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<p>This thesis research builds upon prior work that developed separate SPECT and CT
(computed mammotomography, or breast CT) devices that were independently capable of
imaging an uncompressed breast in 3D space. To further develop the system as a clinically
viable device, it was necessary to integrate the separate imaging systems onto a single
gantry, and to simultaneously design a patient-friendly bed that could routinely and
effectively position the patient during dual-modality imaging of her uncompressed
breast in the system's common field of view. This thesis describes this process and
also investigates practical challenges associated with dedicated breast imaging of
a prone patient using the integrated SPECT-CT device.</p>
<p>We initially characterized the practicability of implementing the novel x-ray beam
ultra-thick K-edge filtration scheme designed for routine use with the breast CT system.
Extensive computer simulations and physical measurements were performed to characterize
the x-ray beam produced using K-edge filtration with cerium and to compare it to beams
produced using other filtration methods and materials. The advantages of using this
heavily filtered x-ray beam for uncompressed breast CT imaging were then further evaluated
by measuring the dose absorbed by an uncompressed cadaver breast during the course
of a routine tomographic scan. It was found that the breast CT device is indeed capable
of imaging uncompressed breasts at dose levels below that of the maximum utilized
for dual-view screening mammography.</p>
<p>To prepare the separate SPECT and CT systems for integration onto a single platform,
the cross contamination of the image of one modality by primary and scattered photons
of the complementary modality was quantified. It was found that contamination levels
of the emission (SPECT) image by the x-ray transmission source were generally far
less than 2% when using photopeak energy windows up to ±8%. In addition, while there
was some quantifiable evidence of a variation in the transmission image in response
to the presence of <super>99m</super>Tc photons in the patient, the effect of primary
and scattered <super>99m</super>Tc photons on the visibility of 5 mm acrylic photons
in a low contrast x-ray transmission environment was negligible. </p>
<p>A novel, tiered, stainless steel patient bed was then designed to allow dual-modality
imaging using the integrated SPECT-CT system. The performance of the hybrid SPECT-CT
system was evaluated during early stage dual-modality patient imaging trials with
particular emphasis placed on the performance of the patient bed. The bed was successful
in its primary task of enabling dual-modality imaging of a patient's breast in the
common field of view, but practical challenges to more effective patient imaging were
identified as well as some novel solutions to these challenges.</p>
<p>In the final section of the thesis research, the feasibility of using two of these
solutions was investigated with a view to imaging more of the patient's posterior
breast volume. Limited angle tomographic trajectories and trajectories that involve
raising or lowering the patient bed in mid tomographic acquisition were initially
investigated using various geometric phantoms. A very low contrast imaging task was
then tested using an observer study to quantify the effect of these trajectories on
the ability of observers to maintain visibility of small geometric objects. </p>
<p>This initial integrated SPECT-CT imaging system has demonstrated its ability to
successfully perform low dose, dual-modality imaging of the uncompressed breast.
Challenges and solutions have been identified here that will make future SPECT-CT
designs even more powerful and a clinically relevant technique for molecular imaging
of the breast.</p>
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