Contrast media in abdomen CT

About this case study: This study focuses on a 54 year old male patient presented with dyspepsia and abdominal pain. Through tests, it is founded he has pancreatic ductal adenocarcinoma stage T3N1M1 & hepatic metastatic deposits. This patient underwent a 4 phase imaging CT of the abdomen. Questions to  be answered: 1. what type of contrast media is utilised for this scan? why is this contrast media used for this condition/its purpose? what happens if the patient is allergic to this contrast media? what alternatives contrast can be used? 2. what is the amount of contrast media employed? why and what factors affect the amount of contrast media used? 3. what is the timing of contrast administration? what factors affect the timing? why is this timing used/what does this timing of contrast administration aimed to show in the images?