John Herd Thompson

An Anthropomorphic Breast Model for Breast Imaging Simulation and Optimization

RATIONALE AND OBJECTIVES Optimization studies for x-ray-based breast imaging systems using computer simulation can greatly benefit from a phantom capable of modeling varying anatomical variability across different patients. This study aimed to develop a three-dimensional phantom model with realistic and randomizable anatomical features. MATERIALS AND METHODS A voxelized breast model was developed consisting of an outer layer of skin and subcutaneous fat, a mixture of glandular and adipose, stochastically generated ductal trees, masses, and microcalcifications. Randomized realization of the breast morphology provided a range of patient models. Compression models were included to represent the breast under various compression levels along different orientations. A Monte Carlo (MC) simulation code was adapted to simulate x-ray based imaging systems for the breast phantom. Simulated projections of the phantom at different angles were generated and reconstructed with iterative methods, simulating mammography, breast tomosynthesis, and computed tomography (CT) systems. Phantom dose maps were further generated for dosimetric evaluation. RESULTS Region of interest comparisons of simulated and real mammograms showed strong similarities in terms of appearance and features. Noise-power spectra of simulated mammographic images demonstrated that the phantom provided target properties for anatomical backgrounds. Reconstructed tomosynthesis and CT images and dose maps provided corresponding data from a single breast enabling optimization studies. Dosimetry result provided insight into the dose distribution difference between modalities and compression levels. CONCLUSION The anthropomorphic breast phantom, combined with the MC simulation platform, generated a realistic model for a breast imaging system. The developed platform is expected to provide a versatile and powerful framework for optimizing volumetric breast imaging systems.

The pediatric bowel management clinic: Initial results of a multidisciplinary approach to functional constipation in children

The multifactorial nature of functional constipation in children suggests that a multidisciplinary management approach may be effective. The authors tested this hypothesis in a newly created pediatric Bowel Management Clinic (BMC). Detailed data were collected prospectively on all patients seen in the clinic over the first 16 months. Both quantitative and qualitative analyses were performed to describe the index population and to demonstrate the impact of the intervention. Satisfaction with care in the clinic was measured using the Measure of Processes of Care tool, then compared with a normative sample. One hundred fourteen patients, all previously treated unsuccessfully for constipation, were referred to a team comprised of a physician, nurse practitioner, nurse educator, dietitian, and psychosocial nurse specialist. The mean age was 5.4 years with equal gender distribution. Between the first and last visits recorded, several variables including stool consistency and frequency, soiling frequency, abdominal pain, rectal pain, and rectal bleeding all showed statistically significant (P < .05) improvement. Qualitative data analysis showed the significant psychosocial impact of constipation on patients and their families. In the Measures of Processes of Care questionnaire, scores for the BMC were higher than normal on all scales except in provision of information. A multidisciplinary approach to functional constipation leads to both patient and parent satisfaction and significant short-term improvement. Further studies will examine the long-term impact of the clinic.

Entry and Exit: Canadian Immigration Policy in Context

Immigration and the multicultural population that results from it are contentious issues in contemporary Canada. Canada accepts more than twice as many immigrants per capita as does the United States, and a majority of immigrants now comes from nontraditional sources in Asia, the Caribbean, and Central America. Critics of a liberal immigration policy charge that these newcomers threaten Canadas social harmony and challenge its cultural identity and that the country faces unprecedented economic and security problems because of uncontrolled immigration. Historical and contemporary evidence suggests, however, that the situation is neither unprecedented nor a crisis. Canada needs immigrants for the compelling reasons it has always sought them: for economic growth and to replace population lost by emigration to the United States. By any comparative yardstick, the Canadian experiments in immigration and multiculturalism have been a resounding success.

