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18/11/2024 INTRODUCTION CONVENTIONAL,DIGITAL Refers to the way of obtaining image in the fluorescent screen....

18/11/2024 INTRODUCTION CONVENTIONAL,DIGITAL Refers to the way of obtaining image in the fluorescent screen. FLUOROSCOPY AND Digital Conventional fluoroscopy SUBTRACTION ANGIOGRAPHY Modern fluoroscopy Advantages Real-time imaging & visualization of anatomy & dynamic processes. By:Ryner Louise G. Caceres, RRT Also used to position the patient for subsequent image recording or devices for interventional procedures. Possible to examine the patient in different positions & to evaluate profile views of abnormalities found. 1 2 HISTORY Fluoroscopy is actually a rather routine type of x-ray examination In 1896 Thomas Addison discovered fluoroscopy using barium except for its application in the visualization of vessels, called platinocyanide as screen phosphor angiography. – Modified II/TV system with more brightness gain(1948) The fluoroscope is used for examination of moving internal structures – Temporal and energy subtraction (1960) and fluids. – Clinical DSA systems(1977) – Qualitative and quantitative improvements – Image processing advances 3 4  18/11/2024 Early fluoroscopes: Cardboard funnels, open at narrow end for viewing, the wide end closed with a thin cardboard piece that coated on the inside with a layer of fluorescent material. Direct viewing of the fluoroscopic image is defective in Color, Sharpness & contrast than the image produced on the film radiographs. Red adaptation goggles were developed by Wilhelm Trendelenburg in 1916. The resulting red light from it’s filtration correctly sensitized the observer’s eyes prior to procedure. 5 6 Fluoroscopic Acquisition Components Fluoroscopy Composition / Structure Fluoroscopic imaging system, the x-ray tube is usually hidden under the patient table. The image intensifier are set over the patient table. With some fluoroscopes, the x-ray tube is over the patient table, and the image receptor is under the patient table. Some fluoroscopes are operated remotely from outside the x-ray room. During image-intensified fluoroscopy, the radiologic image is displayed on a television monitor or flat panel monitor. Image intensifier that converts x-rays into visible light at high intensity 7 8  18/11/2024 Image-Intensifier Tube During fluoroscopy, the x-ray tube is operated at less than 5 mA. The image-intensifier tube is approximately 50 cm long. Despite the lower mA, however, the patient dose is considerably The image-intensifier tube is a complex electronic device that higher during fluoroscopy than during radiographic examinations receives the image-forming x-ray beam and converts it into a visible- because the x- ray beam exposes the patient constantly for a light image of high intensity. considerably longer time. The kilovolt peak (kVp) of operation depends entirely on the section of the body that is being examined. 9 10 Image-Intensifier Tube Glass envelope 1. Glass envelope Maintains tube vacuum to allow control of electrons flow. 2. Input phosphor When installed, the tube is mounted inside a metal container to 3. Photocathode protect it from rough handling and breakage. 4. Electrostatic focusing lens The tube components are contained within a glass or metal envelope that provides structural support. 5. Output phosphor 11 12  18/11/2024 Input phosphor X-rays that exit the patient and are incident on the image intensifier 1st Generation Image Intensifiers tube are transmitted through the glass envelope and interact with the Input phosphor – Zinc Cadmium Sulfide input phosphor, which is cesium iodine. Output phosphor – Zinc Cadmium Sulfide The CsI crystals are grown as tiny needles and are tightly packed in a layer of approximately 300 μm, Each crystal is approximately 5 μm in 2nd Generation Image Intensifiers diameter. Input Phosphor – Cesium Iodide When an x-ray interacts with the input phosphor, its energy is (smaller crystals with greater packing density) converted into visible light. Output phosphor – Zinc Cadmium Sulfide 13 14 Photocathode Electrostatic Focusing Lens It is bonded directly to the input phosphor with a thin, transparent, Located along length of the tube, responsible for focusing the adhesive layer. electrons across the tube from input to output phosphor. The photocathode is a thin metal layer, usually composed of cesium Image is reversed from input to output phosphor (right becomes left, and antimony compounds, that respond to stimulation of light with superior to inferior) the emission of electron. This process is known as photoemission. The concave input screen reduces distortion by keeping the same The number of electrons emitted by the photocathode is directly distance between all points on the input and output screens. proportional to the intensity of light that reaches it. The photocathode emits electrons when illuminated by the input phosphor. 