Spectroscopic Imaging Sequence Research Articles

Adiabatic multi‐echo 31P spectroscopic imaging (AMESING) at 7 T for the measurement of transverse relaxation times and regaining of sensitivity in tissues with short T2* values

An adiabatic multi-echo spectroscopic imaging (AMESING) sequence, used for (31) P MRSI, with spherical k-space sampling and compensated phase-encoding gradients, was implemented on a whole-body 7-T MR system. One free induction decay (FID) and up to five symmetric echoes can be acquired with this sequence. In tissues with low T2 and high T2 , this can theoretically lead to a potential maximum signal-to-noise ratio (SNR) increase of almost a factor of three, compared with a conventional FID acquisition with Ernst-angle excitation. However, with T2 values being, in practice, ≤400 ms, a maximum enhancement of approximately two compared with low flip Ernst-angle excitation should be feasible. The multi-echo sequence enables the determination of localized T2 values, and was validated with (31) P three-dimensional MRSI on the calf muscle and breast of a healthy volunteer, and subsequently applied in a patient with breast cancer. The T2 values of phosphocreatine, phosphodiesters (PDE) and inorganic phosphate in calf muscle were 193 ± 5 ms, 375 ± 44 ms and 96 ± 10 ms, respectively, and the apparent T2 value of γ-ATP was 25 ± 6 ms. A T2 value of 136 ± 15 ms for inorganic phosphate was measured in glandular breast tissue of a healthy volunteer. The T2 values of phosphomonoesters (PME) and PDE in breast cancer tissue (ductulolobular carcinoma) ranged between 170 and 210 ms, and the PME to PDE ratios were calculated to be phosphoethanolamine/glycerophosphoethanolamine = 2.7, phosphocholine/glycerophosphocholine = 1.8 and PME/PDE = 2.3. Considering the relatively short T2 values of the metabolites in breast tissue at 7 T, the echo spacing can be short without compromising spectral resolution, whilst maximizing the sensitivity.

Whole-brain magnetic resonance spectroscopic imaging measures are related to disability in ALS.

To demonstrate the sensitivity of a recently developed whole-brain magnetic resonance spectroscopic imaging (MRSI) sequence to cerebral pathology and disability in amyotrophic lateral sclerosis (ALS), and compare with measures derived from diffusion tensor imaging. Whole-brain MRSI and diffusion tensor imaging were undertaken in 13 patients and 14 age-similar healthy controls. Mean N-acetylaspartate (NAA), fractional anisotropy, and mean diffusivity were extracted from the corticospinal tract, compared between groups, and then in relation to disability in the patient group. Significant reductions in NAA were found along the course of the corticospinal tracts on whole-brain MRSI. There were also significant changes in fractional anisotropy (decreased) and mean diffusivity (increased) in the patient group, but only NAA showed a significant relationship with disability (r = 0.65, p = 0.01). Whole-brain MRSI has potential as a quantifiable neuroimaging marker of disability in ALS. It offers renewed hope for a neuroimaging outcome measure with the potential for harmonization across multiple sites in the context of a therapeutic trial.

In vivo 3D spatial/1D spectral imaging by spatiotemporal encoding: A new single‐shot experimental and processing approach

A novel method for acquiring and processing quality multislice spectroscopically resolved 2D images in a single shot is introduced and illustrated. By contrast to the majority of single-scan spectroscopic imaging sequences developed so far, the method here discussed is not based on the acquisition of echo planar data in the k/t-space, but rather on the use of recently proposed spatiotemporal encoding methods. These techniques provide a robust alternative to classical techniques, as they can scan two spatial plus one spectral dimension by oscillating a single imaging gradient. This work demonstrates that the use of extended spectral/spatial super-resolution algorithms coupled to new experimental spatiotemporal encoding formulations based on swept inversions rather than on chirped excitations can lead to novel spatiotemporal encoding-based tools for resolving complex multisliced 2D images according to the chemical shifts in subsecond experiments. A number of phantom-based models were explored to clarify the relative merits of this technique and estimate its sensitivity performance. In vivo results of fat and water separation on abdominal imaging of mice at 7 T and on human breast imaging at 3 T are presented.

