Fig 1.
MRI data from study Subject 1 and corresponding 3D head model.
A. Coronal (left), axial (middle) and sagittal (right) views of original Gadolinium enhanced T1 MRI patient data showing left parietal glioblastoma (radiological orientation). B. Volume reconstruction of gray matter (gray), white matter (white), tumor tissue (yellow), and a peritumoral region (blue). C. Surface reconstruction of patient skull rotated to present the craniectomy boneflap outlined as a darkened area above the tumor (left). The rightmost image shows the same view, but with the bone flap removed to display the underlying tumor and peritumoral region. D. Surface reconstruction of the head model showing the optimized electrode layout used for simulation (NovoTAL ™). Electrodes are paired orange with white and gray with blue.
Fig 2.
MRI data from study Subject 2 and corresponding 3D head model.
A. Coronal (left), axial (middle) and sagittal (right) views of original T2 MRI patient data showing a deeply seated WHO III astrocytoma (radiological orientation). The tumor was non-enhancing on T1 with Gadolinium enhancement. B. Volume reconstruction of gray matter (gray), white matter (white), tumor tissue (yellow), and a peritumoral region of interest (blue). C. Surface reconstruction of patient skull rotated to present the circular 50 mm craniectomy boneflap outlined as a darkened area above the tumor on the right side. The rightmost image shows the same view, but with the bone flap removed to display the underlying cortical surface. D. Surface reconstruction of the head model showing the optimized electrode layout used for simulation (NovoTAL™). Electrodes are paired orange with white and gray with blue.
Fig 3.
Effect of craniectomy without tumor resection.
Percentage of tissue exposed to field strengths above the corresponding value on the abscissa (craniectomy—stippled line; no craniectomy—solid line). Rows represent different tissues and columns the L/R and A/P electrode pairs, as indicated. Craniectomy significantly increased the electrical field strengths in tumor tissue and the peritumoral region compared to no craniectomy. The distributions of field strengths in healthy tissues were largely unaffected.
Fig 4.
Topographical effect of craniectomy without tumor resection.
A. Field strength distributions with and without craniectomy (coronal, axial, and sagittal sections from left to right, colorbar 0–300 V/m). B. Paired difference between craniectomy and no craniectomy scenarios, i.e. Δ|E| = |E|craniectomy—|E|no craniectomy, for both electrode pairs. Leftmost panels show a rotated surface view of the region of pathology. Craniectomy produced a marked and focal increase in electrical field strength in the regions of pathology underlying the craniectomy, while healthy tissues were largely unaffected.
Fig 5.
Effect of craniectomy on current density.
A. Current density distribution (color indication 0–180 A/m2) on the brain surface with and without craniectomy (no resection). The skin surface (with placed electrodes) is shown for orientation. Craniectomy significantly increases the current density in the region of pathology underlying the craniectomy (black ellipse, Fig 1C). This in turn leads to increased field strength in the affected region. B. Topographical distribution of the current density on the skin surface with and without craniectomy (range 0–250 A/m2). Craniectomy causes the current to be shunted through the skull defect thereby lowering the current density in the skin region between the active electrodes. The figure also shows how individual electrodes in the arrays contribute differently in the two situations.
Fig 6.
Effect of craniectomy after tumor resection.
Percentage of tissue exposed to field strengths above the corresponding value on the abscissa (craniectomy—stippled line; no craniectomy—solid line). Rows represent different tissues and columns the L/R and A/P electrode pairs, as indicated. Craniectomy significantly increases the field strength in the peritumoral region compared to the situation with no craniectomy. The field strengths in healthy tissues were largely unaffected.
Fig 7.
Topographical effect of craniectomy after tumor resection.
A. Topographical maps of field strength distributions (coronal, axial, and sagittal from left to right, colorbar 0–300 V/m) with and without craniectomy and for both electrode pairs as indicated. B. Paired difference between craniectomy and no craniectomy scenarios, i.e. Δ|E| = |E|craniectomy—|E|no craniectomy, for both electrode pairs. Leftmost panels show a rotated surface view of the resection cavity and the surrounding region of pathology. Craniectomy produced a marked and focal increase in electrical field strength in the peritumoral region underlying the craniectomy, while leaving the healthy tissues largely unaffected.
Fig 8.
Effect of craniectomy size and configuration on field distribution.
A. Median and 99th percentile field strengths (ordinate) in the tumor and peritumoral tissues at different craniectomy diameters (abscissa). Results are shown for both the L/R (red line) and A/P (black line) array pairs. Asterisk symbols represent equivalent results obtained using a model with four 15 mm burr holes located above the tumor region. The results are displayed at 30 mm craniectomy diameter as these configurations had the same total area. B. Equivalent results as displayed in A but after resection of the tumor. C. Surface view of selected craniectomies and the corresponding field distributions obtained before tumor resection. Color bar represent the range of field strengths displayed.
Fig 9.
Topographical effect of craniectomy for a deeply seated tumor.
A. Field strength distributions with and without craniectomy (coronal, axial, and sagittal sections from left to right, colorbar 0–300 V/m). B. Paired difference between craniectomy and no craniectomy scenarios, i.e. Δ|E| = |E|craniectomy—|E|no craniectomy, for both electrode pairs. Leftmost panels show a surface view of the region of pathology. Craniectomy caused no considerable changes in electrical field strength in the regions of pathology, but rather induced a significant increase in field strength in the healthy tissues immediately underlying the skull defect.