:: ios 2000 abstracts and talks
The annual UK Radiological Congress, known this year as IOS, was held in Birmingham from 22-24 May 2000. Members of ImPACT presented a number of papers at the meeting. The abstracts are listed below, and the Powerpoint slides from the presentations can also seen by clicking on the link next to the abstracts.
A comparison of the design features of multi-slice CT scanner models.
Anne Hill, Maria Lewis, Sue Edyvean, ImPACT Group
Development of new phantoms for the physical assessment of multi-slice CT scanners.
Dr SA Sassi, N Keat, MA Lewis, JF Carden, S Edyvean
Can multi-slice helical CT achieve a better noise-dose relationship than single-slice?
JF Carden, MA Lewis, N Keat and S Edyvean
A comparison of methods for measuring the limiting spatial resolution of a CT scanner.
B Warr, A Hill, N Keat, Dr S Sassi, S Edyvean
A comparison of the design features of multi-slice CT scanner models.
Anne Hill, Maria Lewis, Sue Edyvean, ImPACT Group
Since the introduction of CT scanning into clinical practice in the early 1970s, the technology has matured greatly. The latest innovation, multi-slice CT scanning, allows the simultaneous imaging of four slices in a single rotation. This, together with reduced rotation times, results in decreases in examination time of up to a factor of seven, for a similar image quality as a single slice, 1-second scanner. A significant number of multi-slice systems are already in clinical use world-wide. In the UK four systems had been installed by November 1999, and it is anticipated that this figure will increase rapidly. Four CT manufacturers currently offer multi-slice scanners, based on three different design principles. Due principally to variations in the detector array design and rotation drive mechanism, the systems have varying capabilities with respect to the length imaged in a single rotation, range of slice widths available and rotation speed. The scanners also have differing specifications for reconstruction times and x-ray tube heat capacity, as well as for the standard image quality and dose parameters. The various multi-slice scanner designs are presented and their capabilities compared. Implications of the design principles on image quality and dose are discussed.
Development of new phantoms for the physical assessment of multi-slice CT scanners. (view slides)
Dr SA Sassi, N Keat, MA Lewis, JF Carden, S Edyvean
PURPOSE: Multi-Slice scanners offer a wide range of slice thicknesses and scan combinations, which should be catered for in developing phantoms for the assessment of these scanners. With nearly two decades of experience in developing physical phantoms for CT scanner assessment at ImPACT, we embarked on developing new phantoms suitable for the assessment of Multi-Slice scanners. METHODS: Quad-Slice scanners have up to four times more volume coverage per rotation than Single Slice scanners scanned at the same pitch. This needs to be reflected in the extra length of the phantoms required. They also offer a wider range of slice thicknesses between 0.5mm and 10mm requiring consistently high contrast for widely variable partial volume averaging. The new phantoms can be divided into two categories; water filled phantoms for noise and uniformity measurements, and inserts, which fit into existing CTDI phantoms for high contrast spatial resolution and slice sensitivity measurements. The high contrast spatial resolution insert is a 0.1mm diameter 140mm long tungsten wire cast in Perspex. The z-sensitivity insert is a 6mm diameter 0.05mm thick tungsten disk embedded in Perspex. RESULTS: The phantoms and the individual inserts provide the tools for the physical assessment of spiral and axial CT image quality including image noise, uniformity, high contrast spatial resolution and slice sensitivity. Preliminary evaluation data has been obtained from single slice GE CT/i scanner and a GE Lightspeed QX/i Multi-Slice scanner. CONCLUSION: The new phantoms meet the increased demands of spiral Multi-Slice CT on phantom design, particularly z-axis length and uniformity.
Can multi-slice helical CT achieve a better noise-dose relationship than single-slice? (view slides)
JF Carden, MA Lewis, N Keat and S Edyvean
Manufacturers claim that multi-slice CT scanners exhibit performance peaks at certain helical pitches, whereas in single-slice CT the image noise remains unchanged with pitch and the slice sensitivity profile steadily deteriorates with increasing pitch. The inference is that, by combining optimized pitch with a new form of helical interpolation algorithm, an improved relationship between noise and dose at a given effective slice thickness can be achieved in multi-slice scanning compared with single-slice scanning. Most of the evidence that has appeared in the literature is based on computer simulations. The aim of our study was to obtain experimental data for the relationship between noise, dose and slice profile at the available pitches on both a multi-slice and a single-slice scanner. We used standard ImPACT phantoms and protocols to measure noise, dose and slice profiles on a single-slice IGE HiSpeed CT/i scanner and on a multi-slice IGE LightSpeed QX/i scanner. A comparison of the results demonstrates the extent to which the manufacturer's claims for multi-slice CT performance are borne out.
A comparison of methods for measuring the limiting spatial resolution of a CT scanner. (view slides)
B Warr, A Hill, N Keat, Dr S Sassi, S Edyvean
The use of CT as a widespread diagnostic imaging tool necessitates the accurate assessment of a scanner's capabilities, specifically spatial resolution. The test tool provided for the assessment of high contrast spatial resolution is usually a bar pattern for subjective visual analysis. The design of these bar phantoms varies between different manufacturers, and although suitable for QA procedures, it does not allow for reliable comparisons between different scanner models. Therefore, it is important that these subjective checks can be related to one another, as well as the more objective methods used by the ImPACT group. The aim of this project was to determine the correlation between techniques so that fair comparisons can be made when required. Measurements were conducted on an IGE HiSpeed CT/i scanner recently installed at St.George's Hospital, London. We used a range of both objective and subjective methods. These included Fourier analysis of Edge Spread Function data, from our own phantom, to calculate MTF 10% & 50% values, the Droege method of analysis (related to the modulation of a bar pattern) on IGE's own QA phantom and visual analysis on a 'Catphan'. By upgrading our image analysis software we were able to test a new wire insert made to fit into one of ImPACT's existing phantoms, which allows us another method of objectively measuring, via the Point Spread Function, MTF 10% & 50% values for, axial, helical and multi-slice scanning. Results are presented showing the correlation between the different methods.