Safety Code 35: Safety Procedures for the Installation, Use and Control of X-ray Equipment in Large Medical Radiological Facilities

Section C: Quality Assurance Program

3.0 Quality Control Testing Procedures and Equipment

Quality control testing must be carried out during routine operation of a radiological facility. This section sets out the required and recommended quality control tests, the associated test equipment and testing frequencies.

Quality control testing of a medical X-ray system includes several major steps. They are:

1. the verification of the system mechanical integrity and stability, including safety mechanisms, automatic patient release, power drives, interlocks;
2. the verification of the performance of ancillary equipment such as film processors and display units;
3. the verification of X-ray performance; and
4. the verification of imaging or diagnostic performance, including assessments of dose.

Test equipment required to perform daily to monthly quality control tests, must be readily available to the individuals responsible for performing these tests. All test equipment must be calibrated and verified to be operating accurately. Individuals performing quality control tests must be trained in the proper operation of the test equipment and in performing the tests.

In the following sections, the descriptive text for each test indicates whether performance of the test is required or recommended. In addition, not all equipment will be subject to the full set of tests listed in the following sections. For example, for film-based systems, the evaluation of noise is not necessary since this item is for the evaluation of digital systems. The type of imaging system, whether film-based, CR, DR, radioscopic or CT, to which the quality control tests apply is identified. Note that both radiographic and radioscopic imaging equipment employing CR and DR digital image acquisition technologies must perform the required tests listed for these systems. Alternative tests can be performed in place of those specified if it can be shown that the test is capable of verifying the necessary parameter or performance.

3.1 Daily Quality Control Testing

3.1.1 Quality Control Tests List

Daily quality control tests are listed in Table 11. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.1.2, are provided.

Table 11: Daily Quality Control Tests

Quality Control Procedures Under Evaluation	Film-based System	CR System	DR System	Radioscopic System	CT System
Daily Quality Control Tests
Equipment Warm-up	D1	D1	D1	D1	D1
Meters Operation	D2	D2	D2	D2	D2
Equipment Conditions	D3	D3	D3	D3	D3
System Movements				D4
Darkroom Cleanliness	D5			D5
Film Processor Function	D6			D6
Overall Visual Assessment of Electronic Display Devices		D7	D7	D7	D7

3.1.2 Daily Quality Control Tests

Daily Quality Control Tests. Daily Quality Control tests must be performed at the beginning of each day before commencing patient examinations.

• D1. Equipment Warm-up--The manufacturer's recommended warm up procedure must be followed. The warm up procedure must be repeated if the equipment is left idle for an extended period of time. It is important to note that all components of the imaging system which are routinely used must be warmed up, including computer display devices and printers.
• D2. Meters Operation--Meters and visual and audible indicators should be checked for proper function.
• D3. Equipment Conditions--X-ray equipment conditions should be visually inspected for loose or broken components and cleanliness. The X-ray source assembly should be checked for motion or vibration during operation. Visual inspection should also be conducted of all other components of the imaging systems.
• D4. System Movement--System movement should be checked for proper function. For systems where the X-ray source is below the table, verify the performance of the power assist and locks by moving the tower in all directions. For systems where the X-ray source is above the table, verify the motion of the X-ray tube assembly.
• D5. Darkroom Cleanliness--In order to maintain the cleanliness of the darkroom all working surfaces, tops of counters and the floor should be cleaned daily. Dust and debris can more easily be seen using a UV-B lamp.
• D6. Film Processor Function--Film processor function must be evaluated every morning before performing clinical examinations, after the processor has been turned on and has reached the required development temperature; and at other times as required, such as after a replenishment rate change. Facilities operating spotfilm equipment must also perform the following quality control tests on the film processing system.
  1. The film processing solution levels must be checked to ensure agreement with the manufacturers' recommended baseline levels for the particular processor and film type, for the given number of films processed daily.
  2. The displayed processor temperature must be checked to ensure agreement with the manufacturers' recommended baseline level for the particular processor and film used.
  3. Sensitometric strip processing must be performed in order to monitor the performance of the image processing system.
     • The base plus fog must be within + 0.05 of the established operating level.
     • The mid-density must be within ± 0.15 of the established operating level.
     • The density difference must be within ± 0.15 of the established operating level.
• D7. Overall Visual Assessment of Electronic Display Devices--The performance of electronic display devices used for interpretation of clinical images must be assessed. Displaying the image of a test pattern, an assessment must be made of the general image quality and for the presence of artifacts. The SMPTE or the TG18-QC test patterns can be used for this test and should be displayed using the software routinely used to display clinical images. It is recommended that the test pattern image be viewed from a distance of 30 cm from the front of the display device. The results of the assessment must be within established limits.

3.1.3 Daily Quality Control Test Equipment

Test equipment for the daily quality control testing are listed in Table 12.

Table 12: Daily Quality Control Test Equipment

Item	Equipment	Systems	Reference
Note: FS: Film Screen, CR: Computed Radiography, DR: Digital Radiography, RA: Radioscopy, SF: Spotfilm, CT: Computed Tomography
1	Phantom (if needed for manufacturer's recommended warm up procedure)	FS, CR, DR, RA, SF, CT	D1
2	Ultraviolet Light	FS, SF	D5
3	Sensitometer (21 steps optical attenuator with densities ranging from approximately 0.00 to 4.80 in steps of 0.15) Accuracy: ± 0.02 log exposure units Reproducibility: ± 0.02 log exposure units	FS, SF	D6
4	Densitometer Accuracy: ± 0.02 O.D. at 1.0 O.D. Reproducibility: ± 0.01 O.D. at 1.0 O.D.	FS, SF	D6
5	Test Pattern Image (ex.: SMPTE or TG18-QC)	CR, DR, RA, CT	D7

3.2 Weekly Quality Control Testing

3.2.1 Quality Control Tests List

Weekly quality control tests are listed in Table 13. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.2.2, are provided.

