QC of CT using Catphan 600

Performance Testing in Computer Tomography using CATPHAN 600 Asim Gilani Radiation Protection Unit Medical Physics Department Dubai Hospital 08/07/09

CTP 404 Slice Geometry and Sensitometry Module

CTP 404 Diameter = 150 mm Thickness = 25 mm 4 wire Ramps at an angle of 23 ° 5 Acrylic spheres 8 sensitometry samples 4 rods

CTP 404 Phantom position verification Patient alignment system Circular symmetry Scan width Sensitometry

Phantom Alignment Align phantom dots with the lasers

Phantom Alignment Scan 6 or 8 axial slices with minimum slice width Start 3 or 4 slices before the zero position

Phantom oriented to right side

How to verify ? Switch ON grid to check the Phantom Alignment

CUATION Once the phantom is centered and aligned DO NOT touch or move the phantom by hand Only move or align it by table movements

Test 1: LASER Accuracy Align the phantom to lasers by moving the table Align all the dots to X, Y and Z LASERS as precisely as possible Scan axially with minimum slice thickness If the Image is same as previous one then LASERS are perfectly aligned OTHERWISE !

Measurement of Z Axis Misalignment

Z-axis Misalignment Measure the distance between center of the phantom and center of the slice Multiple by 0.42 to find the z-axis misalignment 4.99 x 0.42 = 2.1 mm

X and Y Misalignment Switch ON grid and measure distance of the center of the grid to center of the image in X and Y direction and multiply by 0.42

X and Y Misalignment X = 4.61 x 0.42 1.9 mm Y = 3.26 x 0.42 1.4 mm

Test 2: Patient Alignment System Take Scanogram or Scout Take an axial Scan at the crosswire Measure the accuracy of the scan

Test 3: Circular Symmetry Take an axial Scan of the CTP 404 Image must be circular not elliptical Measure diameter of the phantom in X & Y Measure distance between Teflon pins Additionally angle accuracy can be verified

Test 4: Slice Width Accuracy Axially scan CTP 404 with different slice widths Measure slice with at (FWHM) ‏ Full Width at Half Maximum Slice Thickness = FWHM * 0.42

Test 5: Slice Sensitometry Scan the phantom with different slice widths Measure CT Numbers of Different samples

Material CT # Air PMP LDPE Water Polystyrene Acrylic Delrin Teflon - 1000 - 200 - 100 0 - 35 120 340 990

Table Movement Select axial scan with minimum slice width Move table according to figure and scan Verify that you see the dot above

Water and kV Accuracy Axially scan at different kV's Verify that water CT number lies between -7 to + 7

Volume Verification The volume of five spheres ????

CTP 591 Diameter = 150 mm Thickness = 40 mm 2 pairs of coarse ramps (39 beads each)‏ 1 pair of precision ramp (25 Beads each)‏ 2 Isolated beads for MTF and SSP 1 Steel wire of 50 µm diameter

Slice Thickness Verification Make helical scan at different slice widths Verify that all slices are of same thickness

Pitch Verification Make helical scan with different Pitches available Verify the pitch by measuring the center to center difference in adjacent scan and subtracting by the slice width Turn grid ON for help

MTF Measurement The beads are for SSP and MTF measurements We need software for these measurements

CTP 528 High Resolution Module

CTP 528 Diameter = 150 mm Thickness = 40 mm Radial gauge from 1 to 21 lines per cm 2 mm thick aluminum 2 beads of 0.28 mm 20 mm above and below the center in Y-axis & 2.5 mm and 10 mm past the center in Z-axis

The beads are used for MTF and SSP measurements HOW ????????????

CTP 515 Diameter = 150 mm Thickness = 40 mm 39 cylindrical rods 3 contrasts, 0.3 %, 0.5 % & 1.0 % 3, 5, 7 & 40 mm length 2 to 9 & 15 mm diameter

Contrast Verification (Measured Contrast) * (Smallest Diameter Discernible)  Constant (1.0) * (3.0) = 3.0 (0.5) * (5.0) = 2.5 (0.3) * (9.0) = 2.7

Contrast Measurements Take ROI on 155 mm circles Note down the CT # Take ROI immediately around the circle Subtract the 2 ROI's It should be 10, 5 and 3

CTP 486 Diameter = 150 mm Thickness > 40 mm Uniform Module CT # between 0 to 2 % of water

Artifact Analysis Change Window Width and level and observe any artifacts

QC of CT using Catphan 600

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