Dual-rotation C-arm cone-beam computed tomography to increase low-contrast resolution

Interventional imaging with C-arm Cone-Beam Computed Tomography (CBCT) lacks low-contrast resolution. The use of bow-tie filters is common in diagnostic Computed Tomography (CT), as they reduce both patient dose and the dynamic range of the signal at the detector. Without a bowtie filter, a single-rotation acquisition results either in underexposed areas where the object is thick, or in over-exposed areas where the object is thin. Here, we propose to acquire two rotations in order to compensate for the absence of a bowtie filter: an un-truncated acquisition at low exposure and a truncated acquisition at higher exposure. We allow the rotations not to be acquired at the exact same positions, and introduce a reconstruction strategy to make full use of our redundant data and reconstruct the full field-of-view. The method is extended to volume-of-interest tomography. Results on a quality assurance phantom show that an angularly finely sampled acquisition of truncated intensity projections increases low-contrast resolution of C-arm CBCT, when combined with a (sub)set of un-truncated, low-intensity projections. Depending on the angular sampling of the un-truncated data, improvement is observed either over the entire field-of-view or over the truncated field-of-view.