Search

Purpose: Sodium triple quantum (TQ) signal has been shown to be a valuable biomarker for cell viability. Despite its clinical potential, application of Sodium TQ signal is hindered by complex pulse sequences with long scan times. This study proposes a method to approximate the TQ signal using a single excitation pulse without phase cycling. Methods: The proposed method is based on a single excitation pulse and a comparison of the free induction decay (FID) with the integral of the FID combined with a shifting reconstruction window. The TQ signal is calculated from this FID only. As a proof of concept, the method was also combined with a multi‐echo UTE imaging sequence on a 9.4 T preclinical MRI scanner for the possibility of fast TQ MRI. Results: The extracted Sodium TQ signals of single‐pulse and spin echo FIDs were in close agreement with theory and TQ measurement by traditional three‐pulse sequence (TQ time proportional phase increment [TQTPPI)]. For 2%, 4%, and 6% agar samples, the absolute deviations of the maximum TQ signals between SE and theoretical (time proportional phase increment TQTPPI) TQ signals were less than 1.2% (2.4%), and relative deviations were less than 4.6% (6.8%). The impact of multi‐compartment systems and noise on the accuracy of the TQ signal was small for simulated data. The systematic error was <3.4% for a single quantum (SQ) SNR of 5 and at maximum <2.5% for a multi‐compartment system. The method also showed the potential of fast in vivo SQ and TQ imaging. Conclusion: Simultaneous SQ and TQ MRI using only a single‐pulse sequence and SQ time efficiency has been demonstrated. This may leverage the full potential of the Sodium TQ signal in clinical applications. [ABSTRACT FROM AUTHOR]

At ultrahigh magnetic field strengths ( B0 ≥ 7.0 T), potassium (39K) MRI might evolve into an interesting tool for biomedical research. However, 39K MRI is still challenging because of the low NMR sensitivity and short relaxation times. In this work, we demonstrated the feasibility of 39K MRI at 21.1 T, determined in vivo relaxation times of the rat head at 21.1 T, and compared 39K and sodium (23Na) relaxation times of model solutions containing different agarose gel concentrations at 7.0 and 21.1 T. 39K relaxation times were markedly shorter than those of 23Na. Compared with the lower field strength, 39K relaxation times were up to 1.9- ( T1), 1.4- ( T2S) and 1.9-fold ( T2L) longer at 21.1 T. The increase in the 23Na relaxation times was less pronounced (up to 1.2-fold). Mono-exponential fits of the 39K longitudinal relaxation time at 21.1 T revealed T1 = 14.2 ± 0.1 ms for the healthy rat head. The 39K transverse relaxation times were 1.8 ± 0.2 ms and 14.3 ± 0.3 ms for the short ( T2S) and long ( T2L) components, respectively. 23Na relaxation times were markedly longer ( T1 = 41.6 ± 0.4 ms; T2S = 4.9 ± 0.2 ms; T2L = 33.2 ± 0.2 ms). 39K MRI of the healthy rat head could be performed with a nominal spatial resolution of 1 × 1 × 1 mm3 within an acquisition time of 75 min. The increase in the relaxation times with magnetic field strength is beneficial for 23Na and 39K MRI at ultrahigh magnetic field strength. Our results demonstrate that 39K MRI at 21.1 T enables acceptable image quality for preclinical research. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

High magnetic fields expand our capability to use sodium MRI for biomedical applications. The central goal of this review is devoted to the unique features of sodium MRI in tumor animal models, mainly in glioma, performed at 9.4 and 21.1 T. The ability of sodium MRI to monitor tumor response to therapy was evaluated. It is noteworthy that sodium MRI can detect glioma response to chemotherapy earlier than diffusion MRI. Especially attractive is the ability of sodium MRI to predict tumor therapeutic resistance before therapy. The non-invasive prediction of tumor chemo-resistance by sodium MRI presents a potential to individualize strategies for cancer treatment. Specifics of sodium MRI and technical aspects of imaging are also presented. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study investigates the comparative changes in the sodium MRI signal and proton diffusion following treatment using a 9L rat glioma model to develop markers of earliest response to cancer therapy. Sodium MRI and proton diffusion mapping were performed on untreated ( n = 5) and chemotherapy 1,3-bis(2-chloroethyl)-1-nitrosourea-treated rats ( n = 5). Animals were scanned serially at 2- to 3-day intervals for up to 30 days following therapy. The time course of Na concentration in a tumor showed a dramatic increase in the treated brain tumor compared to the untreated tumor, which correlates in time with an increase in tumor water diffusion. The largest posttreatment increase in sodium signal occurred 7-9 days following treatment and correlated to the period of the greatest chemotherapy-induced cellular necrosis based on diffusion and histopathology. Both Na MRI and proton ADC mapping revealed early changes in tumor sodium content and cellularity. This study demonstrates the possibility of Na MRI to function as a biomarker for monitoring early tumor treatment and validates the use of monitoring changes in diffusion MRI values for assessing tumor cellularity. Magn Reson Med 53:85-92, 2005. © 2004 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

