1. CALIBRATION IN MEDICAL ULTRASOUND
Measurement and Calibration of Medical Device
CALIBRATION IN MEDICAL ULTRASOUND
Organizer:
Malaysian Society of Quality in Health (MSQH)
& National Metrology Institute of Malaysia (NMIM)
30th April 2018
Presenters:
Shahrul Nizam Abdul Rashid
Acoustics, Ultrasound & Vibration Laboratory
All rights reserved. © 2015 SIRIM Berhad.

2. MEDICAL ULTRASOUND
Introduction

3. Evolution in Medical Ultrasound

4. Conventional Wisdom of Medical Ultrasound
Resolution depends on wavelength.
Short wavelength will produce high resolution and simultaneously increased the diagnostic power.
Penetration depth depends on frequency and attenuation.
When high frequency apply, the attenuation also increase.

5. MEDICAL ULTRASOUND
Treatment or Surgery using Focused Ultrasound

6. Sources : Report from Focused Ultrasound Foundation 2018
MEDICAL ULTRASOUND
Treatment or Surgery using Focused Ultrasound
Sources : Report from Focused Ultrasound Foundation 2018

7. Principle of ultrasonic pulse echo diagnostic
MEDICAL ULTRASOUND
Principle of ultrasonic pulse echo diagnostic
Transmitter
Receiver
Signal Processor
Target
Transducer probe

8. Transducer types for diagnostic and therapeutic
MEDICAL ULTRASOUND
Transducer types for diagnostic and therapeutic
Diagnostic
Sector scanning transducer
Linear array transducer
Curved linear array transducer
Phased array transducer
Mechanical 2D array transducer
Electric 2D array transducer
Therapeutic
Plane circular transducer
Focusing transducer
Annular array transducer

9. Medical ultrasonic equipment
MEDICAL ULTRASOUND
Medical ultrasonic equipment
ULTRASONIC DIATHERMY (MODERN TERM FOR ACUPUNTUR)
- Devices configured to stimulate the body
through ultrasound for therapeutic and
other purposes
- Ultrasonic diathermy is intended to generate
deep heat within body tissues for the
treatment of selected medical conditions
such as pain, muscle spasms and joint
contractures, but not for the treatment of
malignancies.
Ultrasound diathermy unit

10. Medical ultrasonic equipment
MEDICAL ULTRASOUND
Medical ultrasonic equipment
2. HIGH INTENSITY FOCUSED ULTRASOUND (HIFU) - A surgical tool towards a non-invasive local treatment of tumors. - These days, most of aesthetician use HIFU for slimming process, face lift machine, non surgical deep cleansing etc.

11. Medical ultrasonic equipment
MEDICAL ULTRASOUND
Medical ultrasonic equipment
3. EXTRA-CORPOREAL SHOCK WAVE THERAPY
- A technique of lithotripsy using shock waves
generated externally.
- Medical shock wave is acoustic pressure waves.
- Therapeutic shock waves reflect and focus through
the reflector to create high energy.
- At this time, the shock wave accelerated while
focusing on the target and has high pressure.
- High pressure ( MPa) - Speed rise time (<100 ns) - Short pulse duration (<1 ns) - Low tensile wave component

12. Basic terminology in Medical Ultrasound
Ultrasound: Sound waves of frequencies exceeding the range of human hearing and their propagation in medium
Medical diagnostic ultrasound: modality that uses ultrasound energy and the acoustic properties of the body to produce an image from stationary and moving tissues
Acoustic Intensity: Average rate of flow of energy through a unit normal to the direction of propagation. Fundamental units are watts per square meter (W/m2). The instantaneous rate at which work is done per unit area by one element of fluid on an adjacent element is pu. The intensity is the time average of this rate,
I = <pu>t = 1 𝑡 0 𝑡 𝑝𝑢 𝑑𝑡
where the integration is taken over a tine corresponding to the period of one complete cycle.
Acoustic Power (watt): Surface integral of acoustic intensity

13. MEDICAL ULTRASOUND Exposure Parameter in Medical Ultrasound
(based on IEC & IEC 62359)
Total acoustic output power & Radiation conductance
Equivalent beam area
Equivalent beam diameter
Pressure pulse square integral
Pulse duration
Pulse average intensity
Temporal average intensity
Pulse repetition rate
Duty ratio
Pulse intensity integral
Spatial average temporal average intensity
Spatial peak temporal peak intensity
Spatial peak pulse average intensity
Thermal Index
Mechanical Index
Radiation Force Balance Method
Time domain by hydrophone
Scanning hydrophone method
Determine from above measurement

14. Mechanical Index, MI
The mechanical index (MI) measure part of an ultrasound beam's bioeffects. The MI is found on most ultrasound display screens, along with the thermal index.
Mechanical index is proportional to an ultrasound beam's peak negative pressure.It is also inversely proportional to the frequency of the beam. Therefore, higher frequencies have a lower mechanical index.
Mechanical index = peak negative pressure / √(center frequency of the US beam)
MI is an indication of an ultrasound beam's ability to cause cavitation-related bioeffects, and this is currently thought a reasonable proxy for micromechanical damage. It is "strictly a cavitation index," but is meant to be interpreted more broadly as tissue mechanical stress/damage.
In the U.S. the FDA mandates that the MI be kept below 1.9.

15. Thermal Index, TI
The thermal index (TI) is intended as a measure of an ultrasound beam's thermal bioeffects. It is often displayed on ultrasound screens.
Absorption of sound waves may cause heating in tissue. The thermal index depends on:
- a measure of time-averaged acoustic power
- assumptions of the properties of the tissue being heated
- assumptions about the path of the ultrasound beam
The TI is directly related to the output power of the system:
Thermal index = Wp / Wdeg
Wp: relevent (attenuated) acoustic power at the depth of interest
Wdeg: estimated power necessary to raise the tissue equilibirum temperature by one degree C
If the acoustic power of the ultrasound beam is enough to raise the tissue temperature by one degree C, then the TI = 1.0. It should be noted that this is a relative risk of heating, not an absolute scale of tissue heating.

