Neuroinflammation
is implicated in the pathophysiology of a growing
number of human disorders, including multiple sclerosis, chronic pain,
traumatic brain injury, and amyotrophic lateral sclerosis. As a result,
interest in the development of novel methods to investigate neuroinflammatory
processes, for the purpose of diagnosis, development of new therapies,
and treatment monitoring, has surged over the past 15 years. Neuroimaging
offers a wide array of non- or minimally invasive techniques to characterize
neuroinflammatory processes. The intent of this Review is to provide
brief descriptions of currently available neuroimaging methods to
image neuroinflammation in the human central nervous system (CNS)
in vivo. Specifically, because of the relatively widespread accessibility
of equipment for nuclear imaging (positron emission tomography [PET];
single photon emission computed tomography [SPECT]) and magnetic resonance
imaging (MRI), we will focus on strategies utilizing these technologies.
We first provide a working definition of “neuroinflammation”
and then discuss available neuroimaging methods to study human neuroinflammatory
processes. Specifically, we will focus on neuroimaging methods that
target (1) the activation of CNS immunocompetent cells (e.g. imaging
of glial activation with TSPO tracer [11C]PBR28), (2) compromised
BBB (e.g. identification of MS lesions with gadolinium-enhanced MRI),
(3) CNS-infiltration of circulating immune cells (e.g. tracking monocyte
infiltration into brain parenchyma with iron oxide nanoparticles and
MRI), and (4) pathological consequences of neuroinflammation (e.g.
imaging apoptosis with [99mTc]Annexin V or iron accumulation
with T2* relaxometry). This Review provides an overview of state-of-the-art
techniques for imaging human neuroinflammation which have potential
to impact patient care in the foreseeable future.