08/07/09 1

Performance Testing in Computer Tomography using

CATPHAN 600

Asim Gilani

Radiation Protection UnitMedical Physics DepartmentDubai Hospital

CATPHAN 500 & 600

CATPHAN 500 & 600

Mounting

CATPHAN 600

CATPHAN 600

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

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 widthStart 3 or 4 slices before the zero position

Phantom oriented to right side

Phantom oriented to left side

Phantom Tilted

Aligned Image

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 tableAlign all the dots to X, Y and Z LASERS as precisely as possibleScan axially with minimum slice thicknessIf 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 0.421.9 mm

Y = 3.26 x 0.421.4 mm

Test 2: Patient Alignment System

Take Scanogram or ScoutTake an axial Scan at the crosswireMeasure the accuracy of the scan

Test 3: Circular Symmetry

Take an axial Scan of the CTP 404Image must be circular not ellipticalMeasure diameter of the phantom in X & YMeasure distance between Teflon pinsAdditionally angle accuracy can be verified

Distance Accuracy

AngleAccuracy

Test 4: Slice Width Accuracy

Axially scan CTP 404 with different slice widthsMeasure slice with at (FWHM)M Full Width at Half MaximumSlice Thickness = FWHM * 0.42

6.00 * 0.42 = 2.52 mm

Test 5: Slice Sensitometry

Scan the phantom with different slice widthsMeasure CT Numbers of Different samples

CTP 404

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 widthMove table according to figure and scanVerify that you see the dot above

Water and kV Accuracy

Axially scan at different kV'sVerify that water CT number lies between -7 to + 7

Volume Verification

The volume of five spheres

????

CTP 591

Bead Geometry Module

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

High Resolution Measurements

7 lp / cm visible

The beads are used for MTF and SSP measurements

HOW ????????????

CTP 515

Low Contrast Module

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

Uniformity Module

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

Questions

Suggestions

Thanks