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Biomedical subjects

A Welch

Publications and source records attributed to A Welch.

At least 55 records · Page 3Linked to original sources
PubMed1999

Structure of the standardized computerized 24-h diet recall interview used as reference method in the 22 centers participating in the EPIC project. European Prospective Investigation into Cancer and Nutrition.

A computerized 24-h diet recall interview program (EPIC-SOFT) was developed for use in a large European multi-center study, namely the European Prospective Investigation into Cancer and Nutrition (EPIC). This program, which was adapted for each participating country and translated into nine languages, was developed to standardize interviews between the 22 EPIC centers. Common rules were pre-entered into the system to describe, quantify and probe approximately 1500-2200 foods and 150-350 recipes. Common methods used to classify and export the EPIC-SOFT dietary data facilitate their exchange, comparison and analysis. So far, EPIC-SOFT is the only available computerized 24-h diet recall system developed to provide comparable food consumption data between several European countries.

Databases, Factual↗
PubMed1999

Evaluation of 18F-FDG positron emission tomography in gastric and oesophageal carcinoma.

The aim of this study was to evaluate 18F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) in gastric and oesophageal carcinoma. 16 patients with biopsy proven oesophageal or gastric carcinoma had PET scans. Four patients had advanced disease and received palliative treatment. The remaining 12 patients were randomized to immediate surgery or neoadjuvant chemotherapy. Three patients had repeat PET scans following chemotherapy. PET detected the primary tumour in all cases including stage T1 lesions. Involved locoregional nodes (N1, N2) were not identified separately from the primary tumour. Semiquantitative analysis was performed in the form of tumour to liver activity ratios (TLR). In general, the TLR values were higher in the higher T stages, although there was only one case each of T1 and T2 lesions. PET scanning using 18F-FDG is a sensitive method for detecting primary oesophageal and gastric cancers but is limited in locoregional staging.

Adult↗
PubMed1998

Detection of response to chemotherapy using positron emission tomography in patients with oesophageal and gastric cancer.

BACKGROUND: The aim of the study was to determine whether 2-[18F]-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET) could detect response to chemotherapy in patients with oesophageal and gastric cancer. METHODS: Fourteen patients underwent imaging before and after chemotherapy using FDG-PET. Computed tomography (CT), dysphagia scores and weight changes were used for comparison of evidence of response. Tumour to liver ratios (TLRs) and influx constants for FDG (K) were used for quantification purposes. RESULTS: Thirteen of 14 lesions were successfully imaged before therapy. Changes were seen in all follow-up scans, ranging from a complete response to a 15 per cent increase in tumour FDG uptake. Response was demonstrated by CT in four patients; all four had large reductions in FDG uptake after chemotherapy. Two patients with an increase in FDG uptake reported no improvement in dysphagia and continued to lose weight during therapy. CONCLUSION: Changes in tumour FDG uptake were seen in all tumours after chemotherapy. FDG-PET may have a role to play in the assessment of patients with upper gastrointestinal malignancy receiving chemotherapy.

Adenocarcinoma↗
PubMed1997

An investigation into the effect of input function shape and image acquisition interval on estimates of washin for dynamic cardiac SPECT.

Dynamic cardiac SPECT and PET can be used to measure myocardial perfusion by estimating the kinetic rate constant describing the washing of radioactive-labelled tracers from the blood to the extravascular myocardial tissue. Because of differences in photon statistics and data acquisition techniques, protocols which produce optimal estimates of the washin for dynamic cardiac PET may give suboptimal estimates if applied in dynamic cardiac SPECT. Two important factors in the estimation of washin are the shape of the tracer input function and the image acquisition interval. This study uses computer simulations to investigate the effect of varying the tracer infusion length and image acquisition interval on the bias and variance of estimates of washin obtained with dynamic cardiac SPECT and 99mTc-labelled teboroxime. Bias in parameter estimates can be introduced by aliasing, integration of the time-varying radioactivity by the detector, and detector motion. This bias can be reduced by decreasing the acquisition interval and using a longer-duration input function. However, this results in poor photon statistics, which generate large variance, and can also introduce bias in the estimates of the washin. Our studies indicate that better estimates of the washin are obtained by using an acquisition interval that is of sufficient duration to obtain adequate photon statistics even if this is at the expense of temporal resolution. The increase in bias caused by using a 10 or 20 s acquisition interval instead of a 5 s acquisition interval is minimal when compared with the reduction in variance. Variance in estimates is also reduced by using a sharp input function, resulting in higher peak counts during washin. It is also shown that the variance of estimates of the washin increases generally when faster kinetics are observed. This variance can, however, be reduced by using longer acquisition intervals.

