Hyperpolarized3He microspheres as a novel vascular signal source for MRI

Chawla, Mark S.; Chen, X. Josette; Cofer, Gary P.; Hedlund, Laurence W.; Kerby, Matthew B.; Ottoboni, Thomas B.; Johnson, G. Allan

doi:10.1002/(sici)1522-2594(200003)43:3<440::aid-mrm16>3.0.co;2-m

Cited by 18 publications

(23 citation statements)

References 27 publications

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“…We hypothesize that with centric or half-Fourier phase encoding a higher flip angle can be used, with an inherent increase in SNR. This substantiates the qualitative observations reported by other groups that used centric ordering in morphologic imaging studies (17,19,20). Applications that will benefit from this approach include thin-slice 2D experiments, which requires a more precise knowledge of the slice integrity than that attainable using thick slices or the non-slice-selective projection approaches in the literature (4 -6,10,11).…”

Section: Discussionsupporting

confidence: 82%

“…Applications that will benefit from this approach include thin-slice 2D experiments, which requires a more precise knowledge of the slice integrity than that attainable using thick slices or the non-slice-selective projection approaches in the literature (4 -6,10,11). Centric-ordered strategies may be advantageous in experiments using 3 He gas at much lower volume concentrations, such as infusions of microsphere-encapsulated 3 He (19,26); studies using either lower levels of polarization or smaller volumes of polarized gas because of the technical limitations of gas polarization (27); and studies involving 129 Xe, with its weaker signal due to a lower level of polarization and smaller magnetic moment. A half-Fourier approach potentially offers an increased SNR at high flip angles when compared to full-Fourier sequential encoding, with less of a compromise in spatial resolution than would be experienced with full-Fourier centric encoding.…”

Section: Discussionmentioning

confidence: 99%

“…In a qualitative study, Zhao et al (17) compared SNR and the resolution of boundaries of images of sealed cells of hyperpolarized 129 Xe acquired with sequential and centric phase-encoding strategies. Chawla et al (19) made a similar qualitative comparison of the influence of phase-encoding strategies on the SNR of in vitro images of samples of 3 He encapsulated in microspheres. They observed an increase in SNR with centric phase encoding as compared to sequential encoding.…”

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confidence: 99%

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k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized ³He MRI: Spatial resolution and signal‐to‐noise ratio considerations

Wild

Paley

Viallon

et al. 2002

Magnetic Resonance in Med

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In this work some of the factors that can influence the signal-tonoise ratio (SNR) and spatial resolution in MR images of inhaled hyperpolarized gases are systematically addressed. In particular, the effects of RF depletion of longitudinal polarization and image gradient diffusion dephasing were assessed in terms of their contribution to a k-space filter. By means of theoretical simulations and a novel method of experimental validation using a variable transverse magnetization of the 1 H signal, systematic quantitative and qualitative investigations of the effects of k-space filtering intrinsic to imaging of hyperpolarized gas were made. A 2D gradient-echo image is considered for a range of flip angles with centric, sequential, and half-Fourier Cartesian phase-encoding strategies, and the results are assessed in terms of SNR and spatial resolution in the reconstructed images. Centric phase encoding was found to give the best SNR at higher flip angles, with a trade-off in spatial resolution compared to sequential phase encoding. A half-Fourier approach potentially offers increased SNR through the use of higher flip angles without compromising the spatial resolution, which is comparable to that achieved with sequential encoding. Magn Reson Med 47:687-695, 2002.

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Section: Discussionsupporting

confidence: 82%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized ³He MRI: Spatial resolution and signal‐to‐noise ratio considerations

Wild

Paley

Viallon

et al. 2002

Magnetic Resonance in Med

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“…Of course, the SSFP method is not restricted to gaseous xenon. Many other applications of hyperpolarized noble gases are referenced in the literature, particularly the use of 3 He in microspheres (13). Because the SSFP method offers both speed and accuracy, it is expected that this method will serve to characterize a large number of gaseous vectors.…”

Section: Discussionmentioning

confidence: 99%

Fast measurement of relaxation times by steady‐state free precession of ¹²⁹Xe in carrier agents for hyperpolarized noble gases

