Researchers of the National Research Council of Canada (NRC) conducted the first 3D images of the masterpiece, using a complex laser scanner.
A team of NRC researchers went to Paris in October 2004 to conduct the research at the request of the French state museum agency Centre de Recherche et de Restauration des Musees de France (CRRMF).
The scans revealed that the woman made famous by her enigmatic smile was originally painted with her hair tied back in a bun, although it now appears loose on her shoulders.
That discovery settles an old controversy because only girls or women of bad virtue wore their hair loose in 16th century Italy, CRRMF project leader Bruno Mottin said.
One of her garments, similar to fashions that pregnant or nursing women wore in this period, was also lost under yellow varnish and no longer visible to the naked eye, the infrared scans showed.
The real Mona Lisa had three children. Da Vinci was commissioned by wealthy Florentine businessman Francesco del Giocondo to paint his wife between 1503 and 1506 after the birth of their second child, but he kept it and worked on it until his death, likely changing her hair and other features.
In the “original” Mona Lisa the scans showed the subject gripped her chair more tightly, and that she is not resting against the back of her chair, as thought, but sitting upright.
Finger painting
Researchers also gleaned insights about the Da Vinci's painting technique, including his sfumato or smoke technique of soft, heavily shaded modelling, said Mr Mottin.
"There is no special mystery in the painting like in (Dan Brown's book) The Da Vinci Code," he said. "But, in that painting, Leonardo tried to capture the essence of life ... It embodies all his skills ... That is the true mystery we've uncovered."
Researchers identified a lack of brushstrokes, suggesting that Da Vinci may have used his fingers to paint, except there are no fingerprints on the artwork.
Scans of the Mona Lisa revealed that darker areas, such as the eyes and corners of her smile, are thicker and "composed of a succession of thinly applied glaze layers," said NRC scientist Francois Blais.
But how Da Vinci actually applied his layers of pigment and oil medium remains a mystery.
"It's extremely thinly painted and extremely flat, and yet the details of the curls of hair, for example, are extremely distinct. So, the technique is unlike anything we've ever seen before," said John Taylor of the NRC.
The Mona Lisa is seen by seven million visitors a year.