Publications (28) View all
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Conference Proceeding: A robust parametric method for bias field estimation and segmentation of MR images
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ABSTRACT: This paper proposes a new energy minimization framework for simultaneous estimation of the bias field and segmentation of tissues for magnetic resonance images. The bias field is modeled as a linear combination of a set of basis functions, and thereby parameterized by the coefficients of the basis functions. We define an energy that depends on the coefficients of the basis functions, the membership functions of the tissues in the image, and the constants approximating the true signal from the corresponding tissues. This energy is convex in each of its variables. Bias field estimation and image segmentation are simultaneously achieved as the result of minimizing this energy. We provide an efficient iterative algorithm for energy minimization, which converges to the optimal solution at a fast rate. A salient advantage of our method is that its result is independent of initialization, which allows robust and fully automated application. The proposed method has been successfully applied to 3-Tesla MR images with desirable results. Comparisons with other approaches demonstrate the superior performance of this algorithm.Computer Vision and Pattern Recognition, 2009. CVPR 2009. IEEE Conference on; 07/2009 -
Conference Proceeding: A robust parametric method for bias field estimation and segmentation of MR images.
2009 IEEE Computer Society Conference on Computer Vision and Pattern Recognition (CVPR 2009), 20-25 June 2009, Miami, Florida, USA; 01/2009 -
Article: Normal cerebral, renal and abdominal regional oxygen saturations using near-infrared spectroscopy in preterm infants.
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ABSTRACT: The aim of this study is to characterize baseline regional oxygen saturations (rSO(2)) in stable preterm infants during the first weeks of life. Cerebral, renal and abdominal rSO(2) were continuously monitored from the time of birth to 21 days in twelve preterm infants of 29-34 weeks gestation. Regional saturations were evaluated for trends over time, variability and differences between gestational ages (GAs) and reported pediatric values. Both cerebral (66-83%) and renal (64-87%) rSO(2) baselines were within the range of reported neonatal values but consistently decreased over the first weeks of life (P<0.01). The baseline abdominal rSO(2) was 32-66% and increased with GA (P=0.05). The rSO(2) variability was lowest for cerebral measurements and highest at the abdomen. Abdominal rSO(2) variability decreased over time (P≤0.05). Daily baseline rSO(2) in preterm infants changes over the first weeks of life, especially at the abdomen. Evolution in baseline rSO2 over time may indicate regional developmental maturation of physiological oxygen balance.Journal of perinatology: official journal of the California Perinatal Association 01/2011; 31(1):51-7. · 1.59 Impact Factor -
Article: Using high-resolution MR imaging at 7T to evaluate the anatomy of the midbrain dopaminergic system.
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ABSTRACT: Dysfunction of DA neurotransmission from the SN and VTA has been implicated in neuropsychiatric diseases, including Parkinson disease and schizophrenia. Unfortunately, these midbrain DA structures are difficult to define on clinical MR imaging. To more precisely evaluate the anatomic architecture of the DA midbrain, we scanned healthy participants with a 7T MR imaging system. Here we contrast the performance of high-resolution T2- and T2*-weighted GRASE and FFE MR imaging scans at 7T. Ten healthy participants were scanned by using GRASE and FFE sequences. CNRs were calculated among the SN, VTA, and RN, and their volumes were estimated by using a segmentation algorithm. Both GRASE and FFE scans revealed visible contrast between midbrain DA regions. The GRASE scan showed higher CNRs compared with the FFE scan. The T2* contrast of the FFE scan further delineated substructures and microvasculature within the midbrain SN and RN. Segmentation and volume estimation of the midbrain SN, RN, and VTA showed individual differences in the size and volume of these structures across participants. Both GRASE and FFE provide sufficient CNR to evaluate the anatomy of the midbrain DA system. The FFE in particular reveals vascular details and substructure information within the midbrain regions that could be useful for examining structural changes in midbrain pathologies.American Journal of Neuroradiology 12/2010; 32(4):688-94. · 2.93 Impact Factor -
Article: Failure to direct detect magnetic field dephasing corresponding to ERP generation.
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ABSTRACT: Functional magnetic resonance imaging (fMRI) has become the method of choice for mapping brain activity in human subjects and detects changes in regional blood oxygenation and volume associated with local changes in neuronal activity. While imaging based on blood oxygenation level dependent (BOLD) contrast has good spatial resolution and sensitivity, the hemodynamic signal develops relatively slowly and is only indirectly related to neuronal activity. An alternative approach termed magnetic source magnetic resonance imaging (msMRI) is based on the premise that neural activity may be mapped by magnetic resonance imaging (MRI) with greater temporal resolution by detecting the local magnetic field perturbations associated with local neuronal electric currents. We used a hybrid ms/BOLD MRI method to investigate whether msMRI could detect signal changes that occur simultaneously at the time of the production of well-defined event-related potentials, the P300 and N170, in regions that previously have been identified as generators of these electrical signals. Robust BOLD activations occurred after some seconds, but we were unable to detect any significant changes in the T2*-weighted signal in these locations that correlated temporally with the timings of the evoked response potentials (ERPs).Magnetic Resonance Imaging 06/2008; 26(4):484-9. · 1.99 Impact Factor
