a total of 220 patients with takayasu arteritis underwent ct examinations in our hospital during the 12 years , from january 1994 to december 2005 . to satisfy the inclusion criteria , the patients had to have active takayasu arteritis and to have had the follow - up ct examination done . the criteria for the active disease at the time of the initial ct included systemic features , an elevated erythrocyte sedimentation rate ( esr , normal range in females : 0 20 mm / hr , in males : 0 9 mm / hr ) and abnormal mural changes according to the initial ct evaluation . eighteen patients were included in this retrospective study to evaluate the interval changes of the ct findings in takayasu arteritis . their ages ranged from 11 to 53 years , with the mean age of 31.2 years at the time of the initial ct examination . from two to four ct examinations the clinical findings of the 18 patients are summarized in table 1 , including the number of the ct examinations , the modified ueda type of extent of disease , the levels of esr and c - reactive protein , along with the medical and surgical or interventional treatments . the esr was elevated in all except two patients ( cases 1 and 8) , who showed an elevated esr on a repeated examination performed within one month . the course of disease was modified ueda type i in four patients , type ii in two patients , type iii in nine patients and type iv in three patients . all the patients , except one patient with active pulmonary tuberculosis , were treated with prednisolone alone , or with methotrexate or cyclophosphamide . by the follow - up evaluation , the disease was defined as inactive if the esr was normal at least for six months without steroid medication . otherwise , the disease was defined as active . according to the above criteria , the disease was active in all 18 patients at the time of the initial ct evaluation . the disease was considered as inactive in five patients and active in 13 patients at the time of the last follow - up ct . because of the long period for collecting the cases , more than 10 years , various ct scanners were used for the patients scanning ; these scanners varied from a single slice spiral ct to a 16-channel multidetector ct ( mdct ) scanner including single slice spiral ct ( somatom plus - s , somatom plus-4 , siemens , erlangen , germany ) , the 4-channel mdct ( mx8000 , marconi medical systems , cleveland , oh ) , the 8-channel mdct ( lightspeed ultra , ge medical systems , milwaukee , wi ) and the 16-channel mdct ( sensation 16 , siemens , erlangen , germany ) . an 18- , or 20-gauge needle was placed into the antecubital vein , and 150 ml of nonionic contrast material , iopromide ( ultravist 370 ; schering , berlin , germany ) was injected at a rate of 2.5 3.0 ml / sec with using a power injector ( envision ct ; medrad , indianola , pa ) . we used the bolus - tracking method at the ascending aorta level and set 100 hu as the triggering threshold for the arterial phase . the venous phase scan was taken at 5 to 10 minutes after initiating the injection of the contrast material . the scanning parameters varied according to the type of the scanner , but the following basic concept for scanning of the aorta was followed : the slice thickness was kept as thin as possible for the scanning phase of the precontrast phase , the arterial phase and the venous phase . for the arterial phase , the slice thickness was 3 mm on the single spiral ct and the 4-channel mdct with 2 mm reconstruction intervals , and it was 1.5 mm on the 8-channel and the 16-channel mdct with 1 mm reconstruction intervals . for the precontrast and the delayed venous phase scans , the pitch value was 2 for the single spiral ct and 1 to 1.5 for mdct . mdct could cover the whole aorta during the time of a single breath - hold , and each scan was done with a single breath - hold . in case of the single slice spiral ct , the whole aorta for the arterial phase was covered with two breath - hold scans , one for the thoracic aorta and the other for the abdominal aorta . the high density of the aortic wall and the mural calcification on the precontrast ct scan and the low - attenuated ring on the arterial and the venous phase ct scan were examined by two collaborating radiologists . the mural findings of the follow - up ct were compared with those of the initial ct . in cases of multiple follow - up evaluations , the two radiologists measured the mural thickness on the transverse image of the arterial phase and the ct attenuation of the aortic wall in the precontrast , arterial and venous phases . the mean ct attenuation value in hounsfield units was calculated based on three or more measurements with a region of interest of 2 - 7 mm . the measurement was performed at the location with a maximum mural thickness , including the ascending aorta , the arch , the left common carotid and abdominal aorta . the arterial