Osteo-articular, mammographic and thoracic films: clinical evaluation of digital view box versus conventional view box

PURPOSE

To compare in a clinical setting a conventional view box with a digital view box (Smart Light 2000 Digital Film Viewer System, Smart Light, Israel) in the identification of osteo-articular, mammographic and thoracic lesions.

MATERIALS AND METHODS

Six radiologists (two for each imaging procedure), experts in osteo-articular, mammographic and thoracic diseases, independently, compared 600 plain films (100 patient with two projections for each imaging procedure). The radiologists evaluated the films by filling-out a multiple choice questionnaire containing questions concerning the type of pathology seen and the technical quality of the radiography in terms of exposure along with specific questions concerning each of the imaging procedures.

RESULTS

We observed a higher sensitivity of the digital view box for lesion identification (p<0.05); furthermore, we analyzed a greater number of radiographs, recovering technically unsuitable films, because of over or under-exposure (high or low optical density). The interreader agreement was also good (> 0.75). The better lesion perception derived from the increase luminance of the digital view box in the evaluation of higher film densities, such as in overexposed films. DISCUSSION. The technical characteristics of the digital view box reduce or eliminate negative factors that reduce perceptional performance, and often permit the recovery of films that would have otherwise been considered technically unreadable.

Evaluation of respiratory movement during gated radiotherapy using film and electronic portal imaging

PURPOSE

To evaluate the effectiveness of a commercial system(1) in reducing respiration-induced treatment uncertainty by gating the radiation delivery.

METHODS AND MATERIALS

The gating system considered here measures respiration from the position of a reflective marker on the patient's chest. Respiration-triggered planning CT scans were obtained for 8 patients (4 lung, 4 liver) at the intended phase of respiration (6 at end expiration and 2 at end inspiration). In addition, fluoroscopic movies were recorded simultaneously with the respiratory waveform. During the treatment sessions, gated localization films were used to measure the position of the diaphragm relative to the vertebral bodies, which was compared to the reference digitally reconstructed radiograph derived from the respiration-triggered planning CT. Variability was quantified by the standard deviation about the mean position. We also assessed the interfraction variability of soft tissue structures during gated treatment in 2 patients using an amorphous silicon electronic portal imaging device.

RESULTS

The gated localization films revealed an interfraction patient-averaged diaphragm variability of 2.8 +/- 1.0 mm (error bars indicate standard deviation in the patient population). The fluoroscopic data yielded a patient-averaged intrafraction diaphragm variability of 2.6 +/- 1.7 mm. With no gating, this intrafraction excursion became 6.9 +/- 2.1 mm. In gated localization films, the patient-averaged mean displacement of the diaphragm from the planning position was 0.0 +/- 3.9 mm. However, in 4 of the 8 patients, the mean (over localization films) displacement was >4 mm, indicating a systematic displacement in treatment position from the planned one. The position of soft tissue features observed in portal images during gated treatments over several fractions showed a mean variability between 2.6 and 5.7 mm. The intrafraction variability, however, was between 0.6 and 1.4 mm, indicating that most of the variability was due to patient setup errors rather than to respiratory motion.

CONCLUSIONS

The gating system evaluated here reduces the intra- and interfraction variability of anatomy due to respiratory motion. However, systematic displacements were observed in some cases between the location of an anatomic feature at simulation and its location during treatment. Frequent monitoring is advisable with film or portal imaging.

Imaging of 1.0-mm-diameter radiopaque markers with megavoltage X-rays: an improved online imaging system

PURPOSE

To improve an online portal imaging system such that implanted cylindrical gold markers of small diameter (no more than 1.0 mm) can be visualized. These small markers would make the implantation procedure much less traumatic for the patient than the large markers (1.6 mm in diameter), which are usually used today to monitor prostate interfraction motion during radiation therapy.

METHODS AND MATERIALS

Several changes have been made to a mirror-video based online imaging system to improve image quality. First, the conventional camera tube was replaced by an avalanche-multiplication-based video tube. This new camera tube has very high gain at the target such that the camera noise, which is one of the main causes of image degradation of online portal imaging systems, was overcome and effectively eliminated. Second, the conventional linear-accelerator (linac) target was replaced with a low atomic number (low-Z) target such that more diagnostic X-rays are present in the megavoltage X-ray beam. Third, the copper plate buildup layer for the phosphor screen was replaced by a thin plastic layer for detection of the diagnostic X-ray components in the beam generated by the low-Z target.

RESULTS

Radiopaque fiducial gold markers of different sizes, i.e., 1.0 mm (diameter) x 5 mm (length) and 0.8 mm (diameter) x 3 mm (length), embedded in an Alderson Rando phantom, can be clearly seen on the images acquired with our improved system. These markers could not be seen on images obtained with any commercial system available in our clinic.

