Bowel artifact meaning5/1/2023 ![]() ![]() However, if repeating a stress 201Tl study significant redistribution could have occurred and scheduling the patient for a different day may be preferable. If significant motion is detected and reconstruction artifacts are present, a new acquisition is recommended. ![]() On the other hand, a single motion episode will be duplicated with a dual-head camera since it will be "seen" simultaneously by both detectors at different angles. Multiheaded detector systems have been beneficial to decrease SPECT image acquisition time, improve patient tolerance, and thereby decrease the possibility of patient motion. Commercially available arm holders are useful for this purpose. Although SPECT can be performed with both arms at the side, in order to minimize detector distance and avoid the attenuation caused by the arms, elevation of at least the left arm above the head is preferable. The lumbar curvature of the back should be supported, the knees slightly elevated and supported in order to minimize back strain, and the left arm and shoulder supported and restrained. SPECT acquisition should be fully explained to the patient and he/she should be encouraged not to talk, yawn, sigh or fall sleep (and snore). The technologist can be of great help in minimizing patient motion. Motion correction can be attempted although most software approaches are imperfect and sometimes represent additional sources of error by themselves. The overall visual effect is known as the "hurricane sign" in the short axis views, while in the horizontal long axis misalignment of the lateral and septal wall towards the apex can be apparent as described for COR errors. Frequently the image contains "tails" streaming from the edges of the defect. Characteristically, with patient motion reconstructed images demonstrate opposed defects in contralateral walls. A change in body position at the middle of the acquisition is much worse in consequence. Respiratory motion is very prominent in some patients but the images are often still of diagnostic value, because there is a periodical movement of the heart in the axial direction causing some blurring of the backprojected image but usually not simulating a perfusion defect. During reconstruction, data are backprojected onto different points of the volumetric matrix, and thereby a misregistration error occurs. The cause of the reconstruction artifact is similar to that due to an erroneous COR, but with patient motion the heart itself is at a different location during different portions of the SPECT acquisition. Whether patient movement is abrupt or gradual, myocardial perfusion image artifacts may be created. The best means to detect patient motion is to observe the planar raw images of the SPECT acquisition in cine mode, but condensed images such as sinogram and linogram are also useful. During SPECT acquisition, patients may move in the vertical (axial), lateral or rotational direction. This is one of the most common sources of SPECT myocardial perfusion artifacts. ![]()
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