Some embodiments are directed to a needle assembly including at least N injection needles where N is at least four and a multiple of two. The needle assembly also includes a first liquid port adapted to be connected to an injection device, and N second liquid ports connected to one of the N injection needles. N/2 main liquid pathways each have an entrance connected to the first liquid port and an exit, further including N/2 secondary liquid pathways that have two extremities each opening on one of the N second liquid ports, and a mid portion connected to the exit of one of the main liquid pathways. The main liquid pathways and the secondary liquid pathways define N liquid flow paths between the first liquid port and the N second liquid ports dimensioned so a pressure drop between them is similar.