Resolution, sensitivity, and contrast in gamma-camera design: a critical review

The performance of present-day gamma-cameras is examined from a historical perspective and the prospects for further improvements assessed. The author attempts to show quantitatively that spatial resolution of 25-cm field-of view cameras has reached a point where further advances can bring only diminishing returns clinically, unless improvements in sensitivity, or alternatively, in photon yield of the clinical procedure, are also realized. However, better image contrast due to developments in display technology and emission computed tomography may improve lesion detectability more directly than would an increase in resolution.

[Comparison of screens and screen-film-systems (author's transl)]

Important details are to be payed attention in comparison of different scrreens resp. screen-film-systems: 1. Physical characteristics of different groups of luminescent materials: f.i. calcium tung-state, rare-earths compounds, double halogenides. - 2. Different types of screens: highest details up to highest speed intensifying screens, have to be defined more specifically and differentiated against to each other too. - 3. Besides intensification, resolution has to be included into consideration since one of these dates alone does not allow any statement on the total function of a screen or a screen-film-system. - 4. The technical methodological conditions of apparatuses, object and its positioning have to be defined, f.i. X-ray quality, distances, grid, and in automatically controlled exposition, if necessary, position of ionization chamber as well as absorption of cassetts and screen. - 5. Considering these points gradation curves have to include the whole necessary or interesting diagnostic range. - 6. Due to functional correlation between intensification and resolution, the resolution has to be taken in consideration due to application; its interdependence of density and object (f.i. scattered radiation) is often not taken enough in consideration.

The mechanism of opening of the aortic valve

The mechanism of opening of the aortic valve was investigated in dogs by attaching radiopaque markers to the commissures and the leaflets. Analysis of abnormal cardiac cycles demonstrated that, when the ventricular pressure first equalled the aortic pressure, the intercomissural distances increased 9 percent, and the valve opened with a stellate orifice without forward flow and without a rise in aortic pressure. Further opening of the aortic valve was dependent on forward flow over a narrow range. A new mechanism of aortic valve opening is proposed. This mechanism results in minimal flexion stresses on the leaflets and is important for the longevity of the normal aortic valve. It can occur only if the leaflets arise from an expansile aortic root.

Evaluation of pH monitoring as a method of processor control

Sensitometry and pH values of the developer solution were compared in controlled over-replenishment, developer depletion, fixer contamination experiments, and on a daily quality control basis. The purpose of these comparisons was to evaluate the potential of pH monitoring as a method of processor control, or a supplement to sensitometry as a method of quality control. Reasonable correlation was found between pH values and film density in two of the three experiments but little or no correlation was found in the third experiment and on a day-to-day basis. The conclusion drawn from these comparisons is that pH monitoring has several limitations which render it unsuitable as a method of daily processor quality control as either a primary or supplementary technique. Sensitometry takes into account all the variables encountered in film processing and is the clear method of choice for processor quality control.

[The uni-quatro camera - a new camera for documentation of monitor pictures (author's transl)]

A new camera system is described, which was devised to take pictures of monitor screens on special X-ray film, and it is compared with conventional methods of documentation. Quality of pictures obtained with this method is optimal, handling is quick and simple, and, in spite of that, the camera is smaller and less expensive than other multiformate cameras. Polaroid, special X-ray films and other films may be used interchangeable for all sorts of monitor screens. A report is given about the routine use of this system in ultrasonography.

Motion of bones and volume changes in the neurocranium after craniectomy in Crouzon's disease. A roentgen stereometric study

Craniectomy was performed on a boy with Crouzon's disease at 22 months of age. Metallic implants (tantalum balls, 0.5 mm in diameter) were inserted in the calvaria during surgery, and the child was examined postoperatively by roentgen stereometry at intervals of about 100 days (total observation time, 309 days). The thyroid radiation dose was 250 muGy for one examination. The effect of craniectomy was recorded with a high degree of accuracy in terms of motion of bones and volume changes in the calvaria. Expansion occurred almost entirely through motion of free bone flaps in the frontal region, while a linear craniectomy in the region of the sagittal suture caused small changes. The rate of expansion decreased rapidly and stabilization was recorded about 250 days after surgery.

A slim 198gold-grain implanter loaded with standard Royal Marsden 14-grain magazines

We designed a slim gold-grain implanter with adaptable lengths to implant areas accessible only through long, narrow, examining instruments, such as a suspension laryngoscope. The implanter is loaded with the same 14-grain magazine designed for and supplied with the Royal Marsden "gun." The simplicity of the loading mechanism with a minimum of moving parts makes the instrument practically trouble free. Although it is designed to be used along narrow examining instruments, it can also be used in any situation in which a permanent implant is required, for instance, prostatic cancer and pelvic recurrences in cancer of the uterine cervix previously treated by external and intracavitary irradiation.

Evaluation of several sensitometers for use in processing quality assurance

Sensitometry is becoming a widely used tool to measure and allow correction of changes in the processing of radiographs before those changes become clinically significant. To be effective, the inherent variability of the sensitometer must at least be smaller than the processing variations to be monitored. Results of performance evaluations are given for several commercially available sensitometers. All were found to be useful and dependable quality assurance tools when properly used with life-expectancies of at least five years.

A head holder for operative serial angiography

An apparatus was developed to combine two functions--a versatile neurosurgical head clamp and a compact film changer for operative serial angiography. The construction costs were +15,000, and provided a programmer, six cassettes, and attachments to position the film changer over much of the skull surface. Exposures are obtained by a mobile x-ray machine.