How cryonics works: Process of freezing bodies explained

The process involves removing blood and replacing it with a preserving solution.

Cryonics involves using extremely low temperatures to preserve bodies in the hope that scientists will one day be able to revive them.

After a landmark ruling involving a 14-year-old girl who was granted the right to undergo the controversial procedure, we look at how it works - and what the critics say. 

:: What is the difference between cryonics and cryogenics?

Cryogenics is a branch of science that looks at preserving materials through very low temperatures. The word comes from the Greek "kryos" meaning "frost" and "genic" meaning "to produce". 

Cryonics refers to the technique used after a person's death to store the body at a very low temperature in the hope that they can be revived when a cure is found for their illness.

In reality, in layman's terms, the understanding of the words has been blurred so that we usually refer to people being cryogenically - rather than cryonically - frozen as a means of preservation after death.

:: What is the process?

When a person is declared legally dead, the first thing the response team has to do is ensure that the person's blood is kept pumping around the body. 

Speed is of the essence. The response team will be at the hospital so that, at the point of death, it can move in immediately.

After that, the body is packed in ice and injected with various chemicals to reduce the risk of blood clotting and damage to the brain.

The body is then cooled to just above water's freezing point and the blood is removed.

The body's blood vessels are injected with a "cryoprotectant" solution to try to stop ice crystal formation in the organs and tissues and the corpse is cooled to -130C. 

:: What happens to the body?

Once the team is satisfied with its work, the body is placed in a container which is lowered into a tank of liquid nitrogen, kept at -196C.

The body is then transferred to the storage facility - in the case of the British girl, in Michigan in the US.

 How much does it cost?

It is expensive. The process for the teenage girl in this case cost £37,000 but it can go up to more than £100,000. 

:: Where did the idea come from?

The concept was developed in the early 20th century. The first person on whom the process was performed after his legal death was Dr James Bedford, who died of cancer on 12 January 1967. His body has been moved several times and is now at Alcor Life Extension Foundation in Arizona. 

The day of Dr Bedford's death and cryopreservation is marked within the community as Bedford Day. 

:: What are the criticisms?

This is a highly contentious area. Alcor's co-founder Linda Chamberlain says the company is providing a realistic service that gives hope.

Others are dismissive. Many scientists and doctors argue that it is unlikely that revival in such a way can be achieved because organs such as the heart and kidneys cannot be successfully frozen and thawed. They suggest cells will be damaged during freezing and cannot be returned to living tissue.

Ethics experts say it poses greater problems as a whole for society, as it would appear to be a way of delaying the acceptance of the death of a loved one.

The girl's body is being stored at the Cryonics Institute (Michigan)