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Ultrasound in MedicineHans Torp
Department of Circulation and Medical ImagingNTNU
Hans TorpNTNU, Norway
Ultrasound in Medicine
• No injury/inconvenience for the patient
• Portable equipment• Real-time imaging• Velocity measurements in blood and
muscular tissue
Diagnostic ultrasound have a number of advantages
Ultrasound in Medicine
• Lecture 1, October 5th:
Overview and basic principles
• Lecture 2, October 12th:
Ultrasound imaging in 2D and 3D
• Lecture 3, November 16th:
Ultrasound blood flow velocity measurements
Hans TorpNTNU, Norway
What is ultrasound?
medical ultrasound
440 Hz
audible range
40 MHz1 MHz20 kHzend of piano4.2 kHz
…piano med “ultrasound keys”
start of piano27.5 Hz
Figur av Martijn Frijlink
What is ultrasound? •Sound waves–Propagation speed c–Wave length L–Frequency f–Relation: L = c / f
•Audible sound – f = 20 - 20.000 Hz
•Ultrasound– f > 20.000 Hz
•Diagnostic ultrasound–f > 2.000.000 Hz
L c f Male voice: ~ 1 - 2 meter 330 m/s (air) 165 - 330 HzFemale voice: ~ 0.5 - 1 meter 330 m/s (air) 330 - 660 Hz
Diagnostic ultrasound: 0.1 - 1 mm 1540 m/s 1.5 - 15 MHz
Sound field depends on source size and wavelength
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Echo
Hoi !
Hoi !Hoi !
Echo is reflected sound-waves
Hoi !
By measuring the time delay for the echo, the distance can be estimated
1001, 1002,….
How are ultrasound images made?
Ultrasound images represent the echoes we get back when short high frequency pulses are sent into the body.
Department of circulationand medical imagingFigure by Martijn Frijlink
Ultrasound M-Mode Sonar applied to the human heart
Hans TorpNTNU, Norway
Focused ultrasound beam Echo from tissue structures are visualized
Echocardiography started in 1953
In Lund, Sweeden, by Edler and Hertz
Real-time Ultrasound B-mode 1974
N. Bom & al. “Multiscan EchoCardiograph” Ultrasound in Medicine aug. 74
Video
Ultrasound probe
Fokus
Fokus
Focusing Steering and Focusing
50-200 elements
Real-time 2D B-modeWall motion assessment
))) )))
Hans TorpNTNU, Norway
Ultrasound Probes
Linear arrayHigh resolutionLimited width
Curve-linear arrayLarge image widthLarge near field
Phased arraySmall footprint90 deg. sector format
Hans TorpNTNU, Norwa
Ultrasound imaging can be applied to almost all human organs
Liver Fetus 3 ½ mnd
Kidney
Twin fetus
Ultrasound imaging:Measure dimensions, areas, volumesStudy anatomical detailsAssessment of muscle contractionHeart-valve function
Heart, 4 chamber view
- However, ultrasound are attenuated by air or bone structures- Brain imaging is difficult
Brain18 weeks fetus
Hans TorpNTNU, Norway
Ultrasound imaging can be applied to almost all human organs
Ultrasound guidance in brain surgery
Hans TorpNTNU, Norway
Image resolution
Daperture
F: F
ocal
dep
th
F-number f# = F/D
Wavelength: L
”Dot-size”: f# L
Camera exampleL = 0.9 e-3 mmf# = 5.6Resolution: 0.005 mm ~ 50000 dpiInfrared camera gives lower resolution
Ultrasound exampleL = 0.5 mm (3 MHz)f# = 8cm/2cm= 4 Resolution: 2 mm ~ 125 dpi
Larger probe -> improved resolutionHigher frequency -> improved resolution
Probe-diameterD
F: F
ocal
dep
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L
•Computer-simulated ultrasound image•Higher frequency -> better resolution
Embryo 7 weeks. Ca 13 mm length
3D Transvaginal ultrasoundThe Lancet:
In-vivo three-dimensional ultrasound reconstructions in the embryonic and early fetal period
Harm-Gerd Blaas 1, Sturla H. Eik-Nes 1,Sevald Berg 2, Hans Torp 2;
Blood transfusionin a fetus
Harm-Gerd Blaas, Norwegian national center for fetal medicine
Ultrasonic bio-effects • Thermal effects
– Local and temporal temperature increase– Physioterapy: Heating of muscular tissue– Thermal indeks TI = temperature increase (centdegree).
Recommendation: TI < 3
• Mechanical effects: – Excessive vibrations may cause cavitation– Therapy: Kidney stone disintegration– Mechanical Index MI. Recommendation: MI < 1.9
• Diagnostic ultrasound is safe as long as MI and TI are kept below recommended limits
Hans TorpNTNU, Norway
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