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Biomedical subjects

R N Bryan

Publications and source records attributed to R N Bryan.

At least 145 records · Page 8Linked to original sources

MRI in motor delay: important adjunct to classification of cerebral palsy.

Cranial magnetic resonance imaging (MRI) was performed prospectively in 45 children (ages 3-27 months) with clinically documented motor delay to evaluate the ability of MRI to determine etiologic factors, to determine whether myelination correlated with motor delay, and whether the clinical category corresponded with the imaging findings. Of the 22 children diagnosed clinically as having major motor delay (i.e., cerebral palsy), 77% had magnetic resonance imaging abnormalities. In 23%, etiologic associations were established from MRI alone and in 32% a clinically suspected etiology was supported. No children had myelination delay as the sole abnormality. In 23 children with minor motor delay, only 17% had abnormal scans. Clearly, MRI provided useful information in the majority of children with cerebral palsy; therefore, a classification system is proposed in which MRI can be used in conjunction with clinical assessment to specify more precisely the etiologic factors in cerebral palsy.

Atrophy↗

Detection of nucleic acids by cycling probe technology on magnetic particles: high sensitivity and ease of separation.

Cycling Probe Technology (CPT) is a signal amplification system that allows detection of nucleic acid target sequences without target amplification. CPT employs a sequence specific chimeric probe, typically DNA-RNA-DNA, which hybridizes to a complementary target DNA sequence and becomes a substrate for RNase H. Cleavage occurs at the RNA internucleotide linkages and results in dissociation of the probe from the target, thereby making it available for the next probe molecule. This communication describes the use of oligonucleotides attached to solid supports for target capture and release followed by solution and solid phase cycling. Through the attachment of chimeric probes to Sera-Mag magnetic particles (SMP) a simple and effective method of separating the cleaved probe from non-cycled probe has been developed. By capturing the target DNA on particles and separating it from the extraneous non-specific DNA we are able to dramatically reduce background and thus discriminate between samples of Methicillin Resistant (MRSA) and Methicillin Sensitive (MSSA) Staphylococcus Aureus. We conjugated oligonucleotide probes to SMPs (approximately 1 um) and Nylon beads (NB) which were coated with ID Biomedical's proprietary coating materials (R, patent pending). The general structure of the constructs is shown below: [table: see text]

Magnetics↗

Effects of radiographic contrast agents on spinal cord physiology.

Segmental reflexes in the spinal cords of cats anesthetized with chloralose were used to evaluate the neurophysiologic effects of radiographic contrast agents. The exposed lumbar spinal cord was bathed with concentrations of ionic and nonionic agents including saline, sodium meglumine diatrizoate, meglumine iothalamate, meglumine iocarmate, and metrizamide. The following responses were evaluated: flexor and extensor monosynaptic reflex; polysynaptic flexion reflexes; spontaneous ventral root activity. Hypertonic solutions generally produced a transient decrease in all reflex activity for up to 1 hour. Isotonic solutions produced no significant changes in the monosynaptic responses, but an increase in amplitude of polysynaptic responses, and increased spontaneous activity. The usual facilitory effects of flexion reflex on the flexor monosynaptic reflex were unchanged, but the expected inhibitory effect of flexion reflex on the extensor monosynaptic reflex was changed to excitatory. The relative ability to produced these effects was sodium meglumine diatrizoate greater than meglumine iothalamate greater than meglumine iocarmate greater than metrizamide.

Action Potentials↗

Neuronal effects of water-soluble contrast agents.

The in vitro rat hippocampus slice preparation has been utilized to examine the direct neurotoxicity of water-soluble contrast agents. Intraneuronal recordings were obtained from pyramidal cells in the CA1 field of rat hippocampus slices. Synaptic activity was evoked by Schaffer's collateral stimulation. The effects of Na-diatrizoate and metrizamide were studied. Test solutions were 300 to 345 mOsm and had iodine concentrations of 22.5 to 30 mg I/ml which are probably near clinical concentrations. The two effects of the contrast agents are apparent within 10 minutes and reversible within 30 to 45 minutes. The first is an epileptogenic property reflected by repetitive action potentials arising from an early prolonged depolarization. The second effect is a depression of electrical activity characterized by hyperpolarization of the resting membrane potential. Na-diatrizoate predominantly produced the first effect. Metrizamide principally produced the second effect. These results indicate that contrast agent seizure activity is not due to hyperosmolarity but a more direct chemical effect. The depression, however, may be related to a hyperosmolar effect. The differences between the dominant effects of the ionic vs. nonionic agents observed in these experiments seem to correlate with clinical experience and may indicate the etiology of central nervous system neurotoxicity of these drugs.