Table 13: Weekly Quality Control Tests

Quality Control Procedures Under Evaluation	Film-based System	CR System	DR System	Radioscopic System	CT System
Weekly Quality Control Tests
Visual Inspection of Cleanliness of Imaging Systems	W1	W1	W1	W1	W1
Viewboxes Condition	W2	W2	W2	W2	W2
Laser Film Printer Operation		W3	W3	W3	W3
CT Number Accuracy					W4
CT Noise					W5
CT Uniformity					W6
Digital Subtraction Angiography System Performance				W7

3.2.2 Weekly Quality Control Tests

• W1. Visual Inspection of Cleanliness of Imaging Systems-- Imaging systems must be inspected for dust and dirt on or near the image reception area where they may negatively affect image quality. For CR systems, the imaging plates must be inspected. The imaging plate loading and unloading mechanism must be cleaned and lubricated if necessary. The image receptors for direct-capture systems must be kept clean of dust, dirt and other items which may come into contact with them. Laser scanning digitizers must also be checked for cleanliness.
• W2. Viewboxes Condition--Viewboxes must be inspected visually for cleanliness, viewing area discolouration and improper illumination.
• W3. Laser Film Printer Operation--The quality of images obtained from the laser film printer must be checked. Depending on the system, this may or may not require using pre-established window and level settings on the display. Ensure that the viewbox used to assess printed films has sufficient luminance. The SMPTE, TG18-QC and TG18-PQC test patterns should be used. A hardcopy image of the test pattern must meet the following criteria:
  1. the 5% patch must be just visible inside of the 0% patch,
  2. the 95% patch must be just visible inside the 100% patch,
  3. no geometrical distortion upon visual inspection,
  4. no artifacts upon visual inspection.
• W4. CT Number Accuracy--An evaluation of the accuracy of the CT number of water must be made. Using a uniform water phantom, the mean CT number of water and the standard deviation, within a large region of interest, must remain within the established baseline and acceptable limits of variation. The CT number for water must be in the range of 0 ± 4HU. For quantitative CT application, a phantom containing the material of interest for the particular application should be used for this test. It is recommended that this test be performed at two CT conditions of operation, one representing a typical axial head scan and one representing a typical axial body scan.
• W5. CT Noise--A measurement of CT noise must be made. Noise is given by the variation of CT numbers from a mean value in a defined area in the image of a uniform phantom. Its magnitude is equal to the standard deviation of the CT number values within the region of interest. For noise evaluation, the diameter of the region of interest should represent 40% of the diameter of the uniform phantom image. Noise can be quantified in HU or expressed as a percentage of the linear attenuation coefficient for water (see section B2.5.5). The noise in a CT system must not deviate from the established baseline value by more than ± 10% or 0.2 HU, whichever is larger. The established baseline noise levels in a CT system should not deviate from the manufacturer specified noise value by more than ± 15%. It is recommended that this test be performed at two CT conditions of operation, one representing a typical axial head scan and one representing a typical axial body scan.
• W6. CT Uniformity--Uniformity is defined as the consistency of the CT numbers of an image of a homogeneous material across the scan field. Uniformity is calculated using the following equation:
  
  where
  
  
  CT_m,c

  is the mean CT number in the centre of the image,
  CT_m,p

  is the mean CT number at the periphery of the image.
  
  
  The mean CT number must be determined for 5 regions of interest, one in the centre and 4 at the peripheries of the phantom. The diameter of each region of interest should represent 10% of the diameter of the phantom.
  
  The difference between the mean CT number at the centre of the phantom and the periphery must not exceed 2 HU from the established baseline values. The baseline uniformity of the CT number for water must not be greater than ± 5 HU from the centre of the phantom to the periphery. It is recommended that this test be performed at two CT conditions of operation, one representing a typical axial head scan and one representing a typical axial body scan.
• W7. Digital Subtraction Angiography System Performance--Following equipment warm up and prior to clinical use, the image quality of the DSA system should be evaluated using a phantom containing image quality test objects

3.2.3 Weekly Quality Control Test Equipment

Test equipment for the weekly quality control testing are listed in Table 14.

Table 14: Weekly Quality Control Test Equipment

Item	Equipment	Systems	Reference
1	Test Pattern Image	CR, DR, RA, CT	W3
2	Water Filled Uniform Phantom	CT	W4, W5, W6
3	Digital Subtraction Angiography Image Quality Phantom	RA	W7

3.3 Monthly Quality Control Testing

3.3.1 Quality Control Tests List

Monthly quality control tests are listed in Table 15. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.3.2, are provided.

Table 15: Monthly Quality Control Tests

Quality Control Procedures Under Evaluation	Film-based System	CR System	DR System	Radioscopic System	CT System
Monthly Quality Control Tests
Cassette, Screen, and Imaging Plate Cleaning	M1	M1		M1
Darkroom Temperature and Humidity Conditions	M2			M2
Darkroom Light Conditions	M3			M3
Film Processor Operation	M4			M4
Retake Analysis	M5	M5	M5
Electronic Display Device Performance	M6	M6	M6	M6	M6
Laser Film Printer Operation	M7	M7	M7	M7	M7
CT Tomographic Section Thickness					M8
Calibration of CT Number					M9
CT Number Linearity					M10

