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IAEA International Atomic Energy Agency RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY L16.1: Optimization of protection in fluoroscopy.

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Presentation on theme: "IAEA International Atomic Energy Agency RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY L16.1: Optimization of protection in fluoroscopy."— Presentation transcript:

1 IAEA International Atomic Energy Agency RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY L16.1: Optimization of protection in fluoroscopy IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

2 IAEA 16.1: Optimization of protection in fluoroscopy2 Introduction Subject matter : fluoroscopy equipment and accessories Different electronic component contribute to the image formation in fluoroscopy. Good knowledge of their respective role and consistent Quality Control policy are the essential tools for an appropriate use of such equipment.

3 IAEA 16.1: Optimization of protection in fluoroscopy3 Topics Example of fluoroscopy systems Image intensifier component and parameters Image intensifier and TV system

4 IAEA 16.1: Optimization of protection in fluoroscopy4 Overview To become familiar with the components of the fluoroscopy system (design, technical parameters that affect the fluoroscopic image quality and Quality Control).

5 IAEA International Atomic Energy Agency Part 16.1: Optimization of protection in fluoroscopy Topic 1: Example of fluoroscopy systems IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

6 IAEA 16.1: Optimization of protection in fluoroscopy6 Used to visualize motion of internal fluid, structures Operator controls activation of tube and position over patient Early fluoroscopy gave dim image on fluorescent screen Modern systems include image intensifier with television screen display and choice of recording devices Fluoroscopy: a see-through operation with motion

7 IAEA 16.1: Optimization of protection in fluoroscopy7 X-ray transmitted trough 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 Upper GI series, Barium Swallow Lower GI series Barium Enema Fluoroscopy

8 IAEA 16.1: Optimization of protection in fluoroscopy8 Direct Fluoroscopy: obsolete In older fluoroscopic examinations radiologist stands behind screen and view the picture Radiologist receives high exposure; despite protective glass, lead shielding in stand, apron and perhaps goggles Main source of staff exposure is NOT the patient but direct beam

9 IAEA 16.1: Optimization of protection in fluoroscopy9 Older Fluoroscopic Equipment (still in use in some countries) Staff in DIRECT beam

10 IAEA 16.1: Optimization of protection in fluoroscopy10 AVOID USE OF DIRECT FLUOROSCOPY Directive 97/43Euratom Art 8.4. In the case of fluoroscopy, examinations without an image intensification or equivalent techniques are not justified and shall therefore be prohibited. Direct fluoroscopy will not comply with BSS … performance of diagnostic radiography and fluoroscopy equipment and of nuclear medicine equipment should be assessed on the basis of comparison with the diagnostic reference levels Direct fluoroscopy

11 IAEA 16.1: Optimization of protection in fluoroscopy11 Modern Image Intensifier based fluoroscopy system

12 IAEA 16.1: Optimization of protection in fluoroscopy12 Automatic control display brightness radiation dose film exposure Timer Display control Modern fluoroscopic system components

13 IAEA 16.1: Optimization of protection in fluoroscopy13 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.

14 IAEA 16.1: Optimization of protection in fluoroscopy14 Different fluoroscopy systems 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

15 IAEA International Atomic Energy Agency Part 16.1: Optimization of protection in fluoroscopy Topic 2: Image Intensifier component and parameters IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

16 IAEA 16.1: Optimization of protection in fluoroscopy16 The image intensifier (I.I.) + I.I. Input Screen I.I.Output Screen Photocathode Electrode E 1 Electrode E 3 Electrode E 2 Electrons Path

17 IAEA 16.1: Optimization of protection in fluoroscopy17 Image intensifier systems

18 IAEA 16.1: Optimization of protection in fluoroscopy18 Image intensifier component * Input screen: conversion of incident X Rays into light photons (CsI) * 1 X Ray photon creates 3,000 light photons * Photocathode: conversion of light photons into electrons * only 10 to 20% of light photons are converted into photoelectrons * Electrodes : focusing of electrons onto the output screen * electrodes provide the electronic de-magnification * Output screen: conversion of accelerated electrons into light photons

19 IAEA 16.1: Optimization of protection in fluoroscopy19 Image intensifier parameters (I) * Conversion coefficient (Gx): the ratio of the output screen brightness to the input screen dose rate Gx = cd.m -2 Gys -1 3 Gx depends on : * the applied tube potential * the diameter ( ) of the input screen * I.I. input screen ( ) of 22 cm Gx = 200 * I.I. input screen ( ) of 16 cm Gx = 200 x (16/22) 2 = 105 * I.I. input screen ( ) of 11 cm Gx = 200 x (11/22) 2 = 50

