Korean J Radiol.  2018 Dec;19(6):1077-1088. 10.3348/kjr.2018.19.6.1077.

Iodine Quantification on Spectral Detector-Based Dual-Energy CT Enterography: Correlation with Crohn's Disease Activity Index and External Validation

• Kim YS
• Kim SH
• Ryu HS
• Han JK

• KMID: 2424847
• DOI: http://doi.org/10.3348/kjr.2018.19.6.1077

Abstract

OBJECTIVE
To correlate CT parameters on detector-based dual-energy CT enterography (DECTE) with Crohn's disease activity index (CDAI) and externally validate quantitative CT parameters.
MATERIALS AND METHODS
Thirty-nine patients with CD were retrospectively enrolled. Two radiologists reviewed DECTE images by consensus for qualitative and quantitative CT features. CT attenuation and iodine concentration for the diseased bowel were also measured. Univariate statistical tests were used to evaluate whether there was a significant difference in CTE features between remission and active groups, on the basis of the CDAI score. Pearson's correlation test and multiple linear regression analyses were used to assess the correlation between quantitative CT parameters and CDAI. For external validation, an additional 33 consecutive patients were recruited. The correlation and concordance rate were calculated between real and estimated CDAI.
RESULTS
There were significant differences between remission and active groups in the bowel enhancement pattern, subjective degree of enhancement, mesenteric fat infiltration, comb sign, and obstruction (p < 0.05). Significant correlations were found between CDAI and quantitative CT parameters, including number of lesions (correlation coefficient, r = 0.573), bowel wall thickness (r = 0.477), iodine concentration (r = 0.744), and relative degree of enhancement (r = 0.541; p < 0.05). Iodine concentration remained the sole independent variable associated with CDAI in multivariate analysis (p = 0.001). The linear regression equation for CDAI (y) and iodine concentration (x) was y = 53.549x + 55.111. For validation patients, a significant correlation (r = 0.925; p < 0.001) and high concordance rate (87.9%, 29/33) were observed between real and estimated CDAIs.
CONCLUSION
Iodine concentration, measured on detector-based DECTE, represents a convenient and reproducible biomarker to monitor disease activity in CD.

Keyword

Crohn's disease; Dual-energy computed tomography; Activity index; Iodine quantification

MeSH Terms

Consensus
Crohn Disease*
Humans
Iodine*
Linear Models
Multivariate Analysis
Retrospective Studies
Iodine

Figure

• 

  Fig. 1 Flow diagram of enrolled patients.CA = contrast agent, CD = Crohn's disease, CDAI = Crohn's disease activity index, DECTE = dual-energy CT enterography

• 

  Fig. 2 ROI application.Radiologists applied ROI (green line, right image) to diseased bowel wall (arrows) that showed strongest enhancement in most conspicuous part of small and large bowels on iodine concentration maps generated from enteric phase CT. In this particular patient, iodine concentration measured 3.56 mg·I/mL. Ar = area, Av= average, ROI = region-of-interest, SD = standard deviation

• 

  Fig. 3 Scatter diagram of iodine quantification by two radiologists.Inter-reader agreement was very good, with correlation coefficient of 0.838 (p < 0.001).

• 

  Fig. 4 28-year-old male with known CD.A. On DECTE enteric-phase image, subtly-enhancing eccentric wall thickening (arrow) is visible in distal ileum. Relative enhancement of this lesion measured 131%. B. On iodine map of DECTE, iodine concentration of lesion (arrow) was 1.6 mg·I/mL. Therefore, estimated CDAI with linear regression equation (CDAI = 53.549 × iodine concentration + 55.111) was 141, which was score for remission (CDAI < 150). Patient's real CDAI score was 24, which also indicated remission state.

• 

  Fig. 5 41-year-old female with known CD.A. On DECTE enteric-phase image, focal enhancing and concentric wall thickening (arrow) is visible in terminal ileum. Relative enhancement of this lesion was 201%. B. On iodine map of DECTE, iodine concentration of lesion (arrow) measured 2.5 mg·I/mL. Therefore, estimated CDAI with linear regression equation (CDAI = 53.549 × iodine concentration + 55.111) was 189.0, which was score for mild activity (CDAI: 150–219). Patient's real CDAI score was 164, which also indicated mildly active state of CD.

• 

  Fig. 6 17-year-old female with known CD.A. On DECTE enteric-phase image, focal enhancing and eccentric wall thickening (arrow) is clearly visible in distal ileum. Relative enhancement of this lesion was 310%. B. On iodine map of DECTE, iodine concentration of lesion (arrow) measured 3.3 mgI/mL. Therefore, estimated CDAI with linear regression equation (CDAI = 53.549 × iodine concentration + 55.111) was 231.8, which was score for moderate activity (CDAI: 220–450). Patient's real CDAI score was 262, which also indicated moderately active state of CD.

• 

  Fig. 7 36-year-old female with known CD.A, B. On coronal (A) and axial (B) images of DECTE obtained during enteric phase, multifocal, asymmetrically enhanced bowel wall thickenings (arrows) are prominently visible in ileum. Bilaminar pattern of enhancement (arrowheads) is also demonstrated on involved bowel. Note enterocutaneous fistula (thin arrows) between distal ileum and periumbilical area. Comb signs showing mild venous dilation (grade 2) and severe perienteric fat infiltration (grade 3) were also depicted. Relative enhancement of lesion showing strongest enhancement was 247%. C. On iodine map of DECTE, iodine concentration of involved bowel wall measured 4.7 mg·I/mL. Therefore, estimated CDAI with linear regression equation (CDAI = 53.549 × iodine concentration + 55.111) was 306.8, which was score for moderate activity (CDAI: 220–450). Patient's real CDAI score was 305, which also indicated moderately active state of CD.

• 

  Fig. 8 Scatter-plots between real and estimated CDAI in 33 validation patients.A. On Pearson's correlation test, there was significant correlation (r = 0.925) between real and estimated CDAI scores (p < 0.001). B. In Bland-Altman test, these scoring methods had mean measurement bias of −16.6 and limits of agreement ranging from −150.7 to 117.4.

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