CONCLUSION

This work demonstrates the visibility of small-diameter radiopaque markers with an improved online portal imaging system. These markers can be easily implanted into the prostate and used to monitor the interfraction motion of the prostate.

Developments in digital radiography: an equipment update

Digital X-ray imaging technology has advanced rapidly over the past few years. This review, particularly aimed at those involved in using and purchasing such technology, is an attempt to unravel some of the complexities of this potentially confusing subject. The main groups of X-ray imaging devices that are considered are digitisers of conventional radiographs, image-intensifier-based fluorography systems, photostimulable phosphor computed radiography, amorphous selenium-based technology for thorax imaging and flat-panel systems. As well as describing these different systems, we look at ways of objectively assessing their image quality. Concepts that are used and explained include spatial resolution, grey-scale bit resolution, signal-to-noise ratio and detective quantum efficiency. An understanding of these basic parameters is vital in making a scientific assessment of a system's performance. Image processing and techniques are also briefly discussed, particularly with reference to their potential effects on image quality. This review aims to provide a basic understanding of digital X-ray imaging technology and enables the reader to make an independent and educated assessment of the relative merits of each system.

Precise image-receptor calibration and monitoring of beam quality with a step wedge

OBJECTIVE

To describe an extended bootstrap calibration procedure that uses a step-wedge absorber and minimal equipment for rapid, accurate calibration of image receptors and simultaneous monitoring of beam quality.

METHODS

Multiple radiographs of a step wedge are made at different exposures, with a precision dosimeter as a reference. An iterative least-squares minimization procedure is used to fit the data with a single calibration function. The calibration range can be extended by varying two exposure parameters in addition to stepwedge thickness. Small variations in beam quality and other experimental artifacts can be detected by testing redundant data for self-consistency. As a demonstration, two photostimulable phosphor (PSP) systems were calibrated, one with a well-regulated X-ray source and the other with a poorly regulated source.

RESULTS

The first PSP system was calibrated over a range of 3.2 orders of magnitude with a relative standard deviation of the estimate of only 0.36%. The slope of the calibration curve agreed with the nominal, factory-set value within 0.8% (on a logarithmic scale). The second PSP system had a nearly linear response with a relative standard deviation of the estimate of 0.44% over the upper 97% of its range. Both X-ray sources showed easily detectable variations in tube potential.

CONCLUSIONS

The new calibration method eliminates many of the sources of error of previous techniques such as inverse-square sensitometry. If a suitably precise X-ray source is available, the relative accuracy is limited only by the precision of the receptor system.

Digital x-ray systems. Part 1. An introduction to DX technologies and an evaluation of cassette DX systems

Film is an effective means for capturing diagnostic information. However, film images cannot be easily integrated into a digital communication system. Thus, as the number of healthcare facilities moving toward a digital work-flow increases, so too does the interest in digital x-ray (DX) systems, which produce images as collections of digital data, rather than as static films. In this first part of our two-part series on DX systems, we present an overview of DX technology, we review the cost factors to consider when deciding whether to invest in DX technology, we offer guidance to help facilities determine which type of system--cassette or cassetteless--will best meet their needs, and we evaluate cassette DX systems from four suppliers. Part 2 of our series, which features an evaluation of cassetteless DX systems, will be published later this year. Our testing of DX systems identifies whether a system can provide at least the same amount of diagnostic information as a screen-film system while significantly increasing the efficiency of operations. We found all the evaluated systems to be effective, but we rank the systems from two suppliers above the others because their user interfaces allow easier and more efficient operation.

Image quality of dry-processed film

Recently, a lot of dry film processors and its radiographic films have been favorably used in hospitals. We have evaluated the diagnostic capability and measured the image quality of these dry processed films, comparing it with those of conventional wet processed films. It is found that (1) dry processed film has almost the same diagnostic capability to that of wet processed film, and (2) dry film had strong absorption at 804 nm which brought a reddish color tone to dry film and gave radiologists problems in diagnosis. These situations have been improved through this study to some extent.

Mammography technology overview

As you can see, there are many options in mammography units. This article is not meant to recommend one unit or manufacturer over another, but rather to inform consumers that all units have assets to help technologists acquire the perfect mammogram. This article is meant to make you think about the pros and cons as you consider purchasing new mammography equipment. Though it may seem wise and certainly easier to equip your multiple-unit site(s) with one manufacturer's equipment or even one model, it might truly be wise to have a little variety; this addresses shortcomings of a particular unit. If you provide technologists with a mammography system with which they are comfortable and feel they can address any issues-accommodating disabled patients, patients with breast implants or patients with dense breast tissue-you will see the perfect mammograms you desire.

