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Biomedical subjects

U Welander

Publications and source records attributed to U Welander.

At least 55 records · Page 3Linked to original sources
PubMed1993

Radiographic interproximal angulations: implications for rotational panoramic radiography.

Axial radiographs were taken on 160 subjects at the screening clinic of the Dental School, University of Texas Health Science Center at San Antonio. Intermeatal and midsagittal lines, together with coordinate axes and polynomial curves that represent the average dental arch form, were overlaid on each radiograph. Coordinate references for interproximal tangents at 3154 contacts along the average dental arch form were digitized and angulations between the arch form and midsagittal plane calculated. Interproximal angulations at the average arch form were found to vary greatly but the average fluctuated around 90 degrees over the length of the arch. Optimal beam angulations were shown to be considerably different from central ray angulations of current panoramic machines, and although most machines demonstrated favorable interproximal beam angulation in the anterior region, discrepancy in the premolar region ranged from 15 degrees to over 40 degrees. Overall the OrthOralix SD (Gendex Dental Systems, S.r.l., Monza, Italy) orthogonal projection and PM 2002 CC (Planmeca Inc. Helsinki, Finland) deviate least from optimal interproximal angulation over most of the dental arch. However, the Planmeca gives a better angulation in the canine/premolar region, whereas the OP5/10 (Palomex Instrumentarium Corp., Helsinki, Finland) is comparable with the OrthOralix SD in the molar region.

Analysis of Variance↗
PubMed1993

Basic technical properties of a system for direct acquisition of digital intraoral radiographs.

The Sens-A-Ray system for direct digital intraoral radiography may be used with any computer compatible with an IBM PC/AT. The system relies on a charge-coupled device designed for direct conversion of x-ray energy to an electronic signal. It is the first such device for direct acquisition of radiographs. Technical properties of charge-coupled device detectors when exposed to radiation energies in the range of x-rays used in dental radiography have been studied. Even in the absence of light or x-radiation there is a spontaneous generation of charge within a charge-coupled device detector that gives rise to a background signal, a dark current. It was found that the dark current is a linear function of exposure time. The dose response of the charge-coupled device detector was determined at nominal kilovoltages that range from 50 to 90 kVp. The dose response was shown to be a linear function of exposure. The functions for all kVp settings were practically identical. The charge-coupled device detector is more sensitive to x-radiation than conventional dental films and, consequently, its exposure range is more narrow. The signal-to-noise ratio was calculated from the digital radiographs used for the dose response test. The ratio is above 10 for exposures higher than about 2 microC/kg. The line spread function was determined from test radiographs of a 10 microns wide slit in a test object of 1.5 mm thick tantalum. After curve fitting, the line spread function could be expressed as the sum of a Gaussian and an exponential function. Presampling modulation transfer functions valid at the detector plane and at an object plane were calculated from fitted data on the line spread function. It is concluded that the Sens-A-Ray system has such technical properties that it may replace conventional film-based systems.

Computer Graphics↗
PubMed1993

Dimensional reproduction in direct digital rotational panoramic radiography.

A linear x-ray detector array can be used to perform rotational panoramic radiography provided a technique for data acquisition is used that emulates the dimensional reproduction of a conventional rotational panoramic radiographic system. This may be accomplished with the use of a variable integration time throughout the excursion. The required interval depends upon the scanning geometry, the selected image plane, and the size of pixels used in the digital image. In a prototype device developed around an Orthopantomograph Model OP10 with 0.225 mm square pixels, the integration times range from about 8 milliseconds to 28 milliseconds. An experimental test was performed by radiographing a number of steel spheres positioned at different object depths. Within the limits of experimental error, there was satisfactory agreement between the measured and theoretical magnification.

Humans↗
PubMed1993

Layer thickness in panoramic radiography as defined by different noise-equivalent passbands.

The layer thickness in rotational panoramic radiography is presented with the use of the concept of the noise-equivalent passband. Conventionally, the layer thickness has been calculated only from one-dimensional data in the horizontal or rotational dimension of panoramic radiography. In the present study, results from calculations using both one- and two-dimensional data are presented. When the vertical dimension is included in the calculations, the layer is wider than when calculated from data in the horizontal dimension only. It is pointed out that the wider layer that follows from the introduction of the vertical dimension may be the most reliable measure of layer thickness in panoramic radiography.

