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D McLean

Publications and source records attributed to D McLean.

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

DullRazor: a software approach to hair removal from images.

Recently, there has been a growing number of studies applying image processing techniques to analyze melanocytic lesions for atypia and possible malignancy and for total-body mole mapping. However, such lesions can be partially obscured by body hairs. None of these studies has fully addressed the problem of human hairs occluding the imaged lesions. In our previous study we designed an automatic segmentation program to differentiate skin lesions from the normal healthy skin, and learned that the program performed well with most of the images, the exception being those with hairs, especially dark thick hairs, covering part of the lesions. These thick dark hairs confused the program, resulting in unsatisfactory segmentation results. In this paper, we present a method to remove hairs from an image using a pre-processing program we have called DullRazor. This pre-processing step enables the segmentation program to achieve satisfactory results. DullRazor can be downloaded as shareware from http:/(/)www.derm.ubc.ca.

Algorithms↗
PubMed1997

Breast composition and radiographic breast equivalence.

The composition of the female breast is an elusive variable in screen-film mammography that has a vital role in determining both the radiographic image quality and breast radiation dose. Despite the large volume of research in mammography only two studies known to the author define the chemical composition of the two major breast constituents, fibrous glandular tissue and adipose tissue. Unfortunately there is not complete agreement between these two studies. Upon this basis, a variety of breast phantom materials have been suggested and developed. This paper examines the radiographic equivalence of some of these materials dealing notably with formulations given by Hammerstein et al and ICRU Report 44, as well as BR12, water, and lucite. Radiographic equivalence was calculated using a computer simulation of mammographic spectra (after the example of Birch and Marshall and Tucker et al, and fitted to available FDA data) applied to attenuation data of phantom materials, in turn based on elemental linear attenuation coefficient data. A software algorithm was written that iteratively calculates the thickness of a nominated material required to match the attenuation of another material of particular thickness. The equivalence of 2-8 cm of lucite to various phantom materials was calculated for molybdenum target, molybdenum filter (Mo/Mo) x-ray beams from 25 to 35 kVp and for Mo/Rh and Rh/Rh beams from 27 to 35 kVp. It was found that for Mo/Mo beams the equivalent thickness of breast phantom material for certain thicknesses of lucite was largely independent of x-ray beam energy with the range of thickness equivalences being less than 3% at 8 cm of lucite and less than 0.5% at 2 cm of lucite. The RMI 156 breast phantom was found to be equivalent to 42 mm of Hammerstein et al. 50% glandular/50% adipose phantom material for Mo/Mo beams at 27 kVp, increasing to 43 mm for the range of Rh/Rh beams. While some questions remain on the accuracy of the present composition of breast constituents, it is clear that various breast compositions can be successfully simulated by using an appropriate thickness of lucite material. The use of lucite breast phantoms is then seen as an effective and reliable way of evaluating mammographic image quality and for calculating breast dose for varying required breast compositions.

Adipose Tissue↗
PubMed1997

X-ray intensifying screen visible light detection meter.

A light meter has been designed and built for the purpose of measuring the light emitted from an intensifying screen during x-ray irradiation. The meter uses a photodiode detector with a minimal drift amplification system. The meter repeatability was better than 0.5% and was found to be linear. A significant x-ray induced signal was recorded during measurement which needed to be subtracted from readings to deduce the intensification screen light output. The energy response of four screen types was subsequently measured.

Radiometry↗
PubMed1997

Review of the first 50 cases completed by the RACR mammography QA programme: phantom image quality, processor control and dose considerations.

The Mammography Quality Assurance Programme, recently established by the Royal Australasian College of Radiologists, has processed the first 50 applications. This programme, which closely follows the programme of the American College of Radiology (ACR), utilizes phantom film images, thermoluminescent dosimetry measurement of mean glandular dose, processor control charts, clinical images, equipment reports and required survey information to establish that a centre conforms to a minimum standard in mammography. The present paper describes the initial results of the first phantom images, dose measurements, processor control and survey information. A film review panel of six members has been trained in phantom film reading. Their evaluation of phantom films was compared with film readings by members of the ACR and was found to be in close agreement. Fifty films have been evaluated up to the present time with a failure rate of 26%. The major causes of failure were unacceptable film artefacts and poor contrast (as indicated by reduced fibre and mass visibility). A surprising result was the high failure in processing, where 23% of units reviewed had significant problems, including failure to keep the processor within required control limits. Only one centre recorded a mean glandular dose above 2 mGy with no centre over the 3 mGy limit. A review of the frequency of the quality control testing shows that the acceptance of quality assurance in mammography, while greater than in the initial stages of the ACR programme, is less than current US practice. These initial results for the accreditation process probably reflect an initial period of adjustment, as seen by the high pass rate achieved by centres that have resubmitted material to gain accreditation.

Accreditation↗
PubMed1996

Scatter-to-primary ratio and absorption efficiency in screen-film and computed radiography systems.

PURPOSE: To determine whether the scatter-to-primary (s/p) ratio, measured on a screen-film or computed radiographic (CR) system, varies with chemical composition or primary attenuation properties. MATERIALS AND METHODS: The s/p ratios of four Gd2O2S screens, three CaWO4 screens and a CR screen, were determined under uniform irradiation conditions. One simulated low scatter conditions, such as in lung imaging, and the other simulated high scatter conditions as in abdominal imaging. The absorption efficiency of each screen was measured and calculated. RESULTS: The measured s/p ratio varied within each set of screens. The s/P ratio was related to the absorption efficiency of primary radiation for the screen-film and CR system. No difference in the s/p ratio was seen between screen-film and CR systems when normalised for the primary absorption efficiency. CONCLUSIONS: Absorption efficiency of the imaging system is a major indicator of s/p ratio, for both screen-film and CR systems.

Abdomen↗
PubMed1996

K-characteristic photon absorption from intensifying screens and other materials: theoretical calculations and measurements.

When an extended object is irradiated with primary x rays, K-characteristic radiation is produced throughout the object. At a given location, the ratio of the K-characteristic radiation received to the primary radiation is not well understood. Knowledge of this ratio is important in the consideration of image detector design, as K-characteristic radiation generated within or proximal to the imaging detector may be considered as secondary radiation and as a specialized form of scatter to primary ratio, will reduce image contrast. This article models the production of K-characteristic radiation and calculates the K-characteristic to primary exposure and absorbed energy ratios for a number of sample materials, geometries, and detector types. Calculations have been experimentally verified for tin and gadolinium oxysulphide sample materials in some geometries using an ionization chamber detector. It was found from calculation that the magnitude of the K/p exposure and absorbed energy ratio were closely related to the ratio of the field size to the detector-to-sample distance when the detector-to-sample distances are small compared to the source-to-detector distance. It was also found that the K/p exposure and absorbed energy ratios were maximal and constant when the field size to detector-to-sample ratio was greater than 20:1 for an intensifying screen detector and greater than 100:1 for ionization chamber measurements. Calculation, also confirmed experimentally, indicated that significant ratios of K/p absorbed energy could be detected using intensifying screens proximal to fluorescing sample material.

Algorithms↗
PubMed1995

Assessment of fluoroscopic systems with a simple test object.

A non-invasive test protocol and simple to use test object (the Westmead test object) has been devised to evaluate image quality of the complete fluoroscopic system, including the grid, under automatic brightness control (ABC). The new protocol tests the overall fluoroscopic system rather than individual components such as the image intensifier (II) tube, using the kVp and dose rate as determined by the ABC. A radiographic absorber is required to simulate clinical conditions by giving patient equivalent scatter, beam quality and exit beam intensity. Twenty (20) cm of water was used as an absorber and compared to commonly used copper sheet. It was found that no single thickness of copper gave both patient equivalent beam hardness and patient equivalent absorption under ABC conditions. The two absorbers, 1 mm copper and 20 cm water, were also trialed with the new test object in a survey of 23 fluoroscopic systems using the ABC protocol. Results for two test object features, Threshold Contrast and Contrast-Detail (Low Contrast Resolution), indicated an increased spread in the results for the water absorber when compared to the copper absorber. Of 15 units having a 23 cm field size, 10 units gave better Contrast-Detail results using a copper rather than a water absorber, with 5 results equivocal. Similarly, ten (10) units gave better Threshold Contrast results with copper, while 4 units were equivocal and 1 unit gave a poorer result with copper absorber when compared to a water absorber. It is therefore concluded that the test object and protocol should be used with a patient equivalent absorber (such as 20 cms water) for acceptance tests. Good image quality discrimination between units can then be obtained by correlating x-ray input dose with test object results, such as is given using the Contrast-Detail feature under ABC conditions.