Novel magnetic technology for intraoperative intracranial frameless navigation: in vivo and in vitro results

OBJECTIVE

To characterize the accuracy of the Magellan electromagnetic navigation system (Biosense Webster, Tirat HaCarmel, Israel) and to demonstrate the feasibility of its use in image-guided neurosurgical applications.

DESCRIPTION OF INSTRUMENTATION

The Magellan system was developed to provide real-time tracking of the distal tips of flexible catheters, steerable endoscopes, and other surgical instruments, using ultra-low electromagnetic fields and a novel miniature position sensor for image-correlated intraoperative navigation and mapping applications.

METHODS

An image registration procedure was performed, and static and qualitative accuracies were assessed in a series of phantom, animal, and human neurosurgical studies.

EXPERIENCE AND RESULTS

During the human study phase, an accuracy error of up to 5 mm was deemed acceptable. Results demonstrated that this degree of accuracy was maintained throughout all procedures. All anatomic landmarks were reached with precision and were accurately viewed on the display screen. Navigation that relied on the system was also successful. No interference with operating room equipment was noted. The accuracy of the system was maintained during regular surgical procedures, using standard surgical tools.

CONCLUSION

The system provides precise lesion localization without limiting the line of vision, the mobility of the surgeon, or the flexibility of instruments. Electromagnetic navigation promises new advances in neuronavigation and frameless stereotactic surgery.

[Technologic developments in radiotherapy and stereotactic radiosurgery]

We present a review of current technological progress enabling improvement in the quality of stereotactic irradiations: imaging fusion; individual adaptation of dosimetric planning to the shape of the target thanks to several collimation systems, spatial modulation of the beam with the use of multileaf microcollimators, beam intensity modulation, robotisation of the materials, owing to hardware and software developments.

Who says you can't treat pituitary carcinoma on a breast board?

A hospital-manufactured aquaplast head and neck immobilization system was constructed in tandem with a unique custom-built breast board. It was developed in conjunction with the breast board for patients unable to achieve and maintain the desired head flexion needed in the treatment of pituitary lesions. (This custom design provides an alternative to accomplishing this desired head angle needed to position the patient's eyes out of the treatment area, realizing that the lenses are situated in the anterior 1 cm of the globes.) By using the angled breast board, reproducibility of setup and patient comfort were addressed throughout the simulation, computed tomography planning and treatment process. The custom designed boards were constructed with available materials at relatively low cost to the department.

[FVR setting mode and the adjustment of SHIMADZU S/V 1250 X-ray machine]

The tube current of the x-ray machine is one of the essential factors that decide the quality of a photogram taken by the machine. FVR setting mode introduced in this article takes advantage of the computer technology to adjust the tube current and thus to improve the quality of the photograph.

[An integrated medical diagnostic X-ray unit controlled by microcomputer]

This article introduces an integrated medical diagnostic X-ray unit controlled by microcomputer. It is a practical and low-priced spot-film radiography device, and it is applicable to conventional local control unit. If you select a set of X-rayimage intensification, it can be remotely controlled. This device utilizes DC servo motor and fine precision feedback variable resistor and closed loop control so it has the advantage of fine static control and low mechanical noise. The whole radiographic process is automatically controlled by microcomputer, and can be operated easily.

Regulation of medical devices in radiology: current standards and future opportunities

Today's radiology community depends heavily on cutting-edge diagnostic and therapeutic medical devices to serve patients. These products are regulated by the U.S. Food and Drug Administration (FDA) under a system that grants marketing approval for only those indications for which the safety and effectiveness have been established. Although this complex system is the result of a societal decision to ensure device safety and effectiveness, it has the potential to delay product marketing and impede innovation. Medical device regulation recently has undergone major changes with the enactment of the Food and Drug Administration Modernization Act of 1997 (FDAMA), legislation that is intended to increase system efficiency while retaining the requirement of safety and effectiveness. However, many of the envisioned improvements cannot occur without cooperative interaction between stakeholders in the device development process, including the FDA and the clinical medicine community. The radiology field must continue to build on its strong history of productive dialogue with the FDA to transform the legislative vision of FDAMA into regulatory reality. Such action will ensure timely access to the new device technologies that are necessary for the growth of our specialty and the effective care of our patients.

Quality control of the automatic processor

An often ignored component of a radiology quality control program is daily sensitometric testing of automatic film processors. Sensitometric strip tests can reveal fluctuating chemical activity levels of developing solutions that can have a detrimental effect on developing films. By performing a daily sensitometric strip test before patient films are developed, time, cost, and patient radiation exposure are minimized, which reduces the number of retakes as a result of processing problems. Sensitometric strip tests also assist in quality control by making troubleshooting more specific.

