A novel method is proposed for the measurement of signal-to-noise ratio (SNR) for the purpose of quality assurance (QA) in MRI. A boxcar filtering technique is applied which allows estimation of signal and noise from a single image. The method has been used to estimate SNR in a large set of images acquired in a consistent manner using various scanner models, coils and phantoms. Performance is evaluated by comparison with the double-image subtraction technique incorporating temporal instability correction. The limits of agreement between the techniques are comparable to typical variability in daily SNR, and significantly superior to the performance of other single-image methods published to date. Single-image methods are preferable as they halve the image acquisition time of the recommended double-image approach. Major inaccuracies are identified in methods of SNR measurement currently used for QA in MRI.

Background Radiation induced pulmonary fibrosis is a devastating side effect of radiation therapy of intra-thoracic malignancies; however there is currently no effective pharmacologic agent for its prevention. Since oxidative stress is implicated in the pathogenesis of lung fibrosis we hypothesized that augmenting the lung antioxidant defense by increasing dietary selenium intake prior to and following thoracic radiation in mice would ameliorate fibrosis. Selenium (Se) is a micronutrient, present in protective antioxidant selenoenzymes such as glutathione peroxidase (GPx). Methods We evaluated a 10-fold supplemented Se diet (10X) as compared to a Se adequate (1X) and Se deficient (0X) diet (1.8 and 0.18 vs. 0.00 ppm Se, respectively) with respect to fibrosis and survival by 4 months post a single fraction 13.5 Gy thoracic X-ray treatment (XRT). Mice (n=15 per group) were fed the respective diets at least 4 weeks prior to XRT to ensure augmented lung activity levels of GPx. Fibrosis was evaluated by lung hydroxyproline (OH-Pro) and histology. Results OH-Pro content of irradiated mouse lungs (μg/g lung) decreased significantly in the 10X-Se group (89±2) and the 1X (113±4) as compared to the 0X (171±12). In addition, survival was significantly higher in the 10X irradiated group (80%) as compared to the 1X (66.7%) and the 0X (0%) group. Conclusion Selenium-enriched diets may have a protective effect on the development of radiation fibrosis. Funded by: AICR and U. Penn Research Foundation (MCS)

Background Flaxseed, a nutritional supplement, has high contents of omega-3 fatty acids and lignans with known anti-inflammatory and anti-oxidant properties. Its use in acute lung disease has never been evaluated. In this study we tested flaxseed (FS) diets in three experimental murine models of acute lung injury (ALI). Methods Mice were fed 10% FS for several weeks to determine kinetics of lignan accumulation in blood using liquid chromatography tandem mass spectrometry. Mice fed control and 10% FS diets were challenged by Hyperoxia (80% O2), intratracheal (i.t.) LPS or acid aspiration (AA). Bronchoalveolar lavage (BAL) was evaluated for white blood cells (WBC), neutrophils (PMN), and proteins 24 hours post i.t. challenge of acid or LPS or 6 days after hyperoxia. Lung lipid peroxidation was determined by malondialdehyde (MDA) tissue levels. Results Plasma FS lignans, enterodiol and enterolactone, peaked in the first week and decreased to steady state by 2–3 weeks. Following hyperoxia, FS mice showed a significant decrease in BAL proteins, a measure of lung edema, and a trend with AA while lung inflammation and MDA levels were significantly decreased in both models. In strong contrast, LPS injury and inflammation was not ameliorated by FS. Remarkably, serum lignan levels decreased dramatically in both AA and hyperoxic mice but not in LPS mice. Conclusion Dietary FS is protective against experimental ALI, inflammation and lung lipid peroxidation in vivo. Funded by: AICR (MCS), NIH-HL64063 (YA), U. Penn Research Foundation (MCS, YA).

Computed Radiography image acquisition, processing and analysis techniques have been developed to allow extraction of objective and quantitative measures of bone thickness and morphology from serially acquired images in patients treated for diaphyseal tibia fractures using either intramedullary nails or Ilizarov frames. Monte Carlo techniques have been used to simulate the imaging process and to allow the development and testing of scatter removal algorithms followed by decomposition of the image into bone only and soft tissue only images. Fracture gap and periosteal callus bone thickness have been determined for both treatment regimes at a number of time points post surgery and display changes consistent with the regeneration and remodelling of bone. A novel parameter, based upon image fractal dimension, has been developed and used to characterize morphological aspects of the fracture gap with changes observed being consistent with an increased uniform distribution of bone in the fracture gap.

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.

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.

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.

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.

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.

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.

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.

During 1990 The UK Department of Health installed two Photostimulable Phosphor Computed Radiography (PPCR) systems in the General Infirmary at Leeds with a view to evaluating the clinical and physical performance of the technology prior to its introduction into the NHS. An issue that came to light from the outset of the projects was the radiologists reservations about the influence of the standard PPCR computerized image processing on image quality and diagnostic performance. An investigation was set up by FAXIL to develop an algorithm to produce single format high quality PPCR images that would be easy to implement and allay the concerns of radiologists.