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PubMed2004

Experience with removing Palmaz stents with a rigid bronchoscope.

BACKGROUND: The Palmaz stent can relieve congenital malacia or stenosis of airway, but reports on the indications and results of stent removal are rare. The authors report their experience in removing Palmaz stents and discuss the indications for removal. METHODS: Thirteen stents in 12 patients were removed by a rigid bronchoscope for various reasons. The indications were expected recovery (n = 5), severe granulations and expected recovery (n = 2), stent collapse (n = 2), and stent migration and/or fracture (n = 4). RESULTS: The course after removal was smooth in 9 patients and complicated in 3. The indications for stent removal in these 3 complicated cases were all expected recovery. One of the 3 complicated cases needed emergent cardiopulmonary bypass and tracheostomy for a collapsed stent that occluded airway, 1 failed for intractable bleeding, and 1 failed for intense vagal reflex causing cardiac arrest. At 6 months of follow-up, satisfactory results were seen in all but one case that needed further procedures for an iatrogenic tracheoesophageal fistula. CONCLUSIONS: Most Palmaz stents can be removed smoothly with a rigid bronchoscope; however, lethal complications can happen. The authors suggest that indications for stent removal should be intractable airway symptoms caused by the stent rather than expected recovery. Muscle relaxants should be avoided during anesthesia to maintain spontaneous breathing, and cardiopulmonary bypass should be on standby.

Bronchoscopes↗

PubMed2006

Resolution of the excitation-emission spectra of FMN in rigid poly(vinyl alcohol) matrices.

The excitation-emission spectra of flavin mononucleotide (FMN) were measured in rigid PVA films for concentrations ranging from 6.92 x 10(-4)M to 1.03 M. The theoretical three-linear decomposition of the excitation-emission spectra indicated the presence of two absorption and emission centers corresponding to FMN monomer and dimer, respectively. The component of the fluorescence profile corresponding to the FMN monomer has a large negative part which is the mirror image of the emission band profile of the dimer. The elimination of this part by taking a linear combination of the emission components of the monomer and of the dimer resulted in emission spectrum, which is in a very good agreement with the monomer spectrum measured directly. The appearance of a negative part of the monomer emission profile obtained by trilinear decomposition of the emission-absorption spectra of FMN can be explained in terms of the non-radiative reverse energy transfer from the FMN dimers to the FMN monomers. The presented results confirm that the FMN molecules in rigid PVA form dimers but not higher order aggregates. Moreover, they enable to obtain fluorescence spectra of dimers and suggest that FMN dimers may take part in the process of non-radiative energy transfer occurring in photoreception phenomena.

Dimerization↗

PubMed2005

Extensive circumferential endoscopic mucosal resection with a new rigid esophagoscope: an animal study.

OBJECTIVE: Current endoscopic mucosal resection techniques are suboptimal for large circumferential mucosal resections intended to treat Barrett mucosa with multicentric foci of high-grade intraepithelial neoplasia or early adenocarcinomas. A rigid modified endoscope was developed for extended endoscopic mucosal resection in the esophagus. This pilot animal study investigated the feasibility of circumferential endoscopic mucosal resections of different lengths in the sheep esophagus. METHODS: Circumferential esophageal endoscopic mucosal resections of 2.2 cm (n = 6), 3.3 cm (n = 6), 4.4 cm (n = 7), and 5.5 cm (n = 5) were performed in 24 sheep. Circumferential resections consisted of two opposite hemicircumferential mucosectomies. Animals were followed up with endoscopic examinations at 1 week and then monthly to 6 months, or until complete re-epithelialization without stenosis eventually ensued. Strictures were treated with a single or repeated dilatations with Savary bougies. RESULTS: Circumferential resections 2.2 to 5.5 cm in length were successfully performed in 23 of 24 of the animals. One perforation occurred directly after mucosectomy. Accurate depth of resection through the submucosa was obtained in 85% of the specimens. Cicatricial stenosis was controlled in 95% by bougienage. CONCLUSION: Endoscopic mucosal resection performed with the rigid esophagoscope allowed extensive circumferential resections in a single session. There is thus potential to eradicate complete Barrett esophagus with high-grade intraepithelial neoplasia or early adenocarcinomas.

Animals↗

PubMed2006

The evaluation of benign glottic lesions: rigid telescopic stroboscopy versus suspension microlaryngoscopy.

