Fluoroscopy-Rohit.pptx

FLUOROSCOPY IS DESCRIBED IN DETAIL IN THIS PPT.
CONTENT TAKEN FROM MULTIPLE BOOKS AND JOURNALS.

1. FLUOROSCOPY ROHIT BANSAL Assistant Professor Department of Radio-Diagnosis MAMC, Agroha

2. HISTORY OF FLUOROSCOPY: Fluoroscopy invented by Thomas A. Edison in 1896. Conventional film radiography is restricted to static patient exams. Fluoroscopy is an imaging technique that used to obtain real time moving images of the internal structures of a patient through the use of a Fluoroscope. Fluoroscopy is basically a dynamic imaging, where the radiologists view images of moving organs continuously, while the X-ray beam is ON. PURPOSE: To perform dynamic studies. Visualize anatomical structures in real time or motion. View the motion and function of anatomic organs.

3. FLUOROSCOPIC UNIT Fig: A Fluoroscope and its associated parts

4. FLUOROSCOPY

5. INTRODUCTION: X-ray transmitted through patient. The photographic plate replaced by fluorescent screen. Screen fluoresces under irradiation and gives a live image. Older systems— direct viewing of screen. Screen part of an Image Intensifier system. Coupled to a television camera. Radiologist can watch the images “live” on TV-monitor; images can be recorded. Fluoroscopy often used to observe digestive tract 1) Upper GI series, Barium Swallow. 2) Lower GI series Barium Enema.

6. Direct Vision Fluoroscopy In direct vision fluoroscopy, the X-rays that are transmitted through the patient are passed on to a scintillation phosphor screen (ZnS), which gives an image as faint scintillations. The radiologists had dark adapted his eyes by wearing red goggles for 20-30 minutes prior to the examination. The thick phosphor converts the X-rays into light proportionally, but the brightness is too low.

7. It was discontinued due to the following reasons:- The light output of the fluorescent screen is very poor, for a given exposure rate. The light conversion efficiency of the screen is also very low and the spatial resolution is very poor. Since the images are so faint, it has to be viewed under dark conditions with red goggles. In addition, the patient may receive higher dose of radiation and hence this modality is not in use to day.

8. DIFFERENT FLUOROSCOPY SYSTEMS: Remote control systems: Not requiring the presence of medical specialists inside the X Ray room Mobile C-arms: Mostly used in surgical theatres.

9. Interventional radiology systems: Requires specific safety considerations. In interventional radiology the physician can be near the patient during the procedure. Multipurpose fluoroscopy systems: Can be used as a remote control system or as a system to perform simple interventional procedures .

10. FLUOROSCOPY -MODES OF OPERATION: Manual Mode: Allow the use to select the exact MA and kVp required. AEC Mode: Allow the unit to drive the kVp and mAs to optimize dose and image quality. Pulsed Digital mode: Modifies the fluoroscopic output by cutting by cutting out exposure between pulses With the pulsed mode, it can be set to produce less than the conventional 25 or 30 images per second. This reduces the exposure rate.

11. IMAGE INTENSIFIERS

12. INTRODUCTION: We consider the production of an image on a fluorescent screen by means of X-Rays and the use made of this for fluoroscopy. We saw then that the direct fluoroscopic image is inferior to the radiographic one in respect of: 1. brightness; 2. detail sharpness; 3. contrast. The process of brightening the image during fluoroscopy is called “ Image intensification ”. The association of closed circuit television with apparatus for image intensification is virtually universal.

13. BASIC IMAGING CHAIN: Fig: Basic imaging chain

14. X-RAY IMAGE INTENSIFIER TUBE: The image-intensifier tube is a complex electronic device that receives the image forming x-ray beam and converts it into a visible-light image of high intensity. The process of brightening the image during fluoroscopy is called image intensification. Fig: Principle of an image intensifier tube

15. CONSTRUCTION AND FUNCTION OF IMAGE INTENSIFIER TUBE: An evacuated glass—or in some instances metal—envelope; An input screen(input phosphor) which is in intimate contact with a photocathode; An electron focusing and accelerating system (electron lens); An output screen (output phosphor). Fig: An X-Ray image intensifier tube

16. INPUT PHOSPHOR: Constructed of cesium iodide (CsI). Responsible for converting the incident photons energy to a burst of visible light photon which is similar to intensifying screens in cassettes. Standard size varies from 10-35 cm. Normally used to identify the image intensifier tubes. Fig: X-Ray photon reaching the input phosphor.

17. Why CsI rather than silver activated zinc cadmium sulfide ? CsI has three physical characteristics which makes it superior:  vertical orientation of the crystals.  greater packing density.  more favorable effective atomic number. Packing density of CsI is 3 times greater than zinc cadmium sulfide Reduced phosphor thickness with improved resolution

18. PHOTO CATHODE: Thin metal layer bonded directly to the input phosphor. Usually made of cesium & antimony compounds that respond to light stimulation. Responsible for photo emission. Electron emission after light stimulation. The number of electrons emitted is directly proportional to the intensity of light & to the intensity of the incident x-ray photon. Fig: Showing Photo cathode in image intensifier tube .

