Biomedical subjects

V M Haughton

Publications and source records attributed to V M Haughton.

At least 19 recordsLinked to original sources

PubMed2002

Test-retest precision of functional magnetic resonance imaging processed with independent component analysis.

This study was designed to compare the test-retest precision of functional magnetic resonance imaging (fMRI) data processed with independent component analysis (ICA) and the same data analyzed with a conventional model-dependent method (Student's- t mapping). Volunteers underwent two or three iterations of visual and auditory stimuli, while data were collected for fMRI scans. The scan data were separately processed with ICA and with Student's- t mapping (STM). As a measure of test-retest precision, concurrence ratios were calculated for each subject and each task as the number of voxels that were activated by two iterations of a task divided by the average number of voxels activated in each repetition. In 28 test-retest comparisons, the average concurrence ratio was 0.69+/-0.10 for ICA and 0.65+/-0.13 for the conventional method, a statistically insignificant difference. In fMR image data of block stimulus paradigms, ICA had similar test-retest precision to a conventional model-dependent method.

Acoustic Stimulation↗

PubMed2001

Morphologic changes in the lumbar intervertebral foramen due to flexion-extension, lateral bending, and axial rotation: an in vitro anatomic and biomechanical study.

STUDY DESIGN: A biomechanical and anatomic study with human cadaveric lumbar spine. OBJECTIVES: The purpose of this study is to examine the morphologic changes in the intervertebral foramen during flexion, extension, lateral bending, and axial rotation of the lumbar spine and to correlate these changes with the flexibility of the spinal motion segments. SUMMARY OF BACKGROUND DATA: Previous studies showed morphologic changes in the intervertebral foramen during flexion and extension; however, those changes during lateral bending and axial rotation were not well known. METHODS: There were 81 motion segments obtained from 39 human cadaveric lumbar spines (mean age 69 years). The motion segments were imaged with CT scanner with 1-mm thick consecutive sections. For biomechanical testing each motion segment was applied with incremental pure moments of flexion, extension, lateral bending, and axial rotation. Rotational movements of the motion segment were measured using VICON cameras. After application of the last load, the specimens were frozen under load, and then CT was performed with the same technique described above. Six parameters of the intervertebral foramen were measured, including foraminal width (maximum and minimum), foraminal height, disc bulging, thickness of ligamentum flavum, and cross-sectional area of the foramen. RESULTS: Flexion increased the foraminal width (maximum and minimum), height, and area significantly while significantly decreasing the disc bulging and thickness of ligamentum flavum (P < 0.05). However, extension decreased the foraminal width (maximum and minimum), height, and area significantly. Lateral bending significantly decreased the foraminal width (maximum and minimum), height, and area at the bending side, whereas lateral bending significantly increased the foraminal width (minimum), height, and area at the opposite side of bending. Likewise, axial rotation decreased the foraminal width (minimum) and area at the rotation side significantly while significantly increasing the foraminal height and foraminal area at the opposite side. The percent change in the foraminal area was found significantly correlated with the amount of segmental spinal motion except for the extension motion. CONCLUSIONS: This study showed that the intervertebral foramen of the lumbar spine changed significantly not only on flexion-extension but also on lateral bending and axial rotation. The percent change in cross-sectional foraminal area was correlated with the amount of segmental motion except for extension motions. Further studies are needed to assess the morphologic changes in the intervertebral foramen in vivo and to correlate clinically.

Adult↗

PubMed2001

Functional MR imaging assessment of a non-responsive brain injured patient.

Functional magnetic resonance imaging (fMRI) was requested to assist in the evaluation of a comatose 38-year-old woman who had sustained multiple cerebral contusions from a motor vehicle accident. Previous electrophysiologic studies suggested absence of thalamocortical processing in response to median nerve stimulation. Whole-brain fMRI was performed utilizing visual, somatosensory, and auditory stimulation paradigms. Results demonstrated intact task-correlated sensory and cognitive blood oxygen level dependent (BOLD) hemodynamic response to stimuli. Electrodiagnostic studies were repeated and evoked potentials indicated supratentorial recovery in the cerebrum. At 3-months post trauma the patient had recovered many cognitive & sensorimotor functions, accurately reflecting the prognostic fMRI evaluation. These results indicate that fMRI examinations may provide a useful evaluation for brain function in non-responsive brain trauma patients.

Accidents, Traffic↗

PubMed2001

Frequencies contributing to functional connectivity in the cerebral cortex in "resting-state" data.

BACKGROUND AND PURPOSE: In subjects performing no specific cognitive task ("resting state"), time courses of voxels within functionally connected regions of the brain have high cross-correlation coefficients ("functional connectivity"). The purpose of this study was to measure the contributions of low frequencies and physiological noise to cross-correlation maps. METHODS: In four healthy volunteers, task-activation functional MR imaging and resting-state data were acquired. We obtained four contiguous slice locations in the "resting state" with a high sampling rate. Regions of interest consisting of four contiguous voxels were selected. The correlation coefficient for the averaged time course and every other voxel in the four slices was calculated and separated into its component frequency contributions. We calculated the relative amounts of the spectrum that were in the low-frequency (0 to 0.1 Hz), the respiratory-frequency (0.1 to 0.5 Hz), and cardiac-frequency range (0.6 to 1.2 Hz). RESULTS: For each volunteer, resting-state maps that resembled task-activation maps were obtained. For the auditory and visual cortices, the correlation coefficient depended almost exclusively on low frequencies (<0.1 Hz). For all cortical regions studied, low-frequency fluctuations contributed more than 90% of the correlation coefficient. Physiological (respiratory and cardiac) noise sources contributed less than 10% to any functional connectivity MR imaging map. In blood vessels and cerebrospinal fluid, physiological noise contributed more to the correlation coefficient. CONCLUSION: Functional connectivity in the auditory, visual, and sensorimotor cortices is characterized predominantly by frequencies slower than those in the cardiac and respiratory cycles. In functionally connected regions, these low frequencies are characterized by a high degree of temporal coherence.

Adult↗

PubMed2001

Reliability of functional MR imaging with word-generation tasks for mapping Broca's area.

BACKGROUND AND PURPOSE: Functional MR (fMR) imaging of word generation has been used to map Broca's area in some patients selected for craniotomy. The purpose of this study was to measure the reliability, precision, and accuracy of word-generation tasks to identify Broca's area. METHODS: The Brodmann areas activated during performance of word-generation tasks were tabulated in 34 consecutive patients referred for fMR imaging mapping of language areas. In patients performing two iterations of the letter word-generation tasks, test-retest reliability was quantified by using the concurrence ratio (CR), or the number of voxels activated by each iteration in proportion to the average number of voxels activated from both iterations of the task. Among patients who also underwent category or antonym word generation or both, the similarity of the activation from each task was assessed with the CR. In patients who underwent electrocortical stimulation (ECS) mapping of speech function during craniotomy while awake, the sites with speech function were compared with the locations of activation found during fMR imaging of word generation. RESULTS: In 31 of 34 patients, activation was identified in the inferior frontal gyri or middle frontal gyri or both in Brodmann areas 9, 44, 45, or 46, unilaterally or bilaterally, with one or more of the tasks. Activation was noted in the same gyri when the patient performed a second iteration of the letter word-generation task or second task. The CR for pixel precision in a single section averaged 49%. In patients who underwent craniotomy while awake, speech areas located with ECS coincided with areas of the brain activated during a word-generation task. CONCLUSION: fMR imaging with word-generation tasks produces technically satisfactory maps of Broca's area, which localize the area accurately and reliably.

Brain Mapping↗

PubMed2000

The effect of disc degeneration and facet joint osteoarthritis on the segmental flexibility of the lumbar spine.

