MOTION ARTIFACT PLUS
MOTION ARTIFACT FREE

16.3, where the respiratory and cardiac motion artifacts are highlighted. An example of the inconsistence is illustrated in the sagittal view CT image of a patient in Fig. The maximum and minimum amplitudes are by convention assigned to end-inspiration and end-expiration phases, respectively. End-inspiration phase is 0 % and end-expiration phase is around 40вЂ“60 %. On the other hand, end-expiration phases correspond to a local minimum in amplitude. A phase is determined as a percentage in a breath cycle between two consecutive end-inspiration phases, which typically correspond to a local maximum in amplitude.

MOTION ARTIFACT FREE

However, these 2D CT images, almost free of respiratory motion artifacts, cannot guarantee consistency of the 3D CT anatomy in the craniocaudal direction because each CT image is a snapshot of the anatomy at a particular phase of a respiratory cycle when the patient free-breathes during the CT data acquisition of a PET/CT scan. Fast CT gantry rotation time of sub-second improves the temporal resolution of the CT image to sub-second, making the CT image almost free of respiratory motion artifacts. The 3D volume of a CT scan is composed of a stack of 2D CT images acquired in the craniocaudal direction. On the other hand, combination of a slow gantry rotation cycle time of 1 s, a smaller X-ray collimation of 1 cm for a 16-slice or 2 cm for a 64-slice CT, and a pitch factor of 1 would make the scan speeds of 1 and 2 cm/s for a 16-slice and 64-slice CT, respectively. A faster CT scan can be accomplished with a fast gantry rotation cycle time of 0.5 s, the X-ray collimation of 2 cm for a 16-slice or 4 cm for a 64-slice CT, and a pitch factor of 1.375 for the scan speed of 5.5 and 11 cm/s for a 16-slice and 64-slice CT, respectively. The speed of helical CT is determined by the following three components: gantry rotation cycle time, width of X-ray collimation, and pitch factor defined as the ratio of table translation distance per rotation to the width of X-ray collimation. 1 A helical CT scan of 100 cm from the orbit to the mid-thigh in a typical PET/CT scan can be performed in less than 20 s on a 16-slice or less than 10 s on a 64-slice PET/CT. The detector coverage along the craniocaudal or table direction at the imaging center or isocenter is 2 cm for a 16-slice or 4 cm for a 64-slice GE CT scanner.

MOTION ARTIFACT PLUS

A CT scanner is composed of an X-ray source and a bank of detector modules arranged in fan beam, which needs to rotate at least 180В° plus 60В° fan angle to produce a tomographic image. CT is mostly a 2D whereas PET is a 3D imaging device.

Motion artifact