Brain Health in Neuroradiology

Abstract

Neuroradiology, as a modern branch of the neurosciences and radiological sciences, has an impact on global health, particularly on brain health. On the one hand, neuroradiology directly impacts diseases of the nervous system, such as stroke and inflammatory diseases, by providing an all-in-one package combining imaging, diagnosis, treatment, and follow-up. This has been impacted by the continuous evolution over the last decades of both diagnostic and interventional tools in parallel: this was the case in stroke, where the endovascular treatment was followed closely by developments in fast MRI techniques and multi-slice CT imaging. Additionally, inflammatory diseases of the brain, as well as tumors of the central nervous system, can be imaged and localized in order to set in place both an early diagnosis and initiate treatment. Neurodegenerative diseases such as Alzheimer’s disease, in which treatment options are appearing on the horizon, also benefit from the use of modern neuroimaging techniques. On the other hand, neuroradiology plays an important role in the prevention and prediction of brain diseases and helps in building up the so-called digital twin, often from birth till late in life. Additionally, the practice of neuroradiology itself is evolving to not only improve patient health but also the health of the practitioners of neuroradiology themselves. By improving the overall work environment also, neuroradiologists will be working under better conditions and will suffer less fatigue and burn-out, thereby providing better service to patients and population. By using less radiation for diagnostic tests and shifting to techniques that rely more and more on either magnetic resonance or ultra-sound techniques, the radiation load on the population and on the neuroradiologists will decrease. Furthermore, using less contrast, such as gadolinium, has been shown to result in fewer deposits in the brains of patients, as well as less pollution at the ocean level, thus contributing to general well-being. Additionally, the implementation and use of artificial intelligence at many levels of the diagnostic and treatment chain will be beneficial to patients and physicians. In this paper, we discuss the place and potential not just of the techniques but of neuroradiology and the neuroradiologist as promoters of brain health and thus global health.

1. Introduction

Neuroradiology is a modern branch of medicine that has seen enormous progress since the development of digital subtraction angiography and high-speed planar imaging such as magnetic resonance (MR) and computed tomography (CT) [1]. This progress allows it to combine with other neuroimaging techniques, such as electroencephalography (EEG) and magnetoencephalography (MEG), for the evaluation of higher brain function [2]. The availability of these techniques in highly specialized centers has enabled modern neuroradiology to develop both its diagnostic and interventional arms [3]. Neuroradiology is also a transversal branch in many ways by providing both advanced planar imaging and non-invasive methods for treatment [4]. It serves all patients with diseases of the central nervous systems, as well as the specialties that care for them, across all ages, from the pre-natal period until the end of life. In this sense, it follows the process of population growth and decline over time, providing a unique insight through digital datasets that can be accessed for diagnosis, treatment, and research purposes, benefiting both individual patients and the population. This will also be made possible with the creation of so-called digital twins of patients, on which simulations can be performed [5,6]. Thus, neuroradiology is already able to provide personalized solutions to many patient issues [7]. During its early stages of development, neuroradiology was performed by a variety of specialists: initially, many were neurologists, neurosurgeons, radiologists, or even psychiatrists. However, with the multiplication of techniques and more and more complex possibilities for patient diagnosis and treatment, the idea of neuroradiology as a subspeciality or even specialty on its own has emerged. This has impacted even more the organization at the level of hospitals where neuroradiology is more and more identified as an independent entity, lead to the creation of units, sections divisions, or even some entities calling themselves departments of neuroradiology in many countries. This independence of action from other specialties has not only allowed neuroradiology to become a full actor in modern medicine but also to provide an important contribution to brain health. In Switzerland, neuroradiology is a subspeciality with two diplomas of advanced training in diagnostic and invasive neuroradiology, with an independent curriculum of 4 years after the acquisition of the main specialty [8]. While historically seen as one subspecialty, the level of expertise and knowledge needed to practice either of the two subspecialties has rendered a certain supra-specialization in diagnostic and interventional neuroradiology necessary. Training, while traditionally reserved for radiologists in most European countries, has shown to be favorably seen to open up to clinicians coming from close fields, mainly from the clinical neurosciences (neurology and neurosurgery).

