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 Field coverage / size advantage to flat panel Image distortion advantage to flat panel Flatpanel II

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 x 128

Matrix size 128 x x 512

Edge enhancement

Bits (gray scale)

Bits 4 bits8 bits

Temporal averaging

Last image hold (lih)

DSA

Digital Tomosynthesis: reduce structured noise 3 cm above detector 9 views, + to - 30 ° 1.4 x dose Tomographic ramp Shift images to select plane Add to create tomogram Left Right Niklason, L.T. et.al. Radiology 205: