 Introduction/Background Urinary tract stones are thought to result from either excessive excretion or precipitation of salts in the urine or a relative lack of inhibiting substances. Men are more commonly affected than women, and the incidence increases with age until 60 years of age. For example, it is estimated that 19% of men and 9% of women will be diagnosed with a kidney stone by 70 years of age [1]. Stones also tend to be recurrent with recurrence rates shown to be higher in those with 2 or more previous stone episodes [2]. Special Imaging Considerations CT urography (CTU) is an imaging study that is tailored to improve visualization of both the upper and lower urinary tracts. There is variability in the specific parameters, but it usually involves unenhanced images followed by intravenous (IV) contrast-enhanced images, including nephrographic and excretory phases acquired at least 5 minutes after contrast injection. Alternatively, a split-bolus technique uses an initial loading dose of IV contrast and then obtains a combined nephrographic-excretory phase after a second IV contrast dose; some sites include arterial phase. CTU should use thin-slice acquisition. Reconstruction methods commonly include maximum intensity projection or 3-D volume rendering. For the purposes of this document, we make a distinction between CTU and CT abdomen and pelvis without and with IV contrast. CT abdomen and pelvis without and with IV contrast is defined as any protocol not specifically tailored for the evaluation of the upper and lower urinary tracts and without both the precontrast and excretory phases. In an effort to minimize patient radiation dose, low-dose CT examinations can replace traditional noncontrast CT examinations and are often performed using a combination of lowering milliampere-seconds, kilovoltage peak, and
Acute Onset Flank Pain Suspicion of Stone Disease Urolithiasis .  Introduction/Background Urinary tract stones are thought to result from either excessive excretion or precipitation of salts in the urine or a relative lack of inhibiting substances. Men are more commonly affected than women, and the incidence increases with age until 60 years of age. For example, it is estimated that 19% of men and 9% of women will be diagnosed with a kidney stone by 70 years of age [1]. Stones also tend to be recurrent with recurrence rates shown to be higher in those with 2 or more previous stone episodes [2]. Special Imaging Considerations CT urography (CTU) is an imaging study that is tailored to improve visualization of both the upper and lower urinary tracts. There is variability in the specific parameters, but it usually involves unenhanced images followed by intravenous (IV) contrast-enhanced images, including nephrographic and excretory phases acquired at least 5 minutes after contrast injection. Alternatively, a split-bolus technique uses an initial loading dose of IV contrast and then obtains a combined nephrographic-excretory phase after a second IV contrast dose; some sites include arterial phase. CTU should use thin-slice acquisition. Reconstruction methods commonly include maximum intensity projection or 3-D volume rendering. For the purposes of this document, we make a distinction between CTU and CT abdomen and pelvis without and with IV contrast. CT abdomen and pelvis without and with IV contrast is defined as any protocol not specifically tailored for the evaluation of the upper and lower urinary tracts and without both the precontrast and excretory phases. In an effort to minimize patient radiation dose, low-dose CT examinations can replace traditional noncontrast CT examinations and are often performed using a combination of lowering milliampere-seconds, kilovoltage peak, and