Contrast medium viscosity and IV catheter size are important factors in determining maximum injection rates. "if a rapid injection rate is desired through a smaller gauge size IV catheter and contrast medium viscosity is high, two problems can potentially result. First, the desired injection flow rate may not be achieved. Second, high pressure may cause catheter failure and vessel injury."
American College of Radiology - ACR Manual on Contrast Media,
Version 7, 2010. Page 37.