I. Necessary radiological examination of pediatric urinary. 1, ultrasound: the preferred examination, non-invasive, helps in the diagnosis of prenatal fetal hydronephrosis, urinary tract infection, renal tumors, kidney stones, testicular torsion, testicular masses and other diseases. Effective radiation dose: 0 mSv . 2.CT:Using contrast agent, it can show three time-phase changes for comparative study, with high diagnostic accuracy for renal tumors, stones, arterial stenosis, urinary tract malformation, etc. CTU can show the three-dimensional structure of the urinary tract, and CTA can show the situation of arterial and venous and their direction, which is conducive to intraoperative dissection. However, it is contradictory in clinical use. On the one hand, CT is good for diagnosis; on the other hand, CT has radiation, which is risky for pediatric use. It should be used after weighing the pros and cons. Effective radiation dose: -8 mSv. MR: The examination takes 40 minutes to one hour, is noisy, requires breathing and sedation. It is used for tumor monitoring, pelvic and vascular anatomy, assessment of infection status, etc. It provides functional information.MRU provides three-dimensional images of the urinary system. No radiation. Effective radiation dose: 0 mSv . 4. VCUG:The 2011 AAP guidelines changed and VCUG is no longer the recommended test for a first febrile urinary tract infection unless kidney and bladder ultrasound suggests hydronephrosis, scarring, or other findings such as high-grade vesicoureteral reflux or urinary tract obstruction. Currently, VCUGj is the gold standard for diagnosing reflux and evaluating lower urinary tract abnormalities, especially in boys. Effective radiation dose: 0.3 mSv . 5, Retrograde urography: used to assess urethral injury and stricture. II. Nuclide 1. Nephrogram: assessment of renal function, characterization of parenchymal function, understanding of urinary tract obstruction, transplantation renal assessment, glomerular filtration rate. Effective radiation dose: 0.6 mSv. 2, Renal parenchyma imaging: renal localization, subrenal function, parenchymal anatomical function, infection/scarring. Effective radiation dose: 0.6-1.0 mSv. 3, Radionuclide cystography (RNC): assessment of vesicoureteral reflux, initial diagnosis in older children, follow-up studies in spontaneous remission or postoperative period, sibling monitoring, 4, Radionuclide GFR: more reliable than creatinine clearance. Advantages: direct measurement of glomerular filtration rate, accurate, can be obtained quickly, reliable results. Disadvantages: radiation exposure.