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Biomedical subjects

J C Heggie

Publications and source records attributed to J C Heggie.

At least 19 recordsLinked to original sources
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↗
PubMed2001

Recommendations for a mammography quality assurance program.

In 1989 the ACPSEM published a position paper entitled "A Quality Assurance Programme for Mass Screening in Mammography". This paper described test parameters and performance specifications for the equipment related aspects of a mammography quality assurance program. Advice on test equipment selection was also provided. In the intervening period of time there have been considerable advances in mammography technology creating a need to review a number of the paper's recommendations. There have also been considerable developments in the mammography quality assurance (QA) field, not the least of which includes the American College of Radiology Mammography Accreditation Program (ACR-MAP) and the similarly structured Royal Australian and New Zealand College of Radiologists' Mammography Accreditation Program (RANZCR-MAP). In light of these developments it was decided by the Radiology Interest Group to review the ACPSEM position on those aspects of mammography QA that fall within the medical physicist's area of expertise. This document represents the outcome of those deliberations.

Australia↗
PubMed2001

A comparison of mammography spectral measurements with spectra produced using several different mathematical models.

Due to the relatively complex nature of spectral measurements from x-ray machines, many researchers use mathematical models to simulate the spectra they need. However, there is concern over their accuracy, and hence the impact that their accuracy may have, on subsequent calculations that rely upon the spectra modelled. With this in mind spectral measurements have been performed on a mammography machine and a comparison with spectra calculated using several different models is presented. Several different techniques have been investigated in the spectral measurements to allow for pulse pileup and other effects of high count rate. Comparison with half value layer (HVL) measurements shows that the use of a gating signal in conjunction with the air-free path provides accurate results without the need for a pinhole collimator. Comparison of the measured spectra with those calculated using different models proposed in the literature suggests that accurate results can be produced by all models, but only if the user attempts to match the calculated HVL of the modelled spectrum with the physically measured HVL. If this is not done the modelled spectra may be in error. The impact of such an error is demonstrated in calculations of mean glandular dose, which indicate a possible underestimate of the dose by up to 20%.

Female↗
PubMed2000

Radiation doses from common radiographic procedures: a ten year perspective.

Using a semi-empirical model patient doses for a number of plain film radiographic procedures following the implementation of Computed Radiography (CR) technology in our Hospital have been evaluated. The results are presented in terms of the entrance surface dose (ESD) and the effective dose. A comparison of these results, with those reported previously for 1988, suggests that with the exception of chest radiography, patient doses have decreased although in many instances the decreases are not statistically significant. The finding for chest examinations stands apart from all others in that the introduction of CR technology has resulted in a substantial increase in patient dose for the PA view by at least 18%. The major reason for these apparently contradictory findings has its roots in the effectively variable speed of CR systems and the willingness of radiologists to accept more noise in some CR images.

Adult↗
PubMed1999

An investigation into the impact of anatomical variation upon mean glandular dose produced within a standard breast.

By using the EGS4 Monte Carlo computer program the normalised mean glandular dose (MGD) was calculated for a breast model that is intended to reflect the composition of an "average" breast. The reliability of the calculation was established by comparing the predictions with previously published values for a breast model. The breast model used was then altered in order to reflect the possible extremes in glandular distribution that could occur within a compressed breast. These results show that the MGD could vary by up to a factor of four depending upon where the majority of glandular tissue is located within the breast. The impact of this variation in MGD upon risk assessment within mammography is then discussed.

Adipose Tissue↗
PubMed1997

Determination of correct AEC function with computed radiography cassettes.

