In stage 2, the investigators will look to determine the ability of the contrast enhanced ultrasonography method to detect renal transplant rejection using Sonazoid. For this stage the investigators will recruit subjects with biopsy confirmed renal transplant rejection. Once subjects are consented, they will undergo contrast enhanced ultrasonography with Sonazoid and have images taken. These images will be compared to images of renal transplant patients that have displayed no rejection or clinical issues. These clinically normal subjects will have previously consented to a medical record review so that the investigators may use their images.