Respiratory Motion in Positron Emission Tomography/Computed Tomography: A Review

https://doi.org/10.1053/j.semnuclmed.2008.01.002Get rights and content

The development of positron emission tomography/computed tomography (PET/CT) scanners has allowed not only straightforward but also synergistic fusion of anatomical and functional information. Combined PET/CT imaging yields an increased sensitivity and specificity beyond that which either of the 2 modalities possesses separately and therefore provides improved diagnostic accuracy. Because attenuation correction in PET is performed with the use of CT images, with CT used in the localization of disease, accurate spatial registration of PET and CT image sets is required. Correcting for the spatial mismatch caused by respiratory motion represents a particular challenge for the requisite registration accuracy as a result of differences in temporal resolution between the 2 modalities. This review provides a brief summary of the materials, methods, and results involved in multiple investigations of the correction for respiratory motion in PET/CT imaging of the thorax, with the goal of improving image quality and quantitation. Although some schemes use respiratory-phase data selection to exclude motion artifacts, others have adopted sophisticated software techniques. The various image artifacts associated with breathing motion are also described.

Section snippets

Respiratory-Motion Tracking Systems

Although respiratory gating is not yet standard in the context of PET imaging, several related techniques are already in use. The studies performed to date have investigated a large number of different respiration monitoring systems to account for breathing during gated radiotherapy, 4-dimensional (4D)-CT, 4D cone beam CT, or gated PET. Such motion tracking systems are described herein.

Respiratory Motion Artifacts in CT

Respiration can introduce severe artifacts in CT images caused by internal organ motion.32, 35, 36, 37 The main cause of these artifacts is the dynamic interaction between transaxial image acquisition and the asynchronous motion of tumor and normal tissues.1 Commonly observed artifacts include distortion of the dome of the liver at the lung-diaphragm interface, splitting of a tumor into 2 distinct parts, shuffling of the transaxial slices out of order, and creation of discontinuities in the

Respiratory Motion Correction

The misalignment between PET and CT can, of course, reduce the diagnostic accuracy of PET/CT for lesion detection for the same reasons as discussed above Methods to correct for respiratory motion in the 3 modalities, CT, PET, and PET/CT, are discussed in the subheadings to follow.

Conclusion

In this work, 7 approaches to correct for respiratory motion in PET images have been reviewed. Each has its advantages and disadvantages, and the optimum clinical approach remains to be determined. The main concern with 4D-CT is the increased radiation dose. 4D-CT provides information about the extent of tumor motion, information critical for radiotherapy planning. However, when used for diagnostic purpose, only one high-quality, motion-free image set would be required. Although any of the

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