3.3.2 Monthly Quality Control Tests

• M1. Cassette, Screen and Imaging Plate Cleaning-- Cassettes, screens and imaging plates must be cleaned and inspected for damage. Manufacturer recommended cleaners and cleaning procedures should be used. An inspection for dust particles should be done with an ultraviolet light. Cassettes must be checked for cleanliness, wear, warping, fatigue of foam compression material and closure mechanism, light leaks.
• M2. Darkroom Temperature and Humidity Conditions--A monthly check of the darkroom temperature and humidity should be conducted. The temperature should be between 18°C and 23°C and the humidity between 40% and 60%.
• M3. Darkroom Light Conditions-- A weekly visual test must be performed in the darkroom to ensure the room is light tight. Particular attention must be paid to the door seal and the mounting of the film processor, if the film insertion to the processor is done through a wall. The assessment of darkroom light conditions should be made after a 10 to 15 minute period of adaptation to the dark conditions with safelights turned off.
• M4. Film Processor Operation--Facilities performing spot-film must also perform quality control tests on the film processing system.
  1. The accuracy of the processor temperature display must be checked against a non-mercury thermometer. The processor developer temperature should be accurate to within 0.5°C.
  2. The replenishment rate must be compared with the manufacturers' recommended baseline level for the particular processor and film type, for the given number of films processed daily and for the method of processing.
  3. All processing solutions should be changed and processor solution tanks cleaned.
  4. Fixer retention tests should be performed to ensure fixer is adequately removed from processed films according to established baseline levels.
• M5. Retake Analysis--Facilities must maintain records of every retake, including the reason for the retake along with any corrective actions. An analysis must be done of the retake records to identify and correct any trends or repeated errors. The retake rate should be less than 5%, not including quality control films. If images contain some patient diagnostic information, they should be maintained in the patient file.
• M6. Electronic Display Device Performance--The performance of all electronic display devices used to view images from digital systems, as well as those obtained through scanning of radiographic films, must be checked using a test pattern such as the SMPTE or a TG18 test pattern. For closed systems, where a suitable test pattern is not available on the system, a test pattern generator equipped with the appropriate test patterns must be utilized. Where a system does not have the capability to display an externally provided pattern, the manufacturer recommended quality control procedures must be followed. The quality control procedures and acceptance criteria recommended by the AAPM (AAPM 2005) should be used.
• M7. Laser Film Printer Operation--The quality of images obtained from the laser film printer must be checked. Depending on the system, this may or may not require using pre-established window and level settings on the display. Ensure that the viewbox used to assess printed films has sufficient luminance. The SMPTE, TG18-QC and TG18-PQC test patterns should be used. A hardcopy image of the test pattern must meet the following criteria:
  1. the 5% patch must be just visible inside of the 0% patch,
  2. the 95% patch must be just visible inside the 100% patch,
  3. the optical density of various patches (for example 0%, 10%, 40% and 90%) must be within acceptable limits from the established baseline values, for the particular film used at the facility.
  4. no geometrical distortion greater than ± 1 mm,
  5. no artifacts upon visual inspection.
• M8. CT Tomographic Section Thickness--An evaluation of the tomographic section thickness must be made. Measurement of the tomographic section thickness are made with a test device containing one or two ramps positioned at an angle to the scan plane. For nominal tomographic section thicknesses of 2 mm or more, the measured tomographic section thickness must not vary by more than ± 1 mm from the established baseline tomographic section thickness. For nominal tomographic section thicknesses of 2 mm to 1 mm, the measured tomographic section thickness must not vary by more than ± 50% from the established baseline tomographic section thickness. For nominal tomographic section thicknesses of less than 1 mm, the measured tomographic section thickness must not vary by more than ± 0.5 mm from the established baseline tomographic section thickness. For multislice CT equipment, this test must be performed for both outer tomographic sections and one inner tomographic section. For helical scanning, a test device consisting of a thin disk or bead, mounted in a medium, should be used. The linear attenuation coefficient should be equal to or greater than that of aluminum so that the resulting signal-to-noise ratio is high. Upon scanning of this test device, the tomographic section is defined as the full width at half maximum of the sensitivity profile as a function of the z position.
• M9. Calibration of CT number--At all clinically used voltage settings, the mean CT number and standard deviation should be measured. The mean CT number and standard deviation should be calculated for a 2-3 cm² area of water and air in the reconstructed image. The same location should be used each time this test is performed. The CT number for water must be 0 ± 4 HU. The CT number for air must be -1000 ± 10 HU.
• M10. CT number linearity--At all clinically used voltage settings, the CT number linearity should be assessed. The CT number linearity should be assessed by scanning a phantom containing uniform objects of known materials with a wide range of CT numbers. The measured CT numbers of the materials should be compared with the nominal values provided by the phantom manufacturer and with previously measured values. The measured values must remain within established limits for the CT scanner.

3.3.3 Monthly Quality Control Tests Equipment

Test equipment for the monthly quality control testing are listed in Table 16.

Table 16: Monthly Quality Control Test Equipment

Item	Equipment	Systems	Reference
1	Ultraviolet Light	FS, SF	M1
2	Hygrometer	FS, SF	M2
3	Thermometer (non-mercury) Accuracy: ± 0.3°C Reproducibility: ± 0.1°C	FS, SF	M2, M4
4	Fixer Retention Test Kit	FS, SF	M4
5	Test pattern(s) for evaluation of electronic display device performance and laser film printer (ex. SMPTE, TG18-QC, TG18-PQC)	FS, CR, DR, RA, SF, CT	M6, M7
6	Densitometer Accuracy: ± 0.02 O.D. at 1.0 O.D. Reproducibility: ± 0.01 O.D. at 1.0 O.D.	CR, DR, RA, CT	M7
7	Ruler	FS, CR, DR, RA, SF, CT	M7
8	Test device containing ramps, thin disk or beads	CT	M8
9	Water filled uniform phantom	CT	M9
10	Phantom with imbedded uniform objects of known materials	CT	M10

3.4 Quarterly Quality Control Testing

3.4.1 Quality Control Tests List

Quarterly quality control tests are listed in Table 17. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.4.2, are provided.

