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Biomedical subjects

J A Baker

Publications and source records attributed to J A Baker.

At least 55 records · Page 3Linked to original sources
PubMed1994

Scatter compensation in digital chest radiography using the posterior beam stop technique.

A new scatter compensation technique for computed radiography based on posterior beam stop (PBS) sampled scatter measurements and the bicubic spline interpolation technique was proposed. Using only a single exposure, both the clinical image and an array of scatter measurements, which were interpolated into a smooth scatter-only image, were simultaneously acquired. The scatter was subtracted from the clinical image to generate the primary-only image. To gauge the accuracy of scatter estimation, both quantitative and interpolation errors were evaluated. The PBS measurements were compared against the standard beam stop method at 16 locations in an anatomical phantom, resulting in quantitative errors of 2.7% relative to the scatter or 6.8% relative to the primary. Also measured were the interpolation error over 64 interpolation sample locations and 64 midpoint sample locations in the anatomical phantom. The combined interpolation error was 1.9% relative to the scatter or 8.0% relative to the primary. At the interpolation sample locations, the errors were identical between the phantom radiograph and digital portable chest radiographs from five patients. By summing the quantitative and interpolation errors in quadrature, the overall error of the PBS SISTER (scatter interpolation-subtraction technique for radiography) method was 3.3% relative to the scatter or 10% relative to the primary, which was adequate for dual-energy imaging purposes (less than 10% error relative to the scatter or 20% relative to the primary). The change of image contrast, noise, and signal-to-noise ratio (SNR) at six locations in the anatomical phantom were quantitatively analyzed. Contrast and noise were equally enhanced in all anatomical regions, resulting in approximately the same SNR before and after compensation.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1993

Cognitive inflexibility after archicortical and paleocortical prefrontal lesions in marmosets.

The behaviour and cognitive abilities of marmosets with bilateral ablations of either the archicortex on the mediodorsal surface or the paleocortex on the ventrolateral surface of the frontal lobes were assessed in terms of the types of information being handled, the mode of action (inhibitory versus productive mechanisms), and the level of functioning of these frontal areas. Although there was a tendency for the ventrolateral ablation to produce a greater impairment on object than on spatial discrimination in comparison to the mediodorsal ablation, the differences between the two groups was not marked in this respect. The effect of ablations of either of these areas was more marked on tasks which required the inhibition of prepotent responses than on tasks where novel or arbitrary responses were appropriate. The major effect of both lesions was the production of perseverative behaviour which occurred at the level of motor output in the first few days after surgery but was then observed at the level of choice behaviour and attentional set in formal cognitive tests. Impairments were also seen on postoperative retention of tasks learnt prior to surgery. It is suggested that all these impairments arise from an inability to use or modify stored information.

Animals↗
PubMed1993

Observer evaluation of scatter subtraction for digital portable chest radiographs.

RATIONALE AND OBJECTIVES: The authors compared standard digital portable chest radiographs (DPCXR) to scatter-subtracted DPCXR: METHODS: Thirty DPCXR were obtained using a photostimulable phosphor digital imaging system and a posterior beam stop (PBS) technique that allowed measurement of the scatter component of the DPCXR: The scatter component was subtracted from the clinical image to form a scatter-subtracted image. Six observers recorded preference for the standard image or scatter-subtracted image for identifying five radiographic landmarks and for image quality. RESULTS: A statistically significant preference was demonstrated for the scatter-subtracted images and for viewing the tracheo-bronchial tree, right paratracheal stripe, vertebral column, and support apparatus position. For unprocessed images, there was a statistically significant preference for viewing the pulmonary vasculature. No statistically significant preference was demonstrated for overall image quality. CONCLUSIONS: These results suggest that PBS scatter subtraction holds promise for improving visualization of structures in high-scatter regions of chest radiographs.

Evaluation Studies as Topic↗
PubMed1993

Human pathologic correlation with PET in ischemic and nonischemic cardiomyopathy.