and delayed enhancements of the aortic wall were compared with the attenuation of the back muscle of the same image , and this was expressed as a ratio . the ratio of the attenuation of the enhanced aortic wall over the attenuation of the back muscle in the initial ct was compared with that of the follow - up ct . the luminal findings , in addition to the mural changes , were also considered on the initial and follow - up ct examinations . for the statistical tests between the two groups , mann - whitney u test was used for continuous variables , and the fisher exact test was used for categorical variables . the wilcoxon signed rank test was applied for statistically testing the follow - up evaluation . a two - tailed p value of 0.05 or less was considered to indicate statistical significance , and spss 10.0 statistical computer software ( spss , chicago , il ) was used . because of the long period for collecting the cases , more than 10 years , various ct scanners were used for the patients scanning ; these scanners varied from a single slice spiral ct to a 16-channel multidetector ct ( mdct ) scanner including single slice spiral ct ( somatom plus - s , somatom plus-4 , siemens , erlangen , germany ) , the 4-channel mdct ( mx8000 , marconi medical systems , cleveland , oh ) , the 8-channel mdct ( lightspeed ultra , ge medical systems , milwaukee , wi ) and the 16-channel mdct ( sensation 16 , siemens , erlangen , germany ) . an 18- , or 20-gauge needle was placed into the antecubital vein , and 150 ml of nonionic contrast material , iopromide ( ultravist 370 ; schering , berlin , germany ) was injected at a rate of 2.5 3.0 ml / sec with using a power injector ( envision ct ; medrad , indianola , pa ) . we used the bolus - tracking method at the ascending aorta level and set 100 hu as the triggering threshold for the arterial phase . the venous phase scan was taken at 5 to 10 minutes after initiating the injection of the contrast material . the scanning parameters varied according to the type of the scanner , but the following basic concept for scanning of the aorta was followed : the slice thickness was kept as thin as possible for the scanning phase of the precontrast phase , the arterial phase and the venous phase . for the arterial phase , the slice thickness was 3 mm on the single spiral ct and the 4-channel mdct with 2 mm reconstruction intervals , and it was 1.5 mm on the 8-channel and the 16-channel mdct with 1 mm reconstruction intervals . for the precontrast and the delayed venous phase scans , the pitch value was 2 for the single spiral ct and 1 to 1.5 for mdct . mdct could cover the whole aorta during the time of a single breath - hold , and each scan was done with a single breath - hold . in case of the single slice spiral ct , the whole aorta for the arterial phase was covered with two breath - hold scans , one for the thoracic aorta and the other for the abdominal aorta . the high density of the aortic wall and the mural calcification on the precontrast ct scan and the low - attenuated ring on the arterial and the venous phase ct scan were examined by two collaborating radiologists . the mural findings of the follow - up ct were compared with those of the initial ct . in cases of multiple follow - up evaluations , the two radiologists measured the mural thickness on the transverse image of the arterial phase and the ct attenuation of the aortic wall in the precontrast , arterial and venous phases . the mean ct attenuation value in hounsfield units was calculated based on three or more measurements with a region of interest of 2 - 7 mm . the measurement was performed at the location with a maximum mural thickness , including the ascending aorta , the arch , the left common carotid and abdominal aorta . the arterial and delayed enhancements of the aortic wall were compared with the attenuation of the back muscle of the same image , and this was expressed as a ratio . the ratio of the attenuation of the enhanced aortic wall over the attenuation of the back muscle in the initial ct was compared with that of the follow - up ct . the luminal findings , in addition to the mural changes , were also considered on the initial and follow - up ct examinations . for the statistical tests between the two groups , mann - whitney u test was used for continuous variables , and the fisher exact test was used for categorical variables . the wilcoxon signed rank test was applied for statistically testing the follow - up evaluation . a two - tailed p value of 0.05 or less was considered to indicate statistical significance , and spss 10.0 statistical computer software ( spss , chicago , il ) was used . the mural changes found on the initial and follow - up ct evaluations of the 18 patients are summarized in table 2 . on the precontrast ct , the high density of the aortic wall was noted in 15 patients ( 83% ) . curvilinear or dot - like