Magnetic resonance imaging (MRI) uses a powerful magnetic field, radiofrequency (RF) waves and a computer to produce detailed images of the inside of the body. Children are more sensitive to the effects of radiation, so it is advantageous that MRI does not use x-rays. Its superb soft tissue resolution gives detailed anatomical information.
In the pediatric population, MRI may be used to non-invasively diagnose, characterize or follow-up treatment of a wide array of conditions affecting the body due to illness, injury or a congenital abnormality. Some examples are listed below:
Brain and spinal cord
- Evaluate cysts, tumors, bleeding, abnormal blood vessels
- Infectious diseases e.g. encephalopathy or encephalitis
- Evaluate chronic headaches, dizziness, blurry vision or seizures
- Workup for developmental delay
- Evaluate congenital or acquired spinal abnormalities
- Diagnose sports-related injuries
- Detect the presence of an otherwise hidden tumor or infection in a joint
- Diagnose developmental joint abnormalities in children
- Often used to complement echocardiogram
- Anatomical details of heart and surrounding blood vessels
- Post-cardiovascular surgery changes
Abdomen and pelvic region
- Diagnose some causes of abdominal pain including evaluation for appendicitis
- Diagnose and monitor infectious or inflammatory disorders e.g. Crohn’s disease
- Monitor response to cancer treatment
MRI in the Paediatric population is associated with special considerations.
We mention a few below.
Pre procedural screening
This is an important step in ensuring patient safety prior to any MRI exam. A questionnaire elicits the patient’s medical history, prior imaging exams, known contrast/other allergic reactions, surgery or other treatment interventions (e.g. prior radiation). The screening interview area is private. Older children and teenagers should also be questioned separately from parents or guardian; this may increase the patient’s likelihood to disclose sensitive implants or potential dangers. e.g. piercings that parents are unaware of.
On occasion, younger children may request toys or other comfort objects. Use of such items in/near the scanner is discouraged, but might be deemed allowable after consultation with the overseeing radiologist and careful check with a handheld magnet/ferromagnetic detector outside the MRI suite.
The magnetic field and RF waves are not themselves harmful, but they may cause some medical or implanted electronic devices to overheat or malfunction. Examples of these devices include drug delivery patches (some contain metallic foil backing), cardiac pacemakers, cochlear implants, hearing aids, orthopedic implants. Careful pre-examination screening and discussion with the patient’s primary physician and the Radiologist will determine whether it is safe to proceed with the MRI study.
Obtaining high quality diagnostic images requires a patient to remain still for the length of the MRI test. Depending on developmental status and other factors, some children may require anxiolytic techniques and/orsedation to help achieve this.
There are s mall but important risks associated with sedation, including airway/respiratory difficulties and death. Associated morbidity rates are greater for neonates versus adults1,2. At our institution several factors are considered to increase likelihood of safe sedation, including: patient age/developmental status, past and current medical history, the active agent and route used for sedation (e.g. chloral hydrate or midazolam; oral versus IV; mild sedation versus general anaesthesia).
Infants and neonates may benefit from “feed and sleep” technique, 10 but some still require medications to be incorporated to facilitate the study. In our facility, younger children who are unable to fully understand/execute instructions and patients <8 years will usually have some assistance with medication. Our team of professionals are careful to discuss what to expect with older children, and they are usually able to successfully undergo the procedure without sedation.
Hearing protection is routinely used to cancel noise from the MRI scanner. Exposure to excessive noise is associated with hearing loss, and the risk is likely higher in preterm newborns whose auditory sense is still maturing.
If required, the contrast material used in MRI exams is unlikely to produce an allergic reaction (risk 0.004 –0.7%)8. Any reactions that occur usually are mild and easily controlled by medication.
After undergoing an MRI examination, trace amounts of gadolinium may be retained (>24 hours) in some body tissues (brain, bone skin). There is currently no evidence that retained gadolinium retention is harmful to patients with normal kidney function. Current consensus opinion is that the benefit of an accurate diagnosis outweighs any potential risk. However, contrast will still only be administered if considered medically necessary for diagnosis.
1. Cohen MM et al (1990).Pediatric Anesthesia Morbidity and Mortality in the Perioperative Period. Anesthesia and Analgesia 70.160-7
2. Jeana E. at al (2016),Preterm Versus Term Children: Analysis of Sedation/Anesthesia Adverse Events and Longitudinal Risk. Pediatrics 137(3).
3. Antonov NK et al. (2016) Feed and Wrap MRI Technique in Infants. Clin Ped 56(12), page(s): 1095-1103
4 Tsai LL et al (2015) A Practical Guide to MR Imaging Safety: What Radiologists Need to Know. Radiographics 35(6).
6. Machata AMet al (2009) “ Effect of Brain MRI on Body Core Temperature in Sedated Infants and Children” British Journal of Anaesthesia 102(3):385-9.
7. American Academy of Pediatrics: Committee on Environmental Health. Noise: a hazard for the fetus and newborn. Pediatrics 100(4), 1997, p. 724-727.
8. 2017 ACR manual in contrast manual, version 10.3pg 80
10. Neubauer et al., 2011. Acta Paediatrica 100:12; page1544
13. ACR Guidance Document on MR Safe Practices: 2013