What is the term rate rise in injection?
- A rate rise is another way that a power injection of contrast material can be modified and describes the time in seconds that it takes from the beginning of the injection to reach the desired injection rate.
- For an injection of “20 for 40” with no rate rise, the velocity of contrast agent in the catheter immediately jumps from 0 to 20 mL/s.
- If a rate rise of 0.6 second is used, it takes 0.6 second for the injection to reach maximum velocity.
- Rate rises are used to minimize the recoil of the catheter during rapid injections.
- Rapid contrast injection rates, at 3.0-5.0 mL/sec, through the Arrow-Howes multilumen central venous catheter are feasible and safe in the clinical setting
- That is, no rate rise implies a step function.
A study conducted with an objective to assess the effects of the i.v. injection rate of contrast material on arterial phase hepatic CT.
Subjects and methods: One hundred patients were randomly divided into four groups of 25 with different injection rates of 90 ml of contrast material: 2, 3, 4, or 5 ml/sec. Single-level serial CT was performed at the level of the middle section of the main portal vein before injection and every 2 sec from 12 sec to 60 sec after injection of contrast material. The enhancement value was calculated as the difference in attenuation value between the unenhanced and contrast-enhanced images for the aorta and liver parenchyma. The duration of the arterial phase was defined as the interval beginning when the enhancement value for the aorta reached 100 H and ending when the value for the liver parenchyma reached 20 H.
The results of the study – Faster injection rates increased the maximum enhancement of the aorta. Although faster injection rates decreased the time from injection to the beginning and the end of the arterial phase, faster injection rates did not decrease the duration of the arterial phase itself.
Conclusion of this study – A faster injection rate increases arterial enhancement of the liver, and the duration of the arterial phase remains the same as that occurring with a slower injection rate. It was hypothesized that faster injection rates can provide better results using CT to reveal hypervascular liver tumors.
Another study evaluated our current port injection practice and carried out step-wise changes to our port apparatus to improve flow rates ex-vivo followed by comparison of patient scans before and after the changes.
In contrast to short, peripheral IV catheters, a power port injection requires the proper placement of an access needle into the port hub and then utilizes a long tubing connection to the injector, both of which can vary in diameter and length.In our high volume practice, prior to this study, we frequently encountered pressure-limiting injections that resulted in contrast flow rates significantly below the 5 mL/s for which the power ports are rated. For high injection rate examinations, this required placement of a peripheral IV, which resulted in patient discomfort and decreased efficiency of operations.
This study evaluated the port injection components used at our institution and found that there were larger diameter options for the injection tubing and gauges for the access needles. Ex-vivo testing showed that using the larger diameter tubing and a 19 G needles could improve our injections rates up to 4.2 mL/s. Furthermore, by then using warmed contrast, delivered rates could reach 5 mL/s without pressure limitation given the resultant decrease in viscosity.
In summary, using a 19 G port access needle, larger inner diameter connector tubing and warm contrast media markedly improved our power port injection rates, which now achieve injection rates up to the device manufacturer specifications.
A faster injection rate increases arterial enhancement of the liver, and the duration of the arterial phase remains the same as that occurring with a slower injection rate. Faster injection rates can provide better results using CT to reveal hypervascular liver tumors.