To assess the correlation between myocardial perfusion, metabolism and histologic findings in patients with cardiomyopathy, we evaluated myocardial perfusion and metabolism using positron emission tomography (PET) with 13NH3 (ammonia) and 18FDG (fluoro-2-deoxy-glucose) in nine patients prior to undergoing orthotopic cardiac transplantation. Four patients had ischemic cardiomyopathy (ISCM) and five had nonischemic cardiomyopathy (NISCM). Normalized circumferential profile analyses of representative mid-ventricular perfusion and metabolism PET images were performed for each patient. A corresponding mid-ventricular transaxial slice was obtained from the formalin fixed explanted heart and processed for routine histology. Hematoxylin-eosin stained and Masson trichrome stained sections were evaluated and the percentage of the slice occupied by infarct was determined planimetrically at 10-degree intervals in a circumferential manner. A significant correlation was found between circumferential normalized PET count density profile of perfusion and metabolism in both the ischemic and nonischemic groups (ISCM range r = 0.65-0.75; NISCM range, r = 0.70-0.87). Furthermore, there was a correlation in the ISCM group between the extent of matched perfusion/metabolism defects and transmural infarct involvement (r = 0.66-0.88). PET perfusion and metabolic data closely correlate with pathologic infarction in human hearts of ischemic cardiomyopathy patients.

Adult↗
PubMed1992

Posterior beam-stop method for scatter fraction measurement in digital radiography.

The authors presented a new posterior beam-stop (PBS) technique for measuring the ratio of scattered to total-detected photon flux (scatter fraction) in a radiographic examination while preserving the diagnostic quality of the image. The scatter measurement was made using a standard imaging geometry with both beam stops and an additional x-ray detector placed behind the standard imaging detector. This PBS geometry differs from the standard beam-stop (SBS) technique for scatter measurement. With SBS, a beam-stop shadow appears on the image. To evaluate the PBS technique, scatter fraction measurements were performed on an anatomic phantom using both the PBS and SBS techniques. When compared with the standard technique, PBS provided accurate estimation of scatter fractions. Since the measurement can be performed without degrading a standard clinical radiographic examination, the PBS technique allows simultaneous acquisition of scatter measurements from human patients in combination with a standard radiographic examination.

Filtration↗
PubMed1992

A comparison of glycine, sarcosine, N,N-dimethylglycine, glycinebetaine and N-modified betaines as liposome cryoprotectants.

Glycinebetaine has previously been shown to be effective at reducing leakage from liposomes which are frozen then thawed. This study involved the preparation of a series of N-modified betaines and the comparison of their cryoprotective activities with those of glycine, sarcosine, N,N-dimethylglycine and glycinebetaine. All the compounds investigated, with the exception of (dimethyloctylammonio)acetate, reduced the degree of leakage, after freezing and thawing, with additive concentrations up to 0.6 M. Reducing the degree of N-terminal methylation of glycinebetaine appeared to increase the leakage from liposomes at additive concentrations between 0.2 and 0.6 M. (Dimethylethylammonio)acetate, (dimethylisopropylammonio)acetate and (N,N,N',N'-tetramethylethylenediammonio)-N,N'-diacetate appeared to be no more effective than glycinebetaine, whereas improved protection was afforded by (triethylammonio)acetate and (diethylmethylammonio)acetate at most concentrations. This study demonstrates that the cryoprotective activity of glycinebetaine may be improved with modifications to the N-terminal.

Amaranth Dye↗
PubMed1992

Measurement of scatter fractions in clinical bedside radiography.

The authors present measurements of scatter fraction (SF), the ratio of scattered to total imaged photons, from clinical bedside radiographs of 102 patients. These measurements were obtained by using a new posterior beam-stop technique that does not alter the diagnostic image but that simultaneously provides SF measurements at 224 locations in the image. The SF values in the lung were found to be consistent with previous measurements, while the SF values in the mediastinal and retrocardiac areas were larger than previously reported. SFs in diseased lung were significantly larger than SFs in normal lung. The range of SF values was large for all anatomic locations. For applications in which accurate scatter estimation is required, this wide range of values suggests that SFs should be measured in each individual image.

