When the entire upper tract is not visualized or degraded by motion artifact, MRU sequences can be repeated without fear of added radiation risk. Inherent higher contrast resolution of MRU is particularly beneficial for small tumor detection. Takahashi et al [62] performed a retrospective review of 110 patients who had undergone MRU to identify patients with small (<2 cm) tumors. They concluded that gadolinium-enhanced 3-D spoiled gradient echo MRU helped detect 74% of small UCs. Nephrographic and excretory-phase images are essential for helping detect small UCs. No direct comparison of MRU to CTU for UTUC exists, however, overall, MRU takes much longer to perform. Technical challenges for MRU also include the poorer detection of nonobstructing stones than by CT, which is critical when evaluating hematuria, and MRU is much more prone to motion and peristalsis artifacts with overall lower spatial resolution than CTU. A retrospective study of 91 MRU examinations by Takahashi et al [124] found a sensitivity of 69% and a specificity of 97% for upper tract malignancy. Another retrospective review by Obuchi et al [125] of patients over a 5-year time period who had undergone MRI within 2 months of surgery showed that MRI T staging improved with gadolinium-enhanced fat-suppressed T1- weighted images in combination with morphologic changes and signal intensity changes. For UTUC arising in the renal pelvis, assessment for any renal extension for T staging is important. A retrospective review of 40 patients with renal pelvic tumors and MRI showed that T2-weighted imaging plus DWI enabled a 98% detection rate. For discriminating tumors with macroscopic renal invasion from those with microscopic renal invasion or less, T2-weighted imaging plus DWI (93%) was significantly more accurate than T2-weighted imaging alone (75%) [126]. MRU Without IV Contrast Noncontrast enhanced MRU can be used to assess the renal collecting systems and ureters using a heavily T2- weighted sequence [63].
Pretreatment Staging of Urothelial Cancer. When the entire upper tract is not visualized or degraded by motion artifact, MRU sequences can be repeated without fear of added radiation risk. Inherent higher contrast resolution of MRU is particularly beneficial for small tumor detection. Takahashi et al [62] performed a retrospective review of 110 patients who had undergone MRU to identify patients with small (<2 cm) tumors. They concluded that gadolinium-enhanced 3-D spoiled gradient echo MRU helped detect 74% of small UCs. Nephrographic and excretory-phase images are essential for helping detect small UCs. No direct comparison of MRU to CTU for UTUC exists, however, overall, MRU takes much longer to perform. Technical challenges for MRU also include the poorer detection of nonobstructing stones than by CT, which is critical when evaluating hematuria, and MRU is much more prone to motion and peristalsis artifacts with overall lower spatial resolution than CTU. A retrospective study of 91 MRU examinations by Takahashi et al [124] found a sensitivity of 69% and a specificity of 97% for upper tract malignancy. Another retrospective review by Obuchi et al [125] of patients over a 5-year time period who had undergone MRI within 2 months of surgery showed that MRI T staging improved with gadolinium-enhanced fat-suppressed T1- weighted images in combination with morphologic changes and signal intensity changes. For UTUC arising in the renal pelvis, assessment for any renal extension for T staging is important. A retrospective review of 40 patients with renal pelvic tumors and MRI showed that T2-weighted imaging plus DWI enabled a 98% detection rate. For discriminating tumors with macroscopic renal invasion from those with microscopic renal invasion or less, T2-weighted imaging plus DWI (93%) was significantly more accurate than T2-weighted imaging alone (75%) [126]. MRU Without IV Contrast Noncontrast enhanced MRU can be used to assess the renal collecting systems and ureters using a heavily T2- weighted sequence [63].