Rigid telescopic strobo-video-laryngoscopy (RTS) is a primary clinical assessment methodology in the office evaluation of benign glottic lesions. However, diagnostic observations can be made only at the time of suspension microlaryngoscopy (SML). The records of 100 consecutive patients undergoing microlaryngoscopy for benign glottic lesions were retrospectively reviewed. Nine of 100 patients were found to have additional glottic lesions during SML. Sixteen additional lesions were noted in these nine patients. Fifteen of 16 lesions were sulci and/or mucosal bridges. Forty-five percent (4/9) of the patients with additional lesions underwent a management change intraoperatively. Three patients underwent additional surgical dissection, and one underwent less dissection than was planned. The discrepancy in diagnosis between rigid telescopic strobo-video-laryngoscopy and suspension microlaryngoscopy highlights certain key points: (1) During office endoscopy, tangential views of the medial surface of the glottis limit the diagnostic sensitivity. (2) Sulci and mucosal bridges are most subject to this limitation. (3) Informed consent should address the potential need for a change in intraoperative management. It is advisable to discuss the possibility for dissection in both vocal folds, even if a unilateral lesion is observed in the office. (4) Microlaryngoscopy is the final diagnostic step in the evaluation of glottic pathology. Meticulous inspection and palpation of the glottis are recommended during SML.

Adult↗

PubMed2005

On calculating the finite centre of rotation for rigid planar motion.

In this technical note, a simpler least squares derivation for calculating the angle of rotation and finite centre of rotation of a set of marker points undergoing rigid planar rotation and translation is shown. The major advantage of the approach, other than the simple derivation, is the automatic inclusion of the calculation of a scaling factor between the two point sets - the calculation of which was not obvious in previous approaches [Challis J. Estimation of the finite center of rotation in planar movements. Med Eng Phys 2001;23(3):227-33, Spoor C, Veldpaus F. Rigid body motion calculated from spatial coordinates of markers. J Biomech 1980;13:391-3]. The final numerical calculations are similar to those of [Challis J. Estimation of the finite center of rotation in planar movements. Med Eng Phys 2001;23(3):227-33] and are trivial to implement. A matlab routine for computing the two quantities, and the scaling factor, is included. We demonstrate the method on a clinical example using lateral radiographs of the lumbar spine.

Algorithms↗

PubMed2004

Thoracic non-rigid registration combining self-organizing maps and radial basis functions.

An automatic three-dimensional non-rigid registration scheme is proposed in this paper and applied to thoracic computed tomography (CT) data of patients with stage III non-small cell lung cancer (NSCLC). According to the registration scheme, initially anatomical set of points such as the vertebral spine, the ribs, and shoulder blades are automatically segmented slice by slice from the two CT scans of the same patient in order to serve as interpolant points. Based on these extracted features, a rigid-body transformation is then applied to provide a pre-registration of the data. To establish correspondence between the feature points, the novel application of the self-organizing maps (SOMs) is adopted. In particular, the automatic correspondence of the interpolant points is based on the initialization of the Kohonen neural network model capable to identify 500 corresponding pairs of points approximately in the two CT sets. Then, radial basis functions (RBFs) using the shifted log function is subsequently employed for elastic warping of the image volume, using the correspondence between the interpolant points, as obtained in the previous phase. Quantitative and qualitative results are also presented to validate the performance of the proposed elastic registration scheme resulting in an alignment error of 6 mm, on average, over 15 CT paired datasets. Finally, changes of the tumor volume in respect to each reference dataset are estimated for all patients, which indicate inspiration and/or movement of the patient during acquisition of the data. Thus, the practical implementation of this scheme could provide estimations of lung tumor volumes during radiotherapy treatment planning.

Adult↗

PubMed2005

A non-rigid registration approach for quantifying myocardial contraction in tagged MRI using generalized information measures.

We address the problem of quantitatively assessing myocardial function from tagged MRI sequences. We develop a two-step method comprising (i) a motion estimation step using a novel variational non-rigid registration technique based on generalized information measures, and (ii) a measurement step, yielding local and segmental deformation parameters over the whole myocardium. Experiments on healthy and pathological data demonstrate that this method delivers, within a reasonable computation time and in a fully unsupervised way, reliable measurements for normal subjects and quantitative pathology-specific information. Beyond cardiac MRI, this work redefines the foundations of variational non-rigid registration for information-theoretic similarity criteria with potential interest in multimodal medical imaging.

Adult↗

PubMed2006

Retrospective evaluation of a topology preserving non-rigid registration method.

