The Bolus Chase option provides more flexibility in lower peripheral vasculature imaging. Automated exposure control, peripheral filters and precise speed control assure a high quality image with rarely a need for repeat exposures.

In the bolus chase technique for peripheral angiography, the bolus of contrast medium is precisely followed through the vessels of the legs, from the abdominal aorta down to the feet, in one continuous movement, under the radiologist's direct control.

The patient is placed on the table with the head over the table support, i.e. reversed with respect to the recommended manner. The reason for this choice is that it allows easier positioning for lateral views of the lower legs and feet, as the C-arm can be steeply angled without the image being obstructed by the metal in the sides of the table at the pedestal end.

We prefer to use the Omni Flush catheter (AngioDynamics, Glens Falls NY, Fig. 1). The examination begins with an abdominal aortogram. The catheter is then positioned so that the sideholes are just above the aortic bifurcation. The timing run is performed with 5 ml of 30 % contrast injected at 5 ml/s, with the image centred on the fibular head. The time entered in the Integris V 3000 automatic bolus chase system as the KAT (Knee Arrival time) is, in fact, the time the contrast takes to reach the trifurcation, rather than the knee joint.

After the KAT has been entered, the system presents a recommended volume and rate for
the injection. We generally use these values, but may deviate from them if an injection rate above 7 ml/s is suggested, as we have never found it necessary to inject faster than 7 ml/s. If the KATs for the two legs are very different, we take an average, and increase the injection volume to lengthen the bolus.

We always use the ‘auto bolus chase’ mode rather than the interactive bolus chase, because the dilute contrast agent we use cannot always be seen below the knee on the unsubtracted run, making accurate interactive table movement impossible.

We acquire the mask run first, and then the contrast run. If the mask is acquired following the contrast run, there might be some contrast remaining in the veins which could cause subtraction artifacts (Fig. 2). Following the runs, the subtracted images are reviewed with pixel shift, filmed and evaluated. The study is filmed with pixel shift for the right leg down the left side of the film and that for the left leg down the right side (Fig. 3).

The automatic bolus chase usually provides adequate visualization down to the mid or distal calves on both sides. In patients where more information on the contralateral distal circulation is needed, the Omni Flush catheter can be used to rapidly cross the aortic bifurcation for more selective injections via the distal external iliac artery (usually using 10–15 ml of 30 % I at 5–7  l/s) in order to image the distal tibial and pedal arteries. The ipsilateral distal circulation can also be similarly studied by withdrawing the Omni Flush catheter into the ipsilateral external iliac artery.