Essentials of Digital Imaging

Transcription

1 Essentials of Digital Imaging Module 4 Transcript 2016 ASRT. All rights reserved.

2 Essentials of Digital Imaging Module 4 Image Analysis 1. ASRT Animation 2. Welcome Welcome to Essentials of Digital Imaging: Module 4 Image Analysis. 3. License Agreement 4. Objectives After completing this module, you will be able to: Evaluate the effects of exposure changes on the appearance of a digital image. Evaluate the appearance of a digitally acquired image to assess quantum mottle and saturation. Discuss the relationship between exposure field recognition and the appearance of a digital image. Recognize motion on a digital image. Locate different types of artifacts on a digital image and state their probable cause. 5. Evaluating Digital Images The changes in exposure that affect density and contrast for film do not have as much of an effect on the appearance of digital images. This is due to digital processing that creates the image for display. However there are a number of factors that can affect the brightness of the image and also the contrast. The overall appearance of a digital image can be affected by a number of factors such as under exposure, or quantum mottle, over exposure, or saturation, scatter radiation, grid cut, and motion from the patient. Additional factors that can impact image quality are exposure field recognition errors, an unexpected attenuator in the field of view, or the menu selection for the procedure. 6. Quantum Mottle Quantum mottle, more often referred to as noise, in a digital image can be caused by multiple factors that affect the appearance of the image. Noise results in a mottled, or grainy, appearance caused by random variations of signal intensity on the image. Noise caused by low exposure to the image receptor means a low number of x-ray photons strike the receptor resulting in the phenomena known as quantum mottle. Basically, quantum mottle in digital images is caused by insufficient signal strength. Remember that the distribution of photons in the x-ray beam is not uniform. On occasion, when low levels of radiation are used to produce an image, the captured data are the random pattern of x-ray photons within the beam along with patient anatomical information. In other words, there are not enough x-ray photons striking the receptor. Oftentimes the only way to correct for the quantum mottle is to produce a new image that has an increased number of x-ray photons striking the image receptor. When the repeated image is produced with a greater number of photons striking the receptor it results in an image of better diagnostic quality. 7. Evaluating Noise In addition to quantum mottle the exposure index for the image indicates that the image was obtained with a low level exposure. The only way to reduce the amount of noise present in the image would be to

3 increase the amount of x-ray photons striking the image receptor which increases the signal strength available to create the image. The impact of quantum mottle is most noticeable when assessing the low contrast resolution of a radiograph. The impact on visibility from quantum mottle of low contrast structures is easily demonstrated using a low contrast detail phantom. As quantum mottle increases the ability to visualize subtle differences in differential attenuation is decreased. The circles in the phantom represent variations in tissue attenuation. 8. Over Exposure A misconception about digital imaging systems is that the system has the capability of correcting for errors involving receptor exposure. Digital systems are designed to analyze the signal extracted from the image receptor and to display that image with a specific image appearance. The image will fail to display properly due to the over exposure in instances where the signal strength approaches or exceeds the system s dynamic range. Saturation is the result of over exposure to the point where the dynamic range of the digital system is no longer capable of accurately reproducing the image data for display. The point at which saturation occurs is dependent upon the digital imaging system being used. An example of this is a thoracic spine image that demonstrates saturation in the lung field. The presence of saturation in the image results in an inability to visualize the lung field within the over exposed area regardless of manipulating image brightness. 9. Saturation The elbow radiograph on the left represents an acceptable level of exposure in the image. The image on the right represents a level of exposure that has resulted in saturation. The level of receptor exposure beneath the soft tissue portions of the saturated image exceeded the dynamic range of the pixel values. The outcome is that the soft tissues surrounding the bony anatomy are not able to be visualized. To correct for saturation the technologists must reduce the level of exposure striking the image receptor. The lateral cervical spine image on the left shows a level of exposure with a signal strength that exceeded the dynamic range of the pixel values in soft tissue areas and some bony structures. Attempts to adjust the brightness of the image in order to demonstrate soft tissue and bony detail were unsuccessful. The image must be repeated at a lower level of exposure in order to produce a satisfactory image. The repeat image was performed at a lower level of exposure which eliminated saturation and allows for the visualization of soft tissue and bony detail. 10. Scatter Radiation Scatter radiation does not contribute useful information to the radiographic image. In situations where scatter makes up a significant portion of the radiation striking the image receptor, there is a decrease in the image contrast. An example of scatter affecting image quality is observable on an abdominal radiograph where a significant portion of radiation striking the image receptor seemingly is composed of scattered photons. The image was produced without using a grid which clearly demonstrates the loss of visibility because of scatter radiation hitting the receptor. When a grid was used during the repeat examination, much of the scatter was attenuated. The visibility of structures is significantly improved by reducing the amount of scatter radiation striking the image receptor.

