hepatic fibrosis ( hf ) is the deposition of excess extracellular matrix that is rich in collagen , proteoglycans , and other macromolecules . the most common causes of hf include viral infections , alcoholic and nonalcoholic steatohepatitis , toxic substances intake , metabolic disorders , and so on . fibrosis leads to end - stage cirrhosis and hepatocellular carcinoma , which are the most common causes of morbidity and mortality in developed countries . early detection and evaluation of hf are very important . magnetic resonance imaging ( mri ) the common functional methods , which have been used in hf studies , include mr elastography ( mre ) , diffusion - weighted imaging ( dwi ) , dynamic contrast - enhanced mri , and so on . among these methods , mre is a promising technique used for quantitatively assessing the stiffness of the liver , using propagating mechanical shear waves . the mechanical properties of tissues can correlate with the extent of hf . in recent studies , mre has been shown to be useful for staging hf with its high reproducibility and favorable diagnostic ability . on the other hand , dwi is a fast , noninvasive imaging technique which can offer the valuable information to differentiate normal tissue from anomalous lesions at a cellular level . some prior studies have demonstrated that the apparent diffusion coefficient ( adc ) value of hepatic parenchyma is a promising biomarker in identifying moderate to severe fibrosis . our study was aimed to compare the sensitivity and specificity of mre and dwi for staging hf in an animal model . all studies were conducted with the approval of the animal care committee at our institute . the experiments were conducted on 53 healthy new zealand white rabbits ( weighing 2.02.5 kg ) . all rabbits were divided into two groups : control group ( n = 9 ) and hf group ( n = 44 ) . in addition , the hf group was divided into two subgroups : group a ( n = 32 ) and group b ( n = 12 ) . if rabbits from group a died during the experiment , the rabbits from group b would be used to meet the shortage of group a. hf was induced by subcutaneous injection of 50% carbon tetrachloride ( ccl4 ) oil once a week . the dose of ccl4 was gradually increased ( 0.1 ml / kg at week 13 ; 0.2 ml / kg at week 46 ; 0.3 ml / kg at week 710 ) . a , mri examinations were performed in random eight rabbits at 4 , 5 , 6 , 10 weeks , respectively , after first injection . all examinations were performed on a 3.0 t scanner ( siemens , erlangen , germany ) by use of an 18-channel phased array knee coil . the imaging protocol included an axial t1-weighted flash sequence ( repetition time [ tr]/echo time [ te ] , 165/2.9 ms ; field of view ( fov ) , 140 mm  160 mm ; matrix size , 168  256 ; slice thickness , 5 mm ; gap 1 mm ; bandwidth , 310 hz / pixel ) , and an axial t2-weighted haste sequence ( tr / te , 1000/92 ms ; fov , 160 mm  160 mm ; matrix size , 134  192 ; section thickness , 5 mm ; gap 1 mm ; bandwidth , 355 hz / pixel ) . magnetic resonance elastography the acoustic driver system for mre developed by mayo clinic was used for this study . all the rabbits were imaged in the supine position with an 8 cm - diameter , 1.5 cm - thick , cylindrical passive longitudinal shear wave driver . a two - dimensional ( 2d ) gradient echo sequence was used to collect axial wave images . the parameters of the mre gradient echo sequence were as follows : tr / te , 50/22.7 ms ; flip angle , 30 ; fov , 130 mm  160 mm ; matrix size , 128  84 ; slice thickness , 5 mm . mre was generated by processing the acquired images of propagating shear waves with a 2d multi - scale direct inversion algorithm . diffusion - weighted imaging diffusion - weighted images were acquired in the transverse plane using a spin - echo echo - planar imaging sequence with diffusion - gradient encoding in three orthogonal directions . the parameters were as follows : tr 3000 ms , te 67 ms , fov 180 mm  136 mm , matri  98  56 , section thickness 5 mm , gap 1 mm , and b values of 50 , and 800 s / mm . the adcs were calculated according to the formula adc = ( ln [ si1/si2])/(b2  b1 ) , where si1 and si2 are signal intensities by sequence s1 and s2 , b1 ( = 50 ) and b2 ( = 800 ) are gradient factors of sequences s1 and s2 , respectively . adc maps were automatically calculated inline on a pixel - by - pixel basis with incorporated software on a commercial workstation ( syngo ; siemens healthcare , erlangen , germany ) . one experienced radiologist ( 15 years of experience in abdominal mri ) evaluated all mri on a commercial workstation ( syngo , siemens healthcare , erlangen , germany ) , who was blinded to the histopathological results . in order to measure liver stiffness ( ls ) values of the hepatic parenchyma , three round - shaped ( 23 cm in diameter ) regions of interest ( roi ) were placed in liver on the elastogram map referring to t1-weighted image , avoiding major hepatic vessels and branches , large bile ducts , liver edges , and motion artifacts . the average ls values ( in kpa ) were calculated as the mean value of rois . diffusion - weighted imaging and adc maps three circular roi were , respectively , placed in the hepatic parenchyma , avoiding vessels , large bile ducts , liver edges , and motion artifacts . the mean adc values were calculated as the mean value of the total three adc measurements obtained . an experienced pathologist with 8 years of experience in histologic analysis prepared the samples and performed the histologic analysis , who was blinded to the information of the animal model establishment . the serial 5 m - thick sections were cut and then were stained with hematoxylin and eosin . fibrosis stages were assessed using the scheuer scoring system on a scale of s0 to s4 as follows : s0 , no fibrosis ; s1 , portal fibrosis without septa ; s2 , portal fibrosis with few septa ; s3 , numerous septa without cirrhosis ; and s4 , cirrhosis . statistical analysis was performed using spss ( version 16.0 ; spss , chicago , il , usa ) and medcalc ( version 11.4.2.0 ; medcalc for windows , mariakerke , belgium ) . one - way analysis of variance was used to evaluate the difference in ls and adc values at different hf stages . correlations among ls , adc values , the scheuer score were assessed using the spearman rank correlation . receiver operating characteristics ( rocs ) analysis was performed to compare the diagnostic value of mre and dwi . in order to evaluate diagnostic values of mre and dwi by roc analysis , all animals were divided into some various stage grouping as follows : s0:s1 - 2 - 3 - 4 ( s1 ) , s0 - 1:s2 - 3 - 4 ( s2 ) , s0 - 1 - 2:s3 - 4 ( s3 ) , and s0 - 1 - 2 - 3:s4 ( s4 ) . the areas under the roc curves ( aucs ) for ls and adc values used for staging hf were compared . a difference of p < 0.05 was considered significant . all studies were conducted with the approval of the animal care committee at our institute . the experiments were conducted on 53 healthy new zealand white rabbits ( weighing 2.02.5 kg ) . all rabbits were divided into two groups : control group ( n = 9 ) and hf group ( n = 44 ) . in addition , the hf group was divided into two subgroups : group a ( n = 32 ) and group b ( n = 12 ) . if rabbits from group a died during the experiment , the rabbits from group b would be used to meet the shortage of group a. hf was induced by subcutaneous injection of 50% carbon tetrachloride ( ccl4 ) oil once a week . the dose of ccl4 was gradually increased ( 0.1 ml / kg at week 13 ; 0.2 ml / kg at week 46 ; 0.3 ml / kg at week 710 ) . a , mri examinations were performed in random eight rabbits at 4 , 5 , 6 , 10 weeks , respectively , after first injection . all examinations were performed on a 3.0 t scanner ( siemens , erlangen , germany ) by use of an 18-channel phased array knee coil . the imaging protocol included an axial t1-weighted flash sequence ( repetition time [ tr]/echo time [ te ] , 165/2.9 ms ; field of view ( fov ) , 140 mm  160 mm ; matrix size , 168  256 ; slice thickness , 5 mm ; gap 1 mm ; bandwidth , 310 hz / pixel ) , and an axial t2-weighted haste sequence ( tr / te , 1000/92 ms ; fov , 160 mm  160 mm ; matrix size , 134  192 ; section thickness , 5 mm ; gap 1 mm ; bandwidth , 355 hz / pixel ) . magnetic resonance elastography the acoustic driver system for mre developed by mayo clinic was used for this study . all the rabbits were imaged in the supine position with an 8 