The Evaluation Of Renal Injury After Injection Iodinated Contrast Agent Using BOLD And ASL Perfusion FMRI At 3.0T

Research background and significance:The use of iodinated contrast agents are becoming more widespread,with the increase of intervention surgery and the widespread applications of CT in clinic. Contrast medium induced renal dysfunction had caused widespread concern and research.Renal function maybe lose temporality or even persistently due to the potential side effects of iodinated contrast agent.This damage,known as contrast agent induced nephropathy.At present,kidney damage caused by iodinated contrast agent has been the third main reason of iatrogenic acute renal failure following surgery and low blood pressure,accounting 10%for iatrogenic acute renal failure incidence.And increase mental and economic burden in the patients obviously.At the same time,a marked increase in society financial burden.Early detection and prevention of renal damage due to iodinated contrast agent were very important in clinic.Measuring serum creatinine concentration was the most commonly method for patients of renal damage.But the study shown that serum creatinine changes were not sensitive to early renal function damage.Therefore,the discovery of effective means for early diagnosis of kidney damage caused by iodinated contrast agent had clinical significance.Many studies have shown that the blood flow of kidney medulla play an important role in contrast agent induced nephropathy.Changes in medullary blood flow,thus giving rise to changes in oxygen content medulla.Invasive means were always used for the research of renal blood flow and oxygen content in animals. Invasive laser Doppler probe were used for measurement of renal medullary blood flow traditionally.Invasive means of monitoring kidney in humans were difficult to implement and impractical method.The use of non-invasive means of monitoring renal medullary blood flow and oxygen content of iodinated contrast agent induced nephropathy at physiological conditions was essential.With the advance of magnetic resonance equipment,functional magnetic resonance imaging provides a powerful means for the early detection of many diseases.Some studies had shown that blood oxygen level dependent function magnetic resonance imaging(BOLD-fMRI) technology could monitor the changes in oxygen metabolism of renal medulla effectively.Arterial Spin Labeling function magnetic resonance imaging(ASL-fMRI) could detect the perfusion of tissues and organs quantitatively without exogenous contrast agents,using only their own blood flow.At present,the research has made significant results,useing BOLD and ASL imaging technologys to kidney diseases such as hypertensive nephrosis,diabetes, arteriosclerosis of renal and kidney cancer.Therefore,BOLD and ASL technique had a very large potential value in diagnosis and evaluation of kidney disease.Nowadays, there were very little research literature about the application of BOLD and ASL technology in evaluating kidney function after using iodinated contrast agent.Using functional MRI imaging BOLD and ASL technology to monitor renal function such as perfusion and oxygen metabolism changes in physical condition after injection of iodinated contrast agent,proviced non-invasive,simple and feasible means for the study of kidney disease.objective:1.To discuss the experimental research of normal kidney in rat with 3.0T BOLD and ASL function magetic resonence imaging.2.To discuss the experimental research of injury in the rat kidney after injection iodinated contrast agent with 3.0T fMRI-BOLD imaging.3.To discuss the experimental research of injury in the rat kidney after injection iodinated contrast agent with 3.0T fMRI-ASL imaging.Materials and methods:1.Preparation of laboratory animalsTo purchase 29 SD rats,with weight of 109.60g±14.26g.Each rat was fasting and water deprivation for 4 hours before MRI scaning.The MRI scans were performed after intraperitoneal anesthesia in 30 minutes later.Each time point 3 rats were executed to check renal pathological observation.2.MRI scan2.1 Scan Sequence①Three planar orientation:transverse,sagittal and coronal.②Conventional MRI sequences:T2WI axial,T2WI coronal,T1WI axial,fast spin echo(FSE) sequence.③BOLD imaging sequences:coronal,(multiple fast gradient recalled echo,MFGRE) sequence.