Preliminary Study Of The Stria Of Gennari In Healthy Adults By Using High-resolution MR Phase Difference Enhanced Imaging

ObjectiveTo assess the delineations of the stria of Gennari in healthy adults using phase-difference enhanced imaging (PADRE) technique and measure the phase values in striate cortex and optic radiation, discussing the feasibility of studying the myeloarchitecture of human cortex in vivo using PADRE technique.Materials and MethodsThe study was approved by the Review Board of Shandong Medical Imaging Institute, and informed consents were obtained from all subjects. Thirty-four healthy adult volunteers (20men,14women; range,21-50years; mean age:30.4±8.0years) were enrolled in this study. MRI was performed on a3.0T whole-body MRI system (Philips Achieva, TX, the Netherlands) with an eight-channel phased array head coil. PADRE imaging was performed in all subjects, and VE, TE and PADRE images were reconstructed from the source images.(1) Evaluation of the delineation of the stria of Gennari:Two experienced neuroradiologists blinded with the image-reconstruction modes accessed the visualization of grey matter and white matter, with the emphasis on the delineation of the stria of Gennari in three sets of images by using a four-point grading scale:score of0, the stria of Gennari could not be visualized;1, the stria of Gennari were barely discernible and equivocally identified;2, the stria of Gennari were unequivocally but discontinuously displayed, or unequivocal but unable to identify their exact locations within cortex;3, the stria of Gennari were unequivocally and continuously visualized, as well as their exact locations within cortex. In addition, intensity line profiles through the striate cortex on all three-set images were made to see whether there were "intensity dips" corresponding to the stria of Gennari. The inter-rater agreement for the qualitative grading was estimated using a weighted κ test. For comparison of the grades on the identification of the stria of Gennari in the PADRE images against the VE and TE images, the Wilcoxon signed rank test was performed, p<0.05was considered statistically significant.(2) Measurement of phase value in primary visual cortex and optic radiation: Save the raw data of PADRE technique in form of DICOM and to transfer them to a specific computer. High-pass filtering was performed to create a filtered-phase image (FPI) from the original unwrapped phase image by SPIN software. Round regions of interest (ROIs) within the FPI were manually set on the cortex located at the front and rear of the calcarine sulcus to measure the phase values in primary visual cortex, the phase values of optic radiation were also measured. Kolmogorov-Smirnov testing were performed to test whether the measured phase values were normally distributed, as there were normally distributed, a paired t test was used to evaluate the differences. p<0.05was considered statistically significant.ResultsIn all34healthy subjects, grey matter displayed high intensity signal, and white matter showed low intensity signal in three post-processed images from PADRE technique. The stria of Gennari could be identified in all the images and were depicted as hypointense bands parallel to the surface of primary visual cortex. TE images also displayed good contrast between gray matter and white matter, but the stria of Gennari was delineated as faint dark bandings. VE images could clearly identify the stria of Gennari, but the defining interface of gray-to-white matter and the exact locations in cortex could not be discerned. PADRE images displayed good contrast between gray matter and white matter, and white matter regions showed decreased signal intensity relative to gray matter regions, which provided a better visualization of the stria of Gennari and their exact locations in cortex. In the intensity line profiles through the striate cortex on all three-set images,"intensity dips" corresponding to the stria of Gennari were seen, respectively.Evaluation scores of two raters on differentiating the stria of Gennari in TE, VE and PADRE images are1.79±0.44,1.84±0.37,2.84±0.37;1.76±0.43,1.82±0.38,2.79±0.41, respectively. There was a substantial agreement between two raters (k=0.823). The mean scores were1.78±0.43,1.83±0.38,2.82±0.39, respectively, which demonstrated significant differences. PADERE images were superior to TE images as well as VE images in delineating the stria of Gennari (Z=-13.337,P<0.01; Z=-13.458,p<0.01).The phase values of the striate cortexes and optic radiation in the left and right side were0.218±0.080,0.216±0.080;-0.458±0.113,-0.436±0.128, respectively. There was no statistical difference (t=0.150,p>0.05; t=-1.136,p>0.05) between two sides. The mean phase values of the striate cortexes and optic radiation in both sides were0.217±0.068,-0.447±0.106, respectively and there was statistical difference (t=29.681, p<0.01).ConclusionThe PADRE technique can identify the stria of Gennari in vivo, particularly in the PADRE image, indicating PADRE technique could be used to image the intracortical myelinated nerve fibers in vivo by MR, which may provide a novel tool for the investigation of myeloarchitecture in different cortical areas to establish correspondence between the anatomical and functional specialization in vivo.