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RAD 1333 - Exam 2 Questions and
Correct Answers Latest 2025 Rated A
- ANSComposed of barium fluorohalide crystals doped with europium which is referred to as a Photostimulable phosphor or (PSP) This type of phosphor emits visible light when stimulated by a high intensity laser, a phenomenon termed photostimulable luminescence. Phosphor layer is what gives off light for the LATENT IMAGE _____ ______ the ability of the image receptor (IR) to accurately capture the range of photon intensities that exit the patient. - ANSdynamic range Digital IRs with a wide dynamic range can accurately detect a wide range of radiation intensities and that small degrees of underexposure or overexposure would still result in a quality diagnostic image. _____ is a measure of the imaging system's ability to display the contrast of anatomic objects that vary in size. - ANSModulation Transfer Function - MTF MTF values range between 0 and 1
- 0 = No difference in brightness levels
- 1 = Maximum difference in brightness levels The higher the MTF of an imaging system the better the visibility of anatomic detail!\
An MTF of 1 is easier to achieve with large objects having low spatial frequency. It is more difficult to visualize smaller objects with high spatial frequency. So thats why we need a system with high MTF?Yes. The book says that 1 is hard to achieve and that most systems have a value of less than 1 ______ _______ _________ refers to various computer algorithms (mathematical computations) applied to digital images for the purpose of optimizing the image for display. Benefit to film-screen - ANSdigital image processing ______ _______ is a value that reflects the difference between the desired or target exposure to the IR and the actual exposure to the IR. - ANSDeviation Indicator (DI)
- universal standard indicator exposure
- overexposed is plus 1
- under is negative 1 _______ ___ ________: the range of histogram data set that should be included in the displayed image. - ANSValues of interest (VOI) _______ _________ - the computer compares the acquired image histogram to stored histograms for the same anatomic part. It will then "rescales" the brightness, or gray scale, according to what it "thinks" it should be for that part. - ANSautomatic rescaling
sampling pitch these are both part of the sampling process ________ provide the means to alter original pixel values to improve the brightness and contrast (grayscale) of a digital image using computer algorithms. - ANSlook up tables (LUTs) provide a means to adjust the contrast or grayscale necessary to adequately view the anatomic region _________ is a method of describing the contrast resolution compared with the amount of noise apparent in a digital image. - ANScontrast to nosie ratio - CRN This is a system that can distinguish between more shades of gray Increasing the CNR increases the visibility of anatomic details where as decreasing crn decreases visibility _________ reflects the precision with which each sampled point is recorded. - ANSquantization During the process of quantization, each pixel is assigned a numerical value which controls the number of shades of gray.
2^16 = 65000 shades of gray __________ is the practice of diagnostic image interpretation outside the facility (off-site) from where the imaging data is acquired. - ANSteleradiology _____________ provides a numerical value indicating the level of radiation exposure to the digital image receptor.b - ANSexposure indicator 2 types of Flat Panel Detectors: Indirect & Direct - ANSIndirect - Use a scintillator to convert exit radiation into visible light which is then converted into an electrical charge. Direct - Convert exit radiation directly into electrical charge. 3 Important Stages of Digitizing the CR Latent Image: - ANSscanning, sampling, and quantization THIS IS WHAT HAPPENS WHEN WE GO FROM PMT TO ADC a term used to evaluate the accuracy (sharpness) of anatomic structural lines displayed on an image - and refers to the smallest object that can be detected in an image - ANSspatial resolution anonymization of patients PHI is referring to: - ANSthe removal of the patients identifiable information from the PHI
- .2 millimeters per line pair has a spacial frequency of 5 Large objects are associated with low spatial frequency.
- A twenty mm line pair has a spacial frequency of. figure 4-6 on slide 15 of ch. 4 (part 1) Detective Quantum Efficiency (DQE) value is impacted by: - ANSThe type of material used in the IR to capture the exit radiation The energy of the x-ray beam The spatial frequency The MTF dicom - ANSdefinition talks about the communication standard not HR Difference btwn unstructured and structured scintillators - ANSUnstructured
- go in different directions
- gadolinium oxysulfide ( ) (Unstructured scintillator) structured go in straight up and down because they are vertical crystals
- cesium iodide (CsI) (Structured scintillator) Digital artifacts may be classified as: - ANSThose coming from the detector
- either CR plate or TFT array of the FPD. Those occurring during image data extraction before the ADC.
