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M B Smith

Publications and source records attributed to M B Smith.

At least 55 records · Page 3Linked to original sources
PubMed1998

A birdcage coil tuned by RF shielding for application at 9.4 T.

The design and performance of an inductively fed low-pass birdcage radiofrequency (RF) coil for applications at 9.4 T are described where tuning is accomplished by mechanically moving a concentric RF shield about the longitudinal axis of an RF coil. Moving the shield about the RF coil effectively changes the mutual inductance of the system, providing a mechanism for adjusting the resonant frequency. RF shield tuning eliminates adjustable capacitors on the legs of the RF coil, eliminates current imbalances and field distortions, and results in improved B1 field homogeneity and high quality (Q) factors. RF shield tuning and inductive matching provide an isolated resonance structure which is both physically and electrically unattached. Experimental analysis of shield position on both B1 field homogeneity and resonant frequency is provided. Computer simulations of B1 field homogeneity as a function of shield position and shield diameter are also presented. Magnetic resonance microimaging substantiates the usefulness of this design.

Animals↗
PubMed1998

Energy expenditure during gait using the walkabout and isocentric reciprocal gait orthoses in persons with paraplegia.

OBJECTIVE: To compare the energy expenditure during walking using the Walkabout Orthosis (WO) and the Isocentric Reciprocal Gait Orthosis (IRGO) in persons with paraplegia. DESIGN: A randomized cross-over design. PATIENTS: Ten individuals with complete T9-12 paraplegia. INTERVENTIONS: Subjects were trained to walk using the WO and the IRGO with elbow crutches. MAIN OUTCOME MEASURES: Subjects' energy expenditures during walking using each orthosis over three different terrains--flat tile, flat carpet, and 4 degrees uphill ramp--were compared. Data collected included expired ventilation (L/min), heart rate (beats/ min), speed of walking (m/min), oxygen uptake (VO2; L/min and mL/kg/min), oxygen cost (O2 cost; mL/kg/m), and Physical Cost Index (PCI; beats/m). Subjects walked at a self-selected pace. RESULTS: Subjects walked significantly slower with the WO than with the IRGO, regardless of the surface (p < .05). The average speed of walking ranged from 5.2+/-1.3 for the WO on the tiled surface to 11.5+/-2.3m/min for the IRGO on the carpeted surface. Despite marked differences in self-selected walking speeds between the two orthoses, there were no differences in either heart rate or VO2 among orthoses or surfaces. However, the O2 cost of gait was significantly greater for the WO (range, 3.95 to 4.91mL/kg/m) compared with the IRGO (range, 1.6 to 1.8mL/kg/m). Likewise, the PCI was significantly greater using the WO (range, 8.4 to 10.3beats/m) than the IRGO (range, 4.3 to 7.0beats/m). CONCLUSIONS: This study shows that the metabolic demands of walking with the WO are greater than walking with the IRGO in individuals with T9-12 paraplegia.

Adult↗
PubMed1998

A numerical study of radiofrequency deposition in a spherical phantom using surface coils.

The electromagnetic fields induced by a surface coil in a spherical phantom, having a wide range of electrical properties, is studied using numerical methods of calculation. The specific absorption rate (SAR), radiofrequency magnetic field (B1), magnetic field energy within the phantom (EB), and the volume-averaged SAR ( ) are calculated at 10, 63, and 200 MHz. They are analyzed with respect to dielectric constant, wavelength, and skin depth effects, which become increasingly important in high field magnetic resonance imaging (MRI) where safety and field homogeneity issues need further study. Particular attention is given to solutions representing neural tissue at each frequency. In general, the data at high field strengths have local maxima, with a quasi-harmonic behavior, when the following two resonant conditions are satisfied: 1) skin depth becomes comparable to, or larger than, the sample diameter Ds; and 2) Ds is near an integral multiple of the wavelength. These are also the solutions with maximum EB values and the least homogeneous B1. Samples undergoing resonance at 200 MHz are shown to have important off-axis B1 maxima (affecting field homogeneity) and large values. Some non-resonating 200-MHz phantoms, including simulations consistent with neural tissue, contain larger SAR maxima than the resonating samples, posing safety concerns in high field imaging of biologic tissue.

Computer Simulation↗
PubMed1998

Altered mechanisms of sympathetic activation during rhythmic forearm exercise in heart failure.

