Magnetic resonance images of patients wearing a surgical halo may have unacceptable artifacts if the halo has a conductive loop structure. This study shows that the observed artifacts are predominantly due to eddy currents generated in the halo by switching field gradients, and that these artifacts can be substantially reduced by adjusting the phase encoding direction in MRI sequences so that it is parallel to the axis of the halo.

Artifacts↗

PubMedDate not supplied

Teen Pregnancy Service. An interdisciplinary health care delivery system utilizing certified nurse-midwives.

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Adolescent↗

PubMedDate not supplied

Attention deficit hyperactivity disorder among adults with severe and profound mental retardation.

The present study investigated the incidence of attention deficit hyperactivity disorder in a sample of 86 adults with severe to profound mental retardation. Participants were evaluated by supervisory staff using the diagnostic criteria from the Diagnostic and Statistical Manual of Mental Disorders (American Psychiatric Association, 1994) and Conners' (1990) Hyperactivity Index. Using the most conservative measure, 15% of the sample met the diagnostic criteria. This measure was not influenced by the subjects' chronological age, adaptive age, IQ, or gender. Implications of this finding for continued research and practice were discussed.

Adolescent↗

PubMedDate not supplied

A general method for optimizing tissue discrimination in magnetic resonance imaging.

The basic partial differential formulation for small differences has been applied to the equations for the inversion recovery and saturation recovery sequences with spin-echo rephase pulses and the spin-echo sequence itself. The result is a generalized expression which is proportional to tissue discrimination expressed as the signal-difference-to-noise ratio for a pair of tissues. The expression is a function of the fractional differences in the tissue relaxation times and proton densities, T1, T2, and n, respectively, and the sequence parameters TR and TI, or TE. From it can be derived the conditions which lead to optimum tissue discrimination for a given pulse sequence. It is also possible to predict the optimum pulse sequence to use for any pair of tissues of interest. The method requires a knowledge of the fractional differences in T1, T2, and n for both tissues.

Biophysical Phenomena↗

PubMedDate not supplied

Chronic exposure to hypergravity affects thyrotropin-releasing hormone levels in rat brainstem and cerebellum.

In studies to determine the neurochemical mechanisms underlying adaptation to altered gravity we have investigated changes in neuropeptide levels in brainstem, cerebellum, hypothalamus, striatum, hippocampus, and cerebral cortex by radioimmunoassay. Fourteen days of hypergravity (hyperG) exposure resulted in significant increases in thyrotropin-releasing hormone (TRH) content of brainstem and cerebellum, but no changes in levels of other neuropeptides (beta-endorphin, cholecystokinin, met-enkephalin, somatostatin, and substance P) examined in these areas were found, nor were TRH levels significantly changed in any other brain regions investigated. The increase in TRH in brainstem and cerebellum was not seen in animals exposed only to the rotational component of centrifugation, suggesting that this increase was elicited by the alteration in the gravitational environment. The only other neuropeptide affected by chronic hyperG exposure was met-enkephalin, which was significantly decreased in the cerebral cortex. However, this alteration in met-enkephalin was found in both hyperG and rotation control animals and thus may be due to the rotational rather than the hyperG component of centrifugation. Thus it does not appear as if there is a generalized neuropeptide response to chronic hyperG following 2 weeks of exposure. Rather, there is an increase only of TRH and that occurs only in areas of the brain known to be heavily involved with vestibular inputs and motor control (both voluntary and autonomic). These results suggest that TRH may play a role in adaptation to altered gravity as it does in adaptation to altered vestibular input following labyrinthectomy, and in cerebellar and vestibular control of locomotion, as seen in studies of ataxia.

Adaptation, Physiological↗

PubMedDate not supplied

Regional cerebral blood flow utilizing the gamma camera and xenon inhalation: reproducibility and clinical applications.

A modified collimator and standard gamma camera have been used to measure regional cerebral blood flow following inhalation of radioactive xenon. The collimator and a simplified analysis technique enables excellent statistical accuracy to be achieved with acceptable precision in the measurement of grey matter blood flow. The validity of the analysis was supported by computer modelling and patient measurements. Sixty-one patients with subarachnoid haemorrhage, cerebrovascular disease or dementia were retested to determine the reproducibility of our method. The measured coefficient of variation was 6.5%. Of forty-six patients who had a proven subarachnoid haemorrhage, 15 subsequently developed cerebral ischaemia. These showed a CBF of 42 +/- 6 ml X minute-1 X 100 g brain-1 compared with 49 +/- 11 ml X minute-1 X 100 g brain-1 for the remainder. There is evidence that decreasing blood flow and low initial flow correlate with the subsequent onset of cerebral ischaemia.

