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RADT 465
Image Production
| Term | Definition |
|---|---|
| IP=imaging plate | -PSP within and no light sensitive -No need to be light-tight -Has a thin lead foil in the back to absorb backscatter |
| PSP=photostimulable phosphor | -Composed of europium doped barium fluorohalide coat in a granular or turbid phosphor -Always on so don’t store in x ray room as it is sensible to background radiation |
| Example of turbid phosphor | Gadolinium oxysulfide (Gd2O2S) and rubidium chloride |
| Needle-shaped phosphor and columnar phosphor | Better x ray absorption and less light diffusion |
| PSP Layers | 1. Protective layer 2. Barium fluorohalide 3. Reflective layer 4. Base 5. Antistatic layer 6. Lead foil |
| PSP Latent image | In 8 hours loses approximately 25% of its energy as the F center fades |
| Reflective layer | Helps direct light toward the CR reader |
| Lead foil | Absorbs backscatter |
| Immediate luminescence | Primary excitation |
| F center | Color center |
| Photostimulated luminescence (PSL) | Secondary excitation |
| Subscan motion | Movement of the PSP under the high intensity helium-neon laser o solid state laser beam scan |
| Phosphor activation | Movement of the PSP under the high intensity helium-neon laser o solid state laser beam scan |
| Aliasing | Moire effect: direction of lead strips and grid line per inch (grid frequency) matches the scan frequency the scanner or reader. -Can also occur when sampling frequency is insufficient or less than twice the bandwidth of the input signal |
| Grid recommendation for DR | High grid ratio |
| Fading | Increases a temperature increases |
| Erase PSP prior to use | If it is unused and stored for 48 hours or more |
| Lase jitter | -Inconsistent scanning motion, resulting distorted images -Evaluate monthly as part of CR QA monitoring |
| Windowing | Changes contrast- number of gray shades (width) and brightness (level) |
| Nyquist theorem | The sampling frequency must be more than twice the frequency input signal to best duplicate that original signal |
| Exposure field recognition/partition pattern recognition/segmentation | CR reader identifies and analyzes the region of interests when more than one exposure is made to a single PSP |
| Histogram | -Graphic representation of pixel value distribution -Demonstrates: quantity of exposure, number of pixels, and their value -Black/ left -White/ right |
| Histogram | -Narrow histogram: low-contrast image; more grays -Wide histogram: high-contrast image; more black and whites |
| Lookup table-LUT | A characteristic curve that best matches the anatomic part being image -It identifies each of the tonal values and their distribution in the x ray image |
| CR resolution increases as | PSP phosphor size decreases Laser beam size decreases Monitor matrix size increases |
| Automatic rescaling | Enables compensation for approximately 80% underexposure and 500% overexposure |
| Shuttering | It is used to remove the bright unexposed areas outside of the collimated field that contribute to veil glare |
| DR | -Don’t use PSP -Direct vs indirect capture -Immediate image display -Uses FPD: solid state detector plates |
| Indirect | -Uses Thin film transistors (TFT) or charge couple devices (CCD) -Both involve scintillation -Uses CsI or Gd2O2S X rays to light to electrons |
| Direct | -Uses amorphous selenium (a-Se)-semiconductor and TFT -Thicker detector to improve detection to compensate for lo x-ray absorption of Se -Has the highest DQE No scintillation X rays to electrons |
| CMOS | Lower DQE-detective quantum efficiency |
| HIS | Hospital information system: network that allows the archiving and distribution of the vast amounts of image information from all modalities, managing it all in a single system |
| RIS | Radiology information system: centrally process and store image data within hospital, enables image retrieval from the server by any department over the hospital network |
| PACS | Picture archiving and communications systems: digital images can be sent anywhere there is an equipment to receive and display them |
| DICOM | Digital imaging and communications in medicine: is the international standard to communicate and manage medical images and data |
| HL7 | Health level 7: HL7 stands for Health Level 7 and it is a set of clinical standards and messaging formats that provide a framework for the management, integration, exchange, and retrieval of electronic information across different healthcare systems. |
| EMR/EHR=Electronic medical record/Electronic health record | Allows the electronic entry, storage, and maintenance of digital medical data. Contains the patient's records from doctors and includes demographics, test results, medical history, history of present illness (HPI), and medications. |
| Beam restriction | Limit the exposure by decreasing the x ray field size and hence protects patient from unnecessary exposure |
| X ray generators | Change mechanical energy into electrical energy |
| High frequency generator | Small in size; produce constant potential waveform |
| AC- alternating current | Characterized by varying amplitude and periodic reversal of polarity. -In the US, 60 Hz or 60 cps |
| Amplitude | Maximum high of the wave/impulse and represent electrical potential (voltage) |
| Frequency | Number of cycles per unit of time |
| Faradays | A magnetic field will induce an electric current in a conductor if there is motion of either the magnetic field or the conductor; used in high-voltage transformer |
| X ray transformers | Operate under mutual induction |
| High voltage transformer | -Voltage to kilo voltage -Higher ratio= higher voltage increase Decrease amperage proportionally |
| Autotransformers | Operate on the principle of self-induction and function to provide a selection of kilovoltage |
| Rectification | Change AC to a more useful unidirectional current through solid-state diodes made of semiconductive materials such as silicon, selenium, or germanium that conduct electricity in only one direction |
| Location of rectifications | -Located between the secondary coil of high voltage transformer and the x ray tube |
| Induction | Mutual induction: 2 coils Self-induction: 1 coil |
| Choke coil | Operates with principle of self-induction -It is a part used in electrical circuits to allow DC current to flow through while blocking AC current from passing. |
| Digital images | -Best viewed in low-lighting levels to avoid screen glare -If viewed on bright lit area, image appears dark |
| Quality control | Refers to equipment and its safe and accurate operation |
| Congruence | Describes the relationship between the collimator light field and the actual x ray field. +/-2% within SID |
| Kilovoltage | Test using an electronic kilovoltage meter and should be within +/-4 kV |
| Reproducibility | Radiation output should be consistent within +/-5% |
| Spatial resolution | Recorded detail/sharpness |
| Smaller input phosphor | Increases detail sharpness/ resolution |
| Fluoro Magnification | Increases spatial resolution but increases dose |
| Most useful x rays | Passes through the port window |
| Parallel plate ionization chamber | Type of AEC; radiolucent chamber between pt. And IR that ionizes air within it when photon emerges, terminating the exposure automatically |
| KV relationship with quantity of radiation | The quantity of radiation produced increases as the square of the kilovoltage |
| Rating charts | Enable the radiographer to determine the maximum safe milliamperage, exposure time, and kilovoltage for a particular exposure using a particular x ray tube |
| Relationship between energy, frequency, and wavelength | Increase Energy= higher frequency and shorter wavelength |
| Photon interactions with matter | Photoelectric Compton Coherent/classical |
| Bremsstrahlung | -“Breaking” radiation; compromises 70 to 90% of the x ray beam -High speed e- is attracted and slowed down by positively charged nucleus. It is deflected from its course with a loss of energy in the form of x ray photon Continuous energy spectrum |
| Characteristic | High speed e- with energy of at least 70 keV ejects an atom from the k shell (inner shell). The energy of characteristic x ray equal to the difference in energy between k (69) and L (12) shell energy levels= 57 Discrete energy spectrum |
Created by:
Eva Chung
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