Digital Radiology

1. Digital RadiologyDr M A OghabianMedical Physics GroupTehran University of Medical Scienceswww.oghabian.net

2. Digital Radiology • Aim: To become familiar with the digital imaging techniques in projection radiography and fluoroscopy. Add module code number and lesson title

3. Transition from conventional to digital radiology • Digital images can be numerically processed • Digital images can be easily transmitted through networks and archived • Attention should be paid to the potential increase of patient doses due to tendency of : • producing more images than needed • producing higher image quality not necessarily required for the clinical purpose Add module code number and lesson title

4. What is “dynamic range”? • Wide dose range to the detector, allows a “reasonable” image quality to be obtained • Flat panel detectors (discussed later) have a dynamic range of 104 (from 1 to 10,000) while a screen-film system has approximately 101.5 Add module code number and lesson title

5. Characteristic curve of CR system 3.5 3 2.5 2 1.5 1 0.5 0 HR-III CEA Film-Fuji Mammofine CR response Density 0.001 0.01 0.1 1 Air Kerma (mGy) Add module code number and lesson title

6. Analogue versus digital Analogue: A given parameter can have continuous values Digital: A given parameter can only have discrete values NUMERO

7. What is digital radiology? • In conventional radiographic images, spatial position and blackening are analogue values • Digital radiology uses a matrix to represent image • A matrix is a square or rectangular area divided into rows and columns. The smallest element of a matrix is called ”pixel” • Each pixel of the matrix is used to store the individual grey levels of an image, which are represented by positive integer numbers • The location of each pixel in a matrix is encoded by its row and column number (x,y) Add module code number and lesson title

8. Digital radiology process • Image acquisition • Image processing • Image display • Importance of viewing conditions • Image archiving (PACS) • Image retrieving • Importance of time allocated to retrieve images Add module code number and lesson title

9. Digitizing conventional films • Conventional radiographic images can be converted into digital information by a “digitizer”, and electronically stored • Such a conversion also allows some numerical post-processing • Such a technique cannot be considered as a “ digital radiology” technique. Add module code number and lesson title

10. Different number of pixels per image: original was 3732 x 3062 pixels x 256 grey levels (21.8 Mbytes). Here, resized at 1024 x 840 (1.6 MB). Add module code number and lesson title

11. Scintillation-based DR Gadolinium Oxy-sulphide Detector

12. Digital Radiography Systems • Phosphor photostimulable plates (PSP). • So called CR (computed radiography) • Conventional X-ray systems can be used • Direct digital registration of image at the detector (flat panel detectors). • Direct conversion (selenium) • Indirect conversion (scintillation) Add module code number and lesson title

13. Computed Radiography (CR) • CR utilises the principle of photostimulable phosphor luminescence • Image plate made of a suitable phosphor material are exposed to X-rays in the same way as a conventional screen-film combination • The CR image plate retains most of the absorbed X-ray energy, in energy traps, forming a latent image Add module code number and lesson title

14. Computed Radiography (CR) • A scanning laser is then used to release the stored energy producing luminescence. • The emitted light, which is linearly proportional to the locally incident X-ray intensity is detected by a photo multiplier/ADC configuration and converted to a digital image • The resultant images have a digital specification of 2,370 x 1,770 pixels (for mammograms) with 1,024 grey levels (10 bits) and a pixel size of 100 mm corresponding to a 24 x 18 cm field size Add module code number and lesson title

15. The principle of PSP ADC PMT CB Trap Excitation Storage Emission Add module code number and lesson title

16. كــريــستــال هــالـيــد فــلــوريــد بــاريــم فــعــال شــده بـا يــوروپــيــوم (Europium Activated Barium FluoroHalide) BaFX:Eu , (X= Cl, Br, or I) Add module code number and lesson title

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18. Casette and PSP PSP digitizer (Images courtesy of AFGA) Workstation Add module code number and lesson title

19. DR Detecting Systems Add module code number and lesson title

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21. Direct vs indirect conversion detectors Add module code number and lesson title

22. CCD Based Detection System Add module code number and lesson title

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25. Digital detector Add module code number and lesson title

26. Amorphous Selenium Detector Add module code number and lesson title

27. Digital fluoroscopy • Digital fluoroscopic systems are mainly based on the use of image intensifiers (I.I.) • In conventional systems the output screen of the I.I. is projected onto a video camera system or a CCD camera • The output signals of the camera are converted into a digital image matrix (1024 x 1024 pixel in most systems). • Some new systems start to use flat panel detectors instead of image intensifier. Add module code number and lesson title

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30. Tendency to increase dose ? • For digital detectors, higher doses result in a better image quality (less “noisy” images) • When increasing dose, the signal to noise ratio is improved • Thus, a certain tendency to increase doses could happen specially in those examinations where automatic exposure control is not usually available. Add module code number and lesson title

31. The digital radiology department • In addition to the X-ray rooms and imaging systems, a digital radiology department has two other components: • A Radiology Information management System (RIS) that can be a subset of the hospital information system (HIS) • A Picture Archiving and Communication System (PACS). Add module code number and lesson title

32. Results To Webserver • Modality Worklist Information DICOM Images Verified HL7 HL7 HL7 Radiologist WorkStation Broker Voice Rec. Server Transcription Pool E-gate HIS RIS Add module code number and lesson title

33. Data management RIS PACS • We write a report! • Link both PACS and RIS. • Report compares Orders on RIS with Images on PACS. • Report highlights RIS orders with No images! Add module code number and lesson title

34. DICOM • DICOM (Digital Imaging and Communications in Medicine) is the industry standard for transferal of radiological images and other medical information between different systems • All recently introduced medical products should therefore be in compliance with the DICOM standard • However, due to the rapid development of new technologies and methods, the compatibility and connectivity of systems from different vendors is still a great challenge Add module code number and lesson title

35. DICOM format images: • Radiology images in DICOM format contain in addition to the image, a header, with an important set of additional data related with: • the X ray system used to obtain the image • the identification of the patient • the radiographic technique, dosimetric details, etc. Add module code number and lesson title