The Study Of Acoustic Radiation Force Impulse In The Diagnosis Of Renal Tumors

The differentiation of renal malignant and benign tumors, as well as different subtypes of renal tumors, has been a hot point in the field of imaging diagnosis. The definitive diagnosis of renal tumors has a great impact on the treatment strategy planning and can influence prognosis. Color flow Doppler image (CDFI), contrast-enhanced ultrasound (CEUS), contrast-enhanced computed tomography (CECT) and magnetic resonance image (MRI) are the commonly used modalities for the detection and diagnosis of renal tumors, which is based on the observation of the morphology, intertumoral structure and the blood supply of the tumors. Acoustic radiation force impulse (ARFI), as a new developed modality, can evaluate the rigidity of the tumor. Together with the quantitative analysis, it can afford an innovative way for the differential diagnosis of renal tumors.ARFI is one of the novel ultrasound elasticity imaging techniques, and its image principle is based on the longitudinal compression and lateral vibration caused by the acoustic pulse radiation. The longitudinal compression, which is expressed as a picture composed of black and white pixels, reflects the tissue relative rigidity, and it is defined as virtual touch tissue imaging (VTI). Meanwhile, the shear wave velocity (SWV), which can be calculated by the time difference of the adjacent waves and their wavelength, can be quantitatively presented and it is an indirect index of tissue elasticity. This technique is defined as virtual touch tissue quantification (VTQ).The purpose of our study is to analyze the correlation between ARFI and renal tumor rigidity and to evaluate its clinical value in the differentiation of different renal tumors.Part One:The study of the VTQ in the differential diagnosis of renal tumorsObjective To evaluate the clinical value of VTQ in the differential diagnosis of renal tumors.Methods 199 renal tumors in 199 patients were enrolled in this study. The region of interest (ROI) was placed in the tumor and the renal cortex at the same depth, respectively to measure the shear wave velocity (SWV). The measurement was repeated ten times and their median value was defined as the SWV of the tumor or the renal cortex. SWV ratio was defined as tumor SWV/cortex SWV. These quantitative parameters were achieved in all cases and compared in each other to evaluate the reproducibility of this quantitative technique, the difference of SWV between malignant and benign renal tumors and its clinical value.Results All the tumors were proved by pathology, including 43 benign tumors (40 angiomyolipomas,2 mesoblastic nephromas and 1 oncocytoma) and 156 malignant ones (129 clear cell renal cell carcinomas,11 papillary renal cell carcinomas,9 chromophobe renal cell carcinomas,5 Renal urothelial carcinomas,1 mesenchymal malignant tumor and 1 Wilm’s tumor). The interclass correlation coefficient of VTQ in the renal cortex at different depths was greater than 0.75 and they made significant differences. The SWV and SWV ratio between malignant and benign renal tumors were significant different. With SWV higher than 2.120m/s as the cutoff point of the diagnosis criteria of malignant renal tumor, the sensitivity, specificity were 59.6%and 65.1%,respectively, and with SWV ratio higher than 0.835 as the cutoff point of the diagnosis criteria of malignant renal tumor, the sensitivity, specificity were 64.7%and 69.8%, respectively.Conclusions Though VTQ analysis can be influenced by different depth, it is stable in the evaluation of the renal cortex rigidity as well as that of the renal tumors. The diagnostic value of SWV ratio is greater than that of SWV.Part Two:The study of the VTI in the differential diagnosis of renal tumorsObjective To evaluate the clinical value of VTI in the differential diagnosis of renal tumors.Methods 124 renal tumors in 124 patients were enrolled in this study. The elastic pictures in renal tumors and renal cortex were derived by VTI. The brightness of tumor and renal cortex in each elastic picture were interpreted by 2 experienced sonologists and the brightness between two observers and between malignant and benign renal tumors wer statistically analyzed. Furthermore, correlation analysis between brightness and SWV ratio was also conducted.Results All the tumors were proved by pathology, including 27 benign tumors (25 angiomyolipomas and 2 mesoblastic nephromas) and 97 malignant ones (79 clear cell renal cell carcinomas,5 papillary renal cell carcinomas,7 chromophobe renal cell carcinomas,5 Renal urothelial carcinomas and 1 mesenchymal malignant tumor). The inter-observer consistency coefficient was moderate and was not significant different. Furthermore, there made no significant difference between malignant and benign renal tumors with the brightness on VTI picture, nor did there correlation between brightness on VTI and SWV ratio on VTQ.Conclusions VTI can reflect the elasticity of renal tumors with moderate inter-observers consistency, and it makes little sense in the differentiation of different renal tumors.