A Van Cements in Digital

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ADVANCEMENTS IN

DIGITAL RADIOGRAPHY

Moderator :Mr. Ram Singh (Lecturer)

Deptt. of Radio-Diagnosis & ImagingPGIMER, Chandigarh-160012

Presented By:Debendra Prasad Gupta

M. Sc. Med. Tech. (Radiodiagnosis) – 1st Year Student

Deptt. of Radio-Diagnosis & Imaging

PGIMER, Chandigarh-160012

12th September, 2009

1



DIGITAL RADIOGRAPHY:

Definition: -

It is defined as the image data acquired from

the numeric value i.e. in discrete binarydigits by use of computers .

Whereas in Conventional Radiography

information is represented in the analog or

continuous form rather than a discrete

fashion.2



History: - In 1980 researchers at “ Fuji Laboratories”

developed an erasable X-ray imaging device

based on the x-ray excitation of a phosphor layer

and subsequent reading of the stored image data

with the help of infrared laser (i.e.

Photostimulable Luminescence).

Results showed that the imaging plate was moresensitive than conventional X-ray Film with

intensifying screens.

3



Since the clinical use of x-rays in 1895, majority of radiographic examinations have been carried out by the

conventional method.

The beam is projected through the patient and the transmitted

beam, which has information about the body structures, ismade to strike the cassette containing the film and the

intensifying screens. This way the latent image is produced on

the film.

The latent image can be made visible and permanent by processing it with suitable chemicals.

This conventional method of obtaining radiographs has

dominated the field of radiography for many years. But now, it

has been realized that the FS system has its own limitations.

INTRODUCTION:

4



LIMITATIONS OF FS :

1. After the film has been exposed, the information contentscannot be enhanced.

2. If the radiograph is too dark (Over-Exposed) or too light

(Under-Exposed) either by Exposure Factor, Film Fault or

Processing Faults, it has to be repeated i.e. No Post-Processing option which results in extra exposure to the

patient.

3. The completion of the examination is delayed as the film

has to be processed to convert the latent image into a permanent one.

4. A magnifying glass may be required to see very small

structures in detail i.e. No Zooming & Panning Option.

5



5. Copied radiographs are of inferior quality than original ones.

6. The film is a physical object and so it requires considerable morespace for storage i.e. Storage & Retrieval Cost.

7. Films can only be in one place at a time and they also get

deteriorated with passage of time.

8. Film can not be stored for longer time when required.

9. Dynamic range of x-ray film is limited (i.e. 0.2 – 3).

These limitations can be overcome by the incorporation of

computer technology into the diagnostic x-ray imaging.

With DR system conventional analog information is converted into

digital form, processing the digital data and displaying the image

on the monitor that surprisingly looks like a conventional image.

Cont…

6



MILESTONE IN DIGITAL

RADIOGRAPHY:

Year Year Development: -Development: -

19801980 Scan Projection Radiography (SPR).Scan Projection Radiography (SPR).

19831983 Computed Radiography (CR), Storage Phosphors.Computed Radiography (CR), Storage Phosphors.

19901990 Charge-Coupled Device (CCD) Slot-Scan DirectCharge-Coupled Device (CCD) Slot-Scan Direct

Radiography (DR).Radiography (DR).

19941994 Selenium Drum Direct Radiography (DR).Selenium Drum Direct Radiography (DR).

19951995 Amorphous Silicon - Based–Cesium Iodide ( Scintillator )Amorphous Silicon - Based–Cesium Iodide ( Scintillator )

Flat-Panel Detector in Indirect DR.Flat-Panel Detector in Indirect DR.

19951995 Selenium-Based Flat-Panel Detector in Direct DR.Selenium-Based Flat-Panel Detector in Direct DR.19971997 Amorphous Silicon-Based - Gadolinium ( Scintillator ) Flat-Amorphous Silicon-Based - Gadolinium ( Scintillator ) Flat-

Panel Detector in Indirect DR.Panel Detector in Indirect DR.

20012001 Dynamic Flat-Panel Detector for Digital Fluoroscopy inDynamic Flat-Panel Detector for Digital Fluoroscopy in

DSA.DSA.7



Digital Radiography (DR)

SPR

NaI – Scintillator

Photodiode

Indirect

Conversion

Storage Phosphor

Plate (IP)

BaFX:Eu+2

CR

Indirect Conversion Direct Conversion

DR

Photoconductor +

TFT (a:Se-DFPD)

Selenium Drum

Scintillator + Photodiode

(a:Si) + TFT (IFPD)

Scintillator + CCDCsI:Tl or CsI:Na &

Gd2O2S:Tb3+

According to the nature, design and function of the detector the

Digital radiography can be divided mainly in the following way: -

8



SCAN PROJECTION SYSTEM:

Earlier Scan projection radiography (SPR) was

performed on a computer tomography CT system by

translating the patient through the CT gantry aperture.

It is based on CT–Technology, another projection

radiography technique was developed using a narrowfan beam of X-Rays intercepted by linear array of

detectors called “Scan Projection Radiography”.

Basically, SPR involves the use of the existing CT-

Gantry & Computer to generate an image that looks

surprisingly like Conventional Radiography.

9



The X-ray beam is shaped into a fan by

collimators that confine the beam to a 2-10

mm thickness through on arch of 300 – 450.

There are two collimators: -

1) The pre-patient collimators which shape the beam,

reduced scatter radiation & control patient dose.

2) The post-patient collimators which further reduce

the scatter radiation rejection.

