| Ⅰ.T2-Prepared Segmented 3D-Gradient-Echo for Fast T2-Weighted High-Resolution Three-Dimensional Imaging of the Carotid Artery Wall at 3T:A Feasibility StudyObjective:The multi-contrast assessment of the carotid artery wall has become an important diagnostic tool for the characterization of atherosclerotic plaque and vessel wall thickening.For providing the required T1-,T2-,and proton density weighted con-trast,multi-slice turbo spin echo(TSE)techniques are normally applied.The straight-forward extension of the TSE techniques to volumetric imaging of large sections of the carotid arteries is limited by the resulting long acquisition times.Where the acquisition of a T1-weighted contrast can be accelerated by applying a T1-weighted fast gradient echo technique,acceleration of the T2-weighted contrast is not as straightforward.Methods:In this work,the combination of a T2 preparation and a conventional fast gradient echo technique(T2P-3DGE)was evaluated for rapid acquisition of a T2-weighted image contrast.Acquisition parameters were optimized in an initia1.in vitro study in direct comparison to the conventional T2-weighted TSE(T2W-3DTSE)technique.Subsequently,the T2P-3DGE technique was evaluated in vivo.Results:In direct comparison,the T2P-3DGE sequence provided similar T2 contrast as the respective T2W-3DTSE sequence.After correction of an observed intensity offset,most likely caused by the additional T1-weighting of the T2P-3DGE sequence,no sig-nificant difference between the two T2-weighted sequences were observed in phan-tom data.The good correlation of the image contrast between the two sequences was confirmed in the initial in-vivo study,proving a potential reduction of the scan time for T2P-3DGE to 25%of the respective T2W-3DTSE techniqueConclusion:The in vitro as well as the in vivo results clearly indicate the potential of the T2P-3DGE technique for providing similar T2 image contrast as in the conventional techniques.Thereby,the acquisition times could be substantially reduced to about 25%of the respective 3D-TSE techniqueⅡ.Cardiac MR Imaging in the Rat Model on a Clinical 3Tesla Whole-Body SystemObjective:The aim of this study is to show the feasibility of structural and functional cardiac MR imaging in rats using a non-modified clinical 3T whole body MR systemMethods:5 Wistar rats were investigated.Each rat underwent the imaging protocol two times within one week.Anesthesia was established by isoflurane(2%saturation)MR scans included black-blood(DIR)turbo spin echo acquisitions(structural analysis)and a cardiac phase resolved steady-state gradient echo scan(functional analysis).For heart rates above 300bpm,prospective triggering was used.In case of less than 300bpm retrospective triggering was used.Since the heart rate of the animals varied between 250bpm and 420bpm in subsequent days,in all animals prospective and retrospective triggering was used.Data was acquired with a set of contiguous short-axial slices covering the entire left ventricle for cardiac functional analysis All data were acquired with conventional 8 channel SENSE knee coil.Ejection fraction(EF),EDV,ESV and SV was determined independently in each scan.Cardiac function was evaluated with QMass MR softwareResults:MR imaging was successful in all rats.Black-blood contrast as well as cine images could be obtained with reproducible imaging quality.SNR,CNR,spatial and temporal resolution were sufficient for identification of the inner and outer myocardial wall.Even tiny structures could be visualized with sufficient image quality.Image quality was slightly degraded by flow artifacts during systole.The mean ejection fraction resulted as 77.5%±4.1%,which agrees well with values obtained on high field MR systems.The reproducibility of the EF was better than 6%in all scans.Variation in EDV,ESV,and SV was below 10%.All quantified properties did not show any significant(p<0.05)differences between subsequent scans or between prospectively and retrospectively triggered acquisitionsConclusion:Accurate quantification of cardiac function and heart structures can be obtained on a clinical whole-body 3T system with sufficient spatial and temporal resolution.Acquisition time can be kept below 60 minutes for a comprehensive functional and structural examination of the rat heart... |
