Biomedical subjects

I A Tsalafoutas

Publications and source records attributed to I A Tsalafoutas.

11 recordsLinked to original sources

PubMed2004

Threshold selection in virtual bronchoscopy: phantom study and clinical implications.

PURPOSE: To investigate the effect of the threshold selection on the apparent diameter of a virtual bronchus and the virtual wall morphology and to examine the parameters that can affect the selection of the appropriate threshold for virtual bronchoscopy with single slice computed tomography. MATERIAL AND METHODS: A bronchial phantom containing plastic tubes simulating the airways of the tracheobronchial tree was constructed. The diameters of the virtual images of these tubes were measured using various thresholds for two different materials surrounding the tubes: air and water. These measurements were correlated with the density in HU of the walls. Furthermore, data from 20 virtual bronchoscopies in patients were retrospectively analyzed in the same way. RESULTS: The diameter of a virtual bronchus is strongly affected by the selected threshold. The appropriate threshold for accurate diameter representation depends on the density of the bronchial wall. CONCLUSION: Our results suggest that in clinical practice a single threshold value cannot be used for imaging all segments of the tracheobronchial tree. While a value of -520 is appropriate for the trachea and lobar segments, values down to -720 could be needed on the level of segmental and subsegmental bronchi. At these levels, a threshold value about 65 HU more negative than the value where the artificial holes appear on the virtual bronchial walls could be used.

Bronchoscopes↗

PubMed2004

Variation of the sensitometric characteristics of seven mammographic films with processing conditions.

The effect of different processing conditions on the sensitometric characteristics of mammographic films was investigated and the implications of this effect on clinical practice are discussed. Three Agfa (MR5-II, HDR and HT), two Kodak (MinR-M, MinR-2000), one Fuji (AD-M) and one Konica (CM-H) single emulsion mammographic films were used. For each film type a 21-step sensitometric strip was developed in seven different processing conditions involving the use of four processors, five developing times and four chemistries. The different processing conditions produced a variable effect on the sensitometric characteristics of the mammographic films. While some films seemed relatively insensitive, others were greatly affected. Furthermore, not all the sensitometric parameters of a film were affected in the same way. For example, a change of processing conditions in some cases increased speed and decreased contrast but in some other cases increased both speed and contrast. Different mammographic films present different sensitometric characteristics that can be altered by processing conditions. Thus, in a mammographic facility any change in film processor/processing cycle or chemistry should be carefully investigated before mammograms of patients are acquired. Furthermore, the results of film comparisons under certain processing conditions should not be generalized to other processing conditions.

Female↗

PubMed2004

Quality control of a laser camera with the SMPTE test pattern: optical density variations with printing format and frame position.

The purpose of this study was to investigate the use of the Society of Motion Picture and Television Engineers (SMPTE) test pattern in the quality control of a modern laser camera and the variations in the optical density (OD) of the film when different formats are used. The SMPTE pattern was printed on all the available frames in eight different formats. Furthermore, six films were produced using the same format to check for any reproducibility problems. The OD values of the 11 step greyscale of the SMPTE patterns were measured with a densitometer, as well as the OD of steps 10 and 11 of the 16 step monitor greyscale printed to the left of each frame along with the SMPTE pattern. Variations up to 0.2 were observed in the OD of the same step when different formats and different frames within the same film were compared. Furthermore, the OD variations with frame position were found to follow a specific pattern. The OD variations observed with printing format and frame position can not be explained with certainty. They may indicate a laser camera malfunction and, if this is the case, limits to the maximum variation allowed should be set.

Data Display↗

PubMed2003

A semiempirical method for the description of off-center ratios at depth from linear accelerators.

A semiempirical method for the description of the off-center ratios (OCR) at depth from linear accelerators is presented, which is based on a method originally developed for cobalt-60 (60)Co units. The OCR profile is obtained as the sum of 2 components: the first describes an OCR similar to that from a (60)Co unit, which approximates that resulting from the modification of the original x-ray intensity distribution by the flattening filter; the second takes into account the variable effect of the flattening filter on dose profile for different depths and field sizes, by considering the existence of a block and employing the negative field concept. The above method is formulated in a mathematical expression, where the parameters involved are obtained by fitting to the measured OCRs. Using this method, OCRs for various depths and field sizes, from a Philips SL-20 for the 6 MV x-ray beam and a Siemens Primus 23, for both the 6-MV and 23-MV x-ray beams, were reproduced with good accuracy. Furthermore, OCRs for other fields and depths that were not included in the fitting procedure were calculated using linear interpolation to estimate the values of the parameters. The results indicate that this method can be used to calculate OCR profiles for a wide range of depths and field sizes from a measured set of data and may be used for monitor unit calculations for off-axis points using a standard geometry. It may also be useful as a quality control tool to verify the accuracy of lacking profiles calculated by a treatment planning system.

Algorithms↗

PubMed2003

Radiation doses to patients from endoscopic retrograde cholangiopancreatography examinations and image quality considerations.

The purpose of this investigation was to measure the dose-area product (DAP) and the other relevant dosimetric quantities in diagnostic and therapeutic endoscopic retrograde cholangiopancreatography (ERCP). Furthermore, the dependence of patient dose and image quality on the tube potential was investigated. A DAP meter was used for dose monitoring in seven diagnostic and 21 therapeutic ERCPs. For each ERCP the DAP meter readings, fluoroscopy time, number of radiographs and exposure data were recorded. From these data the fluoroscopy and radiography contributions to DAP, the entrance skin dose and the effective dose for each examination were estimated. For the investigation of the effect of tube potential on patient dose and image quality, a water phantom containing syringes filled with diluted contrast media was used. The average DAP was 13.7 Gy cm2 in diagnostic and 41.8 Gy cm2 in therapeutic ERCP whereas the average fluoroscopy times were 3.1 and 6.0 min respectively. DAP was strongly correlated to the fluoroscopy time. Measurements in the phantom showed that a good compromise between image quality and patient dose is obtained for tube potentials around 80 kV. Therapeutic ERCPs deliver on average higher doses to patients than diagnostic ERCPs. However, for a difficult diagnostic ERCP more patient exposure may be required than for a simple therapeutic ERCP.

