Rotational angiography

Rotational angiography is a medical imaging technique based on x-ray, that allows to acquire CT-like 3D volumes during hybrid surgery or during a catheter intervention using a fixed C-Arm. The fixed C-Arm thereby rotates around the patient and acquires a series of x-ray images that are then reconstructed through software algorithms into a 3D image. Synonyms for rotational angiography include flat-panel volume CT and cone-beam CT.
Technical background.
In order to acquire a 3D image with a fixed C-Arm, the C-Arm is positioned at the body part in question so that this body part is in the isocenter between the x-ray tube and the detector. The C-Arm then rotates around that isocenter, the rotation being between 200° and 360° (depending on the equipment manufacturer).
Such a rotation takes between 5 and 20 seconds, during which a few hundred 2D images are acquired. A piece of software then performs a cone beam reconstruction. The resulting voxel data can then be viewed as a multiplanar reconstruction, i.e. by scrolling through the slices from three projection angles, or as a 3D volume, which can be rotated and zoomed.
Clinical applications.
3D angiography or Rotational Angiography is used in interventional radiology, interventional cardiology and minimally-invasive surgery (e.g., Hybrid cardiac surgical procedure").
CT versus rotational angiography.
Classically, CT imaging has been the method of choice for acquiring 3D data pre- or postoperatively. Choosing between CT and rotational angiography depends on several factors.
Image quality is not only defined through artifacts but also through temporal, spatial, and contrast resolution. The physical characteristics of a flat-panel detector decrease the temporal resolution as the one of the ceramic detectors used in multidetector CT systems. By contrast, the spatial resolution of flat-panel volume CT (rotational angiography using a C-Arm) can be much better than that of a multislice CT scanner, with resolution ranges between 200 and 300 μm in high-resolution mode, compared to up to 600μm for a multislice CT.
Contrast resolution, measured in hounsfield units (HU), is only marginally inferior than with a multidetector CT, the difference in attenuation from the background being 5 HU with flat-panel volume CT (=rotational angiography) compared to 3 HU for a multidetector CT. This difference is negligible for most therapeutical applications.
Radiation dose.
X-ray radiation is ionizing radiation, thus exposure is potentially harmful. Compared to a mobile C-Arm, which is classically used in surgery, CT scanners and fixed C-Arms may deliver higher dose and may be operated for longer periods during surgery. It is therefore important to monitor radiation dose to both patient and the medical staff.
Rotational angiography may increase the exposure of workers to scattered radiation, as the X-ray source moves around the patient. Lead curtainsare often used at the table side to protect the lower body region, but these are less effective with rotational work. Patient doses can be reduced with techniques common to fluoroscopic imaging such as use of pulsed modes, appropriate collimation and short imaging times.