Digital Imaging

Week 10 Week 9 Image Receptors Image Receptors Digital Imaging Film Imaging Film Construction Cassette Construction Film Handling Darkroom Digital Imaging Cassette Digital Imaging Direct Digital Imaging Week 9 Week 10

Digital Radiography Computed Direct-to-Digital Radiography Radiography Capture Indirect Capture Computed Radiography (CR) Direct-to-Digital Radiography (DDR)

Computed Radiography Similar to F/S Uses cassettes as imaging plate (IP) Imaging plate is termed PSP

History of CR INDUSTRY Theory of “filmless radiography” first introduced in 1970 1981 Fuji introduced special cassettes with PSP plates (replaces film) Technology could not support system First clinical use in Japan - 1983

Predictions 1980 – Bell Labs believed that Unix would be the worlds dominant operating system 1982 – Bill Gates thought 640K of main memory would suffice for workplace operating systems ( This presentation is 80,000 kb) 1984 – IBM predicted that personal computers would not amount to anything

How does it differ ? Uses the same general equipment as F/S

Computed Radiography How is it different from F/S? How the image is captured How the image is stored How the image is viewed How the image is processed after taken

Computed Radiography Review of F/S image production: Primary beam Exit radiation Hits phosphors of intensifying screens, lights helps form image-latent image Some photons hit film directly-latent image Film is processed to develop manifest image Film stored, duplicated to be seen by others

Computed Radiography Computed Radiography Image Production: Primary beam-same as film Exit radiation-same as film Interacts with CR cassette image plate- latent image -similar to film CR cassette is place in CR reader, laser translates image to analog signal-different Analog signal converted to digital signal Image can be viewed on computer monitor-manifest image Image can be post-processed-not possible with F/S Image is stored in computer system (PACS) Image can be viewed by anyone with access to system Image can be printed on film with a laser printer

Cassette with film CR with PSP Film Cassette CR cassette with PSP

Photostimulable Phosphor Computed Radiography Photostimulable Phosphor Responds to radiation by trapping energy in the locations where x-rays strike, creating the latent image PSP run scanned by a CR reader, converted to analog image, then to digital image, then image viewed on monitor.

Photostimulable Phosphor CR Reader- scans the PSP plate using a RED laser light, releases trapped electrons which then emit BLUE light which is converted to analog image.

Computed Radiography Exit radiation exposes CR cassette Uses red light to scan Detects the Blue light emitted

CR – PSP plate Stimulated by a RED LIGHT Energy is RELEASED in a form of BLUE light LIGHT captured by photomultiplier tube (PMT) Changed to a digital signal

Computed Radiography The CR system is not much faster than film screen cassettes. It is really not faster it is just different. We can manipulate the image and it is better quality images.

CR Phosphor Plates ABSORPTION EMISSION X-RAY LIGHT LASER STIMULATION ELECTRON TRAP ELECTRON TRAP X-RAY LIGHT Raster pattern scans the phosphor plate.

How CR works Blue released light is captured by a PMT (photo multiplier tube)(laser reader) This light is sent as a digital signal to the computer The intensity (brightness) of the light – correlates to the density on the image

ERASING PLATE After image is recorded Plate is erased with high intensity white light Cassettes are reused Remember RED, WHITE AND BLUE…..but really it goes Red, Blue White…

Digital Radiography Computed Direct-to-Digital Radiography Radiography Capture Indirect Capture Computed Radiography (CR) Direct-to-Digital Radiography (DDR)

Directed Digital Radiography (DDR) Directed digital radiography, a term used to describe total electronic imaging capturing. Eliminates the need for an image plate altogether. There is no cassette at all. Supposed to be faster, digital is faster the CR.

Direct Digital Radiography Cassette-less imaging Uses TFT-Thin Film Transistor No film, so no developing, No PSP, so CR reader needed Immediate image viewing Post Processing capabilities Multiple viewing stations

Amorphous Selenium detector technology for DR Direct Radiography Transitors are coated with amorphous selenium.

Direct Digital Radiography No cassette used, device similar to Bucky used Contains thin film transistor Captures x-ray photons, converts to electron energy, Electron energy transferred to digital image Displayed on monitor for IMMEDIATE viewing

Patient is missing a shield Patient is missing a shield. This is a lot faster but it is a problem for an educator. It is hard to know if they always have someone around with them when they do repeats.

Imaging Systems Be able to compare all the different imaging systems. Compare the advantages, disadvantages of each system.

COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY & FILM SCREEN IMAGE CAPTURE FS - Film inside of cassette CR – Photostimulable Phosphor Plate (PSP) DR(DDR) - Thin Film Transistor (TFT) Don’t forget about Direct Exposure !!

