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Biomedical subjects

D McLean

Publications and source records attributed to D McLean.

At least 19 recordsLinked to original sources
PubMed2006

Quantitative assessment of breast density from digitized mammograms into Tabar's patterns.

We describe a semi-automated technique for the quantitative assessment of breast density from digitized mammograms in comparison with patterns suggested by Tabar. It was developed using the MATLAB-based graphical user interface applications. It is based on an interactive thresholding method, after a short automated method that shows the fibroglandular tissue area, breast area and breast density each time new thresholds are placed on the image. The breast density is taken as a percentage of the fibroglandular tissue to the breast tissue areas. It was tested in four different ways, namely by examining: (i) correlation of the quantitative assessment results with subjective classification, (ii) classification performance using the quantitative assessment technique, (iii) interobserver agreement and (iv) intraobserver agreement. The results of the quantitative assessment correlated well (r2 = 0.92) with the subjective Tabar patterns classified by the radiologist (correctly classified 83% of digitized mammograms). The average kappa coefficient for the agreement between the readers was 0.63. This indicated moderate agreement between the three observers in classifying breast density using the quantitative assessment technique. The kappa coefficient of 0.75 for intraobserver agreement reflected good agreement between two sets of readings. The technique may be useful as a supplement to the radiologist's assessment in classifying mammograms into Tabar's pattern associated with breast cancer risk.

Absorptiometry, Photon↗
PubMed2006

Pine dust, atopy and lung function: A cross-sectional study in sawmill workers.

An increased risk of asthma symptoms has previously been shown in 772 pine sawmill workers. The aim of the current study was to assess the association between dust exposure, lung function and atopy. Subjects with (n = 59) and without (n = 167) asthma symptoms were randomly selected from the previous survey. Lung function and atopy were determined using spirometry and skin-prick tests, respectively. Inhalable dust levels were measured on the same day. The geometric mean dust concentration was 0.52 mg x m(-3). Exposure to dry but not to green dust was associated with asthma symptoms. Green dust was associated with atopic sensitisation, particularly against outdoor allergens; no association was found for dry dust. Forced vital capacity, forced expiratory volume in one second and peak expiratory flow were significantly lower in workers exposed to high levels of green dust (-350 mL, -260 mL and -860 mL x s(-1), respectively) and dry dust (-230 mL, -190 mL and -850 mL x s(-1), respectively). These associations were observed both in subjects with and without asthma symptoms. No associations with cross-shift changes in lung function were found. Exposure to green pine sawdust may be a risk factor for atopy. Both green and dry dust were associated with obstructive as well as restrictive pulmonary effects.

Adult↗
PubMed2006

Paediatric and adult computed tomography practice and patient dose in Australia.

The current practice for CT scanning of paediatric patients in Australia has been assessed through a survey sent to the site of all CT scanners licensed in New South Wales and all dedicated children's hospitals in Australia. The survey addressed demographic details, CT scanner details and scanning parameters for four imaging scenarios (brain CT, chest CT, abdomen/pelvis CT and high-resolution chest CT for three different age groups (8 weeks, 5-7 years and adult patients). The effective dose for each imaging scenario and age group was calculated and compared for 52 sites representing 53 CT scanners. For any age group and imaging scenario, there was a large spread of effective dose. For comparable CT examinations, the effective dose varied by up to 36-fold between centres. There was a clear trend for centres that frequently carry out CT scans on paediatric patients to have the lowest radiation doses. Four age group/imaging scenarios showed significantly lower effective doses for hospital-based CT than for nonhospital sites. There was also a trend for doses to be lower at dedicated paediatric centres. Effective dose was closely associated with mAs, with most centres using lower mAs for younger patients, but few centres reduced the kVp for paediatric patients. The results of the survey emphasize the need for continuing education and protocol review, particularly in paediatric CT examinations, in a complex and fast changing environment.

Adult↗
PubMed2005

Recommendations for a technical quality control program for diagnostic X-ray equipment.

