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Biomedical subjects

K E Muller

Publications and source records attributed to K E Muller.

At least 19 recordsLinked to original sources
PubMed1997

Hepatic enhancement and metastatic lesion conspicuity on CT scans: influence of intravenous glucagon and oral CT contrast material.

PURPOSE: To determine the effect of glucagon and orally administered contrast material on hepatic enhancement and metastatic lesion conspicuity on computed tomographic (CT) scans. MATERIALS AND METHODS: Nine patients with a history of hepatic metastasis underwent two CT examinations with intravenously administered contrast material. Each patient was given orally administered CT contrast material for the first examination. No oral contrast material was given in the second examination. Five patients underwent the initial CT with intravenous administration of 1 mg of glucagon; the second examination was performed without glucagon. Four patients were administered glucagon before the second examination, but no glucagon was administered before the first. Attenuation in the liver, portal vein, and aorta was measured by observers blinded to whether the patient had been given glucagon. Lesion conspicuity was rated on a continuous scale. RESULTS: Greater mean hepatic enhancement was noted on scans of patients in whom oral contrast material was administered (mean, 52 HU) versus those in whom no oral contrast material was administered (mean, 47 HU; P = .019). Glucagon was not associated with greater hepatic enhancement. Neither oral contrast material nor glucagon had a significant effect on lesion conspicuity. CONCLUSION: Oral CT contrast material is associated with a small increase in hepatic enhancement that does not appear to be clinically important. Glucagon does not appear to affect hepatic enhancement or lesion conspicuity in humans.

Administration, Oral↗
PubMed1995

Introduction to perceptual linearization of video display systems for medical image presentation.

The perceptual linearization of video display systems should play a significant role in medical image presentation. It maximizes the faithfulness of information transfer to the human observer; it provides a method for standardizing the appearance of images across different display devices; and it allows for calculation of the inherent contrast resolution of different display devices. This paper provides insight into the process of perceptual linearization by decomposing it into the digital driving level-to-monitor luminance relationship, the monitor luminance-to-human brightness perception relationship, and the construction of a linearization function derived from these two relationships. A discussion of previous work in these areas is given. We then compare and contrast the results of previous work with recent experiments in our laboratory and related work in vision and computer science. We conclude that (1) sufficiently good visual models exist for agreeing on a standard method of calculating the perceptual linearization function; (2) improvements in the resolution and luminance distribution of the digital-to-analog circuitry in display systems are required for medical imaging; and (3), methods for calculating a linearization remapping from a perceptual linearization function currently have significant error and should be replaced with methods that minimize perceptual error.

Analog-Digital Conversion↗
PubMed1995

A review of therapeutic studies of idiopathic membranous glomerulopathy.

The treatment of idiopathic membranous glomerulopathy remains an enigma. We have reviewed many of the important clinical trials concerning membranous glomerulopathy using a meta-analysis and a secondary pooled analysis to test the effects of corticosteroid or alkylating, therapy compared with no treatment on renal survival and complete remission of the nephrotic syndrome. A search was performed using MEDLINE (1968 through 1993) for articles on idiopathic membranous glomerulopathy and glomerulonephritis. Bibliographies of articles were reviewed for completeness. Sixty-nine articles were reviewed. Meta-analysis was performed for four trials that evaluated corticosteroids compared with no treatment and for three trials that evaluated alkylating therapy compared with no treatment. Pooled analysis was performed on randomized and prospective studies (10 studies) and then with 22 case series added. All studies evaluated renal biopsy-proven disease. Meta-analysis was performed on the relative chance of being in complete remission for each study. Renal survival could be evaluated by pooled analysis only. For pooled analyses, Cox's proportional hazard and logistic regression models were used to test the effect of therapy on renal survival and the nephrotic syndrome, respectively. Data concerning gender, nephrotic syndrome, and geographic region were used in all statistical models. Evaluation of renal survival revealed no differences by treatment group (P > 0.1). By meta-analysis, the relative chance of complete remission was not improved for corticosteroid-treated patients (1.55; 95% confidence interval, 0.99 to 2.44; P > 0.1), but was improved for patients treated with alkylating agents (4.8; 95% confidence interval, 1.44 to 15.96; P < 0.05) when compared with no treatment. Pooled analysis of randomized and prospective studies, as well pooled analysis with all studies, supported the findings of the meta-analysis. Corticosteroids or alkylating therapy did not improve renal survival in idiopathic membranous glomerulopathy. Complete remission of the nephrotic syndrome was observed more frequently with the use of alkylating agents.

