Prostate spectroscopy at 3 Tesla using two-dimensional S-PRESS

Sialylated milk oligosaccharides alter neurotransmitters and brain metabolites in piglets: an In vivo magnetic resonance spectroscopic (MRS) study

Background: Human milk contains high concentrations and diversity of sialylated oligosaccharides that have multifunctional health benefits, however, their potential role in optimizing neurodevelopment remains unknown.Objective: To investigate the effect of sialylated milk oligosaccharides (SMOS) intervention on neurotransmitters and brain metabolites in piglets.Methods: 3-day-old piglets were randomly allocated to one of three groups and fed either standard sow milk replacer (SMR) alone (n = 15), SMR supplemented with sialyllactose 9.5 g/kg (SL, n = 16) or a combination of SL and 6'-sialyllactosamine 9.5 g/kg (SL/SLN, n = 15) for 35 days. Brain spectra were acquired using a 3T Magnetic Resonance Spectroscopic (MRS) system.Results: SMOS fed piglets were observed to have significantly increased the absolute levels of myo-inositol (mIns) and glutamate + glutamine (Glx), in particular, the SL/SLN group. Similar findings were found in the relative amount of these metabolites calculated as ratios to creatine (Cr), choline (Cho) and N-acetylaspartate (NAA) respectively (P < .05). In addition, there were significant positive correlations of brain NAA, total NAA (TNAA), mIns, total Cho (TCho), total Cr (TCr), scyllo-Inositol (SI) and glutathione (Glth) with total white matter volume; Glu and SI with whole brain volume; and SI with whole brain weight respectively (P < .01). SLN and 3'SL intake were closely correlated with the levels of brain Glu, mlns and Glx in the treatment groups only (P < .01-.05).Conclusions: We provide in vivo evidences that milk SMOS can alter many important brain metabolites and neurotransmitters required for optimizing neurodevelopment in piglets, an animal model of human infants.

1D-spectral editing and 2D multispectral in vivo1H-MRS and 1H-MRSI - Methods and applications

This article reviews the methodological aspects of detecting low-abundant J-coupled metabolites via 1D spectral editing techniques and 2D nuclear magnetic resonance (NMR) methods applied in vivo, in humans, with a focus on the brain. A brief explanation of the basics of J-evolution will be followed by an introduction to 1D spectral editing techniques (e.g., J-difference editing, multiple quantum coherence filtering) and 2D-NMR methods (e.g., correlation spectroscopy, J-resolved spectroscopy). Established and recently developed methods will be discussed and the most commonly edited J-coupled metabolites (e.g., neurotransmitters, antioxidants, onco-markers, and markers for metabolic processes) will be briefly summarized along with their most important applications in neuroscience and clinical diagnosis.

ProFit revisited

PURPOSE

An enhanced version of the ProFit fitting tool was developed and validated to improve the quantification of two-dimensional JRPESS spectroscopic data.

METHODS

The proposed enhancements were achieved by flexible organization of prior knowledge, configurations for different situations, the inclusion of measured macromolecular baseline contribution, additional baseline splines and a model-free lineshape based on self-deconvolution. The new software was tested and tuned on simulated data and subsequently applied to in vivo intrasubject and intersubject data.

RESULTS

Fit results of simulated and acquired spectra show good overall quality suggesting the potential reliable detection of up to 18 metabolites on a 3T system yielding Cramer-Lower-Bounds below 20%.

CONCLUSION

The proposed enhanced version of ProFit together with two-dimensional J-resolved spectroscopy offers the opportunity to reliably detect a wide selection of important brain metabolites on 3T.

Two-dimensional J-resolved LASER and semi-LASER spectroscopy of human brain

PURPOSE

Two-dimensional J-resolved localized and semi-localized by adiabatic selective refocusing (LASER and semi-LASER) spectroscopy, named "J-resolved LASER" and "J-resolved semi-LASER", were introduced to suppress chemical shift artifacts, additional J-refocused artifactual peaks from spatially dependent J-coupling evolution, and sensitivity to radiofrequency (RF) field inhomogeneity.

