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.