MRU & Bladder
David Childs1

1Wake Forest Baptist Health

Synopsis

MR urography has proven to be a robust technique for the assessment of the urothelium in both the pediatric (congenital anomalies) and adult (urothelial carcinoma) populations. Technical challenges (motion, contraindication to contrast, etc.) remain, although newer MRI techniques are increasingly providing solutions to these issues. The increasing use of diffusion and perfusion-weighted imaging has also provided the benefit of multi-parametric data. While the detection of urothelial carcinoma can be achieved with various endoscopic and urographic imaging tests, the accurate staging of tumors (both T and N stage) remains a challenge. Advances have been achieved in anatomic MRI, perfusion MRI, and diffusion weighted imaging for the T-staging of bladder carcinoma, although the assessment of nodal status remains a significant challenge. Newly described PET/MRI methods have shown promising results in improving both the specificity of focal urothelial lesions and accurate determination of nodal status, though research is ongoing.

Target Audience

(1) Private practice radiologists who wish to learn the practical points of utilizing magnetic resonance urography for their patient population; (2) Academic radiologists who wish to review practical applications as well as the current state of advanced MR and PET/MR techniques for the detection and staging of urothelial malignancy.

Educational Objectives

1. Understand the components of a MR urography protocol

  • Anatomic sequences
  • Excretory urographic sequences
  • Hydrographic urographic sequences
  • Advanced MR techniques (diffusion weighted imaging, perfusion imaging, texture analysis)

2. Understand how to correct image artifacts and other technical challenges commonly encountered in the performance of MR urography

  • Susceptibility artifact
  • Motion artifact
  • Poor distention of the collecting system and ureters

3. Appreciate the use of advanced MR techniques for the detection, characterization, and staging of urothelial neoplasms

  • Current societal guidelines
  • When to choose MR urography over CT urography
  • Benefits over CT urography

4. Understand the current limitations of MRI in the detection and staging of urothelial malignancy

  • Specificity of focal urothelial findings (tumor versus treatment effects)
  • Nodal status (poor sensitivity in small or borderline nodes)
  • Assessment of bladder muscle invasion

5. Understand the current usage and potential benefits of PET/MRI in the detection and staging of urothelial malignancy, as well as future research directions

  • Advantages over anatomic imaging and PET/CT
  • Technical challenges and potential solutions (accumulation of excreted FDG, attenuation correction, motion correction)

Methods

1. Brief review of MR urography protocol

2. Use of case examples which demonstrate how to troubleshoot common image artifacts encountered during the performance of MR urography

3. Use of case examples to demonstrate the use of advanced MR techniques for the detection, staging and characterization of urothelial tumors

4. Review the newest applications of PET/MR for the detection and staging of urothelial malignancy, using case examples

5. Review current shortcomings of MRI and PET/MRI, and potential research opportunities

Conclusions

MR urography has proven to be a robust technique for the assessment of the urothelium in both the pediatric (congenital anomalies) and adult (urothelial carcinoma) populations. Technical challenges (motion, contraindication to contrast, etc.) remain, although newer MRI techniques are increasingly providing solutions to these issues. The increasing use of diffusion and perfusion-weighted imaging has also provided the benefit of multi-parametric data.

While the detection of urothelial carcinoma can be achieved with various endoscopic and urographic imaging tests, the accurate staging of tumors (both T and N stage) remains a challenge. Advances have been achieved in anatomic MRI, perfusion MRI, and diffusion weighted imaging for the T-staging of bladder carcinoma, although the assessment of nodal status remains a significant challenge. Newly described PET/MRI methods have shown promising results in improving both the specificity of focal urothelial lesions and accurate determination of nodal status, though research is ongoing.

Acknowledgements

I would like to thank the members of both the International Society for Magnetic Resonance in Medicine and the European Society for Magnetic Resonance in Medicine and Biology for the opportunity to participate in this meeting.

References

1. Wang F, Wu LM, Hua XL, Zhao ZZ, Chen XX, Xu JR. Intravoxel incoherent motion diffusion-weighted imaging in assessing bladder cancer invasiveness and cell proliferation. J Magn Reson Imaging. 2018;47(4):1054-1060.

2. Panebianco V, De Berardinis E, Barchetti G, et al. An evaluation of morphological and functional multi-parametric MRI sequences in classifying non-muscle and muscle invasive bladder cancer. Eur Radiol. 2017;27(9):3759-3766.

3. Pandey A, Yoruk U, Keerthivasan M, et al. Multiresolution imaging using golden angle stack-of-stars and compressed sensing for dynamic MR urography. J Magn Reson Imaging. 2017;46(1):303-311.

4. Rosenkrantz AB, Friedman KP, Ponzo F, et al. Prospective pilot study to evaluate the incremental value of PET information in patients with bladder cancer undergoing 18F-FDG simultaneous PET/MRI. Clin Nucl Med. 2017;42(1):e8-e15.

5. Chung AD, Schieda N, Shanbhogue AK, et al. MRI evaluation of the urothelial tract: pitfalls and solutions. AJR Am J Roentgenol. 2016;207(6):W108-W116.

6. Parikh N, Ream JM, Zhang HC, et al. Performance of simultaneous high temporal resolution quantitative perfusion imaging of bladder tumors and conventional multi-phase urography using a novel free-breathing continuously acquired radial compressed-sensing MRI sequence. Magn Reson Imaging. 2016;34(5):694-8.

Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)