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Biomedical subjects

A L Williams

Publications and source records attributed to A L Williams.

At least 145 records · Page 8Linked to original sources
PubMedDate not supplied

A clinical evaluation of xenon enhancement for computed tomography.

Xenon increases the attenuation coefficients of tissues in which it dissolves and, therefore, enhances lipid-rich material. The authors evaluated xenon enhancement for computed tomography. Patients and normal subjects were given xenon in subanesthetic concentrations and were scanned in a large aperture CT scanner. Patients tolerated 30-50% inhaled xenon well. Cerebral tissues and lung were enhanced by this concentration of xenon. Xenon inhalation in subanesthetic concentrations will be a useful technique for characterizing abnormal lipid tissues and for estimating cerebral blood flow.

Adult↗
PubMedDate not supplied

High-intensity signals within the posterior pituitary fossa: a study with fat-suppression MR techniques.

Five different theories have been proposed to explain the high-intensity signals within the posterior pituitary fossa seen on MR: (1) a paramagnetic effect of phospholipids in the posterior lobe, (2) lipid in pituicytes in the posterior lobe of the pituitary, (3) neurosecretory granules in the posterior lobe, (4) fat within the sella but outside the pituitary gland, and (5) fat in bone marrow in the dorsum sellae. Previous reports have contained conflicting evidence on which of these structures is the cause of the high-intensity signals within the posterior sella. The purpose of this study was to examine the high-intensity signals of the normal posterior sella with fat-suppression MR techniques to reevaluate the contribution of fat to those signals. The sellae of 19 normal volunteers and two cadavers were imaged with MR with a commercially available unit and a research fat- water-suppression technique. High-intensity signals in the posterior sella were observed in all 21 subjects on conventional T1-weighted MR images. In two volunteers, the high-intensity signals in the posterior sella were suppressed with fat-suppression techniques; in 17 subjects the signals were suppressed with water-suppression techniques. In two volunteers the results were indeterminate. The high-intensity signals in the posterior sella do not behave like lipid in the majority of cases. Our study supports the conclusion that high-intensity signals in the posterior sella may have more than one source. It appears that most of these sources do not suppress with fat-suppression techniques.

Humans↗
PubMedDate not supplied

MR imaging of optic nerve lesions: value of gadopentetate dimeglumine and fat-suppression technique.

Eleven patients with known or suspected optic nerve lesions and eight normal subjects were examined with spin-echo technique at 1.5 T with unenhanced T1-weighted imaging, IV gadopentetate-dimeglumine-enhanced T1-weighted imaging, and enhanced T1-weighted imaging with fat suppression. Two pathologically proved and four presumed optic nerve meningiomas demonstrated significant enhancement and were best seen with the fat-suppression technique. None of the three presumed optic nerve gliomas nor the optic nerves of normal subjects demonstrated qualitative enhancement. We conclude that the use of a fat-suppression technique with gadopentetate dimeglumine enhancement improves delineation of enhancing optic nerve lesions. This technique should be useful for evaluating other anatomic regions where enhancing tissue marginates fat.

Adult↗
PubMedDate not supplied

The cervical nerves and foramina: local-coil MR imaging.

A detailed study of the magnetic resonance (MR) appearance of the cervical nerves and neural foramina is presented. Using a "butterfly" local coil and a 1.5-T GE Signa MR system, the authors obtained 3-mm-thick axial, parasagittal, and 45 degrees oblique MR images of the cervical neural foramina in four normal volunteers. For the oblique images, subjects were rotated 45 degrees toward the right posterior oblique. Neural and vascular structures in the foramina were identified by correlation of the MR images with corresponding cryomicrotomic sections from four cadavers. The 45 degrees oblique images were more useful than axial or parasagittal images for demonstrating anatomic relations in the neural foramina. MR imaging with local coils demonstrates the complex anatomy of cervical neural foramina in various planes.

Adult↗
PubMedDate not supplied

MR imaging of prolactin-secreting microadenomas.

