Biomedical subjects

Jerry Allison

Publications and source records attributed to Jerry Allison.

9 recordsLinked to original sources

PubMed2006

Use of capillaries in the construction of an MRI phantom for the assessment of diffusion tensor imaging: demonstration of performance.

Although diffusion tensor imaging (DTI) shows great potential for the diagnosis of a variety of pathologies, no consensus for an appropriate assessment standard of DTI exists. This study examined the feasibility of using water-filled arrays of glass capillaries to construct a DTI phantom suitable for making repeated and reproducible measurements required in a quality assessment program. Three phantoms were constructed using arrays of capillaries with three inner diameters (23, 48, and 82 microm). Data were acquired using DTI protocols; the fractional anisotropy (FA), mean apparent diffusion coefficient (ADC) and principal eigenvectors of the diffusion tensors were calculated. This study demonstrated four results: (1) echo-planar images show that susceptibility within the capillary arrays does not lead to substantial differences in precessional frequency in regions containing the arrays and neither do the regions show noticeable image distortion; (2) principal eigenvectors of the diffusion tensors agree to within<10.3 degrees of the array orientations; (3) mean FA values (0.18-0.50) and ADC values (1.40-1.93x10-(3) mm2/s) within specified regions of interest are in general agreement with simulations after a simple noise correction; and (4) these array performance characteristics are observable using a typical clinical DTI protocol.

Anisotropy↗

PubMed2005

Study of subclinical cerebral edema in diabetic ketoacidosis by magnetic resonance imaging T2 relaxometry and apparent diffusion coefficient maps.

Cerebral edema is the most significant complication in children with diabetic ketoacidosis (DKA). Our goal was to study whether subclinical cerebral edema was preferentially vasogenic or cytotoxic. Magnetic resonance imaging (MRI)--diffusion-weighted imaging (DWI) and T2 relaxometry (T2R)--were obtained in pediatric patients presenting with severe diabetic ketoacidosis (DKA) 6-12 hours after initial DKA treatment and stabilization and 96 hours after correction of DKA. T2 relaxometry was significantly increased during treatment in both white and gray matter, in comparison to the absolute T2R values 96 hours after correction of DKA (p = .034). Classic intracellular cytotoxic edema could not be detected, based on the lack of a statistically significant decrease in ADC values. ADC values were instead elevated, implying a large component of cell membrane water diffusion, correlating with the elevated white and gray matter T2R We discuss the findings in relation to cerebral blood volume, cerebral vasoregulatory dysfunction, and cerebral hyperemia.

Adolescent↗

PubMed2003

Influence of physical training on plasma leptin in obese youths.

Little is known about the effects of different intensities of physical training on plasma leptin. This study examined the effect of two intensities of physical training on leptin in obese teenagers, and explored correlates at baseline and in response to 8 months of physical training. The participants were 55 obese youths 12-16 years of age who completed both baseline and posttesting. The youths were randomized to engage in lifestyle education only (LSE), moderate-intensity physical training and LSE, or high-intensity physical training and LSE. Baseline leptin was positively associated with fat mass. Girls had higher leptin levels at lower levels of fasting insulin than boys. The 8-mo physical training doses prescribed to obese teenagers did not result in significant group differences in mean change in leptin, although there was large variability in individual response. The change in leptin was inversely associated with baseline leptin and change in cardiovascular fitness. Diet, physical activity level, visceral adiposity, and glucose concentrations were not associated with leptin, neither at baseline nor in response to physical training. At baseline, total fat mass rather than visceral adiposity was associated with higher leptin levels. Over the 8-mo intervention period, regardless of group membership, youths who had the lowest increase in cardiovascular fitness tended to have the highest increase in leptin.

Adipose Tissue↗

PubMed2003

18F protection issues: human and gamma-camera considerations.