Fourier Analysis↗
PubMed1997

Validation of dietary assessment methods in the UK arm of EPIC using weighed records, and 24-hour urinary nitrogen and potassium and serum vitamin C and carotenoids as biomarkers.

BACKGROUND: In the UK EPIC validation studies, the accuracy of several methods was assessed by comparison with to-day weighed records and the biomarkers, 24-hour urine nitrogen (N) and potassium (K), plasma carotenoids and plasma vitamin C. METHODS: Comparisons between methods were made on 156 women, studied over 1 year at 3-monthly intervals at home. On each of four occasions, volunteers completed 4 days of weighed records and provided two 24-hour urine collections and a fasting blood sample. RESULTS: In comparison with the 16 days of weighed records, a food frequency questionnaire (FFQ) yielded higher values mainly due to greater reported consumption of milk and of vegetables. A 24-hour recall was as good as the FFQ in placing individuals in the distribution of habitual diet from weighed records. Results obtained from a 7-day estimated record were closest to those obtained from the weighed record. Correlations between 24-hour urine excretion and dietary N intake from weighed records were high (0.78-0.87) as were those with estimated food diaries (0.60-0.70). Correlations between urine N and the FFQ and 24-hour recall were lower (0.10 to 0.27), but improved by energy adjustment using residuals for N and K which are correlated with total energy intake. Comparisons between dietary estimates and urinary K and serum carotenoids and vitamin C showed broadly similar results. Limited biomarker information amongst 200 UK EPIC participants supported the findings of the validation study. CONCLUSIONS: UK EPIC uses three methods (the 7-day diary, an improved FFQ, and the 24-hour recall) to assess diet. 93% of first food diaries are returned completed by participants. Repeated diaries are the main dietary assessment method for nested case-control analyses.

Aged↗
PubMed1997

Toward accurate attenuation correction in SPECT without transmission measurements.

The current trend in attenuation correction for single photon emission computed tomography (SPECT) is to measure and reconstruct the attenuation coefficient map using a transmission scan, performed either sequentially or simultaneously with the emission scan. This approach requires dedicated hardware and increases the cost (and in some cases the scanning time) required to produce a clinical SPECT image. Furthermore, if short focal-length fan-beam collimators are used for transmission imaging, the projection data may be truncated, leading to errors in the attenuation coefficient map. Our goal is to obtain information about the attenuation distribution from only the measured emission data by exploiting the fact that only certain attenuation distributions are consistent with a given emission dataset. Ultimately this consistency information will either be used directly to compensate for attenuation or combined with the incomplete information from fan-beam transmission measurements to produce a more accurate attenuation coefficient map. In this manuscript the consistency conditions (which relate the measured SPECT data to the sinogram of the attenuation distribution) are used to find the uniform elliptical attenuation object which is most consistent with the measured emission data. This object is then used for attenuation correction during the reconstruction of the emission data. The method is tested using both simulated and experimentally acquired data from uniformly and nonuniformly attenuating objects. The results show that, for uniform elliptical attenuators, the consistency conditions of the SPECT data can be used to produce an accurate estimate of the attenuation map without performing any transmission measurements. The results also show that, in certain circumstances, the consistency conditions can prove useful for attenuation compensation with nonuniform attenuators.

Algorithms↗
PubMed1997

Implementation of a model-based nonuniform scatter correction scheme for SPECT.

In this paper four scatter-compensation schemes are considered. The four schemes are all based on a previously developed two-dimensional (2-D) scatter model. Reconstruction is achieved using the iterative expectation-maximization maximum-likelihood (EM-ML) algorithm. The schemes consist of: 1) including the model in both the forward and back projector; 2) just including the model in the forward projector; 3) and 4) implementing the model in a subtraction and addition scheme, respectively. Monte Carlo simulated projection data are used to test the accuracy, convergence properties, and noise properties of the four scatter-compensation schemes. Data are simulated for both uniformly and nonuniformly attenuating objects. The results show that all four correction schemes yield images which are similar in terms of accuracy to that obtained from reconstructing scatter-free data. The subtraction scheme is shown to converge faster than the other compensation schemes, both in terms of iterations and actual time required for reconstruction. The scheme in which the model is only used in the forward-projector and the scatter-addition scheme both performs slightly better, in terms of signal-to-noise ratio (SNR), than the subtraction scheme. However, the forward projector scheme requires significantly more CPU time for reconstruction. The correction scheme in which the scatter model was included in both the forward and backprojectors is shown to produce accurate images with SNR's higher than even a perfect scatter rejection scheme. While the scatter correction scheme with the model in both the forward projector and backprojector has superior noise properties to the other algorithms, the results suggest that the faster subtraction/addition schemes will probably prove most useful for routine clinical scatter compensation.

