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Biomedical subjects

B J McParland

Publications and source records attributed to B J McParland.

At least 19 recordsLinked to original sources
PubMed2001

X-ray image intensifier performance and patient doses for combinations of supplemental beam filters and vascular contrast agents.

We present an investigation of the fluoroscopic imaging and dosimetric performances of iodine- and gadolinium-based vascular contrast agents in combination with K-absorption edge filters of atomic numbers between 50 (tin) and 82 (lead). These combinations were studied using a theoretical model for a range of diagnostic x-ray spectra (55 to 100 kVp) and for water phantoms representative of thin and thick anatomies. Performance was characterized by radiographic contrast, a derived image quality index, the patient integral and entrance skin doses, and the x-ray tube load. For a given thickness of anatomy, an optimum combination of spectrum kVp, contrast agent and supplemental filter was defined by maximum imaging performance for a minimum or tolerable x-ray tube load and patient dose. It was possible to both improve imaging performance and reduce dose by the use of an appropriate combination of spectrum kVp and filter. For gadolinium-based contrast, performance was optimized with tungsten filtration at 90 kVp for both thin and thick anatomies. It was not possible, however, to optimize the iodinated contrast performance with a single combination of supplemental filter and spectrum kVp. The optimal performance for iodinated contrast was achieved with gadolinium filtration at 60 kVp for thin anatomy and with ytterbium filtration at 80 kVp for thick anatomy. The best performance for thin anatomy was that of the combination of iodinated contrast/gadolinium filter at 60 kVp and the best performance for thick anatomy was that of the combination of gadolinium-based contrast/tungsten filter at 90 kVp.

Chromatography, Gel↗
PubMed2000

A comparison of fixed and variable kVp technique protocols for film-screen mammography.

Mammographic image quality, contrast and dose for a variable tube potential (kVp) technique protocol for film-screen mammography have been investigated. In this protocol, the tube potential is increased for larger breast thicknesses. Comparisons were made with fixed kVp protocols, in which the tube potential is kept constant and the breast thickness compensated for by prolonging the exposure ("fixed kVp" protocol). All measurements were performed on a mammography unit with a molybdenum target and filter. Image quality was quantified by image contrast, image detail detection and the minimum detectable dimension of low contrast objects. It was demonstrated that for a compressed breast thickness of less than about 40 mm, varying the tube potential had a negligible effect upon dose but a significant effect upon image quality. For a compressed breast thickness greater than about 60 mm, the effect of the tube potential upon image quality was much reduced; however, the effect upon dose was significantly greater. The variable kVp protocol takes advantage of this feature to yield a significantly lower dose for thicker breasts with a small reduction in image quality, often only within experimental uncertainty. For an exposure under automatic exposure control, increasing the tube potential from 26 kVp to 30 kVp for a breast of a reference tissue composition (50% adipose and 50% glandular) with a compressed thickness of 60 mm reduced the mean glandular dose from 6 mGy to 3.9 mGy (-35%), but increased the minimum detectable dimension of a low contrast mass from 0.8 (+/- 0.1) mm to 1.1 (+/- 0.1) mm. Adopting a variable kVp protocol led to a median patient mean glandular dose per film of 2.7 mGy, nearly independent of compressed breast thickness. In our survey, the mean age of women presenting for mammography is younger and the mean compressed breast thickness is less than reported from screening centres. This suggests that there will be a higher proportion of denser, glandular tissue in the breasts incorporated within this survey than for surveys from screening centres. The clinical use of the variable kVp protocol allows the extraction from patient data of separate changes in breast composition which are due to patient age and breast thickness. It is concluded that the reference breast tissue composition is not an accurate representation of the women presenting at this centre.

Adolescent↗
PubMed2000

Image quality and dose in film-screen magnification mammography.

Extended exposure times in magnification mammography are a result of the reduced X-ray tube currents required for a small focal spot. The consequences of this are the potential for reduced image quality through motion blur during exposure as well as the onset of film reciprocity law failure. Previous investigators have suggested increasing the X-ray tube potential as a practical mechanism for reducing exposure times in magnification mammography and have demonstrated negligible image quality degradation at least up to 32 kVp. This paper describes a film-screen magnification mammography study that expands upon this previous work to investigate the magnitude of the reduction of breast mean glandular dose and exposure time and the changes in subjective image quality (visibility of low contrast details in an RMI 152 phantom) with increases in tube potential between 28 kVp and 35 kVp. Measures of changes in the radiographic contrast and in the scatter-to-primary ratio (SPR) in magnification geometry as a function of tube potential were also obtained. Evidence for reciprocity law failure was also assessed. For a constant film optical density, increasing the X-ray tube potential from 28 kVp to 35 kVp reduced the mean glandular dose from 3.9 mGy to 2.7 mGy and reduced the exposure time from 3.2 s to 1.0 s. Over this range, the detection rate of fibrils and microcalcification-mimicking specks did not vary with tube potential at the 0.05 level of significance. It was found that only the low contrast mass detail detection rate at 35 kVp was significantly less than that at 28 kVp. The measured radiographic contrast decreased with tube potential and the SPR increased with tube potential. However, both changes were weak, and linear regressions determined that the 95% confidence intervals of the slopes relating both contrast and SPR with tube potential encompassed zero. It is concluded that magnification mammography performed at 34 kVp yields significant reductions in exposure time and mean glandular dose, with a detail detection capability similar to that at 28 kVp.

