 The ultrasound equipment must be of sufficiently high quality in order to give a correct image processing result , which can then provide invaluable information , mainly at the superficial level . It must be able to provide both color and Doppler imaging ; technologies that developed alongside the development of ultrasound . The use of Doppler measurements which trace the echoes of the generated soundwaves received by the probe , enable the direction and the velocity of the blood flow , to be depicted . The overlay of color onto the Doppler information lets these images be seen more clearly . The choice of a probe will depend on the depth needed to be studied . For example , the superficial venous system ( SVS ) can be very well examined using a high frequency probe of 12 MHz . For patients who have thick adipose tissue a probe of 7 @.@ 5 MHz will be required . Deep veins require probes of around 6 MHz whilst the abdominal vessels are better studied with probes of between 4 and 6 MHz . In summary , three probes are needed together with a top level scanner . Also , the proper use of the scanner calls for a high level of expertise , so that the examiner must be well qualified and experienced in order to give effective results . In contrast to arterial ultrasonography the wall of the vein is not relevant and importance is given to the hemodynamic conclusions that the examiner can obtain in order to provide a valuable report . ( <unk> is the study of blood flow and of the laws that govern the circulation of blood in the blood vessels ) . It follows that the examiner knowledge of venous hemodynamics is crucial , which can be a real barrier to a radiologist untrained in this field , who might wish to carry out these examinations . Specialized training in venous ultrasonography is not undertaken in some countries , which undermines best practice , mainly when varicose veins need to be examined . 
