Two-year-old Matheryn Noavaratpong is the youngest person to be cryonically preserved, or frozen at a very low temperature, in the hope that she can be resuscitated in the future.

Only her brain was preserved in a procedure known as a "neuro", short for neurocryopreservation.

Is the procedure science fiction, or can those now being held in vats of liquid nitrogen really be brought back to life?

Even proponents of cryonics admit that revival is out of the reach of current technology. However, they are optimistic that future technology can not only cure the conditions that led to death, but regenerate or repair bodies that have been held in suspension.

Here's what you need to know about having a (very small) second chance at life:

1. How does it work?

There are two main stages to cryonic preservation. Moments or minutes after the heart stops, circulation needs to be maintained so that the brain avoids injury through the lack of oxygen and glucose.

Thereafter, blood and water in the body is replaced with cryoprotectants before being cooled. The cryoprotectants prevent the formation of ice crystals which can cause damage to cell membranes.

The process of deep cooling without freezing is known as vitrification.

2. How much does it cost?

The Arizona-based Alcor Life Extension Foundation charges US$80,000 to preserve the brain and about US$200,000 to keep the whole body in storage.

Quite a bit of the cost goes into the procedures and chemicals required for cryopreservation, but US$115,000 goes into a "patient care trust fund". The funds are managed by the Patient Trust board.

The projected returns from the money is meant to cater for the customer's eventual return, Dr Max More, Alcor's CEO, has said in an interview with online magazine Motherboard.

The Cryonics Institute, also based in the US, says its minimum fee is US$28,000.

KrioRus, a Russian outfit, charges US$36,000 for full body preservation and US$12,000 for preserving the head, according to its website.

A common way of paying for it is through the payout from a life insurance policy.

3. How uncommon is the procedure?

The first person to be cryogenically frozen was 73-year-old psychologist James Bedford, who was suspended in 1967.

Alcor, one of the world's largest cryonic companies, froze its first "patient" in 1976 and Matheryn was their 134th customer. There are more than 1,000 people who have signed up to be preserved by the company when they die.

The Cryonics Institute, started by math professor Robert Ettinger, has 130 "patients" currently. Dr Ettinger, who died in 2011 at age 92, was patient 106. According to its website, there are also 110 pets preserved at the Michigan facility.

Their members - living individuals who have signed up to be preserved - numbered 1,180 in March this year. There are two members from Singapore, while the majority are from the US.

The South China Morning Post reported last September that Alcor may be setting up a team in China as interest in Asia grows.

4. Is a person in "suspension" dead?

Death is not a clear-cut boundary for cryonicists and as medical technology advances, it has become an increasingly blurred line for doctors.

Alcor claims that while their patients are legally dead, they can be kept "biologically alive" with the cryonic process.

After a person's heart stops and blood stops circulating, other parts of the body lose function when deprived of oxygen and glucose.

The brain is one of the first to sustain damage, and it can survive for up to about six minutes after the heart stops. Detached limbs can be re-attached hours or even days without blood circulation if refrigerated.

Legally, the preserved "patients" in cryonic facilities are seen as organ donations and tissue samples, but Alcor views them as "potential persons".

Cryobiologist Dr Dayong Gao from the University of Washington, Seattle, told the BBC: "We simply don't know if they've been damaged to the point where they've 'died' during vitrification because the subjects are now inside liquid nitrogen canisters."

5. How can one bring a body back to life?

Simple tissues, small insects and embryos have been successfully preserved and brought back to life.

A rabbit kidney was vitrified and successfully transplanted in 2002, but in general, the deep-freezing of organs, much less whole mammals, is not feasible yet.

There are numerous obstacles that have to be overcome before attempting to bring back cryonically preserved persons.

Firstly, the knowledge and technology to reverse old age or cure the diseases they suffered prior to death will have to be in place.

The supercooling process is likely to have damaged their bodies. Many cryoprotectants are toxic, and their effects on the human body are unclear.

Cooling a body to -196 deg C can also make it extremely brittle, and prone to fracture.

Proponents of cryonics pin their hopes on scientific breakthroughs such as nanotechnology (the manipulation of matter at a molecular level) to repair the bodies of those preserved, or re-generate bodies for preserved brains.

Sources: Motherboard, How Stuff Works, Alcor Life Extension Foundation, BBC