In congestive heart failure (CHF), the mechanisms of exercise-induced sympathoexcitation are poorly defined. We compared the responses of sympathetic nerve activity directed to muscle (MSNA) and to skin (SSNA, peroneal microneurography) during rhythmic handgrip (RHG) at 25% of maximal voluntary contraction and during posthandgrip circulatory arrest (PHG-CA) in CHF patients with those of an age-matched control group. During RHG, the CHF patients fatigued prematurely. At end exercise, the increase in MSNA was similar in both groups (CHF patients, n = 12; controls, n = 10). However, during PHG-CA, in the controls MSNA returned to baseline, whereas it remained elevated in CHF patients (P < 0.05). Similarly, at end exercise, the increase in SSNA was comparable in both groups (CHF patients, n = 11; controls, n = 12), whereas SSNA remained elevated during PHG-CA in CHF patients but not in the controls (P < 0.05). In a separate control group (n = 6), even high-intensity static handgrip was not accompanied by sustained elevation of SSNA during PHG-CA. 31P-nuclear magnetic resonance spectroscopy during RHG demonstrated significant muscle acidosis and accumulation of inorganic phosphate in CHF patients (n = 7) but not in controls (n = 9). We conclude that in CHF patients rhythmic forearm exercise leads to premature fatigue and accumulation of muscle metabolites. The prominent PHG-CA response of MSNA and SSNA in CHF patients suggests activation of the muscle metaboreflex. Because, in contrast to controls, in CHF patients both MSNA and SSNA appear to be under muscle metaboreflex control, the mechanisms and distribution of sympathetic outflow during exercise appear to be different from normal.

Adult↗
PubMed1998

Effects of the ovarian cycle on sympathetic neural outflow during static exercise.

We compared reflex responses to static handgrip at 30% maximal voluntary contraction (MVC) in 10 women (mean age 24.1 +/- 1.7 yr) during two phases of their ovarian cycle: the menstrual phase (days 1-4) and the follicular phase (days 10-12). Changes in muscle sympathetic nerve activity (MSNA; microneurography) in response to static exercise were greater during the menstrual compared with follicular phase (phase effect P = 0.01). Levels of estrogen were less during the menstrual phase (75 +/- 5.5 vs. 116 +/- 9.6 pg/ml, days 1-4 vs. days 10-12; P = 0.002). Generated tension did not explain differences in MSNA responses (MVC: 29.3 +/- 1.3 vs. 28.2 +/- 1.5 kg, days 1-4 vs. days 10-12; P = 0.13). In a group of experiments with the use of 31P-NMR spectroscopy, no phase effect was observed for H+ and H2PO-4 concentrations (n = 5). During an ischemic rhythmic handgrip paradigm (20% MVC), a phase effect was not observed for MSNA or H+ or H2PO-4 concentrations, suggesting that blood flow was necessary for the expression of the cycle-related effect. The present studies suggest that, during static handgrip exercise, MSNA is increased during the menstrual compared with the follicular phase of the ovarian cycle.

Adult↗
PubMed1998

Postpartum sleep in the hospital. Relationship to taking-in and taking-hold.

This descriptive, correlational study examined the relationship of sleep in the hospital to the new mother's progression through Rubin's phases of taking-in and taking-hold in 120 women who had delivered vaginally. The Martell and Mitchell Postpartum Questionnaire, which measured taking-in and taking-hold, was completed the evening of delivery and the following two mornings. The Verran and Snyder-Halpern Visual Analog Sleep Scale was completed each morning. Both taking-in and taking-hold were present on the evening of delivery. There were small decreases in taking-in and small increases in taking-hold between the evening of delivery and the first morning. Sleep disturbance was high, and sleep effectiveness was low, on the first evening. Neither sleep measure was a predictor of change in taking-in or taking-hold. Findings indicate that taking-in and taking-hold are both present on the day of delivery and that increases in taking-hold take place despite high levels of sleep disturbance.

Adaptation, Psychological↗
PubMed1997

Multi-gradient echo with susceptibility inhomogeneity compensation (MGESIC): demonstration of fMRI in the olfactory cortex at 3.0 T.

