Navigated intraoperative ultrasound in pediatric brain tumors

Abstract

Purpose: The aim of this study was to evaluate the diagnostic value and accuracy of navigated intraoperative ultrasound (iUS) in pediatric oncological neurosurgery as compared to intraoperative magnetic resonance imaging (iMRI).

Methods: A total of 24 pediatric patients undergoing tumor debulking surgery with iUS, iMRI, and neuronavigation were included in this study. Prospective acquisition of iUS images was done at two time points during the surgical procedure: (1) before resection for tumor visualization and (2) after resection for residual tumor assessment. Dice similarity coefficients (DSC), Hausdorff distances 95th percentiles (HD95) and volume differences, sensitivity, and specificity were calculated for iUS segmentations as compared to iMRI.

Results: A high correlation (R = 0.99) was found for volume estimation as measured on iUS and iMRI before resection. A good spatial accuracy was demonstrated with a median DSC of 0.72 (IQR 0.14) and a median HD95 percentile of 4.98 mm (IQR 2.22 mm). The assessment after resection demonstrated a sensitivity of 100% and a specificity of 84.6% for residual tumor detection with navigated iUS. A moderate accuracy was observed with a median DSC of 0.58 (IQR 0.27) and a median HD95 of 5.84 mm (IQR 4.04 mm) for residual tumor volumes.

Conclusion: We found that iUS measurements of tumor volume before resection correlate well with those obtained from preoperative MRI. The accuracy of residual tumor detection was reliable as compared to iMRI, indicating the suitability of iUS for directing the surgeon's attention to areas suspect for residual tumor. Therefore, iUS is considered as a valuable addition to the neurosurgical armamentarium.

Trial registration number and date: PMCLAB2023.476, February 12th 2024.

Keywords: Brain tumor; Intraoperative MRI; Intraoperative ultrasound; Navigation; Pediatrics.

Fig. 1

Navigated intraoperative acquisition set-up. Left image: set-up during iUS acquisition. Reference array (r) and transducer (t) are both optically tracked by stereotactic camera (c). The live ultrasound image is shown on the ultrasound machine (m) and the navigated image is overlaid on MRI (n). Right image: N13C5 transducer (BK5000, BK Medical, Denmark) (t), draped in a sterile cover with the sterile array (a) for optical navigation is attached (Brainlab, Munich, Germany)

Fig. 2

Workflow of data processing and analysis is divided into (1) creation of transformation matrices, multiplying matrices to obtain one transformation to the destination image; (2) rigid image transformation, applying the transformation matrix; and (3) calculation of quantitative metrics, i.e., volume difference, Dice similarity coefficient (DSC), and Hausdorff distance 95th percentile (HD95)

Fig. 3

Flowchart showing different acquisition, processing, and analysis steps with the number of patients involved

Fig. 4

Example segmentations in preoperative and intraoperative MRI and US images. The first row shows the tumor segmentation in A preoperative MRI, B iUS1, and C for both modalities in an overlay. The second row shows the remnant segmentation in D intraoperative MRI, E iUS2, and F for both modalities in an overlay

Fig. 5

Volume based metrics of iUS acquisitions compared to MRI. A The absolute volume plotted per patient for iUS1 and preoperative MRI. A regression line is plotted and shows a coefficient of 0.942. The Pearson correlation coefficient is 0.996. C The absolute volume plotted per patient with a remnant visible on both iUS2 and iMRI. The regression line coefficient of 0.658 and a Pearson correlation coefficient of 0.863 were found. B and D Bland–Altman plots, in which the differences between iUS and MRI are plotted against their averages. B The tumor volumes before resection and D remnant volumes as seen on iUS2 and iMRI. Median volume differences of 0.16 cm³ and 0.60 cm³ were found for iUS1 and iUS2, respectively. The first and third quartiles are shown in blue