Digital imaging systems for medical applications must bebased upon highly efficient detectors to ensure low patientdose. This is particularly important in screening mammographybecause of the large number healthy women that is examined. Amammography system must also provide high spatial and contrastresolution. Different approaches are compared in this thesis,and it is argued that a system based on photon countingdetectors in a scanned multi-slit geometry provides aperformance superior to established technologies. The system is realized using silicon strip detectorsirradiated at a small angle relative to the wafer surface,thereby offering large absorption depth. A linear pixelarray isscanned across the breast to obtain the complete image.Pulse-processing electronics rejecting all detector andelectronics noise count the number of photons that aredetected, forming the pixel values of the image. Optimization of the detector design is discussed in detail.The detector has been carefully simulated to investigate chargemotion and signal formation after photoninteraction. Based onthese simulations, the impact of the detector characteristicson the image quality has been evaluated. Detectors have been manufactured and evaluated both assingle components and as part of experimental imaging devicesincluding custom readout electronics. Presented in this thesisare the measured detector characteristics including a verifi-cation of charge collection efficiency and confirmation thatthe quantum efficiency is 90% for a typical mammographyspectrum. Modulation transfer functions and noise power spectrawere recorded and the detective quantum efficiency calculated.A prototype mammography system was also assembled and themodulation transfer function recorded. The interpretation ofthe modulation transfer function and detective quantumefficiency is discussed for digital systems in general and fora scanned multi-slit system in particular. <b>Keywords:</b>x-ray, imaging, silicon, detector, digital,mammography, scanning, photon counting.

This thesis presents techniques constructed to aid the radiologists in detecting breast cancer, the second largest cause of cancer deaths for western women. In the first part of the thesis, a computer-aided detection (CAD) system constructed for the detection of stellate lesions is presented. Different segmentation methods and an attempt to incorporate contra-lateral information are evaluated. In the second part, a new method for evaluating such CAD systems is presented based on constructing credible regions for the number of false positive marks per image at a certain desired target sensitivity. This method shows that the resulting regions are rather wide and this explains some of the difficulties encountered by other researchers when trying to compare CAD algorithms on different data sets. In this part an attempt to model the clinical use of CAD as a second look is also made and it shows that applying CAD in sequence to the radiologist in a routine manner, without duly altering the decision criterion of the radiologist, might very well result in suboptimal operating points. Finally, in the third part two dual-energy imaging methods optimized for contrast-enhanced imaging of breast tumors are presented. The first is based on applying an electronic threshold to a photon-counting digital detector to discriminate between high- and low-energy photons. This allows simultaneous acquisition of the high- and low-energy images. The second method is based on the geometry of a scanned multi-slit system and also allows single-shot contrast-enhanced dual-energy mammography by filtering the x-ray beam that reaches different detector lines differently. / QC 20100819

Mammography screening aims to reduce the number of breast cancer deaths by early detection of the disease, which is one of the leading causes of deaths for middle aged women in the western world. The risk from the x-ray radiation in mammography is relatively low but still a factor in the benefit-risk ratio of screening. The characterization and optimization of a digital mammography system is presented in this thesis. The investigated system is shown to be highly dose efficient by employing a photon counting detector in a scanning multislit geometry. A novel automatic exposure control (AEC) is proposed and validated in clinical practise. The AEC uses the leading detector edge to measure the transmission of the breast. The exposure is modulated by altering the scan velocity during the scan. A W-Al anode-filter combination is proposed. The characterization of the photon counting detector is performed using the detective quantum efficiency. The effect of the photon counting detector and the multislit geometry on the measurement method is studied in detail. It is shown that the detector has a zero-frequency DQE of over 70\% and that it is quantum limited even at very low exposures. Efficient rejection of image-degrading secondary radiation is fundamental for a dose efficient system. The efficiency of the scatter rejection techniques currently used are quantified and compared to the multislit geometry. A system performance metric with its foundation in statistical decision theory is discussed. It is argued that a photon counting multislit system can operate at approximately half the dose compared to several other digital mammography techniques. / QC 20100825

