Quality assurance in modern X-ray breast imaging

One of the requirements for breast cancer screening is high-quality mammography. Quality assurance programs are thus important and strict quality standards need to be set, monitored and met. Moreover, the risk associated with this screening exam should be small since asymptomatic women are examined. Due to these demands, manufacturers constantly improve and up-date X-ray systems to increase performance. This results in better and more complex X-ray systems. This thesis evaluates current physical technical performance measurements on these modern X-ray breast imaging systems. Part 1 of this thesis evaluates and optimizes procedures for phantom based average glandular dose (AGD) assessment. We proposed alternative phantoms assuming a homogeneous distribution of the glandular tissue. The estimated AGD values obtained with these phantoms were in reasonable agreement with patient AGD values. However, due to the homogeneous nature of these phantoms, variations in densities of real breasts are not taken into account, which may lead to differences depending on the automatic exposure control system. Such differences can be reduced by including local densities in the phantoms. In part 2 of this thesis we propose objective measurements of image quality of digital mammography systems. Currently, objective image quality measurements are performed on unprocessed images. We evaluated whether model observers, mathematical computer-based observers, have potential to evaluate image quality of processed images. We found that model observers can predict human observer performance for a simple task independent of the image quality level which suggests that model observers can be used for objective image quality assessment

Dose assessment in contrast enhanced digital mammography using simple phantoms simulating standard model breasts

Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas

Can the channelized Hotelling observer including aspects of the human visual system predict human observer performance in mammography?

Item does not contain fulltextPURPOSE: In mammography, images are processed prior to display. Model observers (MO) are candidates to objectively evaluate processed images if they can predict human observer performance for detail detection. The aim of this study was to investigate if the channelized Hotelling observer (CHO) can be configured to predict human observer performance in mammography like images. METHODS: The performance correlation between human observers and CHO has been evaluated using different channel-sets and by including aspects of the human visual system (HVS). The correlation was investigated for the detection of disk-shaped details in simulated white noise (WN) and clustered lumpy backgrounds (CLB) images, representing respectively quantum noise limited and mammography like images. The images were scored by the MO and five human observers in 2-alternative forced choice experiments. Results : For WN images the most useful formulation of the CHO to predict human observer performance was obtained using three difference of Gaussian channels without adding HVS aspects (RLR2=0.62). For CLB images the most useful formulation was the partial least square channel-set without adding HVS aspects (RLR2=0.71). The correlation was affected by detail size and background. CONCLUSIONS: This study has shown that the CHO can predict human observer performance. Due to object size and background dependency it is important that the range of object sizes and allowed variability in background are specified and validated carefully before the CHO can be implemented for objective image quality assessment

Can the non-pre-whitening model observer, including aspects of the human visual system, predict human observer performance in mammography?

Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas

Phantoms for quality control procedures in digital breast tomosynthesis: dose assessment

The recent introduction of digital breast tomosynthesis into clinical practice requires quality control procedures. In this study we have investigated whether the assessment of the average glandular dose for modelled standard breasts can be performed using a combination of polymethyl methacrylate (PMMA) and polyethylene (PE) slabs that matches standard breast thicknesses. For this purpose the energies absorbed per unit area of the image receptor when imaging standard breasts and PMMA-PE slabs have been matched taking account of both primary and scattered photons. To achieve this a two-step approach was used. Firstly, the behaviour of the scatter-to-primary ratio (SPR) of PMMA-PE phantoms and standard breasts was investigated using Monte Carlo simulations for various conditions. For imaging without an anti-scatter grid, it was found that the values of standard breast and phantom SPR were significantly different and it follows that these differences are relevant when matching the absorbed energy. In the second part, a set of PMMA-PE combinations is proposed which, for dosimetric purposes, can be used to simulate standard breasts in the thickness range 20 to 100 mm. The dosimetric error when using these PMMA-PE slabs was found to be below 6% for thicknesses up to 7 cm and increases to 10% for 10 cm thickness

Toward image quality assessment in mammography using model observers: Detection of a calcification-like object

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SIMULATING LOCAL DENSE AREAS USING PMMA TO ASSESS AUTOMATIC EXPOSURE CONTROL IN DIGITAL MAMMOGRAPHY

Imaging- and therapeutic targets in neoplastic and musculoskeletal inflammatory diseas

Impaired hematopoiesis in mice lacking the transcription factor Sp3

As the zinc-finger transcription factor specificity protein 3 (Sp3) has been implicated in the regulation of many hematopoietic-specific genes, we analyzed the role of Sp3 in hematopoiesis. At embryonic day 18.5 (E18.5), Sp3-/- mice exhibit a partial arrest of T-cell development in the thymus and B-cell numbers are reduced in liver and spleen. However, pre-B-cell proliferation and differentiation into immunoglobulin M-positive (IgM+) B cells in vitro are not affected. At E14.5 and E16.5, Sp3-/- mice exhibit a significant delay in the appearance of definitive erythrocytes in the blood, paralleled by a defect in the progression of differentiation of definitive erythroid cells in vitro. Perinatal death of the null mutants precludes the analysis of adult hematopoiesis in Sp3-/- mice. We therefore investigated the ability of E12.5 Sp3-/- liver cells to contribute to the hematopoietic compartment in an in vivo transplantation assay. Sp3-/- cells were able to repopulate the B- and T-lymphoid compartment, albeit with reduced efficiency. In contrast, Sp3-/- cells showed no significant engraftment in the erythroid and myeloid lineages. Thus, the absence of Sp3 results in cell-autonomous hematopoietic defects, affecting in particular the erythroid and myeloid cell lineages