SPR Cont…

10



PRINCIPLE OF S.P.R.:

X-Ray beam after passing through patient isdetected by detector array. The signal have been image information of the body parts aretransferred to the computer where they get

digitized & processed to reconstruct theimage.

To obtain a complete image of the body part,

X-Ray tube & detector assembly remainsstationary & the patient is translated throughthe X-ray beam or alternatively patientremains stationary, while the X-Ray tube-detector assembly translates .

SPR Cont…

11



COMPONENTS OF S.P.R. SYSTEM:

1. X-Ray Tube.

2. Pre-Patient Collimator.

3. Post-Patient Collimator.

4. Detector Array.

SPR Cont…

12



X-RAY TUBE ASSEMBLY:

X-Ray tube of high heat loading capacityusually above 1 MHu is required because of long imaging time. Usually 20 – 50 cm

body part of patient is imaged at atranslation speed of 1 – 20 cm/s.

Two types of detector can be used: -

1. A Gas Filled.2. Scintillation Detectors couple with Solid

State Photodiode, i.e. CCD.

SPR Cont…

13



Advantage: -

In SPR X-ray beam is collimated in a fan x-ray beam by Pre-

Patient & Post-Patient Collimators . i.e.: -

1. High Amount of Associated Scatter Rejection.

2. High Radiographic Image Contrast.3. High Dynamic Range (i.e. Low Contrast Detectibility).

4. Image Manipulation.

Disadvantages: -1. Scanning Time is More.

2. Poor Spatial Resolution &

3. More Radiation Dose to the patient.

SPR Cont…

14



ADVANCEMENT:

At the present time, SPR is re-emerging with

some modification as a promising adjunct to

Digital Mammography Tomosynthesis

(DMT).

The purpose of all forms of Tomography is

to improve image contrast, and i.e. the goalof Digital Mammography Tomosynthesis

(DMT).

15



COMPUTED RADIOGRAPHY:

Definition: - Digital way of doing General Radiography with

Conventional X-ray machines except ConventionalScreen/Film and dark room is known as Computed

Radiography.

Principle: -

It is based upon Photostimulated Luminescence in

which the radiographic data is captured from aconventional X-ray machine and processed the datadigitally to produce crisp and high qualityradiographic images.

16



The CR Cassette is exposed with transmitted x-rays beam in a similar

fashion as the conventional cassette. The latent image is formed in the phosphor layer of the Imaging Plate in the

form of Electrical Charge .

Then the latent image is made visible on monitor by processing or scanned

and read that exposed imaging plate by a laser scanning device called

Image Reader. The output signal from the image reader is fed to an image array processor

where the digital gray – scale image is formed.

The digital image generated by the image reader is stored temporarily on a

local hard disk which is processed a/c to need and the resulting image can

be displayed either as soft (Video Display) copy on monitor or send itdirectly to laser printer that make hard (Film) copies of the digital image.

The digital image can then be stored on an optical or magnetic disk for long

term archiving or connected to the PACS through DICOM for Tele-

radiology.

Working:

17



18



19



COMPONENTS OF THE C.R.

SYSTEM:

3.) Image Reader: -

4.) Image Processor: -

Cassette With Imaging Plate

2.) Image Recorder: -

1.) General X-ray Equipment: -

20



Material: -• Body: - ABS ( Acrylonitryl butadiene styrene).

• Corners: - PUR (Polyurethane rubber).

• Hinges: - PP (Polypropylene).

• Inner lining: - Felt.

Sizes: -• Same as that of conventional cassette.

Identification: -

• Embedded memory chip.

•

Contactless RF identification. Backscatter Protection: -• 150 μm lead.

CASSETTE:

21



THE IMAGING PLATE ( IP ):

The Imaging Plate (IP) is also known as ComputedRadiography (CR) Plate or Storage Phosphor Screen

(SPS) or Photostimulable Phosphor (PSP) detector to

record the radiographic image in place of the

conventional film/screen cassette.

The imaging plate is housed in a rugged cassette &

appears similar to a screen/film cassette.

It is available in the same sizes as conventionalcassettes.

It is handled in the same manner as a screen/film

cassette.22



It is not loaded & unloaded in a dark room. Rather, it is

handled in the manner of a screen/film daylight loader. A typical IP can store a latent image for a considerable

period of time. However, it will lose about 25% of the

stored signal b/w 10 min. to 8 hrs after an exposure

resulting in the loss of energy through spontaneous

phosphorescence.

It retains the image for 24 hours, but some degradation

may occur with passage of time. Imaging plate shows a linear response to the intensity

of x-ray exposure over a broad range.

Cont…

23



CONSTRUCTION OF IMAGING

PLATE (IP):

Protective layer : -

- Fluorinated Polymer Material

Phosphor Layer: -- Ba FX: Eu +2 , 0.4mm thick.

Anti-halo Layer + Reflecting Layer

- Prevent laser light from passing through.

Base:-- PET- Polyethylene teraphtalate

Backing Layer: -

- Protects the base from damage &

reduces back scatter X-rays.

- 150 μm lead. 24



THE IMAGING PLATE: A Protective Layer composed of “Fluorinated Polymer”

which make resistant to the abrasion, damaged & scratchescaused on the IP during storage and transfer.

The Phosphor Layer consist of a family of Photostimulable Phosphor crystals i.e. BrFX:Eu2+ where X can be any of halogens i.e. Chlorine (Cl), Bromine (Br) or Iodine (I) or an

arbitary mixture of them. A typical Phosphor Layer composed of about 85% - BaFBr

& 15% - BaFI , activated with a very small quantity of Europium (Eu) as activator in crystal.

