Inferior vena cava filter. This device is placed in the vena cava vein of patients at risk of developing a blood clot that could lead to a fatal pulmonary embolism. This type of IVC filter, known as a Gunther Tulip, is a relatively small device, only about 5 centimetres long. The hook at lower left is used to retrieve the device if it needs to be removed. Placement of the device can be done surgically, but modern types are placed using a catheter inserted through the leg, neck or arm, to reach the required location.