Female↗
PubMed1992

A flap augmentation technique for Achilles tendon repair. Postoperative strength and functional outcome.

The efficacy of tendo-Achilles rupture repair by a modified version of Lindholm's technique was studied biomechanically and functionally. The procedure involves secondary reinforcement of a conventionally reapproximated rupture site by means of a backfolded augmentation flap. The flap cross section consisted of approximately one third of the proximal stump. In 18 paired fresh anatomic Achilles tendons, flap augmentation repairs had an average strength of 217.5 N (SD = 44.7), whereas conventional repairs (two interrupted Kessler sutures) failed at an average of 153.9 N (SD = 30.2). In a series of seven augmentation flap patients evaluated clinically and by Cybex dynamometry, an excellent result (by the Percy/Conochie rating) was obtained in six, and a good result in one. Plantar flexion strength in full extension averaged 94% of that of the uninvolved leg. There were no reruptures. These data suggest that flap augmentation may be a useful adjunct to conventional suture repair.

Achilles Tendon↗
PubMed1991

Propofol: bolus or continuous infusion. A day case technique for the vaginal termination of pregnancy.

Forty patients undergoing vaginal termination of pregnancy were randomly allocated to receive a propofol anaesthetic using either a repeat bolus or infusion technique. The Ohmeda 9000 Infusion Pump was used in the study. Patients in the infusion group recorded significantly longer induction times, greater maintenance doses and prolonged immediate recovery characteristics. Both techniques offered cardiovascular stability but no advantages were demonstrated for the infusion technique over a conventional repeat bolus method.

Abortion, Induced↗
PubMed1991

The effect of metabolic milieu on cardiac PET imaging using fluorine-18-deoxyglucose and nitrogen-13-ammonia in normal volunteers.

Cardiac PET imaging using 13N-ammonia and 18FDG was performed on 17 normal volunteers in the glucose-loaded and fasted states. PET images (glucose-loaded and fasted) were subjected to qualitative visual analysis using the descriptors: image quality, FDG blood-pool activity, ammonia lung field activity, and clinical interpretability. Glucose-loaded studies had better image quality, diminished FDG blood-pool activity, and were more often clinically interpretable compared to fasted studies. Dietary state did not affect 13N-ammonia study parameters. Using a semi-quantitative region of interest method, 18FDG myocardial activity was homogeneous and significantly affected by dietary state (2.48 +/- 1.0 fold increase in myocardial-to-blood pool ratio in glucose-loaded versus fasted states). Serum glucose, insulin, and free-fatty acid concentrations responded physiologically to glucose loading and fasting but showed no correlation with myocardial 18FDG uptake. PET imaging using 13N-ammonia and 18FDG appears optimal in the glucose-loaded state.

Adult↗
PubMed1989

Breast self-examination and the older woman: field testing an educational approach.

The effectiveness of a theoretically based educational strategy was compared with a standard breast self-examination educational strategy. It was found that women in the experimental treatment group (n = 68) were significantly (p = .029) more likely to perform breast self-examination appropriately 3 months following instruction than women in the standard treatment comparison group (n = 66) after controlling for pretest scores and age.

Aged↗
PubMed1988

Seventeen years' experience of a voluntarily based drug rationalisation programme in hospital.

