Introduction

Renal angiomyolipoma without visible fat (RAMLwvf) is one of the most common renal tumors, accounting for 39%. It is composed of mature adipose tissue, thick walled blood vessels and smooth muscle. When the fat content in the tumor is poor, the imaging manifestations are not typical, and it is easy to be misdiagnosed as renal cell carcinoma^[1]. Clear renal cell carcinoma（ccRCC） is the most common renal malignancy. RAMLwvf usually does not need surgery.However, ccRCC must be resected when found because of its high degree of malignancy. It is necessary to make a definite differential diagnosis of the two carcinomas before operation. IDEAL-IQ technology is a new scanning sequence based on the principle of three-point Dixon asymmetric echo technology. The images of water phase, lipid phase, in-phase, reverse phase, fat fraction and R2* relaxation images can be generated at the same time in one scan to realize the quantitative measurement of fat fraction^[2].

Methods

The data of patients who met the following criteria from July 2012 to June 2020 were analyzed retrospectively.The inclusive criteria were as follows: (1) ccRCC or renal RAMLwvf confirmed by surgery and pathology, with complete clinical and pathological data;(2) No MRI contraindications, scanning sequence containing IDEAL-IQ sequence; (3) No radiotherapy, chemotherapy or other treatment before examination; (4) Good image quality, no false shadow area affecting the observation and data measurement of the lesions; (5) The lesions were clearly displayed major diameter > 1.5 cm.Finally, there were 12 cases of ccRCC and 7 cases of RAMLwvf,which were scanned by GE signa hdxt 1.5T MR scanner.The image data of IDEAL-IQ is transmitted to aw 4.6 workstation, and the image is post processed to obtain R2* and FF images, as shown in Figure 1. Two radiologists (observers 1 and 2) with 3 and 15 years of experience in abdominal MR diagnosis completed the data measurement respectively, but they did not know the pathological diagnosis of the patient. According to the conventional MR images, the largest section of the tumor was selected to delineate ROI, the area was larger than 1 / 3 of the solid part of the lesion, and the necrosis, hemorrhage and cystic change areas were avoided. The observer drew 1 ROI on each of the two adjacent layers and took the average value. Two kinds of ideal-iq post-processing images can be converted to each other in the workstation to ensure that ROI is placed in the same position on the two images.Software SPSS 26.0 was used for statistical analysis. Shapiro-Wilk was used to test whether each data conforms to the normal distribution. Those conforming to the normal distribution are represented by x±s, and those conforming to the skewed distribution are represented by the median (P25, P75). The intra-group correlation coefficient (ICC) was used to test the consistency of the measurement results of the two observers on the parameter values of the two groups of cases. 0.4 and 0.75 were used as the cut-off points for the evaluation of poor, medium, and good consistency, and the measurement results of the senior observer The average value is analyzed.Independent sample t test (normal distribution) or Mann-Whitney U test (skew distribution) was used to compare the differences between the ESWAN parameter values of the two groups. Draw the ROC curve for the different parameters, obtain the area under curve(AUC), and obtain the cut-off value, sensitivity and specificity of the corresponding parameter diagnosis according to the maximum Youden index. P<0.05 indicates that the difference is statistically significant.

Results

Measurement consistency between the two observers was good (ICC > 0.75). The R2* value of the ccRCC group was greater than that of the RAMLwvf group, and the FF value was lower than RAMLwvf group, the difference was statistically significant (P <0.05), as shown in Table 1. The AUC value, threshold, sensitivity, and specificity of R2* value and FF value for identifying ccRCC with RAMLwvf groups are 0.893、31.2、91.7%、71.4％and 0.905、6.25、85.7%、83.3%, ROC curve is shown in Figure 2.

Discussion

R2* value is the quantitative expression of tissue oxygenation level, that is the transverse relaxation rate, which is positively correlated with the concentration of deoxyhemoglobin in tissues. The R2* value of ccRCC group is higher than that of RAMLwvf group, which may be due to the higher malignant degree of ccRCC, the active cell proliferation state, the increase of cell number per unit volume and the improvement of metabolic level, aggravating oxygen consumption, resulting in the increase of R2* value. IDEAL-IQ technology corrects many mixed factors that interfere with fat quantification, such as T2* attenuation, fat multispectral peak distribution, magnetic field inhomogeneity, T1 relaxation, noise bias and eddy current. Finally, accurate quantitative image fat ratio is generated，which was named FF value. The FF value of RAMLwvf group was higher than that of ccRCC group. Although RAMLwvf contained less fat, the difference between RAMLwvf and ccRCC group was increased by quantitative measurement of FF value, which made it possible to identify the two before operation_[3-4].

Conclusion

In conclusion, the R2* and FF values of IDEAL-IQ sequence can differentiate ccRCC from RAMLwvf. It is a noninvasive, non enhancement method, and has certain clinical application value.

Acknowledgements

Thanks to my dear teacher and all my friends,sincerely.

References

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