<title>Dynamic geometrical calibration for 3D cerebral angiography</title>

Abstract

Recently there has been increasing interest in obtaining three-dimensional reconstructions of arterial vessels from multiple planar radiographs (obtained at angles around the object). Interventional angiography is the motivating application behind this research. Different methods have been proposed to acquire the planar data such as a gantry mounted x-ray image intensifier (XRII) or a C-arm mounted XRII. In order to obtain a threedimensional reconstruction from a C-arm mounted XRII the trajectory of the source and detector system must be characterized.We have designed a calibration system that provides the necessary trajectory information using uniquely identifiable markers positioned on a cylinder. This calibration ring is to be placed around the patient's head, and consists of steel balls positioned in a predefined arrangement on a cylindrical acrylic support. The balls are arranged such that calibration can be done from almost any partial view, allowing reconstruction of a region of interest (ROl). Steel balls are placed around an acrylic cylinder, restricted to a band approximately 8.5 mm wide, thereby obscuring only a small fraction of the image. In this case the radiograph includes the region of interest (ROT) as well as a partial view of the calibration ring. This enables us to recover the geometry of X-ray imaging system from each individual frame. We call this process "dynamic calibration" as opposed to "off-line" calibration procedures which try to characterize the motion of C-arm before introducing the patient.

Geometric calibration of a mobile C‐arm for intraoperative cone‐beam CT

“…2 In general, geometric calibration relates the 3D coordinates ͑x , y , z͒ of voxels in the reconstructed image to the 2D coordinates ͑u , v͒ of pixels in the projection domain. [18][19][20][21][22][23][24][25][26][27][28] Geometric calibration consists of two stages: ͑i.͒ characterization of pose across the range of source-detector orbit; and ͑ii.͒ correction of geometric nonidealities in the process of 3D reconstruction. Methods of pose characterization include the use of stereoscopic tracking systems to monitor mechanical motion 25 and, more commonly, image-based methods that operate directly on projection data acquired either from a prior calibration 2,18,23,24 or simultaneous with imaging.…”

Low-dose preview for patient-specific, task-specific technique selection in cone-beam CT

“…A previously developed geometric calibration phantom was used to measure the source-detector position of each projection relative to the C-arm isocenter, which was represented as projection matrices. [33][34][35] The x-ray source was operated in pulsed-fluoroscopic mode, with the tube potential fixed at 100 kVp while the tube output of the scan was varied from 20-320 mAs in the head and 30-480 mAs in the body.…”

Deformable registration of the inflated and deflated lung in cone‐beam CT‐guided thoracic surgery: Initial investigation of a combined model‐ and image‐driven approach

“…Projection data processing was described by Schmidgunst et al, 49 and geometric calibration was performed as in Navab et al 50 CBCT volumes were reconstructed using a variation of the filter backprojection algorithm, 51 using a smooth reconstruction kernel and isotropic voxel size of 0.6 mm. A lateral truncation correction was applied based on projection domain extrapolation.…”