Evaluation Studies as Topic↗
PubMed1994

Gonadotropin stimulation regimens for follicular aspiration and in vitro embryo production from calf oocytes.

Crossbred beef x dairy calves were randomly allocated at 3 wk of age to different gonadotropin treatment regimens for stimulation of follicle development and induction of oocyte maturation in vivo. Follicular responses were assessed laparoscopically, and oocytes were aspirated for assessment of maturational state or for in vitro fertilization (IVF) and culture to determine developmental capacity. Follicle-stimulating Hormone (FSH), administered in a single subcutaneous injection together with a low dosage of PMSG, was as effective as the same total dosage of FSH administered in 6 injections over a 3-d period. Without accompanying PMSG, this dose of FSH was ineffective in stimulating follicle development. The mean number of preovulatory follicles (> 5mm, with hyperemic appearance) doubled with each successive stimulation at 3-wk intervals, reaching 35 follicles per calf at 9 wk of age. Oocyte yields ranged from 55 to 81% of follicles aspirated, and did not differ significantly among age, FSH regimen and oocyte maturation stimulus. A combination of LH + FSH was more effective in stimulating cumulus cell expansion than LH by itself (73 vs 22% of recovered oocyte-cumulus cell complex (OCC) respectively; P<0.05). Of 33 unselected immature oocytes (cumulus unexpanded) subjected to in vitro maturation (IVM) and IVF, 30% developed to blastocysts during co-culture with bovine oviduct epithelial cells, which was not significantly different from 25% of 36 oocytes from adult ovaries which reached the blastocyst stage under similar conditions. The results indicate that follicle responses of calf ovaries to FSH stimulation increase progressively from 3 to 9 wk of age, and that oocytes recovered laparoscopically from these follicles produce blastocysts in culture at rates similar to oocytes from adult cattle ovaries collected at slaughter. The approach offers promise for embryo production from donor calves of superior genetic merit for embryo transfer, thereby enhancing the rate of genetic gain above that attainable by conventional breeding or by embryo transfer in adult cattle.

Journal Article↗
PubMed1994

Modifying fluoroscopic views reduces operator radiation exposure during coronary angioplasty.

OBJECTIVES: This three-part study examined the feasibility of reducing operator radiation exposure during coronary angioplasty. BACKGROUND: As case loads and complexity increase, some cardiologists are receiving increasing radiation scatter doses. Techniques to reduce this are therefore becoming more important. METHODS: First, the determinants of the operator dose were assessed by measuring the differences in scatter dose with different camera views. The relative contribution of fluoroscopy as opposed to cine was then quantified. Finally, operators were provided with these data, and subsequent changes in technique were evaluated. RESULTS: Left anterior oblique views resulted in 2.6 to 6.1 times the operator dose of equivalently angled right anterior oblique views. Increasing steepness of the left anterior oblique view also resulted in a progressive increase in operator dose, with left anterior oblique 90 degrees causing eight times the dose of left anterior oblique 30 degrees and three times that of left anterior oblique 60 degrees. In the 45 coronary angioplasty cases prospectively analyzed, fluoroscopy was found to be a greater source of total radiation than cine by a 6.3:1 ratio (range 1.1 to 15.8). Once operators were made aware of the importance of left anterior oblique fluoroscopy, there was a marked reduction in its use. When this was not feasible, there was a reduction in the steepness of the angulation. Left anterior oblique fluoroscopy during angioplasty of the left anterior descending and circumflex coronary arteries was reduced from 40% of total screening time to approximately 5%, and left anterior oblique angulation for fluoroscopy during angioplasty of the right coronary artery decreased from 43.6 degrees (+/- 9.1 degrees) to 29.4 degrees (+/- 2.2 degrees). Success rates (90% vs. 89%) and screening times (19.5 vs. 20.7 min) remained unchanged in 200 coronary angioplasties performed after the study. Average operator radiation dose (measured by radiation badges worn under lead at waist level) was reduced from 32.6 to 14.3 microSv/operator per week despite a slight increase in case load. CONCLUSIONS: Fluoroscopy is the major source of total radiation exposure during coronary angioplasty, with left anterior oblique views providing the highest dose. Modification of views is feasible and will result in significant reduction of operator radiation dose.

