PubMed Health⌕ Search

Biomedical subjects

W R Nemzek

Publications and source records attributed to W R Nemzek.

16 recordsLinked to original sources
PubMed2000

Monte Carlo assessment of computed tomography dose to tissue adjacent to the scanned volume.

The assessment of the radiation dose to internal organs or to an embryo or fetus is required on occasion for risk assessment or for comparing imaging studies. Limited resources hinder the ability to accurately assess the radiation dose received to locations outside the tissue volume actually scanned during computed tomography (CT). The purpose of this study was to assess peripheral doses and provide tabular data for dose evaluation. Validated Monte Carlo simulation techniques were used to compute the dose distribution along the length of water-equivalent cylindrical phantoms, 16 and 32 cm in diameter. For further validation, comparisons between physically measured and Monte Carlo-derived air kerma profiles were performed and showed excellent (1% to 2%) agreement. Polyenergetic x-ray spectra at 80, 100, 120, and 140 kVp with beam shaping filters were studied. Using 10(8) simulated photons input to the cylinders perpendicular to their long axis, line spread functions (LSF) of the dose distribution were determined at three depths in the cylinders (center, mid-depth, and surface). The LSF data were then used with appropriate mathematics to compute dose distributions along the long axis of the cylinder. The dose distributions resulting from helical (pitch = 1.0) scans and axial scans were approximately equivalent. Beyond about 3 cm from the edge of the CT scanned tissue volume, the fall-off of radiation dose was exponential. A series of tables normalized at 100 milliampere seconds (mAs) were produced which allow the straight-forward assessment of dose within and peripheral to the CT scanned volume. The tables should be useful for medical physicists and radiologists in the estimation of dose to sites beyond the edge of the CT scanned volume.

Computer Simulation↗
PubMed2000

MR, CT, and plain film imaging of the developing skull base in fetal specimens.

BACKGROUND AND PURPOSE: The developing fetal skull base has previously been studied via dissection and low-resolution CT. Most of the central skull base develops from endochondral ossification through an intermediary chondrocranium. We traced the development of the normal fetal skull base by using plain radiography, MR imaging, and CT. METHODS: Twenty-nine formalin-fixed fetal specimens ranging from 9 to 24 weeks' gestational age were examined with mammographic plain radiography, CT, and MR imaging. Skull base development and ossification were assessed. RESULTS: The postsphenoid cartilages enclose the pituitary and fuse to form the basisphenoid, from which the sella turcica and the posterior body of the sphenoid bone originate. The presphenoid cartilages will form the anterior body of the sphenoid bone. Portions of the presphenoid cartilage give rise to the mesethmoid cartilage, which forms the central portion of the anterior skull base. Ossification begins in the occipital bone (12 weeks) and progresses anteriorly. The postsphenoid (14 weeks) and then the presphenoid portion (17 weeks) of the sphenoid bone ossify. Ossification is seen laterally (16 weeks) in the orbitosphenoid, which contributes to the lesser wing of the sphenoid, and the alisphenoid (15 weeks), which forms the greater wing. CONCLUSION: MR imaging can show early progressive ossification of the cartilaginous skull base and its relation to intracranial structures. The study of fetal developmental anatomy may lead to a better understanding of abnormalities of the skull base.

Gestational Age↗
PubMed1999

Acute cervical spine injuries: prospective MR imaging assessment at a level 1 trauma center.

PURPOSE: To determine the weighted average sensitivity of magnetic resonance (MR) imaging in the prospective detection of acute neck injury and to compare these findings with those of a comprehensive conventional radiographic assessment. MATERIALS AND METHODS: Conventional radiography and MR imaging were performed in 199 patients presenting to a level 1 trauma center with suspected cervical spine injury. Weighted sensitivities and specificities were calculated, and a weighted average across eight vertebral levels from C1 to T1 was formed. Fourteen parameters indicative of acute injury were tabulated. RESULTS: Fifty-eight patients had 172 acute cervical injuries. MR imaging depicted 136 (79%) acute abnormalities and conventional radiography depicted 39 (23%). For assessment of acute fractures, MR images (weighted average sensitivity, 43%; CI: 21%, 66%) were comparable to conventional radiographs (weighted average sensitivity, 48%; CI: 30%, 65%). MR imaging was superior to conventional radiography in the evaluation of pre- or paravertebral hemorrhage or edema, anterior or posterior longitudinal ligament injury, traumatic disk herniation, cord edema, and cord compression. Cord injuries were associated with cervical spine spondylosis (P < .05), acute fracture (P < .001), and canal stenosis (P < .001). CONCLUSION: MR imaging is more accurate than radiography in the detection of a wide spectrum of neck injuries, and further study is warranted of its potential effect on medical decision making, clinical outcome, and cost-effectiveness.

