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Biomedical subjects

J Law

Publications and source records attributed to J Law.

At least 55 records · Page 3Linked to original sources
PubMed1997

Film viewing conditions in mammography.

A requirement for a minimum viewing box brightness of 3000 cd m-2 for reading mammograms has been widely advocated. Some recent work has challenged that opinion by reporting no significant variation in visibility of low contrast and fine detail objects over a wide range of brightness levels. This paper provides further experimental evidence to support the latter conclusion, at least over the range 1340-4190 cd m-2, and suggests that the currently recommended minimum viewing box brightness levels need to be revised. The importance of reducing room lighting levels is fully confirmed.

Breast Neoplasms↗
PubMed1997

A comparison of image quality on 28 mammography X-ray sets in the UK.

Image quality has been assessed using three different phantoms on 28 mammographic X-ray units in the National Health Service Breast Screening Programme within the UK. The results show only relatively minor differences between different models of X-ray unit and between the 14 associated film processors, but more marked differences between different film-screen combinations. Medium screens give significantly lower image quality scores than fine screens from the same manufacturer. It is suggested that, to improve mammographic image quality, a change of screen type may bring greater benefit than a change of X-ray set model, as well as being much more cost effective.

Humans↗
PubMed1996

Checking the consistency of sensitometers and film processors in a mammographic screening programme.

Quality control procedures in relation to speed and contrast in X-ray film processors, both in X-ray departments and breast screening centres, are based on the use of film sensitometers. Calibrations of these instruments, or simple checks of their constancy with time, are not readily available. A procedure is described in which a reference sensitometer is compared on a 3-monthly basis with the local sensitometer in seven breast screening centres (13 processors) in a region. This demonstrated long-term stability of speed and contrast in both sensitometers and processors. The results may also be used to compare speed and contrast between processors in centres using film of a single type. Standard deviations for single measurements are estimated to be approximately 1% for step density on a single sensitometer, less than 3% for comparison of two sensitometers, about 6% for comparison of processor speed, and between 4 and 5% for processor contrast.

Calibration↗
PubMed1996

Short communication: a comparison of fine and medium screens for mammography.

Intensifying screens for mammography may be categorized as fine, giving priority to image quality, or medium, achieving a lower dose at the expense of some image quality. It is important to be aware of the possible consequences of changing from a fine to a medium screen. The relative image quality and dose of four film-screen combinations (Fuji MIMA/UMMA film with Fuji HR Mammo Fine and HR Mammo Medium screens, Kodak MinRE film with Kodak MinR and MinR Medium screens) were evaluated using Leeds TOR(MAM) and Ackermann test objects. In each case, the performance of the medium screen was compared with that of the fine screen from the same manufacturer; it was not the purpose of this study to compare one manufacturer's products with the other's. Both medium screens showed measurably poorer image quality than the corresponding fine screens. The reduction in dose was only 30-40%. Careful evaluation of other dose reduction methods is recommended before changing from fine to medium screens.

Humans↗
PubMed1996

Consistency of film optical density in mammographic screening programmes.

Maintaining a constant and appropriate mean film optical density in mammography is an essential part of quality assurance in a breast screening programme. It depends on stability in X-ray exposure controls, film supplies, intensifying screens and film processing. A programme of weekly monitoring is described which helps to trace the source of any irregular or step-wise changes in any of the relevant parameters. Its results are also used to investigate by statistical methods the degree of film optical density variation achieved in periods of several weeks of apparent general stability. Results are presented for 20 X-ray sets and a total of 32 record periods of 8-10 weeks each. The mean standard deviation for density of a single film of a Perspex block was found to be 3.5%. For processor speed index it was the same while for X-ray set variations it was less than 2%. Neither of these last two variables showed any strong correlation with block film optical density.

Breast Neoplasms↗
PubMed1996

Short communication: kilovoltage measurement with rhodium target and filters on mammography X-ray machines.