Breast Diseases↗
PubMed1999

A comparison of two mammography film-screen combinations designed for standard-cycle processing.

This paper presents comparisons of the Kodak Min-R 2000 mammography film-screen combination designed for standard-cycle processing with that of the older Min-RM/Min-R combination. Comparisons were performed in terms of characteristic curves and relative image quality. The Min-R 2000 combination had a speed of 1.7 relative to the Min-RM/Min-R combination to yield an optical density of 1.25; the maximum gradients of the characteristic curves for the two combinations were 4.6 and 2.7, respectively. Image quality was evaluated in a breast detail phantom study. It was demonstrated that image qualities of the film-screen combinations were comparable.

Female↗
PubMed1998

A study of patient radiation doses in interventional radiological procedures.

Patient radiation doses received during interventional radiological procedures can be significant. To aid in the establishment of reference dose levels, a patient dose survey has been conducted of such procedures. A total of 288 non-coronary procedures (177 classified as diagnostic and 111 as therapeutic) were accrued into the study. For each procedure, the fluoroscopy screening time and the fluoroscopic and digital radiographic dose-area products were recorded in a computer database. For example, median dose-area product values (due to fluoroscopy and digital radiography combined) of 24.2, 27.9, 69.6 and 74.7 Gy cm2 were obtained for nephrostomy, biliary stent removal/insertion, cerebral angiography and percutaneous transhepatic cholangiography procedures. While the effective dose is not an accurate measure of patient risk, it is convenient for comparing the radiological risks associated with various procedures. Effective doses were estimated from the total dose-area products. The respective median estimated effective dose values for the four procedures noted above were 3.9, 4.5, 7.0 and 12.0 mSv. While an infrequently performed procedure at this institution (n = 4 during this survey), the transjugular intrahepatic portosystemic shunt (TIPS) procedure had the greatest median dose-area product and effective dose values: 347 Gy cm2 and 55.5 mSv, respectively. Excluding the extreme case of TIPS, it was found that among commonly-performed procedures, those that are categorized as therapeutic do not necessarily present a statistically significant greater radiation risk than those which are diagnostic. Comparisons between dose-area product values obtained from this study are made with data from other interventional radiology patient dose surveys and reasons for some differences noted are discussed.

Angiography↗
PubMed1998

Optimizing optical density of a Kodak mammography film-screen combination with standard-cycle processing.

The optimization of optical density in film-screen mammography is crucial in attaining good image quality. While a target range for film optical density of 1.4-1.8 has been recommended for centres participating in the National Health Service Breast Screening Programme (NHSBSP), past investigations have shown that combinations of mammography film and screen and processor conditions can have various optimum densities, some of which are outside this recommended range. The optimum optical density of the film/screen/processor conditions combination used at our institution (the Kodak MIN-RM/MIN-R combination designed for standard-cycle processing) was evaluated using a breast detail phantom study. It was found that the optimum optical density was 1.25 OD. We recommend that an individual institution determines the optimum optical density for the film-screen combination it uses and the processing conditions specific to it.

Mammography↗
PubMed1998

Entrance skin dose estimates derived from dose-area product measurements in interventional radiological procedures.

Patient skin doses resulting from interventional radiological procedures have the potential to exceed threshold doses for deterministic effects such as erythema and epilation. If the irradiation geometry is known, the entrance skin dose can be estimated from the measured dose-area product. For each of 10 non-coronary interventional procedures, a nominal geometry was identified. From a previous survey of patient dose-area products, the entrance skin doses were estimated under the assumption that all procedures were performed with the nominal geometry specific to it. An analysis of the uncertainties in these doses caused by realistic deviations from the nominal geometry was also performed and it was shown that the estimated entrance skin dose values are at least to within 40%, and generally to within about 30%, of those actually received. For example, the median estimated entrance skin doses for the posteroanterior and lateral projections of cerebral angiography were 100 and 110 mGy. respectively, and for hepatic angiography 425 mGy. The largest entrance skin dose estimate for a single projection was for the angiography component of a CT arterial portography procedure at 670 mGy. Comparisons between entrance skin dose estimates obtained from this study are made with data from other interventional radiology patient dose surveys.

Angiography↗
PubMed1996

Radiology in the neonatal intensive care unit: dose reduction and image quality.

