CT Q/C Quiz Flashcards
When should the frequency of equipment testing be increased?
If the system is used for specialized studies such as biopsies and radiation therapy treatment plans
Semi-Annually QC tests?
- Accuracy of gantry tilt
- Patient dose
- CT accuracy of automatic positioning of tomographic plane
- CT Laser light accuracy
CT Radiation dose and scout image acceptable limits? How often is it performed?
- dose delivered must remain within within +/-20% of nominal value
- annual
CT number dependence on phantom position acceptable limits? How often is it performed?
- ensures HU do not vary when scanning a water filled phantom place in various positions
- must not vary by more than +/-5HU
- Annual
What is QC? Primary objective? Focus?
Quality control is the process of ensuring products and services meet consumer expectations (make sure equipment is working the way the manufacturer said it would)
- primary objective: equipment testing
- focus on detecting deficiencies and defects with equipment and instrumentation
What needs to happen for a QC program to run smoothly?
- QC test performed on a regular basis (daily, weekly, monthly, or yearly)
- Results need to be recorded and maintained
- Results must be interpreted promptly: compared to both the specs of the scanner and previous results
Annual QC tests?
- Radiation dose profile
- Protective equipment integrity
- General preventative maintenance
- Electronic display performance
- Radiation dose and Scout image
- CT # dependence on phantom position
3 steps of QC
- Acceptance testing (usually done by physicist): ensured scanner was delivered as ordered, tests stability, integrity, and safety of scanner, includes slice thickness, CT # linearity, spatial contrast resolution, noise (inherent and electronic), and dose output
- Routine Performance Evaluation (done by tech and/or physicist): daily, weekly, monthly, or yearly, monitors components of a CT scanner that affect image quality and dose
- Error Correction: if the values of the QC test are outside the acceptance limits or tolerance limits the scanner needs to be serviced
Quarterly QC tests?
- CT patient support movement
- Low contrast detectability
- Spatial resolution
Two performance standards for QC test results
- Acceptable (essential): performance must be within certain tolerances, if not, equipment can’t be used
- Achievable (desirable): indicates the level of performance that should be attained under favourable circumstances
What does the SC35 define?
Safety procedures for the installation, use, and control of x-ray equipment in large medical radiological facilities
What is QA? What is its primary objective and focus?
Quality assurance is the way we measure and guarantee the quality of a product
- primary objective: enhancement of patient care
- focus: PREVENTION of defect and deficiencies
- emphasis on human factors that can lead to variation in quality patient care
3 mandates of QC?
- Must be performed on a regular basis: scheduling is a compromise between downtime, regulatory requirements, and expected benefits
- Prompt interpretation of measurements: helps techs recognize when CT scanner is not operating within acceptable limits
- Consistent and accurate record keeping: results should be maintained for as long as the CT scanner is active
CT Patient support movement acceptable limits? How often is it performed?
- ensure entire volume of patient is scanned
- +/-1mm of intended movement
- quarterly
Monthly QC tests?
- Calibration of CT number
- Electronic display device performance: CT number linearity
- CT tomographic section thickness
- CT linearity
What does QC equipment testing ensure?
- all acquired images are diagnostic
- compliance with ALARA standards: radiation protection, minimize patient dose
- evaluation of data collected by the QC tests: image quality issues can be solved faster
CT Number Accuracy acceptable limit. How often is it performed
-200-300 ROI on uniform water phantom
0 +/-4HU
Weekly
What additional complexities afflict CT?
- Multi-motional gantry
- Interactive Components
- Multiple computers
CT Tomographic Section Thickness acceptable limits? How often is it performed?
-test device containing ramps, discs, or beads placed at an angle to the plane
-2mm+ = +/- 1mm
-1-2mm = +/-50%
-<1mm = +/-0.5mm
Monthly
Accuracy of automatic position of the tomographic place acceptable limits? How often is it performed?
- location of the actual scan plane is compared with the scanned projection
- within +/-2mm of the actual scan plane
- semi-annual
Low contrast detectability acceptable limits? How often is it performed?
- measures smallest object that can be detected when its density differs from that if its background
- done using phantom with 1% (10HU) difference to surrounding material
- subjective
- quarterly
What is the goal of the QC program?
To ensure timely diagnosis and treatment at a minimum dose to patients and staff
CT Uniformity acceptable limits? How often is it performed?
-the consistency of CT numbers of an image across a scan field on an image of homogenous material (5 ROIs)
-the difference between the mean CT numbers at the center of the phantom and the periphery must not exceed 2HU from the baseline
Weekly
What is acceptance testing?
Ensure scanner was delivered as ordered
Tests stability, integrity, and safety of scanner
Why are more advanced QC tests performed less frequently?
- Complex tests require more downtime: more expensive
- Tests that are less important do not need to be completed as frequently: less likely to malfunction, impact on image quality is not detrimental to diagnosis
- Typically performed by physicist
Patient Dose acceptable limit? How often is it performed?
- dosimetry phantom is placed on table without any additional attenuating material
- must be within +/-20% of established baseline values
- *should be performed by a medical physicist
- semi-annual
What is the intended purpose of the ACR phantom?
To demonstrate to patients and personnel of the CT imaging facility the safety and effectiveness of the imaging services
When should daily QC tests be performed?
Test should be repeated whenever equipment is idle for extended periods of time
If system is on 24/7, test should be done at the same time every 24hr period
Daily QC tests?
- Equipment warm up
- Meters Operation
- Equipment Condition
- Overall Visual Assessment of Electronic Display Devices
What types of tests will acceptance testing include?
- Slice thickness
- noise
- dose output
- CT linearity
- spatial and contrast resolution
Integrity of protective equipment acceptable limit? How often is it performed?
- x-ray equipment to look for defective areas
- lead aprons: defective area must not be greater than 670mm^2
- other PPE: defect must not be larger than a 5mm diameter of a circle
- annual
How to choose a technique for QC tests?
- technique should remain the same for a specific test from day to day
- select one of two representative techniques
- use techniques that match a frequently used clinical technique
Spatial resolution acceptable limits? How often is it performed?
- measures smallest object that can be recorded/detected by the CT system
- MTF or line pairs phantom
- Visual assessment: 1mm or less
- MTF: within 0.5lp/mm or +/-15% of baseline
- quarterly
What tests can an ACR phantom be used for?
- positioning accuracy
- CT # accuracy
- slice thickness
- light accuracy alignment
- low contrast resolution
- CT image uniformity
- high contrast resolution
- distance measurements
Calibration of the CT Number acceptable limit? Ho often is it performed?
-2-3cm^2 area of water and air in reconstructed image
-Water = 0 +/-4HU
-Air = -1000 +/-10HU
Monthly
CT Radiation dose profile acceptable limits? How often is it performed?
- ensures radiation beam does not exceed prescribed scan width
- measured directly from density profile of resultant film or computed from digital profile
- should not exceed the prescribed width by more than the manufacturer specs
- annual
Who determines who performs QC testing?
- regulatory bodies such as Health Canada
- manufacturer can also recommend evaluative procedures
Weekly QC tests?
- CT number accuracy
- Visual Inspection of Cleanliness
- CT Noise
- CT uniformity
Who’s responsibility is it to identify when the physicist is required to complete service repairs?
Ours
CT Noise acceptable limit. How often is it performed?
-Measures the mean value and SD of CT numbers within an RIO 40% of the diameter of the uniform phantom
must be +/-10% or 0.2HU from established baseline noise levels (whichever is larger)
Weekly
Accuracy of gantry tilt acceptable limits? How often is it performed?
- expose film placed upright and parallel to the sagittal laser at various tilt angles (at least 3: no tilt, 2 extremes)
- angles should correspond to display to within +/-3 degree
- semi-annual
Types of phantoms used?
- Image performance phantoms: subjective
- Geometric Phantoms: ensure object shape, size, positions are being represented appropriately
- Dosimetry Phantoms: ensures ALARA principles are adhered to
- Quantitative Phantoms: objective, statistical measurements, make sure HU are accurate
CT Laser light accuracy acceptable limits? How often is it performed?
-needle to puncture holes in film at positions of laser lights (axial)
-place a thin absorber entered in the tomographic place at the intersection of light (sagittal and coronal)
-difference between scanned area and pin pricks = +/-2mm
= +/-5mm for alignment with the center of the SFOV
-Semi-annual
CT Number Linearity acceptable limits? How often is it performed?
- phantom containing objects of known materials with a wide range of CT values
- Measured values must fall within established limits for the CT scanner
- relationship must be straight line
- Monthly
What kind of difficulties are CT imaging systems subject to?
- Miscalibration
- Malfunctioning
- Misalignment
Equipment testing must commence….
-after a major component has been replaced, serviced, or adjusted
