micronodules may be found during neck examination for non - nodular thyroid diseases , as well as in nodular thyroid disease when a clinical thyroid nodule is found to be associated with other non - clinically detected thyroid micro - nodules . generally , most patients with thyroid nodules lacked symptoms , with 5~10% of nodules having potential for malignancy . therefore , early diagnosis and adequate treatment are urgently needed to decrease the incidence of thyroid carcinoma . in 2009 , the thyroid imaging reporting and data system ( ti - rads ) , modeled on the breast imaging reporting and data system ( bi - rads ) and the initial ti - rads scores , classified and determined the risk of thyroid nodule malignancy with ultrasound scanning . ti - rads scores range from 1 ( normal gland ) to 6 ( proven malignancy ) ; ti - rads 3 and ti - rads 4 correspond to highly probable benign nodule and high suspicion for malignancy , respectively . multiple diagnostic tools are currently available for thyroid nodules , including ultrasonography ( us ) , thyroid nuclear scan , and fine - needle aspiration cytology ( fnac ) . differentiation between benign and malignant lesions is difficult in many cases because of the overlap of grey - scale and color doppler us findings . as a major improvement in ultrasound , contrast - enhanced ultrasonography ( ceus ) with ultrasound contrast agents ( ucas ) in addition , ceus has several advantages over traditional imaging techniques , including cost - effectiveness , portability , lack of radiation , non - invasiveness , and better patient compliance , which may be why ceus performs better than us in the diagnosis of renal cystic lesions . ceus plays an important role in the identification of malignant lesions in various organs , such as colon , gallbladder , pancreas , and kidney [ 1315 ] . although the improvement in diagnostic performance of conventional us combined with ceus in the differentiation capability for benign from malignant breast masse has been elucidated in previous data , there is limited data on conventional us combined with ceus in differentiating solitary thyroid nodule ( stn ) and micronodules from normal thyroid tissue . we performed the current study to investigate the diagnostic performance of conventional us combined with ceus in micronodules with categories of ti - rads 3 and ti - rads 4 . the study was conducted according with the protocols proposed by the ethics committee of sichuan provincial people s hospital . written informed consent was obtained from each subject before the study . all procedures in this study were in compliance with the declaration of helsinki . from september 2012 to july 2014 , patients with thyroid disease who underwent conventional us or ceus in sichuan provincial people s hospital were considered as candidates for inclusion . the inclusion criteria were : nodules with a hypoechoic aspect , normal thyroid tissue with homogeneous echogenicity , maximum diameter for thyroid nodules 10 mm , and category 3 or 4 in ti - rads . the exclusion criteria were : ( 1 ) patients with neck deformity , ( 2 ) patients with cystic nodules or mixed nodules with less parenchymal nodules , ( 3 ) solid components that can not be revealed in nodules due to macrocalcification ; ( 4 ) patients with severe allergies ; and ( 5 ) patients who were pregnant . after applying the inclusion and exclusion criteria , a total of 102 patients ( 29 males and 73 females ) were included , with age range 1980 years . the thyroid lesions collected from included subjects had maximum diameter of 2.80~9.65 mm ( mean , 6.691.70 mm ) . among the included lesions , lesions with maximum diameter < 5 mm accounted for 17.6% ( 18/102 ) and 5 mm for 82.4% ( 85/102 ) . thyroid lesions were confirmed either by surgery or biopsy and pathological examination was considered as the criterion standard . the mylab90 ( mylab gold platform ) color doppler ultrasonic diagnosis set ( esaote , genoa , italy ) was used for conventional us measurement . linear array transducer la523 with a center frequency of 4~13 mhz and la522 with a center frequency of 3~9 mhz were equipped for all conventional us . routine gray scale ultrasonography was used to observe the nodule location , number , size , shape , margin , and internal echogenicity . then color doppler and spectrum doppler were used to observe the characteristics of the blood supply in lesions . after conventional us was conducted and ucas and vein passageways were prepared , ceus was performed within a section to fully expose lesions and the surrounding normal thyroid tissue . after the linear array transducer was fixed , patients were told to stop swallowing and to breathe calmly . contrast turned imaging ( cnti ) was set with a frequency of 6~8 mhz , capacity of 3% , sound pressure of 45 kpa , gamma of 46% , and depth of 3.0~4.0 cm . then patients were injected in the median cubital vein with 1.0 ml of bubble disruption , which was diluted and shaken for 30 s , followed by 5 ml of normal saline . each contrast imaging acquisition at 120~180 s and the process of the ultrasound contrast were preserved in the ultrasonic instrument . the measurement was performed by 3 physicians who had ultrasonic experience of more than 3 years with the same instruction standards in order to minimum the bias from different operators . general information on thyroid nodules echogenicity , size , shape , margins , aspect ratio ( a / t ) , microcalcification , and presence / absence of lymphadenectasis in the neck was described based on