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At least 1,729 records · Page 96Linked to original sources
PubMed2000

The effects of pedicle screw adjustments on neural spaces in burst fracture surgery.

STUDY DESIGN: An in vitro biomechanical study of experimental burst fractures and a pedicle screw device. OBJECTIVES: To investigate the effects that adjustments of a pedicle screw device have on the neural spaces of the burst fracture. SUMMARY OF BACKGROUND DATA: Decompression of the neural spaces is important for the recovery of neural function after a burst fracture. No studies, experimental or clinical, are available that have attempted to relate the pedicle screw device adjustments to the decompression of the neural spaces. METHODS: Burst fractures were produced at L1 vertebra in nine human lumbar spine specimens. Pedicle screw devices were attached to T12 and L2. Eight device adjustments, consisting of pure translations (distraction or compression), pure extension, and combinations of translation and extension were applied. The dimensional changes in the canal and the superior and inferior intervertebral foramens were measured. Functions of restoration and improvement were determined for the adjustments to evaluate the effects of each adjustment and to determine the optimal adjustment. Analysis of variance was used to find statistically significant differences, with significance set at P values less than 0.05. RESULTS: Significant differences were observed in the results of the eight adjustments. The most effective adjustments were the combination of 5-mm distraction with 6 degrees extension or 10-mm distraction alone. The worst adjustment was 5 mm of compression. CONCLUSIONS: Restoring compromised neural spaces in a patient with burst fracture is necessary. The choice of a device adjustment was found to be an important factor in the decompression of the neural spaces after the burst fracture. Combined distraction with extension and distraction alone were found to decompress the canal andintervertebral foramens maximally in a burst fracture.

Adult↗
PubMed1999

Transplantation of autologous iris pigment epithelium to the subretinal space in rabbits.

BACKGROUND: Transplantation of autologous iris pigment epithelium (IPE) into the subretinal space has been suggested as one approach for the treatment of age-related macular degeneration. Autologous rabbit IPE cells were transplanted to the subretinal space to define the technique of transplantation and examine the survival of the transplanted cells. METHODS: Autologous IPE cells were harvested by iridectomy and transplanted directly to the subretinal space of the fellow eye in 25 rabbits, using the parsplana approach. Animals were killed over a period of 5 months, and the retinas were examined morphologically by light and electron microscopy. RESULTS: Autologous IPE cells survived and formed a polarized monolayer above the retinal pigment epithelium in the subretinal space, with apical microvilli adjacent to photoreceptors. Fragments of phagocytosed photoreceptor rod outer segments were observed in phagosomes in the cytoplasm of IPE cells. Adjacent rod outer segments remained healthy throughout the experimental period. No signs of a cell-mediated immunologic response were observed. CONCLUSIONS: Our results show that in rabbits, autologous IPE cells transplanted to the subretinal space survive and do not adversely affect the photoreceptors. These results suggest that in humans, IPE cells might provide a substitute for retinal pigment epithelium cells as autologous transplants for the treatment of age-related macular degeneration.

Animals↗
PubMed2003

Reduction of disc space distraction after anterior lumbar interbody fusion with autologous iliac crest graft.

STUDY DESIGN: A retrospective review with long-term clinical and radiologic assessment was conducted. OBJECTIVE: To assess the severity and reasons for the reduction of disc space distraction after successful autograft fusion of the lumbar spine and its clinical consequences. SUMMARY OF BACKGROUND DATA: Anterior lumbar interbody fusion is an established treatment for lumbar disc degeneration. It is not firmly established whether the grafted level narrows after surgery, and if so, what the clinical consequences are. METHODS: This study assessed 67 patients who underwent anterior lumbar interbody fusion at L4-L5 with autologous iliac crest graft. The disc space height and angle between L4 and L5 were serially measured. Times until fusion and the presence of symptoms before and after surgery and at the latest follow-up assessment were noted. RESULTS: The mean follow-up period was 14 years (range, 2.5-32 years). The fusion rate was 96% (64 of 67 patients), and the mean time to fusion was 9 months. In the group that had successful fusion, there was an initial increase in disc space distraction followed by a reduction in 55 patients (86%). The mean preoperative disc space height was 12.1 mm, which increased immediately after surgery to 16.2 mm, but had been reduced to 12.6 mm at the latest follow-up assessment. The reduction in distraction occurred within the first 3 months after surgery and was correlated with age, but not with recurrence of symptoms, the amount of initial distraction, or the gender of the individual. A similar trend was seen with L4-L5 segmental angulation. CONCLUSIONS: Reduction of disc space distraction after anterior lumbar interbody fusion using tricortical iliac crest bone graft is a common finding. Despite this, the fusion rate is high, and there is no association with symptom recurrence.

Adolescent↗
PubMed2003

Spontaneous symptomatic pseudoarthrosis at the T11-T12 intervertebral space with diffuse idiopathic skeletal hyperostosis: a case report.

STUDY DESIGN: We report on a 69-year-old male who had severe back pain due to spontaneous symptomatic pseudoarthrosis at the T11-T12 intervertebral space with diffuse idiopathic skeletal hyperostosis. OBJECTIVE: To describe a rare clinical entity and successful treatment by spinal fusion with a 4-year follow-up. SUMMARY OF BACKGROUND DATA: There have been a few reports of spontaneous symptomatic pseudoarthrosis of an intervertebral space associated with diffuse idiopathic skeletal hyperostosis, but there have been no reports of surgical treatment for this clinical condition. METHODS: Plain radiographs of the patient, who was admitted to our hospital with severe back pain but no history of trauma, revealed manifestations of diffuse idiopathic skeletal hyperostosis and a pseudoarthrosis at the T11-T12 intervertebral space. Posterior instrumentation from T9 to L2 and anterior bone grafting at the T11-T12 intervertebral space were performed. RESULTS: The patient has been followed for 4 years and is currently asymptomatic. CONCLUSIONS: A rare case of spontaneous symptomatic pseudoarthrosis at the T11-T12 intervertebral space with diffuse idiopathic skeletal hyperostosis was treated successfully by spinal fusion.

Aged↗
PubMed2007

Aeration of Prussak's space is independent of the supradiaphragmatic epitympanic compartments.

HYPOTHESIS: This study's aim was to find out how well various microdissection approaches reveal the basic anatomy of the epitympanum, especially the pathways of aeration to Prussak's space, without the help of serial sections, which many find difficult to interpret. BACKGROUND: The basic studies where made during the latter half of the 19th and the first half of the 20th century. Conflicting concepts have later been published, and doubtful information has been included even in textbooks. METHODS: We have studied 145 temporal bones via microdissection to record the state of the soft tissue structures of the epitympanum, particularly upon Prussak's space with its boundaries. A normal surgical otomicroscope was used in the evaluation, and the findings were recorded via black and white and/or color photography; for recent cases, a digital video camera was used. RESULTS: The epitympanic diaphragm separates the large upper floor compartments from the small, laterally placed lower floor unit. The latter consists of Prussak's space and the posterior pouch, at times also of the lower lateral attic. The tympanic isthmus connects the upper unit to the medial tympanum. Defects in the diaphragm create additional airways to the upper unit, in 29% via the tensor fold and in 19% via the lateral incudomalleal fold. In only 7% was there a small opening in the roof of Prussak's space connecting it to the upper unit. Effective aeration of Prussak's space was independent of the upper floor compartments. CONCLUSION: Microdissection is a reliable and sufficient method for teaching epitympanic anatomy. All important structures can be identified and defects in the epitympanic diaphragm verified. Data obtained via serial sections are invaluable in research but not essential in the training of ear surgeons. The two-floor structure of the epitympanum with an independent aeration of the two units should be the starting point for all anatomy teaching.

Adolescent↗
PubMed2005

Implantation of esterified hyaluronic acid in microdissected Reinke's space after vocal fold microsurgery: first clinical experiences.

