Using Immersive Virtual Reality in the Pre-Procedural Planning in Separating Conjoined Twins

Introduction

With surgery, there is always a high-risk factor that recipients must acknowledge, and this only increases for individuals with unique or rare physical conditions. One method that has proven extremely promising is 3D visualization through immersive virtual reality. Virtual reality is to immerse a user inside an artificial world, often generated to mimic real life. This is achieved through various equipment including a Head-Mounted Display and handsets. There are many instances in which 3D visualization has proven to be a high-value asset to complex operations in the medical field. Studies have shown that the use of virtual reality provides results of a reduced operating room time and a higher success probability. Furthermore, a study has also shown that 14 of 16 participants see an increase in confidence in the operating room when they have practiced in VR beforehand. Virtual reality is currently being used in health care to give surgeons spatial awareness of patient-specific anatomical features’. This gives surgeons almost a complete understanding of the environment in which they will be operating and this has revolutionized healthcare as it drastically decreases the risk that comes with a unique patient in need of surgery.

Challenge

Paediatric Surgeon Daniel Saltzman had the task of performing surgery to separate two sisters, Paisleigh and Paislyn, who were thoracopagus conjoined twins who had been joined from the lower two-thirds of the breast bone to the belly button. They had both been color-coded as the red twin and the blue twin. It is incredibly difficult to plan procedures without the information required for such a complex procedure as conjoined twins are often joined in small but critical places. The twins had an interatrial communication in the hepatic artery and internal thoracic and mammary arteries which created blood flow between them and there had also been the question of an interatrial cardiovascular connection between them too although this could not have been known with current, traditional methods. It was the latter connection that increased one of the twins’ shares of the total cardiac output. The planning hemodynamics of this separation was especially difficult for this reason. The surgery had to be moved closer than their hoped date as this was unexpected and urgently needed attention. This study will evaluate the efficiency of using 3D visualization in the preparation stage of a high-risk surgery that requires last-minute thinking in the event of an unexpected discovery.

Method

The first step was ‘Imaging’. For this, the pediatricians had collaborated with researchers at the Earl E Bakken Medical Devices Centre who had invented the machine used in this planning procedure, which was only one of five that exist. This process was done as CT angiograms of the chest and abdomen of the twins had been performed with a Siemens SOMATOM Definition Flash scanner. Two high-pitch spiral acquisitions were performed with prospective EKG triggering; one 18 s after the intravenous power injection of 50% dilute Isovue 370 at 0.7 cc/s into the BLUE twin followed by a similar scan after injecting the RED twin. The first scan was performed on the blue twin for multiple reasons, such as the known heart anomalies of the blue twin’s heart and the possible connection which was only noticed once the doctors had reviewed the models. Each of the scans formed roughly a quarter of the patients’ anatomies, to help align each scan for modeling.

Step two was ‘Segmentation’. This process took months as the professionals had to ensure that the anatomies of both sisters had been accurately segmented and it aided them in making all the diagnoses. In the segmentation process, all data retrieved from the CT scans were split up and analyzed with Mimics software which allowed them to produce models of cardiac blood volumes, lungs, and thoracic skeletal anatomies of both sisters. Once fully compiled, hollow heart models were formed from these scans which showed the insides of the heart cavities. Finally, the models were exported as stereolithography files.

Adjustments had to be made in this process as the initial alignment had not accurately depicted an interatrial connection between the hearts. It was finally aligned by matching the hepatic venous vasculature, giving a correct portrayal of their anatomies and representation of diagnoses, relative to each other.

The third step was visualization. The models were converted into OBJ and MTL files and a text-based software-specific scene file was used to finally create the virtual reality system. The equipment used for this included: a 96” rear-projected stereoscopic screen with a 50” monitor using the FTIR-based method overlay to detect the touch interactions. Space was tracked with 5 Flex 13 cameras. The surgeons wore active shutter glasses to further immerse them whilst they used the touch to control the subjects.

Results

The models in 3D visualization proved to be essential in the success of the twins’ complex surgical treatment. Many key alterations and observations had been made after careful study of the high-resolution models. The confirmation of the interatrial vascular communication alone proves the machine’s significance as if this went unnoticed the children would have most likely died. It is thought that 18% of all conjoined twins survive. The stereoscopic images allowed the teams to communicate in an environment well-catered to expressing their thoughts, opinions, and suggestions. Furthermore, the stereoscopic visualization also impacted the placement of each twin during and after the surgery. It was found that there would be better cardiac access if the blue twin was on the left, putting the red twin on the right. This was initially vice versa. Additionally, it was beneficial for the blue twin to remain in the primary operating room due to them also needing advanced cardiac equipment (which had not been part of the original plan) present. This modification of the plan was thought to have reduced the amount of operations the twins required thus directly improving their chance in survival. 2 years post-separation shows that both patients continue to develop healthily.

References

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