2. Technological Aspects

While heavily dependent on clinical knowledge, Neuroradiology has been at the forefront of technological developments in imaging since its inception. Indeed, there has been a constant evolution and progress from the simple use of X-ray images to the advanced imaging techniques we know today. Overall, even in cases of trauma, X-ray images are extremely rarely used, and the two most commonly used techniques today are computed tomography and magnetic resonance imaging. Both techniques are used as complements to each other, with CT being used more in emergency situations and MRI being much more versatile and flexible due to the possibility of using different sequences. Cerebral angiography, which was the main diagnostic tool before CT and MRI arrived, has become more and more a purely interventional technique that has seen a boom in utilization due to the development of minimally invasive techniques to treat, among others, cerebrovascular diseases.

(A)

Computed tomography: Basically a rotating X-ray unit, CT has known immense advances since its early days, when the EMI-scanner was developed by G. Hounsfield [9]. With the development, at first, of faster rotating CT units and then of spiral scanning, allowing the acquisition of volumes [10] and, today, of multi-detector scanners and of scanners able to acquire images at various energies, as well as photon counting CTs [11], the technique has become very powerful and fast. Due to its speed and capacity to detect absorption of X-rays by an organ, it is very suited to emergency situations, where blood (containing iron) will be easily detected and bone alterations can be seen easily. CT can also provide examinations of the blood vessels with CT angiography, which is very helpful in the setting of stroke or hemorrhage, for example. CT is, however, associated with radiation, which has increased with its usage over the last few decades.

(B)

Magnetic resonance imaging: Magnetic resonance Imaging is a technique that relies on the use of scanners capable of creating a very high local magnetic field; radiofrequency pulses are sent that then are recuperated in order to create an image. This technique has the immense advantage of allowing even better multi-modality imaging due to its capacity to perform a series of sequences that will detect various types of information on the organ being examined: T1 and T2 images will demonstrate anatomy well, images of diffusion (DWI for diffusion weighted imaging) will detect water motion and are used in stroke and a variety of diseases [12], or perfusion using contrast [13] or not will demonstrate hemodynamic changes; it is also possible to demonstrate alterations in brain physiology by using for example spectroscopic MRI or even performing images using sodium instead of water as the molecule being investigated. Advanced imaging techniques such as fMRI, perfusion MRI, and diffusion tensor MRI play an increasingly important role in the management of patients with brain diseases but have the distinct problem of increasing examination time and post-processing needs that may make them less ideal for the global evaluation of large patient cohorts. These are only a few of the reasons why MRI has become the technique of choice to investigate the brain both clinically and for research purposes.

(C)

Neuro-angiography: Angiographic techniques that were the gold-standard techniques for examining the brain before the advent of CT and MRI have remained important techniques in modern neuroradiology. The focus has shifted towards vascular interventions that have now been made feasible by the development of modern catheterization techniques, as well as devices for treating aneurysms, stroke, and more complex malformations [14].

(D)

Other techniques: Nuclear medicine techniques such as PET and SPECT, while not directly in the domain of neuroradiology, have always been important for the investigation of the brain; their use in neuro-degenerative diseases and in neuro-oncology has increased over the last few decades, especially with the development of combined techniques, i.e., PET-CT and PET-MRI, in the interpretation of which neuroradiologists are increasingly involved. Indeed, both of these examinations provide the high spatial resolution of either CT and MRI but also have the capacity to detect alterations in local physiology detected by using various specific brain tracers for PET or even SPECT. Ultrasonic examination of the carotids, while an important established adjunct for monitoring patients with, for example, chronic cerebrovascular disease, is a technique mostly not in the hands of neuroradiologists [15].

