Khan, Ahmad Ali, et al. “RETROGRADE AIR INJECTION FOR IDENTIFYING PRECISELY POSTERIOR CALYX: A VERY USEFUL TOOL WHILE PERFORMING MINI-PERCUTANEOUS NEPHROLITHOTOMY”. Pakistan Armed Forces Medical Journal, vol. 69, no. 3, June 2019, pp. 600-04, https://pafmj.org/PAFMJ/article/view/3038.