Short image acquisition times and sensitivity to magnetic susceptibility favor the use of gradient echo imaging methods in functional MRI (fMRI). However, magnetic susceptibility effects attributed to air-tissue interfaces also lead to severe signal loss in images of the large inferior frontal and lateral temporal cortices of the human brain, which renders these regions inaccessible to fMRI. The signal loss is caused by the local field gradients in the silce selection direction. A multigradient echo with magnetic susceptibility inhomogeneity compensation method (MGESIC) is proposed to overcome this problem. The MGESIC method effectively corrects the susceptibility artifacts and maintains the advantages of gradient echo methods to both BOLD sensitivity and fast image acquisition. The effectiveness of the MGESIC method is demonstrated by fMRI experimental results within the olfactory cortex.

Humans↗
PubMed1997

A method to create an optimum current distribution and homogeneous B1 field for elliptical birdcage coils.

For a birdcage coil with elliptical cross-section, a sinusoidal current pattern does not provide a homogeneous B1 field. A simple theory was developed to create an optimized current distribution for elliptical birdcage coils. This optimized current pattern can create a perfectly homogeneous B1 field inside any elliptical shape. To verify the theory, a 16-element high-pass elliptical birdcage coil was built inside a circular RF shield. The current was optimized by using the inductance characteristics of the coil components to calculate the end-ring capacitances. The B1 field was theoretically calculated and experimentally mapped for the optimized elliptical bird-cage coil and a nonoptimized coil. The results demonstrate that by optimizing the current distribution, a very homogeneous B1 field is produced. This method can be directly applied in design and construction of elliptical birdcage coils for imaging of the naturally occurring elliptical cross-sectional geometries in the human body.

Computer Simulation↗
PubMed1997

Functional outcomes attained by T9-12 paraplegic patients with the walkabout and the isocentric reciprocal gait orthoses.

OBJECTIVE: To compare the functional outcomes attained by persons with paraplegia using the Walkabout Orthosis (WO) and the Isocentric Reciprocal Gait Orthosis (IRGO). DESIGN: A randomized crossover design. PATIENTS: Ten subjects with complete lesions between T9-T12. INTERVENTIONS: Over two 8-week periods, subjects were taught to use each orthosis in conjunction with elbow crutches. MAIN OUTCOME MEASURES: After each 8-week training period, subjects were assessed on their ability to perform five different sets of key skills associated with functional ambulation. RESULTS: There were no differences between orthoses in the ability of subjects to don and doff the orthoses, get up and down stairs and curbs, or walk on a flat surface. Subjects required significantly more assistance when using the WO to walk over inclined surfaces (median IRGO = "independent," median WO = "minimal assistance"; p = .03) but less assistance when using the WO to get from sitting to standing and standing to sitting (median IRGO = "moderate assistance," median WO = "minimal assistance"; p = .03). In addition, subjects walked significantly faster with the IRGO both on the flat (mean IRGO = .34 m/sec +/- .18, mean WO = .14 m/sec +/- .12; p = .002) and on inclined surfaces. CONCLUSIONS: Although it is easier to stand up and sit down with the WO, the IRGO facilitated a faster and more independent gait. Neither orthosis enabled subjects to be fully independent in the key skills necessary for functional ambulation after 8 weeks of training.

Activities of Daily Living↗
PubMed1997

Second malignant neoplasms in children after treatment of soft tissue sarcoma.

Currently, approximately 67% of children diagnosed with cancer can be expected to survive more than 5 years. Among the most significant late effects of cancer therapy is the development of second malignant neoplasm (SMN). This study was performed to identify the factors associated with the development of second malignant neoplasms after treatment for soft tissue sarcomas in childhood. Retrospectively the charts of 20 children who developed second malignant neoplasms after treatment for primary childhood soft tissue sarcoma were reviewed. Presentation, age at diagnosis, tumor histology, extent of tumor, treatment, family histories (when available), and outcome were recorded. The mean age of the patients (10 boys, 10 girls) was 8.5 years of age (range, 1 to 20 years). Most primary tumors were rhabdomyosarcoma (14/20) and occurred in an extremity (10/20). Ninety percent of the patients (18/20) had a complete response to treatment of the primary cancer. Eleven out of 20 received combined chemotherapy and radiation therapy. The most common secondary malignancy was a bone sarcoma (6/20), followed by brain tumors (n = 3), leukemia (n = 2), and other sarcomas (n = 2). Four of the bone sarcomas developed in the field of radiation treatment. Median follow-up was 16 years (range, 1 to 26 years). The median time to development of a SMN was 11.4 years (range, 1.5 to 21 years). Survival after a second malignancy was only 30%. Two patients developed a third malignant neoplasm. The occurrence of a secondary malignancy represents a serious complication of childhood cancer. Certain tumors are related directly to treatment such as osteosarcoma within irradiated fields and secondary leukemias or lymphomas after certain chemotherapy regimens. Combined radiotherapy and chemotherapy may play an additive role in the development of second malignant neoplasms. Genetic factors may predispose affected patients to the development of both primary and secondary malignancies. Close surveillance of children previously treated for childhood cancers is warranted.

