John Hale

Transmission Scanning: A Useful Adjunct to Conventional Emission Scanning for Accurately Keying Isotope Deposition to Radiographic Anatomy

In 1952 Mayneord (1) proposed the usefulness of a transmission counter for plotting outlines of organs. Later, he produced images of lead letters by recording the transmitted beam from a Tm170 (84 keV) source which was maintained in direct alignment with the aperture of a scintillation detector during scanning (2, 3). In 1963, Cameron and Sorenson reported use of Am241 (60 keV) and I125 (30 keV) sources to determine bone mineral content by measuring the change in intensity of a transmitted photon beam moved across a bone (4). No clinical application of transmission scanning for forming images of body structures was reported by these authors. We have explored transmission scanning as a means of improving the orientation of the radionuclide emission scan (5). Accurate evaluation of a radionuclide distribution in the body requires that the spatial relationships of emission scan data be oriented to the anatomy of the patient. Usually, data on the scan record are keyed to anatomy either by using reference mark...

A high-contrast photographic recorder for scintillation counter scanning.

During the past four years, in the Hospital of the University of Pennsylvania, external scintillation counter scanning has been used to provide information relative to the distribution of radioactive isotopes in patients. Attention has been centered largely on representation of the thyroid gland, detection of functioning metastases of thyroid carcinoma, and the outlining of intraperitoneal and intrapleural radioactive colloidal gold distributions. We have been dissatisfied with the standard mechanical relay recording systems, such as those which print marks on paper to indicate the. rate of counting gamma-ray activity. Recently, there have been described several recording devices which attempt to provide better representation of radioactive distributions (1-4). While differing in construction, these instruments are alike in that, with constant scanner speed, the spacing of marks produced on paper or film is proportional to the time required to accumulate a pre-set number of counts. Such a recorder will ou...

Calculation of the Dose Distribution About Californium-252 Needles in Tissue'

Abstract Dose distribution around a point source of 252Cf in tissue due to neutron interaction has been evaluated by Monte Carlo methods. The dose due to neutron and gamma rays emitted by a 2 cm needle source was calculated and compared with published experimental data. The effect of absorber size on neutron dose was also determined.

Supervoltage and multiple simultaneous roentgenography; new technics for roentgen examination of the chest.

While the survey chest roentgenogram is one of our best diagnostic tools, experience has shown that conventional roentgenographic methods fail to record some significant lesions, most notably those which occur within the mediastinum (1). Bronchogenic carcinoma frequently involves the structures of the mediastinum before peripheral roentgenographic evidence of disease is apparent. It is felt, therefore, that the development of a roentgenographic technic adaptable to mass screening methods, which would demonstrate the lung fields and the mediastinal structures, would be of great value in the early detection of cancer of the lung. It is possible, to be sure, to study both the mediastinum and the lung fields with conventional technics. The authors believe, however, that these conventional methods are not satisfactory for mass survey studies, since they require multiple exposures. As the number of exposures needed per patient increases, the cost of the examination rises, the roentgen dose to the patient become...

The Homogeneity Factor for Pulsating Potential X-Ray Beams in the Diagnostic Energy Region

Since the homogeneity factor (HF = first h.v.l./ second h.v.l.) might be useful in specifying diagnostic x-ray beam quality for radiation safety purposes, a study of HF data for pulsating potentials was undertaken. Aluminum, of 2S grade, transmission curves were determined for a half-wave therapy apparatus with a Thermax tube, and for a full-wave diagnostic machine with a Dynamax 20 tube. These tubes have inherent filtration equivalent to 0.5 mm Al. Visualization of beam wave-forms with a photo-multiplier showed little smoothing effect of cable capacitance. Potentials were determined by the K-level excitation method. The focus-chamber-distance and the irradiated area were chosen so that the measured h.v.l. values were within 1 per cent of the unique h.v.l. Appropriate corrections were made for the energy dependence of the measuring chamber. Table I shows that the steeper target angle of the diagnostic tube, as compared to the therapy tube, increases both the first and second h.v.l. at a given kVp. The h.v...

Calibration of Potential of X-ray Generators in the Diagnostic Energy Region

Several methods for determining the peak potential applied to an X-ray tube with an accuracy of ± 1 kv by measuring characteristics of the X-ray beam, have been evaluated. The methods included the attenuation ratio technique, techniques based on detection of the threshold energy for photoelectric absorption, and observation of the upper limit of the bremsstrahlung spectrum. Ion chambers, solid state detectors, and scintillation counters were used as radiation detectors. In the determination of the threshold X-ray tube potential needed to excite K-fluorescent radiation in a secondary radiator, it was found that normalizing the ionization chamber response to constant incident exposure simplifies the experimental set-up of the Greening-Trout procedure without loss in accuracy. The simplest and most accurate method for the determination of the threshold is to observe the fluorescent X-rays from a secondary radiator directly with a pulse-height analyser set for the energy of the characteristic X-ray.

Radiation Safety Evaluation of Fluoroscopes

The problems of estimating patient exposure and the scattered radiation exposure to the operator during fluoroscopy are made difficult by the nature of fluoroscopic procedures. Field size and position change widely and rapidly and, for a given examination, the extent of exposure will depend to a large extent on the technic of the fluoroscopist. In each case the exposure to both patient and operator is related to the exposure dose rate, the quality of the radiation produced by the machine, and the scatter from the machine. These factors may be called the inherent radiation characteristics of the machine, since they depend on the x-ray unit itself and not on the manner of its use. During the past ten years we frequently have had the opportunity to examine fluoroscopes with regard to inherent radiation safety factors. While it is not possible to determine the safety of a particular unit according to an absolute scale, it is possible, by comparison, to discover whether a given machine measures up to a good st...

Step-wedge sensitometry.

An aluminum step-wedge filter placed far from the film cassette provides the constant variation of subject contrast required for quantitative sensitometry while virtually eliminating scatter radiations. Attenuation curves made with this configuration are almost exponentially linear.

Radiation Therapy Records and Record Keeping

It must have been early indeed that the need for accurate records of therapeutic applications of ionizing radiation to patients was recognized. The first recorded reference (1) in Radiology was in 1929, but even this begins with an apology for the presumption of “again introducing the subject of records.” Ever since, it has been the constant effort of radiologists to keep their records abreast of existing information. This is good, for it is largely because of these records, by means of which a valid estimate of what was accomplished by the method could be made, that the specialty has developed to its present status. Radiation therapy in this country is just now getting out of knee pants. It stands at the threshold of an era of development which will take it out of what has in a large part been an empirical art and put it into a position permitting a more real appreciation of what happens as a biochemical or biophysical event. In order to take maximal advantage of these developments, the need for complete...

Positive prints of dense roentgenograms; a teaching aid.

The technique of making a positive contact print of a roentgenogram on readily available commercial film was developed as the first stage of a common method of radiographic subtraction. This technique is useful in transcribing the range of densities in an “overexposed” roentgenogram to a density range in a positive transparency which can be conveniently interpreted on a conventional view box. The technique is particularly helpful in producing prints of dark films for instruction purposes. A method for producing the positive copy is presented together with the sensitometry of the photographic process and examples of the usefulness of the technique.