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UNIT 5 Medical Imaging 1 DEEPAK.P CT Scan 2 DEEPAK.P CT Scan Computed axial tomography (CAT or CT scanning) is a medical imaging procedure that utilizes computerprocessed X-rays to produce tomographic images or 'slices' of specific areas of the body. These cross-sectional images are used for diagnostic and therapeutic purposes in various medical disciplines. Unlike other medical imaging techniques, such as conventional x-ray imaging (radiography), CT enables direct imaging and differentiation of soft tissue structures, such as liver, lung tissue, and fat. 3 DEEPAK.P CT Scan Due to the short scan times of 500 milliseconds to a few seconds, CT can be used for all anatomic regions. 4 DEEPAK.P CT Scan Machine 5 DEEPAK.P CT Scan Principle CT is based on the fundamental principle that the density of the tissue passed by the X-ray beam can be measured from the calculation of the attenuation coefficient. The CT process involves several steps: Scanning 2. Reconstruction 3. Visualization 4. Data collection 1. 6 DEEPAK.P CT Scan Principle 7 DEEPAK.P CT Scan Principle 8 DEEPAK.P CT Scan Principle 9 DEEPAK.P Advantages of CT Scan Relatively inexpensive compared with MRI and PET scanning 2. Accurate, 3-dimensional data including attenuation information 3. Rapid acquisition of data and no need for patients to remain for planning process 1. 10 DEEPAK.P Components in CT Scan 4 BASIC STEPS OF CT SCANNING 11 1. X-Ray Production 2. Data Acquisition 3. Data Processing 4. Image Display DEEPAK.P Components in CT Scan 12 DEEPAK.P Components in CT Scan 13 DEEPAK.P Types of CT Scan X-ray Computed Tomography: This is the conventional CT scanner that scans a particular section of the subject at a time and sends it across to a computer for further processing Spiral or Helical Computed Tomography: These provide accurate information on the internal organs. In spiral CT, the X-ray beam is emitted on a continuous basis and rotates around the subject, as the subject is moved through. Micro Computed Tomography: In micro CT, the pixel size of the images is in micrometer. It is used in cases involving small animals, biomedical samples and other studies where minute detailing is desired. 14 DEEPAK.P Types of CT Scan Micro Computed Tomography: In micro CT, the pixel size of the images is in micrometer. It is used in cases involving small animals, biomedical samples and other studies where minute detailing is desired. • Cone Beam Computed Tomography: • The Cone Beam CT is a recent addition, where the X-ray source is cone shaped and the resultant image is in 3-D. 15 DEEPAK.P Types of CT Scan 16 DEEPAK.P X- Ray 17 DEEPAK.P X-RAY •In 1895 Conrad Rontgen, a German physicist, discovered a previously unknown type of radiation while experimenting with gas-discharge tubes. •X-radiation (composed of X-rays) is a form of electromagnetic radiation. • X-rays have a wavelength in the range of 0.01 to 10 nanometers, •X-radiation is also called Rontgen radiation •An X-ray generator is a device used to generate X-rays. •The heart of an X-ray generator is the X-ray tube. 18 DEEPAK.P X-RAY 19 DEEPAK.P Electro Magnetic Spectrum 20 DEEPAK.P Uses of X- Ray 21 DEEPAK.P Uses of X-RAY These devices are commonly used by radiographers to acquire an x-ray image of the inside of an object (as in medicine or non-destructive testing) but they are also used in sterilization or fluorescence. X-ray machines are used in health care for visualizing bone structures and other dense tissues such as tumors. Non-medicial applications include security and material analysis. The two main fields in which x-ray machines are used in medicine are radiography and fluoroscopy. 22 DEEPAK.P Uses of X-RAY Diagnostic still picture X-Ray Examine bones and internal organs Diagnostic continuous picture X-Ray(Fluoroscopy) Examine internal organs as they functioning Diagnostic motion picture X-Ray Examine circulatory systems and its functioning Diagnostic still picture X-Ray Scans CT scan Therapeutic X-Ray For treatment 23 DEEPAK.P X-RAY in Radiography Some forms of radiography include: Orthopantomogram — a panoramic x-ray of the jaw showing all the teeth Mammography — X-rays of breast tissue Tomography — X-ray imaging in sections Radiotherapy — the use of x-ray radiation to treat malignant cancer cells, a non-imaging application 24 DEEPAK.P X-RAY in Fluoroscopy Fluoroscopy is used in cases where real-time visualization is 25 necessary (and is most commonly encountered in everyday life at airport