Ultrasound–CT fusion in ureteral stone Follow-Up: A prospective accuracy study benchmarked against ureteroscopy

To assess the diagnostic accuracy of radiation-free ultrasound–CT (US–CT) fusion imaging for ureteral stone detection in patients scheduled for ureteroscopy (URS). In this prospective study (NCT02539004), adults with a single ureteral stone on non-contrast CT (NCCT) and scheduled for URS were consecutively enrolled. Exclusion criteria included multiple stones, pacemaker, ureteral stent, or nephrostomy tube. On the day of surgery, US–CT fusion (Logiq E9, GE Healthcare) was performed using electromagnetic tracking and prior 3D NCCT data. The primary analysis assessed sensitivity, specificity, accuracy, positive and negative predictive values (PPV; NPV). Secondary analyses stratified outcomes by patient and stone characteristics. Thirty-one patients were enrolled (mean age 52.2 ± 15.1 years; 71% male). Stones were upper ureter in 51% and mid–lower ureter in 49%, mean diameter 6.9 ± 2.1 mm. Twenty-nine patients (93.5%) underwent URS and were evaluable. US–CT fusion yielded 15 true positives (51.7%), 8 true negatives (27.6%), and 6 false negatives (20.7%), with no false positives. Sensitivity, specificity, PPV, NPV, and accuracy were 71.4%, 100%, 100%, 57.1%, and 79.3%, respectively. Sensitivity was highest for SSD > 10 cm (81.8%), BMI ≤ 30 (75.0%), right-sided stones (88.9%), absence of hydronephrosis (83.3%), and size > 5 mm (81.3%); and lowest for size ≤ 5 mm (40.0%) and radiolucent stones (44.4%). NPV ranged from 33.3% for SSD ≤ 10 cm to 75.0% for SSD > 10 cm and right-sided stones. US–CT fusion demonstrated excellent specificity/PPV but moderate sensitivity - useful for confirming, not excluding, stones - and may reduce repeat CT in selected patients, pending validation by larger head-to-head studies defining performance, indications, and cost-effectiveness.