Patient’s selection
This prospective study was approved by our institutional review board (IRB no. 17100795). Written informed consent was obtained from each patient after receiving information about the details of the study. Between February 2018 till December 2018, 51 patients with CRC that was proved preoperatively by endoscopy were eligible for this study (26 (51%) males, 25 (49%) females; mean age, 53.87 ± 16.13 years; range, 19–86 years). The examined tumors were located in rectum (n = 21), sigmoid colon (n = 14), hepatic flexure (n = 5), descending colon (n = 4), transverse colon (n = 2), ascending colon (n = 4), and splenic flexure (n = 1), that is based on CT findings and confirmed by endoscopy. Patients were excluded if they had (1) severe renal disease (n = 2), (2) pre-operative radiation therapy or chemotherapy (n = 4), (3) no surgical intervention after CT (n = 0), (4) contraindication to contrast media (n = 2), (5) no pathological reports (n = 3), (6) pathologically benign colorectal mass (n = 10), and (7) tumor depth less than 2 cm based on CT (n = 5).
CT technique
Pre-operative PCT scans were performed on all patients by using a 16 detector CT scanner (Bright Speed, GE Healthcare Technologies). After 4 h of fasting, 1000 ml of water was ingested 30 min prior to scanning to opacify the small bowel according to normal practice in our institution. Twenty milligrams of spasmolytic agent hyoscine butylbromide (Buscopan; Boehringer Ingelheim, Ingelheim am Rhein, Germany) was administered intravenously to all patients immediately prior to data acquisition to minimize bowel peristalsis during the CT. Opacification of large intestine with saline was done for all the patients prior to the CT examination, using balloon enema nozzle connected with a tube to an enema bag containing 1.5 l of saline.
An abdominopelvic CT was performed initially to localize the colorectal tumor without IV contrast for cine imaging in perfusion examination using the following parameters (120 kV; 140 mA; 5 mm slice thickness; 1.5 s speed; 36 cm FOV). Identification of the tumor margin was done by two radiologists with consensus (ME and LMRK with experience 15 and 10 years respectively in abdominal CT imaging). Then plan of the perfusion study after coordination of the scan was performed.
For the perfusion study, a pump injector was used to inject 100 ml of iopromide 370 mg of iodine per milliliter intravenously (Ultravist 370; Bayer) at a rate of 5 ml/s, using the following parameters: 120 kV; 100 mA; 5 mm slice thickness; 4i/rot speed rotation; FOV 36 cm. Four contiguous sections were obtained, each collimated to 5 mm (tumor coverage was 2 cm). Dynamic PCT scans began 7 s after the start of IV injection and continued for 65 s. All patients underwent surgery and histopathological study after perfusion PCT was performed.
Image analysis
Image analysis was performed using commercial software based on deconvolution analysis (Body protocol Perfusion; GE Healthcare Technologies). The radiologists reviewed the images and selected one image that has the best-visualized and the mostly enhanced tumor with consensus.
An arterial input was selected by using the mouse to place a circular ROI 1 = 20 mm2 in the area of the best-visualized artery (aorta, iliac, or femoral artery) (Figs. 1a and 2a). By using the software, the arterial time enhancement curve was done automatically then a parametric map was produced. The mean values of BF, BV, and PS were recorded, also their three perfusion maps (Figs.1b–d and 2b–d) were generated for two ROIs, that is similar in size and different in position; (a) ovoid or circular ROI 2 = 30 mm2 were manually selected at the most enhanced area at tumor edge (Figs.1a and 2a), (b) another circular or ovoid ROI 3 = 302 mm were manually selected that placed at the most enhance area at the tumor center (Figs.1a and 2a). Care was taken to exclude peri-rectal or peri-colonic fat and intraluminal gas when present, by viewing a cine loop of the perfusion CT images. A time attenuation curve for the selected tumor tissue and the mean values for BF, BV, and PS for each ROI were then derived automatically.
Tumor grades
The surgical specimens were fixed with 10% formaldehyde and embedded in paraffin. The differentiation of the grades was assessed by an experienced gastrointestinal pathologists and was divided into three subgroups: well, moderately, and poorly differentiated CRC.
Statistical analysis
Data was collected and analyzed those using SPSS (Statistical Package for the Social Science, version 20, IBM, and Armonk, New York). Continuous data were expressed in the form of mean ± SD or median (range) while nominal data were expressed in the form of frequency (percentage). A Student t test was used to compare different perfusion parameters with the two positions of the ROIs while the ANOVA was used to compare different perfusion parameters based on grades of CRC. Level of confidence was kept at 95%; P value < 0.05 was considered significant. Sensitivity, specificity, and accuracy for each significant perfusion parameter in the prediction of tumor grade were calculated using cut off values chosen on the basis of receiver operating characteristic (ROC) curves.