Ultrasound Fetal Thymus

ObjectiveTo investigate the methodology of fetal thymus volume measurement with three-dimensional ultrasound. And to establish the preliminary normal growth curve of fetal thymus among Chinese patients.Materials and MethodsFrom2011April to2012February,271singleton fetuses with gestantional age ranging from16to38+6weeks were enrolled in this study.The measurement of two dimensional parameters, acquisition and measurement of three dimensional thymus volume(TV) were defined, including standard plane for measurement of two dimensional parameters, initial plane of volume acquisition and definition of details of volume measurements. Two dimensional parameters included transverse diameter(TD), anterioposterior diameter(APD), perimeter and transverse area(TA).The intraobserver and interobserver reliability of different rotational angle (30°,15°,9°) of VOCAL and multiplanar measurement was examined in20cases.VOCAL15°was used for its good reliability and convenience to calculate fetal thymus volumes of all enrolled fetuses. Pearson’s correlation coefficient, curve estimation and polynomial regression models was used to evaluate the correlation of fetal thymus volume, two dimensional parameters with gestational age and estimated fetal weight(EFW), as well as the correlation of thymus volume and two dimensional parameters.Results 1. Intra-class correlation coefficient (ICC) between VOCAL30°and VOCAL15°,9°and multiplanar method were0.999,0.998,0.997respectively; ICC between VOCAL15°and VOCAL9°was1.0. Inter-observer and intra-observer ICC of VOCAL30°were0.998and0.997; inter-observer and intra-observer ICC of VOCAL15°were1.0and0.997; inter-observer and intra-observer ICC of VOCAL9°were1.0and0.998; inter-observer and intra-observer ICC of multiplanar method were0.997and0.997.2.Using GA as the independent variable and the thymus volume(TV) as the dependent variable, the best fit regressing equation was TV(mL)=0.014×GA×GA-0.104×GA-1.745(R2=0.952, p=0.000). The Pearson’s correlation coefficient between fetal TV and GA was0.967.3.Using GA as the independent variable and the transverse diameter(TD), anterioposterior diameter(APD), perimeter and transverse area(TA) as the dependent variables, the best fit regressing equations were:TD=0.137×GA-0.85(R2=0.885, p=0.000); APD=0.062×A-0.494(R2=0.822, p=0.000); perimeter=0.393×GA-1.867(R2=0.854, p=0.000); TA=0.393×GA-1.867(R2=0.902, p=0.000)。The Pearson’s correlation coefficient of TD, APD, pefimeter, TA with GA was0.941,0.907,0.924and0.949respectively.4.TV is closely correlated with EFW than two dimensional parameters, the best fit regressing equation was:TV=0.006×EFW-5.957×EFW×EFW/107-0.240,(R2=0.955, p=0.000). The Pearson’s correlation coefficient between TV and EFW was0.970.5.TV is correlated with TA best with the Pearson’s correlation coefficient0.960。Conclusions1. VOCAL15°volume measurement of fetal thymus had excellent reliability.2.The growing pattern of fetal thymus volume fitted with a quadratic polynomial function, while the growing pattern of fetal transverse diameter, anterioposterior diameter, perimeter and transverse area fitted with linear regression model.3. The fetal thymus volume was closely correlated with EFW 4. The fetal thymus volume was best correlated with transverse area. ObjectiveTo investigate the effects of gestational age and scanning angle on the three dimensional measurement of thymus volume in the third trimester.Methods138singleton fetuses with gestantional age ranging from28to38+6weeks From2011April to2012February were enrolled in this study.The quality of the thymus volume block was categorized into degree1-6according to the number of planes that had a clear outline during VOCAL30°measurement. The effects of the gestational age and sono-thoracic angle in volume acquisition on the quality of volume block was analyzed.Results1. The quality of the thymus volume blocks decreased significantly during31-38+6gestational weeks than in28-28+6gestational weeks (P=0.006)2. The sono-thoracic angel46-90°significantly increased the quality of thymus volume blocks than the sono-thoracic angle91-135°(P=0.000)Conclusions1.The quality of the thymic volume blocks decreased with the gestational age.2. Sono-thoracic angle ranging46-90°significantly increased the quality of the thymic volume blocks.