OBJECTIVE: Two main issues in protecting radiation workers and the general public from (18)F radiation-distance from and lead shielding for an (18)F source-were investigated. We also examined the effect of an (18)F source on the counting rate of a neighboring gamma-camera. METHODS: The dose rates of an (18)F vial and a water-filled cylinder were measured using an ionization chamber at different distances with or without lead shielding. In addition, the counting rates of gamma-cameras in the presence of the (18)F cylinder were measured with different detector orientations, distances, and energy windows. RESULTS: The dose rate of a point or an extended source in air was proportional to the inverse square of the distance from the source. At 2 m, the dose rate for a 370-MBq (18)F source was less than 20 micro Gy in any single hour, which is the limit for unrestricted areas. The dose rate with 0.318-cm-thick lead shielding decreased to about 60%, and that with 5.08-cm-thick lead shielding decreased to about 4%; these rates were higher than those estimated using the narrow-beam attenuation formula. The scattered photons and characteristic x-rays from the lead brick and surrounding structures may have contributed to this result. The decrease in dose rate resulting from a 33% increase in distance was similar to the effect from shielding the source with 0.318-cm-thick lead. At 3 m from a 185-MBq (18)F source, the counting rate in the (99m)Tc window of an Orbiter camera was about 120,000/min when the detector faced the source. This rate was comparable to that of a typical (99m)Tc clinical study ( approximately 200,000/min). Only when the distance was increased to 11 m and the detector did not face the source did the counting rate decrease to the background level (3,234/min). The counting rate also depended on the energy window of the gamma-camera. On a Vertex camera, the counting rate of (18)F in the (99m)Tc window versus that in the (201)Tl (or (67)Ga) window was 1:1.7 (or 1:2.7). CONCLUSION: (18)F dose rate can be significantly reduced with distance. Lead shielding is not as effective as was predicted. (18)F sources should be kept substantial distances away from gamma-cameras to avoid contamination of image quality.

Environmental Exposure↗

PubMed2002

Effects of exercise intensity on cardiovascular fitness, total body composition, and visceral adiposity of obese adolescents.

BACKGROUND: Little is known about how the intensity of exercise influences cardiovascular fitness and body composition, especially in obese adolescents. OBJECTIVE: Our goal was to determine the effects of physical training intensity on the cardiovascular fitness, percentage of body fat (%BF), and visceral adipose tissue (VAT) of obese adolescents. DESIGN: Obese 13-16-y-olds (n = 80) were assigned to 1) biweekly lifestyle education (LSE), 2) LSE + moderate-intensity physical training, or 3) LSE + high-intensity physical training. The intervention lasted 8 mo. Physical training was offered 5 d/wk, and the target energy expenditure for all subjects in physical training groups was 1047 kJ (250 kcal)/session. Cardiovascular fitness was measured with a multistage treadmill test, %BF with dual-energy X-ray absorptiometry, and VAT with magnetic resonance imaging. RESULTS: The increase in cardiovascular fitness in the high-intensity physical training group, but not in the moderate-intensity group, was significantly greater than that in the LSE alone group (P = 0.009); no other comparisons of the 3 groups were significant. Compared with the LSE alone group, a group composed of subjects in both physical training groups combined who attended training sessions >or=2 d/wk showed favorable changes in cardiovascular fitness (P < 0.001), %BF (P = 0.001), and VAT (P = 0.029). We found no evidence that the high-intensity physical training was more effective than the moderate-intensity physical training in enhancing body composition. CONCLUSIONS: The cardiovascular fitness of obese adolescents was significantly improved by physical training, especially high-intensity physical training. The physical training also reduced both visceral and total-body adiposity, but there was no clear effect of the intensity of physical training.

Adipose Tissue↗

PubMed2002

Relations of adiposity and effects of training on the left ventricle in obese youths.

PURPOSE: 1) To determine the relations of left ventricular (LV) structure and function to total body composition, visceral adipose tissue (VAT), and hemodynamics in obese children; 2) to determine the effects of 4-month of physical training (PT) on LV structure and function and hemodynamics; and 3) to explore determinants of individual variability in response to PT. METHODS: Measurements included LV structure/function with echocardiography, total body composition with dual-energy x-ray absorptiometry, VAT with magnetic resonance imaging (MRI), and resting and exercising hemodynamics with a Dinamap monitor and Doppler-echocardiography. Youths were randomly assigned to engage in PT for the first or second 4-month periods of the 8-month intervention period. RESULTS: Correlation and regression at baseline showed that elevated LV mass was associated with excess general and visceral adiposity, and elevated cardiac output. Although the PT had favorable effects on percent body fat and VAT, no significant changes were found in LV or hemodynamic variables. Over the 4-month period of the PT intervention, those who increased the most in VAT tended to increase the most in LV mass. CONCLUSION: General and visceral adiposity were associated with elevated LV mass. However, no evidence was provided that 4 months of PT had a significant effect on LV or hemodynamic variables.

Adipose Tissue↗

PubMed2002

Physical training improves insulin resistance syndrome markers in obese adolescents.

