QA And QC

Question 1

What is Quality Assurance

Answer 1

Management program used to ensure excellence in health care. The responsibility of the owner to established a QA program for the staff to follow. Focuses on preventing defects and deficiencies

Question 2

What is Quality Control

Answer 2

Part of a QA program that deals with techniques used in monitoring and maintaining the technical elements of the system that affect the quality of the image

• deals with instrumentation and equipment
• focuses on detecting deficiencies and defects

Question 3

QC schedule

Answer 3

Tests performed on a daily, weekly, monthly, quarterly, semi-annual, and annual basis
Results must be recorded and maintained
Results must be interpreted promptly to ensure the scanner is meeting performance specifications

Question 4

What is acceptance testing

Answer 4

Usually done by physicist
Ensures the scanner was delivered as ordered
Tests the stability, integrity and safety of the scanner

Question 5

Acceptance tests include

Answer 5

Slice thickness verification
CT number linearity 
Spatial (high) and Contrast (low) resolution 
Noise 
Dose output

Question 6

3 mandates of QC

Answer 6

Tests that make up the program must be performed on a regular basis
Results from all tests must be recorded using a consistent format
Documentation should indicate whether the tested parameter is within specified limits

Question 7

2 performance standards for QC tests are

Answer 7

Acceptable (essential)
- indicates that performance must be within a certain tolerances, if not equipment should not be used
Achievable (desirable)
- indicates the level of performance that should be attained under favourable circumstances, the level at which the facility should work if feasible

Question 8

ARC phantom parts

Answer 8

Module 1 - assess positioning and alignment, CT accuracy and slice thickness
Module 2 - assess low contrast
Module 3 - assess CT # uniformity and accuracy of in plane distance measurements
Module 4 - assess spatial resolution (high contrast)

Question 9

Test frequency considerations

Answer 9

Replacement of major components, equipment service or adjustments require immediate testing
If used for accurately localizing tissue (biopsies/rad therapy) increase in test frequency of appropriate tests
Complexity of test performed, decrease the test frequency, slows down the DI department and no money made

Question 10

Daily Tests

Answer 10

Equipment warm up
Meters operation
Equipment condition
Overall visual assessment of electronic display devices

Question 11

Weekly Tests

Answer 11

Visual inspection of cleanliness
CT uniformity
CT noise
CT Number accuracy

Question 12

Monthly Tests

Answer 12

Electronic Display Device Performance
Section Thickness
Calibration of CT numbers
CT number linearity

Question 13

Quarterly Tests

Answer 13

CT patient support movement
Spatial resolution (high contrast)
Low contrast detectability

Question 14

Semi-Annual Tests

Answer 14

Accuracy of automatic position of tomographic plane
Accuracy of gantry tilt
Patient dose
Laser light accuracy

Question 15

Annual Tests

Answer 15

CT number dependence of phantom position 
Radiation dose profile 
General preventative maintenance
Protective equipment 
Radiation dose and scout image

Question 16

CT Number Accuracy QC Test

Answer 16

Weekly QC test
Use a water phantom
Mean CT number of water and the standard deviation within large ROI must remain within established limits
CT number for water must remain in a range of +/- 4 HU
Recommended that the test if performed at 2 CT conditions of operation (body/head)

Question 17

CT Noise QC test

Answer 17

Weekly QC test
Given variation of CT numbers for a mean value in a defined area in the image of a uniform phantom
Use a water phantom
Noise evaluation - diameter of the ROI should rep 40% of the Diameter of uniform phantom image
Noise most not deviate from the established baseline value by more than +/-10% or 0.2HU

Question 18

CT uniformity

Answer 18

Weekly QC test
Use a phantom of water or uniform density
Uniformity - the consistency of the CT #’s in an image of a homo material across the scan field
Mean CT # must be determined for 5 ROI’s (1 middle, 4 periphery)
Diameter of each ROI = 10% of the phantom diameter
No more than +/- 2HU variation from the center of ROI to any at periphery

Question 19

CT Slice Thickness

Answer 19

Monthly QC test
Use a phantom containing a ramp, spiral, or step wedge of known size and thickness
Evaluates tomographic section thickness
AST of 2mm or more section thickness must not vary more than +/- 1mm from baseline value
AST of 2-1mm section thickness must not vary more than +/- 50% of the baseline value
AST >1mm section thickness must not vary more than +/- 0.5mm of the baseline value

Question 20

Calibration of CT Numbers

Answer 20

Monthly QC test
Mean CT # and standard deviation are measured
Calculated for a 2-3cm2 area of water and air in the reconstructed image
Same location should be used for each test
CT # of water must be 0 +/- 4HU
CT # of air must be -1000 +/- 10HU

Question 21

CT # linearity

Answer 21

monthly QC test
Using a phantom containing uniform objects of known materials with a wide range of CT numbers
Tests are completed at all clinically used voltage settings (80,120,140 kVp). CT # range of -1000 - +1000 are checked
Measured CT #’s are compared with the values provided by the phantom manufacturer and with previously measured values
Measured values must stay within the established limits of CT scanner
Acceptable limit achieved when values form a straight line

Question 22

CT Spatial Resolution

Answer 22

Quarterly QC test
Evaluated by physicists by determining MTF
Imaging line pairs phantom done by tech
Phantom has lead strips with different strip width and spacing to determine lp/mm
At min spatial res should be equal to the manufacturer specifications for the scanner

Question 23

Low Contrast Resolution/Detectability

Answer 23

quarterly QC test
Using a phantom of objects of varying size with about 1% or 10HU contrast to the surrounding material
Measured using different reconstruction algorithms routinely used by the scanner
Baseline value is subjective due to the visual acuity of the observer
Value determined as the smallest sized object seen at a specified contrast level to the background when imaged under certain conditions

Question 24

CT Support Movement

Answer 24

Quarterly QC test
Test is performed using an even weight load of no more than 135 kg
Measured of support movement must be within +/- 1mm of the intended movement when the pt support move in and out of the gantry

Question 25

Interlocks

Answer 25

Quarterly QC test

Prevent the x-Ray equipment from producing radiation when the door is open

Question 26

Laser Light Accuracy

Answer 26

Semi-annual QC test
Lasers are located in/outside the gantry, used for patient positions and alignment
Indicates the location of the radiation beam relative to the external anatomical structures of the patient
Radiation should align with the laser light within 2mm

Question 27

Accuracy of Automatic Position of the Tomographic Plane

Answer 27

Semi annual QC test
Localization of the scan plane prescribed by using the scanned project radiograph must be within +/-2mm of the actual scan plane
Assessment of scout images
Ensures the accuracy of the localizer with the digital display function

Question 28

CT Accuracy of Gantry Tilt

Answer 28

Semi-annual QC test
Ensures that the physical tilt of the gantry corresponds to the tilt angle indicated by the CT display
Test at no tilt and each extreme angles
Angles measured on film should correspond with computer display within +/- 3mm

Question 29

CT # Dependence of Phantom Position

Answer 29

Annual QC test
Ensure HU accuracy of varied patient positions within the gantry
CT # of water must not vary by more than +/- 5HU when the position of the water filled phantom is varied over clinically relevant positions

Question 30

CT Radiation Dose Profile

Answer 30

Annual QC test
Collimation of beam is assessed to ensure it doesn’t exceed the prescribed scan width
Should exceed manufactures specifications
Variation of the intensity of the x-Ray beam in the z-plane
Section thickness