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. 2010 Jul;256(1):184-90.
doi: 10.1148/radiol.10091411.

Detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy CT

Naoki Takahashi  1 , Terri J Vrtiska, Akira Kawashima, Robert P Hartman, Andrew N Primak, Joel G Fletcher, Cynthia H McCollough
Affiliations

Detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy CT

Naoki Takahashi et al. Radiology. 2010 Jul.

Abstract

Purpose: To evaluate the detectability of urinary stones on virtual nonenhanced images generated at pyelographic-phase dual-energy computed tomography (CT).

Materials and methods: This retrospective HIPAA-compliant study was institutional review board approved. All included patients had previously consented to the use of their medical records for research. Sixty-two patients (38 men, 24 women; age range, 35-91 years) had undergone CT urography, which consisted of nonenhanced and pyelographic-phase dual-energy CT performed by using a dual-source scanner. Commercial software was used to create virtual nonenhanced images by suppressing the iodine signal from the pyelographic-phase dual-energy CT scans. Two radiologists, in consensus, evaluated the virtual nonenhanced images for the presence of stones. Sensitivity for detecting stones was calculated on a per-stone basis. Sensitivity, specificity, and accuracy were also calculated on a per-renal unit (defined as the intrarenal collecting system and ureter of one kidney) basis. The true nonenhanced scan was considered the reference standard. A jackknife method was used because any patient may have multiple stones.

Results: Of 62 patients with 122 renal units, 21 patients with 25 renal units had a total of 43 stones (maximal transverse diameter range, 1-24 mm; median, 3 mm). The overall sensitivity for detecting stones was 63% (27 of 43 stones) per stone. Sensitivities were 29% (four of 14 stones) for 1-2-mm stones, 64% (nine of 14 stones) for 3-4-mm stones, 83% (five of six stones) for 5-6-mm stones, and 100% (nine of nine stones) for 7-mm or larger (7, 7, 7, 8, 8, 9, 11, 15, and 24 mm) stones. All three ureteral stones (3, 4, and 8 mm) were correctly identified. The sensitivity, specificity, and accuracy for detecting stones on a per-renal unit basis were 65% (17 of 26 renal units), 92% (88 of 96 renal units), and 86% (105 of 122 renal units), respectively.

Conclusion: Virtual nonenhanced images generated at pyelographic-phase dual-energy CT enabled the detection of urinary stones with moderate accuracy. The detection of small (1-2-mm) stones was limited.

