Purpose: To evaluate the effects of four anatomical parameters (angle between superior and inferior temporal retinal
arteries [inter-artery angle, IAA], optic disc [OD] rotation, retinal curvature, and central retinal vessel trunk entry point
location [CRVTL]) on retinal nerve fiber layer thickness (RNFLT) abnormality marks by OCT machines.
Methods: Cirrus OCT circumpapillary RNFLT measurements and Humphrey visual fields (HVF 24-2) of 421 patients
from a large glaucoma clinic were included. Ellipses were fitted to the OD borders. Ellipse rotation relative to the
vertical axis defined OD rotation. CRVTL was manually marked on the horizontal axis of the ellipse on the OCT fundus
image. IAA was calculated between manually marked retinal artery locations at the 1.73mm radius around OD. Retinal
curvature was determined by the inner limiting membrane on the horizontal B-scan closest to the OD center. For each
location on the circumpapillary scanning area, logistic regression was used to determine if each of the four parameters
had a significant impact on RNFLT abnormality marks independent of disease severity. The results are presented on
spatial maps of the entire scanning area.
Results: Variations in IAA significantly influenced abnormality marks on 38.8% of the total scanning area, followed by
CRVTL (19.2%) and retinal curvature (18.7%). The effect of OD rotation was negligible (<1%).
Conclusions: A natural variation in IAA, retinal curvature, and CRVTL can affect OCT abnormality ratings, which
may bias clinical diagnosis. Our spatial maps may help OCT manufacturers to introduce location specific norms to
ensure that abnormality marks indicate ocular disease instead of variations in eye anatomy.
KEYWORDS: 3D modeling, Breast, Computer aided diagnosis and therapy, Radon transform, 3D image processing, Image classification, Mammography, Computed tomography, Cancer, Breast cancer
Current computer aided diagnosis (CADx) software for digital mammography relies mainly on 2D techniques. With the emergence of three-dimensional (3D) breast imaging modalities such as breast Computed Tomography (BCT), there is an opportunity to analyze 3D features in the classification of calcifications. We previously reported our initial work on automated 3D feature detection and classification based on morphological descriptions for single microcalcifications within clusters [1]. In this work, we propose the expansion of the 3D classification methods to include novel microcalcification morphological feature detection such as including more morphological classes and replacing the 2D Radon transform by a 3D Radon transform. Results show that the classification rate improved compared to the previously reported results from a total of 546 to 559 consistently classified calcifications out of 635 total calcifications. This slight improvement is due to the use of the 3D Radon transform and incorporating methods to detect two classes not previously implemented. Future work will focus on adding feature detection and classification of cluster patterns.
Breast CT (BCT) using a photon counting detector (PCD) has a number of advantages that can potentially improve
clinical performance. Previous computer simulation studies showed that the signal to noise ratio (SNR) for
microcalcifications is higher with energy weighted photon counting BCT as compared to cesium iodide energy
integrating detector (CsI-EID) based BCT. CsI-EID inherently weighs the incident x-ray photons in direct proportion to
the energy (contradicting the information content) which is not an optimal approach. PCD do not inherently weigh the
incident photons. By choosing optimal energy weights, higher SNR can be achieved for microcalcifications and hence
better detectability. In this simulation study, forward projection data of a numerical breast phantom with
microcalcifications inserted were acquired using CsI-EID and PCD. The PCD projections were optimally weighed, and
reconstructed using filtered back-projection. We compared observer performance in identifying microcalcifications in
the reconstructed images using ROC analysis. ROC based results show that the average area(s) under curve(s) (AUC) for
AUCPCD based methods are higher than the average
AUCCsI-EID method.
KEYWORDS: Computed tomography, Sensors, Breast imaging, Tumors, Reconstruction algorithms, Breast cancer, X-ray computed tomography, Monte Carlo methods, Diagnostics, X-rays
Dedicated CT breast imaging using a flat-panel detector system holds great promise for improving the detection
and diagnosis of early stage breast cancer. It is currently unclear whether dedicated CTBI systems will be useful
for screening of the general population. Possibly a more realistic goal will be contrast-enhanced, flat-panel CTBI
to assist in the diagnostic workup of suspected breast cancer patients. It has been suggested that the specificity of
CE-CTBI can be improved by acquiring a dynamic sequence of CT images, characterizing the lesion enhancement
pattern. To make dynamic CE-CTBI feasible, it is important to perform very fast CT acquisitions, with minimal
radiation dose. One technique for reducing the time required for CT acquisitions, is to use a half-scan cone-beam
acquisition, requiring a scan of 180° plus the detector width. In addition to achieving a shorter CT scan, half-scan
acquisition can provide a number of benefits in CTBI system design. This study compares different half-scan
reconstruction methods with a focus on evaluating the quantitative performance in estimating the CT number of
iodinated contrast enhanced lesions. Results indicate that half-scan cone-beam acquisition can be used with little
loss in quantitative accuracy.