16. Physical Mechanism in Medical Ultrasound
THERMAL
NON-THERMAL
NON CAVITATION
ACOUSTIC RADIATION FORCE
ACOUSTIC STREAMING
ACOUSTIC RADIATION TORQUE
CAVITATION
NON INERTIAL CAVITATION
INERTIAL CAVITATION

17. I (𝑟)= 𝑘𝐴Δ𝑇(𝑟,𝑡) 𝛼𝑉 [1− exp − 𝑡 𝜏 ]
MEDICAL ULTRASOUND
Governing equation for thermal physical mechanism
Heat transfer equation
Temperature rise
Spatial average temporal average intensity
𝛼IV−𝜌 c 𝑝 𝑉 𝑑𝑇 𝑑𝑡 - 𝜅Α 𝑇− 𝑇 0 =0
𝜏= 𝜌 𝑐 𝑝 𝑉 𝜅𝐴
ΔΤ=Τ− 𝑇 0 = 𝛼𝛪𝑉 𝜅𝛢 1−𝑒𝑥𝑝 − t 𝜏
I (𝑟)= 𝑘𝐴Δ𝑇(𝑟,𝑡) 𝛼𝑉 [1− exp − 𝑡 𝜏 ]
The increase in temperature by ultrasonic waves is caused by the absorption of the ultrasonic waves in the tissue. It depends on acoustic intensity (exposure) and acoustic thermal properties of tissue.

18. Physical Mechanism in Medical Ultrasound
THERMAL
NON-THERMAL
NON CAVITATION
ACOUSTIC RADIATION FORCE
ACOUSTIC STREAMING
ACOUSTIC RADIATION TORQUE
CAVITATION
NON INERTIAL CAVITATION
INERTIAL CAVITATION

19. Inertial and non inertial cavitation
MEDICAL ULTRASOUND
Inertial and non inertial cavitation

20. Why the measurement technique is important?
MEDICAL ULTRASOUND
Why the measurement technique is important?
The use of ultrasound in medicine: From oscillator (probe) medium (treatment, surgery) reception measurement (diagnosis)
Direct exposure of energy to the body Excessive exposure causes side effects
Standard and guidelines for the safe use of ultrasound for medical from FDA known as FDA: 20 safety related test items
Reliability of measurement must undergo traceability and third party verification.
Effort to determine international harmonized measurement method by promotion of International standards based on IEC TC87 (Ultrasonics): Determination of TI (Thermal Index) and MI (Mechanical Index) in IEC 62359

21. Why Medical Ultrasound need calibration
Wear and tear over time – impacts on performance accuracy
Minimize the risk or uncertainty – regular calibration
Life and death matters – quality of treatment
Required by regulatory authorities – certifications and licenses

22. Medical Ultrasound calibration traceability
Ultrasound Probe (Power)
Ultrasound Probe (Pressure)
Phantom
Radiance Force Balance (RFB)
Acoustics Intensity Measurement System (AIMS)
Mass, Voltage
Hydrophone
National Metrology
Institute / Lab
Users, suppliers,
clinics & hospitals
Calibration Lab,
Manufacturer

23. Medical Ultrasound calibration methods
Phantom – Imaging accuracy
Ultrasound Power Meter or Radiation Force Balance – Ultrasound power
Ultrasound Scanning – Ultrasound pressure and intensity

24. Ultrasound Power Measurement Setup
MEDICAL ULTRASOUND
Ultrasound Power Measurement Setup
Source : ONDA Corp.

25. Acoustics Intensity Measurement System (AIMS) Setup
MEDICAL ULTRASOUND
Acoustics Intensity Measurement System (AIMS) Setup
Source : ONDA Corp.

26. Ultrasound Power Measurement (RFB)
MEDICAL ULTRASOUND
Ultrasound Power Measurement (RFB)
PURPOSE
To determine the Ultrasound Power on medical devices.
Compliant with regulatory requirements including IEC 61161, and with associated IEC standards.
CAPABILITY
Power Ranges (selectable): 1 mW to 2W with standard (flat) absorbing target, up to 20W (cone) and up to 100W (brush)
Measurement uncertainty: <10% at 95% confidence level
Measurement Cycle Time: default 4s (15 measurements per minute)
Traceability : PTB
Calibration System

27. Acoustics Intensity Measurement System (AIMS)
MEDICAL ULTRASOUND
Acoustics Intensity Measurement System (AIMS)
PURPOSE
Measure, calculate and plot pulse waveform and pulse intensity integral plots
Intensity: pulse average(Isppa), temporal peak(Isptp), temporal average(Ispta), pulse duration
Mechanical Index
In-water and derated intensity values
Pressure: positive and negative peak values
Acoustic power by planar integration
Beam dimensions (1 and 2 dimensions)
Center frequency and bandwidth
Calibration System

28. Acoustics Intensity Measurement System
MEDICAL ULTRASOUND
Acoustics Intensity Measurement System
CAPABILITY
Axes: 5-axis (3 standard & 2 rotation)
Scan step resolution: 5.5 µm
Firing orientation: any angle (with angular positioner)
Frequency range: 250 KHz to 60 MHz
Travel: 57.5 x 42.5 x 49.5 cm (AST3-L)
Software: Onda Soniq version 5.1
Maximum Speed: 11 mm per second
Traceability : NPL
Fiber Optic
Membrane
Needle
Bullet
Hydrophone