Each of two detectors used in our Positron Emission Mammography (PEM) system consists of four 36mm x 36mm x 20mm bismuth germanate (BGO) detector blocks coupled to a crossed-wire anode photomultiplier tube (PMT). To achieve a high spatial resolution, the crystal blocks have been finely pixelated using a diamond saw. In each detector, 36 x 36 1.9mm x 1.9mm crystal elements are coupled directly to the PMT window and, on the opposite face of the blocks, 35 x 35 elements are offset by 0.9mm along both the x- and y-axes of the PMT. Techniques developed for the successful machining and surface-preparation of the detector blocks are described. Results indicating the detector block performance in terms of spatial and energy resolution are presented. / As part of a system calibration routine, a novel method for crystal element identification has been developed. This robust and reproducible algorithm succeeds in identifying 59 x 49 crystal elements on each detector face. The results are used to generate a Look-Up-Table (LUT) that is accessed during data acquisition for the effective correction of spatial distortion inherent in the detectors. Crystal identification also facilitates an improvement of the capability for accurate energy discrimination, since the detector gain and energy resolution are considered on an element-by-element basis by accessing an energy LUT. Employing a third LUT, which contains the relative efficiencies of individual crystal elements results in a significant improvement in detector uniformity.

X-ray mammography is currently the modality of choice for breast cancer screening. However, X-ray mammography cannot provide a positive diagnosis for cancer. A novel, dedicated breast imaging modality has been developed based on the principles of Positron Emission Tomography (PET). The Positron Emission Mammography (PEM) system is a sensitive, high resolution ($ sp sim2$ mm) breast scanner. PEM detects increased cell metabolism (indicating the presence of cancer) by imaging the distribution of tumour-specific metabolic radiotracers. The accurate co-registration of metabolic and X-ray breast images is important for localizing and characterizing suspicious lesions. Traditionally, registration between different imaging modalities has been difficult. PEM simplifies the image registration process by acquiring an X-ray image and a metabolic image consecutively, without moving the breast between scans. The PEM detectors are integrated into a conventional mammography unit and a co-registration tool has been developed. By providing metabolic information about a suspicious breast lesion, the number of invasive biopsy procedures (currently used to diagnose breast cancer) can be reduced.

Purpose. To evaluate the role of endovaginal sonography (EVS) and Doppler ultrasound in detecting endometrial carcinoma in women presenting with postmenopausal bleeding. / Materials & methods. We prospectively evaluated 421 women with EVS over a 5-year period. Of these 31 (7.4%) were diagnosed with endometrial carcinoma at histopathology. For each patient, biometric and morphologic parameters, as well as Doppler indices of the endometrium were obtained. / Results. Applying a combination of biometric and morphologic criteria, EVS diagnosed malignancy with a sensitivity of 77% (95% CI: 59%--90%) and a specificity of 84% (80%--87%). Using only biometric criteria (endometrial thickness >2mm indicating malignancy), EVS achieved a sensitivity of 100% (91%--100%) and a specificity of 24% (20%--29%), whereas the corresponding sensitivity and specificity for endometrial thickness >5mm was 74% (55%--88%) and 59% (54%--64%), respectively. The most predictive Doppler index was peak venous velocity (95% CI for odds ratio: 1.08--1.40). / Conclusion. Using a combination of biometric and morphologic sonographic criteria achieves the best accuracy in diagnosing patients with endometrial carcinoma, however at the cost of a decreased sensitivity.

No description available.

<p> In the spring of 2012, based on recommendations from the International Commission on Radiological Protection (ICRP), the Nuclear Regulatory Commission (NRC) proposed three amendments to reduce current radiation exposure limits for radiation workers. The NRC proposals have caused some concern within the radiopharmaceutical industry. The regulatory changes may affect the ability of radiopharmacy workers to remain on the job, thereby inflicting additional costs to radiopharmacies if they are required to replace workers who have reached their yearly exposure limits. </p><p> This research sought to determine whether or not the new regulatory proposals will in fact have a financial impact on the radiopharmaceutical industry. This research was a retrospective case study that analyzed four radiopharmaceutical production facilities and their employee radiation exposure reports. Results of the study suggest that the NRC's proposed amendments to reduce radiation levels will not have a great adverse effect, either financially or from an employee exposure standpoint, on the current radiopharmacy system. The research demonstrated that existing as low as reasonably achievable (ALARA) standards have resulted in radiopharmacy workers receiving exposures well below the current limits, and within the NRC proposed limits. Of 77 employees studied over a 10 year period, only seven employees (9 %) would have been removed from the production process for overexposure to any one of the NRC's proposed limits. However, this research reviewed small a subset of four radiopharmacies and did not examine other industries and professions utilizing ionizing radiation.</p>

In the treatment of Parkinson's disease some cases require the ablation of a specific region in the basal ganglia. The accurate localization of this region inside the patient's brain is essential and because direct visual anatomical information for such deep brain structures is not available, the surgeon has to rely on other sources of information such as MRI, CT and x-ray of the patient's brain. However these imaging techniques do not provide sufficient anatomical information, requiring the use of a subcortical brain atlas book to assist in the localization of the different structures. This way of proceeding is cumbersome and results in a certain lack of accuracy in the localization of the different brain structures. / We developed a method that aids the surgeon to obtain the sufficient anatomical information in a simpler and more accurate manner. We provide him with a segmentation of the patient's MRI scan based on the Schaltenbrand and Wahren subcortical atlas. To achieve such segmentation a volumetric version of the atlas was obtained and was then mapped to a model brain MRI using landmark matching. Using an automated tool for the three-dimensional registration of two MRI volumes the deformation transformation between the model brain MRI and the patient's brain MRI was obtained. By applying this same transformation to the volumetric atlas, we obtain a superposition of a volumetric subcortical atlas onto the MRI of the patient's brain in the stereotactic space. This method results in a more accurate localization of the surgical lesion, thus reducing the number of additional interventions which are often necessary when the results of the first procedure are shown to be unsatisfactory. The whole guidance system is now used routinely at the Montreal Neurological Institute and is part of the standard surgical procedure.

