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[Signal contamination problem in three-dimensional localization technique of MR spectroscopy--experiment and an
Abstract:
Signal contamination from the surrounding volume was studied using the ISIS sequence, a three-dimensional localization technique. In phantom experiments, contamination decreased with the increase of Tr, regardless of where the contamination originated from. In 52 localized liver spectra with a Tr of 2 sec, PCr contamination was estimated at 3 to 4%, and contamination of ATP signals from the surrounding liver tissue at less than 1%, because of the relatively short T1 of ATP in the liver. In the spectra of brain neoplasms obtained using the simultaneous double-volume selection technique, the PCr ratio in the tumor relative to the control area was high in low grade astrocytoma (0.80, n =8) and low in others (0.45, n = 11). Considering contamination and spectral noise, a PCr ratio of less than 0.4 does not strongly suggest the existence of PCr in tumors. Among 25 cases whose therapeutic processes were monitored by MRS, signal disappearance was observed in two cases in the localized spectra after therapy. In both of them, tumor necrosis was proved pathologically and correlated well with spectroscopic findings. It was found that the ISIS technique suppressed signal contamination to the level of several percents, providing spectra of acceptable quality through localization.
Insights
The ISIS technique minimizes signal contamination in magnetic resonance spectroscopy (MRS), improving spectral quality for liver and brain tumor studies. This method aids in accurate assessment of metabolites like PCr and ATP, crucial for diagnosing and monitoring disease progression.
Area of Science:
- Biomedical Engineering
- Magnetic Resonance Imaging
- Spectroscopy
Context:
- Signal contamination is a significant challenge in magnetic resonance spectroscopy (MRS).
- The ISIS (Image Selected In Vivo Spectroscopy) technique offers a method for spatial localization.
- Understanding and quantifying signal contamination is crucial for accurate metabolite analysis.
Purpose:
- To evaluate signal contamination in MRS using the ISIS technique.
- To assess the impact of repetition time (Tr) on signal contamination.
- To investigate PCr and ATP contamination in liver spectra and PCr ratios in brain neoplasms.
- To correlate MRS findings with pathological outcomes in tumor therapy monitoring.
Summary:
- Phantom experiments showed that increasing Tr reduced signal contamination.
- In liver spectra, PCr contamination was 3-4% and ATP contamination <1% with Tr=2 sec.
- In brain neoplasms, PCr ratios varied by tumor grade, with <0.4 suggesting low PCr presence.
- ISIS technique effectively suppressed contamination to a few percent, yielding acceptable localized spectra.
- Observed signal disappearance in localized spectra post-therapy correlated with pathological tumor necrosis.
Impact:
- Provides a reliable method for acquiring high-quality localized spectra using MRS.
- Enhances the diagnostic accuracy of MRS in liver and brain tumor characterization.
- Facilitates non-invasive monitoring of therapeutic response in oncology.
- Contributes to the understanding of metabolite changes in disease states.