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PubMedDate not supplied

Randomized long interstimuli interval flash-VEP and SSEP.

Randomized long interstimuli interval stimulations are recommended in the literature for the examination of different evoked potentials because of the probable effects of habituation and of contingent negative variation on the wave form, especially of its late components. The results of (randomly stimulated) SSEP and Flash-VEP elicited with randomized ISI of 3 to 5 seconds were analysed and normative values for these EP's were given. The results were compared with the latency data in the literature where fixed and short ISI were used. The comparison suggests that in cases where for practical reasons the time consuming (randomized long ISI) stimulation is not possible regular stimulation with interstimulus interval of somewhat more than one second also gives satisfactory results.

Adult↗
PubMedDate not supplied

Pattern reversal and flash evoked potentials following acute triethyltin exposure.

Until recently, pattern reversal visual evoked potentials (PREPs) had not been used to examine effects of neurotoxic agents, despite their clinical utility. Acute exposure to triethyltin (TET), which produces cerebral edema and myelin splitting, increased flash evoked potential (FEP) latencies in previous reports [17,18]. We recorded PREPs and FEPs in adult Long-Evans hooded rats before, and 24 hr after, exposure to 0, 4.5 or 6.0 mg/kg IP of TET bromide. Significant increases in latency and changes in amplitude of PREP peaks were found in the 6 mg/kg rats. FEP peak latency increases did not meet the criterion for statistical significance. Thus, under the conditions recorded, PREPs were better than FEPs as a measure of TET-induced neurotoxicity.

Animals↗
PubMed1982

[Inhibition with light flashes of negative delta-waves in the rabbit visual cortex].

To elucidate the nature of negative and positive phases of background delta-waves (BDW), their interaction with evoked potentials was studied in the rabbit visual cortex. BDW appeared after injection of drugs synchronizing ECoG: amyzyl, aminozin, barbiturates, and during asphyxia. The flashes evoked slow positive responses lasting about 0.5 to 1.0 s. These responses blocked the negative BDW. The results of the study and published data suggest that background delta-activity consists of segments which reflect the desynchronized state and correspond to positive BDW, and of segments which reflect active inhibition in the cerebral cortex and correspond to negative BDW.

Animals↗
PubMed1982

One-electron photoreduction of bacterial cytochrome P-450 by ultraviolet light. II. A study using laser flash photolysis of the dynamics of the reduction of bacterial cytochrome P-450 in the presence of carbon monoxide. The role of the protein conformation.

The intramolecular photoreduction of the bacterial cytochrome P-450 demonstrated by the formation of the complex of reduced cytochrome m with camphor and CO has been studied by photolysis with a laser flash at 265 nm. This photoreduction of the heme follows the photoionization of a proximal aromatic amino acid residue and especially tryptophan in the nanosecond time scale as evidenced by the N2O effect on the reduction yield. However most of the hydrated electrons released in the solution do not react with the ferric porphyrin. In agreement with steady state studies, the quantum yield for formation of the complex of reduced cytochrome m with camphor and CO is proportional to the concentration of the high-spin species. The low-spin ferric porphyrin is thus not reducible by photoejected electrons. It is also shown that the growth kinetics of the transient absorbance at 446 nm characterizing the complex of reduced cytochrome m with camphor and CO correspond to a structural change affecting the protein and not to the formation of the complex of CO with the camphor-bound reduced cytochrome in which occurs on a shorter time scale in the present experimental conditions.

Carbon Monoxide↗
PubMed1982

Measuring the average evoked response to light flashes: the contribution of eye-blink artifact to augmenting-reducing.

There have been numerous reports relating individual differences in stimulus intensity control to psychopathology and personality. Most of these studies record the averaged evoked response (AER) to light flashes of different brightness and assess the relationship between response amplitude and stimulus intensity. The present investigation used procedures commonly employed in these studies to examine the effects of eye blinks on the AER. Twenty normal subjects were tested twice over a 1-week interval while the AER and electroocculographic (EOG) response generated by a blink were recorded. The averaged EOG was digitally subtracted from the AER to yield a blink-corrected AER. Various comparisons of amplitude measures derived from corrected and uncorrected AERs and the averaged EOG revealed that blinking contributed a pronounced artifact that tended to reduce the magnitude of AER amplitude, especially to the more intense stimuli. These findings raise questions about the validity of interpretations drawn from studies of AER augmenting-reducing, very few of which control for eye-blink artifact. The linearity of the amplitude-intensity relationship for each subject was also assessed. This analysis revealed that the data points were poorly described by a straight line and therefore that the use of linear slope to characterize the amplitude-intensity relationship is unwarranted.