OBJECTIVE: In this pilot study are presented the first clinical experiences of the use of a resorbable bioimplant made of esterified hyaluronic acid inserted in the microdissected superficial layer of the lamina propria (SLLP), also called Reinke's space, after a flap excision procedure for a benign vocal fold lesion. Laryngeal and vocal evolution of implanted patients are depicted and discussed. STUDY DESIGN: Eleven bio-implants have been inserted in microdissected SLLP of 11 cases presenting with benign vocal fold lesions. The surgical procedure consisted of the excision of primary lesion by a microflap technique immediately followed by implantation of esterified hyaluronic acid in Reinke's space. METHODS: All patients underwent rigid laryngoscopy and a microsurgical procedure under general anesthesia. The cordal lesion was treated with cold instrumentation of Bouchayer (7 cases) or with a mixed technique using CO(2) laser (4 cases). After the classical freeing-up of Reinke's space and the creation of a mucosal flap, a few fibers of esterified hyaluronic bioimplant are gently arranged in Reinke's space before redraping the ligament and closing the cordal incision with a few drops of fibrin glue. Laryngeal and vocal assessments were performed pre- and postoperatively in all patients using videostroboscopy as well as perceptual and objective voice evaluation. All patients were followed in a longitudinal manner: between two and five postoperative evaluations were performed. The longest follow-up was 19 months and the shortest 2 months. RESULTS: All cases exhibited postsurgical improvement of the pliability of the SLLP. None of them developed an adverse scarring process. Improvement of SLLP's pliability was maintained in time in all cases. Vocal improvement was observed in all. Temporary inflammation was noted in one case. There were no serious adverse effects apparent during the follow-up period. CONCLUSION: Bio-implantation of esterified hyaluronic acid in Reinke's space is technically easy and well tolerated. All treated cases exhibited postoperative good pliability of the SLLP compared with their preoperative evaluation.

Absorbable Implants↗
PubMed2005

Ocular examination for trauma; clinical ultrasound aboard the International Space Station.

BACKGROUND: Ultrasound imaging is a successful modality in a broad variety of diagnostic applications including trauma. Ultrasound has been shown to be accurate when performed by non-radiologist physicians; recent reports have suggested that non-physicians can perform limited ultrasound examinations. A multipurpose ultrasound system is installed on the International Space Station (ISS) as a component of the Human Research Facility (HRF). This report documents the first ocular ultrasound examination conducted in space, which demonstrated the capability to assess physiologic alterations or pathology including trauma during long-duration space flight. METHODS: An ISS crewmember with minimal sonography training was remotely guided by an imaging expert from Mission Control Center (MCC) through a comprehensive ultrasound examination of the eye. A multipurpose ultrasound imager was used in conjunction with a space-to-ground video downlink and two-way audio. Reference cards with topological reference points, hardware controls, and target images were used to facilitate the examination. Multiple views of the eye structures were obtained through a closed eyelid. Pupillary response to light was demonstrated by modifying the light exposure of the contralateral eye. RESULTS: A crewmember on the ISS was able to complete a comprehensive ocular examination using B- and M-mode ultrasonography with remote guidance from an expert in the MCC. Multiple anteroposterior, oblique, and coronal views of the eye clearly demonstrated the anatomic structures of both segments of the globe. The iris and pupil were readily visualized with probe manipulation. Pupillary diameter was assessed in real time in B- and M-mode displays. The anatomic detail and fidelity of ultrasound video were excellent and could be used to answer a variety of clinical and space physiologic questions. CONCLUSIONS: A comprehensive, high-quality ultrasound examination of the eye was performed with a multipurpose imager aboard the ISS by a non-expert operator using remote guidance. Ocular ultrasound images were of diagnostic quality despite the 2-second communication latency and the unconventional setting of a weightless spacecraft environment. The remote guidance techniques developed to facilitate this successful NASA research experiment will support wider applications of ultrasound for remote medicine on Earth including the assessment of pupillary reactions in patients with severe craniofacial trauma and swelling.

