Biomedical subjects
V M Haughton
Publications and source records attributed to V M Haughton.
Recent advances in MR spectroscopy expand its applications in neurologic disease.
MRS extends the diagnostic power of MRI by displaying the biochemical composition of a selected tissue or region. When MR imaging shows a lesion, the evaluation of the chemical composition by MRS can help determine whether biopsy, observation or medical treatment is indicated. It can save some patients from biopsy prior to radiation or chemotherapy. In the future, both the image information and the spatial distribution of chemical constituents throughout the brain will be displayed with techniques such as chemical shift imaging (CSI). MRS improves the accuracy of MRI diagnosis and prognosis. MRS is performed at many sites in the country and is reimbursed by many insurers. MRS has been approved by the AMA for a CPT-4 code for reimbursement.
Anatomic changes of the spinal canal and intervertebral foramen associated with flexion-extension movement.
STUDY DESIGN: A cadaveric study was done to analyze the dimensional changes in the spinal canal and intervertebral foramen of the lumber spine with flexion and extension movements. OBJECTIVES: To investigate the relationship between flexion and extension movements and morphologic changes in the spinal canal and the intervertebral foramen. SUMMARY OF BACKGROUND DATA: Previous studies have reported that the dimensions of the spinal canal and the intervertebral foramen may change significantly with motion. The purpose of this study was to assess the quantitative changes in the spinal canal and the intervertebral foramen with segmental flexion-extension movements. METHODS: Nineteen fresh cadaveric spines yielding 25 motion segments were used. The lumbar motion segments were frozen and then imaged in axial and sagittal projections by a computed tomography scanner. They were thawed then, and the motion segments were loaded to 5.7 Nm in flexion (13 motion segments) and in extension (12 motion segments) specimens. While in flexion or extension, the specimens again were frozen and imaged by computed tomography scan. The frozen specimens than were sliced using a cryomicrotome in the sagittal plane to study the dimensions of the intervertebral foramen. Eighteen other fresh cadaveric spines were sliced sagittally for study in the neutral position. RESULTS: The axial computed tomography scans showed that extension significantly decreased the canal area, midsagittal diameter, and subarticular sagittal diameter, whereas flexion had the opposite effects. The sagittal computed tomography scans showed that extension decreased all the foraminal dimensions significantly, whereas flexion increased all the foraminal dimensions significantly. The translational changes were associated with the bulging of the disc and the presence of traction spurs. The cryomicrotome sections showed the cross-sectional area of the foramen to be 12% greater for the flexion group and 15% smaller for the extension group than the cross-sectional area of the neutral group. Nerve root compression in the foramen was found to be 21.0% in neutral, 15.4% in flexion, and 33.3% in extension groups. CONCLUSIONS: The study supports the concept of dynamic spinal stenosis. In addition to static anatomic changes, careful dynamic studies may be required to evaluate better the central canal and the foramen.
Functional magnetic resonance imaging mapping of the motor cortex in patients with cerebral tumors.
OBJECTIVE: The purpose of this study was to determine the usefulness of functional magnetic resonance imaging (FMRI) to map cerebral functions in patients with frontal or parietal tumors. METHODS: Charts and images of patients with cerebral tumors or vascular malformations who underwent FMRI with an echoplanar technique were reviewed. The FMRI maps of motor (11 patients), tactile sensory (12 patients), and language tasks (4 patients) were obtained. The location of the FMRI activation and the positive responses to intraoperative cortical stimulation were compared. The reliability of the paradigms for mapping the rolandic cortex was evaluated. RESULTS: Rolandic cortex was activated by tactile tasks in all 12 patients and by motor tasks in 10 of 11 patients. Language tasks elicited activation in each of the four patients. Activation was obtained within edematous brain and adjacent to tumors. FMRI in three cases with intraoperative electrocortical mapping results showed activation for a language, tactile, or motor task within the same gyrus in which stimulation elicited a related motor, sensory, or language function. In patients with > 2 cm between the margin of the tumor, as revealed by magnetic resonance imaging, and the activation, no decline in motor function occurred from surgical resection. CONCLUSIONS: FMRI of tactile, motor, and language tasks is feasible in patients with cerebral tumors. FMRI shows promise as a means of determining the risk of a postoperative motor deficit from surgical resection of frontal or parietal tumors.
Determination of language dominance using functional MRI: a comparison with the Wada test.
We performed functional MRI (FMRI) in 22 consecutive epilepsy patients undergoing intracarotid amobarbital (Wada) testing and compared language lateralization measures obtained with the two procedures. FMRI used a single-word semantic decision task previously shown to activate lateralized language areas in normal adults. Correlation between the two tests was highly significant (r = 0.96; 95% CIs 0.90 to 0.98; p < 0.0001). These results validate the FMRI technique and suggest that "active" areas observed with this semantic processing task correspond to those underlying hemispheric dominance for language. This strong correlation observed supports the view that language lateralization is a continuous rather than a dichotomous variable. In addition to lateralization information, FMRI consistently demonstrated focal regions of activity in lateral frontal and temporo-parieto-occipital cortex. These functional maps may be helpful in defining the boundaries of surgical excisions.
Correlative MR-anatomic study of the median nerve.
OBJECTIVE: The purpose of our study was to evaluate the effectiveness of MR imaging for showing the intrinsic anatomy of a peripheral nerve. Cadaver wrist specimens that included the median nerve were imaged with MR imaging at 3 T, then sectioned, stained, and inspected grossly and microscopically. The size, shape, and signal intensity of the sheath and axonal structures in the median nerve were identified in MR images by comparison with anatomic sections. CONCLUSION: This study suggests that MR imaging with sufficiently high-resolution techniques shows the internal structure of peripheral nerves. These results suggest that MR imaging may be a means to distinguish neuritis, tumor, degeneration, or fatty proliferation in a peripheral nerve and to evaluate the nerve before microsurgical anastomosis.
Ipsilateral hemisphere activation during motor and sensory tasks.
PURPOSE: To compare activation of the ipsilateral cerebral hemisphere during tactile sensory and motor tasks involving the right and left hands. METHODS: Eight volunteers had functional MR imaging to measure the extent of cerebral hemisphere activation during a motor task and sensory task involving each hand. Hemispheric indexes (left hemisphere activation minus right hemisphere activation)/(left hemisphere activation plus right hemisphere activation) were computed for each hand and each task. The indexes for two tasks and the two hands were compared. RESULTS: The left-hand motor tasks activated the ipsilateral hemisphere in right handers significantly more than did the right-hand tasks. Motor tasks produced a greater activation of the ipsilateral hemisphere than did the sensory tasks. No significant differences were found between the hemispheric indexes for the right-hand and left-hand sensory tasks. CONCLUSION: This study confirms findings of a previous study, showing that the left hemisphere is active in left-hand motor tasks. Activation of the ipsilateral hemisphere is significantly less pronounced during sensory tasks than during motor tasks.
MR appearance of the internal architecture of Ammon's horn.
PURPOSE: To determine whether the four subdivisions of Ammon's horn and six layers of CA1 seen histologically can be demonstrated with MR imaging. METHODS: Specimens of cadaver brains were imaged in a 3.0-T MR imager with a 3.0-cm solenoid coil. The specimens were sectioned, stained, and examined histologically. On anatomic sections, the four subdivisions of Ammon's horn and six layers of CA1 were identified. The MR images were then compared with the anatomic sections. RESULTS: Using geographic characteristics, we identified the four subdivisions of Ammon's horn. In CA1, the six layers could be identified by variations in signal intensity, width, and location. CONCLUSION: This study suggests that, with MR imaging of sufficiently high resolution, the internal architecture of Ammon's horn may be identified.
Test-retest precision of functional MR in sensory and motor task activation.