calcifications were found in six patients ( 33% ) . on the arterial phase of ct , the wall was slightly enhanced in various portions of the aorta and its branches , and the mean ratio of attenuation of the wall over that of the back muscle was 1.4 . a circumferential low - attenuation ring was demonstrated for the patients with substantial arterial enhancement . in the venous phase , the mural enhancement was more pronounced in all the patients with an attenuation ratio from 1.2 to 2.6 ( the mean value : 1.9 ) . the low - attenuation ring was well demonstrated between the contrast - filled lumen and the enhanced outer wall in 15 patients ( 83% ) in the venous phase ( fig . no significant stenosis was shown , even for the four patients with significant mural changes . variable degrees of the luminal changes , including stenosis and dilatation , were noted in the aorta and its branches in 14 patients . on the follow - up ct evaluation , with a mean follow - up period of 55.6 months , the precontrast image showed the high density ring in two more patients ( table 2 ) . the mean attenuation ( hu ) of the aortic wall on the precontrast phase increased significantly from 48.9 to 56.5 ( p = 0.04 ) ( table 3 ) . the mural calcifications noted in 10 patients were more extensive . the mean mural thickness measured on the arterial phase was 2.4 mm , and it was significantly decreased from 4.1 mm as measured by the initial ct evaluation ( p = 0.001 ) . the mean ct attenuation ratio of the wall ( aortic wall / muscle ) in the venous phase decreased significantly from 1.9 to 1.3 ( p = 0.001 ) . the low - attenuation ring in the venous phase was identified in seven patients ( 39% ) with active persistent disease . the mural thickness decreased , and the mural enhancement also decreased significantly in both the group of patients with inactive disease and in the group of patients with active persistent disease ( figs . 2 , 3 ) . in the group of the inactive disease patients ( n = 5 ) , the low - attenuation ring , initially shown in four patients ( 80% ) , disappeared in all the patients by the last follow - up ct ( fig . 2 ) . however , each of the individual ct findings had no statistically significant correlation with the esr - based disease activity on comparison between the both groups . luminal stenosis was improved along with the mural changes by the follow - up ct after medical treatment in two patients ( cases 7 and 16 ) . in one patient ( case 1 ) , the lumen of the abdominal aorta and the proximal left renal artery had recovered , while focal stenosis developed at the middle of the left renal artery . the mural changes found on the initial and follow - up ct evaluations of the 18 patients are summarized in table 2 . on the precontrast ct , the high density of the aortic wall was noted in 15 patients ( 83% ) . curvilinear or dot - like calcifications were found in six patients ( 33% ) . on the arterial phase of ct , the wall was slightly enhanced in various portions of the aorta and its branches , and the mean ratio of attenuation of the wall over that of the back muscle was 1.4 . a circumferential low - attenuation ring was demonstrated for the patients with substantial arterial enhancement . in the venous phase , the mural enhancement was more pronounced in all the patients with an attenuation ratio from 1.2 to 2.6 ( the mean value : 1.9 ) . the low - attenuation ring was well demonstrated between the contrast - filled lumen and the enhanced outer wall in 15 patients ( 83% ) in the venous phase ( fig . no significant stenosis was shown , even for the four patients with significant mural changes . variable degrees of the luminal changes , including stenosis and dilatation , were noted in the aorta and its branches in 14 patients . on the follow - up ct evaluation , with a mean follow - up period of 55.6 months , the precontrast image showed the high density ring in two more patients ( table 2 ) . the mean attenuation ( hu ) of the aortic wall on the precontrast phase increased significantly from 48.9 to 56.5 ( p = 0.04 ) ( table 3 ) . the mural calcifications noted in 10 patients were more extensive . the mean mural thickness measured on the arterial phase was 2.4 mm , and it was significantly decreased from 4.1 mm as measured by the initial ct evaluation ( p = 0.001 ) . the mean ct attenuation ratio of the wall ( aortic wall / muscle ) in the venous phase decreased significantly from 1.9 to 1.3 ( p = 0.001 ) . the low - attenuation ring in the venous phase was identified in seven patients ( 39% ) with active persistent disease . the mural thickness decreased , and the mural enhancement also decreased significantly in both the group of patients with inactive disease and in the group of patients with active persistent disease ( figs . 2 , 3 ) . in the group of the inactive disease patients ( n = 5 ) , the low - attenuation ring , initially shown in four patients ( 80% ) , disappeared in all the patients by the last follow - up ct ( fig . 