PubMed Health⌕ Search

Biomedical subjects

S K Hilal

Publications and source records attributed to S K Hilal.

At least 19 recordsLinked to original sources
PubMed1992

Paramedian thalamopeduncular infarction: clinical syndromes and magnetic resonance imaging.

We prospectively examined 11 patients with magnetic resonance imaging-documented infarction in the paramedian thalamopeduncular region, which is supplied by the superior mesencephalic and posterior thalamosubthalamic arteries. Variations in the size and rostral-caudal extent of infarction correlated with the following three clinical patterns: (1) With unilateral paramedian mesencephalic infarction, an ipsilateral third nerve paresis was accompanied by mild contralateral hemiparesis or hemiataxia. Contralateral ptosis and impaired upgaze were observed in two patients; one of them showed additional damage to the posterior commissure. (2) With bilateral infarction in the thalamopeduncular junction, involving the mesencephalic reticular formation, supranuclear vertical gaze defects were accompanied by impaired consciousness or memory, and mild aphasia in some patients. Persistent amnesia was observed only when the dominant anterior nucleus or mamillothalamic tract was damaged. (3) With larger thalamopeduncular infarcts, partial or complete third nerve paresis was combined with supranuclear gaze disturbance and delayed contralateral tremor. An unusual gaze disorder, a variant of the vertical "one-and-a-half syndrome," occurred with a small strategically placed lesion at the thalamopeduncular junction, best explained by selective damage to supranuclear pathways or partial nuclear involvement. The primary cause of these infarctions was embolism to the basilar apex or local atheroma at the origin of the posterior cerebral artery.

Adult↗
PubMed1992

Phase-scrambled RF excitation for 3D volume-selective multislice NMR imaging.

An RF excitation technique with which one can improve the effective dynamic range of the receiver and reduce the interference between slices for 3D volume-selective multislice MRI is described. The basic idea of the technique is to use phase scrambling in conjunction with slice encoding through the use of RF pulses. The spins in each slice are encoded by RF pulses which have the scrambled as well as slice-encoded phase components along the slice-selection direction. The scrambled, or randomly distributed, phase reduces the peak signal intensity, thereby reducing the dynamic range of the signal. Since the proposed technique utilizes RF slice encoding together with phase scrambling, interslice image interference is greatly reduced and the dynamic range is improved. In addition, the method has several advantages such as a reduction in the power requirement for the RF pulses and the elimination of the necessity for hardware such as nonlinear gradient coils.

Algorithms↗
PubMed1991

Hylan gel composition for percutaneous embolization.

Viscoelastic, pseudoplastic, radiopaque injectable hylan gel for percutaneous embolization was developed and evaluated by in vitro and in vivo tests. The embolization gel is composed of cross-linked hylan (hyaluronan, hyaluronate), tantalum, microcrystalline cellulose, hexamethonium chloride, and thrombin. Upon delivery through small-lumen catheters to the appropriate vascular site, the gel induces formation of a solid blood/gel coagulum. Results from animal studies (rat aorta, rabbit auricular artery) demonstrate that formation of complete and long-lasting arterial blockage is readily achievable without complications due to blood flow, partial vessel obstruction, uncontrolled polymerization, or movement of the gel or its components (specifically thrombin and hexamethonium chloride) into the circulation. Microscopic evaluation indicates that arterial occlusion initially occurs as a result of the injected gel and formed fibrin; at 7 weeks and beyond, arteries are occluded by injected gel, inflammatory cells and fibrosis (scar tissue).

Animals↗
PubMed1991

New spatial localization method using pulsed high-order field gradients (SHOT: Selection with High-Order gradienT).

A new spatial localization method using an additional set of high-order magnetic field gradients is described. The method uses a nonlinear part of high-order magnetic field gradient patterns which allows us to select a volume in conjunction with the selective radiofrequency (RF) pulse. Unlike the other existing volume selection methods such as ISIS or SPARS, the proposed selection method requires only one RF-gradient pulse pair to select a volume in two directions. The center of the selected volume can be moved to any arbitrary location within the body by the addition of precalculated lower order gradients which are simultaneously pulsed with the high-order gradient. The method also has the potential for localized spectroscopy from the FID signal which can be realized by using oscillating second- and first-order gradients for 3D selection with a single RF pulse. By using the proposed localization method, it is possible to design more flexible pulse sequences, e.g., the shorter echo-time spectroscopic pulse sequence. We have designed and constructed a six-loop r2 (or x2 + y2) gradient coil for initial application. By simultaneously applying this second-order gradient and proper x, y, and/or z gradients, 2D selections were achieved in arbitrarily selected positions in conjunction with a single selective RF pulse. Phantom and animal experiments have been performed and the results appear promising, especially in areas of NMR spectroscopic imaging applications where spatial localization is essential.

