For 8 voxel models of a compressed breast (4-7 cm thickness and two orientations for each thickness) and 14 radiation qualities commonly used in mammography (HVL 0.28-0.50 mm Al), tissue dose conversion coefficients were calculated for a focus-to-film distance of 60 cm using Monte Carlo methods. The voxel models were segmented from a high-resolution (slice thickness of 1 mm) computed tomography data set of an ablated breast specimen fixated while being compressed. The contents of glandular tissues amounted to 2.6%, and were asymmetrically distributed with regard to the midplane of the model. The calculated tissue dose conversion coefficients were compared with the recent literature values. These earlier tissue dose conversion coefficients were also calculated using Monte Carlo methods and breast models of various thickness, but these consist of homogeneous mixtures of glandular and adipose tissues embedded in 5 mm pure adipose tissue both at the entrance and exit sides. The results show that the new glandular tissue dose conversion coefficients agree well with the literature values for those cases where the glandular tissue is predominantly concentrated in the upper part of the model. In the opposite case, they were lower by up to 40%. These findings reveal a basic problem in patient dosimetry for mammography: glandular dose is not only governed by the average breast composition, which could be derived from the breast thickness, but also by the local distribution of glandular tissue within the breast, which is not known.

The European Commission (EC) quality criteria for screen-film mammography are used as a tool to assess image quality. A new set of criteria was developed and initially tested in a previous study. In the present study, these criteria are further evaluated using screen-film mammograms that have been digitised, manipulated to simulate different image quality levels and reprinted on film. Expert radiologists have evaluated these manipulated images using both the original (EC) and the new criteria. A comparison of three different simulated dose levels reveals that the new criteria yield a larger separation of image criteria scores than the old ones. These results indicate that the new set of image quality criteria has a higher discriminative power than the old set and thus seems to be more suitable for evaluation of image quality in mammography.

The RADIUS (Radiological Imaging Unification Strategy) project addresses the assessment of image quality in terms of both physical and clinically relevant measures. The aim is to unify our understanding of both types of measure as well as the numerous underlying factors that play a key role in the assessments of imaging performance. In this way it is expected to provide a solid basis for the improvement in radiological safety management, where not only radiation risks are considered but also diagnostic risks of incorrect clinical outcomes (i.e. false positive/false negative). The project has applied a variety of relevant experimental and theoretical methods to this problem, which is generic to medical imaging as a whole. Digital radiography of the chest and the breast has been employed as the clinical imaging domain vehicles for the study. The project addressed the problem from the following directions: role and relevance of pathology, human observer studies including receiver operating characteristics, image quality criteria analysis, structural noise analysis, physical measurements on clinical images, physical measurements on imaging system, modelling of imaging system, modelling of visual processes, modelling of doses delivered and IT-based scientific support strategies. This paper presents an overview of the main outcomes from this project and highlights how the research outcomes actually apply to the real world. In particular, attention will be focused on new and original findings and methods and techniques that have been developed within the framework of the project. The relevance of the project's outcomes to future European research will also be presented.

Though mammography is one of the most sensitive methods to detect breast cancer, the benefit of the mammography screening programmes is still not clearly proven. One of the reasons is the radiation dose delivered by the examinations. Simulations of the radiation transport based on realistic breast phantoms are a useful tool to estimate the dose for the risk relevant parenchymal tissue. Specimens of real breasts have been fixated using a specially designed process while being compressed as in mammography. They have been scanned using the high-resolution mode of a CT. A segmentation has been carried out by assigning the voxels to different tissues. The resulting voxel phantom allows the assessment of tissue doses by Monte-Carlo calculations and can be used to simulate the diagnostic outcome of different imaging procedures. Three different tissues were separated: skin, adipose and 'breast tissue'. This allows reasonable calculations of the average glandular doses in mammography.

The "European Guidelines on Quality Criteria for Diagnostic Radiographic Images" do not address the choice of the film characteristic (H&D) curve, which is an important parameter for the description of a radiographic screen-film system. The image contrast of clinical lumbar spine and chest radiographs was altered by digital image processing techniques, simulating images with different H&D curves, both steeper and flatter than the original. The manipulated images were printed on film for evaluation. Seven experienced radiologists evaluated the clinical image quality by analysing the fulfilment of the European Image Criteria (ICS) and by visual grading analysis (VGA) of in total 224 lumbar spine and 360 chest images. A parallel study of the effect of the H&D curve has also been made using a theoretical model. The contrast (DeltaOD) of relevant anatomical details was calculated, using a Monte Carlo simulation-model of the complete imaging system including a 3D voxel phantom of a patient. Correlations between the calculated contrast and the radiologists' assessment by VGA were sought. The results of the radiologists' assessment show that the quality in selected regions of lumbar spine and chest images can be significantly improved by the use of films with a steeper H&D curve compared with the standard latitude film. Significant (p<0.05) correlations were found between the VGA results and the calculations of the contrast of transverse processes and trabecular details in the lumbar spine vertebrae, and with the contrast of blood vessels in the retrocardiac area of the chest.

Ziele: Das Ziel dieser Studie ist es, eine Methodik zur Verfügung zu stellen, die eine effektive Strahlenbelastung und die Dosisverteilung bei einer Röntgenuntersuchung der weiblichen Brust möglichst genau abzuschätzen gestattet. Die zur Abschätzung benutzten Verfahren wie zum Beispiel Monte-Carlo-Berechnungen erfordern ein möglichst realistisches und genaues Modell der Verteilung unterschiedlicher Gewebearten. Methode: Es wurden drei Mammapräparate, die durch eine spezielle Präparationstechnik in einem der Mammographie entsprechenden komprimierten Zusatnd fixiert worden waren, im High-resolution Modus computertomographisch geschichtet (Schichtdicke 1mm, 512er Matrix, 80 und 120 kVp). Die gewonnenen Daten wurden segmentiert und die Voxel den einzelnen Gewebearten zugeordnet. So entstand ein Voxelphantom der weiblichen Brust, für das mittels Monte-Carlo-Rechnung der Strahlentransport und damit auch die effektive Strahlenbelastung bei einer Mammographie simuliert werden kann. Ergebnis: Es gelang, drei unterschiedliche Gewebearten in den 3D- Volumendaten voneinander abzugrenzen. Damit lässt sich bereits eine recht exakte Abschätzung der Strahlenbelastung und der Dosisverteilung bei der Mammographie ermitteln. Schlussfolgerung: Für eine noch genauere Ermittlung der Strahlendosis bei der Mammographie wäre eine Einteilung des Brustgewebes in fünf verschiedene Gewebearten wünschenswert. Nach projektionsradiographischen Voruntersuchungen wird dies im Weichstrahl-CT möglich sein. Da sich das Präparat nicht bewegt, kann ein solches CT auch mittels einer Flächendetektoranordnung erzeugt und ausgewertet werden. Durch den Vergleich der Ergebnisse lässt sich eine Abschätzung über die benötigte Komplexität von Phantomen zur Simulation des Strahlentransports gewinnen.

Purpose: To investigate the relative importance of spatial resolution and noise on the image quality of clinical radiographs. Methods: The spatial resolution and noise of fifteen digitized lumbar spine radiographs were altered with image processing. Three different MTF curves and three different Wiener spectra were combined into seven different combinations of spatial resolution and noise. These seven combinations were applied to the original data set, and the resulting images were printed on film. Seven expert radiologists evaluated the clinical image quality of the resulting images with visual grading analysis (VGA) of structures based on the European Image Criteria. Results: The results show that added noise is more deteriorating than reduced spatial resolution for the clinical image quality. For a given MTF and noise level, the worst was the one with increased noise followed by the one with both reduced MTF and added noise (mimicking a faster screen-film combination). Reduced MTF only gave the highest rating. Conclusions: It is more important to find methods for removing noise than to try to improve the MTF of a radiographic system. A noisy image can sometimes be improved by reducing the spatial resolution.

