Techniques : extra rotations in helical scanning

• To reconstruct the first and last image in a helical series, data is gathered from outside the nominal scan volume

• Irradiation outside the scan volume can depend on various factors (collimation, slice width, pitch, recon. technique)

  • More significant for short multi-slice scans, with small no. of rotations

• Worth considering different collimation or axial scanning in these situations