Hyperpolarized Xenon MR Imaging of the Brain
Exciting prospects for developing hyperpolarized xenon magnetic resonance imaging (HP 129
Xe MRI) for the
clinical assessment of brain anatomy and function are now on the horizon. The ultimate goal is to develop a new method that is practical
for clinical use that can be used in conjunction with proton MRI to diagnose and evaluate treatment of brain diseases, and to ascertain
information about normal human brain anatomy and function. Several characteristics make HP
Xe MRI exquisitely well suited for studies of brain anatomy and function.
• HP Xenon acts as a biochemical sensor
. Different chemical environments affect the resonance frequency (chemical shift) of
the HP 129
Xe spin, resulting in separated spectral peaks detectable by MR spectroscopy. Because HP 129
Xe presents one of
the largest NMR chemical shift ranges of all nuclei that demonstrate magnetic resonance, it is extremely sensitive to its
chemical environment, which may allow differentiation of diseased and normal tissue. Such shifts in resonance frequency can be
exploited in MR chemical shift imaging (CSI) to produce spatial images of the different frequencies. Thus, CSI allows an anatomical
map to be made of the separate spectral components, and thus the distinct brain tissue that they originate from.
• HP Xenon can detect oxygen concentration
. Both the relaxation time (T1 ) and chemical shift of HP 129
Xe are highly sensitive to the oxygen saturation of blood, making HP129
Xe MRI potentially useful for studies of functional brain activity and for determining areas of hypoxia following brain injury or stroke. In addition, HP129
Xe may be beneficial for imaging patients with brain disease or trauma as evidenced by recent findings showing xenon exerts neuroprotective effects against neurotoxic and ischemic damage.
• HP Xenon can yield absolute, quantitative measures of cerebral blood flow
. Because xenon is considered an ideal perfusion tracer, HP129
Xe MRI is ideally suited for studies of cerebral blood flow. The element xenon has proven its usefulness as a perfusion tracer; xenon enhanced computed tomography (CT) and single positron emission CT (SPECT) using 133
Xe have long been used to measure brain blood flow and perfusion. These methods have set the standard for measures of cerebral blood flow because they yield both an absolute and quantitative measurement of perfusion.
• HP Xenon brain images are not degraded by background signal
. HP 129
Xe gas is not inherent in biological tissue, and so produces no background signal, which in turn results in high contrast HP 129
Xe MR images of the brain.