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MRT Year 1 Semester 2 > CT Q/C Quiz > Flashcards

CT Q/C Quiz Flashcards

1
Q

When should the frequency of equipment testing be increased?

A

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

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2
Q

Semi-Annually QC tests?

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

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

A
  • dose delivered must remain within within +/-20% of nominal value
  • annual
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4
Q

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

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

What is QC? Primary objective? Focus?

A

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
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6
Q

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

A
  • 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
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7
Q

Annual QC tests?

A
  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
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8
Q

3 steps of QC

A
  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
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9
Q

Quarterly QC tests?

A
  1. CT patient support movement
  2. Low contrast detectability
  3. Spatial resolution
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10
Q

Two performance standards for QC test results

A
  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
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11
Q

What does the SC35 define?

A

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

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12
Q

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

A

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
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13
Q

3 mandates of QC?

A
  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
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14
Q

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

A
  • ensure entire volume of patient is scanned
  • +/-1mm of intended movement
  • quarterly
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15
Q

Monthly QC tests?

A
  1. Calibration of CT number
  2. Electronic display device performance: CT number linearity
  3. CT tomographic section thickness
  4. CT linearity
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16
Q

What does QC equipment testing ensure?

A
  • 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
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17
Q

CT Number Accuracy acceptable limit. How often is it performed

A

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

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18
Q

What additional complexities afflict CT?

A
  • Multi-motional gantry
  • Interactive Components
  • Multiple computers
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19
Q

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

A

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

20
Q

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

A
  • location of the actual scan plane is compared with the scanned projection
  • within +/-2mm of the actual scan plane
  • semi-annual
21
Q

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

A
  • 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
22
Q

What is the goal of the QC program?

A

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

23
Q

CT Uniformity acceptable limits? How often is it performed?

A

-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

24
Q

What is acceptance testing?

A

Ensure scanner was delivered as ordered

Tests stability, integrity, and safety of scanner

25
Q

Why are more advanced QC tests performed less frequently?

A
  • 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
26
Q

Patient Dose acceptable limit? How often is it performed?

A
  • 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
27
Q

What is the intended purpose of the ACR phantom?

A

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

28
Q

When should daily QC tests be performed?

A

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

29
Q

Daily QC tests?

A
  1. Equipment warm up
  2. Meters Operation
  3. Equipment Condition
  4. Overall Visual Assessment of Electronic Display Devices
30
Q

What types of tests will acceptance testing include?

A
  • Slice thickness
  • noise
  • dose output
  • CT linearity
  • spatial and contrast resolution
31
Q

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

A
  • 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
32
Q

How to choose a technique for QC tests?

A
  • 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
33
Q

Spatial resolution acceptable limits? How often is it performed?

A
  • 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
34
Q

What tests can an ACR phantom be used for?

A
  • positioning accuracy
  • CT # accuracy
  • slice thickness
  • light accuracy alignment
  • low contrast resolution
  • CT image uniformity
  • high contrast resolution
  • distance measurements
35
Q

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

A

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

36
Q

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

A
  • 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
37
Q

Who determines who performs QC testing?

A
  • regulatory bodies such as Health Canada

- manufacturer can also recommend evaluative procedures

38
Q

Weekly QC tests?

A
  1. CT number accuracy
  2. Visual Inspection of Cleanliness
  3. CT Noise
  4. CT uniformity
39
Q

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

A

Ours

40
Q

CT Noise acceptable limit. How often is it performed?

A

-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

41
Q

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

A
  • 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
42
Q

Types of phantoms used?

A
  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
43
Q

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

A

-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

44
Q

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

A
  • 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
45
Q

What kind of difficulties are CT imaging systems subject to?

A
  • Miscalibration
  • Malfunctioning
  • Misalignment
46
Q

Equipment testing must commence….

A

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

MRT Year 1 Semester 2 (11 decks)

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