Complex tests are under way at a Singapore Hospital to determine if Iranian Siamese twins joined at the head can be surgically separated. Specialists have previously ruled out the procedure, maintaining one or both of the women could die. More than 1,000 X-ray images have been taken of the brains of Iranian Siamese twins seeking separation surgery at Raffles Hospital, and doctors said Friday many more complex tests will be carried out in the days ahead.

Laddan and Laleh Bijani, whose two brains are encased in a single cranial cavity, are hoping the Singapore neurosurgeons who successfully separated Nepalese babies in a similar operation last year will also be able to give them independent lives.

Doctors have refused to try in the past. In Germany five years ago, physicians concluded that one or both could die in an attempt to separate them.

Dr. Keith Goh, the neurosurgeon who presided over the 97-hour surgery on the Nepalese girls here, said technology is better than it was five years ago, and medical progress has been tremendous in many areas. Once the tests are evaluated, he said the surgeons in Germany and elsewhere will be consulted.

Dr. Goh said such an operation carried out on adults would be a first, since all co-joined twins have been separated as babies or during childhood. "So to separate an adult pair of co-joined twins is completely unprecedented," he said. "How difficult is it? It's hard to quantify the risks at this point. These things have to be considered in terms of survival, quality of life in a functional status, all these kinds of things. So it has to be a very, very complete evaluation and you know we need to give it a lot of very deep thought."

The twins graduated from Tehran University earlier this year, acquiring law degrees. Laden Bijani said she and her twin sister are not worried, and are feeling well.

They arrived in Singapore Tuesday. When they have not been undergoing tests, they have watched television, talked with other patients and e-mailed family and friends. The hospital has said that the doctors involved have offered to do the initial tests for free, and will waive their fees if the operation goes ahead.