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A R Cowen

Publications and source records attributed to A R Cowen.

At least 37 records · Page 2Linked to original sources
PubMed1994

Dual-energy digital mammography utilizing stimulated phosphor computed radiography.

Dual-energy subtraction is a radiographic technique for the acquisition of a material selective image by the weighted subtraction of low- and high-energy digital X-ray images. This is achieved by exploiting the energy dependence of the X-ray attenuation components in the image. This can allow the removal of background morphology to enhance the presentation of otherwise obscured details. The detection of microcalcifications in a mammogram by dual-energy techniques has previously been investigated. These investigations indicated that, using dual-energy techniques, small microcalcifications could be extracted from the background breast morphology with sufficient signal to noise ratio (SNR) to be full visualized. The authors present the extension of a theoretical dual-energy model to incorporate practical considerations and then compare the results with experimentally derived data using a commercially available computed radiography system. In particular the extended model now takes into account the energy dependent detective quantum efficiency of a system. This is thought to be a major factor in reducing the efficiency of dual-energy mammography. The theoretical model predicts that dual-exposure dual-energy mammography, utilizing HRIII image plates, could not provide a detail SNR of five for calcifications smaller than 470 mu m. The experimental results verify this and indicate that dual-energy subtraction mammography, utilizing computed radiography, is currently not a viable technique for the detection of clinically significant microcalcifications. Further advances in X-ray image detector efficiency will be required if the full potential of this technique is to be achieved.

Breast Diseases↗
PubMed1994

A clinical comparison between conventional and digital mammography utilizing computed radiography.

Previous work utilizing a specially designed mammographic test object has indicated that the image quality of computed radiography (CR) approaches that of a conventional film-screen technique of equivalent radiographic speed. In an attempt to correlate these results with the clinical situation a subjective rating study of the primary physical parameters of noise, sharpness, and contrast has been conducted. Using a randomized viewing sequence two radiologists experienced in mammography were asked to score these parameters utilizing a 5 point scale. A total of 138 images was used, 62% containing no abnormalities and 38% containing either microcalcifications, masses or both. Additionally, the observers scored their confidence of correct classification, and these results were then used to construct receiver operating characteristic (ROC) curves. The subjective rating of the physical parameters results produced similar results to those obtained using the test object, with CR images providing greater contrast than film. The resolution of CR, however, was lower than for film. Overall the noise levels were similar for both modalities, but the digital images occasionally contained high levels of dust artefacts. In one case these artefacts were mistaken for a cluster of microcalcifications. The test object results and the parameter rating results indicate that CR approaches the performance of film-screen images. Statistically the ROC curves produced indicate CR images to be comparable to the film-screen combination. This may be because the increased contrast compensates for resolution limitations and these findings correlate with our clinical experience.

Breast Diseases↗
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↗
PubMed1994

Earthquake.

On January 25, 1 week after the most devastating earthquake in Los Angeles history, the Southern California Hospital Council released the following status report: 928 patients evacuated from damaged hospitals. 805 beds available (136 critical, 669 noncritical). 7,757 patients treated/released from EDs. 1,496 patients treated/admitted to hospitals. 61 dead. 9,309 casualties. Where do we go from here? We are still waiting for the "big one." We'll do our best to be ready when Mother Nature shakes, rattles and rolls. The efforts of Los Angeles City Fire Chief Donald O. Manning cannot be overstated. He maintained department command of this major disaster and is directly responsible for implementing the fire department's Disaster Preparedness Division in 1987. Through the chief's leadership and ability to forecast consequences, the city of Los Angeles was better prepared than ever to cope with this horrendous earthquake. We also pay tribute to the men and women who are out there each day, where "the rubber meets the road."

California↗
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↗
PubMed1992

A preliminary investigation of the imaging performance of photostimulable phosphor computed radiography using a new design of mammographic quality control test object.

Leeds Test Object TOR[MAM] has been designed to supplement the current FAXIL mammography test object TOR[MAX]. It contains a range of details that have a more natural radiographic appearance and has been designed as a test that more closely approximates the image quality achieved in clinical mammography. Physical aspects of the design and implementation of TOR[MAM] are presented. The TOR[MAM] has been used in a preliminary physical evaluation of the comparative image qualities produced by conventional (screen-film) and photostimulable phosphor computed mammography and the results are discussed. TOR[MAX] results are also presented. The influence of digital image processing (enhancement) on the image quality of computed mammograms is also considered. The results presented indicate the sensitivity of TOR[MAM].

Female↗
PubMed1989

A physical evaluation of the imaging performance of a high-resolution fluorography system.

A physical evaluation of the imaging performance of a unique high-resolution fluorography system is presented. Measurements have been made of contrast performance, unsharpness (modulation transfer function) and noise (Wiener spectrum and threshold contrast detectability), and the results have been compared with those measured from medium-fast calcium tungstate and rare-earth screen--film combinations and a standard fluorography system. The results have proved sufficiently encouraging that a full-scale trial is now underway to evaluate the system's performance in routine clinical application.

Humans↗
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↗
PubMed1987

A set of X-ray test objects for image quality control in digital subtraction fluorography. I: Design considerations.

A set of X-ray test objects has been developed for quality control in digital subtraction fluorography (DSF). Factors which can be assessed include dynamic range, highlight overload and signal-to-noise ratio, low contrast sensitivity, unsharpness, and systematic misregistration. These test objects complement, both in design and calibration, those previously developed to evaluate the imaging performance of television fluoroscopy and small-format fluorography systems. In this article, the first of two, we describe the Leeds DSF test objects, paying particular attention to the reasoning behind their design.

Equipment Design↗
PubMed1987

A set of X-ray test objects for image quality control in digital subtraction fluorography. II: Application and interpretation of results.

In the previous article we introduced a set of test objects for quality control of digital subtraction fluorography (DSF) systems. These test objects have been evaluated using several commercial DSF systems in their clinical environment. In this second article we present test images and results obtained during these trails and explain how the test objects can be used to analyse the imaging performance of DSF systems.

Fluoroscopy↗
PubMed1986

Patient absorbed doses in digital grey-scale fluorography.

This article describes a preliminary comparison between the levels of patient dose used in digital grey-scale fluorography (DGF) and screen-film radiography. Patient doses were measured in three common radiographic examinations, postero-anterior chest, antero-posterior lumbar spine and lateral lumbo-sacral junction, using thermoluminescent dose-meters and an anthropomorphic phantom. Within the limitations of the image quality currently available in DGF, the findings indicate that digital radiography with the large-field X-ray image intensifier promises significant savings in patient dose compared with conventional radiography.

Film Dosimetry↗
PubMed1985

A set of X-ray test objects for quality control in television fluoroscopy.

The history of performance testing in Leeds of television fluoroscopic systems is briefly outlined. Using the visual, physical and technological requirements as a basis, a set of nine test objects for quality control in television fluoroscopy is described. The factors measured by the test objects are listed in the introduction; the test objects and their function are fully described in the remainder of the paper. The test objects, in conjunction with a television oscilloscope, give both subjective and objective information about the X-ray system. Three of the test objects enable the physicist or engineer to adjust certain aspects of the performance of the X-ray system. The set of nine test objects is available commercially.

Fluoroscopy↗