(RAO) Right anterior oblique is a direction, lying close to the right diagonal.

See Radiology Information System.

(R) R is a unit to express exposure to radiation (x-rays or gamma rays). 1 R corresponds to the generation of approximately 2.08 x10⁹ ion pairs (1 electrostatic unit of charge) (in 1 cm³ of dry air at 0 °C and 760 torr). 1 R, converted to SI, equals 2.58 x10^-4 coulombs per kg of air.

(rem) The rem is the dose equivalent of the absorbed dose considering the biological efficiency of the radiation, also called quality factor. With a quality factor of 1 is 1 rem equal to 1.07185 roentgens. One millirem is one thousandth of one rem.
In the SI system of units the rem is replaced by the sievert (Sv), which is numerically equal to the absorbed dose in gray modified by a radiation weighting factor. The conversion factor has been readjusted from 1 to 1.07185 so that 100 rem are equal to 1 Sv.

Read Only Memory, computer equipment to store data once, not changeable.