The impact of increased Al filtration on x-ray tube loading and image quality in diagnostic radiology

Previous work has shown that for nine common radiographic projections (AP abdomen, AP cervical spine, LAT cervical spine, PA chest, LAT chest, AP hip, AP lumbar spine, LAT lumber spine, and AP pelvis) increasing the total x-ray tube filtration from 2.5 mm Al equivalent (the regulatory minimum for general diagnostic radiology) to 4.0 mm Al equivalent, reduces the average effective dose and average skin entrance dose by 9% and 16%, respectively, using a 400 speed screen-film system. In this study, the effects of this filtration increase on x-ray tube loading and image quality were assessed. For the above projections and filtration increase, mean absolute and percentage increases in tube loading were 2.9 mAs and 15%, respectively, for a constant film density and fixed kVp. Tube current (mA) increases of 25% (a worst case) resulted in no statistically significant loss in focal spot resolution due to blooming for both large (1.2 mm) and small (0.6 mm) focal spot sizes, except at high mA low kVp techniques. The latter losses were below 10%, and when the image receptor blur was incorporated, the total system spatial resolution losses were on the order of one-quarter to one-half these values for typical clinical geometries. Radiographs of a contrast phantom taken with 2.5 and 4.0 mm total Al equivalent x-ray tube filtration were compared at 60, 70, 81, 90, 102, and 121 kVp. No statistically significant changes were observed with regard to (1) test object conspicuity as reported by three observers, (2) image contrast, as measured using a densitometer with a 3 mm aperture (+/-0.0017 OD, 95% confidence level), and (3) pixel value image noise, image contrast-to-noise ratios, and image signal-to-noise ratios, as measured using a scanning densitometer with a 12-bit acquisition depth and 85 micron pixel size (+/-2.5%, +/-3.1%, and +/-2.5%, 95% confidence levels, respectively). These results, combined with the linear no-threshold model for radiation risk and the ALARA principle, suggest that general radiography should be carried out using a minimum of 4.0 mm total Al equivalent filtration.     

Advances in three-dimensional diagnostic radiology

The maturity of current 3D rendering software in combination with recent developments in computer vision techniques enable an exciting range of applications for the visualisation, measurement and interactive manipulation of volumetric data, relevant both for diagnostic imaging and for anatomy. This paper reviews recent work in this area from the Image Sciences Institute at Utrecht University. The processes that yield a useful visual presentation are sequential. After acquisition and before any visualisation, an essential step is to prepare the data properly: this field is known as ‘image processing’ or ‘computer vision’ in analogy with the processing in human vision. Examples will be discussed of modern image enhancement and denoising techniques, and the complex process of automatically finding the objects or regions of interest, i.e. segmentation. One of the newer and promising methodologies for image analysis is based on a mathematical analysis of the human (cortical) visual processing: multiscale image analysis. After preprocessing the 3D rendering can be acquired by simulating the ‘ray casting’ in the computer. New possibilities are presented, such as the integrated visualisation in one image of (accurately registered) datasets of the same patient acquired in different modality scanners. Other examples include colour coding of functional data such as SPECT brain perfusion or functional magnetic resonance (MR) data and even metric data such as skull thickness on the rendered 3D anatomy from MR or computed tomography (CT). Optimal use and perception of 3D visualisation in radiology requires fast display and truly interactive manipulation facilities. Modern and increasingly cheaper workstations (<$10000) allow this to be a reality. It is now possible to manipulate 3D images of 256³ at 15 frames per second interactively, placing virtual reality within reach. The possibilities of modern workstations become increasingly more sophisticated and versatile. Examples presented include the automatic detection of the optimal viewing angle of the neck of aneurysms and the simulation of the design and placement procedure of intra-abdominal aortic stents. Such developments, together with the availability of high-resolution datasets of modern scanners and data such as from the NIH Visible Human project, have a dramatic impact on interactive 3D anatomical atlases.     

The impact of technology on medicine

This article is the fifth in the series which discusses the impact of technology in the various specialist fields of modern medicine. Previous articles from the Presidents or representatives of the Royal Colleges of Psychiatrists, Surgeons, General Practitioners and Physicians were published in the May, July and September issues (1980) of the Journal.     