Angioplasty, Balloon↗
PubMed1994

Phantom evaluation of the effect of film processing on mammographic screen-film combinations.

Mammographic image quality should be optimal for diagnosis, and the film contrast can be manipulated by altering development parameters. In this study phantom test objects were radiographed and processed for a given range of developer temperatures and times for four film-screen systems. Radiologists scored the phantom test objects on the resultant films to evaluate the effect on diagnosis of varying image contrast. While for three film-screen systems processing led to appreciable contrast differences, for only one film system did maximum contrast correspond with optimal phantom test object scoring. The inability to show an effect on diagnosis in all cases is possibly due to the variation in radiologist responses found in this study and in normal clinical circumstances. Other technical factors such as changes in film fog, grain and mottle may contribute to the study findings.

Mammography↗
PubMed1993

Immunogenicity and adverse reactions of influenza vaccination in elderly patients given acetaminophen or placebo.

The objective was to examine the antibody responses to influenza immunization in an elderly population and the effect of prophylactic acetaminophen on adverse responses due to inactivated whole virus vaccine containing influenza A (H3N2 and H1N1) and B antigens. During the autumn of 1990, 100 patients 65 years or older were immunized and randomly allocated to receive placebo or 1,950 mg (2 x 975 mg) of acetaminophen. They recorded any local and systemic side effects over a 3-day period. Serology was performed on pre- and post (4-6 weeks) -vaccination sera. Age and gender distribution in the study were: 47% who were 75 years or older, and 61% of the patients were female. Most of the patients (97%) had pre-existing antibodies to Influenza A or B. Average peak preimmunization antibody titers were 40 to B Yamagata and A Taiwan (H1N1) and 80 for A Shanghai (H3N2). Half of each treatment group had a 4-fold or greater rise in antibody titer in response to the vaccine. Only 30% of patients immunized the previous year but 80% of those never vaccinated previously demonstrated a 4-fold or greater serological response to the vaccine. However, measurement of protection rates (HI >/= 40) before and after vaccination indicated 81.1-100% protection for the 3 viruses not influenced by treatment, gender or a history of previous vaccination. Both treatment groups had equally small numbers of patients who recorded systemic symptoms of drowsiness, myalgia, fever and chills and about 50% had arm soreness. Although about 80% of previously unimmunized adults mounted a 4-fold antibody rise to influenza vaccine antigens whereas booster effects were seen in only 30% of those immunized the previous year, protection rates were high (81-100%) after immunization and were not affected by acetaminophen treatment. Adverse effects (15% systemic and 50% local) were not ameliorated by 1950 mg of acetaminophen in these elderly patients.

Journal Article↗
PubMed1993

Computer model to optimise contrast in chest radiography.

X-ray imaging of the chest is challenging because of the large differences in x-ray attenuation between the mediastinal and lung regions of the chest. This large dynamic range of chest exit exposure, along with associated large changes in the scatter component of the beam, makes film based chest imaging difficult to optimise in terms of image contrast and image receiver latitude. Chest radiographic contrast has been studied in terms of intensifying screen luminance differences, as a function of kVp and scatter rejection. An anatomical model has been derived from CT studies and includes simulation of typical lung, retrocardiac and mediastinal regions with the contrast medium of a 5 mm water equivalent mass. Information has also been obtained on the range of luminance generated in the receptor between the three regions. Comparative patient doses have also been calculated. The computer model consists of analytical algorithms, beginning with the primary spectra generated after the method of Birch and Marshall. The generation of secondary radiation is achieved by an algorithm that parameterises published Monte Carlo data. Grid transmission is calculated for both primary and secondary radiation. The energy absorbed in the screen is calculated to include the absorption of K-characteristic radiation. Simulation of energies from 60-120 kVp with a variety of grids (including no grid) showed that contrast, in all areas of the chest radiograph, was a weak function of kVp and a strong function of scatter rejection. This was most evident in thicker regions such as the mediastinum.(ABSTRACT TRUNCATED AT 250 WORDS)

Computer Simulation↗
PubMed1992

Pregnancies and live birth from in vitro fertilization of calf oocytes collected by laparoscopic follicular aspiration.

