Introduction to Biomedical Imaging

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Introduction to Biomedical Imaging

Introduction to Biomedical ImagingAlejandro Frangi, PhDComputational Imaging LabDepartment of Information & Communication TechnologyPompeu Fabra Universitywww.cilab.upf.edu


Ultrasound ImagingIntroduction to Biomedical Imaging


Ultrasound ImagingBasic principles. Comparison to X-rays• Ultrasound > 20kHz• Medical/Diagnostic Ultrasound 1-15 MHz• Sound spreads in all directions• Ultrasound can be formed into a narrow beam (it is more “light-like”)• Periodic motion yields pressure waves• Speed of sound vs. speed of light• Ultrasound requires a medium to propagate (no sound in vacuum)• X-rays can be scattered. US can be reflected, refracted and focusedIntroduction to Biomedical Imaging


Ultrasound ImagingUltrasound pulse/continuous wave modes• Pulsed Wave Mode• Short DC pulse is applied to the crystal producing its instantaneousexpansion an tissue compression• Due to elastic tissue properties: high pressure wave front (compression)travels through the body at speed ν followed by a low wave front(decompression or rarefaction)• Multiple frequencies are present in the signal and echo (bandwidth)• Continuous Wave Mode• AC voltage applied to crystal• Periodic pattern of compression and rarefaction will travel across thebody with speed ν and wavelength λ• The frequency is given by the AC voltage applied to the transducercrystal: ν = λ fIntroduction to Biomedical Imaging


Ultrasound ImagingUltrasound pulse/wavegeneration:transmissionUltrasound signaldetectionIntroduction to Biomedical Imaging


Ultrasound transducer frequency vs. resolutionUltrasound ImagingIntroduction to Biomedical Imaging


Ultrasound ImagingPiezoelectric crystals, beam forming and transducersIntroduction to Biomedical Imaging


Ultrasound ImagingPiezoelectric crystals, beam forming and transducersIntroduction to Biomedical Imaging


Ultrasound ImagingPiezoelectric crystals, beam forming and transducersConvex probe(abdominal)Linear probe(superficial)GynecologyObstetricsIntroduction to Biomedical Imaging


Ultrasound ImagingUltrasound system overviewTime-gaincompensationIntroduction to Biomedical Imaging


Ultrasound ImagingA-mode Ultrasound (A = amplitude)Now obsolete in medical imaging. Wave spikes are represented when a singlebeam passes through objects of different consistency and hardness. The distancebetween these spikes (for example A and B ) can be measured accurately bydividing the speed of sound in tissue (1540 m/sec) by half the sound travel time.depthIntroduction to Biomedical Imaging


M-mode Ultrasound (M = motion)Ultrasound ImagingA single beam in an ultrasound scan can be used to produce an M-mode picturewhere movement of a structure such as a heart valve can be depicted in a wavelikemanner. Because of its high sampling frequency (up to 1000 pulses persecond) This is useful in assessing rates and motion and is still used extensivelyin cardiac and fetal cardiac imaging.depthMitral valveLV (parasternalviewtimeIntroduction to Biomedical Imaging


Ultrasound ImagingB-mode Ultrasound (B = brightness)Same as A-mode, but one dimensionalgraphical display with brightnesscorresponding to amplitude of reflectedsound2D real-time ultrasoundMost modern ultrasound devices are realtime2D imaging systems. Multiplecrystals (linear, curved or phased-array)or moving crystalSequential B-mode pulses sweepingacross a plane to display the image ineither a linear or ‘sector’ formatDisplayed as real time imaging with up to100 images per second.Introduction to Biomedical Imaging


Ultrasound ImagingSummary A-, B-, M-mode ultrasoundIntroduction to Biomedical Imaging


Ultrasound 2D piezoelectric arraysAllows real-time volumetric scans• Arbitrary multiplanar reslicing is possible restrospectively• Real time volume renderingUltrasound ImagingBrest biopsyIntroduction to Biomedical Imaging


Examples of 3D US• Allows real-time volumetric scans• Arbitrary multiplanar reslicing is possible restrospectively• Real time volume renderingUltrasound ImagingMiltral valve3D Color DopplerIntroduction to Biomedical Imaging


Ultrasound ImagingDoppler Ultrasound• Measures the Doppler frequencyshift between the transducer andthe red blood cells• Higher frequency = blood towardtransducer• Lower frequency = blood awayfrom transducerIntroduction to Biomedical Imaging


Ultrasound ImagingDoppler Ultrasound• In practice non zero Doppler angleIntroduction to Biomedical Imaging


Ultrasound ImagingDoppler Ultrasound• Continuous wave (CW)• Use two crystals, one to send and one toreceive.• Doppler signals are obtained from allvessels in the path of the ultrasound beamIntroduction to Biomedical Imaging


Ultrasound ImagingDoppler Ultrasound• Continuous wave (CW)• Use two crystals, one to send and one toreceive.• Doppler signals are obtained from allvessels in the path of the ultrasound beam• Pulsed Wave (PW)• The transducer both sends and receivesthe signal.• The returned signal is gated so that onlyinformation about the desired depth iscomputed.• Color Flow (CF)• Information of the whole image (Dopplerequivalent of B-mode)• Velocity is encoded as a colorIntroduction to Biomedical Imaging


Doppler Ultrasound modesColor Doppler image (top) andPulse wave Doppler of a carotidartery (bottom). The samplevolume is located at the centreof the vessel.Ultrasound ImagingColor Doppler imaging of the heartCW Doppler representingmoderate to severe mitralregurgitation from an apical 4chamber view.Introduction to Biomedical Imaging


Ultrasound ImagingModern ultrasound systemsGE Vivid7GE Voluson 750Introduction to Biomedical Imaging

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