Objective: The cone-beam helical computed tomography (CT) can scan the long object

but conventional x-ray CT imaging is based on the assumption that the entire cross-section of an object is illuminated with x-rays at each view angle. When inspecting large object

the conventional scanning mode is limited due to the width of planar detector. As an alternative

this paper developed field of view (FOV) half-cover scan such that slightly more than one half of required projection data is acquired. Method: When scanning

the gantry is translated horizontally

which direction is vertical to center ray. Then the conventional helical scan is executed. During reconstruction

the extended FDK (Feldkamp-Davis-Kress) algorithm is proposed with no rebinnging needed

and it is computationally as efficient as conventional helical cone-beam FDK algorithm. Result: Experimental results indicate that the FOV half-cover scan can extend the field of view up to 1.86 times

and the image quality

which is reconstructed by improved algorithm with small planar detector

is almost similar to the conventional algorithm with large planar detector. The reconstruction time is reduced 376.66 seconds due to the decrease of projections. Conclusion: The half-cover scan of helical cone-beam CT can extend the diameter of the field of view

and extended FDK algorithm is efficient.