Experimental determination of dose calibrator settings and study of associated volume dependence in v-vials for rhenium-186 perrhenate solution sources

OBJECTIVE

Accurate activity measurements of glass conical v-vials are only possible if dose calibrator dial settings are experimentally determined for the specific vial and volume range over which the measurements of a particular radionuclide is to be made. V-vials are used to transport and store unit doses of radiopharmaceuticals containing high-energy beta-emitters, such as 186Re. We have determined the correct dose calibrator dial settings for measuring 186Re in 3-mL glass conical v-vials from 2 manufacturers.

METHODS

The 186Re solutions used were calibrated for radioactivity content at the National Institute of Standards and Technology (NIST) using liquid scintillation counting with 3H-standard efficiency with a maximum expanded (k = 2) uncertainty of 1.2% on the activity. Volumes of the solutions then were accurately dispensed into a set of v-vials from each of the 2 manufacturers and assayed in the dose calibrator maintained at NIST.

RESULTS

For filling volumes above 1 mL, the dose calibrator response was found to be constant for both of the vials studied, enabling a single dial setting to be used for each vial type. The expanded uncertainties on the activity from uncertainty in the dial setting in that volume range were 0.4%-0.7%. Variability in vial construction contributed another 0.2%-0.3% in the uncertainty in the activity determination.

CONCLUSION

These studies indicate a strong volume dependence on the response of the dose calibrator and highlight the need for experimental verification of dose calibrator settings for nonstandard geometries.

Design of a dual CCD configuration to improve the signal-to-noise ratio

The noise of a digital charge coupled device (CCD) detector increases with the readout speed, causing problems in a number of important applications, such as x-ray fluoroscopy and micro-CT. In this paper, we present an approach for the design of a dual-CCD configuration to improve the average signal-to-noise ratio, and hence provide an inexpensive solution within the constraint of the current technology.

[A radiation method of determining the voltage of x-ray radiation generation. Its status and the outlook]

The paper reviews currently available methods for noninvasive determination of the voltage of X-ray radiation generation. It describes their advantages and disadvantages. The technical data of some commercially produced devices are presented. The paper shows it necessary to develop a standard for noninvasive X-ray tube voltage control and describes the main points of the standard presently developed in the framework of the International Electrical Committee 62C.

[Russian medical x-ray equipment enters the year 2000 with confidence]

The paper analyzes the state-of-the-art in medical X-ray engineering by the year 2000 by using the display units of the Moscow International Exhibition "Health-99". Particular emphasis is laid on small-dose digital fluorographic devices.

Dosimetry in mice exposed to 1.6 GHz microwaves in a carrousel irradiator

We have developed a carrousel irradiator for mice which delivers a head-first and near-field radiofrequency exposure that more closely simulates cellular telephone and radio use than conventional whole body exposure systems. Mouse cadavers were placed on the carrousel irradiator and exposed with their noses 5 mm from the feedpoint of a 1.6 GHz antenna. Local measured specific absorption rates (SAR) in brain regions corresponding to the frontal cortex, medial caudate putamen, and midhippocampal areas were 2.9, 2.4, and 2.2 W/kg per watt of irradiated power, respectively. In addition, average SAR was estimated to be 3.4 W/kg per watt along the sagittal plane of the brain, 2.0 W/kg per watt along the sagittal plane of the body, and between 6.8 and 8.1 W/kg per watt at peak locations along the sagittal plane at the body surface. This detailed SAR information in mice is critical to the interpretation of biological studies of IRIDIUM exposure, and similar analysis should be included for all studies of in vivo exposure of small animals to microwaves.

The radial transmission line as a broad-band shielded exposure system for microwave irradiation of large numbers of culture flasks

The problem of simultaneously exposing large numbers of culture flasks at nominally equivalent incident power densities and with good thermal control is considered, and the radial transmission line (RTL) is proposed as a solution. The electromagnetic design of this structure is discussed, and an extensively bench-tested realization is described. Referred to 1 W of net forward power, the following specific absorption rate (SAR) data were obtained: at 835.62 MHz, 16.0+/-2.5 mW/kg (mean+/-SD) with range (11-22); at 2450 MHz, 245+/-50 mW/kg with range (130-323). Radio-frequency interference from an RTL driven at roughly 100 W is so low as to be compatible with a cellular base station only 500 m distant. To avoid potential confounding by temperature differences among as many as 144 T-75 flasks distributed over 9 RTLs (six irradiates and three shams), temperature within all flasks was controlled to 37.0+/-0.3 degrees C. Experience with over two years of trouble-free operation suggests that the RTL offers a robust, logistically friendly, and environmentally satisfactory solution to the problem of large-scale in vitro experiments in bioelectromagnetics.