Animals↗
PubMed1991

An optimized multislice acquisition sequence for the inversion-recovery MR imaging.

An optimized multislice data acquisition scheme for inversion-recovery MR imaging is proposed and experimental results are presented. In this new scheme, instead of forming a set of multislice inversion-recovery sequences in series for a given phase encoding step, 180 degrees inversion pulses corresponding to different slices are interwoven with the spin echo data acquisition sequence in an optimal way depending on the desired inversion-recovery time. For example, between the 180 degrees inversion RF pulse and the spin-echo imaging sequence, a number of imaging and inversion sequences are inserted with different slice combinations, i.e., long inversion-recovery time is effectively utilized for the other slice pre-inversion and data acquisition. With the optimized sequence, imaging time has been reduced by as much as a factor of four compared with the existing methods.

Brain↗
PubMed1990

MR findings in patients with subacute necrotizing encephalomyelopathy (Leigh syndrome): correlation with biochemical defect.

MR studies were correlated with biochemical results in nine children who presented with lactic acidosis and/or abnormal MR findings in the basal ganglia. Neurologic development was delayed in all nine children. Seven of these patients were diagnosed as having subacute necrotizing encephalomyelopathy (SNE, or Leigh syndrome) on the basis of history, clinical findings, and biochemical studies; of the remaining two, one had congenital lactic acidosis and the other had familial bilateral striatal necrosis with no known biochemical correlate. Although the clinical presentation of these patients was similar, we found distinctive MR abnormalities in characteristic locations in the seven patients with SNE, with or without detectable specific mitochondrial enzyme deficiency in cultured skin fibroblast assays. In our case studies of SNE patients with detectable enzyme deficiency states, defects in pyruvate dehydrogenase complex and cytochrome c oxidase have been found. The MR finding of note in SNE is the remarkably symmetrical involvement, most frequently of the putamen. In our study, lesions were also commonly found in the globus pallidus and the caudate nucleus, but never in the absence of putaminal abnormalities. Other areas of involvement included the paraventricular white matter, corpus callosum, substantia nigra, decussation of superior cerebellar peduncles, periaqueductal region, and brainstem. In patients who present with lactic acidosis and whose MR findings show symmetrical abnormalities in the brain, but with sparing of the putamen, the diagnosis of SNE is in doubt.

Acidosis, Lactic↗
PubMed1979

Recognition and differential diagnosis of enlarged extraocular muscles in computed tomography.

We found enlargement of the extraocular muscles in 70 patients out of 603 orbit studies, of whom 310 had exophthalmos. The majority (46 of 70) had the eye signs of Graves' disease. Arteriovenous malformations and carotid cavernous fistulas can cause enlargement of the extraocular muscles by a diffuse increase in orbital venous pressure, Acute orbital myositis can be distinguished from other forms of pseudotumor by the presence of a single enlarge extraocular muscle with associated inflammatory findings which responds to corticosteroid therapy. Neoplasms may invade extraocular muscles or compress their venous drainage causing secondary muscle enlargement. In all these patients the presence of a mass was correctly identified. The ability of the computed tomography scanner to recognize abnormalities of the extraocular muscles represents a significant advance in classification and diagnosis of the causes of exophthalmos.

Adult↗
PubMed1979

Computed tomography of the orbit.

Computerized tomography (CT) has revolutionized the analysis of patients with orbital tumors. A new CT scanner devised by the author resolves structures less than 1 mm with an image section as thin as 2 mm. This improved resolution shows all the extraocular muscles, including the obliques; enlargement of the optic nerve to the orbital end of the optic canal; and the sclera, crystalline lens, aqueous, and vitreous. Experience with 700 orbital studies shows that CT scanning now identifies pathologic changes in the orbital soft tissues with the same diagnostic accuracy as bone pathology.

Cranial Nerve Neoplasms↗
PubMed1979

Neonatal polycystic encephalomalacia: four new cases and review of the literature.

