Owing to its superior detection of fluid with T2-weighted sequences, MRU has been shown to be more sensitive than noncontrast CT in the detection of secondary signs of obstruction in the presence of urolithiasis such as hydronephrosis and perinephric fluid [28]. MRU Without IV Contrast MRU can also evaluate the urinary system without the use of IV contrast. In an early study performed in patients with acutely obstructed kidneys, noncontrast MRU was found to be 100% sensitive for diagnosing obstruction with perirenal fluid seen in 87% of cases, with the site of the obstruction seen in 80% of these obstructed kidneys. In an early study, when referenced to IVU, corresponding filling defects at MRU were seen in 12 of 18 patients with ureteric obstruction caused by a stone ranging from 4 to 20 mm in size [26]. In a more recent study performed at 3T, in patients presenting with renal colic, noncontrast MRU only detected stones in 50% of patients compared with 91% with noncontrast CT. However, the combination of stone or perinephric fluid and ureteral dilation gave MRU a sensitivity of 84%, specificity of 100%, and accuracy of 86% for stone detection when compared with CT [28]. Radiography Intravenous Urography IV urography (IVU) was once considered the reference standard for the diagnosis of urolithiasis. With the administration of contrast, IVU provides additional information beyond radiography including structural and functional information about kidneys, ureters, and urinary bladder, including the site and degree of obstruction from urolithiasis. A study comparing IVU with noncontrast CT demonstrated a sensitivity and specificity of IVU to be 75% and 92%, respectively, compared with 85% and 98%, respectively, at noncontrast CT [31]. Another study demonstrated significantly greater performance of noncontrast CT over IVU with sensitivities and specificities of 96% and 100%, respectively, for CT versus 87% and 94%, respectively, for IVU [32].
Acute Onset Flank Pain Suspicion of Stone Disease Urolithiasis . Owing to its superior detection of fluid with T2-weighted sequences, MRU has been shown to be more sensitive than noncontrast CT in the detection of secondary signs of obstruction in the presence of urolithiasis such as hydronephrosis and perinephric fluid [28]. MRU Without IV Contrast MRU can also evaluate the urinary system without the use of IV contrast. In an early study performed in patients with acutely obstructed kidneys, noncontrast MRU was found to be 100% sensitive for diagnosing obstruction with perirenal fluid seen in 87% of cases, with the site of the obstruction seen in 80% of these obstructed kidneys. In an early study, when referenced to IVU, corresponding filling defects at MRU were seen in 12 of 18 patients with ureteric obstruction caused by a stone ranging from 4 to 20 mm in size [26]. In a more recent study performed at 3T, in patients presenting with renal colic, noncontrast MRU only detected stones in 50% of patients compared with 91% with noncontrast CT. However, the combination of stone or perinephric fluid and ureteral dilation gave MRU a sensitivity of 84%, specificity of 100%, and accuracy of 86% for stone detection when compared with CT [28]. Radiography Intravenous Urography IV urography (IVU) was once considered the reference standard for the diagnosis of urolithiasis. With the administration of contrast, IVU provides additional information beyond radiography including structural and functional information about kidneys, ureters, and urinary bladder, including the site and degree of obstruction from urolithiasis. A study comparing IVU with noncontrast CT demonstrated a sensitivity and specificity of IVU to be 75% and 92%, respectively, compared with 85% and 98%, respectively, at noncontrast CT [31]. Another study demonstrated significantly greater performance of noncontrast CT over IVU with sensitivities and specificities of 96% and 100%, respectively, for CT versus 87% and 94%, respectively, for IVU [32].