1. Digital Imaging
CHAPTERS 1, 4-7
CARTER

2. CHAPTER 1 Conventional radiography Film/screen system
Light exposes film
Film processed with chemicals
Film taken to radiologist for interpretation

3. Let’s compare rooms for
Conventional (Film) CR DR

4. Let’s compare image formation/acquisition
Film CR DR

5. Let’s compare image processing
Film CR DR

6. CR- Chapter 4 IP layers Protective Phosphor/active Reflective
Conductive
Color
Support
Backing
barcode
Protects phosphor
PSP-barium fluorohalide
Sends light forward when released in the reader
Absorbs/reduces static electricity
Absorb stimulating light (laser)/reflects emitted light
Protects the back of cassette
Match image with patient

7. Reading the IP Red laser light scans in a raster pattern at 2 eV
Laser scans multiple times as IP moves through reader =translation
Light produced –detected by photomultiplier

8. DIGITIZING PHOSPHOR STORAGE CENTER IS SCANNED
RELEASED ELECTRON ENTER DIGITIZER DIVIDES THE ANALOG SIGNAL INTO SQUARES (MATRIX).
EACH SQUARE IS ASSIGNED A NUMBER BASED ON THE BRIGHTNESS OF THE SQUARE
SQUARE IS CALLED A PIXEL

9. SPATIAL RESOLUTION Film screen = 10 line pairs per mm
CR =2.55 to 5 line pairs per mm (lp/mm)
Less detail in CR but more tissue densities seen given the appearance of better detail
Wider dynamic recording range

10. speed Film – determined by size and layers of crystals and phosphors
CR – amount of photostimulable luminescence given off = 100 film speed screen (approx)

11. EXPOSURE –CASSETTE BASED-chapter 5
What is the relationship between selecting the correct body part and computer interpretation of the image?
Too much kVp (above 120) and too little (below 45) can over excite or produce too little excitation of the phosphors
Does the pixel size of a 2000 x 2000 matrix change when using an 8 X10 vs
a 14 x 17 CRcassette?
How does the change in pixel size impact resolution?

12. MOIRE PATTERN
Grid lines from a stationary grid can cause a wavy artifact known as a moire pattern. The grid lines and the scanning laser run parallel

13. Exposure Indicators Exposure indicator number
Fuji, Philips, Konica – S number-indirect relationship
Kodak –Exposure index (EI)-direct relationship
Page 88 tables 5-1 and 5-2

14. HISTOGRAM
Graphic representation of the numerical tone (grays/blacks/whites) of an x-ray exposure
Important in CR
Four modes of date recognition
Automatic data recognition
Semiautomatic mode
Multiple manual selection mode
Fixed mode

15. OTHER ARTIFACTS Plate artifacts Plate reader artifacts
Adhesive tape residue
cracks
Plate reader artifacts
Line patterns
Plate reader loads multiple IP in one cassette
Image processing artifacts
Incorrect erasure (ghosting)
moire
Printer artifacts
White lines

16. CASSETTELESS -Chapter 6
Direct and indirect
DR plate (amorphous selenium) or(a-Se)-converts radiation into an electrical signal –CCD or silicon detectors
Signal stored in a Thin film transmitter (TFT)

17. INDIRECT DIRECT Two step process X-rays convert to light
Light converted to electrical signal
Sent to TFT
X-rays converted directly to an electrical signal
Sent to TFT

18. DQE Detective Quantum Efficiency
Ability to convert an x-ray signal into a useful image
Of the following-which do you think has the most efficient DQE?
Film or CR or indirect capture DR or direct capture DR?

19. Digital Radiographic Image Processing and Manipulation
Chapter 7

20. CR image *sampling (*conversion from analog to digital)
Histogram
X axis = amount of exposure read
Y axis = number of pixels for each exposure
Low kVp= wider histogram
High kVp = narrower
Histogram is anatomy specific

21. NYQUIST THEOREM
When sampling(converting from analog to digital) a signal, the sampling frequency must be greater than the bandwidth of the input signal

22. Sample? Try this at home

23. ALIASING
When the spatial frequency is greater than the Nyquist frequency and the sampling occurs less than twice per cycle, information is lost causing a moire effect.

24. Automatic Rescaling
Fixing the image
Why is this dangerous?

25. LUT and Windowing
Automatic rescaling to achieve appropriate contrast on an image

26. LATITUDE
Find the percentage the exposure can be greater or less than before it impacts the image in CR

27. IMAGE MANIPULATION cont.
Window- how light or dark an image should be
Level-contrast
Background removal or shuttering
Removing the unexposed borders or to blacken the white borders

28. MTF Modular Transfer function
Reproducing the spatial resolution of an object as a diagnostic image
100% of the spatial resolution of the object can never be perfectly reproduced – even with DR and CR – why? -See Bushong – pgs

29. acronyms PSP CRT ADC IP CR DR PACS SNR CNR 10. CCD 11. FOV 12. LUT
13. DICOM
14. RIS
15. HIS
16. TFT
17. DQE

30. Photostimulable phosphor-europian activated barium fluorohalide
Cathode-ray tube or computer monitor
Analog to digital converter
Imaging plate
computed
/digital radiography
Picture archiving communication systems

31. SIGNAL TO NOISE RATIO PG 410 –BUSHONG The higher the signal the less the noise.
CONTRAST TO NOISE RATIO can be manipulated until noise becomes too apparent-limited by the SNR
Charge coupled device- crystal silicon- small, replaces vidicon in fluoro, device used in DR
Field of View –how much of the patient is imaged in the matrix
Look up Table – plotting grays on a scale
Digital imaging and communications in medicine -blending PACS and other imaging modalities
Radiology Information system
Hospital Information system

32. Thin Film Transmitters- indirect and direct conversion detector in DR
Thin Film Transmitters- indirect and direct conversion detector in DR. Stores electronic charge (from converted light) before computer processes it.
Detective Quantum Efficiency converting x-ray intensities into a radiographic image