cm - diameter , 1.5 cm - thick , cylindrical passive longitudinal shear wave driver . a two - dimensional ( 2d ) gradient echo sequence was used to collect axial wave images . the parameters of the mre gradient echo sequence were as follows : tr / te , 50/22.7 ms ; flip angle , 30 ; fov , 130 mm  160 mm ; matrix size , 128  84 ; slice thickness , 5 mm . mre was generated by processing the acquired images of propagating shear waves with a 2d multi - scale direct inversion algorithm . diffusion - weighted imaging diffusion - weighted images were acquired in the transverse plane using a spin - echo echo - planar imaging sequence with diffusion - gradient encoding in three orthogonal directions . the parameters were as follows : tr 3000 ms , te 67 ms , fov 180 mm  136 mm , matri  98  56 , section thickness 5 mm , gap 1 mm , and b values of 50 , and 800 s / mm . the adcs were calculated according to the formula adc = ( ln [ si1/si2])/(b2  b1 ) , where si1 and si2 are signal intensities by sequence s1 and s2 , b1 ( = 50 ) and b2 ( = 800 ) are gradient factors of sequences s1 and s2 , respectively . adc maps were automatically calculated inline on a pixel - by - pixel basis with incorporated software on a commercial workstation ( syngo ; siemens healthcare , erlangen , germany ) . one experienced radiologist ( 15 years of experience in abdominal mri ) evaluated all mri on a commercial workstation ( syngo , siemens healthcare , erlangen , germany ) , who was blinded to the histopathological results . in order to measure liver stiffness ( ls ) values of the hepatic parenchyma , three round - shaped ( 23 cm in diameter ) regions of interest ( roi ) were placed in liver on the elastogram map referring to t1-weighted image , avoiding major hepatic vessels and branches , large bile ducts , liver edges , and motion artifacts . the average ls values ( in kpa ) were calculated as the mean value of rois . diffusion - weighted imaging and adc maps were evaluated on the workstation . referring to t2-weighted image , three circular roi were , respectively , placed in the hepatic parenchyma , avoiding vessels , large bile ducts , liver edges , and motion artifacts . the mean adc values were calculated as the mean value of the total three adc measurements obtained . an experienced pathologist with 8 years of experience in histologic analysis prepared the samples and performed the histologic analysis , who was blinded to the information of the animal model establishment . the serial 5 m - thick sections were cut and then were stained with hematoxylin and eosin . fibrosis stages were assessed using the scheuer scoring system on a scale of s0 to s4 as follows : s0 , no fibrosis ; s1 , portal fibrosis without septa ; s2 , portal fibrosis with few septa ; s3 , numerous septa without cirrhosis ; and s4 , cirrhosis . statistical analysis was performed using spss ( version 16.0 ; spss , chicago , il , usa ) and medcalc ( version 11.4.2.0 ; medcalc for windows , mariakerke , belgium ) . one - way analysis of variance was used to evaluate the difference in ls and adc values at different hf stages . correlations among ls , adc values , the scheuer score were assessed using the spearman rank correlation . receiver operating characteristics ( rocs ) analysis was performed to compare the diagnostic value of mre and dwi . in order to evaluate diagnostic values of mre and dwi by roc analysis , all animals were divided into some various stage grouping as follows : s0:s1 - 2 - 3 - 4 ( s1 ) , s0 - 1:s2 - 3 - 4 ( s2 ) , s0 - 1 - 2:s3 - 4 ( s3 ) , and s0 - 1 - 2 - 3:s4 ( s4 ) . the areas under the roc curves ( aucs ) for ls and adc values used for staging hf were compared . a difference of p < 0.05 was considered significant . nine rabbits had a scheuer score of s0 ; 8 , a score of s1 ; 8 , a score of s2 ; 8 , a score of s3 ; and 8 , a score of s4 . the mean ls values of hf stages were 1.023  0.13 kpa ( s0 ) , 1.334  0.24 kpa ( s1 ) , 1.405  0.16 kpa ( s2 ) , 2.004  0.50 kpa ( s3 ) and 1.986  0.44 kpa ( s4 ) . the mean ls value increased , along with the increasing hf stage [ figure 1 ] . significant differences of ls values were present among hf stages ( f = 14.665 , p < 0.005 ) [ figure 2 ] . no