Synopsis
This presentation will review selected new
techniques and applications for the imaging of human brain tumors, from the
point of view of the MR physicist. A particular emphasis will be on metabolic
MR neuroimaging techniques, including chemical exchange saturation transfer
methods. The challenges involved in developing a new MR imaging technique for
clinical use in humans will be considered.Abstract
While the neuroimaging of brain tumors has been revolutionized since
the advent of MRI, clinical impact in terms of improved overall survival has
been limited, in large part due to their aggressive biology (particularly of
high-grade tumors) and limited treatment options. Nevertheless, new treatments
are being developed, and imaging plays an important role in the diagnosis and
selection of patients for treatment, and following response to treatment.
Traditional, anatomical MR sequences (with and without administration
of Gd-based contrast agents) are renowned for their exquisite sensitivity in
detecting tumors in the central nervous system; however, their relative lack of
specificity is well-known; grading of tumors, distinguishing tumor infiltration
from edema, distinguishing tumor regrowth from radiation necrosis
(‘pseudo-response’ and ‘pseudo-progression’) are all areas where conventional
MRI is known to have significant limitations. Many more advanced functional and
physiological MR techniques, such as diffusion MRI, perfusion MR (either based
on Gd-bolus dynamic-susceptibility contrast (DSC) methods, or arterial
spin-labeling (ASL)), MR spectroscopic imaging (MRSI) all show promise in these
areas, but are not yet widely used for these purposes outside of specialist
academic medical centers. Chemical-exchange (CEST) based MRI measurements have
also shown promise for characterizing brain tumors non-invasively, particularly
the so-called amide-proton-transfer (APT) MRI. Other potential tumor markers
have also recently emerged, such as the onco-metabolite 2-hydroxyglutarate
(2-HG), or (in preclinical models) the use of hyper-polarized 13C compounds
such as pyruvate. However, clinical application of these methods is still at an
early stage.
This presentation will review some of these techniques and
applications, and will consider, from the physicists point of view, some of the
many challenges encountered in taking a new imaging technique from its
demonstration in preclinical models, through development in humans, to clinical
trials, regulatory approval and integration into clinical practice.
Acknowledgements
Some of the material to be presented in this lecture was prepared by Dr Jinyuan Zhou and Dr Peter van Zijl.References
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