15 16  18/11/2024 Anode Output Phosphor Anode is usually charged with 25kV and used to accelerate electron The output Phosphor is usually made up of zinc cadmium sulfide across the tube. crystals. Electrons produced by photoemission will be accelerated to the Each photoelectron that arrives at the output Phosphor results in anode. approximately 50-70 times magnification. The anode is a circular plate with a hole in the middle through which The output phosphor is the site where electrons interact and electrons pass to the output phosphor, which is just the other side of produce light. the anode and is usually made of zinc cadmium sulfide. 17 18 For the image pattern to be accurate, Summary the electron path from the Glass envelope photocathode to the output Surrounds all of the components and provides mechanical support of internal components has a vacuum tube. phosphor must be precise. Input phosphor The engineering aspects of Receives incident x-rays from the x-ray tube and converts them maintaining proper electron travel into light Composed of cesium iodide are called electron optics. Photocathode Attached to the input phosphor by an adhesive layer, Converts The interaction of these high-energy light from input phosphor to electrons by photoemission Negative portion of the tube electrons with the output phosphor Anode produces a considerable amount of Positive portion of the tube. A circular plate with a hole in it in light. which electrons are focused to which goes to the output phosphor Each photoelectron that arrives at Electrostatic focusing lenses the output phosphor produces 50 to Focuses electron path form photocathode to anode by means of 75 times as many light photons as repulsion were necessary to create it. Output phosphor Converts electrons from anode to light 19 20  18/11/2024 Camera The glass envelope serves the same function that it does for the X-ray tube; The television camera consist of to maintain a vacuum and provide cylindrical housing, approximately mechanical support for the internal 15 mm in diameter by 25 cm in elements. length, that contains the heart of These internal elements include the the camera, TV camera tube. cathode, its electron gun, assorted elelctrostatic grids, and a target It also contains electromagnetic coils assembly that serves as an anode. that are used to properly steer the The electron gun is a heated filament electron beam inside the tube. that supplies a constant electron A number of such television camera current by thermionic emission. tubes are available for television Theses electrons are formed into an fluoroscopy, but the vidicon and its electron beam by the control grid, modified version, the plumbicon, which also helps to accelerate the are used most often. electrons to the anode. 21 22 The target of a television camera At the anode end of the tube, tube conducts electrons, creating the electron beam passes a video signal only when through a wire mesh- like illuminated. structure and interacts with the target assembly. The target Image intensifiers and television assembly consist of three layers camera tubes are manufactured that are sandwiched together. so that the output phosphor of the image intensifier tube is the 1. Window same diameter as the window of 2. Signal plate the television camera tube, 3. Target usually 2.5 or 5cm. 23 24  18/11/2024 Optical coupling The simplest method is to use a bundle of fiber optics. One advantage of this type of Television camera tubes and coupling is its compact assembly, charge coupled devices (CCDs) which makes it easy to move the are coupled to an image image intensifier tower. This intensifier tube in two ways. coupling is rugged and can A. Fiberoptics withstand relatively rough handling. B. Lens system The principal disadvantage is that it cannot accommodate the additional optics required for devices such as cine or photospot cameras. 25 26 Lens Coupling: THREE FORMS OF FLUOROSCOPY To accept a cine or photoshot camera, lens coupling is required. This type of DIRECT FLUOROSCOPY coupling results in a much larger assembly that should be handled with TV FLUOROSCOPY care. Working: DIGITAL FLUOROSCOPY The objective lens accepts light from the output Phosphor and converts it into a parallel beam. When an image is recorded on film, this beam is interrupted by a beam-splitting mirror so that only a portion is transmitted to the television camera; the remainder is reflected to a film camera. Such a system allows the fluroscopist to view the image while it being recorded. 27 28  18/11/2024 DIRECT FLUOROSCOPY DIRECT FLUOROSCOPY 29 30 DIRECT FLUOROSCOPY TV FLUOROSCOPY Photo: Suitcase portable x-ray unit & hand fluoroscope 31 32  18/11/2024 TV FLUOROSCOPY TV FLUOROSCOPY Image intensifier- TV system 33 34 DIGITAL FLUOROSCOPY IMAGING SYSTEM WHY DIGITAL FLUOROSCOPY? A digital fluoroscopy examination is conducted in the much same manner as a conventional fluoroscopic study but a computer has Image acquistion faster been added and have multiple monitors and a more complex Post processing is done operating system Linear response Low patient dose(last frame hold) Pulse progessive fluoroscopy Temporal frame averaging 35 36  18/11/2024 DIGITAL FLUOROSCOPY IMAGING SYSTEM Digital Fluoroscopy Imaging System contains: alphanumeric and special function keys for patient data and communication with the computer, Additional special function keys for data acquisition and image display, Computer interactive video control, A pad for cursor and Region of interest (ROI) manipulation or trackball, joystick, mouse. Al least two monitors- one for edit patient and examination data and to annotate final image and other for subtracted images. 37 38 DIGITAL FLUOROSCOPY IMAGING SYSTEM CHARGE-COUPLED DEVICE During DF, the X-ray tube actually operates in the radiographic mode. A major change from conventional fluoroscopy to Digital fluoroscopy This is not a problem as images from Digital Fluoroscopy are obtained by is the use of a charge-coupled device (CCD) instead of TV camera pulsing the X-ray beam in a manner called Pulse-Progressive Fluoroscopy. pickup tube. PPF contains 3 stages: Developed in 1970s for military applications especially in night vision INTERROGATION TIME scopes. EXTINCTION TIME The application of CCD in fluoroscopy is a recent development. DUTY TIME The Sensitive component is a layer of crystalline silicon. DF system must incorporate high frequency generators with very rapid switching on and off with interrogation time and extinction times of less than 1 ms. 39 40  18/11/2024 CHARGE-COUPLED DEVICE CHARGE-COUPLED DEVICE 41 42 CCD ADVANTAGES OF CCD CCDs can be tiled to receive the light from an area X-ray beam as it interacts with a High spatial resolution scintillation phosphor such as Cesium High signal to noise ratio Iodide (CsI). High quantam detective efficiency The scintillation light from a CsI phosphor is No warm up required efficiently transmitted through fiber optic No spatial distortion bundles to the CCD array. No maintenance The result is the high X-ray capture Unlimited life efficiency and good spatial resolution – up Not affected by magnetic field to 5lp/mm. Linear response CsI/CCD is an indirect Digital Fluoroscopic Low patient dose process by which X-rays are first converted into light and then to electric signal. 43 44  18/11/2024 CCD The spatial resolution of a CCD is determined by its physical size and FLAT PANEL IMAGE RECEPTOR(FPIR) pixel count. 1024 matrix can produce images with 10lp/min spatial resolution. Next development in Direct Fluoroscopy. Composed of either cesium iodide(CsI) or amorphous silicon and amorphous selenium(a-Se) Two types: Direct conversion FPIR Indirect conversion FPIR 45 46 INDIRECT CONVERSION INDIRECT CONVERSION Indirect conversion FPIR involves the use of CsI to capture the X-ray as well as transmission of the resulting scintillation light to a collection element. The collection element is silicon sandwiched as a Thin Film Transistor(TFT). Silicon is a semiconductor that usually is grown as a crystal but when identified as amorphous Silicon (a-Si), silicon is not crystalline but is fluid that can be painted onto a supporting surface. CsI has a high photoelectric capture as Cs