This Europium activation procedure, also called doping,creates defects in the BaFBr crystals that allow electrons totrapped more efficiently i.e. increases more DQE of crystal.

Te Reflecting Layer lies b/w phosphor & base layer. which

prevents the reflection of light is also applied. 25



The Base Layer composed of “ PolyethyleneTeraphtalate Resign” over which a layer of

photostimulable phosphor (Europium doped BariumFluoro Bromide crystals- BaFBr:Eu+2) is coated.

The next is Backing Layer composed of “Lead”which prevents the base from damage & reduces back scatter X-rays.

The last is the Bar-Code Label which contains thenumber assigned to the imaging plate.

This Bar-Code provides a mechanism for associatingeach imaging plate with Patient identification, Related examination & Positioning Information.

The imaging plate is flexible and less than 1mm

thick.

Cont…

26



LATENT IMAGE FORMATION IN IP:

To prepare the imaging plat for an x-ray exposure, the

plate is exposed to the intense light to erase any

previous image. For X-ray imaging, the IP is placed in a cassette and is

used just like a film/screen cassette with standard

radiographic equipment. When exposed to X-ray, the Europium atoms in the

phosphor crystalline lattice are ionized & converted

from Eu2+ - Eu 3+ by librating a Valance Electron:

Eu2+ - X-ray Irradiation - Eu3+ + e-

These electron are raised to Higher Energy state in the

Conduction Band where they can moved through out

the crystal lattice. 27



The presence of impurities (e.g Bromine) introduce energy

level in the Forbidden Zone called F – centre.

Once in the Conduction Band , the electron travel freelyuntil they trapped in the F – centre in the Metastable State

with an energy level slightly below that of Conduction

Band but higher than that of Valance Band .

The no. of trapped electron is proportional to the amountof X-ray absorbed locally.

The trapped electron in the form of metastable state

constitute the Latent Image.

Due to thermal motion electron will slowly be liberatedfrom traps, and the Latent Image should there for be read

without too much delay. At room temp, the image should, however, be readable up

to 8 hrs. after exposure.

Cont…

28



LIFETIME OF THE IP: -

One of the major advantages of CR is that the imaging

plate is reusable and thousands of exposures can bemade on it.However, there are a number of factors that

may affect the lifetime of an imaging plate: - The plates are subjected to normal wear and tear from

scratches, scuffs, cracks, and contamination with dust

and dirt, which may interfere with the production of a

good image. The establishment of a well organised quality control

program will play an important role in assessing the

clinical quality of the imaging plate. This may easily

be carried out by artefact assessment and uniformity

evaluation across the plate.29



Dust and dirt build up on CR phosphor plates, leading to image artifacts. Toavoid this, plates need cleaning atregular intervals.

Solvent: Ethanol - 99.7%.

Additives: Catanac SN (Cyastat SN50) - 0.3%.

Safety Precautions: -

- Highly flammable.

- Keep container closed.

- Keep away from sources of ignition.

IMAGING PLATE CLEANER:

30



The CR image reader is alsoknown as Analog to Digital Converter (ADC).

Definition: -

It is a device which converts theContinuous Analog Image of Imaging Plate into the DigitalImage.

Construction: - It is consists of three parts: -

1. Mechanical Feature.

2. Optical Feature &

3. Computer Control.

IMAGE READER:

31



When the CR cassette is inserted into the CR reader,the IP is removed and is fitted to a Precision drivemechanism.

The drive mechanism moves IP constantly, yet slowly(Slow Scan) along the long axis of IP.

Small fluctuations in velocity can result in bandingartifacts, so the motor drive must be absolutelyconstant.

When the IP is being transported in the slow scan

direction a deflection device such as rotating polygonor an oscillating mirror deflexed the laser beam back and forth across the IP.

These drive mechanisms are coupled so the laser beam is blanked during retrace.

1. MECHANICAL FEATURE:

32



The error tolerance for this mechanism is fractions of

pixel. Image edges from a CR Reader that is out of

tolerance appear wavy. Another method is for the cassette to be placed in the

reader vertically with the IP withdrawn downward. As this occurs the cassettes is scanned by horizontal

laser. The IP barely leave the cassette, so, it is not subject

to roller damage. Further more, the scan is nearly always located atright angels to the direction of any grid lines, in thisway, aliasing artifacts are reduced.

Cont…

33



The challenged to the CR Reader is to preciselyinterrogate each Metastable Electron of the latent

image in a precise fashion.

Components of the optical subsystem includes the

Laser, Beam Shaping Optics, Light Collecting Optics,Optical Filters & Photo Detector .

The laser is source of stimulating light; however, it

spreads as it travels to the rotating/oscillating reflector. This laser beam is focused on to the reflector by a lens

system that keeps the beam diameter small - less than

100 µm.

2. OPTICAL

FEATURES:

34



As the laser beam is deflected across the IP, it changes

size & shape that is controlled by a Special BeamShaping Optics which keeps constant, the beam Size,

Shape, Speed & Intensity.

The laser beam scan s the IP in a transverse direction

while the IP is moved past the scanning beam.

After scanning with laser beam, emitted light from the

IP is collected using a funnel like Fiber Optic

Collection assembly i.e. Light Guide and is directed atthe Photodetector or PMT or CCD where the light is

converted to an electrical signal which is

logarithmically amplified to an electric output signal.

Cont…

35



This signal is converted by ADC into digital signalwhich is stored in a computer as a digital image matrix.

Before photo-detection occurs, the light is filtered with

the help of Optical Filter device embedded infront of

the Photodetector so that none of the long wavelength

stimulation light reaches the Photodetector & swamps

emitted lights.

