This study aimed to investigate the effect of dose reduction on diagnostic accuracy and radiation risk in digital mammography. Simulated masses and microcalcifications were positioned in an anthropomorphic breast phantom. Thirty digital images, 14 with lesions, 16 without, were acquired of the phantom using a Mammomat Novation (Siemens, Erlangen, Germany) at each of three dose levels. These corresponded to 100%, 50% and 30% of the normally used average glandular dose (AGD; 1.3 mGy for a standard breast). Eight observers interpreted the 90 unprocessed images in a free response study, and the data were analysed with the jackknife free response receiver operating characteristic (JAFROC) method. Observer performance was assessed using the JAFROC figure of merit (FOM). The benefit of radiation risk reduction was estimated based on several risk models. There was no statistically significant difference in performance, as described by the FOM, between the 100% and the 50% dose levels. However, the FOMs for both the 100% and the 50% dose were significantly different from the corresponding quantity for the 30% dose level (F-statistic = 4.95, p-value = 0.01). A dose reduction of 50% would result in three to nine fewer breast cancer fatalities per 100,000 women undergoing annual screening from the age of 40 to 49 years. The results of the study indicate a possibility of reducing the dose to the breast to half the dose level currently used. This has to be confirmed in clinical studies, and possible differences depending on lesion type should be examined further.

Observer performance studies are time-consuming tasks, both for the participating observers and for the scientists collecting and analysing the data. A possible way to optimise such studies is to perform them in a completely digital environment. A software tool-ViewDEX (Viewer for Digital Evaluation of X-ray images)-has been developed in Java, enabling it to function on almost any computer. ViewDEX is designed to handle several types of studies, such as visual grading analysis (VGA), image criteria scoring (ICS) and receiver operating characteristics (ROC). The results from each observer are saved in a log file, which can be exported for further analysis in, for example, a special software for analysing ROC results. By using ViewDEX for an ROC experiment, an evaluation rate of approximately 200 images per hour can be achieved, compared to approximately 25 images per hour using hard copy evaluation. The results are obtained within minutes of completion of the viewing. The risk of human errors in the process of data collection and analysis is also minimised. The viewer has been used in a major trial containing approximately 2700 images.

Purpose: The aim of this work was to implement different International protocols to estimate average glandular dose levels for the first Sectra MicroDose Mammography (MDM) unit used in routine mammography screening (Helsingborg, Sweden). Method and Materials: The Sectra MDM is a scanning multislit digital mammography system which uses a direct photon counting technique with a solid‐state detector, Si(B). A substantial dose reduction can be expected due to high photon absorption in the detector (90%) and scatter rejection (97%) as well as improved energy weighting compared to other mammography systems on the market. The multislit pre‐collimator scans with a distance of only 115 mm above the breast support making it impossible to follow the usual procedure for half value layer (HVL) measurement. Instead, a sensitive and well‐collimated solid state detector with simultaneous correction for the energy dependence (Barracuda X‐ray multimeter, RTI Electronics AB, Sweden) is used for non‐invasive measurements of the HVL. Results: The average glandular dose was found to be e.g. 0.28 mGy for a 50 mm standard breast with 50 % glandularity simulated with 45 mm PMMA according to the so‐called European protocol from 1996. Conclusion: Methods of how to perform absorbed dose measurements according to European and American protocols on the Sectra MDM have been developed. The average glandular dose is much lower than for any other mammography unit on the market today. However, for increased accuracy, the dose protocols should be revised to account for the anode/filter combination used with the Sectra unit (W/Al), the scattered radiation from the multislit pre‐collimator device and the occurrence of a dose profile in the scanning direction.

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.

In this study a set of structures has been simulated to represent a range of clinically relevant breast cancer mammographic lesions including solid tumours and microcalcifications. All structures have been created using simple random-based mathematical functions and have been inserted into a subset of digital mammography images at appropriate contrast levels into various regions of the breast, including dense fibroglandular and adipose tissue. These structures and their appearance in these clinical images were evaluated in terms of how realistic they looked. They will be used as the input to a large-scale clinical trial designed to examine the effect of significant dose reduction in digital mammography by comparing the detectability of such structures in images acquired at full and quarter automatic exposure control (AEC) dose level and in images with simulated noise levels in between.

The purpose of this work was to study how the pixel size of digital detectors can affect shape determination of microcalcifications in mammography. Screen-film mammograms containing microcalcifications clinically proven to be indicative of malignancy were digitised at 100 lines/mm using a high-resolution Tango drum scanner. Forty microcalcifications were selected to cover an appropriate range of sizes, shapes and contrasts typically found of malignant cases. Based on the measured MTF and NPS of the combined screen-film and scanner system, these digitised images were filtered to simulate images acquired with a square sampling pixel size of 10 μm x 10 μm and a fill factor of one. To simulate images acquired with larger pixel sizes, these finely sampled images were re-binned to yield a range of effective pixel sizes from 20 μm up to 140 μm. An alternative forced-choice (AFC) observer experiment was conducted with eleven observers for this set of digitised microcalcifications to determine how pixel size affects the ability to discriminate shape. It was found that observer score increased with decreasing pixel size down to 60 μm (p<0.01), at which point no significant advantage was obtained by using smaller pixel sizes due to the excessive relative noise-per-pixel. The relative gain in shape discrimination ability at smaller pixel sizes was larger for microcalcifications that were smaller than 500 μm and circular.

