Figure 4c. Transverse CT images numbered (a) 10, (b) 14, (c) 18, and (d) 22 in the image set obtained in a patient examined with scanner B show a hypoattenuating artifact (arrow) that is less apparent on some images than on others because of the presence of normal anatomic structures. When the artifact appears in the intraventricular region, as in c, and has approximately the same attenuation as that of cerebrospinal fluid, it is nearly invisible.