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Biomedical subjects

A Workman

Publications and source records attributed to A Workman.

At least 19 recordsLinked to original sources
PubMed2007

Patient dose from 3D rotational neurovascular studies.

The use of image-guided interventional radiological techniques is increasing in prevalence and complexity. Imaging system developments have helped improve the information available to interventionalists to plan and guide procedures. Information on doses to patients resulting from alternative imaging techniques or protocols is useful for both the process of justifying particular procedures and in optimizing the resultant exposures. Such information is not always available, especially for new or developing imaging techniques. We have undertaken a study of doses to patients associated with two alternative imaging methods for pre-intervention assessment of intracranial aneurysms. In the first technique the aneurysm is assessed from a series of digital subtraction angiography (DSA) runs taken at different imaging projections. The second technique involved acquiring images from one single image run while the imaging system rotated 180 degrees around the patient's head. In this technique, the aneurysm was then evaluated from a 3D reconstruction of the projection images. Effective doses were calculated using a computer model to simulate the exposure geometry and parameters. The mean dose from the DSA protocol used at our centre was 3.4 mSv and from the 3D rotational angiography (RA) technique was 0.20 mSv.

Angiography, Digital Subtraction↗
PubMed2002

A comparison of the imaging properties of CCD-based devices used for small field digital mammography.

The objective imaging characteristics of three systems that use charge coupled devices (CCD) for small-field digital mammography (SFDM) have been compared in terms of spatial resolution and signal to noise ratio. The results indicate that although they are designed for nominally the same tasks of stereotactic localization and spot imaging these detectors have significantly differing physical imaging properties. Imaging system design parameters such as the phosphor screen type and thickness, screen configuration and method of optically coupling the phosphor to the CCD have significant effects on the imaging performance of the detectors.

Humans↗
PubMed2002

Assessment of distortion in a three-dimensional rotational angiography system.

The purpose of this project was to determine the degree of geometrical distortion in a three-dimensional (3D) image volume generated by a digital fluorography system with rotational image acquisition capabilities. 3D imaging is a valuable adjunct in neuroangiography for visualization and measurement of cerebral aneurysms and for determination of the optimum projection for intervention. To enable spatially accurate 3D reconstruction the system must correct for geometrical distortion in the image intensifier television system as well as for deviations in gantry motion. 3D volumes were reconstructed from 100 X-ray projections acquired over a 180 degrees arc over a period of 8 s. A phantom was constructed to assess geometrical distortion in the three dimensions. The phantom consisted of 1 mm diameter ball bearings embedded in Perspex in a cubic lattice configuration. The ball bearings were placed at 20 mm intervals over a 140 mm cubic volume. Distortion was assessed by taking measurements between points of known separation and using a differential distortion measurement. The maximum error in the 3D location of objects was found to be 1.4 mm, while the differential distortion was found to range from -1.0% to +2.3%. The 3D images were found to have negligible visual distortion, enabling subjective assessments to be made with confidence to aid intervention.

Artifacts↗
PubMed2001

Radiation doses to patients during ERCP.

BACKGROUND: There is a scarcity of data regarding the radiation dose and associated risks to patients during ERCP. Dose area product (DAP) measurements can be used to estimate an effective dose (ED) to patients undergoing ERCP. This measure allows radiation risk associated with such procedures to be quantified. The aim of this study was to evaluate the ED to patients undergoing ERCP. METHODS: A DAP meter was fitted to the x-ray tube before each ERCP. DAP reading (Gy-cm(2)), fluoroscopy time, average screening kVp, number of films, and kVp per film were recorded. Mean ED was estimated by using DAP readings and Monte Carlo computer software to model radiation exposure conditions. RESULTS: Data were recorded on 20 subjects. Average DAP was 13.5 Gy-cm(2) (6.8-23.9) for diagnostic and 66.8 Gy-cm(2) (28.7-108.5) for therapeutic ERCP (p < 0.05). Average fluoroscopy time was 2.3 minutes (1.1-5.3) for diagnostic and 10.5 minutes (5.9-16.6) for therapeutic ERCP (p < 0.05). DAP showed a linear relationship with fluoroscopy time (R(2) = 0.928). Mean number of diagnostic and therapeutic films was 2.8 and 3.7, respectively. Fluoroscopic exposure represented 69% of the DAP for diagnostic ERCP and 90% of the DAP for therapeutic ERCP. Average ED was 3.1 mSv for diagnostic and 12.4 mSv for therapeutic ERCP. CONCLUSIONS: Therapeutic ERCP is associated with significantly higher radiation exposure than diagnostic ERCP. ED in therapeutic ERCP is a result largely of fluoroscopy time as opposed to number of films.