Blinking↗
PubMedDate not supplied

[Phasic reactions of visual cortex neurons to different conditions of stimulation with light flashes].

In experiments on rabbits in conditions of quiet wakefulness, most of the activation phases in responses of neurones in the visual cortex to diffuse light flashes set in independently of each other within two short time intervals after the stimulus: the early--20 to 40 ms and the late one--190 to 250 ms. In the after-effect of reticular stimulation changes concern mainly the nature of temporal distribution of late activation phases of the specific responses; the early phases do not undergo any substantial reorganization. In quiet wakefulness differences were found in the distribution of activation phases in neuronal responses of different cortical layers, not observed in the after-effect of reticular stimulation.

Animals↗
PubMed1981

[Repeat flash static perimetry according to Enoch: a simple technique for evaluating neuro-ophthalmological patients (author's transl)].

A static perimetry technique is described, which was first introduced by Enoch. The test-target is flashing and the increment threshold is recorded continuously for five minutes. In this way, using a commercially available Goldmann perimeter, it is possible to find a time-dependent decrease in sensitivity in patients with lesions of the optic pathways. No significant loss in sensitivity is found in patients with pre-disc pathologies, who show visual field deficits. This drop in sensitivity is at least of one log unit. The phenomenon is considered to be a "fatigue" in transmission of visual information and is presumably due to lesions in the conduction system (myelin). The test, which is easily performable, can be used follow-up the lesion: when this resolves, the decrease in sensitivity also disappears. Two patients with retro-bulbar neuritis with the typical characteristics of the above mention phenomenon are presented.

Adult↗
PubMed1995

Reducing marginal flash in the fabrication of direct provisional restorations: a new technique using light-cured resin and transparent silicone.

The optimum placement of bonded indirect restorations depends to a large extent on establishing and maintaining the patient's gingival health during the provisional treatment phase, as inflamed sulcular tissues may compromise subsequent isolation efforts. Gingival health is best achieved by providing provisional restorations of correct emergence profile and accurate margination. This paper introduces a fully-cured direct provisionalization technique that minimizes marginal flash and improves the accuracy of the restoration in a fraction of the production time needed for traditional direct techniques requiring remargination. The technique, which relies on the use of a unique transparent over-impression registration material and visible light-curing provisional composite resin, is described in a case report.

Adult↗
PubMed1995

[Functional magnetic resonance tomography of the basal ganglia. Use of FLASH sequences for mapping activity with BOLD contrast ane high resolution].

The activation pattern of putamen, internal and external division of globus pallidus was investigated during rapid pronation and supination of the right and left hand in 12 normal volunteers using a FLASH sequence with high resolution for functional magnetic resonance imaging (fMRI) at 1.5 T. The chosen paradigm for motor function led to a signal increase within the basal ganglia between 3 and 23%, depending on the structure and individual subject. In all cases significant activation could be found contralateral to the moving hand. In six cases activation was also found on the ipsilateral side. The activated areas within putamen, internal and external division of globus pallidus were less than 5 mm2. These first results indicate that fMRI studies of basal ganglia are feasible and might be suitable for analyzing basal ganglia disorders.

Adult↗
PubMedDate not supplied

Basic analysis of dynamic study in cases of hepatocellular carcinoma using inversion recovery snap shot FLASH MR imaging with Gd-DTPA.

Twenty patients with hepatocellular carcinoma were studied by dynamic sequential inversion recovery snap shot fast low angle shot (FLASH) imaging after the bolus injection of various amounts of Gd-DTPA. We determined the optimal dose of Gd-DTPA for depicting tumors as early marked enhancement and compared the method with dynamic CT by matching data acquisition time. The optimal dose was estimated to be 0.1 mmol/kg. Compared with dynamic CT, dynamic MRI showed rapid short-term enhancement in the early phase, while the contrast enhancement in the late phase lasted longer and was stronger than that of CT.