Eight proven and three presumed prolactin-secreting microadenomas were studied with magnetic resonance (MR) imaging. All 11 cases had CT evidence of a tumor. Technical factors for MR included use of 1.3-1.5 T MR systems, 3 mm slice thickness, short repetition time (TR) (T1-weighted) and long TR (T2-weighted) spin-echo pulse sequences. Six microadenomas were demonstrated with MR. Four tumors had a long T1 and long T2, one had a long T1 and short T2, and one bromocriptine-treated tumor had a short T1 and short T2. MR failed to delineate the focal mass within the pituitary gland in the other five patients. The cause of the MR failures was not determined; however, tumor size did not appear to be a factor. MR signals arising from microadenomas are variable and possibly related to the activity of the prolactin-secreting cells. Correlation of findings from MR imaging, spectroscopy, and electron microscopy may lead to an understanding of the variable MR appearance of microadenomas.

Adenoma↗
PubMedDate not supplied

MR imaging of the optic nerve and sheath: correcting the chemical shift misregistration effect.

The interface between soft-tissue structures and adipose tissue may be obscured by the chemical shift misregistration effect on MR images. In the orbit, this effect occurs at the edges at the optic nerve, even on high-resolution local coil images. In both phantom and clinical studies with a 1.5 T local coil imaging system, it was found that the chemical shift misregistration effect can be minimized by positioning the patient so that the optic nerve is parallel to the frequency encoding gradient. Alternatively, the effect can be corrected by using a computer program to combine "lipid" and "water" proton images. The sensitivity of MR for optic nerve lesions should be improved by these technical modifications.

Child↗
PubMedDate not supplied

Spinal epidural lymphomas: CT features in seven patients.

The computed tomographic (CT) images and records of seven patients with epidural lymphomas were reviewed to analyze their CT characteristics. Although no single specific pattern was identified, several signs were seen: (1) an intraspinal epidural irregular mass extending over several vertebral levels; (2) a mass with osteolysis or sclerosis; and (3) a combined intra- and extraspinal mass. Lymphoma must be considered in epidural masses when there are associated bone changes.

Adult↗
PubMedDate not supplied

MR of the diaphragma sellae.

The appearance of the diaphragma sellae is described in cryomicrotomic sections and on MR in patients with and without intra- and suprasellar masses. On MR, it appears as a thin band of negligible signal that is best shown when adjacent CSF or a mass has greater signal intensity. Its position or absence can be used to differentiate intrasellar masses with suprasellar components from suprasellar masses.

Adenoma↗
PubMedDate not supplied

Facial nerve enhancement in MR imaging.

The significance of facial nerve enhancement after IV gadolinium administration has not been determined. We evaluated the MR appearance of facial nerves (nonenhanced and enhanced) in patients without and with masses involving the temporal bone, internal auditory canal, or cerebellopontine angle. In patients without such masses, no facial nerve enhancement was seen. In the other group, four of 11 patients showed facial nerve enhancement and geniculate ganglion masses. Three of these four patients had neurofibromatosis; one had surgical verification of a facial nerve neurofibroma. Enhanced MR facilitates identification of abnormal facial nerves.

Brain Neoplasms↗
PubMedDate not supplied

Neuroepithelial cysts of the lateral ventricles: MR appearance.

The MR imaging appearance of neuroepithelial cysts in the lateral ventricle is reported. Two cases of proven and two of presumed intraventricular neuroepithelial cysts are presented. In one case, MR observations documented spontaneous regression of a large intraventricular cyst. Theories regarding the origin of neuroepithelial cysts are briefly reviewed. Standard T1- and T2-weighted spin-echo pulse sequences were used to study cysts in the lateral ventricles in axial, coronal, and sagittal planes. The cyst wall can be demonstrated reliably with MR images, eliminating the need for CT and/or contrast ventriculography. MR may also be useful in monitoring cyst size on serial examinations.

Adult↗
PubMedDate not supplied

"Truncation" artifact in MR images of the internal auditory canal.

Dry skulls and a phantom were studied to determine whether an intracanalicular dark band in MR images of some acoustic neuromas could be artifactual. A "truncation" artifact was detected in the internal auditory canals of the dry skulls and in a simulated internal auditory canal of the phantom when the width of the canal approximately equaled 4 X (field of view) /N, where N equals 128 or 256, depending on the number of gradient steps chosen. The "truncation" artifact should not be confused with CSF between normal nerves when a canal contains tumor.

Humans↗