Flat-panel digital radiology with amorphous selenium and active-matrix readout

The influence of respiratory activity of the abdominal muscles on their reaction time in a postural task was evaluated. The electromyographic (EMG) onsets of the abdominal muscles and deltoid were evaluated in response to shoulder flexion initiated by a visual stimulus occurring at random throughout the respiratory cycle. Increased activity of the abdominal muscles was produced by inspiratory loading, forced expiration below functional residual capacity, and a static glottis-closed expulsive maneuver. During quiet breathing, the latency between activation of the abdominal muscles and deltoid was not influenced by the respiratory cycle. When respiratory activity of the abdominal muscles increased, the EMG onset of transversus abdominis and internal oblique, relative to deltoid, was significantly earlier for movements beginning in expiration, compared with inspiration [by 97-107 ms (P < 0.01) and 64-90 ms (P < 0.01), respectively]. However, the onset of transversus abdominis EMG was delayed by 31-54 ms (P < 0.01) when movement was performed during a static expulsive effort, compared with quiet respiration. Thus changes occur in early anticipatory contraction of transversus abdominis during respiratory tasks but they cannot be explained simply by existing activation of the motoneuron pool.     

X-ray imaging using amorphous selenium: determination of Swank factor by pulse height spectroscopy

The use of photoconductors, especially amorphous selenium (a-Se), in x-ray imaging is currently of interest. A critical performance parameter of an imaging detector is the Swank factor for degradation of the signal to noise ratio, or DQE(0), due to variations in the detector response. The Swank factor is evaluated from measured pulse height spectra generated by the absorption of monoenergetic x-ray photons. The spectra show an additional width over previous theoretical expectations, but the Swank factor is still close to the high values previously predicted theoretically.     

X-ray quantum limited portal imaging using amorphous silicon flat-panel arrays

We have measured the linearity, spatial resolution (MTF), noise (NPS), and signal-to-noise characteristics (DQE) of an electronic portal imaging device (EPID) based on an amorphous silicon flat-panel array. The array has a 128 x 128-pixel matrix and each pixel is 0.75 x 0.75 mm2 in dimension so the array covers an area of 96 x 96 mm2. The array acts like a large area light sensor and records the optical signals generated in a metal plate/phosphor screen x-ray detector when the detector is irradiated by a megavoltage x-ray beam. In addition, approximately 0.5% of the total signal is generated by nonoptical processes. The noise measurements show that the device is quantum noise limited with the noise power generated by the x-ray quanta being up to 100 times greater than the noise added by the external readout electronics and flat-panel light sensor itself. However, the flat-panel light sensor does reduce the spatial resolution (compared to a perfect optical sensor with infinitesimal pixel size) because of its moderate pixel size and because optical spread can occur in the transparent glues used to attach the phosphor screen to the flat-panel light sensor. The response of the sensor is very linear and does not suffer from the glare phenomenon associated with TV camera-based EPIDs--characteristics which suggest that the amorphous silicon EPID will be well suited to transit dosimetry. Nevertheless, some limitations need to be overcome before these devices can be used clinically. These include developing larger flat-panel light sensors, the elimination of "noisy" pixels with high dark signal, and improvements in the uniform sensitivity of the sensors. This last requirement is only needed for transit dosimetry applications where it would greatly simplify calibration of the device. In addition, an image acquisition scheme must be developed to eliminate artifacts created by the pulsed x-ray beam generated by linear accelerators. Despite these limitations, our studies suggest that the amorphous silicon EPIDs are very well suited to portal imaging.     

Technical report: Initial experiences with an experimental solid-state universal digital X-ray image detector

This paper presents a brief technical evaluation and first review of clinical experiences with an experimental direct digital X-ray image detector designed to support both dynamic and snap-shot imaging. Derivatives of this type of image detector can potentially fulfil the majority of the fluoroscopic and radiographic imaging requirements of clinical radiology departments, and initial results suggest that imaging systems using the new technology will provide a high quality dose-efficient solution to the search for a universal digital X-ray image detector.     

