Clinical Indications for Rapid Sequence MRI in Pediatric Neurosurgical Patients and the Limitations and Barriers to Implementation

Summary

Here, we present a protocol to increase the use of rapid sequence magnetic resonance imaging (RS-MRI) for pediatric patients for spine, traumatic brain injury (TBI), and hydrocephalus while documenting limitations and barriers to universal implementation.

Abstract

Rapid and fast magnetic resonance imaging (MRI) protocols have become increasingly popular for pediatric neurosurgical patients as they are a great way to reduce ionizing radiation and sedation. While their popularity has increased, there are hurdles to overcome when transitioning to using them clinically, such as cost, staffing training, and motion artifact. Through this paper, we developed a protocol for clinical applications where rapid MRI can be a substitute or adjuvant in diagnostic workup. Further, we outline the relevant literature for the use of RS-MRI for the spine, TBI, and hydrocephalus pathologies while expanding upon the limitations and logistical barriers when transitioning to their use, a few of which are discussed above. Through this, we conclude that RS-MRI can be used diagnostically for spinal pathologies such as syrinx and hydrocephalus. Further, its lack of sensitivity for TBI findings makes rapid sequence magnetic resonance imaging (RS-MRI) a strong adjuvant with other advanced imaging or computed tomography (CT) for traumatic brain injury (TBI) pathologies.

Introduction

Historically, computed tomography (CT) has been a first-line imaging study in many scenarios for screening for and monitoring neurologic pathology. In the pediatric patient population, multiple studies have advocated the reduction in CT imaging to reduce radiation exposure. Kessler et al. state that the effective radiation dose of head CT (HCT) is proportionally higher in young children, and a single HCT can have a lifetime cancer mortality risk of 0.07%. Leukemias and brain malignancies are the most common pathologies associated with increased exposure to radiation¹.

Standard MRI, although without radiation, may require sedation to reduce motion artifacts in pediatric patients. Repeated sedation raises concerns and may have neurotoxic effects on the developing brain¹. Flick et al. did a large, matched cohort study that showed repeated exposure to anesthesia before age 2 may be more likely to lead to the development of learning disabilities².

With the concern for radiation exposure and sedation when performing CT and MRI, Rapid Sequence MRIs (RS-MRI) are increasingly used in the clinical environment. Early RS-MRIs were used in the evaluation of hydrocephalus. Since then, additional indications for RS-MRI have developed due to the short scan times, absence of ionizing radiation, and sedation, which is important for risk factor reduction. Through this systematic review, we aim to discuss the clinical applications where RS-MRI can be substituted or adjuvant in diagnostic workup and the limitations and barriers to implementation.

Protocol

This protocol follows the guidelines of the institutional human research ethics committee of the University of North Carolina, as it was created secondary to a literature review and did not require real human subjects. Required permissions from volunteers and for filming have been obtained. The representative RS-MRI images used in this study have been deidentified.

NOTE: A review of the literature was conducted using keywords like "rapid MRI" and "fast brain". A total of 15 articles were reviewed, and the imaging protocols were retrieved and combined to create the protocol below.