Action Potentials↗

Iohexol cerebral angiography. Multicenter clinical trial.

Ionic contrast media currently used in cerebral angiography frequently cause discomfort due to hyperosmolality. This double-blind, multicenter trial compared two ionic media, meglumine iothalamate and meglumine-Na diatrizoate, with the new nonionic agent, iohexol, in 277 patients undergoing cerebral angiography. Vital signs, cardiovascular changes, and neurologic status were evaluated before, during, and after injection. Patients were observed for adverse reactions for up to 24 hours following studies. Patient discomfort and image quality were evaluated. Visualization was good or excellent with all media studied. No significant physiological differences were observed between the ionic and iohexol groups, but fewer iohexol patients experienced large increases (greater than 20 mmHg) in systolic blood pressure. Iohexol patients experienced significantly less discomfort; ionic patients reported severe discomfort 21/2 times more often. This finding was attributed to iohexol's low osmolality. Iohexol may be indicated particularly for use in selective angiograms where discomfort is a factor and for patients suspected of having blood-brain barrier disruption.

Adult↗

Anatomical localization for PET using MR imaging.

Accurate localization of an imaging plane of interest is often needed prior to a positron emission tomographic (PET) study. We have developed a simple method for accurate and reproducible selection of an imaging plane for PET using magnetic resonance (MR) imaging. This method is useful when optimal sampling of specific brain structures, such as small subcortical nuclei, or when a specific imaging angle is required for the PET study. An external localizing device, consisting of a series of tubes visible on MR, is affixed to an individually fitted thermoplastic mask. This mask system is worn by the patient during both the MR and PET studies. A plane of interest is planned from the sagittal MR image and defined by its relation to the localizing device and to the MR scanner's "landmark" or reference position. This plane is transferred to the mask by means of a calibrated alignment laser. The coplanar acquisition of MR and PET images allows individualized analysis of brain structure-function relationships. Phantom studies demonstrated the accuracy and reproducibility of imaging plane selection by this method to be within 1 mm and 1 degree. Application of the localization protocol in a human subject is also presented.

Adult↗

Intradural spinal metastases in pediatric patients with primary intracranial neoplasms: Gd-DTPA enhanced MR vs CT myelography.

Recently, the application of intravenous gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) has been shown to improve the detection of intradural extramedullary spinal disease in adults. The ability of Gd-DTPA enhanced magnetic resonance (MR) to detect intradural extramedullary spinal metastases was studied in pediatric brain tumor patients. Spinal MR images before and after intravenous injection of Gd-DTPA were analyzed retrospectively in eight pediatric patients with known intracranial neoplasms and clinically suspected subarachnoid tumor seedings. Contrast enhanced spinal MR was compared with CT myelography in four of these patients. In our pediatric population Gd-DTPA enhanced images revealed tumor seeding not appreciable on noncontrast images. Although CT myelography has been the accepted standard investigation in the evaluation of suspected spinal metastases in children, we found that contrast enhanced MR is equal or superior in sensitivity to CT myelography. Spinal MR also provided information not obtainable via CT myelography. In the future, Gd-DTPA enhanced spinal MR should be considered in the initial evaluation of suspected subarachnoid spinal metastases in pediatric patients with known primary brain tumors.

Adolescent↗

A computerized approach for morphological analysis of the corpus callosum.

OBJECTIVE: A new technique for analyzing the morphology of the corpus callosum is presented, and it is applied to a group of elderly subjects. MATERIALS AND METHODS: The proposed approach normalizes subject data into the Talairach space using an elastic deformation transformation. The properties of this transformation are used as a quantitative description of the callosal shape with respect to the Talairach atlas, which is treated as a standard. In particular, a deformation function measures the enlargement/shrinkage associated with this elastic deformation. Intersubject comparisons are made by comparing deformation functions. RESULTS: This technique was applied to eight male and eight female subjects. Based on the average deformation functions of each group, the posterior region of the female corpus callosum was found to be larger than its corresponding region in the males. The average callosal shape of each group was also found, demonstrating visually the callosal shape differences between the two groups in this sample. CONCLUSION: The proposed methodology utilizes the full resolution of the data, rather than relying on global descriptions such as area measurements. The application of this methodology to an elderly group indicated sex-related differences in the callosal shape and size.

