Units of measurement

For units of measurement the use of SI units in articles and cases on Radiopaedia.org is preferred. This is in line with best scientific practice and helps maintain consistency across the site.

Terminology

By scientific convention, if the unit is named after an individual, then when writing the symbol it is capitalised but the full written-out unit is not capitalised, e.g. tesla is the correct form - not Tesla - but the symbol is T.

Conversely, if the unit is not eponymous, e.g. ‘second’, then neither the full name nor the symbol is capitalised, i.e. ‘s’.

Length

The SI unit is the metre but clearly, for most of our purposes it is too long and we prefer the centimetre/cm or millimetre/mm. For cases, like imaging reports, try to stick to one unit rather than switching between them e.g. "1 cm calculus in the gallbladder with a 0.4 cm wall", rather than a 4 mm wall.

Volume

For liquid/gas volumes or for organ size (e.g. testis), we prefer mL or millilitre rather than ml, cc or cubic centimetre.

For solidssolid lesions e.g. lung nodules, mm³ or cm³, are best.

Mass

The SI unit of mass is the kilogram or kg.

Time

The SI unit of time is the second or s.

Electricity

Current is measured in amps (strictly amperes) or A.For tube current, mAs, milliampere-seconds.

Ionising radiation

Absorbed dose

The derived SI unit is the gray (Gy), although the old term the rad is still seen, especially in the USA.

Equivalent dose

The derived SI unit is the sievert (Sv), although the old term the rem is still seen, especially in the USA.

Radioactivity

For doses in nuclear medicine, the derived SI unit - the becquerel (Bq) - is used not the curie (Ci), which is the old c.g.s. unit. As one Bq is a tiny unit, nuclear medicine doses are most commonly expressed in megabecquerels (MBq).

Magnetism

The derived SI unit of magnetic field strength is the tesla, the symbol is T. When stating the strength of an MRI scanner, the normal scientific convention is followed. Therefore 1.5 T and 3 T, not 1.5T and 3T.