Techniques in Pediatric MRI – Tips for Imaging Children - Siemens ...

How-I-do-it1A1B1 Longer TR and TE times are generally required when imaging very young children. The high water content in neonatal brains, coupled with the lackof fatty myelin results in a reduction in contrast-to-noise ratio (CNR) and grey/white matter differentiation. Restore pulses on T2w imaging can improve CSFcontrast and allow shorter TR times to reduce scan time.Techniques in Pediatric MRI –Tips for Imaging ChildrenGlenn CahoonRoyal Children’s Hospital, Melbourne, AustraliaMagnetic resonance imaging (MRI) examinationsof children require a particularset of skills and expertise in order to successfullyobtain diagnostic images withminimal distress to the patients and theirfamily. There have been many developmentsin MRI in recent years, whichhave lead to a dramatic increase in thenumber and types of referrals we are nowseeing for pediatric MR examinations.This paper provides an overview of thechallenges that pediatric patients raisein the MR setting, and some of thedifferent techniques that may beemployed to overcome these difficulties.While some technical modificationsare described, the focus is on practicalrecommendations that can assist youngchildren to comply with the MR procedure,and minimize the use of anesthesiawith this vulnerable population.Pediatric MR imaging can be considereda series of subspecialties. Each area,neurology, cardiac, MSK, oncology, allhave their own subtle nuances that alteras patients mature. In our facility we routinelyscan patients from the early fetal*stages right through to young (and not soyoung) adults with complex congenitalconditions. Each of these fields, andstages of development requires their ownspecialized skills, knowledge, and equipmentto be performed appropriately,however, there is a number of commonchallenges and techniques that apply toimaging pediatric patients.6 MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world

How-I-do-itChallenges ofscanning childrenSafetyMRI of children poses a number of specificsafety issues with patient heatingbeing the primary concern. Neonatesand infants in particular have immaturethermoregulation mechanisms, andhigher core body temperatures makingthem particularly sensitive to RF heatingeffects [1]. These mechanisms are furtheraffected by sedation and anesthesiacommon in pediatric imaging [2], orwhen babies are swaddled for imaging[1]. Children also have a greater surfacearea to weight ratio than adults. Thismeans for a given weight we often needto expose a greater surface area of thepatients to the RF field. This can lead toincreased heating in children, anddecrease their ability to dissipate thisheat. There is intrinsic uncertainty incurrent specific absorption rate (SAR)predictions based on extrapolated datafrom phantom models [3] particularlydue to factors such as body shape, size,composition, and position within the MRscanner. While definitive data on safetyrisks are not yet available, close monitoringof children, particularly critically illor compromised infants, is desirablewhen using higher field strengths andhigh SAR scan techniques [1].Anesthesia is an important safety considerationin pediatric MRI. While seriouscomplications such as death are rare,there are significantly higher rates ofmorbidity, particularly amongst neonates,when compared to adult anesthesia [2].Aside from adverse events there are anumber of common side effects includingnausea, vomiting, drowsiness andagitation upon awakening, which affectabout one third of pediatric patients [2].The challenge of monitoring patients inthe MR environment coupled with thereduced ability for the patient to communicateadverse events creates significantadditional risks [4]. If sedation is required,the associated risks need to be takeninto account when deciding to imageyoung children.AnatomyNormal structures in children are smallerthan in the average adult. This createsa challenge both in terms of the availablesignal, and the limits of our scan resolution.Anatomy is further complicated bycongenital anomalies and malformationsas well as developmental changes [5].At birth we are about 75% water and wedry out as we age to about 55–65%water for an average adult. This is bestappreciated in the neonatal brain. Thehigh water content, and lack of fattymyelin, requires an increase in TE onT2-weighted imaging to around 150–160 ms to improve contrast. With somuch of the available hydrogen in looselybound water, there often is not muchto influence relaxation. The use of fastrecovery (restore) pulses at the end ofthe echo train improves the signal-tonoiseratio (SNR) while allowing forshorter TRs to be used (Fig. 1).T1 contrast can be particularly flat requiringan increase in TR to around 1,200 msat 1.5 Tesla. The use of inversion recoverytechniques, and magnetization prepared3D imaging such as MPRAGE, are evidentat many institutions, particularly athigher field strengths [5].2PathologyChildren are notoriously poor reportersof symptomatology, and their oftenvague and non-specific symptoms canbelie the seriousness of their condition.Clinical examination is often very difficult,so MRI requests are seldom specific.There are many transient appearanceson MR images that can be considerednormal at some stages of developmentand abnormal at others. Recognizing theappearance of normal from abnormaldevelopment on MR images and determiningthe optimal sequences and factorsto best display them presents a challengeto technologists with little pediatricexperience.An awareness of the conditions thatare commonly found in the pediatricpopulation is necessary to tailor scansappropriately.PhysiologyPulse rate, blood flow, and respirationrates are considerably faster in children,with normal heart rates that can be inexcess of 140 bpm and respiratory ratesof 40/min [5]. Children typically find itdifficult to satisfactorily hold their breath,creating significant challenges in cardiac,2 Coronal PD-weighted image of an osteo-chondral defect (OCD) of the distal phalynx of theright toe.MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world 7