20 IAEA 16.1: Optimization of protection in fluoroscopy20 Image intensifier parameters (II) Brightness Uniformity: the input screen brightness may vary from the center of the image intensifier to the periphery Geometrical distortion: all X Ray image intensifiers exhibit some degree of pincushion distortion. This is usually caused by a local magnetic field. Uniformity = (Brightness(c) - Brightness(p)) x 100 / Brightness(c)

21 IAEA 16.1: Optimization of protection in fluoroscopy21 Image distortion

22 IAEA 16.1: Optimization of protection in fluoroscopy22 Image intensifier parameters (III) Spatial resolution limit: the value of the highest spatial frequency that can be visually detected it provides a sensitive measure of the state of focusing of a system it is quoted by manufacturer and usually measured optically and under fully optimized conditions. This value correlates well with the high frequency limit of the Modulation Transfer Function (MTF) it can be assessed with a resolution pattern which contains several sets of patterns at various frequency

23 IAEA 16.1: Optimization of protection in fluoroscopy23 Line pair gauges

24 IAEA 16.1: Optimization of protection in fluoroscopy24 Line pair gauges GOOD RESOLUTIONPOOR RESOLUTION

25 IAEA 16.1: Optimization of protection in fluoroscopy25 Image intensifier parameters (IV) Overall image quality - threshold contrast-detail detection X Ray, electrons and light scatter process in an I.I. can result in a significant loss of contrast of radiological detail. The degree of contrast exhibited by an I.I. is defined by the design of the image tube and coupling optics. Spurious sources of contrast loss are: accumulation of dust and dirt on the various optical surfaces reduction in the quality of the vacuum aging process (deterioration of phosphor screen) Sources of noise are: X Ray quantum mottle photon-conversion processes, film granularity, film processing

26 IAEA 16.1: Optimization of protection in fluoroscopy26 Image intensifier parameters (V) Overall image quality can be assessed using a suitable threshold contrast-detail detectability test object which comprises an array of disc-shaped metal details and gives a range of diameters and X Ray transmission Sources of image degradation such as contrast loss, noise and unsharpness limit the number of details that are visible. If performance is regularly monitored using this test, any sudden or gradual deterioration in image quality can be detected as a reduction in the number of low contrast or small details.

27 IAEA 16.1: Optimization of protection in fluoroscopy27 Overall image quality

28 IAEA International Atomic Energy Agency Part 16.1: Optimization of protection in fluoroscopy Topic 3: Image Intensifier and TV system IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

29 IAEA 16.1: Optimization of protection in fluoroscopy29 Image intensifier - TV system Output screen image can be transferred to different optical displaying systems: conventional TV 262,5 odd lines and 262,5 even lines generating a full frame of 525 lines (in USA) 625 lines and 25 full frames/s up to 1000 lines (in Europe) interlaced mode is used to prevent flickering Cine film 35 mm film format: from 25 to 150 images/s photography roll film,105 mm: max 6 images/s film of 100 mm x 100 mm

30 IAEA 16.1: Optimization of protection in fluoroscopy30 VIDICON FILM PM REFERENCEkV CONTROLLER X Ray TUBE kV GENERAL SCHEME OF FLUOROSCOPY

31 IAEA 16.1: Optimization of protection in fluoroscopy31 VIDICON FILM PM CONTROLLER X Ray TUBE kV CINE MODE I2I2 Ref. I3I3 C1C1 I1I1 C2C2

32 IAEA 16.1: Optimization of protection in fluoroscopy32 Type of TV camera VIDICON TV camera improvement of contrast improvement of signal to noise ratio high image lag PLUMBICON TV camera (suitable for cardiology) lower image lag (follow up of organ motion) higher quantum noise level CCD TV camera (digital fluoroscopy) digital fluoroscopy spot films are limited in resolution, since they depend on the TV camera (no better than about 2 c/mm) for a 1000 line TV system

33 IAEA 16.1: Optimization of protection in fluoroscopy33 TV camera and video signal (I) The output phosphor of the image intensifier is optically coupled to a television camera system. A pair of lenses focuses the output image onto the input surface of the television camera. Often a beam splitting mirror is interposed between the two lenses. The purpose of this mirror is to reflect part of the light produced by the image intensifier onto a 100 mm camera or cine camera. Typically, the mirror will reflect 90% of the incident light and transmit 10% onto the television camera.

34 IAEA 16.1: Optimization of protection in fluoroscopy34 TV camera and video signal (II) Older fluoroscopy equipment will have a television system using a camera tube. The camera tube has a glass envelope containing a thin conductive layer coated onto the inside surface of the glass envelope. In a PLUMBICON tube, this material is made out of lead oxide, whereas antimony trisulphide is used in a VIDICON tube.

