Researchers in Germany and the US have developed a new approach to magnetic resonance imaging (MRI) thermometry using encaged hyperpolarized xenon as a temperature sensor. The method allows absolute temperature mapping with an unprecedented accuracy of 0.1˚C at low and ultralow sensor concentrations.
The new technique, which has the potential to become a helpful tool in clinical diagnostics and therapy monitoring, is presented online in ChemPhysChem. According to Franz Schilling, now a researcher at the Technical University of Munich and lead author of the paper, the method benefits from all the advantages of MRI including its non-invasiveness and the ability to image in any scan orientation with good spatial and temporal resolution.
Many magnetic resonance parameters are inherently temperature-sensitive; for example, proton resonance frequency (PRF), diffusion coefficient or transverse and longitudinal relaxation times. The accuracy of many conventional thermometry methods such as PRF is however limited and although such techniques provide useful relative temperature results, MRI thermometry based on encapsulated hyperpolarized xenon appears to be a more promising technology for in vivo applications because it can be used to map absolute temperatures.
Hydrogen is the most frequently imaged nucleus in MRI, but any nucleus with a net nuclear spin can potentially be imaged, including xenon (129Xe). Such gaseous isotopes must be hyperpolarized before use as their net magnetization is too low to yield a good signal under normal conditions. Schilling and co-workers have introduced xenon sensors as a temperature contrast agent for MRI thermometry to gain both high accuracy and sensitivity. They have achieved this by hyperpolarization through spin exchange optical pumping, which increases the equilibrium net spin polarization by three to four orders of magnitude.
The new technique is based on the temperature-dependent chemical shift of hyperpolarized xenon in a cryptophane-A cage. This shift is linear with a slope of 0.29 ppm per °C, which is almost 30 times higher than that of the proton resonance frequency that is currently used for MRI thermometry. According to Schilling, this new direct mapping concept allows absolute temperature mapping with a previously unmatched accuracy of 0.1˚C at a sensor concentration of 150 µM. But the researchers have also demonstrated an indirect temperature detection technique, via chemical exchange saturation transfer of hyperpolarized xenon (Hyper-CEST, introduced previously by co-author Leif Schröder who currently works at the Leibniz Institute for Molecular Pharmacology in Berlin), which makes temperature mapping with nanomolar agent concentrations as low as 10 nM possible. “This absolute temperature imaging concept offers high temperature accuracy at ultralow agent concentrations”, Schilling says. The new sensors consist of three major components: a cryptophane-A cage for hosting the xenon atom, a linker, and a peptide for sufficient water solubility.
Author: Franz Schilling, Alexander Pines, Lawrence Berkeley National Laboratory, Berkeley (USA), http://www.lbl.gov/
Title: MRI Thermometry Based on Encapsulated Hyperpolarized Xenon
ChemPhysChem 2010, 11, No. 16, Permalink to the article: http://dx.doi.org/10.1002/cphc.201000507
Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care
Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses