QC Testing for Computed Tomography (CT) Scanner

QA - Quality Assurance All planned and systematic actions needed to provide confidence on a structure, system or component. all-encompassing program, including quality control, that extends to administrative, educational, and preventive maintenance methods. WHO: QA in Diagnostic Radiology: To provide consistent production of adequate diagnostic information with minimum exposure of both patient and personnel

NCRP: Goal of QAP in Diagnostic Radiology Principal goal: accurate and timely diagnosis Secondary goal: minimization of radiation exposure and risk and of discomfort and cost to the patient and community. Secondary goals must always be balanced against the primary goal

QC Quality Control Part of the QAP that deals with techniques used in monitoring and maintenance of the technical elements of the systems that affect the quality of the image. Part of the QAP that deals with instrumentation and equipment Purpose in diagnostic radiology: to ensure continuing production of diagnostic images with optimum quality, using minimum necessary dose to the patient

List of Safety and Performance Testing

QC Testing for CT Scanner 1. Scan Localization 1.1: Axial scan localization light accuracy 1.2: Isocenter alignment, sagittal & coronal light accuracy 1.3: Gantry tilt accuracy 1.4: Table positioning 1.5: Image Scan Width 1.6: Dose Profile 1.7: Accuracy of scan prescription from scout image

QC Testing for CT Scanner 2. Generator Performance 2.1: kv accuracy 2.2: Timer accuracy 2.3: Coefficient of Linearity

QC Testing for CT Scanner 3. Computed Tomography Dose Index (CTDI)

QC Testing for CT Scanner 4. Quantitative Accuracy 4.1: Accuracy of Distance Measurement 4.2: CT Number Calibration 4.3: CT Number Constancy 4.4: CT Number Uniformity 4.5: CT Number Dependence on Scan Thickness 4.6: CT Number Dependence on Reconstruction Algorithm 4.7: CT Number Dependence on kv 4.8: CT Number Dependence on Phantom Size 4.9: CT Number Dependence on Phantom Position 4.10: CT Number Linearity

QC Testing for CT Scan 5. Image Quality 5.1: Image Artifacts 5.2: Image Noise 5.3: High Contrast Resolution 5.4: Low Contrast 5.5 Image Display (Visual & Hard Copy)

QC Testing for CT Scan 6. Leakage & Scattered Radiation 6.1: Leakage Radiation 6.2: Scattered Radiation

QC Test for CT Scan List of Test Tools

List of Test Tools 1. Water Phantom 2. Catphan 3. CTDI Head & Body Phantom 4. Multi Function Meter 5. Survey Meter 6. Measuring Tape 7. Ready-pack Film 8. Angle ruler

Water Phantom SIEMENS

Water Phantom Toshiba

Water Phantom GE

CATPHAN

CTDI Head & Body Phantom Head Body

Multi Function Meter

Survey Meter

1. Scan Localization 1.1 Axial Scan Localization Light Accuracy Purpose: To test congruence of scan localization light and scan plan Frequency: Annually Test Tools: Ready-pack film Needle

1. Scan Localization 1.1 Axial Scan Localization Light Accuracy make a line on ready-pack film turn on the internal axial localization light mark light location on film by piercing film pack with pin at several points along the middle of illuminated line make an exposure with the thinnest scan width - process the film measure the marked position from the exposed line on the film

1. Scan Localization 1.1 Axial Scan Localization Light Accuracy Internal Light External Light Deviation Acceptable limit: Maximum deviation: 2mm

1. Scan Localization 1.2 Isocenter alignment, sagittal & coronal light accuracy Purpose: To determine the scan field and the localization light are centered at the same location Frequency: Annually Test Tools: Catphan

1. Scan Localization 1.2 Isocenter alignment, sagittal & coronal light accuracy position Catphan at the center of the light make an exposure commonly used from the visual display, use the centering software (scale grid) to determine the center of the catphan

1. Scan Localization 1.2 Isocenter alignment, sagittal & coronal light accuracy measure the deviation of the sagittal, coronal & isocenter marker on the phantom from the scale grid Acceptable limit: Maximum deviation: 5mm