This paper proposes a comprehensive evaluation of a monomodal B-spline-based non-rigid registration algorithm allowing topology preservation in 3-D. This article is to be considered as the companion of [Noblet, V., Heinrich, C., Heitz, F., Armspach, J.-P., 2005. 3-D deformable image registration: a topology preservation scheme based on hierarchical deformation models and interval analysis optimization. IEEE Transactions on Image Processing, 14 (5), 553-566] where this algorithm, based on the minimization of an objective function, was introduced and detailed. Overall assessment is based on the estimation of synthetic deformation fields, on average brain construction, on atlas-based segmentation and on landmark mapping. The influence of the model parameters is characterized. Comparison between several objective functions is carried out and impact of their symmetrization is pointed out. An original intensity normalization scheme is also introduced, leading to significant improvements of the registration quality. The comparison benchmark is the popular demons algorithm [Thirion, J.-P., 1998. Image matching as a diffusion process: an analogy with Maxwell's demons. Medical Image Analysis, 2 (3), 243-260], that exhibited best results in a recent comparison between several non-rigid 3-D registration methods [Hellier, P., Barillot, C., Corouge, I., Gibaud, B., Le Goualher, G., Collins, D.L., Evans, A., Malandain, G., Ayache, N., Christensen, G.E., Johnson, H.J., 2003. Retrospective evaluation of intersubject brain registration. IEEE Transactions on Medical Imaging, 22 (9), 1120-1130]. The topology preserving B-spline-based method proved to outperform the commonly available ITK implementation of the demons algorithms on many points. Some limits of intensity-based registration methods are also highlighted through this work.

Algorithms↗

PubMed2006

Automatic elastic image registration by interpolation of 3D rotations and translations from discrete rigid-body transformations.

We present an algorithm for automatic elastic registration of three-dimensional (3D) medical images. Our algorithm initially recovers the global spatial mismatch between the reference and floating images, followed by hierarchical octree-based subdivision of the reference image and independent registration of the floating image with the individual subvolumes of the reference image at each hierarchical level. Global as well as local registrations use the six-parameter full rigid-body transformation model and are based on maximization of normalized mutual information (NMI). To ensure robustness of the subvolume registration with low voxel counts, we calculate NMI using a combination of current and prior mutual histograms. To generate a smooth deformation field, we perform direct interpolation of six-parameter rigid-body subvolume transformations obtained at the last subdivision level. Our interpolation scheme involves scalar interpolation of the 3D translations and quaternion interpolation of the 3D rotational pose. We analyzed the performance of our algorithm through experiments involving registration of synthetically deformed computed tomography (CT) images. Our algorithm is general and can be applied to image pairs of any two modalities of most organs. We have demonstrated successful registration of clinical whole-body CT and positron emission tomography (PET) images using this algorithm. The registration accuracy for this application was evaluated, based on validation using expert-identified anatomical landmarks in 15 CT-PET image pairs. The algorithm's performance was comparable to the average accuracy observed for three expert-determined registrations in the same 15 image pairs.

Algorithms↗

PubMed2005

The influence of planarity, rigidity and internal heavy atom upon fluorescence parameters and the intersystem crossing rate constant in molecules with the biphenyl basis.

Fluorescence properties of 10 specially chosen aromatic compounds with the biphenyl basis, differing in the degree of planarity, rigidity and in the nature of the internal heavy atom, but family-related in pi-structure are experimentally studied at room temperature (293K). The quantum yield of fluorescence, gamma, and fluorescence decay time, pi(f), of deaerated and non-deaerated cyclohexane solutions are measured. The oscillator strength, f(e), of S0-->S1 transition, fluorescence rate constant, k(f), natural lifetime, tau0(T), and intersystem crossing rate constant, k(ST), are calculated for each compound. It was observed that the increase in planarity and rigidity causes the k(ST) value to decrease very significantly. Any disturbance of the pi-system by the torsional vibrations of the substituted part of the molecule causes the k(ST) value to increase. The introduction of a heavy atom instead of the methylene bridge of fluorene leads to the increase in the k(ST) value and to the decrease in the f(e) of the 1A-->1La transition. The absence of laser action of fluorene is explained.

Biphenyl Compounds↗

PubMed2004

Tiered environmental risk assessment of methyltins from heat stabilizers in rigid PVC in Sweden.

