Surface EMG crosstalk between knee extensor muscles: experimental and model results

Surface electromyographic (EMG) crosstalk between vastus lateralis, vastus medialis, and rectus femoris muscles was evaluated by selective electrical stimulation of one muscle and recording from the stimulated and another muscle with linear surface arrays of eight electrodes. The ratio between the amplitude of the signals recorded over nonstimulated and stimulated muscles and their correlation coefficient were used as indices to quantify crosstalk. Single-differential and double-differential detection systems were used with interelectrode distances in the range 10-40 mm. The multichannel EMG signals clearly showed that crosstalk is largely due to nonpropagating potentials that correspond in time to the end of the propagation of the action potentials generated by the stimulated muscle. The crosstalk signal increased with increasing interelectrode distance and was statistically higher for single- than for double-differential recordings. The correlation-based indices of crosstalk were poorly correlated with the amplitude-based indices. Moreover, the characteristic spectral frequencies of the signals detected over the nonstimulated muscles were statistically higher than those from the stimulated muscles. A mathematical model of signal generation was used to explain the experimental findings. This study clarifies many controversial findings of past investigations and creates the basis for crosstalk interpretation, simulation, and reduction.     

In vivo animal functional MRI: improved image quality with a body-adapted mold

PURPOSE: To reduce functional magnetic resonance imaging (fMRI) susceptibility distortion at the air/tissue interphase in animal experiments. MATERIALS AND METHODS: We investigated the applicability of a body-adaptable flexible mold consisting of a fast-setting alginate. This technique was implemented for subcutaneous growing tumors in rats and for the brains of monkeys. RESULTS: The T(2)*-weighted gradient-echo, echo-planar imaging (GE-EPI) data obtained with the body-adapted mold showed a reduction of susceptibility artifacts and improved image quality. With both rat tumor and monkey brain, an optimized match with the anatomical T(1) images was possible. CONCLUSION: The present mold methodology is a rapid, easy, and inexpensive way to reduce magnetic susceptibility during animal GE-EPI.     

MR imaging and proton MR spectroscopy in adult Krabbe disease

We present the MR imaging findings in four patients (two pairs of siblings from two unrelated families) with adult Krabbe disease. In the first family, clinical presentation mimicked familial spastic paraplegia. Their MR images showed selective, increased signal intensity on T2-weighted sequences along the corticospinal tracts, most prominently in the proband and barely detectable in her brother. Proton MR spectroscopy showed increased choline and myo-inositol in the affected white matter. In the second family, the clinical presentation differed in that the signs of pyramidal tract involvement were asymmetrical, with concomitant asymmetry on MR images in one. In adults, Krabbe disease may present on MR imaging with selective pyramidal fiber involvement.     

Clinical features and genetic analysis of a new form of spinocerebellar ataxia

BACKGROUND: The autosomal dominant cerebellar ataxias (ADCA) are a clinically heterogeneous group of disorders. The mutations for SCA1, SCA2, SCA3, SCA6, SCA7, SCA8, and SCA-12 are identified and caused by an expansion of a CAG or a CTG repeat sequence of these genes. Six additional loci for SCA4, SCA5, SCA-10, SCA-11, SCA-13, and SCA-14 are mapped. The growing heterogeneity of the autosomal dominant forms of these diseases shows that the genetic etiologies of at least 20% of ADCA have yet to be elucidated. METHODS: The authors ascertained and clinically characterized a four-generation pedigree segregating an autosomal dominant phenotype for SCA. Direct mutation analysis, repeat expansion detection analysis, and linkage analysis for all known SCA loci were performed. RESULTS: Direct mutational analysis excluded SCA1, 2, 3, 6, 7, 8, and 12; genetic linkage analysis excluded SCA4, 5,10, 11, 13, and 14, giving significant negative lod scores. Examination of the family showed that all affected members had gait ataxia and akinesia with variable features of dysarthria, hyporeflexia, and mild intellectual impairment. Eye movements were normal. Head MRI showed atrophy of the cerebellum without involvement of the brainstem. In 10 parent-child pairs, median onset occurred 10.5 years earlier in offspring than in their parents, suggesting anticipation. CONCLUSION: This family is distinct from other families with SCA and is characterized by cerebellar ataxia and extrapyramidal signs.     