1. Scan Localization 1.3 Gantry tilt accuracy Purpose: To determine accuracy of tilt indicators Frequency: Annually Test Tools: Ready-pack film / CR Cassette

1. Scan Localization 1.3 Gantry tilt accuracy tape film/cassette to the side of supporting object center film/cassette to alignment light make an exposure using the narrowest slice tilt the gantry to different angle and make another scan process the film/cassette measure the angle indicated on the film with angle ruler

1. Scan Localization 1.3 Gantry tilt accuracy Acceptable limit: Maximum deviation: ±3º

1. Scan Localization 1.4 Table Positioning Purpose: To determine accuracy of longitudinal table motion Frequency: Annually Test Tools: Measuring tape

1. Scan Localization 1.4 Table Positioning tape the measuring tape along the patient couch move the table along the movement axis and check the indicator from the actual movement from the measuring tape repeat the movement few times for different direction Acceptable limit: Maximum deviation: ±2mm

1. Scan Localization 1.5 Image Scan Width Purpose: To determine the actual width of the imaged slice Frequency: Annually Test Tools: Catphan

1. Scan Localization 1.5 Image Scan Width center the catphan to the gantry axis and align to the scan alignment light scan the catphan with different slice setting How to measure slice width? Measure Full Width Half Maximum (FWHM) Slice Width = FWHM x 0.42

1. Scan Localization 1.5 Image Scan Width Catphan:

1. Scan Localization 1.5 Image Scan Width Tan 23º = Opposite Adjacent Opposite Zmm 23º FWHM Adjacent

1. Scan Localization Adjacent 1.5 Image Scan Width Tan 23º = 0.42 0.42 = Z FWHM Zmm = FWHM x 0.42 23º FWHM Zmm Opposite

1. Scan Localization 1.5 Image Scan Width Example: 10mm Slice Thickness

1. Scan Localization 1.5 Image Scan Width Example: 10mm Slice Thickness determine the CT number (mean) for the background near the wire ramp using ROI function Mean: 99.4

1. Scan Localization 1.5 Image Scan Width Example: Close down the CT window opening to 1 or the minimum setting Move the CT scanner level to the point where the ramp image just totally disappears CT scanner level at this position is your peak/maximum value CT # peak: 263

1. Scan Localization 1.5 Image Scan Width Example: Calculate 50% net peak FWHM 50% net peak = (CT number + CT level peak) 2 = (99.4 + 263) = 181 2 move CT scanner level to 50% net peak measure FWHM

1. Scan Localization 1.5 Image Scan Width Example: 10mm slice thickness Slice Width = FWHM x 0.42 SW #A = 22.9 x 0.42 = 9.62 SW #B = 22.3 x 0.42 = 9.37 SW #C = 21.7 x 0.42 = 9.11 SW #D = 22.5 x 0.42 = 9.45 mean = 9.39mm

1. Scan Localization 1.5 Image Scan Width Example: 10mm slice thickness Deviation = mean slice thickness = 9.39 10.0 = -0.61mm Acceptable limit: For slice thickness <5mm, maximum deviation: 0.5mm For slice thickness 5mm, maximum deviation: 1.0mm

1. Scan Localization 1.6 Radiation Dose Profile Purpose: To determine accuracy of pre-patient collimator setting Frequency: Annually Test Tools: Ready-pack film

1. Scan Localization 1.6 Radiation Dose Profile place ready pack film on table make an exposure with different slice thickness setting on film make sure each exposure do not intercept each other with moving the film in/out of gantry

1. Scan Localization 1.6 Radiation Dose Profile Acceptable limit: Maximum Deviation: Single slice CT: 1mm Multi-slice CT: Within manufacturer s specifications

1. Scan Localization 1.7 Accuracy of scan prescription from scout image Purpose: To determine the accuracy of the planed location during scout localization mode Frequency: Annually Test Tools: Catphan

