Higher Tube Voltage Research Articles

Experimental determination of detector gain, zero frequency detective quantum efficiency, and spectral compatibility of phosphor screens: comparison of CsI : Na and Gd 2O 2S : Tb for medical imaging applications

Gd 2O 2S : Tb and CsI : Na phosphors mostly used in X-ray medical imaging detectors were compared at various X-ray tube voltages between 50 and 150 kVp. Laboratory prepared test screens of 80, 110, and 150 mg/cm 2 coating weight were evaluated on the basis of the number of emitted photons per incident X-ray (NEP) and DQE, both expressing the signal-and-noise transfer properties of image receptors. NEP and DQE were determined by a method employing luminescence and emission spectrum measurements. The spectral compatibility of the two phosphors with films, photocathodes and the Si photodiode was also examined. CsI : Na exhibited high performance in the 60–90 kVp X-ray tube voltage range while Gd 2O 2S : Tb was found better at higher X-ray energies. The CsI : Na – film combination could provide an excellent X-ray radiographic detector, if effectively protected from humidity. Gd 2O 2S : Tb is more suitable for high tube voltage digital imaging but also adequate for conventional imaging.

Patient and staff radiation dose in fluoroscopy-guided TIPS procedures and dose reduction, using dedicated fluoroscopy exposure settings.

Fluoroscopy guided interventions, such as transjugular intrahepatic portosystemic shunt (TIPS) procedures, can results in relatively high radiation doses to patients and staff. The purpose of this study was to evaluate the possible benefit of dedicated fluoroscopy exposure factors in the reduction of doses. Doses to patients and staff were measured during fluoroscopy-guided TIPS procedures in two Dutch university hospitals. Patient doses were calculated from dose-area product (DAP) measurements, entrance beam dimensions and DAP conversion factors. Staff doses were measured outside lead aprons using electronic personal dosemeters. Average patient entrance skin dose (ESD) rate during fluoroscopy was 49 mGy min-1 (13 cases, average fluoroscopy duration 32 min) in one hospital, and 6 mGy min-1 (10 cases, average fluoroscopy duration 50 min) in the other. Estimated staff effective dose per procedure was 28 microSv average in the first hospital compared with 4 microSv average in the other. The use of dedicated fluoroscopy exposure factors, with a relatively high tube voltage and lower tube current resulted in a significant dose reduction for patient and staff in this type of radiological intervention.

Added copper filtration in digital paediatric double-contrast colon examinations: effects on radiation dose and image quality.

Paediatric double-contrast barium enema examinations are usually performed at high tube voltage, 102-105 kV. The aim of this study was to investigate how much the effective dose to the child could be reduced by increasing the X-ray energy further by adding copper filter in the beam, and if this dose reduction could be achieved without endangering image quality. Organ doses to an anthropomorphic phantom simulating a 1-year-old child was measured using thermoluminescence dosimetry for assessment of the effective dose and this value was compared with the energy imparted which was obtained from kerma-area product measurements. To verify that the image quality achieved with this added filtration was still diagnostically acceptable, the study included 15 patient examinations. Since the increased X-ray energy will most probably affect low-contrast objects, image quality was also evaluated with two different phantoms containing low-contrast objects. Effective dose for a complete examination can be decreased 44 % and energy imparted 77 % when a 0.3-mm copper filter is inserted in the beam at tube voltage 102 kV. The patient study did not show any significant deterioration of image quality, whereas phantom measurements of contrast-detail resolution and signal-to-noise ratio was marginally impaired by the added copper filtration. This technique is now in clinical practice for paediatric colon examinations.

Sens-A-Ray characteristics with variations in beam quality

This study examined the relationship between x-ray beam quality and image characteristics with the use of the Sens-A-Ray (Regam Medical Systems, Sundsvall, Sweden). To evaluate the x-ray response, properties of the image sensor, dark current and statistical noise, sensitivity, and contrast resolution were measured. Tube voltage, tube current, and exposure time were varied. Exposures were determined with the use of an ionization chamber. Pixel values beneath a lead strip were used to calculate dark current effects. Contrast was measured with pixel values from the images of a step-wedge. Dark current noise increased in proportion to exposure time. Although the sensitivity at each tube voltage was linear and proportional to the exposure, the gradient was inversely proportional to increased tube voltage. After subtraction of the dark current and statistical noise, the gradient of the sensitivity at low tube voltage remained steeper than at high tube voltages. Hence, sensitivity decreased with increased tube voltage. Sensitivity gradients at each different tube current were similar. Irrespective of exposure, contrast resolution between adjoining step-wedge steps > or = 9 mm were too small to distinguish at 50 kVp. The gray levels for each step below 12 mm in thickness were distinguishable with 90 kVp. Increased dark current noise consequent to long exposure times narrowed the available gray scale range. Lower tube voltage resulted in higher sensitivity with larger gradients than higher tube voltages.