1. Patient positioning

1. Before patient positioning, ensure that a thorough review of contraindications to the use of MRI has been completed. Tell the patient that contraindications for RS-MRI currently include various types of metallic implants such as vascular clips, foreign bodies, prosthetic heart valves, and other types of metal devices. Scan the patient with a metal detector to ensure no loose metal objects.
2. Patients who have anxiety or claustrophobia may need special attention to patient positioning to reduce exacerbations of these conditions. Give patients an alarm bell with an explanation for its use.
   1. Consult members of the Child Life Specialist team. Request that they review videos with patients to prepare them for what to expect.
3. Some RS-MRI coils have mirrors. Fix them so the patient may see out of the MRI scanner. Ensure accurate patient positioning is practiced in pediatric patients and proper coils are chosen to optimize the RS-MRI images.
4. Cranial imaging
   1. For a brain MRI, position the patient supine and centered on the brain coil with the chin tilted upwards³. Use landmarking, touch sensors, or laser marking with the patient's eyes closed.
   2. Provide earplugs for patient comfort and safety and immobilization pads to decrease motion and noise.
5. Spine imaging
   1. Cervical spine
      1. Place the patient in the supine position, with the larynx aligned to the center of the brain coil³. Use the same patient safety measures applied above.
   2. Thoracic spine
      1. Place the patient in the supine position. Utilize a spine coil and the center of the spine coil to align with the sternum³.
   3. Lumbar spine
      1. Position the patient in the supine position. Use the spine coil and align it centrally about 5 cm superior to the iliac bones³. Use an upright MRI if there is difficulty obtaining the image⁴.
6. Comforting techniques
   1. Use comforting techniques to reduce motion artifacts during RS-MRI. Attempt comforting techniques, including feeding, swaddling, and standard restraints⁵.
   2. Request guardian involvement to assist with soothing techniques. If a guardian is unavailable, involve experienced staff members like Child Life Specialists to attempt soothing techniques.
   3. Always attempt conservative soothing methods before the escalation of care. If standard restraints are required, do a thorough skin check after removal to assess for bruising.
7. Sedation
   1. If the patient continues to remain inconsolable despite soothing techniques, consult anesthesiology for sedation recommendations and dosing. Obtain guardian consent with an escalation in care.

2. Spine evaluation

1. The following RS-MRI protocol recommendations capture sequences for the routine detection and evaluation of spinal pathologies. Perform these sequences using a 1.5 Tesla (T) or 3T scanner⁶.
   1. Review representative parameters such as matrix size, field of view (FoV), repetition time (TR), and echo time (TE). Follow institution parameters or the parameters listed below.
2. Adjust the full spine series field of view to single or separate (cervical-upper thoracic, lower thoracic-lumbar/sacral). Calculate adjustments based on the patient's body habitus.
3. Syrinx evaluation
   1. Using the NUMARIS/4 software, select the Patient tab in the top left corner. From the drop-down menu, select Patient Browser.
   2. A separate screen will display a list of options. From this list, select Scheduler. Click once on the patient's name, followed by the register button in the lower half of the screen.
   3. A separate screen will display the patient's Name, Date of Birth, Height, and Weight. Review these parameters to ensure they are correct.
   4. Under patient positioning, select Head First- Supine. On the same screen, under Study, select SYRINX/TETHERED CORD NON-SEDATION EVALUATION protocol.
   5. At the start of the imaging study, ensure the localizer sequence is running. This sequence determines the orientation of the study. Run this sequence 2-3 times in spine cases.
   6. Next, run the selected T2 weighted half-Fourier acquisition single-shot turbo spin echo (HASTE) axial and sagittal sequences.
      1. Follow the imaging protocol listed here: slice thickness 3.0 mm, FoV 240 mm, TE 82 ms, TR 1500 ms.
   7. After the study, repeat step 2.3.1. From the separate screen display, select Local Database.
   8. Select the patient's name and the study completed. Click Transfer at the top left corner, followed by Transfer to PACS.
   9. Notify the support team that the study is concluded and transfer the patient out of the MRI scanner room. Once the patient is safely removed, reunite the patient with a guardian.
4. Other spinal pathologies
   1. If a clinical indication or suspicion of a cord pathology, Add a T2 Short-Ti Inversion Recovery (STIR) sequence. Include this sequence in the protocol above by repeating step 2.3.1.
   2. Select ______- SPINE WO sequence. Select the sequence relevant to the portion of the spine that is being imaged (i.e., C-SPINE WO).
   3. From the list of additional sequences that populate in the right column, select the STIR sequence. Follow these protocol parameters: slick thickness 3.0 mm, FoV 280 mm, TE 58.0 ms, TR 4000 ms.
      1. Of note, STIR nullifies fat tissue, which helps with tissue distinction. STIR has better sensitivity for cord pathologies than HASTE, which is more useful for CSF and cord differentiation.
   4. Repeat steps 2.3.7-2.3.8 to transfer the additional images for interpretation by the radiologist.

