Solving a "Big" problem in Radiology

"We can't x-ray him, he's too big!"...This was a statement I had from a radiology student earlier today when approached with an abdominal x-ray on a morbidly obese patient. My answer? "Too bad, figure it out". Yes, the patient was on the upper end of 400 pounds, and yes, he was extremely difficult to radiograph, however, it had to be done. All too often a student (or even a seasoned technologist for that matter) will come to wits end on a proper approach to imaging the morbidly obese, and sadly, sometimes the patient's life can depend on the quality and, in turn, the interpretation of that radiograph. This is becoming a looming issue in our field and unfortunately the issue isn't going away.

According to the CDC, about one-third of U.S. adults (33.8%) are obese and approximately 17% (or 12.5 million) of children and adolescents aged 2—19 years are obese. During the past 20 years, there has been a dramatic increase in obesity in the United States and rates remain high. In 2010, no state had a prevalence of obesity less than 20%. Thirty-six states had a prevalence of 25% or more; 12 of these states (Alabama, Arkansas, Kentucky, Louisiana, Michigan, Mississippi, Missouri, Oklahoma, South Carolina, Tennessee, Texas, and West Virginia) had a prevalence of 30% or more.

The problem with having an obesity epidemic is having obesity-related diseases. Obesity-related morbidity encompasses a large number of disorders, including: type II diabetes, dyslipidemias, hypertension and cardiovascular disorders, hepatobiliary disease, osteoarthritis, sleep apnea,and even certain malignancies (endometrial, breast, and colon cancer). This is where our job comes into play. We are continuously required to image these people, and sometimes we don't have a clue on how to approach it. I typically try to appeal to the general public on this blog, but this is where I may lose you. If you don't know the difference between a KUB and kVp, you may continue reading, but you'll probably want to pick up an issue of Bontrager's Positioning for Radiography book. If you're a seasoned technologist, this might not be a bad "refresher" course. If you are a student, this should be considered required reading. Enjoy.

The biggest issue we have as an x-ray technologist is simply getting the patient on the imaging table. The key is to have a lot people for "lifting help" and to use an ergonomically practical approach. If gathering a few people to give you a hand isn't realistic, your imaging facility needs to have some sort of protocol for transporting heavy patients, whether it's using a lift of some sort or taking an alternate approach. If you're simply unable to transport the patient to the imaging table, an all too often used solution may be to image the patient with a mobile x-ray machine in their bed.

Once the transport issue has been resolved, another question typically arises. How do we radiograph someone that we simply can't penetrate? Well the answer to that question is a basic step that we learned in the very beginning of our training. Out of all the factors utilized in performing a radiograph, the most important for improving penetration is to increase our kVp. Obviously increasing our kVp will have extenuating circumstances with risks that we must carefully weigh against the rewards of a diagnostic image. With a higher kVp comes MUCH more scatter photons that will dramatically lower the image contrast. Remember to implement a grid if the subject thickness is greater than 10 cm and when using a kVp greater than 70 (which will typically be the case when imaging larger patients).

Once an adequate kVp has been determined, the mAs will most likely also need to be increased. Due to increased subject absorption and attenuation of the x-ray beam, the "quantity" of the x-ray beam will need to be compensated for. The compromise of having a long exposure time will also require you to increase your mA. The goal should be to use the shortest exposure time possible...because it's still going to be long (we just don't want it to be THAT long). If we can cut down on the motion artifacts caused by a long exposure, we can dramatically improve an already inferior image quality.

A couple other quick tips that might help are to increase your film-screen speed (if that's an option), make sure to be on your game with collimation and consider decreasing source-to-image distance. An increased film-screen speed can dramatically decrease the amount of mAs required which will make your life a million times easier (this may not be an option in a digital imaging setting). You will increase image contrast, lower your exposure time, and limit your motion artifacts. Once again, image resolution will be the expense but chances are, if you're resorting to using a higher film-speed screen, image resolution will be one of your lower priorities.

As with any radiograph, tight collimation is essential to producing a quality image. When imaging an obese patient, the importance of good collimation cannot be overstated. We all know that the larger the patient, the more scatter photons are produced. The easiest way to avert that is to limit the field of view in which the photons are being emitted. This will increase your image contrast considerably, especially with the use of a grid. Your image density will be compromised a little, but the density you get from scatter radiation is only deteriorating the quality of the image anyhow. This is a very good tip that is typically an oversight when imaging "in a hurry".

The next step, and hopefully the last one is to decrease your source-to-image distance. This is something that you'll NEVER see recommended in a text book and this is something that a radiography instructor would scoff at, however, I'm looking for real world solutions, and it works. Yes, bringing the tube closer to the patient WILL increase absorbed dose, and yes, you WILL be going against everything you ever learned by the "never shoot anything at less than 40 inches" rule that's been ingrained in you since you donned your first pair of brand new scrubs, BUT...IT WORKS. When making this recommendation to the student today he responded, "That doesn't quite follow ALARA radiation (As Low As Reasonably Achievable) principles". I responded with "Well let's repeat these x-rays 4 or 5 times at 40 inches and calculate the absorbed dose versus one exposure at 34 inches...I'm pretty sure an RSO (Radiation Safety Officer) would be proud of my defiance of your ALARA principles." By following the inverse square law, you will increase your image density considerably, which may be limited depending on the type of x-ray machine you're using. Just a quick disclaimer, this would absolutely be your last resort.

These are all my tips and tricks on how to get a quality image on a very large patient. This particular patient habitus seems to be increasing in the population faster than the technology to image them is produced. Until an x-ray machine manufacturer comes up with a more practical approach, this is the one I'll use. I hope I've helped solve one of the "big" problems in our field.


Curtis J. Carpenter R.T. (R)(CT)