④ASL imaging sequences:coronal,flow sensitive alternating inversion recovery, FAIR),(single-shot fast spin echo,SSFSE),FAIR-SSFSE sequence.2.2 MRI Scanning MethodUsed epuipment:3.0T MRI scanner,50mmbirdcage experimental animals dedicated coil.Head first,in supine position.MRI scans were performed before and after 20mins, 24hrs,48hrs,72hrs of injection iodinated contrast agent.The former as the control group.The scanning sequences were T1WI,T2WI,BOLD,ASL-FAIR.The scanning time was 14 mintues and 12 seconds.4 times MRI scanning were performed at each time point with T2WI coronal,BOLD,ASL-FAIR after injection iodinated contrast agent.Each scanning time was 6 minutes and 14 seconds.3.MRI Images Analysis3.1 Image Quality Analysis2 experienced MR diagnosis of physicians respectively analyzed the image quality of each sequence,including the image sinal to noise ratio,contrast,resolution, artifacts and whether or not the anatomical structure could be demonstracted clearly.3.2 The T2*value and R2*value measurements IN BOLD imaging The four-layer scanning was performed on each kidney,with each layer received 8 different T2* images of different TE time(2.2ms～14.7ms).All the images were submitted to obtain T2* Map image by functool software on workstation.The T2* value was measured on T2*Map image.R2 * values in accordance with the formula: R2*=1/T2*,With mean±standard deviation.3.3 The ASL-RBF value measurement of ASL imagingThe four-layer scanning was performed on each kidney,with each layer received 20 different images.All the images were submitted to access renal perfusion images by functool-fair software on ADW4.3 workstation.The blood flow value of cortex,outer medullary and inner medullary were measured on renal perfusion,with mean±standard deviation.3.4 ROI MeasurementThe region of interest(ROI) selected on each kidney of the same experimental subject had the same size and shape.Each ROI had the area of 1.5mm~2～2.5mm~2, contained at least 5 pixels.6-10 ROIs were measured on cortex and medulla,with the average±standard deviation.The ROIs of placement avoid distortion,artifact and large vessels.4.Pathological Observation3 mice were selected on each time point.The kidneies were fetched immediatedly after scanning.The capsules were removed and discissioed along the renal pedicle coronal.and then were fixed in 10%formalin solution after washing with normal saline.The kidney specimens were procedured by alcohol dehydration,xylene transparent,Baptist wax and paraffin-embedded by routine pathological examination,which were cut 3um thick slices for conventional pathological HE staining,mount and so on.Then were observed under 80,400 times microscope respectively,some specimens had photograph.5.Statistical AnalysisData entry and analysis were performed by SPSS16.0 statistical software using mean±standard deviation,inter-group comparison using t test,variance analysis, before and after the group used their own matching t test,non-normal distribution or variance of arrhythmia using rank sum test.Different time point measurements of changes in the use of line graph.Results1.The Experimental Results29 SD rats,number as 1th to 29th respectively,13 male and 16 female among the total.Rats No.1 to 3 were used to preliminary test,datas were not recorded.The test includes 26 Rats.The rats were abandoned for anesthetic death.Some images were ruled out for the bad quality.The test analysis different cases in different groups.2.Image Quality Analysis2.1 Transverse and coronal T2 weighted image had the best quality without any artifacts,and showed a clear tissue structure.ASL image is better,with a few artifacts, and also showed a clear tissue structure.More artifacts could be seen in BOLD image, the signal to noise ratio and resolution were comparatively lower,but image analysis and measurements were not affected.3.Statistical Analysis Results3.1 There were significant differenct of R2* values in cortex,epiopticon and opticon of both kidney,intercomparison t test,The same group is no significant difference (P＜0.05).3.2 There were significant differenct of ASL-RBF values in cortex,epiopticon and opticon of both kidney,intercomparison t test,The same group is no significant difference(P＜0.05).3.3 R2* values compared between normal control rats.To left kidney:R2* values in peripticon were of the highest(32.77±3.07second-1),but there were significant difference(P=0.041＜0.05) between renal cortex,peripticon and opticon intercomparison among them.To right kidney:The highest R2* values was 31.76±2.73 second-1 in peripticon,there were significant difference(P＜0.05) between renal cortex,peripticon and opticon intercomparison.3.4 Rat's medulla and cortex R2* values intercomparison between time groups with paired t-test:(1).To left kidney:There was no significant difference between rat's R2* values of renal cortex in control group and in each different time group after injection of iodinated contrast agent.R2* values of opticon were significant difference between control group and 24 hours group,24 hours group and 72 hours group(P＜0.05),but there were not significant difference between other groups.R2* values in peripticon,Significant difference could be found between control group and each different groups after injection of iodinated contrast agent(P＜0.05);no significant difference between 48 hours and 72 hours group(P=0.055),but there were significant difference between other groups(P＜0.05).(2).To right kidney:The R2* values in cortex of control group were significantly different to 20 minutes,24 hours and 48 hours group(P＜0.05);there were no significant difference between 24 hours group and 48 hours,72 hours,between 48 hours and 72 hours(P＜0.05).R2* values in peripticon significant difference could be found between control group and 20 minutes,24 hours,48 hours group(P＜0.05),but between control group and 72 hours, no significant difference(P=0.106).R2* values in opticon,significant difference could be found between control group and 20 minutes,24 hours group(P＜0.05),but no significant difference between others.3.5 Intercomparison of ASL-RBF values in rats medulla and cortex between each groups with paired t-test:(1).To left kidney:There was no significant difference between ASL-RBF values of renal cortex in control group and in each different time group after injection of iodinated contrast agent(P＞0.05).ASL-RBF values of opticon were significant differenct between control group and 20 minutes group,20 minutes group and 24 hours,48 hours group(P＜0.05),and no significant difference between other groups.ASL-RBF values in peripticon,Significant difference could be found between control group and 20 minutes,24 hours,48 hoursand 72 hours groups (P＜0.05);no significant difference between 20 minutes group and 24 hours group(P =0.216).(2).To right kidney:There was no significant difference between ASL-RBF values of renal cortex in control group and in each different time group(P＞0.05), Significant difference could be found between 20 minutes group and 24 hours,48 hours group and 72 hours(P＞0.05).ASL-RBF values of opticon were significant differenct between 20 minutes group and 24 hours group(P=0.003),and no significant difference between other groups(P＞0.05). 3.6 The R2* value and ASL-RBFvalue were negative correlation in renal cortex, peripticon and opticon of Experimental Group.The R2* value and ASL-RBFvalue were significant difference in 24hr group opticon.There were no significant difference in others groups(P＞0.05)4 Pathological ResultsPathology HE staining were done to both kidney of different time group rats, contained pre-injection of iodinated contrast agent and 20 minutes,24 hours,48 hours,72 hours after injection iodinated contrast agent.Observed under light microscope by 80,400 times,findings as follow:20 minutes after injection iodinated contrast agent,part of the proximal convoluted tubule epithelial cells cloudy swelling, a few could be seen dissolved,part of the distal convoluted tubule lumens narrowing, also a few epithelium dissolved and disappeared,interstitial substance angiectasis, lightly congestion.Over time:24 hours after injection,small amounts cellular swelling were observed in glomerulus,but no atrophy and fibrosis.Part of proximal and distal convoluted tubule epithelial cells cloudy swelling,no fatty degeneration, hyalinization,cellular necrosis,and so on.The majority of interstitial blood vessels and telangiectasia,congestion,rupture.48 hours after injection,glomerulus cells swelling,atrophy could be seen,part of proximal tubule and distal convoluted tubule epithelial cells cloudy swelling,fatty degeneration,hyaline degeneration and necrosis, occurred.The majority of interstitial vasodilation,hyperemia,most of the expansion of capillary bleeding.72 hours,glomerulus structure occurred fibrosis,atrophy.Part of proximal tubule and distal convoluted tubule epithelial cells cloudy swelling,no steatosis,hyaline degeneration and necrosis changes.A small amount of interstitial vasodilator,congestive.a few capillary a had expansion,hemorrhage.Conclusions:1.3.0 TMRI rat kidney BOLD imaging technology,R2* values can reflect the changes of oxygen content quantitatively in the kidney tissue after contrast agent injected.2.3.0T MRI rat kidney ASL imaging technique,ASL-RBF values can reflect the changes of blood flow quantitatively in the kidney after contrast agent injected. 3.The combination of 3.0T MRI BOLD and ASL-fMRI imaging technology can be more accurately reflect the kidney perfusion and oxygen metabolism changes in rat kidney after iodinated contrast agent injection,and can be used as the evaluation of kidney damage by iodinated contrast agent.Innovations Of The SubjectFirst proposed using 3.0T MRI BOLD and ASL-fMRI functional imaging techniques to monitor the kidney blood flow and oxygen metabolism changes after injection iodinated contrast agent.To consider that 3.0T MRI BOLD and ASL-fMRI imaging techniques can be used to monitoring the Change of renal function after injection of iodinated contrast agent feasibility at physiological conditions.