On the utility of spectroscopic imaging as a tool for generating geometrically accurate MR images and parameter maps in the presence of field inhomogeneities and chemical shift effects

Lack of spatial accuracy is a recognized problem in magnetic resonance imaging (MRI) which severely detracts from its value as a stand-alone modality for applications that put high demands on geometric fidelity, such as radiotherapy treatment planning and stereotactic neurosurgery. In this paper, we illustrate the potential and discuss the limitations of spectroscopic imaging as a tool for generating purely phase-encoded MR images and parameter maps that preserve the geometry of an object and allow localization of object features in world coordinates.Experiments were done on a clinical system with standard facilities for imaging and spectroscopy. Images were acquired with a regular spin echo sequence and a corresponding spectroscopic imaging sequence. In the latter, successive samples of the acquired echo were used for the reconstruction of a series of evenly spaced images in the time and frequency domain. Experiments were done with a spatial linearity phantom and a series of test objects representing a wide range of susceptibility- and chemical-shift-induced off-resonance conditions.In contrast to regular spin echo imaging, spectroscopic imaging was shown to be immune to off-resonance effects, such as those caused by field inhomogeneity, susceptibility, chemical shift, f0 offset and field drift, and to yield geometrically accurate images and parameter maps that allowed object structures to be localized in world coordinates.From these illustrative examples and a discussion of the limitations of purely phase-encoded imaging techniques, it is concluded that spectroscopic imaging offers a fundamental solution to the geometric deficiencies of MRI which may evolve toward a practical solution when full advantage will be taken of current developments with regard to scan time reduction. This perspective is backed up by a demonstration of the significant scan time reduction that may be achieved by the use of compressed sensing for a simple phantom.

Fully adiabatic 31P 2D‐CSI with reduced chemical shift displacement error at 7 T — GOIA‐1D‐ISIS/2D‐CSI

A fully adiabatic phosphorus (31P) two-dimensional (2D) chemical shift spectroscopic imaging sequence with reduced chemical shift displacement error for 7 T, based on 1D-image-selected in vivo spectroscopy, combined with 2D-chemical shift spectroscopic imaging selection, was developed. Slice-selective excitation was achieved by a spatially selective broadband GOIA-W(16,4) inversion pulse with an interleaved subtraction scheme before nonselective adiabatic excitation, and followed by 2D phase encoding. The use of GOIA-W(16,4) pulses (bandwidth 4.3-21.6 kHz for 10-50 mm slices) reduced the chemical shift displacement error in the slice direction ∼1.5-7.7 fold, compared to conventional 2D-chemical shift spectroscopic imaging with Sinc3 selective pulses (2.8 kHz). This reduction was experimentally demonstrated with measurements of an MR spectroscopy localization phantom and with experimental evaluation of pulse profiles. In vivo experiments in clinically acceptable measurement times were demonstrated in the calf muscle (nominal voxel volume, 5.65 ml in 6 min 53 s), brain (10 ml, 6 min 32 s), and liver (8.33 ml, 8 min 14 s) of healthy volunteers at 7 T. High reproducibility was found in the calf muscle at 7 T. In combination with adiabatic excitation, this sequence is insensitive to the B1 inhomogeneities associated with surface coils. This sequence, which is termed GOIA-1D-ISIS/2D-CSI (goISICS), has the potential to be applied in both clinical research and in the clinical routine.

Application of compressed sensing to multidimensional spectroscopic imaging in human prostate

The application of compressed sensing is demonstrated in a recently implemented four-dimensional echo-planar based J-resolved spectroscopic imaging sequence combining two spatial and two spectral dimensions. The echo-planar readout simultaneously acquires one spectral and one spatial dimension. Therefore, the compressed sensing undersampling is performed along the indirectly acquired spatial and spectral dimensions, and the reconstruction is performed using the split Bregman algorithm, an efficient TV-minimization solver. The four-dimensional echo-planar-based J-resolved spectroscopic imaging data acquired in a prostate phantom containing metabolites at physiological concentrations are accurately reconstructed with as little as 20% of the original data. Experimental data acquired in six healthy prostates using the external body matrix "receive" coil on a 3T magnetic resonance imaging scanner are reconstructed with acquisitions using only 25% of the Nyquist-Shannon required amount of data, indicating the potential for a 4-fold acceleration factor in vivo, bringing the required scan time for multidimensional magnetic resonance spectroscopic imaging within clinical feasibility.

Spectral decomposition of susceptibility artifacts for spectral-spatial radiofrequency pulse design.