3. Traumatic brain injury evaluation

1. Perform the recommended protocol with a 1.5 T or 3 T scanner. Select scanners from the list available in Table 1.
2. Ensure that traumatic brain injury (TBI) sequences include but are not limited to axial fluid-attenuated inversion recovery (FLAIR), axial gradient echo sequences (GRE), axial diffusion-weighted imaging (DWI)- single-shot turbo spin echo, and axial and coronal HASTE.
3. Be aware that insignificant variations may exist in TE, TR, matrix size, and field of view. Follow institutional imaging protocols or the parameters listed below.
   1. Of note: T2 GRE and T2 HASTE sequences most likely identify traumatic pathology.
4. Hemorrhage
   1. Follow steps 2.3.1-2.3.3 to select the patient for the study. After selecting patient positioning as Head First Supine, under Study, select NEURO BRAIN.
   2. An additional list of protocols will populate, and from that list, select PEDS TRAUMA. Review this list to ensure it contains the sequences listed above in step 3.2.
   3. For suspected hemorrhage, ensure that a radiologist interprets the GRE images. Use these parameters for best GRE imaging quality: slice thickness 4.0 mm, FoV 230 mm, TE 2.46 ms, TR 240 ms.
      NOTE: This sequence is notable for increased detection of extra-axial hemorrhage when compared to CT imaging.
   4. Repeat steps 2.3.7-2.3.8 to transfer the additional images for interpretation by the radiologist.
5. Diffuse axonal injury
   1. In addition to the GRE sequence, add an additional axial susceptibility weighted image (SWI) to the evaluation for diffuse axonal injury.
      NOTE: SWI images are more sensitive than GRE in terms of volume and number of detected hemorrhagic lesions.
   2. Repeat steps 3.4.1-3.4.2. Use these parameters for best SWI imaging quality: slice thickness 3.0 mm, FoV 220 mm, TE 20 ms, TR 27 ms.
   3. SWI imaging may result in longer acquisition times when compared with GRE and, therefore, is more likely to be degraded by motion artifacts. Review the soothing techniques above to assist in reducing motion artifacts.
6. Skull fractures
   1. For suspected skull fractures, the above sequences have little sensitivity. Add a black bone MRI sequence to the protocol above.
   2. Select the black bone sequence by returning to the Patient Browser tab. From this tab, select the Neuro Brain protocol.
   3. From the list of additional protocols displayed on the left, select PEDS Trauma followed by the Black Bone sequence.
   4. The black bone sequence is a GRE sequence with shorter TE and TR and an optimal flip angle to differentiate soft tissue and bone. Select these imaging protocols^1,7: TE 4.20 ms, TR 8.60 ms, and flip angle of 5° under the Routine tab of the study properties screen.
   5. Head CT is the gold standard for evaluating skull fractures, as seen in Figure 1. Discuss risks and benefits with guardians and determine the most appropriate course. If the patient has completed a skeletal survey in TBI workup, examine the skull radiograph before initiating Head CT.

