kV Settings Research Articles

Organ doses and subjective image quality of indirect digital panoramic radiography.

To determine if slight variations in exposure will affect diagnostic image quality and absorbed radiation doses for digital and analogue panoramic radiography. Thermoluminescent dosimeters were placed in the thyroid gland, eyes, submandibular glands, parotid glands and skin of two human cadaver heads. Three different exposure settings were used: 70 kV, 120 mAs; 77 kV, 75 mAs; and 81 kV, 60 mAs. Subjective image quality was assessed using a phantom head. Storage phosphor (SP) images were printed on film and both analogue and SP images were assessed for their subjective image quality on a five-point rating scale. The results were statistically analysed using logistic regression analysis and chi(2) tests. Highest organ doses were measured for the submandibular glands, followed by the parotid glands. Salivary gland doses tended to be higher at lower kV settings. Image quality was not statistically different for the different exposure settings. Imaging technique did not seem to influence diagnostic image quality, except for the periapical status of upper premolars where SP was better. The main reason for any differences appeared to be interobserver variation. Analogue and SP panoramic radiography performed equally well for subjective diagnostic image quality. No significant differences could be found at the exposure settings used in this study. Radiation doses were highest for the salivary glands, especially at lower kV settings.

Scientific Instrument for a Controlled Choice of Optimal Photon Energy Spectrum: A Comparison Between Calculational Mehods and Laboratory Irradiations of Comparable Hard Tissue Phantoms

Basic performance parameters are defined and analysed in order to optimise physical image quality in relation to the energy imparted to the patient in dental radiology. Air cavities were embedded in well-defined multimaterial, hard tissue phantoms to represent various objects in dento-maxillo-facial examinations. Basic performance parameters were: object contrast (C), energy imparted (_) to the patient, signal-to-noise ration (SNR), C2/_ (film) and (SNR)2/_ (digital imaging system) as functions of HVL (half-value layer), used to describe the photon energy spectrum. For the film receptor, the performance index C2/_ is maximum (optimal) at HVL values of 1.5-1.7 mm Al in the simulated Incisive, Premolar and Molar examinations. Other imaging tasks (examinations), not simulated here, may require other optimal HVL. For the digital imaging system (Digora) the performance index (SNR)2/_, theoretically calculated, indicates that a lower value of HVL is optimal than with film as receptor. However, due to the limited number of bits (8 bits) in the analogue to digital converter (ADC) contrast resolution is degraded and calls for use of higher photon energies (HVL). Customised optimisations with proper concern for patient category, type of examination, diagnostic task is the ultimate goal of this work. The conclusions stated above give some general advice on the appropriate choice of photon energy spectrum (HVL). In particular situations, it may be necessary to use more dose demanding kV settings (lower HVL) in order to get sufficient image quality for the diagnostic task.

Use of an Ivory Wedge as a Test Phantom in Analysing the Influence of Scattered Radiation and Tube Potential on Radiographic Contract in Intraoral Dental Radiology

Contrast, noise and spatial resolution are fundamental physical concepts used to describe image quality. Contrast is one of the most important parameters in conventional film radiography. To facilitate the analysis of the radiographic contrast over a wide range of optical densities, an ivory wedge representative of objects with marked tissue discontinuities has been constructed. It can be used either separately or included within a PMMA phantom representing the middle face to simulate realistic scatter conditions. It is thus possible to investigate how radiographic contrast may be influenced by kV setting, beam filtration, type of generator (constant potential or single pulse) and type of film. The phantom has been used in optimising image quality relative to radiation risk, with the radiographic contrast being determined both theoretically and experimentally in terms of type of film (D and E speed), radiation and object contrast. The importance of controlling physical parameters when investigating image quality and how to achieve this using a well defined phantom is clearly demonstrated.

Efficacy of a porcelain refinishing system in restoring surface finish after grinding with fine and extra-fine diamond burs

Commercial porcelain refinishing kits are claimed to restore the surface finish on porcelain after adjustments in circumstances that preclude reglazing. This study investigates the efficacy of one such kit in restoring a Vitadur N porcelain surface finish after grinding with fine (30 μm grit-red band) and extra-fine (15 μm grityellow band) high-speed diamond burs. The production of the porcelain test samples, the refinishing procedures, and the refinishing times were standardized throughout. Techniques were selected to simulate clinical practice. Randomly selected examples of surfaces created during refinishing were subjected to scanning electron microscopy, using standard kV and tilt angle settings, and to surface profilometry tracings. Roughness average (Ra) readings were recorded for each test specimen for every surface finish. Ra readings were analyzed statistically using a two-way unbalanced model for analysis of variance. Although refinishing after grinding with a 15 μm grit bur produced surfaces significantly smoother than on specimens previously ground with the 30 μm grit burs, the surfaces remained significantly rougher than when originally glazed. It is concluded that, using the type of kit tested, burs of a grade finer than the existing 15 μm grit yellow band types would be appropriate for porcelain adjustments to permit subsequent refinishing to a surface smoothness comparable to the original glaze.