4 11. Grid Use Using a grid for certain radiographic examinations can aid the technologist in improving image quality. An abdominal radiograph produced without the use of a grid demonstrates decreased image contrast resulting in poor visibility. After attempts to manipulate the brightness and contrast of the image it still was not possible to achieve an optimal level of visibility of structures that is achieved by producing a radiograph on the same patient with a grid. Regardless of the imaging system used the presence of significant scatter will result in worsened image quality. 12. Grid Cutoff Proper alignment with the central ray can be difficult when performing a radiographic examination using a grid. The grid is designed to attenuate scatter radiation to improve image quality. Failure to properly align the central ray with the grid also will result in the absorption of the portion of the primary beam that represents anatomical information. The effect on the finished radiograph is an image that is displayed with a significant reduction in visibility referred to as grid cutoff. More specifically, grid cutoff occurs when the beam is not centered transversely to the grid. In addition to poor image display, in some circumstances the exposure to the image receptor is low enough to produce visible quantum mottle because of the insufficient signal striking the receptor. The presence of grid cutoff often is accompanied by an exposure indicator that suggests a low level of radiation exposure was used to produce the image. Additionally, grid cutoff might occur from an off level grid error or when using an improper SID or an upside down focused grid. 13. Off Center Grid Another complication in medical imaging associated with improper transverse alignment of the central ray and the grid is the impact of grid cutoff on image contrast. It might appear that an image is degraded by significant scatter radiation striking the image receptor. In reality, the exposure indicator proves that a low level of exposure was used to produce the image and the presence of quantum mottle tells the radiographer that poor image contrast is a result of grid cutoff. Image quality is easily improved by accurately aligning the central ray to the grid. 14. Inverted Focused Grid When a focused grid is inverted, grid cutoff is visible along the edges of anatomy on the finished radiograph. The diminished image quality results because the lead strips of the grid are no longer parallel to the divergent primary x-ray beam. 15. Knowledge Check 16. Knowledge Check 17. Improper SID Grid cutoff also can occur as a result of a source-to-image receptor distance, or SID, that is too close to the grid. The cutoff is demonstrated along the lateral margins of the radiograph. In addition to the presence of grid cutoff, the exposure index likely will indicate a low level of exposure was used for the examination even if the technologist has selected proper exposure factors. Sometimes two different types of grid cutoff can be visualized on a single radiograph. An example is an elbow radiograph demonstrating misalignment between the x-ray tube and the grid that is performed using a SID that is too short. The system was a cassette-less DR unit with a built in grid. The technologist