The effect of pixel size on shape determination in screening digital mammography systems was studied using a shape identification task as the measured outcome. Ten microcalcifications on screen-films were digitised to a range of pixel sizes (2.5-200 microm) and extracted from computed radiography (CR) images (50 microm) acquired under equivalent imaging conditions. Fifteen observers attempted to identify the shape of each microcalcification at each pixel size. The results were collated to provide a fraction of correct responses vs. pixel size curve for each microcalcification. Averaging over all shapes, pixel values >100 microm lead to a significant decrease in shape determination ability (p < 0.01) for digitised screen-film. For CR images, half the shapes were not properly identified. Hence, although 20-100 microm was sufficient for microcalcification shape determination for digitised screen-film images, 50 microm was only borderline sufficient for the CR digital images.

The Sectra MicroDose Mammography system is based on direct photon counting (with a solid-state detector), and a substantially lower dose to the breast than when using conventional systems can be expected. In this work absorbed dose measurements have been performed for the first unit used in routine mammography screening (at the Hospital of Helsingborg, Sweden). Two European protocols on dosimetry in mammography have been followed. Measurement of half value layer (HVL) cannot be performed as prescribed, but this study has demonstrated that non-invasive measurements of HVL can be performed accurately with a sensitive and well collimated solid-state detector with simultaneous correction for the energy dependence. The average glandular dose for a 50 mm standard breast with 50% glandularity, simulated by 45 mm polymethylmethacrylate, was found to be 0.21 and 0.28 mGy in March and December 2004, respectively. These values are much lower than for any other mammography system on the market today. It has to be stressed that the measurements were made using the current clinical settings and that no systematic optimisation of the relationship between absorbed dose and diagnostic image quality has been performed within the present study. In order to further increase the accuracy of absorbed dose measurements for this unit, the existing dose protocols should be revised to account also for the tungsten/aluminium anode/filter combination, the multi-slit pre-collimator device and the occurrence of a dose profile in the scanning direction.

From 1960 to 1980 and between 1987 and 1994 the whole-body content of 17Cs, and when possible also 134Cs, was measured in a group of subjects living in the city of Lund, Sweden (55.7 degrees N, 13.2 degrees E). The results have been analyzed to estimate the effective ecological half-time of fallout radiocesium in humans living in the area. The Lund area (The Province of Skåne) was subjected to a deposition of about 2 kBq m(-2) of pre-Chernobyl 137Cs from nuclear weapons testing and 1 kBq m(-2) of 137Cs from Chernobyl fallout in May 1986. The radiocesium from the nuclear weapons tests in the 1950's and 1960's still gave a significant contribution to the total 137Cs levels in humans in the post-Chernobyl study period (1987-1994) of about 0.4 Bq per kg body weight, which was about 10% of the peak post-Chernobyl concentration level of 137Cs (3.5-4 Bq kg(-1)) in 1987. The effective ecological half-time for 137Cs from Chernobyl was found to be 1.8 +/- 0.2 y. The aggregate transfer factor from deposition to mean activity concentration in man was estimated to be 3.6 Bq kg(-1)/kBq m(-2). These values may be compared with an effective ecological half-time of 1.3 y found in the reference group in the 1960's, and an aggregate transfer factor of 10 Bq kg(-1)/kBq m(-2). This difference is largely explained by the continuous nature of the global fallout leading to contamination on growing crops whereas the Chernobyl fallout occurred just prior to the South Swedish growing season, leading to less efficient transfer to crops and to human diet. The average committed individual effective dose (50 y) from ingested 137Cs from the Chernobyl fallout was estimated to be 0.02 mSv and from the nuclear weapons fallout (1945-1995) to be 0.20 mSv.

The equivalent biological half-times, Te, of 137Cs and 40K in a South-Swedish urban population have been determined through whole-body measurements and urinary excretion analysis. The Te - values for 137Cs found in males were on average, significantly lower than what is given in the literature. The relatively low average whole-body content of 40K,QK, in the males could explain the discrepancy, taking into consideration that a positive correlation between the Te and QK has been suggested in an earlier work. Furthermore, the potassium-normalized caesium urinary excretion was determined for the subjects in the study, and values were found to be in accordance with earlier results. A literature study of previous experimental data on the potassium-normalized caesium excretion however raises some questions about its applicability as a method for estimating the whole-body burden of 137Cs through urine analysis.

