Method for magnetic resonance spectroscopic imaging
Inventors
Balchandani, Priti • Spielman, Daniel • Pauly, John
Assignees
NATIONAL INSITUTES OF HEALTH (NIH) US DEPARTMENT OF HEALTH AND HUMAN SERVICES (DHHS) US GOVERNMENT • National Institutes of Health NIH
Publication Number
US-7966053-B2
Publication Date
2011-06-21
Expiration Date
2027-11-26
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Abstract
A method for performing spectroscopy using an interleaved readout for at least two species. A B0 field is applied. A first spatial-spectral (SPSP) position resolved spectroscopy sequence (PRESS) excitation with a sufficiently narrow band to excite a first species without exciting a second species is applied. A first readout that measures the first species is performed. A second SPSP PRESS excitation with a sufficiently narrow band to excite the second species without exciting the first species is applied. A second readout that measures the second species is performed.
Core Innovation
This invention provides a method for performing magnetic resonance spectroscopy using an interleaved readout approach to excite and measure at least two different species separately. By applying a static magnetic field (B0), the method involves applying a first spatial-spectral (SPSP) position resolved spectroscopy sequence (PRESS) excitation with a sufficiently narrow spectral band which excites a first species without exciting a second species, followed by a readout to measure the first species. Subsequently, a second SPSP PRESS excitation is applied with a narrow band to excite the second species without exciting the first species, followed by a second readout measuring the second species.
The method addresses significant challenges in high-field (e.g. 7 Tesla) proton magnetic resonance spectroscopic imaging (1H MRSI), such as increased B1 and B0 inhomogeneity and chemical shift localization (CSL) errors which degrade conventional sequences. Using adiabatic spatial-spectral refocusing pulses in an interleaved narrow-band PRESS sequence allows excitation of multiple narrow spectral bands in succession within the same TR, gaining insensitivity to B1 variation and eliminating CSL error because the transmit frequency is separately adjusted for each spectral band.
The invention enables improved spatial coverage and increased overall signal-to-noise ratio (SNR) relative to conventional PRESS sequences. The use of SPSP 90° pulses followed by two phase-matched adiabatic SPSP 180° pulses, each with bandwidths narrow enough to selectively excite respective species without overlap, allows robust measurements despite B0 and B1 field variations. Additionally, interleaving the excitation and readout of multiple species provides spectral coverage of a broad frequency range without increasing scan time.
Claims Coverage
The patent claims include several independent claims directed to methods, computer-implemented methods, and apparatus for performing magnetic resonance spectroscopic imaging with interleaved SPSP PRESS excitations for multiple species. The inventive features focus on selective, narrow-band excitations and interleaved readouts.
Interleaved narrow-band SPSP PRESS excitation and readout method
A method applying a B0 field and performing interleaved position resolved spectroscopy sequence (PRESS) excitations using spatial-spectral (SPSP) pulses with sufficiently narrow spectral bands. The method excites one species without exciting another species, then performs readouts for each species separately. The narrow bands and interleaved sequence allow multiple species to be measured within the same TR without cross excitation.
Narrow-band SPSP pulse design for selective excitation
Each SPSP PRESS excitation comprises a SPSP 90° pulse followed by two adiabatic SPSP 180° pulses that have spectral profiles centered on the resonant frequency of the species they excite. These pulses have narrow bandwidths sufficient to avoid exciting other species. The 90° SPSP pulse shares the same spectral profile as the adiabatic 180° pulses.
Computer-implemented method with interleaved cycles
A computer-implemented method performing, in repeated cycles, applying the first SPSP PRESS excitation and readout for the first species, then applying the second SPSP PRESS excitation and readout for the second species, generating spectroscopic outputs by interleaving these readouts.
Magnetic resonance imaging apparatus with processor and controller
An apparatus comprising a magnetic resonance imaging excitation and detection system and a controller with a display and processor storing computer-readable code. The controller executes code to apply B0, perform first and second SPSP PRESS excitations with narrow bands selective to different species, perform corresponding readouts, generate spectroscopic images by interleaving the readouts, and display the images.
The independent claims cover the inventive method, computer-implemented method, and apparatus for selectively exciting and measuring multiple species using interleaved narrow-band spatial-spectral PRESS sequence excitations and readouts. They emphasize the design of narrow-band adiabatic SPSP pulses centered on specific species to avoid cross excitation, interleaved acquisition to maintain scan time, and generation of spectroscopic images from acquired data.
Stated Advantages
Greater immunity to B1 and B0 field inhomogeneity during spectroscopic imaging at high field strengths.
Virtual elimination of chemical shift localization errors by shifting transmit frequencies for each interleaved spectral band.
Improved spatial coverage and increased overall signal-to-noise ratio (SNR) compared to conventional PRESS sequences.
Interleaving allows excitation of a large spectral range without increasing scan time.
Adiabatic SPSP pulses enable insensitivity to RF power variations and allow 180° refocusing pulses within SAR limits and below RF amplifier peak limits.
The sequence suppresses water signal completely in metabolic interleaves, eliminating the need for additional water suppression techniques.
Documented Applications
Measurement of brain metabolites such as choline-containing compounds, creatine/phosphocreatine, and N-acetyl aspartate using 1H magnetic resonance spectroscopic imaging at ultra-high field (7 T).
Non-invasive identification, visualization, and quantification of brain biochemical markers and neurotransmitters.
Assessment of abnormalities in injured or diseased brain tissue and longitudinal monitoring of degenerative diseases and therapeutic interventions.
Multinuclear spectroscopy and spectroscopic imaging applications, especially for nuclei with large chemical shift ranges such as 13C.
Spectroscopy on a single voxel or on a grid of voxels in various organs including prostate and breast with spectral bands centered on metabolites of interest.
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