Aged↗

An image-processing system for qualitative and quantitative volumetric analysis of brain images.

In this work, we developed, implemented, and validated an image-processing system for qualitative and quantitative volumetric analysis of brain images. This system allows the visualization and quantitation of global and regional brain volumes. Global volumes were obtained via an automated adaptive Bayesian segmentation technique that labels the brain into white matter, gray matter, and cerebrospinal fluid. Absolute volumetric errors for these compartments ranged between 1 and 3% as indicated by phantom studies. Quantitation of regional brain volumes was performed through normalization and tessellation of segmented brain images into the Talairach space with a 3D elastic warping model. Retest reliability of regional volumes measured in Talairach space indicated errors of < 1.5% for the frontal, parietal, temporal, and occipital brain regions. Additional regional analysis was performed with an automated hybrid method combining a region-of-interest approach and voxel-based analysis, named Regional Analysis of Volumes Examined in Normalized Space (RAVENS). RAVENS analysis for several subcortical structures showed good agreement with operator-defined volumes. This system has sufficient accuracy for longitudinal imaging data and is currently being used in the analysis of neuroimaging data of the Baltimore Longitudinal Study of Aging.

Aged↗

A probabilistic ribbon model for shape analysis of the cerebral sulci: application to the central sulcus.

PURPOSE: An approach for quantifying the shapes of the cerebral sulci is presented, utilizing a probabilistic geometric model, and it is applied to the central sulcus. METHOD: The geometric structure of the central sulcus is determined from a set of outlines on cross-sectional images and is used by a procedure that automatically labels the major crest lines, i.e., curves of locally maximal curvature, along the sulcus. An automated procedure then determines a parametric representation of the central sulcus that is consistent across individuals, in that it assigns the same parametric coordinates to corresponding regions of the sulcus. RESULTS: The method is applied to the central sulci from 20 subjects. The use of this shape representation in cortical morphometric analysis applications is demonstrated, in particular in obtaining local depth and curvature measurements of a sulcus as well as in determining average shapes and variability. CONCLUSION: With this method, we were able to build parametric representations of the sulcal ribbons by preserving anatomical homologies.

Anatomy, Cross-Sectional↗

Accurate T2 NMR images.

We present a method for producing accurate calculated T2 nuclear magnetic resonance (NMR) images. A modified Carr-Purcell-Meiboom-Gill pulse sequence is used to obtain a series of images with progressive T2 dependence. This image series is then analyzed pixel by pixel to generate a T2 and initial signal strength image. Tests performed using four samples of known T2 indicate accuracies of better than 9%.

Image Enhancement↗

Accurate T1 and spin density NMR images.

We present a method for producing accurate calculated T1 and spin density nuclear magnetic resonance images. A modified Carr-Purcell-Meiboom-Gill pulse sequence is used to obtain a series of images containing both T1 and T2 dependence. The image series is first analyzed to remove the T2 dependence. The resulting images are then analyzed, pixel by pixel, to generate an image containing T1 values and an image containing values proportional to spin density (SD). Tests performed on two phantoms containing solutions of various known T1's and H2O/D2O concentrations indicate that the T1 image values are accurate to better than 11% and the relative SD values agree to within one standard deviation.

Humans↗

Quantitative proton MR spectroscopic imaging in acute disseminated encephalomyelitis.

Serial MR imaging and quantitative proton MR spectroscopic imaging (MRSI) findings of a 4-year-old boy with acute disseminated encephalomyelitis (ADEM) are reported. Over a 2-month period characterized by an initial illness and two relapses, each with full recovery, MR imaging exhibited the appearance and disappearance of multifocal lesions throughout the CNS that correlated only partly with the neurologic impairment. During one relapse, MRSI revealed low levels of N-acetylaspartate (NAA) within the regions of prolonged T2 signal intensity. All other metabolites were normal. At follow-up, the MR imaging and MRSI abnormalities had fully resolved. MRSI might play an important role in the diagnosis of ADEM, as well as in the elucidation of underlying pathophysiologic processes in this poorly defined disorder of children. This case demonstrates that reduced levels of NAA are not always associated with neuronal loss, irreversible tissue damage, or poor neurologic outcome.

