) and three doses ( approximately 3, 30 and 300 microGy), in order to obtain a complete estimation of the detector performances. In general, the CdTe sensor shows a clear superiority with a maximal DQE(0) of approximately 1, thanks to its high efficiency ( approximately 100%). The DQE of the Si sensor is more dependent on the radiation quality, due to the energy dependence of its efficiency its maximum is approximately 0.4 with respect to the softer radiation. Finally, we compare the XPAD3-S DQE with published curves of other digital devices in a similar radiation condition. The XPAD3-S/CdTe detector appears to be the best with the highest DQE at low frequency, although some improvements are expected to reduce the increase of noise with the counts statistics and to guarantee a better stability of the detector response.

Evaluation of Gd-EOB-DTPA Uptake in a Perfused and Isolated Mouse Liver Model

OBJECTIVES

The aim of this work was to quantitatively evaluate the pharmacokinetic pattern of Gd-EOB-DTPA in a model of isolated and perfused mouse liver by using magnetic resonance imaging (MRI) and monochromatic quantitative computed tomography (MQCT).

MATERIALS AND METHODS

For MQCT, perfusions were realized with the gallbladder spared; for MRI, with gallbladder spared, severed, or clamped. Inductively coupled plasma (ICP) was performed at the end of the imaging protocols.

RESULTS

MQCT, MRI, and ICP showed that perfused mice livers with spared gallbladder can be divided in 2 groups depending on their uptake profile of the contrast agent. Livers with severed gallbladders behave as the group internalizing more contrast agent, whereas Gd-EOB-DTPA uptake looks impaired in the case of a clamped gallbladder.

CONCLUSIONS

For the first time, MQCT and MRI have been performed in parallel to investigate the same physiological problem. The existence of 2 liver groups seems to be the result of some instability of the protocol likely to be related to surgery.

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.

Synchrotron radiation-based experimental determination of the optimal energy for cell radiotoxicity enhancement following photoelectric effect on stable iodinated compounds

This study was designed to experimentally evaluate the optimal X-ray energy for increasing the radiation energy absorbed in tumours loaded with iodinated compounds, using the photoelectric effect. SQ20B human cells were irradiated with synchrotron monochromatic beam tuned at 32.8, 33.5, 50 and 70 keV. Two cell treatments were compared to the control: cells suspended in 10 mg ml⁻¹ of iodine radiological contrast agent or cells pre-exposed with 10 μM of iodo-desoxyuridine (IUdR) for 48 h. Our radiobiological end point was clonogenic cell survival. Cells irradiated with both iodine compounds exhibited a radiation sensitisation enhancement. Moreover, it was energy dependent, with a maximum at 50 keV. At this energy, the sensitisation calculated at 10% survival was equal to 2.03 for cells suspended in iodinated contrast agent and 2.60 for IUdR. Cells pretreated with IUdR had higher sensitisation factors over the energy range than for those suspended in iodine contrast agent. Also, their survival curves presented no shoulder, suggesting complex lethal damages from Auger electrons. Our results confirm the existence of the 50 keV energy optimum for a binary therapeutic irradiation based on the presence of stable iodine in tumours and an external irradiation. Monochromatic synchrotron radiotherapy concept is hence proposed for increasing the differential effect between healthy and cancerous tissue irradiation.

In Vivo Measurement of Gadolinium Concentration in a Rat Glioma Model by Monochromatic Quantitative Computed Tomography

RATIONALE AND OBJECTIVES

Monochromatic quantitative computed tomography allows a nondestructive and quantitative measurement of gadolinium (Gd) concentration. This technique was used in the C6 rat glioma model to compare gadopentetate dimeglumine and gadobutrol.

METHODS

Rats bearing late-stage gliomas received 2.5 mmol/kg (392.5 mg Gd/kg) of gadopentetate dimeglumine (n = 5) and gadobutrol (n = 6) intravenously before the imaging session performed at the European Synchrotron Radiation Facility.

RESULTS

Monochromatic quantitative computed tomography enabled in vivo follow-up of Gd concentration as a function of time in specified regions of interest. Surprisingly, after gadobutrol injection, Gd concentrations in the center and periphery of the tumor were higher than those after gadopentetate injection, although identical in normal and contralateral area of the brain.

CONCLUSION

The in vivo assessment of absolute Gd concentrations revealed differences in gadobutrol and gadopentetate dimeglumine behaviors in tumoral tissues despite injections in the same conditions. These differences might be attributed to different characteristics of the contrast agents.

