Biomedical subjects
Publications and source records attributed to Michael B Smith.
A case of acute, invasive, sinusitis caused by the dematiaceous mold Exserohilum rostratum is presented. Herein we examine the subtypes of fungal sinusitis and briefly discuss some characteristics, pathologic and microbiologic differential diagnoses and management strategies of Exserohilum sinus infection in an immunocompromised patient.
All participants provided informed consent to participate in this study, which was approved by the institutional review board of Milton S. Hershey Medical Center. The purpose of the study was to determine the feasibility of cartilage T2 mapping in the evaluation of response of femoral and tibial cartilage to running exercise. Quantitative magnetic resonance (MR) T2 maps of weight-bearing femoral and tibial articular cartilage were obtained in seven young healthy men before and immediately after 30 minutes of running by using a 3.0-T MR imager. There was no statistically significant change in T2 profiles of tibial cartilage. There was a statistically significant decrease in T2 of the superficial 40% of weight-bearing femoral cartilage after exercise. These in vivo observations agree well with published ex vivo results and support the hypothesis that cartilage compression results in greater anisotropy of superficial collagen fibers.
Porphyromonas gingivalis, a recognized periodontal pathogen, synthesizes free ceramides as well as other phosphorylated ceramide lipids. The purpose of this study was to separate complex lipids of P. gingivalis by high-performance liquid chromatography (HPLC) and determine the structures and biological activities of the major ceramide classes. Using gas chromatography-mass spectrometry, electrospray tandem mass spectrometry (ESI-MS/MS) and NMR analyses, three major classes of dihydroceramides were identified in specific HPLC fractions, with all classes containing the same dihydroceramide base structures (3-OH isoC(17:0) in amide linkage to saturated long-chain bases of 17, 18, or 19 carbons). The free dihydroceramide class recovered in HPLC fractions 7-8 revealed little biological activity. HPLC fraction 20 dihydroceramides, substituted with 1-O-phosphoglycerol and isoC(15:0) linked to the hydroxyl of 3-OH isoC(17:0), significantly potentiated interleukin-1beta (IL-1beta)-mediated prostaglandin secretion and produced marked alterations in fibroblast morphology. HPLC fraction 28 dihydroceramides, substituted with 1-O-phosphoethanolamine, demonstrated little capacity to potentiate IL-1beta-mediated prostaglandin secretion. The novel phosphorylated dihydroceramides synthesized by P. gingivalis demonstrate varying biological activities based on the phosphorylated head group substitution and/or the addition of esterified fatty acid. These results also demonstrate the strong virulence capacity of phosphoglycerol dihydroceramides of P. gingivalis to promote inflammatory factor secretion from IL-1beta-treated fibroblasts and to produce marked alterations in cell morphology in culture.
Experimental results for changes in brain temperature during functional activation show large variations. It is, therefore, desirable to develop a careful numerical model for such changes. Here, a three-dimensional model of temperature in the human head using the bioheat equation, which includes effects of metabolism, perfusion, and thermal conduction, is employed to examine potential temperature changes due to functional activation in brain. It is found that, depending on location in brain and corresponding baseline temperature relative to blood temperature, temperature may increase or decrease on activation and concomitant increases in perfusion and rate of metabolism. Changes in perfusion are generally seen to have a greater effect on temperature than are changes in metabolism, and hence active brain is predicted to approach blood temperature from its initial temperature. All calculated changes in temperature for reasonable physiological parameters have magnitudes <0.12 degrees C and are well within the range reported in recent experimental studies involving human subjects.
The purpose of this study was to evaluate feasibility of magnetic resonance (MR) T2 mapping of the proximal interphalangeal joint of the index finger. Cartilage T2 maps with an in-plane resolution of 39 microm were obtained from five asymptomatic subjects-four men and one woman, aged 24-45 years-by using a 3.0-T MR imager. Image acquisition time was 9.6 minutes. All cartilage T2 maps demonstrated spatial variation similar to that reported previously for knee cartilage, with T2 values increasing toward the articular surface. These results demonstrate the feasibility of acquiring cartilage T2 maps of small joints in the hand. Application of T2 mapping techniques to non-weight-bearing joints may provide a means for differentiation of local biomechanical and systemic factors that can affect cartilage T2 values.