Adolescent↗
PubMed1995

Interpretation time of serial chest CT examinations with stacked-metaphor workstation versus film alternator.

PURPOSE: Interpretation time of serial staging chest CT cases, which each contained current and previous examinations, with a simple prototype workstation called filmstack was experimentally compared with interpretation time with a film alternator. MATERIALS AND METHODS: The filmstack displayed a "stack" of sections for each examination; user controls allowed rapid selection of preset attenuation windows and both synchronized and unsynchronized scrolling. Eight radiologists were timed as they used the filmstack and the film alternator to interpret four ergonomically complex serial CT cases. RESULTS: All reports dictated on the basis of findings with filmstack and film were of acceptable clinical accuracy. The time to examine a case with filmstack was significantly faster than the time with film, including the time to load and unload the alternator (99% confidence [P = .01]). There was no statistically significant difference in interpretation time between filmstack and prehung film. CONCLUSION: Use of a low-cost stacked CT workstation with a single 1,024 x 1,024 monitor is an effective means of interpreting cases that require comparison of multiple CT examinations.

Computer Systems↗
PubMed1994

A method for determination of optimal image enhancement for the detection of mammographic abnormalities.

We present a paradigm for empirical evaluation of digital image enhancement algorithms for mammography that uses psychophysical methods for implementation and analysis of a clinically relevant detection task. In the experiment, the observer is asked to detect and assign to a quadrant, or indicate the absence of, a simulated mammographic structure characteristic of cancer embedded in a background image of normal breast tissue. Responses are indicated interactively on a computer workstation. The parameter values for the enhancement applied to the composite image may be varied on each trial, and structure detection performance is estimated for each enhancement condition. Preliminary investigations have provided insight into an appropriate viewing duration, and furthermore, suggest that nonradiologists may be used under this methodology for the tasks investigated thus far, for predicting parameter values for clinical investigation. We are presently using this method in evaluating several contrast enhancement algorithms of possible benefit in mammography. These methods enable an objective, clinically relevant evaluation, for the purpose of optimal parameter determination or performance assessment, of digital image-processing methods potentially used in mammography.

Algorithms↗
PubMed1993

Portal film enhancement: technique and clinical utility.

We report on the results a 3-year project which had as its goal the development of methods to enhance radiation portal films to improve their readability. We had previously reported on a portal film enhancement technique, contrast limited adaptive histogram equalization, which could enhance low contrast detail, but degraded sharply contrasted edges. A new method, unsharp masking followed by contrast limited adaptive histogram equalization, now appears to overcome this problem. A clinical trial to test whether enhanced portal films could be read more accurately than standard ones was undertaken. The trial involved 12 readers from two institutions doing 276 readings. In this trial the enhanced films were judged to be of higher quality than the non-enhanced films (p < .001) and were read more accurately (p = .026). The usefulness and difficulties of routinely performing portal film enhancement in a busy radiation therapy department are discussed.

Humans↗
PubMed1993

Interpretation of CT studies: single-screen workstation versus film alternator.

A prototype single-screen workstation with a 2,048 x 2,560-pixel high-brightness monitor, 0.11-second image display time, and simple ergonomic design was compared to a conventional horizontal film alternator in diagnostic interpretation of chest computed tomography (CT) studies. Four radiologists used either the workstation or film alternator in interpretation of studies obtained in 10 patients. A counterbalanced within-subject repeated measures experimental design was used. Response times were analyzed for both methods of interpretation. Grades of excellent, acceptable, and unacceptable were assigned by a blinded "grader" to reports of the radiologists. The average time needed for an interpretation at the workstation was 5.65 minutes. No interpretations were graded unacceptable. Retrospective power analysis showed that 16 observers rather than four would have been required to show that use of the workstation was faster than the alternator. With this 95% confidence interval, the workstation interpretation time is clinically equivalent to that with the alternator. These data show that this type of workstation has practical application in interpretation of CT, magnetic resonance imaging, and ultrasound studies.

Humans↗
PubMed1993

Predictors of individual differences in acute response to ozone exposure.

