Showing papers on "Imaging phantom published in 1971"

Analyses of Electromagnetic Fields Induced in Biological Tissues by Thermographic Studies on Equivalent Phantom Models

Abstract: One of the most vexing problems in studies involving the interaction of electromagnetic fields and living biological systems and tissues is the quantification of the fields induced in the tissues by nearby sources. This paper describes a method for rapid evaluation of these fields in tissues of arbitrary shape and characteristics when they are exposed to various sources including plane wave, aperture, slot, and dipole sources. The method, valid for both far- and near-zone fields, involves the use of a thermograph camera for recording temperature disitributions produced by energy absorption in phantom models of the tissue structures. The magnitude of the electric field may then be obtained anywhere on the model as a function of the square root of the magnitude of the calculated heating pattern. The phantoms are composed of materials with dielectric and geometric properties identical to the tissue structures which they represent. The validity of the technique is verified by comparing the results of the experimental approach with the theoretical results obtained for the case of plane layers of tissue exposed to a rectangular aperture source and cylindrical layers of tissue exposed to a plane-wave source. This technique has been used successfully by the author for improving microwave applicators.

Microwave Heating of Simulated Human Limbs by Aperture Sources

Abstract: Microwave heating of phantom models of human limbs by aperture sources is investigated theoretically and experimentally. These phantom models consist of triple-layered circular lossy dielectric cylinders. The three layers of dielectric materials simulate human tissues of fat, muscle, and bone. In the theoretical investigation, apertures operating in the frequency range of 433 to 2450 MHz are used as microwave sources for heating the dielectric materials. The theoretical investigation makes use of the technique of summation of cylindrical waves. A high-speed computer is used to calculate the numerical results. For the experimental investigation, an aperture is designed and built to operate at the frequency of 918 MHz. The resulting temperature patterns in the phantom models are detected by the use of a thermograph camera. The theoretical results are shown to be in agreement with the experimental results. The technique and results of this investigation may be applied towards the design of applicators for therapeutic heating of human tissues.

Image aberrations produced by multichannel collimators for a scintillation camera.

Abstract: An interference pattern which distorted the representation of a parallel-line phantom containing a radionuclide was observed during a study of the quality of the image produced by a commercial Anger camera equipped with “diverging” and other multichannel collimators. Discontinuities occurred in the individual phantom line images, forming a Moire pattern. The effect was maximal close to the face of the collimator and disappeared at a distance from it. Further study has shown this to be a property of all camera collimators with thick septa between the linear arrays of collimator holes.

A liver phantom for evaluating camera and scanner performance in clinical practice

Abstract: An assessment of the resolution of different cameras and scanners may be made using phantoms which bear no physical resemblance to human antomy. Examples are the “slice” and “grid” types of phantom. In the former, there are areas of increased and diminished radioactive concentration relative to that of background. In the grid types, linear sources may be constructed using polythene tubing and then embedded in a Perspex block, or a series of parallel lead strips separated by a distance equal to their width, may be attached to a Perspex plate and placed over a uniform bath of activity. They will produce a valid comparison between detection systems, but the observed resolution characteristics cannot be precisely related to tumours seen in clinical practice. It is suggested that an anatomically realistic phantom will provide additional useful information and should be used to complement, rather than replace those already mentioned.

An improved I.A.E.A. neck phantom for thyroid uptake series

Abstract: The neck phantom recommended by the group of consultants of the International Atomic Energy Agency was compared with a wax model of the human neck used as a thyroid phantom in the Northern Ireland Radiotherapy Centre. Marked differences were found using both Geiger- Muller and scintillation counting systems. The wax phantom was examined and found to be a more accurate representation of the human neck; the I.A.E.A. phantom was therefore modified to give equivalent results. The form finally accepted was a 10 cm diameter Perspex cylinder; the other dimensions were as recommended.

Heating of Simulated Human Limbs by Aperture Sources

Abstract: A bsfract—Microwave heating of phantom models of human limbs by aperture sources is investigated theoretically and experimentally. These phantom models consist of triple-layered circular 10SSY dielectric cylinders. The three layers of dielectric materials simulate human tissues of fat, muscle, and bone. In the theoretical investigation, apertures operating in the frequency range of 433 to 2450 MHz are used as microwave sources for heating the dielectric materials. The theoretical investigation makes use of the technique of smnmation of cylindrical waves. A high-speed computer is used to calculate the numerical results. For the experimental investigation, an aperture is designed and built to operate at the frequency of 918 MHz. The resulting temperature patterns in the phantom models are detected by the use of a thermograph camera. The theoretical results are shown to be in agreement with the experimental results. The technique and results of this investigation may be applied towards the design of applicators for therapeutic heating of human tissues.

Neck phantoms for thyroid uptake measurements

Abstract: In their Instrumental and Technical Note entitled “An improved I.A.E.A. neck phantom for thyroid uptake series' (Gillespie and Keyes, 1971) the authors show that considerable differences result when a neck phantom of 10 cm diameter is used rather than the I.A.E.A. recommended diameter of 15 cm.