Intravenous angiography using scanned projection radiography: preliminary investigation of a new method.

The use of digital subtraction techniques combined with fluoroscopy has rekindled interest in arteriography using intranvenous injections of contrast media. A new method is proposed for intravenous angiography in which an x-ray source and xenon detector array from a computed tomographic (CT) scanner are used to scan a region of interest to produce projection image. In order to provide adequate visualization of small concentrations of iodine in blood vessels, a subtraction scheme is used to remove the contribution from overlapping soft tissue and bone. Initial experiments with a temporal subtraction algorithm on phantoms have demonstrated the ability to image simulated blood vessels of 1.7-mm diameter containing dilute diatrizoate with an iodine concentration of 3.7 mg/cc, at an exposure of less than 100 mR. Vascular structures 5-8 mm in diameter have been imaged in dogs with iodine concentrations of less than 37 mg/cc using temporal subtraction. Principal advantages of the method over other film or fluoroscopic subtraction techniques are: 1) wide dynamic range an low noise of the (CT) detectors, providing excellent iodine sensitivity; 2) high scatter rejection; and 3) efficient utilization of x-ray dose.

Reconstruction of objects from diverging x rays.

Rotation of a system consisting of a single x-ray source and a linear detector array allows rapid collection of x-ray projection data from which transaxial cross sections can be reconstructed. In this paper, we present an algorithm which makes possible rapid computerized reconstruction from such data. We describe some experiments aimed at investigating the optimal choice of some of the parameters associated with the algorithm. We report on reconstructions using our algorithm of the intact thorax of a dog and also of cross sections of the human female breast from x-ray data obtained by a computerized mammography machine.

Intravenous arteriography using scanned projection radiography.

Visualization of arteries using intravenous injections of contrast material requires an imaging system capable of (a) excellent sensitivity to dilute concentrations of contrast media and (b) adequate temporal resolution to minimize the effects of motion during the exposure. A line-scanned radiography system based on a CT fan-beam detector (high-pressure xenon ionization chamber) was used for phantom and animal studies of intravenous arteriography to demonstrate the potential advantages of this method. Even though line-scanned systems require long scan times compared to existing radiographic methods, they are capable of showing rapidly moving arteries without blurring. Concentrations of 3 mg/ml of iodine could be seen in vessels 2 mm in diameter. Phantom studies using kVp switching showed that bone or soft tissue could be selectively cancelled.