has atomic no. 55 and Iodine has 53 47 48  18/11/2024 CsI/a-Si is an indirect Direct Fluoroscopy process by which X-rays are converted first to light by CsI and then to electrical signal by a-Si. The image receptor is fabricated into individual pixels which has light sensitive face of a-Si with a capacitor and a TFT embedded in it. The geometry of each individual pixel is very important as a portion of the pixel face is occupied by conductors, capacitors and TFT. It is not totally sensitive to the incident image forming X-ray beam. The percentage of the pixel face that is sensitive to X-rays is the fill factor, which is approximately 80%; therefore 20% of the X-ray beam does not contribute to the image. As the pixel size is reduced, spatial resolution improves but at the expense of the patient radiation dose. With smaller pixels, the fill factor is reduced and the X-ray intensity must be increased to maintain adequate signal strength. 49 50 DIRECT CONVERSION Amorphous Selenium is the direct DF FPIR 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. Amorphous-Se is both the capture element and the coupling element. Amorphous-Se is approx. 200 m 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. 51 52  18/11/2024 FPIR Field coverage / size advantage to flat panel Image distortion advantage to flat panel 53 54 FPIR FPIR image guided catheter navigation. FPIR is much small and lighter and is manipulated more easily than an image intensifier. FPIR imaging suite provides easier patient manipulation and radiologist/technologist movement. No radiographic cassettes No pincushion distortion 55 56  18/11/2024 FINAL COMPARISION IMAGE DISPLAY-VIDEO SYSTEM A 525-line system of conventional fluoroscopy is inadequate for DF. Limitations of conventional video that restrict its application in digital techniques are: Interlaced mode of reading the target of the television camera can significantly degrade image. Conventional television camera tubes are relatively noisy which have SNR about 200:1 where as 1000:1 is necessary of DF. Interlaced Versus Progressive Mode: Conventional television camera tube reads its target assembly by interlaced mode, wherein two fields of 262½ lines are read individually in 1/60s (17ms) to form a 525-line video frame in 1/30s (33ms). In DF, the TV camera tube reads in progressive mode in which the electron beam of the TV camera sweeps the target assembly continuously from top to bottom in 33 ms. 57 58 IMAGE DISPLAY-VIDEO SYSTEM FLAT PANEL IMAGE DISPLAY The video image is formed similarly on the television monitor. No interlace of one field with another. Flat Panel Display technology is rapidly replacing the Cathode Ray Produce a sharper image with less flicker. Tube (CRT) in all applications like Television, Computer. Signal-to-noise Ratio: Radiography and fluoroscopy is the similar field in which CRTs are Background noise rapidly being replaced by the Flat Panel Image Display. As conventional TV camera tubes have and SNR 200:1, the maximum In fluoroscopic image viewing, Flat Panel Image Display is usually output signal will be 200 times greater than the background electronic Active Matrix Liquid Crystal Display (AMLCD) noise. Liquid crystals materials -a natural molecular dipole. SNR 200:1 is not sufficient for DF because the video signal is rarely at maximum and lower signals become even more lost in the noise. This affect in subtraction techniques and image contrast resolution is severely degraded by a system with a low SNR. 59 60  18/11/2024 Active Matrix Liquid Crystal Display (AMLCD) DIFFERENCES BETWEEN CRT AND AMLCD Display Characteristics: AMLCDs are fashioned pixel by pixel. A 1-megapixel display will have a 1000 x 1000 pixel arrangement and a high resolution monitor of 5-megapixel display has 2000 x 2500 pixel arrangement. Image luminance: Better grayscale definition than CRTs. Not limited by Veiling glare or reflections in the glass faceplate AMLCDs have less intrinsic noise than that of a CRT. Ambient light: Designed to better reduce the influence of ambient light on image contrast. Angular dependence 61 62 TOTAL PROCESS Automatic Brightness Control Acquisition Processing Display Automatic Brightness control (ABC) is a mechanism, which can keep the brightness of the image constant ate the monitor. COMPUTER Basically a feedback circuit, which measure the light intensity of the FLUORO HARDWARE FLAT