An isocentric teletherapy cobalt unit provides a viable alternative to an isocentric linac as a radiation source for radiosurgery. An isocentric cobalt unit was evaluated for its potential use in radiosurgery in three areas: (1) the physical properties of its radiosurgical beams, (2) the quality of radiosurgical dose distributions obtained with 4 to 10 non-coplanar arcs, and (3) the accuracy with which the radiosurgical dose can be delivered. In each of these areas the 10 MV beam of a linear accelerator served as a standard for comparison. / The difference between the 80%--20% penumbras of the radiosurgical fields of the cobalt-60 and 10 MV photon beams is remarkably small, with the cobalt-60 beam penumbras on the average only about 0.7 mm larger than those of the linac beam. Differences between the cobalt-60 and 10 MV plans in terms of dose homogeneity within the target volume and conformity of the prescribed isodose volume to the target volume are also minimal, and therefore of limited clinical significance. Moreover, measured obtained isodose distributions of a radiosurgical procedure performed on the isocentric cobalt unit agreed with calculated distributions to within the +/-1 mm spatial and +/-5% numerical dose tolerances which are generally accepted in radiosurgery. The viability of isocentric cobalt units for radiosurgery would be of particular interest for centers in developing counties where cobalt units, because of their relatively low costs, provide the only megavoltage source of radiation for radiotherapy, and could easily and inexpensively be modified for radiosurgery.

It is known that slight variations in total dose delivered to the patient in external beam photon radiotherapy can significantly alter the probability of tumour control. For this reason, ICRU has recommended a goal of $ pm$5% precision in the dose delivery to the target volume. Several investigators have analyzed the degree of precision routinely achieved and have come to the conclusion that ICRU's goal can be attained, but in practice this is just barely so. / We have measured the degree of precision which exists in our institution by examining each step of the radiotherapy process on a cobalt unit and a 10 MV linear accelerator. Our study finds beam intensity uncertainties of $ pm$3.8% (one standard deviation) and beam positional uncertainties of $ pm$5.5 mm (one standard deviation). The effect of these uncertainties on the dose to the patient is illustrated for a typical case.

The utilization of ultrasound in diagnostic medicine has increased since the 1950's. Ultrasound is a non-invasive two dimensional (2D) imaging technique that provides useful information about underlying soft tissue anatomical structures. Developed recently, three dimensional (3D) reconstruction algorithms convert a series of sequential 2D ultrasound images into 3D data sets. 3D reconstruction is one phase in a pipeline for 3D ultrasound volume visualization that typically takes upwards of 2 minutes to complete. The objective of this research focuses on high speed 3D ultrasound reconstruction by comparing reconstruction speeds on parallel and sequential processors. To decrease reconstruction times, optimizations such as; conversion from floating point to fixed point, multithreading, in-line coding, and mathematical analysis were performed. Optimizations achieved a 15%--50% performance increase. Although parallel processors are not a requirement for 3D reconstruction, they will be necessary to achieve the ultimate goal of real-time 3D ultrasound volume visualization.

Background: Cognitive processing in diagnostic oral radiology requires a solid foundation in the basic sciences as well as knowledge of the radiologic changes associated with disease. Although it is generally assumed that in dentistry, students must acquire both knowledge sets, little is known about the role or impact of the basic sciences on clinical reasoning because the two have traditionally been taught separately in the curriculum. Objectives: This dissertation investigates the role of basic sciences in oral radiology and its effects on diagnostic accuracy. The studies were designed to satisfy the following research aims: 1) to examine and compare the effects of integration and segregation of the basic and clinical sciences on diagnostic accuracy; 2) to examine the effects of basic science instructional methodology and diagnostic strategy on diagnostic outcomes; 3) to explore the potential interactions between instructional methodologies used to teach disease categorization and diagnostic strategies; and 4) to examine the effects of testing the basic sciences on diagnostic accuracy in an integrated instructional methodology. Methods: We conducted three quantitative studies, all of which involved a learning phase and an immediate testing phase that assessed diagnostic performance and memory. In each of the studies, learning strategies, and or testing frequency were varied. We also included performance assessment of diagnostic ability and memory, one week after the initial learning phase. Results: Our results show that students who learned basic sciences explanations had higher diagnostic accuracy when using a holistic System 1 type diagnostic strategy than those who did not. We also demonstrated that basic science knowledge was the most effective when directly integrated with the clinical sciences, and this result is further enhanced with testing. Conclusions: We conclude that integrated basic science learning provides a coherent framework that has the potential to significantly improve the diagnostic accuracy of training dentists.