Computed Radiography

COMPUTED RADIOGRAPHY

filmless’ radiology departments

Diagnostic radiographers

have traded their ______and ______

for a ______and ______

advance for Rad Sci Prof, 8/9/99

What Is Digital Imaging?

Digital imaging is the

acquisition of images to

a computer rather than

directly to film.

New Technology

CR SYSTEM COMPONENTS

n CASSETTES (phosphor plates)

n ID STATION

n IMAGE PREVIEW (QC) STATION

n DIGITIZER

n VIEWING STATION

History of CR

Predictions

n 1980 – Bell Labs believed that Unix would be the worlds dominant operating system

n 1982 – Bill Gates thought 640K of main memory would suffice for workplace operating systems ( This presentation is 80,000 kb)

n 1984 – IBM predicted that personal computers would not amount to anything

History of CR

n By 1998 – over 5,000 CR systems in use nationwide

n 1998 – Local area hospitals begin to incorporate CR systems in their departments

n (Riverside Co. Hosp builds new hospital in Moreno Valley) – completely CR system – 1st generation equipment

TERMINOLOGY

n F/S - ______

n CR - ______

n DR - ______

n DDR - ______

IMAGE CREATION

n SAME RADIOGRAPHY EQUIPMENT USED

n THE DIFFERENCE IS HOW IT IS

n ______

Conventional vs. Digital Imaging

n Conventional X-ray imaging systems

n Produce an analog image (radiographs, & fluoroscopy).

n Using x-ray tube with films & cassettes

Conventional vs. Digital Imaging

n Digital radiography systems require that the electronic signal be converted to a digital signal –

n Using x-ray tube –

n CR cassettes with phosphor plate (PSP)

n DR systems with transistors (TFT)

COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY
& FILM SCREEN
IMAGE CAPTURE

FS - Film inside of cassette

CR – Photostimuable Phosphor Plate (PSP)

DR(DDR) - Thin Film Transitor (TFT)

Cassette with film CR with PSP

Directed Digital Radiography
(DDR)

Directed digital radiography, a

term used to describe total

electronic imaging capturing.

Eliminates the need for an image plate altogether.

IMAGE CAPTURE

n ______

n PSP – photostimulable phosphor plate

n Replaces film in the cassette

n ______– No cassette-

n Photons captured directly onto TFT

n Sent directly to a monitor

CR vs. FS

n PSP in cassette

n Digital image

n Scanned & read- CR reader

COMPUTER

n Image stored on computer

n Viewed on a Monitor

n Hard copy (film) can be made with laser printer

FILM

n Film in cassette

n loaded in a darkroom

n Processed in a processor

FILM

n Hard copy image – stores the image

n Viewboxes – view the images

CR BASICS

• Eliminates the need for film as a recording, storage & viewing medium.

• PSP Plate – receiver

• Archive Manager – storage

• Monitor - Viewing

General Overview CR

n PSP cassette exposed by

conventional X-ray equipment.

n Latent image generated as a matrix of trapped electrons in the plate.

CR – PSP plate

n Photostimulable phosphor (PSP) plate

n Captures photons

n Stored in traps on plate (latent image)

n PLATE scanned in CR READER

CR – PSP plate

n Stimulated by a ______LIGHT

n Energy is ______in a form of _____ light

n LIGHT captured by photomultiplier tube (PMT)

n Changed to a ______signal

How CR works

n Blue released light is captured by a PMT (photo multiplier tube)

n This light is sent as a digital signal to the computer

n The intensity ______of the light – correlates to the ______on the image

Densities of the IMAGE

n The light is proportional to amount of light received

n Digital values are then equivalent (not exactly the same) to a value of optical density (OD) from a film, at that location of the image

ERASING PLATE

n After image is recorded

n Plate is erased with high intensity ______light

n Cassettes are reused

CR VS. DR

n CR -______ where the image is first captured on plate and stored = then converted to digital signal

n DDR -______ where the image is acquired immediately as a matrix of pixels – sent to a monitor

DIRECT RADIOGRAPHY

n Uses a transistor receiver (like bucky)

n Captures and converts x-ray energy directly into digital signal

n Images seen immediately on monitor

n Sent to PACS/ printer/ other workstations FOR VIEWING

CR vs DR

n Imaging plate

n Processed in a Digital Reader

n Signal sent to computer

n Viewed on a monitor

n Transistor receiver (like bucky)

n Directly into digital signal

n Seen immediately on monitor

Image Resolution –
(how sharply is the image seen)

• 4000 x 4000

• Image only as good a monitor*

• 525 vs 1000 line

• More pixels = more memory needed to store

• CR 2 -5 lp/mm

• RAD 3-6 lp/mm

• DR ?

• IMAGE APPEARS SHARPER BECAUSE CONTRAST CAN BE ADJUSTED BY THE COMPUTER –

• (DIFFERENCES IN DENSITY)

ADVANTAGE OF CR/DR

n Can optimize image quality

n Can manipulate digital data

n Improves visualization of anatomy and pathology

n AFTER EXPOSURE TO PATIENT

ADVANTAGE OF CR/DR

n Changes made to image after the exposure

n Can eliminate the need to repeat the exposure

ADVANTAGE OF CR/DR vs FS

n Rapid storage

n Retrieval of images NO LOST FILMS!

n PAC (storage management)

n Teleradiology - long distance transmission of image information

n Economic advantage - at least in the long run?