Susceptibility induced signal loss is a limitation in gradient echo functional MRI. The through-plane artifact in axial slices is particularly problematic due to the inferior position of air cavities in the brain. Spectral-spatial radiofrequency pulses have recently been shown to reduce signal loss in a single excitation. The pulses were successfully demonstrated assuming a linear relationship between susceptibility gradient and frequency, however, the exact frequency and spatial distribution of the susceptibility gradient in the brain is unknown. We present a spiral spectroscopic imaging sequence with a time-shifted radiofrequency pulse that can spectrally decompose the through-plane susceptibility gradient for spectral-spatial radiofrequency pulse design. Maps of the through-plane susceptibility gradient as a function of frequency were generated for the human brain at 3T. We found that the linear relationship holds well for the whole brain with an optimal slope of -1.0 μT/m/Hz.

Metabolic MR imaging of regional triglyceride and creatine content in the human heart

An optimized echo-planar spectroscopic imaging sequence is proposed to facilitate spatial mapping of triglyceride and total creatine content in the human heart. The sequence integrates local-look field of view reduction, cardiac and respiratory gating, and dedicated reconstruction steps to account for gradient channel delays, field inhomogeneity, and phase incoherence due to residual motion. The technique is demonstrated in 12 volunteers in comparison to single voxel point-resolved spectroscopy in the septal wall at 1.5 T. Triglyceride-to-water and total creatine-to-water ratios derived from echo-planar spectroscopic imaging (0.48 ± 0.18% and 0.06 ± 0.03%) and point-resolved spectroscopy (0.52 ± 0.17% and 0.07 ± 0.02%) were found to agree well. In the septal region, intraclass correlation coefficients ranging from 0.67 to 0.72 were estimated. A relatively weak agreement (intraclass correlation coefficients: 0.34 and 0.52) was found for sectors in the lateral wall due to field gradients induced by the posterior vein and limited sensitivity of the receive coil array in this area. On the basis of the findings, it is concluded that fast spectroscopic imaging of both cardiac triglyceride and total creatine content is feasible. Shimming and sensitivity challenges in the lateral region remain, however, to be addressed.

Metabolite Mapping with Extended Brain Coverage Using a Fast Multisection MRSI Pulse Sequence and a Multichannel Coil

Multisection magnetic resonance spectroscopic imaging is a widely used pulse sequence that has distinct advantages over other spectroscopic imaging sequences, such as dynamic shimming, large region-of-interest coverage within slices, and rapid data acquisition. It has limitations, however, in the number of slices that can be acquired in realistic scan times and information loss from spacing between slices. In this paper, we synergize the multi-section spectroscopic imaging pulse sequence with multichannel coil technology to overcome these limitations. These combined techniques now permit elimination of the gaps between slices and acquisition of a larger number of slices to realize the whole brain metabolite mapping without incurring the penalties of longer repetition times (and therefore longer acquisition times) or lower signal-to-noise ratios.

Neurologic 3D MR Spectroscopic Imaging with Low-Power Adiabatic Pulses and Fast Spiral Acquisition

To improve clinical three-dimensional (3D) MR spectroscopic imaging with more accurate localization and faster acquisition schemes. Institutional review board approval and patient informed consent were obtained. Data were acquired with a 3-T MR imager and a 32-channel head coil in phantoms, five healthy volunteers, and five patients with glioblastoma. Excitation was performed with localized adiabatic spin-echo refocusing (LASER) by using adiabatic gradient-offset independent adiabaticity wideband uniform rate and smooth truncation (GOIA-W[16,4]) pulses with 3.5-msec duration, 20-kHz bandwidth, 0.81-kHz amplitude, and 45-msec echo time. Interleaved constant-density spirals simultaneously encoded one frequency and two spatial dimensions. Conventional phase encoding (PE) (1-cm3 voxels) was performed after LASER excitation and was the reference standard. Spectra acquired with spiral encoding at similar and higher spatial resolution and with shorter imaging time were compared with those acquired with PE. Metabolite levels were fitted with software, and Bland-Altman analysis was performed. Clinical 3D MR spectroscopic images were acquired four times faster with spiral protocols than with the elliptical PE protocol at low spatial resolution (1 cm3). Higher-spatial-resolution images (0.39 cm3) were acquired twice as fast with spiral protocols compared with the low-spatial-resolution elliptical PE protocol. A minimum signal-to-noise ratio (SNR) of 5 was obtained with spiral protocols under these conditions and was considered clinically adequate to reliably distinguish metabolites from noise. The apparent SNR loss was not linear with decreasing voxel sizes because of longer local T2* times. Improvement of spectral line width from 4.8 Hz to 3.5 Hz was observed at high spatial resolution. The Bland-Altman agreement between spiral and PE data is characterized by narrow 95% confidence intervals for their differences (0.12, 0.18 of their means). GOIA-W(16,4) pulses minimize chemical-shift displacement error to 2.1%, reduce nonuniformity of excitation to 5%, and eliminate the need for outer volume suppression. The proposed adiabatic spiral 3D MR spectroscopic imaging sequence can be performed in a standard clinical MR environment. Improvements in image quality and imaging time could enable more routine acquisition of spectroscopic data than is possible with current pulse sequences.