Those that occur during the ADC process and subsequent signal processing. Direct Radiography (DR) combines the 2 processes. - ANSAs a result, DR images are available almost instantly, but DR IRs are more fragile and much more expensive than CR IRs disaster recovery processes - ANSoffsite storage and servers supported by a secure network and third-party vendor. distance measured from the center of one pixel to the center of an adjacent pixel. - ANSpixel pitch decreasing pixel pitch (which is done by decreasing pixel size) increases spatial resolution as well as contrast resolution ] Smaller pixel = smaller pixel pitch Larger bit depth = more shades of gray DR Flat-panel detectors are solid-state image receptors that utilize an active matrix array of electronic components. These detectors are constructed with several layers for signal storage, signal readout, and electronic components for digitizing: - ANS1st layer: X- ray converter 2nd layer: Thin Film Transistor (TFT) 3rd layer: Glass substrate
Edge enhancement - (high-pass filtering) - ANSTechnique that improves the visibility of small, high-contrast structures (However, image noise may also be slightly increased) like contrast in the spine Equalization - - ANSPostprocessing function whereby underexposed areas (bright areas) are made darker and overexposed areas (dark areas) are made lighter. Erasing the latent image PSPs can be reused The expected life of a PSP is ≈ 10,000 exposures - ANSBefore the IP can be returned to service, it is exposed to intense white light to release any residual energy that could affect future exposures. Fixed Matrix size - a larger IP will have larger sized pixels and therefore, lower spatial resolution (This is where you would want to use the smallest IR size for the anatomy you are imaging) - ANSMost of the time we will not know if it has a fixed matrix size or fixed sampling frequency. This is why we always use a smaller IP for the smaller anatomy Fixed sampling frequency - a larger IP has a larger matrix to maintain spatial resolution - ANSThe pixel size stays the same here because the matrix is cahnging with the sampling frequency
FPD - Direct Detector - ANSAmorphous selenium-coated (a-Se) detector converts exit radiation directly into electrical charges. With direct detectors there is less opportunity for loss of signal. Therefore, excellent spatial resolution is maintained. FPD - Indirect Detector - ANS- Convert exit radiation into visible light.
- Photodetectors convert visible light to proportional electrical charges.
- Electrical signals sent to the ADC for digitization. gadolinium oxysulfide ( ) (Unstructured scintillator) cesium iodide (CsI) (Structured scintillator) These are phosphors indirect uses scintillators to convert light to electrical charges Generally, digital image processing can be described in two stages: - ANSPRE-processing to prepare the data for processing and display default (preset) or POST-processing which include computer operations available before and after the image is displayed. How do we know if we go far outside the exposure latitude of an image? - ANSWe know for sure from the EI/DI or from noise or brightness of an image
is the number of pixels per unit area. - ANSpixel density KAP is the same as DAP and is the product of the total air kerma and the area of the x-ray beam at the entrance of the patient. - ANSKap differs in that it is the air kerma Laser printers use either a wet or dry printing method: - ANSWet laser printers use liquid chemicals (developer and fixer) to process the image. Dry printing the image is created using heat instead of liquid chemicals. The chemicals are part of the film. luminance is measured in ... - ANScandela per square meter (cd/m²). optical system in CR IP reader - ANSlaser, beam-shaping optics, collecting optics, and optical filters phosphor layer of the ip - ANSComposed of barium fluorohalide crystals doped with europium which is referred to as a Photostimulable phosphor or (PSP) This type of phosphor emits visible light when stimulated by a high intensity laser, a phenomenon termed photostimulable luminescence. Phosphor layer is what gives off light for the LATENT IMAGE
Pixel bit depth, or number of bits (2n), which determines the number of shades of gray that can be displayed on an image. 0- The larger the bit depth the greater the number of shades of gray that can be displayed. 0- A system that can digitize and display a greater number of shades of gray has better contrast resolution and spatial resolution (sharpness) - ANSBit depth is determined by an analog-to-digital converter (ADC). Example: 12-bit depth (2^12) can display 4096 shades of gray Pixels are measured in microns - ANS100 mircrons = .1 mm postprocessing techniques: - ANSDual-energy subtraction Contrast Enhancement Edge enhancement Inversion Smoothing Equalization Pre-processing: To process the latent digital image, the computer creates a HISTOGRAM (graphic representation of a data set) of the image. - ANSThe histogram includes all the pixel values that represent the latent image (released energy) after the software corrections were applied.
