Several medical imaging techniques are capable of producing tomographic images, corresponding to cross-sections through the body. A stack of adjacent sections contains three dimensional information about the organs of interest, and this can be presented on a two dimensional screen using shaded surface techniques. In order to facilitate the routine use of such images, algorithms and techniques were developed on a conventional medical imaging computer system in a hospital environment. Several object representation schemes were compared, and two new schemes were devised. The 'solid binary object' technique facilitated exploration of the interior of an object, while the 'ordered surface list' technique enabled real time display of object surfaces. Several shading algorithms were compared, and a local polynomial fitting routine was devised. This was found to be superior to other methods using objective evaluation of the accuracy of surface normal estimations, and subjective evaluation of the corresponding image appearance. The techniques developed were applied to a variety of data obtained using xray computed tomography, nuclear magnetic resonance and emission computed tomography. For display of myocardial tomograms, a technique was devised for superposition of colour coded coronary arteries, showing their relationship to observed perfusion defects. For display of time varying images of the heart, a rapid display routine was developed to enable ventricular wall motion to be evaluated from any angle. Colour display techniques were also applied to this data to produce single images which incorporated kinetic as well as morphological information. The results obtained have confirmed that shaded surface images can be produced using computers currently available in hospital imaging departments. Interactive object modification and real time object display can be achieved without requiring special hardware.

A testing method was to he developed based on previous experience on computer tomography. It has been known for some time that an image of a cross-section of an object could be reconstructed using projections or scans at different angles describing 180 degrees around the cross-section. Sound velocity, attenuation and sound reflection are the parameters used in ultrasonic computerised-tomography. The object under investigation in this work is a cylinder of acoustic properties like plastic enclosed in a steel casing. The task was to find defects in the cylinder and these defects were of a nature such, that echoes received from them are low and therefore the pulse echo technique cannot be used in their detection. A reconstruction method, based on the "Algebraic Reconstruction Techniques" (ART) is used here to detect these defects. The main achievements are that these recionstructions are obtained from constrained-scans, due to total reflection of ultrasound near the edge of the field, and a technique of obtaining an image with no background speckles. square An extensive computer simulation was done using a mathematical model of the object, which generated scan data similar to that obtained by actual experiment. Different processing techniques were tried to improve the image quality and testing reliability especially to remove the above mentioned problems. A successful method was chosen such that it will be easy to implement in a real testing situation. Successive marking of defect-free areas of the different scans resulted in a well defined defect structure. No-scan areas were identified by experiment and both the no-scan areas due to total reflection and those due to different modes of propagation received the same treatment. Using a marking technique together with the known coordinates of these areas an integrated image was obtained. The implementation of the system was done using a microcomputer together with a commercial flaw detector. The flaw detector was coupled to a digital counter to measure the transit time. The datawere acquired by interfacing the counter to the microcomputer. Data acquisition, control and processing together with the reconstruction programme constituted the software which was developed for this system.