A study was carried out analysing the operation of a drug rationalisation programme in a central London teaching district that had evolved from experience over 17 years. Creation of a limited list of about 700 drugs had been achieved by local consensus. Drug selection was based on appraisal of efficacy, safety, and cost and was undertaken by means of collaborative participation of most consultant specialists in the district. Educative and other non-restrictive strategies for reinforcing the rationalisation policy had achieved a consistently high rate of compliance in prescribing recommended drugs. The concept of selectivity in drug use and its continuous local reappraisal had a beneficial impact on the prescribing habits of doctors at all levels of seniority as well as on the training of medical undergraduates and nurses in the therapeutic use of medicines. Peer review and self audit were encouraged by use of an extensive monitoring system which incorporated continuous "facilitative" dialogue between ward pharmacists and prescribers. Two models of drug rationalisation programme were studied, the second of which together with other local initiatives had been associated with substantial and sustained reductions in drug spending each year over nine years since 1978. It is concluded that the second drug rationalisation programme model substantially improves the cost effective use of drugs in hospital and furthermore has the potential of being extended to general practice, especially in types of prescribing that are common to both forms of patient care.

Drug Prescriptions↗
PubMed1988

Assessment of depression in persons with mental retardation.

The psychometric characteristics of the Self-Report Depression Questionnaire (SRDQ, Reynolds, in press a), a 32-item self-report measure of depressive symptomatology in persons with mental retardation, were examined. The SRDQ was orally administered to 89 adults living in community-based settings. An internal consistency reliability coefficient of .90, and an 11-week test-retest reliability of .63 were obtained. Criterion-related validity was demonstrated by a high degree of relationship, r = .67, p less than .001, between the SRDQ and individual clinical interviews using the Hamilton Depression Rating Scale. An exploratory factor analysis of the SRDQ items was also presented.

Adult↗
PubMed1986

The relative influence of health beliefs, parental and peer behaviors and exercise program participation on smoking, alcohol use and physical activity.

This research specifies a model for lifestyle health behavior which includes socialization, social environmental and cognitive influences on smoking, alcohol use and exercise. Survey respondents were participants in university conditioning classes, academic health classes and a community fitness program. Of the socialization influences, drinking by both parents was directly related to drinking by females and drinking by the mother to that of males. Physical activity level of the father was associated with the activity of both genders. Parental smoking was not related to that of the respondents. Income was positively correlated with alcohol consumption in both genders and with smoking among women. In the immediate environment, drinking and smoking by male and female friends were directly associated with that of both male and female respondents with congruent gender relationships being strongest. Exercise by male friends was positively associated with activity level for both genders, as was exercise by female friends for women only. For college students, program participation was related to lower alcohol consumption among men only and higher activity level for women only. It was not related to the likelihood of smoking. For cognitive factors, belief in the efficacy of lifestyle change was inversely related to alcohol consumption for both genders and to smoking for women. Susceptibility to heart disease was associated with a low exercise frequency and smoking, while generalized susceptibility was directly related to activity level and to smoking. Self control over health was positively related to activity level. With one exception, the peer modeling variables had the strongest relationships of any of the model elements in the multivariate analyses. Gender specificity for modeling of behavior was found for peers, but not for parents. These findings suggest that prevention programs incorporate strategies to maximize peer support for healthful behavior and to counteract the effects of unhealthful behavior modeled by peers. Interventions to increase beliefs in the efficacy of lifestyle change to reduce risk are appropriate to encourage behavior change. When the change is underway, discussion of lowered susceptibility as a function of program compliance should reinforce the new behavior.

Adolescent↗
PubMed1986

Reverse phase high-performance liquid chromatography and secondary ion mass spectrometry. A strategy for identification of ten human hemoglobin variants.

Ten abnormal hemoglobins were detected and characterized in individual cases referred to our laboratory for evaluation of hematological problems. Six of these variants were electrophoretically silent and could be detected by reverse phase high-performance liquid chromatography (HPLC) analysis. HPLC was also used to analyze the tryptic peptides of each individual variant. In most of these variants, secondary ion mass spectra of the mixture of the tryptic peptides could reveal the aberrant peptide and predict possible substitution through the mass difference between the normal and abnormal peptide. The mass spectra of the isolated abnormal peptide generally contained sufficient fragment ions to define the position of the amino acid substitution, obviating the need for lengthy sequencing procedures. Combination of the two techniques.

Amino Acid Sequence↗