Detection and Characterization of Renal Stones by Using Photon-Counting-based CT

Abstract

Purpose To compare a research photon-counting-detector (PCD) CT scanner to a dual-source, dual-energy CT scanner for the detection and characterization of renal stones in human participants with known stones. Materials and Methods Thirty study participants (median age, 61 years; 10 women) underwent a clinical renal stone characterization scan by using dual-energy CT and a subsequent research PCD CT scan by using the same radiation dose (as represented by volumetric CT dose index). Two radiologists were tasked with detection of stones, which were later characterized as uric acid or non-uric acid by using a commercial dual-energy CT analysis package. Stone size and contrast-to-noise ratio were additionally calculated. McNemar odds ratios and Cohen k were calculated separately for all stones and small stones (≤3 mm). Results One-hundred sixty renal stones (91 stones that were ≤ 3 mm in axial length) were visually detected. Compared with 1-mm-thick routine images from dual-energy CT, the odds of detecting a stone at PCD CT were 1.29 (95% confidence interval: 0.48, 3.45) for all stones. Stone segmentation and characterization were successful at PCD CT in 70.0% (112 of 160) of stones versus 54.4% (87 of 160) at dual-energy CT, and was superior for stones 3 mm or smaller at PCD CT (45 vs 25 stones, respectively; P = .002). Stone characterization agreement between scanners for stones of all sizes was substantial (k = 0.65). Conclusion Photon-counting-detector CT is similar to dual-energy CT for helping to detect renal stones and is better able to help characterize small renal stones. © RSNA, 2018.

Figure 1:

Study flowchart. DSCT = dual-source CT, EID = energy-integrating detectors, GU = genitourinary, PCD = photon-counting detectors.

Figure 2:

Energy-integrating detector (EID) and photon-counting detector (PCD) scans in a 67-year-old male study participant with known urolithiasis. A small stone (<3 mm; arrow) in the left kidney was detected with questionable confidence (rating of 3) on the, A, EID 1-mm mixed-kilovolt image (enlarged in B). The same stone was visually detected with high confidence (rating of 1) on the, C, PCD low-energy threshold image at the same image thickness (enlarged in D).

Figure 3:

Renal stone (arrow) in a 48 year-old female participant in the lower left renal pole detected with confidence of 1 in the EID, A, mixed-kilovolt and, B, low-kilovolt images, and in the, D, PCD T_L and, E, bin 1 images. The stone was not automatically segmented and characterized by using the, C, EID images, whereas the PCD images allowed for automatic segmentation and characterization, which showed, F, a non–uric acid composition.