Preamble
The European Association of Nuclear Medicine (EANM) is a professional non-profit medical association that facilitates communication worldwide among individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985.
These recommendations are intended to assist practitioners in providing appropriate nuclear medicine care for patients. They are not inflexible rules or requirements of practice and are not intended, nor should they be used, to establish a legal standard of care.
The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by medical professionals taking into account the unique circumstances of each case. Thus, there is no implication that an approach differing from the recommendations, standing alone, is below the standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set out in the recommendations when, in the reasonable judgment of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources, or advances in knowledge or technology subsequent to publication of the recommendations.
The practice of medicine involves not only the science but also the skills to deal with the prevention, diagnosis, alleviation, and treatment of disease.
The variety and complexity of human conditions make it impossible to always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment. Therefore, it should be recognized that adherence to these recommendations will not ensure an accurate diagnosis or a successful outcome.
All that should be expected is that the practitioner will follow a reasonable course of action based on current knowledge, available resources, and the needs of the patient to deliver effective and safe medical care. The sole purpose of these recommendations is to assist practitioners in achieving this objective.
Introduction
Diagnostic nuclear medicine (NM) includes a wide variety of procedures that can be applied to adult and paediatric patients. Management in paediatric patients requires a special set of skills, which should be developed by the nuclear medicine professionals who are involved in the procedures. NM teams face several challenges while performing diagnostic procedures on the youngest population, as many technical details and requirements may change according to the patient’s physical characteristics (e.g., weight or body mass index) as well as behavioral and psychological aspects related to the stage of development [
1]. An advanced understanding of how to adapt to each paediatric patient includes the ability to optimize the administered activity and acquisition details for each patient to deliver the lowest possible dose, while attaining a good quality image. Additionally, the capability of communicating effectively with the child and the caregivers is crucial. Strategies for relieving anxiety and promoting patient cooperation are essential for best practice [
2]. Developing the communication ability and the capacity to better understand the needs of each patient in each patient’s stage of development will enable the application of a personalized approach [
3]. Having a more relaxed patient and caregiver helps in reducing many common image artifacts, such as patient motion, while increasing comfort for both the patient and caregivers. Tailoring the exam to the paediatric patient requires consideration at each step of the process, from scheduling the scans to the final words, before children leave the department.
Goals
The purpose of this EANM procedural recommendation is to highlight best practices by identifying strategic options for patient compliance and dose optimization in the NM technologist’s interaction with children throughout all stages of the imaging procedure.
Hybrid imaging and CT dose optimization
From the first developments of hybrid imaging, the additional radiation exposure due to CT was a significant concern. Indeed, exposure levels were much higher in the early years. Chawla et al. [
74] reported in their study that, from 2002 to 2007, effective doses due to PET/CT ranged from 2.7 to 54.2 milliSieverts (mSv) for the CT scanning and from 0.4 to 7.7 mSv for the PET procedure [
75]. Some authors [
76‐
79] reported that a non-optimized CT scan can contribute up to 80% of the whole radiation burden in paediatric NM exams. In this context, the
Image Gently’s slogan seems more important than ever: “
One size does not fit all” [
80].
In the first instance, the nuclear medicine physician must identify for each patient the body volume to be investigated during the PET/CT or SPECT/CT examination to lower the radiation burden [
4]. The physician should also specify whether to include arms in the scanning field of view. The interposition of arms in the field of view often leads to a significant deterioration of image quality and to an increase in the radiation level to compensate for noise [
81].
The ALARA principle must always be considered and put into perspective with the benefit-risk ratio of the examination. The optimization of CT in hybrid imaging is mainly based on adjusting acquisition parameters [
82‐
88] as well as reconstruction algorithms [
89,
90]. Imaging tests and subsequent standardization of the most common protocols used in the department can help reduce patient exposure [
76,
91] and quantify any bias that may be introduced using a very low dose CT for attenuation correction [
92,
93].