Multislice 1H MRSI of the human brain at 7 T using dynamic B0 and B1 shimming

Proton MR spectroscopic imaging of the human brain at ultra-high field (≥7 T) is challenging due to increased radio frequency power deposition, increased magnetic field B(0) inhomogeneity, and increased radio frequency magnetic field inhomogeneity. In addition, especially for multislice sequences, these effects directly inhibit the potential gains of higher magnetic field and can even cause a reduction in data quality. However, recent developments in dynamic B(0) magnetic field shimming and dynamic multitransmit radio frequency control allow for new acquisition strategies. Therefore, in this work, slice-by-slice B(0) and B(1) shimming was developed to optimize both B(0) magnetic field homogeneity and nutation angle over a large portion of the brain. Together with a low-power water and lipid suppression sequence and pulse-acquire spectroscopic imaging, a multislice MR spectroscopic imaging sequence is shown to be feasible at 7 T. This now allows for multislice metabolic imaging of the human brain with high sensitivity and high chemical shift resolution at ultra-high field.

Multi-Echo-Based Echo-Planar Spectroscopic Imaging Using a 3T MRI Scanner.

The use of spin-echoes has been employed in an Echo-Planar Spectroscopic Imaging (EPSI) sequence to collect multiple phase encoded lines within a single in a Multi-Echo-based Echo-Planar Spectroscopic Imaging technique (MEEPSI). Despite the dependence on the amplitude of the spin-echoes, the Full Width at Half Maximum (FWHM) of the derived multi-echo Point Spread Function (PSF) is shown to decrease, indicating an improved overall spatial resolution without requiring any additional scan time. The improved spatial resolution is demonstrated in the one-dimensional (1D) spatial profiles of the N-Acetyl Aspartate (NAA) singlet along the phase encode dimension in a gray matter phantom. Although the improved spatial resolution comes at the expense of spectral resolution, it is shown in vivo that peak broadening due to decay is more significant than the loss of resolution from using spin-echoes and therefore does not affect the ability to quantify metabolites using the LCModel fitting algorithm.

Implementation of multi-echo-based correlated spectroscopic imaging and pilot findings in human brain and calf muscle

To implement a spatially encoded correlated spectroscopic imaging (COSI) sequence on 3 Tesla (T) MRI/MR spectroscopy scanners incorporating four echoes to collect four phase-encoded acquisitions per repetition time (TR), and to evaluate the performance and reliability of this four-dimensional (4D) multi-echo COSI (ME-COSI) sequence in brain and calf muscle. Typical scan parameters for the 4D datasets were as follows: repetition time = 1500 ms, 2000 Hz bandwidth, 8 × 8 spatial encoding, one average, 64 Δt(1) increments and the scan duration was 25 min. The performance and test-retest reliability of ME-COSI were evaluated with phantoms and in the occipitoparietal brain tissues and calf of six healthy volunteers (mean age = 32 years old). Regional differences in concentrations of lipids, creatine (Cr), choline (Ch), and carnosine (Car) were observed between spectra from voxels located in tibial marrow, tibialis anterior, and soleus muscle. Diagonal and cross-peak resonances were identified from several brain metabolites including N-acetyl aspartate (NAA), Ch, Cr, lactate (Lac), aspartate (Asp), glutathione (GSH), and glutamine\glutamate (Glx). Coefficients of variation (CV) in metabolite ratios across repeated measurements were <15% for diagonal and <25% for cross-peaks observed in vivo. The ME-COSI sequence reliably acquired spatially resolved 2D Correlated Spectroscopy (COSY) spectra demonstrating the feasibility of differentiating spatial variation of metabolites in different tissues. Multi-echo acquisition shortens scan duration to clinically feasible times.

