The White Apos: American Governors on the Cordillera Central

https://digitalcommons.cedarville.edu/alum_books/1354/thumbnail.jp

Hyperpolarized carbon-carbon intermolecular multiple quantum coherences

Intermolecular multiple quantum coherences (iMQCs) can provide unique contrast with sub-voxel resolution. However, the characteristic growth rate of iMQCs mostly limits these effects to either hydrogen or hydrogen-coupled systems for thermally polarized samples. Hyperpolarization techniques such as dynamic nuclear polarization (DNP) allow for significant increases in the carbon signal (even more signal than that from hydrogen), making carbon iMQCs achievable. We present the first intermolecular multiple quantum signal between two carbon nuclei

Absolute temperature imaging using intermolecular multiple quantum MRI

Purpose: A review of MRI temperature imaging methods based on intermolecular multiple quantum coherences (iMQCs) is presented. Temperature imaging based on iMQCs can provide absolute temperature maps that circumvent the artefacts that other proton frequency shift techniques suffer from such as distortions to the detected temperature due to susceptibility changes and magnetic field inhomogeneities. Thermometry based on iMQCs is promising in high-fat tissues such as the breast, since it relies on the fat signal as an internal reference. This review covers the theoretical background of iMQCs, and the necessary adaptations for temperature imaging using iMQCs. Materials and methods: Data is presented from several papers on iMQC temperature imaging. These studies were done at 7T in both phantoms and in vivo. Results from phantoms of cream (homogeneous mixture of water and fat) are presented as well as in vivo temperature maps in obese mice. Results: Thermometry based on iMQCs offers the potential to provide temperature maps which are free of artefacts due to susceptibility and magnetic field inhomogeneities, and detect temperature on an absolute scale. Conclusions: The data presented in the papers reviewed highlights the promise of iMQC-based temperature imaging in fatty tissues such as the breast. The change in susceptibility of fat with temperature makes standard proton frequency shift methods (even with fat suppression) challenging and iMQC-based imaging offers an alternative approach

Optimized, unequal pulse spacing in multiple echo sequences improves refocusing in magnetic resonance

A recent quantum computing paper (G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007)) analytically derived optimal pulse spacings for a multiple spin echo sequence designed to remove decoherence in a two-level system coupled to a bath. The spacings in what has been called a "Uhrig dynamic decoupling (UDD) sequence" differ dramatically from the conventional, equal pulse spacing of a Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo sequence. The UDD sequence was derived for a model that is unrelated to magnetic resonance, but was recently shown theoretically to be more general. Here we show that the UDD sequence has theoretical advantages for magnetic resonance imaging of structured materials such as tissue, where diffusion in compartmentalized and microstructured environments leads to fluctuating fields on a range of different time scales. We also show experimentally, both in excised tissue and in a live mouse tumor model, that optimal UDD sequences produce different T2 -weighted contrast than do CPMG sequences with the same number of pulses and total delay, with substantial enhancements in most regions. This permits improved characterization of low-frequency spectral density functions in a wide range of applications

Increasing hyperpolarized spin lifetimes through true singlet eigenstates

The sensitivity limitations for magnetic resonance imaging of organic molecules have recently been addressed by hyperpolarization methods, which prepare excess nuclear spin polarization. This approach can increase sensitivity by orders of magnitude, but the enhanced signal relaxes away in tens of seconds, even in favorable cases. Here we show theoretically that singlet states between strongly coupled spins in molecules can be used to store and retrieve population in very-long-lived disconnected eigenstates, as long as the coupling between the spins substantially exceeds both the couplings to other spins and the resonance frequency difference between them. Experimentally, 2,3-carbon-13-labeled diacetyl has a disconnected eigenstate that can store population for minutes and is read out by hydration to make the two spins inequivalent