The impact of information technology on histopathology

Pathology is one of the most computer intensive areas of medicine and as a result diagnostic pathologists in histopathology have often been at the cutting edge of computer literacy. The majority of laboratories use laboratory information systems to issue and store pathology reports. Many of these systems provide the diagnostician with the ability to retrieve reports and cases using coding systems such as SNOMED, but more advanced computer facilities that might assist the pathologist in the diagnosis or interpretation of a case are often lacking. In recent years advances in computer technology have begun to have a much wider impact on the practice of medicine and newer technologies are beginning to find their way into the reporting room. In this review, I cover some of the recent and emerging advances in IT that have the potential to revolutionize the practice of diagnostic histopathology in the next 5 years. The major area of telepathology has been a subject of several recent reviews and will not be covered here.     

Using diagnostic radiology in human evolutionary studies

This paper reviews the application of medical imaging and associated computer graphics techniques to the study of human evolutionary history, with an emphasis on basic concepts and on the advantages and limitations of each method. Following a short discussion of plain film radiography and pluridirectional tomography, the principles of computed tomography (CT) and magnetic resonance imaging (MRI) and their role in the investigation of extant and fossil morphology are considered in more detail. The second half of the paper deals with techniques of 3-dimensional visualisation based on CT and MRI and with quantitative analysis of digital images.     

The impact of endoscopic technology on gastrointestinal pathology.

Since its introduction in the 1950s, fiberoptic endoscopy has dramatically altered the scope and practice of gastrointestinal (GI) pathology. Whereas examination by rigid instruments was generally restricted to the proximal digestive foregut and distal 25 cm of the large bowel, fiberoptic endoscopy extended these limits considerably, which resulted in a greater volume of biopsies submitted to the pathology laboratory. Furthermore, this technique is associated with a lesser degree of patient discomfort and a lower risk of complications compared to rigid or semiflexible endoscopy. In established endoscopy units, flexible endoscopy is performed increasingly with the videoscope rather than the fiberscope. With the added advantage of direct visualization, flexible endoscopy has eclipsed barium radiology as the premier investigative modality for GI diseases. Although upper GI endoscopy and colonoscopy account for the majority of biopsy material, there are other flexible endoscopic techniques, including endoscopic retrograde cholangiopancreatography and enterostomy. Flexible endoscopy has not only impacted the diagnosis of important disease entities (eg, reflux esophagitis, H. pylori gastritis, celiac disease and GI polyps and neoplasia), but it has also become a key component of surveillance protocols for dysplasia in Barrett's esophagus and idiopathic inflammatory bowel disease. Predicting major trends that may emerge from (GI flexible endoscopy in the future is somewhat difficult, but promising new avenues of investigation include increased use of endoluminal ultrasound and trans-bowel fine needle aspiration. Biopsy material will be submitted with more frequency for genetic molecular studies such as tumor development and progression and identification of infections agents; the priorities for handling biopsy material may have to be re-examined. Gastrointestinal (GI) biopsies constitute a substantial proportion of the surgical pathology load in most tertiary care medical centers. Based on topographic site of origin, the GI tract is the single largest component of the biopsy service in this institution. This relates in part to the high frequency of patients' complaints referable to the digestive tract and is also a result of the advances in GI endoscopy that have led to more widespread application of this technique. To gain a better appreciation of the impact of the changes in endoscopic techniques on gastrointestinal pathology, it is pertinent to examine the historical perspective from which the technology arose.     

Monte Carlo studies of x-ray scattering in transmission diagnostic radiology

Monte Carlo methods have been used to simulate the scattering of x rays in polystyrene and water phantoms. In particular, the ratio of the scattered to total x-ray fluence (scatter fraction) has been calculated for monoenergetic x-ray beams in the energy region relevant to diagnostic radiology and nuclear medicine (30-660 keV). Simulations have been made for representative values of the pertinent geometrical factors; phantom thickness from 5 to 21 cm, x-ray beam diameters of 10 and 25 cm, and scatterer-to-image-plane separations from 0 to 20 cm. As a function of x-ray energy, the scatter fraction was found to vary slowly between 30 and 100 keV, and to decrease between 100 and 660 keV. The present results were generated with a special transport code which included the effects of special geometries and the response of the x-ray detector. With the inclusion of these effects, the results resolved inconsistencies and showed good agreement with previous measured and calculated data.     

