LITE-1 mediates behavioral responses to X-rays in Caenorhabditis elegans.

Rapid sensory detection of X-ray stimulation has been documented across a wide variety of species, but few studies have explored the underlying molecular mechanisms. Here we report the discovery of an acute behavioral avoidance response in wild type Caenorhabditis elegans to X-ray stimulation. The endogenous C. elegans UV-photoreceptor protein LITE-1 was found to mediate the locomotory avoidance response. Transgenic expression of LITE-1 in C. elegans muscle cells resulted in paralysis and egg ejection responses to X-ray stimulation, demonstrating that ectopic expression of LITE-1 can confer X-ray sensitivity to otherwise X-ray insensitive cells. This work represents the first demonstration of rapid X-ray based genetically targeted (X-genetic) manipulation of cellular electrical activity in intact behaving animals. Our findings suggest that LITE-1 has strong potential for use in this minimally invasive form of neuromodulation to transduce transcranial X-ray signals for precise manipulation of neural activity in mammals, bypassing the need for invasive surgical implants to deliver stimulation.

A suggested method for setting up GSI profiles on the GE Revolution CT scanner.

"GSI Assist" is the automatic exposure control (AEC) system for dual-energy acquisitions on the GE Revolution CT scanner. This paper describes the user options of GSI Assist, and describes the method developed at UAB Medical Center to simplify the use of GSI Assist without adversely affecting the AEC Operation.

High-ratio grid considerations in mobile chest radiography.

PURPOSE: Grids are often not used in mobile chest radiography, and when used, they have a low ratio and are often inaccurately aligned. Recently, a mobile radiography automatic grid alignment system (MRAGA) was developed that accurately and automatically aligns the focal spot with the grid. The objective of this study is to investigate high-ratio grid tradeoffs in mobile chest radiography at fixed patient dose when the focal spot lies on the focal axis of the grid. METHODS: The chest phantoms (medium and large) used in this study were modifications of the ANSI (American National Standards Institute) chest phantom and consisted of layers of Lucite™, aluminum, and air. For the large chest phantom, the amount of Lucite and aluminum was increased by 50% over the medium phantom. Further modifications included a mediastinum insert and the addition of contrast targets in the lung and mediastinum regions. Five high-ratio grids were evaluated and compared to the nongrid results at x-ray tube potentials of 80, 90, 100, and 110 kVp for both phantoms. The grids investigated were from two manufacturers: 12:1 and 15:1 aluminum interspace grids from one and 10:1, 13:1, and 15:1 fiber interspace grids from another. MRAGA was employed to align the focal spot with the grid. All exposures for a given kVp and phantom size were made using the same current-time product (CTP). The phantom images were acquired using computed radiography, and contrast-to-noise ratios (CNR) and CNR improvement factors (k(CNR)) were determined from the resultant images. The noise in the targets and the contrast between the targets and their backgrounds were calculated using a local detrending correction, and the CNR was calculated as the ratio of the target contrast to the background noise. k(CNR) was defined as the ratio of the CNR imaged with the grid divided by the CNR imaged without a grid. RESULTS: The CNR values obtained with a high-ratio grid were 4%-65% higher than those obtained without a grid at the same phantom dose. The improvement was greater for the large chest phantom than the medium chest phantom and greater for the mediastinum targets than for the lung targets. In general, the fiber interspace grids performed better than the aluminum interspace grids. In the lung, k(CNR) for both types of grids exhibited little dependence on kVp or grid ratio. In the mediastinum, k(CNR) decreased 4%-10% with increasing kVp, and varied up to 5.3% with grid ratio. CONCLUSIONS: When the focal spot is accurately aligned with the grid, the use of a high-ratio grid in mobile chest radiography improves image quality with no increase in dose to the phantom. For the grids studied, the performance of the fiber interspace grids was superior to the performance of the aluminum interspace grids, with the fiber interspace 13:1 grid producing the best overall results for the medium chest phantom and the fiber interspace 15:1 producing the best overall results for the large chest phantom.

Density measurements of dentin by dual-energy radiography.

