Injecting at a rate of 2 cc per second works in most places, and is a good starting point for every clinician. Although most people are using 2 cc per second, everyone is looking more closely at using different rates for different parts of the body, and time will show what these experiments produce. There are pluses and minuses to injecting faster and slower. Injecting faster than 2 cc per second will produce a larger difference between the arterial and venous enhancement, which is beneficial. However, there will be an increased soft tissue signal, and an increased blurring of vessel contours.
Slower rates lead to a longer arterial time window before venous enhancement.
Injecting gadolinium through a syringe in 10 seconds, particularly through a 23-gauge butterfly, requires great strength. It may be impossible. A power injector uses a small butterfly, and techs can inject by themselves. Another timing technique is the automatic bolus detection. In renal cases, the clinician would put the monitoring voxel over the midabdominal aorta, because the renal arteries are in that area.