19. ELECTROSTATIC FOCUSING LENSES The lens is made up of positively charged electrodes that are usually plated onto the inside surface of the glass envelope of the image intensifier tube. These electrodes maintain proper focus of the photoelectrons emitted from the photo cathode. Electron focusing inverts and reverses the image. This is called point inversion because all the electrons pass through a common focal point on their way to the output phosphor. They are located along the length of the image intensifier tube. The focusing lenses assist in maintaining the kinetic energy of the photo electrons to the output phosphor.

20. ACCELERATING ANODE: Accelerating anode is resent at the neck of the image intensifier tube. Its function is to accelerate electrons emitted from the photocathode towards the output screen. The anode has a positive potential of 25 to 35 kv relative to the photocathode. So it accelerates electrons to a tremendous velocity.

21. OUTPUT PHOSPHOR: Output fluorescent screen of image intensifiers is made up of silver-activated zinc cadmium sulfide. Crystal size & layer thickness (0.5-1 inch)are reduced to maintain resolution in minified image. Emits more light photons than were originally resent in input phosphor. The output phosphor image is viewed either directly through a series of fiberoptic lenses & mirrors or indirectly by closed circuit television where it is converted into a series of electrical pulses called the video signal.

22. TELEVISION PROCESS: Television contains many detailed elements of technical complexity but making the simplest assessment possible-we can concerned in principle: Principle 1: Light (Visual) information becomes Electrical information. Principle 2: Electrical information becomes Visual information. TV camera tubes work on a principle of photoconductivity or photoemission. There are several kinds of TV camera tubes used in Medical Radiology.

23. TELEVISION CAMERA TUBE (VIDICON). We may obtain a general understanding of a photoconductive system if we consider first the camera tube which is called a vidicon. The photoconductive material used in vidicon tubes is antimony sulfide (Sb2S3). The vidicon camera tube have three main sections. A. A target section. B. An electron gun. C. A scanning section. Fig: Three Vidicon camera tubes with different diameters.

24. Fig: A Vidicon camera tube.

25. A TARGET SECTION: The target of vidicon is Photoconductive . Target Passes electric current when light is falling upon it and resists electron flow in absence of light. Higher the intensity of light greater will be the conductivity, and higher will be current caused to flow. TARGET CONSISTS OF: Target material used is Antimony Trisulphide. At the front of the tube, A Glass Face-plate. Back of glass face-plate, a conductive transparent layer of Zinc Oxide . Target Antimony Trisulphide is coated thinly upon the presenting surface of the transparent signal plate.

26. AN ELECTRON GUN: Function of electron gun is to produce beam of electrons. ELECTRON GUN CONSISTS OF: A cathode- emits electrons. A Grid (electrode)- controls density of electron flow. A second grid- Accelerates and focuses the stream of electrons. Beam enters then to scanning section of tube.

27. OTHER CAMERA TUBES: As well as the vidicon, other television camera tubes of a photoconductive type are in use for television fluoroscopy. Perhaps the best known of these is the Plumbicon . PLUMBICON: Works on principle of Photoconductivity. Photoconductor used is Lead Monoxide ( PbO ). Larger than vidicon Faster response, less movement blur is seen. Resolution of detail is poorer. Virtually no dark current is present. Fig: Plumbicon camera tube

28. CATHODE RAY TUBE: Cathode ray tube is a funnel shaped evacuated glass tube contain an electron gun, control grid, anode, focusing coil and deflecting coils. Its narrow end contains an electrical system designed to emit, accelerate and focus a stream of electrons. The expanded end of the tube forms a special screen which is coated with a material which will fluorescence when the electrons strike it. Fig: Cathode ray tube

29. ELECTRICAL SYSTEM: Like other vacuum tubes known to the student radiographer  the X-Ray tube itself and television pick-up tubes  the cathode ray tube contains a heated filament ( the cathode) and depends for its function on the emission of electrons from this filament. The electrons so produced are accelerated towards the screen at the other end of the tube by; a) a potential difference between the cathode and the screen. b) a high positive voltage on the anodes,

30. FLUORESCENT SCREEN: Many substances will fluoresce when electrons strike them. Zinc phosphates, silicates and sulphides are all examples of phosphors which will fluoresce under electronic bombardment. It is usual to employ one as a base and to add other material which modify the response of the phosphor. Fig: Fluorescent screen

31. It is usual to employ one as a base and to add other materials which modify the response of the phosphor. These are  Activators – change the color of the fluorescence;  Killers – affects the image retention in the phosphor. In the case of the tube in a television monitor the phosphor on the screen should:  Have maximum sensitivity.  Have long life.  Exhibit short image retention.

32. Digital Fluoroscopy

33. Digital Fluoroscopy The signal from the video camera can be converted into digital format and fed into the computer. The computer will display high resolution digital images, that can be viewed like a movie. Digital fluoroscopy has faster image acquisition and storage and image manipulation. In digital fluoroscopy, either charge coupled device or flat panel detectors are used.

