They played Elgar as the nurse strapped me down. I was wearing just paper underwear, and it was, she said, for my own good. I was at the San Francisco branch of Ameriscan, a company offering full body MRI (magnetic resonance imaging) scans for anyone with $1,000 to spare. You don't need a referral and anyone can walk in off the street. One hour later you will emerge with a CD-Rom of images of your insides and either peace of mind or a diagnosis of serious illness.

In a country where getting sick is expensive, the level of health checking offered by Ameriscan is increasingly popular. More than 10,000 people have been scanned in Ameriscan centres, most of which are in shopping malls across California and Arizona.

The ability to see into arteries or lungs and check out organs offers far more than a stethoscope and a tongue depressor ever could. And it's effective: Ameriscan claims that 10% of customers discover a condition that requires immediate treatment - without any symptoms.

Founded by 35-year-old Dr Craig Bittner, Ameriscan is taking advantage of advances in MRI technology, the internet, and the ubiquity of personal computers in the home. A scanner now costs about $1.5m - a relatively small outlay for a business charging $1,000 for a 15-minute procedure. The expectation is that the patient will also have a PC.

The centre sends images over the internet to radiologists. After scanning, the patient is given a quick run through of the results by a doctor and a CD-Rom of the images. Ten days later, the radiologist at Ameriscan's head office writes to the customer with a more in-depth review.

MRI works like this. By placing your body inside a massively strong magnetic field, the machine causes all the atoms in your body to line up and spin in the direction of the field. Some will point from your head to your feet, the others from your feet to your head. Most pair up with another pointing the other way, and stay locked together. But in a few cases (a handful per million), they will not match up.

Those lonesome atoms will be free to point in either direction or, given the chance, change direction. The chance is given by the second stage of the MRI procedure - the radio frequency pulse. By tuning an RF pulse to affect only hydrogen atoms, which make up 63% of the body, the machine causes the unpaired hydrogen atoms to absorb energy and spin in a different direction.

Here's the clever bit: when you turn the RF pulse off, the excess energy in these lone atoms is released, and can be detected. By combining the detection of the energy given off by each atom, and by varying the magnetic field and the frequency of the RF pulse, the MRI imaging software can create images of the different types of tissue in the body, and where it is.

One feature of the MRI is the ability to take images very quickly, and then line them up after each other. The images on your CD-Rom are in the Dicom standard, the official format for medical image data. Dicom contains information to let you ani mate these images - providing you with videos of your heart beating, and so on.

But MRI isn't totally safe. The magnets are immensely strong - people with pacemakers are banned, as is anyone with shrapnel in the body: it could be ripped out. One problem, according to Ameriscan, is the prevalence of cheap hip transplants from Mexico. Americans sometimes pop over the border, and come back with a hip joint made of metal that could be attracted to the magnet.

For the same reason, no metal is allowed into the scanning room. Neither is it particularly comfortable when you are strapped down and slid inside the noisy scanner.

Not everyone is convinced of the scan's efficacy. The American Cancer Society says that while they are good for finding heart conditions, they are too expensive and unproven to detect lung cancers. Others are concerned that customers may be scanned too often, exposing themselves to radiation levels higher than normal. Ameriscan disagrees, saying people could have five a year without exceeding the recommended dosage.

Full body scanning is not the only advanced medical procedure to become available on the high street in the US: laser eye surgery, plastic surgery, blood testing and even DNA testing are available in shopping malls or through the post.

What did they find with me? Not much, thankfully. One bunged sinus and a lower back showing signs of future gyp, but free arteries, tiptop liver and vibrant lungs. For peace of mind alone, it could be well worth the price.