Direct to Digital Radiography or Direct Capture Radiography

1
Direct to Digital Radiographyor Direct Capture
Radiography

• Bushong Ch. 26 29
• Carter Ch. 6

2
Late 1990s

• A new approach to imaging appeared
• DR or DDR or Direct Capture imaging
• NEW - Wireless DR Detector

3
Directed Digital Radiography(DDR)

• Directed digital radiography, a
• term used to describe total
• electronic imaging capturing.
• DR is hard-wired or Wi-Fi to the image processing
  system. Eliminates the need for an image
  plate altogether.

4
(No Transcript)
5
DDR Systems
6
IMAGE CAPTURE

• CR
• PSP photostimulable phosphor plate
• REPLACES FILM IN THE CASSETTE
• DR NO CASSETTE LIGHT or E-
• Captured directly
• On to a transistor, photodiode or charge-coupled
  device
• Sent directly to a monitor

7
DIRECT RADIOGRAPHY

• uses a TFT, CCD, or photodiode to receive image
  data (like bucky)
• that captures and converts x-ray energy
• directly into digital signal
• seen immediately on monitor
• then sent to PACS/ printer/ other workstations
  FOR VIEWING

8
CR vs DR

• CR
• imaging plate
• processed in a Digital Reader
• Signal sent to computer
• Viewed on a monitor

• DR
• CCD, TFT or photodiode receiver (like bucky)
• directly into digital signal
• seen immediately on monitor

9
Digital Radiography
DDR
CR
Direct Capture
Indirect Capture
Computed Radiography (CR) - PSL
Direct-to-Digital Radiography (DDR)-Selenium
Direct-to-Digital Radiography Silicon Scint.
Laser Scanning Digitizers
10
Digital Radiography
Fundamentals of Digital Radiography

11
Flat-Panel Detectors

• Flat-panel detectors consist of a photoconductor,
  amorphous selenium (a-Se), which holds a charge
  on its surface that can then be read out by a
  TFT. This category also includes silicon and CCD
  detectors.

12
Capture Element

• Where the remnant photons are captured.
• DR Cesium iodide (CsI), Gadolium oxysulfide
  (GdOS), or Amorphous selenium (a-Se).
• And for CR? What is the name of the compound?

13
Direct vs Indirect Conversion

• In direct conversion, x-ray photons are absorbed
  by the coating material and immediately converted
  into an electrical signal. The DR plate has a
  radiation-conversion material or scintillator,
  typically made of a-Se. This material absorbs
  x-rays and converts them to electrons, which are
  stored in the TFT detectors.

14
Collection element

• Collects converted x-ray signal.
• Types Photodiode, A charge-coupled device (CCD),
  or A thin-film transistor (TFT).
• Photodiode CCD collect light. TFT is charge
  sensitive and collects E-.

15
TFT

• The thin-film transistor (TFT) is a
  photosensitive array made up of small (about 100
  to 200µm) pixels. Each pixel contains a
  photodiode that absorbs the electrons and
  generates electrical charges.

16
Active Matrix Array (AMA)Pixels are read
sequentially, one at a time

• Each TFT or CCD detector represents a pixel
• DEL charge collecting detector element

17
DR

• A field-effect transistor (FET) or silicon TFT
  isolates each pixel element and reacts like a
  switch to send the electrical charges to the
  image processor.

18
Amorphous Selenium

• No scintillation phosphor is involved
• The image-forming x-ray beam interacts directly
  with amorphous selenium (a-Se),
• producing a
• charged pair.

19
Amorphous Selenium

• The a-Se is both the capture element and the
  converting element.
• a-Se is a direct DR process by which x-rays are
  converted
• to electric signal

20
DDR only using amorphous selenium (a-Se)

• The exit x-ray photon interact with the a-Si
  (detector element/DEL). Photon energy is trapped
  on detector (signal)
• The TFT stores the signal until readout, one
  pixel at a time

21
Indirect Conversion

• Indirect conversion is a two-step process x-ray
  photons are converted to light, and then the
  light photons are converted to an electrical
  signal.
• A scintillator converts x-rays into visible
  light. The light is then converted into an
  electric charge by photodetectors such as
  amorphous silicon photodiode arrays or
  charge-coupled devices (CCDs).

