5th CT users group meeting: 13/01/2004
The 5th meeting of the CT Users Group was held in Edinburgh on 13/01/2004. 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Please note: information provided in the slides is not peer-reviewed, is for educational use only and is explicitly not to be used for sales or marketing purposes.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 Computerised image quality measurements - Nick Keat, ImPACT
10:20 Auto QA Lite image quality measurement software - Andrew Reilly - Edinburgh Cancer Centre
The IRIS Inc AutoQA Lite™ package is capable of performing a fully automated analysis of CT images of a range of CT phantoms, including those in the Catphan series (410, 412, 424, 440, 500), the InnerVision (Toshiba) phantom and the Siemens QA phantom. In this presentation, 18 months' experience using a loan copy of the software to analyse Catphan 500 images is described.
An overview of the AutoQA Lite™ software is presented, along with the context in which the Catphan 500 is used in our centre. The software is then evaluated against 5 broad criteria: (i) software installation, (ii) import of CT images, (iii) quality, accuracy and robustness of image analysis and results reporting, (iv) retrospective trend analysis, and (v) overall impressions of the package. To fully assess the accuracy of the measurement algorithms a range of test scenarios is considered, simulating alignment errors and other situations which might arise during testing.
It was found that the software is only able to analyse a particular format of DICOM file (implicit VR little-endian). However, once images are correctly imported into the system the software is generally robust and produces results in good agreement with those found by external analysis. AutoQA LiteTM is extremely quick and would be a useful tool for analysis of images as part of a routine QA programme. Although it is possible to fine-tune the software for particular requirements there is only limited potential for extending it to undertake measurements other than those provided automatically.10:40 The Assessment of Siemens Caredose software for pelvic CT - Gareth Iball, David Brettle, Alexis Moore, Joanna Hartley - Leeds Teaching Hospitals NHS Trust, Leeds Nuffield Hospital
An anatomically shaped PMMA phantom has been used to assess the effect of the Siemens ‘CARE Dose’ dose modulation software on CT scans of the pelvis. The effect of the software on the absorbed dose (CTDI100) and the signal to noise ratio have been assessed. The signal to noise ratio was calculated using PTFE and distilled water phantom inserts; PTFE was used to represent bony structure and distilled water was used to represent soft tissue abscesses.
Pelvis protocols identified from the UK CT Dose Survey 2002 were assessed and compared with those provided by Siemens Medical. These protocols were tested individually on one Siemens Sensation 4 CT scanner, with and without ‘CARE dose’ applied.
Results will be presented which show the effect of the ‘CARE Dose’ software on both dose and image quality and whether one of the protocols provides optimal results.
Acknowledgements: The authors would like to acknowledge the invaluable support of - Harrogate District Hospital, York District Hospital, Leeds Nuffield Hospital, ImPACT, Dr Paul Shrimpton and the UK CT Dose Survey 2002.11:00 Single and multi-slice doses using a rapid CT dose calculator - Nick Weir, Royal Infirmary of Edinburgh
11:35 Findings from a CT dose survey - Sarah Morris and Lesley Leavesley - Southampton General Hospital
Aim: To determine and analyse doses delivered during frequent scans performed on six CT scanners within the catchment area served by Southampton Radiological Physics Group. Comparisons were to be made between the centres in the study; with European reference levels and with previous results obtained in 2001.
Method: Exposure factors were determined for frequent examinations, where ‘frequent’ has been defined as more than 10 per month. To obtain the information needed radiographers were interviewed and images were analysed on remote workstations. Measurements of dose were made for each of the scanners in either a head or body sized Perspex phantom, using a 10cc, 10cm long ionisation chamber calibrated in terms of absorbed dose in air. Calculations of CTDIw were made for a combination of exposure factors suited to the individual centres. In each case kilovoltage, mAs and slice thickness were varied. Effective dose and dose length product were calculated using the ImPACT CT dosimetry calculator.
Results: The scanners in the survey varied in age and design. For example a multislice scanner was included as well as a single slice scanner employing gas filled detectors. Despite the poorer efficiency of gas filled detectors the doses delivered were never greater then 50% of the European reference levels (ERL’s) and were comparable to doses delivered in the other centres in the study. There was a vast range in the percentage of ERL’s delivered, from 4% to 82%. 4% was attributable to the three-year-old multislice scanner in the study whilst 82% was attributable to a 10-year-old scanner in continuous use taking emergency cases.
Conclusions: Reference levels are a good way of ensuring doses do not creep up over time however the results of this study suggest that the European reference levels are too high to be useful. Therefore setting local reference levels that take into consideration local factors such as the age of the scanner; whether it is used for routine cases or emergencies; whether protocols are rigidly followed by the consultants or not, could prove to be a more helpful.11:55 Dose optimisation software and the effect on IQ and patient dose (DRL) - Eugenia Kulama, Hammersmith Hospital
12:10 Dose optimisation of high resolution CT chest examinations - Julie Smyth, Ninewells Hospital and Medical School, Dundee
12:30 Business meeting
13:40 IPEM Report 77 revision proposals - Jaddy Czajka - Christie Hospital Manchester
Following on from the CT Testing survey that was conducted by questionnaire in 2002, a draft revision to the CT chapter of Report 77 has been made. The questionnaire responses were used as the basis for confirming the need for a certain test, for suggesting amendments to existing tests and for adding further tests. The proposed changes will be circulated to the CT Users Group members prior to the meeting. A request for evidence based feedback will be made. The revised chapter will be presented for discussion at the meeting.
14:40 A comparison of radiation dose in multi slice CT coronary angiography and conventional coronary angiography - Negus, I; Smail, M; Coles, D; Wilde, P; Baumbach, A; Karsch, K; Oberhoff M - UBHT, Bristol; Bristol Heart Institute
Developments in technology have made CT a viable modality for cardiac imaging. A group in Bristol is clinically comparing MSCT Coronary Angiography with conventional coronary angiography carried out using an image intensifier. This presentation compares the effective dose delivered by each modality for diagnostic procedures during the pilot phase of this study.
Effective doses from CT scans of individual patients were estimated from Dose Length Product data. These were compared to estimations using the ImPACT Patient Dosimetry Calculator/NRPB SR250 and with other published data. Doses from calcium scoring scans of the same patients were also estimated.
Effective doses were also estimated for pilot phase patients whose conventional coronary angiogram had been purely diagnostic and for whom a study report was available. The projection and exposure factors from the study report were used to calculate effective doses for each view using the Monte Carlo package PCXMC. This allowed a comparison of doses between the two techniques.
The potential for optimisation of CT exposure factors has also been considered. This work is ongoing.15:15 Relative CTDI measurements in Perspex and tissue equivalent phantoms for a range of CT scanners - Maria Lewis, ImPACT
15:35 Effect of ROI size on noise measurements - Sue Edyvean, ImPACT
15:55 Is the Cristy Dosimetry Phantom Good Enough? - Elly Castellano, Royal Marsden
Round table discussion:
16:10 Measuring HVLs - Potential pitfalls - Elly Castellano, Royal Marsden
16:10 The Auto mA feature on the latest wave of GE scanners - Elly Castellano, Royal Marsden
