*3.2.2 Volume flow: time averaged velocity X vessel cross sectional area*

AVF itself shows aliasing color flow within it. Blood flow more than 500 to 600 mL/min is required in mature AVF along with the maximum venous diameter about 5 to 6 mm. Presence of both of these criteria confirms maturity in about 95% of AVF. National Kidney Foundation's Kidney Disease Outcomes Quality Initiative clinical practice guidelines defines a "rule of sixes," for maturation of AVF stating that it should have blood flow of ≥600 ml/min, a diameter of ≥6 mm, and a depth of ≤6 mm from the surface of the skin. Along with scanning of AVF, feeding artery and draining veins; evaluation of deep and neck veins should also be a routine practice in Postoperative imaging to rule out any complication at early stage.

## *3.2.3 Important points for postoperative evaluation of AVF*


Due to higher incidence of infection, stenosis and pseudoaneurysm; AVGs are less preferred over AVF. Preoperative vascular mapping for AVF is done in the same manner as in AVF. AVGs are assessed by USG or CDI if palpable focal mass is seen adjacent *Hemodialysis AV Fistula: What a Radiologist Should Know? DOI: http://dx.doi.org/10.5772/intechopen.100485*

to AVG. In such cases there may be graft stenosis. CDI differentiates hematoma from pseudoaneurysm. Symptomatic AVGs should be referred for angiography where it may be treated with angioplasty with or without stent placement if stenosis is present. However, in some cases graft degeneration also causes focal area of larger diameter presenting as palpable mass. In Postoperative evaluation of AVG, feeding artery, AVG, arterial and venous anastomosis and draining vein are evaluated. In loop grafts, identification of direction of blood flow is first step to facilitate identification of arterial and venous limb. The PSV is calculated at 2 cm proximal to arterial anastomosis (seen in the feeding artery) and 2 cm distal to venous anastomosis (seen in the AVG). If visible stenosis is present, PSV ratio (described earlier) is calculated at anastomosis. In presence of upper arm AVG, subclavian vein may show monophasic waveform even if there is no central stenosis. If the venous outflow from the graft is greater than the feeding arterial capacity, arterial steal occurs distal to arterial anastomosis [5].
