Geometric leaf placement strategies.

Geometric leaf placement strategies for multileaf collimators (MLCs) typically involve the expansion of the beam's-eye-view contour of a target by a uniform MLC margin, followed by movement of the leaves until some point on each leaf end touches the expanded contour. Film-based dose-distribution measurements have been made to determine appropriate MLC margins--characterized through an index d90--for multileaves set using one particular strategy to straight lines lying at various angles to the direction of leaf travel. Simple trigonometric relationships exist between different geometric leaf placement strategies and are used to generalize the results of the film work into d90 values for several different strategies. Measured d90 values vary both with angle and leaf placement strategy. A model has been derived that explains and describes quite well the observed variations of d90 with angle. The d90 angular variations of the strategies studied differ substantially, and geometric and dosimetric reasoning suggests that the best strategy is the one with the least angular variation. Using this criterion, the best straightforwardly implementable strategy studied is a 'touch circle' approach for which semicircles are imagined to be inscribed within leaf ends, the leaves being moved until the semicircles just touch the expanded target outline.

Technique for detecting early rheumatoid arthritis.

The authors are of the opinion that the controversy surrounding the value of radiography in the early diagnosis of RA and subsequent assessment of drug therapy is due to the poor resolution of the radiographs used in many of these studies. Given that radiographic findings correlate with the pathological changes occurring in the hands and wrists of the RA patient, the ARA 1987 revised criteria for the classification of RA requires a PA projection of the hands and wrists. With this in mind, it is obvious that a standard radiographic technique offering high-resolution be developed and implemented. Direct magnification procedures as previously described offer high-resolution, however, they are either too cumbersome to use, require specialized, limitedly available equipment, produce partial images, have prolonged exposure times leading to part motion and are too expensive. In addition, radiation dosages to the skin are higher. These problems also preclude their use in the establishment of screening procedures for early RA. By comparison, the authors' optical magnification technique eliminates the major problems encountered in direct magnification. More importantly, the described optical magnification technique provides high-resolution radiographs utilizing readily available equipment and offers a practical means for the effective screening and diagnosis of early RA.

Radiographic methods in total hip arthroplasty.

Widespread acceptance of total hip arthroplasty has occurred in the United States. A review of the literature indicates the following: 1. Better binding material and methods of total hip arthroplasty will be developed. 2. Total hip arthroplasty will be done on younger patients. 3. There will be an increase in total hip replacements. 4. An increase in simultaneous bilateral total hip replacement will occur. 5. There is a need for standardization of the technique and positioning when radiographing the patient who undergone total hip replacement. A radiographic routine for the patient with a total hip replacement should include the following: 1. An anteroposterior projection of the pelvis or an anteroposterior projection of the hip. Either projection should be obtained with the toes pointing upward and not inverted. The entire prosthesis should be included on the radiograph. 2. A lateral projection of the entire prosthesis using the 15 degree posterior angle method. The advantages to this routine are:no special equipment is required, the lack of movement required by the patient and the ease in obtaining these projections regardless of the patient's condition.

Adaptation of the technique for radiography of the glenohumeral joint in the lateral position.

This article emphasizes the importance of obtaining opposing right angle views of the shoulder as a routine part of the examination. It analyses standard projection techniques and presents an adaptation of the transaxillary axial projection that is invaluable to the radiologist in diagnosing that eight per cent of lesions that can be missed by not using this projection.