35 IAEA 16.1: Optimization of protection in fluoroscopy35 Photoconductive camera tube Focussing optical lens Input plate Steering coils Deviation coil Alignement coil Accelarator grids Control grid Electron beam Video Signal Signal electrode Field grid Electrode Electron gun Iris Photoconductive layer

36 IAEA 16.1: Optimization of protection in fluoroscopy36 TV camera and video signal (III) The surface of the photoconductor is scanned with an electron beam and the amount of current flowing is related to the amount of light falling on the television camera input surface. The scanning electron beam is produced by a heated photocathode. Electrons are emitted into the vacuum and accelerated across the television camera tube by applying a voltage. The electron beam is focussed by a set of focussing coils.

37 IAEA 16.1: Optimization of protection in fluoroscopy37 TV camera and video signal (IV) This scanning electron beam moves across the surface of the TV camera tube in a series of lines. This is achieved by a series of external coils, which are placed on the outside of the camera tube. In a typical television system, the image is formed from a set of 625 lines. On the first pass the set of odd numbered lines are scanned followed by the even numbers. This type of image is called interlaced. The purpose of interlacing is to prevent flickering of the television image on the monitor, by increasing the apparent frequency of frames (50 half frames/second). In Europe, 25 frames are updated every second.

38 IAEA 16.1: Optimization of protection in fluoroscopy38 Different types of scanning INTERLACED SCANNING PROGRESSIVE SCANNING 12 2 14 4 16 18 6 1 8 20 13 15 17 10 11 3 21 19 5 7 9 3 5 18 16 14 12 10 8 6 4 2 7 9 11 13 15 17 1 625 lines in 40 ms i.e. : 25 frames/s

39 IAEA 16.1: Optimization of protection in fluoroscopy39 TV camera and video signal (V) On most fluoroscopy units, the resolution of the system is governed by the number of lines of the television system. Thus, it is possible to improve the high contrast resolution by increasing the number of television lines. Some systems have 1,000 or 2,000

40 IAEA 16.1: Optimization of protection in fluoroscopy40 TV camera and video signal (VI) Many modern fluoroscopy systems used CCD (charge coupled devices) TV cameras. The front surface is a mosaic of detectors from which a signal is derived. The video signal comprises a set of repetitive synchronizing pulses. In between there is a signal that is produced by the light falling on the camera surface. The synchronizing voltage is used to trigger the TV system to begin sweeping across a raster line. Another voltage pulse is used to trigger the system to start rescanning the television field.

41 IAEA 16.1: Optimization of protection in fluoroscopy41 Schematic structure of a charged couple device (CCD)

42 IAEA 16.1: Optimization of protection in fluoroscopy42 TV camera and video signal (VII) A series of electronic circuits move the scanning beams of the TV camera and monitor in synchronism. This is achieved by the synchronizing voltage pulses. The current, which flows down the scanning beam in the TV monitor, is related to that in the TV camera. Consequently, the brightness of the image on the video display is proportional to the amount of light falling on the corresponding position on the TV camera.

43 IAEA 16.1: Optimization of protection in fluoroscopy43 TV image sampling SYNCHRO 12 µs LIGHT INTENSITY SAMPLING 64 µs VIDEO SIGNAL (1 LINE) 52 µsIMAGE LINE SINGLE LINE TIME DIGITIZED SIGNAL ONE LINE IMAGE 512 x 512 PIXELS WIDTH 512 HEIGHT 512

44 IAEA 16.1: Optimization of protection in fluoroscopy44 Digital radiography principle Clock Memory ADC I Iris t t ANALOGUE SIGNAL DIGITAL SIGNAL See more in Lecture L20

45 IAEA 16.1: Optimization of protection in fluoroscopy45 Digital Image recording In newer fluoroscopic systems film recording is replaced with digital image recording. Digital photospots are acquired by recording a digitized video signal and storing it in computer memory. Operation fast, convenient. Image quality can be enhanced by application of various image processing techniques, including window-level, frame averaging, and edge enhancement. But the spatial resolution of digital photospots is less than that of film images.

46 IAEA 16.1: Optimization of protection in fluoroscopy46 It is possible to adjust the brightness and contrast settings of the TV monitor to improve the quality of the displayed image. TV camera and video signal (VIII)

47 IAEA 16.1: Optimization of protection in fluoroscopy47 Summary The main components of the fluoroscopy imaging chain and their role are explained: Image Intensifier Associated image TV system

48 IAEA 16.1: Optimization of protection in fluoroscopy48 Where to Get More Information The Essential Physics of Medical Imaging. JT Bushberg, JA Seibert, EM Leidholdt, JM Boone. Lippincott Williams & Wilkins, Philadelphia, 2011 The physics of diagnostic imaging, Dowsett et al, Hodder Arnold, 2006 Interventional Fluoroscopy: Physics, Technology, Safety, S. Balter, Wiley-Liss, 2001


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