This interesting article has an "Etiology" section that neatly summarizes whiplash biomechanics:
"Neck pain among car occupants may follow an impact from any direction, though rear-end impacts cause it almost twice as often as frontal collisions. An 8-mile/h rear-end collision with a 2-g (2 times the gravitational force of earth) acceleration of the vehicle may result in a 5-g acceleration of the head, and experiments using volunteers have shown that a 10-mile/h rear-end collision generates a 9-g acceleration of the neck and 23 g of the frontal cortex. Sprains of the neck occur in 10-60% of car occupants after an accident. Those wearing seatbelts have more neck sprains than those not wearing them. Head restraints reduce the incidence of whiplash injuries in rear-end impacts by 10% in cars with adjustable head restraints and by 17% in cars with fixed restraints."
The authors go on to evaluate the different imaging techniques, with particular focus on the strengths and weaknesses of each: