1. Rad Tech 265

2. 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.

3. 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

4. Digital Fluoroscopy Room

5. Flat panel vs. Image IntensifierII
Field coverage / size advantage to flat panel
Image distortion advantage to flat panel

6. Flat vs. Fat

7. 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.

8. 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.

9. 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.

10. Direct v. Indirect

11. Direct v. Indirect Resolution

12. Digital v Conventional Film

13. Digital v. Analog

14. Acquisition steps

15. 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.

16. Pixels (matrix)

17. Matrix size
32 x 32
128 x 128

18. Matrix size
128 x 128
512 x 512

19. Edge enhancement

20. Bits (gray scale)

21. Bits
4 bits
8 bits

22. Temporal averaging

23. Last image hold (lih)

24. DSA

25. DSA

26. DSA

27. Digital Tomosynthesis: reduce structured noise
Shift images to select plane
Add to create tomogram
Left
Right
3 cm above detector
9 views, + to - 30°
1.4 x dose
Digital radiographic imaging offers capabilities just not possible with conventional imaging. One of the major problems with projection imaging is the overlying and underlying normal anatomy superimposed on the pathology, often obscuring the visualization and detection of the cancer. A method for reducing this superimposition is to acquire multiple low dose images at several angular positions about the breast. Each image projects the content in the breast volume with different shifts depending on the distance of the object from the detector. With high-speed digital readout, each of the images can be processed with a variable shift and add procedure, that allows the creation of a geometric tomogram, that has the effect of reinforcing information at different depths. Multiple such images can be produced, and in areas of suspicion, the pathology (tumor) can be more readily detected. This comes with the price of more images to view, but on the other hand, could lead to a superior diagnosis that might save a patient an unneeded biopsy or provide guidance for early treatment of a pathological process.
Tomographic ramp
Niklason, L.T. et.al. Radiology 205:

28. Advantages/Disadvantages of CR

29. Advantages Potential lower patient dose when utilized properly
Higher DQE
Exam
Decrease in dose
UGI 5%
Pelvis
12%
Chest
14-20%
IVP
50%

30. Lower repeat rate
Better contrast resolution
No darkroom costs
Edge enhancement
Easy storage and retrieval

31. Disadvantages of CR Initial costs Lower spatial resolution
Collimation and centering are critical
Potential for overexposure
Exposure creep

32. Fuji ‘S’ Value Inversely proportional of plate exposure
1 mR at 80 kVp reads as an ‘S’ number of 200.
0.1 mR equals ‘S’ # of 2000
10 mR = ‘S’ # of 20
Ideal value is between

33. Kodak exposure index Directly proportional 1 mR at 80 kVp = 2000
Properly exposed

34. Underexposure with CR Will produce quantum mottle
This is why overexposure is ‘better’
Overexposure produces decreased contrast.
Think processor that is too hot.