The purpose of this work was to implement the European Protocol on Dosimetry in Mammography in Sweden. The standard average glandular dose, AGD, was measured on 32 mammography units in southern Sweden, according to the European protocol as well as to the Nordic protocol. The most important difference is that the European protocol evaluates the half value layer, HVL, of the X ray beam with the compression paddle present, while it is absent in the Nordic protocol. This results in considerably higher HVL values from the European protocol and thus to higher conversion factors for the calculation of the standard AGD. When the European protocol is used instead of the Nordic protocol the standard AGD is increased by 5 +/- 2% (total variation 0-9%) at clinical settings and by 9 +/- 3% (4-17%) at a standardised net optical density of 1.00. These results should be considered in quality control programmes and optimisation procedures as well as in interpretation of trends and in future legislation programmes.

INTRODUCTION The aim of this study was to investigate the time variation of the whole-body burden levels of Cs in a south Swedish population after the Chernobyl fallout in 1986 (1, 2) and to compare the results with data obtained from the same reference group during the 1960s and 70s (3, 4, 5), as well as with contemporary studies on other Swedish populations. Radiocaesium from the nuclear weapons fallout consisted almost solely of Cs (6) and it was estimated that the intake of dairy and beef products accounted for a large part of the Cs intake in the Lund reference group (4), which is in accordance with international observations (7). Between 1960 and 1980 the cumulated deposition of fallout Cs from atmospheric bomb tests was about 2 kBq m in the Lund region (8, 9), which is in reasonable agreement with results from similar latitudes in the northern hemisphere except for areas with very high precipitation (10, 11). The ground deposition levels from the Chernobyl fallout in the province of Skåne was typically 1 kBq m (9), which is low in comparison with most other regions in Sweden (11). Furthermore the aggregate transfer of caesium from soil deposition to man through the ingestion of contaminated foodstuffs was calculated based on detailed deposition data in the region (9) in combination with the results of in vivo concentration in the control group.

X-rays from a laser-produced plasma were analysed using single-photon counting germanium detectors. Special attention was given to the extremely high photon flux, requiring either a long source-detector distance and narrow collimated measurement geometry in order to avoid severe pile-up of pulses in the spectrometer, or the use of a Compton scattering geometry. With the use of these techniques, individual characteristic K-lines were resolved for the first time. Efficiencies for the conversion of the laser light into X-rays were determined, being up to 10−4 for Bremsstrahlung, and up to 10−5 for the characteristic K-line emission. Electron temperatures of ∼100 keV were assessed.

Radionuclide measurements of left ventricular volumes, ejection fractions and stroke volumes were performed by an equilibrium technique in nine patients using left anterior oblique projection and individual depth correction. Phantom studies were made in order to evaluate attenuation and scattering of the radiation. It was found that a simple depth correction factor, k(d) = e mu d, can be used under certain conditions. However, the determination of left ventricular volume by radionuclide techniques is not a truly absolute method. The depth correction factor to be used is dependent on the condition of measuring and evaluation, for instance how the region of interest for the left ventricle is selected. Therefore, this method should be carefully standardized, evaluated and compared to other techniques. Stroke volume measured by radionuclide and dye-dilution technique showed a correlation coefficient of 0.76 (nine patients) at rest and 0.77 (seven patients) at work. This method can be easily performed during routine ejection fraction determination and can thus be useful in clinical studies.

Local blood flow in the thigh was measured with 133Xe clearance technique in eight male distance runners after compression with a foam rubber compress and a standard elastic bandage. Two degrees of compression were tested, and an initial experiment with rested subjects was followed by a similar experiment immediately after running. Maximum compression exerted a cutaneous pressure of 85 (+/- 8) mm Hg and caused an immediate cessation of intra-muscular blood flow in the compressed area. Moderate compression gave a cutaneous pressure of 40 (+/- 5) mm Hg and resulted in a reduction of blood flow by approximately 50%. During compression, there were no significant differences in the blood flow of rested subjects compared to subjects immediately after running. In acute soft tissue injuries, a maximum compression bandage should effectively reduce or eliminate the formation of an intra-muscular hematoma, and an additive effect on blood flow of ice should not be expected.

Local blood flow was measured with 133Xe clearance technique in eight male distance runners, where one leg was cooled for 20 min by applying two "instant cold packs" on the quadriceps muscle. An initial cooling period after resting was followed by a second cooling period 10 min after running. Skin temperature was maximally reduced after 4.5 min of cooling, both at rest and after running, by 15 degrees C and 14.9 degrees C, respectively. During the first 5 min of cooling no reduction of blood flow was seen. After 10 min of cooling blood flow was significantly reduced in the cooled compared to the control leg by 49% (P less than 0.05) after resting and 34% (P less than 0.05) after running. A maximum reduction of blood flow by 66 and 69% (P less than 0.01), respectively, was seen 10 min after the cooling period. In the event of an acute injury, this delayed reaction of cryotherapy on intramuscular blood flow should be carefully considered.