CR/DR VS FILM/SCREEN

n FILM these can not be modified once processed

n If copied – lose quality

n DR/CR – print from file – no loss of quality

“No fault” TECHNIQUES

F/S: RT must choose technical factors

(mAs & kvp) to optimally visualize anatomic detail

CR: the selection of processing algorithms and anatomical regions controls how the acquired latent image is presented for display

n HOW THE IMAGE LOOKS CAN BE ALTERED BY THE COMPUTER – EVEN WHEN “BAD” TECHNIQUES ARE SET

n Initial expense high

n Very low dose to pt –

n Image quality of 100s using a 400s technique

n Therefore ¼ the dose needed to make the image

Storage /Archiving

FILM/SCREEN

n Films: bulky

n Deteriorates over time

n Requires large storage & expense

n Environmental concerns

CR & DR

n 8000 images stored on CD-R

n Jukebox CD storage

n No deterioration of images

n Easy access

Transmission of Images

n ______ - Picture Archiving & Communications System

n ______- Digital Images & Communication in Medicine

n ______ -Remote Transmission of Images

Benefits of Computer (web)-based Viewing Systems

n Hardcopy studies are no longer misplaced or lost- eliminates films

n Multiple physicians may access same patient films

n Patients do not have to wait in Radiology for films once study is completed

“Film-less” components

n CR or DR

n CD-ROM or similar output

n Email capability

n Digitizing capability or service

PACS

Histogram Analysis

n A histogram is a plot of gray scale value

n vs. the frequency of occurrence

n (# pixels) of the gray value in the image

n HISTOGRAM – a bar graph depicting the density distribution (in numerical values) of the imaging plate

n ALGORITHM – a set of mathematical values used to solve a problem or find an average

Basics of Digital Images

n Digital images are a (matrix) of pixel (picture element) values

n The algorithm attempts to distinguish among the parts of the histogram which represent the range of densities from bone to soft tissue

n Histograms set for specific exams (body parts)

n Should produce digital images that are consistent (regardless of kVp or mAs used)

n Correct Algorithm (body part) must be selected prior to processing imaging plate

Methods to Digitize an Image

1. ______- Teleradiography system (PACS, DICOM)

2. ______(vidicon or plumbicon)

3. ______

4. ______

FILM DIGITIZER

Analog vs Digital

n ______- one value blends into another

n like a thermometer

n ______- distinct separation

n 98.6

n exact

ANALOG TO DIGITAL IMAGE

n Conversion of conventional analog films

n To digital format for PACs and teleradiology applications

n With scanning laser digitizers

CONTRAST & DENSITY

n Most digital systems are capable of 1024 shades of gray –

n but the human eye can see only about 30 shades of gray

n The Optical Density and Contrast can be adjusted after the exposure by the Radiographer.

n This is POST - PROCESSING

Basics of Digital Images

n Pixel values can be any bit depth (values from 0 to 1023)

n Image contrast can be manipulated to stretched or contracted to alter the displayed contrast.

n Typically use “window width” and “window level” to alter displayed contrast

n Then the COMPUTER corrects any exposure errors

n Therefore almost ANY technique can be used on the patient –

n The computer will fix it

DOSE IMPLICATIONS

n More exposure to the patient

n Techniques established

n Higher kVp = Less mAs

n Less patient dose

Dose Implications

n Images nearly always look better at higher exposures.

n Huge dynamic range means nearly impossible to overexpose.

POST PROCESSING

TECHNIQUE CONISDERATIONS

n KVP Dependant

n Now COMPUTER controls CONTRAST

n Higher kVp to stimulate electron traps

EMERGING PROBLEMS

n Better – not necessarily faster

n Learning curve for technologists and physicians

n Student applications and issues

n Pitfalls of CR

• _____ and proper ______are critical to good imaging outcomes

• Just like Phototiming, it can magnify your mistakes

COLLIMATION CRITICAL

n As the computer reads the density value of each pixel- it is averaged into the total

n Close collimation= Better contrast

n Bad collimation= more grays and less detail

• Digital imaging is not the end all, cure all for imaging problems

• It is still technologist dependent

To Produce Quality Images

For Conventional Projection

or CR Radiography:

The same rules, theories, and laws still apply and can not be overlooked FFD/OFD (SID/SOD) Inverse Square Law Beam Alignment Tube-Part-Film Alignment Collimation Grids

Exposure Factors: KVP, MaS

Patient Positioning

ECC CR 800

KODAK AUTORAD

NEW IMAGE

• Towel that was used to help in positioning a child

• CR is MORE sensitive to

• ARTIFACTS

CR image – NEW IMAGE

n Line caused from dirt collected in a CR Reader

High resolution with digital imaging

Total
body
scan
for
trauma