Bengt Hemdal

Dose dependence of mass and microcalcification detection in digital mammography: free response human observer studies.

The purpose of this study was to evaluate the effect of dose reduction in digital mammography on the detection of two lesion types-malignant masses and clusters of microcalcifications. Two free-response observer studies were performed-one for each lesion type. Ninety screening images were retrospectively selected; each image was originally acquired under automatic exposure conditions, corresponding to an average glandular dose of 1.3 mGy for a standard breast (50 mm compressed breast thickness with 50% glandularity). For each study, one to three simulated lesions were added to each of 40 images (abnormals) while 50 were kept without lesions (normals). Two levels of simulated system noise were added to the images yielding two new image sets, corresponding to simulated dose levels of 50% and 30% of the original images (100%). The manufacturers standard display processing was subsequently applied to all images. Four radiologists experienced in mammography evaluated the images by searching for lesions and marking and assigning confidence levels to suspicious regions. The search data were analyzed using jackknife free-response (JA-FROC) methodology. For the detection of masses, the mean figure-of-merit (FOM) averaged over all readers was 0.74, 0.71, and 0.68 corresponding to dose levels of 100%, 50%, and 30%, respectively. These values were not statistically different from each other (F= 1.67, p=0.19) but showed a decreasing trend. In contrast, in the microcalcification study the mean FOM was 0.93, 0.67, and 0.38 for the same dose levels and these values were all significantly different from each other (F = 109.84, p < 0.0001). The results indicate that lowering the present dose level by a factor of two compromised the detection of microcalcifications but had a weaker effect on mass detection.

In-plane artifacts in breast tomosynthesis quantified with a novel contrast-detail phantom

The purpose of this work was to develop a contrast-detail phantom that can be used to evaluate image quality in breast tomosynthesis (BT) and as a first step use it to evaluate in-plane artifacts with respect to object size and contrast. The phantom was constructed using a Polylite® resin as bulk material, as it has x-ray mass attenuation properties similar to polymethyl methacrylate (PMMA), a common phantom material in mammography. Six different materials - polyoxymethylene (POM), bakelite®, nylon, polycarbonate (PC), acrylonitrilebutadienestyrene (ABS) and polyethene (PE) - were selected to form the phantom details. For each of the six materials, five spherical objects were manufactured (diameters of 4, 8, 12, 16, and 20 mm) resulting in 30 objects that were embedded with their centres approximately aligned at the central plane of a 26 mm thick Polylite® block (210 mm x 300 mm). A 20 mm thick PMMA block was added to yield a phantom with attenuation properties similar to 45 mm PMMA that could simulate a so-called standard breast (50 mm thick, 50% glandular tissue). Images of the phantom were acquired using a BT prototype system that employs filtered backprojection for image reconstruction. The magnitude of the in-plane artifacts was evaluated and was found to increase linearly with increasing contrast (signal) level and size of the embedded objects. The contrast-detail phantom was found to be a useful tool for evaluating BT in-plane artifacts and might also be used to study out-of-plane artifacts and the effect of different acquisition and reconstruction parameters on image quality in BT.

Potential for lower absorbed dose in digital mammography: a JAFROC experiment using clinical hybrid images with simulated dose reduction

Purpose: To determine how image quality linked to tumor detection is affected by reducing the absorbed dose to 50% and 30% of the clinical levels represented by an average glandular dose (AGD) level of 1.3 mGy for a standard breast according to European guidelines. Materials and methods: 90 normal, unprocessed images were acquired from the screening department using a full-field digital mammography (FFDM) unit Mammomat Novation (Siemens). Into 40 of these, one to three simulated tumors were inserted per image at various positions. These tumors represented irregular-shaped malignant masses. Dose reduction was simulated in all 90 images by adding simulated quantum noise to represent images acquired at 50% and 30% of the original dose, resulting in 270 images, which were subsequently processed for final display. Four radiologists participated in a free-response receiver operating characteristics (FROC) study in which they searched for and marked suspicious positions of the masses as well as rated their degree of suspicion of occurrence on a one to four scale. Using the jackknife FROC (JAFROC) method, a score between 0 and 1 (where 1 represents best performance), referred to as a figure-of-merit (FOM), was calculated for each dose level. Results: The FOM was 0.73, 0.70, and 0.68 for the 100%, 50% and 30% dose levels, respectively. Using Analysis of the Variance (ANOVA) to test for statistically significant differences between any two of the three FOMs revealed that they were not statistically distinguishable (p-value of 0.26). Conclusion: For the masses used in this experiment, there was no significant change in detection by increasing quantum noise, thus indicating a potential for dose reduction.

High-resolution spectroscopy of laser-produced plasmas in the photon energy range above 10 keV.

