Fluoroscopy

FLUOROSCOPY

1. Fluoroscopy Presenter: Sujan Karki B.Sc. MIT 2nd year National Academy of Medical Sciences, Bir Hospital

2. Topics Included History IITV system Digital Fluroscopy

3. Direct Fluoroscopy Thomas Edison experimenting with the fluoroscope he designed. The subject is his assistant, Clarence Dally.

4. Historical development

5. TV FLUROSCOPY

6. Fluoroscopic imaging chain

7. X-ray Generator Selection of KVP and MA that is delivered to x-ray tube. similar design as of radiography with added circuitry for automatic brightness control and low continuous tube current or rapid pulsed exposure. Methods used to energize xray tube in fluoroscopy: 1) Pulsed Exposure 2) Continuous Exposure

8. X-ray Tube X-ray tubes are produced with anode angle ranges of 7°–20°. For radiography and fluoroscopy systems, bi-focus tubes are common. A small focal spot (0.3–0.6 mm) is used for fluoroscopy, and either the small or the large focal spot (1.0–1.2 mm) can be used for image recording when high tube currents are needed. small focal spot may be essential for sharp images of fine vasculature or guide wires

9. Collimator multiple sets of radiopaque shutter blades that define the shape of the x-ray beam Two sets of blades are generally present within the collimator : round and rectangular. A round iris conforms the x-ray beam to the circular FOV Rectangular blades can be brought in manually to further reduce the beam size

10. CONTD Most fluoroscopy systems used for angiography and interventional applications also contain equalization filters. also called contour or wedge filters Further beam shaping in addition to collimation. Equalization filters reduce glare from unattenuated radiation near the edge of the patient and equalize light exposure to the video camera. The filters are made from tapered lead-rubber or lead-acrylic sheets.

11. Filter The penetrating ability of an x-ray beam is determined by measuring the half-value layer (HVL), where the HVL is the thickness of some attenuating material that reduces the beam intensity by one-half at a specified kilovolt peak. Federal regulations require that the minimum HVL for both radiography and fluoroscopy be 2.3 mm Al at 80 kVp . However, it is recommended that the minimum HVL be increased to 3.0 mm Al at 80 kVp to reduce patient dose, particularly for fluoroscopy. Aluminum is the most common added filtration material. Copper can also be used for improved low-energy x-ray filtering  The use of copper filtration material has become more prevalent in fluoroscopy systems used for high-dose procedures such as angiography and interventional applications.

12. These lead-rubber  (a)  and lead-acrylic  (b)  blades are mounted at the collimator with controls provided to adjust the blade location and rotation in order to conform to patient regions of low attenuation. a b

13. Grid Anti-scatter grids are used to improve image contrast by reducing the scattered x rays that reach the image receptor The grid ratios for fluoroscopy range from 6:1 to 10:1 , which is generally lower than common radiographic grid ratios (8:1 to 16:1). Image contrast loss will be minimal when the FOV is reduced or the patient or body part examined is small a grid is not needed if a large air gap between the patient and the image intensifier is required for geometric magnification, access to the patient, or access to interventional devices. With the grid removed, patient exposure can be reduced by about 50%. Although some fluoroscopy systems allow for easy grid removal, exchanging the grid can be cumbersome or impossible on others. 

14. Image Intensifier The image intensifier converts incident x rays into a minified visible light image and, in the process, amplifies the image brightness by about 10,000 times for better visibility to the viewer Image intensifiers are available with different diameter input windows of 10–40 cm. Fluoroscopic systems designed for extremities may be configured with a 10–15-cm-diameter image intensifier, whereas a 40-cm-diameter unit is useful for imaging the abdomen or peripheral vasculature.

15. Optical Coupling distributes light from the image intensifier output window to a video camera and other image recording devices The optical distributor may include a partially silvered, beam-splitting mirror, which directs a portion of the light from the image intensifier output window to an accessory device for image recording and passes the remainder to the video camera .

16. Television System A closed-circuit television system is used to view the image intensifier output image.   The television system consists of a video camera that converts the image to a voltage signal and a monitor that receives the signal and forms the image display. Advantages of TV monitor are: Brightness can be adjusted Multiple obserber can see the display at the same time Image storage at the electronic format

17. Working of TV Camera

18. MAGNIFICATION Magnification is achieved electronically with electronic focusing of the electron beam. Because less signal is used, the image is less bright and, therefore, a higher dose is needed. However, as the image magnified, the resolution is better . Reduce the FOV , irradiate only smaller volume of tissue and the image appear magnified, since it fills the entire screen on the monitor.

