DMI 50b digital radiography modified

Digital Radiography DMI 50B Kyle Thornton What Does That Mean? Digital has a higher dynamic range than film  The response is linear v sigmoidal  It provides more information at the low and high exposure levels  Digital v Computed v Direct Capture Radiography  Computed Radiography   Uses a cassette with an imaging plate Digital Radiography  Uses a linear array of radiation detectors • Similar to Computed Tomography  Direct Capture  Uses a solid-state radiation detector device Computed Radiography  A cassette is used  Contains a photostimulable phosphor imaging plate • Looks like an intensifying screen • Contains a layer of europium-doped barium fluorohalide crystals • When struck with x-rays, a new semistable state is produced • The latent image is stored on this plate The Imaging Plate  Made up of multiple layers         A polyester support layer The phosphor layer A clear protective layer Reflective layer Conductive layer Support layer Backing layer Bar code label on the bottom • Contains a number assigned to the image plate The Imaging Plate Very flexible  Can maintain a latent image for about 24 hours  Can be exposed to light  Some image degradation may occur with extended storage time and light exposure  The Image Reader      Converts the analog information from the latent image to a digital format The image plate is scanned by laser The portion of the plate struck by laser emits light The light is directed to photomultiplier tubes that convert it to digital electric signals Most modern readers can process 110 – 140 plates per hour Terminology  Rotation/inversion   Anatomic measurements   The ability to change the image presentation, or turn the image from a negative to positive The ability to measure certain areas of interest Short-term database functions  Allows user to locate images, create lists of images, image interpretation, and maintain teaching files More Terminology  Gradation Processing   Spatial Frequency   Controls the range of densities used to display structures on the image Controls the sharpness of boundaries between two structures of different densities Dynamic Range Control  Provides a wide diagnostic field • Allows for visualization of bone and soft tissue in a single image display Even More Terminology  Magnification   Allows enlargement of a specific area to enhance viewing and diagnosis Subtraction  Allows the user to enhance certain areas of interest while fading other areas from view • Enhancing from vascular detail while fading superimposing bony detail Image Storage Magnetic tape and optical disk  Each CR image contains app megabytes of data  CR Image Characteristics  Image resolution Dimension of the crystals in the imaging plate  Size of the laser beam in the reader  The image reading matrix  • CR images average – lp/mm • Standard film demonstrates – lp/mm Digital Radiography  X-ray tubes for DR have a high heat capacity   In excess of MHU DR does not use cassettes A radiation detector array is used  These detectors are gas-filled  The more detectors, the better the spatial resolution  Direct Capture Radiography  Image forming x-rays interact with cesium iodide phosphors Patient dose is less with this approach  Or   They interact with a thin layer of selenium  There is no spreading of light and spatial resolution is improved Digital Fluoroscopy  A computer and two video monitors are required One video monitor is used to edit patient data  One monitor displays the image   The operating console is more complex  Allows for the input of patient data Digital Fluoroscopy     The video monitor is often a 1000 line system as opposed to 525 The video signal is read in a progressive mode The electron beam of the of the TV camera tube sweeps the target assembly continuously from top to bottom in 33 ms There is no interlace of fields  The image is sharper with less flicker Digital Fluoroscopy and Dose Static images are made with a lower dose rate than with 105mm spot film cameras  Most DF x-ray beams are pulsed  The dose to the patient is about half that of conventional image intensified fluoroscopy  PACS  Picture Archive and Communication System Allows for the digitization of conventional radiographs  Allows for acquisition, interpretation, and storage of images  The Three Components of a PACS Display System  Network  Storage System  Display System    This is a cathode ray tube monitor Provides a workstation for the operator Must be very high resolution   Ranges from 256 X 256 – 1024 X 1024 This is lower than the spatial resolution of film • The operator is able to subtract, use edge enhancement, window-level, highlight, pan, scroll and zoom on the monitor The Image Matrix   A layout of cells in rows and columns Each cell is a specific location in the matrix   Each cell is called a pixel Each digital image consists of a matrix of cells   The matrix has various brightness levels The level of brightness depends upon the atomic number and mass density of the tissue that has received x-rays Network     A number of computers connected to one another In a PACS, many people have access to an image for different purposes Data from one unit to another is first digitized Images can be transferred to another workstation for interpretation  This is known as teleradiology Storage System PACS is able to archive  Images are not lost  The file room is replaced by a magnetic or optical memory device  Electronically, images can be recalled to any workstation in seconds  Pitfalls and Acceptance of CR and DR       The acceptance of the system is increasing  This is the future and in many imaging departments, the future is now! Department efficiency is increased It does not provide a traditional format Some resolution is lost Edge enhancement artifacts may actually create pathology Due to the increased latitude in image production, the patient may be exposed to too much radiation CR – DR and Patient Dose  If used correctly patient dose can be decreased CXR – 5% decrease  UGI – 5% decrease  IVP – 10% decrease  Pediatric examinations – 15 – 30% decrease  ... Mean? Digital has a higher dynamic range than film  The response is linear v sigmoidal  It provides more information at the low and high exposure levels  Digital v Computed v Direct Capture Radiography. .. levels  Digital v Computed v Direct Capture Radiography  Computed Radiography   Uses a cassette with an imaging plate Digital Radiography  Uses a linear array of radiation detectors • Similar... image to a digital format The image plate is scanned by laser The portion of the plate struck by laser emits light The light is directed to photomultiplier tubes that convert it to digital electric