NMIJ measurement service on ultrasonic field parameters available to demonstrate performance and safety of ultrasonic medical equipment

Transcription

1 NMIJ measurement service on ultrasonic field parameters available to demonstrate performance and safety of ultrasonic medical equipment Masahiro Yoshioka National Metrology Institute of Japan (NMIJ) National Institute of Advanced Industrial Science And Technology (AIST)

2 Needs of ultrasonic measurement for ultrasonic medical equipment Demonstration of performance and safety required in International Standards Output control to balance efficiency and safety on diagnostic and therapy

3 NMIJ ultrasonic standards to provide measurement services Ultrasonic power Ultrasound pressure (Hydrophone sensitivity) Ultrasonic field parameters

4 Ultrasonic field characterization for Medical diagnostic equipment using IEC Ultrasonic field Measurement Ultrasonic power Ultrasound pressure Measurement, Calculation Ultrasonic field parameters Characterization Thermal Index Mechanical Index

5 Calibrated devices by NMIJ ultrasonic measurement services Hydrophone:Microphone for ultrasound in water Ultrasonic transducer: Ultrasound source Ultrasonic wave

6 Ultrasonic power standard Ultrasonic power: Energy per unit time of ultrasonic wave passing a certain plane (Unit: W) Ultrasonic power on sound source of medical equipment is indispensable for evaluation of ultrasonic output

7 Ultrasonic power calibration system using Radiation force balance Absorbing target Ultrasonic transducer Electric balance

8 Development of high output ultrasonic power standard Back ground Need has emerged for measurement of therapeutic high power ultrasound Problem on Radiation Force Damage of absorbing target by high power ultrasound exposure High power calibration system using calorimetric method is developed in NMIJ

9 High ultrasonic power calibration using calorimetric method Ultrasonic transducer

10 Ultrasound pressure standard Ultrasound pressure: Variation from static pressure by ultrasonic wave at a certain point (Unit: Pa) Parameters characterizing ultrasonic field is derived using instantaneous ultrasound pressure or that spatial distribution Ultrasound pressure standard is indispensable for demonstrating performance and safety of medical equipment

11 Ultrasound pressure standard is provided by hydrophone sensitivity calibration (Unit: V/Pa) Membrane type Needle type

12 Reciprocity calibration system of hydrophone sensitivity up to 1 MHz Receiver (Hydrophone, Ultrasonic transducer) Transmitter (ultrasonic transducer) Absorber

13 Hydrophone calibration system using laser interferometry for frequency Laser interferometer range up to 40 MHz Pellicle reflecting optically Small diameter (2 mm) ultrasonic transducer developed for expanding calibration frequency range up to 40 MHz

14 Ultrasonic field parameter standard Manufacture or distributor of ultrasonic medical diagnostic equipment required to demonstrate performance and safety of their products according to International Standards For validation of ultrasonic field measurement by manufacture or distributor, 3 ultrasonic field parameters are calibrated with reference transducer in NMIJ

15 Calibrated ultrasonic field parameters Peak-rarefactional acoustic pressure p r (Unit: Pa) Maximum of modulus of negative instantaneous acoustic pressure Spatial-peak temporal-average intensity I spta Spatial-average temporal-average intensity I sata (Unit: W/cm 2 ) (Acoustic) Intensity: Ultrasonic power per unit area at a certain point

16 Block diagram of ultrasonic field parameter calibration system Motorized stage Calibrated device Thermo -meter Water vessel Ultrasonic wave Hydrophone calibrated in NMIJ AD converter Clock Trigger Clock generator Computer Ultrasonic transducer Signal generator Frequency counter

17 Ultrasonic power Hydrophone sensitivity Ultrasonic field parameters Summary of NMIJ ultrasonic measurement services Method Radiation force balance Calorimetry Calibration range 1 mw mw (15 MHz - 20 MHz) 1 mw - 15 W (0.5 MHz - 15 MHz) 15 W - 100W (1 MHz - 3 MHz) Expanded uncertainty (Level of confidence 95 %) 5 % - 12 % 9 % Reciprocity 100 khz - 1 MHz 10 % - 13 % Laser 0.5 MHz - 40 MHz interferometry 6.1 % - 17 % p R 7 % - 10 % Plane scan 0.5 MHz - 20 MHz I SPTA 14 % - 20 % I SATA 14 % - 21 %

18 Ultrasonic power Future works Expanding calibration range: 200 W Hydrophone sensitivity Expanding frequency range: 50 khz -100 MHz Technique for phase response calibration Ultrasonic field parameter Adding Effective radiating area, Beam nonuniformity ratio required for ultrasonic physiotherapy equipment