CHAPTER 5 QC Test For Radiographic Equipment Prepared by:- Kamarul Amin bin Abdullah @ Abu Bakar School of Medical Imaging KLMUC
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
CHAPTER 5QC Test For Radiographic Equipment
Prepared by:-Kamarul Amin bin Abdullah @ Abu Bakar
School of Medical ImagingKLMUC
Lesson Outcomes
• Describe the objectives of each QC test done.(importance)
• Define the term ‘reproducibility’ and ‘linearity’.
• Identify the required QC test for specific x-ray devices.
• Identify QC tools and equipments involved in each QC test.
• Discuss the analysis of result of QC.
• Discuss the procedure of QC test.
QC Tests (All)
1. AUTOMATIC EXPOSURE CONTROL (AEC)A. Exposure ReproducibilityB. Response timeC. Backup timerD. Exposure timerE. AccuracyF. ReproducibilityG. Dead-man exposure switch
2. KILOVOLTAGEA. AccuracyB. Reproducibility
3. RADIATION OUTPUT (mAs)A. LinearityB. Programmed timerC. Reproducibility
4. HALF-VALUE LAYER (HVL)5. BEAM AND COLLIMATION ALIGNMENT6. GRID ALIGNMENT7. FOCAL SPOT
QC Tests (Theory and Practical)
1. kV reproducibility
2. mA linearity
3. Timer accuracy
4. HVL
5. Grid alignment
6. Beam and collimation alignment
1. kV reproducibility
Objective:
• To determine the variation in average kVp over a number of exposures at the same generator setting.
Equipment:
• Digital kV meter/multifunction meter
• Lead backing sheet
• Energized radiographic unit
Reproducibility
• ability of radiographic unit to produce the same exposure even though in the short intervals.
Sample of Data Collection
X= 70 Kvp
Data Analysis
Discussion on Analysis
• Kilovoltage settings tend to drift over time, primarily as a result of tubing aging.
• Reproducibility should be maintained within ±2%.• The problem maybe because:
1. X-ray tube problems2. Inaccurate reading of the detector.
• The generator in that room did not function very well. It did not have the capability to produce the same exposure even though in the short intervals.
mA linearity
Objective:
• To evaluate the linearity of a generator for commonly used exposure settings
Equipment:
• Energized radiographic unit
• Digital dosimeter
Linearity
• ability of radiographic unit to produce a constant radiation output for various combinations of mAand exposure time.
Sample of Data Collection
Data Analysis
Sample of Data Analysis
Discussion on Analysis
• Linearity means that the ratio of exposure to total charge in mR/mAs is constant over the entire range of mAs values.
• The average mR/mAs obtain at any tube current settings (mA) shall not differ by more than 0.10.
• Linearity should be maintained to ±10% over the entire working range of the generator regardless of the number mA stations at fixed kVp.
• This test attempts to establish if the same film density is achieved using the same kVp and mAsbut different mA and time values.
Timer Accuracy
Objective:
• To evaluate the accuracy of an exposure timer.
Equipment:
• Energized radiographic unit
• Digital exposure timer (multi-function meter)
Sample of Data Collection
Data Analysis
Discussion on Analysis
HVL
Objective:• To assess the x-ray beam quality and determine
the adequacy of filtration.
Equipment:• Energized radiographic unit• Digital dosimeter • Lead backing sheet• Aluminiumfilters• Tape for positioning filters
HVL
• HVL is that amount of absorbing material that will reduce the intensity of the primary beam to one-half its original value.
Sample of Data Collection
General Analysis
Data in table are typical for half-value layer determination.
• Referring to the data, the HVL is 2.4mm Al.
• At zero filtration, x-ray quantity appears to be approximately 118 mR.One half of the 118mR is 59mR.
• At the level of 59mR, a horizontal line is drawn from the y-axis until it intersects the plotted curve.
• From that intersection, a vertical line is dropped to the x-axis where, it intersects at 2.4mm Al, which is the HVL.
Discussion on Analysis
• FILTRATION IS NECESSARY TO REMOVE LOW-ENERGY PHOTONS FROM THE X-RAY BEAM.
• THE BEST METHOD TO DETERMINE ADEQUATE FILTRATION IS BY MEASURE THE HALF-VALUE LAYER (HVL).
• HVL IS THE AMOUNT OF THE FILTRATION THAT WILL REDUCE THE EXPOSURE RATE TO ONE HALF OF ITS INITIAL VALUE.
• THE DOSIMETER WHICH IS RAD CHECK THAT BEING USED IN LAB IS TO MEASURE THE HVL BY DETECTING THE QUALITY OF ALUMINIUM FILTRATION THAT WILL REDUCE THE BEAM INTENSITY TO HALF THE ORIGINAL VALUE.
Grid alignment
Objective:
• To detect an upside-down focused grid or incorrect tube to grid distance.
Equipment:
• Energized radiographic unit (60kV, 2mAs)
• RMI grid alignment test tool
• 18 x 24 cm cassette with film
• Densitometer
Sample of Data Collection
Data Analysis
• Which hole represents the highest OD? Why?
Discussion on Analysis
• If the grid is misalignment, it may be because of several causes.
• One of the causes is due to the position of grid (off-center) or its construction (upside down grid)
• It also because of reciprocating action of the grid itself where grid motion and the beginning of the x-ray exposure are not simultaneously
Beam and Collimation Alignment
Objective:• To check misalignment of the light field and the x
ray field
Equipment:• Energized radiographic unit• RMI Collimator Test Tool and the RMI Beam
Alignment Test Tool• Cassette 8 X 10 inch• The bubble level
Sample of Data Collection
• upper steel ball superimposed with lower steel ball.
• collimation beam fall at the same scale of number in the test tool.
• upper steel ball is not superimposed with lower steel ball.
• rating scales are not at the same number on both superior, inferior and lateral side. The collimation beam is less on left and inferior side and vice versa.
• overlapped of the steel balls in the center.
• collimation falls within the rectangular frame.
Data Analysis
Collimation
• Misalignment must not exceed ±2% of the SID.
• If an edge of the x-ray field falls on the first spot ±1 cm, it shows that the edge of the x-ray field and the light field are misaligned by 1% of SID.
Beam
• If both steel balls overlapped, the central ray is perpendicular, indicates good alignment.
Discussion on Analysis
Collimation
• Misalignment must not exceed ±2% of the SID.
• If an edge of the x-ray field falls on the first spot ±1 cm, it shows that the edge of the x-ray field and the light field are misaligned by 1% of SID.
Beam
• If both steel balls overlapped, the central ray is perpendicular, indicates good alignment.
Other QC Test Objectives
• To measure the minimum response time of the AEC.
• To ensure that the backup timer is functioning and backup time does not exceed the specified time.
• To ensure that the exposure is terminated by removing pressure from the exposure switch.
• To determine how the measured kVpcompares with the generator setting.
Related Documents
