Evaluation of magnetic resonance imaging issues for implantable microfabricated magnetic actuators

The mechanical robustness of microfabricated torsional magnetic actuators in withstanding the strong static fields (7 T) and time-varying field gradients (17 T/m) produced by an MR system was studied in this investigation. The static and dynamic mechanical characteristics of 30 devices were quantitatively measured before and after exposure to both strong uniform and non-uniform magnetic fields. The results showed no statistically significant change in both the static and dynamic mechanical performance, which mitigate concerns about the mechanical stability of these devices in association with MR systems under the conditions used for this assessment. The MR-induced heating was also measured in a 3-T/128-MHz MR system. The results showed a minimal increase (1.6 °C) in temperature due to the presence of the magnetic microactuator array. Finally, the size of the MR-image artifacts created by the magnetic microdevices were quantified. The signal loss caused by the devices was approximately four times greater than the size of the device.     

Rhombencephalosynapsis as a cause of aqueductal stenosis: an under-recognized association in hydrocephalic children

Background

Rhombencephalosynapsis is a rare genetic aberration characterized by variable vermian hypoplasia/aplasia in conjunction with united cerebellar hemispheres. Genetic defects in the isthmic organizer at the mesencephalic–metencephalic junction are presumably responsible for the associated aqueductal stenosis.

Objective

We performed a retrospective review of 20 children with rhombencephalosynapsis to evaluate for and emphasize the association of aqueductal stenosis and hydrocephalus.

Materials and methods

We retrospectively reviewed the MR and CT images of 20 children (0–11 years old) with rhombencephalosynapsis encountered at two academic children’s hospitals. Rhombencephalosynapsis spectrum severity was graded based on pre-existing literature. We analyzed examinations for ventriculomegaly and degree of aqueductal stenosis. The collicular distances were measured from the collicular apices. Imaging studies were also analyzed for malformations of cortical and cerebellar development.

Results

Thirteen of the 20 children (65%) with rhombencephalosynapsis presented with clinical or imaging evidence of hydrocephalus and aqueductal stenosis, principally involving the caudal cerebral aqueduct. All children with aqueductal stenosis had collicular fusion. All six children with complete rhombencephalosynapsis had aqueductal stenosis. The cerebral aqueduct varied from normal to stenotic in children with incomplete rhombencephalosynapsis. Corpus callosum dysgenesis was present in four children.

Conclusion

Aqueductal stenosis in the setting of rhombencephalosynapsis is an under-recognized cause of noncommunicating hydrocephalus. Our findings support the hypothesis that a defect involving the common gene(s) responsible for the differentiation and development of both the roof plate and midline cerebellar primordium at the mesencephalon/first rhombomere junction may be responsible for the association of aqueductal stenosis and rhombencephalosynapsis.     

X-linked mental retardation with thin habitus,osteoporosis, and kyphoscoliosis: Linkage to Xp21.3-p22.12

We reevaluated a family previously described as having nonspecific X-linked mental retardation (XLMR) by Snyder and Robinson [1969: Clin Pediatr 8:669–674] (MIM 309583). Clinical and DNA studies were conducted on 17 relatives, including 6 males with mild-to-moderate mental retardation, 3 carrier females, and 8 normal males. In contrast to the normal appearance and minimal clinical findings reported 22 years ago, affected males were found to have a characteristic set of clinical findings. These developed gradually over the first 2 decades, and included thin body build with diminished muscle mass, osteoporosis and kyphoscoliosis, slight facial asymmetry with a prominent lower lip, nasal speech, high narrow or cleft palate, and long great toes. Carrier females were clinically normal. Multipoint linkage analysis indicated linkage to markers distal to the 3′ end of DMD (DXS41 and DXS989), with a maximal lod score of 4.7. On the basis of these findings, this entity is redefined as XLMR syndrome. © 1996 Wiley-Liss, Inc.     

Synthesis and characterization of substituted benzoylhydrazones of naloxone

Naloxone benzoylhydrazone (NalBzoH) has proved a valuable tool in the investigation of opioid receptor subtypes. In the present study, we have examined a series of derivatives of NalBzoH in which substitutions have been made on the benzoyl ring. Overall, we see dramatic effects on the binding affinities of derivatives against the various opioid receptor subtypes. Although the range of affinities against the mu receptors is quite modest, ranges of the others vary almost 30-fold for kappa₃, 50-fold for kappa₁ and 100-fold for delta and kappa₂ binding. Few substituted derivatives display greater affinity than NalBzoH for any of the receptors, except for delta sites where several derivatives have affinities almost tenfold greater than NalBzoH. Along with the wide variations in affinity, the compounds also appear to exhibit widely divergent activities in traditional biosasays. © 1996 Wiley-Liss, Inc.     

Plasma hyaluronidase activity in mucolipidoses II and III: Marked differences from other lysosomal enzymes

A nearly pathognomonic finding of the lysosomal storage disorders mucolipidoses II and III is the marked increase of plasma lysosomal enzyme activities. The genetic lesion in ML II and III causes defective function of the enzyme UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-l-phosphotransferase. Defective function of this enzyme results in deficient phosphorylation of lysosomal enzyme asparagine-linked oligosaccharides and a consequent misrouting of many newly synthesized lysosomal enzymes. These enzymes are secreted from cells instead of being targeted to lysosomes, with resultant marked elevations of multiple lysosomal enzyme activities in plasma. We report here that plasma hyaluronidase activity, an endoglycosidase of presumably lysosomal origin, is not increased in the plasma from individuals with mucolipidoses II and III, unlike most lysosomal enzymes. Our data suggest the possibility that hyaluronidase is not targeted to lysosomes by a lysosomal enzyme phosphosmannosyl recognition mechanism. Alternatively, hyaluronidase activity may not be present in the cell type(s) responsible for the lysosomal enzyme hypersecretion in mucolipidoses II and III which, along with its deficiency in fibroblasts and leukocytes, would constitute an unusual tissue distribution of activity for a soluble lysosomal enzyme. © 1996 Wiley-Liss, Inc.     

Comparison of Clinical and Echocardiographic Outcomes After Surgical Redo Mitral Valve Replacement and Transcatheter Mitral Valve-in-Valve Therapy

Objectives

There are minimal data regarding clinical outcomes and echocardiographic findings after transcatheter mitral valve-in-valve replacement (TMVR) compared with redo surgical mitral valve replacement (SMVR).