Comprehensive and accurate diagnosis and treatment planning is crucial in successful orthodontics. An essential part of the diagnostic exercise is to determine whether there is a tooth size/arch length discrepancy (Bishara, 2001). The mixed dentition space analysis is one method of determining this (Moyers, 1973). The procedure requires the measurement of the anteroposterior dimension of the crowns of erupted teeth and the prediction of the size of the crowns of the unerupted permanent canine and premolar teeth. The comparison of tooth sizes enables the calculation of the ‘leeway space’, which may provide for the transition to the full intercuspation of the first permanent first molars as well as the relief of a certain amount of crowding in the arch (Gianelly, 1995). To date, the application of data of methods of measuring and estimating tooth size have been limited by the relative complexities of the method (Paredes et al, 2006), and the application of the data has been limited by the demographic profile of the patient (Schirmer and Wiltshire, 1997; Khan, 2006). The aim of this study is to develop a technique of precisely measuring the mesiodistal tooth size of the crowns of teeth from computerized images of panoramic x-rays, using the Leica QWin© System of Image Analysis (Leica, UK(Pty) Ltd). Ideally, this method would be accurate, reproducible and easy to use by a clinician. Thirty sets of study casts and the corresponding panoramic radiographs of patients in the mixed dentition stage of dental development were chosen, according to specific criteria, from the archived records of the Undergraduate Clinic at The School of Oral Health Sciences, University of the Witwatersrand. On the study casts, the mesio-distal widths of the second deciduous molar (‘e’) and of the first permanent molar (‘6’) teeth in each quadrant were measured with a digital vernier caliper. The corresponding radiographs were digitally photographed at a fixed distance, and uploaded onto the computer programme. A magnification factor was determined using the image of a premeasured object. The images of the ‘e’ and the ‘6’, together with the image of the unerupted second premolar tooth (‘5’) were measured with the calibrated linear function of the Leica QWin© System. The data was thus corrected for by the relevant magnification factor. The size differential between the ‘e’ and the ‘5’, representative of the leeway space, was then calculated. A calculation of the intra-examiner repeatability demonstrated a low co-efficient of variation of the measurements recorded on both the study casts and on the computer. The measurements of the teeth taken on the study casts were compared with the corrected measurements of the same teeth taken from the computer images of the teeth. Tooth size measurements taken with the Leica QWin System were greater than those taken with the vernier calipers. In both methods the sizes of the teeth were larger in the mandible than in the maxilla. This observation was also reported by Kraus et al (1969). The values for leeway space were calculated in both jaws. The mean values of leeway space in the maxilla were 0.81mm on the left hand side and 1.08mm on the right hand side, and 2.43mm on the left hand side and 2.59mm on the right hand side in the mandible. These values were similar to those recorded by Nance (1947) and by Bishara et al (1988) who also found that values of leeway space were smaller in the maxilla than in the mandible. The accuracy of the measurements taken with the proposed method was found to be dependent upon correct patient positioning in the focal trough of the machine at the time of panoramic radiographic exposure, the use of a marker known in size placed at the site to be measured in order to correct measurements for magnification and the definition of corresponding mesio-distal points on the teeth from which measurements would be taken on both sets of records.

Forest insect and disease pests alter the appearance of trees, thereby impacting visual resources. Because of the complexity of most forest landscapes, the degree of visual impact of pest-infested forest stands is difficult to quantify. This paper describes a method of measuring visual impacts of pest-infested forest stands. Photographs of healthy Ponderosa pine trees were entered into a computer video-image-processing system. Using this system, images of trees were altered to simulate different degrees of infestation by limb rust, a forest pathogen. The altered and unaltered images were shown to groups of observers who rated the scenes in terms of "scenic beauty." The great majority of individuals were able to detect a change in the appearance of trees infected with limb rust disease even when only small sections of a tree were altered. There was also general agreement within the groups of observers that the presence of limb rust disease had a detrimental effect on the visual quality of the forest scenes. The tests also suggested that the location of infestation in the tree crown, the amount of crown mortality, and the number of infected Ponderosa pine in a stand influenced the degree to which visual quality was impacted.

Past studies evaluating the esthetics of orthodontic treatment have been done using 2-D images. New 3-D imaging offers an improved, real-life representation of a subject. The purpose of this study was to determine how laypeople perceived differences in lip position (flat versus ideal lip fullness) in 2-D compared to 3-D. 3dMD images of 8 Caucasian subjects were adjusted to an ideal and flat lip position in 3-D and then in 2-D from the profile view. 2 surveys were created with paired ideal and flat images on the screen, either in 2-D or 3-D, and evaluators were asked to choose which image they preferred and by how much. Evaluators were more likely to be neutral, and were less decisive of their preference in 3-D compared to 2-D. People might be less sensitive to small differences in facial soft tissue and esthetics than previous research in 2-D has led orthodontists to believe.