Image Processing, Computer-Assisted↗
PubMed1996

Correcting for ethnicity when defining large for gestational age infants in diabetic pregnancies.

The large-for-gestational-age (LGA) infant, defined as > 90th birthweight percentile, is associated with mild disturbances of maternal glucose tolerance. In the UK the same birthweight percentile charts are used for all ethnic groups when assessing LGA infants. The influence of maternal hyperglycaemia on LGA infants of Asian (Indian Subcontinent) mothers in the UK is likely to be under-reported, as Asian birthweights tend to be lower than White/Europid birthweights. We assessed the number of LGA infants born consecutively to 21 Asian and 26 White/Europid mothers with gestational diabetes mellitus (GDM), delivered between 37 and 42 weeks gestation, and also in 34 Asian and 121 White/Europid mothers with a positive screening test for GDM but a normal 75 g oral glucose tolerance test (OGTT). Large-for-gestational-age infants were identified using both the standard UK percentile charts of the Medical Research Council and percentile charts constructed from 30,418 Asian and 162,477 White/Europid singleton births, delivered between 37 and 42 weeks gestation to non-diabetic mothers delivered in the North West Thames Region of England. The standard Medical Research Council percentile charts, compared with the ethnically derived charts, identified fewer LGA Asian (7/56 vs 15/56) but more White/Europid infants (33/147 vs 21/147). When correcting for ethnicity more Asian than White/Europid GDM mothers delivered LGA infants (9/21 vs 3/26, chi 2 = 4.76, p < 0.05). The maternal 2 h OGTT plasma glucose was a significant independent contributor to birthweight in the Asian (r2 = 0.319, p < 0.0005) but not the White/Europid infants, in whom gestational age and maternal height were significant independent contributors to birthweight (r2 = 0.158, p < 0.0001). We conclude that ethnic influences are important when defining LGA infants and that mild disturbances of maternal glycaemia have a greater influence on the birthweight of Asian than White/Europid infants.

Adult↗
PubMed1996

The standard primipara as a basis for inter-unit comparisons of maternity care.

OBJECTIVE: To assess the suitability of the standard primipara (a subset of the obstetric population that has relatively low risk or intervention and of adverse outcome) for making inter-unit comparisons of indicators of the process and outcome of maternity care. DESIGN: Inter-unit comparison of 10 indicators of obstetric intervention and adverse outcome derived from routinely collected computerised data held on the St Mary's Maternity Information System. SETTING: Fifteen maternity units in the former North West Thames Region. PARTICIPANTS: 15,463 primiparae who were delivered in 1992. MAIN OUTCOME MEASURES: Proportion of primiparae within the standard definition; degree to which standard primiparae are associated with lower rates of intervention and adverse outcome, as compared to other primiparae. RESULTS: Within the database, 42.6% of all primiparae were found to be standard, with rates varying between units from 25.9% to 57.7%. As expected, the standard primiparous woman is at less risk of intervention or adverse outcome than other primiparae. All but one component variable of the standard definition is a significant risk factor for at least four of the 10 indicators. Statistically significant differences in indicator rates are seen between standard and nonstandard primiparae within units. Within the standard group, significant differences in rates of intervention and adverse outcome are seen between units. Units with relatively high levels of intervention within the higher risk nonstandard group also have relatively high levels of intervention within the standard group. CONCLUSIONS: Use of the standard primipara, rather than the whole obstetric population, as the basis for inter-unit comparisons of maternity care will control for the substantial difference in case mix seen in different units, thereby increasing the validity of those comparisons. The technique has the additional benefit of clarifying the relationship between everyday clinical decision making and a unit's performance in comparative indicator reports. The approach must be combined with a separate study of the other groups in the case mix, such as multiparae and high risk primiparae. Additional nonoverlapping groups, homogeneous in terms of risk factors, should be defined and used to extend the basis on which comparisons may be made.

Adult↗
PubMed1995

Relation between maternal haemoglobin concentration and birth weight in different ethnic groups.

