Introduction The use of imaging protocols allows the standardization of procedures and workflow as well as consistency of image quality. With appropriate training, radiographers can select and implement imaging protocols with relatively little requirement for radiological involvement. This use of skill mix provides radiographers with an expanded role and greater responsibility that increases job satisfaction and staff retention. Imaging protocols can also provide guidance for radiologists and radiographers for patients in shared care between secondary and tertiary care institutions. The use of protocols set up by the referring centre will prevent repeat MR scanning with the additional burden on MR scanner time. These advantages are offset by the minor disadvantage that radiologists’ personal preferences and the intricacies of individual scanners are not taken into consideration. At Great Ormond Street Hospital (GOSH), MRI protocols have been implemented for nearly 20 years and have been modified as scanners are replaced and new sequences developed. Our success is measured by the minimal number of patients recalled (less than 1%). Increasingly, we are asked about our MR protocols by departments throughout the United Kingdom and have set them out here to make them freely available to those who may find them beneficial to patient care. The protocols provided are confined to conventional imaging techniques and diffusion-weighted imaging (DWI), and do not include the advanced imaging techniques of perfusion imaging, diffusion tensor imaging and MR spectroscopy that remain largely within the research domain. Practical issues of MRI in children 1 2 2 Commercial MR machines are designed for adult practice and few manufacturers make provision for the issues encountered in paediatric practice. Currently, most children are imaged in units that have a wider adult practice with only a handful of institutions throughout the world having dedicated paediatric MR facilities. The structures we need to examine in children are generally small and we aim for a maximum slice thickness of 5 mm in the brain and 3 mm in the spine. The slice thickness is reduced to 3 mm when acquiring images of the pituitary gland and orbits. We do not recommend ultrafast ‘breath-hold’-type T2-weighted (T2-W) sequences that have reduced contrast to noise as an alternative to sedating a child, as achieving high contrast to noise is of utmost importance given the small size of the paediatric head. Advances in coil design have improved signal-to-noise and we now use multichannel head and spine coils. Practical consideration of the changing brain with age 3 4 1 5 Fig. 1 a b c  6 7 8 Factors influencing sequence choice For any imaging protocol, it is the specific combination of sequences that determines the diagnostic efficacy of the examination. It is clear that imaging protocols vary between institutions. This is largely because rapid advances in imaging technology and variations between manufacturers, applied in the context of investigating relatively rare disorders, precludes an effective evidence-based approach to sequence choice. The main advantages that MRI offers over alternative imaging modalities is the ability to demonstrate different tissue contrasts (principally T1-W, T2-W and spin density, but also flow and diffusion) in multiple imaging planes (principally sagittal, coronal and axial). The disadvantage of MRI is the artefacts that it generates in almost every image. The choice of sequence combination should reflect the multicontrast and multiplanar capabilities of MRI. We have found that applying the generic principle of combining T2-W images in two planes, supported by T1-W imaging in two planes, as the basis of our imaging protocols, serves to optimize the benefits of MRI whilst minimizing the impact of artefacts. Standard MRI studies Brain 9 In those under 2 years of age, the T2-W sequence is replaced by a dual-echo axial STIR sequence (see above). In some cases, a T2*-W gradient-echo (GE) sequence (“susceptibility-weighted” sequence), sensitive to changes in local field inhomogeneity caused by the breakdown products of haemoglobin, is added. The sequence is particularly useful in trauma and vascular malformations such as multiple cavernomas. Spine 10 Our standard spine imaging includes sagittal, fast spin-echo T1- and T2-W sequences (3-mm-thick slices). Both axial T1-W and T2-W images are acquired through any abnormality. Unlike most adult spine imaging protocols, groups of axial images through disc levels are not applied because degenerative disc disease is rare. Children with scoliosis and/or suspected spinal dysraphism routinely have axial T1-W images through the conus and filum terminale to detect lipomas of the filum