Pneumonia in Children: Ultrasound or X-Rays?

Pneumonia is the most frequent respiratory disease in children and can even cause death. That is why it is extremely important to make an accurate diagnosis as quickly as possible. If this requires imaging tests, normally X-rays are taken. But there is an alternative: ultrasound. MEDICA.de talks with Dr. Jörg Detlev Moritz about the risks of X-rays for children and the benefits of ultrasound scans.

Dr. Moritz, why are X-rays risky particularly for children?

Dr. Jörg Moritz: Maybe you can best imagine it like this: cells are damaged most during the cell division phase. A child’s organism is still growing. That’s why there is a higher rate of cell division that might easier lead to damages. The following damages might occur:

X-radiation can induce cancer for example. The latency period is approximately 20 years. Due to the higher life expectancy of children, the probability of radiation-induced cancer to clinically manifest is much higher compared to older adults.

If X-ray radiation causes damage to DNA in the ovaries or testes, it may lead to hereditary diseases. Since children may be parents someday, these inherited defects can manifest.

Another set of problems comes from child body proportions. A child’s organism is far smaller than that of an adult. That’s why the organs lie much closer together. When X-rays pass through the body, it generally also produces scattered radiation, that being radiation that travels in arbitrary directions and cannot be completely shielded. For example, if X-rays are taken of a little girl’s thorax, the ovaries are hit with relatively more scattered radiation than would occur with the ovaries of an adult woman.

That is why X-rays for children need to be taken very carefully with strict indications. The risk of damages caused by X-rays is subject to the laws of probability. There is no threshold. Having said that, the risk of radiation damage from a single X-ray image is negligible.

What is the difference between an ultrasound and X-ray imaging procedure?

Moritz: They are essentially two entirely different procedures. Corresponding to their density, X-rays are attenuated at varying degrees by the different types of tissues as they pass through the body. X-rays are only slightly attenuated by air. In the case of pneumonia, the air in the lungs is pushed aside by inflammatory secretions and X-rays are correspondingly more strongly attenuated. That is why pneumonia appears as a densification on an X-ray image.

Meanwhile, in the case of ultrasound, sound waves are sent into the body. The ultrasonic waves are reflected at boundaries and then sent back to the receiving transducer. How strongly sound waves are reflected depends on the characteristics of tissue – propagation speed for sound in the tissue and the density of the tissue. Ultrasonic waves are completely reflected at the air surface so that it is impossible to image through air with ultrasound. However, in the case of pneumonia, the air is pushed aside by the inflammatory fluid. With ultrasound, the soft tissue structure with trapped remaining air shows in the bronchial tubes.

If there is an increased amount of fluid in the alveolar septum, the ultrasound scan shows certain reflections, so-called B-lines. This, in turn, is an indication of lung disease. You can reliably diagnose a pleural effusion, a relatively common finding in pneumonia, by using ultrasound. Very small levels of pleural effusion are better detectable using ultrasound versus X-rays.

Recently your colleagues at the Icahn School of Medicine at Mount Sinai, New York, published a study in CHEST magazine. What type of study is this?

Moritz: The study explored whether X-ray and ultrasound exams are comparable in diagnosing pneumonia. The physicians of one hospital examined all children with suspected pneumonia, who required imaging by using both X-rays and ultrasound imaging.

The physicians formed two groups. First, the children in the first group were examined using ultrasound imaging. If the results of this exam were unclear, additional X-rays were taken. The children in the second group were primarily examined via X-rays and were subsequently also tested using ultrasound imaging. There was no patient in the first group where pneumonia could not be detected right away. Having said that, it was also apparent that the sensitivity of the ultrasound test hinged on the examiner’s experience with ultrasound. Those experienced with using the ultrasound technique needed an additional X-ray far less to reach a diagnosis than those with lesser experience. All in all, the first group, which primarily received ultrasound imaging, required 40 percent fewer X-rays.

How reliable is ultrasound imaging to diagnose pneumonia?

Moritz: Several studies were able to show that ultrasound imaging is just as reliable as X-ray examinations. Sometimes, pneumonia presents with very small sources of irritation that are not yet visible on an X-ray but are already detectable with ultrasonic testing. However, there are also types of inflammation where changes only occur in the core of the lungs. These are not detectable in an ultrasound scan.

So essentially it would be better to first use ultrasound and if things are unclear to add X-rays?

Moritz: That might be the ideal case. However, this would exceed our capacities since ultrasound scans are fairly time-consuming. Even though the study states that ultrasonic testing takes less time, you have to remember that the study was conducted in the U.S. In the U.S., ultrasonic testing is done by ultrasound technicians and the images are then evaluated by physicians. Unlike in Germany, where ultrasonic testing is done by physicians. Needless to say, we also conduct ultrasonic testing in children to diagnose pneumonia because depending on the patient and problem, this can yield important additional information. However, doing an ultrasound of every patient first is so far not a routine procedure here.

There have already been some prior studies that showed diagnostic sonography to be useful in diagnosing pneumonia. In light of that, why are X-rays still routinely done?

Moritz: So far, X-rays have definitely been the gold standard to diagnose this particular illness. Ultrasonic testing still needs to take root as a routine procedure. Another example is bone fractures. I was able to prove that ultrasonic testing is just as effective in detecting fractures as X-rays. Ultrasonic testing is gradually finding its way into routine diagnostic tests. Yet X-rays are still the preferred method. I believe that we first need to go through a learning stage to increasingly establish ultrasonic testing as a routine method. Having said that, there will always be indications for X-ray imaging to diagnose pneumonia.