Table 17: Quarterly Quality Control Tests

Quality Control Procedures Under Evaluation	Film-based System	CR System	DR System	Radioscopic System	CT System
Quarterly Quality Control Tests
Collimator Operation	Q1	Q1	Q1	Q1
Interlocks	Q2	Q2	Q2	Q2	Q2
Table Angulation and Motion				Q3
Compression Devices Operation				Q4
Chronometer Operation				Q5
Protective Devices				Q6
Park Position Interrupt				Q7
CT Patient Support Movement					Q8
CT Spatial Resolution					Q9
CT Low Contrast Detectability					Q10

3.4.2 Quarterly Quality Control Tests

• Q1. Collimator Operation--Using each collimating option, a test should be performed to ensure smooth collimator blade motion. If applicable, vary the SID to assure the collimator tracks (i.e., automatically maintain the field size) as the SID changes.
• Q2. Interlocks--If there are interlocks on the door(s), they must be tested to ensure that they prevent the X-ray equipment from producing radiation when the door is open. For radioscopic equipment, it must not be possible to activate the X-ray tube unless the entire radioscopic beam is intercepted by the image receptor.
• Q3. Table Angulation and Motion--The table should move freely to the upright position and stop at the appropriate spot. The table angle indicator and the actual table angle should coincide to within 2 degrees.
• Q4. Compression Devices Operation--Check that available compression devices easily move in and out of the X-ray beam and function correctly.
• Q5. Chronometer Operation--The chronometer accuracy should be verified with a stopwatch.
• Q6. Protective Devices for Radioscopic Equipment--A protective curtain or drape, of at least 0.25 mm lead equivalence at 100 kV, must be in place and move freely so that it can be placed between the patient and any personnel in the radioscopic room. Lead drapes should be affixed to the image intensifier (under table systems) and have no creases or gaps that may subject the operator to unnecessary scatter radiation. If the unit is an under table radioscopic system, check that the shield covering the cassette holder entrance during radioscopy is working as intended. The shield should provide the equivalent protection of at least 0.5 mm of lead at 100 kV.
• Q7. Park Position Interrupt--When the image receptor is in the parked position, it should not be possible to energize the X-ray tube. This many be checked while wearing a lead apron and depressing the radioscopic irradiation switch to see if the system is activated.
• Q8. CT Patient Support Movement--The accuracy of the patient support movement ensures that the desired volume of the patient is scanned. This becomes important when performing contiguous scans where the scan interval equals the scan width to image an entire volume of the patient. If the scan interval is larger than the scan width, then gaps are present in the imaged volume. If the scan interval is smaller than the scan width, then the scans will overlap. The measured patient support movement must be within ± 1 mm of the intended movement when the patient support moves both into and out of the gantry. To simulate the weight of the patient, a phantom or other weights (not exceeding 135 kg) must be place on the support when performing this test.
• Q9. CT Spatial Resolution--The spatial resolution must be tested, with the CT conditions of operation of the scanner, using one of the following three methods. The recommended method of measuring the spatial resolution is using the modulation transfer function curve, obtained from the Fourier transform of the point-spread function. The test device is a high contrast wire, typically 2 mm in diameter or less, placed in a tube of minimally attenuating material. The measurement of the 50% point and the 10% point of the MTF curve must be within 0.5 lp/cm or ± 15% of the established baseline value, whichever is greater.
  
  A quantitative measurement of modulation can be made using a bar pattern test device which contains line-pair patterns of different spatial frequencies. Using region of interest measurements, individual points along the MTF curve can be obtained. When measurements are made using a test object with line-pair patterns of varying spatial frequency or by noting the spatial frequency at which the measured modulation transfer function drops to 5%, the limiting high contrast resolution should be 5 line pairs per centimetre or more.
  
  An alternate method is through visual assessment using a test device consisting of a repeated pattern of holes, bars or lines. When measuring the limiting high contrast resolution using a phantom for high contrast resolution having sets of test objects of equal diameters and spacing, the high contrast resolution must be 1 mm or less.
• Q10. CT Low Contrast Detectability--Measurements should be made of the low contrast detectability to ensure it is within established limits. Low contrast detectability is typically specified as the smallest sized object at a specified contrast level to the background which can seen in a particular phantom when imaged under specified conditions. The phantom used for this test should have objects with less than 1% or 10 HU contrast to the surrounding material. The limiting detectability should be measured with the reconstruction algorithm of the scanner which is routinely used, as well as other clinically relevant reconstruction algorithms. The baseline performance level must be stated for a given phantom at specific scan conditions, including radiation dose, viewing conditions, and visualization criteria. It should be noted that this visual test for establishing low contrast detectability is subjective since it depends on a number of factors including the visual acuity of the observers and ambient lighting conditions.

3.4.3 Quarterly Quality Control Tests Equipment

Test equipment for the quarterly quality control testing are listed in Table 18.

Table 18: Quarterly Quality Control Test Equipment

Item	Equipment	Systems	Reference
1	Stopwatch	RA	Q5
2	Dosimeter Accuracy: ± 5% Reproducibility: ± 1%	RA	Q6
3	Weight (not exceeding 135 kg)	CT	Q8
4	Ruler	CT	Q8
5	Pre-packaged film (ex. "Ready Pack")	CT	Q8
6	Needle (for puncturing holes in film)	CT	Q8
7	CT Spatial Resolution Test Device	CT	Q9
8	CT Spatial Resolution Test Device	CT	Q10

3.5 Semi-Annual Quality Control Testing

3.5.1 Quality Control Tests List

Semi-annual quality control tests are listed in Table 19. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.5.2, are provided.

