Kidney transplantation is the treatment of choice for many patients with end-stage renal disease which kidneys are unable to filter wastes from the body, maintain the proper balance of water and chemicals, or produce urine .
This study included 40 patients, their ages ranging from 10 to 50 years old and a total mean age ± SD = 32.03 ± 9.9 years. The female (14) patients representing 35% and the male patients (26) representing 65% of the patients match the study published by Ozkan et al., 2013 , which included 42 patients with (18) females and (24) males (mostly male) with mean age 38.7 ± 11.8 and agreed with Tatar et al. (2014)  which included (28) patients with (10) females and 18 males with mean age 39 ± 11. So, we can conclude that the incidence of renal failure and renal transplantation is more likely at these age groups with male predominance.
All included patients in this study were examined by ultrasound, color duplex Doppler, and sono-elastography. Ultrasonography is often the imaging method chosen for transplant evaluation early in the postoperative period, and it can be used for long-term follow-up as well. It is also used to guide diagnostic and therapeutic interventions, such as biopsy . Color Doppler US has traditionally been the principle noninvasive imaging method for transplant evaluation. It is rapid, safe, portable, and easy to use in unstable postoperative patients .
The sono-elastography (SE) provides quantitative information on tissue elasticity distribution for the assessment of renal pathological changes .
The final diagnosis of the studied sample was based on histopathology by ultrasound-guided biopsy.
As regards the perfusion grades among our patients and its correlation with histopathological results, we classified our patients on three-grade scale: 13 patients with normal renal tissue and good cortical perfusion (Grade 0), 13 patients with ATI with good cortical perfusion (Grade 0), 14 patients with CAI including 12 reasonable perfusion (Grade 1), and 2 patients with patchy perfusion (Grade 2). Our results matched the results of Hilboen et al. (2014)  who studied 18 patients and classified their patients on the same three-grade scale. A study was done by Laszlo et al. (1990)  who studied that 9 patients had ATI also used the same perfusion scale.
In between 40 patients who were included in our study, 13 normal patients (32.5%), 13 ATI patients (32.5%), and 14 CAI patients (35%), it means that the incidence of CAI in our study was greater than ATI and normal renal allografts, and this was in agreement with the study done by Yang et al. (2017)  which included 50 patients; 15 of them were normal (30%),15 were ATI (30%), and 20 were CAI (40%).
In our study, the mean renal allograft elasticity in normal patients was 3.99–9.91 Kpa, and this was in agreement with Gennisson et al. (2012)  who reported that mean elasticity values were 15.4 ± 2.5 Kpa and 10.8 ± 2.7 Kpa, respectively, in abnormal and normal patients. The mean elasticity of CAI range was 30.32–36.90 Kpa which agreed with Brocchi et al. (2014)  who stated that the mean renal allograft stiffness value in patients with CRI with stable creatinine was 34.06 ± 10.72 Kpa. The mean elasticity in patients with ATI was 18.24–24.52 Kpa according to our study during the examination.
The mean ± SD of resistive index(RI) was 0.63 ± 0.06 in normal group, 0.76 ± 0.03 in ATI group, and 0.66 ± 0.05 in CAI group; these results matched with the study done by Farina et al. (2007)  who studied 3 groups: (A) patient without disease, (B) patient with chronic rejection, and (C) patient with acute tubular necrosis; the range of RI for the Group A was 0.6–0.72, the Group B was 0.69–.79, and the group C was 0.68–78. On the other hand, our results disagreed with Ozkan et al (2013)  who reported that there was no significant correlation between renal parenchymal stiffness and RI in his population, and this is maybe due to the smaller studied group with ATI in his study.
In our study, there is no significant correlation between serum creatinine and elasticity values which agreed with Brocchi et al. (2014)  who studied 45 kidney transplant recipients and stated that the mean kidney stiffness value in patients with stable creatinine was 34.06 ± 10.72 Kpa and no correlation with renal function (single S-creatinine value) was found while disagreed with Yang et al. (2017)  who studied 50 patients and stated that there was positive correlation between serum creatinine levels and elastography scores.
In the present study, there is no significant correlation between serum creatinine and perfusion which agreed with Hilboen et al. (2014)  who studied 18 patients and stated no significant correlation between the vascular grade perfusion and the mean serum creatinine levels.
In this study, there was no significant correlation between serum creatinine and RI which agree with Hilboen et al. (2014)  who studied 18 patients and stated that the percentage correlation between the vascular grades and the RI was 26.4% (p = 0.7) using person product-moment correlation test, indicating that there was no significant correlation between the vascular grade and the mean RI.