Modeling and optimization of rotational C-arm stereoscopic X-ray angiography

Stereoscopy can be an effective method for obtaining three-dimensional (3-D ) spatial information from two-dimensional (2-D) projection X-ray images, w ithout the need for tomographic reconstruction. This much-needed informatio n is missed in many X-ray diagnostic and interventional procedures, such as the treatment of vascular aneurysms. Fast C-arm X-ray systems can obtain m ultiple angle sequences of stereoscopic image pairs from a single contrast injection and a single breath hold. To advance this solution, we developed a model of stereo angiography, performed perception experiments and related results to optimal acquisition. The model described horizontal disparity f or the C-arm geometry that agreed very well with measurements from a geomet ric phantom. The perceptual accommodation-convergence conflict and geometry limited the effective stereoscopic field of view (SFOV). For a typical lar ge image intensifier system, it was 28 cm x 31 cm at the center of rotation (COR). In the model, blurring from finite focal-spot size and C-arm motion reduced depth resolution on the digital display. Near the COR, the predict ed depth resolution was 3-11 mm for a viewing angle of 7 degrees, which agr eed favorably with results from recently published studies. The model also described how acquisition parameters affected spatial warping of curves of equal apparent depth. Pincushioning and the difference between the acquisit ion and display geometry were found. to introduce additional distortions to stereo displays. Preference studies on Xray angiograms indicated that the ideal viewing angle should be small (1-2 degrees), which agreed with some p reviously published work. Perceptual studies indicated that stereo angiogra ms should have high artery contrast and that digital processing to increase contrast improved stereopsis. Digital subtraction angiograms, with differe nt motion errors between the left and right-eye views, gave artifacts that confused stereopsis. The addition of background to subtracted images reduce d this effect and provided other features for improved depth perception. Us ing the modeling results and typical clinical angiography requirements, we recommend acquisition protocols and engineering specifications that are ach ievable on current high-end systems.