FS vs. CR CR FILM PSP in cassette Film in cassette Digital image Scanned & read- CR reader COMPUTER Image stored on computer Viewed on a Monitor Hard copy (film) can be made with laser printer FILM Film in cassette loaded in a darkroom Processed in a processor Hard copy image – stores the image Viewboxes – view the images

CR vs DR CR Imaging plate Processed in a Digital Reader Signal sent to computer Viewed on a monitor DR Transistor receiver (like bucky) Directly into digital signal Seen immediately on monitor

COMPUTED RADIOGRAPHY & DIRECT RADIOGRAPHY & FILM SCREEN IMAGE CAPTURE

Image Resolution (how sharply is the image seen) CR 2 -5 lp/mm RAD 10 lp/mm DR ? IMAGE APPEARS SHARPER BECAUSE CONTRAST CAN BE ADJUSTED BY THE COMPUTER – (DIFFERENCES IN DENSITY) CR 4000 x 4000 Image only as good a monitor* More pixels = more memory needed to store

ADVANTAGE OF CR/DR Can optimize image quality Can manipulate digital data Improves visualization of anatomy and pathology AFTER EXPOSURE TO PATIENT

CR/DR VS FILM/SCREEN FILM- these can not be modified once processed If copied – lose quality 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 HOW THE IMAGE LOOKS CAN BE ALTERED BY THE COMPUTER – EVEN WHEN “BAD” TECHNIQUES ARE SET 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 HOW THE IMAGE LOOKS CAN BE ALTERED BY THE COMPUTER – EVEN WHEN “BAD” TECHNIQUES ARE SET

Storage /Archiving FILM/SCREEN Films: bulky Deteriorates over time Requires large storage & expense Environmental concerns CR & DR 8000 images stored on CD-R Jukebox CD storage No deterioration of images Easy access

ADVANTAGE OF CR/DR vs FS Rapid storage Retrieval of images NO LOST FILMS! PACS- DICOM (storage management) Teleradiology - long distance transmission of image information Economic advantage - at least in the long run?

Transmission of Images PACS - Picture Archiving & Communications System DICOM - Digital Images & Communication in Medicine TELERADIOGRAPHY -Remote Transmission of Images

Basics of Digital Images Digital images are a (matrix) of pixel (picture element) values Computer can see 256 shades of gray.

Analog vs Digital Analog - one value blends into another like a thermometer Digital - distinct separation 98.6 exact Analog is not exact. Where digital is an exaxt.

CONTRAST & DENSITY Most digital systems are capable of 1024 shades of gray – but the human eye can see only about 30 shades of gray The Optical Density and Contrast can be adjusted after the exposure by the Radiographer. This is POST - PROCESSING

High displayed contrast – narrow window width Short scale of contrast. Different algorithms High displayed contrast – narrow window width

Low displayed contrast (stretched) – wide window width Long scale of contrast Low displayed contrast (stretched) – wide window width

Basics of Digital Images Pixel values can be any bit depth (values from 0 to 1023) Image contrast can be manipulated to stretched or contracted to alter the displayed contrast. Typically use “window width” and “window level” to alter displayed contrast

80 KVP 5 30 5 15 100 200 500 These all look the same regardless of the dosage given to the patient. This a a concern because technologists can overexpose patients.

Danger of Digital Then the COMPUTER corrects any exposure errors Therefore almost ANY technique can be used on the patient – The computer will fix it

DOSE IMPLICATIONS More exposure to the patient Techniques established-F/S techniques Higher kVp = Less mAs Less patient dose Goes Contrary to what good techs have been taught

80 kvp 200mas 10 mas 80 kvp Note Quantum Mottle

Dose Implications Images nearly always look better at higher exposures. Huge dynamic range means nearly impossible to overexpose.

POST PROCESSING These are all from one exposure.

TECHNIQUE CONSIDERATIONS kVp Dependent Now COMPUTER controls CONTRAST Higher kVp to stimulate electron traps

(replaces film, storage & viewboxes) CR – Reader (replaces Darkroom & Processor & Chemicals Diagnostic Viewer (replaces film, storage & viewboxes) EXPLAIN EQUIPMENT

EMERGING PROBLEMS Better – not necessarily faster Learning curve for technologists and physicians-increase repeat rate? Student applications and issues Pitfalls of CR

Learning Curve Positioning and proper collimation are critical to good imaging outcomes Just like Phototiming, it can magnify your mistakes

COLLIMATION CRITICAL As the computer reads the density value of each pixel- it is averaged into the total Close collimation= Better contrast Bad collimation= more grays and less detail

To Produce Quality Images For Conventional Radiography or CR Radiography: The same rules, theories, and laws still apply and can not be overlooked SID, Inverse Square Law, Beam Alignment ,Tube-Part-Film Alignment, Collimation, Grid, Exposure Factors: kVp, mAs Patient Positioning PATIENT POSITIONING Accounts for 85% of the total number of repeat exposures. Has a direct affect on exposure technique.

Quality Images Patient positioning Accounts for 85% of the total number of repeat exposures. Has a direct affect on exposure technique.

Towel that was used to help in positioning a child CR/DR is MORE sensitive to ARTIFACTS

Digital Imaging