Synopsis

Keywords: Image acquisition: Quantification, Neuro: Brain, Image acquisition: Multiparametric

In addition to the previous talks, this lecture is devoted to an overview of quantitative MRI methods in neuroimaging in the scope of personalized medicine. Advanced techniques such as MR elastography (MRE), chemical exchange saturation transfer (CEST), magnetic resonance spectroscopy (MRS), arterial spin labeling (ASL), dynamic contrast-enhanced (DCE) imaging, and X-nuclei imaging will be addressed. Measuring tissue stiffness, characterizing tissue content and organization, mapping metabolic state or assessing tissue perfusion are among information MRI can provide today. This comprehensive overview will highlight the potential of quantitative MRI in personalized healthcare for neurological disorders.

Abstract

Multi-parametric quantitative MRI methods have emerged as powerful imaging techniques for a better understanding and diagnosis of diseases, thus improving personalized medicine. This lecture provides a structured panorama of key techniques, including magnetic resonance elastography (MRE), chemical exchange saturation transfer (CEST), magnetic resonance spectroscopy (MRS), arterial spin labeling (ASL), dynamic contrast-enhanced (DCE) imaging, and X-nuclei imaging. The principle of each technique is briefly described. The quantified parameters are discussed and their relevance in the context of specific neurological pathologies are presented.
MRE is a non-invasive technique designed to measure tissue stiffness and providing crucial insights into the mechanical properties of the brain tissues. Applying external mechanical vibrations synchronized with motion encoding gradients, the wave propagation can be captured and then processed to quantify shear stiffness. This parameter has proven to be valuable in neurodegenerative diseases, stroke, or traumatic brain injuries, where alterations in tissue biomechanical properties appears (Streitberger, 2012). It is a potential biomarker of pathological changes (Bunevicius, 2020). MRE requires specific hardware and processing that still need to be improved and standardized.
CEST imaging exploits the exchange of protons between water and other molecules, offering a unique method to study molecular dynamics. By selectively saturating the resonances of specific compounds, such as proteins or metabolites, CEST enables the quantification of their concentration and chemical exchange rates (Cai, 2012). This method holds promise in characterizing tumors, as changes in cellular composition and metabolism can be indicative of malignancy and personalized treatment strategies guidance.
MRS provides insights into the biochemical composition of tissues by measuring the resonance frequencies of specific nuclei (Ladd, 2018). Commonly applied to study brain metabolites like N-acetyl-aspartate, choline, and creatine, MRS allows for the quantification of metabolite concentrations. In neuro-oncology, MRS aids in differentiating tumor types and assessing treatment response, driving tailored therapeutic approaches based on the metabolic profile of individual patients. Neurodegeneration and neuroinflammation can also be characterized with MRS.
ASL is a perfusion imaging technique based on the magnetic labeling of arterial blood as an endogenous contrast agent. By quantifying cerebral blood flow (CBF), ASL provides critical information about tissue perfusion (Alsop, 2015). This method proves valuable in neurovascular diseases, such as ischemic stroke, where assessing regional perfusion abnormalities aids in treatment decision-making, including the identification of viable tissue for reperfusion therapy.
DCE imaging involves the administration of contrast agents to assess tissue perfusion and microvascular permeability (Yablonskiy, 2013). By tracking dynamic distribution of the contrast agent, DCE imaging gives access to blood volume and permeability. In neuro-oncology, DCE imaging aids in tumor characterization, grading and monitoring treatment response helping in driving therapeutic strategies based on vascular properties of individual tumors.
X-nuclei imaging involves the utilization of non-proton nuclei, such as sodium or phosphorus, for imaging purposes. X-nuclei imaging provides information about cellular function, energy metabolism, and ion homeostasis (Hu, 2020). In neurological disorders such as multiple sclerosis, alterations in sodium concentration are indicative of tissue inflammation and demyelination (Shah, 2016), making sodium imaging a valuable tool for disease characterization and treatment monitoring. Nevertheless, it is still limited to few centers equipped with specific X-Nuclei chain.
In conclusion, the exploration of multi-parametric quantitative MRI methods underscores their major role in neuroimaging toward personalized medicine. Each technique offers unique insights into different aspects of neurological pathophysiology, enabling tailored approaches to diagnosis, prognosis and treatment. The integration of these quantitative methods into clinical practice could change the management of neurological disorders, paving the way to an era of truly personalized and precision medicine.