Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session H19: Focus Session: New Frontiers in Imaging IV |
Hide Abstracts |
Sponsoring Units: DCP Chair: Jeffrey Reimer, University of California, Berkeley Room: Colorado Convention Center 104 |
Tuesday, March 6, 2007 8:00AM - 8:36AM |
H19.00001: Molecular Dynamics Underlie the Nature of MRI Signals: The NMR Shutter-Speed Invited Speaker: Motions of the spin-bearing molecules can have profound effects on the very nature (the exponentiality) of the macroscopic NMR signal. Quantitative mechanistic protocols often involve varying the equilibrium molecular kinetics (usually by temperature~change) relative to the ``NMR time-scale'' (SS$^{-1})$, usually ill-defined as the absolute difference of resonance frequencies [$\vert \Delta \omega \vert $] in sites between which spins are exchanged. This holds true for the equilibrium water molecule exchange between tissue compartments and distinct populations. However, \textit{in vivo} studies must [by regulation] be isothermal, and the tissue $^{1}$H$_{2}$O MRI signals remain essentially isochronous [$\Delta \omega $ = 0]. In NMR, an equilibrium process is manifest in the context of its ``exchange condition.'' It only ``appears'' to be fast or slow by comparison of its actual rate~constant with its \textit{system} ``shutter{\-}speed'' (SS). [A~nonzero $\Delta \omega $ is the first, but not only, SS: its~dimension is reciprocal time.] The process kinetics can be measured only if its NMR condition is varied at least partway between the fast- and slow exchange limits. In an isothermal study with no catalyst, this can be accomplished only by varying the pertinent SS. An MRI contrast reagent (CR) increases the laboratory frame $^{1}$H$_{2}$O relaxation rate constant, R$_{i}$ [$\equiv $~(T$_{i})^{-1}$; i = 1,2]. For an isochronous exchange process, the SS is the intrinsic $\vert \Delta $R$_{i}\vert $ for the sites. In~quantitative dynamic-contrast-enhanced (DCE) studies, analytical pharmacokinetic modeling is accomplished on region-of-interest (ROI) or pixel by pixel $^{1}$H$_{2}$O signal time-courses following bolus CR injections. Accounting for the equilibrium transendothelial and transcytolemmal water interchange processes (a three-site exchange situation) is crucial for modeling accuracy: the relevant SS values vary during the CR bolus passage. This is so for DCE studies of cancer, multiple sclerosis, and myocardial blood flow variation. It is necessary for the successful discrimination of malignant and benign breast and prostate lesions. One can expect a SS for almost any NMR experiment. This includes diffusion weighted and rotating-frame longitudinal relaxation of\textit{ in vivo} $^{1}$H$_{2}$O signals. In~these latter cases, the pertinent SS can be manipulated solely by adjustment of pulse sequence parameters, leading to completely non-invasive protocols. [Preview Abstract] |
Tuesday, March 6, 2007 8:36AM - 8:48AM |
H19.00002: Human Regional Pulmonary Gas Exchange with Xenon Polarization Transfer (XTC) Iga Muradian, James Butler, Mirko Hrovat, George Topulos, Elizabeth Hersman, Iulian Ruset, Silviu Covrig, Eric Frederick, Stephen Ketel, F.W. Hersman, Samuel Patz Xenon Transfer Contrast (XTC) is an existing imaging method (Ruppert et al, Magn Reson Med, 51:676-687, 2004) that measures the fraction F of $^{129}$Xe magnetization that diffuses from alveolar gas spaces to septal parenchymal tissue in lungs in a specified exchange time. As previously implemented, XTC is a 2-breath method and has been demonstrated in anesthetized animals. To use XTC in humans and to avoid issues associated with obtaining identical gas volumes on subsequent breath-hold experiments as well as precise image registration in post-processing, a single breath XTC method was developed that acquires three consecutive gradient echo images in an 8s acquisition. We report here initial measurements of the mean and variance of F for 5 normal healthy subjects as well as 7 asymptomatic smokers. The experiments were performed at two lung volumes ($\sim $45 and 65{\%} of TLC). We found that both the mean and variance of F increased with smoking history. In comparison, standard pulmonary function tests such as DLCO FEV1 showed no correlation with smoking history. [Preview Abstract] |
