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Biomedical subjects

A L Williams

Publications and source records attributed to A L Williams.

153 records · Page 9Linked to original sources
PubMedDate not supplied

The MR appearance of gray and white matter in the cervical spinal cord.

Artifacts that can distort the appearance of the cervical spinal cord are caused by data truncation during MR image reconstruction. We used a phantom and then correlated anatomic sections with MR images in cadavers and normal volunteers to evaluate the effect of truncation artifacts on the MR appearance of the spinal cord. When truncation artifacts are minimized, the gray matter and major white-matter columns in the cervical cord can be recognized. T2-weighted gradient-echo MR techniques can best differentiate gray from white matter.

Humans↗
PubMedDate not supplied

Gradient recalled echo MR imaging of the jugular foramen.

Axial T1-weighted spin-echo MR images have not proved to be effective in identifying normal structures in the jugular foramen. By correlating cryomicrotomic sections and axial T1-weighted gradient recalled echo images, we identified the neural and vascular contents of the jugular foramen. Further work with gradient recalled echo images is needed to determine the signal characteristics of jugular foraminal lesions.

Glomus Jugulare Tumor↗
PubMedDate not supplied

Magnetic susceptibility artifacts in gradient-recalled echo MR imaging.

Artifacts related to magnetic susceptibility differences between bone and soft tissue are prevalent on gradient-recalled echo images, particularly when long echo delay times are used. These susceptibility artifacts spatially distort and artifactually enlarge bone contours. This can alter the apparent shape of the spinal canal and exaggerate the degree of spinal stenosis seen in patients with cervical spondylosis. The effects of magnetic susceptibility artifacts in gradient echo imaging were studied in a phantom model and the results were correlated with MR images obtained in patients with cervical spondylosis.

Cervical Vertebrae↗
PubMedDate not supplied

MR measurement of normal and pathologic brainstem diameters.

The dimensions of the brainstem were measured on magnetic resonance (MR) images to provide criteria for detecting brainstem enlargement. Twenty-eight normal adult subjects had MR imaging with sagittal partial-saturation and spin-echo sequences. Four patients with brainstem gliomas and three with cerebellar atrophy were also studied. Five measurements were made: (A) the distance between the interpeduncular fissure and the aqueduct, (B) the distance from the anterior surface of the cerebral peduncles to the aqueduct, (C) the distance between the anterior surface of the pons midway between the mesencephalon and medulla to the fourth ventricular floor, (D) the shortest anteroposterior diameter of the medulla at the pontomedullary junction, and (E) the shortest anteroposterior diameter of the medulla at the medullospinal junction. Pontine diameter could be measured more reproducibly and accurately than mesencephalic or medullary diameters. In four patients with glioma, one or more of the measured diameters were more than 2 SDs above the average in normal volunteers, and abnormally small measurements were found in the patients with atrophy.

Adult↗
PubMedDate not supplied

CT recognition of subcortical hematomas.

Subcortical hematomas develop in brain trauma and less commonly in hypertensive intracerebral hemorrhage. Six cases are reported that exhibit a spectrum of computed tomographic (CT) findings in this entity. Pathologic correlates in four cases are presented. It is theorized that subcortical hematomas form in trauma secondary to shearing stresses in the brain. Differential movement of gray and white matter may disrupt cortical medullary vessels. Rupture of degenerative vessels at this junction may account for hypertensive hematomas.

Adolescent↗
PubMedDate not supplied

Mesencephalic anatomy: demonstration by computed tomography.

Although gray and white matter are distinguished by computed tomography (CT) in the cerebrum and cerebellum, their resolution in the mesencephalon has not been reported. CT and anatomic sections of the mesencephalon were compared to determine the relative densities of the superior cerebellar peduncles (white matter) and red nuclei and central gray matter. The normal low attenuation of the superior cerebellar peduncle should not be misinterpreted as infarction or demyelination.

Cerebellar Nuclei↗
PubMedDate not supplied

The flocculus in computed tomography.

The flocculus may simulate a cerebellopontine angle mass in computed tomography (CT). The CT appearance of the flocculus was compared with acoustic neuroma. Normal internal auditory canals, symmetric cerebellopontine angle cisterns, modest contrast enhancement, and a location posterior to the porus acousticus distinguish the flocculus from an acoustic neuroma.

Cerebellopontine Angle↗
PubMedDate not supplied

CT recognition of optic nerve sheath meningioma: abnormal sheath visualization.

Optic nerve sheath meningiomas and optic nerve gliomas can be difficult to differentiate by computed tomography (CT). Three patients with optic nerve sheath meningiomas were studied with a CT/T 8800 scanner with 1.5-mm-thick axial sections and intravenous contrast material. In each case, an abnormal optic nerve sheath was identified by CT. A soft-tissue mass arose from one side of the sheath in one patient, and the entire sheath was enlarged in two patients. This provides a basis for distinguishing optic nerve sheath meningioma from optic nerve glioma.

Contrast Media↗