OBJECTIVE: Because the magnetic resonance imaging (MRI) transverse relaxation time (T2) of cartilage is sensitive to organization of collagen fibers in the cartilage, it may be a noninvasive image marker for senescent changes in cartilage collagen and early cartilage degeneration. The purpose of this study was to determine age-dependent differences in cartilage T2 values in healthy asymptomatic women. METHODS: Quantitative T2 maps of patellar cartilage from 30 asymptomatic women ages 22-86 years were obtained using a 3.0T MRI scanner. The study population was stratified by age into 4 cohorts: 18-30, 31-45, 46-65, and 66-86 years. Spatial differences in cartilage T2 were determined as a function of normalized distance from bone. Older groups were compared with the 18-30-year-old group to determine the effects of age on cartilage T2 values. Regions were considered statistically significantly different if the mean T2 values between groups differed at P < 0.05. RESULTS: Mean cartilage T2 profiles were nearly identical for the 2 youngest cohorts. Compared with the 18-30-year-old group, T2 values were statistically significantly longer in the superficial 40% of cartilage in the 46-65-year-old group and over the entire cartilage thickness in the 66-86-year-old group. CONCLUSION: The location of T2 elevations in women over the age of 45 years is consistent with the theory that senescent changes of cartilage collagen begin near the articular surface and progress to the deeper cartilage with advancing age.
PURPOSE: To determine if gender is a significant variable for in vivo magnetic resonance imaging (MRI) T2-mapping of knee articular cartilage in young asymptomatic volunteers. MATERIALS AND METHODS: Cartilage MRI T2 mapping was performed in a young healthy population consisting of seven male and 10 female volunteers, 22 to 29 years of age. High-resolution in vivo T2 maps were obtained of patellar, tibial, and weight-bearing femoral articular cartilage. Spatial dependency of cartilage T2 between groups was evaluated through a comparison of cartilage T2 as a function of normalized distance from bone. RESULTS: Bulk cartilage T2 values were similar at all three anatomic sites, and between male and female volunteers. All volunteers demonstrated similar spatial variation in cartilage MRI T2 values, with a minimum located in the radial zone and increasing T2 values toward the articular surface. There was no difference in spatial dependency of cartilage T2 between males and females. CONCLUSION: In young, healthy volunteers, the magnitude and spatial dependency of cartilage T2 does not differ with gender.
PURPOSE: To examine relationships between specific energy absorption rate (SAR) and temperature distributions in the human head during radio frequency energy deposition in MRI. MATERIALS AND METHODS: A multi-tissue numerical model of the head was developed that considered thermal conductivity, heat capacity, perfusion, heat of metabolism, electrical properties, and density. Calculations of SAR and the resulting temperature increase were performed for different coils at different frequencies. RESULTS: Because of tissue-dependent perfusion rates and thermal conduction, there is not a good overall spatial correlation between SAR and temperature increase. When a volume coil is driven to induce a head average SAR level of either 3.0 or 3.2 W/kg, it is unlikely that a significant temperature increase in the brain will occur due to its high rate of perfusion, although limits on SAR in any 1 g of tissue in the head may be exceeded. CONCLUSION: Attempts to ensure RF safety in MRI often rely on assumptions about local temperature from local SAR levels. The relationship between local SAR and local temperature is not, however, straightforward. In cases where high SAR levels are required due to pulse sequence demands, calculations of temperature may be preferable to calculations of SAR because of the more direct relationship between temperature and safety.
We modeled four different end-ring/shield configurations of a birdcage coil to examine their effects on field homogeneity and signal-to-noise ratio (SNR) at 64 MHz and 125 MHz. The configurations are defined as: 1) conventional: a conventional cylindrical shield; 2) surrounding shield: a shield with annular extensions to closely shield the end rings; 3) solid connection: a shield with annular extensions connected to the rungs; and 4) thin wire connection: a shield with thin wires connected to the rungs. At both frequencies, the coil with conventional end-ring/shield configuration produces the most homogeneous RF magnetic (B1) field when the coil is empty, but produces the least homogeneous B1 field when the coil is loaded with a human head. The surrounding shield configuration results in the most homogeneous B1 and highest SNR in the coil loaded with the human head at both frequencies, followed closely by the solid connection configuration.
A phantom design method suitable for high-field MRI based on the RF field wave characteristics of sample and experimental validations at 7.0 T and 3.0 T are presented. The RF field distribution in a phantom with a given RF coil system is primarily determined by the sample size relative to the wavelength inside the sample, and the ratio between the displacement and conduction currents. Experimental results demonstrate that the MR image intensity patterns associated with wave behavior in human samples at a given field strength can be reproduced with a phantom at the same or different field strengths once the dimension and penetration constant are scaled by the corresponding wavelength in the sample medium.