Table 19: Semi-annual Quality Control Tests

Quality Control Procedures Under Evaluation	Film-based System	CR System	DR System	Radioscopic System	CT System
Semi-annual Quality Control Tests
CT Laser Light Accuracy					SY1
CT Accuracy of Automatic Positioning of Tomographic Plane (using the scanned projection radiograph)					SY2
CT Accuracy of Gantry Tilt					SY3
CT Patient Dose					SY4

3.5.2 Semi-Annual Quality Control Tests

• SY1. CT Laser Light Accuracy--Laser light accuracy must be determined for both axial scan localization lights, which indicate the location of the radiation beam relative to the external anatomical structures of the patient, and the sagittal and coronal scan localization lights, which centre the anatomic structure of interest in the scan field of view.
  1. Axial Scan Localization Lights--Axial scan localization light accuracy is tested either by imaging a thin wire (approximately 1 mm diameter) or by using a needle to puncture holes in film at the positions of the laser lights and exposing the film using the smallest available scan width. The difference between the exposed areas on the film and the locations of the pin pricks must be less than ± 2 mm.
  2. Isocentre Alignment and Sagittal and Coronal Scan Localization Lights--Place a thin absorber (pencil) centred in the tomographic plane at the intersection of the sagittal and coronal positioning light fields. The intersection of the sagittal and coronal scan localization lights must indicate the centre of the field of view. The midline of the table should be coincident with the sagittal scan alignment light. The results must be within the manufacturer's recommended values and tolerances. A limit of ± 5 mm should be achievable.
• SY2. CT Accuracy of Automatic Positioning of Tomographic Plane (using the scanned projection radiograph/scout localization)--The location of the scan plane prescribed by using the scanned projection radiograph must be within ± 2 mm of the actual scan plane.
• SY3. CT Accuracy of Gantry Tilt--The accuracy of the indicated CT gantry tilt should be verified. When performing non-orthogonal scans, it is important to ensure that the physical tilt of the gantry corresponds to the tilt angle indicated on the CT display. This is generally done by exposing film placed upright and parallel to the sagittal laser at various gantry tilt angles. At least 3 irradiations need to be made on the film: no tilt (0 degrees) and each of the extreme angles. The angles measured on the film should correspond with the computer display to within ± 3 degrees.
• SY4. Patient Dose--The CTDI₁₀₀ must be determined for both head and body scanning techniques, using the CT dosimetry phantom placed on the patient support without any additional attenuating material present. For each technique, the CTDI₁₀₀ must be determined at the centre and periphery of the phantom as well as in air using the manufacturer's recommended techniques and setting. The values of CTDI₁₀₀ are used to calculate CTDI_w which must be within ± 20% of the established baseline values and the manufacturer's specifications when a fixed technique is used. It is highly recommended to strive for an agreement with manufacturers' specification of ± 10%. This test should be performed by a medical physicist.

3.5.3 Semi-annual Quality Control Tests Equipment

Test equipment for the semi-annual quality control testing are listed in Table 20.

Table 20: Semi-annual Quality Control Test Equipment

Item	Equipment	Systems	Reference
1	Thin wire	CT	SY1, SY2
2	Pre-packaged film (ex. "Ready Pack")	CT	SY1, SY3
3	Sharp needle (for puncturing holes in film)	CT	SY1
4	Pencil	CT	SY1
5	Ruler	CT	SY1
6	Protractor	CT	SY3
7	CT Dosimetry Phantom--Head Circular cylinder constructed of polymethyl methacrylate Density 1.19 ± 0.01gm/cm3, length 14 cm, diameter 16 cm	CT	SY4
8	CT Dosimetry Phantom--Body Circular cylinder constructed of polymethyl methacrylate Density 1.19 ± 0.01gm/cm3, length 14 cm, diameter 32 cm	CT	SY4
9	Dosimeter and CT Dose Probes	CT	SY4

3.6 Annual Quality Control Testing

3.6.1 Quality Control Tests List

Annual quality control tests are listed in Table 21. The imaging systems to which the tests are applicable, and the test numbers corresponding to those in section 3.6.2, are provided.

Table 21: Annual Quality Control Tests

Quality Control Procedures Under Evaluation	Film-based System	CR System	DR System	Radioscopic System	CT System
Annual Quality Control Tests
Safelight Test	Y1			Y1
Film/Screen Contact	Y2			Y2
Accuracy of Loading Factors	Y3	Y3	Y3	Y3
Radiation Output Reproducibility	Y4	Y4	Y4	Y4
Radiation Output Linearity	Y5	Y5	Y5	Y5
X-ray Beam Filtration	Y6	Y6	Y6	Y6
Automatic Exposure Control	Y7	Y7	Y7	Y7
X-ray Field and Light Field Alignment	Y8	Y8	Y8	Y8
X-ray Beam Collimation	Y9	Y9	Y9	Y9
Grid Performance	Y10	Y10	Y10	Y10
Response Function		Y11	Y11
Exposure Index		Y12	Y12
Dynamic Range	Y13	Y13	Y13	Y13
Noise, Uniformity and Image Artifacts		Y14	Y14
Spatial Resolution	Y15	Y15	Y15	Y15
Contrast Detectability	Y16	Y16	Y16	Y16
Digital Detector Residual Images		Y17	Y17
Phantom Dose Measurements	Y18	Y18	Y18	Y18
Typical Image Intensifier Air Kerma Rate				Y19
Maximum Image Intensifier Air Kerma Rate				Y20
Automatic Intensity Control				Y21
Image Lag				Y22
CT Number Dependence on Phantom Position					Y23
CT Radiation Dose Profile					Y24
CT Radiation Dose--Scout Localisation Image					Y25
Viewboxes	Y26	Y26	Y26	Y26	Y26
Electronic Display Device Performance		Y27	Y27	Y27	Y27
Integrity of Protective Equipment	Y28	Y28	Y28	Y28	Y28
General Preventive Maintenance	Y29	Y29	Y29	Y29	Y29