STUDY DESIGN: A biomechanical and imaging study of human cadaveric spinal motion segments. OBJECTIVE: To investigate the effect of both disc degeneration and facet joint osteoarthritis on lumbar segmental motion. SUMMARY OF BACKGROUND DATA: Spinal degeneration includes the osteoarthritic changes of the facet joint as well as disc degeneration. Disc degeneration has been reported to be associated with spinal motion. The association of facet joint osteoarthritis with lumbar segmental motion characteristics and the combined influence of disc degeneration and facet osteoarthritis has not yet been investigated. METHODS: A total of 110 lumbar motion segments (52 female, 58 male) from 44 human lumbar spines were studied (mean age = 69 years). Magnetic resonance images were used to assess the disc degeneration from Grade I (normal) to Grade V (advanced) and the osteoarthritic changes in the facet joints in terms of cartilage degeneration, subchondral sclerosis, and osteophytes. Disc height, endplate size, and facet joint orientation and width also were measured from the computed tomographic images. Rotational movements of the motion segment in response to the flexion, extension, lateral bending, and axial rotational moments were measured using a three-dimensional motion analysis system. RESULTS: Female motion segments showed significantly greater motion (lateral bending: P < 0. 001, flexion: P < 0.01, extension: P < 0.05) and smaller endplate size (P < 0.001) than male ones. The segmental motion increased with increasing severity of disc degeneration up to Grade IV, but decreased in both genders when the disc degeneration advanced to Grade V. In male segments, the disc degeneration-related motion changes were significant in axial rotation (P < 0.001), lateral bending (P < 0.05), and flexion (P < 0.05), whereas female segments showed significant changes only in axial rotation (P < 0.001). With cartilage degeneration of the facet joints, the axial rotational motion increased, whereas the lateral bending and flexion motion decreased in female segments. In male segments, however, motion in all directions increased with Grade 3 cartilage degeneration and decreased with Grade 4 cartilage degeneration. Subchondral sclerosis significantly decreased the motion (female: axial rotation, P < 0. 05; extension, P < 0.05 vs.- male:flexion,P < 0.05). Severity of osteophytes had no significant association with the segmental motion. CONCLUSION: Axial rotational motion was most affected by disc degeneration, and the effects of disc degeneration on the motion were similar between genders. Facet joint osteoarthritis also affected segmental motion, and the influence differed for male and female spines. Further studies are needed to clarify whether the degenerative process of facet joint osteoarthritis differs between genders and how facet joint osteoarthritis affects the stability of the spinal motion segment.

Cadaver↗

PubMed2000

Combining independent component analysis and correlation analysis to probe interregional connectivity in fMRI task activation datasets.

A new approach in studying interregional functional connectivity using functional magnetic resonance imaging (fMRI) is presented. Functional connectivity may be detected by means of cross correlating time course data from functionally related brain regions. These data exhibit high temporal coherence of low frequency fluctuations due to synchronized blood flow changes. In the past, this fMRI technique for studying functional connectivity has been applied to subjects that performed no prescribed task ("resting" state). This paper presents the results of applying the same method to task-related activation datasets. Functional connectivity analysis is first performed in areas not involved with the task. Then a method is devised to remove the effects of activation from the data using independent component analysis (ICA) and functional connectivity analysis is repeated. Functional connectivity, which is demonstrated in the "resting brain," is not affected by tasks which activate unrelated brain regions. In addition, ICA effectively removes activation from the data and may allow us to study functional connectivity even in the activated regions.

Adult↗

PubMed2000

Pediatric epilepsy surgery: neuroimaging, neuropsychology, and anticonvulsants.

Neuroimaging and the neuropsychological evaluation are important components of the presurgical evaluation for epilepsy surgery. Advances in neuroimaging over the last decade, to a large part, underlie improvements in pediatric epilepsy surgery outcomes. The neuropsychological evaluation plays an important role in the evaluation of the older child and adolescent, particularly in the evaluation of mesial temporal sclerosis. However, its role in the young child being considered for surgery remains to be defined. This section reviews the definition of medical intractability, issues related to medication withdrawal during video-EEG monitoring, recent neuroimaging advances, and the neuropsychological evaluation.

Adolescent↗

PubMed2000

Magnetic resonance imaging in patients with central nervous system pathology: a comparison of OptiMARK (Gd-DTPA-BMEA) and Magnevist (Gd-DTPA).

RATIONALE AND OBJECTIVES: The objective of the two pivotal phase 3 studies was to evaluate the safety and efficacy of OptiMARK (Gd-DTPA-bis(methoxyethylamide) [Gd-DTPA-BMEA]) compared with Magnevist (Gd-DTPA) in magnetic resonance imaging of the central nervous system. METHODS: Two multicenter, randomized, double-blind, parallel group studies were conducted in 395 patients with known or suspected central nervous system pathology. Subjects were randomized to receive a single 0.1 mmol/kg intravenous injection of either Gd-DTPA-BMEA or Gd-DTPA. The safety of Gd-DTPA-BMEA and Gd-DTPA was monitored for up to 72 hours after study drug administration. Precontrast and postcontrast administration magnetic resonance scans were acquired using identical imaging planes and techniques. RESULTS: No deaths or unexpected adverse events were reported in either group. A comparison of adverse events by intensity and relation demonstrated no statistically significant differences between the two groups. Gd-DTPA-BMEA and Gd-DTPA were equivalent with respect to confidence in diagnosis, conspicuity, and border delineation. CONCLUSIONS: Gd-DTPA-BMEA and Gd-DTPA demonstrated comparable efficacy profiles, and the safety profiles were considered similar.

Adult↗

PubMed2000

Flexibility of lumbar spinal motion segments correlated to type of tears in the annulus fibrosus.

OBJECT: The authors conducted a study in which their objective was to measure the effect of tears in the annulus fibrosus on the motions of lumbar spinal motion segments. METHODS: Lumbar spinal motion segments were harvested from human cadavers and studied using a 1.5-tesla magnetic resonance imager. The motion segments were subjected to incremental flexion, extension, rotation, and lateral bending torques. Displacements and rotations were measured using a kinematic system. The segments were sectioned on a cryomicrotome to verify the presence of tears in the annulus fibrosus. CONCLUSIONS: Tears in the annulus fibrosus increase the amount of motion that results from a torque applied to the motion segment. Radial and transverse tears of the annulus fibrosus have a greater effect on motions produced by an axial rotatory torque than on those produced by flexion, extension, or lateral bending torques. The difference between normal discs and discs with annular tears is more marked during moments of axial rotational than during those of flexion, extension, or lateral bending.

Aged↗

PubMed2000

Functional MR imaging activation after finger tapping has a shorter duration in the basal ganglia than in the sensorimotor cortex.

BACKGROUND AND PURPOSE: Repetitive motor tasks that produce sustained neuronal activity in the sensorimotor cortex produce transient neuronal activity in subcortical regions. We tested the hypothesis that a reference function modeling a transient hemodynamic response would more reliably detect activation in the basal ganglia than would a conventional reference function, which models a sustained hemodynamic response. METHODS: Functional MR imaging data were acquired in eight subjects performing an alternating-hand finger-tapping task. Postprocessing was performed by cross-correlation to two types of reference functions: one that models a sustained hemodynamic response to finger tapping and one that models an initial transient hemodynamic response. Activation in the sensorimotor cortex, supplementary motor area, cerebellum, thalamus, and corpus striatum was tabulated for each reference function. RESULTS: With the conventional boxcar reference function, activation was detected in the sensorimotor cortex, supplementary motor area, and cerebellum, but intermittently in the corpus striatum in all subjects. With the reference function for a transient response, activation in the corpus striatum was not detected in all subjects. CONCLUSION: In the corpus striatum, activation is detected more frequently with a reference function that models a transient response. Activated cortical and subcortical regions can be mapped with an alternating-hand finger-tapping paradigm and a combination of reference functions.

Adult↗

PubMed2000

Whole-brain functional MR imaging activation from a finger-tapping task examined with independent component analysis.

BACKGROUND AND PURPOSE: Independent component analysis (ICA), unlike other methods for processing functional MR (fMR) imaging data, requires no a priori assumptions about the hemodynamic response to the task. The purpose of this study was to analyze the temporal characteristics and the spatial mapping of the independent components identified by ICA when the subject performs a finger-tapping task. METHODS: Ten healthy subjects performed variations of the finger-tapping task conventionally used to map the sensorimotor cortex. The scan data were processed with ICA, and the temporal configuration of the components and their spatial localizations were studied. The locations with activation were tabulated and compared with locations known to be involved in the organization of motor functions in the brain. RESULTS: Components were identified that correlated to varying degrees with the conventional boxcar reference function. One or more of these components mapped to the sensorimotor cortex, supplementary motor area (SMA), putamen, and thalamus. By means of ICA components, sensorimotor cortex, supplementary motor area, and superior cerebellar activation were identified bilaterally in 100% of the subjects; thalamus activation was contralateral to the active hand in 80%; and putamen activation was contralateral to the active hand in 60%. CONCLUSION: ICA processing of multislice fMR imaging data acquired during finger tapping identifies the sensorimotor cortex, SMA, cerebellar, putamen, and thalamic activation. ICA appears to be a method that provides information on both the temporal and spatial characteristics of activation. Multiple task-related components can be identified by ICA, and specific activation maps can be derived from each separate component.

Brain↗

PubMed2000

Mapping functionally related regions of brain with functional connectivity MR imaging.

BACKGROUND AND PURPOSE: In subjects who are performing no prescribed cognitive task, functional connectivity mapped with MR imaging (fcMRI) shows regions with synchronous fluctuations of cerebral blood flow. When specific tasks are performed, functional MR imaging (fMRI) can map locations in which regional cerebral blood flow increases synchronously with the performance of the task. We tested the hypothesis that fcMRI maps, based on the synchrony of low-frequency blood flow fluctuations, identify brain regions that show activation on fMRI maps of sensorimotor, visual, language, and auditory tasks. METHODS: In four volunteers, task-activation fMRI and functional connectivity (resting-state) fcMRI data were acquired. A small region of interest (in an area that showed maximal task activation) was chosen, and the correlation coefficient of the corresponding resting-state signal with the signal of all other voxels in the resting data set was calculated. The correlation coefficient was decomposed into frequency components and its distribution determined for each fcMRI map. The fcMRI maps were compared with the fMRI maps. RESULTS: For each task, fcMRI maps based on one to four seed voxel(s) produced clusters of voxels in regions of eloquent cortex. For each fMRI map a closely corresponding fcMRI map was obtained. The frequencies that predominated in the cross-correlation coefficients for the functionally related regions were below 0.1 Hz. CONCLUSION: Functionally related brain regions can be identified by means of their synchronous slow fluctuations in signal intensity. Such blood flow synchrony can be detected in sensorimotor areas, expressive and receptive language regions, and the visual cortex by fcMRI. Regions identified by the slow synchronous fluctuations are similar to those activated by motor, language, or visual tasks.

Adult↗

PubMed1999

The clinical applications of functional MR imaging.

Functional MR imaging, similar to positron-emission tomography, shows the regions in which cerebral blood flow changes as neurons are active in the performance of cognitive tasks. Blood flow increases (activation) exceed that needed to supply oxygen for the increased metabolic needs for the increased neuronal activity. Therefore, in regions with activation, the deoxyhemoglobin concentration in the capillary blood decreases below levels found in the brain where neurons are not active.

Auditory Cortex↗

PubMed1998

The stiffness of lumbar spinal motion segments with a high-intensity zone in the anulus fibrosus.

STUDY DESIGN: Biomechanical and anatomic study of human cadaveric spinal motion segments. OBJECTIVES: To measure the stiffness of spinal motion segments by disc type and by load type (flexion, extension, axial rotation, or lateral bending). To compare stiffness in motion segments with and without a high-intensity zone or radial tear in the anulus fibrosus. SUMMARY OF BACKGROUND DATA: The high-intensity zone, that is a linear zone of high-intensity on T2-weighted magnetic resonance images corresponding to a radial tear in the anulus fibrosus, is a marker for a painful disc at discography. The high-intensity zone is hypothetically associated with diminished stiffness of the motion segment. METHODS: Human cadaveric lumbar spinal motion segments with normal disc morphology or a high-intensity zone of the anulus fibrosus were selected on the basis of magnetic resonance imaging. The motion segments were subjected to incremental flexion, extension, rotation, and lateral bending torques. Rotation was measured with a kinematic system. Torque-rotation curves and stiffness were calculated for each motion segment and for each torque. The motion segments were sectioned on a cryomicrotome to verify the disc morphology as normal or as that of a radial tear. RESULTS: In four motion segments with normal discs, stiffness was greater in axial rotation (8.4 Nm/degree) than in lateral bending (2.3 Nm/degree), flexion (1.8 Nm/degree), or extension (2.6 Nm/degree). In 16 motion segments with a high-intensity zone, stiffness was 2.4 Nm/degree in axial rotation, and less severely reduced in lateral bending, flexion, and extension. Stiffness in motion segments with a high-intensity zone was significantly less with smaller than with larger axial rotation loads. CONCLUSIONS: The presence of a high-intensity zone in the intervertebral disc is associated with reduced stiffness of motion segments. The reduction is greater in axial rotation than in other torques. The reduction is more in smaller than in larger axial torques.

Aged↗

PubMed1998

Focal brain lesions: effect of single-voxel proton MR spectroscopic findings on treatment decisions.