Oregioni

Parizel

Sousa

et al. 2003

Magnetic Resonance in Med

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Hyperpolarized gases (129 Xe and 3 He) are being used increasingly in both MRI and NMR spectroscopy studies. However, it has been shown that carrier agents are required to preserve the long relaxation times of gases in biological fluids. Optimized gas transport can be achieved through controlled T 1 and T 2 measurements of 129 Xe gas at equilibrium, using the steadystate free precession method (SSFP). The accuracy of the method was proven with the use of CuSO 4 -doped water samples and xenon dissolved in chloroform. The optimization of recently developed laser-polarized xenon techniques, which are being used increasingly in NMR spectroscopy (1) and MRI (2), requires that relaxation time measurements be obtained. Gaseous xenon initially was used for diffusion studies in the gas phase, and subsequently has been used to investigate porous materials or lungs. In the biomedical domain, most of the current studies involving xenon focus on its properties in blood and its use in cerebral perfusion measurements. For such applications, gaseous xenon must be implemented into a biocompatible vector, in which the Ostwald coefficient of xenon must be as high as possible. When the target organ is far from the injection point, the direct injection of the vector-xenon combination into the body offers two advantages: an increase in the concentration of hyperpolarized 129 Xe at the site of interest, and a persistence of magnetization owing to the longer relaxation times of 129 Xe in biocompatible delivery agents. The aim of this work was to measure 129 Xe relaxation times in order to optimize the transfer of hyperpolarized gas. The low signal of gases precludes the use of conventional relaxation time measurement methods. However, it should be noted that even with hyperpolarized gases there is a discrepancy in T 1 results, and that very few T 2 measurements were obtained. If 129 Xe is not hyperpolarized, the signal is too low to perform measurements under good conditions with a conventional method. We implemented the SSFP method to determine whether it could produce accurate and reproducible results.The SSFP sequence was originally used to increase the signal-to-noise ratio (SNR) of low-signal samples with long relaxation times (3). It was later used to determine the relaxation times of exotic nuclei in liquid solutions (4). More recently, SSFP has been used successfully with a gaseous mixture of xenon and O 2 (5). We proposed to test this technique for its ability to measure the relaxation times of thermally polarized xenon in biological carriers, before tackling its use in more delicate hyperpolarized gas applications. For this purpose, SSFP was first applied to a water sample in a 1 H NMR experiment. The high SNR in the water sample allowed us to test the theoretical description of the method. It was subsequently performed on a sample containing xenon in a chloroform solution. This enabled us to test the sequence on gas, under favorable conditions (the SNR was not too low, and the solution was almost homogeneous). Finally, the S...

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“…The Ostwald coefficient for xenon in pure blood is much lower, approximately 0.17 (93). For 3 He-gas encapsulated in microbubbles, the concentration depends on the concentration and size of the bubbles in the carrier suspension (12,17). The HP 13 C-nucleus is part of a water-soluble molecule, and the deliverable concentration is in this case only limited by the concentrations that can be reached during the polarization procedure (paper IV).…”

Section: Discussionmentioning

confidence: 99%

Contrast-enhanced magnetic resonance angiography

Jonas

2003

Acta Radiol

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Svensson J. Contrast-Enhanced Magnetic Resonance Angiography. Development and optimization of techniques for paramagnetic and hyperpolarized contrast media. Stockholm 2001. ISBN 91-628-5322-8. Contrast-enhanced magnetic resonance angiography (CE-MRA) is a diagnostic method for imaging of vascular structures based on nuclear magnetic resonance. Vascular enhancement is achieved by injection of a contrast medium (CM). Studies were performed using two different types of CM: conventional paramagnetic CM, and a new type of CM based on hyperpolarized (HP) nuclei.The effects of varying CM concentration with time during image acquisition were studied by means of computer simulations using two different models. It was shown that a rapid concentration variation during encoding of the central parts of k-space could result in signal loss and severe image artifacts. The results were confirmed qualitatively with phantom experiments.A postprocessing method was developed to address problems with simultaneous enhancement of arteries and veins in CE-MRA of the lower extremities. The method was based on the difference in flow-induced phase in the two vessel types. Evaluation of the method was performed with flow phantom measurements and with CE-MRA in two volunteers using standard pulse sequences. The flow-induced phase in the vessels of interest was sufficient to distinguish arteries from veins in the superior-inferior direction. Using this method, the venous enhancement could be extinguished.The possibility of using HP nuclei as CM for CE-MRA was evaluated. Signal expressions for a flow of HP CM imaged with a gradient echo sequence were derived. These signal expressions were confirmed in phantom experiments using HP 129 Xe dissolved in ethanol. Studies were also performed with a new CM based on HP 13 C. The CM had very long relaxation times (T 1,in vivo /T 2,in vivo % 38/1.3 s). The long relaxation times were utilized in imaging with a fully balanced steady-state free precession pulse sequence (trueFISP), where the optimal flip angle was found to be 1808. CE-MRA with the 13 C-based CM in rats resulted in images with high vascular SNR ($500).CE-MRA is a useful clinical tool for diagnosing vascular disease. With the development of new contrast media, based on hyperpolarized nuclei for example, there is a potential for further improvement in the signal levels that can be achieved, enabling a standard of imaging of vessels that is not possible today.

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Hyperpolarized3He microspheres as a novel vascular signal source for MRI

Cited by 18 publications

References 27 publications

k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized ³He MRI: Spatial resolution and signal‐to‐noise ratio considerations

k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized ³He MRI: Spatial resolution and signal‐to‐noise ratio considerations

Fast measurement of relaxation times by steady‐state free precession of ¹²⁹Xe in carrier agents for hyperpolarized noble gases

Contrast-enhanced magnetic resonance angiography

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Hyperpolarized3He microspheres as a novel vascular signal source for MRI

Cited by 18 publications

References 27 publications

k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized 3He MRI: Spatial resolution and signal‐to‐noise ratio considerations

k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized 3He MRI: Spatial resolution and signal‐to‐noise ratio considerations

Fast measurement of relaxation times by steady‐state free precession of 129Xe in carrier agents for hyperpolarized noble gases

Contrast-enhanced magnetic resonance angiography

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Product

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k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized ³He MRI: Spatial resolution and signal‐to‐noise ratio considerations

k‐Space filtering in 2D gradient‐echo breath‐hold hyperpolarized ³He MRI: Spatial resolution and signal‐to‐noise ratio considerations

Fast measurement of relaxation times by steady‐state free precession of ¹²⁹Xe in carrier agents for hyperpolarized noble gases