METHODS

Three pairs of adiabatic pulses were employed for voxel localization in J-resolved LASER and two pairs in J-resolved semi-LASER. The first half of t1 period was inserted between the last pair of adiabatic pulses, which was proposed in this work to obtain two-dimensional adiabatic J-resolved spectra of human brain for the first time. Phantom and human experiments were performed to demonstrate their feasibility and advantages over conventional J-resolved spectroscopy (JPRESS).

RESULTS

Compared to JPRESS, J-resolved LASER or J-resolved semi-LASER exhibited significant suppression of chemical shift artifacts and additional J-refocused peaks from spatially dependent J-coupling evolution, and demonstrated insensitivity to the change of RF frequency offset over large bandwidth.

CONCLUSION

Experiments on phantoms and human brains verified the feasibility and strengths of two-dimensional adiabatic J-resolved spectroscopy at 3T. This technique is expected to advance the application of in vivo two-dimensional MR spectroscopy at 3T and higher field strengths for more reliable and accurate quantification of metabolites.

Improved efficiency on editing MRS of lactate and γ-aminobutyric acid by inclusion of frequency offset corrected inversion pulses at high fields

γ-Aminobutyric acid (GABA) and lactate are metabolites which are present in the brain. These metabolites can be indicators of psychiatric disorders or tumor hypoxia, respectively. The measurement of these weakly coupled spin systems can be performed using MRS editing techniques; however, at high field strength, this can be challenging. This is due to the low available B1 (+) field at high fields, which results in narrow-bandwidth refocusing pulses and, consequently, in large chemical shift displacement artifacts. In addition, as a result of the increased chemical shift displacement artifacts and chemical shift dispersion, the efficiency of the MRS method is reduced, even when using adiabatic refocusing pulses. To overcome this limitation, frequency offset corrected inversion (FOCI) pulses have been suggested as a mean to substantially increase the bandwidth of adiabatic pulses. In this study, a Mescher-Garwood semi-localization by adiabatic selection and refocusing (MEGA-sLASER) editing sequence with refocusing FOCI pulses is presented for the measurement of GABA and lactate in the human brain. Metabolite detection efficiencies were improved by 20% and 75% for GABA and lactate, respectively, when compared with editing techniques that employ adiabatic radiofrequency refocusing pulses. The highly efficient MEGA-sLASER sequence with refocusing FOCI pulses is an ideal and robust MRS editing technique for the measurement of weakly coupled metabolites at high field strengths.

Selective spectral modulation of strongly coupled spins with an echo top refocusing pulse in PRESS sequences

The double spin echo is the basis of the point resolved spectroscopy (PRESS) sequence. In this study we sought to investigate the effects of a broadband 180° pulse - incorporated in the PRESS sequence at the location of the first echo (gPRESS) - on the citrate resonances, chosen as a model of strongly coupled spin system. A significant signal modulation generated by the additional 180° pulse was predicted with simulations and observed experimentally in the citrate resonances. No effects were observed on the singlet resonance of glycine and the weakly coupled resonances of lactate. The phenomenon observed in gPRESS was attributed to the off-diagonal Hamiltonian elements responsible for a coherence transfer occurring throughout the evolution periods. The results of this study show that it is necessary to assess the effects of broadband 180° pulses on strongly coupled spin systems, since these pulses can selectively modify the spectral shape of strongly coupled resonances.

A decade in prostate cancer: from NMR to metabolomics

Over the past 30 years, continuous progress in the application of nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance spectroscopic imaging (MRSI) to the detection, diagnosis and characterization of human prostate cancer has turned what began as scientific curiosity into a useful clinical option. In vivo MRSI technology has been integrated into the daily care of prostate cancer patients, and innovations in ex vivo methods have helped to establish NMR-based prostate cancer metabolomics. Metabolomic and multimodality imaging could be the future of the prostate cancer clinic--particularly given the rationale that more accurate interrogation of a disease as complex as human prostate cancer is most likely to be achieved through paradigms involving multiple, instead of single and isolated, parameters. The research and clinical results achieved through in vivo MRSI and ex vivo NMR investigations during the first 11 years of the 21st century illustrate areas where these technologies can be best translated into clinical practice.