Aged↗
PubMed1995

[Knee joint cartilage in magnetic resonance tomography. MR chondrovolumetry (MR-CVM) using fat-suppressed FLASH 3D sequence].

UNLABELLED: The objective of this study was to optimize the demonstration of articular cartilage with magnetic resonance tomography (MRT) and to assess its accuracy in determining the articular cartilage volume of the knee joint. METHODS: A fat-suppressed FLASH-3D sequence was optimized on healthy volunteers. A fresh cardaveric knee joint was removed from a 82-year-old man and immediately imaged without being frozen or fixed. MRT was carried out at 1.5 T and 25 mT/m (Vision, Siemens, Erlangen, Germany) with a conventional CP knee coil. Sagittal and transverse sections were acquired perpendicular to the articular surfaces, and then, parallel to these imaging planes, anatomical sections were obtained with a diamond band saw. The volumes of the patellar, tibial and femoral cartilages were determined from both the images and the sections, using an image analysing system. RESULTS: Signal intensities and contrast-to-noise ratios depend on the parameters used. The highest contrast between the cartilage and the periarticular tissues was obtained at a flip angle of 30 degrees (TR = 60 ms, TE = 11 ms). However, a flip angle of 60 degrees was judged to provide optimal subjective image quality. Using these parameters, the deviations between the radiological and the anatomical cartilage volumes were -4.7% in the patella, -3.1% in the tibial plateau and -4.2% in the femur. CONCLUSIONS: The volumes of the knee-joint cartilages may be accurately determined with MRT if an appropriate pulse sequence is chosen. From a clinical point of view the differences between MR images and anatomical sections can be considered negligible. These differences may be explained on the basis that MRT delineates uncalcified cartilage only and that the calcified layer is demonstrated as part of the subchondral bone plate. However, close correlation of the thicknesses of the uncalcified and the calcified layer has been reported in the literature, so the relative distribution of articular cartilage should be accurately reflected in MR images.

Aged↗
PubMed1994

Visual evoked potentials in response to flashes in the cat cortex.

A model is presented of visually evoked potentials (VEPs) in the cerebral cortex of cats after binocular stimulation by means of flashes. The VEPs consist of four components: P1, N1, P2 and N2 which appear during the first 100 ms after the stimulation is produced. This model has been found in all the animals used in the experiments and is repeated with small variations at almost all the recording points. After studying the data obtained, a hypothesis is put forward for the possible origin of the four components in the primary visual area.

Animals↗
PubMed1994

[Sequelae of cannabis use--results of a survey of experts on traffic accidents and "echopsychoses" (flash-back)].

There is a lack of knowledge in the judgement of the effects and the dangerousness of cannabis. Specially in the judgement of the delinquency of traffic the effects must be clarified. Cannabis plays often a fundamental role in road accidents. Obviously flash-backs of consumers of cannabis are observed more often than documented in the literature hitherto. The existing but not published experiences of experts have to be considered extensively to get an idea more complete of the diverse effects of cannabis in traffic offences.

Accidents, Traffic↗
PubMedDate not supplied

Dynamic contrast enhancement of intracranial tumors with snapshot-FLASH MR imaging.

PURPOSE: To investigate whether exact evaluation of the dynamic contrast enhancement pattern within intracranial tumors can help to classify tumor histology and vascularity. METHOD: Forty-nine patients suffering from different intra- and extraaxial intracranial tumors underwent MR-examination in a 1.5-T superconductive whole body system. After rapid injection of Gd-DTPA, 48 images were acquired during the first 1.5 to 2 minutes of contrast enhancement within the tumors. A fast snapshot-FLASH imaging technique allowed measurement times of 1 second per image. Appearance of Gd-DTPA in a venous sinus served as a temporal reference point. Transformation of 48 discrete measurement points (mean signal values of the enhancing tumor region) into a continuous curve, using a cubic spline approximation, allowed calculation of the time of maximum signal increase (Tm1) and the following time of half maximum increase (Tm2). These time parameters were compared to histopathologic findings, especially the degree of tumor vascularization. RESULTS: Significantly different dynamic patterns of the early enhancement period were found for the different tumors. All eight neurinomas, typically less vascularized than most meningiomas, showed a characteristically prolonged contrast enhancement with a long Tm2. Histopathologic findings concerning the degree of vascularization showed two subtypes in meningiomas (n = 17) as well as in pituitary macroadenomas (n = 7). This was confirmed by dynamic evaluation in all cases, in the sense that short Tm1 and Tm2 were found in cases with higher degrees of vascularization. Negatives values of Tm1 were measured in two glomus jugulare tumors, reflecting the arterialization of these vascular tumors. In neuroepithelial tumors (n = 15), the glioblastomas (n = 7) showed very short Tm1 compared to the lower grade gliomas (n = 8). This is explained by histologic findings of pathologic vessels with arteriovenous shunts. CONCLUSION: The evaluated dynamic time parameters can be used to narrow differential diagnostic possibilities and to infer the degree of vascularization of intracranial tumors.