Administration, Intranasal↗

PubMedDate not supplied

Perceptual structure of monophthongs and diphthongs in English.

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Humans↗

PubMedDate not supplied

Perception of prominence by Estonian and English listeners.

This study deals with the perception of prominence in speech and nonspeech signals by listeners who are native speakers of Estonian or English. The stimuli consisted of repetitions of the synthetic syllable [ba] at a constant fundamental frequency (F0) or signal-correlated noise tokens whose amplitude envelope matched that of the [ba]. The basic token was 400 msec in duration. Listeners heard sequences of four stimulus tokens separated by 120 msec of silence. One token in the sequence could be lengthened to 425, 450, 475, or 500 msec and/or increased in amplitude by 3 or 6 dB; changes in duration and amplitude were independent. The speech ([ba]) and nonspeech (noise) listening tests were run separately. The listeners' task was to indicate which of the four tokens was "most prominent". The responses showed that, for English-speaking listeners, amplitude cues overrode duration cues, while Estonian listeners were more responsive to duration cues. For both groups of listeners, smaller increments in duration and/or amplitude sufficed to produce perceived prominence in the noise condition than in the speech condition. This is interpreted as being due to the absence of F0 variation. In spoken language, F0 is a significant component of stress both in production and perception. Thus the absence of F0 variation should have greater effect on the perception of speech-like stimuli than noise stimuli. The results of the experiments show this to be the case.

Auditory Perception↗

PubMedDate not supplied

Treatment recommendations for respiratory tract infections associated with aging.

Age-related changes, for example reduced elasticity and earlier airways collapse, predispose the elderly to respiratory infection. Other factors such as a lifetime of smoking, the use of hypnotics, or the development of stroke also predispose. Pneumonia becomes increasingly common with advancing age, and both morbidity and mortality increase with associated disease burden. Diagnosis of pneumonia may be more difficult in the aged because of physiological changes. However, careful physical examination with accurate, regular recording of body temperature will usually reveal the characteristic features of pneumonia, which should be confirmed by chest radiograph. In the frail elderly, the onset of impaired function, such as confusion, immobility, falling or incontinence, should raise suspicion of infection. Pneumonia is classified as community-acquired, nursing home-acquired or nosocomial, which helps in the empirical choice of antibiotics. Streptococcus pneumoniae is the most common organism in the community, then Haemophilus influenzae and Branhamella catarrhalis. Gram-negative organisms like Klebsiella and Escherichia coli are more common in nosocomial infections. Nursing home patients with pneumonia tend to be more frail than those in the community. Treatment is directed at eradication of the organism with the appropriate antibiotic, maintaining hydration and oxygenation, as well as managing impaired mobility, faecal loading, urinary incontinence and confusion. Influenza vaccination is strongly recommended for the frail elderly. Tuberculosis remains an important diagnosis in the frail elderly and should always be considered, especially in patients with respiratory infection who fail to respond to conventional therapy.

Aged↗

PubMedDate not supplied

Transmembrane versus soluble stem cell factor expression in human testis.

The interaction between stem cell factor (SCF), a ligand produced by Sertoli cells, and its c-kit receptor on germ cells is necessary for successful spermatogenesis in animal models. SCF can be alternatively spliced into soluble and transmembrane forms, and it is the transmembrane form that is required for spermatogenesis in rodents. c-Kit receptors are also present on Leydig cells, and soluble SCF has been implicated in the regulation of testosterone production. This study had two goals: To test the hypothesis that the extent of germ cell production in human males is correlated with the expression of transmembrane SCF, and to examine the relationship between testosterone production and the expression of soluble SCF in humans. Reverse transcriptase polymerase chain reaction was used to determine the ratio of transmembrane-to-soluble SCF in testicular tissue. Clinical analysis, hormonal measurements, and histological methods were used to evaluate the causes of infertility and to seek correlations with the pattern of SCF expression. SCF was preferentially expressed as the transmembrane type in all testicular samples, regardless of the state of germ cell production. Furthermore, the percent of transmembrane SCF expression was independent of clinical and histopathological diagnosis (r(s) = 0.111, n = 28) and unrelated to the extent of spermatogenesis. This contrasts with rat models of testicular injury that exhibit a decreased proportion of transmembrane SCF with atrophy. A significant correlation (r(s) = 0.665, P < .02, n = 16) was found between testosterone levels and percent soluble SCF, which suggests that, in humans, there may be a regulatory interaction between soluble SCF and testosterone.

Biopsy↗