CT Q/C Quiz

Question 1

When should the frequency of equipment testing be increased?

Answer 1

If the system is used for specialized studies such as biopsies and radiation therapy treatment plans

Question 2

Semi-Annually QC tests?

Answer 2

1. Accuracy of gantry tilt
2. Patient dose
3. CT accuracy of automatic positioning of tomographic plane
4. CT Laser light accuracy

Question 3

CT Radiation dose and scout image acceptable limits? How often is it performed?

Answer 3

• dose delivered must remain within within +/-20% of nominal value
• annual

Question 4

CT number dependence on phantom position acceptable limits? How often is it performed?

Answer 4

• ensures HU do not vary when scanning a water filled phantom place in various positions
• must not vary by more than +/-5HU
• Annual

Question 5

What is QC? Primary objective? Focus?

Answer 5

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

Question 6

What needs to happen for a QC program to run smoothly?

Answer 6

• 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

Question 7

Annual QC tests?

Answer 7

1. Radiation dose profile
2. Protective equipment integrity
3. General preventative maintenance
4. Electronic display performance
5. Radiation dose and Scout image
6. CT # dependence on phantom position

Question 8

3 steps of QC

Answer 8

1. 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
2. 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
3. Error Correction: if the values of the QC test are outside the acceptance limits or tolerance limits the scanner needs to be serviced

Question 9

Quarterly QC tests?

Answer 9

1. CT patient support movement
2. Low contrast detectability
3. Spatial resolution

Question 10

Two performance standards for QC test results

Answer 10

1. Acceptable (essential): performance must be within certain tolerances, if not, equipment can’t be used
2. Achievable (desirable): indicates the level of performance that should be attained under favourable circumstances

Question 11

What does the SC35 define?

Answer 11

Safety procedures for the installation, use, and control of x-ray equipment in large medical radiological facilities

Question 12

What is QA? What is its primary objective and focus?

Answer 12

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

Question 13

3 mandates of QC?

Answer 13

1. Must be performed on a regular basis: scheduling is a compromise between downtime, regulatory requirements, and expected benefits
2. Prompt interpretation of measurements: helps techs recognize when CT scanner is not operating within acceptable limits
3. Consistent and accurate record keeping: results should be maintained for as long as the CT scanner is active

Question 14

CT Patient support movement acceptable limits? How often is it performed?

Answer 14

• ensure entire volume of patient is scanned
• +/-1mm of intended movement
• quarterly

Question 15

Monthly QC tests?

Answer 15

1. Calibration of CT number
2. Electronic display device performance: CT number linearity
3. CT tomographic section thickness
4. CT linearity

Question 16

What does QC equipment testing ensure?

Answer 16

• 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

Question 17

CT Number Accuracy acceptable limit. How often is it performed

Answer 17

-200-300 ROI on uniform water phantom
0 +/-4HU
Weekly

Question 18

What additional complexities afflict CT?

Answer 18

• Multi-motional gantry
• Interactive Components
• Multiple computers

Question 19

CT Tomographic Section Thickness acceptable limits? How often is it performed?

Answer 19

-test device containing ramps, discs, or beads placed at an angle to the plane
-2mm+ = +/- 1mm
-1-2mm = +/-50%
-<1mm = +/-0.5mm
Monthly

Question 20

Accuracy of automatic position of the tomographic place acceptable limits? How often is it performed?

Answer 20

• location of the actual scan plane is compared with the scanned projection
• within +/-2mm of the actual scan plane
• semi-annual

Question 21

Low contrast detectability acceptable limits? How often is it performed?

Answer 21

• 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

Question 22

What is the goal of the QC program?

Answer 22

To ensure timely diagnosis and treatment at a minimum dose to patients and staff

Question 23

CT Uniformity acceptable limits? How often is it performed?

Answer 23

-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

Question 24

What is acceptance testing?

Answer 24

Ensure scanner was delivered as ordered

Tests stability, integrity, and safety of scanner

Question 25

Why are more advanced QC tests performed less frequently?

Answer 25

- 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

Question 26

Patient Dose acceptable limit? How often is it performed?

Answer 26

- 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

Question 27

What is the intended purpose of the ACR phantom?

Answer 27

To demonstrate to patients and personnel of the CT imaging facility the safety and effectiveness of the imaging services

Question 28

When should daily QC tests be performed?

Answer 28

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

Question 29

Daily QC tests?

Answer 29

1. Equipment warm up 2. Meters Operation 3. Equipment Condition 4. Overall Visual Assessment of Electronic Display Devices

Question 30

What types of tests will acceptance testing include?

Answer 30

- Slice thickness - noise - dose output - CT linearity - spatial and contrast resolution

Question 31

Integrity of protective equipment acceptable limit? How often is it performed?

Answer 31

- 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

Question 32

How to choose a technique for QC tests?

Answer 32

- 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

Question 33

Spatial resolution acceptable limits? How often is it performed?

Answer 33

- 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

Question 34

What tests can an ACR phantom be used for?

Answer 34

- positioning accuracy - CT # accuracy - slice thickness - light accuracy alignment - low contrast resolution - CT image uniformity - high contrast resolution - distance measurements

Question 35

Calibration of the CT Number acceptable limit? Ho often is it performed?

Answer 35

-2-3cm^2 area of water and air in reconstructed image -Water = 0 +/-4HU -Air = -1000 +/-10HU Monthly

Question 36

CT Radiation dose profile acceptable limits? How often is it performed?

Answer 36

- 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

Question 37

Who determines who performs QC testing?

Answer 37

- regulatory bodies such as Health Canada | - manufacturer can also recommend evaluative procedures

Question 38

Weekly QC tests?

Answer 38

1. CT number accuracy 2. Visual Inspection of Cleanliness 3. CT Noise 4. CT uniformity

Question 39

Who's responsibility is it to identify when the physicist is required to complete service repairs?

Answer 39

Ours

Question 40

CT Noise acceptable limit. How often is it performed?

Answer 40

-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

Question 41

Accuracy of gantry tilt acceptable limits? How often is it performed?

Answer 41

- 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

Question 42

Types of phantoms used?

Answer 42

1. Image performance phantoms: subjective 2. Geometric Phantoms: ensure object shape, size, positions are being represented appropriately 3. Dosimetry Phantoms: ensures ALARA principles are adhered to 4. Quantitative Phantoms: objective, statistical measurements, make sure HU are accurate

Question 43

CT Laser light accuracy acceptable limits? How often is it performed?

Answer 43

-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

Question 44

CT Number Linearity acceptable limits? How often is it performed?

Answer 44

- 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

Question 45

What kind of difficulties are CT imaging systems subject to?

Answer 45

- Miscalibration - Malfunctioning - Misalignment

Question 46

Equipment testing must commence....

Answer 46

-after a major component has been replaced, serviced, or adjusted