The Commission of the European Communities (CEC) research project "Predictivity and optimisation in medical radiation protection" addressed fundamental operational limitations in existing radiation protection mechanisms. The first part of the project aimed at investigating (1) whether the CEC image quality criteria could be used for optimization of a radiographic process and (2) whether significant differences in image quality based on these criteria could be detected in a controlled project with well known physical and technical parameters. In the present study, chest radiographs on film were produced using healthy volunteers. Four physical/technical parameters were varied in a carefully controlled manner: tube voltage (102 kVp and 141 kVp), nominal speed class (160 and 320), maximum film density (1.3 and 1.8) and method of scatter reduction (grid (R=12) and air gap). The air kerma at the entrance surface was measured for all patients and the risk-related dose H(Golem), based on calculated organ-equivalent dose conversion coefficients and the measured entrance air kerma values, was calculated. Image quality was evaluated by a group of European expert radiologists using a modified version of the CEC quality criteria. For the two density levels, density level 1.8 was significantly better than 1.3 but at the cost of a higher patient radiation exposure. The correlation between the number of fulfilled quality criteria and H(Golem) was generally poor. An air gap technique resulted in lower doses than scatter reduction with a grid but provided comparable image quality. The criteria can be used to highlight optimum radiographic technique in terms of image quality and patient dose, although not unambiguously. A recommendation for good radiographic technique based on a compromise between image quality and risk-related radiation dose to the patient is to use 141 kVp, an air gap, a screen-film system with speed 320 and an optical density of 1.8.

The 'European Guidelines on Quality Criteria for Diagnostic Radiographic Images' do not address the choice of film characteristic (H/D) curve, which is an important parameter for the description of a radiographic screen-film system. Since it is not possible to investigate this influence by taking repeated exposures of the same patients on films with systematically varied H/D curves, patient images of lumbar spine were digitised in the current study. The image contrast was altered by digital image processing techniques, simulating images with H/D curves varying from flat over standard latitude to a film type steeper than a mammography film. The manipulated images were printed on film for evaluation. Seven European radiologists evaluated the clinical image quality of in total 224 images by analysing the fulfilment of the European Image Criteria and by visual grading analysis of the images. The results show that the local quality can be significantly improved by the application of films with a steeper film H/D curve compared to the standard latitude film. For images with an average optical density of about 1.25, the application of the steeper film results in a reduction of patient absorbed dose by about 10-15% without a loss of diagnostically relevant image information. The results also show that the patient absorbed dose reduction obtained by altering the tube voltage from 70 kV to 90 kV coincides with a loss of image information that cannot be compensated for by simply changing the shape of the H/D curve.

The objective of this study is to establish a comprehensive set of backscatter factors for mammography based on the exposure model proposed by the European Protocol on Dosimetry in Mammography. The Monte Carlo calculated backscatter factors (BSFs) presented in this study are for various exposure conditions encountered in mammographic practice as well as in calibration procedures. The data demonstrate the variation of the BSF as a function of the exposure parameters, hence enabling a better match with calibration conditions and, at the same time, reviewing the BSF data already recommended by the European Protocol. Furthermore, earlier data for BSF for general diagnostic radiology are validated.

The voxel phantom Golem was used for the dosimetric part of the EU research project 'Predictivity and Optimisation in Medical Radiation Protection'. A risk-related dose quantity, H-Golem, was evaluated using calculated organ equivalent dose conversion coefficients and entrance air kerma values measured during the clinical examinations. Two types of examinations were considered: chest PA examinations, which were performed in 16 groups involving different speed classes, mean optical densities, tube voltages and methods of scatter reduction; and lumbar spine AP examinations, for which four different combinations of speed class and tube voltage were used. For the chest examinations, the expected effects of different examination techniques are clearly mirrored by the dosimetric results. For the lumbar spine examinations, part of the expected results was concealed by the unwanted influence of the patient diameters on the doses, which could be partially eliminated by adapting the voxel phantom to different sizes.

Backscatter factors were determined for x-ray beams relevant to diagnostic radiology using Monte Carlo methods. The phantom size considered most suitable for calibration of dosimeters is a cuboid of 30 x 30 cm2 front surface and 15 cm depth. This phantom size also provides a good approximation to adult patients. Three different media were studied: water, PMMA and ICRU tissue; the source geometry was a point source with varying field size and source-to-phantom distance. The variations of the backscatter factor with phantom medium and field geometry were examined. From the obtained data, a set of backscatter factors was selected and proposed for adoption as a standard set for the calibration of dosimeters to be used to measure diagnostic reference doses.

