Asymmetry analysis of nuclear Overhauser enhancement effect at ‐1.6 ppm in ischemic stroke
Yu Zhao, Aqeela Afzal, Zhongliang ZuAbstract
Background
The nuclear Overhauser enhancement (NOE)‐mediated saturation transfer effect at ‐1.6 ppm, termed NOE(‐1.6 ppm), has demonstrated potential for detecting ischemic stroke. However, the quantification of the NOE(‐1.6 ppm) effect usually relies on a multiple‐pool Lorentzian fit method, which necessitates a time‐consuming acquisition of the entire chemical exchange saturation transfer (CEST) Z‐spectrum with high‐frequency resolution, thus hindering its clinical applications.
Purpose
This study aims to assess the feasibility of employing asymmetry analysis, a rapid CEST data acquisition and analysis method, for quantifying the NOE(‐1.6 ppm) effect in an animal model of ischemic stroke.
Methods
We examined potential contaminations from guanidinium/amine CEST, NOE(‐3.5 ppm), and asymmetric magnetization transfer (MT) effects, which could reduce the specificity of the asymmetry analysis of NOE(‐1.6 ppm). First, a Lorentzian difference (LD) analysis was used to mitigate direct water saturation and MT effects, providing separate estimations of the contributions from the guanidinium/amine CEST and NOE effects. Then, the asymmetry analysis of the LD fitted spectrum was compared with the asymmetry analysis of the raw CEST Z‐spectrum to evaluate the contribution of the asymmetric MT effect at ‐1.6 ppm.
Results
Results show that the variations of the LD quantified NOE(‐1.6 ppm) in stroke lesions are much greater than that of the CEST signals at +1.6 ppm and NOE(‐3.5 ppm), suggesting that NOE(‐1.6 ppm) has a dominating contribution to the asymmetry analysis at ‐1.6 ppm compared with the guanidinium/amine CEST and NOE(‐3.5 ppm) in ischemic stroke. The NOE(‐1.6 ppm) variations in the asymmetry analysis of the raw CEST Z‐spectrum are close to those in the asymmetry analysis of the LD fitted spectrum, revealing that the NOE(‐1.6 ppm) dominates over the asymmetric MT effects.
Conclusion
Our study demonstrates that the asymmetry analysis can quantify the NOE(‐1.6 ppm) contrast in ischemic stroke with high specificity, thus presenting a viable alternative for rapid mapping of ischemic stroke.