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Figures

Figure 1:
Figure 1:
Flowchart of patient exclusion and inclusion for dual-energy CT urography and the presence or absence of urinary tract stones.
Figure 2a:
Figure 2a:
Transverse CT images in 61-year-old woman with multiple renal stones. (a, b) True nonenhanced scans show 2-mm (a) and 5-mm (b) calyceal stones (arrow) in lower pole of right kidney. (c, d) Corresponding pyelographic-phase images show iodinated contrast material (arrowheads) in collecting systems, obscuring renal stones. (e, f) Corresponding virtual nonenhanced images created from pyelographic-phase scans show removal of iodine signal from collecting systems. The 5-mm stone (arrow in f) in right kidney is visible as high-attenuating material, but the 2-mm stone is not identifiable in e owing to oversubtraction of stone signal.
Figure 2b:
Figure 2b:
Transverse CT images in 61-year-old woman with multiple renal stones. (a, b) True nonenhanced scans show 2-mm (a) and 5-mm (b) calyceal stones (arrow) in lower pole of right kidney. (c, d) Corresponding pyelographic-phase images show iodinated contrast material (arrowheads) in collecting systems, obscuring renal stones. (e, f) Corresponding virtual nonenhanced images created from pyelographic-phase scans show removal of iodine signal from collecting systems. The 5-mm stone (arrow in f) in right kidney is visible as high-attenuating material, but the 2-mm stone is not identifiable in e owing to oversubtraction of stone signal.
Figure 2c:
Figure 2c:
Transverse CT images in 61-year-old woman with multiple renal stones. (a, b) True nonenhanced scans show 2-mm (a) and 5-mm (b) calyceal stones (arrow) in lower pole of right kidney. (c, d) Corresponding pyelographic-phase images show iodinated contrast material (arrowheads) in collecting systems, obscuring renal stones. (e, f) Corresponding virtual nonenhanced images created from pyelographic-phase scans show removal of iodine signal from collecting systems. The 5-mm stone (arrow in f) in right kidney is visible as high-attenuating material, but the 2-mm stone is not identifiable in e owing to oversubtraction of stone signal.
Figure 2d:
Figure 2d:
Transverse CT images in 61-year-old woman with multiple renal stones. (a, b) True nonenhanced scans show 2-mm (a) and 5-mm (b) calyceal stones (arrow) in lower pole of right kidney. (c, d) Corresponding pyelographic-phase images show iodinated contrast material (arrowheads) in collecting systems, obscuring renal stones. (e, f) Corresponding virtual nonenhanced images created from pyelographic-phase scans show removal of iodine signal from collecting systems. The 5-mm stone (arrow in f) in right kidney is visible as high-attenuating material, but the 2-mm stone is not identifiable in e owing to oversubtraction of stone signal.
Figure 2e:
Figure 2e:
Transverse CT images in 61-year-old woman with multiple renal stones. (a, b) True nonenhanced scans show 2-mm (a) and 5-mm (b) calyceal stones (arrow) in lower pole of right kidney. (c, d) Corresponding pyelographic-phase images show iodinated contrast material (arrowheads) in collecting systems, obscuring renal stones. (e, f) Corresponding virtual nonenhanced images created from pyelographic-phase scans show removal of iodine signal from collecting systems. The 5-mm stone (arrow in f) in right kidney is visible as high-attenuating material, but the 2-mm stone is not identifiable in e owing to oversubtraction of stone signal.
Figure 2f:
Figure 2f:
Transverse CT images in 61-year-old woman with multiple renal stones. (a, b) True nonenhanced scans show 2-mm (a) and 5-mm (b) calyceal stones (arrow) in lower pole of right kidney. (c, d) Corresponding pyelographic-phase images show iodinated contrast material (arrowheads) in collecting systems, obscuring renal stones. (e, f) Corresponding virtual nonenhanced images created from pyelographic-phase scans show removal of iodine signal from collecting systems. The 5-mm stone (arrow in f) in right kidney is visible as high-attenuating material, but the 2-mm stone is not identifiable in e owing to oversubtraction of stone signal.
Figure 3a:
Figure 3a:
Transverse CT images in 44-year-old man with left distal ureteral stone. (a) True nonenhanced scan shows 3-mm stone (arrow) in distal left ureter. (b) Pyelographic-phase image shows iodinated contrast material in ureters and bladder, obscuring nonobstructing ureteral stone. (c) Virtual nonenhanced image created from pyelographic-phase scan shows removal of iodine signal from ureters and bladder. Left distal ureteral stone (arrow) is visible as high-attenuating material.
Figure 3b:
Figure 3b:
Transverse CT images in 44-year-old man with left distal ureteral stone. (a) True nonenhanced scan shows 3-mm stone (arrow) in distal left ureter. (b) Pyelographic-phase image shows iodinated contrast material in ureters and bladder, obscuring nonobstructing ureteral stone. (c) Virtual nonenhanced image created from pyelographic-phase scan shows removal of iodine signal from ureters and bladder. Left distal ureteral stone (arrow) is visible as high-attenuating material.
Figure 3c:
Figure 3c:
Transverse CT images in 44-year-old man with left distal ureteral stone. (a) True nonenhanced scan shows 3-mm stone (arrow) in distal left ureter. (b) Pyelographic-phase image shows iodinated contrast material in ureters and bladder, obscuring nonobstructing ureteral stone. (c) Virtual nonenhanced image created from pyelographic-phase scan shows removal of iodine signal from ureters and bladder. Left distal ureteral stone (arrow) is visible as high-attenuating material.
Figure 4:
Figure 4:
Transverse virtual nonenhanced CT image created from pyelographic-phase scan in 51-year-old man with left renal stone shows iodinated contrast material (arrowheads) in renal collecting system and ureter due to failed iodine signal removal. Stone in left kidney is not detectable because of nonsubtracted iodine signal (not shown).
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