Acute Disease↗
PubMed1998

Allergic fungal sinusitis: CT findings.

PURPOSE: To determine the computed tomographic (CT) findings in patients with allergic fungal sinusitis. MATERIALS AND METHODS: The authors retrospectively reviewed CT scans and surgical and histopathologic reports in 45 patients (27 male, 18 female; age range, 8-68 years) with allergic fungal sinusitis from multiple institutions. The median age (25 years) and demographics of the patients were determined. Two head and neck radiologists together evaluated the CT scans for the presence of intrasinus high-attenuation areas, extent of sinus involvement, bone expansion and thinning, bone erosion, and extension of disease into the adjacent soft tissues. RESULTS: Allergic fungal sinusitis was more common in male patients and in patients aged 20-30 years. All patients had increased intrasinus attenuation at non-contrast material-enhanced CT. Multiple sinus involvement occurred in 43 patients. Bilateral involvement was more common than unilateral disease. Forty-four patients had complete opacification of at least one of the involved sinuses; 43 of these patients had expansion of an involved sinus, 42 had remodeling and thinning of the bony sinus walls, and 41 had erosion of the sinus wall. CONCLUSION: Allergic fungal sinusitis is a distinct clinical entity with nonspecific symptoms that may be initially suggested by the CT findings. These findings should alert the clinician to the possibility of allergic fungal sinusitis and prompt other diagnostic studies to establish the diagnosis and treatment plan.

Adolescent↗
PubMed1998

Perineural spread of head and neck tumors: how accurate is MR imaging?

PURPOSE: Our aim was to determine the precision of MR imaging evaluation of perineural spread of head and neck tumors. METHODS: Nineteen patients had complete extirpation of head and neck tumors (10 squamous cell carcinomas, four adenoid cystic carcinomas, one poorly differentiated carcinoma, one salivary duct carcinoma, one mucoepidermoid carcinoma, one chordoma, and one meningioma) with histologic confirmation of perineural spread. Findings at presurgical contrast-enhanced MR imaging were compared with findings at pathologic examination. RESULTS: The sensitivity of MR imaging for detection of perineural spread was 95%; however, the sensitivity for mapping the entire extent of perineural spread fell to 63%. CONCLUSION: MR imaging may fail to depict microscopic foci of perineural tumor infiltration, leading to underestimation of the extent of perineural spread. Nevertheless, with careful analysis of foraminal architecture and MR enhancement patterns, one can reliably identify the presence if not the extent of perineural spread.

Adult↗
PubMed1996

Phase III clinical trial comparing iodixanol and iohexol in cerebral angiography.

RATIONALE AND OBJECTIVES: We report on our early clinical experience in the United States with the nonionic dimeric (6:1 ratio) contrast medium iodixanol in cerebral angiography. Iodixanol has an osmolality less than half that of monomeric, nonionic contrast media such as iohexol at equivalent iodine concentrations and is isosmotic to blood. METHODS: Forty-nine adult patients undergoing elective cerebral angiography were studied in a phase III, double-blind, randomized, parallel-design clinical trial comparing the safety and diagnostic efficacy of iodixanol at 320 mg I/ml (IOD-320) and iohexol 300 mg I/ml (IOH-300). Diagnostically adequate cerebral angiograms were routinely obtained with both contrast agents. RESULTS: A total of 37% of the patients experienced adverse events (48% in the IOD-320 group and 25% in the IOH-300 group). No statistically significant differences were noted between the two groups studied in the proportion of patients with one or more adverse events or in the intensity of the adverse events. The most common adverse event was headache. There were no deaths or serious complications related to either contrast medium in this study. CONCLUSION: The results of this phase III trial support the conclusion that iodixanol at a concentration of 320 mg I/ml is comparable to iohexol at 300 mg I/ml in terms of efficacy (overall radiographic diagnostic visualization) and safety.

