Hans Torp NTNU, Norway TTK 4165 Signalbehandlingsteknikker i medisinsk bildediagnostikk Signal Processing in Medical Imaging Faglærer: Hans Torp Institutt for sirkulasjon og bildediagnostikk
Hans Torp NTNU, Norway lecture overview • Physical principles of ultrasound • Ultrasound imaging • Ultrasound Doppler and flow imaging • Overview TTK4165
Sound field depends on source size and wavelength
Echoes from tissue structures are received and displayed First Cardiac trials by Edler and Hertz in 1953 Hans Torp NTNU, Norway Ultrasonic M-Mode (Motion Mode)
Hans Torp NTNU, Norway Real-time Ultrasound B-mode 1974 Vis film N. Bom & al. “Multiscan EchoCardiograph” Ultrasound in Medicine aug. 74
Blood velocity Mitral inflow Normal relaxation Delayed relaxation Doppler blood flow meter Pedof 1976
Fourier transform - measure bloodflow • Gaussian Random process - ultrasound signal • Analog computer diff. equation solver- model of the cardiovascular system • Bernouli equation- from blood velocity to pressure
Ultrasound probe Focusing Steering and Focusing 50-200 elements
2 Received Echoes from close objects 1 Objects probe elements
A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 A / D 134 134 134 134 134 134 134 134 134 134 134 134 134 134 134 Digital Beam Former #Channels: 128 # samples per channel: 10.000 • Data per scanline: 2*10.000*128 = 2.5 Mb • Data per image: 2.5*100 = 250 Mb • Data per second: 40* 250 Mb = 10 Gb
1996 System Five 128 channels Elektronic scanning Mekanisk scanning 2000 Vivid 7 128 kanaler Elektronisk scanning 1986 CFM 700 5 channels Mekanisk scanning
Hans Torp NTNU, Norway Real-time 2D B-modeWall motion assessment ))) )))
Linear array High resolution Limited width Curve-linear array Large image width Large near field Phased array Small footprint 90 deg. sector format Hans Torp NTNU, Norway Ultrasound Probes
Heart, 4 chamber view Kidney Fetus 3 ½ mnd Liver Twin fetus Ultrasound imaging can be applied to almost all human organs Ultrasound imaging: Measure dimensions, areas, volumes Study anatomical details Assessment of muscle contraction Heart-valve function
Probe-diameter D F: Focal depth L Image resolution D aperture F-number f# = F/D Wavelength: L ”Dot-size”: f# L F: Focal depth Camera example L = 0.9 e-3 mm f# = 5.6 Resolution: 0.005 mm ~ 50000 dpi Infrared camera gives lower resolution Ultrasound example L = 0.5 mm (3 MHz) f# = 8cm/2cm= 4 Resolution: 2 mm ~ 125 dpi Larger probe -> improved resolution Higher frequency -> improved resolution
Embryo 7 weeks. Ca 13 mm length • Computer-simulated ultrasound image • Higher frequency -> better resolution
3D Transvaginal ultrasoundThe Lancet:In-vivo three-dimensional ultrasound reconstructions in the embryonic and early fetal periodHarm-Gerd Blaas 1, Sturla H. Eik-Nes 1, Sevald Berg 2, Hans Torp 2;
18 weeks Limb development in Norway 20th century 12 weeks
PW Doppler: Velocity from one point Color flow imaging: Velocities in the whole image Color M-mode: Velocities along a line Color Doppler velocity imaging
Curved M-mode Systole Atrial systole Early relax. Hans Torp NTNU, Norway Tissue Velocity Imaging Moving upward Moving downward
Wall motion quantification Curved M-mode Systole Atrial systole Early relax. Strain rate Tissue velocity Strain rate v1 SR L v2 Shortening No change Elongation Adapted from J-U. Voigt and A. Heimdal
Real-time 3D imaging2D matrix array 50 x 1 elements • 32-192 elements in a 1D array • 32*32 ... 96*96 elements in a 2D array • 1000 - 10000 elements • Cable • Electronics • Beamformer 50 x 50 =2500 elements
Azimuth Elevation Sanntid 3D
4D Volume Imaging Increased elevation width Standard setup • No ECG gating • Volume rendering / orthogonal slicing • Volume size: ~20 x 80º / ~35 x 45º • Volume rate: 17-25
4D Color Imaging (ECG Gated) • Gated from 7 heart beats • High frame rates (17-35 frames / second) • High Color sensitivity • High Color resolution
TTK4165 Overview • Pulse Echo principle • Ultrasound beamforming • General imaging system • Ultrasound imaging system • Doppler – blood velocity measurement and imaging • Patient safety issues • Ultrasound contrast imaging • 3D imaging