security). Some medical applications of fluoroscopy include: Angiography — used to examine blood vessels in real time Barium enema — a procedure used to examine problems of the colon and lower gastrointestinal area Barium swallow — similar to a barium enema, but used to examine the upper gastroinstestional area biopsy — the removal of tissue for examination DEEPAK.P X- Ray Tube 26 DEEPAK.P X-RAY Generation Like any vacuum tube, the X-ray tube contains a cathode, which directs a stream of electrons into a vacuum, and an anode, which collects the electrons. The anode in an X-ray tube is made of tungsten, molybdenum, or copper. The electrons are then focused and accelerated by an electrical field towards an angled anode target. The point where the electron beam strikes the target is called the focal spot. 27 DEEPAK.P X-RAY Generation When electrons collide with the anode, about 1% of the resulting energy is emitted as X-rays, with the remaining 99% released as heat. A cooling system is necessary to cool the anode; many X-ray generators use water or oil re-circulating systems The intensity of X rays depends on the current through the tube. This current can be varied by varying the heater current. 28 DEEPAK.P X-RAY Generation •The wavelength of the X rays depends on the target material and the velocity of the electrons hitting the target. It can be varied by varying the target voltage of the tube. 29 DEEPAK.P X ray tube 30 DEEPAK.P Generation of X- ray from X ray tube 31 DEEPAK.P Block Diagram 32 DEEPAK.P X-RAY Generation •The intensity of X rays depends on the current through the tube. •This current can be varied by varying the heater current. •The wavelength of the X rays depends on the target material and the velocity of the electrons hitting the target. It can be varied by varying the target voltage of the tube. 33 DEEPAK.P Simple Block Diagram 34 DEEPAK.P Block Diagram 35 DEEPAK.P Collimators 36 DEEPAK.P Collimators A collimator is a device that narrows a beam of particles or waves. In optics, a collimator may consist of a curved mirror or lens with some type of light source and/or an image at its focus. 37 DEEPAK.P Collimators in X-rays In X-ray, and gamma ray optics, a collimator is a device that filters a stream of rays so that only those traveling parallel to a specified direction are allowed through. 38 DEEPAK.P Collimators in X-rays 39 DEEPAK.P Collimators 40 DEEPAK.P Collimators in X-rays This may be a sheet of lead or other material opaque to the incoming radiation with many tiny holes bored through it. Only rays that are travelling nearly parallel to the holes will pass through them—any others will be absorbed by hitting the plate surface or the side of a hole. It allows the radiographer to control the exposure of radiation to expose a film. 41 DEEPAK.P Gantry detectors 42 DEEPAK.P Gantry detectors The gantry is the 'donut' shaped part of the CT scanner that houses the components necessary to produce and detect xrays to create a CT image. The x-ray tube and detectors are positioned opposite each other and rotate around the gantry aperture. This gantry can rotate 360 degrees around its axis. 43 DEEPAK.P Gantry detectors 44 DEEPAK.P Gantry detectors 1. gantry aperture (720mm diameter) 2. microphone 3. sagittal laser alignment light 4. patient guide lights 5. x-ray exposure indicator light 6. emergency stop buttons 7. gantry control panels 8. external laser alignment lights 9. patient couch 10. ECG gating monitor 45 DEEPAK.P Gantry detectors CT scanner with cover removed to show internal components. T: X-ray tube D: X-ray detectors X: X-ray beam R: Gantry rotation 46 DEEPAK.P X-Ray Detectors 47 DEEPAK.P X-Ray detectors The two most common types of X-ray detector used are the scintillation and the gas-filled detectors. Scintillation detectors work by converting x-rays to optical photons in special materials and then detecting the light with a photomultiplier tube or a photodiode. The X-ray photon collides with a phosphor screen, or scintillator and produces photons in the blue region of the visible spectrum. These are subsequently converted to voltage pulses by means of a photomultiplier tube attached directly behind the scintillator. 