A needle comprises an elongated first shaft element with a C-shaped cross section and an elongated second shaft element with a C-shaped cross section. The first shaft element and the second shaft element are adapted to be detachably connected to each other. This is achieved by an overlap of respective end sections of the first and second shaft elements. Within the channel formed by the shaft elements, an optical probe may be accommodated from which the shaft elements may be removed by separating the two shaft elements from each other.