Role of Virtual Imri in Brain High Grade Glioma Surgery: Advantages, Limitations and Correlation with Ict and Brainshift

Introduction: Elastic Image Fusion (EIF) using intraoperative CT scan may enhance neuronavigation accuracy and compensate for brainshift. This study evaluates safety and reliability of EIF algorithm (Virtual iMRI Cranial 4.5, Brainlab, AG) for identification of residual tumour in glioblastoma surgery. Moreover, the impact of brainshift on software reliability is assessed.

Methods: This ambispective study included 80 patients with a diagnosis of glioblastoma. Pre-operative MRI was elastically fused (Virtual iMRI) with intraoperative CT scan (BodyTom; Samsung-Neurologica). Diagnostic specificity and sensitivity of each tool was determined. Impact of brain shift on residual tumour was statistically analysed. Analysis of accuracy was performed through Target Registration Error (TRE) measurement after Rigid Image Fusion (RIF) and EIF. A qualitative evaluation of each Virtual MRI was performed.

Results: Virtual iMRI (VMRI) identified residual tumour in 34/80 patients (42.5%), confirmed either by intraoperative CT or post-operative MRI. Of those, iCT failed to recognize residual tumour in 17/80 (21.2%) cases while in other 17/80 (21.2%) intraoperative CT successfully reported residual tumour. In 27/80 cases (33.8%) VMRI reported residual tumour that was present neither on iCT nor on post-operative MRI. i-CT showed sensitivity of 50% and specificity of 100%; Virtual iMRI demonstrated sensitivity of 100% and specificity of 41%. Spearman correlation analysis showed a moderate correlation between pre-operative volume and Virtual iMRI tumour residual. Moreover, tumour involving insula or infiltrating more than one lobe displayed higher median values (p=0.023) of “false” virtual residual tumour.
A statistically significant reduction towards lower TRE values after EIF was observed for test structures.

Conclusion : Virtual iMRI has proven to be a feasible option to detect residual tumour. Its integration within a multimodal imaging protocol may provide neurosurgeons with intraoperatively updated imaging.