significant differences of ls values were present between s0 and s1 ( p > 0.05 ) , s1 and s2 ( p > 0.5 ) , and s3 and s4 ( p > 0.5 ) . the ls values significantly correlated with the extent of hf ( r = 0.838 , p < 0.001 ) [ figure 3 ] . t1-weighted image ( a and c ) and magnetic resonance elastography ( b and d ) of two rabbits with hepatic fibrosis ( hf ) . one rabbit in the top row with mild hf ( s2 ) shows mean ls value of 1.66 kpa , whereas the other ( s4 ) in the lower row has significantly elevated liver stiffness ( mean liver stiffness value = 2.59 kpa ) . the plot shows the significant differences of liver stiffness values among all hepatic fibrosis stages except for s0 versus s1 , s1 versus s2 , and s3 versus s4 . scatterplot shows the relationship between the liver stiffness ( ls ) value and hepatic fibrosis ( hf ) stages . the ls values significantly correlated with hf stages ( r= 0.838 , p < 0.001 ) . the mean adc values of hf stages were ( 1.392  0.29 ) 10 mm / s ( s0 ) , ( 1.247  0.27 ) 10 mm / s ( s1 ) , ( 1.381  0.29 ) 10 mm / s ( s2 ) , ( 1.032  0.20 ) 10 mm / s ( s3 ) and ( 0.932  0.23 ) 10 mm / s ( s4 ) . the mean adc value decreased , along with the increasing hf stage [ figure 4 ] . significant differences of adc values were present among hf stages ( f = 5.344 , p < 0.005 ) [ figure 5 ] . no significant differences of adc values were present among s0 , s1 , and s2 ( p > 0.1 ) . there was also no significant difference of adc values between s1 and s3 ( p > 0.1 ) and s3 and s4 ( p > 0.1 ) . the adc values significantly correlated with the hf stages ( r = 0.527 , p < 0.001 ) [ figure 6 ] . diffusion - weighted imaging ( a and c ) and apparent diffusion coefficient ( adc ) ( b and d ) maps of two rabbits with hepatic fibrosis ( hf ) . one rabbit in the top row with mild hf ( s2 ) shows mean adc value of 1.216  10 mm / s , whereas the other ( s4 ) in the lower row has significantly decreased adc values ( mean adc value = 0.757  10 mm / s ) . the plot shows significant differences of apparent diffusion coefficient values between s0 and s3 , s0 and s4 , s1 and s4 , s2 and s3 , and s2 and s4 . scatterplot shows the relationship between the apparent diffusion coefficient ( adc ) value and hepatic fibrosis ( hf ) stages . the adc values significantly correlated with hf stages ( r= 0.527 , p < 0.001 ) . the areas under roc curve for ls values were greater than those for the adc values in all hf stages ( 0.979 vs. 0.712 for  s1 , 0.922 vs. 0.699 for  s2 , 0.949 vs. 0.867 for  s3 , and 0.843 vs. 0.795 for s4 ) [ figure 7 ] . but no significant differences of aucs for ls values and adc values were present in two groups ( s3 and s4 ) . the cut - off values of ls and adc values in all stage grouping were listed in tables 1 and 2 . the receiver operating characteristic ( roc ) analysis on evaluating the diagnostic value of magnetic resonance elastography and diffusion - weighted imaging ( s1 , a;s2 , b;s3 , c;s4 , d ) . the areas under roc curve for liver stiffness values were greater than those for the apparent diffusion coefficient values in all hepatic fibrosis stages ( s1 , 0.922 vs. 0.699 for s2 , 0.949 vs. 0.867 for s3 , and 0.843 vs. 0.795 for s4 ) . diagnostic value of ls values at different hf stages ls : liver stiffness ; hf : hepatic fibrosis . diagnostic value of adc values at different hf stages adc : apparent diffusion coefficient ; hf : hepatic fibrosis . nine rabbits had a scheuer score of s0 ; 8 , a score of s1 ; 8 , a score of s2 ; 8 , a score of s3 ; and 8 , a score of s4 . the mean ls values of hf stages were 1.023  0.13 kpa ( s0 ) , 1.334  0.24 kpa ( s1 ) , 1.405  0.16 kpa ( s2 ) , 2.004  0.50 kpa ( s3 ) and 1.986  0.44 kpa ( s4 ) . the mean ls value increased , along with the increasing hf stage [ figure 1 ] . significant differences of ls values were present among hf stages ( f = 14.665 , p < 0.005 ) [ figure 2 ] . no significant differences of ls values were present between s0 and s1 ( p > 0.05 ) , s1 and s2 ( p > 0.5 ) , and s3 and s4 ( p > 0.5 ) . the ls values significantly correlated with the extent of hf ( r = 0.838 , p < 0.001 ) [ figure 3 ] . t1-weighted image ( a and c ) and magnetic resonance elastography ( b and d ) of two