The purpose of this study was to identify personal characteristics that predict individual differences in acute FEV1 response to ozone exposure. Response and predictor data were collected on 290 white male volunteers 18 to 32 yr of age who were each exposed to one of six concentrations of ozone between 0.0 and 0.40 part per million. The sample was divided into an exploratory sample of 96 and a confirmatory sample of 194 subjects. Exploratory analysis indicated that ozone, age, and several other variables explained a significant proportion of the variance in response. In the confirmatory sample, only age and ozone concentration predicted FEV1 decrement. For the combined sample ozone explained 31% of the variance, with age accounting for an additional 4%. The model predicted a decreasing response with increasing age for all nonzero ozone concentrations. For exposure to 0.40 ppm, the model predicts decrements in FEV1 of 1.07 and 0.47 L for 18- and 30-yr-old subjects, respectively. We concluded that for white male subjects age was a significant predictor of response, with older subjects being less responsive to ozone. Furthermore, we demonstrated that exploratory analysis without control of type I statistical error rates may result in apparent findings that cannot be replicated.

Adolescent↗
PubMed1992

Treatment of progressive membranous glomerulopathy. A randomized trial comparing cyclophosphamide and corticosteroids with corticosteroids alone. The Glomerular Disease Collaborative Network.

OBJECTIVE: To determine if deterioration in renal function could be ameliorated by adding cyclophosphamide to corticosteroid therapy in patients with progressive membranous glomerulopathy. DESIGN: Randomized, controlled treatment trial. Patients were followed for a mean of 29.2 +/- 17.1 months. SETTING: Collaborative network of 120 university and private-practice nephrologists. PARTICIPANTS: Patients with membranous glomerulopathy whose renal function deteriorated (as evidenced by doubling of the serum creatinine level, a 50% fall in the glomerular filtration rate, or a sustained serum creatinine level of greater than 2.0 mg/dL [reciprocal creatinine value, 0.5], or whose nephrotic range proteinuria persisted in association with morbid complications. Of 156 patients with biopsy-proven membranous glomerulopathy, 36 became eligible for randomization. Twenty-six of these 36 patients were randomly assigned to receive one of the two treatments. INTERVENTIONS: Pulse methylprednisolone, oral corticosteroids, and 6 months of intravenous cyclophosphamide or alternate-day corticosteroid therapy alone. MAIN RESULTS: At entry, no statistical differences were found between the treatment groups in duration of renal disease, age, gender, serum creatinine level, 24-hour urine protein excretion, or biopsy stage. The groups showed no difference in mean arterial blood pressure during follow-up. Four of the 13 patients receiving corticosteroids alone and 4 of the 13 patients receiving corticosteroids plus intravenous cyclophosphamide progressed to end-stage renal disease during follow-up. Reciprocal creatinine values tested at 6-month intervals showed no statistical differences between treatment groups at any time point. The log of the 24-hour protein excretion values showed no statistical differences between treatment groups after treatment. The power to detect a substantial improvement in renal function, defined as a doubling of the reciprocal of the serum creatinine, at the 0.05 significance level was 0.92. CONCLUSIONS: Combination therapy with intravenous cyclophosphamide and corticosteroids, when compared with corticosteroid therapy alone, does not improve renal function in patients with progressive membranous glomerulopathy.

Adult↗
PubMed1988

Babble and random-noise masking of speech in high and low context cue conditions.

"Perceptual" masking of speech by multitalker speech (babble) has been widely reported but poorly quantified. Furthermore, the validity of the construct of perceptual masking is questionable. This report describes an experiment using a newly standardized test of speech perception in noise (SPIN) with both babble and spectrally matched random-noise maskers. Classical psychophysical ogive curves were used to model speech recognition as a function of signal-to-noise ratio (S/N). The two maskers yielded speech recognition functions of the same steepness but different locations on the S/N axis. The high-context items of SPIN yielded speech recognition curves with steeper slope and different locations on the S/N axis than the low-context items. These data are used to argue that perceptual masking was not documented (under certain assumptions) and that the superior masking of babble may be explained in purely acoustical terms. Speculations are offered about the possible acoustical differences that could be responsible for the differences in masking effect.

Acoustics↗
PubMed1984

Toluene levels in blood and brain of rats as a function of toluene level in inspired air.