It has long been recognized that the assessment of Automatic Exposure Control (AEC) function is an important criterion in the assessment of any general radiographic x-ray installation. Of the tests commonly performed on an AEC, only Beam Quality Dependence relates intimately with the optical density produced on the resultant radiograph. In this test the AEC function is ascertained as being satisfactory or otherwise, on the basis of whether the optical density on the radiograph is controlled within well defined limits. With computed radiography (CR), where the conventional screen-film combination is replaced by a storage phosphor screen, the process by which the digital image is presented on film restricts the resultant optical densities to an extremely tight range, independent of the air kerma incident upon the CR phosphor plate. The implication of this is that the measurement of optical density can not be used as a direct measure of AEC function, and a test such as Beam Quality Dependence cannot be performed in the conventional manner. To overcome this, the relationship between incident air kerma and a computer generated index supplied with the CR system was investigated for two commercially available systems, one supplied by Fuji Medical Systems and the other by Kodak. The relationship between the index and incident air kerma could then be used as a substitute for optical density in monitoring AEC performance with respect to beam quality. It has been determined that an inverse linear relationship exists between the incident air kerma and the Sensitivity Number for the Fuji CR system and that a logarithmic relationship exists between the Exposure Index and incident air kerma for the Kodak CR system. In order to quantify these relationships further, the dependence of Sensitivity Number and Exposure Index on beam quality and incident kVp have been investigated. Using the results from the above investigations, acceptable limits for both Sensitivity Number and Exposure Index, can be established to test for correct AEC function, with respect to Beam Quality Dependence.

Air↗
PubMed1996

Survey of doses in screening mammography.

A survey was conducted over a period of several weeks to ascertain the mean glandular dose (MGD) to breast tissue arising from screening mammography. This survey found a MGD of 2.26 mGy per film for a sample of 2051 films and an average value of the MGD for each woman screened of 4.6 mGy for the 490 women included in the sample. The results revealed that there was a slight but significant trend towards lower MGD values with increasing age over 60. This study offers a method whereby from a knowledge of the X-ray tube potential, breast thickness and the recorded mAs a relatively reliable estimate of the MGD may be obtained for individual women.

Adult↗
PubMed1993

Computed tomography pelvimetry: accuracy and radiation dose compared with conventional pelvimetry.

Several publications in the past few years have indicated that computed tomography (CT) pelvimetry is preferable to conventional pelvimetry when considering accuracy and radiation dose. Many of the previous publications have, however, compared state of the art CT pelvimetry with outmoded conventional pelvimetry techniques. This study compared both the accuracy and the radiation dose of CT pelvimetry with conventional pelvimetry as practised in two large teaching obstetric hospitals in Melbourne. The study did not demonstrate any significant difference in the accuracy between the two methods. The radiation dose to the fetal gonads was also similar. The radiation dose using CT pelvimetry could be significantly lowered if the axial CT section through the ischial spines were excluded from the CT technique.

Female↗
PubMed1992

The usefulness of K-edge filters in automatic brightness controlled fluoroscopy and digital subtraction angiography.

This paper presents the results of a study in which the efficacy of using high atomic number K-edge filters in place of non-selective filters, in Automatic Brightness Controlled fluoroscopy and Digital Subtraction Angiography was examined. Filters investigated in the study were copper, and aluminium [as examples of non-selective filters], gadolinium, erbium and tantalum. The results of this study would suggest, with the possible exception of gadolinium as an added filter in angiography of thin anatomical parts, that the selective K-edge filters offer no particular advantage over the non-selective filters from the viewpoint of either patient dose reduction or image contrast. Further, for imaging of all but the thinnest anatomical parts, their use adds substantially to the problems of x-ray tube loading.

Angiography, Digital Subtraction↗
PubMed1991

Radiation absorbed dose calculations for samarium-153-EDTMP localized in bone.

Calculations have been undertaken to estimate the likely radiation dose received by patients undergoing treatment with samarium-153-EDTMP. Previously known bone structure parameters have been employed to partition correctly the energy absorbed in the bone matrix between red bone marrow, yellow marrow, and various types of mineral bone. Both uniform surface and volume distribution of the radioactivity are considered. The key findings of the calculations can be stated in terms of the MIRD "S-factors" for red bone marrow and the endosteal layer of cells on bone surfaces. In particular, the S-factor for red bone marrow is either 0.0276 mGy/MBq.h or 0.0077 mGy/MBq.h for surface and volume distributed radioactivity, respectively. For the endosteal layer of thickness (10 microns) on bone surfaces, the corresponding values are 0.0723 mGy/MBq.h and 0.0213 mGy/MBq.h, respectively.