OBJECTIVE: To assess the relation of the lowest haemoglobin concentration in pregnancy with birth weight and the rates of low birth weight and preterm delivery in different ethnic groups. DESIGN: Retrospective analysis of 153,602 pregnancies with ethnic group and birth weight recorded on a regional pregnancy database during 1988-91. The haemoglobin measurement used was the lowest recorded during pregnancy. SETTING: North West Thames region. SUBJECTS: 115,262 white women, 22,206 Indo-Pakistanis, 4570 Afro-Caribbeans, 2642 mediterraneans, 3905 black Africans, 2351 orientals, and 2666 others. MAIN OUTCOME MEASURES: Birth weight and rates of low birth weight (< 2500 g) and preterm delivery (< 37 completed weeks). RESULTS: Maximum mean birth weight in white women was achieved with a lowest haemoglobin concentration in pregnancy of 85-95 g/l; the lowest incidence of low birth weight and preterm labour occurred with a lowest haemoglobin of 95-105 g/l. A similar pattern occurred in all ethnic groups. CONCLUSIONS: The magnitude of the fall in haemoglobin concentration in pregnancy is related to birth weight; failure of the haemoglobin concentration to fall below 105 g/l indicates an increased risk of low birth weight and preterm delivery. This phenomenon is seen in all ethnic groups. Some ethnic groups have higher rates of low birth weight and preterm delivery than white women, and they also have higher rates of low haemoglobin concentrations. This increased rate of "anaemia," however, does not account for their higher rates of low birth weight, which occurs at all haemoglobin concentrations.

Africa↗
PubMed1995

Validation of weighed records and other methods of dietary assessment using the 24 h urine nitrogen technique and other biological markers.

Results from analysis of 24 h urine collections, verified for completeness with para-amino benzoic acid, and blood samples collected over 1 year were compared with 16 d weighed records of all food consumed collected over the year, and with results from 24 h recalls, food-frequency questionnaires and estimated food records in 160 women. Using the weighed records, individuals were sorted into quintiles of the distribution of the urine N excretion:dietary N intake ratio (UN:DN). UN exceeded DN in the top quintile of this ratio; mean ratio UN:DN = 1.13. Individuals in this top quintile were heavier, had significantly greater body mass indices, were reportedly more restrained eaters, had significantly lower energy intake:basal metabolic rate ratios (EI:BMR), and had correlated ratios of UN:DN and EI:BMR (r -0.62). Those in the top quintile reported lower intakes of energy and energy-yielding nutrients, Ca, fats, cakes, breakfast cereals, milk and sugars than individuals in the other quintiles but not lower intakes of non-starch polysaccharides, vitamin C, vegetables, potatoes or meat. Correlations between dietary intake from weighed records and 24 h urine K were 0.74 and 0.82, and between dietary vitamin C and beta-carotene and plasma vitamin C and beta-carotene 0.86 and 0.48. Correlations between dietary N intake from weighed records and 24 h urine excretion were high (0.78-0.87). Those between N from estimated food records and urine N were r 0.60-0.70. Correlations between urine N and 24 h recalls and food-frequency questionnaires were in the order of 0.01 to 0.5. Despite problems of underreporting in overweight individuals in 20% of this sample, weighed records remained the most accurate method of dietary assessment, and only an estimated 7 d diary was able to approach this accuracy.

Basal Metabolism↗
PubMed1995

A transmission-map-based scatter correction technique for SPECT in inhomogeneous media.

In this paper a method of modeling the distribution of scattered events in emission projection data is developed and applied. This method is based on the use of a transmission map to define the inhomogeneous scattering object. The key point is the use of the set of line integrals calculated as part of the attenuation correction technique, as the basis of a model of the distribution of scattered events. The probability of a photon being scattered through a given angle and being detected in the emission energy window is approximated using a Gaussian function. The parameters of this Gaussian are determined using Monte Carlo generated parallel-beam scatter line spread functions from a nonuniformly attenuating phantom. The model is incorporated into a two-dimensional projector-backprojector and used with the Expectation-Maximization-Maximum-Likelihood algorithm for the reconstruction of fan-beam phantom data. The correction is shown to perform well for a phantom that varies slowly in the axial direction. For the more clinically realistic situation of a torso phantom, the method produces improvements in terms of blood pool to myocardium contrast, but does not restore the contrast to the level exhibited in a reconstruction from "scatter free" data.

Humans↗
PubMed1995

An investigation of the effect of finite system resolution and photon noise on the bias and precision of dynamic cardiac SPECT parameters.

