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What is the Moiré effect?
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What is the relationship between OID and magnification?
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Img Prod - RADT465
ARRT Registry Review covering for Image Production content area
| Question | Answer |
|---|---|
| What is the Moiré effect? | Also known as Aliasing artifact, it has the appearance of somewhat wavy linear lines and can occur in computed radiography when using stationary grids. |
| What is the relationship between OID and magnification? | Inversely related. OID +, magnification - |
| How is the anode heel effect more prominent? | Using short SIDs, large IRs, small anode angles, and imaging parts having uneven tissue densities. |
| What is the function of the back up timer? | Protect the patient from overexposure and the x-ray tube from excessive heat load. |
| Technical factor that regulates receptor exposure: | mAs |
| How can SID compensate OID? | An increase of 7 inch SID compensates for every inch of OID |
| How are lp/mm and LSP measure? | Line pairs per millimeter (lp/mm) measure using a resolution test pattern. Line-spread function (LSP) measure using 10mm x-ray beam |
| MTF | Modulation transfer function: measures the amount of information lost between the object and the IR |
| Loss of signal at the lateral edges can mean : | SID is above or below the recommend focusing distance, the useful beam will not coincide with the angled lead strips at the lateral edges. Grid cutoff. |
| kVp adjustments for increase in patient thickness | for each centimeter of increase in thickness, 2 kV is added to the exposure |
| Additive pathologies | Ascites Rheumatoid arthritis Paget's disease Pneumonia Atelectasis Congestive heart failure Edematous tissue |
| Destructive Pathologies | Osteoporosis Osteomalacia Pneumoperitoneum Emphysema Degenerative arthritis Atrophic and necrotic conditions |
| PSP Layers | Protective layer Phosphor layer Electroconductive/conductor Support layer Light shield/Reflective layer Protective (Backing) layer |
| Bit depth | the number of bits required to describe the gray level that each pixel can take on |
| As matrix size increases (fixed FOV) | pixel size is smaller and better image resolution results |
| As FOV increases (fixed matrix size) | the size of each pixel increases and spatial resolution decreases |
| What produces the most receptor exposure? | The combination of highest milliampere seconds value and shortest SID |
| How is image resolution improved? | Small DEL size and large fill factor |
| Window level | associated with image brightness changes |
| Window width | changes in image contrast |
| Reproducibility | consistency in exposure output during repeated exposures at a particular setting |
| Linearity | Quality assurance term use to describe consistency in exposure at adjacent mA station |
| When increasing SID | The effect of excessive OID decreases. However, increased SID usually requires a significant increase in exposure factors. |
| Types of grids | Parallel/non-focused grids Angled/focused grids Moving grids Stationary grids |
| Types of grid error (grid cutoff) | Upside-down focused grid Off-focus grid Off level/angulation error Off center/lateral decentering |
| Parallel/Non-focused grid | Lead strips in the grid are parallel Used in fluoro and mobile radiography |
| Angled/focused grid | lead strips in the grid are angled to match the divergence of the x-ray beam allows more photons to pass through |
| Moving grids | Vibrate during the exposure to blur the grid lines. Requires a connection to the imaging equipment and source of electricity. Used only in table or wall mounted Bucky's. |
| Stationary grids | Used in tabletop or mobile radiography where there is no connection of the IR to the system. |
| Upside-down focused grid error | Occurs with focused grids only. Grid lines are opposite of the beam's divergence. Results in a loss of exposure along edges of image. |
| Off-focus/focus-grid distance decentering error grid | Occurs when using an SID that is outside the manufacturers range for a focused grid. Loss of exposure on the outside or one side of the image. Also called focus-grid decentering. |
| Off level/Angulation error | Result of the beam being angled against the gridlines. Caused by the tube or the IR not being aligned to each other. Occurs with focused or non-focused grids. Results in loss of exposure across entire image. |
| Off center/Lateral decentering grid error | Beam is not aligned to the center of the focused grid. Beam divergence doesn't match the angle of the lead strips. Results in overall loss of exposure. |
| Preprocessing (Acquisition processing) functions | flat-field corrections, correction for noise reduction as a result of DEL dropout, rescaling, exposure field recognition, segmentation recognition, and histogram analysis |
| Equalization (dynamic range control) | DRC - postprocessing function compresses the contrast scale, remove densities that obscure image details |
| HVL | the amount of material necessary to decrease the intensity of the beam to one-half its original value, thereby effecting a change in both beam quality and quantity. |
| Absorption | when an x-ray photon interacts with matter and disappears (photelectric effect) |
| Scattering | when there is partial transfer of energy to matter (Compton effect) |
| Attenuation | the reduction in the intensity of an x-ray beam as it passes through matter (in the form of absorption and scattering) |
| Scatter absorption is improved by having | High grid ratio, low grid frequency (the number of lead strips per inch) |
| How do we produce short scale image contrast? | The lower the kilovoltage, the less penetration, and shorter the scale contrast. |
| X-ray beam off-center and off-off focus below the focusing distance | the image below the focus will show increased receptor exposure |
| X-ray beam off-center and off-focus above the focusing distance | the image below will show decreased receptor exposure |
| Reciprocity Law | A particular milliampere seconds value, regardless of the combination of milliamperes and time, will reproduce the same receptor exposure. |
| Nyquist theorem | the sampling frequency must be greater than twice the frequency of the input signal so that the reconstruction of the original image can be close to the original signal |
| Maximal spatial resolution in digital imaging | is equal to the Nyquist frequency, 1/2 x pixel pitch (mm) |
| Histogram | graphic representation of pixel value distribution |
| Factors that affect histogram | Positioning, centering, collimation, selection of the correct processing algorithm, changes in scatter, SID, OID (anything that affects scatter or dose) |
| Exposure latitude | The range of exposure diagnostic image values the image detector is able to produce. Dependent on image detector = +dynamic range of detector, +values are detected |
| LUT | look-up table used as a reference to evaluate the raw information and correct the luminance values. a characteristic curve that best matches the anatomic part being imaged. |
| Attenuation: the higher the kilovoltage | the less is the attenuation |
| Attenuation: the greater the effective atomic number of the tissues | the greater the beam attenuation |
| Attenuation: the greater the volume tissue (subject density and thickness) | the greater beam attenuation |
| Primary or Low-Voltage Circuit Devices | AC supply (main power supply) main power switch Circuit braker Autotransformer fuses line voltage compensator line voltage meter kV selector exposure switch exposure timer primary side of step-up transformer (V) |
| Secondary Circuit | Secondary side step-up transformer (kV)-secondary coil of high voltage transformer mA meter rectifiers x-ray tube |
| Filament Circuit | Rheostat/mA selector step down transformer cathode filament focal spot selector |
| Primary Circuit is | Low Voltage (V) |
| Secondary Circuit is | High Voltage (kV) |
| Filament circuit is | High Amperage (mA) |
| References | Saia, D.A. (2022). Image Production. In S. Barnes, C. M. Thomas (Eds.), Lange Q & A: Radiography Examination (12th ed., pp. 189-211,). Chicago, IL: McGraw-Hill Education. |
| References | Schmuck, H. (2023). RADT465 Unit 2 Image Production Worksheet (Unpublished course reference). University of Southern Indiana, Evansville, IN. |
Created by:
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