Astronauts↗
PubMed1989

Evolution of resistance with sequential application of insecticides in time and space.

The effect, on the evolution of resistance, of alternating two unrelated insecticides in space or in time (or both) is studied. Transient polymorphism is shown to occur under certain conditions of mating, selection and migration. In some situations, the transient polymorphism can show a sharp decline before the alleles recover to fixation. Alternating a single insecticide in space, and in space and time, is also considered. Neither alternation in space nor in time shows any advantage with regard to delaying the onset of resistance. The most promising mode is to alternate the presence and absence of a single insecticide in both space and time, especially if it is applied at the larval stage and if some form of biological control is used in the regions where no insecticide is applied.

Animals↗
PubMed1996

Growth and photosynthetic responses of wheat plants grown in space.

Growth and photosynthesis of wheat (Triticum aestivum L. cv Super Dwarf) plants grown onboard the space shuttle Discovery for 10 d were examined. Compared to ground control plants, the shoot fresh weight of space-grown seedlings decreased by 25%. Postflight measurements of the O2 evolution/photosynthetic photon flux density response curves of leaf samples revealed that the CO2-saturated photosynthetic rate at saturating light intensities in space-grown plants declined 25% relative to the rate in ground control plants. The relative quantum yield of CO2-saturated photosynthetic O2 evolution measured at limiting light intensities was not significantly affected. In space-grown plants, the light compensation point of the leaves increased by 33%, which likely was due to an increase (27%) in leaf dark-respiration rates. Related experiments with thylakoids isolated from space-grown plants showed that the light-saturated photosynthetic electron transport rate from H2O through photosystems II and I was reduced by 28%. These results demonstrate that photosynthetic functions are affected by the microgravity environment.

Carotenoids↗
PubMed1976

Boron uptake by excised barley roots: I. Uptake into the free space.

At 2 C, all boron accumulated by excised barley roots (Hordeum vulgare L. cv. Herta) remains in the free space; i.e. active uptake is nil at this temperature. Three component fractions of free space B were apparent: (a) a surface contaminant film of B on blotted roots, (b) water free space B, and (c) B reversibly bound in the cell walls. A stoichiometric release of H(+) from the roots in the presence of B indicated that B was bound by borate complexes with polysaccharides in the cell walls. Polysaccharide-borate complexes are much less stable than those of monosaccharides, and the bound B fraction could be readily removed by rinsing the roots in the presence of a monomeric polyol possessing the necessary cis-diol configuration. Cell wall material separated from excised barley roots had a B binding capacity 66% greater than that of intact roots.A 30-minute rinse in distilled H(2)O or 0.5 mm CaSO(4) was required to remove all cell wall-bound B from the roots after a 30-minute uptake period. Thus, although B in the contaminant surface film and the water free space is rinsed from the roots within 10 minutes, a 30-minute rinse is essential if all reversibly accumulated B is to be removed from the free space.

Journal Article↗
PubMed1990

Spacing between GT-1 binding sites within a light-responsive element is critical for transcriptional activity.

Dissection of the light-responsive element (LRE) located between -166 and -50 of rbcS-3A from pea has revealed critical spacing requirements between the two GT-1 binding sites for light-responsive transcription. An increase in spacing between the two sites by as little as 2 bp reduces dramatically the rbcS-3A transcript levels in vivo. Mutation of the 10 bp between the binding sites leads to slightly lower transcript levels, as do deletions of either 3 bp or 8 bp. Deletions of 5 bp or 7 bp from between the GT-1 binding sites do not affect rbcS-3A transcript levels; however, a deletion of 10 bp virtually abolishes the activity of this element. These spacing changes within the light-responsive element similarly affect transcription of a divergently oriented and truncated nopaline synthase promoter. Most spacing changes between the two GT-1 binding sites, however, do not impair the binding of GT-1 to this element in vitro. Together with previous observations, these results suggest that the nuclear factor GT-1 may interact with the binding sites in either a productive or nonproductive manner and that GT-1 binding is necessary but not sufficient for light-responsive transcription. We also discuss our results in relation to the observed spacing of similar sequence elements present within other light-responsive promoters.