5 performing the examination did not ensure that the beam and grid were properly aligned before making the exposure and the incorrect SID was displayed on the DICOM header of the image. 18. Exposure Field Recognition Recognition of the edges of the exposure field play an important role in ensuring an image will display correctly. An exposure field recognition error occurs when the computer fails to identify collimated borders of a radiograph. When the computer can t find the borders, it causes a rescaling error, which often affects the brightness and contrast of an image. An exposure field recognition error during image processing will often result in an image displayed with inadequate brightness. An example of when this error can occur is when 2 exposures can be made on 1 image receptor. The individual exposure fields should be recognized during image processing although; sometimes the analysis of the image data fails to recognize the exposure field borders. Details about the examination suggest that the radiographic exposure was accurate for the examination evident by the absence of quantum mottle. Mottle, or noise, would normally be present if a low level of exposure produced the image. This validates that the diminished image quality is the result of an exposure field recognition error. In this instance, the area within the white box determined the level of image brightness as well as the exposure index. The lack of exposure within the region of interest, or ROI, led to a rescaling error that produced a low level of brightness and the exposure indicator reflected a low level of exposure even though the level of exposure was adequate. 19. Recognition Errors Some radiographic exams can present a unique challenge in attempting to produce diagnostic quality images. An example is a cross table lateral lumbar spine. Locating the spine and properly centering the anatomy of interest to the image receptor is not difficult to achieve but is a skill that is acquired after much practice. Improper alignment of the body part with the central ray and image receptor can result in an exposure field recognition error. An exposure field that is not accurately localized during image processing produces a final image that fails to display the proper brightness even though the appropriate level of radiation exposure was used. The system has the ability to reprocess the image data by realigning the region of interest to match the collimation margins. Upon making that adjustment, the image can be significantly improved. 20. Unexpected Attenuator Joint replacement surgery is common and is something that the technologist needs to be aware of before obtaining a radiographic image. Knowing about the surgery beforehand can aid the technologist in selecting the most appropriate technique for the examination. When an unexpected, highly attenuating material is present, it might negatively impact the brightness of the image when it is displayed. Metal rods contribute to an image displayed with inadequate brightness. Rescaling, following the computer s analysis of the image data, can result in a radiograph that is too dark. The rods represent a significant portion of low exposure within the data and therefore the rescaling process adjusts image brightness to take into account the low level of radiation exposure to the area of interest. 21. Menu Selection

6 The menu selected for image processing is critical to displaying the image properly. The menu selected for each unique examination contains specific levels of brightness, contrast, edge enhancement, and equalization. Selecting a menu that is not assigned to the examination being performed because it displays the image better can lead to potential medicolegal concerns. In some circumstances, selecting the incorrect processing menu can provide a more pleasing appearance to the viewer even though it holds changes in image processing that might be unacceptable for the exam. Keep in mind, the change in processing also can produce an exposure indicator that suggests there was an increase in radiation exposure to the patient, when in fact; there is no difference in exposure between the images being displayed. Image processing menus are carefully developed and should only be used for the examinations that they have been assigned to. 22. Image Blur Blurred images are caused by motion or changes in a geometric factor during image production. Motion is the predominant cause of blur in radiographic images. Technologists can minimize geometric blur when selecting technical factors, such as SID, OID, and focal spot size. Blur caused by geometric factors is best assessed using specific test phantoms. Image blur often is caused by patient movement. It is sometimes difficult to immediately recognize motion on radiograph but when using the zoom feature blur from motion becomes apparent when the edges of bony structures of interest are fuzzy or unclear. When motion produces blurring in an image it is often difficult to observe on the technologist workstation without using image zoom. The image zoom feature is essential for assessing the presence of motion in an image. Image zoom enlarges the radiograph making some of the finer details easier to see when motion is otherwise undetected. This function makes any blurred anatomy clearly visible and indicates the need to repeat the examination. 23. Size Distortion Radiographic distortion occurs as a result of changes in the relationship between the primary beam and image receptor. Size distortion is a misrepresentation of the true size of the object due to changes in distance between the tube, body part, and image receptor. An example of size distortion is magnification. The size of the image receptor affects the size of the image display. This change in display size should not be confused with magnification from changes in SID and OID. The two most common factors that are responsible for size distortion because of their effect on the distance between the object of interest and the image receptor are source-to-image receptor distance and object-to-image receptor distance. The Waters method is used to demonstrate the orbits. By tilting the head and placing the patient's chin on the image receptor, a 25- to 37-degree angle is formed between the orbitomeatal line and image receptor. This angulation not only projects the petrous portion of the temporal bones below the inferior border of the orbits, allowing the orbits to be evaluated free of superimposition by the petrous ridges but also brings the orbital margins further from the image receptor resulting in slight magnification of the structures. The combination of these effects makes it possible to better evaluate the orbits for injury such as blow out fractures. 24. Shape Distortion

