Spectral photon-counting CT imaging of colorectal peritoneal metastases: initial experience in rats

Abstract

Computed tomography imaging plays a major role in the preoperative assessment of tumor burden by providing an accurate mapping of the distribution of peritoneal metastases (PM). Spectral Photon Counting Computed Tomography (SPCCT) is an innovative imaging modality that could overcome the current limitations of conventional CT, offering not only better spatial resolution but also better contrast resolution by allowing the discrimination of multiple contrast agents. Based on this capability, we tested the feasibility of SPCCT in the detection of PM at different time of tumor growth in 16 rats inoculated with CC531 cells using dual-contrast injection protocols in two compartments (i.e. intravenous iodine and intraperitoneal gadolinium or the reverse protocol), compared to surgery. For all peritoneal regions and for both protocols, sensitivity was 69%, specificity was 100% and accuracy was 80%, and the correlation with surgical exploration was strong (p = 0.97; p = 0.0001). No significant difference was found in terms of diagnostic performance, quality of peritoneal opacification or diagnostic quality between the 2 injection protocols. We also showed poor vascularization of peritoneal metastases by measuring low concentrations of contrast agent in the largest lesions using SPCCT, which was confirmed by immunohistochemical analyses. In conclusion, SPCCT using dual-contrast agent injection protocols in 2 compartments is a promising imaging modality to assess the extent of PM in a rat model.

Figure 1

Experimental protocol.

Figure 2

Illustration of SPCCT features of peritoneal metastases (PM) used to assess the radiological peritoneal cancer index (r-PCI). (LS: lesion size; s-PCI: surgical peritoneal cancer index).

Figure 3

Examples of true-positive and false-negative lesions on SPCCT with surgical correlation (r-LS: radiological lesion size; s-LS: surgical lesion size; POI: peritoneal opacification index of the region).

Figure 4

SPCCT sensitivity (Se) according to lesion size (LS).

Figure 5

(a) Comparison of radiological (r-PCI) and surgical peritoneal cancer index (s-PCI) for each rat according to timepoint and injection protocol. (b) Box-and-whisker plots of the distribution of r-PCI and s-PCI for all protocols (A + B).

Figure 6

(A) Example of contrast agent concentration measurements in a peritoneal nodule in regions 10–11 (EP: Early phase, LP: Late Phase). (B) Concentrations of contrast agents measured on early and late-phase contrast material maps in the largest peritoneal tumor nodule, liver, and omental cake (if present). Data are presented as mean ± standard deviation of mean concentration.