William J. Ohley

Fractional Brownian Motion: A Maximum Likelihood Estimator and Its Application to Image Texture

Fractals have been shown to be useful in characterizing texture in a variety of contexts. Use of this methodology normally involves measurement of a parameter H, which is directly related to fractal dimension. In this work the basic theory of fractional Brownian motion is extended to the discrete case. It is shown that the power spectral density of such a discrete process is only approximately proportional to |f|a instead of in direct proportion as in the continuous case. An asymptotic Cramer-Rao bound is derived for the variance of an estimate of H. Subsequently, a maximum likelihood estimator (MLE) is developed to estimate H. It is shown that the variance of this estimator nearly achieves the minimum bound. A generation algorithm for discrete fractional motion is presented and used to demonstrate the capabilities of the MLE when the discrete fractional Brownian process is contaminated with additive Gaussian noise. The results show that even at signal-to-noise ratios of 30 dB, significant errors in estimation of H can result when noise is present. The MLE is then applied to X-ray images of the human calcaneus to demonstrate how the line-to-line formulation can be applied to the two-dimensional case. These results indicate that it has strong potential for quantifying texture.

Fractal dimension in the analysis of medical images

The analysis of cardiac magnetic resonance (MR) images and X-rays of bone is considered. Each image type is approached using a different form of fractal parameterization. For the MR images, the goal of the study is segmentation, and to this end small regions of the image are assigned a local value of fractal dimension. For the bone X-rays, rather than segmentation, the large-scale structure is parameterized by its fractal dimension. In both cases, the use of fractals leads to the classification of the parameters of interest. When applied to segmentation, this analysis yields boundary discrimination unavailable through previous methods. For the X-rays, texture changes are quantified and correlated with physical changes in the subject. In both cases, the parameterizations are robust with regard to noise present in the images, as well as to variable contrast and brightness.<<ETX>>

Rapid induction of therapeutic hypothermia using convective-immersion surface cooling: Safety, efficacy and outcomes

Therapeutic hypothermia has become an accepted part of post-resuscitation care. Efforts to shorten the time from return of spontaneous circulation to target temperature have led to the exploration of different cooling techniques. Convective-immersion uses a continuous shower of 2 degrees C water to rapidly induce hypothermia. The primary purpose of this multi-center trial was to evaluate the feasibility and speed of convective-immersion cooling in the clinical environment. The secondary goal was to examine the impact of rapid hypothermia induction on patient outcome. 24 post-cardiac arrest patients from 3 centers were enrolled in the study; 22 agreed to participate until the 6-month evaluations were completed. The median rate of cooling was 3.0 degrees C/h. Cooling times were shorter than reported in previous studies. The median time to cool the patients to target temperature (<34 degrees C) was 37 min (range 14-81 min); and only 27 min in a subset of patients sedated with propofol. Survival was excellent, with 68% surviving to 6 months; 87% of survivors were living independently at 6 months. Conductive-immersion surface cooling using the ThermoSuit System is a rapid, effective method of inducing therapeutic hypothermia. Although the study was not designed to demonstrate impact on outcomes, survival and neurologic function were superior to those previously reported, suggesting comparative studies should be undertaken. Shortening the delay from return of spontaneous circulation to hypothermic target temperature may significantly improve survival and neurologic outcome and warrants further study.

Fractal analysis of bone X-ray tomographic microscopy projections

Fractal analysis of bone X-ray images has received much interest recently for the diagnosis of bone disease. Here, the authors propose a fractal analysis of bone X-ray tomographic microscopy (XTM) projections. The aim of the study is to establish whether or not there is a correlation between three-dimensional (3-D) trabecular changes and two-dimensional (2-D) fractal descriptors. Using a highly collimated beam, 3-D bone X-ray tomographic images were obtained. Trabecular bone loss was simulated using a mathematical morphology method. Then, 2-D projections were generated in each of the three orthogonal directions. Finally, the model of fractional Brownian motion (fBm) was used on bone XTM 2-D projections to characterize changes in bone structure that occur during disease, such a simulation of bone loss. Results indicate that fBm is a robust texture model allowing quantification of simulations of trabecular bone changes.

