Radiography: Past and Present

Welcome to this web based training on Radiography Past & Present. Within this training we will explore radiography, how it has evolved over the years, and the differences between analog and digital imaging. You have now completed the course Radiography: Past and Present.  You should now be able to: - Identify significant innovations related to radiography - Compare the components of analog imaging versus digital flat detectors - List the steps included in the imaging process - Identify methods to reduce dose - Identify and manipulate functions for image processing - Discuss Workflow improvements using digital radiography   Upon completeion of this course you will be able to: - Identify significant innovations related to radiography - Compare the components of analog imaging versus digital flat detectors - List the steps included in the imaging process - Identify methods to reduce dose - Identify and manipulate functions for image processing - Discuss Workflow improvements using digital radiography   Below is an example of film radiography from 1912.  Glass plates were used as a base since they were able to support the emulsion and they were transparent.  This is also the source behind the phrase "flat plate". Film emulsion is composed of silver bromide crystals suspended in a  gelatin Silver bromide crystals are about 1 - 5 microns in size Once coated on the film base, the emulsion layer is about 5 - 10 microns thick   In the 1960's flexible polyester became the gold standard for radiography.  Film base made from polyester is still used today.   The intensifying screen intensifies the action of the x-rays.  It does this by emitting visible light which would expose the x-ray film.  This has two advantages: - the amount of radiation required was reduced - the contrast of the image was improved Challenges for X-ray films include:  Film has to do it all - it was used as the image receptor - it was used to display the image on the view box - used when archiving a patient's study Usually there was only one copy.  If something happened to that film there was no replacement which meant there was no record of that exam.   - Computed radiography utilizes a cassette - CR does not use film, only an imaging plate - The plate is exposed and then sent to a reader - The reader scans the plate to bring out the image - Computed radiography is based on the photostimulation principle - CR cassettes are inserted into a CR reader where the image is read by a laser - The latent image is converted to a visible light image then displayed on a monitor - Imaging plates must be erased so they can be used again Computed Radiography Workflow - The CR imaging cassette acquires the image - Once read, the display of the image is seen on a monitor - Archiving of the image is done in a digital format - CR imaging plates operate and respond best in a certain kV range Digital imaging detectors can be fixed in a table or wallstand, or they can be mobile. The operating principle for digital detectors is different.     DR technology uses a process that converts x-rays into an electronic signal The electronic signal is then displayed onto a monitor as the image This is known as the Opto-Direct principle Film Cassette Workflow 1.  Cassettes used in procedure room 2.  Cassettes carried to darkroom passbox 3.  Films processed in film processor  4.  Films critiqued by censor/technolgist 5.  Films taken to film library 6.  Films taken to reading room Direct exposure on film  - 60 kV, 100 mAs on AP ankle Rare earth intensifying screens with film (400 speed)  - 55 kV, 5 mAs on AP ankle CR imaging plates (250 speed)  - 60 kV, 4 mAs on AP ankle DR imaging plate (400 speed)  - 50 kV, 2 mAs on AP ankle   Exposure made to the detector Not an indication of the exposure the patient received Affected by SID, kV, mAs, filtration Expressed in a numerical value Direct relationship – as the exposure is increased, the EXI increases     EXI is a global standard set forth by the IEC EXI is calculated from the pixels that have anatomical data on them An exposure of 1 micro-gray will yield an EXI of 100 An exposure of 2.5 micro-gray will yield an EXI of 250 EXI can be displayed as Clinical or Physical. Recommended to use Clinical since Physical would only be used for medical physics and constancy testing. Once the Clinical EXI value is selected, then that information will be a part of each image as well as part of the DICOM header. The EXI information will then go along with the image even on the network. The majority of digital X-ray detectors provide a linear, direct proportional relationship between image receptor, dose, and signal response.     The increased dynamic range of DR images implies that all of the anatomy has density values that can be displayed and visualized when compared to conventional systems, as we can see on the current image. You also have the ability to compensate for underexposures and overexposures through postprocessing functions.   What you see is what you get...   CR–QC Review station provides the following functionalities: - Annotation - Image rotation/flip - Change Look up Tables (LUT) - Change window values DiamondView allows you to see adaptive spatial filtering as well as visualize bony detail and skin line on extremities. Harmonization reduces the dynamic range of the image.  It does this by compression of coarse structure contrast. Notice how the very bright whites and very dark blacks are gone on the image on the right. . Advanced Image Processing Functions - Annotation/graphics - Look Up Tables (LUT’s) - Image flip/rotation - Window values Annotation Look Up Tables (LUT) Effect of Gradation Curve (LUT)            Image Flip/Rotate & Window Values   MTF Features   The ability to transfer contrast from the object being radiographed to the image receptor at a specific resolution This leads to spatial frequency and a system’s ability to display image resolution or detail   Usually displayed in line pairs/mm   Siemens digital detector – 3.4 line pairs/mm With film cassettes, they would travel to the procedure room, to the dark room for the film to be processed. Then the films would have to be QC’d by the technologist, then taken to the film library to be put in the patient’s film jacket or matched up with a previous exam. It would then sent to the reading room.   With CR the imaging plates are used in the procedure room and then brought to the CR reader where the imaging plate is read. Once read, the imaging plate will be erased. After reviewing, the image is sent over the network to the reading room or printed onto film. Digital detectors are far more efficient. They eliminate the tasks associated with cassettes. The DR image is displayed within 8 seconds after the exposure is made. The detector does not need to be erased, and the image, once reviewed, is sent over the network to the reading room. DQE = Detector Quantum Effeciency Highest possible image signal; lowest possible noise   The benchmark in describing the efficiency of a digital imaging plate Expressed as a %; the higher, the better   Captures radiation and converts it to visible light and an electronic signal   Increases signal and reduces noise