Improved Spatial Localization for Spectroscopic Imaging R21-CA011092
The goal of this collaboration is to develop and clinically apply a new hybrid spatial encoding method called PSF-Choice that maintains the simplicity of standard Fourier encoding but includes the flexibility of non-Fourier encoding to shape the point-spread-function (PSF). With this method, practical spectroscopic imaging of the prostate that is free from lipid contamination can be achieved at no additional cost in imaging time or loss in resolution or signal-to-noise ratio. When the project is completed, an improved spectroscopic sequence to guide prostate interventions will be available to the prostate program and can also be disseminated to external groups.
To date, researchers have completed the method using the PROSE sequence and tested it in phantoms at 1.5T and 3T on GE MRI at 11.0, 12.0, and 14.0 as well with a number of patients both at 1.5T and 3T. The team has also implemented the method to work in two phase-encode directions: a relatively significant modification. A major focus is to test it with prostate patients and to use a truncated protocol with the unmodified PROSE and the sequence with PSF-Choice to minimize acquisition time and to acquire using the unmodified PROSE and the sequence with PSF-Choice. The aim is to demonstrate that, with PSF-Choice, significantly less contamination of spectra arises from the out-of-voxel fat signal. More on this project, including latest results... In 2009, results of an evaluation in phantoms and a clinical feasibility study with 16 patients were presented at the 2009 ISMRM conference in an oral spectroscopy session.
Status of MR Spectroscopy
In vivo MR proton spectroscopy has been shown to be clinically valuable for assessing and localizing prostate tumors. However, due to the inherently low signal-to-noise ratio (SNR) in MR spectroscopic imaging (MRSI), measurement times can be very long. Thus, to be practical for clinical prostate MRSI, duration must be reduced. In MRSI, spatial resolution is generally very low and, related to low-resolution data acquisition, significant ringing, i.e., occurs (a kind of bleeding of signal contamination into the voxel-of-interest) from neighboring and even distant voxels. Contamination from unsuppressed lipid or water signal can be especially problematic in some cases, rendering prostate spectra useless for diagnosis.
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Publications
This collaboration produced abstracts acknowledging the R21-CA011092 and the U41 RR019703 (NCIGT):
- Panych LP, Roebuck JR, Mulkern RV, Tang Y, Madore B, Chen N-K. Improving spatial localization in MR spectroscopic imaging with PSF-Choice. ISMRM 2009.
- Panych LP, Roebuck JR, Mulkern RV, Madore B, Chen NK. A new method to improve spatial localization in MR spectroscopic imaging of the prostate. RSNA SSM19-06. 2007.
- Panych LP, Roebuck JR and Chen N-K. Correcting for center frequency variations in MRSI data using the partially suppressed water signal. ISMRM 2007.