X-Ray Generators and Ancillary Radiographic Equipment Chapter 7 Quality Control of X-Ray Generators and Ancillary Radiographic Equipment

X-ray Generators Single Phase Generator – uses single phase of alternating current

X-ray Generators (cont’d) Single Phase Generator – half-wave rectified

X-ray Generators (cont’d) Single Phase Generator – full-wave rectified

X-ray Generators (cont’d) Three Phase Generators – utilize 3 sources of alternating current

X-ray Generators (cont’d) Three Phase Generators – 3-phase, 6-pulse

X-ray Generators (cont’d) Three Phase Generators – 3-phase, 12-pulse

X-ray Generators (cont’d) High Frequency Generator – increases frequency of incoming alternating current

X-ray Generators (cont’d) Three main components: Control or Operating Console High Voltage Generator X-ray Tube, Tube Accessories and X-ray Table

Quality Control for Radiographic Units Three Components: Visual Inspection Environmental Inspection Performance Testing

Radiation Measurement Most performance testing performed with gas-filled chamber detectors Three different type of these detectors: Ion Chamber – most often used Proportional counter Geiger-Muller Counter

Performance Testing X-ray Generator Reproducibility or Exposure Same technical factors should always produce the same radiation output Testing requires measuring output with detector at same technical factors Any variation found during testing cannot exceed ± 5%

Performance Testing X-ray Generator (cont’d) Radiation Output Measures amount of radiation exposure per mAs of technique Units are either mR/mAs or μCkg-1/mAs Determined using radiation detector and making exposure at 10 mAs Current and previous values are compared All values should remain within ± 10%

Performance Testing X-ray Generator (cont’d) Radiation Quality and Filtration Measured by determining Half Value Layer (HVL) Determined by using a radiation detector and making exposures at 80 kVp adding aluminum filters in 1 mm increments Minimum HVL at 80 kVp is 2.3 mm aluminum equivalent

Performance Testing X-ray Generator (cont’d) Kilovolt peak (kVp) Accuracy Can be determined by using a special test cassette or a digital kVp meter Determines whether or not the kVp value on the control console corresponds with the maximum energy of the actual x-ray beam Variations between the stated kVp and the actual x-ray beam quality must be within ± 5%

Performance Testing X-ray Generator (cont’d) Timer Accuracy Testing can be performed by using either the spinning top test or a digital timer The variability allowed for timer accuracy is ± 5% for exposure times greater than 10 milliseconds (ms) and ± 20% for exposures less than 10 milliseconds (ms)

Performance Testing X-ray Generator (cont’d) Voltage Waveform Visualizes voltage waveform through x-ray tube

Performance Testing X-ray Generator (cont’d) Reciprocity The same mAs should produce the same radiation output regardless of mA and time selected Testing utilizes a radiation detector and exposures using same mAs but different mA and time stations Any variation between exposures cannot exceed ± 10%

Performance Testing X-ray Generator (cont’d) Linearity Any sequential change in mAs should produce the same sequential change in radiation output Testing involves making exposures of a radiation detector at mAs values that are double that of previous exposure Any variation between exposure cannot exceed ± 10%

Performance Testing X-ray Tube and Tube Accessories Focal Spot Size Evaluated to determine if focal spot blooming has occurred Level of blooming must not exceed NEMA standards

Performance Testing X-ray Tube and Tube Accessories (cont’d) Focal Spot Size Testing can be performed by one of three devices: Pinhole camera Focal Spot Test Tool Star or slit resolution patterns

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Restriction System Light Field-Radiation Field Congruence Assures that light field of collimator is the same area struck by x-rays The light field must be congruent to within ± 2% of the SID Evaluation can be performed by the use of either a collimator test tool or 8-penny test

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Restriction System Image Receptor-Radiation Field Alignment Determined with collimators equipped with Positive Beam Limitation (PBL) Variation between the x-ray field and image receptor size must be within ± 3% of the SID

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Restriction System Accuracy of the X-Y Scales Size of field selected by collimator adjustment knobs must correspond to the actual field size to within ± 2% of SID Can be tested with collimator test tool or 8-penny test

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Restriction System Illuminator Bulb Brightness Determined using a photometer placed tabletop at a 100 cm SID The illumination of the light source must be at least 15 foot-candles (ft-cd) or 160 lux when measured at a 100-cm (40”) distance

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Alignment X-ray beam must be mounted properly in its metal housing and aligned to the center of the bucky tray Items to evaluate include perpendicularity and x-ray beam/bucky tray alignment

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Alignment Perpendicularity The x-ray tube must be mounted in its housing so that the x-ray beam is within 1 degree of perpendicular Testing is performed with a commercially available beam alignment tool

Performance Testing X-ray Tube and Tube Accessories (cont’d) Beam Alignment X-ray beam/Bucky tray alignment Also known as central ray congruency The x-ray beam/Bucky tray alignment must be within ± 1% of SID Testing can be performed using either a beam alignment tool or the washer or coin method