Aged↗

PubMed2003

A model for calculating shielding requirements in diagnostic X-ray facilities.

In this study a new model for calculating shielding requirements in diagnostic X-ray facilities is presented. It is based on the combination and modification of models and concepts originally proposed by other authors in order to calculate barrier requirements in diagnostic X-ray facilities accurately and realistically without unjustified exaggerations. With this model, multiple sources of radiation operating at different potentials, leakage radiation reduction when operating at potentials less than the maximum rated value, secondary radiation use factors reduction for primary barriers, attenuation by image receptor hardware and existing building materials are all taken into account. Examples of shielding calculations for typical cases are given illustrating the differences between the various models and concepts proposed, as well as the potential reduction in shielding requirements without compromising the radiation protection of public and staff.

Humans↗

PubMed2001

The diagnostic X-ray protection characteristics of Panelcrete, Aquapanel, Betopan and Gypsoplak Superboard.

Panelcrete, Aquapanel and Betopan are cement-based building materials with uses similar to those of gypsum wallboard, whose properties as a diagnostic X-ray shielding material have been extensively studied. The X-ray attenuation characteristics of these cement-based boards as well as those of a gypsum wallboard, Gypsoplak Superboard, are investigated for broad beam geometry conditions and for tube potentials of 50 kVp, 70 kVp, 100 kVp, 125 kVp and 140 kVp. Comparisons between these materials as well as with published data for gypsum wallboard are made. An example of their use as secondary barriers is given. Furthermore, it is confirmed that when building materials are considered for diagnostic X-ray shielding, calculations based on data for similar materials and corrected for density differences can be used only as an approximation.

Construction Materials↗

PubMed2001

Differences in effective dose estimation from dose-area product and entrance surface dose measurements in intravenous urography.

In this study, measurements of dose-area product (DAP) and entrance surface dose (ESD) were carried out in a sample of 25 adult patients who underwent intravenous urography (IVU). These measured quantities were used to estimate the effective dose E from the IVU examination, a quantity closely correlated to radiation risk. Estimating E involves the use of conversion coefficients that have been determined for specific X-ray views in a mathematical phantom. These are obtained under conditions which are not usually met in clinical practice. As a result, the E estimates using the two different measurable quantities can be quite different. Analysis of the calculation procedure suggests that the E estimate using the DAP measurements, in addition to being more practical, could be more accurate than using ESD measurements, as DAP is sensitive to the X-ray field size settings. Furthermore, it is shown that in the absence of the appropriate equipment, a reliable E estimate can be obtained from the ESD calculated using the exposure data for each X-ray view.

Adult↗

PubMed2000

Dose calculations for asymmetric fields defined by independent collimators using symmetric field data.

Several methods have been developed for the dosimetry of asymmetric radiation fields formed by independently moving collimator jaws. Three of these methods, based on different principles and modified to comply with our set of available data, are utilized for the calculation of asymmetric field dose profiles. All three methods use output factors and per cent depth doses or tissue maximum ratios of symmetric fields. In the first method, calculation of the off-centre ratio (OCR) of the asymmetric field is based on the symmetric field from which the asymmetric is originated, by setting the one jaw in an asymmetrical position. In the second method the OCR of the symmetric field is used for the OCR calculation of the asymmetric field of the same size; whereas the third method does not allow for the asymmetric OCR calculation. The results obtained using data for the 6 MV photon beam of a Philips SL-20 linear accelerator indicate that both the first and second method can accurately reproduce asymmetric field profiles from symmetric field data; the third method does not allow for penumbra reproduction, but it is accurate at the central part of the asymmetric field. The problems encountered in the application of the three methods are reported and their accuracy is compared.

Humans↗

PubMed1999

Patient doses from barium meal and barium enema examinations and potential for reduction through proper set-up of equipment.

Patient doses for barium meal and barium enema examinations, performed at two Greek hospitals, were measured using a dose-area product meter. The results were analysed to obtain the contributions of fluoroscopy and radiography to the dose as well as a number of other dose related parameters for each examination. The doses observed are within the range of values reported by other authors and comply with the dose reference levels (DRLs), proposed from relevant surveys in the UK and The Netherlands. However, comparison between the two hospitals revealed significant differences in the contributions to dose from the various parts of the examinations. To determine the reasons for these differences, measurements of dose related parameters were made using a Plexiglas phantom and standard clinical X-ray machine settings. Factors contributing to increased dose delivery were determined and recommendations have been made concerning ways in which doses might be reduced in each hospital, without degradation of the diagnostic quality of these examinations.

Barium Sulfate↗

PubMed1998

The diagnostic X-ray protection characteristics of Ytong, an aerated concrete based building material.

Ytong is a widely used building material. The X-ray attenuation properties of Ytong for broad beam geometry conditions and for tube potentials in the 50-140 kVp range are investigated. Comparisons with published data for concrete and other building materials are made. The results suggest that Ytong is not suitable for primary X-ray shielding in common diagnostic installations. However, walls of Ytong, typically 15-20 cm thick, may offer adequate protection in dental and mammography installations, as well as in low workload diagnostic installations as a secondary barrier.

Construction Materials↗