Design, construction, and validation of a large capacity rodent magnetic field exposure laboratory

A magnetic field exposure laboratory has been constructed to support National Toxicology Program studies for the evaluation of the toxicity and carcinogenicity of pure, linearly polarized, 60 Hz magnetic fields in rodents. This dual corridor, controlled access facility can support the simultaneous exposure of 1200 rats and 1200 mice. The facility contains fully redundant electrical and environmental control systems and was constructed using non-metallic materials to maintain low levels of background (ambient), stray, and cross-talk magnetic fields. The exposure module design provides for large uniform exposure volumes with good control of stray and cross-talk fields, while allowing the use of roll-around cage racks for simplified animal husbandry. Stray fields and cross-talk have been further reduced by the inclusion of "steering coils" in each exposure module. Ambient 60 Hz fields (less cross-talk) in all exposure rooms are <0.1 microT (1 mG), and static magnetic fields have been mapped extensively. Magnetic field strength, waveform, temperature, relative humidity, light intensity, noise level, vibration, and air flow in all animal holding areas are tightly regulated, and are monitored continuously during all studies. Field uniformity in the animal exposure volumes is better than -/+l0%; a systematic program of cage, rack, and room rotation controls for possible positional effects within the exposure system. Magnetic fields are turned on and off over multiple cycles to prevent the induction of transients associated with abrupt field level changes. Total harmonic distortion is <3% at all field strengths. The facility has been used to study magnetic field bioeffects in rodent model systems in experiments ranging in duration from 8 weeks to 2 years.

Food and Drug Administration low-level extremely-low-frequency magnetic field exposure facility

We describe the design, construction details, and performance characteristics of an exposure system designed to provide very well controlled extremely-low-frequency magnetic field exposures of in vitro samples. This system uses Helmholtz coils placed inside temperature-controlled mu-metal chambers to provide simultaneous ac and dc field exposures at any relative angle with minimal residual background field. The system has both exposed and sham-exposed chambers and is operated under computer control in such a way as to ensure blind exposure of samples.

Doppler sonography in breast pathology

Breast sonography has been a standard complementary procedure to mammography for more than 10 years. In recent years, a tremendous technological evolution has taken place both at the level of the equipment, electronics and software, and in probe technology. This has resulted in a substantial increase in image quality (contrast ans spatial resolution) and in Doppler sensitivity. The use of linear probes of at least 7 MHz is mandatory, and frequencies of over 10 MHz are becoming standard now. Sonography of the breast not only permits differentiation between solid and cystic lesion, but also gives additional morphological details which enable differentiation between benign and malignant lesions. US increases both sensitivity and specificity of the breast exam when combined with X-ray mammography. It is also the method of choice for guiding interventional procedures, such as hook wire placement, FNAC, or core biopsy. Doppler has been used since the seventies (continuous wave Doppler), but more recently the use of color Doppler has proven to be valuable in the study of the vascularity of breast lesions.

Is your technetium generator eluate sterile?

OBJECTIVE

This study was performed to assess the sterility of multidose 99mTc generator eluate vials at the end of a working day.

METHODS

Expired 99mTc generator eluate vials were collected over a period of 10 wk and stored until the activity reached background. Four batches of 10 vials each were selected randomly and sent to an independent microbiology laboratory for sterility testing.

RESULTS

No eluate showed any microbial growth after 14 d incubation in growth media.

CONCLUSION

Retrospective sterility testing of 99mTc generator eluate confirmed the validity of our departmental protocol for radiopharmaceutical preparation. Sterility testing has become part of our quality control program.

Simulated bone erosions in a hand phantom: detection with conventional screen-film technology versus cesium iodide-amorphous silicon flat-panel detector

PURPOSE

To assess the diagnostic performance of an active-matrix flat-panel x-ray detector for reduced-dose imaging of simulated arthritic lesions.

MATERIALS AND METHODS

A digital x-ray detector based on cesium iodide and amorphous silicon technology with a panel size of 43 x 43 cm, matrix of 3,000 x 3,000 pixels, pixel size of 143 micrometer, and digital output of 14 bits was used. State-of-the-art screen-film radiographs were compared with digital images obtained at doses equivalent to those obtained with system speeds of 400, 560, and 800. The phantom was composed of a human hand skeleton on an acrylic plate with drilled holes simulating bone erosions of different diameters and depths. Results of four independent observers were evaluated with receiver operating characteristic curve analysis.