<p>Breast cancer screening is currently performed by mammography, which is limited by overlying anatomy and dense breast tissue. Computer aided detection (CADe) systems can serve as a double reader to improve radiologist performance. Tomosynthesis is a limited-angle cone-beam x-ray imaging modality that is currently being investigated to overcome mammography's limitations. CADe systems will play a crucial role to enhance workflow and performance for breast tomosynthesis.</p><p>The purpose of this work was to develop unique CADe algorithms for breast tomosynthesis reconstructed volumes. Unlike traditional CADe algorithms which rely on segmentation followed by feature extraction, selection and merging, this dissertation instead adopts information theory principles which are more robust. Information theory relies entirely on the statistical properties of an image and makes no assumptions about underlying distributions and is thus advantageous for smaller datasets such those currently used for all tomosynthesis CADe studies.</p><p>The proposed algorithm has two 2 stages (1) initial candidate generation of suspicious locations (2) false positive reduction. Images were accrued from 250 human subjects. In the first stage, initial suspicious locations were first isolated in the 25 projection images per subject acquired by the tomosynthesis system. Only these suspicious locations were reconstructed to yield 3D Volumes of Interest (VOI). For the second stage of the algorithm false positive reduction was then done in three ways: (1) using only the central slice of the VOI containing the largest cross-section of the mass, (2) using the entire volume, and (3) making decisions on a per slice basis and then combining those decisions using either a linear discriminant or decision fusion. A 92% sensitivity was achieved by all three approaches with 4.4 FPs / volume for approach 1, 3.9 for the second approach and 2.5 for the slice-by-slice based algorithm using decision fusion.</p><p>We have therefore developed a novel CADe algorithm for breast tomosynthesis. The techniques uses an information theory approach to achieve very high sensitivity for cancer detection while effectively minimizing false positives.</p> / Dissertation

<p>A 3D microwave imaging system suitable for clinical trials has been developed. The anatomy, histology, and pathology of breast cancer were all carefully considered in the development of this system. The central component of this system is a breast imaging chamber with an integrated 3D antenna array containing 36 custom designed bowtie patch antennas that radiate efficiently into human breast tissue. 3D full-wave finite element method models of this imaging chamber, complete with full antenna geometry, have been developed using Ansoft HFSS and verified experimentally. In addition, an electronic switching system using Gallium Arsenide (GaAs) absorptive RF multiplexer chips, a custom hardware control system with a parallel port interface utilizing TTL logic, and a custom software package with graphical user interface using Java and LabVIEW have all been developed. Finally, modeling of the breast (both healthy and malignant) was done using published data of the dielectric properties of human tissue, confirming the feasibility of cancer detection using this system.</p> / Dissertation

Cancer is the second leading cause of death among the world and it has an increasing share among all causes of death. Economical burden of cancer is increasing especially in high and middle-income countries. Leaving cancer in competitive markets would lead to inefficiencies / hence governments should intervene in the market and make public decisions in struggling cancer. Among all cancer types breast cancer has the highest incidence and mortality rates in females. Causes of breast cancer still remains indeterminate and only way to cope with breast cancer are by early diagnoses. Early diagnoses can best be achieved by regular mammography screenings. This study analyzes the possible outcomes of implementing regular breast cancer mammography screening program in Turkey. A simulation model is constructed and run for 10 years, to obtain the costs and benefits of such a screening program. Costs of such a program include the screening costs and costs due to abnormal mammograms. Benefits, on the other hand are reduced treatment costs due to early diagnosis, reduced mortality and morbidity. Simulation model is run for 11 different screening strategies for determining the optimal screening strategy in terms of screening interval and minimum age to screen. The necessary data is obtained from hospital records, Cancer Early Diagnosis and Treatment Center records, IMF, WHO and TUIK databases and literature. Results of the simulation suggest that women over 40 in Turkey should be screened biennially for economical efficiency.

<p>Digital imaging systems for medical applications must bebased upon highly efficient detectors to ensure low patientdose. This is particularly important in screening mammographybecause of the large number healthy women that is examined. Amammography system must also provide high spatial and contrastresolution. Different approaches are compared in this thesis,and it is argued that a system based on photon countingdetectors in a scanned multi-slit geometry provides aperformance superior to established technologies.</p><p>The system is realized using silicon strip detectorsirradiated at a small angle relative to the wafer surface,thereby offering large absorption depth. A linear pixelarray isscanned across the breast to obtain the complete image.Pulse-processing electronics rejecting all detector andelectronics noise count the number of photons that aredetected, forming the pixel values of the image.</p><p>Optimization of the detector design is discussed in detail.The detector has been carefully simulated to investigate chargemotion and signal formation after photoninteraction. Based onthese simulations, the impact of the detector characteristicson the image quality has been evaluated.</p><p>Detectors have been manufactured and evaluated both assingle components and as part of experimental imaging devicesincluding custom readout electronics. Presented in this thesisare the measured detector characteristics including a verifi-cation of charge collection efficiency and confirmation thatthe quantum efficiency is 90% for a typical mammographyspectrum. Modulation transfer functions and noise power spectrawere recorded and the detective quantum efficiency calculated.A prototype mammography system was also assembled and themodulation transfer function recorded. The interpretation ofthe modulation transfer function and detective quantumefficiency is discussed for digital systems in general and fora scanned multi-slit system in particular.</p><p><b>Keywords:</b>x-ray, imaging, silicon, detector, digital,mammography, scanning, photon counting.</p>

