CT Users Oct 2007

S. Edyvean, Jim WestonImaging Performance Assessment of CT ScannersSt. Georges Hospital, London

www.impactscan.org

Some images courtesy of Cynthia McCulloughMayo Clinic, Rochester, USA

Gammex RMI CT Phantom, 438

(ACR CT Accreditation phantom, 464)

ImPACT ImPACT

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CT Users Oct 2007

Gammex RMI CT Phantom, 438

• David Aikman– Gammex RMI Ltd.,Nottingham

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CT Users Oct 2007

4 3 2 1

20 c

m

4 cm

Head Foot

Alignment

CT #

Image width

Low contrast

resolution

Uniformity & noise

Distance accuracy

SSP

High contrast

resolution

Gammex RMI CT Phantom

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CT Users Oct 2007

Gammex RMI CT Phantom

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CT Users Oct 2007

Documentation

Manual, also ACR (American College of Radiology) website

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CT Users Oct 2007

https://www.gammex.com

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CT Users Oct 2007

ACR CT Accreditation Program

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CT Users Oct 2007

ACR documentation

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CT Users Oct 2007

Setting up

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CT Users Oct 2007

Air ≈-1000 HU

Water ≈0 HU

Polyethylene ≈ -97 HU

“Bone” ≈+910 HU

Acrylic ≈+120 HU

Module 1: alignment, image thickness, CT number

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CT Users Oct 2007

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 = 1000WL = 0

Module 1: alignment, image thickness, CT number

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CT Users Oct 2007

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CT Users Oct 2007

11 / 2 = 5.5 mm

10 / 2 = 5 mm

Adult abdomen technique

Scan width measured at several scan widths

WW = 400WL = 0

Module 1: alignment, image thickness, CT number

Wires are 0.5 mm apart in z-direction

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CT Users Oct 2007

Adult abdomen technique

CT number measured in 5 materials

CT number of water measured at several scan widths and kVps WW = 400

WL = 0

Air ≈-1000 HU

Water ≈0 HU

Polyethylene ≈ -97 HU

“Bone” ≈+910 HU

Acrylic ≈+120 HU

Module 1: alignment, image thickness, CT number

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CT Users Oct 2007

ACR documentation: module 1

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CT Users Oct 2007

• Low contrast = 6 HU ± 0.5 HU– (cf Catphan 10, 5, 3 HU single object of each size)

Module 2: Low contrast detectability

6 mm

5 mm4 mm

3 mm

2 mm

25 mm

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CT Users Oct 2007

• Catphan is closest to a ‘standard’ phantom

Phantoms for low contrast detectability (LCD)

• Catphan 50010 HU contrast

5 HU contrast

3 HU contrast

2-15 mm diameter

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CT Users Oct 2007

• Low contrast = 6 HU ± 0.5 HU– (cf Catphan 10, 5, 3 HU single object of each size)

Module 2: Low contrast detectability

6 mm

5 mm4 mm

3 mm

2 mm

25 mm

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CT Users Oct 2007

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CT Users Oct 2007

Adult abdomen and head techniques

Measure uniformity and noise

Assess for artifacts

Measure distance accuracy(optional)

WW = 100WL = 0

100 mm

Module 3: uniformity, noise, distance, mtf & ssp

0.3 mm tungsten carbide beads

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CT Users Oct 2007

Adult abdomen, adult head and high-resolution chest techniques

Record the firsthighest frequency bar pattern for which the bars and spaces merge

WW = 100WL ≅≅≅≅ 1100

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59

4

6

7

8

10

Bar patterns:lp/cm

Aluminium in solid water

Module 4: high contrast spatial resolution

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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)

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CT Users Oct 2007

https://www.gammex.com

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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%

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CT Users Oct 2007

Incidental Findings

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CT Users Oct 2007

Incidental Findings

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CT Users Oct 2007

Incidental Findings

CT Users Oct 2007

S. Edyvean, Jim WestonImaging Performance Assessment of CT ScannersSt. Georges Hospital, London

www.impactscan.org

Some images courtesy of Cynthia McCulloughMayo Clinic, Rochester, USA

Gammex RMI CT Phantom, 438

(ACR CT Accreditation phantom, 464)

ImPACT ImPACT