Influence of iodine contrast agent on the range of ion beams for radiotherapy

The basis for the range calculation of heavy ions in tissue is an empirical correlation between x-ray CT numbers and ion ranges measured for tissue equivalent materials. Iodine contrast agents (CA), used during computed tomography (CT) imaging, lead to an increase of the Hounsfield units in tissue with increased CA uptake and cause errors in the calculation of the ranges. The aim of this work is to quantify how accurately ion range is calculated in CA loaded tissue. In order to quantify the mean change in Hounsfield units (HU), a statistical analysis of 25 CT data sets with and without CA was performed. To establish a relation between the change in Hounsfield units due to CA and changes in ion range, the Hounsfield number for various CA concentrations and the range of ions in CA was measured. The analysis of CT data sets showed that after intravenous injection of 100 ml contrast agent (Imeron300) at a concentration of 300 mg iodine/ml an increase of the Hounsfield numbers in tumor tissue of up to 57 HU can be observed. The measured range shift in CA is much smaller than calculated by the treatment planning system (TPS). The maximum error in range resulting from the CA enhanced data is approximately 2.5% and results mainly from this wrong interpretation of HU by the TPS. For a tumor with an extent of 5 cm this leads to an exaggeration of the ion ranges during irradiation of (1.24+/-0.04) mm. This may be clinically relevant in cases where highest precision is needed and where organs at risk are close to the target volume. In view of these findings it may be safer to rely solely on native CT data for the purpose of dose and range optimization in therapy planning for heavy ions and protons.

Medical applications of synchrotron radiation

The medical imaging and therapeutic technologies that are based on the use of radiation are reviewed briefly, with special emphasis on the recent developments of synchrotron radiation (SR) methods. New results have been achieved in all of these areas since the last comprehensive reviews were written in this field. This topical review is intended to make the latest possible results and complete set of references available. The different contrast mechanisms in imaging by x-rays are described. The applications range from whole-body imaging to studies of atomic and molecular structures. The SR imaging applications include coronary angiography, bronchography, mammography, computed tomography, x-ray microscopy and imaging by scattering. The therapy applications include photon activation therapy and microbeam radiation therapy.

Absolute cerebral blood volume and blood flow measurements based on synchrotron radiation quantitative computed tomography

Synchrotron radiation computed tomography opens new fields by using monochromatic x-ray beams. This technique allows one to measure in vivo absolute contrast-agent concentrations with high accuracy and precision, and absolute cerebral blood volume or flow can be derived from these measurements using tracer kinetic methods. The authors injected an intravenous bolus of an iodinated contrast agent in healthy rats, and acquired computed tomography images to follow the temporal evolution of the contrast material in the blood circulation. The first image acquired before iodine infusion was subtracted from the others to obtain computed tomography slices expressed in absolute iodine concentrations. Cerebral blood volume and cerebral blood flow maps were obtained after correction for partial volume effects. Mean cerebral blood volume and flow values (n = 7) were 2.1 +/- 0.38 mL/100 g and 129 +/- 18 mL. 100 g-1. min-1 in the parietal cortex; and 1.92 +/- 0.32 mL/100 g and 125 +/- 17 mL. 100 g-1. min-1 in the caudate putamen, respectively. Synchrotron radiation computed tomography has the potential to assess these two brain-perfusion parameters.

Quantitative functional lung imaging with synchrotron radiation using inhaled xenon as contrast agent

Small airways play a key role in the distribution of ventilation and in the matching of ventilation to perfusion. The purpose of this study was to introduce an imaging method that allows measurement of regional lung ventilation and evaluation of the function of airways with a small diameter. The experiments were performed at the Medical Beamline of the European Synchrotron Radiation Facility. Monochromatic synchrotron radiation beams were used to obtain quantitative respiration-gated images of lungs and airways in two anaesthetized and mechanically ventilated rabbits using inhaled stable xenon (Xe) gas as a contrast agent. Two simultaneous images were acquired at two different energies, above and below the K-edge of Xe. Logarithmic subtraction of the two images yields absolute Xe concentrations. This technique is known as K-edge subtraction (KES) radiography. Two-dimensional planar and CT images were obtained showing spatial distribution of Xe concentrations within the airspaces, as well as the dynamics of filling with Xe. Bronchi down to 1 mm in diameter were visible both in the subtraction radiographs and in tomographic images. Absolute concentrations of Xe gas were calculated within the tube carrying the inhaled gas mixture, small and large bronchi, and lung tissue. Local time constants of ventilation with Xe were obtained by following the evolution of gas concentration in sequential computed tomography images. The results of this first animal study indicate that KES imaging of lungs with Xe gas as a contrast agent has great potential in studies of the distribution of ventilation within the lungs and of airway function, including airways with a small diameter.