Conditions and mechanism for the appearance of interlobar fissures as 5-line signs in axial maximum intensity projection images.

Purpose: To assess the conditions and mechanism for the 5-line sign of normal interlobar fissures revealed on axial maximum intensity projection (MIP).

Subjects And Methods: Fifty subjects (32 males and 18 females aged 16 to 76 years) whose conditions were diagnosed as normal on computed tomography (CT) of the chest were presented. Images for the fissures with a slice thickness of 1.25 mm, a space thickness of 1.25 mm, and an MIP slab thickness of 6.25 mm were reconstructed.

Results: A 5-line shadow of normal interlobar fissures was shown on axial MIP imaging using a slab thickness of 6.25 mm. On axial MIP imaging, 93% of interlobar fissure parts were manifested as clear or barely clear.

Conclusions: On axial MIP imaging using a slab thickness of 6.25 mm, normal interlobar fissures were displayed as 5-line signs, which, similar to the beaded small lung vessels shown on MIP imaging, might be a partial volume-averaging phenomenon.