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Rad Tech 265. More Digital Imaging. Digital Fluoroscopy. Radiation dose Patient dose for DF is significantly less than conventional fluoro At 7.5 pulses/second DF has a 75% drop in exposure At 3 pulses/sec a 90% reduction in dose The lower dose is obviously advantageous for pediatric work.

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Rad Tech 265

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Rad Tech 265

More Digital Imaging


Digital Fluoroscopy

  • Radiation dose

    • Patient dose for DF is significantly less than conventional fluoro

      • At 7.5 pulses/second DF has a 75% drop in exposure

      • At 3 pulses/sec a 90% reduction in dose

  • The lower dose is obviously advantageous for pediatric work.


Types of DF

  • The most common methodology is to add a CCD to the video chain.

  • A truly digital system can be either indirect or direct.

    • Pulse progressive fluoroscopy

      • Uses a high frequency generator with regular mA values


Digital Fluoroscopy Room


Flat panel vs. Image Intensifier

Flat

panel

II

Field coverage / size advantage to flat panel

Image distortion advantage to flat panel


Flat vs. Fat


Direct DF

  • In direct capture or direct to digital systems, x-ray energy is not converted to light. Instead, it is captured by a thin film transistor matrix of a material such as amorphous selenium that changes it into electronic signals. No intensifying screen is required, and none of the energy is lost through scatter, as happens when x-ray energy is converted to light on its way to display of an image.


Indirect DF

  • The indirect capture systems, including some flat panel displays that can be integrated into analog systems, are similar conceptually to the traditional film-screen technology. In one version, a cesium iodide scintillator captures the x-rays as they exit the patient and converts them to light. This light is turned into electronic signals by a matrix of amorphous silicon sensors. Each sensor corresponds to a single pixel of the image and is connected to a readout line. The signals from each cell in the matrix are read out in sequence row by row to obtain the image. High information transfer rates permit the display of moving images.


Indirect v. Direct

  • Notice, that the comparison of direct v. indirect digital fluoroscopy is the same as direct v. indirect digital radiography.

  • In the indirect systems, the photons are converted to a light image first before being digitized.


Direct v. Indirect


Direct v. Indirect Resolution


Digital v Conventional Film


Digital v. Analog


Acquisition steps


Image Manipulation with DF

  • Pan/zoom, background noise reduction, adjustable contrast and brightness, edge enhancement, quantitative analysis of vessel diameter and stenosis severity, subtraction capabilities, roadmapping, and bolus chase are common.


Pixels (matrix)


Matrix size

32 x 32

128 x 128


Matrix size

128 x 128

512 x 512


Edge enhancement


Bits (gray scale)


Bits

4 bits

8 bits


Temporal averaging


Last image hold (lih)


DSA


DSA


DSA


Right

Left

Shift images to select plane

Add to create tomogram

Digital Tomosynthesis: reduce structurednoise

  • 3 cm above detector

  • 9 views, + to - 30°

  • 1.4 x dose

Tomographic ramp

Niklason, L.T. et.al. Radiology 205:399-406


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