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

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ocal

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•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