Contrast and primed tubing can then be attached to the spinal needle for a test injection
under fluoroscopy to ensure that the needle is superficial to the ligament (Figure 8A).
Once the test injection
is complete, a separate filling valve is actuated to refill and restabilize the pressure in the fluid chamber before the next test cycle.
Test injection was initially administered to verify that the local anesthetic spreads within the QL muscle (Figure 10(b)).
Another reason for adding the half-the-air pressure monitor is to reduce the risk of local anesthetic systemic toxicity (LAST) and at the same time save the local anesthetic when the block site is deep with rich vascularity  and needs test injection to confirm the correct spread in the interfascial plane , such as the deep anterior QL block involving the thoracolumbar fascia through which vessels exit from the paravertebral space .
When the arthrography was performed under US-guidance, a test injection
of 2 mL of contrast agent was administered to confirm accurate needle placement, which was followed by injection of approximately 8 mL of contrast agent into the hip joint by using the end of the extension tube as a port.
A test injection
of contrast was delivered through the dilator in the left anterior oblique projection to check for "tenting" of the fossa at the intended puncture site.
After a satisfactory test injection, absolute alcohol was injected.
While some prefer to inject alcohol in increments of 2 ml every 10 to 15 minutes (3), others inject 10 to 15 ml continuously at a rate subjectively decided by the rate of opacification and clearing of contrast material from the epidural soft tissue, as seen on CT images taken in dynamic mode during the test injection (5).
The timing of the contrast bolus for CTA scans is typically determined using either a test injection
or automated bolus-tracking software.
The next phase will be the data processing and the study of the area and the first test injections
of CO2 which are expected to take place throughout 2011 and 2012.
The pounds 120,000-a-year star has already had two test injections
containing a small amount of collagen to make sure she is suitable for the full treatment.