Conjoined twins benefit from rapid prototyping

Objet Geometries’ QuadraTempo system for building 3D models was used to plan the successful separation of conjoined twins in Los Angeles.

Guatemalan twins Maria Teresa and Maria de Jesus Quiej-Alvarez were born joined at the head on July 24, 2001. The twins’ brains were separate and complete, with separated arteries and a dividing membrane. The veins draining the blood, however, were interwoven and fed into each others’ circulatory system.

Separating conjoined twins is a highly complicated procedure, but surgeons at the University of California’s Mattel Children’s Hospital determined that an operation was possible.

The members in the surgical team all had different visualisation needs in order to plan their role in the surgery. The plastic surgeons were most interested in the structure of the skull, while the neurosurgeons were particularly concerned with the arrangement of the blood vessels, some of which were shared by the twins.

The most complex part of the operation was to sort out the veins and re-route the twins’ blood supply. Because the blood vessels were crisscrossed, tracking them using standard, two-dimensional x-rays would be impossible. One of the hospitals’ doctors suggested using 3D rapid prototyping to help the plastic surgeons practice how to separate the girls’ skulls, re-route the blood supply and plan skin grafting to cover the separated brains.

Boston, MA-based Biomedical Modeling Inc. (BMI), an RP fabricator for medical uses, handled the process. The UCLA team supplied BMI with three CT scans at different angles – it wasn’t possible to arrange the twins for one scan. The company then registered and combined the scans of the twins’ brains and the intersection of the two skulls into a single, 3D model.

Biomedical Modeling produced three biomodels – one model of each of the twins’ skulls, which could be studied separately or combined to provide the surgical team with a replica of the conjoined anatomy. The third biomodel showed the region where the twins were joined, enabling the surgeons to easily see the architecture of arteries and veins.

It took Biomedical Modeling three days to process the CT data and create the STL files, about 80 Mbytes each, for rapid prototyping. These were then sent to InterPRO a CT-based RP service bureau via email.

Interpro verified the data and oriented each part for optimum build in an Objet Geometries’ QuadraTempo rapid prototyping system that builds parts by selectively jetting tiny droplets of acrylic photopolymer creating layers and then curing layer-by-layer, using UV light.

Usually, after a part is made, removing support material can be done using jets of water. This time, however, removing the Objet support material took several hours of work. Because the blood vessels were so delicate, it was impossible to blast away the support get with a water jet without damaging the fragile structure. So it was necessary to spoon out and clean off the support material by hand, at times heating the parts with warm water to soften the material.

With models in hand, the surgeons were able to meticulously plan the operation on the two children. The operation itself took 22 hours to complete, but similar procedures in the past have taken as long as 97 hours. Part of the time savings was undoubtedly due to the use of rapid prototyping.