QA And QC Flashcards
What is Quality Assurance
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
What is Quality Control
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
QC schedule
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
What is acceptance testing
Usually done by physicist
Ensures the scanner was delivered as ordered
Tests the stability, integrity and safety of the scanner
Acceptance tests include
Slice thickness verification CT number linearity Spatial (high) and Contrast (low) resolution Noise Dose output
3 mandates of QC
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
2 performance standards for QC tests are
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
ARC phantom parts
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)
Test frequency considerations
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
Daily Tests
Equipment warm up
Meters operation
Equipment condition
Overall visual assessment of electronic display devices
Weekly Tests
Visual inspection of cleanliness
CT uniformity
CT noise
CT Number accuracy
Monthly Tests
Electronic Display Device Performance
Section Thickness
Calibration of CT numbers
CT number linearity
Quarterly Tests
CT patient support movement
Spatial resolution (high contrast)
Low contrast detectability
Semi-Annual Tests
Accuracy of automatic position of tomographic plane
Accuracy of gantry tilt
Patient dose
Laser light accuracy
Annual Tests
CT number dependence of phantom position Radiation dose profile General preventative maintenance Protective equipment Radiation dose and scout image
CT Number Accuracy QC Test
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)
CT Noise QC test
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
CT uniformity
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
CT Slice Thickness
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
Calibration of CT Numbers
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
CT # linearity
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
CT Spatial Resolution
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
Low Contrast Resolution/Detectability
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
CT Support Movement
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
Interlocks
Quarterly QC test
Prevent the x-Ray equipment from producing radiation when the door is open
Laser Light Accuracy
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
Accuracy of Automatic Position of the Tomographic Plane
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
CT Accuracy of Gantry Tilt
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
CT # Dependence of Phantom Position
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
CT Radiation Dose Profile
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