X-ray machines used for mammography have, until recently, almost exclusively employed molybdenum (Mo) as anode material and filtration. In the UK, the RMI model 232 kVp meter is used extensively for the measurement of kilovoltage on such equipment. This unit is provided with switchable internal calibration only for molybdenum and molybdenum, or tungsten and aluminium, as anode and filtration, respectively. However, rhodium (Rh) has recently been introduced for filtration with either a molybdenum or rhodium anode in mammography equipment but, as yet, calibration facilities are not available for rhodium spectra. In this work, appropriate corrections for readings obtained with the RMI 232 kVp meter are derived for use with rhodium as filtration material with either molybdenum or rhodium anode material. An intercomparison between measurements made with four RMI model 232 kVp meters and nine IGE DMR X-ray sets was undertaken. The reproducibility of the instruments was confirmed and measurements of tube potential made on each of the X-ray sets pooled. Measurements were made from a nominal 25-35 kVp using Mo/Mo, Mo/Rh and Rh/Rh target/filter combinations. Corrections for readings obtained with Mo/Rh and Rh/Rh were produced by comparison with readings obtained with Mo/Mo, assuming stability of tube potential between anodes. The results are compared with data recently produced by the manufacturer of the meter.

Calibration↗
PubMed1996

Medication prescribing advice and drug utilization: a review from the United Kingdom.

General Medical Practitioners (GPs) in the United Kingdom are usually the first point of contact with the National Health Service (NHS) for patients. They provide the majority of ambulatory care for their practice population and act as 'gatekeepers' for referral onwards to other services. This article investigates the influence of the purchasing authority prescribing advisors (PAs), including pharmacists and GPs on the prescribing habits in Salford, England, an inner city area in the North of England, close to the city of Manchester. The PAs became known as the prescribing CIA, and used the strategy of Control, progressing to Influence and Autonomy, to develop a mature partnership between the GPs, PAs and other health care professionals. Information collated from prescribing (PACT) data, by the Prescription Pricing Authority, was used to make comparisons between different practices within an area. Savings made by making rational changes in prescribing, were used to enhance practice development for the benefit of patient care.

Data Collection↗
PubMed1995

A novel anti-seminoma monoclonal antibody (M2A) labelled with technetium-99m: potential application for radioimmunoscintigraphy.

OBJECTIVE: To study the potential usefulness of monoclonal antibody (mAb) M2A specific for seminoma to image tumour nodules in a preclinical nude mouse model. MATERIALS AND METHODS: MAb M2A was labelled with technetium-99m (99mTc) following reduction and was administered intraperitoneally to nude mice bearing subcutaneous HEY cell xenografts against which the antibody was originally raised. Biodistribution and gamma scintigraphy studies were performed 24 h after administration of 99mTc-M2A. RESULTS: Biodistribution studies showed specific targeting of 99mTc-M2A to HEY tumours in comparison with control mAb 99mTc-6E8 and 99mTc-2G3 which do not bind to HEY cells. Subcutaneous HEY cell tumours (0.5-1.0 g) were successfully imaged using gamma-scintigraphy following administration of 99mTc-M2A. CONCLUSION: The results of this study indicate the potential usefulness of 99mTc-M2A as a clinical reagent for imaging seminoma metastases.

Animals↗
PubMed1995

A system to generate chromosomal mutations in Lactococcus lactis which allows fast analysis of targeted genes.

A system for generating chromosomal insertions in lactococci is described. It is based on the conditional replication of lactococcal pWV01-derived Ori+ RepA- vector pORI19, containing lacZ alpha and the multiple cloning site of pUC19. Chromosomal AluI fragments of Lactococcus lactis were cloned in pORI19 in RepA+ helper strain Escherichia coli EC101. The frequency of Campbell-type recombinants, following introduction of this plasmid bank into L. lactis (RepA-), was increased by combining the system with temperature-sensitive pWV01 derivative pVE6007. Transformation of L. lactis MG1363 (pVE6007) with the pORI19 bank of lactococcal chromosomal fragments at the permissive temperature allowed replication of several copies of a recombinant plasmid from the bank within a cell because of the provision in trans of RepA-Ts from pVE6007. A temperature shift to 37 degrees C resulted in loss of pVE6007 and integration of the pORI19 derivatives at high frequencies. A bank of lactococcal mutants was made in this way and successfully screened for the presence of two mutations: one in the monocistronic 1.3-kb peptidoglycan hydrolase gene (acmA) and one in the hitherto uncharacterized maltose fermentation pathway. Reintroduction of pVE6007 into the Mal- mutant at 30 degrees C resulted in excision of the integrated plasmid and restoration of the ability of ferment maltose. The integration plasmid (pMAL) was rescued by using the isolated plasmid content of a restored Mal+ colony to transform E. coli EC101. Nucleotide sequencing of the 564-bp chromosomal fragment in pMAL revealed an internal part of an open reading frame of which the translated product showed significant homology with ATP-binding proteins MalK of E. coli, Salmonella typhimurium, and Enterobacter aerogenes and MsmK of Streptococcus mutans. This combined use of two types of conditional replicating pWV01-derived vectors represents a novel, powerful tool for chromosomal gene inactivation, targeting, cloning, and sequencing of the labelled gene.