Local-look navigator gated and cardiac triggered echo-planar spectroscopic imaging of the heart

Single-voxel proton magnetic resonance spectroscopy has been shown to be a promising tool for assessing creatine [1] and myocardial triglycerides in humans [2, 3, 4]. A focus of interest is the correlation between triglyceride content in the myocardium and cardiac dysfunction [5]. While spectral information from a single volume is sufficient when alterations with global effects on the heart are studied, a demand for higher and flexible spatial resolution exists when probing local changes. The objective of the current work was to implement a navigated local-look Echo-Planar Spectroscopic Imaging (EPSI) sequence for assessment of triglyceride and creatine content in the myocardium in vivo.

Widespread extrahippocampal NAA/(Cr+Cho) abnormalities in TLE with and without mesial temporal sclerosis

MR spectroscopy has demonstrated extrahippocampal NAA/(Cr+Cho) reductions in medial temporal lobe epilepsy with (TLE-MTS) and without (TLE-no) mesial temporal sclerosis. Because of the limited brain coverage of those previous studies, it was, however, not possible to assess differences in the distribution and extent of these abnormalities between TLE-MTS and TLE-no. This study used a 3D whole brain echoplanar spectroscopic imaging (EPSI) sequence to address the following questions: (1) Do TLE-MTS and TLE-no differ regarding severity and distribution of extrahippocampal NAA/(Cr+Cho) reductions? (2) Do extrahippocampal NAA/(Cr+Cho) reductions provide additional information for focus lateralization? Forty-three subjects (12 TLE-MTS, 13 TLE-no, 18 controls) were studied with 3D EPSI. Statistical parametric mapping (SPM2) was used to identify regions of significantly decreased NAA/(Cr+Cho) in TLE groups and in individual patients. TLE-MTS and TLE-no had widespread extrahippocampal NAA/(Cr+Cho) reductions. NAA/(Cr+Cho) reductions had a bilateral fronto-temporal distribution in TLE-MTS and a more diffuse, less well defined distribution in TLE-no. Extrahippocampal NAA/(Cr+Cho) decreases in the single subject analysis showed a large inter-individual variability and did not provide additional focus lateralizing information. Extrahippocampal NAA/(Cr+Cho) reductions in TLE-MTS and TLE-no are neither focal nor homogeneous. This reduces their value for focus lateralization and suggests a heterogeneous etiology of extrahippocampal spectroscopic metabolic abnormalities in TLE.

Implementation of 3 T Lactate-Edited 3D 1H MR Spectroscopic Imaging with Flyback Echo-Planar Readout for Gliomas Patients

The purpose of this study was to implement a new lactate-edited 3D 1H magnetic resonance spectroscopic imaging (MRSI) sequence at 3 T and demonstrate the feasibility of using this sequence for measuring lactate in patients with gliomas. A 3D PRESS MRSI sequence incorporating shortened, high bandwidth 180° pulses, new dual BASING lactate-editing pulses, high bandwidth very selective suppression (VSS) pulses and a flyback echo-planar readout was implemented at 3 T. Over-prescription factor of PRESS voxels was optimized using phantom to minimize chemical shift artifacts. The lactate-edited flyback sequence was compared with lactate-edited MRSI using conventional elliptical k-space sampling in a phantom and volunteers, and then applied to patients with gliomas. The results demonstrated the feasibility of detecting lactate within a short scan time of 9.5 min in both phantoms and patients. Over-prescription of voxels gave less chemical shift artifacts allowing detection of lactate on the majority of the selected volume. The normalized SNR of brain metabolites using the flyback encoding were comparable to the SNR of brain metabolites using conventional phase encoding MRSI. The specialized lactate-edited 3D MRSI sequence was able to detect lactate in brain tumor patients at 3 T. The implementation of this technique means that brain lactate can be evaluated in a routine clinical setting to study its potential as a marker for prognosis and response to therapy.

