Magnetic susceptibility is an important physical property of tissues, and can be used as a contrast mechanism in magnetic resonance imaging (MRI). Recently, targeting contrast agents by conjugation ...with signaling molecules and labeling stem cells with contrast agents have become feasible. These contrast agents are strongly paramagnetic, and the ability to quantify magnetic susceptibility could allow accurate measurement of signaling and cell localization. Presented here is a technique to estimate arbitrary magnetic susceptibility distributions by solving an ill-posed inversion problem from field maps obtained in an MRI scanner. Two regularization strategies are considered: conventional Tikhonov regularization and a sparsity promoting nonlinear regularization using the l 1 norm. Proof of concept is demonstrated using numerical simulations, phantoms, and in a stroke model in a rat. Initial experience indicates that the nonlinear regularization better suppresses noise and streaking artifacts common in susceptibility estimation.
The pulmonary nodule is the most common manifestation of lung cancer, the most deadly of all cancers. Most small pulmonary nodules are benign, however, and currently the growth rate of the nodule ...provides for one of the most accurate noninvasive methods of determining malignancy. In this paper, we present methods for measuring the change in nodule size from two computed tomography image scans recorded at different times; from this size change the growth rate may be established. The impact of partial voxels for small nodules is evaluated and isotropic resampling is shown to improve measurement accuracy. Methods for nodule location and sizing, pleural segmentation, adaptive thresholding, image registration, and knowledge-based shape matching are presented. The latter three techniques provide for a significant improvement in volume change measurement accuracy by considering both image scans simultaneously. Improvements in segmentation are evaluated by measuring volume changes in benign or slow growing nodules. In the analysis of 50 nodules, the variance in percent volume change was reduced from 11.54% to 9.35% (p=0.03) through the use of registration, adaptive thresholding, and knowledge-based shape matching.
Computer-aided diagnostics Reeves, Anthony P; Kressler, Bryan M
Thoracic surgery clinics
14, Številka:
1
Journal Article
Recenzirano
The computer can be used in a number of ways to aid the physician to interpret CT lung images. Commercial tools are becoming available to assist the radiologist in growth rate determination, hence ...cancer diagnosis. Computer algorithms are in development that will permit lung health evaluation, including nodule detection. Finally, the results of such efforts will probably produce more detailed visualizations of the lung region, including depictions of the location and state of lung abnormalities. While computer methods have found a first application with the radiologist, these methods should also provide a valuable aid to surgery and pathology.
Magnetic resonance imaging (MRI) is a widely used noninvasive imaging technique. Technological improvements are necessary to allow application to cardiac imaging. This thesis reports on methods that ...improve imaging speed to develop a single breath hold cardiac phase resolved coronary angiography sequence, apply motion compensation to free breathing first pass myocardial perfusion, and employ convex optimization techniques for improved estimation of magnetic susceptibility distributions. In coronary angiography, a cardiac phase resolved imaging protocol is desirable to eliminate the need to accurately determine the period of minimal motion. A phase resolved protocol is developed by applying a spiral trajectory to improve acquisition efficiency and steady state free precession to provide good blood to myocardium contrast. The technique provides adequate spatial and temporal resolution to enable visualization of the coronary arteries in peak-systole and mid-diastole. In perfusion imaging, a patient is injected with a contrast agent that appears bright in MRI and the time course of myocardial enhancement is observed. Complete images are acquired every heartbeat, requiring rapid acquisition. The time course can be quite long and the necessary breath hold may exceed the capabilities of the patient. Parallel imaging techniques are applied to improve acquisition efficiency and a diaphragm navigator is employed to estimate the respiratory motion of the heart, allowing imaging during free breathing. Tracking cells labeled with iron oxide or other contrast agents is of interest to monitor stem cell therapies designed to reduce scarring and improve perfusion after myocardial infarction. Recently, iron oxide based contrast agents have become clinically available. Conventional iron imaging techniques yield qualitative images with negative contrast under MRI. Development of a quantitative positive contrast method to image iron oxide particles is of great interest. Iron oxides have a strong magnetic susceptibility that produces a variation in the resonance frequency of nearby spins. A technique is developed to estimate the susceptibility of each voxel from a phase image, potentially allowing more accurate quantification in cellular MRI.
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