Ultra-Low Dose CT KUB
– by Dr. Jeffrey Yeoh, Radiologist –
Stone Follow-Up CT (Ultra-Low Dose CT KUB)
The Ultra-Low Dose CT KUB examination, Noncontrast CT Abdomen and Pelvis exam, is designed specifically for patients who need follow-up imaging of their known urinary tract calculi. The ultra-low dose CT KUB study is expected to be most often requested by urologists, but any physician may also request this service.
Imaging of Urinary Tract Calculi
CT is the “gold standard” in imaging urinary tract calculi. Urinary tract calculi are usually calcified, and therefore best imaged with CT. For calculi over 3 mm CT has reported sensitivity and specificity of nearly 100%. Traditional dose CT can reliably detect urinary tract calculi as small as 1 mm, and can locate them anywhere within the urinary tract, from kidney, ureter, bladder, and even urethra. Abdominal X-ray (KUB) has reported sensitivity of only 70% and is also limited by lack of specificity, since calcified phleboliths and other calcifications often cannot be differentiated from urinary tract calculi. Ultrasound can detect urinary tract calculi, when larger, and in areas well visualized by ultrasound, like the kidney and bladder, but the ureters are usually obscured by bowel gas. Therefore ureteral calculi are more often not seen, even when present.. Ultrasound may detect hydronephrosis and/or hydroureter, which might suggest an unseen obstructing ureteral calculus.
Urinary tract calculi often afflict younger patients, who will likely need many more years of imaging follow up. Frequent imaging of urinary tract calculi is often needed because of the rapid changes in the course of the disease, as the stones may quickly form/dissolve, migrate down or upstream, or possibly obstruct urine flow. Therefore, since this type of imaging follow-up may be needed frequently and in close succession in the same patient, the Ultra-Low Dose CT KUB provides the lowest possible radiation dose that would still allow adequate evaluation of the size, number, and position of the known urinary tract calcified calculi.
Traditional Noncontrast CT Abdomen and Pelvis protocols effective radiation dose is about 15 mSv. In the interest of limiting radiation to our patients, Hawaii Diagnostic Radiology Services, HDRS, limits the dose to about 5 to 10 mSv. Our brand new GE dual energy CT and VEO supercomputer, one of three in the nation, at our St. Francis Liliha location,utilizes cutting edge technology to improve image quality at ultra-low doses. At this location, we can perform follow up CT KUB exams at about 1-2 mSv. (3-5 mSv in larger patients.)