Geometric distortion, signal-loss, and image-blurring artifacts in echo planar imaging (EPI) are caused by frequency shifts and T(2)(*) relaxation distortion of the MR signal along the k-space trajectory due to magnetic field inhomogeneities. The EPI geometric-distortion artifact associated with frequency shift can be reduced with parallel imaging techniques such as SENSE, while the signal-loss and blurring artifacts remain. The gradient-echo slice excitation profile imaging (GESEPI) method has been shown to be successful in restoring tissue T(2)(*) relaxation characteristics and is therefore effective in reducing signal-loss and image-blurring artifacts at a cost of increased acquisition time. The SENSE and GESEPI methods are complementary in artifact reduction. Combining these two techniques produces a method capable of reducing all three types of EPI artifacts while maintaining rapid acquisition time.
PURPOSE: Edentulous patients desire restoration of their chewing ability as soon as possible after placement of dental implants. The purpose of this article is to provide clinicians with evidence that immediate loading of implants placed into the anterior mandible can predictably provide the patient with early functional rehabilitation. Two methods are presented that illustrate delivery of the final restoration or a provisional implant-borne prosthesis immediately after implant placement. MATERIALS AND METHODS: A literature search was performed which produced 14 articles in the English literature that provided sufficient evidence that immediate loading is now not experimental and can be recommended as an acceptable treatment alternative. RESULTS: Two practical methods to achieve immediate function are presented in a step-wise manner to illustrate how to deliver this service to the patient. CONCLUSION: Based on our literature review, immediate loading of the edentulous mandible with an implant-borne restoration is an acceptable and predictable method to deliver efficient return of function for the edentulous patient.
The performance of a fully automated, random access, enhanced chemiluminescence immunoassay (Ortho/ECi) for the detection of antibody to hepatitis C virus (HCV) (anti-HCV), HBsAg, and antibody to HBsAg (anti-HBsAg), in human serum was compared to a Abbott second-generation enzyme immunoassay (EIA 2.0). The Ortho/ECi assays employ an immunometric technique with enhanced chemiluminescence for optimal assay performance. With regard to the study of clinical laboratory performance, six groups of sera prescreened with Abbott EIAs were assayed: anti-HCV-negative samples (n = 318), anti-HCV-positive samples (n = 177), anti-HBsAg-negative samples (n = 241), anti-HBsAg-positive samples (n = 239), HBsAg-positive samples (n = 158), and HBsAg-negative samples (n = 312). Sera with discrepant results in the two serological assays were resolved by confirmatory tests. Sera with indeterminate results by one or more confirmatory tests were evaluated by reviewing medical records. The overall concordance between the Ortho/ECi assay and the Abbott EIA were 97.78, 93.54, and 97.66% for anti-HCV antibodies, anti-HBsAg antibodies, and HBsAg, respectively. After resolving the discrepancies, the specificities of the new assay for anti-HCV and anti-HBsAg antibodies and HBsAg were 98.1, 92.8, and 100%, respectively. The sensitivities of the new assay for anti-HCV, anti-HBsAg, and HBsAg were 100, 98.8, and 97.4%, respectively. In conclusion, The Ortho/ECi assays for diagnosis of HCV and hepatitis B virus (HBV) infections are highly specific and sensitive assays. The rapid turnaround time, random access, full automation, and high throughput make it an effective assay system for clinical laboratory diagnosis of HCV and HBV infections.
PURPOSE: To examine how fine a model resolution is necessary for calculation of specific energy absorption rate (SAR) for the human head in regions as small as 1 g. MATERIALS AND METHODS: Here we perform a simple study comparing the maximum SAR averaged over any 1 cm(3) and SAR averaged over the entire head for several models of the same human head within the same radiofrequency coil, but with spatial resolutions varying from 8-100 Yee cells per cm(3). RESULTS: Over the range of model resolutions from 8-100 Yee cells per cm(3), there is only a 16% variation in maximum SAR in any 1 cm(3) of tissue in the head, and only a 7% variation in SAR averaged over the entire head. CONCLUSION: While it is always desirable to perform SAR calculations with the greatest possible accuracy, in calculations of the maximum SAR levels in any 1 cm(3) of tissue, spatial resolutions greater than 5 mm may not yield notably different results than those with a spatial resolution of 5 mm.
