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Biomedical subjects

A D Linney

Publications and source records attributed to A D Linney.

18 recordsLinked to original sources
PubMed1992

A three dimensional analysis of soft and hard tissue changes following bimaxillary orthognathic surgery in skeletal III patients.

The three dimensional changes in the bone and the ratio of soft tissue to bone movement were investigated in a group of 16 Skeletal III patients following orthognathic surgery. Computerised tomogram scans were taken for each patient pre-operatively and 1 year postoperatively. The scans were superimposed, radial measurements calculated, and the changes illustrated by two separate colour scales. There was no constant pattern of movement in the maxilla or mandible in these patients. However, following a Le Fort 1 osteotomy there was commonly a 1:1 ratio in the midline which increased to 1.25:1 at the alar bases and over the canine regions bilaterally. There was also a 1.25:1 ratio or greater over the chin and mentalis regions following mandibular set back.

Adult↗
PubMed1992

A three-dimensional soft tissue analysis of 16 skeletal class III patients following bimaxillary surgery.

A three-dimensional soft tissue study of the results of surgery in a group of 16 skeletal Class III adult patients following orthognathic surgery was carried out using laser scans (Arridge et al., 1985). The patient group was compared to a control group of the same population. Laser scans were taken prior to surgery, 3 months post-surgery, and at least 1 year after retention. Preoperative comparison to the control groups revealed that the facial disproportion related to both the maxilla and the mandible. Le Fort I advancements resulted in broadening of the lateral aspects of the nose, advancement of the dorsum, and overcorrection of the alar bases. There was a degree of change over the cheeks bilaterally, because of alterations in the general drape of the soft tissues. There was a degree of overcorrection in the female group following mandibular set back but the male group were still more prognathic, when compared to the control group. There was a marked degree of relapse in the mandible from 3 months to 1 year postoperatively, with a resultant anterior movement of the maxillary arch. Laser scanning has proved to be a simple non-invasive method of measuring three-dimensionally, and is a very useful tool in auditing surgical outcome and measuring surgical relapse.

Adult↗
PubMed1992

The analysis of profiles using curvature analysis.

The difficulties of localizing landmarks using standardized lateral skull radiographs has been acknowledged. A method is described for producing an objective way of identifying landmarks on the facial profile leading to a useful segmentation and quantitative description of the contours and features of the face. The method uses scale space filtering techniques and curvature analysis, first employed in pattern recognition. The method has been used on two groups: a random sample of twelve-year-old females and a sample of 10 patients with a normal facial morphology who had cephalometric X-rays taken at 5, 9, 13, 16, and 20 years. It demonstrated that the shape of each of the curves is similar in the first group except in the mouth region. The growth study produced meaningful data on the growth of the face.

Adolescent↗
PubMed1992

Comparison of three imaging techniques for assessing endodontic working length.

The accuracy of endodontic working length estimation was investigated using three imaging techniques: radiography (Rd), Xeroradiography (Xr) and Radiovisiography (RVG positive and negative prints). An in-vitro model of extracted single straight roots, mounted in wooden blocks with wax, was employed in the study. Optimum exposures were established for each of the imaging techniques. The magnification of the images was measured and the resolution of the RVG images was also investigated. Comparable Rd (D-speed film), Xr,RVG positive and RVG negative images were made of five roots with size 10 files in situ. Images of 10 standard files were made, ranging from 2.0 mm through the root apex to 2.5 mm short of the apex, resulting in 200 images. Six observers each assessed the working distance on 100 images, measuring the distance from the apical foramen to the file tip. After allowing for the magnification of the images, these results were compared with the 'true' file tip to apical foramen (measured with the aid of a reflex microscope). The inaccuracy of working distance estimations was considered to be of clinical significance (> 0.5 mm) in 6% of measurements made from Rd and Xr, 19.2% of measurements from RVG negative and 32.3% from RVG positive images. In addition, 14% of RVG images were too poorly defined to be assessed. The first-generation RVG system was used in this study. It was therefore concluded that the most accurate estimates of working distance were made from Xr and Rd images, and that RVG images, particularly the RVG positive images, were the least accurate and most difficult to read.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Computer-generated titanium cranioplasty: report of a new technique for repairing skull defects.