the conventional us examination . based on the alder classification , the blood flow signals were classified into grade 0 , grade i , grade ii , and grade iii . dynamic contrast images underwent successive or frame - by - frame playback and were evaluated based on 7 aspects : enhanced time , enhanced uniformity , enhanced pattern , enhanced intensity , size of the enhanced nodules , margins of the enhanced nodules , and rim - like enhancement , which were regarded as indictors for qualitative analysis . the diagnostic criteria for benign thyroid nodules were based on enhanced intensity of the peaked nodules ( hyper - enhancement ) , unchanged nodules size , clear margins of the nodules , and presence of rim - like enhancement in nodule tissues . the malignant thyroid nodules were diagnosed based on slow enhance time , enhance intensity of the peaked nodules ( iso - enhancement / hypo - enhancement ) , nodules size changes , unclear margins of the nodules , and absence of rim - like enhancement in nodule tissues . categorical data are presented with percentage or ratio , while continuous data are expressed as s . each hypothesis was tested using the t test ( homogeneity of variance ) ,  test , or binary logistic regression analysis ( forward selection method , =0.05 ) . receiver operator characteristic ( roc ) curves were used to compare the diagnostic differences among the conventional us , ceus , and combined use of conventional us and ceus . the study was conducted according with the protocols proposed by the ethics committee of sichuan provincial people s hospital . written informed consent was obtained from each subject before the study . all procedures in this study from september 2012 to july 2014 , patients with thyroid disease who underwent conventional us or ceus in sichuan provincial people s hospital were considered as candidates for inclusion . the inclusion criteria were : nodules with a hypoechoic aspect , normal thyroid tissue with homogeneous echogenicity , maximum diameter for thyroid nodules 10 mm , and category 3 or 4 in ti - rads . the exclusion criteria were : ( 1 ) patients with neck deformity , ( 2 ) patients with cystic nodules or mixed nodules with less parenchymal nodules , ( 3 ) solid components that can not be revealed in nodules due to macrocalcification ; ( 4 ) patients with severe allergies ; and ( 5 ) patients who were pregnant . after applying the inclusion and exclusion criteria , a total of 102 patients ( 29 males and 73 females ) were included , with age range 1980 years . the thyroid lesions collected from included subjects had maximum diameter of 2.80~9.65 mm ( mean , 6.691.70 mm ) . among the included lesions , lesions with maximum diameter < 5 mm accounted for 17.6% ( 18/102 ) and 5 mm for 82.4% ( 85/102 ) . thyroid lesions were confirmed either by surgery or biopsy and pathological examination was considered as the criterion standard . the mylab90 ( mylab gold platform ) color doppler ultrasonic diagnosis set ( esaote , genoa , italy ) was used for conventional us measurement . linear array transducer la523 with a center frequency of 4~13 mhz and la522 with a center frequency of 3~9 mhz were equipped for all conventional us . routine gray scale ultrasonography was used to observe the nodule location , number , size , shape , margin , and internal echogenicity . then color doppler and spectrum doppler were used to observe the characteristics of the blood supply in lesions . after conventional us was conducted and ucas and vein passageways were prepared , ceus was performed within a section to fully expose lesions and the surrounding normal thyroid tissue . after the linear array transducer was fixed , patients were told to stop swallowing and to breathe calmly . contrast turned imaging ( cnti ) was set with a frequency of 6~8 mhz , capacity of 3% , sound pressure of 45 kpa , gamma of 46% , and depth of 3.0~4.0 cm . then patients were injected in the median cubital vein with 1.0 ml of bubble disruption , which was diluted and shaken for 30 s , followed by 5 ml of normal saline . each contrast imaging acquisition at 120~180 s and the process of the ultrasound contrast were preserved in the ultrasonic instrument . the measurement was performed by 3 physicians who had ultrasonic experience of more than 3 years with the same instruction standards in order to minimum the bias from different operators . general information on thyroid nodules echogenicity , size , shape , margins , aspect ratio ( a / t ) , microcalcification , and presence / absence of lymphadenectasis in the neck was described based on the conventional us examination . based on the alder classification , the blood flow signals were classified into grade 0 , grade i , grade ii , and grade iii . dynamic contrast images underwent successive or frame - by - frame playback and were evaluated based on 7 aspects : enhanced time , enhanced uniformity , enhanced pattern , enhanced intensity , size of the enhanced nodules , margins of the enhanced nodules , and rim - like enhancement , which were regarded as indictors for qualitative analysis . the diagnostic criteria for benign thyroid nodules were based on enhanced intensity of the peaked nodules ( hyper - enhancement ) , unchanged nodules size , clear margins of the nodules , and presence of rim - like enhancement in nodule tissues . the malignant thyroid nodules were diagnosed based on slow enhance time , enhance intensity of the peaked nodules ( iso - enhancement / hypo - enhancement ) , nodules size changes , unclear margins of the nodules , and