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MR211 Final Review
MR211 Review
| Term | Definition |
|---|---|
| LUT | A list of the pixel values that make up the “ideal” histogram shape for an image of a particular body part |
| Flat field uniformity corrections | Purpose is to correct variations in the image field. Examples include: electronic response and gain offsets, light guide variations, and variable scintillator thickness |
| Image lag | Leftover signal present in next image (ghosting) |
| Automatic rescaling | Remaps the brightness and gray scale of the digital image so that it appears like a “normal” or conventional radiograph |
| Q values | Stored in a permanent LUT, represent the ideal histogram values for every procedure performed |
| S values | Input values received for each exposure taken, creates the histogram |
| Histogram | Bar graph represented by the data within the collimation field indicating the number of pixels counted for each gray scale value |
| Exposure field recognition (EFR) | Used by both CR and DR- Computer recognizes landmarks to determine dark structures within the anatomy from the pitch-black background density, which must be eliminated |
| S-max | Landmark point that represents the darkest density within the body part (right side of histogram) |
| S-min | First landmark scanned on the left that has a non-zero pixel value |
| S-ave | The average density within the anatomy, used to calculate the exposure indicator |
| Histogram analysis | Computer algorithms will search for an SMIN point, an SMAX point, or both, in the acquired histogram. Data outside of the two graph points SMIN and SMAX eliminated from the calculations used to produce the final image (Type I, II, or III) |
| Kernel (preprocessing) | Computer algorithm that creates a sub-matrix to average surrounding pixel values to fill in missing data from dead dels |
| Matrix | A square arrangement of numbers in columns (M) and rows (N), numbers correspond to discrete pixel values |
| Pixel | Picture element, smallest component of a digital image |
| Voxel | Volume element, represents the information contained in a volume of tissue in the patient |
| Bit depth | Number of bits stored per pixel, defines the brightness levels (shades of gray) available for each pixel |
| FOV | Portion of the IR that contains relevant anatomical information and is displayed on the monitor screen |
| Dynamic range | The range of exposures that may be captured by a detector |
| Window width | Adjusts the length of gray scale in the image (contrast) |
| Window level | Adjusts the overall or average brightness of the image |
| Scanning | Image is divided up into a matrix of pixels (1st step of digitization) |
| Sampling | Intensity of light (or x-rays) is measured for each cell (2nd step of digitization) |
| Quantization | A discrete numerical value is assigned to each cell from a pre-designated gray scale (3rd step of digitization) |
| ADC | Analog-to-digital converter; receives the signal from the amplifier, converts the analog signal to digital data sent to the computer |
| Stimulated phosphorescence | The ability to store a latent image over time; requires re-stimulation (ex. Laser) |
| F-centers | Metastable defects in the PSP that cct like “electronic holes” that can trap electrons freed from x-ray ionization of the crystal |
| Photomultiplier tube (PMT) | Component of the CR reader where light emitted by the phosphor plate is changed into an electronic signal and amplified |
| Del | a detector element in the image receptor |
| TFT | : Thin-film transistors; the electronic switching gate used in detector elements of directcapture radiography (DR) |
| Storage capacitor | Component of the del that stores the electrical charge; known as the “heart” of the del |
| Semiconductor | Detection surface of the del; will be primarily sensitive to x-rays or light, depending on the material used (selenium or silicon) |
| Fill factor | The percentage of a del’s square area devoted to the semiconductor detection layer |
| A-Se | Amorphous selenium; del semiconductor material used in direct conversion DR. Absorbs incoming x-rays and converts them to electrical charge |
| A-Si | Amorphous silicon; Del semiconductor material used in indirect conversion DR. Absorbs incoming x-rays and converts them to light |
| CsI | One type of phosphor used in the scintillation layer of indirect conversion DR detectors. Considered a structured phosphor |
| Gd2O2S | One type of phosphor used in the scintillation layer of indirect conversion DR detectors Considered an unstructured or turbid phosphor |
| Gate lines | Network of wires within the AMA; controlled by the address driver. Tell the TFT “gates” to open in sequence |
| Data lines | Network of wires within the AMA; when the charge flows out from each individual del, the data lines send that charge to the amplifier |
| Del pitch | The distance between the center of two adjacent dels |
| Aliasing | Artifact caused by a loss of digital information due to a fluctuating signal |
| DQE | Measures the overall efficiency for converting input exposure data into a useful output image |
| Exposure latitude | The range of exposures which produce quality images at appropriate patient dose |
| Exposure indicator | A readout estimating the exposure level received at the image receptor as derived from the initial pixel values in the acquired image histogram |
| KSTD | A standard exposure typical of that imaging receptor system |
| KIND | The measurement of the radiation that was incident on the image receptor for that particular exposure |
| KTGT | The ideal exposure for each specific body part and view |
| Deviation index (DI) | A standardized readout indicating how far an exposure falls outside the target or “ideal” exposure level expected for a particular projection |
| Fourier transform | Converts image data from the spatial domain to the frequency domain for processing |
| Smoothing | Type of low-pass filtering that removes noise from an image |
| Edge enhancement | Type of high-pass filtering that brings out smaller details by suppressing larger, background areas |
| Dual energy subtraction | Creates a double-exposure is made at two different kVp settings or with filters to produce separate soft tissue and bone images |
| DAP | Calculates dose by multiplying entrance dose (in centigray) by exposure field sized used |
| Dose creep | The use of higher than necessary radiation dose to a patient to avoid repeats caused by underexposure |
| Saturation | Extreme over-exposure, causing a loss of data that results in a flat black appearance of the over-exposed portion of the image |
| DICOM | Allows network communication between a modality and PACS |
| Metadata | Extensive, detailed information stored “behind the image” for every image |
| HL-7 | Software standard for exchanging electronic text information, used for communication between HIS and RIS systems |
| HIS | Hospital Information System, Includes direct patient care information, billing systems, and reporting systems (ex. MRN) |
| RIS | Radiology Information System, System used to order exams and report results (ex. Accession number) |
| EHR/EMR | Electronic health record/ Electronic medical record |
| Aperture ratio | Measure of the image luminance of LCD monitors |
| Refresh rate | A measure of how fast the monitor rewrites the screen |
| Photometer | A device used to measure the light intensity from a display monitor |
| Resolution tool | A lead foil “bar” test pattern (right) can be used to obtain spatial resolution in LP/mm |
| Luminance | The rate of light emitted from a CRT, LCD, or LED monitor |
| Luminance response | A monitor’s ability to accurately display different shades or levels of brightness from a test pattern (aka contrast test) |
| VAD | Rapid loss of luminance at increasing viewing angles of LCD monitors |
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