19. AUTOMATIC BRIGHTNESS CONTROL Automatic brightness control (ABC) is a mechanism, which can keep the brightness of the image constant at the monitor. Basically a feedback circuit, which measure the light intensity of the output screen or videocamera signal. A photomultiplier or a photodiode is used to monitor the light output of the II tube.

20. Fluoroscopic Equipment Configurations R/F Units with Over-Table X-ray Tube R/F Units with Under-Table X-ray Tube

21. Digital fluroscopy The signal from the video camera can be converted into digital format and fed into the computer. Digital fluoroscopy has faster image acquisition and storage and image manipulation.

22. Digital Fluroscopy During DF, the X-ray tube actually operates in the radiographic mode. This is not the problem as images from Digital Fluoroscopy are obtained by pulsing the X-ray beam in a manner called Pulse-Progressive Fluoroscopy. PPF contain 3 stages: Interrogation time : time required for the X-ray tube to be switched on and reach selected levels of kVP and mA. Duty cycle : fraction of time that the X-ray tube is energized. Extinction time : time required for the x-ray tube to be switched off.

23. contd Images may be acquired at 15 frames per second rather than the usual 30 frames per second. Because simply reducing the number of pulses would result in an increase in image noise, manufacturers may increase the milliamperage setting to achieve a similar visual appearance. one would expect a 50% dose reduction when going from 30 to 15 frames per second, but, because of increased milliamperage, the actual dose savings are 25%–28%  With equivalent perceptibility levels, Aufrichtig et al showed average dose savings of 22%, 38%, and 49% at 15, 10, and 7.5 frames per second, respectively.

24. Charge-Coupled Devices (CCDs) The oldest indirect-conversion digital radiography systems used  charge-coupled devices (CCDs)  to acquire the digital image . CCD chip is an integrated circuit, made up of amorphous silicon. The silicon surface is photoconductive. If it is exposed to visible light, electrons are liberated and build up in the pixel. Thus, each pixel act as capacitor and collect charge, proportional to light

25. Movement of charge pockets column by column through bottom row

26. ADVANTAGES OF CCD High spatial resolution High signal to noise ratio High quantum detective efficiency No lag or blooming No spatial distortion Unlimited life Linear response Low patient dose

27. Active-Matrix Flat-Panel Imagers The two main types of x-ray absorption materials currently being used are photoconductors and scintillators . Photoconductors  are materials that absorb x-rays, resulting in an electrical charge Scintillators are phosphors that produce light when absorbing x-rays An AMFPI detector measures the response of these materials to x-ray absorption and is a large area two-dimensional (2-D) array of pixels fastened to a thin glass backing, or substrate.

28. Flat Panal Detector fluoroscopy system

29. Indirect Conversion Indirect detection flat panel systems consist of a Scintillation phosphor, amorphous silicon photo diode (a-Si) and flat TFT arrays. The detector base is the glass substrate, on to which light sensitive a-Si with a capacitor and TFT is embedded in the form of pixels When exposed to X-rays, the scintillation emits visible light The photodiode release electrons, so that charge build up in each detector element, which is stored by the capacitor.

30. Direct conversion Amorphous Selenium is the direct DF process by which X-rays are converted to electric signal as no scintillation phosphor is involved. The imaging forming X-ray beam interacts directly with a-Se producing a charged pair. a-Se is both the capture element and the coupling element. a-Se is approx. 200 micron meter thick and is sand- wiched between charged electrodes. X-rays incident on a-Se create electron hole pairs through direct ionization of Selenium. The created charge is collected by a storage capacitor and remains there until the signal is read by the switching action of the TFT.

31. Artefacts Artefacts in fluoroscopic imaging usually stem from image distortions caused by components of the image chain XRII suffer from several common image distortions including: 1)Veiling Glare 2) Vignetting 3)Blooming 4)Pincushion Distortion 5)S Distortion Flat Panel image receptors are generally freefrom image distortions

32. Veiling Glare degrades object contrast at the output phosphor of the image intensifier. X-ray, electron, and light scatter all contribute to veiling glare. A thick XRII Output Windowis used that may incorporate - Dopants to absorb scattered light, -Sides coated with a light-absorbing material

33. Vignetting A fall-off in brightness at the periphery of an image is called vignetting . As a result, the center of an image intensifier has better resolution, increased brightness, and less distortion. Vignetting can be reduced in some cases by restricting the Aperture Size

34. Pincushion Distortion Pincushion distortion is a geometric, nonlinear magnification across the image. Appearance of straight lines curving towards the edges Results from the curvature of the input phosphor More severe for large fields of view

35. S Distortion External electromagnetic sources affect electron paths at the periphery of the image intensifier more, than those nearer the center. Results from presence of an External magnetic field Manufacturers include a highly conductive metal shield that lines the case in which the vacuum bottle is positioned to reduce the effect of S distortion .