To evaluate noninvasive measures of gene expression and tumor response in a gene-dependent enzyme prodrug therapy (GDEPT), a bifunctional fusion gene between Saccharomyces cerevisiae cytosine deaminase (CD) and Haemophilus influenzae uracil phosphoribosyltransferase (UPRT) was constructed. CD deaminates 5-fluorocytosine (5FC) to 5-fluorouracil (5FU), and UPRT subsequently converts 5FU to fluorouridine monophosphate, and both of these reactions can be monitored noninvasively in vitro and in vivo using 19F magnetic resonance spectroscopy (MRS). Following transient transfection the CD–UPRT fusion protein exhibited both UPRT and CD enzymatic activities as documented by 19F MRS. In addition, an increase in CD activity and thermal stability was witnessed for the fusion protein compared to native CD. Stable expression of CD–UPRT in 9L glioma cells increased both 5FC and 5FU sensitivity in vitro compared to CD-expressing and wild-type 9L cells. Noninvasive 19F MRS of both CD and UPRT gene function in vivo demonstrated that in animals bearing CD-expressing tumors there was limited conversion of 5FC to 5FU with no measurable accumulation of cytotoxic fluorinated nucleotides (F-nucs). In contrast, CD–UPRT-expressing tumors had increased CD gene activity with a threefold higher intratumoral accumulation of 5FU and significant generation of F-nucs. Finally, CD–UPRT yielded increased efficacy in an orthotopic animal model of high-grade glioma. More importantly, early changes in cellular water mobility, which are felt to reflect cellular death, as measured by diffusion-weighted MRI, were predictive of both durable response and increased animal survival. These results demonstrate the increased efficacy of the CD–UPRT GDEPT compared to CD alone both biochemically and in a preclinical model and validate both 19F MRS and diffusion-weighted MRI as tools to assess gene function and therapeutic efficacy. [Copyright &y& Elsevier]

At ultrahigh magnetic field strengths (B0  ≥ 7.0 T), potassium ((39) K) MRI might evolve into an interesting tool for biomedical research. However, (39) K MRI is still challenging because of the low NMR sensitivity and short relaxation times. In this work, we demonstrated the feasibility of (39) K MRI at 21.1 T, determined in vivo relaxation times of the rat head at 21.1 T, and compared (39) K and sodium ((23) Na) relaxation times of model solutions containing different agarose gel concentrations at 7.0 and 21.1 T. (39) K relaxation times were markedly shorter than those of (23) Na. Compared with the lower field strength, (39) K relaxation times were up to 1.9- (T1 ), 1.4- (T2S ) and 1.9-fold (T2L ) longer at 21.1 T. The increase in the (23) Na relaxation times was less pronounced (up to 1.2-fold). Mono-exponential fits of the (39) K longitudinal relaxation time at 21.1 T revealed T1  = 14.2 ± 0.1 ms for the healthy rat head. The (39) K transverse relaxation times were 1.8 ± 0.2 ms and 14.3 ± 0.3 ms for the short (T2S ) and long (T2L ) components, respectively. (23) Na relaxation times were markedly longer (T1  = 41.6 ± 0.4 ms; T2S  = 4.9 ± 0.2 ms; T2L  = 33.2 ± 0.2 ms). (39) K MRI of the healthy rat head could be performed with a nominal spatial resolution of 1 × 1 × 1 mm(3) within an acquisition time of 75 min. The increase in the relaxation times with magnetic field strength is beneficial for (23) Na and (39) K MRI at ultrahigh magnetic field strength. Our results demonstrate that (39) K MRI at 21.1 T enables acceptable image quality for preclinical research. Copyright © 2016 John Wiley & Sons, Ltd., (Copyright © 2016 John Wiley & Sons, Ltd.)