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DECT: GU Applications Ravi Kaza, MD University of Michigan Department of Radiology Disclosures • None Principle of DECT • Acquire attenuation values of same structures at two different energy levels • Measure change in attenuation of voxels between two energies • Differentiate and quantify materials Types of DECT scanners • • • • • Dual-source DECT Rapid-switching DECT Dual-layer DECT Sequential DECT Twin-beam DECT DECT in Urinary Tract Imaging • Renal mass characterization • Urinary calculi characterization • CT Urography Renal Mass Characterization • Distinguish enhancing from non-enhancing renal masses with single phase of image acquisition • Done by detecting iodine in enhancing renal masses • Can eliminate the need for unenhanced imaging • Permit the characterization of incidentally detected renal lesions Renal Mass Characterization 50 HU Hyperdense renal cyst Iodine density image Water density image Renal Mass Characterization 55 HU Renal cell carcinoma Iodine density image Water density image Renal Mass Characterization • Virtual unenhanced images: – Enable measurement of Hounsfield units similar to true unenhanced images • Iodine quantification: – Iodine density measured in mg/cc – Can be used to detect enhancement Renal Mass Characterization * 3.3 mg/cc * 0.6 mg/cc * 89 HU * 93 HU Iodine density image Renal Mass Characterization Virtual unenhanced image Images courtesy of Dr. Alec Megibow Renal Mass Characterization • Limitations: – Higher image noise of VUE images as compared to true unenhanced images – Reduced conspicuity of calcification in renal masses Urinary Calculi Characterization • Knowledge of stone composition prior to stone extraction may guide management – Uric acid vs non-uric acid calculi • Change in stone attenuation at the two energies – Dual-source DECT • Dual-energy Index – Fast-kV switching DECT • Material basis pair images • Effective atomic number (Eff-Z) Urinary Calculi Characterization Images courtesy of Dr. Alec Megibow Urinary Calculi Characterization Calcium:Uric acid basis pair Calcium density image Uric acid density image Urinary Calculi Characterization • Highly accurate in distinguishing – uric acid from non uric acid calculi – calcium containing calculi form non calcium containing calculi • Further classification as struvite and cysteine calculi is feasible Urinary Calculi Characterization • Limitations: – Difficult to characterize • Calculi < 5 mm • Mixed calculi CT Urography • Virtual unenhanced (VUE) images generated from the contrast-enhanced excretory phase images of a DECT urogram permit detection of calculi – May reduce the need for a true unenhanced series • Potential for stone characterization CT Urography Coronal CTU VUE image CT Urography • Limitations: – Potential to miss calculi < 3 mm on VUE images – “Rim artifact” due to incomplete removal of dense iodine can cause false +ve/-ve diagnosis of calculi CT Urography Coronal CTU True unenhanced image VUE image VUE image • • • • DECT in GU Imaging: Advantages Characterize incidental renal lesions Quantify iodine content in renal mass Characterize urinary calculi May permit decreased patient radiation dose by eliminating the need for true unenhanced scan DECT in GU Imaging: Limitations • Higher image noise on VUE images • Artifacts from incomplete iodine subtraction seen on VUE image of CTU • Time and expertise needed for post processing and image generation • Larger image data sets of DECT requiring increased image storage capabilities
