Automated volumetric analysis for comparison of oral sulfate solution (SUPREP) with established cathartic agents at CT colonography

Abstract

Purpose: To objectively compare residual colonic fluid volume and attenuation of oral sulfate solution (OSS) with four different established cathartic regimens using an automated volumetric software tool at CT colonography (CTC).

Methods: This HIPAA-compliant study had institutional review board approval. Volumetric analysis of residual contrast-tagged colonic fluid was performed on CTC studies in 263 adults (mean age 60.1 years; 137M/126F) using an automated volumetric software tool. Twenty-three patients receiving 177 mL OSS (SUPREP; single-bottle purgation) were compared with 60 patients each receiving 45 mL sodium phosphate (NaP), 90 mL NaP (2× NaP), 592 mL (two bottles) magnesium citrate (MgC), and 4,000 mL polyethylene glycol (PEG). All patients received oral contrast cleansing after catharsis. Data were analyzed with unpaired t test with Welch correction and F test.

Results: The mean volume of residual colonic fluid was less with OSS (125 ± 60 mL) than for established cathartic agents: 2× NaP (206 ± 125 mL, P < 0.0001), MgC (184 ± 125 mL, P < 0.01), PEG (166 ± 114 mL, P < 0.05), and NaP (165 ± 135 mL, P = 0.067). Variance of volumes was also significantly lower for OSS (range 28-251 mL) than for established agents (range 4-853 mL) (all P < 0.01). Mean fluid attenuation was higher with OSS (956 ± 168 HU) than for established agents (all P < 0.05): 2× NaP (455 ± 191 HU), MgC (691 ± 154 HU), NaP (779 ± 127 HU), and PEG (843 ± 193 HU).

Conclusions: Automated volumetry allows rapid objective assessment of bowel preparation quality at CTC. Purgation with the novel oral sulfate solution (SUPREP) consistently resulted in less residual colonic fluid and higher fluid attenuation compared with established cathartic regimens.

Figures

Figure 1

CTC examination with automated quantification of residual colonic fluid volume and attenuation in a 57-year-old man. (A) Three-dimensional display map of the correctly segmented colon. The automated volumetric CTC tool allows accurate quantification of the amount and attenuation of the total residual colonic fluid. Automatically calculated total colonic residual fluid in this patient receiving novel OSS regimen was 73 ml. The automatically calculated attenuation of the residual fluid was 826 HU. Two-dimensional axial CTC images before (B) and after (C) automated digital subtraction of residual colonic fluid allow verification of correct segmentation. Note that not only large fluid collections (arrow) are captured but also smallest fluid residues (arrowheads).

Figure 2

Mean volume and attenuation of residual colonic fluid over all established cathartic agents versus OSS regimen as quantified by automated volumetric QA tool. (A) Bar graph shows mean residual colonic fluid volume. The fluid volume was significantly lower for OSS regimen (125±60 ml) than for established cathartic agents (average of 2xNaP, MgC, NaP and PEG) (180±121 ml) (p<0.001). Note the outliers (dots) and extreme outliers (triangles) with high fluid volumes of up to 853 ml when using established cathartic agents, which hamper 3D endoluminal fly-through without electronic cleansing. Dotted line indicates 200 ml threshold of total residual colonic fluid. (B) Bar graph shows the mean attenuation of the residual colonic fluid. The attenuation was significantly higher for the OSS regimen (956±167 HU) as compared to the average of established cathartic agents (692±223 HU) (p<0.0001).

Figure 3

CTC examinations in two patients receiving the new OSS regimen (A) and the established sodium phosphate regimen (B). (A) Axial two-dimensional CTC image from a 62-year-old man who underwent OSS regimen illustrates the calculated low total residual fluid volume (89 ml) with high attenuation (897 HU). (B) Axial two-dimensional CTC image from a 58-year-old man who underwent sodium phosphate regimen illustrates the calculated high residual total fluid volume (853 ml) with low attenuation (440 HU). Note the good conspicuity of colonic fold against the high attenuation fluid after OSS regimen (A, arrow head) as compared to poor conspicuity of a fold against the low attenuation fluid after MgC regimen (B, arrowhead). Both cases also illustrate the inadequacy of the established manual fluid volume and attenuation quantification methods. In (A) the volume of descending colon occupied by fluid would be rated > 50%, albeit this is not due to high fluid volume, but rather due to poor overall distension. In (B) the different attenuations of the fluid within the colon are clearly evident and indicate the sampling error of manual ROI-based methods for attenuation quantification.

Figure 4

Mean volume and attenuation of residual colonic fluid for each cathartic agent as quantified by automated volumetric QA tool. (A) Box and whisker plots showing mean residual colonic fluid volume. The mean residual volume was smallest when using the OSS regimen (125±60 ml) and significantly higher using 2xNaP regimen (206±125 ml) (p<0.0001), MgC regimen (184±125 ml) (p<0.01) and PEG regimen (166±114 ml) (p<0.05). NaP regimen showed also a higher residual volume (165±135 ml) than OSS regimen but without reaching a statistically difference (p=0.067). Note the outliers with high residual volumes with established cathartic agents that are not observed with OSS. Dotted line indicates 200 ml threshold of total residual colonic fluid. (B) Box and whisker plots showing the mean attenuation of the residual colonic fluid. The attenuation was significantly higher for the OSS regimen (955±167 HU) as compared to all of the other established cathartic agents, ranging from 406±191 HU for 2xNaP regimen (p<0.0001) to 843±193 HU for PEG regimen (p=0.012).

Figure 5

Automated volumetric QA tool reveals inverse correlation between volume and attenuation of residual colonic fluid. Graph depicts residual fluid attenuation plotted against the fluid volume across all different cathartic agents. As residual fluid volume increases, the degree of fluid attenuation decreases. Correlation is r= −0.262 (p