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We compare the noise properties of conventional and energy selective X-ray computed tomography. The images produced by the systems are not directly comparable so we discuss their relationship and show that the conventional image is a subset of the energy selective data. We describe how to form a conventional image from the energy selective images and demonstrate that, if this is done at the optimal display energy, the resulting conventional image will have the same noise as that produced by a conventional system with the same dose. But the energy selective system also extracts all the energy dependent information so it produces more information for the same dose than a conventional system.

The technique of computerized photon tomography has been applied in the nondestructive evaluation of a number of inanimate objects. 1,2,3 Hardware and software capabilities for industrial tomographic analysis, particularly of high-density objects, have been developed. Spatial resolution is on the order of 1-2mm for density variations of a few percent.

Both tomographic sections and complete three-dimensional images may be generated from nuclear magnetic resonance signals by a wide variety of techniques. In favorable situations, contrast and resolution may be comparable to those obtained by other imaging techniques, although scanning times will in general be longer. The practical problems encountered in the construction and use of head, limb, and whole-body systems are reviewed, progress toward useful whole-body imaging evaluated, and the effects of flow and motion, the sources and control of contrast, and the prospects for diagnostic tissue characterization discussed.

The application of SPECT as an alternative and/or a complement to other excisting imaging methods in nuclear medicine is being increasingly frequent. Specially designed devices have been developed as well as systems based on conventional devices, such as rotating gamma cameras.

Gamma-ray imaging is a well-established procedure in medical diagnosis. In single photon ECT we wish to measure and display the concentration of radio activity within a thin transverse slice of the body while still retaining the simple, atraumatic, non-invasive nature of the iadionuclide investigation. When Kuhl and Edwards introduced the technique in 1963, it did not involve any fundamental change in the detection-display equipment nor in the accuracy of measurement, as for example with X-ray transmission imaging, but simply pointed the way to develop the emission imaging equipment into a more sophisticated tool for the accurate measurement of in-vivo concentration of radionuclide. This paper attempts to examine the technique and to review the physics and engineering aspects of current ECT systems.

The use of a fluoroscopic imaging system for providing the projection data required in computerized tomography has been explored. The capability of both conventional systems and large flat screen-low light level vidio systems are discussed. The highlights of previously published data are also presented. Specific applications to radiation therapy are illustrated and the equipment described. The differential contrast senditivity is of the order of 0.5%, spatial resolution less than 0.5 mm, and slice thickness approximately 1 mm. Patient skin exposure is expected to be between 150 mR and 300 mR per scan.