Iranian Journal of Neurosurgery
Volume:8 Issue: 2, Spring 2022

Diffusion Tensor Imaging (DTI)-based tractography can help us visualize the spatial relation of fiber tracts to brain lesions. Several factors may interfere with the procedure of diffusion-based tractography, especially in brain tumors. The current study aims to discuss several solutions to improve the procedure of fiber reconstruction adjacent to or inside brain lesions. Illustrative cases are also presented.

Methods and Materials/Patients

 The paper is a narrative review of methods that can improve DTI-based fiber reconstruction in the area of brain tumors. To provide up-to-date information, we briefly reviewed related articles extracted from Google Scholar, Medline, and PubMed.

We proposed five techniques to improve fiber reconstruction. Technique 1 is a very low Fractional Anisotropy (FA) application. Technique 2 includes resampling techniques, such as q-ball and High Angular Resolution Diffusion Imaging (HARDI). Technique 3 is the reconstruction of fiber tracts by defining the separated Region of Interest (ROIs). Technique 4 explains the selection of the ROIs according to functional Magnetic Resonance Imaging (fMRI) since the anatomical configuration is distorted by neoplasm. Technique 5 consists of using unprocessed images for preoperative planning and correlation with the clinical situation.

DTI tractography is highly sensitive to noise and artifacts. The application of tractography techniques can improve fiber imaging in the area of brain tumors and edema.

Numerous efforts have been made over the past century. Various innovation techniques are increasingly gaining attention and gradually establishing the foundation of recent significant developments in the world of neurosurgery, among which varied stereotactic neuro-navigation designs and other novel emerging systems are being developed every day. This narrative review aims to describe basic concepts in frameless stereotaxy and summarize the primary principles of neuronavigation and clarify basic characteristics, such as the accuracy of this technique (frameless navigation), and emphasize the importance of designing phantom.

Methods and Materials/Patients

 The application of brain images to steer the surgeon to a target in the brain by utilizing the stereotactic principle of co-registration of the patient with an imaging study that permits brain surgery to be fulfilled with greater safety and smaller incisions by providing precise surgical guidance of the location of intracranial pathology is highly noticeable. General uses of frameless stereotaxy are explained and common benefits
are highlighted. It is genuinely inevitable to estimate the accuracy of these systems and discover sources of error.

The findings have provided considerable insight into recent findings on principles of frameless stereotactic surgery and novel developments for image-guidance systems.

The unprecedented development of image guidance has been much discussed. As a concluding note, several determinants, including updated imaging/registration, ease of use, robotic instruments, automated registration of increased accuracy, and the program’s potential for expansion to other disciplines, are all under development for image guidance.

Brain mapping is the study of the anatomy and function of the Central Nervous System (CNS). Brain mapping has many techniques and these techniques are permanently changing and updating. From the beginning, brain mapping was invasive and for brain mapping, electrical stimulation of the exposed brain was needed. However, nowadays brain mapping does not require electrical stimulation and often does not require any complex involvement of patients. To perform brain mapping, functional and structural neuroimaging has an essential
role. The techniques for brain mapping include noninvasive techniques (structural and functional magnetic resonance imaging [fMRI], diffusion MRI [dMRI], magnetoencephalography [MEG], electroencephalography [EEG], positron emission tomography [PET], near-infrared spectroscopy [NIRS] and other non-invasive scanning techniques) and invasive techniques (direct cortical stimulation [DCS] and intracarotid amytal test [IAT] or wada test).

Methods and Materials/Patients:

 This is a narrative study on brain mapping in neurosurgery. To provide up-to-date information on brain mapping in neurosurgery, we precisely reviewed brain mapping and neurosurgery articles. Using the keywords “brain mapping”, “neurosurgery”, “brain mapping techniques”, and “benefits of brain mapping”, all of the related articles were obtained from Google Scholar, PubMed, and Medline and were precisely studied.

