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ULTRA SOUND<br />IN<br />MEDICAL IMAGING<br />Mohammad Amir<br />Final Year MBBS<br />JJMMC<br />

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WHAT IS MEDICAL IMAGING<br />?<br />

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MEDICAL IMAGING: The techniques and processes used to create image of the internal as well as external human body parts for clinical purpose .<br />

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Why medical imaging is required?<br /><ul><li>Medical imaging provides a pictorial status of particular organ which is to be treated

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It makes a surgical targets more clear and precise

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It provides a pictorial status of fetus development right from 4th weak to 36th- 38th week

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It make therapeutic targets easy to detect and treat </li></li></ul><li>TYPES OF MEDICAL IMAGING WIDELY USED <br /><ul><li>X-RAY

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MAMOGRAPHY

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CONTRAST RADIOGRAPHY

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ULTRA SOUND

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CT SCAN

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MRI

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SPECT(SINGLE PHOTON EMMISION TOMOGRAPHY)

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PET(POSITRON EMISSION TOMOGRAPHY)</li></li></ul><li><ul><li>PIZOELECTRIC IS DEVELOPED BY THE CURIES IN 1880 USING NATURAL QUARTZ

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SONAR was first time used in war time 1940

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Diagnosis medical application in use since late 1950’s</li></li></ul><li>WHAT IS ULTRA SOUND<br />?<br />

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ULTRA SOUND : MEDICAL DEFINATION!!!<br /><ul><li>DIGNOSTIC MEDICAL ULTRASOUND IS THE USE OF HIGH FREQUENCY SOUND TO AID IN DIGNOSIS AND TREATMENT OF PATIENT.

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FREQUENCY RANGES USED IN MEDICAL ULTRASOUND ARE 2-15 MHZ</li></li></ul><li>

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Ultrasound Production<br /><ul><li>Transducer contains piezoelectric elements/crystals which produce the ultrasound pulses (transmit 1% of the time)

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These elements convert electrical energy into a mechanical ultrasound wave</li></li></ul><li>PULSE<br /><ul><li> Pulse of sounds is send to soft tissues

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Sound interaction with soft tissues= bio effect

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Pulsing is determined by transducer or probe crystal and ins not operated or control</li></li></ul><li>ECHO<br /><ul><li>ECHO IS PRODUCED BY SOFT TISSUES

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TISSUE INTRACTION WITH SOUND = ACOUSTIC PROPAGATION PROPERTIES

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ECHOES ARE RECEIVED BY THE TRANSDUCER CRYSTAL

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ECHOES ARE INTRPRETED AND PROCESSED BY ULTRA SOUND MACHINE</li></li></ul><li>Refraction<br />reflective<br />refraction<br />Scattered<br />echoes<br />Incident <br />Angle of incidence = angle of reflection<br />

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The Returning Echo<br /><ul><li>Reflected echoes return to the scan head where the piezoelectric elements convert the ultrasound wave back into an electrical signal

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The electrical signal is then processed by the ultrasound system</li></li></ul><li>FACTORS AFFECTING ULTRASOUND<br /><ul><li>FREQUENCY

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WAVELENGTH

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BANDWIDTH

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ATTENUATION

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TIME GAIN COMPENSATION</li></li></ul><li>Piezoelectric Crystals<br /><ul><li>The thickness of the crystal determines the frequency of the scan head</li></ul>High Frequency<br />10 MHz<br />Low Frequency<br />3 MHz<br />

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FREQUENCY AND RESOLUTION<br /> HIGH FREQUENCY = HIGH RESOLUTION <br />

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DYNAMIC RANGE<br />

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M-MODE<br />B-MODE<br />

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Power Doppler<br />Color Doppler<br />

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MACHINE COMPONENT<br /><ul><li>Keyboard /cursor

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Diskstorage device

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Printer</li></li></ul><li>

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Transducer Design<br />Size, design and <br />frequency<br />depend upon the<br />examination<br />

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Image Formation<br /><ul><li>Electrical signal produces ‘dots’ on the screen

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Brightness of the dots is proportional to the strength of the returning echoes

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Location of the dots is determined by travel time. The velocity in tissue is assumed constant at 1540m/sec

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Distance = Velocity Time</li></li></ul><li>Image Formation<br /> ‘B’ mode<br />

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Interactions of Ultrasound with <br />Tissue<br /><ul><li>Acoustic impedance (AI) is dependent on the density of the material in which sound is propagated</li></ul> - the greater the impedance the denser the material.<br /><ul><li>Reflections comes from the interface of different AI’s

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greater  of the AI = more signal reflected

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works both ways (send and receive directions)</li></li></ul><li>Attenuation & Gain<br />Sound is attenuated by tissue<br />More tissue to penetrate = more attenuation of signal<br />Compensate by adjusting gain based on depth<br />near field / far field<br />AKA: TGC<br />

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Ultrasound Gain<br />Gain controls<br />receiver gain only<br />does NOT change power output<br />think: stereo volume<br />Increase gain = brighter<br />Decrease gain = darker<br />

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Balanced Gain<br />Gain settings are important to obtaining adequate images.<br />bad far field<br />bad near field<br />balanced<br />

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Reflected Echo’s<br />Strong Reflections = White dots<br />Diaphragm, tendons, bone<br /> ‘Hyperechoic’<br />

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Reflected Echo’s<br /> Weaker Reflections = <br />Grey dots<br />Most solid organs, <br />thick fluid – ‘isoechoic’ <br />

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Reflected Echo’s<br />No Reflections = Black dots<br />Fluid within a cyst, urine, blood<br />‘Hypoechoic’ or echofree<br />

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Ultrasound Beam Profile<br />Beam comes out as a slice<br />Beam Profile<br />Approx. 1 mm thick<br />Depth displayed – user controlled<br />Image produced is “2D”<br />tomographic slice<br />assumes no thickness<br />You control the aim<br />1mm<br />

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Goal of an Ultrasound System<br />The ultimate goal of any ultrasound system is to make like tissues look the same and unlike tissues look different<br />

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Accomplishing this goal depends upon...<br />Resolving capability of the system<br />axial/lateral resolution<br />spatial resolution<br />contrast resolution<br />temporal resolution<br />Processing Power<br />ability to capture, preserve and display the information<br />

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Ultrasound Applications<br />Visualisation Tool:<br />Nerves, soft tissue masses <br />Vessels - assessment of position, size, patency<br />Ultrasound Guided Procedures in real time – dynamic imaging; central venous access, nerve blocks<br />

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Imaging<br />Know your anatomy – Skin, muscle, tendons, nerves and vessels <br />Recognise normal appearances – compare sides!<br />

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Skin, subcutaneous tissue<br />Epidermis<br />Loose connective tissue and subcutaneous fat is hypoechoic<br />Muscle interface<br />Muscle fibres interface<br />Bone<br />

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conclusion<br /><ul><li>Imaging tool – Must have the knowledge to understand how the image is formed

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Dynamic technique

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Acquisition and interpretation dependant upon the skills of the operator.</li></li></ul><li>