Overactive bladder(OAB,Urgency) was determined by International Continence Society as Urinary urgency, usually accompanied by frequency and nocturia, with or without urgency urinary incontinence, in the absence of urinary tract infection (UTI) or other obvious pathology.The SNM treatment involves a two-stage surgical procedure performed under local anesthesia. The device include IPG (implantable programme generator) and lead. In the initial test phase, 1st stage, electrode is placed near the sacral nerve and requires a 2 weeks assessment. This allows your doctors and you to assess your initial response according to your voiding dairy and satisfaction. In 2nd stage, SNM procedure is implantation of the IPG.

X ray guidance is harmful to both patients and doctors, while ultrasound guidance is real time visual guidance ,easy to operate by doctors and a radiation free option to challenge anatomy. Urologists are skilled in both ultrasound operations and anatomy basics and dedicating to developing better guidance technique in surgery.

The study here compare the efficacy and safety of ultrasound versus X ray guidance technique in SNM.

Inclusion Criteria:

1. Age > 16 years;
2. Subjects suitable for SNM surgery;
3. Normal upper urinary tract function;
4. Bladder volume > 100 mL;
5. Good compliance and able to complete the follow-up assessments.

Exclusion Criteria:

1. Psychiatric or neurologic disabilities on neurologic evaluation such as multiple sclerosis, spinal cord injury, epilepsy, Parkinson's disease, stroke;
2. Bladder lithiasis or tumor (cystoscopy or ultrasonography);
3. Stress urinary incontinence;
4. Bladder outlet obstruction;
5. Diuresis > 3 liters per 24 hours;
6. Negative at the test period or previous treatment with SNM;
7. Pregnancy and plan to be pregnancy in 2 years.