Browsing by Author "Enterline, David S"
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Item Open Access Harmonic source wavefront aberration correction for ultrasound imaging.(2010) Dianis, Scott W.Aberration is a correctable phenomenon that degrades diagnostic quality in a significant number of ultrasound images. Previous aberration correction studies have focused on development of aberration estimation algorithms or on aberration reduction by using harmonic imaging. In the past, a major drawback of aberration estimation algorithms has been the assumptions required about the imaging target, assumptions that can limit clinical application where correction for multiple locations within a scan may be required. Harmonic imaging attempts to reduce the effect of aberration, without making assumptions about the imaging target, by using a lower-frequency transmit beam that is less prone to aberration. However, harmonic imaging does not correct for any aberration that may remain. It is hypothesized that a harmonic source wavefront correction technique is capable of creating a point-like acoustical source that allows for estimation and correction of two-dimensional aberration in a clinical setting. Harmonic source wavefront correction utilizes the reduced aberration of harmonic imaging to create a known acoustical source to satisfy the assumptions of the aberration estimation algorithms, thus improving their clinical application. Generation of a point-like acoustical source in the presence of aberration is demonstrated using both spatially correlated and spatially uncorrelated electronic aberrators varying in strength from 0.25π radians to 1.16π radians RMS focusing error. Beam properties of the 2.08 MHz fundamental, 4.16 MHz generated harmonic, and 4.17 MHz imaging beams were compared; in the presence of aberration, relative peak beam amplitude of the 4.16 MHz generated harmonic beam was up to 81% higher than the 4.17 MHz imaging beam, while -6 dB beam width indicated the 4.16 MHz generated harmonic beam was 88% narrower and more point-like than the 2.08 MHz fundamental beam. The feasibility of harmonic source wavefront correction was demonstrated by correcting for spatially uncorrelated electronic aberrators in a water tank using a point target, specular reflector, and speckle region as correction targets. Harmonic source wavefront correction was paired with a cross-correlation algorithm to estimate corrective delays and was most effective in correcting peak amplitude of the 4.17 MHz imaging beam using a point target (up to 94% improvement), followed by use of a specular reflector (up to 83% improvement), followed by use of a speckle region (up to 47% improvement). Aberration correction is sensitive to signal-to-noise ratio (SNR),and correction utilizing the 2.08 MHz fundamental, which provided higher SNR, was more effective than correction utilizing the more point-like 4.16 MHz harmonic for the experimental setup used. A harmonic SNR of 14 dB was estimated as necessary for harmonic-based correction performance to equal or surpass fundamental-based correction, regardless of fundamental SNR. Finally, performance of harmonic source wavefront correction was quantified in a clinical setting. Correction of spatially correlated electronic aberrators was performed using both ex vivo porcine kidneys and the left kidneys of 11 human volunteers as correction targets. Correction utilizing porcine kidney resulted in 10 dB greater improvement in peak beam amplitude than correction utilizing the left kidney of human volunteers. Body wall aberration present in the human volunteers was not accounted for during correction and likely caused the disparity in correction performance. An average upper limit for body wall aberration for the human subjects was estimated at 65 ns (±9 ns) RMSItem Open Access Identification of Chiari Type I Malformation subtypes using whole genome expression profiles and cranial base morphometrics.(BMC medical genomics, 2014-06) Markunas, Christina A; Lock, Eric; Soldano, Karen; Cope, Heidi; Ding, Chien-Kuang C; Enterline, David S; Grant, Gerald; Fuchs, Herbert; Ashley-Koch, Allison E; Gregory, Simon GBackground
Chiari Type I Malformation (CMI) is characterized by herniation of the cerebellar tonsils through the foramen magnum at the base of the skull, resulting in significant neurologic morbidity. As CMI patients display a high degree of clinical variability and multiple mechanisms have been proposed for tonsillar herniation, it is hypothesized that this heterogeneous disorder is due to multiple genetic and environmental factors. The purpose of the present study was to gain a better understanding of what factors contribute to this heterogeneity by using an unsupervised statistical approach to define disease subtypes within a case-only pediatric population.Methods
A collection of forty-four pediatric CMI patients were ascertained to identify disease subtypes using whole genome expression profiles generated from patient blood and dura mater tissue samples, and radiological data consisting of posterior fossa (PF) morphometrics. Sparse k-means clustering and an extension to accommodate multiple data sources were used to cluster patients into more homogeneous groups using biological and radiological data both individually and collectively.Results
All clustering analyses resulted in the significant identification of patient classes, with the pure biological classes derived from patient blood and dura mater samples demonstrating the strongest evidence. Those patient classes were further characterized by identifying enriched biological pathways, as well as correlated cranial base morphological and clinical traits.Conclusions
Our results implicate several strong biological candidates warranting further investigation from the dura expression analysis and also identified a blood gene expression profile corresponding to a global down-regulation in protein synthesis.