Biomedical subjects

J C Falconer

Publications and source records attributed to J C Falconer.

6 recordsLinked to original sources

PubMed1997

Cerebrospinal fluid-suppressed high-resolution diffusion imaging of human brain.

A cerebrospinal fluid (CSF)-suppressed flow-attenuated inversion recovery (FLAIR) double-shot diffusion echo-planar imaging (EPI) sequence was developed and used, along with a non-CSF-suppressed version of the sequence, to determine the extent of the contribution of CSF partial-volume averaging to the apparent diffusion coefficients (ADCs) of normal human brain in vivo. Regional analysis indicates that cortical gray matter and parenchymal tissues bordering the ventricles are most affected by CSF contamination, leading to elevated ADC values. Only slight differences in gray- and white-matter average ADCs were detected after CSF suppression. The human brain average ADCs calculated from high-resolution CSF-suppressed diffusion-weighted images in these studies are similar to those reported in animals. FLAIR diffusion sequences remove CSF as a source of error in ADC determination and ischemic lesion discrimination in diffusion-weighted images (DWI) and ADC maps.

Brain↗

PubMed1996

Characterization of an experimental spinal cord injury model using waveform and morphometric analysis.

STUDY DESIGN: A weight-drop device based on a displacement transducer and feedback detection circuitry was designed to produce consistent experimental spinal cord injuries in a rat model. The device was characterized and evaluated based on biomechanical parameters, quantitative histology, and neurologic behavior. OBJECTIVE: To develop, characterize, and evaluate a spinal cord injury device for use in animal models. SUMMARY OF BACKGROUND DATA: The biomechanical parameters of spinal cord injury, including compression, velocity, force, energy, impulse-momentum, and power, can be derived from the displacement waveform. It has been shown that the magnitude and variability of certain of these injury parameters are correlated with lesion size and neurologic deficit. METHODS: Two groups of six male Sprague-Dawley rats were injured using the device and their injury displacement waveforms digitally recorded on a personal computer equipped with a data acquisition board. Group 1 animals were sacrificed immediately after injury, whereas Group 2 animals were sacrificed 14 days after injury. Quantitative morphometric and numerical analyses were performed on histologic specimens and injury waveforms, respectively. Biomechanical injury parameters were compared with histologic and behavioral measures of injury. RESULTS: All kinetic injury parameters were reproducible to within standard deviations of less than +/- 22%, whereas spinal cord displacement variability was +/- 29%. Motor scores for animals on day 14 animals were 4.3 +/- 0.4, whereas lesion sizes were much more variable, exhibiting percent volumes of 5.5 +/- 2.5 immediately after injury, and 11.9 +/- 7.1 on day 14. CONCLUSION: This device should benefit studies of experimental spinal cord injury in animals by reducing interanimal variations in injury severity, especially in the acute phase of injury.

Animals↗

PubMed1996

Time dependence of N-acetyl-aspartate, lactate, and pyruvate concentrations following spinal cord injury.

The time dependence of N-acetyl-aspartate (NAA) concentrations relative to lactate and pyruvate in the injured rat spinal cord was investigated. Segments of spinal cord from regions rostral, caudal, and at the epicenter of the injury were analyzed. NAA concentrations were determined by gas chromatography-mass spectrometry and lactate and pyruvate concentrations were determined by UV spectroscopy at 20 min, 60 min, 2 h, 8 h, 24 h, 3 days, and 1 week after injury. NAA levels fell most significantly at the epicenter of the injury, reaching 30% of basal levels within 24 h. In all segments, lactate levels increased significantly shortly after injury, peaking at two to five times normal basal levels between 20 and 60 min after injury. Rostral and caudal to the injury site, lactate elevations and NAA reductions were less dramatic. Pyruvate concentrations were not significantly altered in any of the sections after injury. The temporal and spatial relationships of NAA and lactate changes indicated that ischemic conditions due to injury in the upper thoracic rat spinal cord were distributed asymmetrically. Acute ischemia was more severely caudal to the injury site, and NAA concentrations were more severely impaired in the rostral direction. The results suggest that the extent of neuronal degeneration due to spinal cord injury does not correlate directly with acute ischemic severity as measured by the lactate/pyruvate ratio, and may be more closely related to secondary changes in the neuronal environment.

Animals↗

PubMed1994

MRI scanner transport system.

A computer-controlled transport system has been designed and tested for small bore magnetic resonance scanners for animal research. The transport system allows remote animal positioning based on scout images using a graphic interface. The design utilized commercially available components suitable for use in the scanner's strong magnetic field. Tests indicate positioning accuracy of the transport system to be within 0.13 mm.

Animals↗

PubMed1994

Quantitative MRI of spinal cord injury in a rat model.

Sequential in vivo MRI studies of experimental spinal cord injuries (SCI) were performed using a three-dimensional implementation of the FATE (Fast low-Angle spin echo sequence with short TE) sequence. MRI-observed pathology was quantified using a multispectral segmentation algorithm. Neurological analysis was performed on the same animals concurrently, in addition to end-point histology, for comparison with quantitative MRI results. These studies suggest that it is possible to use MRI to detect the onset of secondary injury in the spinal cord. The data also indicate that early detection of MRI-visible pathology may provide the necessary markers for predicting the long-term level of neurologic deficit.

Algorithms↗

PubMedDate not supplied

Reproducibility of nonparametric feature map segmentation for determination of normal human intracranial volumes with MR imaging data.

Semiautomated segmentation of dual-contrast magnetic resonance images was used to determine volumes of total brain, gray matter, white matter, and cerebrospinal fluid (CSF) in healthy volunteers. Reproducibility of the technique was evaluated in terms of intraobserver, interobserver, and study-to-study variations. Intraobserver coefficients of variation ranged from 0.4% to 6.0%, while interobserver values ranged from 0.8% to 9.9%. In both cases, the maximum variations were obtained in volume measurements of tissues with maximum complexity (ie, CSF), and the minimum variation was obtained in determining total brain volume. This was also true in the case of study-to-study variations in volume measurements, for which the coefficients of variation ranged from 0.5% to 8.7%. The use of appropriate preprocessing techniques, which are crucial to the accuracy and reproducibility of the segmentation technique, are described in detail.

Adult↗