COMPUTED RADIOGRAPHY (CR)

Transcription

1 COMPUTED RADIOGRAPHY (CR) Moving with the time Avi Avner BVSc BSc CVR DVDI MRCVS

2 CR-Basics A five step process: 1. X-ray image received on phosphor plate 2. Image extracted from phosphor plate by Laser (Raw image) 3. Raw image processed for quality improvement 4. Final image in DICOM format 5. DICOM image can be either printed, burned on CD, or sent to PACS 2

3 Computed radiography Image Plate Plate reader Quality control monitor Workstation

4 CR 30-X - Workflow 1 NX Receives DMW (*) from RIS 4 Identify image (Direct ID) RIS system 6 Control image quality 2 Take Image 3 Insert cassette in digitizer Firewire connection 7 DICOM Print or Archive PACS system 8 Cassette ready for next image 5 CR 30-X Scans image (*) DMW = DICOM Modality worklist CR 30-X Digitizer and NX Modality Workstation Hardcopy printer

5 IMAGE PLATE Photosensitive phosphor layer (e.g. europium activated barium fluorohalide Thin and flexible Placed in a conventional cassette Stores the latent image after x-ray x exposure

6 Label Clip Format Opening ock Shutter Opening Mechanism

7 CR - Physics Exposure stage Image: Exposure, VALENCE BAND (HIGH ENERGY LEVEL) Trap Capture, Reading, Detection Laser light Reading stage X-Ray Photon UV Photon PhotoElectron CONDUCTANCE BAND (LOW ENERGY LEVEL) PHOSPHOR PLATE 7 PM

8 Scanning Procedure 1. Plate is scanned by the laser 8

9 Scanning Procedure 2. Blue light (diffused) is emitted from the plate and detected by the photomultiplier 3. Plate is erased with light (not laser) and returned to the cassette 9

10 QUALITY CONTROL WORKSTATION Digital data transferred Raw data adjusted by software Processing algorithm Processing Define contrast, latitude and edge enhancement Define contrast,

11 PACS AND WORKSTATION Picture Archiving and Communication System

12 Limitations of Conventional radiography

13 Limitations of conventional radiology Films cannot tolerate a wide range in radiation exposure (D loge curve) One has to chose between good contrast and good latitude Image cannot be adjusted once taken Require space for dark room and film/ chemicals storage.

14 Limitations of screen-film systems Price of films and chemicals is constantly going up (4-10% per year) Need several exposures to show different tissues (bone vs soft tissue)

15 Advantages of CR Image quality comparable with to conventional screen-film systems Wide dynamic range- ability to image structures of different attenuation values (thorax and abd) Reduction of repeat exposures 15

16 Advantages of CR CR is compatible with most conventional x-ray x systems Increased savings: no film, chemicals, dark room and storage room required Computer processing of raw image: brightness, contrast, sharpness enhancement, zooming, measurements

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18 Advantages of CR CR is more tolerant of under / over exposure (wide latitude) Ability to extract information not possible on conventional radiographs (e.g edge enhancement, masking, cropping) Faster image acquisition

19 Advantages of CR DICOM-Digital Digital imaging communications in medicine PACS- Images retrieved from computer archive Teleradiology

20 ADVANTAGE: LATITUDE AND CONTRAST

21 ADVANTAGE: LATITUDE AND CONTRAS

22 ADVANTAGES: BONE AND SOFT TISSUE

23 Disadvantages of CR Initial cost Additional cost Transition to a new system Wider latitude Tend to overexpose- degrade contrast.

24 Disadvantages of CR IP sensitive to fogging: use grid, need to be erased daily

25 UNDEREXPOSURE QUANTUM MOTTLE

26 UNDEREXPOSURE QUANTUM MOTTLE

27 OVEREXPOSURE CLIPPING

28 EDGE ENHANCEMENT `ÜBERSCHWINGER

29 EDGE ENHANCEMENT

30 Optimization of images Erase plate not used for 24hrs Scatter control- Grid Scatter control- avoid overexposure Centering / collimation- histogram should represent anatomy Collimation- reduce scatter and improves contrast

31 Optimization of images Multiple fields per IP- not recommended. If multiple fields: uniform distribution- symmetry, strict collimation- no overlap.

32 Practical tips Systems break- reliable service Computer will eventually crash (3-5yrs) Vendor reliability (going out of business)- Safety net. Back-up your system outside the main server

33 Practical tips Purchase price may only be just the beginning- make sure you know what you are getting (you may not be getting the system that was shown to you) Know who is providing your service Service: contract, software upgrade, computer crashes, replacing computer

34 Practical tips: focus on Image quality Image processing has greatest effect Multi-scale Image Contrast Amplification (MUSICA-Agfa) Agfa) תוכנת עיבוד התמונה (Agfa) MUSICA מאפשרת קבלת תמונה דיאגנוסטית באיכות CR הגבוהה ביותר הקיימת כיום במערכות

35 The tip of the day Where you buy from is as important as what you buy Image quality Image processing has greatest effect (e.g. MUSICA-Agfa) Agfa)