Four patients with pathologically documented polycystic cavitation of the brain had an acute illness characterised by stupor, seizures, CSF erythrocytic and monocytic pleocytosis, increased CSF protein, and diminished CSF glucose. The acute phase was followed by chronic decerebation, disappearance of the CSF abnormalities, and radiological evidence of polycystic cavitation of the brain. In one patient Herpes simplex was isolated from a cutaneous vesicle. The CSF abnormalities in the disorder have received scant attention, and have not previously been correlated with the acute and chronic stages. Clearly some cases are associated with Herpes simplex virus. The clinical profile should now be sufficiently distinctive to permit future identification of the aetiology in more neonates.

Brain↗
PubMed1978

The embolization of vascular malformations of the spinal cord with low-viscosity silicone rubber.

Development of the low-viscosity silicone rubber has made possible the successful embolization and complete obliteration of 9 out of 11 vascular malformations of the spinal cord treated with this material. The procedure is particularly useful in patients where the malformation is fed by a limited number of posterior radicular feeders without any supply from the anterior spinal artery. One patient with a supply from the anterior spinal artery. One patient with a supply from both anterior and posterior feeders was successfully embolized after a temporary occlusion of the anterior spinal radicular feeder. Seven patients out of 11 embolized with silicone rubber showed a clinical improvement of their signs and symptoms.

Adult↗
PubMed1978

Specificity of computed tomography in the diagnosis of supratentorial neoplasms. Consideration of metastases and meningiomas.

A previously unsuspected linear relationship between the initial density and the amount of uptake of various tumors is described. As a rule, initially radiodense neoplasms enhance less than radiolucent neoplasms. For a given amount of enhancement, meningiomas are initially more radiodense than metastases; also, breast metastases are more radiodense than lung metastases. The density versus uptake curve tends to show certain specificity for a given type of neoplasm. Absolute differentiation of histologic types is still not possible on the basis of these curves. The correlation, however, is interesting and seems to be related to the amount of damage to the blood-brain barrier and the degree of calcification, vascularity, and cellularity of the various tumors. With improved precision of scanners the specificity of the CT image may be improved.

Brain Neoplasms↗
PubMed1978

Development and evaluation of a new water-soluble iodinated myelographic contrast medium with markedly reduced convulsive effects.

A new water-soluble myelographic contrast agent with more hydrophilic properties than metrizamide was developed and tested in the primate (Macaca mulatta) and the cat. A new animal model that allows study of the convulsive effects of intrathecally administered contrast agents in the awake monkey was designed. With this sensitive model the new contrast agent was shown to have a remarkable reduced convulsive effect when compared with metrizamide and other media. Intrathecal hypertonic solutions in the cat depress the evoked cortico-spinal responses whereas the neurotoxic effects of the iodinated water-soluble contrast media increase them. The net effect is a combination of the two actions.

Animals↗
PubMed1978

Computed tomographic measurement of the xenon brain-blood partition coefficient and implications for regional cerebral blood flow: a preliminary report.

The calculation of regional cerebral blood flow requires, in addition to the measurement of the clearance, a knowledge of the regional brain-blood partition coefficient. The usual 133Xe washout techniques do not measure this latter parameter but use published values for normal brain tissue. This may lead to large errors in pathological tissue because the partition coefficient changes significantly in brain tumors. Investigations have begun into the use of CT and stable xenon to produce a cross sectional view of the brain in terms of its brain-blood partition coefficients. Results of experiments using an iodine phantom and xenon inhalation in animals are presented.

Animals↗
PubMed1977

Effect of isotonic contrast agents on spinal reflexes in the cat.

The effects of isotonic solutions of three contrast agents, administered intrathecally, were studied in cats. A pronounced increase in the electrically evoked cortico-spinal responses and segmental spinal polysynaptic reflexes was recorded after administration of methylglucamine diatrizoate. Injection of methylglucamine iothalamate resulted in an increase of the amplitudes of these reflexes, while metrizamide did not show any consistent effect. The data suggest that water-soluble media have direct effects upon spinal gray matter.

Animals↗
PubMed1977

Scintigraphic detection of osteoid osteoma.

Bone scanning with 99mTc-diphosphonate disclosed a solitary focus of intense activity in a cervical vertebra of a 17-year-old youth with persistent unexplained neck pain. Surgery subsequently demonstrated a well-circumscribed osteoid osteoma. This experience is further evidence of the efficacy of radionuclide skeletal scintigraphy in the evaluation of benign bone disease.

Adolescent↗