48 DEEPAK.P X-Ray detectors A gas filled detector consists of a rectangular gas cell with thin entrance and exit windows. Inside the detector, an electric field of about 100 V/cm is applied across two parallel plates. Some of the x-rays in the beam interact with the chamber gas to produce fast photoelectrons, 49 DEEPAK.P Solid State X-ray Detectors X-ray interacts in material to produce photoelectrons which are collected by applying a drift field 50 DEEPAK.P Ultra Sound Imaging 51 DEEPAK.P Ultrasound Ultrasound is a mechanical disturbance that moves as a pressure wave through a medium. Ultrasound is high frequency mechanical vibrations or pressure waves above a frequency the human ear can hear. 1. 2. 3. 52 Infra sound Below 20Hz Audible 20Hz and 20 000Hz. Ultrasound Above 20 000Hz DEEPAK.P Ultrasound 53 DEEPAK.P Ultrasound The velocity of propagation of US and the attenuation are the 2 most important parameters. Ultrasonic imaging equipment is designed on the premise that the ultrasonic energy propagates through tissue in a straight line and that the ultrasonic beam is very narrow. When the medium is a patient, the wavelike disturbance is the basis for use of ultrasound as a diagnostic tool. 54 DEEPAK.P Ultrasound in medical field Ultrasound uses a pulse-echo technique of imaging the body. Pulses transmitted into patient and give rise to echoes when they encounter interfaces/reflectors. These interfaces/reflectors are caused by variations in the "acoustic impedance" between different tissues. Echo signals are amplified electronically and displayed on a monitor using shades of grey (from black to white), The transducer is the component of the ultrasound imaging equipment that is placed in direct contact with the patient's body. 55 DEEPAK.P Ultrasound in medical field 56 DEEPAK.P Properties of an ultrasound wave Attenuation is the rate at which intensity wave diminishes with the depth it covers or its penetration. 3 Types: 1. Scattering 2. Absorption 3. Reflection. When an ultrasound wave passes through tissues Attenuation: Reduction in amplitude and intensity of wave Refraction: Change in direction & velocity of wave 57 DEEPAK.P Properties of an ultrasound wave Frequency of wave - Higher the frequency, higher the attenuation and less penetration of the wave Type of tissue the wave is traveling Depth the wave travels - more distance wave has to travel the more energy is lost. 58 DEEPAK.P Properties of an ultrasound wave Like other forms of sonic energy, ultrasound exists as a sequence of alternate compressions and rarefactions of a suitable medium (air, water, bone, tissues etc) and is propagated through that medium at some velocity. Whenever a beam of ultrasound passes from one medium to another, a portion of the sonic energy is reflected and the remainder is refracted 59 DEEPAK.P Properties of an ultrasound wave 60 DEEPAK.P Properties of an ultrasound wave 61 DEEPAK.P Properties of an ultrasound wave The amount of energy reflected depends on the difference in density between the two media and the angle at which the transmitted beam strikes the medium. The greater the difference in media, the greater will be the amount reflected. At interfaces of extreme difference in media, such as between tissues and bone or tissues and a gas, almost all the energy will be reflected and practically none will continue through the second medium. For this reason, the propagation path for ultrasound into or through the body must not include bone or any gaseous medium, such as air. 62 DEEPAK.P Properties of an ultrasound wave In applying ultrasound to the body, an airless contact is usually produced through use of a gel or a water bag between the transducer and the skin. The combined effect of scattering and absorption is called attenuation. Ultrasonic attenuation is the decay rate of the wave as it propagates through material. 63 DEEPAK.P Characteristics of an ultrasound wave Wave parameters PERIOD: time taken for one particle in the medium through which the wave travel, to make one complete oscillation (cycle)about its rest position, in response to the wave FREQUENCY: the number of oscillations per second of the particle in the medium responding to the wave passing through it WAVELENGTH: the distance between 2 consecutive, identical positions in the pressure wave 64 DEEPAK.P Characteristics of an ultrasound wave Wave parameters VELOCITY: the speed of propagation of a sound wave, determined by a combination af the density and compressibility of the medium through which it is propagating PHASE:the stage at which a wave is within a cycle AMPLITUDE:a measure of the degree of change within a medium, caused by the passage of a sound wave and relates to the severity of the disturbance POWER: rate of flow of energy through a given are INTENSITY: the power per unit area 65 DEEPAK.P VELOCITY The velocity