Use of small amounts of ultrasound guided air for injections.

The existence and detection of air in various tissues is of great importance, whether the air has emanated by a disease mechanism (for example, intra-abdominal in gastric lesions, extrapulmonary in thoracic lesions) or been applied as a diagnostic tool. The detection of the air in a diagnostic test may be performed by such diVerent methods as stethoscopy (epidurally in the whoosh test), or radiography (intra-articularly in arthrography ). In ultrasonography the injection of ultrasound contrast agents containing air may increase the diagnostic confidence in the intravascular domain. 5 Atmospheric air, which is much cheaper, may be safely injected in small quantities for diagnostic purposes in extravascular domains—for example, joints, and in our experience also in bursae and tendon sheaths, which all have cavities that can be visualised in this way. In addition to the standard ultrasonic verification of correct needle placement, it is possible to monitor and verify the actual injection of the substance by adding a small amount (0.5–1 ml) of air. Figure 1 shows the inflamed tendon sheath of a patient with rheumatoid arthritis. Before injection of cortisone the correct position of the needle is verified as well as the correct placement of the substances injected through this needle. The air is readily discernible on the screen (fig 2A-D), and the flow of the air in both proximal and distal direction along the tendon can be visualised. The procedure can be performed in an outpatient clinic with the aid of an assistant. We do not propose that all injections should be carried out under the guidance of ultrasound, however, during training of the therapists or in scientific studies the placement of the injection may be assured in this way.