Elsevier

Academic Radiology

Volume 14, Issue 3, March 2007, Pages 340-343
Academic Radiology

Technical report
Manually Adjusted Versus Vendor-Preset Definition of Metabolite Boundaries: Impact on Proton Metabolite Ratios

https://doi.org/10.1016/j.acra.2006.12.011Get rights and content

Rationale and Objectives

Metabolite peak boundary definition is an important postprocessing step in proton magnetic resonance spectroscopy (1H-MRS). We compare metabolite ratios calculated using three different postprocessing strategies: software-rendered default peak boundaries, manually adjusted peak boundaries and a curve-fitting program. The first two of these methods are commercially available.

Materials and Methods

A total of 42 spectra acquired on a 1.5-T MR unit using two-dimensional chemical shift proton MR spectroscopy (TR/TE = 1500/144 ms) were analyzed. Choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) relative concentrations were derived and the following metabolite ratios were calculated: Cho/Cr, Cho/NAA, and NAA/Cr. Metabolite concentrations/ratios were calculated using (a) default peak boundaries rendered by commercially available, postprocessing software (Functool 2000, version 2.6.0); (b) manually adjusted peak boundaries by an experienced spectroscopist, using an option offered by the same commercially available software; and (c) an offline in-house curve-fitting program. Measurements obtained with method (c) were considered as the “gold standard.” Paired t-tests comparing default and adjusted metabolite ratios, as well as default and adjusted ratios with their respective curve-fit values were used for statistical analysis.

Results

Significant differences between default and manually adjusted values were found for Cho/Cr ratios <1.5 and for all Cho/NAA ratios. For Cho/Cr ratios <1.5, significant differences between default and curve-fit values were present; this was not the case when comparing manually adjusted and curve-fit values. Default and manually adjusted Cho/NAA ratios were significantly higher than corresponding curve-fit ratios. Manually adjusted values were, however, closer to the curve-fit values. No significant differences were noted between default and adjusted NAA/Cr values; default and manually adjusted ratios were significantly lower than curve-fit ratios.

Conclusion

There can be significant differences in metabolite ratios calculated using default and manually adjusted peak limits in proton MR spectroscopy. Furthermore, Cho/Cr and NAA/Cho adjusted metabolite ratios are closer to curve-fit values, which are considered the most accurate of the three.

Section snippets

Materials and methods

A total of 42 spectra spanning a range of normal and abnormal spectroscopic features and qualities were included in the study. The 42 spectra were derived from seven subjects, including three healthy adults with unremarkable brain MR examinations (one man and two women, age range 48−52 years, mean age 51 years) and four patients with a brain tumor (four men, age range 7−53 years, mean age 34 years). Institutional board review approval was obtained for the study.

Spectra were acquired using

Results

The preset peak boundaries rendered by the software in rank (i.e., frequency index number) and corresponding ppm were as follows: Cho: 67−77 (3.29−3.17 ppm), Cr: 76−89 (3.18−2.99 ppm), and NAA: 142−155 (2.20−2.00 ppm). These default preset peak boundaries were consistent in all subjects. The default central maxima for the three metabolites were Cho: 70 (3.27 ppm), Cr: 82 (3.09 ppm), and NAA: 145 (2.11 ppm). The manually adjusted peak boundaries in rank and corresponding ppm were as follows:

Discussion

As in vivo proton MR spectroscopy becomes a widely used tool in the characterization of focal brain lesions, assessing postprocessing methods and identifying potential pitfalls assumes increasing importance.

Our findings show that there are significant differences between metabolite ratios rendered by default software-rendered metabolite peaks and those estimated after manual adjustment of the peak boundaries by an experienced spectroscopist. Furthermore, the manually adjusted Cho/Cr and Cho/NAA

Conclusion

Our results suggest that there can be significant differences in metabolite ratios calculated using default and manually adjusted peak limits in proton MR spectroscopy. Furthermore, Cho/Cr and NAA/Cho adjusted metabolite ratios are closer to curve-fit values, which are considered the most accurate of the three.

References (8)

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  • MR Spectroscopy Using Normalized and Non-normalized Metabolite Ratios for Differentiating Recurrent Brain Tumor from Radiation Injury

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    We determined the areas under the various metabolite peaks and calculated the ratios. The integration limits of the respective peaks were manually defined by the same neuroradiologist before computerized calculations (23). Multiple voxels covering the contrast-enhancing lesion were analyzed and the voxel with the most abnormal spectra in terms of changes in the metabolic peaks (ie, significant increase in Cho and/or significant decrease in NAA, Cho, and Cr peaks) were chosen as “diagnostic voxel” for the contrast-enhanced lesion.

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