Virtual reality adds depth to brain aneurysm diagnosis

Radiologists detected brain aneurysms just as accurately by examining CT scans with a virtual reality device as they did by reviewing conventional CT angiography (CTA) and 3D rotational angiography scans, researchers reported in the July issue of Clinical Neurology and Neurosurgery.

First author Dr. Xiujuan Liu and colleagues from the First Affiliated Hospital of Harbin Medical University in China developed a method for viewing volume-rendered CT scans while wearing a virtual reality headset. They found that radiologists using the headset were able to spot brain aneurysms with an accuracy that matched reference standards (Clin Neurol Neurosurg, July 2018, Vol. 170, pp. 93-98).

The virtual reality technique was particularly advantageous for detecting intracranial aneurysms that were small or close to the skull, the researchers noted.

"The true stereoscopic [virtual reality] 3D display system highlights the depth of information," they wrote. "The viewer can better appreciate the spatial relationship of a lesion using the stereoscopic virtual reality display system [rather] than the conventional CT workstation."

'Perfect diagnostic modality'

Early diagnosis of an intracranial aneurysm is critical because of the high mortality risk for patients after rupture, the investigators noted. The gold standard for detecting these brain aneurysms has been 3D rotational angiography. Although it is highly accurate, some clinicians have begun favoring other less invasive and less time-consuming imaging modalities instead.

"The perfect diagnostic modality for the detection of intracranial aneurysms should be fast, accurate, noninvasive, and easy to carry out," they wrote. "Furthermore, it must have a low risk of complications."

Growing in popularity as a diagnostic tool, CTA has proved to be nearly as precise as 3D rotational angiography at spotting aneurysms -- with the added bonuses of being noninvasive and taking less time. Where CTA falls short, however, is in detecting aneurysms that are small (< 3 mm) or close to bone structures, due to inherent depth restrictions with 2D visualization.

"[Viewing scans] on the flat screen of the CT workstation fails to effectively and accurately provide depth information," the authors wrote. "This fundamental restriction significantly limits our ability to perceive and understand complex spatial relationships."

Recognizing this limitation, Liu and colleagues turned to virtual reality technology to help clinicians better appreciate the spatial relationship between an aneurysm and its surrounding anatomical structures. They acquired the imaging data of 42 patients suspected of having a brain aneurysm who underwent both CTA and 3D rotational angiography exams between January 2012 and February 2014. The average age of the patients was 56 years, and 32 were women.

Two technicians processed the CTA scans and rescontructed them as volume-rendered images. They saved these reconstructed images in bitmap file format and transferred them to virtual reality software, which also included a series of algorithms designed to project a separate image to the left and right eyes.

Donning virtual reality glasses, two radiologists were able to review the images in a stereoscopic virtual reality setup previously developed by Liu and colleagues.

Similar diagnostic capacity

The radiologists found 38 brain aneurysms in 36 patients using 3D rotational angiography, but they spotted only 37 aneurysms, including one false-positive and two false-negatives findings, with CTA. On the other hand, they detected 39 aneurysms, including one false positive, with the virtual reality headset.

Overall, there was no statistically significant difference between using conventional CTA and virtual reality to detect aneurysms, though the radiologists did catch two small aneurysms using the virtual reality device that were not visible on the CTA scans.

The accuracy of detecting brain aneurysms with virtual reality was comparable to the accuracy of CTA, but radiologists using the virtual reality technique demonstrated a better ability to spot smaller-sized aneurysms. This advantage could be especially useful for neurosurgeons, who rely on a detailed understanding of aneurysm morphology and spacing to clip an aneurysm before it ruptures, the authors wrote.

Several factors could have biased the results in favor of virtual reality, including the high prevalence of aneurysms in the study population and having displayed the virtual reality images in a predetermined position that provided an optimal view of the aneurysms, according to the group.

The researchers suggested that future studies aim to address these potential biases and develop a virtual reality display method capable of allowing users to rotate the images at any desired angle.