PURPOSE: To determine the influence of single-voxel proton magnetic resonance (MR) spectroscopic findings on the treatment of patients suspected of having a brain tumor. MATERIALS AND METHODS: Medical records were reviewed in 78 patients who underwent MR spectroscopy for evaluation of a focal brain mass suspected of being neoplastic. MR spectroscopic findings were positive for neoplasm in 49 patients and negative in 29. Treatment with or without performance of biopsy was noted. In patients with positive findings who underwent irradiation or chemotherapy without biopsy and in patients with negative findings who were treated medically or followed up for interval changes, MR spectroscopy was classified as having a potential positive influence on treatment. In patients with positive findings with subsequently proved nonneoplastic lesions and in patients with negative findings with subsequently proved tumors, MR spectroscopy was classified as having a potential negative influence. RESULTS: MR spectroscopy in eight (16%) patients with positive findings and in 15 (52%) patients with negative findings had a potential positive influence on treatment. In two (3%) patients, MR spectroscopy had a potential negative influence. CONCLUSION: MR spectroscopy may play a beneficial role in the management of suspected brain tumors. Prospective studies are needed to test the effect of MR spectroscopy on clinical practice and to measure costs and benefits.

Adolescent↗

PubMed1998

Hemispheric language dominance studied with functional MR: preliminary study in healthy volunteers and patients with epilepsy.

PURPOSE: We used functional MR imaging to compare hemispheric language dominance in healthy volunteers and in patients with epilepsy. METHODS: We retrospectively reviewed the functional MR images of 23 healthy volunteers and 16 patients with epilepsy obtained by using an echo-planar technique designed for whole-brain imaging. The activation paradigm used was a silent word generation task. Hemispheric language dominance was assessed as the percentage of activated pixels in the left hemisphere minus the percentage of activated pixels in the right hemisphere x 100. RESULTS: We found no significant difference in language lateralization between right-handed male and right-handed female volunteers. However, a statistically significant difference in language distribution was found between left- and right-handed female volunteers. The left-handed female volunteers showed a more bilateral hemispheric language lateralization. Language lateralization in right-handed male epilepsy patients with early age at seizure onset and seizure locus in the left temporal lobe was not significantly different from that of healthy right-handed male volunteers. Similarly, we found no difference in language lateralization between right-handed female volunteers and right-handed female epilepsy patients with late age at seizure onset and seizures in the left temporal lobe. CONCLUSION: Handedness has a significant influence on hemispheric language dominance in healthy volunteers. Sex has no influence on hemispheric language dominance, regardless of the task used to assess such dominance, nor does age at seizure onset influence language lateralization in patients with left temporal lobe epilepsy. Therefore, hemispheric language dominance can be assessed and compared effectively with functional MR imaging.

Adolescent↗

PubMed1998

Contrast media of high and low molecular weights in the detection of recurrent herniated disks.

PURPOSE: Our goal was to compare contrast enhancement of recurrent herniated disk fragments and scar after intravenous injection of a new high-molecular-weight contrast medium, Gadomer 17 (gadomer), with that after injection of a low-molecular-weight contrast medium, (gadopentetate dimeglumine). METHODS: Recurrent herniated disks were modeled in dogs by placing a fragment of intervertebral disk cartilage in the epidural space at laminectomy. MR imaging was performed with one of the contrast media at 20 and 50 days and with the other medium at 22 and 52 days. The changes in signal intensity from baseline in the disk fragment and in the adjacent scar tissue was measured at 2, 22, and 45 minutes. Differences were tested for significance with a student t-test. RESULTS: At 50 days after surgery, signal intensity in the intervertebral disk fragment increased by an average of 0.52 at 2 minutes after injection of gadomer and by an average of 0.90 after injection of gadopentetate. For scar, the increases in signal intensity were 1.41 (gadomer) and 1.62 (gadopentetate). At 22 and 45 minutes after injection, the signal intensity change in the disk fragment continued to be significantly greater after gadopentetate than after gadomer injection. In comparison with the changes at 50 days, both scar and disk fragment tended to show greater signal intensity changes at 20 days. Signal intensity changes in the disk fragments were significantly less after gadomer than after gadopentetate. Signal intensity changes in scar were slightly less with gadomer than with gadopentetate. CONCLUSION: Greater contrast is achieved between scar and recurrent herniated disk with a higher-molecular-weight contrast medium than with one of lower molecular weight. The difference between the high- and low-molecular-weight contrast media increases with maturation of the scar tissue.

Animals↗