PURPOSE: To determine the test-retest precision of functional MR maps of regions in the brain "activated" by sensory, motor, and cognitive tasks. METHODS: Echo-planar images were acquired at 1.5 T in four subjects during voluntary motor activity involving the thumb and fingers and during tactile stimulation of the palm. Each subject performed the two tasks twice. Functional images of each task were generated at three thresholds. Test-retest precision was calculated in terms of two ratios: 1) the pixels activated in both iterations of the tasks in proportion to the pixels activated by either iteration of the task, and 2) the ratio modified to include first-order neighboring pixels. The first is referred to as pixel precision, and the latter as first-order-neighbor pixel precision. RESULTS: In each subject, activation from the first and second iteration of each task was located in the same region of the same gyrus. Pixel precision was .57 for the two tasks (at a threshold of 0.50). First-order-neighbor precision was greater than .80 for the two tasks at the same threshold. CONCLUSION: High test-retest precision can be obtained in functional MR.
Use of functional MR to map language in multilingual volunteers.
PURPOSE: To use functional MR imaging to compare brain activation during processing of languages in which multilingual volunteers are fluent with brain activation during processing of languages in which they are not fluent. METHODS: Echoplanar images were obtained for five right-handed male multilingual subjects who performed a language task in three languages, one of which was a language in which the subject was not fluent. The functional MR technique included echoplanar images obtained at 1 per second during cycles of rest and performance of the task, from which functional images were processed by means of cross-correlation analysis. The numbers of active pixels in each volunteer and for each language were compared. RESULTS: Activation was noted in the left frontal lobe in all subjects performing language tasks. In each subject, the number of activated pixels was greatest for the language in which the subject was least fluent. CONCLUSION: Functional MR imaging shows differences in the processing of different languages in multilingual volunteer subjects, depending on the level of fluency in the language, and it is an effective functional imaging method for studying the processing of different languages.
Ionic versus nonionic paramagnetic contrast media in differentiating between scar and herniated disk.
PURPOSE: To compare the MR contrast enhancement produced by ionic and nonionic paramagnetic contrast media in herniated disk fragments with that in epidural scar tissue. METHODS: A recurrent herniated disk was modeled in canines by using laminectomy to place a fragment of disk cartilage in the epidural space. The dogs were studied 88 and 90 days after laminectomy with MR imaging enhanced with an ionic or a nonionic paramagnetic contrast medium. Contrast enhancement of the epidural scar tissue and the epidural disk fragment was measured at 2, 22, and 45 minutes after the injection. RESULTS: Contrast enhancement was consistently and significantly higher in scar tissue than in disk fragments, although the difference decreased between 2 and 45 minutes after administration of contrast medium. Enhancement of disk fragments was less with the ionic than with the nonionic contrast medium. Contrast between the disk fragments and scar was also greater with the ionic than with the nonionic medium. CONCLUSIONS: The contrast between recurrent disk fragments and scar tissue is affected by the timing of the scan and the choice of contrast medium. Scans obtained immediately after the injection of contrast medium show more contrast between disk fragment and scar than do delayed scans. Recurrent herniated disk fragments are more effectively shown by ionic than by nonionic media.
Multiplanar MR and anatomic study of the mandibular canal.
PURPOSE: To evaluate the MR appearance of the mandibular canal and its contents. METHODS: Cadaveric mandibles were imaged at 1.5 T and 3 T, then sectioned with a cryomicrotome. The size, shape, signal intensity, and pattern of structures in the mandibular canal were identified on MR images by comparing them with corresponding anatomic sections. RESULTS: The inferior alveolar nerve and connective tissue were identified on the 1.5-T and 3-T images in the mandibular canal. Within the nerve the axon bundles were distinguished from the nerve sheath on the 3-T images. CONCLUSION: This study suggests that MR images can show excellent anatomic detail in the mandibular canal.
Occult lumbar lateral spinal stenosis in neural foramina subjected to physiologic loading.
PURPOSE: To measure the effect of extension, flexion, lateral bending, and axial rotation loads applied to the spine on the anatomic relationship of the spinal nerves in the neural foramen to the ligamentum flavum and the intervertebral disk, anc to determine the effect of disk degeneration on the response to loading. METHODS: Cadaveric lumbar motion segments were examined with CT and MR imaging, loaded with pure moment forces, frozen in situ, reexamined with CT, and sectioned with a cryomicrotome. The morphology of the intervertebral disks was classified on the basis of the appearance of the cryomicrotome sections. The neural foramina were classified as having no evident stenosis, as being stenotic, as having occult stenosis, or as showing resolved stenosis on the basis of the images and sections before and after loading. The stenotic and nonstenotic foramina were stratified by disk level, intervertebral disk classification, and type of loading applied. The effect of spinal level, disk type, and load type on the prevalence of stenosis was studied. RESULTS: On average, extension, flexion, lateral bending, and axial rotation resulted in the ligamentum flavum or intervertebral disk contacting or compressing the spinal nerve in 18% of the neural foramina. Extension loading produced the most cases of nerve root contact, and lateral bending produced the fewest cases. Each of the loading types resulted also in diminished contact between the spinal nerve and the intervertebral disk or ligamentum flavum in some cases. Disk degeneration significantly increased the prevalence of spinal stenosis. All foramina associated with advanced disk degeneration and half of the foramina associated with disks having radial tears of the annulus fibrosus either developed occult stenosis or were stenotic before loading. CONCLUSIONS: The study supports the concept of dynamic spinal stenosis; that is, intermittent stenosis of the neural foramina. Flexion, extension, lateral bending, and axial rotation significantly changed the anatomic relationships of the ligamentum flavum and intervertebral disk to the spinal nerve roots.
MR appearance of the retroisthmic cleft.
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Functional connectivity in the motor cortex of resting human brain using echo-planar MRI.
An MRI time course of 512 echo-planar images (EPI) in resting human brain obtained every 250 ms reveals fluctuations in signal intensity in each pixel that have a physiologic origin. Regions of the sensorimotor cortex that were activated secondary to hand movement were identified using functional MRI methodology (FMRI). Time courses of low frequency (< 0.1 Hz) fluctuations in resting brain were observed to have a high degree of temporal correlation (P < 10(-3)) within these regions and also with time courses in several other regions that can be associated with motor function. It is concluded that correlation of low frequency fluctuations, which may arise from fluctuations in blood oxygenation or flow, is a manifestation of functional connectivity of the brain.
Atypical demyelinating lesions in patients with multiple sclerosis.
We describe an atypical MRI appearance of multiple sclerosis (MS). Lesions characterized on T2-weighted images by a well-defined rim of increased signal intensity and a concentric region of higher signal intensity were seen in 6 of 132 patients with MS. On T1-weighted images these lesions were evident as regions of low signal intensity, often with a rim of contrast enhancement or increased signal intensity. These appearances tended to be shown by new, evolving lesions.
Functional magnetic resonance imaging mapping of the sensorimotor cortex with tactile stimulation.
The purpose of this study is to compare tactile stimulation of the palm with voluntary movement of the fingers as paradigms for mapping the sensorimotor cortex in functional magnetic resonance imaging. In 22 subjects, 24 sets of functional magnetic resonance images were obtained with echoplanar acquisitions and cross-correlation image processing techniques. Two tasks were employed: a motor task in which subjects moved the thumb and index finger of one hand and a sensory task in which the palm was scratched by another person. The activation from the two tasks coincided entirely in 20 sets and partially in 3 sets. In one case, no activation was seen with the motor task. The study suggests that tactile stimulation of the palm is useful and reliable for mapping the sensorimotor cortex.
Functional magnetic resonance imaging of the central auditory pathway following speech and pure-tone stimuli.
Functional magnetic resonance imaging (FMRI) is a new noninvasive technique for imaging cerebral function. Studies of the human central auditory pathway examined responses in eight normal hearing volunteers following auditory stimuli, including narrative speech and pure-tone audiometry. The activation demonstrated by FMRI is modeled on an increase in regional blood flow with increased neuronal activity. The FMRI signals represent deoxyhemoglobin concentration changes in capillaries within the region of the brain that is activated. Brain activation was imaged in the superior temporal gyrus during text reading and pure tones. Activation in both text and pure-tone presentation did not vary with the intensity of the auditory stimulus and elicited a dominant response in the left temporal lobe. These observations demonstrate the capability of FMRI to correlate anatomic and functional relationships in the human central auditory pathway.