Bone Density↗
PubMed1992

Preliminary evaluation of a digital system for rotational panoramic radiography.

A prototype system for direct digital panoramic radiography has been evaluated with respect to density, contrast, magnification, distortion, resolution, and overall image quality. Density and contrast depend on detector calibration and may be modified by the display system or by digital processing of the captured image. Variation of magnification in the horizontal and vertical dimensions gives rise to distortion phenomena that are identical to those encountered in film-based systems. Resolution in the vertical dimension is determined by the pitch of the detector elements. In the horizontal dimension, resolution is limited by the effective width of the detector elements. To evaluate the clinical acceptability of the images, radiologists and general practice residents were asked to assess the perceptibility of important radiographic landmarks in film-based and digital images of both a radiographic phantom and a patient. The digital system performed on a par with film in the representation of normal morphologic structures of the clinical human subject whereas more differences were apparent in the phantom images. The general practice residents consistently rated the digital images higher than their radiologist counterparts did. No consistent trends were found to indicate any inherent deficiencies of the digital system in the depiction of any one area. The results indicate the promise of direct digital acquisition as a method of panoramic imaging.

Evaluation Studies as Topic↗
PubMed1992

Direct digital extraoral radiography of the head and neck with a solid-state linear x-ray detector.

A narrow fan beam of x-rays intercepted by a linear array detector was used to acquire transmission data for a radiographic phantom moved across the beam. The digital data were displayed as images representing a variety of extraoral views of the head and neck. Projections investigated include the straight lateral view, two frontal projections, and a half-axial projection. The digital images appear to provide adequate contrast and resolution for common diagnostic tasks. In addition, the use of a scanning linear detector reduces the amount of scatter, which increases contrast relative to images made with an area detector. The system appears to provide a versatile and convenient means for the acquisition of extraoral views relevant to dental practice while it eliminates the logistical difficulties and errors associated with film processing.

Analog-Digital Conversion↗
PubMed1992

Sens-A-Ray. A new system for direct digital intraoral radiography.

A new system for direct digital intraoral radiography, Sens-A-Ray, is presented. This system is based on a detector with a charge-coupled device that was designed especially for direct exposure to x-ray radiation. The system also includes interface electronics and an IBM AT-compatible personal computer with a digital I/O with frame memory, a super VGA graphics board, a high-resolution monitor, and software for the exposure, capture, storage, and enhancement of images. An external optical mass storage device is used for permanent storage of images in digital format. A video printer may be used to create hard copies. The system produces radiographic images at a significantly lower exposure than required for E-speed intraoral film. Applications of the system are exemplified, and its basic properties are discussed.

Computer Graphics↗
PubMed1992

CT reconstruction algorithm for a dental panoramic x-ray unit.

A variable Jacobian and weighted backprojection algorithm, used for medical CT, was adapted to perform CT reconstructions on data obtained with a dental panoramic x-ray unit. A detector array, fitted to the unit for the purpose of acquiring digital panoramic radiographs, was used to collect the data. Compensations were made for the incomplete (230 degrees) rotation of the panoramic x-ray unit, the non-fixed centre of rotation, the irregular rotation of the x-ray target and detector, and the resulting variances in magnification. The algorithm was tested on mathematically simulated phantoms and on acquired data. Reconstruction of simulated data proved the success of the algorithm. Real data reconstructions showed some defects as a result of inaccuracies in quantifying the experimental panoramic device.

Algorithms↗
PubMed1992

Design and implementation of an image management and communications system (IMACS) for dentomaxillofacial radiology.

An Image Management and Communications System for digital dentomaxillofacial radiology is under development at the Department of Dental Diagnostic Science at the University of Texas Health Science Center at San Antonio, Texas, USA. In its final stage, the system will provide a method of integrating different direct digital image acquisition modalities such as intraoral, panoramic and extraoral radiography. A review of the design criteria necessary for establishing such a system for clinical dentistry is discussed and the first phase of its implementation described.

Computer Communication Networks↗
PubMed1991

Electronic system for digital acquisition of rotational panoramic radiographs.