36. Blooming Blooming is caused by the input of signals to the video camera that exceed its Dynamic Range Such large signals cause Lateral Charge Spreading with in the camera target resulting in a diffuse image that is larger than the original Can be minimized through the use of tight X ray beam Collimation Has largely been eliminated in CCD cameras

37. Minification gain the ratio of input area to the output area of the image intensifier. A smaller output window size will just compress more photons into a smaller area, producing a smaller but brighter image.

38. Flux gain The ratio of the number of light photons striking from the output screen to the ratio of the number of x-ray photons striking the input screen. 1000 light photons at the photocathode from 1 xray photon Output phosphor = 3000 light photons (3 X more than at the input phosphor!) This increase is called the flux gain

39. Brightness Gain and Conversion Factor The brightness gain comes from two sources that are completely unrelated: – the minification gain – the flux gain. Brightness Gain = 𝑀𝑖𝑛𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 𝐺𝑎𝑖𝑛 × 𝐹𝑙𝑢𝑥 𝐺𝑎𝑖𝑛

40. PATIENT RADIATION DOSE The entrance exposure limit for standard operation of a fluoroscope is 10 R/min (100 mGy /min)  Some fluoroscopes are equipped with a high-output or “boost” mode, and the limit for operation in this mode on state-of-the-art equipment is 20 R/min (200 mGy /min ) Dose rates of up to 50 R/min (500 mGy /min) and higher may be encountered during recorded interventional and cardiac catheterization studies. A very long examination involving 30 minutes of fluoroscopy time could result in doses of <90–1,500 rad ( 900 mGy to 15 Gy ). 1,500 rad (15 Gy ) can cause severe skin burns that develop slowly and may take months to heal. ( 18 Gy ) can causes evere skin burns involving dermal necrosis may slowly evolve over many months

41. WHAT TO DO DURING FLUROSCOPY

42. Intermittent Fluoroscopy keeping the x rays on only a few seconds at a time, long enough to view the current catheter position.   View and save images with last-image-hold Fluoroscopy units are also equipped with last-image-hold. This allows for storing and reviewing of the last image without re-exposing the patient to more radiation.

43. Effect of dose spreading by varying the beam incidence angle.

44. KEEP IMAGE INTENSIFIER CLOSE TO THE PATIENT

45. VARIOUS TYPES OF SHIELDINGS

46. SCATTER LEVEL WITH AND WITHOUT SHIELDING

47. References Fluoroscopy: Patient Radiation Exposure Issues, Mahadevappa Mahesh The AAPM/RSNA Physics Tutorial for Residents General Overview of Fluoroscopic Imaging, Beth A. Schueler The AAPM/RSNA Physics Tutorial for Residents Fluoroscopy: Patient Radiation Exposure Issues1,Mahadevappa Mahesh, PhD Radiography and fluoroscopy, 1920 to the present, J S Krohmer Study of scattered radiation during fluoroscopy in hip surgery,Oksana Lesyuk1 Survey of Modern Fluoroscopy Imaging: Flat-Panel Detectors versus Image Intensifiers and More, Edward Lee Nickolof Radiology key Radiology café IAEA FLUROSCOPY THE PHYSICS OF RADIOLOGY AND IMAGING(K THALAYAN) RADIOLOGIC SCIENCE FOR TECHNOLOGIST (STEWART CARLYLE BUSHONG) The AAPM/RSNA Physics Tutorial for Residents Typical Patient Radiation Doses in Diagnostic Radiology1 Robert A. Parry ,  Sharon A. Glaze ,  Benjamin R. Archer

48. QUESTIONS WHAT DO YOU UNDERSTAND BY PULSED FLUROSCOPY ? WHAT ARE THE PARTS OF IMAGE INTENSIFIER TUBE? WHAT DO YOU UNDERSTAND BY MAGNIFICATION IN FLUROSCOPY? WHAT ARE THE TYPES OF ARTIFACTS SEEN IN FLUROSCOPY?