Cryonics: How does the controversial procedure work?
Video report by ITV News Science Correspondent Alok Jha
The High Court decision to allow a terminally ill teenager to be cryogenically preserved has intensified debate over the controversial procedure.
Aside from ethical arguments, experts have cast doubt that the procedure could be a success.
Cryonics expert Dr David Shaw said that it is "very implausible" that the brain of an individual cryo-preserved would survive the procedure.
But hundreds of people are already known to have undergone the procedure and thousands more have signed up for cryonic suspension, hoping that advances in medical technology after they die could be used to give them a second chance of life.
Alcor Life Extension in Arizona currently has 148 cryogenetically preserved patients, 104 men and 39 women and more than 1,100 members.
Among their preserved patients are 73-year-old psychologist Dr James Bedford, the first person to be cryogenically frozen in 1967.
His body, first preserved by the Cryonics Society of California and later transferred to Alcor in 1987, is said to remain in a good condition.
University of Bristol graduate Cormac Seachoy, who died in December 2015 at just 27 years old has also been cryo-preserved.
In his last Facebook post he wrote: "My cancer is extremely aggressive, so chemo is not a viable option and I will most likely die in the coming two or three weeks.
"All my love to everybody, a massive thank you to all the amazing people who made my 27 years so pleasurable!"
Mr Seachoy liaised with Cryonics UK and the US company just two days before his death so that his body could be transported from London to the US to be Alcor's 142nd patient.
Other Alcor Life Extension cryonics patients include Ronald Selkovitch, who was cryopreserved in 2015 after his wife and mother had the procedure.
Other patients include a man who shot himself in 2014 and another, Michael Louis Friedman, that died in 1992 from a shotgun wound to the head.
How is a body cryo-preserved?
Cryonic companies start their procedure at the earliest moment possible to the legal death of the patient.
There are several minutes between the heart stopping and the brain dying which Alcor Life Extension says its "window of opportunity" to artificially restore blood circulation.
As a dying patient becomes critical, medical personnel wait on "standby" to begin life support procedures in the moments after death.
The initial procedure to transport the patient includes:
placing the patient in an ice water bath and restoring blood circulation and breathing by artificial devices.
establishing intravenous lines and administering protective medications to protect the brain to maintain blood pressure during artificial circulation and prevent the brain from "reperfusion" injury (tissue damage).
surgically accessing the femoral arteries and veins and placing the patient on a cardiopulmonary bypass meaning the blood is circulated through an external heart-lung machine.
The transportation procedure is similar to that used to move donor organs around the country.
After this initial procedure, the patient's temperature is reduced to a few degrees above the freezing point of water as blood is replaced with an organ preservation solution specifically designed to support life at low temperature.
Then, when the patient arrives at the cryonic centre:
Major blood vessels are connected to a perfusion circuit by a physician.
A cryoprotectant solution, similar to that used during transport is circulated through the patient at a temperature near 0 degrees Celsius for several minutes to wash out any remaining blood.
The concentration of the solution is increased to 60% over two hours to three hours. Temperature, pressure and cryoptotectant concentration data are continually monitored.
Visual monitoring of the brain is carried out through two small holes in the skull and a dye injection to check there is no swelling or injury.
Patients are then cooled by nitrogen gas to below -124 degrees and as quickly as possible, within three hours, to avoid ice formation to reach a stable "vitrified".
The patient is frozen further over two weeks to -196 degrees and are monitored by "crackphone" instruments to detect fracturing which can happen when objects are cooled to such temperatures.
Cryonic patients are then stored under liquid nitrogen at -196 degrees in a vacuum-insulated unit which is replenished ever few weeks.
The complex procedure, that requires long-term maintenance, is therefore very expensive and thought to cost up to $70,000 (£56,000) for neuro preservation (brain or head only) and $200,000 (£160,000) for the whole body.