Effect of tungsten absorption edge filter on diagnostic x-ray spectra, image quality and absorbed dose to the patient

Dose Reduction and Image Quality Optimization of Pediatric Chest Radiography Using a Tungsten Filter

The use of diagnostic radiology in pediatric patients has increased, and various positive effects have been reported, including methods to reduce radiation doses in children. Research has been conducted to preserve image quality while reducing exposure and doses in pediatric patients. This study aimed to measure four different filters to identify an optimized filter for pediatric patients. The experiment was conducted using four types of filters, including aluminum, copper, molybdenum, and tungsten. The optimal filter thickness was verified using a histogram to visually evaluate the spectrum by filter thickness, effective dose on a pediatric phantom, entrance skin dose, organ absorbed dose using the PC-based Monte Carlo (PCXMC) program version 2.0 simulation, figure of merit (FOM), and image quality. As a result of measuring the spectrum according to the tube voltage and the four types of filters, dose reduction and contrast improvement effects were obtained with a 0.05 mm tungsten filter. Additionally, effective entrance skin and organ absorbed dose decreased with the said filter. The aluminum, copper, and molybdenum filters demonstrated that the effective dose scarcely decreased even when the thickness was increased; meanwhile, the effective dose decreased when the tungsten filter was 0.05 mm. The FOM with a 0.05 mm tungsten increased by 91% in the lung field and 39% in the mediastinal field. The entrance skin and organ absorbed dose in pediatric patients can be reduced by removing low-energy photons that fail in image formation using a tungsten filter.

C-SPECT - a Clinical Cardiac SPECT/Tct Platform: Design Concepts and Performance Potential

Because of scarcity of photons emitted from the heart, clinical cardiac SPECT imaging is mainly limited by photon statistics. The sub-optimal detection efficiency of current SPECT systems not only limits the quality of clinical cardiac SPECT imaging but also makes more advanced potential applications difficult to be realized. We propose a high-performance system platform - C-SPECT, which has its sampling geometry optimized for detection of emitted photons in quality and quantity. The C-SPECT has a stationary C-shaped gantry that surrounds the left-front side of a patient's thorax. The stationary C-shaped collimator and detector systems in the gantry provide effective and efficient detection and sampling of photon emission. For cardiac imaging, the C-SPECT platform could achieve 2 to 4 times the system geometric efficiency of conventional SPECT systems at the same sampling resolution. This platform also includes an integrated transmission CT for attenuation correction. The ability of C-SPECT systems to perform sequential high-quality emission and transmission imaging could bring cost-effective high-performance to clinical imaging. In addition, a C-SPECT system could provide high detection efficiency to accommodate fast acquisition rate for gated and dynamic cardiac imaging. This paper describes the design concepts and performance potential of C-SPECT, and illustrates how these concepts can be implemented in a basic system.

Computed tomography with monochromatic bremsstrahlung radiation

The use of filters with appropriate thickness of different elements produces a method to quasi-monochromatize X-ray beams. In the present study the filters were produced in a boric acid matrix, using the elements Mo, Sb, Cs, Ce and Gd. The thickness of the filters varied from 50 to 300 microm for a high voltage tube operating from 30 to 70 kVp. The parameters analyzed were the beam resolution, measured by its FWHM as a function of filter thickness, and the reduction of beam intensity. The results show a comparison between conventional tomographies obtained with different filters and application in the technique of differential tomography, with double energy for identification of elements such as Zr, Nd, Ba and Sm.

Effective dose in diagnostic radiology as a function of x-ray beam filtration for a constant exit dose and constant film density

