1. Department of Radiology Peking Union Medical College Hospital
Dual/Spectral CT:
Role in Urology Imaging
Hao Sun, MD
Department of Radiology
Peking Union Medical College Hospital
Beijing, China

2. Development of Dual Energy CT (DECT)
J Am Coll Cardiol Img 2015; 8:

3. Types of DECT Scanners
AJR 2017; 208:1185–1192

4. DECT Post-processing Techniques
Tube A: 140kV
Tube B: 80kV
Image set A
Image set B
Material-nonspecific
Virtual monochromatic images
Effective atomic map
Electron density map
Material-specific energy-dependent
Material decomposition
Virtual non-enhanced CT (VNE)
Iodine Map
Material labeling
Urinary stone

5. Dual/Spectral CT: Role in Urology Imaging
Dual-Energy CT Renal Lesion Evaluation
Dual-Energy CT Adrenal Lesions
Dual-Energy CT Urinary Calculi Evaluation
Dual-Energy CT Urography
Dual-Energy CT Radiation Dose

6. Dual/Spectral CT: Role in Urology Imaging
Dual-Energy CT Renal Lesion Evaluation
Dual-Energy CT Adrenal Lesions
Dual-Energy CT Urinary Calculi Evaluation
Dual-Energy CT Urography
Dual-Energy CT Radiation Dose

7. DECT Renal Lesion Evaluation
Advantages of DECT in is its ability to characterize renal lesions with a single contrast-enhanced DECT acquisition without the need for a true unenhanced phase
Iodine（mg I/mL）, a biomarker for enhancing tissue, within a lesion
Thresholds for enhancement vary between platforms.
Iodine density measurements
discriminate between clear cell RCC and papillary RCC
assess response to therapy in cases of metastatic RCC
useful in evaluating patients with multiple renal lesions such as those with polycystic kidney disease or in differentiating post-treatment changes from residual tumor after renal mass ablation …

8. DECT Renal Lesion Evaluation
DECT allows for fast and accurate characterization of renal masses in a single-phase acquisition.
Interpretation of color coded images significantly reduces interpretation time.
Omission of a non-enhanced acquisition can reduce radiation exposure by almost 50%.
Dual-energy CT in a patient with heavily calcified cystic renal cell carcinoma that did not show significant enhancement at DECT or SECT. A, Superimposition of color-coded iodine map and VNE image; B,Virtual nonenhanced image; C, Axial;and D, Coronally reformatted nephrographic phase image. Measured enhancement was 12 HU.
Invest Radiol 2010; 45:

9. DECT Renal Lesion Evaluation
DECT iodine quantification for ccRCC v.s. pRCC, and insights regarding the tumor grade
Radiology 2014; 273:

10. DECT Renal Lesion Evaluation
Dual-energy multi–detector row CT with optimal-energy virtual monochromatic images can overcome renal cyst pseudo-enhancement
Optimal-energy virtual mono-chromatic images can enable un-equivocal diagnosis of simple renal cysts, eliminating the need for additional work-up.
Figure 7:transverse unenhanced a and contrast enhanced 140 kVp polychromatic images and contrast-enhanced(c)80-keV and(d)90-keV virtual monochromatic images in a 54-year-old womanwith an intrarenal 15-mm renal cyst in the right kidney. Pseudoenhancement is observed whenaandbare compared. In spite of a substantial reduction in the postcontrast attenuation increase, a slightpseudoenhancement persists onc. In comparison,dallows for a postcontrast attenuation increase ofless than 10 HU.
Radiology 2014; 273:

11. DECT Renal Lesion Evaluation
66-year-old woman with renal cystic disease. Axial contrast-enhanced spectral detector CT image (top) shows ROI (green box) containing larger low-attenuation lesion anteromedially (arrow) and smaller exophytic high-attenuation lesion posterolaterally (arrowhead). Dual-energy analysis tool shows conventional,virtual unenhanced (VNC), iodine no water, and effectiveZreconstructions (bottom images, left to right) of selected ROI. Anteromedial lesion had measured iodine concentration of 0.3 mg I/mL, confirming that it is nonenhancing cyst; posterolateral lesion had measured iodine concentration of 3.9 mg I/mL, confirming that it represents enhancing mass. WL = window level (in HU), WW = window width (in HU), R = right, P = posterior.
AJR 2017; 208: 1185–1192

12. DECT Renal Lesion Evaluation
DECT helps to evaluate patients with multiple renal lesions such as those with polycystic kidney disease
AJR 2017; 208:1185–1192

