The world of pediatric imaging was revolutionized a couple of decades ago with the introduction of pediatric PET/CT. This subsequently found wide acceptance in pediatric oncological imaging, among other applications.

PET/MRI is a more recent development, approved in pediatric patients by the FDA in 2011. This is an area that is undergoing further study and development as technology improves and it is expanded to more indications.

Here is a brief perspective on pediatric PET in 2020:

Pediatric PET challenges

When PET is combined with CT or MRI, it helps to provide physicians with views of the metabolic processes and physiological condition of the body. Indications for use include areas such as oncologic, cardiovascular and neurologic imaging.

On the whole, any sort of imaging in pediatric patients presents unique challenges that aren’t generally there in adult patients with the same condition. Pediatric radiology requires good knowledge of these issues and of course, rapport with the children who are being imaged.

On the whole, specialized pediatric technologists are spread thinly across the United States. One (somewhat dated) study estimated that only around 3% of all radiologists had a pediatric specialty. This can be a challenge in and of itself.

Some of the common challenges of pediatric PET imaging include:

• Gaining the trust and cooperation of the child. In the mind of a pediatric patient, medical facilities, equipment and the strangers who are operating them can be a frightening prospect.
• Sometimes the challenges with gaining the cooperation of the child result in sedation or anesthesia for the imaging process. One presentation reported on survey results where some facilities sedated as little as 10% of the time, while others did so 85% of the time. Potential neurotoxicity as a result of anesthesia is a known risk among the pediatric population.“The criteria for which children may need anesthesia for a PET scan are similar to those of other lengthy procedures in pediatric nuclear medicine: patients who are mentally impaired, young children who cannot cooperate or tolerate, and those who are claustrophobic. In short, any patient with characteristics that may interrupt or disrupt the PET scan should be considered for sedation or anesthesia.” (Source)
• Establishing intravenous access. Not all pediatric patients will already have a central line in and may require intravenous access. This can be challenging with small veins and balking at multiple attempts to reach them.
• Bladder catheterization is sometimes necessary for clear imaging. The process of applying the catheter to a child can be challenging – anesthesia is often preferable beforehand.
• The need to fast for hours prior to imaging. For some children, this will seem like an eternity and can contribute to their overall mood and cooperation.
• The environment surrounding the imaging area. Children tend to require an environment that will engage them and make them feel more comfortable.“For instance, the walls should have bright colors, with paintings and designs as well as images with toys, play characters, cartoons and toys.” (Source)
• Physical safety. While this is always a concern for all patients, there tends to be an increased need for safety measures with pediatric patients. For example, protection from radiation is imperative and facilities may need to invest in more expensive, lower-dose equipment.
• The relatively smaller anatomic structures in children create a challenge in terms of available signal as well as limit of resolution.

PET combination modalities: The pros and cons

Is PET/CT or PET/MRI preferable in pediatric patients? Each modality has its own pros and cons.

PET/CT

One of the major pros of PET/CT is that it’s much more widely available than PET/MRI at this stage. One of the advantages of being so widespread is that imaging protocols are well-established and the providers ordering the imaging are very familiar with it.

The equipment is less expensive than MRI which contributes to its widespread use. Exams can generally be performed more quickly than MRI, at 30 minutes or less. Among pediatric patients, this can be a crucial factor. Either they’re anesthetized and therefore it is preferable to keep them under for as short a period as possible, or they’re not and for their comfort and cooperation, getting through imaging quickly is necessary.

One of the major concerns over pediatric PET/MRI is exposure to radiation:

“Not only are children more sensitive to the effects of radiation than adults but, following radiation exposure, children have a longer postexposure life expectancy in which to exhibit adverse radiation effects. Both the PET and CT components of the study contribute to the total patient radiation dose, which is one of the most important risks of the study in this population.” (Source)

Radiographers need to consider careful selection of pediatric-specific CT imaging parameters designed for appropriate diagnostic, localization, or attenuation correction only CT, in conjunction with the use of recommended radiotracer administered activities.

Compared to MRI, CT also has limited soft tissue contrast.

PET/MRI

PET/MRI is performed as either a sequential or synchronous procedure. In the former, the PET procedure is conducted first, followed by the MRI on separate equipment which may even be located in a different room. For imaging facilities, this can offer advantages for technical compatibility and cost.

With the latter option, PET and MRI data are obtained at the same time. A single gantry contains the PET detectors, which are located between the body and the gradient coils of the MRI system. This has the effect of reducing the scanning footprint and potentially the amount of time needed to complete a scan.

The amount of time taken is a common concern when compared to CT. MRI frequently takes up to an hour or more to complete – a long time for any child. There are also certain conditions where it may not be suitable, although protocols and indications are continuing to develop for its use.

One of the great drawcards of PET/MRI for the pediatric population (and others) is that it reduces patient exposure to radiation by about 50%. There is also evidence to show that MRI can pick up abnormalities in the brain that CT may miss.

Recent reviews show it to be a promising modality with multiple potential applications in the pediatric space.

Promising studies in pediatric cancer patients

As the applications for PET/MRI in pediatric patients continue to develop, some promising studies have come out. In one recently highlighted by GE, clinicians at the Children’s Hospital of Wisconsin have developed a 30 minute PET/MR exam for pediatric cancer patients.

They addressed the issue of longer scan times for MR by tailoring their MR sequences to fit into the PET acquisition time. Their imaging results proved to be effective, so the bottom line is that they have converted PET/CT scans in pediatric cancer patients to PET/MR.

On the whole, pediatric imaging is progressing in 2020 but there still remains some common challenges, unique to the field of pediatrics. Healthcare organizations should consider these carefully when looking at imaging solutions for their younger patients.