OBJECTIVES: The aim of this study was to apply the dual-energy radiographic technique to teeth and to soft tissue simulated with Lucite and report the visual and quantitative results. STUDY DESIGN: High- and low-energy image pairs were exposed of aluminum and Lucite calibration wedges and human teeth sections. Reconstructed images of the calibration wedges and teeth sections were viewed and measured. RESULTS: The aluminum reconstruction images accentuated the aluminum wedge and the teeth, whereas the Lucite reconstruction images minimized them. Correlations between the nominal direct and dual-energy measurements of the wedges and teeth thicknesses were found to be very good. The root-mean-square deviation of the dual-energy reconstructions from the measured nominal thicknesses was found to be no greater than 0.6 mm. CONCLUSION: These results demonstrate the feasibility of using dual energy as a means of selective cancellation of unwanted tissues and the measurement of posterior tooth density.

An automatic and accurate x-ray tube focal spot/grid alignment system for mobile radiography: system description and alignment accuracy.

PURPOSE: A mobile radiography automatic grid alignment system (AGAS) has been developed by modifying a commercially available mobile unit. The objectives of this article are to describe the modifications and operation and to report on the accuracy with which the focal spot is aligned to the grid and the time required to achieve the alignment. METHODS: The modifications include an optical target arm attached to the grid tunnel, a video camera attached to the collimator, a motion control system with six degrees of freedom to position the collimator and x-ray tube, and a computer to control the system. The video camera and computer determine the grid position, and then the motion control system drives the x-ray focal spot to the center of the grid focal axis. The accuracy of the alignment of the focal spot with the grid and the time required to achieve alignment were measured both in laboratory tests and in clinical use. RESULTS: For a typical exam, the modified unit automatically aligns the focal spot with the grid in less than 10 s, with an accuracy of better than 4 mm. The results of the speed and accuracy tests in clinical use were similar to the results in laboratory tests. Comparison patient chest images are presented--one obtained with a standard mobile radiographic unit without a grid and the other obtained with the modified unit and a 15:1 grid. The 15:1 grid images demonstrate a marked improvement in image quality compared to the nongrid images with no increase in patient dose. CONCLUSIONS: The mobile radiography AGAS produces images of significantly improved quality compared to nongrid images with alignment times of less than 10 s and no increase in patient dose.

Grid line artifact formation: A comprehensive theory.

Linear focused grids are commonly used in general radiography and mammography to control scatter. In these applications, if lines would be visible when the grid was stationary, then the grid is moved during the x-ray exposure to blur out grid lines. Presented is a theoretical framework for estimating grid line artifact magnitude and evaluating artifact suppression techniques. The framework takes as parameters the grid pitch, septum thickness, and exposure time, and allows for a variation in grid velocity and in x-ray tube output during the exposure. Grid line artifacts are evaluated for a variety of conditions. These include a stationary grid, a grid moving at a constant velocity with no kV ripple, a grid moving at a constant velocity with large kV ripple, and a grid moving with decreasing velocity and no kV ripple. Also evaluated are grid line artifacts for a novel suppression technique in which the grid moves at a constant velocity and the x-ray exposure waveform is "feathered," i.e., when the x-ray exposure waveform has a soft start and stop. Of practical interest is that it is possible to effectively eliminate grid line artifacts when the grid moves only a short distance with an appropriately "feathered" exposure waveform. This capability permits one to design efficient and compact coarse strip density grid systems.

A novel technique to suppress grid line artifacts.

It has been established that coarse strip density, air-interspace grid systems can suppress scatter in general radiography and in mammography more effectively than conventional high strip density grids. However, such systems have never gained clinical acceptance due to the large distance the grid needs to move to suppress gridline artifacts and due to their corresponding bulk. We present a novel technique for suppressing grid lines using an x-ray exposure wave form with a soft start and soft stop. The wave form is achieved by varying the x-ray tube current during the exposure. We derive the conditions that the time dependence of the x-ray exposure output needs to meet to suppress gridline artifacts with only a modest grid movement. The technique allows for the design of compact coarse strip density grid systems. We present experimental results that demonstrate the feasibility of the technique.