Adenoma↗
PubMed1993

[Usefulness of 2D FLASH multislice dynamic MR imaging for evaluation of parametrial invasion in cervical carcinoma].

Twenty seconds and 3 minutes after starting rapid injection of Gd-DTPA, multislice dynamic (MD) images were obtained with the 2 dimension fast low-angle shot (2D FLASH) technique. Four of 5 cervical carcinomas showed high signal intensity in the early dynamic phase (20 seconds), so they were readily distinguished from the myometrium that were not enhanced in the same phase. For evaluation of parametrial invasion, MD study showed better contrast between the tumor and the parametrium than did T2-weighted images because the tumor demonstrated a high signal intensity similar to that of the parameterium on T2-weighted images. MD images were able to scan the entire tumor especially in progressive cases and to evaluate the hemodynamics of the tumor. Therefore, MD imaging seemed to be useful for evaluation of parametrial invasion in cervical carcinomas.

Carcinoma, Squamous Cell↗
PubMed1995

A computer simulation of motion in turbo FLASH imaging and echo-planar imaging.

We have experimentally demonstrated motion effects in a turbo FLASH imaging (TFI) using a small cylindrical phantom moving at constant velocity. To further verify these experimental results, image blurring is assessed by using a computer simulation in this study. By applying the same acquisition parameters as phantom experiments, the simulation images are reconstructed to compare with the experimental results. Several kinds of configurations are applied to the simulation of the TFI. A computer simulation of an echo-planar imaging (EPI) is also used to compare the motion effects with TFI.

Computer Simulation↗
PubMed1997

The perimenopausal hot flash: epidemiology, physiology, and treatment.

The "hot flash" (HF), or vasomotor instability, is experienced by 75% of perimenopausal and menopausal women in the United States. The experience for some women is a minor annoyance but for others, the HF is an intensely unpleasant sensation that is disruptive to their lives. The HF is thought to be triggered by a number of external and internal stimuli such as anxiety, stress, ambient high temperatures, caffeine, and alcohol. The thinner woman tends to experience more severe and frequent HFs than the woman with more adipose tissue, probably because of the ability of adipose tissue to transform androstenedione to estrone and estradiol. Smoking history also tends to be associated with the experience of HFs at an earlier age. The etiology of HFs in the decreasing estrogen state is related to the downward resetting of the hypothalamic thermoregulating mechanism, probably by the action of norepinephrine, which is usually modulated by estrogen. The body attempts to dissipate unwanted body heat by vasodilation, thus causing the sensation of the HF. The most successful treatment modalities have been hormone replacement therapy with estrogen and progesterone. Alpha 2-adrenergic blockers have also shown some limited effectiveness. Many alternative therapies such as vitamin E, primrose oil, dong quai, and black cohash have anecdotal support but have not been thoroughly studied. Relaxation, exercise, avoidance of triggering factors, and control of external environment have all been utilized with some success by women.

Adaptation, Psychological↗
PubMedDate not supplied

[Critical frequency of flashes fusion in differential diagnosis of vision disorders in children].

Critical frequency of fusion of flashes (CFFF) was measured in children by CFFF-D device recommended for clinical trials by the Ministry of Health and Medical Industry of the Russian Federation (Protocol No. 4 of June 13, 1996). A total of 213 children with central and peripheral retinal abiotrophy, partial atrophy of the optic nerve, refraction and dysbinocular amblyopia, and healthy children were examined. The most expressed changes of CFFF were observed in children with optic nerve atrophy. The CFFF-D device provides reliable results for the diagnosis.

Adolescent↗