Introductory Chapter: Advances in Neuroimaging

1. Introduction

For over a century, scientists have been working hard to observe the living brain through the protective cover of the human skull, such as X-ray in 1918, ventriculography with contrast agent, pneumoencephalography in 1919, and cerebral angiography in 1926. The emergence of computed tomography (CT), magnetic resonance imaging (MRI), and digital subtraction angiography (DSA) has gradually replaced these examination methods [1, 2, 3]. Nowadays, a series of technologies enable researchers and clinical doctors to create stunning detailed images of our brain structure. Neuroimaging tools, including ultrasound, CT, MRI, functional MRI, DSA, positron emission tomography (PET), and single photon emission computed tomography (SPECT), play a fundamental and important role in neurosurgical and neurological treatments of brain and spine pathologies (Figure 1) [1, 2, 3].

Figure 1.

The chart of the continual advancements in neuroimaging modalities.

2. Traumatic brain injury

Traumatic brain injury (TBI) is the main cause of morbidity and mortality worldwide [4]. Imaging plays a crucial role in the evaluation and diagnosis of TBI, particularly in its triage role in acute situations to determine which patients require emergent neurosurgical intervention [4]. The damage caused by TBI can be divided into primary and secondary mechanisms [4]. Primary injury is usually defined as direct mechanical injury caused by trauma. These injuries are usually acute and obvious, including fractures, intracranial hemorrhage, contusions, and traumatic axonal injuries [4]. This type of injury is best detected using traditional CT and MR structural imaging techniques [5].

Traumatic arterial injury can be caused by various mechanisms, including tearing caused by fracture fragments, blunt or penetrating trauma, and arterial strain [4]. The likelihood of intracranial carotid artery and vertebral artery injury is much lower than that of cervical segment injury [4]. Skull base fracture is one of the most common causes of arterial injury—the appearance of skull base fractures on CT should always prompt consideration of CT angiography (CTA) or MR angiography (MRA) for further evaluation [4]. In some cases, routine angiography may be necessary, especially when the lesion is mild or endovascular treatment is chosen (such as severe bleeding, nosebleeds, or carotid-cavernous fistula) [4]. Molecular markers have potential applications in detecting and monitoring the progression of TBI, with a particular emphasis on microRNAs as a novel molecular regulator for neural tissue damage and repair [4].

3. Brain tumors

Neuroimaging plays a constantly evolving role in the diagnosis, treatment planning, and post-treatment evaluation of brain tumors. The MRI is commonly used in the care of brain tumor patients [5]. The use of advanced MRI sequences for structural and functional imaging (such as perfusion imaging, functional MRI (fMRI), and diffusion MRI (dMRI) sequences) provides basic information for the selection of surgical candidates, customization of personalized surgical plans based on brain structure and functional tissues, and prediction of postoperative functional outcomes [5]. Emerging radiomics techniques will be implemented to improve the diagnostic and prognostic effectiveness of neuroimaging data [5].

4. Functional neurosurgery

Accurate anatomical localization through neuroimaging techniques is crucial for achieving optimal clinical outcomes in functional neurosurgery [5]. Imaging guidance does represent the foundation of many increasingly invasive neurosurgical treatments, primarily used for the treatment of tremors and chronic pain, but has interesting prospects in the treatment of epilepsy, psychiatric disorders, and drug delivery [5]. These structural, functional, and metabolic assessments include MRI, PET, and magnetoencephalography (MEG).

The ablation of various central nervous system targets, especially deep brain stimulation (DBS), is an established tool for treating motor disorders [6]. Accurate targeting of the expected structure is crucial for optimal clinical outcomes. However, most of the targets used in functional neurosurgery are suboptimal visualized on conventional MRI. Specialized MRI sequences can usually visualize common anatomical structures in DBS surgery to a certain extent, including 1.5-T field strength [6].

The latest advances in neuroimaging, including the use of diffusion tensor imaging, diffusion tractography, fMRI, and positron emission tomography (PET), provide higher-resolution descriptions of the structural and functional connections between regions of interest [7]. In addition, new neuroimaging techniques enable DBS patients to be analyzed at the group level and delineate areas related to clinical benefits. These regions may differ from traditional target nuclei and may correspond to the center of white matter tracts or functional networks [7]. Advanced neuroimaging technology is particularly important for guiding personalized DBS-targeted treatment of refractory depression and obsessive-compulsive disorder, as the symptom characteristics and potential disorder circuits of these diseases are more heterogeneous [7].

5. Neurodegenerative disorders

Neurodegenerative diseases include Alzheimer’s disease (AD), frontotemporal lobe degeneration (FTLD), Parkinson’s disease (PD), and related diseases. The most commonly used neuroimaging techniques for neurodegenerative diseases are MRI and PET [8]. In neurodegenerative diseases, significant atrophy patterns on MRI are usually disease-type specific. In addition, the emergence of PET tracers targeting amyloid and tau, two major protein diseases in AD and other diseases, enables clinical trials to detect and monitor disease progression and disease-specific targeting results early on [9].