The relationship of toluene concentration in blood and brain to the concentration of toluene in inspired air has not been explicitly studied. Sixty rats were exposed by inhalation to 50, 100, 500, or 1000 ppm toluene for 3 hr. Immediately following exposure, venous blood samples and whole brains were collected and assayed for toluene levels. For several empirical reasons, the natural logarithm (log) of toluene tissue levels were predicted in a linear model from log toluene levels in air. An additional 10 rats were exposed to 550 ppm toluene for 8 hr in order to verify that the 3-hr exposure was sufficient to produce near-asymptotic levels of toluene in blood and brain. Log brain toluene concentration was significantly higher than log blood concentration by an additive constant. The ratio of brain to blood toluene level was estimated as 1.56/1. Three- and eight-hour exposure results did not differ, thus indicating that these results would hold for toluene exposures of 3 hr or greater.

Animals↗
PubMed1984

Toluene blood level following subcutaneous injection of toluene in the rat.

A model of toluene level in blood following subcutaneous injection of toluene mixed with polyoxyethylated-vegetable-oil vehicle was developed. The purpose was to provide a means of predicting dose received for subsequent toxicologic studies for any time and dose combination. The pharmacokinetics were of secondary interest. Using data from 111 rats, a four-parameter equation was devised to predict the time course of toluene blood level from 20-480 min post dosing, for dose levels of 50-1000 mg/kg. Blood concentrations rose at a rate which was independent of dose level. Maximum blood levels were uniquely determined by dose level. Blood levels fell at different rates depending upon dose level. Injection exposure, when compared to inhalation, has the advantages of (a) low expense, (b) low equipment requirements, and (c) simplicity. The disadvantage is, for some experiments, poor temporal stimulation of the normal route of administration, inhalation.

Animals↗
PubMed1984

Recommendations for appropriate statistical practice in toxicologic experiments.

Appropriate statistical practice in toxicologic research is reviewed. The problem centers on the antagonistic needs to discover toxic effects and avoid false indictments of harmless compounds. Specific problems which distort error rates include having many dependent variables, conducting many tests on a variable, data snooping, lack of statistical power and 5) violations of statistical assumptions. Solution strategies include top down planning, designing efficient experiments, balancing type I and type II error rates, selecting hypotheses and 5) using appropriate statistical analysis methods. Top down planning and the "leapfrog" design strategy are particularly emphasized.

Research Design↗
PubMed1981

Effects of age and body lead burden on CNS function in young children. I. slow cortical potentials.

The effects of body Pb burden on slow cortical potentials were studied in 63 children aged 13-75 months. Slow wave (SW) voltage during sensory conditioning varied as a linear function of blood lead (PbB) level. The slope of this function, moreover, changed systematically with age. For children under 5 years of age, SW voltage tended to be positive at low PbBs and to be negative above 30 micrograms/dl. For children over 5 years of age, SW voltage tended to be negative at low PbBs and to be less negative (or positive) above 30 micrograms/dl. These results provide evidence of altered CNS function at the lowest Pb effect level ever reported.

Aging↗
PubMed1981

Effects of age and body lead burden on CNS function in young children. II. EEG spectra.

This study explored the effects of age and PbB upon EEG power spectra and various measures of hemispheric laterality in children, aged 13-75 months, watching a display (cartoon). The following are the principle conclusions: (1) The delta- and theta-band amplitude decreased with age. (2) When only bilaterally synchronized EEG between P3 and P4 was considered, the amplitude of P3 was estimated as greater than P4 in all frequency bands and for all ages. Previous reports have not shown lateral EEG dominance in children below 75 months. (3) When lateral dominance measures consider only the relationship between synchronized EEG at P3 and P4, bilateral communality in the delta band increased with age. (4) Increased PbB generally produced an increase in the relative amplitude of synchronized EEG between P3 and P4 in all frequency bands. This was true for PbB levels well below 15 micrograms/dl, among the lowest level PbB effects previously reported. No clinical or behavioral effects of PbB values have been reported below 15 micrograms/dl. It appears to be theoretically and practically important to understand the functional significance of bilaterally synchronized activity. The signal processing of the CNS can be explored using these methods. Greater understanding of these data would help define the extent and etiology of PbB effects on the CNS

Aging↗