The use of high-field (3 T) magnetic resonance devices in intraoperative imaging allows for the acquisition of high spatial resolution images, permitting the surgeon to provide optimal tumor excision. However, due to the high sensitivity, it should taken into account that metal instruments such as non-ferromagnetic headrests and surgical equipment will cause sensitivity artifacts. In the study of Pamir et al., a 5-pin headrest-head coil combination specially designed for the system was used to solve this problem [12]. The 3 T MRI unit in our center is apart from the operation room. This design is suitable for both Io and outpatient imaging; its use for routine diagnostic purposes when Io imaging is not required reduces the financial cost.

In our study, 36% (45/125) of patients in the Io MRI group were returned to the operating room, increasing the resection rates. In a similar study by Bunyaratavej et al. that included glioma and non-glioma diagnoses, this rate was found to be 60% (24/40) [13]. These results show that the use of Io MRI in brain tumor surgery offers the possibility of an additional excision during the same surgical procedure in the event that the surgeon did not anticipate residual tumor before the operation.

Low-grade glial tumors are slow-growing, infiltrative masses with a median survival time of 5 to 7 years [14]. Since the response to chemotherapy and radiotherapy is poor [15], the widest possible resection of the tumor is targeted during the operation. Another reason for preferring the greatest acceptable resection is the potential of malignant degeneration of residual LGG [16]. In fact, some studies suggest that supratotal resection is associated with improved survival rates [14, 17]. Therefore, the surgeon may choose a more aggressive resection route when tumor features on the preoperative MRI are compatible with LGG. As expected, in our study, the EOR in lesions that were radiologically compatible with LGG was statistically significantly higher when compared to lesions considered to be HGG.

In the meta-analysis study by Li et al., the effect of using Io MRI on the resection rate and survival was evaluated, and it was concluded that the PFS was longer in the groups that underwent Io MRI compared to conventional neuronavigation (P = 0.012); however, OS rates did not differ between groups (p = 0.799) [6]. They also reported that Io MRI significantly improved PFS and EOR, especially in HGG patients[6]. In a study involving 14 patients diagnosed with glioblastoma, Pietel et al. revealed no significant difference between the median survival rates of patients who underwent Io MRI and those who did not (P = 0.68) [18]. Roder et al. noted that the use of Io MRI in 117 cases of glioblastoma raised the 6-month PFS rate from 32 to 45%, although no statistically significant data could be obtained (P = 0.131) [19]. They related this result to the use of varied adjuvant treatment protocols on patients and the limited number of cases. In the comprehensive meta-analysis published by Caras et al., techniques such as Io MRI, diffusion tensor imaging, and functional MRI were investigated in glioma surgery [20]. It was concluded that the aforementioned intraoperative imaging methods significantly increased OS and GTR compared to standard neuronavigation (35.0 months vs. 14.4 months, P < 0.001 for both parameters).

In studies investigating the effect of tumor localisation on OS, it has been reported that periventricular extension and eloquent area involvement decrease OS. In the study of Liu et al., the decrease in OS in occipitotemporal glioma cases is supported by the results of our current study [21]. It was emphasized that the distance between the center of the third ventricle and the edge of the contrast-enhancing tumor affects the survival time [22]. This distance is shorter in centrally located tumors. Centrally located gliomas can extend more easily through deep white matter tracts, making excision difficult. This may increase the possibility of surgical sequelae and decrease OS.

PFS in the Io MRI group was significantly longer than in the control group in the current study. The absence of a statistically significant difference in OS rates may be due to the use of adjuvant therapy, which varies according to histopathological subtype and molecular profile. In addition, the fact that the HGG/LGG distribution is not homogeneous between the groups can be considered another reason.

Our study has several limitations. The first is the retrospective nature of research design. The second is the limited number of control patients due to presence of an Io imaging system in our institution. The third limitation factor is that the World Health Organization classification of brain neoplasms was updated in May 2021, and the majority of our patients’ histopathological diagnoses were recorded according to the 4th edition published in 2016. According to the last classification, CNS WHO grades of isocitrate-dehydrogenase (IDH) mutant astrocytomas range from 2 to 4; IDH mutant oligodendrogliomas with 1p/19q deletion have both CNS WHO grade 2 and 3 types [23]. Because of this current information, the aforementioned neoplasms are not called LGG without knowing their molecular panel.