absence of rim - like enhancement in nodule tissues . categorical data are presented with percentage or ratio , while continuous data are expressed as s . each hypothesis was tested using the t test ( homogeneity of variance ) ,  test , or binary logistic regression analysis ( forward selection method , =0.05 ) . receiver operator characteristic ( roc ) curves were used to compare the diagnostic differences among the conventional us , ceus , and combined use of conventional us and ceus . among the 102 subjects , 52 patients were included in the malignant group , among which 22 patients had preoperative fine - needle aspiration ( fna ) and 52 patients received surgery . the remaining 50 patients were included in the benign group , among which 36 patients received preoperative fna and 14 patients received surgery . in the malignant group , age range was 30~50 years . a significant difference was detected in age between the 2 groups ( p<0.05 ) , but no significant difference was found for sex ( p>0.05 ) ( table 1 ) . conventional us showed that the micronodules in ptc had the following characteristics : irregular shape , unclear margins , a / t 1 , microcalcification in nodules , majority 0i blood flow signals , and presence of suspicious lymph gland ( figures 1 , 2 ) . there were significant differences in the above characteristics between the malignant group and benign group ( all p<0.05 ) ( table 2 ) . ceus examination with ptc was often characterized by slow enhancement time , centrality enhancement pattern , inhomogeneous enhancement uniformity , iso / hypo - enhancement intensity at peak , size changes of the nodules ( enlarged or decreased ) , unclear margins , and absence of rim - like enhancement . benign nodules were characterized by fast enhanced time , non - centrality enhanced pattern , homogeneous enhanced uniformity , hyper - enhancement at peak , no size change of the nodules , clear margins and presence of rim - like enhancement ( figures 3 , 4 ) . there were significant differences in enhancement time , enhancement pattern , enhancement intensity , size change of nodules , margins , and rim - like enhancement between the malignant group and benign group ( all p<0.05 ) . no significant difference was detected in enhancement uniformity between the 2 groups ( p>0.05 ) ( table 3 ) . binary logistic regression analysis was conducted with pathological diagnosis as the dependent variable and statistically different indexes in convention us , ceus , and conventional us combined with ceus as independent variables . logistic regression analysis was conducted with or > 1 indicating risk factors and or < 1 protective factors . logistic regression analysis of conventional us showed that a / t 1 , irregular shape , microcalcification , and suspicious lymph gland are risk factors for thyroid micronodules ( table 4 ) , whereas logistic regression analysis of ceus showed that slow enhancement time and absence of rim - like enhancement are risk factors for thyroid micronodules ( all p<0.05 , or > 1 ) ( table 5 ) . logistic regression analysis of conventional us combined with ceus demonstrated that a / t 1 , microcalcification , suspicious lymph gland , slow enhancement time , and absence of rim - like enhancement are risk factors ( all p<0.05 , or > 1 ) ( table 6 ) . the roc curve showed that us had an area under the roc curve ( auc ) of 90.0% and ceus had an auc of 90.7% , in contrast to the auc of 99.0% for combined use of conventional us and ceus ( figure 5 ) , which indicated that the combination of these 2 methods had a superior diagnostic value compared with conventional us and ceus alone . among the 102 subjects , 52 patients were included in the malignant group , among which 22 patients had preoperative fine - needle aspiration ( fna ) and 52 patients received surgery . the remaining 50 patients were included in the benign group , among which 36 patients received preoperative fna and 14 patients received surgery . in the malignant group , age range was 30~50 years . a significant difference was detected in age between the 2 groups ( p<0.05 ) , but no significant difference was found for sex ( p>0.05 ) ( table 1 ) . conventional us showed that the micronodules in ptc had the following characteristics : irregular shape , unclear margins , a / t 1 , microcalcification in nodules , majority 0i blood flow signals , and presence of suspicious lymph gland ( figures 1 , 2 ) . there were significant differences in the above characteristics between the malignant group and benign group ( all p<0.05 ) ( table 2 ) . ceus examination with ptc was often characterized by slow enhancement time , centrality enhancement pattern , inhomogeneous enhancement uniformity , iso / hypo - enhancement intensity at peak , size changes of the nodules ( enlarged or decreased ) , unclear margins , and absence of rim - like enhancement . benign nodules were characterized by fast enhanced time , non - centrality enhanced pattern , homogeneous enhanced uniformity , hyper - enhancement at peak , no size change of the nodules , clear margins and presence of rim - like enhancement ( figures 3 , 4 ) . there were significant differences in enhancement time , enhancement pattern , enhancement intensity , size change of nodules , margins , and rim - like enhancement between the malignant group and benign group ( all p<0.05 ) . no significant difference was detected in enhancement uniformity between the 2 groups ( p>0.05 ) ( table 3 ) . binary logistic regression analysis was conducted with pathological diagnosis as the dependent