4th CT users group meeting: 07/11/2002
The 4th meeting of the CT Users Group was held in Nottingham on 07/11/2002. The programme is shown below with links to pdf version of some of the talks.
Please note: information provided in the slides is not peer-reviewed, is for educational use only and is explicitly not to be used for sales or marketing purposes. Any of the authors can be contacted, via the CTUG if no contact information is provided in the slides, to discuss the contents.
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Meeting Programme
10:00 Taking it on the chest: when planning assumptions change - Mike Holubinka, Portsmouth
10:30 New Monte Carlo simulations at NRPB for paediatric CT - Paul Shrimpton - Medical Dosimetry Group, NRPB
Optimisation of protection for paediatric patients undergoing CT is only now beginning to achieve due prominence, following an earlier general lack of awareness of the potentially higher levels of dose to children relative to adults. This unfortunate oversight was fostered, perhaps, by the absence of specific tools for paediatric CT dosimetry. In order to facilitate more comprehensive dose assessment for CT, new Monte Carlo simulations have been performed at NRPB for a complete family of six (MIRD) geometric mathematical phantoms representing ages from newborn to adult. Organ doses have been calculated for CT exposures of contiguous, 1 cm thick, transverse slices in each phantom, and for three CT scanner models (Siemens DRH, GE 9800 and Philips LX) reflecting a range of designs. Calculations have also been carried out in relation to the standard head and body CT dosimetry phantoms. All calculations have been implemented using the MCNP-4C radiation transport code operating on a personal computer (with Pentium III processor).
Rigorous quality assurance procedures have been undertaken so as to validate the models developed. In particular, remarkably good agreement was found with the results of comparable Monte Carlo calculations previously completed at NRPB, in relation to both CT (of adults) and conventional x-ray exposures. Ratios of CTDIw to air kerma were reassuringly close to measured values for the three scanner models.
In general, values of effective dose from CT, when normalised to air kerma, are significantly greater for paediatric patients than for adult patients when using the same technique to scan similar anatomical regions, but with some dependence on the scanner model. The enhancement is greatest for ‘head and neck’ scans, where it is in the range 2.3-2.6 for the newborn across all three scanners. For scans of the whole trunk it ranges from 1.4 for the scanner without a shaped filter, the Siemens DRH, to 2.3 for the GE 9800 scanner.
The results of the calculations highlight the particular need to use CT scan protocols that are tailored to patient size. A summary of the work has already been published (Khursheed et al, Br J Radiol 75: 819-830 (2002)). The organ dose coefficients will also be published as a software report on the NRPB website and will form the basis for a general method for dose assessment in paediatric CT.
© 2002 NRPB10:45 Noise and dose levels in paediatric CT - Jenny Oduko - Bristol
An audit of paediatric CT examinations revealed that a wide range of parameters were being used, especially by on-call radiographers.
A set of simple water-filled phantoms of different sizes were used to make noise measurements, and the results were used to suggest exposure parameters for children of different body sizes (making use of the anthropometric data in NRPB Report R318, ‘Reference Doses and Patient Size in Paediatric Radiology’).11:15 UK CT dose survey: An update - Matthew Dunn, Queen’s Medical Centre, Nottingham
11:20 Results of the CT quality assurance survey - Jaddy Czajka - Christie Hospital NHS Trust, Manchester
The CT Users Group has conducted a survey of Diagnostic CT QA practice in the UK, with the aim of establishing a consensus on core performance tests carried out on a scanner during its lifetime. The survey took the form of a questionnaire to which there were 26 replies. Results will be presented for a range of tests performed during routine testing and a list of recommended tests will be suggested. Frequency of testing will also be discussed.
11:40 Commissioning a dedicated oncology scanner - Andrew Reilly, Edinburgh
12:00 Optimisation of standard protocols on a multislice CT scanner - Ian Negus, Plymouth
14:00 The new CT technology: what are the benefits? - Julia Barrett - ImPACT
Nearly all the CT scanners currently being purchased for UK hospitals are sub-second multi-slice models. Most can acquire 4 slices simultaneously, and may have the option of upgrading to 8, 16 or more slices in the future. Software packages are available which enable a variety of specialised scanning techniques to be performed, and some models incorporate dose-reduction features. Patients undergoing CT scans in these hospitals can expect to benefit in a number of ways from the new technology. Greater diagnostic accuracy may result from improvements in image quality, and a greater range of diagnostic capabilities is now available. Better patient comfort can be expected with faster scanning speeds and the need for less contrast. The high quality 3D images reconstructed from multi-slice acquisitions have important applications in subsequent surgical procedures. In addition, the advances in specialized techniques such as CT angiography, virtual endoscopy and gated cardiac imaging should spare some patients from having to undergo more invasive procedures. This presentation explores the technological developments which have brought about these potential benefits, investigates how far the potential is currently being realised, and examines the ways in which any drawbacks associated with the new technology are being addressed.
14:20 Excess Rotations prior to and following a helical CT run - Catherine Chapman-Jones, Canterbury
14:40 Assessment of the low contrast detectability of multi-slice CT scanners - David Platten, ImPACT
15:00 Effective dose in paediatric computed tomography - Simon Willis, Newcastle
15:20 The relationship between image noise and spatial resolution of CT scanners - Sue Edyvean, ImPACT
15:30 Update on IEC CT acceptance testing standard - Sue Edyvean, ImPACT
15:40 CT calibrations. What can NPL offer? - NPL