2 ) . however , each of the individual ct findings had no statistically significant correlation with the esr - based disease activity on comparison between the both groups . luminal stenosis was improved along with the mural changes by the follow - up ct after medical treatment in two patients ( cases 7 and 16 ) . in one patient ( case 1 ) , the lumen of the abdominal aorta and the proximal left renal artery had recovered , while focal stenosis developed at the middle of the left renal artery . various imaging modalities may reveal the mural changes in patients with takayasu arteritis during the early phase of the disease with or without such luminal changes , as dilatation and stenosis ( 6 , 8 - 10 ) . ct may reveal mural thickening with the arterial and venous enhancement ( 5 , 6 , 8 , 9 ) . sonography shows a homogenous concentric mural thickening of the aorta and its branches , such as the carotid or subclavian arteries ( 9 , 11 ) . the mr imaging reveals the mural thickening of the aorta , the pulmonary artery and its branches , and especially on the gadolinium enhanced t1 weighted images . the mural thickening and the enhancement , as evaluated by each modality , may decrease after appropriate treatment ( 9 - 13 ) . in this retrospective study , we evaluated the mural changes on the follow - up ct examination for the patients with active disease at the time of the initial ct examination . there have been a few reports on the detailed analysis of the mural changes on the follow - up ct evaluation in a group of patients . paul et al . reported on their results of electron beam ct follow - up , in which they noted a decrease of the mural thickening and an increase of the mural calcifications . the outer wall enhancement , initially noted in 81% cases , was found in 37% case on the last ct scans ( 8) . for our results , the mural thickness decreased significantly from 4.1 mm to 2.4 mm . other mural changes seen on the follow - up ct evaluation included increased attenuation of the aortic wall and more extensive mural calcifications on the precontrast ct . the mural enhancement in the venous phase was decreased significantly on the follow - up ct evaluation . it is very difficult to estimate the activity of this disease with using a single parameter of the clinical or imaging diagnosis . there are 4 criteria for the disease activity : systemic features , an elevated esr , features of vascular ischemia and the typical angiographic features ( 7 ) . systemic features such as neck or shoulder pain may fail to represent the real activity of the disease . the angiography may be normal even with an extensive wall thickening if the mural changes did not cause luminal changes , such as narrowing , irregularities or aneurysm ( 6 , 9 ) . so , any cross - sectional imaging modality , including sonography , ct and mr , may be added to make the criteria of activity complete in respect of the angiographic feature . the disease should be regarded as active if there is any new focus or an aggravation of the mural changes according to a cross - sectional imaging modality . on the contrary , the mural changes may resolve completely with appropriate treatment , resulting in an inactivated form of disease . reported that   the contrast - enhanced mr imaging showed more enhancement of the thickened aortic wall as compared with the myocardium , suggesting active disease . for determining the progress of the disease activity , they reported an agreement rate for contrast - enhanced mr imaging as 88.5% with the clinical findings : 92.3% with the esr and 84.6% with the c - reactive protein ( 13 ) . in this study , the disease was defined as inactive by the follow - up evaluation if the esr was normal at least for six months even without steroid medication . after appropriate treatment , the mural thickness decreased significantly in all five cases with inactive disease , as was established by the follow - up ct evaluation . for the microscopic findings of takayasu arteritis , the inflammatory reactions affect mainly the adventitia and the media . the media shows vascularization , and the capillaries originating at the transition zone of the adventitia proliferate to the entire medial layer . following this neovascularization , inflammatory tissue invades the media with infiltration of lymphocytes , plasma cells and giant cells ( 14 ) . the active inflammation of the outer wall contributes mainly to the thickening of the aortic wall in the early phase of takayasu arteritis . the mural enhancement in the arterial or venous phase is most likely associated with the neovascularization and the productive inflammation of the media and the adventitia . the intima is thickened with an increase of the basophilic ground substance during the acute phase ( 14 ) . it can be seen as a