J. N. Otis

Computed tomography using synchrotron radiation

Abstract X-ray computed tomography (CT) is a widely used method of obtaining cross sectional views of objects. The high intensity, natural collimation, monochromaticity and energy tunability of synchrotron X-ray sources could potentially be used to provide CT images of improved quality. The advantages of these systems would be that images could be produced more rapidly with better spatial resolution and reduced beam artifacts. In addition images, in some cases, could be acquired with elemental sensitivity. As a demonstration of the capability of such a system, CT images were obtained of four slices of an excised pig heart, in which the arteries and cardiac chambers were filled with an iodinated medium. Images were taken with incident X-rays tuned successively to energies just above and below the iodine K edge. Iodine specific images were obtained by logarithmically subtracting the low energy image data from the high energy data and then reconstructing the image. CT imaging using synchrotron radiation may become a convenient and non-destructive method of imaging samples difficult to study by other methods.

The application of synchrotron radiation to non-invasive angiography☆

Abstract Synchrotron radiation provides a new source of X-rays highly-suited to iodine K-edge Digital Subtraction Angiography (DSA). The use of such beams provides maximum sensitivity to intra-arterial iodine and virtually eliminates image contrast due to non-vascular body structures. The intensity of the beams permits short exposure times and allows images to be recorded, in line-scan fashion, in sharp focus despite arterial motions. The sensitivity of this method offers the prospect of visualizing arteries, and in particular the coronary arteries, by peripheral venous injection. The principles of DSA have been demonstrated using phantoms and excised animal hearts, and in vivo studies in animals have begun. The instrumentation developed for this purpose and the results obtained to date are summarized.

Transvenous coronary angiography using synchrotron radiation

X-ray-based angiography continues to be the standard method of assessing the severity and the extent of coronary atherosclerosis. The relative insensitivity of conventional X-ray imaging systems to iodine-containing contrast agents necessitates that the images be acquired with essentially undiluted contrast agent in the lumen of the vessels being studied. This, in turn, requires arterial catheterization and the insertion of the catheter tip in or near the ostia of the vessels and the direct injection of the contrast agent. The health risks and monetary costs of the procedure have limited its use to circumstances in which there is a high probability of the presence of severe disease. Despite these problems, coronary angiography has been employed in serial studies to evaluate the effects of drug therapy and diet on coronary atherosclerosis (1).

Coronary angiography using synchrotron radiation (invited)

Imaging of coronary arteries using a venous instead of an arterial injection of contrast agent could provide a much safer method to diagnose heart disease. The tunability, intensity, and collimation of synchrotron radiation x‐ray beams makes possible imaging systems with greatly improved imaging sensitivity. A pair of fan x‐ray beams, a movable patient chair, and a multielement x‐ray detector are used to acquire a pair of x‐ray images above and below the iodine K edge. The logarithmic subtraction of these two images produces an image with excellent sensitivity to contrast agent and minimal sensitivity to bone and tissue. High‐quality images from a dog and preliminary images from five humans have been obtained. Improvements are being made to the system to increase the effective radiation flux and to measure the position of both x‐ray beams.

The angiography program at Stanford

Abstract A program is underway at the Stanford Synchrotron Radiation Laboratory to evaluate at minimally invasive method of visualizing the coronary arteries in man using synchrotron radiation. The design of an X-ray imaging system to accomodate a newly-available X-ray beam 12.3 cm in width is described. The system performance as revealed with test images of phantoms and excised hearts is indicated, and the system components to be tested before clinical studies can begin are identified.

Evaluation of synchrotron X-rays for transvenous coronary angiography

Abstract This study is related to an evaluation of synchrotron radiation for the non-invasive assessment of coronary artery disease in humans. In vivo canine studies are reported for an imaging system developed for use with synchrotron X-ray beams. The probable configuration of an expanded system for pilot human subject studies is described.

Veiling glare of a linear multichannel Si(Li) detector

The effective veiling glare has been measured in a linear, 64 element Si(Li) detector of 5 mm thickness and 0.5 mm center-to-center spacing between adjacent sensitive areas. Each elemental contact was 6 mm high and 0.4 mm wide. The measurement was made in two different ways, both employing a 33 keV beam of synchrotron x-rays at the Stanford Synchrotron Radiation Laboratory. In one method, a lead phantom in the shape of an isosceles triangle was illuminated across its width with a fan beam of 33 keV x-rays 0.5 mm high by 20 mm wide. The x-ray flux passing by the phantom was measured in each channel of the Si(Li) detector. In the second method, a highly collimated beam of 33 keV x-rays (0.5 mm high by 0.025 mm wide) was scanned across 15 channels of the detector in 0.01 mm steps. The measured intensity in each channel of the detector was recorded at each position of the beam. The photon flux fell to less than 0.1% at a distance of 3 mm from the edge of the beam. The results of both measurements were in agreement. They were also compared to calculated results based on the known total x-ray cross sections for Compton scattering and photoelectric absorption. To within the experimental error, the observed and calculated results were found to be in good agreement.

Transvenous coronary angiography in dogs using synchrotron radiation

SummaryThe application of coronary angiography is limited because it requires arterial invasion and the direct injection of contrast agent into the coronary arteries. A prototype system has been developed which achieves sufficient sensitivity to the iodinated contrast agent to allow the visualization of coronary arteries in dogs after its intravenous injection. The system uses two fan beams of x-rays from an electron storage ring and a 300 element linear silicon detector. Two interlaced images, spaced at 150 eV above and below the K absorption edge of iodine (33.2 keV), are acquired and the logarithmic subtraction of these two images produces an image which has maximal sensitivity to iodine and minimal sensitivity to soft tissue and bone. This approach appears suitable for studies on human subjects.

Prospects for non-invasive angiography with tunable X-rays☆

Abstract A safe and sensitive method of visualizing the coronary arteries is needed. The presently available method of visualization is highly invasive and carries too high a risk and cost. The intensity and tunability of synchrotron X-ray beams provides a new source of X-rays highly suited to the in vivo detection of iodinated contrast agents. The method offers the prospect of non-invasive visualization of the arteries by peripheral venous injection of contrast agent. The studies already conducted and those in preparation for human subjects are reviewed.

High-Speed Rotating-Drum X-Ray Beam Choppers for Line-Scan Dual-Energy Medical Imaging

Two 30 cm diameter steel drums with four facets rotating at 1800 RPM have produced high-quality digital-subtraction radiographs by alternately blocking and transmitting dual-energy synchrotron X-ray beams. An eight times faster system with 16.5 cm diameter tenfaceted tin-plated aluminum drums rotating at 5760 RPM is presently under construction.