Toshiba Medical Systems Safety in Ultrasound

and Image manipulation

Erica Oliver Clinical Product Specialist Ultrasound

Diagnostic ultrasound is an imaging modality that is useful in a wide range of clinical applications, and in particular, prenatal diagnosis. There is, to date, no evidence that

diagnostic ultrasound has produced any harm to humans (including the developing fetus).

BMUS STATEMENT

Despite its apparent excellent safety record, ultrasound imaging involves the deposition of energy in the body, and should only be used for medical diagnosis, with the equipment only

being used by people who are fully trained in its safe and proper operation.

It is the scan operator who is responsible for controlling the output of the ultrasound equipment. This requires a good knowledge of scanner settings, and an understanding of their effect on potential thermal and mechanical bio-effects.

BMUS GUIDLINES

BMUS Recommended Range and Scanning Times

1.The thermal index for soft tissue (TIS)This is used when ultrasound only insonates soft tissue, as, for example, during obstetric scanning up to 10 weeks after last menstrual period(LMP).

2. The thermal index for bone (TIB)This is used when the ultrasound beam impinges on bone at or near its focal region, as, for example, in any fetal scan more than 10 weeks after LMP.

3. The thermal index for cranial bone (TIC)This is used when the ultrasound transducer is very close to bone, as, for example, during trans-cranial scanning of the neonatal skull.

BMUS GUIDELINES INDICIES

•A temp elevation of 1.5ºC will cause no harm to tissue•A temp elevation of 4ºC maintained for 5 mins or more is considered harmful to fetal tissue•Some Doppler & Colour modes may reach this level•Other modes this is unlikely in current clinical useIndicated by Thermal Indices (TI) on equipment

Thermal Hazards

•Can happen where there are gas pockets i.e. lung & intestine particularly in neonates•Indicated by mechanical index (MI) value of 0.4 or more•Possibility of damage in small localised areas cannot be excluded•MI displayed on equipment on the monitor

Non-thermal hazard

The ALARA principle (i.e. as low as reasonably achievable).

If however the patient has a larger body habitus it is reasonable to use higher output or longer examination times than in others: for example, the risks of missing a fetal anomaly must be weighed against the risk of harm from potential bioeffects. When overall times longer than those recommended here are essential, the probe should be removed from the patient whenever possible, to minimise exposure.

Consequently, it is essential for operators of ultrasound scanners should be properly trained and fully informed when making decisions of this nature.

ALARA

Ultrasound During 11-14 week scans (or earlier in pregnancy)‘Pulsed Doppler (spectral, power and colour flow imaging) ultrasound should not be used routinely’

Approved by WFUMB Administrative Council, January 27, 2011.This text is identical to that in the statement published by AFSUMB, AIUM, BMUS, EFSUMB and JSUMB

WFUMB/ISUOG Statement on the Safe Use of Doppler

Do you know where your acoustic knob is?Do you know what the acoustic power is set at?Do you know where your Mechanical and thermal Indices can be found?Do you know what the indices do when you put harmonics on?Do you know what the indices do when you put colour Doppler on and Spectral Doppler?

System Optimisation

Mechanical Index found on left hand side of monitor whilst scanning is live

MECHANICAL INDEX

Thermal Index top right hand side of monitor

Thermal Indicies

Located under the TGC

Acoustic Knob

3.9 TIB

Power Outputs with colour and spectral Doppler

Manipulation of the system for optimum image quality

Knobology

The transducers are multi frequency for example 6 Mhz to 1 Mhz the lower the frequency the better the penetration the higher the frequency the better the resolution

Frequency

Aplipure or compounding allows electronic beam steering multiple angles improves continuity of structures and boundaries. Allows better signal to noise ratio contrast resolution whilst maintaining penetration.

Aplipure (compounding)

An electronic edge enhancement separating structures from clutter or noise.

Precision Imaging

The focus can be altered via both these buttons. Focus electronically narrow the beam for better resolution and should be placed just on or just behind the area of interest

Focus

The overall gain amplifies echos across the whole image whereas the TGC amplifies the allocated echos at a given depth selected by the operator

Gain and TGC (time gain compensation)

The depth button when pressed becomes your zoom or magnification the zoom can be selected to be either a pan zoom or a centre zoom the new Aplio series has high definition zoom features to give superior resolution .

Depth and Zoom

The system is capable of storing up to 180 GB of both still images and clips onto the hard drive. This can be transferred to a CD, USB PACs, external database, and black and white print all patient identification can be removed for this purpose if needed.

HDD and storage 180 GB

ter Haar G, Duck FA (eds). 2000. The Safe Use of Ultrasound in Medical Diagnosis , BMUS/BIR, London.

BMUS. 2010. Guidelines for the safe use of diagnostic ultrasound equipment. Ultrasound, 18 52-59.

WFUMB. 1998. World Federation for Ultrasound in Medicine and Biology Symposium on Safety if Ultrasound in Medicine: conclusions and recommendations on thermal and non-thermal mechanisms for biological effects of ultrasound, Barnett SB (editor) Ultrasound Med. Biol, 24, 1-55

References

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