PANEL output screen or video camera signal. AND IMAGE UNIT ADC SOFTWARE DAC DISPLAY A photomultiplier or a photodiode is used to monitor the light output ALGORITHMS of the tube. STORAGE 63 64  18/11/2024 DIGITAL SUBTRACTION ANGIOGRAPHY Digital subtraction angiography (DSA) is a new radiographic technology used in diagnosing vascular disease The digitalized image information makes it possible to “subtract” the pre contrast images from those obtained after contrast injection so as to visualize arterial structures without direct arterial puncture and injection DSA is a gold standard investigation for renal artery stenosis, cerebral aneurysms & arteriovenous malformations (AVM). 65 66 DSA TEMPORAL SUBTRACTION Image contrast can be enhanced electronically and image contrast is Image obtained at one time subtracted from image at later time improved by subtraction techniques which provide instantaneous viewing of the subtracted image during passage of a bolus of contrast Shows only blood vessels with contrast medium. Two types: So Digital fluoroscopy provides better contrast resolution through 1. Mask mode post processing of image subtraction. 2. Time interval display mode(TID) Types of image subtraction: Temporal subtraction Energy subtraction Hybrid subtraction 67 68  18/11/2024 MASK MODE MASK MODE Amount of contrast 4-10 sec delayed image before bolus of CM reaches the anatomic site is taken as mask image and stored in primary memory and is displayed. The mask image if followed by a series of additional images with bolus of CM and stored in adjacent memory locations. These each subsequent images are acquired with subtraction from the mask image and stored in primary memory and displayed in monitor as well 69 70 MASK MODE MASK MODE Image Integration REMASKING On subsequent examination, if the initial mask image is inadequate Imaging sequence after acquisition of the mask can be controlled. e.g. because of the patient motion or improper technique or any other reason, after acquiring mask image after 2 sec. of injection, after 2 sec later images may be used as the mask image. another delay, images are obtained at the rate of 2/s for 3s, 1/s for 5s e.g. if the intended mask image is technically inadequate and maximum and one every other second for another 14 second. contrast appears during the 5th image, a better subtraction image may be obtained by using image number 5 as the mask image rather than image number 1. Several images (e.g. image numbers four through eight) even can be integrated using the composite image as the mask image. Unacceptable masking images can be caused by noise, motion and technical factors. 71 72  18/11/2024 Time-Interval Difference Mode Some examinations call for each subtracted image to be made form a Time-Interval Difference Mode different mask and follow-up frame. TID mode produces subtracted images form progressive masks and In real time, the images observed convey the flow of CM dynamically. following frames. TID images are relatively free of motion artifacts but have less contrast than mask-mode imaging. TID imaging is applied principally in cardiac evaluation. 73 74 ENERGY SUBTRACTION TEMPORAL SUBTRACTION The temporal subtraction techniques take advantage of changing contrast media during the time of examination and require no special demands on MISREGISTRNATION the high voltage generator. If the patient motion occurs between the mask image and a Energy subtraction uses two different X-ray beam alternately to provide a subsequent image, the subtracted image will contain misregistration subtraction image that results form differences in photoelectric interaction. artifacts. Energy subtraction is based on the abrupt change in the photoelectric absorption of the K edge of contrast media compared with that for soft The same anatomy is not registered in the same pixel of the image tissue and bone. matrix. The probability of photoelectric absorption in iodine of CM, bone and This type of artifact can be eliminated by the registration of the mask muscle decreases with the increasing X-ray energy. by shifting the mask by one or more pixels so that superimposition of At an energy of 33 keV, an abrupt increase in absorption is noted in iodine images is again obtained. and a modest decrease in soft tissue and bone. The energy corresponds to the binding energy of the two K-shell electrons of iodine. 