E. Guibelalde

Patient dose values in interventional radiology

Large exposures incurred in interventional radiology procedures make it advisable to establish reference dose values. These dose values should be quoted in quantities representative of the radiological risk to the patient. In Spain, measurement methods were developed to comply with the European Directive on Patient Protection. Dose-area product and, when feasible, surface dose using thermoluminescent dosimetry chips were measured. Both approaches are discussed, as well as their potential use in patient protection programmes. Initial results are presented for a sample of 680 patients in 10 hospital centres in Spain. Mean, median and range are reported for some specific procedures. Mean values of 8750, 6651, 6663, 9292 and 6816 cGy cm2 are reported for percutaneous transluminal coronary angioplasty, coronary angiography, low extremity, renal and cerebral arteriographies, respectively.

Evaluation of the European image quality criteria for chest examinations

The European Commission has published guidelines for image quality, radiographic technique and patient dose. These could be easily checked by staff either during the examination or when reporting the resulting radiographs. The objective was to achieve comparable image quality throughout Europe using optimum techniques. This paper presents an application of the image criteria for chest examinations. The application of criteria to a large number of films helps to correlate scoring films using this method with other alternatives such as the evaluation of physical parameters using phantoms or test objects. The advantages and limitations of the image quality list of criteria are discussed. As a result of its application, some modifications of image quality criteria, based upon simple essential indicators (minimizing the number of criteria) are formulated and presented.

Image quality and dose in lumbar spine examinations: results of a 5 year quality control programme following the European quality criteria trial.

The large dose values found for lumbar spine examinations in a centre participating in the European quality criteria trial have been investigated within a 5 year quality control programme. Actions focused mainly on optimizing the focus-to-film distance, tube potential (kV), film optical density and X-ray beam filtration. These actions lead to overall dose reductions of up to 75% in lumbo-sacral joint examinations and prove the need for a regular survey of patient skin doses.

Patient doses in hysterosalpingography

The results of a survey of doses imparted on 41 patients undergoing hysterosalpingography is presented. Dosimetric evaluations were carried out by measuring both the dose-area product using a transmission ionization type chamber, and the entrance surface dose using thermoluminiscent dosimeters. As a result, a local reference dose value was obtained for this examination. Correlations between the dose-area product and the entrance surface dose data were analysed and compared in order to find the most appropriate dosimetric procedure. The median dose-area product obtained was 713 cGy cm2 (range 247 cGy cm2-1623 cGy cm2). Ovarian doses were also calculated, and a median value of 4.6 mGy was obtained for the whole examination. Effective doses were estimated with a median value of 3.1 mSv, and a range of 1.0 mSv-8.1 mSv.

Image quality and patient dose for different screen-film combinations

Comparisons of image quality and estimations of dose reductions were made for several new screen-film combinations including conventional and rare-earth systems under conditions similar to abdomen radiography. The evaluation was carried out using an ANSI type phantom and the TOR(CDR) image quality object developed by the University of Leeds. The parameters employed for the comparison were: entrance dose, high and low contrast threshold sensitivity and resolution. The advantages and limitations of the method are also discussed. Results show that images with high quality can be obtained with comparatively low patient doses, and that there are still wide differences in image quality for similar speed systems, depending on the manufacturer and on the chosen combination.

Physical image quality comparison of four types of digital detector for chest radiology.

Image quality for similar exposure conditions has been compared for two computed radiography (CR) systems (needle-based and conventional storage phosphor) and two flat-panel (DR) systems from different manufacturers mainly devoted to chest radiology. Image quality was assessed with a contrast-detail object and acrylic material to simulate clinical conditions. Specific image evaluation software was used to measure the contrast and obtain an image quality figure. Phantom and detector incident air kerma were measured for all images. Image quality differences were significant, and in the range of 100-300 microGy (phantom incident air kerma) the needle-based CR system and one of the DR systems show similar image quality and they are quite superior when compared with the conventional CR system.

Quality assurance of viewing boxes: proposal for establishing minimum requirements and results from a Spanish quality control programme

The Medical Physics Group at the Complutense University of Madrid has undertaken a project, during the last 3 years, under a CEC contract on “Optimization of Radiation Protection in Diagnostic Radiology” (Vano, 1989) in which a pilot programme of Quality Control (QC) was included (Gonzalez, 1989). Exhaustive patient and occupational dose measurements showed differences between the test results from similar equipment. This fact moved us to set up a Quality Control Programme (Guibelalde & Llorca, 1989), and then several Quality Assurance (QA) programmes. The necessity to establish minimum performance requirements for image quality, and the convenience of denning objective parameters to make possible further advances in the reduction of patient doses and optimization of image quality, has been pointed out at several Workshops of the Commission of European Communities (CEC) on Image Quality in Diagnostic Radiology. A Working Document of the CEC (1989) has recently been issued emphasizing the need to develop a...

A CDMAM Image Phantom Software Improvement for Human Observer Assessment

A software tool is presented to improve the features of CDMAM image phantom by University Hospital Nijmegen. This software tool ensures that the 4-alternative forced choice method of CDMAM is actually kept, even when is being scored by highly expertise observers familiar on the test object pattern. For digital images, the developed software tool automatically changes the image position of the four corners. It can be selected a fixed rotation angle or a random one, so making impossible that any observer is able to remember the exact corner position of the target disc inside any cell. Two alternative successful algorithms have been tested. ROC curve analysis obtained by 36 observers shows that both original and computer-modified images are indistinguishable. The ROC area was 0.507±0.024 for first algorithm and 0.522±0.026 for the second one, indicating that there was no statistical difference between real and computer-modified images for both of them.

Denoising of PET images by context modelling using local neighbourhood correlation.

Positron emission tomography (PET) images are characterised by low signal-to-noise ratio and blurred edges when compared with other image modalities. It is therefore advisable to use noise reduction methods for qualitative and quantitative analyses. Given the importance of the maximum and mean uptake values, it is necessary to avoid signal loss, which could modify the clinical significance. This paper proposes a method of non-linear image denoising for PET. It is based on spatially adaptive wavelet-shrinkage and uses context modelling, which explicitly considers the correlation between neighbouring pixels. This context modelling is able to maintain the uptake values and preserve the edges in significant regions. The algorithm is proposed as an alternative to the usual filtering that is performed after reconstruction.

Eye lens dose correlations with personal dose equivalent and patient exposure in paediatric interventional cardiology performed with a fluoroscopic biplane system

PURPOSE To analyse the correlations between the eye lens dose estimates performed with dosimeters placed next to the eyes of paediatric interventional cardiologists working with a biplane system, the personal dose equivalent measured on the thorax and the patient dose. METHODS The eye lens dose was estimated in terms of Hp(0.07) on a monthly basis, placing optically stimulated luminescence dosimeters (OSLDs) on goggles. The Hp(0.07) personal dose equivalent was measured over aprons with whole-body OSLDs. Data on patient dose as recorded by the kerma-area product (PKA) were collected using an automatic dose management system. The 2 paediatric cardiologists working in the facility were involved in the study, and 222 interventions in a 1-year period were evaluated. The ceiling-suspended screen was often disregarded during interventions. RESULTS The annual eye lens doses estimated on goggles were 4.13±0.93 and 4.98±1.28mSv. Over the aprons, the doses obtained were 10.83±0.99 and 11.97±1.44mSv. The correlation between the goggles and the apron dose was R2=0.89, with a ratio of 0.38. The correlation with the patient dose was R2=0.40, with a ratio of 1.79μSvGy-1cm-2. The dose per procedure obtained over the aprons was 102±16μSv, and on goggles 40±9μSv. The eye lens dose normalized to PKA was 2.21±0.58μSvGy-1cm-2. CONCLUSIONS Measurements of personal dose equivalent over the paediatric cardiologists apron are useful to estimate eye lens dose levels if no radiation protection devices are typically used.