variable and statistically different indexes in convention us , ceus , and conventional us combined with ceus as independent variables . logistic regression analysis was conducted with or > 1 indicating risk factors and or < 1 protective factors . logistic regression analysis of conventional us showed that a / t 1 , irregular shape , microcalcification , and suspicious lymph gland are risk factors for thyroid micronodules ( table 4 ) , whereas logistic regression analysis of ceus showed that slow enhancement time and absence of rim - like enhancement are risk factors for thyroid micronodules ( all p<0.05 , or > 1 ) ( table 5 ) . logistic regression analysis of conventional us combined with ceus demonstrated that a / t 1 , microcalcification , suspicious lymph gland , slow enhancement time , and absence of rim - like enhancement are risk factors ( all p<0.05 , or > 1 ) ( table 6 ) . the roc curve showed that us had an area under the roc curve ( auc ) of 90.0% and ceus had an auc of 90.7% , in contrast to the auc of 99.0% for combined use of conventional us and ceus ( figure 5 ) , which indicated that the combination of these 2 methods had a superior diagnostic value compared with conventional us and ceus alone . the current study investigated the diagnostic value of conventional us combined with ceus in ti - rads 3 and ti - rads 4 thyroid micronodules . we demonstrated the combination of these 2 technologies showed superior performance compared with single use of convention us or ceus . our results were further enhanced by the use of both logistic regression analysis and roc curve . although data show that the incidence of ptc has been decreasing significantly and the prognosis for this disease has greatly improved , the early detection on this disease still needs to be emphasized because it easily spreads to the lungs and bones [ 2022 ] . , our study investigated the diagnostic value of conventional us combined with ceus in ti - rads 3 and 4 thyroid micronodules . according to the definition of ti - rads , patients with ti - rads 3 presented with hyper- , iso- , or hypoechoic nodules , while ti - rad4 has a suspicious neoplastic pattern or malignant pattern . thyroid micronodules with maximum diameter 10 mm were selected because nodules larger than 1 cm have high potential to develop into clinically significant cancers . with the high sensitivity and specificity of ti - rads , diagnosis of thyroid nodules has shown great improvement using ultrasound contrast . as an important diagnostic tool in predicting thyroid malignancy and selecting thyroid nodules , the characteristics of suspicious thyroid nodules include marked hypo - echogenicity , irregular margins , microcalcifications , and a taller than - wide shape , which contribute to better diagnostic accuracy . consistent with these features , our study , using conventional 2-dimensional and color doppler contrast , demonstrated that the micronodules in ptc had irregular shape , unclear margins , a / t 1 , microcalcifications , blood flow 0-i , and suspicious lymph gland . another meta - analysis , which showed that ultrasound features are important predictors of malignancy for thyroid nodules , reported a similar result regarding the accuracy of conventional us . a meta - analysis by brito found that the value of diagnostic us features , such as internal calcifications , echogenicity , infiltrative margins , and solid vs. cystic content of the nodule , were often overestimated , which is slightly different from the results of the present study . the ready repeatability , lack of risk , and low cost of conventional us make it a particularly attractive modality . in this same setting , our study revealed that ceus had significantly better sensitivity , specificity , and accuracy than conventional us . a previous study found that real - time ceus showed remarkably different images in benign vs. malignant thyroid nodules ; therefore , ceus has clinical value use for differential diagnosis of stn . evidence supports that ceus has a better visualization of the microcirculation and details of stenosis compared with conventional us and power doppler . our study demonstrated that ptc tissues had hypo - enhancement and normal thyroid tissues had hyper - enhancement using ceus . most malignant nodules have fibrosis , calcification , focal necrosis , and aberrant blood vessels , which may lead to hypo - echogenicity on us and hypo - enhancement on ceus . however , research also found that the differential diagnosis between benign and malignant thyroid nodules using conventional imaging methods lacks reliability , and that ceus enhancement patterns varied between benign and malignant lesions . therefore , the combined use of conventional us and ceus may improve accurate diagnosis of benign and malignant lesions compared with convention us or ceus alone , which is reflected in the improved specificity and accuracy and higher auc in our results . our findings are consistent with a previous study describing the value of ceus combined with conventional us in the diagnosis of thyroid micro - carcinoma using a logistic regression model , which found that ceus and conventional us were very effective in thyroid nodule diagnosis . the findings of our study suggest that the combined use of conventional us and ceus has superior diagnostic performance in ti - rads category 3 and 4 thyroid micronodules , compared with conventional us and ceus alone . therefore , the combined use of conventional us and ceus should be advocated in thyroid micronodule diagnosis .