Power Injector

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Neuroendovascular requires practitioner dependent imaging. What does this mean? Essentially the physician responsible for not only performing the procedure, but for also acquiring diagnostic images. A power injector delivers a more perfect, consistent (nearly) square wave bolus with each injection. This is simply better than the variability created with hand injected angiography. Did the flow in a vascular malformation really change pre and post embolization? An accurate answer to this question requires the exact same injection on pre and post embolization angiography. There are two additional compelling reasons to power inject where feasible. One, we use approximately 99% of our radiation during angiographic runs. Power injecting allows the removal of all physicians from the room during highest radiation usage. Two, we find that cone beam CT imaging is best acquired when using approximately half the injection rate of planar angiography and therefore power injecting of planar runs is enabling effective cone beam CT imaging. While you might feel comfortable with most of your injection protocols, what about choosing an injection rate for a super selective occipital artery injection for a dural fistula where the artery is relatively small, but the fistula is moderately high flow? Using approximately half the injection rate of an affective planar run has been affective for our practice.

This setting controls the injection rate, measured in milliliters per second (mL/sec). Adjusting the rate ensures that contrast is delivered at the optimal speed for the vessel size and imaging requirements. For example, higher injection rates are needed for larger vessels to achieve uniform opacification, while lower rates are better suited for smaller or more delicate vessels to reduce the risk of vessel damage or spasm. We aim for super selective injections with each of our arterial selections. We want an injection rate that maximally opacifies the arterial tree or the vessel selected without reflux into an adjacent artery (ICA selection with ECA reflux or vice versa as an example).

The total volume is tied to the injection rate for both planar and 3D acquisition. For planar runs the volume really determines the total duration of the contrast injection. Injecting at 5ml/s? If you want the total duration of the contrast injection to last 1.4 seconds you need to inject 7ml. For a volumetric acquisition the total volume of contrast should be chosen such that you account for the X-Ray delay plus the total scan time. Using a 14s DynaCT with a 2 second X-ray delay and 2 ml/s injection rate? Use 32 mL of contrast, calculated by adding a 2-second delay to the 14-second acquisition (16 seconds total) and multiplying by the injection rate of 2 mL/sec.

Rate rise controls the speed at which the injection reaches its target flow rate. A slower rate rise (higher rate) is ideal for delicate vessels, limited purchase catheter tip position, or if you have concern that the catheter tip is against the vessel wall, which is a risk for dissection and you would like a slower rate initially to create a jet, which propels the catheter tip off the artery wall before reaching the full rate of injection. Conversely, a faster rate rise (lower rate) may be necessary in large vessels or high-flow systems to achieve uniform opacification during short imaging windows.

The pressure limit sets the maximum force the injector will apply during delivery. This is a safety feature designed to prevent overpressurization, particularly in fragile or diseased vessels. Adjusting the pressure limit is essential when dealing with different catheters, as smaller catheters have lower tolerance thresholds.

An X-ray delay is utilized during cone beam CT imaging with contrast injection. Typically speaking, the goal would be to have the entire arterial tree opacified with contrast during the full sweep of the fluoroscopy unit to create the 3D image. We typically use the timing of complete arterial opacification on our planar runs to help determine the delay. for example, if we are imaging a large aneurysm and the aneurysm takes 5 seconds to opacify on our planar run, we would choose a 5 second delay and adjust our total volume accordingly REF. 

Injector delay accounts for the time between initiating the injection and when the imaging machine completes the digital subtraction angiography (DSA) mask. This delay ensures that the injection timing is perfectly synchronized with the imaging acquisition, avoiding premature or delayed contrast delivery.

Properly setting the injector delay is critical in cases where precise alignment of the contrast bolus with the imaging sequence is essential, such as in neurovascular imaging. Misalignment can result in suboptimal images, with either insufficient contrast opacification or premature washout before the scan begins.