A review of 40 cases of titanium cranioplasty fabricated from impressions taken of the defect through the patient's scalp in the conventional way showed that 23% were ill-fitting and 41% of frontal plates had a poor aesthetic result. Attributable factors were difficulty in defining the defect border accurately and limited information of the surrounding tissue architecture which led to strains produced during insertion. Inadequate communication between surgeon and prosthetist compounded these difficulties. A prospective study of six cases fabricated from CT computer-generated models of challenging cranial defects appears to show significant improvements in plate design, resulting in better plate adaptation, stability and aesthetic contour. Plate insertion was rapid (mean time 27 min) thereby minimizing operating time. This paper also discusses the advantages of the enhanced information derived from CT and describes the potential for pre-craniotomy template and matching cranioplasty, thereby permitting a one-stage procedure.

Computer Graphics↗
PubMed1991

A mathematical method for the comparison of three-dimensional changes in the facial surface.

Many attempts have been made to measure and compare the changes in the facial surface brought about by facial reconstructive surgery. Three-dimensional (3-D) analyses have largely consisted of qualitative descriptions rather than a quantitative treatment of these changes. Until recently, the lack of availability of 3-D data for the face and head has limited the advancement of these techniques. However, with 3-D information readily available from a laser scanning system which we have constructed, a technique has been applied which describes mathematically the facial shape and changes occurring in the face in terms of fundamental surface types. The method is described and used to compare the faces of two patients (one a cleft palate patient and the other a long-face, Class II malocclusion patient) before and after surgery along with the clinical description of the surgery, the resulting facial changes, the actual surgery performed, and the predicted surgical expectation. A strong relationship is found between the surface type description and the clinical observations. The implications of the method for surgery, facial aesthetics, and other disciplines are discussed.

Cleft Lip↗
PubMed1991

The relationship and reproducibility of angle ANB and the Wits appraisal.

An analysis is presented of the errors and variations in the Wits analysis and the angle ANB, using computer simulation. The method is applicable to any index where the identification errors have been established for the points and planes used in its derivation. A standard deviation may be determined for the index produced and the statistical distribution of values for any number of observations.

Cephalometry↗
PubMed1991

Methods of three dimensional analysis of patients with asymmetry of the face.

One of the problems of patients with facial asymmetry is that two dimensional analysis of such patients does not give a satisfactory picture of the underlying problem. Various methods have been suggested to overcome this problem, such as stereophotogrammetry (Burke et al. 1983) and Moire fringes (Takasaki 1970, Xenofos and Jones 1979). These methods are time consuming and are not fully automated. At present no 3D method is available which provides a readily analysable, global description of change in the face due to the limitations of the techniques which have been used. The 3D changes in shape of the face which occur during growth and with surgical intervention remain undetermined, either qualitatively or quantitatively. Although the importance of such a development has been pointed out, no method of 3D analysis has been developed. (Cutting et al. 1986). Attempts at three dimensional (3D) measurement of the face for monitoring the growth of children with facial deformities usually use hazardous and invasive techniques of ionizing radiation and metallic implants to assess the growth of the skull. Over the past 10 years the Departments of Orthodontics and Medical Physics and Bio-Engineering at University College London have collaborated in the development of a computer graphics based 3D system for the simulation, planning and prediction of maxillo-facial surgery. The laser scanning system developed measures over 20,000 points over the surface of the face in 10 seconds using a non-invasive and completely non-hazardous technique (Arridge et al. 1985, Moss et al. 1987, Moss et al. 1988). The data acquired is accurate to approximately 0.5 mm. Analytical programmes have been developed to handle the enormous quantity of data produced. These programs form the basis of a practical, user-friendly, clinical system whose performance has been evaluated and is now in routine use (Moss et al. 1989).

Cephalometry↗
PubMed1989

Application of 3-D computer graphics for facial reconstruction and comparison with sculpting techniques.

