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Biomedical subjects

Victor M Haughton

Publications and source records attributed to Victor M Haughton.

9 recordsLinked to original sources
PubMed2003

Peak systolic and diastolic CSF velocity in the foramen magnum in adult patients with Chiari I malformations and in normal control participants.

BACKGROUND AND PURPOSE: Abnormal flow of CSF through the foramen magnum has been implicated in the pathogenesis of clinical deficits in association with Chiari I malformation. The purpose of this study was to test the hypothesis that peak CSF velocities in the foramen magnum are increased in patients with Chiari I malformations. METHODS: Eight adult patients with symptomatic Chiari I malformations and 10 adult volunteers were studied with cardiac gated, phase-contrast MR imaging in the axial plane at the foramen magnum. The spatial uniformity of flow velocity in the foramen magnum was assessed at 14 time frames within the R-R interval. The velocity in each of the voxels at each of the time frames was calculated, and the peak systolic and diastolic velocities were tabulated for the patients and controls. RESULTS: For the normal volunteers, the CSF velocities in the subarachnoid space were relatively uniform throughout the subarachnoid space at each of the time frames. Peak systolic velocity ranged from 1.2 to 3.3 cm/s, and peak diastolic velocity ranged from 1.6 to 4.5 cm/s. In symptomatic patients with Chiari I, velocities in the foramen magnum did not appear as uniform throughout the subarachnoid space in the phase-contrast images. Peak systolic velocities ranged from 1.8 to 4.8 cm/s, and peak diastolic velocities ranged from 2.5 to 5.3 cm/s. Peak systolic velocity was significantly higher (P =.01) in the patients than in the control volunteers. CONCLUSION: Patients with Chiari I malformations have significant elevations of peak systolic velocity in the CSF in the foramen magnum.

Adult↗
PubMed2002

Independent component analysis applied to diffusion tensor MRI.

The accuracy of the outcome in a diffusion tensor imaging (DTI) experiment depends on the acquisition scheme as well as the postprocessing methods used. In the present study, the DTI results acquired after applying different combinations of diffusion-weighted (DW) gradient orientations were initially compared. Then, spatially independent component analysis (ICA) was applied to the T(2) and DW images. In all cases a single component was detected that was similar to the map of the trace of the diffusion tensor, but contained a reduced amount of noise. Furthermore, when no correction for eddy current artifacts was used in the image acquisition scheme, the effects of eddy currents were separated by ICA into independent components. After these components were removed, conventional estimation of the diffusion tensor was performed on the modified data. No artifact was contained in the final rotationally invariant scalar quantities that describe the intrinsic diffusion properties. Additionally, independent components that mapped major white matter fiber tracts in the human brain were identified. Finally, the noise included in the original T(2) and DW images was also separated by ICA into independent components. These components were subsequently removed and a reduction of noise in the final DTI results was achieved.

Adult↗
PubMed2002

Application of image registration to measurement of intervertebral rotation in the lumbar spine.

In this study, the precision and accuracy of a new method for measuring axial rotations of the lumbar vertebrae, which are thought to be increased in patients with degenerative spinal instability, were estimated. A standard image registration algorithm involving a user-selected center of rotation was adapted for this purpose. Accuracy was tested on a phantom containing a rotating lumbar vertebra. Calculated rotations were compared to the known values. Images were also obtained in subjects, using a tilting table that provided rotation between thorax and hips. For these measurements precision was estimated by varying the center of rotation. In the phantom the method had an accuracy of 0.2 degrees. In the human subject measurements the precision was 0.60-1.5 degrees. The method measured rotations of lumbar vertebrae with sufficient accuracy and precision to detect clinically significant differences in patients with back pain.

Biomechanical Phenomena↗
PubMed2002

Preoperative mapping of the supplementary motor area in patients harboring tumors in the medial frontal lobe.

OBJECT: Injury to the supplementary motor area (SMA) is thought to be responsible for transient motor and speech deficits following resection of tumors involving the medial frontal lobe. Because direct intraoperative localization of SMA is difficult, the authors hypothesized that functional magnetic resonance (fMR) imaging might be useful in predicting the risk of postoperative deficits in patients who undergo resection of tumors in this region. METHODS: Twelve patients who had undergone fMR imaging mapping while performing speech and motor tasks prior to excision of their tumor, that is, based on anatomical landmarks involving the SMA, were included in this study. The distance between the edge of the tumor and the center of SMA activation was measured and was correlated with the risk of incurring postoperative neurological deficits. In every patient, SMA activation was noted in the superior frontal gyrus on preoperative fMR imaging. Two speech and two motor deficits typical of SMA injury were observed in three of the 12 patients. The two speech deficits occurred in patients with tumors involving the dominant hemisphere, whereas one of the motor deficits occurred in a patient with a tumor in the nondominant hemisphere. The risk of developing a postoperative speech or motor deficit was 100% when the distance between the SMA and the tumor was 5 mm or less. When the distance between SMA activation and the lesion was greater than 5 mm, the risk of developing a motor or a speech deficit was 0% (p = 0.0007). CONCLUSIONS: Early data from this study indicated that fMR imaging might be useful in localizing the SMA and in determining the risk of postoperative deficits in patients who undergo resection of tumors located in the medial frontal lobe.

Adult↗
PubMed2002

Comparison of independent component analysis and conventional hypothesis-driven analysis for clinical functional MR image processing.

