(kg) The base SI unit of mass of the metric system.
Definition: 1 kilogram is defined as the mass of the standard kilogram, a platinum-iridium bar in the custody of the International Bureau of Weights and Measures (BIPM) near Paris, France.
A traditional unit of mass or weight is also the pound (in general use, e.g. in the United States and Great Britain), with the symbol lb (derived from the Latin word libra).
1 kg is 2.204627 pound (lb. av.)
1 pound (lb. av.) is 0.453 kg.
Smaller units are, e.g.
1 000 gram (g) are 1 kg
1 000 milligram (mg) are 1 g
1 000 microgram (μg) are 1 mg

This dose means the RF power absorbed per unit of mass of an object, and is measured in watts per kilogram (W/kg).
The absorbed dose is dependent on the duty cycle and transmitter-coil type and increases with field strength, radio frequency power and and body size.
The specific absorption rate (SAR) describes the potential for heating of the patient's tissue due to the application of the RF energy necessary to produce the MR signal.

See also Specific Absorption Rate, MRI Safety, and MRI Risks.

(J) The SI unit of work or energy.
Definition: The work done by a force of 1 newton acting to move an object through a distance of 1 meter in the direction in which the force is applied.
Since kinetic energy is one half the mass times the square of the velocity, 1 joule is the kinetic energy of a mass of two kilograms moving at a velocity of 1 m/sec.
The joule is named for the British physicist James P. Joule.

Quantity of matter, the unit is kilogram (kg).

(N) The SI unit of force.
Definition: 1 newton will accelerate a mass of 1 kilogram at the rate of 1 meter per second per second.
The relationship between force (F), mass (m), and acceleration (a) is expressed by the formula F = ma.
The newton is named for Isaac Newton (1642-1727), the British mathematician, physicist, and natural philosopher.