IEEE transactions on bio-medical engineering
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IEEE Trans Biomed Eng · Jun 2006
On the selection of optimal flip angles for T1 mapping of breast tumors with dynamic contrast-enhanced magnetic resonance imaging.
We present a method for selecting optimal flip angles for both precontrast and postcontrast T1 mapping of breast tumors using dynamic contrast-enhanced magnetic resonance imaging; and with the aim of improving accuracy in the estimation of contrast medium concentration. The proposed method can appropriately account for the different ranges of precontrst and postcontrast T1 values by the use of weighting functions, which also allow the flexibility to enhance the accuracy of certain T1 values, corresponding to the tissues of interest. Results of Monte Carlo simulations show that the proposed method could yield significantly lower errors in the estimation of contrast concentration, as compared with an existing approach.
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IEEE Trans Biomed Eng · May 2006
Computation of transmitted and received B1 fields in magnetic resonance imaging.
Computation of B1 fields is a key issue for determination and correction of intensity nonuniformity in magnetic resonance images. This paper presents a new method for computing transmitted and received B1 fields. ⋯ The method is validated using numerical simulations and experimental data from phantom and human scans. The experimental results are in agreement with theoretical expectations.
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IEEE Trans Biomed Eng · May 2006
Surface extraction and thickness measurement of the articular cartilage from MR images using directional gradient vector flow snakes.
The accuracy of the surface extraction of magnetic resonance images of highly congruent joints with thin articular cartilage layers has a significant effect on the percentage errors and reproducibility of quantitative measurements (e.g., thickness and volume) of the articular cartilage. Traditional techniques such as gradient-based edge detection are not suitable for the extraction of these surfaces. This paper studies the extraction of articular cartilage surfaces using snakes, and a gradient vector flow (GVF)-based external force is proposed for this application. ⋯ Thickness is computed based on the surfaces extracted using the proposed algorithm. In order to make the thickness measurement more reproducible, a new thickness computation approach, which is called T-norm, is introduced. Experimental results show that the thickness measurement obtained by the new thickness computation approach has better reproducibility than that obtained by the existing thickness computation approaches.
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IEEE Trans Biomed Eng · May 2006
An analytical model for surface EMG generation in volume conductors with smooth conductivity variations.
A nonspace invariant model of volume conductor for surface electromyography (EMG) signal generation is analytically investigated. The volume conductor comprises planar layers representing the muscle and subcutaneous tissues. The muscle tissue is homogeneous and anisotropic while the subcutaneous layer is inhomogeneous and isotropic. ⋯ The series expansion is truncated for the practical implementation. Representative simulations are presented. The proposed model constitutes a new approach for surface EMG signal simulation with applications related to the validation of methods for information extraction from this signal.
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The magnetic resonance imaging (MRI) coil's radio frequency (RF) field distribution has a strong effect on image quality as well as specific absorption rate. In this paper, a method of probing a coil's RF field distribution over any unoccupied region of the coil is presented. ⋯ Very good agreement was achieved between the infrared measurements and numerical data obtained utilizing an in-house three-dimensional finite-difference time-domain package. The results demonstrate that the proposed technique is practical, robust, and efficient in making accurate measurements of the electric field distributions in loaded and unloaded MRI coils.