Clinical Nuclear Medicine by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9783030394578
Publisher: Springer International Publishing

17.1.2 Motion Artifacts

Motion artifacts are typically presented as blurring in PET or as misalignment between PET and CT data sets, which can lead to both spatial localization errors and incorrect attenuation correction [4]. The dimension of artifacts is mainly dependent on the number and spatial range of motion and the duration of acquisition. PET acquisition is usually performed by a series of consecutive bed positions of 15–20 cm with a duration of 2–3 min each. Therefore, motion particularly causes artifacts image in motion-affected regions. In contrast, the separately acquired helical CT scan acquires 15–20 cm in a few seconds, and motion-affected regions are usually obtained in a locally motion-free state [4].

Motion can be considered as either voluntary (e.g., head motion) or involuntary (e.g., cardiac contraction or respiratory motion). Artifacts can be developed by motion occurring during either the PET or the CT acquisition or from motion that occurs between the two acquisitions.

Patient movement may cause poor-quality and blurred PET images and regions of increased or decreased activity mainly due to incorrect attenuation correction. In addition, PET artifacts can result from erroneous scatter correction if the tracer distribution is not correctly adjusted with the CT due to regions of activity being incorrectly defined as scatter. Changing scatter correction parameters can often reduce this artifact. In addition, good communication with the patient, attention to careful positioning, physical supports, and occasionally, sedation may limit voluntary motion. However, careful inspection of PET/CT images to identify when motion has occurred is probably the most useful method to repeat local imaging when needed.

Involuntary motions causing artifact by respiratory-induced spatial misalignment between PET and CT data sets are potentially more difficult to control. It usually happened at the base part of the lung and the anterior wall of the heart and can lead to attenuation-correction errors and degrading of lesion detection and tumor quantitation (Fig. 17.1) [6–8].

Fig. 17.1 18F-FDG PET (coronal view). Motion artifact. Involuntary motions causing artifact by respiratory-induced spatial misalignment between PET and CT data sets on the base of the lung, so-called mushroom sign, banana sign (arrows)

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