In SPECT/CT, reducing the CT acquisition volume to the region with the SPECT findings can markedly reduce the radiation dose.
Performing paediatric studies on modern cameras with high detector sensitivity (e.g., cadmium-zinc-telluride (CZT) detectors) and advanced CT scanners can reduce the effective dose by facilitating the lowering of injected activity and using the advanced paediatric CT optimization techniques [
94‐
96]. Similarly, SPECT or PET reconstruction with resolution recovery algorithms can improve image quality and allow reduction in the administered radiopharmaceutical activity [
97‐
100].
Configuration of CT scan parameters for paediatric protocols usually involve optimization of both tube voltage and current, for which weight-based classes for paediatric patients can be defined [
82,
89]. Recently, automatic exposure control systems utilizing automatic tube current modulation (ATCM) [
83,
87] and automatic tube voltage selection (ATVS) have been developed. ATVS allows an the automatic choice of kV and mAs settings without impairing the contrast-to-noise ratio [
101,
102] and negligible variation when used for quantification of PET images [
103]. However, exposure control settings will generally still require some weight-based classes to be defined. When the ATVS are not available, tube voltage can be manually adapted for children. Due to the small physical size of children, dose reduction can actually improve image contrast [
103], rather than create the severe image noise associated with adult CT.
CT reconstruction algorithms are also crucial for dose reduction [
104,
105], and novel reconstruction tools are continuously developed. Several iterative reconstruction methods have been implemented through the years and introduced in NM and PET hybrid systems [
106‐
113]. Furthermore, recent advances in artificial intelligence, using deep learning reconstruction [
114,
115], are promising in terms of additional dose reduction and image quality, allowing further adjustment to protocols for specific clinical cases [
116].
Therefore, the NM technologist must be aware of the dose reduction options available on their systems and understand how to optimize them properly.
The purpose of the CT will largely determine the CT settings and the radiation exposure to the child. Certain departments prefer the “one-stop-shop” approach, especially with PET/CT utilizing a contrast-enhanced diagnostic CT, which negates the need for additional radiological studies. Nevertheless, since many children undergo diagnostic CT or magnetic resonance imaging (MRI) in addition to the NM procedure, it is common practice to use a low-dose CT settings for anatomical localization and attenuation correction. This is an essential element that must be considered when undertaking a CT optimization study in comparison to that in the radiology field. Examples of the CT optimization in the nuclear medicine field applied to paediatric patients for the purpose of anatomical localization and attenuation correction and the suggested exposure setting used are reported in Table
1.
Table 1
The reported nuclear medicine studies had purpose in CT optimization in paediatric patients, aiming at attenuation correction and anatomical localization. ASiR™, adaptive statistical iterative reconstruction algorithm; NI™, noise index
| ∙ 10-year-old paediatric equivalent acrylic phantom ∙ NEMA PET phantom™ | PET/CT (a) | 16 | _ | 80–100 | 10–40 | _ | 0.5 | 1.35 | 3.75 |
PET/CT (b) | 40 | _ | 80–100 | 10–40 | _ | 0.19 | 1.35 | 5.00 |
PET/CT I | 16 | _ | 80–100 | 10–40 | _ | 0.5 | 1.35 | 3.75 |
| ∙ Catphan 700 phantom™ ∙ Jaszczak phantom with Esser lid phantom ™ ∙ NEMA IEC Body Phantom™ ∙ 140 patients | PET/CT | 64 | 0–9.4 | 80 | 20–130 | NI™: 30 ASiR™: 100% | n.a | 0.98 | 3.75 |
9.5–18.4 | 100 | 20–160 | NI™: 40 ASiR™: 100% |
18.5–31.4 | 100 | 10–210 |
31.5–55 | 100 | 25–210 |
> 55 | 120 | 32–210 |
| ∙ 27 patients | PET/CT | 128 | 3.1–39 | 100 | 20–40 | ASiR™: n.a | 0.5 | 1.3 | n.a |
Effective dose estimation
Workstations [
118] provide details of expected and delivered exposure in the form of the volume CT dose index (CTDIvol), representing the dose that would be delivered through a slice of a standard phantom (unit: milliGrays, mGy) and the dose length product (DLP = product of CT dose index and the irradiated scan length, expressed in mGy*centimeter, cm). However, the estimated individual patient risk due to the radiation burden is provided by the effective dose (ED), not by the DLP, and its estimation is a complex process [
119,
120] that takes into account the CT parameters, scan range [
121,
122], patient size and age, the irradiated organs, body composition, and tissue weighting factors [
5].
