Rotational angiography | |
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![]() Ceiling-mounted C-arm in a cardiac catheterization lab | |
Purpose | acquire CT-like 3D volumes during hybrid surgery |
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.[1] Synonyms for rotational angiography include flat-panel volume CT[2] and cone-beam CT.[1]
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.[1][3]
3D angiography or Rotational Angiography is used in interventional radiology, interventional cardiology and minimally-invasive surgery (e.g., Hybrid cardiac surgical procedure).[citation needed]
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.[3] 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.[2] 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.[2]
See also: Radiation protection |
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.[6]
Rotational angiography may increase the exposure of workers to scattered radiation, as the X-ray source moves around the patient. Lead curtains are often used at the table side to protect the lower body region, but these are less effective with rotational work.[7] Patient doses can be reduced with techniques common to fluoroscopic imaging such as use of pulsed modes, appropriate collimation and short imaging times.[8]