KEYWORDS: Breast, 3D modeling, Systems modeling, X-ray computed tomography, Sensors, Tumor growth modeling, Tissues, Breast imaging, Data modeling, X-rays
Dedicated x-ray computed tomography (CT) of the breast using a
cone-beam flat-panel detector system is a modality under investigation by a number of research teams. As previously reported, we have fabricated a prototype, bench-top flat-panel CT breast imaging (CTBI) system and developed computer simulation software to
model such a system. We are developing a methodology to use high resolution, low noise CT reconstructions of fresh mastectomy specimens for generating an ensemble of 3D digital breast phantoms that realistically model 3D compressed and uncompressed breast anatomy. These breast models can be used to simulate realistic projection data for both breast tomosynthesis (BT) and CT systems thereby providing a powerful evaluation and optimization
mechanism.
Planar X-ray mammography is the standard medical imaging modality for the early detection of breast cancer. Based on
advancements in digital flat-panel detector technology, dedicated x-ray computed tomography (CT) mammography is a
modality under investigation that offers the potential for improved breast tumor imaging. We have implemented a
prototype half cone-beam CT breast imaging system that utilizes an indirect flat-panel detector. This prototype can be
used to explore and evaluate the effect of varying acquisition and reconstruction parameters on image quality. This
report describes our system and characterizes the performance of the system through the analysis of Modulation Transfer
Function (MTF) and Noise Power Spectrum (NPS). All CT reconstructions were made using Feldkamp's filtered
backprojection algorithm. The 3D MTF was determined by the analysis of the plane spread function (PlSF) derived
from the surface spread function (SSF) of reconstructed 6.3mm spheres. 3D NPS characterization was performed
through the analysis of a 3D volume extracted from zero-mean CT noise of air reconstructions. The effect of varying
locations on MTF and the effect of different Butterworth filter cutoff frequencies on NPS are reported. Finally, we
present CT images of mastectomy excised breast tissue. Breast specimen images were acquired on our CTMS using an
x-ray technique similar to the one used during performance characterization. Specimen images demonstrate the inherent
CT capability to reduce the masking effect of anatomical noise. Both the quantitative system characterization and the
breast specimen images continue to reinforce the hope that dedicated flat-panel detector, x-ray cone-beam CT will
eventually provide enhanced breast cancer detection capability.
In considering a breast CT system, it is important to note that the spectral attenuation profile of a tumor is very similar to that of fibro-glandular tissue. Preliminary evidence based on imaging breast specimens suggest that the CT number of a malignant breast tumor is very similar to that of surrounding fibro-glandular tissue. Therefore, it is expected that radiologists will probably rely more on tumor morphology to distinguish a malignant tumor from fibro-glandular tissue than an increase in contrast per se. Previous studies have shown that iodinated contrast agents can increase the effective attenuation coefficient yielded by a breast tumor thereby providing increased CT tumor contrast. In order to characterize how the intravenous administration of an iodinated contrast agent can affect the performance of CT breast imaging, a computer simulation of such a system was conducted. The two primary goals of this investigation were first to determine how mean glandular dose, choice of x-ray energy spectrum, and iodine contrast agent density affect tumor detection, and second to determine what effect Compton and Rayleigh scattering have on the variability of the attenuation coefficient yielded by CT mammography. The first goal was achieved by making use of a modified version of the Bakic (Med. Phys. 2003) digital breast phantom to model the uncompressed breast, and a 0.5 cm sphere representing a breast tumor was digitally inserted into the ductal region of this phantom. Several projection sets were generated with the tumor containing various densities of iodine contrast agent, different x-ray energy spectra, and different mean glandular dosage (MGD) levels . Slices through the tumor were extracted from the reconstructions of these projections and were used in human observer studies to determine tumor detectability. The second goal was achieved by using the GATE (Geant 4 Application for Tomographic Emission) Monte-Carlo software package to compute the scattering incident on the flat panel detector for an x-ray projection, then using the aforementioned Bakic phantom, a 0.5 cm sphere representing a breast tumor attenuation and a 3.0 mg/ml of Iodinated contrast agent were inserted at various locations with varying attenuation for 100 projection sets with scatter, and 100 projections without scatter. Histograms of the resulting effective attenuation coefficients yielded by Feldkamp filtered backprojection were plotted and compared.
In active Fault Tolerant Control Systems (FTCS), a Fault Detection
and Identification (FDI) algorithm is used to monitor system
performance, to detect the occurrence of a fault and to estimate
system parameters. The natural existence of environmental noises,
disturbances, and small modelling uncertainties will force the FDI
algorithm to estimate system parameters with some inaccuracies. As
a result, the system to be controlled includes parameter
uncertainties. In this paper, plant parameter uncertainties are
assumed to be time-varying unknown-but-bounded. Exponential
stabilization of FTCS for systems with uncertainties is studied,
and a stabilization algorithm is constructed. A numerical example
is presented to demonstrate the potential of the theoretical
developments.
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