Tuesday, March 6, 2007 8:48AM - 9:00AM |
H19.00003: ABSTRACT WITHDRAWN |
Tuesday, March 6, 2007 9:00AM - 9:12AM |
H19.00004: Human Pulmonary Diffusion Weighted Imaging at 0.2T with Hyperpolarized 129Xe Adrian Sindile, Iga Muradian, Mirko Hrovat, Christina Johnson, William Hersman, Sam Patz Unlike hyperpolarized 3He inhalations, which achieve a high degree of gas mixture homogeneity due to the higher diffusion constant, hyperpolarized 129Xe requires additional precautions to assure gas mixture homogeneity. A homogeneous concentration of Xe inside the human lungs is necessary to allow the use of ADC values as a reproducible measure of lung physiology and structure. To determine whether observed ADC differences are due to regional variations in Xe dilution, which would affect diffusitivity, we measured ADC as a function of a number of exhaling/rebreathing cycles (breaths). The results of our investigations into these differences will be presented. [Preview Abstract] |
Tuesday, March 6, 2007 9:12AM - 9:24AM |
H19.00005: Large Production of Hyperpolarized 129-Xe for MRI Applications Iulian Ruset, F.W. Hersman, Jan Distelbrink, Stephen Ketel, Silviu Covrig, Iga Muradian, Adrian Sindile Although 129-Xe was the first hyperpolarized gas to be used in MRI studies, the research community has focused on 3-He, mainly because of the larger quantities of hyperpolarized gas available. Xenon has advantages over helium, such as natural abundance, lower diffusion, and high solubility in blood. It presents a large frequency chemical shift when dissolved in blood, tissue, brain, or trapped in molecular cages. A new design of a high-flow low-pressure spin-exchange optical pumping Rb-Xe polarizer was recently demonstrated by our group. The concept of counterflowing the gas mixture against laser light and dividing the polarizing cell in three operational zones has resulted in an increase with over an order of magnitude in the output magnetization compared with previously reported polarizers. We were able to produce hyperpolarized xenon at 64{\%} polarization for 0.3 liters/hour flow rate and 22{\%} polarization at 6 liters/hour. We also demonstrated a new design of freezing and thawing hyperpolarized xenon with minimum losses. We will present the concept of the high-flow low-pressure counterflowing xenon polarizer, its performance, as well as new optical pumping laser technologies. We will discuss optimization plans for xenon polarizing systems based on experimental observed limitations and theoretical modeling. [Preview Abstract] |
Tuesday, March 6, 2007 9:24AM - 9:36AM |
H19.00006: Rapid Production of Hyperpolarized $^3$He Gas for MRI Benjamin C. Anger, Richard E. Jacob, Kevin R. Minard, Brian T. Saam Hyperpolarized (HP) $^3$He gas created via spin-exchange optical pumping (SEOP) is widely used as a signal source in MRI applications. One drawback to conventional SEOP is the time required for polarization. The process normally requires 10 - 20 hours to achieve 40-50\% polarization in enough gas ($\sim$1 L) for a single imaging experiment. Two recent advances in the physics of SEOP have led to dramatic enhancements in polarization efficiency: the use of spectrally narrowed diode-laser arrays and hybrid SEOP, which employs both potassium and rubidium as alkali-metal intermediaries. We have combined these techniques in constructing two polarizers, a prototype system at Utah and a more fully engineered system at PNNL. We report $>$60\% $^3$He polarization in 0.5 bar{\Large{$\cdot$}}L of gas in valved and refillable glass cells, achieved in under 4 h. With the apparatus described we are able to produce several liters of polarized $^3$He per day. [Preview Abstract] |
Tuesday, March 6, 2007 9:36AM - 10:12AM |
H19.00007: Double Quantum Filtered NMR Spectroscopy and Imaging Invited Speaker: As a result of the anisotropic motion of water molecules interacting with ordered biological tissues the proton-proton dipolar interaction and the deuteron quadrupolar interaction do not average to zero leaving some residual splittings. The technique of double quantum filtered (DQF) NMR capitalizes on this phenomenon, opening new possibilities to probe biological processes and to obtain a new kind of contrast in MRI. In the talk new applications of the DQF pulse sequences to the study of nerves, enabling the measurement of intercompartmental water exchange in sciatic and optic nerves, the study of the fiber architecture in cartilage under normal, compressed and diseased conditions and the imaging of tendons, enabling the monitoring their healing process following injury. [Preview Abstract] |