In this case, emitted light is the signal & stimulatinglight is the Noise; therefore, Proper filtering improves

the Signal to Noise Ratio (SNR).

Cont…

36



The Computer Control of a CR Reader provides: -- Signal Amplification.

- Signal Compression.

- Scanning Control.

- Analog to Digital Conversion &

- Image Buffering.

The out put of the Photodetector is a time varying analog signal

i.e. transmitted to a computer system that has multiple function. The time varying analog signal from the Photodetector is

processed for Amplitude, Scale & Compression that shapes thesignal before the final image is formed.

Then, the Analog Signal is Digitized by Digital to Analog

Converter (DAC), with attention paid to proper Sampling (time b/w samples) & Quantization (the value of each sample).

The Image Buffering occurs usually in a hard disc, this is a placewhere a completed image can be temporarily stored until it istransferred to a workstation for interpretation or for archival in

PACS.

3. COMPUTER CONTROL:

37



What Happens to the Plate in the Reader?

1. Cassette is enter the reader.

2. Image plate is removed from

cassette3. Latent image is scanned by laser

4. Image plate is erased with high

intensity light.

5. Image plate is returned to cassette

and ejected. 38



After exposure the cassette is feeded into image reader system.

Where the cassette is opened automatically and the imaging plateis removed from the cassette inside the reader.

Then the IP is moved along its long axis and scanned sequentially(Horizontally) by a Monochromatic Infrared Laser Beam of

Helium-Neon (He-Ne) Gas or Solid State Laser of intensity ≈

633nm. The laser light stimulates the trapped electron moving them up to

the conduction band where they make their exit returning to thelower energy Valance Band.

This movement involves the transformation of Europium from the

Eu3+

- Eu2+

i.e. Metastable State to Ground State by emission of energy in the form of light ( Blue & Green) having a wavelengthlower than that of the stimulated laser light.

Eu3+ + e-→ (Influenced by IR Laser of 633 nm) → Eu2+ + hf (400 nm).

FUNCTION OR READING PROCESS:

39

C



The intensity of the emitted light is proportional to the

amount of x-ray energy absorbed in the PSP – layer.

By using a Optical Filter , that absorbs red light but is

transparent to Blue & Green light

This emitted light is collected using a Light Guide & isfed to a Photomultiplier Tube where the light is

converted to an Electrical Signal which is amplified to

an Electric Output Signal .

The Electric Output Signal is converted into Digitized

Image Signal by ADC & stored in a computer as a

Digital Matrix.

Cont…

40





42

C



Erasing Process: -

It is necessary to reuse the imaging plate again.

Because residual Latent Image electrons are still

trapped on higher energy level after readout.

If residual latent image remained, ghosting couldappear on subsequent use of the IP in the next exam.

This energy is erased after the readout process using a

high intensity white light from a bank of specially

designed Fluorescent Lamps source that flushes the

traps without reintroducing electron from the ground

energy level.

Cont…

43



WORKSTATION:

Here Radiographic Technologist can be processed

the digital image in a variety of ways depending uponthe clinical application & the final image can berecorded as a hard copy through Multi Format Camera or Laser Imager . In the form of analog

image. Here digital data is stored on the hard disk of a work

station from where it can be processed, viewed, printed through or distributed via a local network to

peripheral stations. The work station provides a DICOM compliant output

which maybe directed to a laser Printer for hardcopies, or networked to other viewing stations or

archived in PACS for Teleradiology. 44



ADVANTAGES OF C.R. SYSTEM:

No special equipment is required. No handling of Processing Chemicals.

The Exposure Latitude is wider i.e. High Dynamic Range(1:10,000) which leads to reduced rates of failed x-ray

exposure so in a single radiograph large densities variationcan be obtained.

Fewer Repeat examinations should be needed due toexposure factors because of the wide exposure Latitude.

The CR system are cassette based, they can easily beintegrated into existing radiographic devices are highlymobile so all types of Radiographic Examination i.e. Mobile, Portable (Bedside), Trauma, Dental Radiographyare possible with the C.R. system.

45

C t



If a single Imaging Plate shows defects, it can easily bereplaced by the radiographer himself with no need for specialized equipment or service person.

The image displayed on the monitor can bemanipulated in a variety of ways: contrastenhancement, edge enhancement, black/white reversal,zooming & panning etc (i.e Post Processing).

The process of storing the images does not requireseparate rooms and is relatively easier.

Cost effective route to digital radiography. The acquired image can be transferred to many

monitors, different places for viewing to large no. of person.

Increased capability for consultation made possible byelectronic transmission of digital images through PACS& Teleradiology (i.e. networking system).

Cont…

46



LIMITATIONS OF THE C.R. SYSTEM:

The technique is Time & Labor Intensive like FSR. Image reader takes time before the image can be displayed so

the time taken is same as that required for FSR.

Lesser spatial resolution as compared to conventional

radiography. Speed Class of 100-200 is similar to that of Medium Speed FSR

system so that radiation dose required is same or more than

FSR.

Radiological technologists receive no direct feedback on theaccuracy of their selection of exposure factors as the resultant

images are of consistent quality regardless of the exposure.

This may lead to undesirable and undetected over exposure to

the patient.47



INNOVATIONS & NEWER

APPLICATIONS IN CR:

Some of the draw backs of CR system ,namely:

- Cassettes Handling.- Long Read Out Time of PSP Plates.

- Low DQE &

- Poor Resolution have been addressed by newer innovations &

technological advances.