BACKGROUND AND PURPOSE: With independent component analysis (ICA), regions of activation can be identified on functional MR (fMR) images without a priori knowledge of expected hemodynamic responses. The purpose of this study was to compare the results of fMR imaging data processed with spatial ICA with results obtained with conventional hypothesis-driven analysis. METHODS: Eleven patients with focal cerebral lesions and one with agenesis of the corpus callosum were enrolled. Each patient performed text-listening, finger-tapping, and word-generation tasks. Conventional activation maps were generated by fitting time courses of each voxel to a boxcar reference function. Maps were created from the same image data with ICA techniques. To compare the maps, a concurrence ratio (CR) (number of voxels activated on both maps to number of voxels activated on either map) was calculated. RESULTS: In the ICA analysis, maps with appropriate spatial and temporal features for auditory, sensorimotor, or language cortices were identified in most patients. Images processed with ICA resembled images processed with conventional means. In patients who moved or performed the task incorrectly, ICA produced a map that resembled the expected activation pattern but differed from the conventional image. CRs averaged 70% for all comparisons in the 12 patients. CONCLUSION: fMR imaging maps for auditory, sensorimotor, and language tasks produced with ICA and conventional techniques were similar in most cases. Differences were consistent with the particular characteristics of the method. In data sets corrupted by motion or incorrect task performance, ICA may produce more accurate maps.

Arousal↗
PubMed2002

Diffusion tensor MR imaging in diffuse axonal injury.

BACKGROUND AND PURPOSE: Disruption of the cytoskeletal network and axonal membranes characterizes diffuse axonal injury (DAI) in the first few hours after traumatic brain injury. Histologic abnormalities seen in DAI hypothetically decrease the diffusion along axons and increase the diffusion in directions perpendicular to them. DAI therefore is hypothetically associated in the short term with decreased diffusion anisotropy. We tested this hypothesis by measuring the diffusion characteristics of traumatized brain tissue with use of diffusion tensor MR imaging. METHODS: Five patients with mild traumatic brain injuries and 10 control subjects were studied with CT, conventional MR imaging, and diffusion tensor imaging. All patients were examined within 24 hours of injury. In each participant, diffusion tensor indices from homologous normal-appearing white matter regions of both hemispheres were compared. These indices were also compared between homologous regions of each patient and the control group. In two patients, diffusion tensor images from the immediate post-trauma period were compared with those at 1 month follow-up. RESULTS: Patients displayed significant reduction of diffusion anisotropy in several regions compared with the homologous ones in the contralateral hemisphere. Such differences were not observed in the control subjects. Significant reduction of diffusion anisotropy was also detected when diffusion tensor results from the patients were compared with those of the controls. This reduction was often less evident 1 month after injury. CONCLUSION: White matter regions with reduced anisotropy are detected in the first 24 hours after traumatic brain injury. Therefore, diffusion tensor imaging may be a powerful technique for in vivo detection of DAI.

Adult↗
PubMed2002

Measuring the axial rotation of lumbar vertebrae in vivo with MR imaging.

BACKGROUND AND PURPOSE: Flexion-extension radiography is neither sensitive nor specific in the diagnosis of degenerative spinal instability, a presumed cause of back pain and an indication for spinal fusion. We tested the hypothesis that with MR imaging and a device to rotate the torso, axial rotations of lumbar vertebrae can be measured with sufficient accuracy and that significantly different rotations can be detected between lumbar segments with degenerated disks and those with normal disks. METHODS: We studied five volunteers without back pain (group 1), five patients who underwent MR imaging because of back pain but were not considered candidates for fusion (group 2), and five patients in whom diskography identified one or more disks with concordant pain (group 3). Each participant was placed on a specially built table that provided separate supports for the torso and for the hips and legs. Series of sagittal images were acquired with a T2-weighted fast spin-echo sequence, with the torso rotated clockwise and then counterclockwise. The amount of rotation was calculated from axial images with use of an automated program. RESULTS: In the five volunteers, rotations of the lumbar motion segments varied between -1.8 degrees and 5.7 degrees, with an average of 0.8 degrees. The abnormal disks in five patients in group 2 rotated from -0.9 degrees to 5.6 degrees, with an average of 3.2 degrees. In group 3, the disks in which concordant pain was elicited rotated from 0.8 degrees to 4.4 degrees, with an average of 2.2 degrees. Difference in rotation between abnormal and normal disks was statistically significant. CONCLUSION: Measurements of rotations of lumbar vertebrae with MR imaging may have value for determining levels that move abnormally in axial rotation.

Adult↗
PubMedDate not supplied

Confounding effect of large vessels on MR perfusion images analyzed with independent component analysis.

BACKGROUND AND PURPOSE: First pass contrast-enhanced MR imaging using gradient-echo acquisitions is commonly used to assess cerebral blood flow, despite the confounding signal from large blood vessels. We hypothesized that removal of this unwanted intravascular signal using independent component analysis would result in a more accurate depiction of cerebral blood flow. METHODS: Images of 11 patients, acquired with our acute stroke imaging protocol, were post processed to produce images of relative cerebral blood flow (rCBF). The same images were processed with independent component analysis to identify and remove the signal from large blood vessels, with a second set of rCBF images produced. Both sets of rCBF maps were pooled, randomized in order, and read in a blinded fashion by two neuroradiologists to assess the level of large artery artifact and overall image quality. Significance was determined using a Wilcoxon signed rank test. RESULTS: Results from both readers indicated that the level of large artery artifact was significantly reduced in the images processed using independent component analysis component removal (P <.05). In addition, both readers indicated significantly (P <.05) improved image quality of the images processed using independent component analysis. CONCLUSION: The removal of the signal resulting from large blood vessels before calculation of rCBF resulted in images with significantly less artifact and higher image quality.

Adolescent↗