1. Tests in Product Development
- Cases of Medical Devices
Raimo Sepponen, prof.
Aalto University
Electronics Department

2. Tests in Medical Device development
• Tests required by Medical Device Directive
• Tests by the quality control and international
standards
• How to test functional safety?
• Special but important problem area:
Electomagnetic Compatiblity (EMC)

3. Mechanical Failure: Falling head of a
radiation therapy unit
These devices are not related to the case – shown only for demonstration!!

4. Electromechanical Failure: Unexpected
movement of C-arc of mammography device
These devices are not related to the case – shown only for demonstration!!
Reason: Opening of electromechanical brakes during drop of mains voltage

5. Increasing risks of poor EMC
FDA + Evaluation Engineer

6. Evaluation Engineer

7. Rapidly changing electromagnetic environment – basis of
standards are old already when the are published
FDA

8. Wireless communication is a major noise source
FDA

9. Failing Apnea Alarm
Apnea alarm with poor
RF filtering detects
modulated field and assumes
FM Transmitter that baby is breathing
Field modulated by
movements
coupled to
sensor mat
Mother moving in kitchen

10. Walkie-talkies and cellphones interfere with medical equipment
Many types of hospital equipment are susceptible to RF radiation from hand-
portable mobile radio transmitters – diagnostic equipment such as ECGs, EEGs,
pulse oximeters and other physiological monitoring equipment; and therapeutic
equipment such as infusion pumps, ventilators and defibrillators. Physiological
monitoring equipment is very sensitive – hence very susceptible.
Example: The type of modulation employed by the mobile transmitter can be
significant. For example, an external pacemaker withstood a GSM signal
(modulated at 217Hz) at 30V/m field strength, but TETRA modulation (17Hz)
caused interference at 3V/m.
www.emcuk.co.uk

11. Fibreglass ambulance roof causes death of patient
Medical technicians taking a heart-attack victim to the hospital in 1992 attached her to a
monitor/defibrillator. Unfortunately, the heart machine shut down every time the
technicians turned on their radio transmitter to ask for advice, and as a result the woman
died.
Analysis showed that the monitor unit had been exposed to exceptionally high fields
because the ambulance roof had been changed from metal to fibreglass (to let in more
daylight) and also fitted with a long-range radio antenna. The reduced shielding from the
vehicle roof combined with the strong radiated signal proved to be too much for the
monitor/defibrillator.
Ambulances in the U.K. are typically fitted with radio transmitters with 100W of
transmitted power (ERP), and the resulting field strengths near the roof, where the
medical equipment is often installed, can exceed 70V/m in a vehicle with a metal roof.
Compare this with the 3V/m and 10V/m RF field susceptibility tests required by the
medical devices safety standard EN 60601-1-2. Equipment for fitting in ambulances and
similar environments must be able to function correctly despite such strong RF fields, so
they need to have greater immunity
www.emcuk.co.uk

12. Static Elecricity
• Example: A fluid dispenser often
malfunctioned when nursing staff entered the
room
• Reason: Static electric discharges in clothing
due to interactions of clothes and items in
pockets

13. Static discharges generated by metal/dielectric contacts –
Electric field
D.C.Smith: EOS/ESD Symposium 99-329

14. Coins in plastic bag – Magnetic field
D.C.Smith: EOS/ESD Symposium 99-329

15. Hazards due to user errors
• Example: Magnetic Resonance Imaging – burn
injury

16. Burn injuries during MRI
L R
loop loop
U
C Cair
skin Cskin
R
skin R skin
Radiology 1996; 200:572-575

17. Testing for Functional Safety
• Know the environment where the product is
used
• The environment is changing continuously
• Collect user experiences – not only from your
own products
• Try to develop non-standard tests which
reveals the unexpected malfunctions

18. Message
Tests according to
standards do not ensure
functional safety