7 Shape distortion is a misrepresentation of the true shape of an object due to a change in the angular relationship of the tube, body part, and image receptor. Shape distortion causes objects of interest to be elongated or foreshortened. When a patient is positioned for an oblique projection of the hip as opposed to using a standard AP projection the site of injury and the orthopedic hardware can be better evaluated. The wing, or ala, of the ilium appears elongated, the pubis is foreshortened, and the ischium is in profile achieving the goal of demonstrating placement of the surgical pin outside of the joint. Another example of shape distortion is a PA axial projection of the scaphoid using ulnar deviation. The scaphoid is elongated because of the 20o angle of the tube to the part and image receptor. Another option is to instead angle the image receptor 20o using a radiolucent sponge. Size distortion also can be applied to the PA axial scaphoid projection by placing a radiolucent positioning device underneath the wrist to bring the wrist further from the image receptor, increasing the OID. 25. Exposure Index It s important to understand what the exposure index values represent, along with factors that affect its accuracy. If exposure index values are outside the optimal range, however, noise or other problems appear. Factors that can influence the accuracy of the exposure indicator, regardless of the system used, include exposure field recognition, collimation, and unexpected structures in the exposure field. The implementation of the international standardized exposure indicator known as the Exposure Index started in The purpose was to establish a common Exposure Index across manufacturers and vendors of digital x-ray equipment. The end result is that the manufacturers utilize an exposure index that is linearly proportional to the amount of radiation received by the detector. Each department then develops a Target Exposure Index that results in the production of quality images at acceptable dose levels. In addition to the Target Exposure Index, the user of the equipment will be able to determine compliance with the desired value by assessing the Deviation Index for the exposure. The Deviation Index is displayed using a scale of minus 3 to plus 3. A Deviation Index of 0 indicates that the exposure matches the Target Exposure Index. A Deviation Index of +1 represents 25% more exposure than the Target Exposure Index where a Deviation Index of -1 represents 20% less exposure than the Target Exposure Index. Furthermore, a Deviation Index +3 represents 2X more exposure than the Target Exposure Index and a Deviation Index of -3 represents that the exposure was about ½ the Target Exposure Index. 26. Evaluating Exposure Indicator When all the exposure received by the receptor, not just the areas within the collimated borders, is included in calculating the exposure indicator, the exposure index likely will be miscalculated. Often this occurs when 2 radiographs are exposed onto a single image receptor. The area between the 2 images represents a very low exposure level. This area was incorporated in the histogram values and subsequently altered the calculated exposure indicator. The result was a value that indicated an insufficient amount of radiation. This 2-on-1 radiograph of the forearm also demonstrates a faulty exposure indicator calculation. The technique used was acceptable, but the exposure field borders weren't recognized, which decreased contrast and brightness. The histogram is very wide with an increase at the lower end of exposure

8 intensities, where it includes the area between collimated fields. If that area had not been included in producing this image, the display would have been appropriate and the exposure indicator would have been properly calculated. 27. Histogram Analysis Error It is possible to produce a chest radiograph using satisfactory kvp and mas values; however, if a lead apron is included in the exposure field the apron can cause an error in the histogram analysis. The apron is an additional attenuator that produces an extra peak at the low-intensity area of the a priori histogram. As a result, the values result in an exposure indicator miscalculation. The miscalculation suggests that the plate is grossly underexposed, when in fact it isn't. Additionally, a rescaling error occurs that leads to an inappropriate display of image contrast and brightness. Another example of a histogram analysis error occurs when including too much of the abdomen in the exposure field for a portable chest examination. The radiograph is processed using a chest menu that expects a chest-shaped histogram therefore; the calculation of the exposure indicator is inaccurate. The low-level exposure area below the diaphragm is included in the histogram and produces an incorrect exposure indicator, leading the technologist to believe that the image receptor was underexposed. Using the zoom feature on the image allows the technologist to evaluate for noise on the radiograph. If no significant noise is found it suggests that the image was not underexposed. Technologists must make sure that collimation is appropriate when looking at exposure indicators. Checking for additional attenuators within the exposure field and being certain the expected anatomy is shown ensures the histogram values are calculated correctly. 28. Recording Multiple Images Recall that recording multiple images on a single receptor can cause overexposed and underexposed areas. Exposure field margins are altered by overlapping exposure fields in the center of the receptor and nonparallel alignment of exposure field edges. The lookup table uses all the data on the plate, rather than just the image data, to produce the image display. The current recommendation is to record only 1 image per receptor to avoid potential data analysis errors. 29. Knowledge Check 30. Knowledge Check 31. Digital Image Artifacts Artifacts in digital imaging can be grouped by image receptor type. The image receptor is a photostimulable phosphor plate, called a PSP, or flat panel detector with a thin-film transistor, or TFT. Artifacts also might be categorized by their causes or where they occur and can be produced by Image receptors, processing equipment or electronic component issues. In addition, artifacts occur because of mistakes made in patient positioning or preparation. The latter errors are called exposure artifacts. 32. PSP Artifacts Various types of artifacts occur with photostimulable phosphor plate systems. These systems use a phosphor plate, transport mechanism, optical components, and assorted electronic components. The potential for unique artifacts that can be replicated are easily identifiable by disruptions in plate transport, dirty or damaged phosphor plates, dirty or damaged optical components, and malfunctioning

