Title:
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Image reconstruction for emission optical projection tomography
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Emission Optical Projection Tomography (eO PT) is a relatively new imag-
ing modality that bridges a gap between micro Magnetic Resonance Imag-
ing and Confocal Laser Scanning Microscopy. eO PT can be used to image
the anatomy and gene expression of intact biological specimens at high
resolution and thus provides an alternative to time consuming methods
such as serial sectioning. Tomographic image reconstruction for eOPT is
currently performed using the Filtered Back Projection algorithm which,
while being fast, does not account for the physics of image formation and
thus can result in reconstructions of reduced resolution and questionable
quantitative consistency.
This thesis describes work that was done on eOPT in three areas, including
image formation, tomographic reconstruction, and memory savings, the
latter of which were required to bring implementation of 3D iterative
reconstruction algorithms within reach for the relatively high-resolution
eO PT imaging modality.
In the area of image formation, measurements were taken to reveal the
effects of optical blurring, diffraction and charge-coupled device (CCD)
camera noise. Accurate models of each of these phenomena were developed
and compared against the measurements.
The subject of image reconstruction was first addressed with a modi-
fication to the FBP algorithm designed to correct for the quantitative
inaccuracies suspected of being introduced by the FBP algorithm when
reconstructing specimens consisting of very fine detail. This was done by
incorporating the quantitative aspects of the model of image formation
into the FBP algorithm. The full model of image formation was incorpo-
rated into the iterative Maximum Likelihood Expectation Maximisation
(MLEM) algorithm.
The third strand of this thesis focuses on various memory saving meth-
ods developed to enable the implementation and testing of a variation of
MLEM known as the Ordered Subsets Expectation Maximisation (OSEM).
, Without such memory saving methods, the implementation of an iterative
3D reconstruction algorithm such as MLEM or OSEM using a full model
of image formation would have remained beyond the capacity of modern
computers for the foreseeable future, requiring several Terabytes of RAM.
Comparisons were made between the quality of and the time required to
produce FBP and OSEM reconstructions of the same data sets given the
availability of limited computing resources. The feasibility of adopting
OSEM reconstructions as an alternative to FBP reconstructions was dis-
cussed, based on the use of currently available cutting edge computing
hardware.
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