Adolescent↗
PubMed1997

Disseminated Histoplasma capsulatum infection presenting as genital ulcerations.

BACKGROUND: Histoplasma capsulatum infection in adults is most often subclinical but can result in disseminated disease with weight loss, fever, hepatosplenomegaly, and oropharyngeal ulcerations. Genital ulceration as the presenting sign of the disease has been reported rarely. CASE: A 63-year-old woman presented with multiple vaginal ulcerations due to chronic disseminated H capsulatum infection. Initial diagnosis was made by Papanicolaou and Giemsa-stained vulvar smears. Ketoconazole therapy resulted in clearing of the lesions in 5 weeks. CONCLUSION: Chronic disseminated histoplasmosis is an insidious and potentially fatal disease that can present rarely as genital mucocutaneous ulcerations in women. Prompt presumptive diagnosis can be accomplished by examination of smears obtained by ulcer abrasion, permitting institution of appropriate therapy.

Antifungal Agents↗
PubMed1997

Evaluation of the Roche AMPLICOR MTB assay for the detection of Mycobacterium tuberculosis in sputum specimens from prison inmates.

The reliability of the Roche Mycobacterium tuberculosis polymerase chain reaction (PCR) assay (AMPLICOR MTB) for the diagnosis of pulmonary tuberculosis was evaluated by testing expectorated sputum specimens from 187 inmates in Texas state prisons and comparing the results to culture and medical history. Of the 80 specimens that were culture positive for mycobacteria, 36 specimens from 16 patients grew M. tuberculosis. Forty-six specimens were smear positive for acid-fast bacilli (AFB), and of these, M. tuberculosis was isolated from 24. On initial testing, 52 specimens were PCR positive. Thirty-one of these 52 were culture positive for M. tuberculosis, and 21 were culture negative, resulting in a PCR sensitivity and specificity of 86.1 and 96.1%, respectively. After resolving discrepancies by review of the medical history and repeat testing, PCR sensitivity, specificity, and positive and negative predictive values, respectively, were 92.8, 99.8, 98.1, and 99.2%. For AFB smear-positive specimens, the sensitivity, specificity, and positive and negative predictive values, were 95.8, 100, 100, and 93.3, respectively; whereas, for AFB smear-negative specimens, these values were 87.5, 99.7, 95.5, and 99.4%, respectively. These results confirm the reliability of the AMPLICOR MTB assay for direct detection of M. tuberculosis in AFB smear-positive sputum specimens and suggest a potential role in evaluating AFB smear-negative sputum specimens.

Humans↗
PubMed1997

A comparison of the attitude of paraplegic individuals to the walkabout orthosis and the isocentric reciprocal gait orthosis.

This study compared the attitude of paraplegic individuals to the Isocentric Reciprocal Gait Orthosis (IRGO) and the Walkabout Orthosis (WO), after they had been given the opportunity of using both. Ten complete T9-12 paraplegic patients participated in this randomised cross-over design. Initially the subjects learned to walk with the first orthosis before taking it home for a 14 week home trial period. The same process of training an trialing the orthosis at home was then repeated with the second orthosis. Attitudes to specific aspects of the orthoses were assessed by an 18 point questionnaire and overall attitudes were inferred after determining the amount of time that subjects used the orthoses at home and determining which orthosis the majority of subjects wanted to keep at the end of the study. The main finding was that subjects did not perceive any significant differences between the two orthoses. That is: (i) the questionnaire did not detect significant differences in attitudes to the two orthoses; (ii) there was no significant difference in the number of subjects tat preferred one orthosis to the other, at the end of the study, and (iii) subjects did not derive more use from one orthosis than the other over the two 14 week home trial periods. In addition, it was found that few subjects wore either orthosis more than once every 2 weeks and that subjects were primarily using the orthoses for therapeutic purposes. This latter finding was supported by the results of the questionnaire that revealed that subjects found both orthoses to be useful for standing but not useful for performing more purposeful tasks. It was concluded that when subjects are primarily using the WO and IRGO for therapeutic purposes, they do not readily perceive differences between the two.