rabbits with hepatic fibrosis ( hf ) . one rabbit in the top row with mild hf ( s2 ) shows mean ls value of 1.66 kpa , whereas the other ( s4 ) in the lower row has significantly elevated liver stiffness ( mean liver stiffness value = 2.59 kpa ) . the plot shows the significant differences of liver stiffness values among all hepatic fibrosis stages except for s0 versus s1 , s1 versus s2 , and s3 versus s4 . scatterplot shows the relationship between the liver stiffness ( ls ) value and hepatic fibrosis ( hf ) stages . the ls values significantly correlated with hf stages ( r= 0.838 , p < 0.001 ) . the mean adc values of hf stages were ( 1.392  0.29 ) 10 mm / s ( s0 ) , ( 1.247  0.27 ) 10 mm / s ( s1 ) , ( 1.381  0.29 ) 10 mm / s ( s2 ) , ( 1.032  0.20 ) 10 mm / s ( s3 ) and ( 0.932  0.23 ) 10 mm / s ( s4 ) . the mean adc value decreased , along with the increasing hf stage [ figure 4 ] . significant differences of adc values were present among hf stages ( f = 5.344 , p < 0.005 ) [ figure 5 ] . no significant differences of adc values were present among s0 , s1 , and s2 ( p > 0.1 ) . there was also no significant difference of adc values between s1 and s3 ( p > 0.1 ) and s3 and s4 ( p > 0.1 ) . the adc values significantly correlated with the hf stages ( r = 0.527 , p < 0.001 ) [ figure 6 ] . diffusion - weighted imaging ( a and c ) and apparent diffusion coefficient ( adc ) ( b and d ) maps of two rabbits with hepatic fibrosis ( hf ) . one rabbit in the top row with mild hf ( s2 ) shows mean adc value of 1.216  10 mm / s , whereas the other ( s4 ) in the lower row has significantly decreased adc values ( mean adc value = 0.757  10 mm / s ) . the plot shows significant differences of apparent diffusion coefficient values between s0 and s3 , s0 and s4 , s1 and s4 , s2 and s3 , and s2 and s4 . scatterplot shows the relationship between the apparent diffusion coefficient ( adc ) value and hepatic fibrosis ( hf ) stages . the adc values significantly correlated with hf stages ( r= 0.527 , p < 0.001 ) . the areas under roc curve for ls values were greater than those for the adc values in all hf stages ( 0.979 vs. 0.712 for  s1 , 0.922 vs. 0.699 for  s2 , 0.949 vs. 0.867 for  s3 , and 0.843 vs. 0.795 for s4 ) [ figure 7 ] . but no significant differences of aucs for ls values and adc values were present in two groups ( s3 and s4 ) . the cut - off values of ls and adc values in all stage grouping were listed in tables 1 and 2 . the receiver operating characteristic ( roc ) analysis on evaluating the diagnostic value of magnetic resonance elastography and diffusion - weighted imaging ( s1 , a;s2 , b;s3 , c;s4 , d ) . the areas under roc curve for liver stiffness values were greater than those for the apparent diffusion coefficient values in all hepatic fibrosis stages ( s1 , 0.922 vs. 0.699 for s2 , 0.949 vs. 0.867 for s3 , and 0.843 vs. 0.795 for s4 ) . diagnostic value of ls values at different hf stages ls : liver stiffness ; hf : hepatic fibrosis . diagnostic value of adc values at different hf stages adc : apparent diffusion coefficient ; hf : hepatic fibrosis . in this study , our results demonstrated that there was a significant difference of ls and adc values among hf stages in a rabbit model . the ls values measured on mre were more strongly correlated with the hf stages than with adc values . but no significant difference of the diagnostic performances of mre and dwi in two groups ( s3 and s4 ) were present . up to now , there are five system of scoring hf , including knodell hai , the scheuer scoring system , ishak 's system , metavir system , and ishak modified hai . the scheuer scoring system can be applied for chronic viral hepatitis as well as nonviral hepatitis . in this present study , so the scheuer scoring system was used to evaluate hf stages . in term of this system , the ls value becomes larger , along with increasing the tissue stiffness . on the elastograms of hf , mre has been used to assess hf caused by various etiologies . in a prior study , yin et al . reported there was a linear correlation between ls and fibrosis extent in an animal model . in our study , this result indicated that the ls values measured on mre can be used to represent the