22 yo male with penetrating trauma near the right superficial femoral artery 40 days ago.

Swirling blood flow in a pseudoaneurysm on ultrasonography …
This appearance resembling ancient chinese symbol : YIN YANG

The yin-yang sign is helpful in facilitating diagnosis of partially thrombosed true arterial aneurysms and false aneurysms.
This sign may be seen on ultrasonography or contrast CT scans ; a well-defined round or oval mass with increased echo or attenuation in half of its area and decreased echo or attenuation in the other half .( Yin and Yang:The Paradox of Advances in Imaging )