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Biomedical subjects

W M Maguire

Publications and source records attributed to W M Maguire.

13 recordsLinked to original sources
PubMed1998

Low-dose spiral computed tomography of the thorax: comparison with the standard-dose technique.

RATIONALE AND OBJECTIVES: This study was conducted to determine whether significant reduction in radiation dose (250 mAs-->50 mAs), in chest computed tomography (CT) using volume acquisition affects image quality or the detectability of pathologic findings in the lung and mediastinum. METHODS: Phantom studies were conducted to evaluate resolution and noise level, then a patient study was then done. Fifty consecutive patients (10 normal and 40 abnormal) cases were examined. After a scan (250 mAs, 120OkVp) of the entire thorax, five additional slices (50 mAs, 120kVp) at the level of the abnormality were obtained. Three independent observers evaluated the visibility of normal lung and mediastinal structures, as well as image noise. The mean score was compared between the standard and low doses. In a second study, an independent evaluation of the presence or absence of pathologic findings was made by four observers. RESULTS: Lucite phantom studies demonstrated diminished low-contrast resolution and increased noise level for the low-dose technique. Observers assessed more noise in the low-dose images (P < 0.001). The normal structures were judged to be more visible with standard dose (P < 0.01), but the magnitude of the judged differences was small especially in the lung. No differences were found in the detection of lung and mediastinal abnormalities (P > 0.10). CONCLUSIONS: The low-dose technique was effective in demonstrating pathologic findings for the lung and mediastinum. Low-dose spiral CT should be considered as a viable alternative to standard-dose spiral CT.

Adult↗
PubMed1996

Cerebral CT venography.

PURPOSE: To produce cerebral venograms with thin-section helical computed tomography (CT) and to assess their diagnostic utility. MATERIALS AND METHODS: Thirty-six CT venograms were obtained in 33 patients after intravenous administration of iodinated contrast material. Eighteen patients had suspected dural sinus thrombosis. Twelve patients had tumor adjacent to a major venous structure. Three patients underwent CT venography during CT angiography. RESULTS: Superior sagittal, transverse, and straight sinuses were identified on every CT venogram. Other veins were seen with high frequency. Dural sinus thrombosis was diagnosed in seven patients, with magnetic resonance (MR) venographic correlation in five patients. CT venograms were easier to interpret and had fewer artifacts than MR venograms. Relationships of tumor to adjacent cerebral venous structures were well shown on CT venograms. CONCLUSION: CT venography yields detailed images of the intracranial venous circulation with consistently high quality. It is a rapid, useful method for diagnosis of dural sinus thrombosis and for preoperative mapping of venous structures in patients with neoplasm.

Adult↗
PubMed1994

Interobserver agreement using computed radiography in the adult intensive care unit.

RATIONALE AND OBJECTIVES: We determined whether computed radiographs in an adult intensive care unit produce greater agreement between readers in descriptions of radiologic findings and interval changes. METHODS: Fifty-six conventional radiographs and 56 computed radiographs were obtained on 28 patients. Computed and conventional radiographs were imaged simultaneously in a single exposure with the use of a sandwich cassette. The two sets of films per patient were taken less than 1 week apart. RESULTS: Four readers evaluated the chest films and judged interval changes with the use of standardized confidence scales. Overall exposure and film quality also were evaluated. Computed radiographs were rated better in overall quality. Tubes and lines were detected with comparable accuracy. Interobserver agreement in the evaluation of radiologic descriptors was generally greater with computed radiographs (intraclass correlation). No differences were noted in interobserver agreement in the judgment of interval changes. CONCLUSIONS: The diagnostic usefulness of computed radiography is comparable to conventional films in the intensive care unit. The higher interobserver agreement rate for radiologic descriptors with computed radiography is an added advantage of the system.

Adult↗
PubMed1993

Mechanical complications of cancer.

Emergency physicians can expect to see more patients with malignancies. Some of these malignancies can lead to life-threatening emergencies, and the emergency physician must suspect and be able to recognize these problems.

Cardiovascular Diseases↗
PubMed1990

Epinephrine-induced vasospasm reversed by phentolamine digital block.

A case of profound digital vasoconstriction caused by the accidental injection of epinephrine from a commercial bee sting kit is reported. One hour later the patient had a cold, painful, blanched finger. A digital block using a 2-mg dose of phentolamine mixed with 2% lidocaine was performed. Thirty minutes after treatment, the finger was pink and warm. The patient reported a marked decrease in pain. Reexamination 12 hours later showed only mild tenderness at the fingertip. No tissue necrosis occurred. One month after injection, there were no apparent sequelae. Although the use of alpha-adrenergic blocking agents by regional infiltration to treat accidental infusion or extravasation of epinephrine has been suggested, no reports of this technique are found in the emergency medicine literature. The mechanism of digital vasoconstriction and the action of phentolamine are discussed.