Tuesday, March 6, 2007 10:12AM - 10:24AM |
H19.00008: Hyperpolarized Krypton-83 as a MRI Contrast Agent Zackary Cleveland, Galina Pavlovskaya, Karl Stupic, John Repine, Thomas Meersmann Hyperpolarized krypton-83 (I = 9/2) yields NMR signal enhancements [1] of 1200 to 4500 times that of thermal equilibrium value depending on the composition of the optical pumping gas mixture. The quadrupolar relaxation of krypton-83 provides surface sensitive contrast in MRI [2] and yields information about surface hydrophobicity [3], surface-to-volume ratio, surface temperature, and surface hydration. These characteristics make hp krypton-83 MRI a promising technique for materials science applications and medical diagnosis. Experimental hp krypton-83 results in model systems with biomedically relevant coatings (e.g. lung surfactant and cigarette tar) are presented. Additionally, preliminary results from hp krypton-83 in excised rodent lungs are discussed. (1) ZI Cleveland, et al., Chem. Phys., 2006. 124(4) 044311. (2) GE Pavlovskaya, et al., Proc. Natl. Acad. Sci. U.S.A.,2005. 102: 18275-18279. (3) KF Stupic, et al., Solid State Nucl. Magn. Reson., 2006. 29: 79-84. [Preview Abstract] |
Tuesday, March 6, 2007 10:24AM - 10:36AM |
H19.00009: Introducing Hyperpolarized Xenon-131 Directly Detected by NMR Spectroscopy Karl Stupic, Zackary Cleveland, Galina Pavlovskaya, Thomas Meersmann Previously, high-field NMR and MRI applications of hyperpolarized (hp) noble gasses focused on the isotopes helium-3 (spin I = 1/2), xenon-129 (spin I = 1/2) [1], and more recently krypton-83 (spin I = 9/2) [2]. In this contribution, hp xenon-131 (spin I = 3/2) was generated by spin-exchange optical pumping and separated from the rubidium vapor for high field NMR detection at 14.1 T field strength. Xenon-131 is of particular interest because of its quadrupolar nature that can be utilized for the study of surfaces [3] and for the investigation of high magnetic field effects on the electronic structure of the noble gas atom [4]. In addition, this isotope is a useful probe for quadrupolar processes during gas transfer and during NMR/MRI detection. Experiments with xenon-131, including multiple quantum filtered NMR spectroscopy [3], provides insights into similar processes present in krypton-83 and its more complicated spin system [5]. [1] D. Raftery \textit{Ann. Rep. NMR Spec.}, \textbf{57}, 208 (2006). [2] G. Pavlovskaya, \textit{et al}., \textit{Pro. Natl. Acad. Sci. U.S.A.} \textbf{102}, 18275 (2005). [3] T. Meersmann \textit{et al.}, \textit{Phys. Rev. Lett. }\textbf{80}, 1398 (1998). [4] T. Meersmann and M. Haake, \textit{Phys. Rev. Lett.} \textbf{81}, 1211 (1998). [5] Z. Cleveland, \textit{et al.}, \textit{J. Chem. Phys.}\textbf{124}, 044312 (2006). [Preview Abstract] |
Tuesday, March 6, 2007 10:36AM - 10:48AM |
H19.00010: Spin relaxation in hyperpolarized krypton-83 and xenon-129 Thomas Meersmann, Zackary Cleveland, Karl Stupic, Galina Pavlovskaya The potential medical application of hyperpolarized (hp) krypton-83 (spin S = 9/2) [1] make a better insight into the NMR relaxation behavior of this isotope desirable, in particular since the relaxation limits the observed signal intensity but also provides a source for MRI contrast. The quadrupolar relaxation of krypton-83 is shown to be highly dependent on temperature, optical pumping gas mixture, the nature of surrounding surfaces and the applied magnetic field strength [2, 3]. The relaxation is mainly caused by quadrupolar interactions during brief surface adsorption periods of the krypton atoms onto the surrounding container walls. In contrast to xenon-129, interactions with paramagnetic impurities in the surface or with gas phase oxygen are not significant. 1) Pavlovskaya, et al. Proc. Natl. Acad. Sci. U.S.A.,2005. 102: 18275-18279; 2) Cleveland, Z.I., et al. J. Chem. Phys., 2006. 124(4) 044311; 3) Stupic, K.F et al. Solid State Nucl. Magn. Reson., 2006. 29: 79-84. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700