Motion gated small animal imaging with a flat-panel CT

Small animal CT gains increasing interest in preclinical research. However, physiological motion compensation like in clinical CT has seldom been employed so far. We present different methods of retrospective motion correction for small animal imaging despite their high respiratory and heart rate. Beside respiratory gating alone the combination of respiratory and simultaneous cardiac gating is shown. In vivo data are acquired with an experimental flat-panel based CT scanner* (Siemens Healthcare, Forchheim Germany). Whole mice or rats fit in the available FOV of 25 * 25 * 4 cm(3), while acquisition rate is 100fps. Extrinsic gating is realized by tracing the physiological motion from a small animal monitoring system with a pneumatic pillow for respiratory motion and ECG for heart motion. At the alternative intrinsic method, the lung motion is directly correlated to the movement of the center of gravity in the acquired projection data. As an advantage of the second method the even low preparation effort per scan is reduced. As long as the rotation time of the gantry is far below the cycle time of heart or the lung a multi-segment reconstruction is used in both methods. Motion artifacts are largely suppressed after gating. While in non gated images, the diaphragm, heart contours, bronchi and lung vessels are already visible, they are more sharply defined in the gated datasets. Four-dimensional assessment of lung motion is possible and lung volume in several phases such as peak inspiration and expiration could be segmented, quantified and compared.