Method of choice for a New born child not passing urine for 36 hours :
Ultrasound of kidney & bladder
CT Scan
Cystoscopy
X–ray pelvis
A history of Anuria suggests Acute Renal failure.
Ultrasonography is the ideal imaging tool in Renal failure because of its non dependence on Renal function.
As it allows visualization of :

Pelvicalyceal system ofAssessment of Renal Size o Structural anomalies and calculi .
Note - In this question DTPA scan has not been provided as an option. So, the best answer is USG.