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Gammex RMI CT Phantom, 438
Gammex RMI CT Phantom, 438 (ACR CT Accreditation phantom, 464) S. Edyvean, Jim Weston Imaging Performance Assessment of CT Scanners St. Georges Hospital, London www.impactscan.org Some images courtesy of Cynthia McCullough Mayo Clinic, Rochester, USA CT Users Oct 2007 ImPACT Gammex RMI CT Phantom, 438 • David Aikman – Gammex RMI Ltd.,Nottingham 2 CT Users Oct 2007 Gammex RMI CT Phantom Head 20 cm 4 High contrast resolution Foot 3 Uniformity & noise Distance accuracy 2 Low contrast resolution 1 Alignment CT # Image width SSP 4 cm CT Users Oct 2007 3 Gammex RMI CT Phantom 4 CT Users Oct 2007 Documentation Manual, also ACR (American College of Radiology) website 5 CT Users Oct 2007 https://www.gammex.com 6 CT Users Oct 2007 ACR CT Accreditation Program 7 CT Users Oct 2007 ACR documentation 8 CT Users Oct 2007 Setting up 9 CT Users Oct 2007 Module 1: alignment, image thickness, CT number Polyethylene ≈ -97 HU “Bone” ≈ +910 HU Water ≈ 0 HU Acrylic ≈ +120 HU Air ≈ -1000 HU 10 CT Users Oct 2007 Module 1: alignment, image thickness, CT number High-resolution chest technique Must see all four BBs (in Modules 1 & 4) Longer wire must have same number of lines above and below (±1) Wires are 0.5 mm apart in z-direction WW = 1000 WL = 011 CT Users Oct 2007 12 CT Users Oct 2007 Module 1: alignment, image thickness, CT number Adult abdomen technique Wires are 0.5 mm width apart in zScan direction measured at several scan widths 11 / 2 = 5.5 mm 10 / 2 = 5 mm WW = 400 WL = 0 13 CT Users Oct 2007 Module 1: alignment, image thickness, CT number Adult abdomen technique Polyethylene -97 HU CT≈number measured in 5 materials Water ≈ 0 HU of CT number water measured at Acrylic ≈ several scan +120 widths andHU kVps “Bone” ≈ +910 HU Air ≈ -1000 HU WW = 400 WL = 0 14 CT Users Oct 2007 ACR documentation: module 1 15 CT Users Oct 2007 Module 2: Low contrast detectability • Low contrast = 6 HU ± 0.5 HU – (cf Catphan 10, 5, 3 HU single object of each size) 25 mm 2 mm 6 mm 3 mm 5 mm 4 mm CT Users Oct 2007 16 Phantoms for low contrast detectability (LCD) • Catphan 500 2-15 mm diameter 10 HU contrast 5 HU contrast 3 HU contrast • Catphan is closest to a ‘standard’ phantom 17 CT Users Oct 2007 Module 2: Low contrast detectability • Low contrast = 6 HU ± 0.5 HU – (cf Catphan 10, 5, 3 HU single object of each size) 25 mm 2 mm 6 mm 3 mm 5 mm 4 mm CT Users Oct 2007 18 19 CT Users Oct 2007 Module 3: uniformity, noise, distance, mtf & ssp Adult abdomen and head techniques 0.3 mm Measure tungsten uniformity and carbide beads noise Assess for artifacts Measure distance accuracy (optional) CT Users Oct 2007 100 mm WW = 100 WL = 0 20 Module 4: high contrast spatial resolution Adult abdomen, Barhead patterns: adult and lp/cm high-resolution chest techniques 12 10 4 Aluminium in Record the first solid water highest frequency bar pattern for which the bars and spaces merge 9 5 6 8 7 WW = 100 WL ≅ 1100 21 CT Users Oct 2007 Gammex RMI CT Phantom • • • • • • Nicely designed phantom Excellent phantom stand Good additional documentation from ACR Slightly limited for axial MSCT? (40 mm modules) Bar pattern doesn’t go to maximum resolution LCD of 6HU different from manufacturers spec. (use 3HU from Catphan) 22 CT Users Oct 2007 https://www.gammex.com 23 CT Users Oct 2007 Gammex RMI CT Phantom • David Aikman – Gammex RMI Ltd.,Nottingham – 01159850808, daa@gammex.com • Cost – List price £5589 (not including stand), – Discount for early sales ~10% 24 CT Users Oct 2007 Incidental Findings 25 CT Users Oct 2007 Incidental Findings 26 CT Users Oct 2007 Incidental Findings 27 CT Users Oct 2007 Gammex RMI CT Phantom, 438 (ACR CT Accreditation phantom, 464) S. Edyvean, Jim Weston Imaging Performance Assessment of CT Scanners St. Georges Hospital, London www.impactscan.org Some images courtesy of Cynthia McCullough Mayo Clinic, Rochester, USA CT Users Oct 2007 ImPACT