RESULTS

The cesium iodide and amorphous silicon detector resulted in better diagnostic performance than did the screen-film combination, with the dose being the same for both modalities (P <.05). For digital images obtained at reduced doses, no significant differences were found.

CONCLUSION

The improved diagnostic performance with digital radiographs obtained with the cesium iodide and amorphous silicon detector suggests that this detector technology holds promise in terms of dose reduction for specific diagnostic tasks, without loss of diagnostic accuracy.

Recent advances in breast sonography

Breast sonography has come to maturity during the past decade. Recent and ongoing technological developments include higher-frequency wideband transducers, 2-D array phased-array technology, extended-field-of-view imaging, three-dimensional sonography, higher-sensitivity color and power Doppler imaging, contrast agents, and harmonic imaging. Applications of breast sonography have thus expanded, with more reliable tissue characterization and differentiation between benign and malignant diseases and improved staging of cancer patients. Sonography has become the guidance technique of choice not only for percutaneous needle biopsy but also for many other interventional procedures involving nonpalpable breast masses. In selected cases, sonography can even be used to biopsy or localize calcifications that can be clearly identified on sonography. A growing field of research is ultrasound-guided percutaneous ablation of breast lesions using cryotherapy or radiofrequency.

Extraoral and panoramic systems

Digital solutions for extraoral and panoramic radiology have been available for more than 15 years. The costs, however, have been too high for adoption in private dental practice. The past 2 years have seen tremendous growth in the number of relatively cost-effective digital options available to the dentist and dental specialist. Furthermore, computer speed and data storage capacities have progressed. This article presents an overview of systems available at present, and their enabling technologies and enhancement capabilities.

Intraoral detectors. CCD, CMOS, TFT, and other devices

The first real-time intraoral detectors were introduced in 1997. Since then, charge-coupled device sensors have dramatically improved. The spatial and gray-scale resolution has increased and the dimensions of the sensitive areas are now comparable to those of conventional film. More recently, complementary metal oxide semiconductors were introduced. This technology offers the potential of integration, manufacturability, and low costs. Digital radiographic technology has matured and clinicians should adopt the systems and invest the time and effort to master them.

Digital detectors in mammography. A technological overview

At a first glance the future of digital mammography seems very bright considering the wealth of offerings for new detectors, made by companies on the market or in journals. However technically spoken, digital mammography is one of the most demanding applications in the spectrum of radiology along with a high degree of cost consciousness in the mammography screening programs. The functional requirements are so high for digital mammography that only the best and most expensive components are good enough to compete with the current screen-film systems. Next difficulties are the lack of quality standards for digital detectors, not at all existing in the past and still under discussion, and the non-existence or changing of approval procedures. This is discouraging the industries to enter the field and is slowing down the phase-in time. After these obstacles are removed, there will come the discussions on acceptance of digital mammography within the professional community, due to the 'look' of the images and also the need to gain confidence with these images.

A theoretical design of a flattening filter to improve field uniformity of a superficial therapeutic X-ray beam

A Monte Carlo model has been developed using the MCNP code to aid the design of a flattening filter, to improve field uniformity of a superficial x-ray machine. The machine is operating at 90 kV and filtered with a 1.1 mm aluminium filter. In the theoretical simulation the original flat filter was replaced by a varying thickness filter to improve the uniformity across field sizes 20, 5 and 2 cm diameter as well as hardening the beam. Simulation results showed that flatness of the beam profile was improved for the 20 cm field size from +/- 7.3% to +/- 1.1% across the anode/cathode direction and from +/- 7.7% to +/- 3.2% in the anode/cathode direction. For the 5 cm field size the improvement was from +/- 4.6% to +/- 3.1% and from +/- 5.5% to +/- 3.4%, and for the 2 cm field size from +/- 3.1% to +/- 2.4% and from +/- 10.2% to +/- 9.5%, in the same directions, respectively. Beam quality simulations were made and the original half-value layer was reduced from 2.21 +/- 0.09 mm aluminium to 2.04 +/- 0.09 mm aluminium. The study demonstrated that it was possible to build a filter capable of flattening the beam profile for different sized applicators without significantly changing the penetrating ability of the beam.

Re-engineering the soft machine: the impact of developing technology and changing practice on diagnostic radiographer skill requirements

This paper describes research to investigate the extent to which new technology and changing work practices in diagnostic imaging have changed the skill requirements of working radiographers. Interviews were conducted with radiography managers, radiologists and industry representatives. While changes in technology were viewed as having a significant impact on skill requirements, levels of resourcing and both national and local policy were seen as key factors driving changes in work practice. Respondents believed that significant changes would be required to pre- and post-registration training requirements for radiographers in the light of changing practice.

