Ultrasonography is the preferred imaging method for diagnosing hypertrophic pyloric stenosis. Key findings on ultrasound include thickening of the pyloric muscle greater than 3mm and elongation of the pyloric channel greater than 17mm. Doppler ultrasound can also detect increased blood flow to the hypertrophied pyloric muscle and mucosa. While upper gastrointestinal studies with barium can identify signs like double tracking, ultrasonography has greater sensitivity and specificity for diagnosing hypertrophic pyloric stenosis.