Sensitivity of amorphous selenium to x rays from 40 kVp to 18 MV: measurements and implications for portal imaging

Recently, the clinical application of electronic portal imaging devices has enabled more frequent verification of patient setup for radiation treatment. However, the image quality has sometimes proven to be inadequate, motivating the investigation of alternative sensors with better image quality. Amorphous selenium (a-Se) is potentially one such sensor since the electrostatic image formation process has high resolution. To fully evaluate the potential of a-Se for portal imaging, it is necessary to investigate all the imaging properties at high x-ray energies. Here, measurements of the sensitivity of a-Se to incident x-ray spectra ranging in energy from 40 kVp to 18 MV and for a-Se thicknesses ranging from approximately 10 to 300 microns under full buildup conditions are described. When x rays or energetic electrons deposit energy in a photoconductor with an applied electric field, F, electrons and holes are released. The x-ray conversion sensitivity may be defined as 1/W +/-, where W +/- is the energy required to release an electron-hole pair. Consistent with the results of previous investigators, W +/- is found to vary approximately with F-2/3. Unexpectedly, over the energy range of 40 kVp to 18 MV, W +/- was found to decrease by a factor of nearly 3. These dependencies are compared to the predictions of two competing charge recombination models, geminate and columnar. The results are explained by a microdosimetric model in which the sensitivity at megavoltage energies is governed by geminate recombination, but at lower energies, both mechanisms are involved. Thus, the sensitivity of a-Se to x rays spanning the diagnostic and radiotherapy range has been measured and the physical basis for this behavior established.     

Validation of procedures for quantitative whole-body autoradiography using digital imaging

The objective of this study was to demonstrate that tissue concentrations of radioactivity derived by digital analysis of autoradiograms were comparable to values derived from direct sampling and analysis of tissues. In addition, we describe the preparation and calibration of standards for use in quantitative whole-body autoradiography. For this study, three male Long-Evans hooded rats were administered 14C radioactivity intravenously. The animals were sectioned for whole-body autoradiography, with concomitant sampling of blood and 16 selected tissues. After 3 weeks of film exposure, the optical densities of the resulting autoradiograms were analyzed with a RAS3000 digital imaging system to estimate tissue concentrations of radioactivity. These concentrations were then compared with those obtained by direct analysis of the tissue samples. The concentrations derived from digital analysis of the autoradiograms were very highly correlated with those determined from direct tissue analysis (r = 0.956). Linear regression analysis yielded a straight line with a slope of 0.97 and a goodness of fit (r2) of 0.913. This analysis suggested that there is an approximate 1:1 correlation between concentration values determined by the two methods. Marked differences between the values derived via the two techniques were observed for only three tissues. However, this subset of the data accounted for only 6% of the total data, and the differences were probably due to contamination from adjacent tissues during excision. Overall, the concentrations of radioactivity derived from digital analysis of the autoradiograms were comparable to those derived from direct analysis of tissue samples. The results indicated that the digital analysis procedure for film can serve as a valuable adjunct to conventional tissue analysis for radioactivity.     

Experience in using at a polyclinic the Siberia low-dose digital X-ray unit

Application interactive CLASS software for stimulating productive binocular cooperation based on random-dot patterns and stereograms was used for treating strabismus and amblyopia in 105 children during a standard course of treatment. The children were divided into 3 groups treated by the CLASS alone (1), Class + two other application programs (2), and CLASS + traditional methods. General positive changes (improvement of visual acuity, decrease of eye deviation, etc.) were similar in these 3 groups. Positive effect of CLASS exercises on binocular visual mechanisms was significant. Due to precise evaluation of binocular interaction provided by CLASS, positive changes in binocular cooperation and stereovision were attained in 93% of children.     