Scanning - The purpose of scanning is to convert the latent image on the IR into an electrical signal (voltage). - ANSThe IP is scanned with a laser beam to release the stored energy as visible light (photostimulable luminescence) continuous pattern of light intensities sent to photomultiplier tube or (PMT). Shuuttering is also called - ANSelectronic masking Smoothing - (low-pass filtering) - ANSA technique that suppresses image quantum noise (However, spatial resolution is degraded) System that can distinguish between more shades of gray has a better .... - ANScontrast to noise ratio The _____ _______ refers to the range of exposures that should be used to produce a diagnostic image. - ANSexposure latitude Lower than necessary x-ray exposures (too few x-rays) (the left side of exposure latitude) = quantum noise Higher than necessary x-ray exposures (the right side of exposure latitude) = Overexposure to the patient (fog) The pixel size is directly proportional to the FOV displayed and inversely related to the matrix size. - ANSIf the FOV is increased (from 10x12 —>
14x17 IR) for a fixed matrix size, the pixel size is also increased (directly related) If the matrix size is increased (2048 x 2048 matrix --> 4000 x 4000) for a fixed FOV (14x17 IR), the pixel size will decrease (inversely related) The size of the pixel and the pixel pitch are determined by the DEL. Therefore, the spatial resolution in a flat panel detector IR is determined by the size of the _____ - ANSDEL
- The smaller the DEL, the better the spatial resolution The thin film transitor (TFT) is divided into square detector elements (DEL)
- ANSEach DEL has a capacitor to store electrical charges and a switching transistor for readout Electrical charges are read out separately from each DEL and then sent to the ADC for digitizing. The x-axis represents the range of pixel values assigned from white to black The y-axis represents the number (frequency) of pixels for each value. The location of the graph along the x-axis represents image brightness levels - shifted right to left - ANSThe right represents areas of black The left represents areas of white The middle is the area of interest
Photodetector Analog to digital convertor (ADC) What does DEL stand for? - ANSdetector elements DEL - not dicom elements. what does the Photodetector do? (such as photomultiplier tube (PMT)) - ANSCollects, amplifies, and converts the visible light to an electrical signal proportional to the range of energies stored in the IP. what does the term electronic masking mean? - ANSaltering the regions viewed on the displayed image. It is not within the standards of practice for radiographers to make decisions about removing information within the radiation-exposed field. What happens if we increase SNR? What if we decrease it? - ANSIncreasing the SNR means that the strength of the signal is high compared to the amount of noise. Increasing the SNR will improve the quality of the digital image. Increased noise (decrease SNR) will decrease visibility of anatomic details.
what is the Nyquist Theorem? - ANS- states that in order to accurately reproduce an image from the continuous analog signal, the sampling rate must be at least two times the highest spatial frequency (lp/mm) in the exit radiation intensities (signal). 2^n What is the technique that alters the pixel values to increase image contrast? - ANScontrast enhancement When the released energy from the IR is digitized, several operations occur to the raw data to account for flaws or imperfections in the electronic IR: - ANSdead pixeling and flat fielding Window level (or center) : brightness sets the midpoint, of the range of brightness visible in the image. - ANSA direct relationship exists between window level and image brightness:
- Increasing the window level increases the image brightness
- decreasing the window level decreases the image brightness. window width or contrast - ANSvaries the range of shades of gray visible in the image. An inverse relationship exists between window width and image contrast: Increased (wide) window width = lower contrast. Decreased (narrow) window width = higher contrast.