3.6.2 Annual Quality Control Tests

• Y1. Safelight Test--An evaluation must be made of the effects of the safelight on film optical density. A film strip exposed to an optical density of 1.2 units must not show an increase in optical density greater than 0.05 units in two minutes exposure to the darkroom light environment. Facilities performing spotfilm must also perform this quality control test.
• Y2. Screen/Film Contact--All cassettes used in the facility must be tested for screen/film contact. Large areas of poor contact that are not eliminated by screen cleaning and remain in the same location during subsequent tests should be replaced. Facilities performing spotfilm must also perform this quality control test.
• Y3. Accuracy of Loading Factors--For any combination of loading factors, the X-ray tube voltage must not deviate from the selected value, by more than 10%, the loading time must not deviate from the selected value by more than (10% + 1 ms), the X-ray tube current, must not deviate from the selected by more than 20%, and the current-time product must not deviate from the selected value by more than (10% + 0.2 mAs).
• Y4. Radiation Output Reproducibility--The X-ray tube radiation output shall be high enough to minimize irradiation time to eliminate perceptible motion artifacts. For any combination of operating loading parameters, the coefficient of variation of any ten consecutive irradiation measurements, taken at the same source to detector distance within a time period of one hour, is no greater than 0.05, and each of the ten irradiation measurements is within 15% of the mean value of the ten measurements
• Y5. Radiation Output Linearity--For any pre-selected value of X-ray tube voltage, the quotient of the average air kerma measurement divided by the indicated current time product obtained at two settings of X-ray tube current or X-ray tube current-time product must not differ by more than 0.10 times their sum, that is,
  
  where X₁ and X₂ are average air kermas (exposures) per current time product. The values of X₁ and X₂ must be determined at
  1. if the X-ray tube current is selected in discrete steps, any two consecutive X-ray tube current settings;
  2. if the X-ray tube current selection is continuous, any two X-ray tube current settings that differ by a factor of 2 or less;
  3. if the current time product is selected in discrete steps, any two consecutive current time product settings; or
  4. if the current time product selection is continuous, any two current time product settings that differ by a factor of 2 or less.
• Y6. X-ray Beam Filtration--The first half-value layer of aluminum must be measured. The measured values must not be less than the values shown in Table 8 in subsection B2.5.1 for a selected X-ray tube voltage.
  
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• Y7. Automatic Exposure Control--For film-based systems, the automatic exposure control must be evaluated to ensure it performs in such a way that the variation in optical density in the resultant radiograms does not exceed the value of
  1. 0.15 when the X-ray tube voltage is variable and the thickness of the irradiated object is constant,
  2. 0.20 when the thickness of the irradiated object is variable and the X-ray tube voltage is constant,
  3. 0.20 when the thickness of the irradiated object and the X-ray tube voltage are both variable, and
  4. 0.10 when the thickness of the irradiated object and the X-ray tube voltage are both constant.
  For digital systems, the performance of the automatic exposure control must be assessed according to the manufacturer's procedures and must be within the manufacturer's specifications. It is recommended that the automatic exposure control should perform in such a way that the variation in the mean linearized data on a constant region of interest does not exceed 20% for constant X-ray tube voltage and constant thickness of the irradiated object, when the X-ray system is operated in conditions representative of the typical clinical use. Compliance is checked by ensuring that the ratio of the highest and the lowest measured values is less than or equal to 1.2 or within the manufacturer's specifications.
• Y8. Light Field and X-ray Field Alignment--The alignment of the light localizer, designed to define the outline of the X-ray field, with the X-ray field must be verified. In the plane of the image receptor, the misalignment, of the edges of the visually defined field with the edges of the X-ray field must not exceed 2% of the focal spot to image receptor distance.
• Y9. X-ray Beam Collimation--(a) An evaluation of the beam limiting device must be made to ensure that the equipment is capable of aligning the centre of the X-ray field with the centre of the image reception area to within 2% of the focal spot to image receptor distance.
  
