![]() Truncation errors can also occur when the field of view between the PET and CT differ, positioning patients away from the in-plane center, or when patient size is too large for the field of view-even though this can mostly be corrected by software. Hard copies of images should be avoided as artifacts such as those related to the printing process and damage to the print medium are common. This can be prevented by equipment maintenance of whole-body uniformity. If multiple passes are used in acquisition or if a continuous acquisition is used, a “zipper” (linear) artifact or banding (often horizontal linear) artifact may be observed, respectively. With any series of static images, misalignment may be a source of error. These artifacts can be prevented by correct calibration after servicing the machine. This can reduce the field of view by overcompensation or misalignment of the field of view (leaving edge effects in view). Electronic masking of the unusable edge of view prevents edge packing effects along the crystal area. įield of view artifacts can involve many mechanisms. Software processing of the image can also reduce collimator artifacts. A dent or defect in the collimator can be caused during the manufacturing process or by mechanical stress. If the damage is more widespread, flood images can be compared between different collimators for detection. Collimator artifacts have no bright rim around the photogenic area, which distinguishes them from crystal defects such as cracks. It does not change spatial resolution or radiation scatter content but increases contrast and helps with locational relationships of structures. Tomographic imaging (PET/CT and SPECT) reconstruction can avoid these artifacts by digital subtraction methods and three-dimension imaging. Certain radioisotopes are used to minimize this effect (99mTc instead of 201Tl). Less energy causes more scatter and more absorbed radiation by the patient. Collimators address the vast majority of gamma camera attenuation potential problems, but Compton scatter artifacts can still occur. Attenuation artifacts can be inherent to gamma radiation due to the energy it has.
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