Adult↗
PubMed1997

Murder-suicide of the jealous paranoia type: a multicenter statistical pilot study.

The authors present a pilot statistical study of murder-suicide comprising 32 cases from the years 1990-1992, collected from the offices of the medical examiners of seven counties in five of the United States. The study includes brief reviews of previous statistical surveys of murder, murder-suicide, and suicide. This present study's conclusions parallel the findings of previous research on the demographic characteristics of the perpetrators of murder-suicide, the relationship between killers and victims, the types of weapon used, locations of the incidents, and the time intervals between the murder and suicide. It also highlights the similarities between the characteristics of the perpetrator of murder-suicide and those of persons who commit only suicide, supporting the thesis that murder-suicide is an extended suicide. Suggestions for prevention of such a type of crime are offered.

Adolescent↗
PubMed1997

Detection of Mycobacterium tuberculosis in BACTEC 12B broth cultures by the Roche Amplicor PCR assay.

To evaluate the ability of the Amplicor MTB Assay to detect Mycobacterium tuberculosis complex (MTBC) organisms in BACTEC 12B broth cultures, 249 cultures with a growth index (GI) of > or = 20 from 160 patients were tested retrospectively. Specimens were processed by standard methods, and then BACTEC 12B vials and Middlebrook 7H11/7H115 plates were inoculated, incubated, and interpreted in accordance with the manufacturer's instructions and laboratory protocol. From 12B vials with a GI of > or = 20, and aliquot of broth was removed and frozen at -20 degrees C until assayed by PCR. PCR results were compared to those obtained by the usual laboratory protocol, whereby MTBC organisms were identified by a DNA probe assay performed on broth from 12B vials with a GI or > or = 300 or on colonies from solid medium. Of the 249 broth cultures evaluated, 142 contained mycobacteria, including 44 that contained MTBC organisms. Of these 44 cultures, 41 were PCR positive; the 3 that were PCR negative were blood specimens collected in an Isolator tube. All 98 cultures with nontuberculous mycobacteria and the 107 that did not contain mycobacteria were PCR negative. Thus, the sensitivity and specificity of PCR were 93 and 100%, respectively. For those culture sin which MTBC organisms were identified by both the DNA probe and PCR assays, the mean time from specimen inoculation to detection and identification of MTBC organisms was 16 (range, 4 to 26) days for the PCR and 28 (range, 13 to 43) days for the DNA probe assay (P < 0.0001). In summary, PCR is a rapid, reliable method for detection of MTBC organisms in BACTEC 12B broth cultures with a GI of > or = 20.

Bacterial Typing Techniques↗
PubMed1997

Spatial variation of T2 in human articular cartilage.

PURPOSE: To determine the spatial variation of in vivo cartilage T2 in young asymptomatic adults. MATERIALS AND METHODS: Quantitative T2 maps of seven asymptomatic young male adults and one male volunteer with a history of previous intraarticular chondroid fragments were calculated by using a multiecho, spin-echo magnetic resonance imaging sequence at 3.0 T. The T2 maps were bilinearly interpolated to generate T2 profiles across the thickness of cartilage. RESULTS: All seven asymptomatic volunteers demonstrated a monotonic increase in T2, which increased from 32 msec +/- 1 in the deep radial zone and 48 msec +/- 1 in the deep transitional zone to 67 msec +/- 2 in the outer transitional superficial zone. The T2 profile of the volunteer with superficial fibrillation observed at arthroscopy demonstrated marked spatial heterogeneity and a statistically significant increase in cartilage T2. CONCLUSION: There is a reproducible pattern of increasing T2 that is proportional to the known spatial variation in cartilage water and is inversely proportional to the distribution of proteoglycans. The authors postulate that these regional T2 differences are secondary to the restricted mobility of cartilage water within an anisotropic solid matrix.

Adult↗