radiolucent ring with a good contrast between the enhanced outer wall and the contrast filled arterial lumen . an improvement of the inflammatory process of the aortic wall may be manifested as a decrease of the thickness , a decrease of the mural enhancement and disappearance of the inner low - attenuation ring on the follow - up ct evaluation . ct may reflect the mural changes on the follow - up evaluation of active takayasu arteritis . however , there was no statistical significance in the correlation between the ct findings and activity of the disease on the basis of the esr in this study . though the esr is a sensitive parameter of active inflammation , it is nonspecific and has certain limitations in representing the activity of this disease . the esr has been reported to be persistently elevated during clinical remission in 56% of the cases ( 7 ) . the ct protocol in this study was variable because different ct scanners were used for the patients who were selected retrospectively over a long period . on the ct angiography for patients with takayasu arteritis , the carotid bifurcation should be included into the examination because involvement of the common carotid artery is common in takayasu arteritis . the thinner the slice thickness is , the easier it is to detect stenosis of the aortic branches such as the renal artery . in addition to the arterial phase data , the venous phase imaging also reveals important mural changes , including the delayed enhancement and the inner low - attenuation ring . however , the thin section acquisition and the additional venous phase imaging may be associated with exposure of patients to a considerable dose of radiation . decreasing the tube current and increasing the slice thickness up to 5 mm in the venous phase it was a retrospective study of ct follow - up in patients with takayasu arteritis with the different intervals between the initial and the ct follow - up examinations being from 10 months to 10 years . there could be bias in selection of the patients with active takayasu arteritis since the clinical criteria of activity were not perfect . the number of cases was not adequate to provide a sufficient statistical analysis with many ct findings . the ct imaging protocols and the imaging systems were not identical , which was due to the evolution of the ct technology during the study period . the regimen and the dosage of the medical treatment were different because the patients included into the study were treated by different clinicians . in summary , the mural changes on the follow - up ct evaluation of patients with active takayasu arteritis include a decrease of the mural thickness , a decrease of the mural enhancement and disappearance of the low - attenuation ring in the venous phase , and an increase of the mural attenuation and calcifications in the precontrast phase . further investigations are necessary to establish the correlation between these mural changes noted over a period of time with the luminal changes and the long - term prognosis of patients with active takayasu arteritis .
objectivewe wanted to evaluate the mural changes by ct on the follow - up examination of patients with active takayasu arteritis.materials and methodsthe study included 18 patients , ( 4 males and 14 females ) , with active takayasu arteritis . 
 a total of 44 ct examinations were done during the follow - up period ( mean : 55.6 months ) . at the time of the last follow - up ct , the disease , on the basis of the erythrocyte sedimentation rate ( esr ) , 
 was found to be inactive in five patients and the disease was active and persistent in 13 patients . the thickness and ct attenuation of the aortic wall on the precontrast , arterial and venous phases were measured on the initial and the follow - up ct examinations . 
 the ratio of the mural attenuation over that of the back muscle on the initial ct was compared with the ratio found on the follow - up ct.resultsthe initial ct findings included high density and calcifications of the aortic wall in the precontrast images and a thickened wall with enhancements in the arterial and the venous phases . 
 a low - attenuation ring was demonstrated in the venous phase in 15 patients ( 83% ) . on the follow - up evaluation , 
 the mean mural thickness decreased significantly from 4.1 mm to 2.4 mm . 
 the mean mural attenuation ratio in the venous phase decreased significantly from 1.9 to 1.3 ( p = 0.001 ) . 
 the low attenuation ring was identified in seven patients ( 39% ) who had only with active , persistent takayasu arteritis.conclusionthe mural changes demonstrated by the follow - up ct evaluations for the patients with active takayasu arteritis included a decrease of the mural thickness and enhancement , disappearance of the low - attenuation ring on the venous phase , and an increase of the mural attenuation and calcification on the precontrast phase .