terminale that may not be visible on sagittal imaging. Contrast medium 1 Table 1 Indications for contrast medium administration Various indications Acute inflammation  Acute disseminated encephalomyelitis (ADEM)  Optic neuritis Acute infection  Abscess  Cerebritis  Discitis  Empyema  Encephalitis  Meningitis  Transverse myelitis Neurocutaneous disorders  Congenital melanocytic naevus  Neurofibromatosis type II Tumours  Benign and malignant  Intracranial  Intraspinal a  Vascular anomalies  Cavernomas  Developmental venous anomalies Vascular disorders  Intraparenchymal haemorrhage  Sturge-Weber syndrome  Vasculitis a MRI protocols for specific areas The strategies applied to the brain are also applied to small parts such as the orbits and pituitary gland. The orbit is scanned using a STIR sequence to benefit from the fat saturation properties of the sequence and improve the conspicuity of lesions within the orbit. The slice thickness is reduced to 3 mm and, to increase the signal-to-noise, the matrix size is reduced, thereby slightly reducing the in-plane resolution. A heavily T2-W 3-D volume sequence of the petrous temporal bones is used to image the membranous labyrinth and is reconstructed in the coronal plane of the petrous temporal bone, and the axial and sagittal plane of the internal auditory meati (IAM). The sagittal plane is used to view the vestibulocochlear nerve in cross section. A constructive interference steady state sequence (CISS), available on Siemens scanners, is acquired and reconstructed at a slice thickness of 0.7 mm. The GE equivalent is the FIESTA sequence and the Philips equivalent is DRIVE. MRI protocols for specific neurological or neurosurgical presentations The majority of children undergoing an MRI brain scan will have epilepsy, stroke or a brain tumour and are often referred to specialists with an interest in these areas. Tumours of the brain and spine Brain 11 The purpose of preoperative imaging of brain tumours is to assess tumour location and type, establish whether there are single or multiple lesions, define its relationship with vital structures and look for any complications such as hydrocephalus. Contrast-enhanced T1-W volumetric acquisitions are also acquired for image-guided surgery. Imaging of the spine is performed in all children with intracranial tumours (not only posterior fossa tumours) and although this requires a change of coil and an additional sequence, we find it beneficial as tumour histology is often not certain at the time of the initial imaging. Some tumours unexpectedly metastasize to the spine and assessment of the postoperative spine is made more difficult in the presence of blood products. 11 12 13 14 15 2 Table 2 Proposed protocols for surveillance imaging in children with ependymoma, medulloblastoma and pilocytic astrocytoma Tumour Timing of postoperative imaging Frequency of study Macroscopically complete excision Incomplete excision Cranial study Spinal study Cranial study Spinal study Ependymoma 24–48 h First None First None 1st year 3–6 months 6 months 3 months 3–6 months 2nd–5th years 6 months 6–12 months 6 months 6–12 months a 24–48 h First None First None 1st year 3–4 months 3–4 months 3–4 months 3–4 months 2nd–6th year 6–8 months 6–8 months 6–8 months 6–8 months b 24–48 h First None First None 1st year 6 months None 6 months None 2nd year At 24 months None 6 months None 3rd year At 3.5 years None 6 months None 4–5th year At 5 years None 1 year None 6th year onwards None None 2 years None a b Spine 3 4 Table 3 Protocols for specific areas Specific areas Protocols Orbits (3-mm slices)  Coronal and axial dual-echo STIR  Coronal and axial T1-W spin-echo Orbits with contrast enhancement (3-mm slices)  Coronal dual-echo STIR  Coronal and axial T1-W spin-echo  Contrast-enhanced coronal and axial T1-W images with fat saturation Pituitary (3-mm slices)  Sagittal and coronal T1-W spin-echo  Coronal T2-W spin-echo Pituitary with contrast enhancement (3-mm slices)  Pituitary protocol  Contrast-enhanced coronal and sagittal T1-W spin-echo Internal auditory meati  3-D volume axial CISS  Brain MRI Face and neck MRI  Coronal and axial dual-echo STIR  Coronal and axial T1-W spin-echo  Fat-saturated contrast-enhanced coronal and axial T1-W spin-echo Midline facial lesions  Axial dual-echo STIR from floor of anterior cranial fossa to hard palate  Sagittal T1-W and T2-W spin-echo (3-mm slices)  Coronal T1-W spin-echo from nose to brainstem Table 4 Standard MRI brain and spine protocols Types of brain and spine MRI Protocols MRI brain (under 2 years old)  Axial and coronal dual echo STIR  Coronal and sagittal T1-W spin-echo  DWI in three planes and calculated ADC map a MRI brain (over 2 years old)  Axial T2-W fast spin-echo  Coronal FLAIR  Coronal and