Individual organ absorbed dose and total effective dose for nine common radiographic projections were investigated as a function of half-value-layer, HVL, and total equivalent filtration for the following cases: (1) with the patient exit dose held constant and (2) with the film density held constant. As expected, the absorbed dose to organs proximal to the x-ray beam entry point tracked with skin dose as a function of HVL, whereas organ dose distal to the x-ray beam entry point was almost independent of HVL. Dose to organs near mid-line showed an intermediate HVL dependence. For the nine radiographic projections, increasing the total filtration from 1.5 to 4.0 mm Al while holding the kVp fixed resulted in mean decreases in the effective dose of 17% for the case of a constant exit dose, and 25% for a constant film density with a "400 speed" rare-earth screen-film system. The decreases in the mean skin entrance doses were 38% and 45%, respectively. With the screen-film system, the average effective dose decreased at 16% per mm of added Al between 1.5 and 2.5 mm Al total filtration, and at 7% per mm between 2.5 and 4.0 mm. These results partially support the NCRP Report No. 102 recommendation that the minimum filtration be 2.5 mm Al for general diagnostic x-ray tubes. They also suggest, using the linear no-threshold radiation risk model, that further significant reductions in stochastic risk to the U.S. population can be achieved by raising the minimum beyond 2.5 mm. Experience over a 12 year period in our tertiary care teaching hospital indicates that adding 1-1.5 mm Al filtration beyond the 2.5 mm minimum does not pose a problem in terms of additional tube loading or reduction in image quality. However, these issues need to be more formally addressed.

Radiation dose reduction in diagnostic x-ray procedures

The performance of K-edge filters to modify the x-ray spectrum is investigated experimentally in a variety of clinical situations involving bone/soft tissue imaging, with the aim of improving the optimization between image contrast and patient exposure. The results show that simultaneous improvement of contrast and reduction of exposure is possible for a wide range of patient sizes. For conditions of fixed contrast skin exposure reductions of better than 50% and integrated dose reductions of up to 30% have been achieved with tolerable increases in tube load. Rare earth salt solutions were used as an inexpensive alternative source of K-edge filtration, and their performance was found to be in no way inferior to that of expensive metal foils.

Clinical evaluation of a samarium/aluminum compound filter

Rare earth compound filters, which offer reduced patient exposure during intraoral radiography, have not been clinically evaluated for their effect on diagnostic yield. This clinical study was conducted to compare the diagnostic yield of bitewing radiographs exposed with a conventional aluminum filter with matched bitewing radiographs exposed with a samarium/aluminum compound filter. One hundred sixty-three pairs of bitewing radiographs were read independently by two reviewers for absence or presence and depth of proximal carious lesions. Degree of agreement between films was assessed by means of the kappa statistic. Results showed good agreement between the radiographs exposed with each filter type. Thus, x-ray machines modified with a samarium/aluminum rare earth compound filter produce bitewing radiographs of comparable diagnostic yield and lower dose when compared with radiographs exposed with a conventional aluminum filter.

Rare earth filters for intraoral radiography: exposure reduction as a function of kV(p) with comparisons of image quality

Radiographs of phantoms were produced using E-speed film and various rare earth X-ray beam filters. The rare earth filters considerably reduced the amount of radiation needed to produce diagnostic quality images and, in many cases, improved image quality. These filters can be implemented easily and inexpensively in a clinical setting, resulting in radiation exposure reductions of up to 71%.

Spectroscopic analysis and dosimetry of diagnostic x-ray beams filtered by rare earth materials

A laboratory investigation was carried out to assess the effect of various types of rare earth filter materials on the energy spectrum and concomitant reduced exposure values of diagnostic x-ray beams at 70, 80, and 90 kVp. An x-ray spectroscope was constructed and used to generate the energy spectra of beams passing through the various rare earth filter materials. Photographs were made of each spectrum, and live-time gross photon counts were recorded. Following spectral determinations, ionization chamber readings were generated for each filter material. Substantial effects on x-ray spectra and reduction of exposure values were noted. The degree of these effects were dependent on the atomic number, k-edge, and thickness of each filter. Metallic forms of rare earth materials proved to be more effective than the salt forms with erbium offering the greatest potential for reduction in exposures over the range of experimental kilovolt (peak) values.

Filter materials for dose reduction in screen-film radiography

A computer program was developed to calculate both integral absorbed dose in a water phantom and entrance exposure, for the imaging of iodine contrast with x-ray intensifying screens. The effect of filtration of the x-ray beam on integral absorbed dose and entrance exposure was studied for 27 different filter materials and four types of intensifying screens. The dose and exposure were calculated, keeping the image contrast and energy absorption in the screens constant. To check the validity of the calculations, a number of measurements were performed, the results of which agreed well with our calculations. A remarkable result is that dose and exposure reduction can be achieved almost equally well with conventional filters (aluminum and copper) as with a number of K-edge filters. This was found for situations commonly encountered in diagnostic radiology (60-80 kV, 20 cm water). This finding is in contrast to a number of earlier studies, in which K-edge filters were found to be superior to conventional filters.