# Ultrasound Elastography: Methods, Clinical Applications, and Limitations: A Review Article
## 5 Clinical Applications of Ultrasound Elastography
### Kidneys
#### 5.2.1 Elastography Techniques in Renal Disease Diagnosis  
The primary function of the kidneys is to filter waste products and excess fluids from the blood, help regulate blood pressure, and maintain electrolyte balance, but developing CKD can interfere and cause the kidneys to function improperly.  
There are five stages of CKD, as measured by glomerular filtration rate (GFR), that can range from mild kidney damage in stage one to possible kidney failure in stage five. CKD can lead to multiple complications throughout the patient's life and can affect a variety of organs in the body. It can lead to cardiovascular diseases, anemia, electrolyte imbalance, and renal fibrosis, but it is important to note that the detection of the disease in its early stages can aid in a quicker treatment and recovery, refraining from adverse treatments such  
Figure 3: The stages of chronic kidney disease (CKD) from 1 to 4 were determined by analyzing data obtained from the National Health and Nutrition Examination Survey conducted between 2017 and March 2020. The analysis utilized the CKD Epidemiology Collaboration GFR estimation equation for the year 2021, which incorporated variables such as serum creatinine levels, age, and sex. For a more comprehensive understanding of the methodologies employed, please refer to the section titled “Calculation of Estimates”.  
as dialysis and renal transplant. Later stages of CKD can result in renal fibrotic pathologies (native and allograft) [87; 88].  
Currently, renal biopsy is the only surefire way to stage renal fibrosis. However, new studies have shown that shear wave imaging (USE) may be able to find and monitor the disease without surgery, so there is less need for an invasive biopsy. SE has an accuracy of about 95% in predicting moderate (F2) and severe (F3) fibrosis in renal transplant patients. Allograft kidneys have the advantage of a superficial location, which makes assessment easier than that of the retroperitoneallyally located native kidneys; therefore, applying external pressure to native kidneys during SE makes for a somewhat false diagnosis of pathology. In addition to the fact that SE cannot distinguish between different stages of CKD, this calls for the use of shear wave imaging [87; 88].  
Shear imaging does not depend on external compression, showing advantages in evaluating both native and allograft kidney fibrosis and CKD as well, depicting a significant correlation between the presence of fibrosis found in elastography and biopsy and between the urinary creatinine levels and transverse elastography measures, unlike liver fibrosis. It has been shown by SWI studies of kidney fibrosis that CKD progression and shear wave velocity are inversely proportional, observing a decline in shear wave velocity as the CKD stages develop in comparison to normal kidneys [88; 89; 90].  
USE can also aid in the detection of renal lesions using SI and susceptibility-weighted imaging (SWI is an MRI sequence that is particularly sensitive to compounds that distort the local magnetic field and, as such, makes it useful in detecting blood products, calcium, etc.), reducing the need for rather time-consuming CT and MRI imaging and eliminating any intravenous contrast media usage. Beneficial masses appear hyperechoic on the scan, but malignant masses tend to appear hypoechoic in approximately 10% of studied cases and hyperechoic in another 10%, although they could be somewhat confused together. The fact that malignant masses have the tendency to be 2.8 times stiffer than benign cells and that shear wave velocity has the ability to differentiate between them can assist in the assessment of the pathology at hand. Most radiologists prefer to use renal USE as an exclusion test rather than a test for diagnosis [91; 92; 93; 94; 95; 96].