Adult↗
PubMed2000

Application of draft European Commission reference levels to a regional CT dose survey.

A survey of CT doses in Northern Ireland in the period between October 1995 and March 1997 was carried out. The survey included all but one of the 10 scanners in use at the time, and, additionally, two others that were replacement machines. The method used was to study standard protocols and calculate doses to the NRPB mathematical phantom, so that a direct comparison could be made with other surveys carried out in a similar fashion elsewhere. The survey addressed the patient radiation dose but not image quality or clinical outcomes. It is estimated that in Northern Ireland the contribution to collective dose to the population from CT is about 40% of that from all medical X-rays. The proposed European Commission reference quantities, weighted CT dose index and dose-length product were computed and their potential use evaluated. A full study of mean values of effective dose per examination revealed the average dose per examination was not significantly different from that found in the 1989 UK survey, although several procedures gave rise to doses that were high enough to be investigated with a view to justification or reduction. One of the scanners was found to give consistently high doses. It is likely that a revision of the mAs values used on this scanner will produce a significant reduction in patient doses without compromising image quality. When compared with the draft EC reference levels, fewer procedures were found to have excessively high dose values. The proposed EC reference levels would therefore be useful for continual monitoring of CT dose status, but do not appear to provide as comprehensive an assessment of patient exposure as that given by consideration of effective doses.

Clinical Protocols↗
PubMed1998

Radiation doses to patients during pharyngeal videofluoroscopy.

Pharyngeal videofluoroscopy (VTF) is a well-recognized technique for investigating and assessing swallowing disorders. There is, however, a paucity of data available regarding the radiation dose to patients during such procedures, but there is general concern that fluorographic imaging modalities are associated with significant radiation exposure. We have recorded the dose received by 23 patients undergoing VTF in our department using a Dose-Area Product (DAP) Meter and have used the data to calculate the effective dose to the patients. The mean effective dose is 0.4 mSv (range 0.027-1.1) which compares favorably with the effective doses associated with other common radiological procedures. We therefore conclude that the radiation detriment associated with pharyngeal VTF is well within acceptable levels.

Adult↗
PubMed1998

Protocol for measurement of patient entrance surface dose rates for fluoroscopic X-ray equipment.

While patient entrance surface dose rate is an important indicator of dose performance for fluoroscopic units, there has been no standardized approach to measuring this. Since results are strongly dependent on the type of phantom used and the relative positions of the X-ray tube, intensifier and phantom, comparisons of the performance for different units are difficult to make. This document sets out a protocol for making these measurements using a standard phantom and standard configurations for different types of X-ray unit Values of dose rates which might be expected are given.

Clinical Protocols↗
PubMed1997

Physical performance measures of radiographic imaging systems.

New systems and technologies for dental radiographic imaging are being introduced at an increasing rate. Established methods of physical measurement allow the imaging performance of these systems to be quantified. These quantitative measures are important when comparing the imaging performance of competing systems. This review presents an overview of the main concepts in the assessment of the physical performance of imaging systems including signal transfer, as described by both the characteristic curve and modulation transfer function (MTF), and image noise, as described by the Noise Power Spectra. These measures can be combined to produce signal-to-noise ratio descriptors such as Noise Equivalent Quanta and Detective Quantum Efficiency which give an overall description of imaging system performance. Subjective means of measuring image quality, which naturally include the performance of the image display system and the observer, are also considered as a gauge of system performance.

Artifacts↗
PubMed1996

The imaging performance of a storage phosphor system for dental radiography.

Direct digital imaging systems are becoming increasingly common in dental radiography. The majority of these systems are based on charge coupled device (CCD) technology. A relatively new system, based on photo-stimulable phosphor luminescence (PSPL), is now commercially available. This system appears to overcome some of the restrictions of CCD systems including those associated with the bulky detector, connecting wire, limited image size and limited exposure latitude. A physical evaluation of the PSPL system was conducted including measurements of sensitometric response, modulation transfer function (MTF), noise power spectrum (NPS), noise equivalent quanta (NEQ) and detective quantum efficiency (DQE). These measurements were compared with results obtained previously for Kodak Ektaspeed (E-speed) film. The results of the evaluation indicate that the PSPL system may be capable of operating at exposures up to 80% lower than for film with comparable image quality.

Humans↗
PubMed1995

Update on the recommended viewing protocol for FAXIL threshold contrast detail detectability test objects used in television fluoroscopy.

