Senft 2011.

Study characteristics
Methods	Randomised controlled trial. Randomisation of participants was done in blocks of 4 on a 1‐to‐1 ratio using BiAS for Windows 9.01 by an assistant who had no clinical involvement in the trial. Sample size: The sample size calculation was done to detect a difference of 25% between groups for the primary endpoint with a power of 80%. Blinding: Investigators who assessed eligibility of participants and scheduled surgeries were masked to treatment group assignment by use of a sealed envelope design. Surgeons and participants were not masked to the treatment group assignment, but the neuroradiologist who analysed MRI data was masked.
Participants	Inclusion criteria: Adults ( ≥ 18 years) with known or suspected gliomas showing distinct contrast enhancement on T1‐ weighted MRI amenable to radiologically complete resection were eligible. Exclusion criteria: Presence of cardiopulmonary or hepatorenal comorbidities; tumours that crossed the midline or were located in the basal ganglia, cerebellum, brain stem, or otherwise in close proximity to eloquent brain structures prohibiting or questioning complete resectability; contraindications to MRI examination (e.g. pacemaker); and inability to give consent due to neuropsychological deficits or a language barrier.
Interventions	Intervention: Mobile intraoperative ultralow field (0.15 Tesla) MRI system (PoleStar N‐20, Odin Medical Technologies, Yokneam, Israel and Medtronic, Louisville, CO, USA). Control: "Conventional micro neurosurgical resection" including Cavitron Ultrasonic Aspirator (CUSA) and neuronavigation. The use of intraoperative ultrasound or fluorescence‐guided surgery with 5‐aminolevulinic acid was not allowed in either group.
Outcomes	Primary: Extent of resection. Secondary: "Volume of residual tumour on postoperative MRI and progression‐free survival (PFS) at 6 months. We also compared the duration of surgery and treatment‐related morbidity."
Notes	Definitions: All participants underwent high‐field MRI at 1.5 T or 3.0 T with and without contrast agent within 7 days before surgery and within 72 h after surgery. 1 masked, independent, and experienced neuroradiologist (AB) assessed MRIs to establish the extent of resection and undertake volumetric analyses of the tumours and tumour residues. Residual tumour was defined as detectable contrast enhancement on T1‐weighted imaging with a volume of more than 0.175 cm3 on postoperative MRI as done previously.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation of participants was done in blocks of 4 on a 1‐to‐1 ratio using BiAS for Windows 9.01 by an assistant who had no clinical involvement in the trial.
Allocation concealment (selection bias)	High risk	Sealed envelope design
Blinding of participants and personnel (performance bias) All outcomes	High risk	Surgeons and participants were not blinded.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Only the neuroradiologist analysing the MRI data was blinded, which is important for assessing extent of resection. Assessors of clinical outcomes were not masked, which would have affected PFS and treatment‐related morbidity.
Incomplete outcome data (attrition bias) All outcomes	High risk	49 of 58 participants analysed (4 excluded in each arm due to diagnosis of a metastasis, and 1 in the iMRI arm withdrew consent).
Selective reporting (reporting bias)	Low risk	All prespecified outcomes reported (extent of resection, residual tumour volume, PFS, and treatment‐related morbidity).
Other bias	High risk	1. Interim analysis/abbreviated trial. Stopped early due to an interim analysis resulting in a reduced sample size from 80 to 58. Due to the possible effect of this adjustment on the alpha error and to avoid over‐interpretation of the data, a P value of less than 0.04 was considered significant for the primary endpoint. 2. Industry sponsorship. No external funding source for the study declared, but one of the authors received an honorarium from Medtronic, which manufactures the scanner used.