  (b) Radiographic X-ray equipment that has a positive beam limiting system must prevent the emission of X-rays until the beam limiting device is adjusted so that
  1. the dimensions of the X-ray field do not exceed those of the image reception area, or the selected portion of that area, by more than 3% of the focal spot to image receptor distance, and
  2. the sum of the absolute values of the differences in the dimensions of the X-ray field and the image reception area, or the selected portion of that area, does not exceed 4% of the focal spot to image receptor distance.
  (c) Radioscopic equipment equipped with a spotfilm device must have a mechanism that, when the X-ray beam axis is perpendicular to the image reception plane, permits the perimeter of the X-ray field to be aligned with that of the selected portion of the image reception area so that
  1. the dimensions of the X-ray field differ from the corresponding dimensions of the image reception area by a distance that does not exceed 3% of the focal spot to image receptor distance, and
  2. the sum of the absolute values of the differences in the dimensions between the X-ray field size and the image reception area does not exceed 4% of the focal spot to image receptor distance.
• Y10. Grid Performance--Grid performance, including movement and uniformity, must be checked annually.
• Y11. Response Function--For digital X-ray imaging systems, the response function of the detector should be assessed. The manufacturer specified relationship between the system response (mean pixel value in a standard region of interest) and exposure to the image receptor, over a range of tube loadings, should be confirmed to be within established limits. The manufacturer's recommended testing procedure should be followed.
• Y12. Exposure Index--For digital X-ray imaging systems, the accuracy and reproducibility of the exposure index, as a function of the dose to the image receptor, must be evaluated. The manufacturer's recommended testing procedure must be followed and the results must be within established limits.
• Y13. Dynamic Range--For film screen systems, a high purity step wedge should be used to monitor the performance of the X-ray generator. When using a 11-step wedge, the acceptable variation in film density should be ± 1 step from the established baseline density, or when using a 21-step wedge, the acceptable variation in film density should be ± 2 steps from the established baseline density. For digital systems, the dynamic range is a measure of the maximum difference in attenuation that the system can simultaneously image, without loss of information due to saturation of pixels. A test object consisting of an attenuating plate terminated with a step wedge of 12 steps should be used. The number of non saturated steps or the thickness of the smallest non saturated step should be within established limits.
• Y14. Noise, Uniformity and Image Artifacts--An assessment must be made of noise, uniformity and image artifacts. The Signal-to-Noise Ratio (SNR) should be calculated by measuring the mean pixel value and standard deviation in a region of interest within the image. The standard deviation of signal values should be determined for three different locations, at the centre, at the top, and at the side of the image. The size of the region of interest should equal approximately 10% of the area of the phantom. The test should be done using homogeneous phantoms having thicknesses representative of patient thickness. The measured noise value must be within established limits. The uniformity of the signal across the different regions of interest at the periphery and the centre of the phantom must be within established limits. Images must be assessed to ensure that unacceptable artifacts are not present.
• Y15. Spatial Resolution--An evaluation must be of the spatial resolution of the equipment. Spatial resolution is the ability to resolve objects in a resultant image when the difference in the attenuation between the objects and the background is large compared to noise. The manufacturer's recommended test procedures must be followed. For each mode of operation, the spatial resolution must within established limits.
• Y16. Contrast Detectability--An evaluation should be made of contrast detectability. The contrast detectability is the ability to resolve different objects from the background when the difference in attenuation between the objects and the background is small compared to noise. The manufacturer's recommended test procedures should be followed. For each mode of operation, the contrast resolution should be within established limits. For DSA applications, it is recommended to use a phantom with contrast levels representative of clinically used iodine contrast levels.
• Y17. Digital Detector Residual Image--There must not be any visible residual image from a previous exposure. The manufacturer's recommended test procedure should be followed.
• Y18. Phantom Dose Measurements--Entrance skin air kerma measurement for frequently performed examinations must be within established limits. Measurements should be performed using the equipment geometry and loading conditions representative of those used clinically. Dose values obtained should be used for the annual review of the facilities Diagnostic Reference values.
  
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• Y19. Typical Air Kerma Rate of Radioscopic Equipment-- Using a uniform phantom place on the patient support, measurements of the typical entrance air kerma rate, including backscatter, should be made for all geometries and modes of operation used clinically. The values should be within established levels.
• Y20. Maximum Air Kerma Rate of Radioscopic Equipment--Radioscopic equipment, other than when recording images, must not operate at any combination of X-ray tube voltage and X-ray tube current that results in an air kerma rate that exceeds
  1. 50 mGy/min when the equipment is not fitted with an automatic intensity control,
  2. 100 mGy/min when the equipment is fitted with an automatic intensity control, and
  3. 150 mGy/min when the equipment is fitted with both an automatic intensity control and a high-level irradiation control when the latter is activated.
  The image intensifier must be protected with sufficient (approximately 6 mm) lead sheets when performing this test.
• Y21. Automatic Intensity Control--An evaluation must be made of the automatic intensity control system of radioscopic systems. The automatic intensity control system is designed to maintain the rate of the X-ray exposure to the image intensifier with changes in thickness and composition of the anatomical region being imaged. Place a dosimeter between a homogenous phantom and the X-ray source. Double the phantom thickness and repeat the exposure. The exposure measurement should be approximately double the first measurement.
• Y22. Image Lag--An evaluation of the image lag should be made to ensure the performance of the TV camera does not cause unnecessary smearing of the radioscopic image. Radioscopic systems used for cardiac catheterization and interventional procedures must have a high frame rate to provide sufficient temporal resolution required by such procedures. Viewing the image of a rotating test tool, the radioscopic system should be able to visualize a wire of diameter 0.013 inch or smaller.
  
