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Parallel magnetic resonance imaging (MRI) methods employ receiver coils sensitivities to reduce imaging time: reconstruction algorithms need RF field maps which must be measured or estimated. Assuming statistical independence of different regions in a MR image, we consider the sensitivity estimation as a blind source separation (BSS) problem that can be solved with independent component analysis (ICA)...
Hyperpolarized 3He gas MRI has a serious potential for assessing pulmonary functions. Due to the fact that the non-equilibrium of the gas results in a steady depletion of the signal level over the course of the excitations, the signal-to-noise ratio (SNR) can be independent of the number of the data acquisitions under certain circumstances. This provides a unique opportunity for parallel MRI for gaining...
The coil separation of phased-array coils is an important issue if a wide area of interest is to be imaged. An equivalent circuit of two circular-shaped coils was used to compute the optimal distance in a two phased-array coil. This circuit included the mutual inductance of two circular coils. An expression for the mutual inductance was derived and the resulting values included in the circuit. With...
Large arrays of RF coils with 16 or more channels are becoming commercially available. However, most MR scanners have eight or fewer receiver channels. In order for these scanners to achieve the SNR benefits of these large arrays, the signals from the array elements must be combined. In this paper, strategies for combining the array elements into 8 or fewer channels are discussed and an analysis of...
Intensity inhomogeneity in MR images is an undesired phenomenon, which often hampers different steps of quantitative analysis such as segmentation or registration. In this paper we propose a novel fully automated method for retrospective correction of intensity inhomogeneity. The basic assumption is that inhomogeneity correction could be improved by combining the information from multiple MR channels...
The diagnosis of cardiovascular disease requires precise assessment of both morphology and function of the heart. Currently, magnetic resonance imaging (MRI) provides a useful tool for accurate and reproducible assessment of regional function of the left ventricle noninvasively. MR tagging produces images of the heart that can be analyzed using harmonic phase (HARP) method to describe the regional...
We are involved in a comprehensive program to characterize atherosclerotic disease using multiple MR images having different contrast mechanisms (T1W, T2W, PDW, magnetization transfer, etc.) of human carotid and animal model arteries. We use specially designed intravascular and surface array coils that give high signal-to-noise but suffer from sensitivity inhomogeneity and significant noise. We present...
In studying bioelectromagnetic problems, finite element method offers several advantages over other conventional methods such as boundary element method. It allows truly volumetric analysis and incorporation of material properties such as anisotropy. Mesh generation is the first requirement in the finite element analysis and there are many different approaches in mesh generation. However conventional...
Magnetic resonance electrical impedance tomography (MREIT) has been developed as a new medical imaging modality providing high-resolution conductivity and current density images. This paper is about MREIT of the breast. To show the feasibility of breast MREIT, we carried numerical simulations and breast phantom experiments. We found that an anomaly with 4 mm diameter can be visualized in a reconstructed...
Performing multi-joint arm movements in controllable dynamic environments during functional magnetic resonance imaging (fMRI) could provide important insights into the brain mechanisms involved in human motor control and related dysfunctions. In order to obtain useful data, these movements must be possible and comfortable for the subject within the narrow bore of the scanner and should not create...
Past neuroimaging studies of acupuncture have demonstrated variable results for important brainstem nuclei. We have employed cardiac-gated fMRI with T1-variability correction to study the processing of acupuncture by the human brain. Furthermore, our imaging experiments collected simultaneous ECG data in order to correlate heart rate variability (HRV) with fMRI signal intensity. Subjects experienced...
This paper presents potential medical applications that an untethered microdevice in the cardiovascular system could perform within an MRI system. Recent developments and continuing evolution in micro/nano fabrication and design techniques will enable the development of functional microdevices able to explore the cardiovascular system. The magnetic resonance submarine (MR-Sub) project is a first step...
This paper describes a mechanical interface to use in conjunction with fMRI, in order to infer the brain mechanisms of human motor learning. Innovative mechanical concepts based on gravity and elastic forces were used to generate typical stable and unstable dynamic interactions at the hand during multijoint arm movements. Two designs were retained and implemented from MR compatible materials. The...
This paper presents the identification and the study of the impact of a real-time MRI-based propulsion and tracking system constraints on the step response using a discrete PID controller. A simplified model for such a system accounts for these constraints such as the time delay, the sampling period, and the blood velocity. This application is intended for minimally invasive operations within the...
MRI system noise often appears in the fMRI timeseries in phantom and human subjects experiments. The predominant characteristic of this MRI system noise is high amplitude at one or a few specific temporal frequencies. These frequencies are immediately found by FFT analysis, but they have also been identified in ICA methods. This study indicates that these frequencies should be considered in the design...
In this work, a new concept in high field RF head coil design for MRI applications is presented. An 8-element phased array head coil operating at 4T is designed based on a hybrid method combining reciprocity theorem and inverse method. Both circularly or linearly polarized head coils can be designed. A FDTD/MOM calculation method is used to model the phased array head coil and to accurately calculate...
The objective of this paper is to present an analytical method to detect lesions or tumors in digitized medical images for 3D visualization. The authors developed a tumor detection method using three parameters; edge (E), gray (G), and contrast (H) values. The method proposed here studied the EGH parameters in a supervised block of input images. These feature blocks were compared with standardized...
In the paper we describe a Web-based interface to view 2-D and 3-D results generated from segmentation and measurement process interactively. Our implementation takes a fully Web-based approach to provide universal access and visualization to a wide range of patient data (i.e. at multiple locations). An example case study is presented: thickness measurement of articular cartilage from MR knee images...
A new method for the propulsion of a spherical ferromagnetic device along a given path in a water filled phantom with no human interaction is presented using an 1.5 T magnetic resonance imaging (MRI) clinical system. A special real time loop is implemented and presented that feeds the scanner with the appropriate gradients amplitudes and directions based on a pre-determined path. This paper studies...
The aim of the present study is to develop a method to detect the neural activity during rest state from fMRI data. According to the high functionally neural connectivity and spatial relationship of a functional group of brain, time series and spatial clustering are sequently applied to detect the functional groups. In the article, the author also discusses the validation of the method applied to...
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