Amino Acid Oxidoreductases↗
PubMed1991

Exact random-walk models in crystallographic statistics. VII. An all-space-group study of the effects of atomic heterogeneity on the P.D.F.'s of magnitude of [E].

Exact expressions have been found for the probability density functions (p.d.f.'s) of the magnitude of the normalized structure factor for all the two-dimensional and most three-dimensional space groups [Part VI: Rabinovich, Shmueli, Stein, Shashua & Weiss (1991). Acta Cryst. A47, 328-335]. The results of that investigation are used in the present article to examine some effects of atomic heterogeneity, in the various space-group symmetries, on the p.d.f.'s. Some typical comparisons are made between p.d.f.'s based on the central limit theorem and p.d.f.'s computed from exact formulae. In addition, the exact results are compared to histograms of simulated values of magnitude of [E]. It is found that the p.d.f.'s for some space groups are influenced rather strongly by the presence of outstandingly heavy scatters, but they are quite insensitive to the presence of such scatterers in other space groups. The often made general statement 'The presence of outstandingly heavy scatterers may invalidate the indications of Wilson's statistics' is made more precise here, insofar as it depends on the particular space group.

Fourier Analysis↗
PubMed1999

Algorithms for deriving crystallographic space-group information.

Algorithms are presented for three-dimensional crystallographic space groups, handling tasks such as the generation of symmetry operations, the characterization of symmetry operations (determination of rotation-part type, axis direction, sense of rotation, screw or glide part and location part), the determination of space-group type [identified by the space-group number of the International Tables for Crystallography (Dordrecht: Kluwer Academic Publishers)] and the generation of structure-seminvariant vectors and moduli. The latter are an algebraic description of allowed origin shifts, which are important in crystal structure determination methods or for comparing crystal structures. The space-group type determination produces a change-of-basis matrix which transforms a given space-group representation to the standard one according to the International Tables for Crystallography. The algorithms were implemented and tested using the SgInfo library. The source code is free for non-commercial applications.

Journal Article↗
PubMed1999

Real-space molecular-dynamics structure refinement.

Real-space targets and molecular-dynamics search protocols have been combined to improve the convergence of macromolecular atomic refinement. This was accomplished by providing a local real-space target function for the molecular-dynamics program X-PLOR. With poor isomorphous replacement experimental phases, molecular dynamics does not improve real-space refinement. However, with high-quality anomalous diffraction phases convergence is improved at the start of refinement, and torsion-angle real-space molecular dynamics performs better than other available least-squares or maximum-likelihood methods in real or reciprocal space. It is shown that the improvements result from an optimization method that can escape local minima and from a reduction of overfitting through the implicit use of phases and through use of a local refinement in which errors in remote parts of the structure cannot be mutually compensating.

Hydroxymethylglutaryl CoA Reductases↗
PubMed1993

Efficient electrode spacing for examining spatial organization during ventricular fibrillation.

Spatial organization has been observed during episodes of ventricular fibrillation (VF) by recording epicardial unipolar electrograms on a grid of electrodes. In such studies, the choice of spacing between electrodes is an important decision, affecting the resolution and the size of the domain to be studied. A basic tenet of sampling theory, the Nyquist criterion, states that an electrode spacing smaller than half the smallest significant wavelength is required to capture the important details of a spatially sampled process. In this paper, we suggest a method to choose a practical interelectrode spacing by examining wavenumber power spectra of high-resolution VF data recorded from a square 11 x 11 array of electrodes spaced 0.28 mm apart. The plaque was sutured on the epicardium near the left ventricular apex in seven anesthetized pigs. VF was induced with ac simulation. Unipolar extracellular electrograms were simultaneously recorded from each channel for 2 s after the induction of VF. Each signal was sampled in time at 1000 Hz. Wavenumber power spectra were calculated for 100 ms segments using the zero-delay wavenumber spectrum method, for a total of 140 power spectra. All spectra had dominant peaks at the origin and fell off rapidly with increasing wavenumber (decreasing wavelength). In all the spectra, every wavelength shorter than 1.4 mm contributed insignificant power. Furthermore, in 134 of 140 spectra (96%), insignificant power levels were associated with every wavelength shorter than 2.8 mm. These results suggest that, for unipolar extracellular electrodes, an intersensor spacing on the order of 1 mm is appropriate to study organization during early VF.

