ARRS 2022 Abstracts

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E1069. Urine Trouble! A Quiz-Based Review of Technique, Findings, and Pitfalls in MR Urography
Authors
  1. Barun Bagga; New York University Langone Health
  2. Myles Taffel; New York University Langone Health
  3. Jay Karajgikar; New York University Langone Health
Background
CT urography is regarded as the first line cross-sectional imaging investigation in patients with hematuria, dilated collecting systems, characterization of congenital abnormalities, and patients with known or presumed cancers of the urinary tract malignancies. Magnetic resonance urography (MRU) is a powerful alternative, especially in patients looking to avoid radiation exposure (young patients requiring multiple follow-up examinations, pregnant patients, or patients with an iodinated contrast allergy). Furthermore, MRU allows advanced tissue characterization with multi-parametric techniques such as DWI and dynamic contrast-enhanced (DCE) imaging. However, optimal acquisition and implementation of MRU is challenging. We intend to explore the nuances of MRU technique in a case-based clinically applicable approach.

Educational Goals / Teaching Points
The goals of this exhibit are to understand the nuanced role of DWI and DCE in early urothelial cancer detection, especially the need for optimization of the temporal and spatial resolution; learn about state-of-the-art fast MRU imaging techniques that have allowed for integration into routine clinical workflow; and demonstrate the role of MRU in tissue characterization and narrowing down a differential diagnosis for urothelial pathologies.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The evaluation from the kidney to bladder requires a wide FOV and trade-offs need to be made between scan time and optimal spatial and temporal resolution. Parallel imaging (PI), using spatial information from multiple receiver coils, has been used to accelerate data acquisition; However, it is limited by the constraints on the signal-to-noise ratio and coil design restrictions. Compressed sensing (CS) is another alternative based on the sparsity of the MR data and using incoherence to reconstruct images from under sampled data. Cartesian acquisition techniques, however, create incoherent aliasing artefacts, which deteriorate the final image quality. Golden-angle radial sparse parallel (GRASP) imaging, combines the two strategies, giving the appropriate high temporal and spatial resolution in a large volumetric coverage. This allows for rapid data acquisition without the need for breath-hold commands or selection of rigid temporal resolution, with reconstructed GRASP images giving DCE images within minutes. We have found this to be invaluable in the detection of small urothelial lesions, which can easily be missed after the contrast reaches the bladder. DWI with high B-values and conventional T2-weighted images add sensitivity to lesion detection and characterizing pathologies, including but not limited to inflammatory pathologies, lymphoma, and congenital anomalies. Lasix injection before dynamic post-contrast image acquisition helps improve the visualization of the upper tracts and ureters.

Conclusion
An optimized MRU is a powerful and fast radiation-free cross-sectional imaging modality, which can add value in urinary tract pathology detection.