1. Scan Localization 1.7 Accuracy of scan prescription from scout image position the catphan & make a scout localization scan through out the phantom plan one axial scan on one of the locator on the phantom move the table to the start scan location before the scan begins, go inside the scanning room and switch on the axial localization light record the deviation of the localization light from the marker of the catphan

1. Scan Localization 1.7 Accuracy of scan prescription from scout image Acceptable limit: Maximum Deviation: 1.0mm

QC Testing for CT Scanner 2. Generator Performance 2.1: kv accuracy 2.2: Timer accuracy 2.3: Coefficient of Linearity

2. Generator Performance 2.1 kv Accuracy Purpose: To determine the accuracy of the tube voltage Frequency: Annually Test Tools: Multi Function Meter; etc: Unfors (RaySafe), RTI Piranha, Victoreen 4000m+

2. Generator Performance 2.1 kv Accuracy from the console, enter into service mode position the tube to the AP position position the multi function meter to the gantry opening align with the light Make an exposure on the meter Repeat with other kv setting with exposure time & ma fixed

2. Generator Performance 2.1 kv Accuracy

2. Generator Performance 2.1 kv Accuracy Calculation: for kv <100kV: kv Accuracy = kvmeasured kvset for kv 100kV: kv Accuracy = (kvmeasured kvset) x 100% kvset Acceptable limit: for kv <100kV, maximum deviation: 5kV for kv 100kV, maximum deviation: 5%

2. Generator Performance 2.2 Timer Accuracy Purpose: To determine the accuracy of the exposure time Frequency: Annually Test Tools: Multi Function Meter; etc: Unfors (RaySafe), RTI Piranha, Victoreen 4000m+

2. Generator Performance 2.2 Timer Accuracy from the console, enter into service mode position the tube to the AP position position the multi function meter to the gantry opening align with the light Make an exposure on the meter Repeat with other exposure time setting with kv & ma fixed

2. Generator Performance 2.2 Timer Accuracy Calculation: Timer,t Accuracy = (tmeasured tset) x 100% tset Acceptable limit: maximum deviation: ±10%

2. Generator Performance 2.3 Coefficient of Linearity Purpose: To determine the linearity of tube output with different mas setting Frequency: Annually Test Tools: Multi Function Meter; etc: Unfors (RaySafe), RTI Piranha, Victoreen 4000m+

2. Generator Performance 2.3 Coefficient of Linearity from the console, enter into service mode position the tube to the AP position position the multi function meter to the gantry opening align with the light Make an exposure on the meter Repeat with other ma setting with kv & exposure time fixed

2. Generator Performance 2.3 Coefficient of Linearity Calculation: Calculate the dose/mas (X) from the results of various ma used Obtain X maximum (Xmax) and X minimum (Xmin) Coefficient of Linearity = (Xmax Xmin) x 100% (Xmax + Xmin) Acceptable limit: maximum deviation: 10%

QC Testing for CT Scanner 3. Computed Tomography Dose Index (CTDI)

3. CTDI 3. Computed Tomography Dose Index (CTDI) Purpose: To determine the radiation dose to patient tissues is within the manufacturer s specification for axial modes scan Frequency: Annually Test Tools: CTDI Head & Body phantom Multi Function Meter (with 10cm pencil beam ion-chamber)

3. CTDI 3. Computed Tomography Dose Index (CTDI) Method: Place the 16cm CTDI Head phantom on the head rest of patient table Align the center axis of the phantom, parallel to the scan rotational axis (center of the gantry)

3. CTDI 3. Computed Tomography Dose Index (CTDI) Method: Put in 10cm pencil beam ion chamber into the centre-hole position (position A) E A B C D

3. CTDI 3. Computed Tomography Dose Index (CTDI) Method: Put in 10cm pencil beam ion chamber into the centre-hole position (position A) A

3. CTDI 3. Computed Tomography Dose Index (CTDI) Method: Set the exposure factor (kv, ma, time, slice thickness) same with the manufacturer s specification setting Make an exposure with axial mode Record the dose from the meter

3. CTDI 3. Computed Tomography Dose Index (CTDI) Method: Repeat the measurement with the other peripheral position (position B, C, D & E) Repeat the whole CTDI measurement with 32cm CTDI Body phantom E A D B C