Aspartic Acid↗

Diagnosis of acute cerebral infarction: comparison of CT and MR imaging.

The appearance of acute cerebral infarction was evaluated on MR images and CT scans obtained in 31 patients within 24 hr of the ictus; follow-up examinations were performed 7-10 days later in 20 of these patients and were correlated with the initial studies. Acute infarcts were visible more frequently on MR images than on CT scans (82% vs 58%). Proton density- and T2-weighted scans usually demonstrated regions of hyperintensity corresponding to acute infarcts, but proton density-weighted scans often showed better definition of the lesion in terms of regional anatomy. Follow-up MR images and CT scans identified approximately 88% of subacute strokes, 54% of which were better defined and/or larger than on the initial examination. In 20% of lesions, "hemorrhagic" characteristics were seen on at least one examination. CT and MR imaging were comparable in delineating acute hemorrhage, but MR detected more cases with evidence of hemorrhage on follow-up examinations. MR appears to be more sensitive than CT in the imaging of acute stroke.

Acute Disease↗

Mechanisms of MR signal alteration by acute intracerebral blood: old concepts and new theories.

We reviewed the current literature and theories pertaining to the appearance of hemorrhage on MR images. New theories were formulated to explain the etiology of spin-echo (SE) and gradient-echo contrast on clinical MR images of hematomas at low and intermediate field strengths. It is our hope that these theories will prompt further experiments to prove or disprove their validity. The discussion of SE contrast focuses on the powerful MR effects mediated by changes in protein concentration. These changes are postulated to occur as a result of (1) clot matrix formation; (2) settling of RBCs, which increases the number of RBCs per unit volume and the total protein concentration; and (3) alterations in intracellular protein concentration caused by changes in RBC hydration. The contribution of acid methemoglobin to image contrast via the proton electron dipole-dipole mechanism is also included. The discussion of gradient-echo contrast focuses on the inhomogeneity that may be present within voxels that contain a blood clot. This inhomogeneity results when the voxel contains regions with different magnetic susceptibilities (i.e., clumped RBCs and serum). Two temporally arranged schemata for T2-weighted and T1-weighted SE scans are presented that illustrate how these factors might interact to explain the diverse appearance of hematomas on clinical SE images. The signal intensity on T2-weighted SE scans appears to be dependent primarily on the state of hydration of the RBC. This factor and the presence or absence of methemoglobin appear to be the major factors that govern contrast on T1-weighted SE images.

Acute Disease↗

MR imaging of intracerebral blood: diversity in the temporal pattern at 0.5 and 1.0 T.

MR scans were obtained at 0.5 and 1.0 T in 40 patients with 46 intracerebral hematomas categorized as hyperacute (0-2 days), acute (3-7 days), subacute (8-14 days), and chronic (15 days to 6 years). In a retrospective review, the signal intensity of the lesions was compared with that of normal white matter of the brain on spin-density, T1-, and T2-weighted spin-echo and T1-weighted gradient-echo sequences. The classic appearance and evolution of hematomas described in the literature at 1.5 T were not found in a significant number of the cases reviewed. In the hyperacute group, only five of eight hematomas had signal intensities that were hypointense relative to brain on T2-weighted images. Two of eight hyperacute hematomas were hyperintense relative to brain on the T1-weighted spin-echo images. However, T1-weighted gradient-echo images reliably demonstrated a hypointense signal in some portion of the hematoma in 45 of 46 cases. We conclude that while there is no constant temporal pattern on spin-echo or gradient-echo sequences, there are signal-intensity changes suggestive of hemorrhage in nearly all hematomas imaged at 0.5 and 1.0 T. Although the inconsistency may be frustrating from a diagnostic standpoint, this variability may reveal important individual differences in hematomas and the brain that surrounds them, and thus be clinically significant. Before these data can be mechanistically analyzed, the reason for contrast on MR scans of hematoma must be better understood.

Cerebral Hemorrhage↗