Digital Radiology Dr M A Oghabian Medical Physics Group Tehran University of Medical Sciences www'og

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Digital RadiologyDr M A OghabianMedical
Physics GroupTehran University of Medical
Scienceswww.oghabian.net
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Digital Radiology

• Aim To become familiar with the digital imaging
  techniques in projection radiography and
  fluoroscopy.

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Transition from conventional to digital radiology

• Digital images can be numerically processed
• Digital images can be easily transmitted through
  networks and archived
• Attention should be paid to the potential
  increase of patient doses due to tendency of
• producing more images than needed
• producing higher image quality not necessarily
  required for the clinical purpose

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What is dynamic range?

• Wide dose range to the detector, allows a
  reasonable image quality to be obtained
• Flat panel detectors (discussed later) have a
  dynamic range of 104 (from 1 to 10,000) while a
  screen-film system has approximately 101.5

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Characteristic curve of CR system
3.5 3 2.5 2 1.5 1 0.5 0
HR-III
CEA Film-Fuji Mammofine
CR response
Density
0.001 0.01 0.1
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Air Kerma (mGy)
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Analogue versus digital
Digital A given parameter can only have discrete
values
Analogue A given parameter can have continuous
values
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What is digital radiology?

• In conventional radiographic images, spatial
  position and blackening are analogue values
• Digital radiology uses a matrix to represent
  image
• A matrix is a square or rectangular area divided
  into rows and columns. The smallest element of a
  matrix is called pixel
• Each pixel of the matrix is used to store the
  individual grey levels of an image, which are
  represented by positive integer numbers
• The location of each pixel in a matrix is encoded
  by its row and column number (x,y)

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Digital radiology process

• Image acquisition
• Image processing
• Image display
• Importance of viewing conditions
• Image archiving (PACS)
• Image retrieving
• Importance of time allocated to retrieve images

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Digitizing conventional films

• Conventional radiographic images can be converted
  into digital information by a digitizer, and
  electronically stored
• Such a conversion also allows some numerical
  post-processing
• Such a technique cannot be considered as a
  digital radiology technique.

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Different number of pixels per image original
was 3732 x 3062 pixels x 256 grey levels (21.8
Mbytes). Here, resized at 1024 x 840 (1.6 MB).

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Scintillation-based DR

• Gadolinium Oxy-sulphide Detector

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Digital Radiography Systems

• Phosphor photostimulable plates (PSP).
• So called CR (computed radiography)
• Conventional X-ray systems can be used
• Direct digital registration of image at the
  detector (flat panel detectors).
• Direct conversion (selenium)
• Indirect conversion (scintillation)

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Computed Radiography (CR)

• CR utilises the principle of photostimulable
  phosphor luminescence
• Image plate made of a suitable phosphor material
  are exposed to X-rays in the same way as a
  conventional screen-film combination
• The CR image plate retains most of the absorbed
  X-ray energy, in energy traps, forming a latent
  image

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Computed Radiography (CR)

• A scanning laser is then used to release the
  stored energy producing luminescence.
• The emitted light, which is linearly proportional
  to the locally incident X-ray intensity is
  detected by a photo multiplier/ADC configuration
  and converted to a digital image
• The resultant images have a digital specification
  of 2,370 x 1,770 pixels (for mammograms) with
  1,024 grey levels (10 bits) and a pixel size of
  100 mm corresponding to a 24 x 18 cm field size

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The principle of PSP
ADC
PMT
CB
Trap
Excitation
Storage
Emission
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???????? ????? ??? ?????????????? (Europium
Activated Barium FluoroHalide) BaFXEu , (X Cl,
Br, or I)
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Casette and PSP
PSP digitizer
(Images courtesy of AFGA)
Workstation
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DR Detecting Systems
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• Direct vs indirect conversion detectors

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CCD Based Detection System
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Digital detector
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Amorphous Selenium Detector
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Digital fluoroscopy

• Digital fluoroscopic systems are mainly based on
  the use of image intensifiers (I.I.)
• In conventional systems the output screen of the
  I.I. is projected onto a video camera system or a
  CCD camera
• The output signals of the camera are converted
  into a digital image matrix (1024 x 1024 pixel in
  most systems).
• Some new systems start to use flat panel
  detectors instead of image intensifier.

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Tendency to increase dose ?

• For digital detectors, higher doses result in a
  better image quality (less noisy images)
• When increasing dose, the signal to noise ratio
  is improved
• Thus, a certain tendency to increase doses could
  happen specially in those examinations where
  automatic exposure control is not usually
  available.

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The digital radiology department

• In addition to the X-ray rooms and imaging
  systems, a digital radiology department has two
  other components
• A Radiology Information management System (RIS)
  that can be a subset of the hospital information
  system (HIS)
• A Picture Archiving and Communication System
  (PACS).

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Radiologist WorkStation
Broker
Voice Rec. Server
Transcription Pool
E-gate
HIS
RIS
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Data management
RIS
PACS

• We write a report!
• Link both PACS and RIS.
• Report compares Orders on RIS with Images on
  PACS.
• Report highlights RIS orders with No images!

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DICOM

• DICOM (Digital Imaging and Communications in
  Medicine) is the industry standard for transferal
  of radiological images and other medical
  information between different systems
• All recently introduced medical products should
  therefore be in compliance with the DICOM
  standard
• However, due to the rapid development of new
  technologies and methods, the compatibility and
  connectivity of systems from different vendors is
  still a great challenge

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DICOM format images

• Radiology images in DICOM format contain in
  addition to the image, a header, with an
  important set of additional data related with
• the X ray system used to obtain the image
• the identification of the patient
• the radiographic technique, dosimetric details,
  etc.