5.0T MR imaging system has solved technical challenges inherent in traditional ultra-high field MRI,such as uneven image signals and difficulty in whole-body imaging,hence significantly improved imaging quality.Currently,5.0T MRI had shown great potential in nervous system,cardiovascular system,skeletal muscle system and abdominal imaging,and multiple innovative technologies had emerged and developed around this system.The clinical application value and research progresses of 5.0T MRI were briefly described in this article.

Objective To explore the optimization for parameters of 5.0T pseudo continuous arterial spin labeling(pCASL)MRI of whole brain.Methods Nine healthy adults were prospectively enrolled,and single-delay pCASL scanning was performed based on a 5.0T MR scanner with 3 sets of labeling gradients:Group A,average gradient(Gavg)=1 mT/m and the ratio of maximum gradient(Gmax)to Gavg(Gratio)=10,group B,Gavg=0.6 mT/m and Gratio=10,group C,Gavg=0.3 mT/m and Gratio=9.The labeling efficiency and cerebral blood flow(CBF)of 3 groups were compared to screen the best labeling gradient group.Results When the marked average blood flow velocity was 40 cm/s,the gradient field tolerance of group C was better than that of group A and B at the situation of reduced B1+and larger B0 offset frequency range.Under the gradient field of group C,the level of labeled artery B1 ranged from 54.19％to 75.36％,with an average of 64.71％.The labeling efficiencies of group C were all ≥85％,and all ≥90％at the average B1 level(64.71％).In the whole gray matter and almost all brain regions,CBF on pCASL under gradient field of group C was significantly higher than that of group A and B(all P＜0.05).Conclusion Low Gavg and low Gmax were the optimal parameters for 5.0T whole brain pCASL MRI.

Objective To observe the value of 5.0T MRI in measuring the volumes of hippocampal formation(HF)subfields in healthy adults.Methods Cranial high-resolution TIWI were prospectively obtained in 23 healthy adult volunteers using 5.0T and 3.0T MR scanners,respectively.HF was divided into 38 subfields,and then the volume of each subfield was measured using FreeSurfer software.The volumes of HF subfield based on 5.0T and 3.0T MR T1WI were compared,and the correlations of the outcomes were analyzed.Results Significant differences of the volumes of bilateral hippocampal tails,left parasubiculum,left molecular layer of hippocampal head,left granular cell-molecular layer-dentate gyrus head,right granular cell-molecular layer-dentate gyrus body,left cornu Ammonis(CA)1 head,left CA3 head,left CA4 head,right fimbria of hippocampus and left hippocampus amygdala transition area were found between 5.0T and 3.0T T1WI(all P＜0.05).The volumes of HF subfields measured based on 5.0T and 3.0T T1WI were moderately to highly positively correlated(all r＞0.5,all P＜0.01).Conclusion 5.0T MRI could be used to measure the volume of HF subfield in adults.

Objective To compare image quality of 5.0T and 3.0T time of flight MR angiography(TOF-MRA)and displaying choroidal anterior arteries(AChA).Methods Data of 80 patients who underwent head 5.0T(5.0T group,n=40)and/or 3.0T TOF-MRA(3.0T group,n=42)were retrospectively analyzed,among them 2 patients underwent both 5.0T and 3.0T TOF-MRA.The subjective scoring and objective evaluation of image quality were performed,and the results were compared between groups.AChA was divided into proximal,intermediate and distal segments(A1,A2,A3 segment),the quantity of left and right AChA shown on 5.0T and 3.0T TOF-MRA were recorded,and the length and diameter of left and right AChA dispalyed on MRA were comparatively observed.Results The subjective scores of image quality of 5.0T group were higher than that of 3.0T group(5.0[4.0,5.0]vs.5.0[3.0,5.0],Z=6.417,P=0.029).The signal-to-noise ratio(91.01±5.04)and contrast-to-noise ratio(72.47±5.14)of 5.0T group were both larger than those of 3.0T group([62.11±4.16],[48.92±4.62],t=28.339,19.681,both P＜0.001).There were 80 segments of AChA-A1,80 of AChA-A2 and 60 segments of AChA-A3 displayed on 5.0T TOF-MRA,while 60 segments of AChA-A1,36 of AChA-A2 and 12 segments of AChA-A3 displayed on 3.0T TOF-MRA,respectively.In 5.0T group,the length of the left and right AChA was(24.01±7.41)mm and(22.72±9.36)mm,with diameter of(1.16±0.12)mm and(1.19±0.14)mm,respectively,whereas in 3.0T group,the relative values were(18.35±8.67)mm,(16.80±6.94)mm,(0.99±0.25)mm and(0.95±0.29)mm,respectively,all in 5.0T group were greater than in 3.0T group(t=3.242,3.183,4.595,3.846,all P＜0.001).Conclusion Compared with 3.0T TOF-MRA,5.0T TOF-MRA of AChA might provide better image quality and clearer vessel depiction,being helpful to clinical diagnosis and treatment of ACHA-related cerebral vascular diseases.