48



AUTOMATED CR SYSTEM WITH

FAST READOUT:

CR system efficiency has been recentlyimproved by reducing the readout time & byremoving the step of cassette handling.

Automated CR system achieve this by line – scan lasers & photodiode detectors that reducethe readout time of a PSP plate to less than 10s.

In these system there is no cassette handling,leading to totally automatic image dataacquisition.

49



NEWER PHOSPHORS FOR IP :

Commercially available IP have unstructured phosphor like Rubidium Chloride (RbCl) or BaFX:Eu

These are scanned in a raster pattern.

A needle – shaped phosphor RbI, CsBr , has been

newly; introduced, e.g. Konica Minolta’s Regius 370

Upright DR & is considered more efficient due to its

structural configuration of crystals.

This crystal structure reduces lateral light diffusion because of the needle shaped configuration that acts aslight guide.

In addition the newer phosphors are more efficient withan increased DQE.

50

Cont



Cont…

51



MOBILE CR SYSTEM:

Bedside radiography of critically ill patients with conventional CR involves physical transport of the cassettes to the CR reader, often

located far away.

The situation gets worse as the no. of ‘portable ‘ films increase.

To save Labor, Time & Improve Workflow, portable compact CR system have been introduced in late 2007, with FugiFilm (FCR

Carbon XL CR Reader) & Carestream Health Inc (Pointof –

CAreCR-ITX 560) machines.

These system basically have a mobile X-ray unit with an integrated

CR reader.

So, they are easy to use & offer quick image availability in less than

25 sec.

52



53



DUAL-ENERGY IMAGING:

It is done by two methods: -

1.) Subtraction Technique &

2.) Double Expose Technique.

1.) Subtraction Technique: -

In this method, x-ray energies are separated by the insertionof a copper filter b/w two image plates which are then givena single exposure.

the low energy image is recorded on the front image plate &a high energy image is recorded on the back.

Owing to the difference in energy the absorption ratio of X-ray through bone & soft tissue will differ for the two images.

By subtracting these two images using weighted factors, bone or soft tissue detail can be selectively displayed.

54

Cont



2.). Double Expose Technique: - In this method, by using a high & low KVp, two images arecreated in the two different image plates.

Soft tissue & bones can be separately depicted by thismethod.

Dual – energy technique are most effective when bothimages are acquired simultaneously.

Similar results are obtained with two exposure within a veryshort period of time.

Uses: - In Chest Radiography, particularly for the evaluation of

partially calcified nodules & pleural plaques.

Cont…

55



AUTOMATIC IMAGE STICHING:

This is useful in determining precise measurement in lengthyanatomical regions like- whole spine, lower limbs or upper limb in a skeletal survey.

Now a days, the largest flat panel DR plates are available in 43X 43 cm.

Using these detectors, only a limited portion of the body partcan be imaged at a time in a single exposure, thus making thesedetectors inadequate for studying the whole spine or the entirelower limb.

To over come this problem, multiple sequential exposures at

different patient positions are acquired in a still patient. Automatic stitching is then performed to reconstruct a larger

composite image.

This special software enables pixel shift and overlap.56



With the recent approval of the Clear View digitalmammography products, FUJIFILM Medical Systems USA

(Stamford, Conn) becomes the first vendor to offer a full-field

digital mammography (FFDM) system based on CR technology

in the United States.

CR for mammography uses imaging plates (IPs) made with

photostimulable phosphor to convert x-rays into digital

information. Existing glass, flat-panel FFDM systems rely on

solid-state detectors.

CR-BASED FFDM

57



The CR Reader, the Clear View CSM, has a unique dual-side readingcapability that permits the capture of x-ray information from both sides of

the Imaging Plate (IP) simultaneously. The 50-µm laser excites the

phosphor, which has a thicker coating compared to standard CR IPs. Light

is emitted from both sides due to a clear base and is captured with dual

light guides.58



SLOT SCAN SYSTEM:

This system uses narrow fan beam X-ray of about 5mm & linear CCD array detector system.

It has mechanically linked x-ray tube & collimator

opposite the narrow CCD array with few rows of detector and scan along the long axis of the patient

anatomy.

It has two precisely aligned moving slit collimators,

one on either side of the patient. Due to which this system provides the ultimate in

scatter rejection & detector efficiency .

59

Cont



Cont…

Thus use of a radiographic grid is not necessary,

significantly using the radiation dose. There are different possible movement of mechanical

linked system & patient couch movement. The exposure time to the patient is about 20 msec. &

readout process time takes about 1 - 3sec. Scan time depends on the area covered i.e. 2 – 30

seconds.

Because of the need for fixed installation, Slot ScanDR system is dedicated to Chest radiography,

Mammography, or Dental Radiography.

60

CCD Slot Scan Direct Radiography



CCD Slot Scan Direct Radiography

61

ADVANTAGES:



ADVANTAGES: Scatter radiation almost totally absent. No grid is required.

Radiation dose is reduced as grid no required. Detector efficiency is more with lower image noise. Longer & large anatomical regions are well covered.

DISADVANTAGES: High initial cost. Longer acquisition time due to narrow fan beam. So, requirement of equipment with high rating of

generator & X-ray tubes. i.e. high tube loading. Poor Spatial Resolution, due to Patient motion which

degrade image quality during scanning. It is a fixed modality method with bulky design. Bedside Radiography is not possible. 62

SELENIUM DRUM DR SYSTEM



Rotating selenium-dotted drum, which has a positive electrical surface charge, is

exposed to x-rays. During exposure, a charge pattern proportional to that of theincident x-rays is generated on the drum surface and is recorded during rotation

by an analog-to-digital converter .