INTRODUCTION: The purpose of this study was to test the hypothesis that physical training (PT), especially high-intensity PT, would have a favorable effect on components of the insulin resistance syndrome (IRS) in obese adolescents. METHODS: Obese 13- to 16-yr-olds (N = 80) were randomly assigned to one of the following 8-month interventions; 1) lifestyle education (LSE)-alone every 2 wk, 2) LSE+moderate-intensity PT, and 3) LSE+high-intensity PT. PT was offered 5 d x wk(-1). Plasma triacylglycerol (TAG), total cholesterol (TC), high-density lipoprotein cholesterol (HDLC), very low-density lipoprotein cholesterol (VLDLC), low-density lipoprotein cholesterol (LDLC), low-density lipoprotein (low density lipoprotein (LDL)) particle size, apolipoproteins AI and B, glucose, insulin, and blood pressure were measured with standardized methods. RESULTS: The intent-to-treat analyses for all subjects who completed pre- and post-tests regardless of their adherence to the interventions showed that the LSE+high-intensity PT group had more favorable changes than the LSE-alone group in TAG level (P = 0.012), TC/HDLC (P = 0.013), and diastolic blood pressure (P = 0.031). For efficacy analyses, all PT subjects who attended at least 2 d x wk(-1) (40%) were combined into one group (LSE+PT) and compared with the LSE-alone group. These two-group analyses showed significant interactions (P < 0.001) between baseline values and group membership for deltaTAG, deltaVLDLC, and deltaTC/HDLC, such that subjects who had the least favorable baseline values showed the most beneficial impact of the PT. Of particular interest was a favorable effect of the PT on LDL particle size. CONCLUSION: PT, especially high-intensity PT, had a favorable effect on several IRS markers in obese adolescents.

Absorptiometry, Photon↗

PubMed2002

Practical aspects of functional MRI (NMR Task Group #8).

Functional MR imaging (fMRI) based upon the Blood Oxygen Level Dependent (BOLD) effect is currently an important new tool for understanding basic brain function and specifically allowing the correlation of physiological activity with anatomical location without the use of ionizing radiation. The clinical role of fMRI is still being defined and is the subject of much research activity. In this report we present the underlying physical, technical and mathematical principals of BOLD fMRI along with descriptions of typical applications. Our purpose in this report is to provide, in addition to basic principles, an insight into the aspects of BOLD imaging, which may be used by the medical physicist to assist in the implement of fMRI procedures in either a hospital or research environment.

Brain↗

PubMed2002

Left ventricular structure and function in obese adolescents: relations to cardiovascular fitness, percent body fat, and visceral adiposity, and effects of physical training.

OBJECTIVE: Little is known about the relations of fitness and fatness to left ventricular structure and function in obese adolescents. This project had 2 purposes: 1) to determine the correlations of cardiovascular fitness and adiposity to left ventricular parameters in obese adolescents; and 2) to see the effect of 8 months of physical training (PT) at low and high intensities. DESIGN: Obese 13- to 16-year-olds (N = 81) were tested at baseline and then randomly assigned to lifestyle education (LSE) alone, LSE plus moderate-intensity PT, or LSE plus high-intensity PT. Follow-up testing was conducted 8 months later. Because no significant differences were found between moderate-intensity and high-intensity PT, the groups were combined to form a LSE + PT group. INTERVENTION: Eight months of PT, offered 5 days per week with the target energy expenditure for all PT participants being 250 kcal/session, and LSE every 2 weeks. Outcome Measures. Left ventricular mass divided by height to the 2.7th power (LVM/Ht(2.7)), midwall fractional shortening (MFS), and relative wall thickness (RWT) were measured using M-mode echocardiography. Cardiovascular fitness was measured by a maximal multistage treadmill test; percent body fat (%BF) with dual-energy radiograph absorptiometry; and visceral adipose tissue (VAT) with magnetic resonance imaging. RESULTS: At baseline, high levels of VAT were associated with higher RWT (r = 0.30) and lesser MFS (r = -0.29). Compared with the LSE-alone group, the LSE + PT group significantly improved in cardiovascular fitness and decreased in %BF and VAT. However, there were no significant differences between groups on changes in LVM/Ht(2.7), MFS, or RWT. Individual changes in cardiovascular fitness, %BF, and VAT did not correlate significantly with interindividual changes in left ventricular structure and function. CONCLUSIONS: High levels of VAT were associated with unfavorable left ventricular structure and function. However, no evidence was provided that an 8-month PT program, which improved cardiovascular fitness and reduced general and visceral adiposity, improved left ventricular structure and function. Future studies consisting of longer training programs and/or greater weight reductions are needed to see whether the adverse left ventricular effects of obesity can be ameliorated by exercise training.

Adipose Tissue↗