PURPOSE:Estimation of radiogenic risks for patient and radiologist in chemoembolisation of hepatocellular carcinoma (HCC) and laser angioplasty of the pelvic arteries. METHODS:In 5 chemoembolisations of HCC (4 males, one female) and 6 laser angioplasties of the pelvic arteries (5 males, one female) the surface doses received by patient and operator were measured using thermoluminescent dosimeters in standardised positions. The organ doses of the patient were derived by conversion factors employed on the measured surface doses. Effective dose was determined according to the recommendations of ICRP 60. RESULTS:The risk of lethal malignant disease and genetic disorder derived from the doses in the patient was found to be of the magnitude of 10(-4)-10(-5). The thresholds for transient erythema of the skin and depression of hematopoiesis can be reached after high expositions. A theoretical maximum of 700 laser angioplasties of the pelvic arteries allowable in one year was calculated based on the dose to the operator's left hand. For chemoembolisation of HCC, the dose to the left eye lens would reach the yearly maximum after approximately 1000 procedures. Remarkable risks for malignant disease of skin and thyroid as well as detectable opacities of the eye lens can occur after frequent interventions for many years. CONCLUSIONS:Because of the lower life expectancy the patient's risk for stochastic effect can be seen as minimal. No clinically relevant deterministic effects will occur. In the case of frequent interventions, the dose absorbed by the radiologist is likely to exceed the prescribed dose limit and to cause remarkable risk for stochastic and non-stochastic effects after many years.

Purpose: Estimation of radiogenic risks for patient and radiologist in chemoembolisation of hepatocellular carcinoma (HCC) and laser angioplasty of the pelvic arteries.Methods: In 5 chemoembolisations of HCC (4 males, one female) and G laser angioplasties of the pelvic arteries (5 males, one female) the surface doses received by patient and operator were measured using thermoluminescent dosimeters in standardised positions. The organ doses of the patient were derived by conversion factors employed on the measured surface doses. Effective dose was determined according to the recommendations of ICRP 60.Results: The risk of letal malignant disease and genetic disorder derived from the doses in the patient was found to be of the magnitude of 10(-4)-10(-5). The thresholds for transient erythema of the skin and depression of hematopoiesis carl be reached after high expositions. A theoretical maximum of 700 laser angioplasties of the pelvic arteries allowable in one year was calculated based on the dose to the operator's left hand. For chemoembolisation of HCC, the dose to the left eye lens would reach the yearly maximum after approximately 1000 procedures. Remarkable risks for malignant disease of skin and thyroid as well as detectable opacities of the eye lens can occur after frequent interventions for many years.Conclusions: Because of the lower life expectancy the patient's risk for stochastic effect can be seen as mini mal. No clinically relevant deterministic effects will occur. In the case of frequent interventions, the dose absorbed by the radiologist is likely to exceed the prescribed dose limit and to cause remarkable risk for stochastic and non-stochastic effects after many years.

In radiation protection of the patient in x-ray diagnosis all three principles of radiation protection should be applied. So-called dose constraints which limit entrance surface doses ensure implicitly that patient doses should not exceed certain levels. With respect to justification, it is believed that there is a large potential for patient dose reduction by avoiding both clinically unjustified examinations and unnecessary repetition of diagnostic procedures. While this appears to be quite straightforward, the strategy for optimisation is more complicated. Here, a reasonable compromise between high image quality and low patient dose has to be found, as often measures aimed at improved image quality lead to an increase of patient dose, and, vice versa, measures aimed at a reduction of patient dose result also in reduced image quality.Whereas the problem to quantitatively assess the quality of a given image is still not solved satisfactorily, the determination of patient doses has become increasingly feasible in recent years. For this purpose, computer codes, often based on Monte Carlo techniques, simulating the radiation transport in material are commonly used together with computational models of the human body. Most of the computational body models in use are so-called mathematical models, that means, mathematical expressions representing simple geometrical bodies are used to describe idealised arrangements of body organs. Additionally, tomographic models were developed in recent years which use computed tomographic data of real persons to provide three-dimensional representations of the body.Using these computational models of the human body, numerous studies concerning organ and tissue doses from diagnostic radiology were performed. Although it is not recommended to apply the calculated doses to assess individual patient doses, the influence of single exposure conditions as, e.g., tube voltage, filtration, field size and location, focus-to-skin distance, on organ and tissue doses can be studied readily, thus resulting in information prerequisite for optimisation in x-ray diagnosis. Additionally, the tomographic models enable to assess the influence of moderate variations of the patient size on organ doses and, therefore, improve to a certain extent the applicability of literature data on patient doses to individuals.