3. Neuroradiology and Population Health

The direct impact of neuroradiology and its neuroimaging techniques on both brain disease and health cannot be underestimated. Indeed, with each technological evolution or revolution, there has been an increase in diagnostic power given to the practicing clinical neuroscientist and neuroradiologist. With the introduction of each subsequent technique (X-ray, angiography, CT, and MRI), neuroradiology has improved its capacity to detect diseases earlier than ever before, which would most often have been missed: the most evident one being the development of MR techniques such as diffusion and perfusion techniques that allow medical professionals to demonstrate both ischemic lesions and the underlying hypoperfusion behind a cerebrovascular event [16]. The development of minimally invasive techniques has also given neuroradiology the ability to intervene with less trauma than regular surgery. Examples include carotid and intracranial stenting, or even vertebroplasty [17].

With the advent of CT and MRI, it became possible to diagnose not just intracranial masses or diseases such as stroke; in stroke, after the positive results in favor of thrombectomy showed clear improvement in outcomes of patients undergoing endovascular treatment [18,19,20,21,22], neuroradiology thus gained a major role by initially selecting patients based on CT or MR criteria; performing clot extraction by thrombectomy or aspiration after clot classification [23]; and then conducting follow-up imaging to assess the success of the therapy, address any complications if present, and predict the final outcome. This has transformed neuroradiology into a full clinical partner in dealing with diseases of the CNS. This has been strengthened by the creation of two curricula for diagnostic and invasive neuroradiology running for two years, each with its own curriculum and log-book.

The capacity of neuroradiological techniques to impact the health and well-being of patients is well documented at the level of the individual patient or of smaller cohorts; however, its use at larger scales and in prevention is somewhat more controversial in the sense of how to implement it. While the gains provided by the techniques have shown themselves to be enormous, the costs and time that healthcare specialists have spent have increased. What is known is that, with time, most modalities tend to become more sophisticated, cheaper, safer, and faster (i.e., CT), so progress in that direction is expected. Using MRI to screen for neurodegenerative diseases in populations that are aging will, at the moment, be associated with immense costs to healthcare systems that are already overloaded. However, smart selection of populations at risk may help to implement screening programs, and the clever use of AI at all levels of the chain may help to resolve the lack and/or cost of associated manpower. The development of such screening programs may, however, have a huge impact on patient well-being and thus reduce, at term, the costs to society as a whole. Neuroradiology, as a specialty, is very often involved with the patient over their whole lifespan, going from the intra-uterine age to the geriatric age.

4. Neuroradiology and Prevention of Brain Diseases

More and more, neuroradiology is involved in the prevention of diseases in the central nervous system [24]. This can be performed in cases of primary prevention, where groups of patients at risk undergo examinations to look for diseases. For example, CT and MR angiography can be used for patients with a known family history of aneurysms: if an aneurysm is found, the patient will be referred to a multidisciplinary board that will discuss the necessity of treating the aneurysm based on its form, location, and other factors [25]. This will also be performed for patients with no previous history and where an incidental aneurysm is found and in whom neuroradiology will often take the lead by providing diagnosis, having a consultation (often with neurosurgeons), and then performing treatment after discussing with the patient and the referring doctor, as well as performing a clinical and radiological follow-up. Other cerebrovascular diseases that may be approached in this way are arterio-venous fistulas, where also most of the imaging, clinical approach, and treatment are guided by neuroradiologists.

Issues with brain health will occur more frequently in the aging population. This is due of course to a multiplicity of factors: the normal aging of the body and brain, as well as factors such as hypertension, vascular disease, diabetes, and other systemic diseases that affect the vessels and blood supply to the brain. There are already a few types of diseases associated with diminished brain performance where neuroradiology plays an important role for screening and treatment: patients with carotid stenosis are usually examined with a combination of CT/MRI/US that is followed and treated by the neuroradiologist in charge, together with the referring clinician. Also, dementia in aging has seen a surge in imaging in patients. For a long time, the role of imaging in these patients was just to exclude the presence or absence of an immediately treatable cause of dementia (e.g., subdural hematoma), but this is no longer the case. The most pertinent example is Alzheimer’s disease, for which new drugs are emerging that might affect the outcome of this common neurodegenerative disease [26]. In this setting, improved imaging strategies, including ultra-high-field imaging (7T), could significantly enhance the power of imaging techniques and improve patient outcomes [27]. Previously, due to the lack of clearly functioning drugs, patients with dementia were often not imaged sufficiently, and now with the advent of possibly potent drugs, it will be necessary to image these patients both in the pre-treatment screening process and to make close imaging follow-up examinations. Indeed, previously, PET imaging and MRI would often demonstrate lesion in advanced cases, but now, when patients have just subjective complaints and those for whom a drug administration may be discussed, MR may be performed in order to detect or not the presence of small hemorrhages due to CAAT, which would be a contra-indication to current drugs, and afterwards, MRI again would be performed with a mix of T2/FLAIR images (to detect edema) and T2* images (to detect hemorrhage). Therefore, neuroradiology is going beyond its initial exclusion role to a more diagnostic one that will also be used for patient triage, and monitoring and follow-up both in clinical trains and the use of drugs in patients.

