Topics covered/ Table of contents
1)Types of radiography
2) Film screen radiography ,digital radiography
3) Computed and direct digital radiography
4) Process of imaging in direct digital radiography
5) Advantages of direct digital radiography
6) Advancement in direct digital radiography
Film screen radiograph
Film itself act as
Medium for image storage
Used for decades in past.
Now largely replaced by digital
Film screen radiography cont...
Uses intensifying screens
Film is placed between two
Screens emit light when x-rays
strike them causing change in
Film is processed chemically
Limitations of film screen radiography
No Manipulation – Cant be manipulated i.e. magnification,
cropping ,windowing, etc are not possible
Storage – Image quality deteriorates over time
- Requires large space and more management for
Transmission – loss of quality during transmission.
- Loss of quality during duplication
When digital detectors are used
to capture information then its
called digital radiography
Films and Screens are replaced by
• Image reception ,display and
storage are done separately.
Advantages of digital radiography
Manipulation – can be magnified ,compressed ,cropped
Storage – stored in digital files requiring much less space
- no reduction in quality on long time storage
Communication – Can me made into multiple copies without
loss of. quality
- Can be easily send anywhere through PACS
Two Types of digital radiography
Computed radiography system i.e. CR
Direct digital radiography system i.e. DR
Computed radiography system CR
Operational in Radiology
department of PMCH
CR contains photo illuminable
Phosphor plates acting as
detecting and storage layer in
place of conventional films.
Coating of europium activated
barium fluorohalide is used in
these phosphor plates.
Process of imaging in computed radiography
On exposure to X ray energy is
absorbed and stored temporarily
by crystals in the plate
Readout process – plate is scanned
with high energy laser beam and
energy stored in .crystals is set free
in form of light photons.
Light thus emitted is collected and
converted into digital images.
Computed Radiography cont...
Imaging plate can be reused after exposure to white light
It can be easily integrated into existing conventional setup and
produce digital images that can be stored and communicated
Imaging plates are expensive and can easily get damaged by
Direct digital radiography
No cassettes reading or film
Signal from X ray receptor is
directly send to computer for
Minimal work is required by
Direct digital radiography
Has flat panel detectors or
charge couple devices which are
connected to computers with
Image is available within
seconds of image capture
But needs new installation in X
DR Readout process
Charges are generated by Direct
and indirect conversion process
Sensed by electric readout
mechanism present in thin film
Analog to digital conversion
performed and images produced
Types –Direct digital radiography
Direct digital radiography can be
of two types
1) Direct conversion type –
amorphous selenium directly
convert X-rays into electrical
Types – DR
2)Indirect conversion type –
involves two steps.
-X ray to visible light by scintillator
-Visible light to charges by photo
Thin film transistors
Used in both direct and indirect conversion
Structure – Deposited in multiple layer on glass substrate.
lowest layer has readout electronics
higher layer has charge collectors
X ray element and light sensitive element are
deposited on top layer
Structure- thin film transistor
Direct converter Indirect converter
X ray element
charge collector array
x ray element
light sensitive element
charge collector array
Thin film transistor cont..
Encased in protective layer for insulation
connected to computers through wire for image reconstruction
Flat panel detector -
Available in size 43 ×43
cm,41×41 cm and 43×35 cm
Image can be generated within
Uses scintillators to convert x
ray into visible light.
Visible light is converted into
charge by photo iodide array.
Charge Collected at photo
iodide is converted to digital
signal by readout electronics.
Types ; scintillator
visible light emitted can spread to
Consists of caesium iodide crystals
on detectors which are parallel
needles channel most signal
directly to photo iodide layer.
Raw data is processed by computers and converted into
Processing includes removing technical artefacts and
Removing unwanted signals called noise
Windowing and reversing of contrast is done for better view
Advantages of DR over CR
Quick image development, within 10 sec
Very less work done by technician so less manpower is
Less radiation dose than film screen or conventional
Image transmission in DR
As image is generated within seconds it can be duplicated and
sent to various departments simultaneously.
Helps in Inter department coordination for better patient
Advancements in Direct digital radiography
Wireless DR system – Data is
transferred to computer without
wire. Useful in difficult regions like
axilla andTM joint
Mobile DR system- useful for
Advancement in DR system
Automatic image stitching – image reconstruction after
multiple sequential exposure. Useful for imaging large
anatomical regions like whole spine in a single film.
Computer aided diagnosis- suspicious looking areas are
marked by computer for review by radiologist.