Objective To observe the value of 5.0T MR susceptibility weighted imaging(SWI)for displaying cerebral small veins and detecting cerebral microbleeds(CMB).Methods Head MR examinations were prospectively performed using both 3.0T and 5.0T MR scanner in 30 stroke patients suspected caused by cerebral small vessel disease.The image quality,effect of displaying cerebral small veins and detecting CMB were compared between 3.0T and 5.0T SWI.Results The image quality scores,signal-to-noise ratios,contrast-to-noise ratios,scores of displaying deep cerebral veins and subcortical veins,the counts of detecting CMB and iron deposition on cortical surface of 5.0T SWI were all higher than those of 3.0T SWI(all P＜0.05).High consistency of CMB positions was found between 3.0T and 5.0T SWI(Kappa=1.0).Conclusion The effect of 5.0T MR SWI for displaying cerebral small veins and detecting cerebral microbleeds were better than 3.0T MR SWI,which could be used to assess stroke caused by cerebral small vascular disease.

Objective To observe the feasibility of 5.0T MR for cardiac imaging.Methods Three patients with heart diseases and 17 healthy volunteers were prospectively enrolled.Cardiac MR(CMR)cine sequence and black blood sequence imaging were performed using 5.0T and 3.0T MR scanner,respectively.The image quality and artifacts degrees were compared between 5.0T and 3.0T CMR images,and the consistency of left ventricular parameters obtained using 5.0T and 3.0T scanners was analyzed.Results No significant difference of image quality nor artifacts degrees was found between 5.0T and 3.0T CMR images(all P＞0.05).The left ventricular end diastolic volume(EDV),end systolic volume(ESV),ejection fraction(EF),stroke volume(SV)and end diastolic mass(EDM)derived from cine images acquired at different fields were in a good agreement(all ICC＞0.75,all P＜0.001).Conclusion 5.0T MR could be used for cardiac imaging,with image quality of cine and black blood sequences comparable to that of 3.0T MR.

Conventional 1.5T and 3.0T cardiac MRI(CMRI)had been widely used.The ultrahigh field MR behaved better in image resolution and signal-to-noise ratio.The domestic 5.0T whole-body ultrahigh field MRI had better balance between the field strength and quality in CMRI,which was expected to improve imaging quality and efficiency.The status challenges and future of 5.0T CMRI were reviewed in this paper.

Objective To observe the value of 5.0T MRI for quantifying proton density fat fraction(PDFF)of liver.Methods Liver chemical shift encoded(CSE)MR scanning were prospectively performed using 5.0T,3.0T and 1.5T scanner in 30 volunteers,respectively,and CSE-PDFF were measured.Then MR spectroscopy(MRS)were performed using 5.0T and 1.5T scanner,respectively,and MRS-PDFF were also measured.The consistency of liver PDFF measured on different images was observed,and the value of 5.0T MRI for liver PDFF was analyzed.Results The overall consistencies of liver CSE-PDFF measured with 5.0T,3.0T and 1.5T MR scanner were all good(all ICC＞0.75,all P＜0.001).The consistency of liver CSE-PDFF based on 5.0T and 3.0T,1.5T MR scanner were both good(ICC=0.989,0.992,both P＜0.001).The overall consistencies of CSE-PDFF based on 5.0T MR and MRS-PDFF based on 5.0T and 1.5T MR were both good(both ICC＞0.75,both P＜0.001).CSE-PDFF had good consistency with MRS-PDFF based on same 5.0T MR scanner(ICC=0.988,P＜0.001),and CSE-PDFF based on 5.0T had good consistency with MRS-PDFF based on 1.5T MR scanner(ICC=0.978,P＜0.001).Conclusion 5.0T MRI had high value for quantifying liver PDFF.

Objective To observe the consistency of 5.0T and 1.5T MR spectroscopy(MRS)for quantitating proton density fat fraction(PDFF)of liver.Methods Lipid emulsion models with lipid content of 0,5％,10％,15％,20％,25％and 30％were prepared.1H-MRS were collected using 5.0T and 1.5T MR scanners,respectively,and PDFF were obtained with jMRUI software.Totally 23 people,including 11 cases of fatty liver and 12 healthy adults were prospectively collected,and volume of interest(VOI)in the liver were selected to acquire 1H-MRS,and PDFF were obtained with jMRUI software and corresponding workstation,respectively.The consistencies of PDFF measured with different methods were analyzed.Results PDFF of lipid emulsion models with lipid content of 0,5％,10％,15％,20％,25％and 30％measured with jMRUI software and workstations based on 5.0T and 1.5T 1H-MRS all had good consistencies and being positively correlated,so were PDFF of liver tissue measured with jMRUI software and workstations based on 5.0T and 1.5T 1H-MRS.Conclusion 5.0T and 1.5T 1H-MRS had good consistency for quantitating liver PDFF.Measuring liver PDFF with workstation in clinical practice was helpful to simplifying workflow.

Objective To observe the value of susceptibility weighted imaging(SWI)based on 5.0T MRI for diagnosing hepatocellular carcinoma(HCC)complicated with vein tumor thrombi.Methods Totally 63 HCC patients were retrospectively enrolled,among them 17 complicated with vein tumor thrombi.The efficacy of 5.0T SWI for detecting vein tumor thrombus was observed,and the image quality were compared between 5.0T and 3.0T.Results 5.0T SWI displayed vein tumor thrombi in 16 cases,except for 1 case with vein tumor thrombi in the upper segment of the left lateral lobe of the left portal vein.The liver edge score,overall image quality score,signal-to-noise ratio and contrast-to-noise ratio of portal venous phase and hepatobiliary phase in 5.0T enhanced MRI were all higher than those in 3.0T(all P＜0.05).Conclusion 5.0T SWI was helpful for diagnosing HCC complicated with vein tumor thrombi.