The exchange of a radionuclide (and similarly of oxygen) between blood and the myocardium is a dynamic process. Dynamic SPECT offers the possibility of directly quantifying the kinetic parameters which describe this process. In this paper we investigate and quantify the effect of typical SPECT system resolution and photon counting statistics on the bias and precision of dynamic cardiac SPECT parameters. System resolution and photon noise are only two of the image degrading processes which occur in SPECT. Therefore, the bias and precision quoted should be viewed as a lower limit on those which could be expected with an experimental study. Dynamic SPECT projection data are simulated using a realistic human torso phantom. Data are simulated assuming both perfect system resolution and a system resolution typical of a clinical SPECT system. A triple detector SPECT system which acquires a full set of projection data in 10 s using continuous detector motion is modelled. Kinetic parameters are estimated using a number of myocardial regions of interest. The results show that the rate constant characterizing the washing of activity into the myocardium is more sensitive to region of interest position than is the washout rate constant. The bias and precision of the dynamic parameters are estimated from multiple realizations of projection data exhibiting various noise levels. The main effect of increased photon noise in the projection data is to decrease the precision of the estimated parameters. However, there is also some evidence that for high noise levels the bias of the parameters may also be affected.

Biophysical Phenomena↗
PubMed1994

Application of convergent-beam collimation and simultaneous transmission emission tomography to cardiac single-photon emission computed tomography.

Single-photon emission computed tomography (SPECT) is the most commonly performed imaging technique for perfusion studies of the heart and brain. However, these organs are much smaller than the crystal surface of gamma cameras. SPECT sensitivity and resolution can be improved by using fan- and cone-beam collimators to magnify the image of these organs over a larger portion of the crystal face. Special orbits and reconstruction algorithms must be used with convergent-beam acquisitions to prevent image distortion. Differential attenuation of source activity in the chest is one of the most vexing problems in cardiac SPECT, especially with Thallium-201. Multi-headed cameras equipped with convergent-beam collimators allow a transmission image to be obtained at the same time as emission images. Applying a transmission map of the chest attenuation values to the emission images produces a truer picture of source distribution in the heart. This article reviews the technical problems associated with convergent-beam geometry and simultaneous transmission emission tomography SPECT imaging of the heart.

Algorithms↗
PubMed1994

Comparison of dietary assessment methods in nutritional epidemiology: weighed records v. 24 h recalls, food-frequency questionnaires and estimated-diet records.

Women (n 160) aged 50 to 65 years were asked to weigh their food for 4 d on four occasions over the period of 1 year, using the PETRA (Portable Electronic Tape Recorded Automatic) scales. Throughout the year, they were asked to complete seven other dietary assessment methods: a simple 24 h recall, a structured 24 h recall with portion size assessments using photographs, two food-frequency questionnaires, a 7 d estimated record or open-ended food diary, a structured food-frequency (menu) record, and a structured food-frequency (menu) record with portion sizes assessed using photographs. Comparisons between the average of the 16 d weighed records and the first presentation of each method indicated that food-frequency questionnaires were not appreciably better at placing individuals in the distribution of habitual diet than 24 h recalls, due partly to inaccuracies in the estimation of frequency of food consumption. With a 7 d estimated record or open-ended food diary, however, individual values of nutrients were most closely associated with those obtained from 16 d weighed records, and there were no significant differences in average food or nutrient intakes.

Diet Records↗
PubMed1993

Profiles of workload in general surgery from linked hospital statistics.

Data from the Oxford Record Linkage Study between 1976 and 1986 were used to analyse statistical profiles of hospital care, taking account of multiple admissions per patient. Admission rates were higher in the elderly than the young, they were higher for men than women, and they increased over time. Episode-based admission rates increased by 15.5 per cent and person-based rates by 11.6 per cent. Most of the increase therefore represented a real rise in the number of people treated rather than an increase in multiple admissions per person. In the latest year of the study there was a mean of 125 admissions per annum per 100 male patients admitted and of 118 admissions per annum per 100 female patients admitted. The mean length of stay per admission and the total time spent in hospital per person per annum declined substantially from 1976 to 1986. Admission rates for prostatectomy, colectomy and varicose vein surgery increased significantly and those for appendicectomy, cholecystectomy and peptic ulcer decreased significantly.

Adolescent↗
PubMed1993

In-vitro and in-vivo characterisation of resistance to colonisation with Clostridium difficile.

In hamsters, resistance to colonisation by Clostridium difficile appears to be mediated by micro-organisms that are present in the gut in relatively low concentrations. Small amounts of normal caecal contents inhibited the growth of C. difficile when added to cultures in vitro or given to animals which had been treated with clindamycin. Filtrates of caecal contents, frozen and thawed contents and contents diluted to 0.1% wet weight lost their inhibitory properties. However, caecal contents retained their protective capacity after culture for 7 days in vitro. Antibiotic treatment altered resistance to colonisation by only a few species of clostridia. Faeces of animals treated with ampicillin but not clindamycin recovered colonisation resistance after incubation at 37 degrees C in vitro. Since human faeces could also restore colonisation resistance to hamsters, the hamster model may be useful for the study of resistance to colonisation by C. difficile in man.

Animals↗