Therapy and diagnostics
People born at the turn of the 20th century were accustomed to the concept of dentures. As they aged, they faced the dismal idea of having their teeth pulled and losing their sense of taste to the layer of uncomfortable, clacking plastic they removed each night and deposited in a glass of fizzing cleaning fluid. Thankfully, modern dental technology has changed all that. It’s no longer unrealistic to expect teeth to last a lifetime.
Over the last few decades, the periodic trip to the dentist has been replaced by the visit to the hygienist. The aim of the exercise remains the same: remove dental plaque and prevent gingivitis and the ensuing irritation that causes receding gums and possible ultimate loss of teeth. Although the original hand descaler is still often used to finalize the job, the periodontal therapy to remove the plaque, which left to its own hardens into calculus (tartar), is nowadays frequently carried out with ultrasonic descalers.
Ultrasonic descalers have a tip that vibrates at high frequency from 25 000 to 40 000 or more cycles per second to break down bacterial matter to which plaque and calculus stick. The cleaning efficiency depends on the vibration amplitude. IEC 61205, Ultrasonics - Dental descaler systems - Measurement and declaration of the output characteristics, defines standard methods of measurement and specifies the essential vibration characteristics of ultrasonic dental descalers.
While providing specifics on the technical parameters such as primary tip vibration excursion, tip vibration frequency and half-excursion force, the International Standard specifies measurements for operating conditions, load conditions, cleaning and the irrigant temperature of an ultrasonic descaler. The WG (Working Group) responsible for the publication (WG 7: Ultrasonic surgical equipment) is part of IEC TC 87: Ultrasonics. IEC TC 87 maintains a close liaison with TC 62: Electrical equipment in medical practice, and TC 29: Electroacoustics.
TC 87 is at present working on a new amendment to the second edition of IEC 61157, which provides a standard means to measure and report the acoustic output of medical diagnostic ultrasonic equipment, particularly used by manufacturers in the literature they provide to prospective purchasers of systems.
Ultrasound in diagnostics
Medical diagnostic ultrasonic equipment is widely used in clinical practice for monitoring and imaging subcutaneous tissues such as internal organs, tendons and so on. It is particularly used during pregnancy for examining the foetus. Equipment consists of an ultrasonic transducer (hand-held probe) that is placed on the patient and coupled with relevant electronics to produce an ultrasound wave that in turn generates a reflected echo that is interpreted as a digital image. Systems normally operate at frequencies in the low megahertz frequency range (from 2 to 18 megahertz), well beyond the limit of human hearing, which is typically accepted as 20 kilohertz.
The ultrasound entering the patient interacts with the patient's tissue, and this interaction can be considered in terms both of its thermal and non-thermal effects.
The heat is on
In October 2010, TC 87 published a new edition of IEC 62359, Ultrasonics - Field characterization - Test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields. It takes into account the thermal effects generated by ultrasound both "at-surface" and "below-surface" when a person is exposed to a particular ultrasonic field during medical diagnosis or monitoring. Using theoretical tissue-equivalent models, the recent publication provides test methods to determine the relevant indices and exposure parameters relating to the temperature rise resulting from the absorption of ultrasound. It also provides methods to determine exposure parameters for certain non-thermal effects.
As technology progresses and scientific understanding increases, so it is expected that the indices will change and the publication see new revisions. At present, the approach and philosophy used in drafting this particular International Standard for the safety of ultrasonic diagnostic equipment are consistent with those of the International Standards of the IEC 60601-2 series that apply to other diagnostic modalities, such as X-ray equipment and magnetic resonance systems.
Find out more
- IEC TC 87Ultrasonics
- IEC 60601-2 seriesMedical electrical equipment
- IEC 61157Standard means for the reporting of the acoustic output of medical diagnostic ultrasonic equipment
- IEC 61205Ultrasonics - Dental descaler systems - Measurement and declaration of the output characteristics
- IEC 62359Ultrasonics - Field characterization - Test methods for the determination of thermal and mechanical indices related to medical diagnostic ultrasonic fields