This paper describes a prospective study of the diagnostic radiation doses received in a neonatal intensive care unit (NICU) for a representative radiological technique used at our institution for a number of years and a "low dose" technique similar to that recommended by the Commission of the European Communities (CEC). A 400 speed film-screen combination was used in both techniques. A total of 363 anteroposterior (AP) chest and abdominal films of 77 neonates were accrued. For each radiograph, the entrance skin dose (FSD), energy imparted (EI) and mean whole body dose were determined. For a neonatal AP chest, there was an 18% reduction in the mean ESD per radiograph from 20.0 muGy for the representative technique to 16.4 muGy for the low dose technique (p < 0.0005). The reduction in the mean EI per radiograph values for the two techniques from 7.9 muJ to 7.1 muJ (10%) was statistically significant at the p < 0.017 level, after compensating for the difference in mean field dimensions between the two patient cohorts. The mean whole body dose per radiograph reduction from 4.4 to 3.5 muGy (20%) was statistically significant at the p < 0.0028 level. It was determined that the ESD and EI could be fitted by an exponential function in the equivalent patient diameter, a single parameter indicative of neonate size. Absolute excess childhood cancer mortality risk per film was estimated using risk factors derived for fetal exposures. A "worst case" absolute excess mortality risk per chest radiograph was estimated to be 1.40 x 10(-7) for the conventional technique and was further reduced to 1.11 x 10(-7) for the low dose technique. A blind comparison of patient-matched film pairs for each technique was performed by three radiologists using criteria similar to those specified by the CEC. No statistically significant difference in clinical image quality was found between the two techniques.

Analysis of Variance↗
PubMed1995

Digital portal image registration by sequential anatomical matchpoint and image correlations for real-time continuous field alignment verification.

Detection of radiotherapy field misalignments with electronic portal imaging devices requires the precise initial registration of the digital portal image with a reference image indicating the prescribed field alignment. Moreover, for real-time continuous detection this registration must be performed rapidly--arguably within 250 ms. The quality of this registration is sensitive to the ability of the user to accurately identify corresponding anatomical landmarks in the image pair. To improve the accuracy of the registration and, ultimately, that of the field misalignment measurement, we have developed a sequential digital portal image registration method using both user-identified anatomical matchpoints and image information. A first pass generates registration parameters from user-provided matchpoint coordinates and explicitly accounts for the uncertainty in matchpoint identification. The second pass uses both the initial registration parameters and image information to further improve the registration quality by maximizing cross correlations between segments of the image pair. As this registration method does not use massive matrix/vector computations common to other algorithms, it is inherently faster and well-suited for real-time field placement error detection. On a platform representative of those controlling many commercial electronic portal imaging devices (486 CPU), this algorithm registers portal images in times of less than 6 ms per matchpoint with errors of less than 2% in magnification, 0.5 degree in in-plane rotation, and less than 1 pixel dimension in in-plane translation. As the algorithm assumes a rigid-body geometry, it is sensitive to out-of-plane rotations. A quantitative analysis of this algorithm is presented, indicates its accuracy, and describes its sensitivity to out-of-plane rotations.

Algorithms↗
PubMed1995

A fluoroscopy credentialling programme for orthopaedic surgeons.

We have developed a teaching programme for non-radiologists who use fluoroscopy, which includes techniques for reducing the radiation received by the patient and the surgeon during orthopaedic procedures. The techniques resolve around the radiation protection concepts of time, distance and shielding. The programme has been very successful in reducing the total fluoroscopy times of orthopaedic surgeons; in our institute, durations have been reduced to about 10% of those before the training started. We review the aims and content of our programme.

Education, Medical, Continuing↗
PubMed1990

The effect of a dynamic wedge in the medial tangential field upon the contralateral breast dose.

The elevated incidence of breast cancer following irradiation of breast tissue has led to concern over the magnitude of the scattered radiation received by the uninvolved contralateral breast during radiation therapy for a primary breast lesion and the risk of an induced contralateral breast cancer. Some linear accelerators use a single dynamic (or universal) wedge that is mounted within the treatment head at an extended distance from the patient. Because of the combined effects of distance and shielding, the contralateral breast dose due to a medial tangent containing a dynamic wedge is expected to be less than that containing a conventional wedge. This paper presents contralateral breast dose (CBD) measurements performed on an anthropomorphic phantom with breast prostheses irradiated with 6 MV X rays from a linear accelerator equipped with a dynamic wedge. Doses were measured at 15 points within the contralateral breast prosthesis with thermoluminescent dosimeters. It was found that the contralateral breast dose per unit target breast dose decreases with the perpendicular distance from the posterior edge of the medial tangent to the dose measurement point and increases with effective wedge angle by factors ranging up to 2.8, in agreement with data presented earlier for a water phantom geometry. This dose elevation showed no statistically significant dependence (p less than 0.05) upon the perpendicular distance from the beam edge. Comparisons with data in the literature show that the contralateral breast dose increase by a dynamic wedge is typically only about half of that reported for a conventional wedge for the same wedge angle and distance from the beam.

Breast↗
PubMed1989

Methods of calculating the output factors of rectangular electron fields.

The dose output of a clinical electron beam exhibits a complex dependence upon field size, beam energy and collimation system design. A variety of methods have been developed in the past to calculate the output of an electron beam of arbitrary field dimensions. This paper describes three of these methods and indicates the advantages and disadvantages of each. Comparisons with measured data are also presented.

Algorithms↗