Low-power adiabatic sequences for in vivo localized two-dimensional chemical shift correlated MR spectroscopy

Novel low-power adiabatic sequences are demonstrated for in vivo localized two-dimensional correlated MR spectroscopy, such as correlated spectroscopy and total correlated spectroscopy. The design is based on three new elements for in vivo two-dimensional MRS: the use of gradient modulated constant adiabaticity GOIA-W(16,4) pulses for (i) localization (correlated spectroscopy and total correlated spectroscopy) and (ii) mixing (total correlated spectroscopy), and (iii) the use of longitudinal mixing (z-filter) for magnetization transfer during total correlated spectroscopy. GOIA-W(16,4) provides accurate signal localization, and more importantly, lowers the SAR for both total correlated spectroscopy mixing and localization. Longitudinal mixing improves considerably (fivefolds) the efficiency of total correlated spectroscopy transfer. These are markedly different from previous 1D editing total correlated spectroscopy sequences using spatially nonselective pulses and transverse mixing. Fully adiabatic (adiabatic mixing with adiabatic localization) and semiadiabatic (adiabatic mixing with nonadiabatic localization) methods for two-dimensional total correlated spectroscopy are compared. Results are presented for simulations, phantoms, and in vivo two-dimensional spectra from healthy volunteers and patients with brain tumors obtained on 3T clinical platforms equipped with standard hardware. To the best of our knowledge, this is the first demonstration of in vivo adiabatic two-dimensional total correlated spectroscopy and fully adiabatic two-dimensional correlated spectroscopy. It is expected that these methodological developments will advance the in vivo applicability of multi(spectrally)dimensional MRS to reliably identify metabolic biomarkers.

Echo-time independent signal modulations for strongly coupled systems in triple echo localization schemes: an extension of S-PRESS editing

The double spin-echo point resolved spectroscopy sequence (PRESS) is a widely used method and standard in clinical MR spectroscopy. Existence of important J-modulations at constant echo times, depending on the temporal delays between the rf-pulses, have been demonstrated recently for strongly coupled spin systems and were exploited for difference editing, removing singlets from the spectrum (strong-coupling PRESS, S-PRESS). A drawback of this method for in vivo applications is that large signal modulations needed for difference editing occur only at relatively long echo times. In this work we demonstrate that, by simply adding a third refocusing pulse (3S-PRESS), difference editing becomes possible at substantially shorter echo times while, as applied to citrate, more favorable lineshapes can be obtained. For the example of an AB system an analytical description of the MR signal, obtained with this triple refocusing sequence (3S-PRESS), is provided.

Difference spectroscopy using PRESS asymmetry: application to glutamate, glutamine, and myo-inositol

A simple, clinically viable technique utilizing PRESS and strong coupling properties is presented for discrimination of coupled brain metabolites. The method relies on signal variation due to alteration of inter-echo timings (PRESS asymmetry) while maintaining a constant total echo time. Spin response of singlets and weakly coupled spins is unchanged due to PRESS asymmetry, allowing difference spectroscopy to detect unobstructed strongly coupled resonances. No changes to the standard PRESS sequence are required except variation of inter-echo timings. The procedure is illustrated for the separate detection of glutamate from glutamine and the detection of myo-inositol in simulation, phantom, and in vivo experiments at 4.7 T. The subtraction yields calculated from the simulation were 53% for glutamate and 75% for myo-inositol, and a resultant contribution of 96% glutamate to the total glutamate/glutamine multiplet in the 2.04-2.14 ppm range. To extend the treatment to other field strengths and metabolites, an analytical approximation based on a strongly coupled AB system was used to model individual spin groups. Subtraction spectroscopy yields for different combinations of coupling parameters were calculated for the detection of various strongly coupled metabolites at common clinical field strengths. The approximation also predicts adequate glutamate/glutamine discrimination at 3.0 T using the difference spectroscopy method.