9 electronic devices. However, it is possible that the cause of an intermittently appearing artifact might not be identified until it is replicated. Artifacts associated with the plate and optical components will reduce the intensity of light collected by the optical system. The reduced intensity causes an artifact to appear bright on the image. Scratches, dents, and stains are artifacts on a PSP plate that can severely damage the phosphors. When the plate is scratched or dented, the affected area can t absorb x-rays. If the plate is stained, light emission is reduced or cannot happen. The artifact along the edge of the image is where the phosphor has chipped away from the support base. The white line in the soft tissue is a scratch and the white specs are dust spots on the phosphor. 33. Plate Based Artifacts At first an artifact might be missed. When looking at an image using magnification the artifact should become more apparent. The bright line artifact in the medial aspect of the humeral head was caused by a dirty plate. Many digital artifacts appear bright, or white, on the finished image. Once identified, the cause can be determined. Primary causes of bright artifacts likely are a damaged or dirty plate or damaged or dirty optical components. Plate based artifacts remain localized to the same area of an individual plate. Sometimes artifacts begin to look familiar. This occurs because the same plate is used for multiple radiographs. If technologists don t notice the artifact on the image, and the plate isn t taken out of service to be cleaned, the artifact will continue to appear degrading numerous patient examinations throughout the day. For this reason, it is important that technologists check images for artifacts continuously. 34. Routine PSP Cleaning PSP plates require routine cleaning and inspection by technologists to make sure the plates produce artifact-free images. One reason it s so important to regularly clean PSP plates is that many artifacts that can t be seen on a technologist s workstation are easily seen by the radiologist on his or her workstation. The quality, resolution, brightness, and contrast resolution capabilities of monitors used by radiologists are far superior to the monitors used by technologists. Sometimes the artifact can't be seen on a technologist s workstation unless the image is significantly magnified and altered. However, on a radiologist s workstation, the artifact might be immediately apparent and look like a foreign body. It also is important that a manufacturer approved cleaning solution is used during the periodic cleaning of PSP plates. Cleaning plates with the wrong solution can cause an irreparable artifact created as the solution soaks into the phosphor layer and leaving a stain. The stain disrupts the normal emission of light from the plate during the plate reading process. The PSP must be removed from service and disposed of according to the facility s waste removal policy. 35. Processor Artifacts Differentiating between the artifacts located on a plate and one that occurs during plate processing can be challenging when the questionable plate is not immediately available. The artifact s appearance generally provides some clues. Plate artifacts generally don t cross the entire axis of a plate; they only appear on images from the defective plate. On the other hand, processing artifacts run along an entire plate axis and appear on nearly all images regardless of the plate used.

