Improved MRI Thermometer

Thermal Bio-mapping

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Courtesy FMP

Online –?? In a recent technical article* in ChemPhysChem entitled MRI Thermometry Based on Encapsulated Hyperpolarized Xenon , Franz Schilling and his co-workers from the USA and Germany described research work showing they could measure the temperature of an object using Magnetic Resonance Imaging (MRI)?? of polarized Xenon (Xe) atoms embedded in another medium.

The sensitivity of the measurement is nearly 30 times that of the sensitivity of protons in the water molecule. Thus, the method indicates significant potential for development embedded biosensors using tagged cells with inert Xenon tracers.

Below is the abstract of the article along with links to the full story at Wiley’s online library.

Abstract**

A new approach to MRI thermometry using encapsulated hyperpolarized xenon is demonstrated. The method 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 perceptibly higher than the shift of the proton resonance frequency of water (ca. 0.01?ppm?per ??C) that is currently used for MRI thermometry.

Using spectroscopic imaging techniques, we collected temperature maps of a phantom sample that could discriminate by direct NMR detection between temperature differences of 0.1???C at a sensor concentration of 150??M.Alternatively, the xenon-in-cage chemical shift was determined by indirect detection using saturation transfer techniques (Hyper-CEST) that allow detection of nanomolar agent concentrations.

Thermometry based on hyperpolarized xenon sensors improves the accuracy of currently available MRI thermometry methods, potentially giving rise to biomedical applications of biosensors functionalized for binding to specific target molecules.

Article first published online: 6 SEP 2010

* Schilling, F., Schr??der, L., Palaniappan, K., Zapf, S., Wemmer, D. and Pines, A. , MRI Thermometry Based on Encapsulated Hyperpolarized Xenon. ChemPhysChem, n/a. doi: 10.1002/cphc.201000507

** Slightly modified for easier reading online

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For more information on BiosensorImaging, visit: Hyper-CEST Detection Schemes at the FMP in Berlin, Germany, a member of the Leibniz-Association called Leibniz-Institut f??r Molekulare Pharmakologie. where:

We are currently developing sensitive magnetic resonance detection techniques for xenon biosensors. For this purpose, we are implementing an indirect detection schemes of the encapsulated xenon that takes advantage of the exchange of the noble gas between the free solution and the biosensor molecule: selective radiofrequency pulses label the biosensor magnetization component that is transferred to the intense solution peak by chemical exchange.

In addition, the work on Biosensors has prospects like:

Using Hyper-CEST, xenon MRI could become an important technique for molecular imaging (MI) and overcome the sensitivity problems of NMR that usually makes other techniques like positron emission tomography (PET) or single photon emission tomography (SPECT) the favourite detection methods in MI.

The ultimate goal is to establish a new kind of MRI approach based on Xe bisosensors tailored for different biomolecular targets. We are therefore working on on pairing various MRI encoding schemes with the Hyper-CEST sensitivity enhancement. Moreover, novel xenon biosensors for different biochemical targets will be tested for their CEST detection characteristics.

References:

This work was brought to our attention by David Bradley’s article, Noble heat mapping – Xenon plays role in new MRI thermometry.

A US Patent has been issued on the method of MRI Temperature measurement Methods for detecting and imaging a temperature of an object by nuclear magnetic resonance”, United States Patent 4558279, Publication Date: 12/10/1985. Other US Patents are also published that deal with applications of the method.