  This test should be repeated using cine cameras and digital recorders to ensure that these systems are delivering optimal image quality.
• Y23. CT number dependence on phantom position--The CT number for water must not vary by more than ± 5 HU when the position of a water filled phantom is varied over clinically relevant positions on the patient support.
• Y24. CT Radiation Dose Profile--The collimation of the radiation beam should be assessed to ensure it does not exceed the prescribed scan width. Scan width is typically defined as the full width half maximum (FWHM) of the radiation dose profile. For each available scan width, the FWHM of the radiation dose profile should not exceed the prescribed scan width by more than manufacturer's specifications. The FWHM of the radiation dose profile can be measured either directly from the density profile of the resultant film or computed from the digital profile upon digitization of the image.
• Y25. CT Radiation Dose-Scan Projection Radiograph/Scout Localization Image--The dose delivered from a scout localization image, which is a scanned projection radiograph, must remain within ± 20% of the nominal value. Changes in this dose can be indicative of problems with collimation or patient support movement. The technique and loading factors used to obtain the scout localization image must be recorded, so that identical test conditions can be used for subsequent tests. It is recommended that this test be performed semi-annually, but must be performed at least annually.
• Y26. Viewboxes--All viewboxes must be tested for compliance with the following requirements. Ensure all view-boxes have been turned on for a minimum of 30 minutes before obtaining measurements.
  1. Luminance. Luminance is the amount of light emitted or scattered by a surface. The view box luminance should be at least 2,500 nits (cd/m2).
  2. Light Output Uniformity. The light output from the viewboxes should be uniform to within 10%. Measurements should not be made near the edges of the viewbox (within 1 to 2 inches), where luminance values may be quite low.
  3. Light Output Homogeneity. The light output homogeneity between a bank of viewboxes should be uniform to within 20% of the mean.
  4. Ambient Light Control. The ambient light within the reading room must be less than 50 lux. A value of 5-10 lux is recommended.
• Y27. Electronic Display Device Performance--The performance of all electronic display devices used for the interpretation of clinical images and guidance during interventional procedures must be verified using a test pattern such as the SMPTE or TG18 test patterns. For closed systems, where a suitable test pattern is not available on the system, a test pattern generator equipped with the appropriate test patterns must be utilized. Where a system does not have the capability to display an externally provided pattern, the manufacturer recommended quality control procedures must be followed. The annual quality control tests recommended by the American Association of Physicists in Medicine (AAPM, 2005), including test procedures and acceptance criteria should be used. An evaluation should be made of geometric distortion, reflection, luminance response, luminance dependencies, resolution, noise, veiling glare and chromaticity. The display system must be warmed up prior to testing and attention must be given to the ensure ambient light levels are appropriate and representative of condition under which clinical images are viewed. A viewing distance of 30 cm is recommended.
• Y28. Integrity of Protective Equipment--All personnel's protective equipment must be examined using radiographic or radioscopic equipment to ensure they are not defective. Lead aprons where the total defective area is greater than 670 mm² are not acceptable. Personnel protective equipment having a defect in the vicinity of the thyroid or the reproductive organs which is larger than the equivalent of a 5 mm diameter circle must not be used. Personal judgement should be used when small defects are located along the edges of the protective equipment and when defects are due to stitching of the equipment. All protective equipment, when not in use, should be stored in accordance to the manufacturers' recommendations.
• Y29. General Preventive Maintenance--Preventive maintenance of the X-ray equipment and accessories is necessary to prolong the life of the equipment. An annual inspection must be conducted for structural integrity, cleanliness, ease of movement of all components and any other procedures recommended by the manufacturers.

3.6.3 Annual Quality Control Tests Equipment

Test equipment for annual quality control testing are listed in Table 22.

Table 22: Annual Quality Control Test Equipment

Item	Equipment	Systems	Reference
1	Densitometer Accuracy: ± 0.02 O.D. at 1.0 O.D. Reproducibility: ± 0.01 O.D. at 1.0 O.D.	FS, SF	Y1, Y7, Y13
2	Stopwatch	FS, SF	Y1
3	Film/screen contact test tool	FS, SF	Y2
4	Non-invasive X-ray tube voltage meter Accuracy: ± 1.5 kV Reproducibility: ± 0.5 kV	FS, CR DR, SF	Y3
5	Irradiation time meter Accuracy: ± 5% Reproducibility: ± 1%	FS, CR DR, SF	Y3
6	Current meter Accuracy: ± 1% Reproducibility : < 0.5%	FS, CR, DR, SF	Y3
7	Dosimeter Accuracy: ± 5% Reproducibility: ± 1% CT dose probes - scout localization dose	FS, CR, DR, RA	Y4, Y5, Y6, Y11, Y12, Y18, Y19, Y20, Y21, Y25
8	Aluminum filter (> 99.9% purity) Accuracy: 1% thickness	FS, CR, DR	Y6, Y17
9	Multiple sheets of uniform, tissue equivalent attenuator (covering range of clinical patient thicknesses)	FS, CR, DR, RA, SF	Y7, Y10, Y11, Y12, Y13, Y14, Y15, Y16, Y17, Y19,Y21
10	Metallic markers	FS, CR, DR, RA, SF	Y8
11	Ruler	FS, CR, DR, RA, SF	Y8, Y9, Y28
12	X-ray Beam Alignment test tool	FS, CR, DR, RA, SF	Y9
13	Stepwedge	FS, CR, DR, RA, SF	Y13
14	Spatial Resolution test tool (specific for type of equipment)	FS, CR, DR, RA, SF	Y15
15	Contrast Detectability test tool (specific for type of equipment)	FS, CR, DR, RA, SF	Y16
16	Phantom for evaluation of Entrance Surface Dose	FS, CR, DR, RA, SF	Y18
17	6 mm lead sheet	RA	Y20
18	Rotatable spoke test tool pattern (steel wires of diameter ranging from 0.005 inches to 0.022 inches, rotatable at 30 rpm)	RA	Y22
19	Electric motor capable of producing 30 rpm	RA	Y22
20	Water filled uniform phantom	CT	Y23
21	Pre-packed film (ex. "Ready Pack")	CT	Y24
22	Scanning Microdensitometer	CT	Y24
23	CT Dosimetry Phantom - Head Circular cylinder constructed of polymethyl methacrylate Density 1.19 ± 0.01 gm/cm3, length 14 cm, diameter 16 cm	CT	Y25
24	CT Dosimetry Phantom - Body Circular cylinder constructed of polymethyl methacrylate Density 1.19 ± 0.01 gm/cm3, length 14 cm, diameter 32 cm	CT	Y25
25	CT Dose Probes	CT	Y25
26	Light meter (for measurement of luminance and illuminance) Accuracy: ± 10% Reproducibility: ± 5%	FS, CR, DR, SF, CT	Y26
27	Test patterns (for evaluation of electronic display system) (ex. TG18 )	CR, DR, RA, CT	Y27