Performance Testing X-ray Tube and Tube Accessories (cont’d) SID Indicator The SID indicator must be installed so that it is accurate to within ± 2% of the SID Testing can be performed with a tape measure or the triangular method

Performance Testing Overload Protection The overload protection mechanism should not permit an exposure that exceeds 80% of the tube capacity for a single exposure Testing involves selecting technical factors that would exceed limit and then depress rotor/prep button on control panel If rotor engages and ready light appears, system fails

Performance Testing (cont’d) X-ray Tube Heat Sensors Usually found on 3-phase equipment Heat sensors should provide a warning when anode heat reaches 75% of the maximum

Automatic Exposure Control Consists of two main components: Detectors – also known as sensors, cells or chambers. Actual devices can be either photodetectors, ion chambers or solid state detectors Comparator – receives signal sent by detectors and terminates exposure when a specific amount of radiation has been measured

Automatic Exposure Control Testing (cont’d) Backup, or Maximum Exposure Time The backup timer should terminate the exposure within 6 seconds or 600 mAs, whichever comes first Testing involves placing a lead apron tabletop over sensors and seeing if exposure terminates within specified values

Automatic Exposure Control Testing (cont’d) Consistency of Exposure with Varying mA System should maintain exposure level with any changes in mA Testing involves making a series of exposures of a homogenous phantom at different mA stations. Images should all be the same. Any variation cannot exceed ± 10%

Automatic Exposure Control Testing (cont’d) Consistency of Exposure with Varying kVp System should maintain exposure with any changes in kVp Testing involves making a series of exposures of a homogenous phantom at different kVp values All images should be similar

Automatic Exposure Control Testing (cont’d) Consistency of Exposure with Varying Part Thickness System should be able to compensate for changes in part thickness Testing involves a series of exposures of a homogenous phantom of varying thickness values Images should be similar

Automatic Exposure Control Testing (cont’d) Consistency of Exposure with Varying Field Sizes System should be able to compensate for any changes in the x-ray field size Testing involves a series of exposures of a homogenous phantom at different field sizes Images should be similar

Automatic Exposure Control Testing (cont’d) Consistency of AEC Detectors Each detector or sensor should function identically to all other detectors Testing involves exposures of a homogenous phantom at each of the sensors available on unit Images should be similar

Automatic Exposure Control Testing (cont’d) Reproducibility Exposures made at the same kVp and mA stations of the same phantom thickness should produce the same exposure Testing involves a series of exposures of a homogenous phantom at the same kVp and mAs Images should be similar

Automatic Exposure Control Testing (cont’d) Density Control Function Density selector should allow for changes in radiation exposure of 25% to 30% for each increment Testing involves a series of exposures of a homogenous phantom at each of the density selector options Each setting should produce an image 25% to 30% greater than the previous setting

Conventional Tomographic Systems Used to create “slices” of the body to remove superimposition and improve contrast in area of interest Two basic types are linear (sometimes called rectilinear) and pluridirectional (sometimes called multidirectional)

Quality Control of Tomographic Systems (cont’d) Section Level Requires specialized test tool The level of the section indicated on the equipment and the actual level should be the same or within ± 5 mm (some manufacturers suggest ± 1 mm for pluridirectional units)

Quality Control of Tomographic Systems (cont’d) Section Thickness Evaluation is made with special test tool

Quality Control of Tomographic Systems (cont’d) Level Incrementation Requires testing with specialized test tool A ruler should be constructed so that changing from one tomographic section to the next is accurate to within ± 2 mm

Quality Control of Tomographic Systems (cont’d) Exposure Angle Testing involves specialized test tool The value indicated on the equipment and the actual angle are the same or within ± 5 degrees for units operating at angles greater than 30 degrees and within ± 2 degrees for units operating less than 30 degrees

Quality Control of Tomographic Systems (cont’d) Spatial Resolution Testing involves imaging a test tool with a mesh pattern containing different size holes Units should be able to resolve at least 40 holes per inch

Quality Control of Tomographic Systems (cont’d) Section Uniformity and Beam Path Radiation output should be consistent throughout exposure Any variation for uniformity should be within optical density value of ± 0.3 Path closure in pluridirectional units should be within ± 10% of the path length for beam path

Quality Control of Tomographic Systems (cont’d) Patient Exposure Patient exposure for tomographic image should not exceed two times the non-tomographic exposure for the same part in the same position

Grid Testing Grid Uniformity Lead strips in grid must be uniformly spaced Image of homogenous phantom is made and optical density of the center and center of each quadrant is made Readings should be within ± 0.10 for proper uniformity

Grid Testing (cont’d) Grid Alignment Center of grid must be aligned with the detent lock position of the x-ray tube Testing requires imaging a special test tool

Portable and Mobile X-ray Generators Portable Generator – small enough to be carried by one person Mobile Generator – pushed on wheels Direct Power Unit Capacitor Discharge Cordless High Frequency