SF 6 is used as a contrast agent for ultrasound imaging. Sulfur hexafluoride microbubbles are administered in solution through injection into a peripheral vein. These microbubbles enhance the visibility of blood vessels to ultrasound.F 6 is used as a contrast agent for ultrasound imaging. Sulfur hexafluoride microbubbles are administered in solution through injection into a peripheral vein. These microbubbles enhance the visibility of blood vessels to ultrasound.
Once constipation (no bowel movement) has gone on for some time, the result can be what is known as an impacted bowel (sometimes called fecal impaction). Essentially, this means that a large lump of dry, hard stool is stuck inside your rectum.
According to the Cleveland Clinic, going more than three days without having a bowel movement is too long. Normal stools should be easy to pass and are typically brown in color. Abnormal changes in the color of your stool can include: 1  black, tarry stools. 2  clay-colored stools. 3  deep red stools.