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Initial clinical experience with a system for the digitization, processing, and display of film radiographs is described. Film is digitized using a high-intensity laser scanner; the recorded image data may then be subjected to a wide variety of processing options, with display of processed images on television monitors. The possibilities of clinical applications to processing and display of chest radiographs and film mammograms are described. A comparison of conventional analog subtraction and digitized film subtraction angiography indicated equivalent diagnostic capability, with the advantage of flexible, interactive image processing with the digital technique. A specially designed, energy-selective cassette permits dual-energy imaging from two films effectively exposed to different x-ray energy spectra. Dual-energy imaging may be capable of the characterization of body materials, including lung nodules, and useful for eliminating obscuring radiographic shadows overlying regions of interest.

An emulsion of Ethiodol and Pluronic was evaluated as a vascular (blood pool) imaging agent with both the GE experimental scanned projection radiography system and conventional computed tomography (CT), 475 mg iodine/kg body weight of emulsion, was injected into 11 rabbits with thigh muscle V2 carcinomas. Both projection radiography scans and CT scans visualized aorta, vena cava, pulmonary, and femoral vessels, and distorted vessels around tumors for 20 min after infusion. This persistent vascular visualization allowed CT scanning at multiple contiguous levels, which could be followed by reformatting in the sagittal and coronal planes. Following diatrizoate in identical iodine/kg doses, vascular visualization persisted for only 1 min after infusion. Blood pool agents are ideal for projection radiography systems and CT reformatting of vascular anatomy.

We have described a prereconstruction method for dual energy (PREDECT) analysis of CT scans. In theory, this method can (a) eliminate beam hardening and produce an accuracy comparable with monoenergetic scans and (b) provide the effective atomic number and electron density of any voxel scanned. Our implementation proves these statements and eliminates some of the objectionable noise. We constructed a phantom with a cylindrical sleeve-like compartment containing known amounts of high atomic number material simulating a removable skull. Conventional scans, with and without this beam hardener, were done of a water bath containing tubes of high electron and high atomic number material. Dual energy scans were then done for PREDECT. To increase the effective separation of the low and high energy beams by using more appropriate tube filtration, we fabricated a beam filter changer containing erbium, tungsten, aluminum, and steel. We used erbium, tungsten, and steel at high energy and aluminum, steel, and erbium at low energy for data acquisition. The reconstructions were compared visually and numerically for noise levels with the original steel only filtration. We found a decrease in noise down to approximately one-half the prior level when erbium/aluminum or tungsten/aluminum replaced the steel/steel filter. Erbium and tungsten were equally effective. Steel/erbium and steel/aluminum also significantly reduced image noise. The noise in the photoelectric (P) and Compton (C) images is negatively correlated. At any pixel, if the noise is positive in the P image, it is most probably negative in the C. Using this fact, the noise was reduced by postreconstruction processing.

Dual energy scanned projection radiography of the abdomen has been performed using an experimental line-scanned radiographic system. Digital images simultaneously obtained at 85 and 135 kVp are combined, using photoelectric/Compton decomposition algorithms to create images from which selected materials are cancelled. Soft tissue cancellation images have proved most useful in various abdominal imaging applications, largely due to the elimination of obscuring high-contrast bowel gas shadows. These techniques have been successfully applied to intravenous pyelography, oral cholecystography, intravenous abdominal arteriog-raphy and the imaging of renal calculi.

Two cases of hiatus hernia causing a soft tissue mass involving the gastric fundus on CT scans are presented. These masses could be mistaken for pathologic processes if hiatus hernia is not included in the differential diagnosis. Methods for resolving such diagnostic problems are discussed.

We have evaluated scanned projection radiography (SPR) for the diagnosis of cancer. Four rabbits with V2 thigh carcinomas and nine patients with a variety of malignant neoplasms were studied with a GE CT/T 8800 scanner modified for SPR. Images were made before injection of intravenous contrast medium, and additional scans were taken after injection. Temporal subtraction was then performed on the digitized data. Rabbit thigh V2 carcinomas and human lung, liver, and extremity neoplasms were visualized. Contrast enhancement was phasic with early vessel demonstration and subsequent visualization of low density central areas of tumoral necrosis. Liver metastases appeared as poorly defined areas of low density. Because of the combination of high contrast sensitivity plus capability of imaging large tissue volumes on one scan, SPR may be valuable in cancer screening.

The combination of [3H]8-methoxypsoralen ([3H]8-MeOP) plus near ultraviolet (UV) light was used to study sister chromatid exchange induction and [3H]8-MeOP-DNA adduct formation in Chinese hamster ovary (CHO) cells. Approx. 2.2 adducts/cell/erg/mm2 light were formed under conditions leading to the induction of 0.011 sister chromatid exchanges/erg/mm2 light during the two cycles following DNA damage. Based on these data, the adduct to sister chromatid exchange ratio is nearly 200. Both DNA monoadducts and crosslinks were produced by the illumination employed; the relative effectiveness of these 8-MeOP-DNA reaction products in sister chromatid exchange induction remains to be determined. The yield of 8-MeOP-DNA adducts did not show appreciable cell cycle dependence, and the efficiency of adduct formation, unlike sister chromatid exchange induction, was the same for DNA which replicated early or late in the DNA synthesis phase. However, substitution of 5-bromodeoxyuridine (BUdR) for thymidine in the DNA led to a nearly 2-fold increase in adduct formation. It is concluded that, while sister chromatid exchanges are typically a much more sensitive index of DNA damage than are chromosome aberrations, these exchanges may still correspond to only a small fraction of the total damage produced.