Oocytes were recovered by laparoscopic aspiration from 3- to 8-week-old calves treated with follicle-stimulating hormone (FSH) followed by human chorionic gonadotropin (hCG) to induce follicular growth and oocyte maturation in vivo. Most of the recovered oocytes either had resumed meiotic maturation at the time of aspiration or were competent to undergo maturation during subsequent culture in vitro. Oocytes matured in vivo following FSH and hCG treatment underwent in vitro fertilization (70%) at rates not significantly different from those of control oocytes recovered from adult cow ovaries at abattoirs and matured in vitro (75%). Calf oocytes that were immature at aspiration exhibited lower fertilization rates after in vitro maturation (36%) but their rate of development to morulae and blastocysts did not differ from that of mature oocytes at aspiration. A total of 91% of the zygotes produced from calf oocytes developed to morula and 27% to blastocyst stages during 6 days of culture. The proportion developing to morulae was significantly higher (P<0.05) than that observed for zygotes resulting from in vitro maturation and fertilization of oocytes recovered from cow ovaries obtained at an abattoir and processed concomitantly (59% to morulae and 18% to blastocysts). Morulae or blastocysts developed from oocytes from 5 to 6-week-old calves, when transferred to synchronized recipient heifers, resulted in 2 confirmed pregnancies, one of which produced a single full-term live calf. The ability to produce embryos from oocytes recovered from newborn or prepubertal calves offers the potential for markedly reducing the generation interval in cattle, thereby substantially accelerating the rate of genetic gain that can be achieved through embryo transfer.

Journal Article↗
PubMed1992

Maturational and experiential components of character formation.

This paper explores the concept of character from the point of view of its use both in everyday language and in psychoanalytic literature. It also examines, with clinical illustrations, some of the complex interactions of maturation and experience in the formation of character.

Adolescent↗
PubMed1992

An evaluation of the effect of processing conditions on mammographic film contrast, fog levels and speed.

While it is well established that extended development times and temperatures will increase mammographic film contrast and speed (1), little work has been done to date in extending this work to encompass all common screen-film types and to study the effect of processing chemistry variations on contrast speed results. This paper reports on four locally available mammographic films which, after exposure in conditions that closely simulate clinical conditions, have been developed with four different development chemicals as a function of development temperature and time. Three development times were used (23, 32 and 42 seconds) in combination with four development temperatures (32, 34, 36 and 38 degrees). The results support the previously published result of increased speed and contrast with extending development time and temperature. It was further found that, for some film types, the film contrast varied significantly over film density when developed with extended processing. Other film types, however, maintained high contrasts over large film density ranges. In some cases the increased contrast was accompanied by elevated film fog levels. The development of mammographic films in non recommended chemistries produced varying results, mostly detrimental, which demonstrated that selection of development chemistry as well as optimal development times and temperatures, is critical for good film performance.

Absorptiometry, Photon↗
PubMed1992

Physiological factors associated with injurious falls in older people living in the community.

Performance in six tests of sensorimotor function was measured in 50 subjects who were admitted to an acute hospital because of a fall (ICD codes E880-888), but who did not suffer a fracture of the lower limbs as a result. Performances in these tests were compared with 50 subjects of the same age and sex who had not fallen in the previous 12 months. It was found that those admitted to hospital because of a fall had decreased tactile sensation, reduced quadriceps strength and increased body sway on firm and compliant surfaces. The fallers also performed poorly in clinical tests of static and dynamic balance. Psychoactive-drug use was associated with falling and a number of test measures, including body sway, static balance, dynamic balance and quadriceps strength. Twenty-seven percent of fallers had poor outcomes, in that 1 year after testing, they had either suffered three or more additional falls, been readmitted to hospital, been transferred to nursing homes or died.

Accidental Falls↗