10 36. Optical Component Artifacts Based on the construction of a plate reader, it might seem improbable for the inside to become dirty. Certain artifacts represent that they assuredly do. The actions of inserting the cassette into and removing the cassette from the reader allow for artifact generating contaminants to be introduced into the equipment. Artifacts such as a piece of hair located on an optical component transmitting light from the plate are a perfect example. A hair stuck to one of the optics can block the signal in that area of the image causing a "wig-wag" pattern as the hair moves back and forth during processing. Some plate readers have a built in cleaning feature that technologists can employ to decontaminate a portion of the optical system, removing the debris from the device. 37. Dirty Light Guide Some artifacts are more subtle than others. Arrows identify a line that runs along the second phalanx. The line represents a loss of image data caused by a dirty light guide in the plate reader. Dirt blocked the plate s signal and therefore the signal couldn't travel up the light guide through the photomultiplier tube to the analog-to-digital converter. The line runs the entire length of the plate and is parallel to the direction the plate traveled through the reader. 38. Flat-panel DEL Artifacts A source of artifact with flat panel units occurs within the detector elements, or DELs. In some cases the artifact is difficult to distinguish on a full-sized image. The arrows point to a small bright line in the chest, just below the humeral head. The partial loss of a row of DELs on the flat-panel detector caused this artifact. To fix this problem, the detector is recalibrated. If the artifact is still present following calibration then a field service engineer should be contacted to further investigate the issue. 39. Image Evaluation Factors There are several factors that are used to evaluate digital images. In the past, factors that were used for analog imaging were simply visual characteristics, such as; density, contrast, image blur, and distortion that couldn t have been manipulated. With digital evaluation, however, factors are a mix of visual cues and numerical values which include brightness, image blur, distortion, noise, and the exposure indicator. To better evaluate the digital image, it can be magnified and the brightness, and contrast levels can be adjusted, to further investigate artifacts and image blur. 40. Knowledge Check 41. Knowledge Check 42. Image Analysis What is causing the degraded image quality? a. exposure field recognition error. b. quantum mottle. c. saturation d. scatter. 43. Image Analysis A 3-on-1 projection of a finger demonstrates an exposure field recognition error. A rescaling error occurred during the computer s analysis of the image data. Because the field borders weren't recognized, the exposure data were included in the image data, including the intrafield area between

11 collimation borders on the receptor. When the values were incorporated into the analysis process there was a rescaling error and the lookup table application didn't display the appropriate brightness. Such 3- on-1 exposures are not uniformly accepted as a method to acquire images of extremities. Using 1-on-1 exposures basically ensures that this type of error won't occur, provided that collimation borders adhere to the rules for exposure field alignment. This error is evident because the image displays too dark and the technical factor selection used were appropriate for the exam. 44. Image Analysis What is causing the degraded image quality in the cervical region? a. exposure field recognition error. b. quantum mottle. c. saturation. d. scatter. 45. Image Analysis The cervical region is saturated. Imaging structures with large variations in part thickness that are adjacent to each other is challenging. The use of a compensating filter would be appropriate in order to create a more uniform attenuation of the beam between the upper thoracic and cervical vertebrae. 46. Image Analysis What is causing the degraded image quality on these radiographs? a. scatter. b. fog. c. grid cutoff. d. saturation. 47. Image Analysis The technologist confirmed that the correct technique was used; however, grid cutoff occurred. Improper alignment of the grid reduces the demonstrated contrast regardless of the receptor used. If this image had been repeated with the grid appropriately aligned with the x-ray beam, the image would have been acceptable. 48. Image Analysis What is causing the degraded image quality? a. exposure field recognition error. b. quantum mottle. c. saturation d. scatter. 49. Image Analysis The grainy appearance of the image represents under exposure. Quantum mottle occurs when there is insufficient exposure to the image receptor. When the strength of the signal is weak from insufficient x- ray photon interaction with the image receptor the result often is a mottled effect, or image noise.

