ROCHESTER, Minn. (AP) - The surgeons who spent hours meticulously separating conjoined twins Abbigail and Isabelle Carlsen in May had a secret weapon on their side: Artists.

Medical illustrators, animation experts and other specialists used information from thousands of medical scans to create drawings, 3-D pictures and computer animations of the girls' organs - hoping to give the surgeons a clear picture of what they could expect.

Normally, medical illustrators draw renderings after a procedure is finished.

"However, this project was unusual in that the lead physicians wanted illustrations designed as preoperative and intra-operative study guides," said Michael King, a medical illustrator whose desk is covered with loose sheets of detailed drawings. "It definitely starts with just the chicken scratch kind of stuff."

The daughters of Jesse and Amy Carlsen of Fargo, N.D., were joined at the chest and abdomen when they were born. They went to the Mayo Eugenio Litta Children's Hospital, where they were successfully separated in May.

The girls had a unique anatomy. Their hearts overlapped and there was concern about a shared bile duct and intestine. CT images were reviewed repeatedly so artists could sketch each vessel.

"Even after all our preparation, we needed the models, drawings, computer images, and scans all right there in the OR," said Dr. Christopher Moir, the lead surgeon for the twins. "In fact, we almost ran out of OR wall space to put it all up."

The illustrators start with freehand drawings and spend hours looking at electronic images to make sure everything is accurate. Sometimes, sketches are drawn, and then drawn again in another way.

"We did a lot of sketching along the way. We did a lot of discussion and revisions. It's unique anatomy. No one else has this," King said.

Surgeons received a virtual tour of the Carlsen twins' organs before surgery so they'd know what to expect.

"I am grateful to all the artists, engineers and computer wizards who were essential to saving Abby and Belle on the day of surgery and ensured a complication-free recovery," Moir said.