SELENIUM DRUM DR SYSTEM:

Advantage:-

It provide good image quality that issuperior to that provided by screen-film

or CR systems.

Disadvantage:-Because of their mechanical design,

selenium drum detectors are dedicatedfor chest stand systems only with no

mobility at all.

63

DIRECT RADIOGRAPHY (DR):



Indirect Conversion Direct Conversion

Direct Radiography (DR)

Photoconductor (a:Se)

+ TFT (DFPD)

Selenium Drum

Scintillator +

Photodiode (a:Si) +

TFT (IFPD)

Scintillator + CCDCsI:Tl or CsI:Na &

Gd2O2S:Tb3+

DIRECT RADIOGRAPHY (DR):

DR technology converts x-rays into electrical charges by

means of a direct readout process using CCD/TFT arrays.

64

INDIRECT DR:



INDIRECT DR: In this case, X-ray energy is first converted into

light photons by an phosphor scintillator (CsI:Tl,Gd2o2S:Tb).

Then the light photons are converted in electric

charge by Photodiode Phosphor (a:Si).

The electric charge is converted in electrical

signal by CCD/TFT which is digitized by ADC in

digital signal & stored in computer.

The stored digital signal in computer is processedand converted in analog signal by DAC to see on

the monitor.

The whole process will take only 1.3 – 3 sec.65

Cont…



Cont…

Convert X-rays into light photonConvert X-rays into light photonafter then electronic signals for after then electronic signals for

digital image formation.digital image formation.

Uses 3 step process : -Uses 3 step process : -

X –rays

Visible Light

Electronic Signals

Image formation

CsI:Tl, Gd2o2S:Tb

a:Si

TFT & ADC

66

DIRECT DR:



DIRECT DR: In this case we do not use the phosphor coating scintillator

layer, thus eliminating the intermediate light producing step. Hence a:Se directly acts as the x-ray detector.

The x-ray beam directly interacts with a thin layer of a:Se

creating electron-hole pairs, which being charged, travel

directly to the TFT. From TFT, the charge pattern is read out by charge amplifier

& digitized by ADC in digital signal & stored in computer.

The stored digital signal in computer is processed and

converted in analog signal by DAC to see on the monitor.

The whole process will take < 1.3 sec.

67

Cont…



Convert X-rays into electronicsignals for digital image formation

Uses 3 step process : -Uses 3 step process : -

X –rays

Electronic Signals

Image formation

a:Si

TFT & ADC

68



69

CONSTRUCTION & WORKING



CONSTRUCTION & WORKING

OF FPD SYSTEM:

The physical dimensions of the detector array are 40 x

50 x 4 cms with 2560 x 3072 pixel matrix.

The matrix is covered with a scintillator layer of CsI:Tl

or Gd 2

O2

S:Tb in case of Indirect FPD only.

The matrix array consists of a glass substrate onto

which a layer of a:Si is evaporated in the case of

Indirect FPD & a:Se in case of Direct FPD.

The a:Si or a:Se is structured in a matrix of individual photo sensors and switching elements, either a TFT or a

CCD which allows the connections of the sensor with

the read out line in column direction.70

Cont…



TFT or CCD are controlled via address lines in thehorizontal direction, in order to read out the singlecharge values of photodiodes.

These signals are multiplexed and converted into

digital signals by an A.D.C. inside the detector housing.

The 2-D digital image data is directly transferred tothe image processing computer via an optic fiber

link. So the image is available in digital form shortly

after the exposure has been made.

71

ADVANTAGES of DR SYSTEM:



ADVANTAGES of DR SYSTEM: Increasing Workflow Efficiency, Saving Time & Labor.

Integrating high power X-ray system of 30 – 1000 KW Rating, veryShort Exposure Time , Eliminating Motion Blur.

Variable Speed Acquisition possible (speed class 100 – 800) dependingon acceptable SNR.

Most DR system have presets available for various anatomical studiesincluding optimized post processing e.g. chest, spine etc.

Automatic tube detector positioning for selected study.

Auto selection filter & Focal Spot Size a/c to the anatomical part.

Automatic tracking for easy positioning.

Immediate availability of image for Quality Check & Diagnosis.

The examination becomes quick as no cassettes have to be fetched fromthe storage area, taken to the examination site, or to the processing unitafter exposure.

Radiography as well as fluoroscopy can be performed.

Post processing can be done. 72

DISADVANTAGES OF DR



DISADVANTAGES OF DR

SYSTEMS:

High initial cost.

Some radiographic view are difficult to obtain as

the detectors are generally not free to be placed in

any position. Careful handling is required due to fragile nature

of most detectors.

Due to its inflexibility, portable or ward

radiography is not possible.

Different equipment is required for different kinds

of work.73



DIGITAL FLUOROSCOPY:

It provides Real Time Imaging of anatomic

structures. As maximum image detail is

required, so image brightness must be high. Image intensifier was developed to replace

the conventional fluoroscopic screen.

With the introduction of computer technology into fluoroscopy, digital images

with better detail can be obtained.

74



EQUIPMENT:

D.F. requires the same fluoroscopy

equipment in addition to a computer, 2 video

monitors, and a more complex operatingconsole.

A high voltage generator.

A video system. A charge couple device.

75



ADVANTAGES:

Less radiation dose as compared to the

I.I.T.V. system.

Better image quality.

76

DEVELOPMENTS IN D F :



DEVELOPMENTS IN D.F. :

Flat panel detector system has replaced the I.I.T.V. system.