12 50. Image Analysis Both images were both produced with the same technique factors. What is causing the difference in appearance of the two images? a. menu selection. b. grid cutoff. c. saturation d. quantum mottle. 51. Image Analysis The selection of the correct menu for an exam is important to ensure an image displays correctly. In some circumstances the exposure indicator is accurate although here the image appearance is different and the exposure indicator values are different by a factor of Image Analysis The image on the left is a PA projection of the wrist and the image on the right is a lateral projection. What is causing the degraded image quality? a. scatter radiation. b. exposure field recognition error. c. underexposure of lateral wrist. d. overexposure of the PA wrist. 53. Image Analysis The thickness of the body part changed the attenuation of the x-ray beam. One fundamental principle of imaging is when the thickness of the object being imaged changes, the level of exposure also must change. Working with a digital image receptor still requires technologists to adjust the exposure level to achieve an appropriate image display. The exposure level for a lateral projection should increase so the same amount of radiation strikes the receptor as in the PA image. In doing so, both images would display with equal brightness and contrast. 54. Image Analysis What is causing the artifact on this radiograph? a. stain. b. scratch. c. dent. d. dirt. 55. Image Analysis The artifact of the scratch on the full image is more apparent using magnification. The bright line in the tibia is a scratch on the photostimulable phosphor plate. 56. Image Analysis What is causing the artifact on this radiograph? a. scratched PSP. b. stained PSP.

13 c. dented PSP. d. dirty PSP. 57. Image Analysis The dirty PSP artifact is difficult to see on a full-sized image but the magnified image makes the artifact more apparent. The bright specks in the upper abdomen are there because the PSP needs to be cleaned. 58. Image Analysis What is causing the artifact on these radiographs? a. scratched PSP. b. stained PSP. c. dented PSP. d. dirty PSP. 59. Image Analysis On the first set of radiographs the arrow points to a small bright dot in the acromial process. On the radiographs of an AP shoulder the arrow points to a similar small bright dot in the soft tissue above the clavicle. The artifact is similar because it is actually the same artifact in both sets of images. Until the plate is cleaned every radiograph produced using this digital unit will demonstrate the same small bright dot. 60. Image Analysis What is causing the artifact? a. dirty light guide. b. corroded optical component. c. hair stuck to an optical component. d. scratch on the PSP plate. 61. Image Analysis The line identified by the white arrows runs through the metacarpals and represents the image data loss caused by a dirty light guide. Dirt blocked the signal from the plate so that the signal couldn t travel to the analog-to-digital converter. The line runs the entire width of the plate and is parallel to the direction the plate passed through the reader. 62. Image Analysis What 2 artifacts are visible on this radiograph? 1. dirty light guide. 2. corroded optical component. 3. hair stuck to an optical component. 4. scratch on the PSP plate. a. 1 and 2 b. 2 and 3 c. 1 and 4 d. 3 and Image Analysis A dirty light guide in the plate reader produced the line identified by the white arrow labeled "A." Dirt blocked the signal from the plate stopping the signal from travelling up the light guide, through the

14 photomultiplier tube, and to the analog-to-digital converter. The horizontal line identified by the white arrow labeled "B" was caused by a scratch on the PSP plate. 64. Conclusion This concludes Essentials of Digital Imaging: Module 4 Image Analysis. You should now be able to: Evaluate the effects of exposure changes on the appearance of a digital image. Evaluate the appearance of a digitally acquired image to assess quantum mottle and saturation. Discuss the relationship between exposure field recognition and the appearance of a digital image. Recognize motion on a digital image. Locate different types of artifacts on a digital image and state their probable cause. 65. References American Association of Physicists in Medicine. AAPM Report No An exposure indicator for digital radiography. Published July Accessed February 14, Bushong SC. Radiologic Science for Technologists: Physics, Biology, and Protection. 10th ed. St Louis, MO: Mosby Elsevier; Carlton RR, Adler AM. Principles of Radiographic Imaging: An Art and A Science. 5th ed. Clifton Park, NY: Thomson Delmar Learning; Carroll QB. Radiography in the Digital Age: Physics, Exposure, Radiation Biology. Springfield, IL: Charles C Thomas; Carter CE, Vealé BL. Digital Radiography and PACS. St Louis, MO: Mosby Elsevier; Practice Standards for Medical Imaging and Radiation Therapy. Radiography practice standards. American Society of Radiologic Technologists website. June 19, Accessed February 14, Seeram E. Digital Radiography: An Introduction for Technologists. Clifton Park, NY: Delmar Cengage Learning; Strategic Document. Version , April 11, Digital Imaging and Communications in Medicine website. Accessed February 14, 2013.