of an ultrasound wave through a medium varies with the 66 physical properties of the medium. In low-density media such as air and other gases, molecules may move over relatively large distances before they influence neighboring molecules. In these media, the velocity of an ultrasound wave is relatively low. In solids, molecules are constrained in their motion, and the velocity of ultrasound is relatively high. Liquids exhibit ultrasound velocities intermediate between those in gases and solids. DEEPAK.P Characteristics of an ultrasound wave One of the most significant characteristics of sound is its frequency. The basic unit for specifying frequency is the hertz, which is one vibration, or cycle, per second. Pitch is a term commonly used as a synonym for frequency of sound. Frequency higher than 20 000Hz (20kHz) Frequencies in the range of 2 MHz (million cycles per second) to 20 MHz are used in diagnostic ultrasound. The Ultrasound frequencies cannot be heard by a normal young adult. 67 DEEPAK.P Characteristics of an ultrasound wave . 68 DEEPAK.P Characteristics of Ultrasound 69 DEEPAK.P Characteristics of Ultrasound 70 DEEPAK.P Doppler effect Doppler Effect is the shift in frequency and wavelength of waves which results from a source moving with respect to the medium, a receiver moving with respect to the medium, or even a moving medium. The perceived frequency (f ´) is related to the actual frequency (f0) and the relative speeds of the source (vs), observer (vo), and the speed (v) of waves in the medium by 71 DEEPAK.P Pulse Echo system 72 DEEPAK.P Characteristics of an ultrasound wave The choice of using the plus (+) or minus (-) sign is made according to the convention that if the source and observer are moving towards each other the perceived frequency (f ´) is higher than the actual frequency (f0). Likewise, if the source and observer are moving away from each other the perceived frequency (f ´) is lower than the actual frequency (f0). 73 DEEPAK.P Doppler effect . 74 DEEPAK.P . 75 DEEPAK.P Applications of Ultrasound 76 DEEPAK.P Applications of Ultrasound: echocardiography Echocardiography has become routinely used in the diagnosis, management, and follow-up of patients with any suspected or known heart diseases. The pictures show the size and shape of your heart. They also show how well your heart's chambers and valves are working. It can provide a wealth of helpful information, including the size and shape of the heart (internal chamber size quantification), pumping capacity and the location and extent of any tissue damage. Echocardiography can also help detect any cardiomyopathy, 77 DEEPAK.P echoencephalography Echoencephalography is the detailing of interfaces in the brain by means of ultrasonic waves.[1 the use of ultrasound to examine and measure internal structures (as the ventricles) of the skull and to diagnose abnormalities and disease The reflected pulses from the skin, brain ventricle, skull, and other head structures are recorded and amplified with a cathode-ray oscilloscope, giving a measure of the distance between the probe and the reflecting surfaces. The method is rapid, painless, and harmless; it is a good screening test 78 DEEPAK.P Ultrasound Transducer . 79 DEEPAK.P Ultrasound Transducer . 80 DEEPAK.P ULTRASOUND BEAMS from source of large dimensions . 81 DEEPAK.P ULTRASOUND BEAMS from source of small dimensions . 82 DEEPAK.P PRESENTATION MODES 83 DEEPAK.P A-scans A-scans can be used in order to measure distances. A transducer emits an ultrasonic pulse and the time taken for the pulse to bounce off an object and come back is graphed in order to determine how far away the object is. A-scans only give one-dimensional information and therefore are not useful for imaging. In the A-mode presentation of ultrasound images, echoes returning from the body are displayed as signals on an oscilloscope. 84 DEEPAK.P A-scans 85 DEEPAK.P A-scans 86 DEEPAK.P A-scans 87 DEEPAK.P B-scans B-scans can be used to take an image of a cross-section through the body. The transducer is swept across the area and the time taken for pulses to return is used to determine distances, which are plotted as a series of dots on the image. B-Scans will give two-dimensional information about the cross- section. 88 DEEPAK.P B-scans 89 DEEPAK.P B-scans 90 DEEPAK.P M-scans in cardiac cycle 91 DEEPAK.P Echo Cardiography (Heart) 92 DEEPAK.P Echo Cardiograph 93 DEEPAK.P Comparison 94 DEEPAK.P Comparison 95 DEEPAK.P Scanners 96 DEEPAK.P Scanner 97 DEEPAK.P Scanners 98 DEEPAK.P