Bakgrund I Sverige ökar antalet insjuknanden i bröstcancer årligen. Diagnostisering med hjälp av mammografi och självundersökning bidrar till tidig upptäckt av cancertumörer vilket ger bättre prognos. För att alla kvinnor ska självundersöka brösten och gå på erbjuden mammografi är kunskap om bröstcancer en god förutsättning. Syfte Syftet med denna forskningsstudie var att undersöka kvinnors kunskap om bröstcancer och självundersökning av brösten. Syftet var också att undersöka huruvida sådan kunskap skiljer sig mellan kvinnor i och utanför det nationella screeningsprogrammet för bröstcancer samt huruvida det finns en skillnad i förekomst av självundersökning. Hänsyn togs även till de eventuella faktorer i kvinnornas bakgrund och vanor som kan ha en inverkan på resultatet. Metod En empirisk studie med kvantitativ ansats. Datainsamling genomfördes via enkäter, vilka besvarades av 130 kvinnliga deltagare. Enkäterna syftade till att undersöka kvinnornas vanor kring självundersökning och mammografi, demografisk bakgrund samt kunskap om bröstcancer. Resultat Resultatet av kunskapstestet visar att kvinnor har god kunskap om bröstcancer och självundersökning då över 80% av kvinnorna svarade rätt på 10 av 14 frågor. En signifikant skillnad i kunskapen mellan de två grupperna kunde ses i en fråga. Fler kvinnor i screeninggruppen än utanför screeninggruppen som utfört självundersökning av brösten. Flera faktorer i kvinnornas bakgrund och vanor hade en påverkan på kunskapen. Slutsats Kunskapen om bröstcancer bland deltagarna i studien var god. Kunskapen mellan kvinnor i och utanför screeningprogrammet skilde sig i få områden. Förekomsten av självundersökning var högre av kvinnor som erhållit undervisning från skola och/eller sjukvård. Därav behövs fortsatt utbildning inom det aktuella området för att främja kvinnors hälsa. / Background In Sweden and the number of breast cancer diagnosis is increasing annually. Diagnosis using mammography and breast self-examination contributes to the early detection of cancerous tumors, which gives a better prognosis. In order to get all women to self-examine their breasts and to get the offered mammography, knowledge about breast cancer is a good precondition. Aim The purpose of this research study was to investigate women's knowledge about breast health and breast self-examination. The aim was also to investigate whether such knowledge differ between women in and outside the national screening program for breast cancer and whether there is a difference in the incidence of self- examination. Consideration was also taken of the potential factors in the women's background and habits that may have an impact on earnings. Methods An empirical study with a quantitative approach. Data collection was conducted through questionnaires, which were answered by an amount of 130 female participants. The questionnaires aimed to investigate women's habits related to self- examination and mammography, demographic background and knowledge of breast cancer. Results The results of the knowledge test shows that women have a good knowledge about breast cancer and self-examination, since over 80% of women answered correctly in 10 out of 14 questions. A significant difference in knowledge between the two groups was seen in a query. There were more women in the screening group than in the non-screening group who performed breast self-examination. Several factors in women's history and habits had an influence on their knowledge. Conclusion Knowledge about breast health among the study participants was overall good. The knowledge among women in and outside the screening program differed in few areas. The prevalence of self-examination was higher among women who received instruction from school and/or medical care. Therefore continued education within the area is necessary in order to promote women's health.