22
CCD Array with a scintillation phosphor
23
Direct vs Indirect DR
24
Charge-Coupled Device

• CCD, which is the light-sensing element.
• The CCD is a silicon-based semiconductor
• has three principal advantageous imaging
  characteristics sensitivity, dynamic range, and
  size.

25
Sensitivity

• is the ability of the CCD to detect and respond
  to very low levels of visible light
• This sensitivity is important for low patient
  radiation dose in digital imaging.

26
Coating for DR

• AMORPHOUS SILICON (indirect)
• AMORPHOUS SELENIUM (direct)
• See pag 372 in Carltons

27
Dynamic range

• is the ability of the CCD to respond to a wide
  range of light intensity, from very dim to
• very bright
• DR should
• lower patient
• dose

28
Size

• A CCD is very small, and this makes it highly
  adaptable to uses in radiology
• The CCD itself measures approximately 1 to 2 cm,
  but the pixel size is an exceptional 100 100
  µm!

29
Coupling Element

• Transfers the x-ray signal to the collection
  element.
• Ex A lens or fiber optic assembly, a contact
  layer, or amorphous selenium.

30
DEL Digital Value

• Digital Value depends on
• Charge collected by DEL.
• Bit depth
• 10 bit 1 1024
• 12 bit 1 - 4096

31
DEL collects x-raysignal
32
F/S DDR imaging systems
33
Unlike CR plates, only the exposed pixels
contribute to the image data base.

• One exposure Detector Readout

34
TFT Array Detectors

• Detector is refreshed after exposure
• If no exposures are produced. . . detector
  refreshed every 30 45 sec
• Built in AEC, An ion chamber between grid and
  detector

35
Advantages/Disadvantages

• CsI phosphors have high detective quantum
  efficiency (DQE) lower patient dose
• DQE of x-rays absorbed by the phosphors
• a-Se only there is no spreading of light in the
  phosphor better spatial resolution

36
Dynamic range

• is the ability of the CCD to respond to a wide
  range of light intensity, from very dim to
• very bright
• DR should
• lower patient
• dose

37
DR

• Initial expense high
• very low dose to pt due to the high DQE over CR
  and F/S. Fewer photons required to produce and
  image.
• image quality of 100s using a 400s technique
• Therfore ¼ the dose needed to make the image

38
Patient Dose

• Important factors that affect patient dose
• DQE when using CsI systems
• Both systems fill factor

39
Digital Image Postprocessing

• Process
• Annotation
• Window and level Magnification
• Image flip
• Image inversion
• Subtraction

• Results
• Label the image
• Expand the digital grayscale to visible
• Improve visualization and spatial resolution
• Reorient image presentation
• Make white-black and black-white
• Improve image contrast

40
Postprocessing

• Region-of-interest
• Edge enhancement
• Pan, scroll, and zoom

41
DDR has all the advantages of CR imaging
techniques

• Post processing PACS

42
DIGITAL IMAGE STORAGE
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
(No Transcript)
48
Redundant Array of Inexpensive Disk(RAID) 
49
(No Transcript)
50
(No Transcript)
51
(No Transcript)
52
DR Image Quality

• Pixel Pitch
• Fill Factor
• Amorphous Selenium vs Amorphous Silicon

53
 

• (RAID) Redundant Array of Inexpensive Disk
• DICOM
• PACS
• HISTOGRAM
• ALGORYTHM
• HIS/RIS

54
IMAGE TRANSMISSION
55
(No Transcript)
56
(No Transcript)
57
(No Transcript)
58
(No Transcript)
59
(No Transcript)
60
(No Transcript)
61
(No Transcript)
62
(No Transcript)
63
(No Transcript)
64
PACS
Questions?