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Content archived on 2024-04-19

Digital medical imaging : optimisation of the dose for the examination studies in QA, dosimetry, optimisation, tolerances and limiting values


Considerable progress has been achieved towards the overall project objectives. This progress is represented by the significant contribution of work by both individual groups and collaborative efforts to the greater body of published literature to areas of image quality assessment, patient and staff dosimetry, radiation protection, dose optimization and Digital Subtraction Angiography (DSA).

Much of the work has focused on image intensifier radiography, where comparisons were made between digital and analogue systems which are paralleled with developing Quality Assurance protocols (since existing QA protocols are restrictive in terms of technique factors and dose rates) and optimization studies utilizing specialised custom built test objects and phantoms. Such a comparison of imaging methods and systems was completed for chest and abdomen examinations. It was also found a large fluoroscopic dosimetry survey using dose area product meters that newer digital screening units offered superior dosimetric possibilities than their older conventional counterparts, with such facilities as variable frame rates. real time image processing (particularly temporal averaging) and last frame digital hold.

Optimization studies, with a particular emphasis on DSA, have been ongoing throughout the contract period. Several approaches to this end have been taken by the various working groups, such as from the perspectives of image quality, dosimetry and clinical simulation with the aid of vascular phantoms with varying degrees of stenosis.

Other areas of interest which been investigated are the present status of multiformat cameras and viewing conditions. Protocols have been developed for the performance of quality assurance measurements for these important aspects of the digital imaging chain, as they are often neglected or not considered as an integral part of presently established QA programmes. This work has highlighted the fact multiformat imagers and viewing conditions are components requiring optimization and rigorous quality assurance.
During the last 2 decades major innovations in Fluoroscopic and Digital Medical Imaging Equipment occurred. The associated clinical applications include Digital Cardiac and Vascular Imaging and new approaches to traditional Barium Studies. In Europe the population dose from the latter alone is comparable with that from CT. Taken together the population doses from Fluoroscopic and Digital Techniques provide the largest single contribution from diagnostic medical sources. This proposal aims to bridge a major gap that has opened up between the rapid and comprehensive development of the equipment and it's clinical applications on the one hand, and the underdeveloped condition of the necessary support studies in Dosimetry, Quality Assurance and Optimization on the other. The need for dosimetry and optimization studies is further exacerbated by the recommendations of ICRP-60, which have radically altered the basis for risk estimates in situations involving irradiation of the abdomen and thorax.
This proposal addresses the Dosimetry, Quality Assurance and Optimization issues raised above. The available patient and Staff Dosimetry literature has serious gaps for the newer clinical techniques, and many of the available assessments are for older equipment which are unlikely to be valid for the present generation of equipment. These questions and those arising from ICRP-60 will be refined and addressed. With regard to Quality Assurance, a set of techniques/protocols suitable to the technology and it's applîcation will be pioneered. The approach involved will be dominated by objective measurements such as Signal to Noise Ratio, Modulation Transfer Function etc., but semi-subjective methods will also be employed as required. Tolerances, Limiting Values and Recommended performance Levels will be prepared for four situations: Acceptance Tests Rigorous Quality Assurance, Routine Constancy Checks and Equipment Write-Off. While the available relevant literature on Dosimetry and Quality Assurance is limited, that on dose reduction and optimization is almost non existent. Hence a series of Optimization studies is proposed both at the level of the Physics/Technology and it's Clinical Application. The later will include a number of studies of the optimum dose for specific clinical applications using specific techniques.


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Federated Dublin Volontary Hospital
EU contribution
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Garden Hill House
8 Dublin

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Participants (2)