Diffusion-weighted imaging with apparent diffusion coefficient mapping and spectroscopy in prostate cancer

Prostate cancer is a major health problem, and the exploration of noninvasive imaging methods that have the potential to improve specificity while maintaining high sensitivity is still critically needed. Tissue changes induced by tumor growth can be visualized by magnetic resonance imaging (MRI) methods. Current MRI methods include conventional T2-weighted imaging, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping and magnetic resonance spectroscopy (MRS). Techniques such as DWI/ADC provide functional information about the behavior of water molecules in tissue; MRS can provide biochemical information about the presence or absence of certain metabolites, such as choline, creatine, and citrate. Finally, vascular parameters can be investigated using dynamic contrast-enhanced MRI. Moreover, with whole-body MRI and DWI, metastatic disease can be evaluated in 1 session and may provide a way to monitor treatment. Therefore, when combining these various methods, a multiparametric data set can be built to assist in the detection, localization, assessment of prostate cancer aggressiveness, and tumor staging. Such a comprehensive approach offers more power to evaluate prostate disease than any single measure alone. In this article, we focus on the role of DWI/ADC and MRS in the detection and characterization using both in vivo and ex vivo imaging of prostate pathology.

Elliptical magnetic resonance spectroscopic imaging with GRAPPA for imaging brain tumors at 3 T

Magnetic Resonance Spectroscopic Imaging (MRSI) is a technique for imaging spatial variation of metabolites and has been very useful in characterizing biochemical changes associated with disease as well as response to therapy in malignant pathologies. This work presents a self-calibrated undersampling to accelerate 3D elliptical MRSI and an extrapolation-reconstruction algorithm based on the GRAPPA method. The accelerated MRSI technique was tested in three volunteers and five brain tumor patients. Acceleration allowed larger spatial coverage and consequently, less lipid contamination in spectra, compared to fully sampled acquisition within the same scantime. Metabolite concentrations measured from the accelerated acquisitions were in good agreement with measurements obtained from fully sampled MRSI scans.

Quantitative J-resolved prostate spectroscopy using two-dimensional prior-knowledge fitting

Two-dimensional (2D) prior-knowledge fitting (ProFit) was adapted and applied for the quantification of J-resolved (JPRESS) spectra acquired at a field strength of 3T from the human prostate in vivo. In contrast to methods based on simple line fitting and peak integration, commonly applied for metabolite quantification in the prostate, ProFit yields metabolite concentration ratios that are independent of sequence and field strength, since it is based on the linear combination of 2D basis spectra. It is demonstrated that ProFit benefits from the increased information content and reduced baseline distortion in JPRESS prostate spectra, in particular for the quantification of coupled metabolites like citrate (Cit), spermine (Spm), and myo-inositol (mI). The method is validated with 10 repetitive prostate measurements on the same subject. Furthermore, a study carried out on 10 healthy subjects shows that the six prostate metabolites creatine (Cr), total choline (Cho), Cit, Spm, mI, and scyllo-inositol (sI) can be reliably detected in vivo, some of which--especially total Cho and Cit--have proven to be useful markers for the detection of prostate cancer.

Two-dimensional MR spectroscopy of healthy and cancerous prostates in vivo

OBJECTIVES

A major goal of this article is to summarize the current status of evaluating prostate metabolites non-invasively using spatially resolved two-dimensional (2D) MR Spectroscopy (MRS).

MATERIALS AND METHODS

Due to various technical challenges, the spatially resolved versions of 2D MRS techniques are currently going through the developmental stage. During the last decade, four different versions of 2D MRS sequences have been successfully implemented on 3T and 1.5T MRI scanners manufactured by three different vendors. These sequences include half and maximum echo sampled J-resolved spectroscopy (JPRESS), S-PRESS and L-COSY, which are single volume localizing sequences, and the multi-voxel based JPRESS sequence.

RESULTS

Even though greater than 1ml voxels have been used, preliminary evaluations of 2D JPRESS, S-PRESS and L-COSY sequences have demonstrated unambiguous detection of citrate, creatine, choline, spermine and more metabolites in human prostates. ProFIT-based quantitation of JPRESS and L-COSY data clearly shows the superiority of 2D MRS over conventional one-dimensional (1D) MRS and more than six metabolites have been successfully quantified. These sequences have been evaluated in a small group of prostate pathologies and pilot investigations using these sequences show promising results in prostate pathologies.