13. DECT Renal Lesion Evaluation
Images obtained with low kVp show greater conspicuity of low-attenuation renal lesions adjacent to normal renal parenchyma during the nephrographic phase compared with images at higher kVp settings.
Axial high-energy (a) and low-energy (b) nephrographic phaseCT images in a 54-year-old man with a Bosniak III category complexcystic lesion in the right kidney.
Eur Radiol 2014; 24:353–362

14. DECT Renal Lesion Evaluation
DECT can provide high-quality VNE data sets, which are a reasonable approximation of TNE data sets.
Integration of DE scanning into a renal mass protocol will lower radiation exposure by 35%.
Radiology 2009; 252:  

15. DECT Renal Lesion Evaluation
Iodine maps improve the detection of tissular portions in cystic lesions
a: unenhanced DECT image;
b: monochromatic reconstruction at 70 keV during the arterial phase;
c: iodine mapping, the concentration of iodine is measured at 2.01ug/cm3indicating a clear cell renal cancer (concentration ofiodine>0.9ug/cm3 .
Bosniak I type， no iodine
Diagn Interv Radiol 2016; 97:

16. DECT Renal Lesion Evaluation
Colour-coded iodine overlay images can provide benefits over conventional greyscale imaging for enhancement in subcentimetre lesions
Iodine signal (purple colour-encoding) is seen within the lesion located at the upper pole, whereas a lack of iodine signal is visible within the cyst of the lower renal pole.
A 66-year-old man with a 7-mm lipid-poor angiomyolipoma of the left kidney.
Eur Radiol 2014; 24: 353–362

17. DECT Renal Lesion Evaluation
Limitations
Accuracy of DECT drops for renal lesions less than 1.5 cm.
A difference in attenuation values of 5–20 HU has been reported in some ROIs between VNE and TNE images, which could lead to mischaracterization of a minimally enhancing renal lesion.
Iodine density threshold for detection of enhancement in renal lesions has varied from 0.5 to 2 mg I/mL, which suggests that reported values are specific to the type of DECT scanner, image processing algorithm, and the contrast-enhanced phase of examination used.
Additional analyses using iodine-calcium basis pair or iodine–calcium–soft-tissue three-material decom-position may be needed to distinguish iodine from calcium when assessing renal lesions with calcification.

18. Dual/Spectral CT: Role in Urology Imaging
Dual-Energy CT Renal Lesion Evaluation
Dual-Energy CT Adrenal Lesions
Dual-Energy CT Urinary Calculi Evaluation
Dual-Energy CT Urography
Dual-Energy CT Radiation Dose

19. DECT Adrenal Lesions
DECT can be used to help differentiate some lipid-poor adrenal adenomas from metastatic lesions.
A decrease in attenuation of an adrenal lesion between 140 kVp and 80kVp is a highly specific sign of adrenal adenoma.
However, because an increase in attenuation at 80 kVp is seen with metastatic lesions and some adenomas, the sensitivity of this test is low.
AJR 2010; 194: 1479–1483

20. DECT Adrenal Lesions
The adrenal protocol with DECT by using VNE CT is a promising tool for diagnosing lipid-poor adenoma and does not require the acquisition of an unenhanced CT scan.
But it may expose patients to additional radiation doses for lipid-rich adenomas that could be diagnosed on an unenhanced CT scan.
Radiology 2013; 267:

21. DECT Adrenal Lesions
The adrenal protocol with DECT by using VNE CT is a promising tool for diagnosing lipid-poor adenoma and does not require the acquisition of an unenhanced CT scan.
But it may expose patients to additional radiation doses for lipid-rich adenomas that could be diagnosed on an unenhanced CT scan.
Radiology 2013; 267:

22. DECT Adrenal Lesions
Significant differences were observed between benign and indeterminate adrenal nodules on both virtual monochromatic spectral (VMS) images at 140keV and VNC images derived from contrast-enhanced single source(fast kVp switch) DECT.
AJR 2014; 203: 329–335

23. DECT Adrenal Lesions
DECT tools can mathematically subtract iodine or minimize its effects in high energy reconstructions, approximating non-contrast imaging and potentially reducing the need for additional studies to triage adrenal nodules detected on post-contrast DECT exams.
DECT images show the nodule in the arterial phase of enhancement (A) and a virtual non-contrast (VNC) image (B) derived from the same series using the iodine:water material basis pair. Calcium in the aorta remains in image B after iodine subtraction. Images C–E are virtual monochromatic spectral (VMS) images at 40, 75 and 140 keV, respectively. Note the decreasing conspicuity of iodine at higher reconstructed monochromatic energy levels. E is similar but not identical to B, with E exhibiting persistent subtle corticomedullary differentiation and less noise.
AJR 2014; 203: 329–335