Estimation of effective dose equivalent to staff in diagnostic radiology

The irradiation of staff in diagnostic radiology was simulated for conditions commonly encountered in fluoroscopy. Scattered radiation distributions were produced from diagnostic x-ray beams generated at tube potentials in the range 60-120 kVp, using the abdomen sections of a Rando phantom. Doses to a number of organs in the head and neck were measured using a Rando phantom loaded with lithium fluoride thermoluminescent dosemeters. The torso sections were placed on a water phantom on top of a stand, with film badge dosemeters positioned on the surface of the phantom at the forehead, neck, chest and waist, and the phantom was placed in the radiation field. Doses to organs in the torso were calculated from the waist-level film badge dosemeter reading using normalised organ dose data. Radiation doses to organs below a lead apron, when worn, were estimated from the unshielded dose values using a transmission factor appropriate to the quality of the scattered radiation. The effective dose equivalent (EDE) to the phantom was calculated for various x-ray beam qualities and lead apron thicknesses and compared with the film badge doses. The results indicate that a dosemeter worn at the waist/chest level under a lead apron generally underestimates the EDE. Conversely, dosemeters worn at the forehead/neck tend to overestimate the EDE. It is recommended that a dosemeter is positioned under a lead apron, if worn.     

The impact of fine-needle aspiration biopsy on a diagnostic electron microscopy laboratory

We retrospectively reviewed the number and types of diagnostic electron microscopic specimens from a 4 1/2-year period. During this period, the number of fine-needle aspirate biopsy specimens processed increased in a linear fashion, from a relatively uncommon occurrence to the current level of activity, in which fine-needle aspiration specimens now represent 40% to 50% of the nonrenal diagnostic material examined by electron microscopy. This study documents the increasing importance of fine-needle aspirate-type specimens in the everyday operation of a diagnostic electron microscopy facility.     

The medical history as a diagnostic technology.

The medical history is a powerful diagnostic technology. However, in seeking to establish an appropriate balance between the history and the other diagnostic modalities more explicit consideration must be given to the performance characteristics of the medical history. Building on recent work undertaken in the UK and elsewhere in Europe it is now feasible to develop a library of setting-specific likelihood ratios and kappa statistics for key elements of the medical history. Of particular importance to those working in primary care, statistically adjusted combinations of information from the medical history can be generated; furnishing clinicians with likelihood ratios of significant magnitudes. It is suggested that developing a more rational approach to the use of the medical history could lead to improvements in diagnostic efficiency and effectiveness, with benefits for individual patient care in addition to the overall NHS budget. When diagnosis is viewed as a processing pathway founded on a robust medical history, it becomes clear than in some situations investigations may become unnecessary and, in other circumstances, their impact will be enhanced.     

An analytical model of the scattered radiation distribution in diagnostic radiology

A simple scatter model is used to analytically derive the point spread function (PSF) for scattered radiation in diagnostic radiology. The resulting equation is a function of four physical parameters; object thickness, object-to-detector distance (air gap), and the linear attenuation coefficients for both primary and scatter radiation. Though the model is based upon single scattering, it is shown that by reducing the scatter attenuation coefficient the analytic model compares well to the multiple scattering PSF determined using Monte Carlo analysis.     

Some properties of photon scattering in water phantoms in diagnostic radiology

Monte Carlo simulation was applied to study the histories of photon interactions in a soft-tissue-equivalent medium under diagnostic imaging conditions. We examined the dependence on incident x-ray energy and phantom thickness of the basic properties of photon scattering, including the probabilities of occurrence of the various interaction processes, and the frequency distributions of scattering events. We investigated the properties of scattered radiation for monoenergetic incident x rays, which provide a basis for deriving the physical properties of scattered radiation for any polyenergetic incident beam. We also included four incident x-ray beams with broad spectra; these represented the incident x rays typically used for diagnostic imaging.     

Aluminum equivalence of materials used in diagnostic radiology and its dependence on beam quality

A semi-empirical theory has been derived that relates the aluminum equivalence of various materials used in diagnostic radiology to their attenuation coefficients. The dependence of the aluminum hardness (AHE) and attenuation (AAE) equivalent on the beam quality is described in terms of effective energy. This 'aluminum equivalence approach' (ALEAP) gives estimates of the aluminum equivalent, regardless of spectral shape, that are usually within +/- 5% except when absorption edges are involved. A reasonable definition for the AHE of K-edge filters is offered. Suggestions are made for methods of testing for compliance with standards and regulations.