Ischemia-induced impairment of left ventricular relaxation: relation to reduced diastolic filling rates of the left ventricle.

An investigation was performed in order to better define the cause of reduced diastolic filling rates of the left ventricle (LV) observed in the setting of acute myocardial ischemia. Seven closed chest, anesthetized pigs were instrumented by placing a micromanometer-tip catheter in the LV and a balloon tip catheter in the midportion of the left anterior descending coronary (LAD) artery. The animals red blood cells were labeled with technetium-99m and LV time-activity curves obtained by means of a computer-controlled, nonimaging cardiac probe (collimated, 3.5 cm DIA, sodium iodide crystal). Nuclear data obtained simultaneously with LV pressure data were used to evaluate diastolic pressure-count rate (i.e., volume) relations of the LV under control conditions and at 5 and 10 minutes after balloon occlusion of the animals LAD. Diastolic filling rates, the time constant (“T”) of ventricular relaxation, the chamber passive stiffness constant (“K”), and maximum negative left ventricular DPDT were computed for each experimental condition. Maximum negative DPDT decreased compared with control (1690 + 699 mm Hg/sec; mean ± 1 SD) at both 5 minutes (1040 ± 493, p < 0.01) and 10 minutes (1360 ± 588, p < 0.05) after occlusion. Likewise “T” was prolonged versus control (45.3 ± 6.4) at both 5 minutes (56.8 ± 12.8, p < 0.01) and 10 minutes (54.0 ± 8.7, p < 0.05) after occlusion. In contrast both “K” and calculated left ventricular pressure at zero counts (i.e., volume) remained constant throughout the study. Left ventricular end-diastolic pressure also did not change significantly during the study. The mean, maximal, and mid to late LV diastolic filling rates all were prolonged significantly (p < 0.05) versus control at 5 minutes and 10 minutes after occlusion. The rate of early diastolic filling of the LV did not change significantly during the study, although it tended to decline along with the other rates. Thus, ischemia-induced changes in diastolic filling rates may be seen in the absence of changes in left ventricular chamber stiffness, and ischemia-induced impairment of left ventricular relaxation alone is sufficient to reduce the rate of diastolic filling of the LV.

Hemodynamic effects of new intra-aortic balloon counterpulsation timing methods in patients: A multicenter evaluation☆☆☆★

BACKGROUND To test whether later intra-aortic balloon pump (IABP) deflation approaching or simultaneous with left ventricular ejection would improve hemodynamics and myocardial efficiency with the use of new balloon deflation methods, 4 IABP timing techniques were evaluated in 43 patients. METHODS AND RESULTS Later balloon deflation produced significantly greater percentage changes in mean aortic pressure (6% vs 1%), systolic pressure time index (-27% vs -20%), diastolic pressure time index (35% vs 19%), and the systolic pressure-time index/diastolic pressure-time index ratio (97% vs 51%), respectively. However, these changes increased peak systolic pressure (-15% vs -11%). Cardiac output and stroke volume indexes were not significantly altered over the 4 settings. CONCLUSIONS These data suggest that systemic hemodynamics and myocardial efficiency may be improved by later balloon deflation approaching left ventricular ejection in comparison to conventional IABP timing.