The focus of other neuroimaging studies is on psychiatric disorders, including anxiety, depression, addiction, and psychosis [9]. Recently, transcranial magnetic stimulation has been proposed as a potential pathological treatment method and biological probe for schizophrenia [9].

Non-central nervous system diseases and related treatments can have an impact on the brain and cognition. For example, non-central nervous system cancers and their chemotherapy and/or hormone therapy are associated with cognitive injury, known as cancer-related cognitive impairment (CRCI). CRCI has been proven to be associated with structural findings on MRI [10]. With the continuous development of new cancer treatment methods, the impact of cancer and CRCI treatment on brain structure, function, and cognition evaluated by neuroimaging is worth considering.

6. Cerebral and spinal vascular diseases

Intracranial aneurysms and vascular malformations are often found after intracranial hemorrhage [11]. CT scanning is the most sensitive method for detecting acute subarachnoid hemorrhage, parenchymal hemorrhage, and intraventricular hemorrhage. The display of small aneurysms on MRI is inconsistent. DSA remains the standard for fully and accurately describing patent aneurysms and arteriovenous and venous malformations (Figure 2).

Figure 2.

A 46-year-old woman with a ruptured posterior communicating artery aneurysm was coiled. A, cranial CT scanning showing the subarachnoid hemorrhage of the left supracellar cistern (arrow). B, lateral view of the left internal carotid artery injection. C, 3-D reconstruction of the left internal carotid artery injection. Showing the aneurysm of the left posterior communicating artery (arrows). D, lateral view of the left internal carotid artery injection showing the first 3-D coil was placed into the pseudo-aneurysm (arrow). E, lateral view of the left internal carotid artery injection after aneurysm coiling showing the disappearance of the aneurysm (arrow). F, unsubtracted image showing the coil mass (arrow).

Giant aneurysms and thrombosed aneurysms present as mass lesions, which are often detected on MRI as a screening examination [12]. MRI is usually more capable of characterizing these lesions than CT or angiography. Patients with vascular malformations with focal neurological symptoms and no bleeding are best evaluated through MRI [13]. It is easy to prove patent vascular malformations, manifested as flow void and other flow-related phenomena [14]. Hidden vascular malformations, including thrombosed arteriovenous, venous, and cavernous malformations, as well as telangiectasia, are also best detected by MRI and are not visible during angiography. The new advances in artificial intelligence and advanced imaging modes, such as PET and MRI scans, have the potential to predict early outcomes in SAH [11].

The Flow-diverter device (FDD) is a next-generation stent placed in the parent artery at the level of the aneurysm neck to disrupt flow within the aneurysm, thereby facilitating thrombus formation within the aneurysm [15]. The use of these stents is mainly suitable for unruptured aneurysms, especially aneurysms located in the internal carotid artery, vertebral artery, and basilar artery, for fusiform and dissecting aneurysms, as well as for saccular aneurysms with large neck and low dome-to-neck ratio. FDD treatment is a feasible and effective technique for unruptured aneurysms with complex anatomical structures (fusiform, dissecting, large neck, bifurcation with side branches), in which coiling and clipping are difficult or impossible [16].

Endovascular therapy has completely changed the treatment of acute ischemic stroke [17]. In the past few years, the indications for endovascular treatment have expanded to include patients receiving treatment at extended windows, such as large ischemic core infarction and basilar artery occlusion thrombectomy, as demonstrated by several randomized clinical trials [18]. Simplifying the neuroimaging protocol in the extended window to allow for non-contrast CT and CTA collaterals has also expanded the scope of mechanical thrombectomy, especially in regions around the world where advanced imaging may not be available.

7. Spinal cord tumors

FMRI of the spinal cord utilizes various methods and stimulation schemes to gain a deeper understanding of the healthy human spinal cord, laying the foundation for its clinical research and practical application [19]. New fMRI techniques and new knowledge about healthy human spinal cord have been established. Spinal cord fMRI advancement and research will further enhance our understanding of various spinal cord diseases and provide the foundation for evaluating existing and developing new treatment plans [20]. Driven by these developments, studying pathology and injury status within the spinal cord, such as fibromyalgia, multiple sclerosis, spinal cord injury, and cervical spondylotic myelopathy, have provided in-depth insights into the temporal processes of spinal cord injury and changes caused by injury, has become the next important direction in spinal fMRI.

8. Tinnitus

Although tinnitus may originate from damage to the peripheral auditory apparatus, its perceptual and painful symptoms are the result of changes in auditory, sensory, and limbic neural networks. Understanding these complex changes can promote the development of targeted therapy. When the diagnosis of Meniere’s disease is unclear, a new MRI technique that can describe the maze in detail may be useful. The advancement of CT, MRI, and DSA has made diagnosis of cerebral aneurysmas, arteriovenous malformations, and dural arteriovenous fistulas possible [15, 21].

9. Conclusions

In the past few decades, neuroimaging has evolved from anatomical imaging to multimodal comprehensive anatomical and functional imaging. The minimally invasive treatment possibilities of interventional neuroradiology, image-guided laser ablation, and MRI-guided high-intensity-focused ultrasound will be used for the treatment of brain and spinal pathology.