It sounds like an item on The Day Today: 'Danish doc uses ultrasound to get the inside story on sex: mysteries of orgasm revealed through Window on Love'.

But it is not a joke. Five years ago Dr Lasse Hessel, the man who invented the female condom, began recruiting couples prepared to use ultrasound scanning techniques while having sexual intercourse. Now Dr Hessel has written a book based on his findings, which he hopes will help people to choose the sexual positions most likely to give women and men orgasms.

It shows, graphically, by reproduction of the scans, explanatory diagrams and pictures the position, movement and interaction of the vagina, uterus and penis to indicate which parts of the male and female anatomy in contact with each other are likely to give the greatest satisfaction.

'Couples would tell me, as a GP, that they were quite happy, but for one thing: the woman could not have orgasms. What were they doing wrong?'

Dr Hessel thought a new line of research might provide some answers. 'Masters and Johnson did their best but their findings are based mostly on interviews. When we are interviewed about our sex life, perhaps we don't tell the truth. We know that certain parts of the vagina are most sensitive. But if you ask a woman, she can't explain which part has been stimulated the most.'

Instead of interviewing couples, he decided to use ultrasound scans 'so we could see what happened during intercourse in different positions'.

This was not without its difficulties. Dr Hessel, who was working in Oxford at the time, advertised for medical students to act as volunteers. 'At first people thought it was a joke,' he says. Eventually he found four willing English couples. The remaining 19 were recruited after he returned to work as a GP in Denmark.

Performing under clinical conditions was not easy. 'The younger couples became familiar with the set-up quite easily but the more mature couples had to come back several times before performing intercourse naturally.'

Not all couples could manage all 10 positions 'due to trouble keeping the ultrasound scanner in the right position during intercourse', and only two of the female testers achieved orgasm; most women found the scanning a distraction.

A number of the volunteers later told him the experience had helped them to improve their sex lives - in private. One couple said: 'Just using our new knowledge we have, in a short time, managed to achieve fully satisfying intercourse.'

'We wanted to learn how the erogenous zones were best stimulated,' Dr Hessel says. 'We managed to get the facts.'

His book is on sale elsewhere in Europe, Scandinavia and North America but the British were more wary. Eventually, he found an Australian company willing to publish his book after a series of British publishers had turned him down. 'They felt looking inside during intercourse was the ultimate in voyeurism,' he says.

Perhaps they had a point? 'I can't help the way people might interpret this work,' says Dr Hessel, 'but to show I have nothing to be ashamed of I am coming to England to promote my book - and I am bringing my wife and our two children.'

The relevant parts of the anatomy have been outlined in yellow yet, even so, the average reader will find it difficult to make much sense of the blurred black and white scan images. But there are also diagrams and drawings, albeit of a young couple so physically perfect and athletic they are more likely to engender feelings of inadequacy rather than a spirit of adventure.

The doctor has included a table at the back of the book rather like a Which? best- buy chart. Each position - the doctor selected 10 of the most common - is rated on 10 aspects that may heighten pleasure.

The best position for women appears to be No 9 (woman sitting on top, facing away from her partner). Traditionalists should perhaps note that the missionary position is one of the worst.

There are bound to be romantics who feel making love is not like choosing a washing machine, but Dr Hessel points out that he has had many letters from grateful readers. 'One German couple wrote to say that their sex life used to be like owning a Porsche without having the keys. Now they can drive fast.'

And if that makes the book sound more like an advanced motorist's manual than a guide to sexual fulfilment, he does not mind. 'It is meant to be a user's handbook. It is important to learn about technique.

'But then you can put the book away and begin your own experiments. People are so conservative in their sex lives. Most people use only one or two positions. Our curiosity should be greater than that.'

'Window on Love, The Ultimate Guide To Sexual Fulfilment' by Dr Lasse Hessel, Crawford House Press, pounds 7.99.

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