This position paper was produced by a working party set up by the Radiology Special Interest Group of the ACPSEM in 2001. It is designed to give the consensus view of College members in Australia and New Zealand on the nature and frequency of tests which should be performed on diagnostic x-ray equipment to maintain adequate quality control of imaging performance and radiation safety. Tests on mammographic equipment have been excluded having been covered in a previous ACPSEM position paper (Australas Phys Eng Sci Med, 24(3):107-131, 2001). Detailed descriptions of test procedures are not given but it is intended that a series of workbooks should be produced giving College recommended test methods for each imaging modality. The recommendations are produced here in an easy-to-read, tabular form giving the nature and purpose of each test and the implications of non-compliance with regard to image quality and radiation safety.

Australasia↗
PubMed2005

The effect of towing a range of relative resistances on sprint performance.

The aim of this study was to compare sprint performance over 10 and 20 m when participants ran while towing resistances, weighing between 0 and 30% of body mass. The sample of 33 participants consisted of male rugby and soccer players (age 21.1 +/- 1.8 years, body mass 83.6 +/- 13.1 kg, height 1.82 +/- 0.1 m; mean +/- s). Each participant performed two sets of seven sprints over 20 m using a Latin rectangular design. The times were recorded at 10 and 20 m using electronic speed gates. The sprints of 13 players were video-recorded to allow calculation of stride length and frequency. For both sprints, a quadratic relationship was observed between sprint time and resistance as sprint time increased from 2.94 s to 3.80 s from 0 to 30% resistance. This relationship was statistically significant but considered not to be meaningful for performance because, over the range of resistances used in this study, the quadratic model was never more than 1% (in terms of sprint time) from the linear model. As resistance increased, the stride length shortened, with mean values of 1.63 +/- 0.13 m at 0% body mass and 1.33 +/- 0.13 m at 30% of body mass. There was no significant change in stride frequency with increasing resistance. The results show that in general there is an increase in sprint time with an increase in resistance. No particular resistance in the range tested (0 - 30%) can be recommended for practice.

Adult↗
PubMed2005

Occupational bladder cancer in New Zealand: a 1-year review of cases notified to the New Zealand Cancer Registry.

AIM: To identify which cases of adult bladder cancer notified to the New Zealand Cancer Registry in 2001 had a probable occupational cause. METHODS: Occupational Safety and Health (OSH), in conjunction with the Massey University Centre for Public Health Research, interviewed and obtained an occupational history for 210 (162 men, 48 women) cases. RESULTS: Of the 162 male cases (response rate 65%), 45 (28%) were considered to be 'probable' occupational cancers. Of the 48 female cases (response rate 76%), three cases (6%) were considered to be 'probable' occupational cancers. The largest occupational group for men was truck drivers, which made up 51% of probable cases. Other common groups were engineering and metal workers (18%), crop farmers/orchardists (7%), textile and leather workers (7%), painters/furniture finishers (7%), and plastics manufacturing workers (4%). The three female cases considered to be of occupational origin included two textile workers and one telephonist. CONCLUSIONS: The percentage of cases considered to be of occupational origin is similar to that reported in Europe and the United States, indicating that occupational cancer is a major occupational health problem in New Zealand as it is in other parts of the world.

Female↗
PubMed2005

Mortality in New Zealand workers exposed to phenoxy herbicides and dioxins.

AIMS: To evaluate mortality in New Zealand phenoxy herbicide producers and sprayers exposed to dioxins. METHODS: Phenoxy herbicide producers (n = 1025) and sprayers (n = 703) were followed up from 1 January 1969 and 1 January 1973 respectively to 31 December 2000. A total of 813 producers and 699 sprayers were classified as exposed to dioxin and phenoxy herbicides. Standardised mortality ratios (SMR) were calculated using national mortality rates. RESULTS: At the end of follow up, 164 producers and 91 sprayers had died. Cancer mortality was reduced for sprayers (SMR = 0.82, 95% CI 0.57 to 1.14) and increased in exposed production workers (SMR = 1.24, 95% CI 0.90 to 1.67), especially for synthesis workers (SMR = 1.69), formulation and lab workers (SMR = 1.64), and maintenance/waste treatment/cleaning workers (SMR = 1.46). Lymphohaematopoietic cancer mortality was increased in exposed production workers (SMR = 1.65, 95% CI 0.53 to 3.85), especially for multiple myeloma (SMR = 5.51, 95% CI 1.14 to 16.1). Among sprayers, colon cancer (SMR = 1.94, 95% CI 0.84 to 3.83) showed increased mortality. CONCLUSIONS: Results showed 24% non-significant excess cancer mortality in phenoxy herbicide producers, with a significant excess for multiple myeloma. Associations were stronger for those exposed to multiple agents including dioxin during production. Overall cancer mortality was not increased for producers and sprayers mainly handling final technical products, although they were likely to have been exposed to TCDD levels far higher than those currently in the general New Zealand population.