The Yield from X Ray Tubes in Terms of Ambient Dose Equivalent

The yield from X ray tubes in terms of the quantity ambient dose equivalent has been determined experimentally, the experimental arrangements used in all three different tubes/generators over the tube potential range from 30 to 300 kV are described and the results are presented. After having established a basis for a comparison between the old data in terms of exposure with the new data in terms of ambient dose equivalent it is demonstrated that the yield is decreased at low tube and increased at high tube voltages by a transition from old to new quantities. With the help of the data presented the strength of radiation protection shielding may be estimated using the quantity ambient dose equivalent.

Digital radiography of the chest: state of the art

Digital image acquisition possesses a number of advantages over conventional systems in radiographic examination of the chest, the most important of which is its greater dynamic range. In addition, one digital images are acquired, they can be processed by computer in ways that cannot be rivalled by conventional analog techniques. Finally, digital images can be stored, retrieved and transmitted to local or remote sites. Here the status of the different digital systems employed in chest radiology and commonly used image processing techniques are reviewed. Also discussed are the current clinical applications of integrating digital chest radiography with a picture archiving and communication system (PACS) along with the difficulties typically encountered. Studies with a variety of digital techniques have been carried out on several fronts. Computer radiography based on photostimulabe phosphor (CR) has replaced screen-film imaging in certain applications (i.e. bedside imaging). However, CR has limitations, namely its poor X-ray utilisation efficiency at high X-ray tube voltages and sensitivity to scatter; therefore, it is not ideal for all applications. Recently, a dedicated digital chest unit with excellent X-ray utilisation efficiency at high X-ray tube potentials has been introduced. On the basis during the past decade, recommendations are made regarding the most desirable equipment specifications for dedicated and bedside digital chest radiography.

The effect of thin K-edge filters on radiation dose in dental radiography.

The use of thin K-edge filters has been found to reduce considerably the radiation dose in intra-oral radiography. The aim of this study was to investigate the effect of filtration on the skin entrance dose and several sites (representing organs or areas of interest within the head) along the central beam axis, at other points within the primary beam and at two points just outside the primary beam. The subject was a sliced head phantom (a human skull embedded in tissue-equivalent material) which was exposed to X rays from a conventional dental X-ray unit in the range of tube voltage 55-85 kVp for each of four filter systems. These were 2.7 mm of aluminium alone (the existing total filtration) or with an added 0.1 mm erbium, 0.1 mm yttrium or 0.05 mm niobium metal foils. Measurements of radiation dose were made using thermoluminescent dosemeters (TLD rods) and were adjusted to simulate the exposure resulting from a typical dental radiograph of a maxillary molar. The results suggest that the use of thin K-edge filters significantly reduces the entrance skin dose and to a certain extent reduces the total dose imparted to the head. However, the dose to the ipsilateral orbit at higher tube voltages may be increased.

Average radiation exposure values for three diagnostic radiographic examinations.

National surveys of more than 600 facilities that performed chest, lumbosacral spine, and abdominal examinations were conducted as a part of the Nationwide Evaluation of X-Ray Trends program. Radiation exposures were measured with use of a set of standard phantoms developed by the Center for Devices and Radiological Health of the Food and Drug Administration, U.S. Public Health Service. X-ray equipment parameters, film processing data, and data regarding techniques used were collected. There were no differences in overall posteroanterior chest exposures between hospitals and private practices. Seventy-six percent of hospitals used grids, compared with 33% of private practices. In general, hospitals favored a high tube voltage technique, and private facilities favored a low tube voltage technique. Forty-one percent of private practices and 17% of hospitals underprocessed their film. Underprocessing in hospitals increased from 17% in 1984 to 33% in 1987. Average exposure values for these examinations may be useful as guidelines in meeting some of the new requirements of the Joint Commission on Accreditation of Healthcare Organizations.

超高感度増感紙の臨床適応

The physical characteristics of ultra-high-speed screen-film systems (UHSS) (i. e. Quanta III (Q III), G8, G12, and KU systems) were studied and the UHSS systems were used in clinical radiography, such as infantile hip joint, fetus (pelvimetry) and urological radiography. When using a thin object and low tube voltage, the relative speeds of the UHSS systems were 2-3.5 times faster than that of a medium speed system, such as Hiscreen-A. On using a thick object and high tube voltage the relative speeds of the UHSS systems were 5-10 times faster than that of the His-A system. The G12 and KU systems showed particularly high speeds. Modulation transfer factors of the Q III and G8 systems were better than that of the other UHSS system. The sharpness of radiographic systems is important in infantile hip joint radiography, and thus the Q III, G8, and KU systems are most suitable for such a case. Because ultra-high-speed is required in fetrography, G12 and KU systems should be most suitable. Urinary organs are constructed from low spatial frequency. The image quality of the G8 system were found to be best for urological radiography.

The quality of disturbed radiation to the ovaries during diagnostic x-ray exminations (author's transl)

Dose measurements and analysis of disturbed spectra have shown that protection of the ovaries against disturbed radiation is worth while, although its effectiveness decreases with higher tube voltages. Increasing tube voltage increases disturbed radiation to the ovaries; the quality of the disturbed radiation is largely independent of the amount of filtration.