34. Detector Technology Main function of detector is conversion of x-ray signal into electronic signal. Types of Detector: Indirect Digital Detector. Direct Digital Detector.

35. Indirect Digital Detector It consists of Scintillation phosphor, Amorphous Silicon Photodiodes. Scintillation Crystal Used: Thallium Activated Cesium Iodide ( CsI:Tl ) Terbium Activated Gadolinium Oxy-Sulfide (Gd2O2S:Tb) Function: X-Ray Signal Light Photon Photodiodes: Amorphous Silicon (Light Sensitive material). Function: Light Signal Electronic Signal

36. Direct Digital Detector As Direct Digital Detector = Amorphous Silicon Photo Conducting Material is used. X-Ray Photon Selenium Photo Conducting Layer Electronic Signal

37. Thin Film Transistor (TFT) It can be used with both direct and indirect digital detector method. It is also known as Flat panel detector. The TFT has three connections. Source = Capacitor. Gate = Connected to Horizontal Lines (Rows). ® Drain = Connected to Vertical lines or read out lines (Column). ©

38. C2 C1 C3 C4 R1 R2 R3 R4 S1 S2 S3 S4

39. TFT is basically an electronic switch that can be made on and off. Negative voltage applied to the gate = Off. Positive voltage applied to the gate = On. Initially, the capacitor of each detector element stores the charge is earthed, so that all the residual charges are passed on ground. During the x-ray exposure, negative voltage to gate is applied, Then TFT is on off position and charge is accumulated in each detector element is stored in capacitor. During the readout process, positive voltage is applied to gate (one row ® at a time) then the switches of detector elements in a given row are On. This will connect vertical wires C1, C2, C3 & C4 to digitizer through switches S1, S2, S3 & S4. Multiplexer selects the column sequentially (one column at a time) and charge is amplified and allowed to move to digitizer.

40. CHARGE-COUPLED DEVICE Charge-Coupled Devices (CCD) forms images from visible light. The charge-coupled device (CCD) is used to get digital format of the Image Intensifier tube light. CCD is an integrated circuit made up of Metal Oxide Crystalline Silicon Capacitor ( MoCSC ). CCD has individual pixel elements; when visible light falls on each pixel; electrons are librated charges from pixel. The electrons in every pixel are sifted to another pixel. The bottom row is readout pixel by pixel and the charge is shifted to the readout electronics; which produces an electronic signal. This signal is digitized by Analog to Digital Converter (ADC) and will be used to construct final image.

41. Spot Film Device Fluoroscopic systems designed for gastrointestinal imaging are generally equipped with a spot film device. The spot film device allows exposure of a conventional screen-film cassette in conjunction with fluoroscopic viewing. This rather familiar system, located in front of the image intensifier, accepts the screen-film cassette and "parks" it out of the way during fluoroscopy. Cassettes may be loaded from the front or rear depending on the design of the system. The X-ray field size is also reduced automatically by the collimators at the time of exposure to minimize scattered radiation and patient radiation dose. The fluoroscopist can override this automatic collimation to further reduce the X-ray field. Spot film imaging uses essentially the same technology as conventional screen-film radiography. One major limitation is the range of film sizes available for spot film imaging. Although some older fluoroscopy equipment is limited to a single size, usually 24 x 24 cm, current equipment allows a range of film sizes to be used, from 20 x 25 cm to 24 x 35 cm. Spot film devices usually allow more than one image to be obtained on a single film.

42. Automatic Film Changers The automatic film changers used in vascular imaging are also screen-film systems. They can be found in several varieties. Some are large, floor-mounted boxes, but systems more commonly used today mount on the image intensifier. The system consists of a supply magazine for holding unexposed film, a receiving magazine, a pair of radiographic screens, and a mechanism for transferring the film. When an exposure is required, the screens are mechanically separated, the film is pulled into place between them, and they are closed. After the film is exposed, the screens separate again. The film is moved to the receiver, and another film is pulled into place for the next exposure. The number of films and filming rates must be preprogrammed for proper operation Because the major requirement is capturing rapid motion of a contrast agent, 800-speed screen-film combinations are typically used in film changers.

43. This speed leads to a dose half that of the more general-purpose 400-speed systems used for gastrointestinal imaging. Resolution is also reduced to about 5 lp /mm. Unlike with spot film devices, the requirement for rapid motion limits the automatic changer to one film size, usually 35 x 35 cm. The typical film changer holds up to 30 films in the receiving magazine. At the maximum rate of four films per second, a 7.5-second run is achieved without changing magazines. A problem common to many film changer systems is that the film changer is mounted perpendicular to the image intensifier. Thus, there is a long delay between fluoroscopic viewing and recording of the images. In some systems, the film changer is mounted in front of the intensifier, limiting the size of the intensifier input field to something smaller than the film size when the changer is in position. Other problems associated with film changers are motion blurring, missed exposures, jamming, inadequate density and contrast, and film fogging.

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