A real-time flat-panel X-ray pixel imaging system for low-dose medical diagnostics and craniofacial applications

The aim of this study was to evaluate on-line performance of a real-time digital imaging system based on amorphous silicon technology and to compare it with conventional film-screen equipment. The digital detecting imager consists of (1) a converter, which transforms the energy of the incident X rays into light; (2) a real-time digital detecting system, capable of producing as many as 10 pictures per second using a large-area pixel matrix (20 x 20 cm2) based on solid-state amorphous silicon sensor technology with a pitch of 400 microns; and (3) appropriate computer tools for control, real-time image treatment, data representation, and off-line analysis. Different phantoms were used for qualitative comparison with the conventional film-screen technique, with images obtained with both systems at the normal dose (used as a reference), as well as with dose reduction by a factor of 10 to 100. Basic image quality parameters evaluated showed that the response of the detector is linear in a wide range of entrance air kerma; the dynamic range is higher compared with the conventional film-screen combination; the spatial resolution is 1.25 lp per millimeter, as expected from the pixel size; and good image quality is ensured at doses substantially lower than for the film-screen technique. The flat-panel X-ray imager based on amorphous silicon technology implemented in standard radiographic equipment permits acquisition of real-time images in radiology (as many as 10 images per second) of diagnostic quality with a marked reduction of dose (as much as 100 times) and better contrast compared with the standard film technique. Preliminary results obtained with a 100-micron pitch imager based on the same technology show better quality but a less substantial dose reduction. Applications in craniofacial surgery look promising.

High-fidelity electronic display of digital radiographs

A fully digital radiography system requires high-fidelity electronic display devices that preserve diagnostic quality. Current cathode-ray tube monitors do not meet desired performance criteria for displaying radiographs and have excessive size, weight, and power consumption. Recent developments in flat-panel display technology (in particular active-matrix liquid crystal displays, field-emission displays, and organic light-emitting displays) suggest that high-fidelity, lightweight displays will be available in the near future. Large-size active-matrix liquid crystal display devices have been demonstrated. High brightness can be easily achieved with bright back illumination. Further developments in optical design for monochrome displays should provide high fidelity and improve the angular dependence of the emitted light. Field-emission display devices have attractive emission distribution and potential for low veiling glare. This technology needs to be extended to a large area, and problems with cathode aging and nonuniformity have to be contemplated. Organic light-emitting displays represent a simple and potentially inexpensive display technology with the ability to achieve high image quality. However, extensive research and development is required to achieve large-area manufacturing methods.

The performance of a fluoroscopic electronic portal imaging device modified for portability

Advances in external beam therapy technology have made routine, efficient conformal therapy a reality. With it comes the increasing need for online treatment verification, which is only achievable at present through the use of electronic portal imaging devices (EPIDs). For a large radiotherapy centre, the provision of one EPID per treatment machine proves extremely expensive. This paper details modifications to the design of a commercial fluoroscopic EPID (the SRI-100) to produce a portable system, capable of providing quick, high quality imaging on more than one treatment machine. We describe the necessary hardware and software changes made to the system, as well as the variety of mechanical and quality control checks performed for testing the stability and quality of the imaging. The modified system has been found to be both electronically and mechanically robust, with associated image quality, scaling, distortion and movement similar to other EPIDs in the department. Although the modification was designed specifically to allow for the acquisition of images from multiple treatment machines, it may also enable the operation of the EPID for other uses such as total body irradiation (TBI) treatment verification and a further range of quality control procedures on the linear accelerator itself.

Effects of collimator size of a dental X-ray unit on image contrast

OBJECTIVES

To examine the effect of collimator size on image contrast in dental radiography.

METHODS

Two conventional collimators, one circular (53 mm in diameter) and one rectangular (35x45 mm2), were compared with a small rectangular collimator (26x39 mm2). Low-contrast and high-contrast resolution was assessed with the aid of contrast-detail and line-pair phantoms.

RESULTS

Shallower holes were observed with the small rectangular collimator. Two-thirds of 17 observers assessing high-contrast resolution considered the small collimator to result in a clearer image than the conventional collimators. The same effect was demonstrated with the line-pair phantom and by microdensitometry. With the small collimator the energy imparted is estimated to be reduced by 54 and 36% compared with the conventional circular and rectangular collimators respectively.

CONCLUSIONS

Decrease of the collimator size to fit the film size used for children will result in improved low-contrast and, under some conditions, improved high-contrast resolution. This improvement might have implications for caries diagnosis and monitoring.

