Bradley D. Clymer

Malignant-lesion segmentation using 4D co-occurrence texture analysis applied to dynamic contrast-enhanced magnetic resonance breast image data.

To investigate the use of four‐dimensional (4D) co‐occurrence‐based texture analysis to distinguish between nonmalignant and malignant tissues in dynamic contrast‐enhanced (DCE) MR images.

Three-dimensional numerical simulations of susceptibility-induced magnetic field inhomogeneities in the human head

Three-dimensional numerical simulations of the static magnetic field in the human head were carried out to assess the field inhomogeneity due to magnetic susceptibility differences at tissue interfaces. We used a finite difference method and magnetic permeability distributions obtained by segmentation of computed tomography images. Computations were carried out for four models, consisting of the head and the neck; the head, neck, and shoulders; the head, neck, and thorax; and the head tilted backwards, including the neck and the shoulders. Considerable magnetic field inhomogeneities were observed in the inferior frontal lobes and inferior temporal lobes, particularly near the sphenoid sinus and the temporal bones. Air/tissue interfaces at the shoulders were found to induce substantial magnetic field inhomogeneities in the occipital lobes and the cerebellum, whereas air/tissue interfaces in the lungs appeared to have less influence on the magnetic field in the brain. Tilting the head backwards could significantly reduce the field inhomogeneities superior to the planum sphenoidale as well as in the occipital lobes and the cerebellum.

Texture detection of simulated microcalcification susceptibility effects in magnetic resonance imaging of breasts

The presence, size, structure and clustering characteristics of microcalcifications can indicate breast cancer. The magnetic susceptibility of microcalcifications differs from soft biological tissues, leading to directional blurring effects that can be detected by statistical image processing methods. A study of the ability of statistical texture analysis to detect simulated localized blurring in magnetic resonance imaging (MRI) of dense breast is presented. This method can detect localized blurring with sensitivity of 88.89% to 94.44%, specificity of 99.72% to 100%, positive predictive value of 73.91% to 100% and negative predictive value of 99.91% to 99.95%. J. Magn. Reson. Imaging 2001;13:876–881.

Three-dimensional texture analysis of cancellous bone cores evaluated at clinical CT resolutions.

The objective of this study was to determine if three-dimensional (3D) Haralick co-occurrence texture measures calculated from low-resolution CT images of trabecular bone correlate with 3D structural indices measured from high-resolution CT images. Thirty-three cubical regions of trabecular bone from human calcanei were analyzed using images obtained from a micro-computed tomography (micro-CT) scanner. 3D measures of bone architecture were calculated. The original images were then subsampled by factors of 5, 10, 15, and 20, and 3D texture features were calculated for each set of subsampled images. Linear regression models showed that co-occurrence texture features were significantly correlated with structural indices. Over 90% of the variation in three different structural indices was explained in two-variable regression models using texture features as predictors when the voxel side length was reduced by a factor of 10. Texture features calculated from clinical images may increase our ability to obtain trabecular bone architectural information when high-resolution images are unobtainable.

An arrhythmia detector and heart rate estimator for overnight polysomnography studies

We present an algorithm for automatic on-line analysis of the ECG channel acquired during overnight polysomnography (PSG) studies. The system is independent of ECG morphology, requires no manual initialization, and operates automatically throughout the night. It highlights likely occurrences of arrhythmias and intervals of bad signal quality while outputting a continual estimate of heart rate. Algorithm performance is validated against standard ECG databases and PSG data. Results demonstrate a minimal false negative rate and a low false positive rate for arrhythmia detection, and robustness over a wide range of noise contamination.

A Control Strategy for Terrain Adaptive Bipedal Locomotion

Rhythmic movements of a five-link sagittal biped with muscle-likeactuators are considered. In walking, as the support phases changecontact is periodically made with the environment. The inputs toevery actuator are modeled after the inputs to muscles in mammals. Thesystem possesses intrinsic position and velocity feedback due to theactuator dynamics. A control strategy is articulated that is novelin that it; a) is physiologically viable; b) simplifies the dynamics;and c) adapts to the speed of walking, going up and down stairs,going up or down inclines, maneuvering over obstacles or holes, andthe tempo and stride length of walking. Walking simulations of afive-link sagittal biped are presented.

Timing Uncertainty For Receivers In Optical Clock Distribution For VLSI

Optical interconnection techniques have been suggested to reduce signal skew for clock distribution for silicon VLSI chips. One optical approach for clock distribution is to holographically map an optical signal from an off-chip source to several photoreceivers within small functional cells on a chip surface. Within each functional cell, the clock is distributed via short surface wires with negligible delays. In such a system, the primary source of timing uncertainty is due to fabrication-related variation of transistor parameters between identically drawn receivers on a chip. We present here an overview of the distribution system and two receiver designs. A test chip has been designed and fabricated, and laboratory measurements of transimpedance receiver parameters are presented. Analysis and simulation studies show that a phase-locked loop receiver based on a voltage-controlled ring oscillator can offer two orders of mag-nitude improvement in receiver skew over a simple transimpedance amplifier design, allowing a total synchronization uncertainty on the order of 55 ps while operating at 100 to 200 MHz and requiring much less layout area than the transimpedance amplifier.

Rocking, Tapping and Stepping: A Prelude to Dance

Dancing to a rhythm, as humans do, is a complex process, andformulation of its dynamics and control are very difficult. Rhythmicexchange of the support surfaces and stability of the overall systemare not well understood. To produce a dancing movement, simplermovements such as rocking, tapping, and stepping can be combined. Therhythm of dancing is usually driven by a music beat. A method thatextracts beats from a wide variety of music in real time ispresented. Work is being done to couple the extracted rhythm of themusic to a dancing biped. The seven degree of freedom sagittal bipedwith sixteen actuators is controlled to move in a rocking, tapping,and stepping fashion. A pattern generator is described which takes amusical beat and generates oscillations. The oscillations are usedto select a finite sequence of predefined desired states, and todrive the system from the current desired state to the next. Thesenext desired states allow derivation of neural excitation inputs tothe sixteen muscle-like actuators. Simulations show the feasibilityof the control strategy moving the biped from desired state todesired state as it traverses the trajectories of these three simplermovements of rocking, tapping, and stepping. In a final simulation,the three movements of rocking, stepping, and tapping are combined ina three-step up and down dancing movement.

A control strategy for adaptive bipedal locomotion

Rhythmic movements of a five-link sagittal biped with muscle-like actuators are considered. In walking contact is periodically made with the environment as the support phases change. The inputs to every actuator are modeled after the inputs to muscles in mammals. The system possesses intrinsic position and velocity feedback due to the actuator dynamics. A control strategy is articulated that is novel in that (a) it is physiologically viable, (b) it simplifies the dynamics, and (c) it adapts to speed of walking, going up and down stairs, going up or dozen inclines, maneuvering above obstacles or holes, and the tempo and stride length of walking. Simulations of the walk of a five-link sagittal biped are presented.

An efficient method of FIR filtering based on impulse response rounding

A new method of implementing efficient FIR filters is presented. It involves approximation of an equiripple FIR by a rounding operation and application of the derived impulse response by a simple recursive equation. The technique is extremely efficient for lowpass, highpass, bandpass, and bandstop filters with sharp transitions and low edge frequencies.