To perform an effective and safe neurosurgical intervention, precise information about the structural and functional anatomy of the brain is obligatory. Based on the information on brain mapping, the selection of suitable patients for the operation, the plan of appropriate operative approach, and good surgical results can be acquired. To provide this information, we can use brain mapping techniques that were formerly applied in neuroscientific brain mapping efforts with noninvasive techniques, such as fMRI, MEG, dMRI, PET, etc and invasive techniques, such as DCS, IAT, etc.

Functional brain mapping is a constantly evolving fact in neurosurgery. All stages in obtaining a functional image are complex and need knowledge of the basic physiologic and imaging features.

The methods to detect brain activation with functional MRI (fMRI), and MRI provide a way to measure the anatomical connections which enable lightning-fast communication among neurons that specialize in different kinds of brain functions. Diffusion tensor imaging (DTI) can measure the direction of bundles of the axonal fibers which are all aligned. Besides mapping white matter fiber tracts, these methods can enable us to detect and characterize white matter disorders in diseases. The objective of this narrative review is to overview current knowledge concerning DTI as one of the
prominent popular MRI techniques that provide a planned tool for comprehensive, noninvasive, functional anatomy mapping of the human brain in both research and practical field. This review summarizes the DTI development in recent years concerning the specificity and utility of this technique in brain surgery.

Methods and Materials/Patients:

 The significance of mapping the structure of white matter tracts, constructively the brain’s wiring by visualization and characterization of white matter fasciculi in two and three dimensions enables us to profound how different brain regions are connected and how diseases affect white matter and cause neurological problems. And we noted that while DTI proposes a potent tool to study and visualize white matter, it suffers from inherent artifacts and limitations. Additionally, some materials about the origin of the DTI signal and unique information on white matter and 3D visualization of neuronal tracts have been raised.

This article focuses on DTI modality and its computational techniques, and investigates significant considerations in this regard. Moreover, an inspection of the white matter structure and integrity of normal and diseased brains (e.g. multiple sclerosis, stroke, aging, dementia, schizophrenia, etc.) have been raised as a clinical application of tractography.

The utilization of advances in diffusion-tensor (DT) imaging techniques considerably enables us to map the white matter tractography (WMT) in the normal brain. These techniques impress the operative decision in a surgical operation, especially concerning cerebral neoplasms. Also, it is possible to judge with the assistance of DTI in each subject.

The extent of resection seems a solid prognostic factor in patients with high-grade gliomas (HGGs). When administered orally, 5-aminolevulinic acid (5-ALA) is exclusively converted into protoporphyrin IX (PPIX) by malignant cells and detects, identifying contrast-enhancing glial lesions under 400 nm blue light. The authors thoroughly assess the efficacy, accuracy, and safety profile of 5-ALA-guided surgery toward the maximal resection of cranial HGGs.

Thirty consecutive patients with HGG adjacent to the corticospinal tract (CST) met our inclusion criteria in a single-arm retrospective study. Bilateral diffusion tensor imaging (DTI)-derived corticospinal tract (CST) tractography was employed using a 1.5 Tesla magnetic resonance imaging (MRI). Oral 5-ALA was ingested with a dose of 20 mg/kg 4 hours prior to operation and was applied to qualify the margins of the local resection cavity. The clinical and volumetric assessments were postoperatively conducted. The mean preoperative tumor volume on T1 contrast-enhanced MRI and fluid-attenuated inversion recovery (FLAIR) images was 16.8 cm3 and 47.6 cm3, respectively. Complete resection of contrast-enhanced lesions was yielded in 27 of 30 patients (90%). All patients improved postoperatively regarding motor deficits and or seizures. No new permanent neurological deficits were detected in the 3-month follow-up.

Fluorescence image-guided surgery (FIGS) using 5-ALA increases the extent of resection (EOR) with further surgical risks in eloquent regions when combined with multimodality visualization- functional mapping. It also provides pathological insights to visualize cranial HGGs and identify infiltration of functional fiber tracts.