Radio Principles Theory 7 & 8 Flashcards

Question

DIGITAL IMAGING | What are the advantages of digital imaging procedures?

Answer 1

reduced long-term operating costs reduced image storage requirements high contrast resolution imaging exceptional imaging latitude. This directly relates to patient dose reduction, as the reduction in retakes due to poor factoring is virtually eliminated.

Answer 2

With digital imaging systems, the x-rays that reach the receptors form an electronic image which are manipulated by the computer and displayed as a matrix of intensities which have a dynamic range of values.

Answer 3

Refers to a layout of cells in rows and columns, with each cell corresponding to a specific location in the image. A number value is assigned to each cell, which represents its brightness. Each cell in the matrix is called a “pixel”. The number of pixels in the matrix helps determine the size of the matrix. For a given field of view (ie, image plate size), the larger the matrix the better the spatial resolution of the image (ie, the sharper the image). With our system, using a 35 x 43 cm cassette, we can process an image with a spatial resolution of 6 pixels/mm (2320 x 2826 matrix) or 10 pixels/mm (3480 x 4240 matrix). The latter matrix would provide better spatial resolution, or image detail, with the trade-off being larger image file size.

Answer 4

Refers to the number of shades of grey that can be represented by the image. A dynamic range of 21 would only have two shades (black and white). The dynamic range of the human eye is ~ 25 (i.e., 32 shades). The dynamic range of the x-ray beam leaving the patient exceeds 210. This range can only be fully appreciated by the computer. The greater the dynamic range, the more gradual the change in shades of gray will be, and the better the contrast resolution. Most digital imaging systems use a dynamic range of 28, 210, 212. Practically, each shade of grey is assigned a numeric value within the range allowed by the system (0 - 255 for 8-bit to 0 - 4095 for 12-bit). This value is “recorded” in each pixel, which in turn creates the various densities on the image. A large dynamic range allows for windowing of the image to optimize contrast and density overall, as well as at specific regions of interest e.g. when the AC joint is “burned out” on a shoulder view, you can manipulate the density of the image to enhance that particular region. Major advantage of digital over analogue imaging

Answer 5

Transitional system Cost-effective Allows for transforming existing analogue-based radiographic equipment into a digital format Film-screen portion replaced with imaging plate in a cassette that looks like traditional cassette Chemical-based film processing system replaced with dry laser-based digital system ``` The functional component of the imaging plate is the phosphor layer, which contains photostimulable phosphors – barium fluorohalide compounds (BaSrFBrl:Eu for our system). The phosphor layer will only maintain the information for a finite period of time, so it is recommended that they be processed within an hour of imaging. ``` The latent image is stored as trapped valence electrons, which are released by exposure to a small, high intensity laser beam. The released electrons return to their valence band, emitting blue light in the process. This light is viewed by a photomultiplier tube, which creates an electronic signal to be digitized and stored for display.

Answer 6

Another film-less system of radiography. Unlike CR, fixed detector arrays are used to produce the image rather than imaging plates. As such, no processor is required – the images are directly sent to the computer. This is the same method used for CT imaging. Detector array technology is highly complex, and will not be discussed in this class. There are two ways the image is acquired that will be touched on here: Fan beam vs. area beam collimation.

Answer 7

The x-ray beam is wide, but thin (~2-10mm). The advantage is greater radiographic contrast as scatter can be dramatically reduced. The disadvantage is that only a narrow band of the region can be imaged, so the patient must: a) be translated through the beam (this is the standard for CT scout views) or b) the tube is moved across the patient, who remains stationary (as with most current DR x-ray systems). This takes several seconds to perform, and patient motion can actually eliminate any advantage gained by scatter reduction

Answer 8

This is the same type of beam used in normal radiographic equipment. The complexity of this method does not lie in the collimation, but in the type of imaging receptor array needed to collect the large amount of information in the area being imaged. The advantages and disadvantages are reversed from fan beam collimation.