The use of detached endcaps for 3 T birdcage coils was investigated both theoretically and experimentally. Finite difference time domain analysis, along with workbench and MRI techniques, were used to map the radiofrequency (RF) B(1) distribution along the coil axis with and without an endcap. Without an endcap the measured B(1) value at the service end of the birdcage was only 45% of the value at the coil's center. This was improved to 85% with a detached endcap of maximum achievable diameter (375 mm), positioned 4 mm from the RF shield. The B(1) field distribution on the patient side of the coil was unaffected by the presence of the endcap. The dependence of the B(1) distribution as a function of endcap diameter was also investigated. Surprisingly, simulations and experiments show that there is an optimum ratio of endcap-to-birdcage coil diameter (approximately 1.08) that gives the best B(1) homogeneity. In the human head the optimized endcap, positioned 16 mm from the RF shield, improves the MRI signal amplitude from 55% to 85% of maximum toward the service end. This novel endcap design is easy to implement with existing birdcage coils, and could prove useful when flexibility in access to the RF coil is required.
CONTEXT: Mycobacterium kansasii is a slow-growing photochromogenic mycobacterium that may infect patients with human immunodeficiency virus (HIV) late in the course of acquired immunodeficiency syndrome (AIDS). The clinical features of pulmonary and extrapulmonary infections have been described in the literature; however, the pathology of infection has not been adequately addressed. OBJECTIVE: This report describes the pathologic features of 12 cases of M kansasii infection in patients with AIDS. DESIGN: The medical records, autopsy protocols, cytologic material, and histologic material from patients with AIDS and concomitant M kansasii infection at a tertiary-care medical center during 1990-2001 were reviewed. RESULTS: Twelve cases were identified, 6 by autopsy, 5 of which were diagnosed postmortem. Four of the 12 cases had cytologic material and 4 cases had histologic biopsies available for review. Pulmonary infection was most common (9/12), and all patients in whom thoracic lymph nodes were assessed showed involvement (7/7). Abdominal infection was less frequent, with only 1 of 6, 2 of 6, and 2 of 6, demonstrating liver, spleen, and abdominal lymph node infection, respectively. Isolated infections without documented pulmonary infection included brain abscess (n = 1), ulnar osteomyelitis (n = 1), and paratracheal mass (n = 1). Cytologic and histologic material showed a wide range of inflammatory reactions, including granulomas with and without necrosis, neutrophilic abscesses, spindle-cell proliferations, and foci of granular eosinophilic necrosis. The M kansasii bacillus was characteristically long, coarsely beaded, and frequently showed folded, bent, or curved ends. Intracellular bacilli were randomly or haphazardly distributed within histiocytes. CONCLUSION: Mycobacterium kansasii infection produces predominantly pulmonary infection in late-stage AIDS with a high incidence of thoracic lymph node involvement and a much lower incidence of dissemination to other sites. Infection is manifest as a wide variety of inflammatory reactions on cytology and histology; however, the characteristic appearance of the bacillus on acid-fast bacilli stain and its intracellular arrangement in histiocytes can allow a presumptive identification.
[reaction: see text] Treatment of aniline with n-butyllithium and then trimethyltin chloride gave the tin amide (PhNH-SnMe(3)) in situ. Without isolation of the tin amide, reaction with bromine and workup with aqueous fluoride ion gave p-bromoaniline in 76% yield, with no dibromoaniline or o-bromoaniline. Application of this sequence to 11 different aromatic amines gave selective bromination in 36-91% yields, without formation of dibromides. This constitutes a good general method for the regioselective bromination of aromatic amines.
Radiofrequency (RF) field wave behavior and associated nonuniform image intensity at high magnetic field strengths are examined experimentally and numerically. The RF field produced by a 10-cm-diameter surface coil at 300 MHz is evaluated in a 16-cm-diameter spherical phantom with variable salinity, and in the human head. Temporal progression of the RF field indicates that the standing wave and associated dielectric resonance occurring in a pure water phantom near 300 MHz is greatly dampened in the human head due to the strong decay of the electromagnetic wave. The characteristic image intensity distribution in the human head is the result of spatial phase distribution and amplitude modulation by the interference of the RF traveling waves determined by a given sample-coil configuration. The numerical calculation method is validated with experimental results. The general behavior of the RF field with respect to the average brain electrical properties in a frequency range of 42-350 MHz is also analyzed.