Agricultural Workers' Diseases↗
PubMed2005

The effect of source to image-receptor distance on effective dose for some common X-ray projections.

A number of studies on the effects of source to image distance (SID) on dose to the patient have been published. These generally assume that the X-ray beam is collimated to a rectangular region of fixed size at the entrance surface of the patient at each SID. This is poor radiographic practice. In this work, effective doses have been determined using the commercially available Monte Carlo simulation package PCXMC. Three collimation cases were considered, namely to regions of clinical interest at the entrance and at the centre of the patient, and a fixed beam size at the image receptor. For cases of collimation to a central region of interest or to the image receptor, the saving in effective dose at increased SIDs is modest.

Dose-Response Relationship, Radiation↗
PubMed2004

The effect of source to image distance on scattered radiation to the image receptor.

In performing experimental or theoretical studies of the effect of source to image distance on dose to the patient, it is conventional to assume that the dose to the image receptor should remain constant at each SID. However, if the proportion of scattered radiation reaching the image receptor depends on the SID, then this assumption will be invalid. In this paper, the effect of SID on the scatter fraction has been determined using a Monte Carlo simulation, using EGSnrcMP. The Monte Carlo code was first benchmarked against three independent experimental studies, and shown to give excellent agreement. In order to obtain agreement with experiment, it was necessary to include Rayleigh scatter and bound Compton effects and to properly simulate multiple scattering. The scatter fraction was then determined for a range of SIDs from 100 to 300 cm, for a range of conditions, including kVp setting, phantom thickness, field size, object to image distance, collimation to entrance surface, centre of phantom and image receptor, and a range of image receptor materials. The results indicate that the scatter fraction is independent of SID within a few percent, except when there is a large object to image distance.

Algorithms↗
PubMed2004

Mortality and cancer incidence in New Zealand meat workers.

AIMS: To ascertain whether there is an increased risk of cancers of the lung and lymphohaematopoietic tissue in workers employed in the New Zealand meat processing industry, and to identify exposures associated with any increased risks. METHODS: A cohort of 6647 individuals assembled from personnel records from three plants was followed from 1988 until 2000. The observed number of deaths and cancer registrations was compared with expected numbers using five year age and gender specific rates for the New Zealand population. Subgroup analyses evaluated the effect of duration of exposure to selected agents, based on job titles and departments. RESULTS: Vital status was determined for 84% of the cohort, and 92% of the total possible person-years. Mortality from all causes and all cancers was increased, and there was a significant excess of lung cancer. There were significant trends of increasing risk of lung and lymphohaematopoietic cancer with increasing duration of exposure to biological material. CONCLUSIONS: Excess risks were observed for mortality from all causes, all cancers, and lung cancer. Although the increased risk of lung cancer may be partly due to confounding by smoking, it is unlikely to be entirely due to this cause. Furthermore, the dose-response relation observed for lung cancer suggests the effect is related to exposure to biological material contained in animal urine, faeces, and blood. Although numbers were small, the risk of lymphohaematopoietic cancer was also associated with increasing duration and level of exposure to biological material.

Adult↗
PubMed2003

The effect of ball carrying method on sprint speed in rugby union football players.