Animals↗
PubMed2000

Correction of MR kappa-space data corrupted by spike noise.

Magnetic resonance images are reconstructed from digitized raw data, which are collected in the spatial-frequency domain (also called kappa-space). Occasionally, single or multiple data points in the k-space data are corrupted by spike noise, causing striation artifacts in images. Thresholding methods for detecting corrupted data points can fail because of small alterations, especially for data points in the low spatial frequency area where the k-space variation is large. Restoration of corrupted data points using interpolations of neighboring pixels can give incorrect results. We propose a Fourier transform method for detecting and restoring corrupted data points using a window filter derived from the striation-artifact structure in an image or an intermediate domain. The method provides an analytical solution for the alteration at each corrupted data point. It can effectively restore corrupted kappa-space data, removing striation artifacts in images, provided that the following three conditions are satisfied. First, a region of known signal distribution (for example, air background) is visible in either the image or the intermediate domain so that it can be selected using a window filter. Second, multiple spikes are separated by the full-width at half-maximum of the point spread function for the window filter. Third, the magnitude of a spike is larger than the minimum detectable value determined by the window filter and the standard deviation of kappa-space random noise.

Artifacts↗
PubMed2006

Self-similar random field models in discrete space.

Self-similar random fields are of interest in various areas of image processing since they fit certain types of natural patterns and textures. Current treatments of self-similarity in continuous two-dimensional (2-D) space use a definition that is a direct extension of the one-dimensional definition, which requires invariance of the statistics of a random process to time scaling. Current discrete-space 2-D approaches do not consider scaling, but, instead, are based on ad hoc formulations, such as digitizing continuous random fields. In this paper, we show that the current statistical self-similarity definition in continuous space is restrictive and provide an alternative, more general definition. We also provide a formalism for discrete-space statistical self-similarity that relies on a new scaling operator for discrete images. Within the new framework, it is possible to synthesize a wider class of discrete-space self-similar random fields and texture images.

Algorithms↗
PubMed2004

Compensation for nonuniform resolution using penalized-likelihood reconstruction in space-variant imaging systems.

Imaging systems that form estimates using a statistical approach generally yield images with nonuniform resolution properties. That is, the reconstructed images possess resolution properties marked by space-variant and/or anisotropic responses. We have previously developed a space-variant penalty for penalized-likelihood (PL) reconstruction that yields nearly uniform resolution properties. We demonstrated how to calculate this penalty efficiently and apply it to an idealized positron emission tomography (PET) system whose geometric response is space-invariant. In this paper, we demonstrate the efficient calculation and application of this penalty to space-variant systems. (The method is most appropriate when the system matrix has been precalculated.) We apply the penalty to a large field of view PET system where crystal penetration effects make the geometric response space-variant, and to a two-dimensional single photon emission computed tomography system whose detector responses are modeled by a depth-dependent Gaussian with linearly varying full-width at half-maximum. We perform a simulation study comparing reconstructions using our proposed PL approach with other reconstruction methods and demonstrate the relative resolution uniformity, and discuss tradeoffs among estimators that yield nearly uniform resolution. We observe similar noise performance for the PL and post-smoothed maximum-likelihood (ML) approaches with carefully matched resolution, so choosing one estimator over another should be made on other factors like computational complexity and convergence rates of the iterative reconstruction. Additionally, because the postsmoothed ML and the proposed PL approach can outperform one another in terms of resolution uniformity depending on the desired reconstruction resolution, we present and discuss a hybrid approach adopting both a penalty and post-smoothing.

Algorithms↗