The Intrex--a constant-potential x-ray unit for periapical dental radiography.
Explore the source record for details and available documents.
Radiation Dosage↗
Biomedical subjects
U Welander
Publications and source records attributed to U Welander.
Blurring effects in rotational panoramic radiography.
Explore the source record for details and available documents.
Models, Theoretical↗
Image distortion in rotational panoramic radiography. VI. Distortion effects in sliding systems.
A mathematical model for calculating the form distortion in rotational panoramic radiographic systems with a sliding beam path and an elliptical form of the sharply depicted plane was developed. The distortion of a spherical model object was calculated for two different systems exemplifying properties of commercially available equipment. The spherical object was distorted toward an ovoid shape in the image. No marked deviations were found between this ovoid distortion and the ellipsoid distortion previously calculated for a theoretical system having a constant effective projection radius and a cylindrical form of the sharply depicted plane. Except for extremely displaced objects in the anterior region the form reproduction in sliding rotational panoramic systems seems to be satisfactory for clinical purposes.
Computers↗
The cephalographic projection. Part I: General considerations.
Explore the source record for details and available documents.
Cephalometry↗
A new method for image layer analysis in rotational panoramic radiography.
The position and form of the image layer in rotational panoramic radiography vary from one manufacture to another. A method utilizing a digital computer to calculate the position, form, and relative thickness of the image layer from data obtained from two test radiographs is described. The image layer analysis permits the performance of different rotational panoramic radiographic units to be compared independent of various parameters such as beam width and magnification. The image layers for several commercially available units are illustrated.
Computers↗
Effects of errors in film speed and beam alignment on the image layer in rotational panoramic radiography.
Explore the source record for details and available documents.
Models, Theoretical↗
Mandibular rami osteotomies and their effect on the gonial angle.
Explore the source record for details and available documents.
Adolescent↗
Image distortion in rotational panoramic radiography. II. Vertical distances.
Films, exposed with rotational panoramic radiography, are generally considered inferior regarding the accuracy of measurements. Theoretic mathematical calculations, confirmed by an experimental test, have been performed in order to evaluate the reliability of measurements of distances that appear vertical in the image. It is demonstrated that, within certain limits, the panoramic film may be used for vertical measurements in clinical practice provided the patient has been properly positioned in the equipment during the exposure.
Mathematics↗
Image distortion in rotational panoramic radiography. III. Inclined objects.
Mathematical calculations have been performed to analyse how accurately the angle between objects, inclined in space, is reproduced on panoramic films. A marked tolerance against angle distortion was found. Angular measurements may be performed on correctly exposed panoramic films, and the values obtained are satisfactorily accurate for most clinical purposes.
Mathematics↗
Image distortion in rotational panoramic radiography. IV. Object morphology; outer contours.
On films exposed with rotational panoramic radiography, distortion effects are often apparent. The distortion of the outer contour of three-dimensional model objects jas been analysed mathematically. The applied mathematical expressions for coordinate transformation between object and film were confirmed experimentally. The distortion of the outer contour is dependent on the basic form of the object; the more rounded the object is, the less marked is the distortion. It is concluded that for practical clinical purposes the correctly exposed panoramic film is reliable when the form of rounded objects is assessed.
Mathematics↗
Image distortion in rotational panoramic radiography. I. General considerations.
The projection system in rotational panoramic radiography is complex in the respect that there are two projections of the object working simultaneously, one in the horizontal and one in the vertical dimension, giving rise to distortion of three-dimensional objects in the image. A mathematical method is presented for transforming data from three-dimensional objects to image data. This method may be used when analysing different distortion effects inherent in panoramic films.
Mathematics↗
Sagittal split technique I. Immediate postoperative conditions. A radiographic follow-up study.
The postoperative appearance of 28 patients was studied following sagittal split osteotomy. A radiological evaluation of the direction and location of the split, secondary unwanted fractures and the area of overlap and contact relationship between the fragments was carried out. In 70% of the cases examined the line of cleavage broke through on the medial surface of the ramus. Unwanted fractures occurred in five of the 56 operated rami, however, these did not influence the postoperative healing to a great extent. The area of overlap between the fragments varied from 3-10 cm2. In some cases diastases of up to 8 mm were noted. The true area of contact as such was significantly less than the area of overlap.
Female↗
Sagittal split technique. II. Radiographic findings during the fixation period. A radiographic follow-up study.
The radiological appearance of 28 patients following sagittal split osteotomy was studied during the fixation period. Larger areas of overlap and smaller diastasis between the fragments were more frequently associated with short periods of fixation (7 weeks or less). This difference was not statistically significant. In 84% of the operated sides varying degrees of decalcification could be seen within the bone structures. Using tomographic images callus formation between fragments could be registered in 75% of the cases before or at the termination of the fixation; these cases were all stable after removal of fixation. With the exception of two cases the remaining 25% were clinically stable, however, although callus formation could not be demonstrated radiographically.
Bony Callus↗
Sagittal split technique. III. Postoperative rest conditions. A radiographic follow-up study.
The radiological appearance of 26 patients was studied 11--53 months postoperatively following sagittal split osteotomy. In 75% of the cases examined an increase in the mandibular angle could be noted compared to pretreatment values. This differences was statistically significant. In 70% of the cases the angle increased by 1--10 degrees. In 25% there was no change or reduction in the angle. The antero-posterior width of the rami was found to decrease; when this was combined with an increase in the mandibular angle, extensive morphological changes were found. These postoperative conditions must be regarded as unsatisfactory and a modification of the technique of sagittal split osteotomy should be considered as for example advocated by EPKER4.
Female↗
The effect of image quality on the identification of cephalometric landmarks.
The effect of rare-earth phosphor intensifying screens on diagnostic image quality was examined. Five observers were asked to identify ten landmarks on each of fifteen cephalometric images having varying screen-film-kvp combinations. The most sensitive screens were found to significantly affect diagnostic image quality and thereby the reliability of landmarks identification. This finding was, however, only established for those landmarks having the lowest standard deviations and the clinical significance is thus questionable. There would appear to be other more important factors than physical image quality involved in the reliability of landmark identification. High intensifying screens are, therefore, recommended for use in cephalometric analyses since they help to reduce patient dose and do not appear to sacrifice diagnostic image quality to the extent that the reliability of cephalometric measurements is significantly affected.
Cephalometry↗
Image distortion in narrow beam rotation radiography. A mathematical analysis.
A general mathematical analysis of the image distortion in narrow beam rotation radiography has been performed. Distortion effects are often evident in panoramic images exposed in clinical practice. It is found that in spite of this general experience panoramic images, exposed with the aid of a rotating narrow beam, are reliable for ordinary clinical demands when the object morphology is to be assessed. This statement is valid provided that the object has been properly positioned at the exposure.
Mathematics↗
Position, form, and thickness of the image layer in narrow beam rotation radiography.
Explore the source record for details and available documents.
Models, Biological↗
Mean energy imparted in relation to the focus to object distance.
The relationship between the energy absorbed by the patient at the exposure of a radiographic image and the focus to object distance is analysed. It is found that the mean energy imparted, or the integral absorbed dose, is the same irrespective of the focus to object distance when the energy fluence and the field size are both normalized at the film plane. When the field size is kept constant within the object whilst the focus to object distance is varied a limited increase in the mean energy imparted occurs when the focus to object distance is decreased; this statement is valid for the focus to object distances which are usually applied in diagnostic radiology. When estimating radiation risks the importance of the focus to object distance is found to be of limited interest.
Absorption↗