Different methods of ball carrying can be used when a player runs with the ball in rugby union. We examined how three methods of ball carrying influenced sprinting speed: using both hands, under the left arm and under the right arm. These methods were compared with running without the ball. Our aim was to determine which method of ball carrying optimizes sprinting speed. Altogether, 48 rugby union players (age 21 +/- 2 years, height 1.83 +/- 0.1 m, body mass 85.3 +/- 12 kg, body fat 14 +/- 5%; mean +/- s) were recruited. The players performed twelve 30-m sprints in total (each player performed three trials under each of three methods of carrying the ball and sprinting without the ball). The design of the study was a form of Latin rectangle, balanced across the trial order for each of the methods and for pairwise combinations of the methods in blocks of four per trial. Each sprint consisted of a 10-m rolling start, followed by a 20-m timed section using electronic timing gates. Compared with sprinting 20 m without the ball (2.58 +/- 0.16 s), using both hands (2.62 +/- 0.16 s) led to a significantly slower time (P < 0.05). Sprinting 20 m with the ball under the left arm (2.61 +/- 0.15 s) or under the right arm (2.60 +/- 0.17 s) was significantly quicker than when using 'both hands' (P < 0.05), and both these methods were significantly slower than when running without the ball (P < 0.05). Accordingly, running with the ball in both hands led to the greatest decrement in sprinting performance, although carrying the ball under one arm also reduced the players' sprinting ability. Our results indicate that to gain a speed advantage players should carry the ball under one arm.

Acceleration↗
PubMed2003

A study of mean glandular dose during diagnostic mammography in Malaysia and some of the factors affecting it.

The primary objective of this study was to determine the mean glandular dose (MGD) during diagnostic mammography in Malaysia. The secondary objective was to evaluate some of the factors affecting MGD. A survey of standard MGD was performed, based upon quality control records for the period October 1999 to August 2001. This covered 30 mammography units from 9 manufacturers. MGD was also measured for a series of patients attending mammography examinations at three other mammography units. MGD per film was estimated from recorded radiographic factors, the compressed breast thickness (CBT) and X-ray unit calibration data. MGD per woman was calculated by summing the MGDs for all films, and averaging it over both breasts. 300 women drawn equally from three major ethnic groups, namely Malay, Chinese and Indian, took part in the study. The difference of MGD per woman between ethnic groups was tested for significance using non-parametric Kruskal-Wallis and median tests. The factors affecting MGD per woman were tested for significance using a multivariate analysis of variance. The MGD for the phantom was 1.23 mGy (range 0.22-2.39 mGy) while the mean patient based MGD per film was 1.54 mGy and 1.82 mGy for the craniocaudal and mediolateral oblique views, respectively. The mean MGD per woman was 3.37 mGy. It was also found that there is no significant difference in MGD per woman among the ethnic groups (p>0.05, Kruskal-Wallis test). However, on the multivariate test two factors, namely half value layer of the X-ray beam and (CBT), had a significant effect on MGD per woman (p<0.05). No significant relationships were seen between MGD per woman with respect to ethnicity, body mass index or age.

Adult↗
PubMed2001

Asthma and other respiratory symptoms in New Zealand pine processing sawmill workers.

BACKGROUND: To study respiratory symptoms in pine sawmill workers. METHODS: A respiratory health questionnaire was administered to 772 pine sawmill workers and the association between symptoms and job-title-based exposure was studied. RESULTS: Asthma in exposed workers (18%, n = 704) was more common than in the general population (12.1%, n = 592; adjusted OR (95% CI): 1.6 (1.1-2.3)). Asthma was also more common in the low exposure group (15.6%, n = 294) and high exposure groups (high exposure to 'green dust'; 20.4%, n = 212 and high exposure to 'dry dust'; 18.8%, n = 198) than in the non-exposed workers (9.2%, n = 65). Adjusted odds ratios were 1.9 (0.7-4.9), 2.7 (0.9-7.6), and 2.1 (0.8-5.7), respectively. Adjusted odds ratios for symptoms of cough were 2.7 (1.2-6.5) for the low, 5.2 (2.1-13.0) for the high 'green dust' and 3.3 (1.4-7.9) for the high 'dry dust' exposure groups. Moreover, eye and nose irritations were significantly more prevalent in the high and low exposure groups. CONCLUSIONS: Working in pine sawmilling is associated with an increased prevalence of asthma and cough symptoms and eye and nose irritation.

Adult↗
PubMed2001

Measurements and modelling of the compliance of human and porcine organs.

