Digital Radiology

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Digital Radiology

•AimAim: To become familiar with the digital : To become familiar with the digital imaging techniques in projection radiography imaging techniques in projection radiography and fluoroscopy.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 neededproducing 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

HR-IIICEA Film-Fuji Mammofine

CR response

Air Kerma (mGy)

0.001 0.01 0.1 1

3.5

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2.5

2

1.5

1

0.5

0

Den

sity

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Analogue versus digital

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Digital: A given Digital: A given parameter can only parameter can only have discrete valueshave discrete values

Analogue: A given Analogue: A given parameter can have parameter can have continuous valuescontinuous values

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C1

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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).

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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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

Computed Radiography (CR)

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The principle of PSP

Excitation Storage Emission

CB

Trap

ADCPMT

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بــاريــم فــلــوريــد هــالـيــد كــريــستــاليــوروپــيــوم بـا شــده فــعــال

(Europium Activated Barium FluoroHalide )BaFX:Eu , )X= Cl, Br, or I)

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18(Images courtesy of AFGA(

PSP digitizer Casette and PSP

Workstation

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DR Detecting Systems

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21•Direct vs indirect conversion detectorsDirect 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 fluoroscopyDigital 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).

32HISHIS

BrokerBroker

RISRIS

Voice Rec. ServerVoice Rec. Server

TranscriptionTranscriptionPoolPool

Radiologist Radiologist WorkStationWorkStation

ResultsResultsTo WebserverTo Webserver

DICODICOMM

Images Images VerifieVerifiedd

HL7HL7

E-gateE-gate

HL7HL7HL7HL7

•Modality Worklist InformationModality Worklist Information

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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!

PACS RIS

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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 imagethe identification of the patientthe radiographic technique, dosimetric details,

etc.