A Case for Wide-Angle Breast Tomosynthesis

RATIONALES AND OBJECTIVES Conventional mammography is largely limited by superimposed anatomy. Digital breast tomosynthesis (DBT) and computed tomography (CT) alleviate this limitation but with added out-of-plane artifacts or limited chest wall coverage. This article presents a wide-angle breast tomosynthesis (WBT), aimed to provide a practical solution to these limitations, and offers an initial study of its utility in comparison with DBT and CT using a singular evaluation platform. MATERIALS AND METHODS Using an anthropomorphic virtual breast phantom, a Monte Carlo code modeled a breast imaging system for three modalities of DBT, WBT, and breast CT (44°, 99°, and 198° total angle range, respectively) at four breast compression levels, all at a constant mean glandular dose level of 1.5 mGy. Reconstructed volumes were generated using iterative reconstruction methods. Lesion detectability was estimated using contrast-to-noise ratio and a channelized Hotelling observer model in terms of the area under the receiver operating characteristic (AUC). RESULTS Results showed improved detection with increased angular span and compression. The estimated AUCs for WBT were similar to that of CT. Comparative performance averaged over all thicknesses between CT and WBT was 4.3 ± 3.0%, whereas that between WBT and DBT was 5.6 ± 1.0%. At compression levels reflective of the modality (7-, 5-, and 4-cm thickness for CT, WBT, and DBT, respectively), WBT yielded an AUC comparable to CT (performance difference of 1.2%) but superior to DBT (performance difference of 5.5%). CONCLUSIONS The proposed imaging modality showed significant advantages over conventional DBT. WBT exhibited superior imaging performance over DBT at lower compression levels, highlighting further potential for reduced breast compression.

Wide-angle breast tomosynthesis: initial comparative evaluation

Conventional mammography is largely limited by superimposed anatomy which is alleviated by breast tomosynthesis and CT. Limited acquisition in tomosynthesis can result in significant out of plane artifacts while large angular acquisition span in CT can limit the imaging coverage of the chest wall near the breast. We propose a new breast imaging modality, wide-angle breast tomosynthesis (WBT), aimed to provide a practical compromise between 3D sampling and chest-wall coverage. This study compares lesion detection between conventional digital breast tomosynthesis, WBT, and breast CT (44°, 99°, and 198° total angle range, respectively) under equal patient dose conditions. A Monte Carlo (MC) code based on the Penelope package modeled a virtual flat-panel breast tomosynthesis system. The modalities were simulated at four breast compression levels. Glandular dose to the breast was estimated and the radiation flux was subsequently adjusted to achieve a constant mean glandular dose level of 1.5 mGy, independent of the breast thickness and acquisition geometry. Reconstructed volumes were generated using iterative reconstruction methods. Lesion detectability was estimated using contrast-to-noise-ratio. Results showed improved detection with increased angular span and compression. Evaluations also showed improved performance of WBT over DBT at lower compression levels, therefore highlighting potential for reduced breast compression when using a larger acquisition angle.

Saskatchewan: A New History (review)

the British hunter to the increasing sophistication and spread of an over-arching environmental imperialism. Indeed, elite American hunters in Eastern Canada during the same period employed much of the same rhetoric. They, too, wrote detailed monographs and mapped out the results of their own explorations and sublime experiences, all illustrated by similar picturesque imagery. By the mid-nineteenth century there was an emerging struggle between British, American, and Canadian sportsmen over the control of hunting territory throughout Canada, and much of it played out in British and provincial courts. Was the British appropriation of Rupert’s Land part of that process? What was unique about British activities there? Perhaps a more thorough understanding of the character of British activities might be better revealed with a more detailed account of the relationship between their ‘British’ values and the animals they chose to hunt, to import, and ultimately to acclimatize in Western Canada. Although a slim volume, this is a well-argued text that adds novel interpretations of little-used sources and provides a model approach for interdisciplinary research and writing that seamlessly integrates concepts in both cultural and environmental history. As such, this work will interest scholars in a range of fields, including nineteenthcentury literature, colonial/imperial studies, and cultural geography, to name only a few. Those working in the nascent field of Canadian environmental history, especially, will find this a rewarding study in the interconnectedness of nature, class, and culture. darin kinsey Université Laval