The Barium Enema

Barium (Ba, element 56) is a contrast agent for x-ray imaging of the gastrointestinal tract. In Chapter 16 of Intermediate Physics for Medicine and Biology, Russ Hobbie and I describe such contrast agents.

Abdominal structures are more difficult to visualize because except for gas in the intestine, everything has about the same density and atomic number. Contrast agents are introduced through the mouth, rectum, urethra, or bloodstream. One might think that the highest-Z [highest-atomic number] materials would be best. However the energy of the K edge rises with increasing Z. If the K edge is above the energy of the x rays in the beam, then only L absorption with a much lower cross section takes place. The K edge for iodine is at 33 keV, while that for lead is at 88 keV. Between these two limits (and therefore in the range of x-ray energies usually used for diagnostic purposes), the mass attenuation coefficient of iodine is about twice that of lead. The two most popular contrast agents are barium (Z = 56, K edge at 37.4 keV) and iodine (Z = 53). Barium is swallowed or introduced into the colon. Iodine forms the basis for contrast agents used to study the cardiovascular system (angiography), gall bladder, brain, kidney, and urinary tract.

In Table 16.7, we mention barium again.

TABLE 16.7. Typical radiation equivalent doses for the population of the United States. (From AAPM Report 96 2008, Table 2)

       Procedure                               Equivalent dose (mSv)
Chest X ray (Anterior Posterior)          0.1-0.2
Mammogram                                        0.3–0.6
Barium enema                                          3-6
Nuclear medicine–cardiac                      13-40
Head CT                                                   1-2
Chest CT                                                   5-7
Abdomen CT                                            5-7
Coronary CT angiography                        5-15

Third in this list is the unpleasant-sounding “barium enema.” What’s that?

In a barium enema, the doctor inserts a lubricated enema tube into the patient’s rectum, fills the colon with the contrast agent barium sulfate, and takes an x-ray. Patients prepare for a barium enema like they prepare for a colonoscopy: the night before they are restricted to a clear liquid diet, take laxatives, and use warm water enemas to clear out stool particles.

I like to learn by experiencing something rather than merely reading about it. I prefer to get my nose out of the book and try things, have new experiences, and live life. However, I DON’T FEEL THAT WAY ABOUT A BARIUM ENEMA. I hope you, dear reader, don’t ever gain first-hand experience with this procedure either.

Enjoy?