Preliminary experimental evaluation of an inverse source imaging procedure using a decoupled coil detector array in magnetic resonance imaging

Results of treatment for 104 forearm shaft fractures in 70 patients have been presented. In all cases included in this study an open reduction of the fracture was followed by AO plate stabilization. Functional and radiological assessment was carried out according to the criteria of Anderson et al. Excellent and good functional results were achieved in 48 cases, fair in 10 and poor in 12 cases. The ulna united in 75%, the radius in 78% (delayed union included). Cross- union occurred in three patients, one case of destabilization at fracture site was observed, no infection has been noted. AO plate osteosynthesis proved to be still valuable mode of treatment for forearm shaft fracture.     

Functional radiology of the liver: magnetic resonance imaging

Magnetic Resonance (MR) images sensitive to the flowing blood are defined as images of MR angiography. Proton movement within a magnetic field modifies both the intensity and the phase of Nuclear Magnetic Resonance (NMR) signal; two techniques of MR angiography are thus distinguished: (TOF) the "time of flight" (intensity) and the "phase-contrast" (phase) technique. In the time of flight MR angiography the blood may appear as hypointense or hyperintense compared to stationary tissues. Blood hypointensity in vessels is due to the flow void phenomenon while hyperintensity is due to the phenomenon of flow-related enhancement. In phase contrast MR angiography, protons moving within a magnetic field modify their phase directly proportional to the displacement velocity and gradient intensity. Moreover, MRI allows noninvasive measurement of blood flow. Flow velocity is measured with TOF sequences or phase-contrast sequences. In TOF sequences quantitative measurement is performed with the bolus tracking procedure. In contrast-phase sequences the velocity is measured based on the extent of signal phase modification induced by the proton displacement velocity. The recent use of liver-specific contrast media supplies information on parenchymal liver function.     

Interpretation of chemically created periapical lesions using direct digital imaging

Perchloric acid (70%) was used to create simulated periapical lesions in tooth sockets of 15 dentate cadaver jaw specimens. Using the Trophy USA direct digital radiographic system, linear images were captured at selected time intervals after initial acid application and altered by contrast reversal, pseudocolor enhancement, and two forms of histogram equalization. The 525 total images were randomized for display on a computer monitor for evaluation by five endodontists. Images were evaluated twice by each rater, with viewings 1 to 2 wk apart. Statistical analysis determined interrater variability, intrarater reproducibility, and the relative merits of each enhancement technique. At 8, 12, 16, and 24 h after acid application, both techniques of histogram equalization yielded a statistically significant improvement over reverse contrast in perception of periapical patholais. Linear and pseudocolor-enhanced images were also significantly more diagnostic than reverse contrast at 12, 16, and 24 h. Intrarater reproducibility showed moderate agreement, but analysis showed only a fair level of interrater agreement.     

Analysis of pathological vocal fold vibrations using high-speed digital imaging

There have been various methods devised to monitor vocal fold vibration. Stroboscopy provides clinically-celevant information concerning pathology of the vocal folds. However, slow motion observation is based on the regularity of the vibration, and this ignores the role of irregularity of the vocal fold vibration in pathological cases. In order to know more about the nature of the vocal fold vibratory pattern, it is essential to monitor the vibration on a cycle by cycle basis. We analysed vocal fold vibrations of 22 pathological larynges using a computer-assisted high-speed digital imaging technique. Observed items included symmetry, regularity, phase difference, glottal closure, amplitude, mucosal wave and periodicity difference. Vibratory patterns were classified by location of lesion, severity of disease, expiratory pressure and laryngeal modulation. Analyses of pathological vocal fold vibrations using high-speed digital imaging techniques are providing the theoretical support for voice therapy and elucidating the causes of hoarseness.     

Web-based digital radiology teaching file: facilitating case input at time of interpretation

OBJECTIVE: Our goal was to develop a software system that allows easy and rapid input of digital radiology images and text reports, at the time of interpretation, into an easily searchable electronic teaching file database using the Internet and the World-Wide Web protocols, servers, and browsers. CONCLUSION: Using the Internet, the World-Wide Web, and our software system, we can rapidly input digital radiology images and associated text reports into an easily searchable database accessed by privileged users. This inexpensive and simple method for building a digital teaching file database allows cross-platform access for users who have a Web browser.     

