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<p>With continuing advances in medical imaging technologies, there is an increased
demand to extract quantitative information from images. This has been particularly
vital in the effort to increase the efficacy and accuracy of diagnoses. Quantitative
information is readily available in images because the acquisition techniques intrinsically
involve physical processes. Quantitative image quality metrics are critical in the
evaluation of medical images for diagnostic merit, particularly when used for the
characterization and comparison of different systems. When such metrics are based
on measurable physical parameters, they can provide valuable information for system
optimization. Image quality describes the "goodness" of an image in displaying information
for a task. This thesis explored methods of measuring image quality for two scenarios:
(1) to characterize 2D flat-panel detector performance and (2) to measure directional
spatial resolution for 3D images from breast tomosynthesis.</p><p>In the first chapter,
two new wireless digital receptors (DRX-1C and DRX-1, Carestream Health, Inc., Rochester,
NY) were evaluated and compared to a conventional flat-panel detector (Pixium 4600,
Trixell, Moirans, France) on the basis of detective quantum efficiency (DQE). A secondary
goal was also to evaluate the filtration to achieve specified beam qualities for the
DQE measurements, closely following the methodology of the International Electrotechnical
Commission (IEC) for radiation qualities RQA5 and RQA9. All three DR systems demonstrated
similar modulation transfer functions (MTFs) at most frequency ranges, while the DRX-1
showed lower values near the cutoff of approximately 3.5 cycles/mm. At each exposure,
the Pixium 4600 and DRX-1C demonstrated similar noise power spectrum (NPS) curves
that indicated better noise performance than the DRX-1. Zero-frequency DQEs for Pixium
4600, DRX-1C, and DRX-1 were approximately 63%, 74%, and 38% for RQA5 and 42%, 50%,
and 28% for RQA9, respectively. In terms of DQE performance, the DRX-1C image receptor
was found to be superior to the Pixium 4600 and DRX-1.</p><p>In the second chapter,
the directional spatial resolution of simulated breast tomosynthesis images was determined
using a cone-based technique and a sphere phantom. Projections were simulated for
a voxelized breast phantom with 12 mm diameter sphere inserts using a fluence modeled
from a 28 kVp beam incident upon an indirect flat-panel detector with 200 µm pixel
size. Characteristic noise and blurring for each projection were added using cascaded
systems analysis. The projections were reconstructed using a standard filtered backprojection
technique, producing a 3D volume with an isotropic voxel size of 200 µm. Regions of
interest (ROIs) that completely encompassed single spheres were extracted, and conical
regions were prescribed along the three axes extending from the centroid. Voxels within
a cone were used to form an edge spread function (ESF), from which the directional
MTF was calculated. A bin size of 0.02 mm and a conical range of 30 degrees were found
optimal for maximizing accuracy and minimizing noise of the MTF. A method for removing
out-of-plane artifacts of the ESFs along in-plane axes was investigated and yielded
a modified MTF. The idea of separating the effective resolution and artifacts from
the measured ESF are expected to facilitate the interpretation of MTF measurements
in breast tomosynthesis. Similar methods may be applied to characterize the spatial
resolution of other 3D imaging modalities.</p>
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