 Venous ultrasonography of the lower limbs is the most demanding of the medical complementary examinations . It is dependent on the examiner 's expertise and training , and the interpretation of the results is subjective and reliant on an understanding of venous hemodynamics . ( A mapping does help the reproducibility and the inter @-@ observer agreement of this examination ) . The examination is made even more difficult because there can be dilated veins without insufficiency , ( by hyper @-@ debit ) , and non dilated but incompetent veins . Moreover , veins can be discretely incompetent in summer but then be normal in winter . Also , by definition of insufficiency , ( insufficient blood flow ) blood may be seen to flow freely in both directions , anterograde and retrograde between two valves . Another problem when dealing with the superficial venous system , is that venous anatomy is not constant ; the position of veins can vary in different patients ; also in the same patient the right lower limb is not identical to the left lower limb . As a further complication to the examination , where venous insufficiency is evidenced , the examination needs to be done with the probe in the transversal position but the mapping must be done showing the veins in their longitudinal aspect . This demands a rapid extrapolation by the physician from the transversal images seen to the longitudinal drawing needed . The dynamic maneuvers also need to be well executed . The need of a specialized training is mandatory which is a huge problem for many countries today . 