Facial reconstruction has until now been carried out by the sculpting technique. This method involves building a face with clay or other suitable material on to a skull or its cast, taking into account appropriate facial thickness measurements together with information provided by anthropologists such as approximate age, sex, race and other individual idiosyncrasies. A method for facial reconstruction is presented using 3-D computer graphics and is compared with the manual technique. The computer method involves initially digitising a skull using a laser scanner and video camera interfaced to a computer. A face, from a data bank which has previously digitised facial surfaces, is then placed over the skull in the form of a mask and the skin thickness is altered to conform with the underlying skull. The advantage of the computer method is its speed and flexibility. We have shown that the computer method for reconstructing a face is feasible and furthermore has the advantage over the manual technique of speed and flexibility. Nevertheless, the technique is far from perfect. Further facial thickness data needs collecting and the method requires evaluation using both known control skulls and later unknown remains.

Computer Graphics↗
PubMed1988

A computer system for the interactive planning and prediction of maxillofacial surgery.

A computer system has been developed for the simulation of facial surgery with interactive three-dimensional graphic techniques and data derived from computed tomographic scans and a purpose-built laser scanning system. The simulation includes the surgery on the hard tissues, and modeling of the soft tissue for prediction of the postoperative facial appearance. The facilities available are described and an example of their use is given.

Computer Graphics↗
PubMed1988

Application of a video image subtraction system to measure and control head position in cephalometry.

Variation in head position in the cephalostat is a potential source of error in cephalometrics as it causes distortion of the radiographic projection of the head. Image subtraction is an electronic technique enabling images to be superimposed and which highlights any differences. Using this method, a study was carried out to assess the reproducibility of the position of the head in the cephalostat. It was also used to find out whether subjects could improve their own head relocation by looking at the monitor and trying to achieve the best possible fit on the original image.

Cephalometry↗
PubMed1986

A low cost system for computer-based cephalometric analysis.

A simple, versatile TV-based measuring system is described which is applicable for cephalometrics and other purposes. It is suitable for large or microscopic objects, and can be used for measuring two-dimensional objects, or three-dimensional objects in two planes. Reproducibility of the system in cephalometrics is assessed and compared with that obtained with the reflex metrograph.

Cephalometry↗
PubMed1985

Three dimensional digitization of the face and skull.

The possibility of using computer-aided design as a tool for the planning and simulation of facial reconstruction surgery is discussed and has been shown to be feasible. Methods of acquiring the essential measurements on the facial surface and the underlying bone structure in a computer-compatible form are described, including a new approach which has been implemented using a system of fanned laser beams and a television camera for data acquisition. A mathematical analysis of the properties of this kind of imaging system is given. Finally the requirements of a complete aid to surgery system based on this approach are outlined and plans for the implementation of such a system are described.

Computers↗
PubMedDate not supplied

Three-dimensional visualization of computerized tomography and laser scan data for the simulation of maxillo-facial surgery.

A system has been developed for the three-dimensional (3D) visualization of the face and skull using data obtained from a purpose-built no-contact laser scanning system and from a series of scans produced by X-ray computerized tomography. Features developed allow the simulation, planning and prediction of maxillo-facial surgery. Realistic skeletal and facial images with a solid 3D appearance are produced from these two datasets using computer graphics techniques. The images can be sectioned for diagnostic purposes or parts can be repositioned for the simulation of surgery. 3D measurements can be made on the images for pre- and post-surgical analysis. An example of the clinical use of the system in the planning of surgery and the prediction of post-surgical facial appearance is given.

Computer Graphics↗
PubMedDate not supplied

Using greyscale voxel databases for improved shading and segmentation.

Many different data representations are possible in computer graphics. Originally, in the medical field, simplified methods were used in order to reduce computation times on small computer systems. Currently a wider range of techniques is developing as costs of hardware continue to fall. In this paper we review a number of possible representations and explain the advantage of one that is greyscale, volumetric and random access. Different segmentation techniques can be used, as well as shading algorithms that give greatly improved appearances. A quantitative analysis of shading methods is derived in terms of the degree of sampling of the 'pseudo-normal' vectors that estimate the direction of the tangent to a surface. The application to a study of multiple sclerosis lesions in the brain using nuclear magnetic resonance data is shown.

Brain↗