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102-2 DIGITAL
| Question | Answer |
|---|---|
| What is Computed Radiography (CR)? | Cassette-based digital imaging modality that uses storage phosphor plates to produce images. |
| *Slow Scan” mechanism | IP plate is pulled out and scanned thinly ALONG THE long axis of the IP |
| “Fast Scan” mechanism | IP plate is scanned across the wide axis of the IP |
| Laser | SOURCE OF STIMULATING LIGHT. Scans the extracted IP with a helium laser beam or solid-state laser diodes. Scans with a red light in a laser pattern and give energy to the trapped electrons |
| Optical Filter | filters laser signals with information on it and filters it out from signals with no information (outside the part) |
| Photodetector | is a photomultiplier tube (PMT) information from optical filter |
| What is the process of the CR reader converting a screen to a digital image? | 1. The CR reader removes the imaging plate and uses laser to scan the imaging plate, releasing the energy stored in the CONDUCTIVE LAYER as BLUE LIGHT)2.releases stored light and converts it to an electrical signal, which is then digitized. |
| Photostimulable Luminescence (PSL) | Defined as light produced by a phosphor (active layer) when struck by light or x-ray photons. PSL occurs following x-ray exposure. However, PSL also occurs some time later when exposed to a different light source |
| DIGITAL RADIGRAPHY(DR) | Hard-wired to the image processing system and is cassette-less. Directly converts x-ray photons into an electrical digital signal. |
| Flat panel or flat field detectors | both the indirect amorphous silicon and the direct amorphous selenium plates that are being used in digital radiography. |
| Direct/Indirect Acquisition DR Main Difference | Direct-WITHOUT scintillator or Indirect-WITH scintillator. |
| Scintillator function | Absorbs x-ray photons and emits light isotropically (in all directions) |
| Direct DR Aka Direct Conversion/Acquisition or Direct SELENIUM Flat Panel Imaging system | Aka Direct Conversion/Direct Acquisition or Direct SELENIUM Flat Panel Imaging system. X-rays absorbed by coating material and immediately converted into an electrical signal. Amorphous Selenium (a-Se) TFT(thin film-transistor) |
| Indirect DR aka Indirect Conversion/Acquisition or Indirect SILICON Flat Panel Imaging System | USES Amorphous Silicon and Cesium Iodide. X-ray photons are converted to light (Amorphous Silicon) THEN the light photons are converted to an electrical signal(Cesium Iodide) |
| Amorphous Selenium (a-Se) | a semiconductor with excellent ray photon detection ability. Converts x-rays to an electrical signal and is sent to TFT (Thin film transistor) detectors |
| Amorphous Silicon (a-Si:H) TFT | Can not directly convert x-rays to an electric charge but works as a light detector to capture fluorescent light. |
| Cesium Iodide (Csl) TFT | A scintillator/ CCD(charged couple device)for Amorphous Silicone Converts x-rays into visible light |
| TFT characteristics | each stores electrical signal and transmits to pone pixel. Positioned in a matric that allow the charge pattern to be read out |
| How much can radiographers reduce the patient dosage for DR? | 20=50% reduced patient dose. |
| What can DR NOT compensate for after exposure? | Excessive noise from quantum mottle (not enough mass). |
| What factors are NOT affected with patient dose (kVp/mAs) in DR? | Contrast does not change. Digital image contrast doesn’t change with does. KVP doesn’t control contrast. Spatial resolution (detail) NOT affected by focal spot size (pixels determine in DR). |
| Relationship between mAs and kVp in DR? | mAs doesn’t control optical density. kVp should be increased as mAs is decreased, vise-versa. |
| Grid selection in CR | Occurs more often due to sensitivity of IP to scatter. Dependant upon:part size, kVp, Scatter, Grid frequency (lines/inch) |
| Grid frequency | number fo grid line/inch. Higher frequency, finer grid lines. Typically 80-152 lines/inch. |
| Moire effect/pattern | When scan laser and grid lines are parallel, creates a WAVY ARTIFACT PATTERN. More likely when laser frequency is closer to grid frequency. |
| Grid ratio | relationship between HEIGHT of lead strips AND SPACE BETWEEN LEAD STRIPS. HIGHER ratio, MORE SCATTER ABSORBED. |
| Focus grid | grid where lead strips are angled to coincide with the divergence of the x-ray beam.MOST GRIDS CHOSEN ARE PARALLEL AND FOCUSED |
| Size of grid | smaller cassette, higher sampling rate, so HIGH FREQUENCY grid should be used for 10x12 cassettes or smaller to eliminate scatter. |
| Shuttering | post-exposure image manipulation, in which a black background can be added around the original collimation edges, eliminating white/clear areas. NOT A REPLACEMENT FOR PRPOPER PRE EXPOSURE COLLIMATION. |
| How many shades of grey can screen-film image display view on a box? | 30 shades of grey |