Amino Acid Sequence↗
PubMed1995

Technical note: perspex blocks for estimation of dose to a standard breast--effect of variation in block thickness.

Mean glandular dose in mammography may be deduced from measurements made using Perspex blocks. This method is almost universally used in the National Health Service Breast Screening Programme. The effect on the estimated mean glandular dose of variations in the measured thickness of Perspex from a nominal thickness of 40 mm was investigated. Results are presented from three UK Regions. Variations in measured Perspex thicknesses ranged from almost 8% below to about 2% above the 40 mm nominal, causing errors in dose estimation, if uncorrected, of about +20% to -6.5%. A means of correcting dose estimates for measured differences in block thickness is presented. An alternative method of ensuring consistent dosimetry would be to use accurately machined Perspex blocks.

Breast↗
PubMed1995

A method for estimating compressed breast thickness during mammography.

Measurements of compressed breast thickness during mammography is necessary for the calculation of breast dose. In theory, it should be possible to calculate breast thickness from the separation of images of radio-opaque markers attached to the compression paddle. Such a technique has been evaluated on two models of X-ray set using simulated and real breasts. The results show that breast thickness at a given position can be determined with an average error of about 2 mm by this method, which is likely to be adequate for dosimetry.

Breast↗
PubMed1995

Risk and benefit associated with radiation dose in breast screening programmes--an update.

This paper discusses and attempts to estimate the very small numbers of women attending the UK Breast Screening Programme for whom the risk of cancer induction may exceed the probability of cancer detection. It updates a previous paper on the same topic. Variations in breast dose between individuals, due to differences in breast size and in numbers of views and films taken, are considered and revised. New data on cancer induction and its variation with age at exposure have been employed. The overall effect of these changes is generally to improve the balance of benefit against risk compared with the previous paper referred to, the very few exceptions being categories where the numbers of women in question remain of the order of one in a million. The implications for certain alternative screening schedules and for some current trials are also discussed, the conclusions being again reasonably reassuring.

Adult↗
PubMed1995

Assessment of mean glandular dose in mammography.

The routine assessment of patient dose in the National Health Service Breast Screening Programme is performed as part of the quality assurance protocol recommended by the Institute of Physical Sciences in Medicine. The mean glandular dose to a standard breast is deduced from measurement of the air kerma at the entrance surface of a 4 cm Perspex phantom by applying a series of conversion factors. The exposure factors for this measurement are those used clinically. The measured mean glandular dose is then compared with nationally accepted action levels. In some centres the assessment of mean glandular dose using Perspex is supplemented by patient dose surveys. The mean glandular dose to a series of patients attending a breast screening unit may be estimated from a knowledge of the exposure factors and compressed breast thickness, using a knowledge of the X-ray tube output. Measurements made on units in the Northern Region of England and in Scotland using both methods are presented. The implication of these measurements with regard to patient dose surveys in mammography and quality assurance programmes are discussed. An analysis of the uncertainties associated with the measurement techniques is presented.

Breast↗
PubMed1995

Treatment of refractory recurrent multifocal atrial tachycardia with atrioventricular junction ablation and permanent pacing.

Multifocal atrial tachycardia is a difficult clinical problem generally associated with acute cardiorespiratory illness. The purpose of this study was to assess the feasibility and clinical utility of atrioventricular junction ablation plus permanent transvenous pacemaker implantation as therapy for uncontrolled refractory multifocal atrial tachycardia. Three patients with uncontrolled refractory multifocal atrial tachycardia underwent atrioventricular junction ablation plus permanent transvenous pacemaker implantation. Complications and outcome of each procedure was monitored and both objective and subjective assessment of physical functional capacity was assessed by a semiquantitative examination. Ablation procedures controlled the ventricular response in all patients. There were no complications related to the ablation procedure or implantation of permanent transvenous pacing system. All patients demonstrated subjective improvement in symptoms. Palpitations were virtually eradicated in these patients and all enjoyed significant improvements in rest and effort dyspnea, exercise tolerance and asthenia. Objective assessment of functional class also demonstrated significant improvements. Atrioventricular ablation plus permanent transvenous pacing offers a safe and effective therapy for uncontrolled refractory multifocal atrial tachycardia.

Aged↗