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 not, vert, similar100 keV were assessed.

Impact of dose on observer performance in breast tomosynthesis using breast specimens

The purpose of this study was to investigate the effect of dose on lesion detection and characterization in breast tomosynthesis (BT), using human breast specimens. Images of 27 lesions in breast specimens were acquired on a BT prototype based on a Mammomat Novation (Siemens) full-field digital mammography (FFDM) system. Two detector modes - binned (2×1 in the scan direction) and full resolution - and four BT exposure levels - approximately 2×, 1.5×, 1×, and 0.5× the total mAs at the same beam quality as used in a single FFDM view with a Mammomat Novation unit under automatic exposure control (AEC) conditions - were examined. The exposure for all BT scans was equally divided among 25 projections. An enhanced filtered back projection reconstruction method was applied with a constant filter setting. A human observer performance study was conducted in which the observers were forced to select the minimum (threshold) exposure level at which each lesion could be both detected and characterized for assessment of recall or not in a screening situation. The median threshold exposure level for all observers and all lesions corresponded to approximately 1×, which is half the exposure of what we currently use for BT. A substantial variation in exposure thresholds was noticed for different lesion types. For low contrast lesions with diffuse borders, an exposure threshold of approximately 2× was required, whereas for spiculated high contrast lesions and lesions with well defined borders, the exposure threshold was lower than 0.5×. The use of binned mode had no statistically significant impact on observer performance compared to full resolution mode. There was no substantial difference between the modes for the detection and characterization of the lesion types.

Optimization of image quality in breast tomosynthesis using lumpectomy and mastectomy specimens

The purpose of this study was to determine how image quality in breast tomosynthesis (BT) is affected when acquisition modes are varied, using human breast specimens containing malignant tumors and/or microcalcifications. Images of thirty-one breast lumpectomy and mastectomy specimens were acquired on a BT prototype based on a Mammomat Novation (Siemens) full-field digital mammography system. BT image acquisitions of the same specimens were performed varying the number of projections, angular range, and detector signal collection mode (binned and nonbinned in the scan direction). An enhanced filtered back projection reconstruction method was applied with constant settings of spectral and slice thickness filters. The quality of these images was evaluated via relative visual grading analysis (VGA) human observer performance experiments using image quality criteria. Results from the relative VGA study indicate that image quality increases with number of projections and angular range. A binned detector collecting mode results in less noise, but reduced resolution of structures. Human breast specimens seem to be suitable for comparing image sets in BT with image quality criteria.

Body burden and excretion of 137-Cs and 40K in subjects from the south of Sweden

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.

Absorbed Dose Measurement in Mammography

Publisher Summary This chapter briefly describes methods to estimate the relevant radiation dose values that are necessary for quality control and optimization, and that also can be used as a basis for risk estimates and comparison between different mammography techniques and groups of women. The dose received by an individual woman during a mammographic examination is influenced by many parameters, such as the breast anatomy and the technical equipment and the examination technique. The parameters related to the mammography unit include the choice of anode (also called target), filter, and voltage (also called potential, in kV or kVp) across the X-ray tube. The patients specific anatomy also has an influence, for example, larger and/or more glandular breasts generally receive a higher dose owing to the necessary increase in exposure. On most modern mammography units, the selection of anode, filter, and tube voltage can be changed so that higher and then more penetrating photon energies are produced in these cases. Some modern mammography units are able to automatically adjust the selection of anode, filter, and tube voltage based on the thickness and even the glandularity of the breast. It is important to differentiate between measurements performed directly on the breast of a patient (or a phantom simulating a breast) and indirect measurements performed in the absence of a patient/phantom. Both phantom and patient measurements play an important role. Phantom measurements can be used to assess the performance of the mammography system. They are also efficient tools for optimization and comparison between mammography units and centers as well as with diagnostic reference levels (DRL) based on standard breasts.

Comparison of screen-film, imaging plate and direct digital mammography with CD phantoms

Low contrast-detail phantoms of glandularity 30, 50 and 70%, and thickness 3, 5, and 7cm were imaged. Screen-film (SF), imaging plate (CR), and full-field digital mammography (FFDM) systems were studied. Images were acquired for a range of anode/filter/tube potential/dose (AGD) combinations. The number of perceivable objects (score) was recorded and AGD determined. For FFDM, image scores similar to those with SF can be achieved at 20–60% of the SF dose. The largest dose reduction potential was found for the thickest phantoms and highest glandularity. With CR, a dose reduction of 10–20% was found, the largest reduction appearing for the thinnest phantom thickness.

Ecological half-time of radiocesium from Chernobyl debris and from nuclear weapons fallout as measured in a group of subjects from the south of Sweden

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 1950s and 1960s 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 1960s, 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.