Positive response to immunomodulatory therapy in an adult patient with Rasmussen's encephalitis

Rasmussen's encephalitis (RE) is a rare and progressive neurologic condition of uncertain etiology that typically has a childhood onset. The authors describe a 45-year-old woman with adult-onset progressive aphasia, right hemiparesis, severe drug refractory epilepsy, and left cerebral hemisphere atrophy. High-dose corticosteroids and plasmapheresis were not effective. She improved with high-dose therapy with human IV immunoglobulin.     

Correlation among amniotic fluid index (AFI), cesarean section rate, and labor length in inducted pregnancies beyond 41 weeks' gestation with unfavorable cervix

This paper evaluated how the pregnancy after 41 completed weeks' gestation with amniotic fluid index (AFI) > 6 has a slower response to the prostaglandin E2 (PGE2) induction. Eighty-one post-term pregnancies (41 completed gestations' weeks) with unfavorable cervix were considered in this follow-up. Induction was performed by means of intracervical PGE2 gel (Dinoprostone 0.5 mg). After 12 hours, if the cervix was still unfavorable, then another gel administration followed. Cases that had oxytocin administration were excluded from the study. The median time of spontaneous delivery in the overall series was 25 hours, 14 minutes. We had 18 cases of cesarean section (22.2%). In the group of pregnancies with AFI > 6 (60 cases) and in the group with AFI < or =6 (21 cases), the median time of spontaneous delivery was 29 hours, 25 minutes and 23 hours, 39 minutes, respectively (p-value = 0.02). The rate of cesarean sections was 26.67 and 9.52, respectively in the two groups (p-value >0.05). Two out of four cases of cesarean sections for fetal distress belonged to the group of AFI > 6. All the 14 cases of cesarean section for dystocia belonged to the group with AFI > 6. Considering just patients who did not deliver within 12 hours (57 cases), median time of spontaneous delivery was 33 hours and 24 hours 40 minutes for group AFI > 6 (42 cases) and AFI < or =6 (15 cases), respectively (p-value = 0.0009). Thirty-one cases out of 57 had another PGE2 gel administration. Adjusted odds ratio was 0.33 (0.16-0.65, 95% C.I.) for AFI < or =6 versus AFI > 6.     

L-2-Hydroxyglutaric aciduria: MRI in seven cases

The MRI findings in 7 patients with L-2-Hydroxyglutaric aciduria (L-2-OHG aciduria) are described and compared with previous neuroradiological reports and the only three published pathological cases. Signal abnormalities involved peripheral subcortical white matter, basal ganglia and dentate nuclei. Cerebellar atrophy was present. Although similar appearances may be seen in other metabolic disorders, the distribution of signal abnormalities in L-2-OHG aciduria is highly characteristic and may suggest the correct diagnosis. Received: 5 January 1998 Accepted: 22 April 1998     

A stereochemical and statistical analysis of metallocene-promoted polymerization

The metallocene catalysts active in propylene polymerization can be divided into five classes, depending on whether the catalytic sites are chirotopic or not, and on the symmetry relationship between the catalytic sites bound to the same metal atom. Under the hypothesis of a purely alternating mechanism for propagation, class III and class IV catalysts, respectively, give rise to prevailingly isotactic and syndiotactic polymers. Four probabilistic schemes have been developed for interpreting the stereosequence distribution of polypropylene in terms of pentads. They take into account the two sources of steric control, chirotopicity of the catalyst site and configuration of the chain end, and the presence, besides the alternating mechanism, of successive addition steps at the same catalytic site.