Creating and curating a pediatric radiology digital library to make the internet a useful reference tool for the radiologist

BACKGROUND AND OBJECTIVE: The endothelial cell count after phacoemulsification serves as a sensitive indicator for the level of corneal damage caused by different phacoemulsification techniques. PATIENTS AND METHODS: In a prospective and randomized study, the "Reversed Tip and Snip" technique and the "Divide and Conquer" technique were performed in groups of 30 patients each. The corneal endothelial cell count was measured preoperatively as well as 4 weeks and 3 months postoperatively. RESULTS: The endothelial cell count showed significant (P < .001) reduction by approximately 10% after the "Reversed Tip and Snip" technique and by approximately 15% (P < .001) after the "Divide and Conquer" technique. The latter produced a significantly (P < .001) greater cell loss. CONCLUSIONS: The "Reversed Tip and Snip" phacoemulsification technique produces less endothelial cell loss than the "Divide and Conquer" technique.     

X-ray digital subtraction angiography to magnetic resonance-digital subtraction angiography using three-dimensional TRICKS. Historical perspective and computer simulations: a review

Seventeen years after the introduction of x-ray digital subtraction angiography (DSA), gadolinium-enhanced magnetic resonance (MR) angiography techniques have become available for the performance of MR-DSA. For the purposes of this article, we will consider this to include two-dimensional and three-dimensional approaches using time-resolved and non-time-resolved applications. Magnetic resonance-DSA is one in a historical progression of techniques which have aimed to produce less invasive forms of angiography. After outlining some historical milestones, several current issues regarding current methods for MR-DSA are discussed.     

Monte Carlo study of grid performance in diagnostic radiology: task dependent optimization for screen-film imaging

An optimization of anti-scatter grid design using Monte Carlo techniques in diagnostic radiology is presented. The criterion for optimization was to find the combinations of the grid parameters (lead strip width, grid ratio and strip density) and tube potential which result in the lowest mean absorbed dose in the patient at fixed image contrast. The optimization was performed in three irradiation geometries, representing different scattering conditions (paediatric examinations, and two adult lumbar spine examinations) and was restricted to grids using fibre materials in covers and interspaces. Grid designs currently available were studied, as were designs which use thinner strips (< 30 microns) and higher grid ratios (> 18). It was found that grids with widely different strip densities (strips cm-1) and grid ratios can have good performance provided that they are used with appropriate strip width and tube potential. With increasing amounts of scatter, the optimal grid requires thicker strips and higher grid ratios. Increasing the strip density and using thinner strips and higher grid ratios are generally required. Grids with low strip density (25 strips cm-1) were found to be less sensitive to alterations in strip width. Optimal grids for paediatric radiology require thinner strips (10-20 microns) than those in currently available grids. Grids on the market are best suited for examinations of the adult body in anteroposterior (AP) view. In the adult lateral view, representing the largest scattering volume, higher grid ratios (> 18) than those in existing grids would be optimal. Examples of good grid designs are given for each examination.     

Rapid monitoring of virus-like particles using an optical biosensor: a feasibility study

The mature major microneme protein of Sarcocystis muris cyst merozoites, which is known as a dimeric lectin with high affinity to galactose and some of its derivatives, was expressed in Escherichia colias a histidine-tagged fusion protein. The recombinant polypeptide, which was recognized by a monoclonal antibody directed against the native lectin, was purified from inclusion bodies after solubilization and refolding, using a combination of metal chelate and lactose affinity chromatography. The apparent molecular mass of the refolded polypeptide as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoreses was 16 kDa, whereas gel filtration chromatography clearly demonstrated that the recombinant protein, like its native counterpart, exists as a homodimer of two non-covalently associated subunits. Inhibition of haemagglutination suggests that the combining site of the recombinant lectin recognizes N-acetyl-galactosamine as the dominant sugar, thus confirming the correct folding of the monosaccharide combining site in the renatured lectin. To the best of our knowledge, this work represents the first reported detailed characterization of a recombinant lectin from apicomplexan parasites, and may contribute to a better understanding of the process of host cell recognition and invasion by these obligate intracellular protozoa.