The methyltins, methyltin 2-ethylhexyl mercaptoacetate and methyltin-2-mercaptoethyloleate sulfide, are used as heat stabilizers in rigid PVC. The degradation products monomethyltintrichloride (MMTTC) and dimethyltindichloride (DMTDC) may leach from the PVC, and enter the environment. A risk assessment was executed for the use of these products in Sweden, with the double aim to (a) assess the potential environmental risks, and (b) explore the possibilities of a tiered risk assessment. An initial assessment was executed with EUSES 1.0. The initial assessment showed no significant environmental risks on a regional scale. On a local scale however, emissions from a sewage treatment plant to the surface water pose a potential risk for the near proximity. In a second tier, this critical exposure route was studied in more detail; an improved exposure scenario was drawn up; and an additional sorption experiment was performed. This refinement resulted in much lower predicted environmental concentrations (<<PNEC). Measured methyltin concentrations in countries where methyltin heat stabilizers are registered, reveal concentrations ranging from < detection limit to intermediate values between concentrations predicted in the initial and refined assessment. The tiered assessment scheme proved valuable. Using this, the environmental risks due to the leaching of MMTTC and DMTDC from rigid PVC in Sweden are of no concern.

Animals↗

PubMed2003

A randomized trial of rigid gas permeable contact lenses to reduce progression of children's myopia.

PURPOSE: To test whether rigid gas permeable (RGP) contact lens wear can reduced the rate of myopia progression in school age children. DESIGN: Randomized clinical trial. METHODS SETTING: Single clinical center. STUDY POPULATION: Both eyes of 428 Singaporean children. INCLUSION CRITERIA: 6 through 12 years of age with myopia between -1 and -4 diopters, astigmatism <or= 2 diopters, no prior contact lens wear, no other ocular pathologies. INTERVENTION: Spectacle or RGP lens correction for myopia. After a 3-month adaptation period, 383 children were followed, and 298 (78%) remained after 24 months. OUTCOME MEASURES: Cycloplegic subjective refraction, keratometry, and axial length measured at 12 and 24 months. RESULTS: Children who adapted to contact lenses wore them for a median of 7 hours per day, but no more than 40% wore them at least 8 hours per day, 7 days per week. Spectacles were worn for a median of 15 hours per day at the time of the 24-month follow-up. There was an increase in the spherical equivalent of -1.33 and -1.28 diopters (P =.64), and axial length increased by 0.84 and 0.79 mm (P =.38) over 2 years among children randomized to contact lenses and spectacles, respectively. Adjustment for baseline differences between the groups and for hours per day of contact lens wear did not alter these findings. CONCLUSIONS: Rigid gas permeable lenses did not slow the rate of myopia progression, even among children who used them regularly and consistently. It is unlikely that this intervention holds promise as a method by which to slow the rate of progression of myopia in children.

Child↗

PubMed1992

Glued-on, rigid gas-permeable contact lens for severe radiation-induced keratitis.

A 68-year-old woman with severe radiation-induced keratoconjunctivitis sicca became progressively unresponsive to conventional medical treatment. Her left eye deteriorated rapidly and required total tarsorrhaphy. In an attempt to stabilize the right eye and preserve some functional vision, we glued a high-Dk rigid, gas-permeable contact lens with tissue-grade cyanoacrylate adhesive to Bowman's membrane. This glued-on contact lens induced rapid and dramatic improvement of the patient's comfort and sight. Recent developments in high-permeability, rigid, contact-lens materials now make artificial replacement of the epithelium a potentially useful treatment for severe ocular surface disease when conventional treatment has failed.

Aged↗

PubMed1991

Fitting of aspheric high gas-permeable rigid contact lenses to scarred corneas.

Scarring of the cornea often results in an irregular corneal surface, which causes scattering in light perception. Therefore, the impaired visual acuity cannot be adequately corrected by spectacles in most cases. In this study, high oxygen-transmissible aspheric rigid lenses were fitted, with computer assistance, in 26 scarred eyes of 23 consecutive patients. In 15 of 26 eyes (57.7%), a successful fitting with good vision, no complications, and a sufficiently long wearing time was accomplished. The main lens-related complications included fluorescein-staining epithelial defects in five of 26 eyes (19.2%) and epithelial edema in two of 26 eyes (7.7%). Computer-aided fitting was of limited value because keratometer readings were not measurable in 50% of the cases. The results of this study indicate that the application of high oxygen-transmissible aspheric rigid contact lenses may obviate corneal surgery.

Adult↗

PubMed1998

Biomechanical study of sternal closure using rigid fixation techniques in human cadavers.