[Slice sensitivity profile and image pixel noise of multi-slice spiral CT in comparison with single slice spiral CT]

PURPOSE

Presentation and evaluation of slice sensitivity profile and pixel noise of multi-slice CT in comparison to single-slice CT.

METHODS

Slice sensitivity profiles and pixel noise of a multi-slice CT equipped with a 2D matrix detector array and of a single-slice CT were evaluated in phantom studies.

RESULTS

For the single-slice CT the width of the slice sensitivity profiles increased with increasing pitch. In spite of a much higher table speed the slice sensitivity profiles of multi-slice CT were narrower and did not increase with higher pitch. Noise in single-slice CT was independent of pitch. For multi-slice CT noise increased with higher pitch and for the higher pitch decreased slightly with higher detector row collimation.

CONCLUSIONS

Multi-slice CT provides superior z-resolution and higher volume coverage speed. These qualities fulfill one of the prerequisites for improvement of 3D postprocessing.

Physical evaluation of a system for direct digital intra-oral radiography based on a charge-coupled device

OBJECTIVES

To determine technical properties of a direct digital intra-oral radiographic system, the Dixel(R) (J Morita Corporation, Kyoto, Japan).

METHODS

A dose response function and the dark current were calculated from two series of exposures to a homogeneous radiation field. The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of an edge. The noise power spectrum (NPS) was determined at three exposures from radiographs exposed to homogeneous radiation fields. Noise equivalent quanta (NEQ) were calculated from the one-dimensional NPS and the MTF. The detective quantum efficiency (DQE) was determined from the NEQ and a representative value of the photon fluence. Signal-to-noise ratios (SNR) were calculated from the NEQs and different signal contrasts.

RESULTS

The dose response function demonstrated a slight curvature. There was no effect of the dark current. NPS ranged from 10-5 - 10-7 mm2 depending on exposure and frequency. At a peak of about 2 cycles/mm the DQE is on an average about 30 per cent. SNRs are favorable.

CONCLUSION

The technical properties found in this study indicate that the Dixel(R) system is suitable for intra-oral dental radiography.

[Medical x-ray equipment on the threshold of the 21st century]

The authors, specialists in medical X-ray engineering, have been engaged in it for about 40 years, forecast that this medical engineering field will be under development and regard its development as transition to a qualitative new level prepared by latest technologies in X-ray apparatus making, digital television, and computed technology rather than an ultimate landmark of evolution.

[Development of the automatic dental X-ray film processor]

This paper introduces a multiple-point detecting technique of the density of dental X-ray films. With the infrared ray multiple-point detecting technique, a single-chip microcomputer control system is used to analyze the effectiveness of the film-developing in real time in order to achieve a good image. Based on the new technology, We designed the intelligent automatic dental X-ray film processing.

A comparison of image reject rates when using film, hard copy computed radiography and soft copy images on picture archiving and communication systems (PACS) workstations

A comparison has been made of the reject rates of plain images for three separate periods when film, computed radiography (CR) and PACS systems were in operation throughout the Hammersmith Hospital, London. There was a statistically significant reduction in the overall percentage reject rate across all examinations from 9.9% to 8.1% when the hospital changed from using a conventional film based system to a CR system. There was a further reduction in the reject rate to 7.3% when the hospital moved to a hospital-wide PACS system, but this change was not statistically significant. Using estimations of the total number of images used, the percentage reject rates were 6.6% for film, 5.5% for CR and 5.5% for PACS. Thus, if the radiation dose for each image is unchanged, and the same types of images are used for the examination of each body area, a move from conventional film imaging to phosphor plate imaging provides the potential to reduce the patient population dose.

The challenge of PACS in a small hospital

Memorial Hospital is located in-North Conway, New Hampshire. Year round, the 35-bed hospital serves mainly tourists and retirees to the area. The imaging department wanted to integrate its services within an existing community network, meet the needs of a transient population and resolve staff utilization and storage problems. Conversion from film to digital in the radiology department took advantage of digital x-ray and PACS. Since the hospital was already using digital technology for CT, MR, ultrasound and fluoroscopy, it made sense to include plain film imaging in the digitization process Memorial Hospital faced a number of challenges. Those in decision-making positions lacked a general knowledge about PACS, and, in particular, about PACS in similarly sized facilities. The hospital also lacked experience working with vendors. A timeline was critical as Memorial Hospital prepared for winter, its busiest season. The facility decided on a phased-in project with no immediate HIS/RIS interface, and computerized radiography with hard-copy films was implemented immediately. The facility has made the transition from a conventional imaging department to a PACS environment. It attributes its success to the way it involved those who would be affected by any future changes in the planning and decision-making processes. Memorial Hospital expects to expand its services and streamline its archival capabilities in the near future.