Beta Particles↗
PubMed1990

A survey of doses to patients in a large public hospital resulting from common plain film radiographic procedures.

A semi-empirical method allowing ready calculation of skin absorbed doses has been applied in a survey of patients undergoing a number of common plain film radiographic procedures in a large public hospital. As an alternative indicator of risk, the quantity Mean Energy Imparted, has also been determined for some procedures. Survey results are compared with those obtained in a recent United Kingdom survey and against the most recent data available for Australia. In the special situation relating to mammography, the results are presented in terms of mean glandular doses.

Hospitals, Public↗
PubMed1986

Metabolic consequences of prolonged hyperinsulinemia in humans. Evidence for induction of insulin insensitivity.

Hyperinsulinemia is frequently associated with a variety of insulin-resistant states and has been implicated causally in the development of insulin resistance. This study examines the metabolic consequences of prolonged hyperinsulinemia in humans. Basally and 1 h after cessation of a 20-h infusion of insulin (0.5 mU X kg-1 X min-1, aimed at elevating plasma insulin levels to approximately 30 mU/L) or normal saline, subjects were assessed for glucose turnover with 3-[3H]glucose; insulin sensitivity, as measured by either the euglycemic glucose-clamp technique or the intravenous glucose tolerance test (IVGTT) minimal model method of Bergman; and monocyte insulin-receptor binding. Hepatic glucose production (Ra) was suppressed by greater than 95% during each euglycemic clamp and during the 20-h insulin infusion. After the insulin infusion, Ra and glucose utilization rate returned to the initial basal level within 1 h, as did insulin levels. At that time, insulin sensitivity was significantly decreased, as measured by the "insulin action" parameter during the 40- to 80-min phase of the clamp (0.049 +/- 0.003 vs. 0.035 +/- 0.007 min-1, P less than .05) and during the 80- to 120-min phase (0.047 +/- 0.005 vs. 0.039 +/- 0.007 min-1, .05 less than P less than .1).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Manipulation of experimental rat and rabbit liver tumor blood flow with angiotensin II.

The effects of angiotensin II on the distribution of blood flow to experimental hepatic tumors in ten rats and rabbits were examined using blood flow tracer microspheres. The ratio of arterially introduced microspheres lodging in tumor tissue compared to the surrounding normal hepatic parenchyma was measured before and after i.v. infusion of angiotensin II-inducing incremental systemic responses. A significant elevation (P less than 0.05) in this ratio was described for both rats (3.0-fold) and rabbits (3.2-fold) following the drug infusion. Ratio elevation occurred in 37 of 40 tumors examined despite the lack of a clear dose-response relationship. In addition, angiotensin II was found to significantly (P less than 0.05) increase the number of microspheres gaining arterial access to the central portions of the tumors. In terms of internal radiation therapy, these results would indicate a substantially enhanced radiation dose reaching tumor tissue after angiotensin II infusion, while relatively sparing the surrounding normal tissue.

Angiotensin II↗
PubMed1983

Hepatic metastases--a physiological approach to treatment.

Hepatic metastases derived from primary malignancy of the gastrointestinal tract have a grave prognosis, with median survival rates varying from 3 to 11 months. Surgery for isolated metastases and intrahepatic artery chemotherapy are the most effective treatment options currently available. We have explored the potential use of radioactive microspheres delivered into the liver by the hepatic artery as a form of internally irradiating metastatic liver cancer. Microspheres containing radioactive Yttrium injected into the hepatic artery concentrate in the metastases rather than normal liver parenchyma, due to the fact that the blood supply of metastases is derived preferentially from the hepatic artery. Using a rabbit tumour model, radioactive microspheres delivered into the hepatic artery have been shown to lodge preferentially in tumour tissue. The therapeutic application of this phenomenon is that metastases may receive many times the radiation dose delivered to normal liver parenchyma when radioactive microspheres are delivered into the hepatic artery. This would mean that a mean dose of 30 Gy delivered to normal liver tissue would result in greater than 150 Gy being delivered to tumour tissue. Current results in experiments suggest that this form of treatment may have considerable potential for prolonging survival of patients with hepatic metastases.

Animals↗