5. Neuroradiology: Illuminating the Path to Public Brain Health

Due to the enormous requirements in imaging and neuroimaging over the last few decades since the introduction of the EMI scanner, the radiation load from X-ray emissions is not negligible. Indeed, X-ray examinations have been shown to contribute more and more to exposure to radiation in the population, especially since the development of CT scanners. However, the radiology community has been aware of this issue for many decades and try to apply the ALARA (as low as reasonably achievable) approach to using radiation in a clinical setting. With the possibility of replacing many of these X-ray-based techniques with other techniques that do not rely on radiation, such as magnetic resonance imaging [28,29], it is now possible to drastically reduce this radiation load. While handling MRI requires some experience, particularly with security measures, due to the magnetic fields, the reading of previously difficult pathologies, such as hemorrhages, is now much easier. Additionally, low-field scanners, which have always been available, are less costly, allow easier handling of patients with implants, and are cheaper to operate [30,31,32]. Also, using faster and cheaper low-field scanners together with AI algorithms would allow us to safely deploy large-scale brain screening programs.

In interventional neuroradiology, efforts have been made to measure and control the dose of radiation to the patient and the neuroradiologist [33], with the advent of flat panel technology being one steppingstone in that direction. As stated before, the newer possibilities provided by both low- and high-field MR scanners should also render many X-ray examinations obsolete. And the idea of developing angiography suites based no longer on X-rays but on MR techniques has been around for a while, even if it has not yet left the research lab.

Thus, while performance has been increased technologically, also measures have been taken to render the examinations themselves faster, more precise, and also more protective of the patients and the physician’s health. Indeed, many X-ray pioneers suffered radiation-induced issues, going from simple cutaneous erythema to sometimes radiation-induced tumors. Awareness of this has been raised over the last decades, and more and more emphasis has been put on the safe use of such techniques.

6. Neuroradiology as a Polluter

As with any activity using technology, neuroradiology is confronted with being a producer of medical waste. Besides the potential waste resulting from the disposal of heavy imaging technology that has to be regularly replaced, new sources of potential ecological damage induced by medical activities have been identified. The use of contrast media, most notably gadolinium chelates, has been observed to be higher in the waters of regions close to high concentrations of scanners [34]. Reducing the use of contrast agents through new sequences or using contrasts with higher relativity could help address this issue, as has been demonstrated [35,36], since they have been shown to deposit in tissues such as the brain. Additionally, using less material in angiography suites by better selecting the type of device before the intervention could be achieved by optimizing the choice of the catheter in stroke thrombectomy through improved analysis of the clot before intervention using AI [37,38]. This has led, among others, the European Society of Neuroradiology to start a Green Committee, which aims to promote sustainable work in neuroradiology. Also, due to the fact that gadolinium has been shown to accumulate in many organs (among others the brain), more and more reflection has been performed lately on replacing it in certain situations, e.g., by replacing contrast-enhanced perfusion with techniques not using contrast, such as ASL. Time-of-flight angiography techniques for MRI also need no contrast and have contributed to this decrease in the use of contrast overall.