architectural distortion in hf . annet et al . demonstrated that the adc of the live rats correlated with the severity of hf . our results also explored that significant differences of adc values were also present among hf stages , and adc values significantly correlated with hf stages . the b - value is a very important factor , which influences the contribution of microperfusion in adc measurements . recommended that a b - value of 750 s / mm or greater can help quantify liver fibrosis accurately . in this present study , large b value ( b = 800 s / mm ) was used to decrease the component of microperfusion . thus , these correlations between adc values and hf stages in our study can be explained by extracellular accumulation of collagen , glycosaminoglycans , and proteoglycans , which can restrict water diffusion . in a recent meta - analysis on evaluating performance of mre and dwi for staging hf , the sensitivity , specificity , and auc of mre for staging f0f1 versus f2f4 and f0f2 versus f3f4 were higher accuracy than those of dwi . wang et al . compared the ability of mre and dwi for staging hf in patients with chronic hepatitis . in his study , mre showed greater capability than dwi in discriminating stage 2 or greater ( f2 ) , stage 3 or greater ( f3 ) , and cirrhosis ( f4 ) , shown as significant differences in auc . meanwhile , mre showed higher sensitivity and specificity in predicting fibrosis scores f2 , f3 , and f4 than those of dwi . but the correlationship between adc values and hf stages was not present in his study . our results demonstrated the sensitivity , specificity , and auc of mre for staging s1 and s2 were higher than those of dwi . no significant differences of aucs between mre and dwi were present in staging  s3 and s4 while the specificity of mre was higher than that of dwi . first , our animal model induced by ccl4 administration other than subjects in prior studies . second , the echo planar imaging sequence is very sensitive to magnetic susceptibility artifacts and motion artifacts , which can influence the measurements of adc values . first , we did not dynamically measure ls values and adc values because the rabbits with hf were not in good healthy conditions and were difficult to complete the continuous examinations . second , we did not evaluate the influence of steatosis , iron overload , and edema on stiffness , and adc measurements . in conclusion , magnetic resonance elastography more strongly correlated with the hf stages than dwi and is more specific in predicting all hf stages .
background : to compare the diagnostic values of magnetic resonance elastography ( mre ) and diffusion - weighted imaging ( dwi ) in staging hepatic fibrosis ( hf ) in an animal model.methods:this study consisted of 44 rabbits served as hf group and 9 normal rabbits . 
 hf group was divided into two subgroups : group a ( n = 32 ) and group b ( n = 12 ) . 
 rabbits in group b were served as a complementary group when rabbits in group a suddenly died during the study . 
 rabbits from control and group a underwent abdominal mr imaging ( mri ) , mre , and dwi . in group 
 a , random eight rabbits underwent mri examinations at 4 , 5 , 6 , 10 weeks after carbon tetrachloride oil subcutaneous injection . 
 liver stiffness ( ls ) and apparent diffusion coefficient ( adc ) values of liver parenchyma were measured . 
 the diagnostic performance of mre and dwi for staging hf was compared using the receiver operating characteristic curve analysis on the basis of the histopathological analysis of hf.results:significant differences of ls and dwi values were present among hf stages ( p < 0.005 ) . 
 the ls values measured on mre ( r = 0.838 , p < 0.001 ) were more strongly correlated with the hf stages than with adc values ( r = 0.527 , p < 0.001 ) . 
 the area under the receiver operating characteristic curve values of ls were significantly larger than those of dwi were for discriminating two stages of hf ( 0.979 vs. 0.712 for  s1 , 0.922 vs. 0.699 for  s2 ) . 
 mre showed higher specificity for predicting all stages of hf compared to dwi.conclusions:mre more strongly correlated with the hf stages than dwi and is more specific in predicting all hf stages .