Fysisk institutt - Rikshospitalet 1. 2 Ultrasound waves Ultrasound > 20 kHz, normally 1-15 MHz i...

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Transcript of Fysisk institutt - Rikshospitalet 1. 2 Ultrasound waves Ultrasound > 20 kHz, normally 1-15 MHz i...

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Fysisk institutt - Rikshospitalet 1 Slide 2 2 Ultrasound waves Ultrasound > 20 kHz, normally 1-15 MHz i medicine When a wave is sent in one direction, it will continue until reflected, deflected or absorbed. Sound speed is independent of frequency but dependent on the medium Sound speed is related to density, compressibility and intensity V = f Because the frequency remains unchanged when the medium is changed, the wavelength has to change because the speed is changed Slide 3 Fysisk institutt - Rikshospitalet 3 Ultrasound waves No transport of US-waves in vacum and poor transport in gases => Air must NOT be present Transducer must be in close contact to the object Use acoustic gel to ensure transmission from transducer to object Bone tissue is a barrier for US Without the audible range for both animals and humans Pulsed or continuous, dependent on the object. Mainly pulsed in image forming US Slide 4 Fysisk institutt - Rikshospitalet 4 Resolution Axial resolution: Ability to discriminate two objects in parallell to the beam. Best at high frequencies Lateral resolution: Ability to discriminate two objects perpendicular to the beam Best at the focal zone Slide 5 Fysisk institutt - Rikshospitalet 5 Ultrasound waves Eccocharacteristics Anechoic (ecco-free) Tissue without acoustic interface looks black Hypoechoic (poor ecco) Tissue with low ecco-genesity will be dark grey Tissue with medium ecco-genesity will be light grey Hyperechoic Ecco rich tissue, from light grey to white Slide 6 Fysisk institutt - Rikshospitalet 6 Handheld probe Slide 7 Fysisk institutt - Rikshospitalet 7 Modern ultrasound devices Slide 8 Fysisk institutt - Rikshospitalet 8 Ultrasound 3D www.theultrasoundzone.com/3dultrasoundphotos.html Slide 9 Fysisk institutt - Rikshospitalet 9 Ultrasound piezo crystal Kilde: Alejandro Frangi Slide 10 Fysisk institutt - Rikshospitalet 10 Piezo-electric disc Slide 11 Fysisk institutt - Rikshospitalet 11 Ultrasound (US), A-mode (amplitude) Slide 12 Fysisk institutt - Rikshospitalet 12 Time motion US, M-mode Slide 13 Fysisk institutt - Rikshospitalet 13 M-mode Ultrasound (motion) Slide 14 Fysisk institutt - Rikshospitalet 14 B-mode Slide 15 Fysisk institutt - Rikshospitalet 15 B-mode (Brightness) Same as A-mode, but twodimensional graphical display where brightness indicates the amplitude to reflected sound Most modern US-systems is realtime 2D or 3D. Multiple crystals or mobile crystals Up to 100 images per second Slide 16 Fysisk institutt - Rikshospitalet 16 Summarized A, B og M-mode Kilde: Alejandro Frangi Slide 17 Fysisk institutt - Rikshospitalet 17 Probes 4-12 MHz Slide 18 Fysisk institutt - Rikshospitalet 18 4 different probe- principles Slide 19 Fysisk institutt - Rikshospitalet 19 Piezoelectric array-probe Volumetric scan realtime Possibilities for multiplan reslicing retrospectively Realtime volume rendering Slide 20 Fysisk institutt - Rikshospitalet 20 Side lobes Slide 21 Fysisk institutt - Rikshospitalet 21 Ultrasound transducer frequency vs resolution A 15 MHz scan has very good resolution but penetrates a short distance only A 3 MHz scan can penetrate far into the body, but the resolution is poor High frequency = High resolution High frequency = Poor range Kilde: Alejandro Frangi Slide 22 Fysisk institutt - Rikshospitalet 22 Piezoelectric crystal, beam shape Kilde: Alejandro Frangi Slide 23 Fysisk institutt - Rikshospitalet 23 Piezoelectric crystal, beam shape Kilde: Alejandro Frangi Slide 24 Fysisk institutt - Rikshospitalet 24 Overview Time-gain compensation Kilde: Alejandro Frangi Slide 25 Fysisk institutt - Rikshospitalet 25 Attenuation Slide 26 Fysisk institutt - Rikshospitalet 26 Sources of error (1) Slide 27 Fysisk institutt - Rikshospitalet 27 Sources of error (2) Slide 28 Fysisk institutt - Rikshospitalet 28 Sources of error (3,4,5) Slide 29 Fysisk institutt - Rikshospitalet 29 3D transducer Slide 30 Fysisk institutt - Rikshospitalet 30 Catheter probe Slide 31 Fysisk institutt - Rikshospitalet 31 Doppler ultrasound Kilde: Alejandro Frangi Higher frequency = blood towards the transducer Lower frequency = blood away from the transducer Slide 32 Fysisk institutt - Rikshospitalet 32 Doppler ultrasound Slide 33 Fysisk institutt - Rikshospitalet 33 Doppler image/velocity Slide 34 Fysisk institutt - Rikshospitalet 34 Colour doppler Slide 35 Fysisk institutt - Rikshospitalet 35 Doppler Slide 36 Fysisk institutt - Rikshospitalet 36 Ultrasound advantages Muscles and soft tissue are suitable for US-imaging, especially transitions between solid substances and liquid filled areas. Real time images = fast diagnosis. Can also be used to biopsy-guiding Shows the organ structure No well-known side effects, not unpleasant for the patient Small scanners compared to other image modalities Inexpensive compared to other image modalities Spatial resolution is better at high-frequency US than most of the other modalities Slide 37 Fysisk institutt - Rikshospitalet 37 Ultrasound disadvantages Unable to penetrate bone tissue Poor performance where gas is present Limited operating range, dependent on the frequency High requrements for the operator, can be difficult to interpret Difficult to track back a scanned volume, as soon as the pictures are aquired no exact anchor-pile is available to navigate in the volume Slide 38 Fysisk institutt - Rikshospitalet 38 Future? Source: General Electric. The next stethoscope of the medical doctor?