Dissertation

Thesis (Ph.D.)--Tufts University, 2004. / Adviser: Sergio Fantini. Submitted to the Dept. of Electrical Engineering. Includes bibliographical references (leaves 201-202). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

This dissertation investigates how policies and financial incentives may affect the use of services within the United States health care system. The research consists of two distinct parts: Part I comprises two studies examining the impact of recently enacted state legislation regarding dense breast tissue on the use of downstream imaging; Part II delves into changes in physician reimbursement and their effect on health care delivery. Dense breast tissue is a common finding that decreases the sensitivity of mammography in detecting cancer. Some states have passed legislation requiring health care providers to notify patients with dense breast tissue that identification of early cancers may be compromised. Others have also aimed to increase access to supplemental screening tests by requiring health plans to include such follow-up options in covered benefits. The legislation has been controversial because supplemental imaging following a negative screening mammogram for patients with no other risk factors provides little benefit compared to its substantial cost. In the first study, we analyzed whether the dense breast tissue notification laws affected the probability of screening mammography follow-up by ultrasound and magnetic resonance imaging (MRI). We found strong evidence that implementing the notification legislation led to an increase in the probability of downstream breast ultrasound imaging in most states, and to an increase in the probability of downstream breast MRI in some states. In the second study, we identified specific characteristics of various state-level dense breast policies that were associated with increased use of downstream breast ultrasound imaging. In Part II of the dissertation, we assessed the extent to which changes in health care prices affect the provision of health services by physicians in various medical and surgical specialties in both Medicare and the private sector. We exploited the considerable changes in the Medicare Physician Fee schedule due to procedural code bundling that happened between 2010 and 2014 as the source of variation in health care prices. Our results showed that volume responses to changes in health care prices are inelastic and vary in both direction and magnitude by specialty and sector. / 2019-10-31T00:00:00Z

<p>This work investigates phantom and subject positioning as well as collecting data with a variety of angular sampling and acquisition trajectories. The overall goal of this work has been to utilize the dedicated, breast SPECT-CT system to acquire the best possible images. A large portion of this work has been to apply corrections to the system for quantitative imaging. The system has been shown to provide high quality images with minimal out-of-field signal contribution. Additionally, the quantification procedure has been shown to be within 10% of the known activity concentration present at the time of imaging for both VAOR and PROJSINE trajectories.</p> / Dissertation

Η ψηφιακή τομοσύνθεση στην τρισδιάστατη απεικόνιση μαστών, είναι μια μέθοδος ανακατασκευής οποιουδήποτε αριθμού τομογραφικών επιπέδων τυχαίου προσανατολισμού, στη βάση ψηφιοποιημένων προβολικών εικόνων της εξεταζόμενης περιοχής, που λαμβάνονται κατά την διάρκεια της περιστροφής του συστήματος ακτινολογική λυχνία-ενισχυτής εικόνας με κέντρο το ισόκεντρο του μηχανήματος και κατά το προεπιλεγμένο τόξο. Δυστυχώς, σε περιπτώσεις αυξημένης πυκνότητας μαστών, η ποιότητα των ανακατασκευασμένων επιπέδων επηρεάζεται από θόρυβο, λόγω των επιπροβαλλόμενων στοιχείων υπερκείμενων ή υποκείμενων επιπέδων. Το αντικείμενο που πραγματεύεται η εργασία, είναι η μελέτη διαφόρων τεχνικών επεξεργασίας των τομών, που θα μπορούσαν να αφαιρέσουν το θόρυβο από τα ανακατασκευασμένα επίπεδα και να βελτιώσουν την ποιότητά τους. Για αυτόν το λόγο, δημιουργήθηκαν τρία πειραματκά phantoms διαφορετικής πολυπλοκότητας, στα οποία προστέθηκαν δυσμορφίες που αντιπροσωπεύουν μικρές ασβεστοποιήσεις και μάζες χαμηλής αντίθεσης. Στη συνέχεια, υποβλήθηκαν στην προσομειωμένη απεικόνιση με ακτίνες Χ, προκειμένου να παραχθεί ένα σύνολο προβολικών εικόνων σε τόξο εύρους από -20° έως +20° κάθε 2°. Οι ακτινοβολημένοι όγκοι ανακατασκευάστηκαν μέσω του αλγόριθμου πολλαπλών προβολών (MPA), γραμμένο σε Matlab. Οι ανακατασκευασμένες φέτες έχουν πλάτος λιγότερο από 1mm, προκειμένου να ανιχνευθούν μικρές ασβεστοποιήσεις. Αναπτύχθηκαν και αξιολογήθηκαν πειραματικά δύο αλγόριθμοι για την περαιτέρω επεξεργασία των λαμβανόμενων τομών. Ο πρώτος είναι βασισμένος στην λογαριθμική μέθοδο αφαίρεσης δομών που βρίσκονται εκτός επιπέδου ενδιαφέροντος, συνδυάζοντας τεχνικές τονισμού της εικόνας. Η δεύτερη τεχνική εκτελεί το φιλτράρισμα της εικόνας, συγκρίνοντας τις τιμές των pixel, σε όλο τoν όγκο προς ανακατασκευή. Η ποιότητα της εικόνας καθορίστηκε μέσω της οπτικής αξιολόγησης των ανακατασκευασμένων επιπέδων καθώς και τον υπολογισμό του CNR. Και οι δύο αξιολογήσεις κατέδειξαν καλή διαχωριστική και αφαίρετική ικανότητα του τομογραφικού θορύβου. Το MPA σε συνδυασμό με τους προτεινόμενους αλγορίθμους αφαίρεσης θορύβου, μείωσε τον τομογραφικό θόρυβο στις ανακατασκευασμένες εικόνες και αύξησε το CNR. Περαιτέρω μελέτες θα περιλαμβάνουν την ανάπτυξη ενός γενικευμένου αλγορίθμου αφαίρεσης θορύβου που θα συνδυάσει τις προτεινόμενες δύο τεχνικές. / Digital tomosynthesis for breast imaging is a method of reconstructing any number of tomographic planes, by using a set of limited angle projections, acquired as the X-ray source moves in an arc around the breast. Unfortunately, in case of dense breasts, the quality of the reconstructed planes is affected by structured noise, due to blur from planes other than the fulcrum plane. The purpose of this project is to study different post-processing techniques that could remove the noise from the reconstructed planes and improve their quality. For this purpose, three software phantoms of different complexity with inserted abnormalities that represent small micro calcifications and low-contrast masses were created. Subsequently, they were subjected to x-ray imaging simulation in order to produce a set of projection images in the gantry arc from -200 to 200 every 20. The irradiated volumes were reconstructed with the Multiple Projections reconstruction Algorithm (MPA) written in Matlab. Reconstructed slices were with width of less than 1mm width, in order to detect the small microcalcifications. Two algorithms for removing unwanted structured noise were explored. The first one is based on the iterative logarithmic subtraction method of unrelated structures combined with image enhancement techniques. The second technique performs a filtering action based on a pixel intensity value comparison, throughout the phantom volume. Image quality was assessed by evaluation of the reconstructed planes in terms of both visual assessment and contrast to noise ratio (CNR). Both evaluations demonstrated good noise discrimination and elimination, followed by an improvement of the contrast and visibility of abnormalities in tomograms. The MPA followed by the proposed noise removal algorithms resulted in less noisy tomosynthesis images, higher CNR and feature contrast for both low- and high contrast details. Further studies include developing of a generalised noise removal algorithm that will combine the proposed two techniques.

