A while ago I heard a researcher talking about a new full-body scanner he had tested on a seemingly healthy female colleague in her early 30s. It revealed a precariously thin bulge - an aneurysm - in one of the main arteries leading to her brain. She had experienced no symptoms whatsoever, but it could have burst at any moment: the scan's locating of it allowed a relatively easy surgical fix.

Having just turned 50 - and with my last visit to a doctor somewhere in the 1970s - I thought that getting some checks like this might be a very good idea. My NHS GP agreed, although explained that, as I wasn't displaying any worrying symptoms, I would have to go private for any detailed insights.

My first stop was Bupa's modern assessment centre in London's Gray's Inn Road. After friendly preliminaries I found myself stretching my arm out and trying not to concentrate too hard on the fast approaching alarmingly large needle. The iron atoms that made my blood so red were created in giant stars, that lived and died more than 4½bn years ago. Now they were floating along in my blood beside sugars, hormones and much else. The needle probing into this inner flow seemed to me like an oil rig drilling deep beneath the North Sea.

Too much sugar could be a sign that my pancreas wasn't working properly, and an early marker of diabetes; too few white blood cells could be a sign of bone marrow problems. More than 20 such indicators were checked, and when the results were delivered an hour later, I came out fine.

Next, we did the overall fitness test. The first one was delightfully low-tech. They measured my height and waist and divided them. Having too much weight floating around in the middle, particularly for men, often indicates cholesterol build-up and sugar problems through the body. Good job I hadn't come a decade earlier, when having little children meant scarcely any time to exercise, and walking by swimming pools was an occasion to see how long I could suck my stomach in without toppling to the ground from a lack of oxygen. The ideal ratio is 0.44, and although I weigh 13st, at 6ft 2in and with a 32in waist, I was bang in the middle.

The most important fitness number though was to be my VO2 max, which is the maximum amount of oxygen in millilitres you can use in one minute, per kilogram of body weight. Here's where the ancient iron atoms are crucial because blood is almost entirely water, yet hardly any oxygen will dissolve into pure water. The oxygen we need will latch on to iron - on the underbody of a car, it's what we call rusting. The test involved pedalling away topless on an exercise bike while wearing a nose-clip and feeling like a dork.

Although I was gasping by the end - and when the electrodes monitoring my heart were tugged off I felt sympathy for women who suffer through waxing - the test showed I was doing a good job. The young medic who conducted it was delighted: I was in the top group of his scores even for 30-year-olds, and in the top half for 20-year-olds as well.

I was pleased to hear that, of course, but since I have always enjoyed exercise - judo when I was younger; then after the pause when my children were younger, kick-boxing pretty frequently - it wasn't a great surprise. My main concern was that my father had died from heart disease when in his 60s. I loved him immensely, and feared I might have inherited his heart condition.

So the second stop on my MOT pilgrimage took me to the Preventicum medicine centre in west London where I was soon slid inside a full-body MRI scanner. I found travelling backwards into what seemed like an infinitely long shiny tube a deeply tranquil experience.

This was the machine that had found the researcher's colleague's hidden aneurysm. It pulls out information from deep within the body, showing three-dimensional inner details that can be investigated on a screen. MRIs use magnets strong enough to lift a small car, so the otherwise easy-going staff had wanted to be sure I didn't have any shrapnel or other metal bits inside me. I waited a while in the machine while they got ready. Then I heard a series of clicks, as the magnets tugged invisibly on the hydrogen atoms in my heart so they lined up, and then as radio waves clicked on, pushing the core of those atoms to one side.

Suddenly the radio waves were switched off and the hydrogen atoms jumped back to their initial position. That massed "jump-back" was enough to send out disturbances that the MRI picked up. No dangerous x-ray radiation had been used, but it was still enough to broadcast a picture out from my core. I felt safer, and more looked after than I had in a long time.

Afterwards, with the radiologist, I watched my heart beating: we could see the valves open, and swirls of my blood flowing through. Everything seemed fine - but there was one, even more detailed test I wanted to try. For this I went to iHealth's one-stop health assessment and imaging centre at Weybridge. It has a remarkable range of specialists working together. An old shoulder injury I had had, for example, was diagnosed and exercises for helping it prescribed, all in less than an hour. There was an excellent physiotherapist, an MRI scanning team he instructed on what to look for, and a shoulder surgeon on hand to help interpret the results. Of most interest to me, however, was the ultra-fast CAT scanner that would spot any plaque that might be accumulating in myarteries. This did use x-rays, spinning quickly around my chest to snatch pictures from multiple angles.

These tests were good too. Almost 15% of British men my age are going to get heart attacks within a decade. I was lucky enough to be doing a lot better than that: my chances were just 1% or less. It feels good to be reassured.

· bupa.co.uk, preventicum.co.uk, ihealthltd.com

· David Bodanis is the author of Electric Universe and E=MC2:a Biography of the World's Most Famous Equation