3. CTDI 3. Computed Tomography Dose Index (CTDI) Calculate CTDI100 & compare the result with the manufacturer s reference

3. CTDI 3. Computed Tomography Dose Index (CTDI) Calculation: CTDI100 = measured dose(mgy) x 100mm beam collimation(mm) compare with manufacturer s reference, Deviation = (CTDI100 measured CTDI100 reference) x 100% CTDI100 reference Acceptable limit: Maximum Deviation: ±20%

3. CTDI 3. Computed Tomography Dose Index (CTDI) CTDIw : CTDIw = 1/3 CTDI100 (center) + 2/3 CTDI100 (periphery) CTDIvol : CTDIvol = CTDIw / pitch *pitch = table distance in one rotation / beam collimation

4. Quantitative Accuracy 4.1 Accuracy of Distance Measurement Purpose: To determine the accuracy of distance measurement for both the axial and transaxial mode Frequency: Annually Test Tools: Catphan

4. Quantitative Accuracy 4.1 Accuracy of Distance Measurement for axial mode: center the catphan to the gantry axis and align to the scan alignment light scan the catphan measure the distance between the four dots Maximum Deviation: 1mm

4. Quantitative Accuracy 4.1 Accuracy of Distance Measurement for transaxial mode: Make a typical scout localization scan on the entire Catphan and measure the distance between the dot that appears on the phantom Maximum Deviation: 1mm

4. Quantitative Accuracy 4.2 CT Number Calibration Purpose: To determine the reference CT number for water and air are within the acceptable limits Frequency: Daily Test Tools: Water phantom

4. Quantitative Accuracy 4.2 CT Number Calibration place water phantom at gantry rotational axis make a scan with a commonly used exposure factor measure the CT number using the ROI at the center of the phantom repeat with a same exposure but without any phantom or object within the scan field measure the CT number for the air

4. Quantitative Accuracy 4.2 CT Number Calibration

4. Quantitative Accuracy 4.2 CT Number Calibration Water Air

4. Quantitative Accuracy 4.2 CT Number Calibration Acceptable Limit: For water value, CT number: 5.0HU For Air value, CT number: 1000 10.0HU

4. Quantitative Accuracy 4.2 CT Number Calibration

4. Quantitative Accuracy 4.3 CT Number Constancy Purpose: To determine the CT number is consistent through out the year and maintain at that standard reference value Frequency: Daily Test Tools: Water phantom

4. Quantitative Accuracy 4.3 CT Number Constancy Method: Repeat test CT Number for water at least 4 times Record CT Number for every images Assessment: The CT Number for water should be constant

4. Quantitative Accuracy 4.4 CT Number Uniformity Purpose: To determine the uniformity of the image Frequency: Monthly Test Tools: Water phantom

4. Quantitative Accuracy 4.4 CT Number Uniformity Method: From image of CT Number calibration test for water, record the CT Number for the ROI in the middle and other four corners of the phantom

4. Quantitative Accuracy 4.4 CT Number Uniformity Calculation: Maximum Edge to Center variation: Deviation = (CT No.MAX @ CT No.MIN)Edge (CT No.Center) Acceptable limit: Head Phantom: Maximum Deviation: ±5HU Body Phantom: Maximum Deviation: ±20HU

4. Quantitative Accuracy 4.4 CT Number Uniformity Center: 1: -1.4HU Edge: 2: -1.0HU 3: -0.9HU 4: -0.8HU 5: -0.9HU Deviation: 0.4HU

4. Quantitative Accuracy 4.4 CT Number Uniformity Center: 1: 0.4HU Edge: 2: 1.5HU 3: 0.9HU 4: 0.1HU 5: 0.9HU Deviation: 1.1HU

4. Quantitative Accuracy 4.5 CT Number Dependence on Scan Thickness Purpose: To determine the CT number dependence on different scan slice thickness Frequency: Annually Test Tools: Water phantom

4. Quantitative Accuracy 4.5 CT Number Dependence on Scan Thickness performed CT Number test continue scanning with same exposure setting BUT with different SLICE THICKNESS scan with all possible slice thickness selection record CT Number at the center for each images Maximum Deviation: ±5HU

4. Quantitative Accuracy 4.6 CT Number Dependence on Reconstruction Algorithm Purpose: To determine the CT number dependence on different reconstruction algorithm Frequency: Annually Test Tools: Water phantom

4. Quantitative Accuracy 4.6 CT Number Dependence on Reconstruction Algorithm performed after CT Number test continue scanning with same exposure setting BUT with different ALGORITHM scan with all possible algorithm selection record CT Number at the center for each images Maximum Deviation: ±5HU

4. Quantitative Accuracy 4.7 CT Number Dependence on kv Purpose: To determine the CT number dependence on different kv Frequency: Annually Test Tools: Water phantom

4. Quantitative Accuracy 4.7 CT Number Dependence on kv performed after CT Number test continue scanning with same exposure setting BUT with different kv scan with all possible kv selection record CT Number at the center for each images Maximum Deviation: ±5HU

4. Quantitative Accuracy 4.8 CT Number Dependence on Phantom Size Purpose: To determine the CT number dependence on phantom size Frequency: Annually Test Tools: Water phantom

4. Quantitative Accuracy 4.8 CT Number Dependence on Phantom Size performed after CT Number test continue scanning with same exposure setting BUT with different PHANTOM SIZE scan with other available water phantom size record CT Number at the center for each images Maximum Deviation: ±20HU

4. Quantitative Accuracy 4.9 CT Number Dependence on Phantom Position Purpose: To determine the CT number dependence on phantom position Frequency: Annually Test Tools: Water phantom

4. Quantitative Accuracy 4.9 CT Number Dependence on Phantom Position performed after CT Number test continue scanning with same exposure setting BUT with different table height move up & down the table (etc: 5cm height different) and scan for every different height record CT Number at the center for each images Maximum Deviation: ±15HU

4. Quantitative Accuracy 4.10 CT Number Linearity Purpose: To determine the CT number linearity with different attenuation coefficient Frequency: Annually Test Tools: Catphan

4. Quantitative Accuracy 4.10 CT Number Linearity Position catphan at the gantry Scan at position where variable material is constructed inside the catphan Determine CT Number for various materials Plot linear graph CT number vs linear attenuation coefficient (μ)

4. Quantitative Accuracy 4.10 CT Number Linearity

4. Quantitative Accuracy 4.10 CT Number Linearity Assessment: CT Number shall change linearly with linear attenuation coefficient of different material

QC Testing for CT Scan 5. Image Quality 5.1: Image Artifacts 5.2: Image Noise 5.3: High Contrast Resolution 5.4: Low Contrast 5.5 Image Display (Visual & Hard Copy)

5. Image Quality 5.1 Image Artifacts Purpose: To assess any artifacts appear on the image Frequency: Monthly Test Tools: Water phantom

5. Image Quality 5.1 Image Artifacts place water phantom at gantry rotational axis scan with a commonly used exposure factor check whether any artifact appear on the screen Assessment: No artifacts should appear on the images

5. Image Quality 5.1 Image Artifacts Ring Artifact

5. Image Quality 5.1 Image Artifacts Cupping Artifact

5. Image Quality 5.2 Image Noise Purpose: To assess the noise level for different scanning parameters Frequency: Annually Test Tools: Water phantom

5. Image Quality 5.2 Image Noise place water phantom at gantry rotational axis scan with a commonly used exposure factor repeat the scan with various mas record CT Number & SD at the center for each images Plot linear graph, SD vs 1/sqrt(mAs)

5. Image Quality 5.2 Image Noise ma Sec mas 1/sqrt (mas) CT No. (HU) SD, noise 50 1.00 50.0 0.1414-0.27 18.80 100 1.00 100.0 0.1000 0.39 12.76 150 1.00 150.0 0.0816 0.04 10.87 200 1.00 200.0 0.0707-0.03 9.05 250 1.00 250.0 0.0632-0.71 8.57 300 1.00 300.0 0.0577-0.35 7.74 SD vs1/ sqrt(mas) R² = 0.9957 20.0 18.0 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 Assessment: The noise (SD) should increases linearly with inverse square of mas