Adult↗
PubMed1996

Evaluation of fetal midface anatomy related to facial clefts: use of US.

PURPOSE: To identify the sonographic appearance of normal fetal midface anatomy of in vitro fetal specimens and to correlate the appearance with that of in utero fetuses to determine which aspects of this anatomy can be evaluated clinically. MATERIALS AND METHODS: The midface structures of 12 normal fetal specimens were examined in the axial, sagittal, and coronal planes with ultrasound. The results were correlated with those of other modalities. One hundred consecutive, normal in utero fetuses were scanned in the same planes in an attempt to identify the same anatomic landmarks identified in the fetal specimens. RESULTS: In the fetal specimens, the upper lip (coronal plane), alveolar ridge, tooth sockets, point of fusion of primary and secondary palates (axial plane), and fusion line of the secondary palate (sagittal plane) were consistently observed. In the 100 in utero fetuses, the same anatomy was visualized in the coronal plane in 95 (95%), in the axial plane in 97 (97%), and in the sagittal plane in 26 (26%). The mean scanning time was 2.8 minutes. CONCLUSION: Important aspects of fetal midface anatomy that relate to facial clefts can be observed in utero at prenatal sonography in the coronal and axial planes.

Cleft Lip↗
PubMed1996

Prediction of major vascular injury in patients with gunshot wounds to the neck.

PURPOSE: To determine whether plain film and CT findings help predict the presence and severity of vascular trauma. METHODS: The records of 65 patients with gunshot wounds of the neck were reviewed. There were 58 men and 7 women ranging in age from 2 to 72 years. All had angiography of the cervical vessels; in addition, 64 had plain radiography, 22 had CT, and 14 had a barium swallow. The results of plain films, barium swallow, and CT scans were correlated. RESULTS: Eighteen patients (28%) had major vascular injury, which included 10 pseudoaneurysms, six vascular occlusions, four intimal injuries, and one arteriovenous fistula. Ten patients had prevertebral soft-tissue swelling (sensitivity, 59%; specificity, 77%), 14 had a bullet fragment close to a vessel (sensitivity, 78%; specificity, 36%), and 13 had missile fragmentation (sensitivity, 72%; specificity, 45%). CONCLUSION: Prevertebral soft-tissue swelling, missile fragmentation, and missiles adjacent to major vessels are useful but nonspecific radiographic signs and are present in many patients with normal angiographic findings. A knowledge of the physical findings, including the entry and exit wounds, plus the results of plain radiography and CT can help define bullet trajectories and guide angiographic evaluation.

Adolescent↗
PubMed1996

The trigeminal nerve.

The trigeminal nerve is described in terms of segmental anatomy and regional pathology. The common brain stem lesions are neoplasms, vascular disease, and demyelinating processes. Common lesions affecting the cisternal segment and Meckel's cave are schwannoma, meningioma, epidermoid, vascular ectasia, and aneurysm. Common lesions affecting the cavernous segment include meningioma, trigeminal schwannoma, lymphoma, metastasis, and vascular lesions. Skull base abnormalities include chordoma, chondrosarcoma, metastasis, bone dysplasias, and Paget's disease. The peripheral divisions of the trigeminal nerve are commonly involved by adjacent inflammatory disease in the sinuses, perineural spread of malignancy, and schwannoma. Unfortunately, the anatomic site of a lesion cannot be accurately predicted on the basis of clinical symptomatology. Successful imaging evaluation must include the entire course of the trigeminal nerve from the brain stem and upper cervical cord through the peripheral branches.

Aged↗
PubMed1996

Imaging findings of the developing temporal bone in fetal specimens.