Accidents↗
PubMed1984

Visuotopic organization of the prelunate gyrus in rhesus monkey.

We have examined topographic organization of the prelunate gyrus and adjacent cortex buried in the lunate and superior temporal sulci. We recorded from cortex of awake rhesus monkeys performing a fixation task. Multiunit receptive fields were mapped with small, stationary spots of light to determine borders and points of strongest driving or "activity centers" of the fields. We found evidence for several distinct subdivisions of this cortex. A representation of the vertical meridian runs across the gyrus, and two crude topographic representations of the central 30 degrees of the lower quadrant, the posteromedial and anterolateral areas (area PM and area AL), share this representation of the meridian. Area AL extends from the prelunate gyrus into the posterior bank of the superior temporal sulcus; it is separated from the MT area by a narrow strip of cortex. Area PM occupies part of the prelunate gyrus and extends into the anterior bank of the lunate sulcus. Receptive field size in both AL and PM is an increasing function of eccentricity and is similar for the two areas. Medial to areas PM and AL on the prelunate gyrus is another cortical region with qualitatively different topographic organization.

Animals↗
PubMed1981

Effects of spatial-frequency specific adaptation and target duration on visual persistence.

Two experiments investigated the properties of visual persistence as functions of spatial frequency, stimulus duration, and pattern-specific adaptation. In Experiment 1, increasing the duration of high spatial-frequency gratings from 50 to 500 msec decreased the duration of visual persistence produced by that grating to an asymptotic level. However, low-frequency gratings produced a constant estimate of visual persistence independent of presentation time. Also, spatial-frequency specific adaptation reduced the persistence of the high-frequency gratings to this asymptotic level, but the lower frequency persistence estimates already at this level were unaffected (Experiment 2). These findings are related to possible temporal properties of the sustained and transient visual systems.

Figural Aftereffect↗
PubMed1980

The McCollough effect in rhesus monkey.

After viewing red vertical stripes and green horizontal stripes, the eye subsequently views white vertical stripes as greenish and white horizontal stripes as pinkish. It has been theorized that this phenomenon, known as the McCollough effect, is related to long-tern adaptation of cells tuned for both color and orientation. Such cells have been found in the visual cortex of the rhesus monkey. We asked whether rhesus monkeys, like man, experience a McCollough effect. Two humans and two rhesus monkeys were adapted by requiring them to fixate a spot moving slowly across alternating horizontal and vertical gratings of complementary color. Following adaptation, a test grating whose color changed from red to green or green to red was presented. Humans and monkeys were instructed or trained to release a response lever during the interval that the grating was white. After adaptation, there were orientation-specific changes in all four subjects' responses as would be predicted if both man and monkey were experiencing a McCollough effect.

Adaptation, Physiological↗
PubMed1977

Spatial frequency and the mediation of short-term visual storage.

The perceived duration of a photopically illuminated, fixated grating presented for 50 milliseconds increased (from 300 to 500 milliseconds) with spatial frequency (0.9 to 15 cycles per degree). This suggests a sustained neural channel contribution to short-term visual storage, and argues against a pure photoreceptor, especially a rod, locus for such storage.

Form Perception↗
PubMedDate not supplied

Comparison of fixed and adjustable window width and level settings in the CT evaluation of diffuse lung disease.

OBJECTIVE: The purpose of this investigation was to assess the utility of allowing free adjustment of window width and level in comparison with the use of a fixed lung window in the CT evaluation of diffuse lung disease. MATERIALS AND METHODS: Six radiologists each judged 36 cases (28 diffuse lung disease and 8 normal) using a standardized form. In half of the sessions, images were viewed in a fixed lung window (level = -500 HU; width = 2,000 HU). In the other sessions, the observer was able to adjust the window and level freely while viewing the images. Each case was seen twice in separate sessions: once in a fixed lung window and once with window width and level adjusted by the reader. A variety of diagnostic features were evaluated using a 5 point scale. These included visibility of fine lung structures, abnormalities of the lung parenchyma, and overall evaluation of the lung. RESULTS: The visibility of lung structures was not improved with adjustable window settings. Receiver operating characteristic (ROC) analysis showed fixed windows to be superior to adjustable windows for overall evaluation of the cases [fixed A(z) = 0.90, adjustable A(z) = 0.84, p < 0.05, jackknife method]. Time to rate each case was increased by 15% with window width and level adjustment. CONCLUSION: Free adjustment of window width and level produced no improvement in reader performance over that achieved with fixed window width and level.

Humans↗