Calculation of radiation dose enhancement factors for dose enhancement therapy of brain tumours

When brain tumours are loaded with iodinated contrast media (CM) and exposed to X-rays, the photoelectrons, Auger electrons and fluorescent X-rays from the iodine enhance the radiation dose absorbed by the tumour. A modified CT scanner, the CTX, can be used to localize the tumour and to deliver the dose enhancement therapy. Monte Carlo calculations are presented of the central-axis radiation depth dose in a brain containing a tumour loaded with an iodine concentration of 5 mg ml-1 and irradiated with the CTX operated at various kV settings. The dose enhancement factor (DEF) is also calculated for various field sizes and for 5 mg ml-1 of gadolinium in the tumour when the CTX is operated at 140 kV. The calculated values of the DEF are close to published experimental results.

Microscopy studies of Tilletia teliospore sheaths

Teliospores of bunts of wheat and rice have a complex multilayered wall. The outer wall layer or sheath may be absent from some Tilletia controversa teliospores and may be difficult to characterize unless it is hydrated. It may also contain surface rodlets. The sheath has been characterized with freeze fracture and thin sectioning studies. By altering the sample processing procedures and by using thin sectioning the sheath can be used to distinguish T. caries teliospores from T. controversa teliospores which is important for wheat marketing. Earlier attempts were made to distinguish the two species using SEM at low kV settings without the use of special procedures to hydrate the sheath. When many samples of each species were studied, variations in wall structure within species were evident, but at 1-15 kV the electrons penetrated the porous outer sheath and imaged the impermeable exospore layer. The purpose of these investigations was to use SEM to study hydrated sheaths of samples of T. caries and T. controversa teliospores at different kV settings.

The application of energy‐dispersive X‐ray fluorescence and the fundamental parameter approach to the analysis of NiFeCr alloys

AbstractThe fundamental parameter approach has been applied to NiFeCr alloys using an energy‐dispersive X‐ray fluorescence spectrometer employing secondary target excitation. The relative distributions of primary, secondary and tertiary fluorescence for these alloys and some of the assumptions inherent in the fundamental parameter approach are discussed both on a theoretical and an experimental basis. For a series of hypothetical NiFeCr alloys, our theoretical calculations show that the tertiary fluorescence contribution to the Cr intensity varies from 0.1 to 7.25% dependent on composition and on excitation energy. Furthermore, a general calibration procedure independent of the sample matrix and the kV, mA and collimator settings is outlined. The analysis results obtained for six reference alloys proved to be accurate within 5% for most elements. The results obtained with and without tertiary fluorescence included in the model deviate 2–5% only. This is partly due to a matrix absorption correction compensation in the latter case.

The tissue-equivalence of the Alderson Rando anthropomorphic phantom for X-rays of diagnostic qualities

Comparative measurements were made of depth-dose profiles in an Alderson Rando phantom and a similarly shaped phantom of water which closely simulates the attenuation properties of human muscle. Measurements were carried out at three different kV settings of the X-ray generator, covering the lower-energy range of normal diagnostic practice over which attenuation differences are likely to be most important. The results show that whilst the Alderson phantom can undoubtedly be extremely useful in medical dosimetry, corrections to the dose distributions observed for diagnostic qualities of radiation may sometimes be necessary to allow for departures from tissue-equivalence.

An inaccuracy in computed tomography: the energy dependence of CT values.

The CT values of a variety of materials were studied in an EMI and a Syntex head scanner. The presence of bone-simulating rings changed the CT values despite the use of constant length water paths and software corrections. Errors due to beam hardening in CT scanning are discussed. These errors could be of significance, particularly in quantitative studies. The changes in CT values with KV setting of the scanner are used to illustrate their energy dependence and the peculiarities of the scaling system introduced by EMI. The difficulty in specifying a standard scale or unit for CT scanners is discussed.

THE GRENZ-RAY OUTPUT CHARACTERISTICS OF A SUPERFICIAL THERAPY MACHINE.

In a superficial X-ray therapy unit, the Dermopan, recently installed at this hospital, an unexpected relationship was observed between X-ray output and tube current when the latter was varied from the specified value at the 10 kV setting. It is thought worth while to record this observation, since failure to appreciate this behaviour could lead to serious errors in dosage. It will also be seen that, by means of a simple adjustment of the control circuit of the machine, this characteristic can be turned to good account by providing improved dose control. The equipment uses a self-rectified tube with a beryllium window. A selector switch on the control panel provides for operation at 10, 29, 43 or 50 kVp. An electrical interlock system ensures that the tube can be energised only when the filter appropriate to the selected kilovoltage is in place. A fine control of line voltage is provided. A tube current of precisely 25 mA is specified at all four X-ray qualities. Tube current control is smooth and adequat...