Early detection of breast cancer on screening mammograms is crucial to reduce mortality rates. Computer-aided detection (CADe) systems for mammography are of great importance since they have been shown to positively assist radiologists in detecting early cancer. However, one area where CADe systems for mammography need improvement is in the early detection and annotation of spiculated lesions, which may represent invasive malignancies, and hence, early detection is crucial. Spicule annotation is important since it can yield useful discriminative information about the suspect lesion location on the mammogram and can also provide rich visual evidence to the interpreting radiologist to make the right follow-up decision. However, spicule annotation is a non-trivial task since spicules are fine scale curvilinear structures that are often not clearly visible amidst the surrounding breast parenchyma. The first contribution of this dissertation is an active contour algorithm called snakules for the annotation of spicules on mammography. Observer studies with experienced radiologists to evaluate the performance of snakules demonstrate the potential of the algorithm as an annotation tool that could be used to augment existing spiculated mass CADe systems. Mammography suffers from a major limitation: the 3-D to 2-D projection process results in anatomical noise due to overlapping of out of plane tissue structures, which hinders both radiologists and CADe systems in finding early cancers. This has motivated the development of 3-D breast imaging in the form of breast tomosynthesis, stereoscopic (stereo) mammography, and breast computed tomography (CT) to augment mammography for early cancer detection. Our second contribution is a novel computational stereo model for estimating a dense disparity map from a pair of stereo mammograms. This problem is very important since this is the first step towards elucidating 3-D information that is essential for conducting 3-D digital analysis on the stereo mammogram images. Nearly all of the 3-D structural information of interest on a stereo mammogram exists as a complex network of multi-layered, heavily occluded curvilinear structures, which is unlike what is seen on optical images of the real world. Our proposed stereo model employs a new singularity index as a constraint in a global optimization framework to obtain better estimates of disparity along critical curvilinear structures. The new singularity index is an important contribution of this work. In-depth theoretical analyses and experiments on several real world images demonstrate the efficacy of the index for detecting multi-scale curvilinear structures. Experiments on synthetic images with known ground truth and on real stereo mammograms highlight the advantages of the proposed stereo model over the canonical stereo model. The final contribution of this dissertation is an observer study, which demonstrates the feasibility of viewing breast tomosynthesis projection images stereoscopically. Unlike stereo mammogram images, each tomosynthesis projection image is acquired at a much lower dose. Stereo viewing of tomosynthesis projection images has the potential to reveal the 3-D structure of the breast, unlike the current cine or slice-by slice viewing modes. The results from our study suggest that stereo viewing could be a viable reading mode for breast tomosynthesis data in the future. / text