CONCLUSION

Implementation of the state-of-the-art 2D MRS techniques and preliminary evaluation in prostate pathologies are discussed in this review. Even though these techniques are going through developmental and early testing phases, it is evident that 2D MRS can be easily added on to any clinical Magnetic Resonance Imaging (MRI) protocol to non-invasively record the biochemical contents of the prostate.

MR imaging of the prostate: 1.5T versus 3T

Over the past several years, evidence supporting the use of MR imaging in the evaluation of prostate cancer has grown. Almost all this work has been performed at 1.5T. The gradual introduction of 3T scanners into clinical practice provides a potential opportunity to improve the quality and usefulness of prostate imaging. Increased signal to noise allows for imaging at higher resolution, higher temporal resolution, or higher bandwidth. Although this may improve the quality of conventional T2-weighted prostate imaging, which has been the standard sequence for detecting and localizing prostate cancer for years, the real potential for improvement at 3T involves more advanced techniques, such as spectroscopy, diffusion-weighted imaging, dynamic contrast imaging, and susceptibility imaging. This review presents the current data on 3T MR imaging of the prostate as well as the authors' impressions based on their experience at Yale-New Haven Hospital.

Implementation and validation of localized constant-time correlated spectroscopy (LCT-COSY) on a clinical 3T MRI scanner for investigation of muscle metabolism

PURPOSE

To implement and evaluate a novel single-volume two-dimensional localized constant-time-based correlated spectroscopy (2D LCT-COSY) sequence on a clinical 3T MR scanner. This sequence exhibits homonuclear decoupling along the F1 dimension, leading to improved spectral resolution compared to that of non-constant-time localized correlated spectroscopy (L-COSY).

MATERIALS AND METHODS

A GE 3T MR scanner equipped with a quadrature transmit and receive extremity coil was used in this study. The 2D LCT-COSY sequence was programmed using General Electric's EPIC compiler. Simulations for a two-spin 1/2 system were performed using GAMMA libraries to evaluate the theoretical performance of the sequences, and were also compared with corresponding phantom experiments using trans-cinnamic acid. Finally, spectra were acquired from the soleus muscle of healthy volunteers in order to evaluate performance in vivo.

RESULTS

Simulations and experimental results confirmed the improved spectral resolution of LCT-COSY over L-COSY, as well as its homonuclear decoupling performance. The behavior of resonance amplitudes as a function of evolution time in the experiment also was appropriately reflected by the simulation. Corresponding results were obtained for the in vivo muscle spectra, in which separation of overlapping olefinic and allylic methylene protons from the intra- and extramyocellular lipids (IMCL and EMCL, respectively) was achieved.

CONCLUSION

Simulations and experimental results in vitro and in vivo demonstrate the strengths of LCT-COSY. This technique can be implemented on systems of any field strength, and has the potential to separate overlapping metabolites in tissue when employed on high-field clinical MRI scanners equipped for proton spectroscopy.

Body and Cardiovascular MR Imaging at 3.0 T

Potential advantages of magnetic resonance (MR) imaging at 3 T include higher signal-to-noise ratios, better image contrast, particularly in gadolinium-enhanced applications, and better spectral separation for spectroscopic applications. In terms of clinical imaging, these advantages can mean higher-spatial-resolution images, faster imaging, and improved MR spectroscopy. However, achieving superior imaging and spectroscopic quality at 3 T can be challenging. This review discusses many of the problems encountered in body and cardiovascular MR imaging at 3 T, such as increased susceptibility, B1 field inhomogeneity, and increased specific absorption rate. The article also considers solutions that are being pursued, such as parallel imaging, variable-rate selective excitation, and variable flip angle sequences. A review of the most commonly used pulse sequences provides practical tips on how these can be optimized for 3-T imaging. In the coming few years, substantial improvements in 3-T technology for clinical imaging and spectroscopy will undoubtedly be seen. An understanding of the basic principles on which these developments are based will help radiologists translate the advances into better imaging studies and, ultimately, better patient care.