BACKGROUND: We believe rigid plate fixation may be superior to wire fixation in sternal closure, as rigid fixation used in the craniofacial skeleton has shown greater stability, lower postoperative pain, and accelerated bone healing. We hypothesize that sterna fixed with titanium plates are more stable mechanically than sterna fixed with wires. METHODS: The sterna from human cadavers were used in this two-phased study. Phase I compared wires to four-hole titanium straight plates. Phase II compared wires to four-hole titanium custom H plates. The sterna were tested biomechanically using all fixation methods. RESULTS: Phase I showed no statistically significant difference in the stiffness or lateral displacement between the wired and straight plated sterna. Phase II showed a statistically significant greater stiffness (p < 0.05) and less lateral displacement (p < 0.05) in the custom plated sterna over the wired sterna. CONCLUSIONS: Our results showed that custom titanium H plates were superior to wire fixation. Furthermore, our results established the importance of plate configuration in sternal fixation. Our study may have beneficial clinical implications, as decreased motion at the sternotomy site could mean less postoperative pain, a decreased incidence of infection, and accelerated bone healing.

Aged↗

PubMed1997

Chilling stress leads to increased cell membrane rigidity in roots of coffee (Coffea arabica L.) seedlings.

Tropical and sub-tropical higher plant species show marked growth inhibition when exposed to chilling temperatures. In root tip segments of coffee seedlings which were subjected for 6 days to temperatures of 10, 15, 20 and 25 degrees C, in darkness, we have detected an increased amount of malondialdehyde formed in the 10 degrees C treatment, accompanied by higher electrolyte leakage. The electron paramagnetic resonance (EPR) technique and the fatty acid spin probes 5-, 12- and 16-doxylstearic acid were used to assess cellular membrane fluidity. At the depth of the 5th and 16th carbon atom of the alkyl chains the nitroxide radical detected more rigid membranes in seedlings subjected to 10 degrees C compared with 15 and 25 degrees C. At the C-12 position of the chains the probe showed very restricted motion and was insensitive to chilling induced membrane alterations. EPR parameters for intact tissues and microsome preparations from root tips showed that the fluidity was essentially the same when evaluated at C-5 and C-16 positions of the chains, and was considerably more fluid for microsomal membranes in the region of the C-12 position of the bilayers. The rotational motion of the nitroxide at C-16 position of the chains experienced a phase transition at about 15 degrees C. The calculated energy barriers for reorientational motion of the probe 16-doxylstearic acid were higher at temperatures of 5-15 degrees C than in the interval of 15-25 degrees C, suggesting that below the phase transition the membrane lipids assume a more ordered and compacted array. Membrane rigidity induced by chilling was interpreted as due to lipid peroxidation that could have been facilitated by higher density of peroxidizable chains below the membrane phase transition.

Coffee↗

PubMed2000

Rigidity of triskelion arms and clathrin nets.

Statistical analysis is applied to a set of electron micrographic images (Kocsis, E., B. L. Trus, C. J. Steer, M. E. Bisher, and A. C. Steven. 1991. J. Struct. Biol. 107:6-14), from which quantitative measures are obtained to support the notion that the three arms of a triskelion have statistically identical properties and exhibit independent structural fluctuations. Additionally, a study of local contour fluctuations, which indicates that the elastic properties of a triskelion arm are approximately constant over the entire arm length, is used along with a small deformation statistical mechanics theory to derive an effective, average flexural rigidity for the arms. This result is used to estimate the bending energy necessary to deform a clathrin patch, and comparison is made with the deformation energy of an equivalent area of non-clathrin-coated membrane. We estimate that the rigidity of the clathrin lattice is at least comparable to that of a typical membrane. Hence, the natural curvature of a clathrin cage can stabilize, and perhaps propel, the formation of intracellular coated vesicles.

Clathrin↗

PubMed2002

Rigid analogues of buspirone and gepirone, 5-HT1A receptors partial agonists.

Rigid analogues of buspirone and gepirone, 5-HT1A receptors partial agonists, were obtained. The compounds exhibited very low affinity to the receptors. Their structural features resembled to a large extent the arrangement of the respective structural elements found in the solid state of buspirone and in the theoretical structure of NAN-190 (5-HT1A postsynaptic antagonist) rigid analogue exhibiting high affinity to the receptor. The obtained results would thus suggest that the bioactive conformation of buspirone might not be the extended one. That would additionally suggest that either both groups of compounds could occupy different areas at the receptor binding sites (or bind to different receptor states) or the constrained structure of 2 does not represent well 5-HT1A receptor binding site requirements.

Binding, Competitive↗