X-rays passing through the patient are converted into

electrical signals by the F.P.D. These are then passed

through the amplifier and ADC where they are converted

into digital signals. The digital image data is directly transferred to an image

storage PC via an optic fiber link at the rate of 30 f/s

This system permits high speed digital image acquisition, processing and display.

Images are of excellent resolution.

77

DYNAMIC FPD FLUOROSCOPY:



Dynamic

Detector- Bi-Plane

DYNAMIC FPD FLUOROSCOPY:

78

INNOVATIONS & NEWER



INNOVATIONS & NEWER

APPLICATIONS IN DR:

Digital Radiography is witnessing rapidinnovations in hardware as well as software

applications. Clinical utility & the true potential of these

applications will be understood better in the

years ahead.Few of the exciting applications are:

79



Cont…



Each absorbed X-ray photon results in a unit count

regardless of the photon energy.

As the electrical pulse generated is much higher than

the electronic noise, this type of DR system produce

images with high SNR. Uses: -

1) Mammography (Sectramicrodose).

2) In gaseous micros trip detectors for Biplane Whole Body Imaging in erect weight bearing position with

excellent result ( EOS of Biospace med).

81



82

Ad



Advantages: -

Radiation dose is reduced as grid is not required. High system DQE. High SNR due to minimal electronic noise. No ghost image (Previous exposure is residue). High contrast & detail resolution.

Disadvantages: -

Exposure time is long. Patients motion may degrade image quality. Requirement of equipment with high rating of generators

& X-ray tubes.83

DIGITAL TOMOSYNTHESIS



DIGITAL TOMOSYNTHESIS:

In this technique multiple low dose exposure aregiven from various angles while the x-ray tubemoves in an arc & the detector remains stationary.

Multiple images with different focal zones are

possible to be created by addition of these low doseimages after pixel shift.

It emphasize contrast in a particular layer of a regionof body.

Generated images can be viewed singly or as a cineloop.

It is also considered to useful in Mammography,Chest, IVU studies.

84

DIGITAL MAMMOGRAPHY



TOMOSYNTHESIS ( DMT ):

It is a recent advanced application of DM. In this technique, an area X-ray beam

interacts with the digitalmammographic image receptor, producing a digital mammogram.

This digital mammogram is repeatedseveral times at different angles.

Each images is available in digitalform & can be reconstructed as a 3DMatrix of values, each representing a

Voxel. With these digital data available, a

tomographic section can bereconstructed with enhanced imagecontrast at acceptable patient

radiation dose.85

MOBILE /PORTABLE DR:



MOBILE /PORTABLE DR:

Now a days flat panel detector portable radiography

is also possible. This method was first invented by Canon.

The FPD are available in 17” X 17” with a cable for portable/mobile radiography.

As a general a FPD connected by a cable to a mobileor portable unit having a monitor.

The use of portable DR system hampered by thefragility of the FPDs & the high costs.

A portable DR system, when compared with an FSR system, avoids all problems related to theavailability, storage, transportation, disposed of films& chemicals. 86



87

WIRELESS FPD



WIRELESS FPDs:

With the introduction of the model Pixium 3543 from Thales,wireless portable DR system is now a reality.

After exposure, it wirelessly transfer image data to the DR system.

Alternatively the image data can be transferred to DR console

via an Ethernet cable. It has no cables & does not interfere with surrounding

machines. So, it is easy to handle as a CR cassettes.

Typically a 17” X 14” image size is made available within 3s.

It is particularly well suited for use with immobilized patients, in operating rooms, intensive care units, emergencysituations, and rooms for exams requiring difficult or unusualX-ray projections.

88

WIRELESS FPD SYSTEM:



X-RayGenerator

Power

Supply

Pixium Portable

Docking Station

WiFi (or back-up cable)

Pixium Portable 3543

Ethernet

Cable

Acquisition

board

Ethernet

Board

RS 232Optical Fiber

Power supply

Pixium RAD 4600

PixRad software

PC

89

FLUOROSCOPY



FLUOROSCOPY:

Real – time digital imaging in DR is possible withthe invention Pixium RF 4343, from Thales.

It facilitates high-quality radiography &

fluoroscopy (up to 30 images/sec.)

This fluoroscopy feature is use in Gastroenterology,

Urology & Vascular applications.

Newer FPDs like Pixium 4700 & Pixium 4800 from

Thales are used for Vascular & Cardiovascular DSAapplications by permitting low – dose fluoroscopy.

90

Integris Allura Integris Allura Flat DynamicFlat Dynamic

D f C diD t t f C di



Detector for CardioDetector for Cardio

Scintillator Photodiode array Refresh light

91

IMAGE QUALITY PARAMETERS:IMAGE QUALITY PARAMETERS:



IMAGE QUALITY PARAMETERS:IMAGE QUALITY PARAMETERS:

Pixel Size, Matrix & Detector Size.

Dynamic Range & Contrast.

Spatial Resolution. Limiting Spatial Resolution (LSR).

Signal to Noise Ratio (SNR). Modulation Transfer Function (MTF).

Detective Quantum Efficiency (DQE). 92

DYNAMIC RANGE & CONTRAST:



DYNAMIC RANGE & CONTRAST:

Contrast levels or film

densities generated over arange of x-ray exposure levels.

Dynamic range is a measure

of the signal response of adetector that is exposed to x-

rays.

Narrow Dynamic Range

Image

Brightness

Toe Part

Shoulder

Straight

X-ray Detected

1:1000

Wide Dynamic Range

Shoulder

StraightToe Part

X-ray Detected

1:10,000

ImageBrightne

ss

93

Cont…



Film-Screen

Detector

Low Contrast

High Contrast

94

LIMITING SPATIAL RESOLUTION



( LSR):

Reso lu t ion

Reso lu t ion

Spatial Resolution refers to the minimum resolvableseparation between high-contrast objects.