75 76  18/11/2024 DIFFERENCES ENERGY SUBTRACTION If monoenergetic X-ray beams of 32 and 34 keV could be used alternately, the difference in absorption of Iodine would be enormous and the resultant subtraction image would have very high contrast. But such is not the case because every X-ray beam contains a wide spectrum of energies. Energy subtraction has the decided disadvantage of requiring some method of providing an alternating X-ray beam of two different emission spectra. Two methods have been devised – alternating pulsing the X-ray beam at 70kVp and then 90 kVp Introducing dissimilar metal filters into the X-ray beam alternately on a flywheel. 77 78 HYBRID SUBTRACTION HYBRID SUBTRACTION Some Digital Fluoroscopy systems are capable of combining Temporal and Energy subtraction techniques – Hybrid Subtraction. In Hybrid subtraction, image acquisition follows the mask-mode procedure. The mask and each subsequent images are formed by an energy subtraction technique. If patient motion can be controlled, hybrid imaging theoretically can produce the highest-quality DF images. 79 80  18/11/2024 DSA ROADMAPPING Roadmapping is a special application of DSA. A mask image is acquired and stored and CM is injected and subtraction images are acquired as in DSA (A). As the catheter is fluoroscopically advanced, the image is formed by subtraction form the second mask (B). Final DSA image shows completer vasculature tree with good contrast (C). This image is inverted and used as the mask for additional DSA images. 81 82 DSA DSA PATIENT DOSE Potential advantage of DF is reduced patient dose. However, DF images appear to be continuous, in fact they are discrete. DF X-ray beams are pulsed to fill one or more 33-ms video frames; so fluoroscopic dose rate is lower than that for continuous analog fluoroscopy. Static images with DF also are made with a lower dose per frame than those attained with a 100-mm spot film camera. Both television camera tube and the CCD have greater sensitivity than the spot film. Digital spot images are so easy to acquire that it is possible to mare more exposures than are necessary. 83 84  18/11/2024 SUMMARY Digital fluoroscopy has replaced the conventional type for its advantages. In case of conventional fluoroscopy, what we get is what we see but in case of digital fluoroscopy many post processing can be done. 85 86 Advances A future prospect is that DSA may be performed with energy The cesium-iodide image intensifier is the standard for production DSA subtraction rather than temporal subtraction. units, but state-of-the-art image intensifiers, such as the Thompson CSF 96 intensifier and the Philips 14-inch (36 cm) intensifier, are proposed for Energy subtraction, an alternative being tested in several centers, is future DSA units. based on subtraction of images of different kilovoltage, rather than in different time. Further modifications will include thicker image phosphors in order to better control and use the light output. The advantage is that the different kilovoltages can be programmed The size of the image intensifier is also an important factor, especially for within milliseconds of each other, so that motion no longer demonstrating large vascular areas, as in the extremities. introduces an artifact. Large intensifiers, such as the Philips 14-inch (36 cm), offer superior Current fluoroscopically based DSA units are incapable of energy contrast resolution capabilities, but have the disadvantages of decrease in subtraction although one manufacturer is planning to provide such a spatial resolution due to the fixed matrix size of the image processor and system in the future. the considerable increase in cost. 87 88  18/11/2024 QUESTIONS??? Newly developed video tubes, such as the Amperex 45-XQ (‘‘frog’s What are the forms of fluroscopy? head’ ‘ plumbicon), as incorporated into a Sierra Scientific camera, Why digital fluroscopy has replaced other forms of fluroscopy? and the lead oxide Videcon tube are examples. What are the advantages of FPIR? Snapshot mode; slow scan video technique where the image is stored Why AMLCD has replaced CRT? on the target of the of the TV pickup tube & then read out digitized. What is meant by DSA and what are its type? What is meant by remasking? What is meant by misregistration and how can it be reduced? How are the temporal and energy substraction differ with each other? 89 90 THANK YOU…… 91