Biomedical subjects
Publications and source records attributed to L A Hayman.
A rapid, simple, and inexpensive computed tomographic technique has been developed for marking the scalp and lateral skull radiograph of patients with small cerebral convexity lesions. The more precise localization provided thereby facilitates planning and performance of surgery.
Oblique projection vertebral angiography is the simplest and most accurate angiographic method of detecting small cerebellopontine angle tumors. The vascular blood supply to the tumor and brainstem is displayed as the surgeon will encounter it during lateral suboccipital craniotomy. The procedure is comfortable for the patient, technically easy to perform, and reproducible. Interpretation is relatively unaffected by variations in vascular anatomy or superimposed vessel or bone images. This method can be used to supplement routine views, or be performed alone with stereoscopic filming.
The diagnostic accuracy of CT scanning in the sellar area can be improved by using a rapid high dose (RHD) contrast technique which visualizes the supraclinoid carotid arteries, cavernous sinus and vascular plexus of the infundibulum. The RHD technique is briefly described and the pertinent anatomy discussed and illustrated.
Ten patients were studied in whom precontrast computed tomography (CT) revealed an isodense mass which obliterated cerebral sulci and deformed the ventricle(s). Upon rapid-high-dose (RHD) contrast enhancement, the cerebral hemispheric surface was so well demonstrated, that in 4 patients the possibility of an isodense subdural hematoma was exluded, while in the other 6 it was correctly diagnosed. Preoperative angiography was not necessary.
The choroid plexus of the fourth ventricle is a sensitive, symmetrical CT landmark which can often be visualized in overlapped scans performed in the orbital plane during rapid infusion of a high dose of iodinated contrast substance. Normal and pertinent abnormal plexus configurations are described and illustrated.
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The poorly reactive and dilated pupil observed in a comatose patient is often thought to represent an acute third nerve palsy owing to brain herniation or aneurysm. In the well patient, however, the isolated dilated pupil is unlikely to be owing to a third nerve palsy. It is more commonly owing to other benign causes such as local iris sphincter abnormalities, pharmacologic dilation, tonic pupil syndrome, or sympathetic irritation. This article presents a diagnostic flowchart to help the primary care physician analyze this problem and prevent costly and unnecessary imaging of these patients.
Temperature readings from standard wire lead thermistor probes and a fluoroptic temperature probe were compared before, during, and after exposure to a spin-echo imaging sequence at 2.35 T. All the probes were placed in saline-filled vials (1-mL capacity) surrounded by dense foam rubber to isolate and preserve local heating effects. There were no consistent differences in the temperatures recorded by the various probes. The authors conclude that wire lead thermistor probes do not exhibit substantial heat deposition when exposed to a standard spin-echo imaging sequence at 2.35 T.
T1 and T2 were measured in unclotted blood samples with 0.24- and 4.7-T spectrometers. The fraction by weight of intracellular water in the red blood cells (RBCs) was varied by either osmotic manipulation or density separation in concentrated (packed RBCs) and dilute (RBCs suspended in buffer or serum) samples. Reducing the cell water content caused a moderate decrease in T1 and a profound decrease in T2 at both 0.24 and 4.7 T. Conversely, increasing the cell water content caused an increase in both T1 and T2. The authors conclude that dehydrated RBCs in an area of hemorrhage would cause a substantial decrease in signal intensity on long TR/TE (T2-weighted) images. Overhydration of RBCs would have the opposite effect.
The MR appearance of clots with different internal structures was compared on gradient-echo (GE) and spin-echo (SE) images. After MR imaging, clots were submitted for histological analysis to allow direct correlation of clot structure with MR image intensity. Normal heterogeneous clots (containing entrapped serum) were hypointense compared to both unclotted blood (Hct 45) and brain on GE MR images. Homogeneous (serum-poor) clots and settled blood were hyperintense to unclotted blood and isointense or hyperintense to brain. These results indicate that the GE technique is quite sensitive to the physical inhomogeneity created (at the voxel level) when blood forms an inhomogeneous clot containing relatively large islands of red blood cells (RBCs) surrounded by lakes of serum. The effect of the different possible clot structures on GE signal intensity thus provides an etiology for the previously unexplained observations of hemorrhage with high signal intensity on GE MR images.