Magnetic resonance mammography (MRM) is a promising technique, since it provides high resolution breast imaging with no use of ionising radiation and with inherently good soft tissue discrimination. The addition of dynamic contrast enhancement kinetics of the breast upgraded the method to a great extend, due to highly differentiated malignant vs. benign lesion hemodynamics resulting from the angiogenetic properties of cancerous cells. Straightforward pharmacokinetic analysis, such as the 3TP algorithm, has been implemented in commercially available CAD systems. Quantitative parameters can be extracted that directly correspond to different aspects of the underlying pathology and can be compared to biopsy results. However, there is a general understanding that straightforward pharmacokinetic analysis (3TP model) requires a very demanding imaging protocol in order to be able to measure such parameters accurately. Fitting the experimental data of the dynamic series to simple mathematical models extracting quantitative features provides a means to evaluate and to shrink the big amount of data of the study to one set of images, in order make the diagnostic process faster and more robust. That could facilitate the clinical routine. The dynamic series of the MRM examinations of the 55 patients were analyzed in this study. Radiologists specialized in MRM have identified and characterized all suspicious lesions according to BIRADS lexicon. Dynamic data were fitted pixel-wise to a simple bilinear model to extract washout, time to peak and washin parameters. Subsequently, those parameters were mapped to Hue, Saturation and Value, respectively, of an HSV color model, which was utilized for characterizing the lesions. Also, Hue heterogeneity was qualitatively assessed for the characterization of lesions. In addition, observers evaluated the haemodynamic properties of the lesions with the conventional hand-drawn ROI based technique (Kuhl system). The results of the two methods were then compared to the histological ground truth to derive their classification performance. Classification performance for the proposed and the conventional one was Az=0.880.05 and Az=0.860.05, respectively, by means of ROC analysis. Results indicate no statistically different performance between the two methods, with the proposed one offering time savings and reproducibility. / Η μαγνητική τομογραφία μαστών (MRM) είναι μια πολλά υποσχόμενη τεχνική, αφού προσφέρει απεικόνιση των μαστών με υψηλή διακριτική ικανότητα αλλά και εγγενή ικανότητα διάκρισης διαφόρων τύπων μαλακών ιστών, χωρίς τη χρήση ιοντίζουσας ακτινοβολίας. Η προσθήκη δυναμικής απεικόνισης των ιστών του μαστού με τη χρήση παραμαγνητικής σκιαγραφικής ουσίας στο εξεταστικό πρωτόκολλο ισχυροποίησε τη μέθοδο αφού υπάρχει σημαντική διαφοροποίηση στην αιμοδυναμική συμπεριφορά ανάμεσα σε καλοήθεις και κακοήθεις παθήσεις λόγω του αγγειακού δικτύου που δημιουργούν οι μεταβολικές ανάγκες των καρκινικών κυττάρων. Υπολογιστικά συστήματα αυτόματης διάγνωσης που διατίθενται εμπορικά, πραγματοποιούν φαρμοκοκινητική ανάλυση της δυναμικής συμπεριφοράς των ιστών του μαστού με χρήση μαθηματικών αλγορίθμων όπως ο αλγόριθμος τριών χρονικών σημείων (3TP). Από τέτοιες αναλύσεις εξάγονται ποσοτικές παράμετροι που έχουν ευθεία συσχέτιση με διάφορα χαρακτηριστικά της υποκείμενης παθολογίας και μπορούν να συγκριθούν με τα αποτελέσματα ιστολογικών μελετών. Παρόλα αυτά είναι γενικά αποδεκτό ότι για να επιτευχθεί ακριβής υπολογισμός των παραμέτρων αυτών απαιτείται η επιλογή ειδικού εξεταστικού πρωτοκόλλου με μεγάλες απαιτήσεις σε χρονική διακριτική ικανότητα. Η επιλογή απλών μαθηματικών μοντέλων για τον υπολογισμό ποσοτικών παραμέτρων με έμμεση συνάφεια με την παθολογία μας δίνει τη δυνατότητα να ελαχιστοποιήσουμε τον όγκο δεδομένων που παρέχει η εξέταση σε ένα σετ εικόνων και να κάνουμε τη διαδικασία της διάγνωσης πιο γρήγορη και ασφαλή από ότι παρουσιάζεται σήμερα στην κλινική ρουτίνα. Η σειρά των εικόνων της δυναμικής μελέτης των εξετάσεων μαγνητικής τομογραφίας μαστών 55 ασθενών αναλύθηκαν για αυτή τη μελέτη. Ακτινολόγοι με εξειδίκευση στην εξέταση κατέταξαν όλες τις ανιχνευθείσες παθολογικές περιοχές κατά BIRADS. Έγινε προσέγγιση των πειραματικών τιμών των pixels των δυναμικών σειρών με ένα απλό διγραμμικό μοντέλο και εξάχθηκαν χάρτες ποσοτικών παραμέτρων έκπλυσης σήματος (washout), χρόνου μέγιστης ενίσχυσης (time to peak) και ενίσχυσης (washin). Στη συνέχεια αυτές οι παράμετροι χρησιμοποιήθηκαν σαν απόχρωση (Hue), κορεσμό (Saturation) και ένταση (Value) της χρωματικής κλίμακας HSV. Με αυτή την αντιστοίχηση δημιουργήθηκαν χάρτες λειτουργικής απεικόνισης οι οποίοι και χρησιμοποιήθηκαν για το χαρακτηρισμό της παθολογίας. Για τον τελικό χαρακτηρισμό εκτιμήθηκε ποιοτικά και η ανομοιογένεια των λειτουργικών χαρτών ως προς την απόχρωση. Επιπλέον η αιμοδυναμική συμπεριφορά των ευρημάτων εκτιμήθηκε με τη συμβατική μέθοδο περιγραφής περιοχής ενδιαφέροντος με το χέρι και εξαγωγής καμπύλης σήματος – χρόνου από αυτήν την περιοχή (μέθοδος Kuhl). Τα αποτελέσματα των δυο μεθόδων συγκρίθηκαν με τα αποτελέσματα της ιστολογικής εξέτασης των ελεγχθεισών παθολογιών και υπολογίστηκε η απόδοση της κάθε μεθόδου. Αυτή βρέθηκε Az=0.880.05 για την προτεινόμενη μέθοδο και Az=0.860.05 για την κλασική, με χρήση ανάλυσης ROC. Τα αποτελέσματα αυτά υποδεικνύουν ότι δεν υπάρχει στατιστικώς σημαντική διαφορά μεταξύ των δυο μεθόδων, με την προτεινόμενη να παρουσιάζει κέρδος χρόνου και αυξημένη επαναληψιμότητα.