Nevertheless, in impromptu situations, the DLP can be used indirectly to ascertain the safety of the CT and identify when an exposure may result in higher doses than expected [
123].
As a practical example, in PET/CT imaging, the NM technologist can evaluate any unnecessary exposure using the DLP and CTDIvol, displayed before the scan, by comparing these values to reference ranges defined for the weight of the patient.
This check helps increase the awareness of the CT exposure that the NM technologist is using. This strategy does not substitute dosimetry, which should be carried out in an audit setting and is based on precise calculations with dedicated software, usually by the Medical Physics Expert.
Image review
After image acquisition is complete, a quality assessment of the raw data should be perfomed to confirm the validity of the available images for diagnostic interpretation.
Patient motion artifacts should be assessed, and if present, correction software should be considered (if available). In some instances, image acquisition may need to be repeated [
124].
Checking for normal biodistribution of the radiopharmaceutical can help identify any abnormal attenuation artifacts caused by an external object that was inadvertently kept by the patient. In this case, if the attenuation is in the target zone, image acquisition should be repeated.
Patient position artifacts should also be checked, as asymmetrical uptake can be misleading in cases where the patient is not properly positioned. When children are very small, minor rotation may still affect the acquired image and can lead to misinterpretation. Use of post processing and reconstruction methods that allow reorientation might be feasible, else a repeat scan should be considered if a software option is not effective.
It is equally important to check for potential registration artifacts, since both studies — SPECT/PET and CT — should perfectly overlap. Regardless of the need of CT for attenuation correction and/or anatomical reference, an error in the registration can lead to important pitfalls. Again, software and reconstruction solutions should be used when available, and manual reorientation of the scans attempted.
All image repetition should be carefully considered, especially when hybrid imaging is used. Repeating a CT scan will increase the radiation burden of the procedure and should be avoided whenever possible. If only the emission image was affected, repetition is relatively easy to perform, provided the patient is still cooperative. It is useful for a department to audit the frequency that repeat images are required as this may highlight where protocols and practice, particularly related to patient cooperation, can be improved.
Recommendations on patient discharge
By the end of the procedure, the patient and caregivers should be discharged in friendly manner, to leave a good lasting memory for the child. NM professionals should inform the child pleasantly that the examination is over, orally reinforce the child’s cooperative behaviors, and offer the previously agreed-upon reward. Younger children are often delighted with bubbles, a colored sticker, a fun activity with the caregiver, or the opportunity to put their handprint on the board of the bravest placed in the waiting room. Older children usually feel rewarded with bravery certificates or stickers, given the opportunity to take a photo of the bravest board after having written their name on it. Giving a positive reinforcement to the paediatric patient can be very beneficial to increase his/her well-being and for future examination needs. Parents should also be thanked for cooperating during the procedure and informed about examination results.
Recommendations to stimulate the radiopharmaceutical biological elimination should be given to the patient and/or caregiver. This is obviously dependent on the radiopharmaceutical and its specific excretion. The majority of the radiopharmaceuticals used in NM have renal excretion, so increased hydration and micturition throughout the day are some of the most common final recommendations. Caregivers should be advised to replace diapers more often to reduce radiation exposure.
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