The significance of varying the viewing conditions that may affect the perceived threshold contrast of X-ray television fluoroscopy systems has been investigated. Factors investigated include the ambient room lighting and the viewing distance. The purpose of this study is to find the optimum viewing protocol with which to measure the threshold detection index. This is a particular problem when trying to compare the image quality of television fluoroscopy systems in different input field sizes. The results show that the viewing distance makes a significant difference to the perceived threshold contrast, whereas the ambient light conditions make no significant difference. Experienced observers were found to be capable of finding the optimum viewing distance for detecting details of each size, in effect using a flexible viewing distance. This allows the results from different field sizes to be normalized to account for both the magnification and the entrance air kerma rate differences, which in turn allow for a direct comparison of performance in different field sizes.

Clinical Protocols↗
PubMed1995

Improved image quality utilizing dual plate computed radiography.

A method of improving image quality in computed radiography (CR) using dual plate exposure has been developed. Two CR image plates are used to increase the fraction of X-ray quanta absorbed from the beam. Spatial registration and combination of images from the two plates leads to an image with improved signal-to-noise ratio characteristics. A cross correlation technique is used to register spatially the images from the front and rear plates. The modulation transfer function and noise power spectrum were measured for the single plate and combined dual plate images. Results indicate a potential increase of approximately 60% in the detective quantum efficiency (DQE) of the dual plate combined image compared with the single plate image. The improvement of DQE at high spatial frequencies is dependent on the accuracy of the registration of the two images. The actual improvement in imaging performance was measured using a contrast detail test piece. A computerized method was used to measure the imaged detail signal-to-noise ratio of the details of different dimension. Results indicate an improvement of 21% in the signal-to-noise ratio of the details imaged with the dual plate arrangement compared with the single plate. This indicates that this technique can result in a significant increase in image quality for the same exposure level. Alternatively this technique could allow reduction in exposure while maintaining the same image quality achievable with the single plate system.

Humans↗
PubMed1994

Physical evaluation of computed radiography as a mammographic X-ray imaging system.

The physical imaging properties of a computed radiography (CR) system operating under mammographic exposure conditions have been measured. These measurements include modulation transfer function (MTF), sensitometric response and noise power spectrum (NPS). These figures were used to derive signal-to-noise ratio (SNR) descriptors of the system performance. The same measures were derived for a mammographic film-screen system. The SNR properties of the CR system indicate superior low frequency performance over a wider dynamic range than the film-screen system. The spatial frequency dependent SNR properties of the CR system are, however, limited. The results of a psychophysical test support the results obtained from physical measurements. These results indicate that despite its limited sharpness, details of dimensions relevant to diagnosis in mammography (circular details 0.25 mm diameter to represent microcalcifications and 3 mm diameter to represent small masses) are reproduced using CR with SNRs which are at least comparable with those of a mammographic film-screen system.

Breast Diseases↗
PubMed1993

Physical aspects of photostimulable phosphor computed radiography.

Currently photostimulable phosphor computed radiography (PPCR) promises to be the digital X-ray image acquisition technology of choice for classical radiography (i.e. X-ray examinations of natural anatomy). For the last two years we have been carrying out a physical evaluation of modern PPCR technology and some of our findings relevant to general radiographic applications are reviewed here. Topics covered include the function of the auto-reader system and the reliability of image reproduction, the radiation exposure requirement and physical image quality. The latter is based upon both objective and subjective measures of image quality. These studies have yielded a favourable comparison of the image quality of modern PPCR technology with that of medium-speed and fast radiographic screen-film combinations. The major advantages of PPCR appear to be the maintenance of high imaging efficiency (DQE) over a much wider range of signal levels than film and consistent image acquisition and presentation independent of exposure level. In general radiographic applications no major limitations due to the comparatively modest limiting spatial resolution of PPCR [maximum limiting resolution = 5 line-pair mm-1] have been experienced. Digital image enhancement is a central element of PPCR image reproduction. The authors believe that advances in image enhancement algorithms remain a potential area for further improving the presented quality of PPCR images.

Image Processing, Computer-Assisted↗
PubMed1988

The computer enhancement of digital grey-scale fluorography images.

In this article we describe the results of a preliminary investigation of computerized processing of digital grey-scale fluorography (DGF) images. Image processing techniques used include dynamic range equalization, adaptive contour enhancement and non-linear transformation of grey-scale data. Original and processed images derived from non-subtractive digital angiography and digital spot-film investigations are used to illustrate our findings. The quality of the processed images confirms the promise of digital image processing in DGF.

Algorithms↗