An ECG may be helpful in diagnosing complications such as hyperkalemia in the clinical setting of hydronephrosis.  Peaked T waves are the earliest sign of hyperkalemia on ECG.
Hydronephrosis electrocardiogram
Hydronephrosis echocardiography or ultrasound
Hydronephrosis physical examination
Pyonephrosis physical examination
Pyonephrosis MRI
Hydronephrosis MRI
Pyonephrosis ultrasound
Pyonephrosis CT