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PURPOSE: To demonstrate the high-resolution numerical simulation of the respiration-induced dynamic B0 shift in the head using generalized susceptibility voxel convolution (gSVC). MATERIALS AND METHODS: Previous dynamic B0 simulation research has been limited to low-resolution numerical models due to the large computational demands of conventional Fourier-based B0 calculation methods. Here, we show that a recently-proposed gSVC method can simulate dynamic B0 maps from a realistic breathing human body model with high spatiotemporal resolution in a time-efficient manner. For a human body model, we used the Extended Cardiac And Torso (XCAT) phantom originally developed for computed tomography. The spatial resolution (voxel size) was kept isotropic and varied from 1 to 10 mm. We calculated B0 maps in the brain of the model at 10 equally spaced points in a respiration cycle and analyzed the spatial gradients of each of them. The results were compared with experimental measurements in the literature. RESULTS: The simulation predicted a maximum temporal variation of the B0 shift in the brain of about 7 Hz at 7T. The magnitudes of the respiration-induced B0 gradient in the x (right/left), y (anterior/posterior), and z (head/feet) directions determined by volumetric linear fitting, were < 0.01 Hz/cm, 0.18 Hz/cm, and 0.26 Hz/cm, respectively. These compared favorably with previous reports. We found that simulation voxel sizes greater than 5 mm can produce unreliable results. CONCLUSION: We have presented an efficient simulation framework for respiration-induced B0 variation in the head. The method can be used to predict B0 shifts with high spatiotemporal resolution under different breathing conditions and aid in the design of dynamic B0 compensation strategies.
Subject(s)
Brain , Compensation and Redress , Head , Human Body , Magnetic Resonance Imaging , Methods , Respiration , TorsoABSTRACT
Objective To investigate the value of intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) based on ISHIM sequence in the grading of astrocytic tumor.Methods We collected excised tumors confirmed by histological diagnosis from 42 patients including high-grade astrocytic tumors (10 WHO grade Ⅲ,18 WHO grade Ⅳ),and 14 low-grade astrocytic tumors (1 WHO grade Ⅰ and 13 WHO grade Ⅱ).All patients underwent conventional MR imaging,ISHIM IVIM-DWI,and contrast-enhanced MR imaging.Parameters of tumor parenchyma region,peripheral edema regions and the contralateral normal brain white matter sites were measured,and the statistical analysis was conducted.Results The D value in tumor parenchyma region was significantly lower,but the D* and f values were higher in high-grade astrocytic tumor when compared with lowgrade one and all had statistical significance;in tumor peripheral edema region,D value was lower in high-grade astrocytic tumor than that in low-grade one,and the difference had statistical significance but there was no significant difference in terms of the D* and f values.There was no significant difference of the D,D* and f values in contralateral normal brain white matter sites in both high-and low-grade astrocytic tumor.Conclusion The D,D* and f values measured by ISHIM IVIM-DWI are helpful to the judgment of tumor grade and it has greatapplication value in the differential diagnosis of high-and low-grade astrocytic tumor.
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Objective To investigate the strengths and weaknesses of SPAIR and WE in iShim-IVIM of breast gland MRI scanning. Methods Twenty patients with breast tumor underwent iShim-IVIM and DCE-MRI scanning by SPAIR and WE technology. SNR ,CNR and ADC of the SPAIR-iShim and WE-iShim imaging were cal-culated and imaging quality were evaluated. Statistical analysis was done afterwards. Results The SNR and CNR of WE technology is higher than those of SPAIR statistically (P<0.05). There is no significant statistical differ-ence in score of the images between SPAIR and WE(P>0.05). The ADC of the center of the tumor has no signifi-cant statistical difference between SPAIR and WE(P>0.05). Conclusion The quality of the images using WE is significantly improved than SPAIR ,but both of them can meet the diagnostic requirements ,and the ADC has no statistical difference as well.
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Objective To investigate the strengths and weaknesses of SPAIR and WE in iShim-IVIM of breast gland MRI scanning. Methods Twenty patients with breast tumor underwent iShim-IVIM and DCE-MRI scanning by SPAIR and WE technology. SNR ,CNR and ADC of the SPAIR-iShim and WE-iShim imaging were cal-culated and imaging quality were evaluated. Statistical analysis was done afterwards. Results The SNR and CNR of WE technology is higher than those of SPAIR statistically (P<0.05). There is no significant statistical differ-ence in score of the images between SPAIR and WE(P>0.05). The ADC of the center of the tumor has no signifi-cant statistical difference between SPAIR and WE(P>0.05). Conclusion The quality of the images using WE is significantly improved than SPAIR ,but both of them can meet the diagnostic requirements ,and the ADC has no statistical difference as well.