Molecular breast imaging (MBI) is a relatively new clinical breast imaging modality, which has the potential to have a significant impact in breast cancer screening and perioperative breast imaging for women with high risk factors for developing breast cancer. Two objectives were proposed in this thesis to increase the use of MBI. First, a magnetic resonance (MR)-compatible gamma camera was developed for combined molecular/MR breast imaging. MBI is a functional imaging technique with high specificity and sensitivity but could benefit from the addition of anatomical information from breast MRI for lesion localization, cancer staging, treatment planning and monitoring. A small area (8cm x 8cm) cadmium zinc telluride (CZT) based gamma camera was developed and tested for MR compatibility in both sequential and simultaneous imaging conditions. Results indicated that the gamma camera was minimally affected during both sequential and simultaneous imaging with a gradient echo (GRE) and spoiled gradient echo (GRE) sequence. Signal to noise ratio (SNR) degradation was observed in the MR images but no geometric distortions were observed. Simultaneous imaging is feasible, but a reassessment of the RF shielding would be required to minimize the noise contribution degrading image quality. Second, backscatter photons were investigated as a potential dose reduction technique for MBI. While the effective dose from MBI is relatively low in comparison to other nuclear medicine procedures, the dose is considered high in relation to mammography and in order to increase acceptance as an alternative breast imaging method, dose reduction is an important objective. Backscatter photons have the same spatial information as primary photons but are typically discarded along with other scattered photons. A scatter compensation method called the triple energy window (TEW) was used to extract backscatter photons from the Compton scattering spectrum and added to the primary photons, increasing count sensitivity by 6%. The noise level matched the increase in contrast leading to negligible change in lesion contrast to noise ratio (CNR). Dose reduction is not justified with this particular technique because of the elevated noise level, but the use of backcsatter photons show potential with improved contrast. / Dissertation / Doctor of Philosophy (PhD)

This study is intended to determine the feasiblity of establishing a high-quality, free-standing MR imaging center dedicated to the breast in or about the City of Redlands.

Introdução: Os enxertos de gordura autóloga (lipoenxertia) são utilizados há muito tempo como material de preenchimento para correção de defeitos de tecido mole, sendo inicialmente utilizados para correção de defeitos faciais. Nos últimos anos, houve um crescente interesse no uso da lipoenxertia em mamas, tanto como método de reconstrução em pacientes submetidas a cirurgias por câncer de mama quanto em procedimentos estéticos. A gordura é considerada um material de preenchimento ideal em decorrência da facilidade de obtenção e da baixa reação imunogênica e alérgica, além de se tratar de material autólogo. Os principais problemas da lipoenxertia são as taxas de reabsorção imprevisíveis do material enxertado (40-60%), a preocupação quanto a sua segurança, principalmente pela hipótese de a gordura estimular o crescimento de células cancerígenas e o fato da necrose do material enxertado poder produzir fibrose, calcificações ou cistos oleosos na mama, os quais poderiam interferir na interpretação das imagens mamográficas. A partir da técnica desenvolvida por Coleman, diversos estudos surgiram mostrando a eficácia e a segurança da lipoenxertia, já que a mesma não parece interferir nas imagens radiológicas, demonstrando que alterações mamográficas após a lipoenxertia são facilmente interpretadas como alterações benignas por radiologistas experientes. Objetivo: Analisar se a lipoenxertia realizada durante a cirurgia conservadora por câncer de mama e posteriormente seguida de radioterapia causa modificações mamográficas. Método: Foi realizado seguimento de 171 pacientes com diagnóstico de câncer inicial submetidas a tratamento conservador e radioterapia no Hospital de Clínicas de Porto Alegre, no período de junho de 2010 a junho de 2013. Trinta e oito dessas pacientes foram submetidas a reconstrução imediata com lipoenxerto segundo a técnica de Coleman. Resultados: A média da idade das pacientes foi de 58,9 anos para as pacientes sem lipoenxerto e 52,5 anos para as com lipoenxerto, e a média do volume enxertado foi de 125 mL. Foram analisadas as alterações mamográficas dessas pacientes 6, 12, 18 e 24 meses após a radioterapia. Constatou-se uma maior incidência de alterações benignas, como cistos oleosos e esteatonecrose, nas pacientes submetidas a lipoenxertia. Não se detectou no presente estudo diferenças quanto a frequência de nódulos, achados suspeitos ou na classificação BI-RADS entre as pacientes com e sem lipoenxerto. Conclusão: Conclui-se, portanto, que a lipoenxertia causa alterações mamográficas facilmente percebidas como benignas, sem elevar a incidência de achados inconclusivos ou suspeitos. Trata-se de um estudo inédito, pois a reconstrução mamária com gordura é realizada no momento da cirurgia conservadora. / Background: Fat grafts have been used for a long time as a filling material for correction of soft tissue defects. There is growing interest in the use of fat grafting as a method of breast reconstruction in patients undergoing surgery for breast cancer. Fat is considered an ideal filler material due to its easy availability and low immunogenic and allergic reaction and because it is an autologous material. However, fat grafts often have high rates of reabsorption and replacement by fibrous scar tissue, calcifications or oily cysts, which can generate sequels and difficulties in the interpretation of radiological images of the breast. Based on the technique developed by Coleman, several studies have emerged showing the efficacy of fat grafting and that it does not seem to interfere with the early diagnosis of breast cancer. Studies have shown that the incidence of mammographic changes after fat grafting does not differ from other surgical procedures of the breast and that they are easily interpreted as benign changes by experienced radiologists in breast imaging. Aim: Analyze mammographic changes in fat grafting performed during conservative surgery for breast cancer and subsequently followed by radiotherapy. Methods: A total of 171 patients diagnosed with early-stage cancer who received conservative treatment and radiotherapy at the Hospital de Clínicas de Porto Alegre from June 2010 to July 2013 were followed in the present study. Thirty-eight of these also underwent immediate reconstruction with fat grafting, as described by Coleman. Results: Mean patient age was 58.9 years for those not exposed to lipomodeling, and 52.5 years in the remainder of the sample. The mean graft volume was 125 ml. In the present study, oncological follow-ups at 6, 12, 18 and 24 months revealed a higher incidence of benign mammographic findings, such as oil cysts and steatonecrosis, in women who had undergone lipomodeling. However, no between-group differences were identified on any other radiological parameter, including scarring, nodules, suspicious findings and BI-RADS categories. Conclusion: These findings suggest that the mammography alterations caused by lipomodeling are easily identified as benign, and that this procedure is not associated with an increased incidence of inconclusive or suspicious findings. This is a unique study because breast reconstruction with fat is conducted at the time of conservative surgery.