PURPOSE: To trace the development of the normal fetal temporal bone by means of plain radiography, MR, and CT. METHODS: Eighteen formalin-fixed fetal specimens, 13.5 to 24.4 weeks' gestational age, were examined with a mammographic plain film technique, CT, and MR imaging at 1.5 T. Temporal bone development and ossification were assessed. RESULTS: The membranous labyrinth grows with amazing rapidity and attains adult size by the middle of the gestation period. The cochlea, vestibule, and semicircular canals are very prominent and easily recognized on MR images. The otic capsule develops from a cartilage model. Ossification of the otic capsule proceeds rapidly between 18 and 24 weeks from multiple ossification centers that replace the cartilaginous framework. The mastoid, internal auditory canal, vestibular aqueduct, and external auditory canal continue to grow after birth. CONCLUSION: The study of fetal developmental anatomy may lead to a better understanding of congenital disorders of the ear. Faster MR scanning techniques may provide a method for in utero evaluation of the fetal temporal bone.

Cartilage↗
PubMed1995

Reversible blindness secondary to acute sphenoid sinusitis.

Sphenoid sinusitis is an elusive diagnosis with significant morbidity if not diagnosed and treated promptly. We have reported an unusual case of acute sphenoiditis mimicking Gradenigo's syndrome. This resulted in virtual bilateral blindness that entirely resolved with aggressive surgical and medical treatment. It is recommended that sphenoid sinusitis be strongly considered in patients with acute headache and fever. A detailed cranial nerve examination should be performed, and CT scans of the skull base and paranasal sinuses should be obtained. Immediate surgery is strongly recommended for acute sphenoid sinusitis at the first suggestion of a complication and in those patients not promptly responding to medical therapy. It is apparent that irreversible damage to the optic nerve can occur before the development of gross intraorbital pathology. Therefore we believe that delaying surgery until the visual acuity is worse than 20/60, as advocated by some authors, may not be in the patient's best interest. Surgery should be directed at removing the purulent material, obtaining cultures, removing irreversibly diseased mucosa, and maintaining drainage of the sphenoid sinus.

Acute Disease↗
PubMed1995

A reappraisal of the radiologic findings of acute inflammation of the epiglottis and supraglottic structures in adults.

PURPOSE: To evaluate the radiologic characteristic of acute inflammation of the epiglottis and supraglottic structures in adults. METHODS: The clinical and radiographic findings in 27 adult patients with epiglottitis (average age, 43 years; range, 28 to 81 years) were compared with those of a control group of asymptomatic subjects (n = 15; average age, 48 years; range, 24 to 79 years). Unusual clinical aspects in the current series included two patients who were positive for human immunodeficiency virus, 1 with acquired immunodeficiency syndrome and Kaposi sarcoma, 3 with emphysematous epiglottitis, 1 with abscess formation, and 1 with laryngeal carcinoma. One patient required emergency tracheostomy. One patient died of pneumonia. RESULTS: The ratio of the soft-tissue parameters to the anteroposterior width of the C-4 vertebral body yielded three key parameters of high statistical significance in adult epiglottitis. The ratio of the width of the epiglottis to the anteroposterior width of C-4 should not be greater than 0.33 (sensitivity, 96%; specificity, 100%). The ratio of the prevertebral soft tissue to C-4 should not exceed 0.5 (sensitivity, 37%; specificity, 100%) and the ratio of the width of the hypopharyngeal airway to the width of C-4 should be less than 1.5 (sensitivity, 44%; specificity, 87%). The aryepiglottic folds were enlarged in 85%, and the arytenoids were swollen in 70% of the patient population (specificity, 100%). CONCLUSION: These defined radiologic parameters should aid in the diagnosis of acute epiglottitis in adults.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Relationship of transient ischemic attacks and angiographically demonstrable lesions of carotid artery.

Eighty-eight percent of arteries in patients with amaurosis fugax or hemispheric transient ischemic attacks had angiographically demonstrable lesions at the carotid bifurcation. Eighty-one percent had stenoses or occlusions at the carotid bifurcation; 7 percent had ulcerative lesions without stenoses at this site. Forty-nine percent of arteries in these patients demonstrated ulcerative lesions with or without stenosis at the carotid bifurcation. There was no significant difference in the incidence or types of ulcerations between those patients with amaurosis fugax and those with hemispheric transient ischemic attacks. Eighty-eight percent of arteries examined in this series were amenable to surgical reconstruction. Amaurosis fugax and hemispheric transient ischemic attacks were of equal value in predicting the possibility of a surgically treatable lesion at the carotid bifurcation.

Blindness↗