24. Dual/Spectral CT: Role in Urology Imaging
Dual-Energy CT Renal Lesion Evaluation
Dual-Energy CT Adrenal Lesions
Dual-Energy CT Urinary Calculi Evaluation
Dual-Energy CT Urography
Dual-Energy CT Radiation Dose

25. DECT Urinary Stone Evaluation-Detection
3rd generation DECT with an additional built-in tin filter.
High-pitch abdominopelvic CT with Sn150kV substantially reduced radiation exposure and scanning time, while maintained stone detection and image quality and prevented breathing-motion artifacts.
Scan time: 0.83±0.04 s
Abdom Radiol 2017; 42:

26. DECT Urinary Stone Evaluation-Detection
No respiratory artifact
A 50-year-old male presented with right renal colic and hematuria.Regular-dose CT image showed a 7.8-mm stone in the right renal pelvis (A) and another 8.1-mm stone in the right ureter (C).Corresponding low-dose CT images also showed the right renal stone (B) and the right ureter stone (D).
Abdom Radiol 2017; 42:

27. DECT Urinary Stone Evaluation-Composition
Factors influencing treatment decisions
Calcium oxalate
Hydroxyapatite
Uric acid
Cystine
Brushite
Struvite
Patient symptoms
Stone characteristics
Location
Size
Composition
UA stonesalkalinization
Calcium based stones difficult to fragment with SWL
How to determine stone composition in vivo?

28. DECT Urinary Stone Evaluation-Composition

29. DECT Urinary Stone Evaluation-Composition
By using custom software that takes advantage of the increased in-spectral separation provided by a tin filter on the high-energy beam of a dual-source CT system, uric acid stones(red) can be distinguished from three groups of non–uric acid stones: cystine (yellow), calcium oxalate/brushite
/struvite (green), and apatite.
).(a)Uric acid stone in a 71-year-old man.(b)Cystine stone in a 63-year-old man.(c)Calcium oxalate stone in a 21-year-old woman.(d)Apatite stone in a 34-year-oldwoman.
Radiology 2015; 276:

30. DECT Urinary Stone Evaluation-Composition
DECT could accurately predict the major component of urinary calculi and detect uric acid, cysteine, and calcium oxalate with a satisfactory accuracy.
Clin Radiol 2016; 71:

31. DECT Urinary Stone Evaluation-Composition
Clin Radiol 2016; 71:

32. DECT Urinary Stone Evaluation-Composition
Limitations
Accuracy decreases when calculi < 3-5mm
But, small stones do not need intervention
Calculi with mixed composition  focus on major component
Small calculi adjacent to urinary tract catheters could be obscured or misclassified.

33. Dual/Spectral CT: Role in Urology Imaging
Dual-Energy CT Renal Lesion Evaluation
Dual-Energy CT Adrenal Lesions
Dual-Energy CT Urinary Calculi Evaluation
Dual-Energy CT Urography
Dual-Energy CT Radiation Dose

34. DECT Urography
To generate VNE images from the contrast-enhanced phase, enabling detection of urinary calculi without the need for a true unenhanced phase.
Large (>2.9mm) and high-attenuation (>387 HU) calculi can be detected with good reliability
Smaller and lower attenuation calculi might be erased from images, especially with in-creased image noise.
Radiology 2012; 264: 119–125

35. Dual/Spectral CT: Role in Urology Imaging
Dual-Energy CT Renal Lesion Evaluation
Dual-Energy CT Adrenal Lesions
Dual-Energy CT Urinary Calculi Evaluation
Dual-Energy CT Urography
Dual-Energy CT Radiation Dose

36. DECT Radiation Dose
The radiation dose from most DECT protocols is equivalent to conventional single energy CT (dose-neutral).
Advances in CT detector hardware and newer iterative image reconstruction algorithms have improved image quality of DECT, which could enable further reduction in radiation dose.
The potential to eliminate the true unenhanced phase of imaging and the need for repeat imaging for incidental renal lesions could lead to further saving in radiation dose while using DECT.
AJR 2017; 208:1185–1192

37. DECT Radiation Dose
With both DSCT generations, abdominal DECT can be routinely performed without radiation dose penalty compared to SECT, while third-generation DSCT shows improved dose efficiency.
Eur Radiol 2017; 27:

38. Thank you
Dr. Hao Sun