Stress-strain data obtained from animal and human tissue have several applications including medical diagnosis, assisting in surgical instrument design and the production of realistic computer-based simulators for training in minimal access surgery. Such data may also be useful for corroborating mathematical models of tissue response. This paper presents data obtained from ex-vivo and in-vivo tissue indentation tests using a small indentor that is similar to instruments used in minimal access surgery. In addition, uniform stress tests provide basic material property data, via an exponential stress-strain law, to allow a finite element method to be used to predict the response for the non-uniform stresses produced by the small indentor. Data are obtained from harvested pig liver and spleen using a static compliance probe. Data for human liver are obtained from volunteer patients, undergoing minor open surgery, using a sterile hand-held compliance probe. All the results demonstrate highly non-linear stress-strain behaviour. Pig spleen is shown to be much more compliant than pig liver with mean elastic moduli of 0.11 and 4.0 MPa respectively. The right lobe of human liver had a mean elastic modulus of about 0.27 MPa. However, a single case of a diseased liver had a mean modulus of 0.74 MPa--nearly three times the stiffness. It was found that an exponential stress-strain law could accurately fit uniform stress test data and that subsequent finite element modelling for non-uniform stress around a small indentor matched measured force characteristics.

Animals↗
PubMed2001

Adult-onset acute leukemia and employment in the meat industry: a New Zealand case-control study.

OBJECTIVES: To assess the risks for adult-onset acute leukemia associated with employment in the New Zealand meat industry. METHODS: A total of 110 incident leukemia cases identified from referrals to one of six treatment centers between 1989 and 1991 were compared with 199 general population controls. Detailed occupational exposure histories were obtained by interview. RESULTS: There was an elevated risk associated with ever having worked in an abattoir (OR = 2.3, 95% CI 1.0-5.2), which appeared confined to those with over 2 years exposure (OR = 4.9, 95% CI 1.5-15.6). The excess risk was confined to abattoir workers having direct contact with animals or animal products (OR = 5.2 95% CI 1.2-22.2). Ever having worked as a butcher was associated with elevated risk (OR = 2.9, 95% CI 1.1-7.2), confined to those individuals who worked as a butcher in an abattoir (OR = 4.8) or who butchered livestock on farms (OR = 8.2). No increased risk was found for work as a retail/wholesale butcher or meatpacker (OR = 1.2). CONCLUSIONS: This study found increased leukemia risks associated with employment in the meat industry. These were confined to abattoir workers with over 2 years employment in the industry, and to persons whose jobs involved contact with animals or animal tissue, implying that biological exposures may be responsible.

Adult↗
PubMed2001

Qualitative methodologies and community participation in examining reproductive experiences: the Harlem Birth Right Project.

OBJECTIVES: Racial disparities in health present a challenge to public health because of the complexity of interacting social forces. The Harlem Birth Right Project sought to improve understanding of these forces by using qualitative and community participatory methods. In this paper we 1) describe the process of qualitative inquiry and community involvement, 2) evaluate the impact of community participation, and 3) present a brief summary of the findings on social context as it relates to pregnancy outcomes of women in Harlem. METHODS: We operationalized the qualitative method by combining participant observation, longitudinal case studies, and focus groups. An ethnographic survey was used to verify and triangulate findings across methods of data collection. We involved the community in the design, implementation, and analysis by collaborating with community-based organizations, setting up a community advisory board, and the use of dialogue groups and community meetings. RESULTS: The use of qualitative methods and community partnership uncovered important aspects of the social context of women's lives that may not have emerged through traditional epidemiologic research. We found that pregnancy may serve as a catalyst to increase perception of the magnitude of preexisting social stressors. Several stressors and chronic strains associated with structural forces were identified. For example, the high percentage of households headed by women is seen as one consequence of larger structural forces. While social support networks serve as an important coping mechanism to buffer against the stress caused by these structural forces, the types of support women seek differs by social strata, and some strategies were identified as being substantially more effective than others. CONCLUSIONS: Qualitative and community participatory research can be successfully conducted to support public health goals and can derive important new information on the social context of women's lives.

Community Participation↗