5. Image Quality 5.3 High Contrast Resolution Purpose: To determine high contrast resolution of the system Frequency: Monthly Test Tools: Catphan

5. Image Quality 5.3 High Contrast Resolution scan catphan with the sharpest reconstruction algorithm and the lowest slice thickness Examine the image by adjusting window level & window width

5. Image Quality 5.3 High Contrast Resolution

5. Image Quality 5.3 High Contrast Resolution 1 5 4 3 2 Acceptable level: 5lp/cm

5. Image Quality 5.4 Low Contrast Purpose: To determine the low contrast of the system Frequency: Monthly Test Tools: Catphan

5. Image Quality 5.4 Low Contrast scan catphan with the lowest reconstruction algorithm and 8 or 10mm slice thickness Examine the image by adjusting window level & window width

5. Image Quality 5.4 Low Contrast

5. Image Quality 5.4 Low Contrast 0.5% 1.0% Acceptable level: 5mm for 0.3% of nominal target contrast 0.3%

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) Purpose: to determine that all of the information in the video signal is displayed on the video display & printout film Frequency: Monthly

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) Method: open SMPTE test pattern image and display it on the monitor adjust the window width & window level so that the entire test pattern is visible print SMPTE image on film using film printer

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) Assessment: The 5% patch should be visible inside the 0% patch The 95% patch should be visible inside the 100% patch The line pair pattern at the center and all four sides of the image should be resolvable The alphanumeric should be sharp & clear

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) 5% inside 0% patch 95% inside 100% patch

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) 5% inside 0% patch 95% inside 100% patch Density Step Ramp (0% to 100%)

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) 5% inside 0% patch 95% inside 100% patch Density Step Ramp (0% to 100%) High Contrast Bars Centre 4 Corners

5. Image Display (Visual & Hard Copy) 5. Image Display (Visual & Hard Copy) 5% inside 0% patch 95% inside 100% patch Density Step Ramp (0% to 100%) High Contrast Bars Centre 4 Corners Low Contrast Bars Centre 4 Corners

QC Testing for CT Scan 6. Leakage & Scattered Radiation 6.1: Leakage Radiation 6.2: Scattered Radiation

6. Leakage & Scattered Radiation 6.1 Leakage Radiation Purpose: To determine any areas of radiation leakage through the x-ray tube housing and to measure this leakage Frequency: Annually Test Tools: Survey Meter Measuring Tape

6. Leakage & Scattered Radiation 6.1 Leakage Radiation Position x-ray tube at the bottom of the gantry using service mode function Cover the collimator with a lead gowns to block the entire primary beam Position survey meter at 1 meter away from tube at front, back, right & left area Select the maximum kv (120, 135 @ 140kV) with a suitable ma & timer Record survey meter reading after each exposure

6. Leakage & Scattered Radiation 6.1 Leakage Radiation Acceptable Level: 100mR in an hour Calculate Correction Factor (CF) for the survey meter used CF = 1 t = exposure time -t/rc 1 e RC = survey meter time constant Multiply measured reading with CF True Reading = measured reading x CF Normalised true reading with Leakage Technique Factor (LTF)

6. Leakage & Scattered Radiation 6.2 Scattered Radiation Purpose: To measure the amount of scattered radiation from the CT room Frequency: Annually Test Tools: Survey Meter Water Phantom

6. Leakage & Scattered Radiation 6.2 Scattered Radiation Position water phantom at the center of the gantry Position survey meter at the area where would like to test Scan the phantom with the highest exposure factor clinically used Record survey meter reading

6. Leakage & Scattered Radiation 6.2 Scattered Radiation Acceptable Level: 10mR per week Calculate Correction Factor (CF) for the survey meter used CF = 1 t = exposure time -t/rc 1 e RC = survey meter time constant Multiply measured reading with CF True Reading = measured reading x CF Calculate Weekly Dose

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