Electrical parameter profiles of human breast images can be used to simulate and analyze the anticipated effects on tissue from its interaction with electromagnetic fields involved in the cancer treatment exposure. In part, the success of this approach depends on the accuracy and precision in identifying the different tissue types. In this work, we propose two methods of segmenting human breast images with malignant tumors. The first method of algorithmic partitioning of the image involves manual color-edge contouring of the tissues using a cursor and subsequent identification of the tissue types. For the second method, MRI T1 values and thresholds are used to perform segmentation and we investigate the potential of incorporating edge detection. The first method is effective, while the second lacks precision, but eliminates the need of manual contouring. The images are imported as BMP files into SEMCAD, an electromagnetic simulation tool based on finite-difference time-domain method, which recognizes the grouped tissues and creates a model of the image. The model allows the user to easily assign electrical parameter values to the grouped tissues, according to the measured values reported in the literature.

Breast CT is a promising modality whose inherent scatter could be used to reconstruct electron density (rho_e) images. This has led us to investigate the benefits of reconstructing linear attenuation coefficient (mu) and (rho_e) images of the breast. First generation CT provides a cost-effective and simple approach to reconstruct (rho_e) images in a laboratory but is limited by the anisotropic probability of scatter, attenuation, noise and contaminating scatter (coherent and multiple scatter). These issues were investigated using Monte Carlo (MC) simulations of a first generation breast scatter enhanced CT (B-SECT) system. A reconstruction algorithm was developed for the B-SECT system and is based on a ring of detectors which eliminates the scatter dependence on the relative position of the scattering centre. The algorithm incorporates an attenuation correction based on the (mu) image and was tested against analytical and MC simulations. MC simulations were also used to quantify the dose per scan. The ring measures a fraction of the total single incoherent scatter which is proportional to ray integrals of (rho_e) and can be quantified even when electron binding is non negligible. The algorithm typically reconstructs accurate (rho_e) images using a single correction for attenuation but has the capability for multiple iterations if required. MC simulations show that the dose coefficients are similar to those of cone beam breast CT. Coherent and multiple scatter can not be directly related to (rho_e) and lead to capping artifacts and overestimated (rho_e) by a factor greater than 2. This issue can be addressed using empirical corrections based on the radiological path of the incident beam and result in (rho_e) images of breast soft tissue with 1% accuracy, 3% precision and a mean glandular dose of 4 mGy for a 3D scan. The reconstructed (rho_e) image was more accurate than the (rho_e) estimate derived from the (mu) image. An alternative correction based on the thickness of breast traversed by the beam provides an enhanced contrast image reflecting the breast scatter properties. These results demonstrate the feasibility of detecting small (rho_e) changes in the intact breast and shows that further experimental evaluation of this technique is warranted.