Effect of intraaortic balloon counterpulsation on regional myocardial blood flow and oxygen consumption in the presence of coronary artery stenosis: Observations in an awake animal model

Abstract The mechanism by which intraaortic balloon pumping ameliorates myocardial ischemia in patients with unstable angina pectoris is uncertain. Accordingly, the following study was performed to determine the effect of intraaortic balloon pumping on regional myocardial blood flow and myocardial oxygen consumption (MVO 2 ) distal to severe coronary artery stenosis. Nine closed chest conscious pigs were instrumented with a 7.5 mm long plastic stenosis which reduced vessel diameter by 82%. Measurements of hemodynamics, regional myocardial blood flow (microsphere technique) and MVO 2 were made (1) before intraaortic balloon pumping, (2) at the end of 15 to 20 minutes of intraaortic balloon pumping, and (3) 20 minutes after its discontinuation. Control endocardial blood flow (ml · min − 1 · g − 1 ) distal to the stenosis (1.04 ± 0.20, mean ± 1 standard deviation [SD]) was less than endocardial flow in myocardium perfused by the unobstructed circumflex coronary artery (1.67 ± 0 0.77, p In response to intraaortic balloon pumping rate-pressure product declined versus control (10,300 ± 2,090 [SD] mm Hg · min − 1 to 9,110 ± 2,010, p − 1 · − 1 ) distal to the stenosis did not change during intraaortic balloon pumping (1.00 ± 0.24) versus control (1.04 ± 0.20). In contrast, during intraaortic balloon pumping epicardial blood flow distal to the stenosis declined versus control (1.16 ± 0.36 to 1.01 ± 0.27, p 2 (ml · min − 1 · 100 g − 1 ) distal to the stenosis also decreased versus control in response to intraaortic balloon pumping (12.90 ± 3.55 to 10.30 ± 2.52, p 2 correlated well ( r = 0.74, p Thus, intraaortic balloon pumping reduces myocardial oxygen demand but does not improve blood flow distal to a severe coronary stenosis; (2) blood flow distal to a severe stenosis may fail to increase with intraaortic balloon pumping because (A) distal coronary mean diastolic pressure may not increase, and (B) blood vessels distal to the stenosis tend to autoregulate in response to a decline in myocardial oxygen demand; and (3) intraaortic balloon pumping ameliorates myocardial ischemia in patients with unstable angina pectoris primarily by reducing oxygen demand rather than by increasing oxygen supply.

Measurement Of Bone Structure By Use Of Fractal Dimension

This paper describes a method to characterize the evolution of bone structural changes by image processing. This is done by assuming a fractal texture model for the images. A directionally oriented implementation of a maximum likelihood estimator of H (related to the Hausdorff Besicovitch dimension) is performed to obtain an evaluation of this parameter for several directions on each image. Two sets of Xray images are ased : images of an excised, bisected femoral head after different times in an acid solution, and images of a human calcaneus (heel) after an injury and immobilization. The results show that the value of H follows the visual evolution of bone structure and that H decreases with the dissolution of calcium.

Dicrotic notch detection using wavelet transform analysis

The objective of this research was to devise a method of accurately and consistently extracting the dicrotic notch from the aortic blood pressure signal for various heart rates and arrhythmias. The aortic blood pressure signal has been analyzed by calculating the wavelet transform at several scales to consistently detect the temporal location of the dicrotic notch. The simultaneous locations of the peaks in the wavelet transforms of the first derivative of the aortic pressure waveform across 2 consecutive scales corresponds to the location of the dicrotic notch. A final algorithm analyzes the transform results and labels the notch point. Locating the dicrotic notch is critical for analyzing systolic time interval.

Analysis of Left Ventricular Mechanics During Filling, Isovolumic Contraction, and Ejection

The left ventricle (LV) was modeled by two confocal ellipsoids truncated in a plane corresponding to the base of the LV. The ellipsoids were approximated by a series of cylindrical shells. During passive filling, the pressure within the ventricular chamber was determined from chamber volume and a stress-strain relationship for myocardium in the relaxed state. The rapid filling phase of diastole was not analyzed. During isovolumic contraction, the cylindrical shells assumed the properties of myocardium in active contraction. Contraction was sequential, beginning at the ventricular apex, and progressing toward the ventricular base. Geometric changes occurred in the LV model as a function of wall stress, material properties, and timing of myocardial activation. During ejection, viscous and inertial forces were determined as were model output pressure and flow waveforms.