Study On Optimization Of Pulse Sequences For Lactate Detection And Its Diagnostic Value In Brain Diseases Using ～1H MR Spectroscopy

Objective Lactic acid is one of metabolites from theglycolysis. Brain anoxia and ischemia will cause accumulation of lactate. Non-invasive detection of lactate using MR spectroscopy has played an important role in diagnosis and treatments of diseases due to anoxia and ischemia. However, peaks related to lactate are usually difficult to be detected in most of cases, which might be an obstacle for the analysis of illness. The purpose of present study was to obtain optimal detection and quantitative analysis of lactate by changing a series of parameters used in the sequences. Moreover, we do more to get the most optimization sequences and carry out more clinical trials to validate the sequences, therefore we can solve the technical problem in detection and quantitativeanalysis of lactate using MRS. Methods The studies were performed on bothphantom and human subjects. The phantom experiment was carried out in a glass model containing lactate. The MR scanner is a 1. 5T system (SignaMR/i, GE). The spectra were obtained by using both point resolved spectroscopy (PRESS) and stimulated echo acquisition (STEAM) sequences. In order to obtain the optimal TE and TR values of the metabolites in the brain and external standard solution, MRS data were collected with different TE values at a constant TR and different TR values at a constant TE. The spectra were processed using a GE software. The peak heights were measured and the curves of the peak heights versus the TE were plotted using Microsoft Excelprogram. Moreover, the optimal sequence combining with other sequences, which including T1WI, T2WI, FLAIR and DWI, were used to acquire proton MRI data for 17 patients with acute cerebral infarction and 20 healthy volunteers. The DWI data with b=0 and b=1000 were processed using Functool software of GE company to get ADC map, and then three slices corresponding to the VOI of MRS were selected to calculate average ADC values. The average ADC values were also calculated at the correspondent location of contralateral normal region. Paired-Samples T test were applied in all volunteers' MRS data with TE=135 ms and TE=270 ms for statistical analyzing. The correlation of the T test result and average ADC value was analyzed.Result All the peaks recorded by STEAM sequence were with the similar performance as those by PRESS sequence. However, the former were weaker than the latter. The curves of lactate peaks versus TE obtained by the model exhibi ted waveform characteristic. The up doublets were recorded with their maximum peak heights using TE values of 26 ms and 270 ms, whereas the down doublets were recorded at their peaks using a TE value between 135 to 160 ms. No evidence of abnormal signal was found on T1WI, T2WI, FLAIR and DWI in all healthy volunteers, and subtle lactate peak was shown in MRS using 1. 5T scanner as well. The scanning results in T1WI, T2WI, FLAIR and DWI of the acute cerebral infarction have shown that different degree of cerebral swelling and abnormal signals found in lesions. The different lactate peaks were observed using optimized sequences. The lactate peaks using TE=135 ras were down doublet whereas the peaks using TE=35 ms and 270 ms were up doublet. However, the lactate peak with TE=26 ms were easily influenced by the signal contributions from water and fat which could disturb the evaluation. Lactate peaks were smaller at TE=135 ms compared with TE=270ms. It was resulted that the lactate peaks were ascending and ADC were descending in 17 patients with cerebral infarction. Lactate peaks were significantly negative correlated with average ADC values( Y =-0. 79).Conclusion ㏕he optimal sequence for lactate detection in model underour scanning condition is PRESS sequence with TR=1500 ms and TE=26, 270 and 135~160 ms. ㏕he results from acute cerebral infarction patients and health volunteers using the optimized sequences shown that MRS sequence with TR 1500 ms and TE 270 ms was the best one in clinical trials. The optimized sequences are able to benefit the detection and quantitative analysis of lact...