7. Neuroradiology Enhances Brain Health for Its Practitioners

Very often, neuroradiologists work long and hard hours due to the increasing number of cases and their passion for their specialty. While this can be rewarding in the short run, it may lead to burnout, depression, or lack of concentration over time. Lack of concentration could result in medical errors, and burnout could lead to a decrease in the availability of certain interventions. Therefore, it is necessary to staff centers sufficiently on both the diagnostic and interventional sides to provide a good work–life balance. Due to various factors, both political and economic, neuroradiology is currently understaffed [39]. Thus, the administrative part should partly be handled by specialists with a specialized knowledge of the specialty in order to understand its optimal function [40].

8. Discussion

Neuroradiology is not the same specialty it initially was and will continue to evolve under the influence of clinical and technological developments. Indeed, it has evolved immensely since the first skull images were performed, and we have seen imaging techniques going from very invasive (e.g., pneumo-cisternography, etc.) to becoming much less so (MR scanners), as well as advances in interventional techniques in parallel to the development of endovascular treatment for stroke and cerebro-vascular malformations. This has led neuroradiology to be a full specialty, offering diagnostic and therapeutic options for many diseases that were previously thought untreatable. This has led to a shift in positioning of the neuroradiologist in the field of clinical neurosciences to a full actor. As we have seen, neuroradiology, in collaboration with clinical scientists, has an enormous impact on the health of the brains of the entire population. Its role goes even beyond this, as it has the capacity and the obligation to reduce exposure to X-rays by using MRI and to use less or more adapted, less polluting contrast media [34]. These are not future wishes; these are things that can be performed now. Additionally, due to the relative hardship involved in the training and work of neuroradiology, neuroradiologists need to take care of their own health for the sake of others. Also, the use of new techniques, such as, on the one hand, high-end techniques such as ultra-high-field imaging with advanced techniques such as spectroscopy and diffusion tensor techniques, and on the other hand, low-field MR techniques that can provide fast, safe, and cheap population-wide screening will provide a full armamentarium to the discipline in order to detect what is pathological or not (with a clever implementation of artificial intelligence) and then go further into the investigation of cases that need a more precise work-up for treatment and follow-up. Additional fields of neuroimaging that have been underexplored by neuroradiology will also open up, such as those related to mental health.

9. Conclusions

Finally, due to its immense contribution to the health of the population by providing diagnostic and interventional help in a variety of life-threatening diseases, neuroradiology should be recognized by peer practitioners, the population, and politicians as a prime mover in the improvement of not just brain health but overall health.

10. Future Directions

Neuroscientists and neuroradiologists need to proactively engage with decision- and policymakers to make them understand the urgency of addressing brain health. Indeed, the brain is a precious but very fragile organ that needs protection to thrive. Additionally, neuroradiologists and neuroscientists should act both within their professional societies and within local and national political entities to make their voices heard by the entire population through educational efforts. Only then will neuroradiology fully help both the neurosciences and brain health to prosper [41]. This can be achieved by using more MR-derived techniques and also by using less irradiating angiography techniques, such as flat-panel techniques, and one-day MR angiography-based interventions may be feasible. It is thus necessary to move away from X-ray techniques for diagnostics and treatment to make these techniques safer for both patients and practitioners. Artificial intelligence techniques are already playing a role in helping the physician to detect lesions on the one hand and to better stratify them on another. Due to the vast increase in data due to the acquisition of more and more datasets of images in an increasing number of patients, it will be necessary to resort to using AI technologies. On the other hand, AI will help the referring physician to better choose the patients he is assigning to an examination. In the scanning process itself, AI already today plays a role by increasing the scanning speed of the machines. Then, once the images are processed, the AI algorithms will help detect relevant alterations in the datasets and help direct patient management. All of this will also impact the way that not just the neuroradiologists but all the involved physicians work. Neuroradiology itself may evolve, as we have seen it evolve from using encephalography to MRI imaging. Indeed, the specialty, in order to provide the services needed by the clinicians, the patients, and the population, must again show flexibility and acquire and master knowledge from the clinical, radiological, and data fields. In order to achieve this, neuroradiologists need to participate actively, along with clinical neuroscientists, in scientific clinical and political activities that promote the brain health of not just their patients but also of themselves and the population as a whole.