sagittal T1-W spin-echo  DWI in three planes and calculated ADC map a MRI brain with contrast enhancement (under 2 years old)  Axial and coronal dual-echo STIR  Coronal T1-W spin-echo  DWI in three planes and calculated ADC map  Contrast-enhanced axial, coronal and sagittal T1-W spin-echo with magnetization transfer a MRI brain with contrast enhancement (over 2 years old)  Axial T2-W fast spin-echo  Coronal FLAIR  Coronal T1-W spin-echo  DWI in three planes and calculated ADC map  Contrast-enhanced axial, coronal and sagittal T1-W spin-echo with magnetization transfer a MRI spine  Sagittal T1-W and T2-W fast spin-echo  Axial T1-W and T2-W fast spin-echo through target area and conus  (Coronal T1-W spin-echo for scoliosis, if patient compliant) MRI spine with contrast enhancement  Sagittal T1-W and T2-W fast spin-echo  Contrast-enhanced sagittal T1-W fast spin-echo  Axial T1-W spin-echo through target area a Epilepsy 16 5 17 Table 5 Protocols for particular clinical indications Types of clinical indication Protocols Brain tumours  MRI brain with contrast enhancement  Contrast-enhanced sagittal T1-W images of whole spine  Contrast-enhanced image-guided images when required Stroke Acute a b  Sagittal T1-W spin-echo DWI in three planes and calculated ADC map Intracerebral 3-D TOF MRA Axial dual-echo STIR and T1-W spin-echo through the neck Extracerebral 2-D TOF MRA of the neck down to the aortic root Non-acute Acute stroke protocol without imaging of the neck Epilepsy a  3-D T1-W volume acquisition reconstructed in three planes b  Coronal FLAIR (or 3-D FLAIR if available)  Hippocampal T2-relaxometry (see text) Intraparenchymal haemorrhage  MRI brain with contrast enhancement  Intracerebral 3-D TOF MRA  MRV Non-accidental head injury  Standard MRI brain  Axial GE “susceptibility-weighted” sequence  Sagittal T2-W spin-echo and GE “susceptibility-weighted” sequence of the cervical spine MPRAGE MRV a b Non-traumatic intraparenchymal haemorrhage 18 Stroke 19 19 20 A 3-D TOF MRA sequence is used for the imaging of the intracranial vessels and a 2-D TOF MRA sequence for the extracranial vessels. The TOF scan times are shorter than phase-contrast (PC) MRA and there is lack of dependence on the choice of correct velocity encoding with obvious advantages when scanning ill children. Intracranial 3-D TOF MRA is also included in the investigation of children with IPH, although its sensitivity to T1 shortening may obscure the underlying abnormality (see above). As CT is often the first-line investigation in children with stroke, the potential of DWI to detect hyperacute cerebral infarction prior to changes on T2-W MRI is not realized. However, inpatients (e.g. cardiac patients, patients with recent-onset stroke) can be imaged early, and in these children DWI can be used to detect infarcts of different ages. Non-accidental head injury 21 22 23 21 Neonatal imaging Conventional imaging can detect patterns of regional brain injury in the neonatal period that can help time the injury, determine underlying mechanisms and ultimately provide some prognostic information. MRI is useful in detecting hypoxic–ischaemic injury, and germinal matrix and intraventricular haemorrhage, and can be useful to distinguish other pathologies that may mimic hypoxic–ischaemic encephalopathy in the neonatal period such as venous infarction, metabolic disease, infection, and congenital developmental abnormalities. Our neonatal imaging protocol is the same as the under-2-year brain protocol. Achieving high signal-to-noise is of utmost importance given the small size of the infant head and is improved by decreasing the slice thickness to 4 mm whilst decreasing the matrix size from 512 × 512 to 256 × 256 in a field-of-view of 180 mm. Although specific neonatal head coils have been developed, most nonpaediatric centres are unlikely to have access to them and improved results can be obtained by using an adult knee coil. Developmental delay Developmental delay, without other clinical features such as epilepsy or dysmorphic features, is not considered an indication for an MRI scan at our institution. This decision was made in conjunction with our neurologists as it was recognized that there is an extremely low yield of clinically relevant abnormalities seen in patients with developmental delay alone. The future The future of paediatric neuroimaging lies in the incorporation of research techniques, such as perfusion imaging and diffusion tensor imaging, into standard imaging protocols once they have been demonstrated to be of value within the clinical arena. The use of higher field strength magnets will have the advantage of increasing signal-to-noise and reducing scanning time, which will be of benefit to the child who is both small and liable to move.