Mr tissue4d

Image processing was performed by using a commercially available software application (Syngo. via VB30, MR Prostate, and MR Tissue4D; Siemens Healthineers, Shanghai, China). The TOFTS model was used to calculate quantitative pharmacokinetic model parameters, including the influx forward volume transfer constant (Ktrans, /min) and rate constant (Kep, /min).
Ktrans and Kep measurements were achieved by a circle tool to delineate the ROI on perfusion maps with the largest three layers of tumor lesions (carefully avoiding necrosis or cystic areas). In this study, two experienced radiologists (with 6 and 10 years of experience in rectal imaging) performed this task blind to the patient’s clinical and pathological information, but they were aware that the patients were rectal cancer patients. The radiologists reviewed the T₂WI and DWI images and determined the location of the tumor. The final Ktrans and Kep values corresponded to the mean values obtained by drawing three different levels of ROI (with areas no less than 1 cm²)^{29 (link)} and taking the average. The Ktrans and Kep values were averaged between the two radiologists for further analysis (Figs. 1, 2).Figure 1

(a–d) Showing the T2WI, ADC map, Ktrans, and Kep of GRASP, respectively.

Figure 2

(a–d) Showing the T2WI, ADC map, Ktrans, and Kep of TWIST, respectively.

A 3T MRI scanner (MAGNETOM Vida, Siemens Healthcare, Erlangen, Germany) with a 30-channel surface coil and a 32-channel or 72-channel spine coil was utilized for all MRI examinations. A power injector operating used to deliver 0.1 mmol/kg gadoterate meglumine (Dotarem, Guerbet, Paris, France) followed by a 20-mL saline flush for DCE MRI. The temporal resolution of DCE MRI was 13.5 seconds for the first two images, 8.4 seconds for 180 seconds, and 13.5 seconds for the remaining 121 seconds. The MRI sequences and parameters are summarized in Supplementary Table E1. Pharmacokinetic maps were generated from DCE MRI after automatic motion correction and registration using a commercially available program (MR Tissue4D in Syngo.via VB40B, Siemens Healthcare): volume transfer constant (K^trans), reverse reflux constant (K_ep), extravascular extracellular volume fraction (V_e). The initial area under the curve (iAUC) was measured for the first 60 seconds. The arterial input function was chosen by having the smallest chi2 value as supplied by the program.