Dose-area product, a quantity easily measured in the X ray room, has been proposed for use as a dose index for patient exposure in diagnostic radiology. The most important aspect of the dose-area product is that it facilitates in practice the exposure dose assessment of individual patients. Furthermore, empirical functions relating dose-area product to organ doses or to effective dose, quantities supposingly expressing the radiation detriment, were estimated by some authors. In this work, a thorough study is attempted to investigate the relation of dose-area product likely to be measured, with the corresponding organ doses for a series of common radiographic examinations. For each examination, the influence of beam quality, field size and shifts of the position of the field on the above relation are also studied. This is achieved by means of organ doses obtained using MIRD-type human phantoms of a male and a female adult and a voxel phantom of a baby. A discussion on the suitability of dose-area product as a quantity to assess dose delivered to the critical tissues of the patient will be included, highlighting the conditions and uncertainties. The correlation of dose-area product and effective dose will be critically discussed.

Computed tomography (CT) offers a hi,bh diagnostic capability, but the dose to the patients is high compared to conventional radiography. For estimating the related radiation risk, the assessment of the doses to individual organs resulting from CT examinations, especially in paediatrics, is necessary. Therefore, a catalogue of organ doses from CT examinations of children was compiled at the GSF. Being applied for special cases rather than for routine examinations, CT is often operated at 'non-standard' situations. For that reason, the doses were calculated for single CT slices of 1 cm width at varying positions throughout the body. The results form a data base from which organ doses for individual paediatric examinations can be derived by suitably combining the calculated values. Two radiation qualities and two exposure geometries were considered as well as the use of asymmetric beams. The organ dose conversion factors are applicable to babies (at the age of about 2 months) and to children between 5 and 7 years but can be used for other ages as well with the appropriate adjustments. For the calculations, the patients were represented by the GSF tomographic anthropomorphic models BABY and CHILD. The radiation transport in the body was simulated using a Monte Carlo method. The doses are presented as conversion factors of mean organ doses per air kerma free in air on the axis of rotation.

The question discussed in this paper is whether effective dose can reflect the risk to patients from radiological procedures and can be used, for example, to optimise procedures and compare risks of various methods, to define dose constraints, and to estimate the risks to individuals or populations attributed to medical exposures. This report demonstrates that the use of effective dose for patients could be misleading or even wrong due to inappropriate simplifications of the underlying biological mechanisms and inappropriateness of the weighting factors connected with the definition of effective dose for a given patient population. We show that the choice of the most meaningful quantities to express patient exposure depends strongly on the respective situation.

Im Rahmen eines EG-Projektes wurde die Patientenexposition bei pädiatrischen Röntgenuntersuchungen in 90 Kinderkliniken durch unmittelbare Dosismessung im Nutzstrahlenbündel ermittelt. Als Dosimeter dienten TLD-chips aus CaF2, die bei 70 kV zur Messung der Oberflächendosis in µGy kalibriert worden waren und mit der Post versandt wurden. Die Dosen pro Röntgenaufnahme liegen je nach Untersuchung zwischen dem unteren Bereich 26 - 80 µGy für Thorax ap bei Frühgeborenen und dem oberen Bereich 597 - 1686 µGy für Schädel ap/pa im Alter von 10 Monaten. Die (hier durch das 1. und 3. Quartil der bei einer bestimmten Untersuchung erhaltenen Dosiswerte dargestellte) Streubreite kann als Hinweis auf noch bestehende Optimierungsmöglichkeiten gewertet werden.

Spectra of the total direct and scattered radiation behind a phantom (30 × 30 × 20 cm3) and an antiscatter grid (8/40) were measured. The results show that the antiscatter grid has a remarkable impact on the spectral distribution and that spectra used up to now for standard sensitometry of film-screen systems differ widely from the spectra as they are in practice; the latter can be simulated by filtration.