This study compares the efficacy of the ultrasound with fluoroscope in guidance of lumbar sympathetic block (LSB). The goals of the study are; 1) To show that US-guided LSB results in shorter performance time compared to fluoroscope-guided LSB, 2) To evaluate the efficacy and safety of US-guided LSB, and 3) To verify that US-guided LSB has similar success rates to fluoroscope-guided LSB. 50 patients who are supposed to undergo LSB due to sympathetically maintained pain, satisfy criteria of inclusion and exclusion, and voluntarily sign the informed consent will be enrolled.