Contrast-enhanced Ultrasound of the Kidney

Inclusion Criteria: To be eligible for the present study, patients must meet the following criteria: 1. Able to provide written informed consent 2. Willing to comply with protocol requirements 3. At least 18 years of age 4. Have kidney disease, defined as either CKD II-VI, determined by estimated glomerular filtration rate (GFR) of \<90 and derived from serum creatinine measurements, or albuminuria/proteinuria, determined by albumin to creatinine ratio or protein to creatinine ratio of \>30mg/gm, or having received a kidney transplant 5. Have at least one kidney lesion identified but incompletely characterized on a non-contrasted US, CT, or MR exam for which the patient's provider recommends follow-up studies or further evaluation with an additional imaging tests. Exclusion Criteria: Patients who meet any of the following criteria will be excluded for enrollment: 1. Critically ill or medically unstable and whose critical course during the observation period would be unpredictable (e.g., chronic obstructive pulmonary disease (COPD) requiring oxygen) 2. Known hypersensitivity to sulfur hexafluoride or to any component of perflutren lipid (Definity®) 3. Right to left shunt, severe pulmonary hypertension (Pulmonary artery pressure \>90mmHg), or adult respiratory distress syndrome 4. Active cardiac disease including any of the following: * Severe congestive heart failure (class IV in accordance with the classification of the New York Heart Association) * Unstable angina. * Severe arrhythmia (i.e. ventricular tachycardia, flutter fibrillation; ventricular premature complexes occurring close to the preceding T- wave, multifocal complexes). * Myocardial infarction within 14 days prior to the date of proposed Definity® administration. * Uncontrolled systemic hypertension (systolic blood pressure (BP) \>180 mm Hg and/or diastolic BP \>100 mm Hg despite optimal medical management 5. Is in an intensive care setting 6. Has an unstable neurological disease (e.g cerebrovascular accident (including transient ischemic attacks (TIAs) within the 3 months before signing of informed consent 7. Has undergone an invasive procedure on kidney lesion (e.g. tissue biopsy, surgery, nonsurgical cytoreductive procedure) since identification of lesion via US without contrast 8. Has any other medical condition or other circumstances that would significantly decrease the chances of obtaining reliable data or of achieving the study objectives such as: * Mental illness * Drug abuse 9. Female patient who is pregnant or lactating (the possibility of pregnancy has to be excluded by negative serum or urine beta human chorionic gonadotropin results, obtained within 24 hours before the perflutren lipid administration, or on the basis of patient history, e.g.: tubal ligation, hysterectomy or a minimum of 1 year without menses) 10. Obesity that limits obtainment of acceptable images \-