Echo planar correlated spectroscopic imaging: Implementation and pilot evaluation in human calf in vivo

Exploiting the speed benefits of echo-planar imaging (EPI), the echo-planar spectroscopic imaging (EPSI) sequence facilitates recording of one spectral and two to three spatial dimensions faster than the conventional magnetic resonance spectroscopic imaging (MRSI). A novel four dimensional (4D) echo-planar correlated spectroscopic imaging (EP-COSI) was implemented on a whole body 3 T MRI scanner combining two spectral with two spatial encodings. Similar to EPSI, the EP-COSI sequence used a bipolar spatial read-out train facilitating simultaneous spatial and spectral encoding, and the conventional phase and spectral encodings for the other spatial and indirect spectral dimensions, respectively. Multiple 2D correlated spectroscopy (COSY) spectra were recorded over the spatially resolved volume of interest (VOI) localized by a train of three slice-selective radiofrequency (RF) pulses (90°-180°-90°). After the initial optimization using phantom solutions, the EP-COSI data were recorded from the lower leg of eight healthy volunteers including one endurance trained volunteer. Pilot results showed acceptable spatial and spectral quality achievable using the EP-COSI sequence. There was a detectable separation of cross peaks arising from the skeletal muscle intramyocellular lipids (IMCLs) and extramyocellular lipids (EMCLs) saturated and unsaturated pools. Residual dipolar interaction between the N-methylene and N-methyl protons of creatine/phosphocreatine (Cr/PCr) was also observed in the tibialis anterior region.

Short echo spectroscopic imaging of the human brain at 7T using transceiver arrays

Recent advances in magnet technology have enabled the construction of ultrahigh-field magnets (7T and higher) that can accommodate the human head and body. Despite the intrinsic advantages of performing spectroscopic imaging at 7T, increased signal-to-noise ratio (SNR), and spectral resolution, few studies have been reported to date. This limitation is largely due to increased power deposition and B(1) inhomogeneity. To overcome these limitations, we used an 8-channel transceiver array with a short TE (15 ms) spectroscopic imaging sequence. Utilizing phase and amplitude mapping and optimization schemes, the 8-element transceiver array provided both improved efficiency (17% less power for equivalent peak B(1)) and homogeneity (SD(B(1)) = +/-10% versus +/-22%) in comparison to a transverse electromagnetic (TEM) volume coil. To minimize the echo time to measure J-modulating compounds such as glutamate, we developed a short TE sequence utilizing a single-slice selective excitation pulse followed by a broadband semiselective refocusing pulse. Extracerebral lipid resonances were suppressed with an inversion recovery pulse and delay. The short TE sequence enabled visualization of a variety of resonances, including glutamate, in both a control subject and a patient with a Grade II oligodendroglioma.

Imaging considerations for in vivo 13C metabolic mapping using hyperpolarized 13C-pyruvate.

One of the challenges of optimizing signal-to-noise ratio (SNR) and image quality in (13)C metabolic imaging using hyperpolarized (13)C-pyruvate is associated with the different MR signal time-courses for pyruvate and its metabolic products, lactate and alanine. The impact of the acquisition time window, variation of flip angles, and order of phase encoding on SNR and image quality were evaluated in mathematical simulations and rat experiments, based on multishot fast chemical shift imaging (CSI) and three-dimensional echo-planar spectroscopic imaging (3DEPSI) sequences. The image timing was set to coincide with the peak production of lactate. The strategy of combining variable flip angles and centric phase encoding (cPE) improved image quality while retaining good SNR. In addition, two aspects of EPSI sampling strategies were explored: waveform design (flyback vs. symmetric EPSI) and spectral bandwidth (BW = 500 Hz vs. 267 Hz). Both symmetric EPSI and reduced BW trended toward increased SNR. The imaging strategies reported here can serve as guidance to other multishot spectroscopic imaging protocols for (13)C metabolic imaging applications.

B1 and T1 insensitive water and lipid suppression using optimized multiple frequency-selective preparation pulses for whole-brain 1H spectroscopic imaging at 3T

A new method for the simultaneous suppression of water and lipid resonances using a series of dual-band frequency-selective radiofrequency (RF) pulses with associated dephasing gradients is presented. By optimizing the nutation angles of the individual pulses, the water and lipid suppression is made insensitive to a range of both T1-relaxation times and B1 inhomogeneities. The method consists only of preparatory RF pulses and thus can be combined with a wide variety of MRSI schemes including both long and short TE studies. Simulations yield suppression factors, in the presence of +/-20% B1 inhomogeneity, on the order of 100 for lipid peaks with three different T1s (300 ms, 310 ms, and 360 ms), and water peaks with T1s ranging from 0.8 s to 4 s. Excellent in vivo study performance is demonstrated using a 3 Tesla volumetric proton spectroscopic imaging (1H-MRSI) sequence for measuring the primary brain metabolites peaks of choline (Cho), creatine (Cr), and N-acetyl aspartate (NAA).