4. Hydrocephalus and shunt evaluation

1. Perform the protocol on 1.5 T or 3 T. Review sequences with standard commercially available hardware and software.
2. Hydrocephalus evaluation
   1. Follow steps 2.3.1-2.3.3 to select the patient for the study. After selecting patient positioning as Head First Supine, under Study, select Neuro Brain.
   2. An additional list of protocols will populate. From that list, select Rapid Sequence.
   3. Begin the study with a localizer sequence named AAHScout. Ensure that this localizer sequence automatically begins at the start of the study.
   4. For evaluation of hydrocephalus, include a TurboFLASH T1-weighted sequence and a HASTE T2 weighted sequence. The TurboFLASH sequence is a modified GRE sequence with shorter TE, TR, and flip angles.
      1. For HASTE T2 performed on a 1.5 T, use the following recommended parameters⁸: Repetition time (TR) 744 ms, echo time 104 ms, flip angle 150°, field of view 230 mm, matrix 256 × 156, number of acquisitions 1, slice thickness 4 mm with a skip of 1 mm, and I-PAT factor of 2.
      2. For HASTE T2 performed on a 3 T, use the following recommended parameters⁸: 3-Tesla: TR 358 ms, echo time 90 ms, flip angle 150°, field of view 220 mm, matrix 256 × 156, number of acquisitions 1, slice thickness 4 mm with a skip of 1 mm and I-PAT factor of 2.
         NOTE: HASTE T2 weight images provide the best imaging quality for ventricular assessment. If a catheter is placed, the TurboFLASH T1-weighted images are better suited for catheter visualization.
   5. Use these imaging protocols for TurboFLASH T1-weighted sequence: slice thickness 4.0 mm, FoV 230 mm, TE 2.46 ms, TR 240 ms. Viewing the Exam tab on the left, ensure both sequences are in three planes- axial, sagittal, and coronal. Multiplanar imaging provides better visualization of the catheter when compared with uniplanar imaging.
   6. Transfer images using steps 2.3.7-2.3.8.
3. Shunt evaluation
   1. Follow the protocol above for hydrocephalus evaluation. Repeat the imaging sequence until a clear visualization of the shunt catheter is obtained.
      NOTE: A summary of recommended sequences can be found below in Table 1. Only high-yield sequences are included.

Results

Spine evaluation
Ryan et al. conducted a prospective study to determine the feasibility of rapid spine MRI in the evaluation of syrinx in pediatric patients. Patients with known or suspected syrinx or Chiari malformations underwent rapid spinal MRI (HASTE) and standard non-contrast MR. Images were blindly reviewed by pediatric neuroradiologists who measured the following outcomes: Presence or absence of syrinx, syrinx measurement, clonus position, cerebellar tonsillar ectopia and degree, and filum ...

Discussion

RS-MRI offers an alternative imaging diagnostic tool in pediatric patients. RS-MRI uses T2 weighted sequences to visualize cranial and spinal pathologies, with faster scan times than traditional neuroimaging modalities.

Through a literature review and observation, we developed a protocol for the use of RS-MRI. We found that the sequences most relevant for diagnosing spinal pathologies were T2 HASTE and STIR. Additionally, T2 GRE and HASTE were most likely to identify traumatic pathology. Lastl...

Materials

Name	Company	Catalog Number	Comments
Alarm bell	Siemens	https://www.siemens.com/global/en/products/buildings/fire-safety/evacuation/notification-ul.html
Brain and spine coils	Siemens	https://www.siemens-healthineers.com/magnetic-resonance-imaging
Consent form to be filled out by parents or guardian	Local Health System	N/A
Ear plugs	3M Classic Ear Plugs	https://www.3m.com/3M/en_US/p/?Ntt=classic+ear+plugs
Ferroguard Metal Detector	Metrasens	https://www.metrasens.com/solution/ferroguard-assure/
Immobilization restraints	Siemens	https://www.siemens-healthineers.com/magnetic-resonance-imaging
Landmarkers, laser markers, or touch sensors	Siemens	https://www.siemens-healthineers.com/magnetic-resonance-imaging
MR power cut-off	Siemens	https://www.siemens-healthineers.com/magnetic-resonance-imaging
MR quench button	Siemens	https://www.siemens-healthineers.com/magnetic-resonance-imaging
MRI scanner	Magnetom Avanto	https://www.siemens-healthineers.com/en-us/magnetic-resonance-imaging/0-35-to-1-5t-mri-scanner/magnetom-avanto	Other brands: Discovery 750, HDXT Signa scanners, GE Healthcare, , Aera and Skyra, Siemens, Erlangen, and Germany
Radiologic technologist	Local Health System	N/A
Radiologist	Local Health System	N/A
Standard MRI hardware and software	NUMARIS	Version 4
Support pads and pillows	Medline	www.medline.com	Alternative: Quality electrodynamics