In Digital Detectors, Spatial Resolution is defined

and limited by the minimum Pixel Size.95

SIGNAL TO NOISE RATIO (SNR):



Decreasing Noise

Increa

singC

ontras

t

High SNR Low SNR

Noise

Signal

Contrast Ratio

Quantum Mottle (QM): - It is an appearance of noise in

the radiographic image due to low SNR of theinformation reaching the image recording system.

( )

96

IMPACT OF NOISE:



Quantum and Electronic noise are unavoidable in a

digital imaging chain. The effect, often expressed asSignal-to-Noise Ratio (SNR), can vary widely fromsystem to system.

Signal Useful Image Formation ------------- = ------------------------------------ Noise Erratic (Unwanted) Information

1:1 SNR 2:1 SNR 5:1 SNR97

MODULATION TRANSFER



FUNCTION (MTF ).

Modulation transfer function (MTF) is the capacity of thedetector to transfer the modulation of the input signal at agiven spatial frequency to its output.

Light Photons

Gd2O2S:Tb + a:Si

High Scattering

Low MTF

CsI:Tl + a:Si

Low Scattering

Good MTF

Electron

a:Se

No Scattering “Perfect”

MTF

Light Photons

X-Ray

Photons:

98

DEECTIVE QUANTUM EFFICIENCY (DQE):



DEECTIVE QUANTUM EFFICIENCY ( DQE ):

Detective Quantum Efficiency (DQE) is one of thefundamental physical variables related to imagequality in radiography.

It is the % of X-ray absorbed by the image receptor.

It depends on: -- Radiation Exposure.

- Spatial Frequency.

- MTF.

- Detector Material.

- Quality of the radiation applied (Voltage & Current).

99

11 Digital Radiographic Room =Digital Radiographic Room = 2.62.6



1 Digital Radiographic Room g g p 2.6

Conventional Screen/Film Room !Conventional Screen/Film Room !

Imaging Technique Average Exam time

Conventional Screen Film Radiography 6:05 Minutes

Computed Radiography 7:02 Minutes

Direct Capture Radiography 2:18 Minutes

100

Technical Features Of Various DR

S t



FeatureFeature X-rayX-rayConverter Converter

ReadoutReadout Detector Detector sizesize

Pixel SizePixel Size Matrix SizeMatrix Size

Screen FilmScreen Film Gd2O2S FilmFilm 14x1714x17 Grain SizeGrain Size

22

………………....

StorageStoragePhosphor Phosphor

BaFBr:EuBaFBr:Eu LASERLASER 14x1714x17 100 - 200100 - 200

µmµm

1760x21401760x2140

Slot scanSlot scanCCDCCD

CsI:TlCsI:Tl CCDCCD 17x1717x17 162 µm162 µm 2736x27362736x2736

Direct FPDDirect FPD a:Sea:Se Active SeActive SeMatrixMatrix

14x1714x17 139 µm139 µm 2560x30722560x3072

Indirect FPDIndirect FPDGd2O2S:Tb Active a:SiActive a:Si

MatrixMatrix17x1717x17 160 µm160 µm 2688x26882688x2688

CsI:TlCsI:Tl Active a:SiActive a:SiMatrixMatrix

17x1717x17 143 µm143 µm 3121x31213121x3121

System:

101

IMAGE RECEPTOR COMPARISION:

FEATURE FILM/SCREEN CR (PSP) DR



FEATURE FILM/SCREEN CR (PSP) DR

RADIATION DOSE Higher Lower Lower

GENERATION OFVISIBLE IMAGE

Chemical, WetProcessing

Laser Scanner, Computer Computer

IMAGE VIEWING Delayed, View boxTransillumination

Delayed, Computer Monitor In few seconds, Computer Monitor

RESOLUTION 16-20 lp/mm 6-8 lp/mm 8-10 lp/mm

CONSTRUCTION Thin, Flexible Thin, Flexible Thick, Rigid & Robust

LIFE SPAN Single Use Reusable after Erasure Reusable (Unlimited)

IMAGEENHANCEMENT

Fixed UnchangeableImage

Multiple Operations: -Contrast, Density,Magnification,

Positive/Negative,Measurement

Multiple Operations: -Contrast, Density,Magnification,

Positive/Negative,Measurement

STORAGE Patient Record, HugeSpace required

Variety of ArchivingMethod: - Server, Zip, OMD,MOD, CD, DVD, PACS

Variety of Archiving Method: -Server, Zip, OMD, MOD, CD,DVD, PACS

102

IDEALIDEAL DR DR SYSTEM:SYSTEM:



Physical Design: -

- Compatible in size with Film Cassette.- Immediate Readout.

- Robust.

- Cost Effective.

Image Capture: -- High Quantum efficiency.

- Low Dose.

Image Quality: -- Spatial & Contrast Resolution as goodas Film/Screen System.

- Wide Dynamic Range.

- DICOM Compatible.103

CONCLUSION:



CONCLUSION: With the advent of computed radiography diagnostic

radiology is advancing towards a film less system.

The replacement of film by detectors and storage

devices eliminated several inherent drawbacks of

conventional radiography and decreases the radiationexposure to the patient and radiographer.

Very soon digital imaging will become more common

and affordable for all aspect of radiography.

With the development of Digital Radiography , theRadiographic Examination becomes more easy, handy

and less time consuming method with good quality of

image. 104



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