Heart rate (HR) and blood oxygen saturation (SaO2) were monitored before and during clinically indicated MR examinations of newborns to (a) identify any temporal relationship between MR scanning and vital sign fluctuations and (b) assess the reliability of SaO2 monitoring of dynamic changes. Fluctuations in HR (but not in SaO2) that are temporally linked to the MR image acquisition occur in most neonates during routine clinical MR examinations.
This report presents a patient who sustained closed head injury with chiasmal trauma. This uncommon injury may not be apparent on routine imaging studies. It is significant, not only from the visual standpoint, but also because of the association with serious conditions, such as panhypopituitarism, traumatic carotid aneurysm, carotid cavernous fistulae, and meningitis associated with leakage of cerebrospinal fluid. This report demonstrates that magnetic resonance imaging (MRI) is the best method for identifying chiasmal abnormalities.
Magnetic resonance (MR) imaging and computed tomography (CT) are routinely performed with the use of contrast materials in the diagnosis of neuro-ophthalmologic disease. Iodinated agents are commonly used in CT scanning and femoral contrast arteriography, and gadolinium is used in MR imaging. While contrast materials contribute greatly to diagnostic accuracy, they may also be responsible for adverse effects, ranging in severity from mild discomfort to death. The most frequent and severe side effects are associated with ionic iodinated contrast agents, while the rate of adverse reactions is less with use of nonionic iodinated contrast agents. Side effects and adverse reactions to gadolinium are uncommon, but they do occur. In neuro-ophthalmologic diagnosis, MR imaging is generally preferred over CT scanning, partly because of its greater ability to delineate soft tissue intracranial structures, but also because of the relative safety of gadolinium as a contrast agent. Properties of contrast agents are discussed in the context of specific imaging techniques and tissues investigated. Types and severity of adverse effects as well as risk factors for incurring such effects are summarized.
This report describes a patient with a headache and a bitemporal hemianopsia immediately following endoscopic ethmoid and sphenoid sinus surgery. Computed tomographic imaging revealed tension pneumocephalus caused by surgical interruption of the boundaries between the sinus(es) and the anterior cranial cavity. The delineation of the central chiasmal injury required follow-up magnetic resonance imaging.
A rare case with intradural-extramedullary cysticercosis is presented here. MR imaging with and without gd-DTPA were performed. There were multiple cysts in the basal cistern, cisterna magna, and cervical subarachnoid space which were isointense with cerebrospinal fluid both on T2- and T1-weighted images. Swelling and increased signal intensity in the cord parenchyma were detected on T2-weighted images. Gadolinium enhanced studies showed rim-shaped enhancement in the cysts and irregular, diffuse enhancement in the meninges.
A technique for alleviating artifacts in excision of cadaver spines for computed tomographic (CT) study is described. It maintains distension of the thecal sac by filling the spinal subarachnoid space with gelatin containing iodinated contrast media. The excision, handling, and storage procedures described prevent all but minute amounts of air from entering the specimen and producing artifacts which can degrade the CT images. The frozen specimen can be sectioned with a band saw in any plane and correlated with the CT images. This technique allows CT-anatomic correlation of not only bony and extrathecal soft tissues of the spine, but also the intrathecal neural elements.
The pharmacokinetics of diatrizoate contrast media were determined following low- (0.7 g I/kg) and high- (1.5 g I/kg) dose intravenous administration. The higher dose of contrast media produced plasma concentrations of iodine which remained approximately twice as high as conventional doses for one hour following infusion. This finding may explain the improved CT images obtained after infusion of higher doses of iodine contrast media. There was no significant long-term change in plasma osmolality noted in venous blood after either dose.