A prototype system for digital panoramic imaging of the maxillofacial complex has been developed. In this system x-ray film is replaced by an electronic sensor that delivers the image information to a computer for storage in digital format. The images, which are similar to conventional panoramic radiographs, are displayed on a high-resolution video monitor and may be stored on optical disk for future use. Hard-copy output is also available. The present prototype system has been installed on an Orthopantomograph model OP10 panoramic x-ray machine is programmed for operation with this machine, but in principle the system can be installed on any such device. The system may be incorporated into the design of future panoramic x-ray systems or may be used to retrofit panoramic x-ray systems now using photographic film to record the radiographic image. Greater sensitivity of electronic sensors should make possible a reduction of x-ray dose to the patient, compared with film-based systems.

Analog-Digital Conversion↗
PubMed1991

Age estimation based on tooth development: a test of reliability and validity.

The precision and accuracy of three commonly used methods for age determination by teeth were studied in 541 children aged 5.5-14.5 yr. These methods rely on estimation of tooth development as seen in radiographs compared with compiled dental charts. It was found that charts made from Scandinavian populations gave a rather good precision, while one from a Canadian population gave a consistent overestimate. Dependent on the method used, sex, and age, the 95% confidence interval for an individual prediction could be more than +/- 2 yr.

Adolescent↗
PubMed1990

Nonrotational scanning in panoramic radiography.

A mathematical analysis of orthoradiography, nonrotational scanning in panoramic radiography, and rotational panoramic radiography shows that they may all be described by the same set of equations. The other two techniques may be regarded as special cases of rotational panoramic radiography.

Humans↗
PubMed1990

Reversed layer position in rotational panoramic radiography.

In rotational panoramic radiography, the image layer is generally positioned between the rotation center of the beam and the film. It is also possible to create a layer that is positioned between the rotation center and the x-ray source. The reversed layer position is useful clinically and gives rise to image properties that are somewhat different from the conventional geometry.

Humans↗
PubMed1990

Applicability of simultaneous rotational panoramic radiography.

The position of the image layer in simultaneous multilayer rotational panoramic radiography using films placed parallel in one cassette was calculated for curved and flat cassettes. Parallel films do not result in parallel layers. The use of a flat cassette results in minor shifts in layer position compared with a curved cassette. The position of the film required to produce parallel curved layers was calculated. Using curved cassettes, extraordinary modifications of the film position would be needed for the anterior region. The use of flat cassettes appears to be practically impossible. Routine use of this technique is therefore unlikely.

Computer Simulation↗
PubMed1989

Image layers in the Zonarc.

The Zonarc (Palomex Oy, Helsinki, Finland) uses the principles of rotational panoramic radiography to image various structures of the head and neck. System parameters obtained from the manufacturer have been used to derive data on the imaging characteristics of the Zonarc when using each of the following programmes: MT, DENT, TMJ, EAR, CV and LAT. The beam path along with the shape, position and relative thickness of the layer has been calculated for each programme, together with the resolution and magnification associated with the different layers.

Humans↗
PubMed1989

Standard forms of dentition and mandible for applications in rotational panoramic radiography.

Mathematical expressions describing the average form and size of the dentition and the mandible are presented. These expressions should be of value in applications of panoramic radiography when reference to an average standard jaw form is of interest. Data were collected from axial radiographs of 35 males and 35 females of three ethnic groups: Mexican-Americans, black Americans and American and Scandinavian Caucasians. Curves were traced on the axial radiographs representing the dentition and the mandible and points along these curves digitized. Mathematical expressions were established using advanced algorithms for orthogonal polynomial curve fitting, i.e. perpendicular distances to the curved dentition and mandible were minimized rather than distances parallel to the y-axis in an arbitrarily chosen coordinate system. The standard deviations around the polynomials defining the average curves are demonstrated and expressions for calculating the continuously varying standard deviations are given.

Dentition↗
PubMed1989

Layer thickness in rotational panoramic radiography: some specific aspects.

It is customary to define the thickness of the image layer in rotational panoramic radiography along the central ray of the X-ray beam. This results in calculated values which overestimate its thickness, especially in regions where the central ray deviates markedly from orthogonality. A supplementary definition is proposed which considers layer thickness in a direction perpendicular to the central plane of the image layer. This provides values which may be more easily related to the thickness of the object being radiographed. A mathematical approximation for calculations involving the supplementary definition is described and illustrated with numerical examples.

Radiography, Panoramic↗