Transcript Digital Radiology

Digital Radiology
Dr M A Oghabian
Medical Physics Group
Tehran University of Medical
Sciences
www.oghabian.net
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
HR-III
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CEA Film-Fuji Mammofine
Density
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1.5
CR response
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0.001
0.01
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Air Kerma (mGy)
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Analogue versus digital
Analogue: A given
parameter can have
continuous values
Digital: A given
parameter can only
have discrete values
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NUMERO
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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
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
PMT
ADC
CB
Trap
Excitation
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Storage
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Emission
‫كــريــستــال هــالـيــد فــلــوريــد بــاريــم فــعــال شــده بـا يــوروپــيــوم‬
(Europium Activated Barium FluoroHalide)
BaFX:Eu , (X= Cl, Br, or I)
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PSP digitizer
Casette and PSP
(Images courtesy of AFGA)
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Workstation
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).
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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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Results
•Modality Worklist Information
To Webserver
DICOM
Radiologist WorkStation
Images
Verified
Broker
Voice Rec. Server
HL7
HL7
HL7
E-gate
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HIS
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Transcription
Pool
RIS
PACS
Data management
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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RIS
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.
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