| What is a key factor for penetration and the type and amount of contrast desired? | kVp |
| What is optimum kVp range for CR? | 60kVp to 110kVp |
| What is critical in determining proper digital IR exposure? | mAs |
| What two important factors should be considered when selecting a CR imaging cassette | Type and size |
| What controls Grid size? | kVp, body part size, film size |
| Quality of data acquired from the IR is measured by what? | Contrast, Noise, Frequency(kVp) |
| What are two principle characteristics of Digital images? | spatial resolution and contrast resolution |
| What is the principle descriptor for contrast resolution in a digital image? | DYNAMIRANGE (grayscale) |
| Dynamic Range | the number of gray shades that in imaging system can reproduce.identified by the bit depth/capacity of each pixel. |
| Spatial Resolution | Ability of an imaging system to resolve and render a detailed image (recorded detail). Determined by matrix size, pixel size and gray scale bit depth. Can be expressed in 3 dimensions, x-y-z .axis |
| What is the spatial resolution “z” axis on a digital image? | the gray scale bit depth (represents the DEPTH of the information on the image. The larger the depth of the pixel, the greater the number of shades of gray available for image display |
| Matrix size | a square of boxes that gives form to the image. Each matrix box is known as picture elements or pixels. Decreasing matrix size decrease number of pixels, decreases quality. |
| Window Leveling | ability of the computer to mathematically bring density differences into the visual range. Directly related to IMAGE DENSITY, inversely related to window width |
| Automatic rescaling | images produced with uniform density and contrast (auto correction). Too little exposure=quantum mottle. Too much exposure=loss of contrast/distinct edges from scatter. |
| Common types of DIGITAL IMAGING artifact | 1.IR Artifacts 2.Object artifacts 3.CR reader Artifacts 4. Printer errors |
| IR Artifacts | Imaging plate artifacts (cracked cassettes) Backscatter(dark line artifacts. Phantom/Ghost images (didn’t erase plate) scratches, light spots (from dust), flipped cassette upside down, heat damage. |
| Object artifacts | from errors with patient positioning, collimation, histogram selection. |
| Why are CR and DR IRs more sensitive to scatter? | due to lower k-edge values. |
| CR Reader Artifacts | Laser film transport artifacts (uneven transport of film) Dropout(dust accumulation in CR reader) |
| ADVANTAGES OF CR/DR SYSTEMS | lower pt dose. Lower repeat rates. High res, wider exposure, more grayscale (dynamic range) no darkroom/film costs, image storage easier, can post process image, PACS and IMACS system |
| PACS | Picture Archiving and Communication System |
| IMACS | Image Management and Communication System |
| What are the post processing functions | 1.Window and level (correct photo with appropriate density/contrast).2, Magnification 3. Shuttering 4.Image Orientation 5. Image Stitching (putting more than one image together in one image. 6.Image Annotation |
| Disadvantages of CR/DR systems | 1.up front cost higher 2.LOWER SPATIAL RESOLUTION. 3.Collimation/part alignment MORE CRITICAL. 4.Radiographers can get away with repeat overexposure. 5. HIGHER CHANCE OF ARTIFACTS. |
| What is the DQE (Detective Quantum Efficiency)? | Measures combined effect of noise and contrast performance. The greater the DQE, the better the digital system is at displaying image quality. Greater DQE increases ability to view small low contrast objects (like mammography) |
| Which digital system has the best mobility? | CR systems are more potable than DR because IR’s can move anywhere. |
| Which digital system has the highest cost? | DR systems cost 3 to 4 times MORE than CR systems. |
| Which digital system is the most functional? | DR systems are less labor intensive and quicker for patient exams than CR. |
| What are the three major categories of Quality Control for digital x-ray systems? | 1.Acceptance Testing(acceptable specifications) 2.Routine Maintenance (ensure running as expected 3. Error Maintenance (fixes if system has a problem.) |
| What are DAILY tests for general digital system inspection? | 1.Cleanliness of cassettes/receptors 2.Cassette Integrity 3.Fully erased imaging plates 4. Verify digital interfaces/network comm. 5.Laser printer functionality |
| What are WEEKLY tests for general digital system inspection? | Verify monitor calibration, Clean CRT interface. Clean/Inspect receptors. Follow QC recommended tests. Inspect CR reader. |
| What are the MONTHLY tests for general digital system inspection? | Reject/repeat analysis survey.Inspect/clean all image plates. |
| What imaging systems have the highest, lowest, middle DQE? | DR systems have highest DQE,then CR,then Film. |
Created by:
bcmoody