F.A. Dilmanian

Computed tomography with monochromatic X-rays from the National Synchrotron Light Source

Abstract A multiple-energy computed tomography (MECT) system that employs monochromatic and tunable 33–100 keV X rays from a superconducting wiggler at the National Synchrotron Light Source is being developed at Brookhaven National Laboratory. The CT configuration is that of a fixed, horizontal fan-shape beam and a subject seated in a rotating chair. Two quantitative CT methods will be used: a) K-edge subtraction of intravenously administered iodine (or a heavier element) to image brain tumors, large blood vessels of the lower head and neck, and arteriovenous malformations; and b) dual photon absorptiometry to obtain two brain CT images that map the low−Z elements and the intermediate−Z elements (i.e. P, S, Cl, K, Ca, and Fe) separately. The system is expected to provide 0.5 mm spatial resolution, horizontally, with unprecedented image contrast and accuracy of quantification. The system will employ a two-crystal monochromator and a high-purity Ge linear array detector.

Design of a multislit, variable width collimator for microplanar beam radiotherapy

Microbeam radiation therapy of the intracerebral 9L gliosarcoma in rats, an experimental surrogate for human malignant gliomas, using mainly 30–130 keV wiggler‐generated x rays, extended the residual lifespans of some rats ten or more times over those of untreated, similar gliosarcoma‐bearing rats. The rats were exposed 300 or 600 times to an upright, 25‐μm‐wide, 4‐mm‐high x‐ray beam. A multislit collimator has been designed to shorten the time required for the therapy.

Monochromatic computed tomography of the human brain using synchrotron x rays: Technical feasibility

Abstract A monochromatic computed tomography (CT) scanner is being developed at the X17 superconducting wiggler beamline at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory, to image the human head and neck. The system configuration is one of a horizontal fan beam and an upright seated rotating subject. The purposes of the project are to demonstrate improvement in the image contrast and in the image quantitative accuracy that can be obtained in monochromatic CT and to apply the system to specific clinical research programs in neuroradiology. This paper describes the first phantom studies carried out with a prototype system, using the dual photon absorptiometry (DPA) method at energies of 20 and 38 keV. The results show that improvements in image contrast and quantitative accuracy are possible with monochromatic DPA CT. Estimates of the clinical performance of the planned CT system are made on the basis of these initial results.

Multiple energy computed tomography (MECT) at the NSLS: Status report

Status of the synchrotron‐based computed tomography system, called multiple energy computed tomography (MECT), is described. MECT, that uses monochromatic beams from the X17 superconducting wiggler beam line at the National Synchrotron Light Source, will be used for imaging the human head and neck. An earlier prototype MECT produced images of phantoms and living rodents. This report summarizes the studies with the prototype, and describes the design, construction, and test results of the clinical MECT system components.

A high‐energy double‐crystal fixed exit monochromator for the X17 superconducting wiggler beam line at the NSLS

A high‐energy double‐crystal x‐ray monochromator has been constructed for use on the X‐17 beam line at the National Synchrotron Light Source (NSLS). Its design is based on the ‘‘boomerang’’ right angle linkage, and features a fixed exit beam, a cooled first crystal, and an energy range of 8–92 keV. The entire mechanism is UHV compatible. The design is described and performance details, obtained in testing at the X17 beam line, are presented.

Guiding hard X rays with glass polycapillary fiber

Abstract X rays can be guided through a polycapillary fiber by multiple total reflections from the smooth channel walls of the fiber. Using monochromatic synchrotron radiation at energies of 22 and 44 keV, we measured the efficiency of transmission of X rays through polycapillary fibers with channel diameters of about 13 μm. Efficiencies of 57.3 and 54.5% for 22 and 44 keV X rays, respectively, were obtained with a 120-mm-long straight polycapillary fiber aligned with the incident beam. These values are close to the open fraction of the fiber, which is about 60%. In addition, transmission efficiency was measured as a function of the tilt angle between the incident beam and the axis of the fiber. We also measured the transmission efficiency as a function of the deflection angle for a 114-mm-long curved polycapillary fiber. The measurements are compared with a ray-tracing simulation.

CT imaging of small animals using monochromatized synchrotron X-rays

Rats and chicken embryos were imaged in vivo with a prototype multiple energy computed tomography (MECT) system using monochromatized X-rays from the X17 superconducting wiggler at the National Synchrotron Light Source (NSLS). The CT configuration consisted of a horizontal, low-divergence, fan-shaped beam, 70-mm wide and 0.5-mm high, and a subject rotating about a vertical axis. A linear-array high-purity Ge detector with 140 elements, each 0.5-mm wide and 6-mm thick, was used with a data acquisition system that provides a linear response over almost six orders of magnitude of detector current. The dual photon absorptiometry (DPA) algorithm was applied to images of the rat head acquired at 20 and 45 keV to obtain two new images, one representing the low-Z and the other the intermediate-Z element group. The results indicate that the contrast resolution and the quantification accuracy of the images improve stepwise; first, with the monochromatic beam and, second, with the DPA method. The system is a prototype for a clinical brain scanner.<<ETX>>

An X-ray monochromator for dual-energy computerized tomography using synchrotron radiation

Abstract Dual-energy CT imaging of the brain will be performed using synchrotron radiation X-ray beams at about 40 and 80 keV to visualize the altered concentrations of the intermediate-Z elements that occur in brain lesions and atherosclerotic plaques. The monochromator designs considered allow rapid switching between these two energies without change in the position or direction of the X-ray beam. One design uses the fundamental and second harmonic radiations from an existing dual-Bragg-crystal Si〈2,2,0〉 monochromator. In this design the 40 and 80 keV beams would be isolated by monochromator detuning or gold filtration, respectively. The other designs utilize fundamental radiations for both energies and would require some modification of the existing monochromator mechanism to achieve adequate tuning speed. These designs use two Si 〈2,2,0〉 crystals, one with a Bragg and the other with either a Bragg or a Laue geometry.

Measurement of rocking curve wings at high x-ray energies

Abstract Measurements done recently at the NSLS have indicated that the level of intensity found in the wings of diffraction peaks from silicon at higher X-ray energies (> 20 keV) far exceeds the value which would be predicted based on the dynamical theory. We have measured Si(220) double crystal rocking curves at the 40 keV fundamental and harmonics with various crystal scattering geometries: Bragg-Bragg, Laue-Bragg, Laue-Laue. The comparison of the Bragg and Laue case diffraction geometries was done to determine scattering volume effects. Comparisons with dynamical theory calculations will be discussed. These measurements have been carried out in order to assess the level of harmonic contamination which will be present from a double crystal monochromator being designed for the X17 superconducting wiggler beamline.

Multiple energy computed tomography with monochromatic X-rays from the NSLS

Monochromatic X-rays from the X17 superconducting wiggler beamline at the National Synchrotron Light Source (NSLS) were used for dual-energy quantitative computed tomography (CT) of a 27-ram-diameter phantom containing solutions of different KOH concentrations in cylindrical holes of 5-mm diameter. The CT configuration was a fixed horizontal fan-shaped beam of 1.5-mm height and 30-mm width, and a subject rotating around a vertical axis. The transmitted X-rays were detected by a linear-array Si(Li) detector with 120 elements of 0.25-mm width each. A two-crystal Bragg-Bragg fixed-exit monochromator with Si<220> crystals was used. Dual photon absorptiometry CT data were taken at 20 and 38 keV. The reconstructed phantom images show the potential of the system for quantitative CT.<<ETX>>