How-I-do-it3chest and abdominal imaging. Increasedflow rates lead to artifacts from bloodvessels and cerebrospinal fluid (CSF)pulsations, creating difficulties withspine and Time-of-Flight (TOF) vesselimaging [5]. Differences and evolutionin pediatric physiology may also leadwto changes in the mechanism of injury,or the types of injuries that occur inchildren, such as growth plate injuriesand osteo-chondral defects (OCD) [6].BehavioralSedation or anesthetic is commonlyrequired for younger children or thosewith significant behavioral problems.Factors such as temperament, stress,pain, and illness play an important rolein patient compliance, creating difficultiesin establishing definitive age limitsfor identifying which children will requirethese procedures [7]. Encouraging childrento co-operate for an MRI examinationand identifying those who cannotare arguably the most significant challengesin pediatric MRI.Techniques in scanningchildren without sedationPreparationAt our institution we begin scanningwithout sedation from about five yearsof age, although some positive outcomeshave been obtained with patientsas young as three years. Adequate preparationof children for the MRI procedurehas been vital in achieving these results.Our facility employs the services of educationalplay therapists who use a rangeof resources to assist children to complywith the procedure, such as brochures,MRI toys and storybooks, discussions withparents, and, most importantly, the‘mock MRI’ procedure.SimulationThe ‘mock MRI’ procedure involves childrenundergoing a simulated scan withthe assistance of a play therapist priorto the actual diagnostic scan. It acts asboth a screening tool, to assist in identifyingchildren who are likely to be ableto comply with the MRI procedure,and also helps to prepare these children,by familiarizing them with the environment,sounds, and equipment, whileteaching them skills (such as breathing,relaxation, or distraction) to cope withthe actual procedure (Fig. 2). Use ofthe ‘mock’ magnet has led to a markedreduction in the numbers of patientswho have required anesthetic [7] andreduced the time required for the diagnosticscan [8]. Several pediatric facilitiesin various countries have introduceda mock procedure in their facilities inrecent years [9].CommunicationSpecialist staff and equipment are clearlyhelpful in assisting children to complywith an MR scan. However, for technologists,an awareness of how to talk to childrenand adolescents at different stagesof development and the use of psychologicaltechniques, such as distraction andrelaxation, can be the critical factor determiningwhether a young person is willing,or able, to carry out the procedure.Many children are withdrawn or uncommunicativewhen nervous about a medicalprocedure, and taking the time tohelp the child to feel safe and secure inthe environment is important. Compliancewith preschool children may befacilitated by engaging in pretend play,where the child can be encouraged toframe the experience in familiar and nonthreateningways [10]. Nonverbal communicationcomprises a significant proportionof a child’s interaction with theworld at this stage, and young childrencan pick up on their parents’ anxiety orthe technologist’s impatience throughnonverbal clues. They may not understandthese feelings and can interpretthem as anger or fear of the examination.Professionals who work with childrentypically take steps to ensure that boththeir verbal communication and body3 Mock MRI simulator – this procedure identifies patients that are able to comply withthe requirements of an MRI examination, as well as prepare them for the clinical scan,saving unnecessary appointments and valuable scanner time.8 MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world

How-I-do-itTable 1: Communicating with childrenEngage with the child Get down on their level Use simple language Maintain eye contactFrame the experience Help them verbalize Involve the child’s past Smiletheir experienceexperiences / playEmpower the child Offer limited choices Praise good behavior Be positive “I know you can do this”language are reassuring and convey calmnessand confidence (Table 1). Positivereinforcement, where the child is praisedfor their efforts at each step, can be veryhelpful.School age children are able to engagemore actively in the procedure, and mayrespond well to efforts to increase theirperceived control. Medical examinationsoften take the locus of control awayfrom the patient, and this is particularlytrue in pediatrics where someone elseusually makes the decisions for thepatient. Empowering children by offeringsome choice in how they can havethe scan can be helpful. This is particularlyimportant during adolescence; aperiod of rapid social and physicalchanges [10], when increased autonomyis important, yet can be hampered byserious illness. Adolescents are less likelythan children or adults to blindly followinstructions, and may be reluctant toaccept or comply with the scan in theabsence of a flexible approach, where thetechnologist is sensitive to their concerns.Distraction and relaxationDistraction can be a powerful tool forreducing anxiety and increasing patientcompliance. Distraction techniquescan be either active or passive. Passivetechniques such as audiovisual aids areuseful during the scan when patients arerequired to lie still in the bore. Havinga point of interest (such as a parent orvideo screen) is helpful in maintainingthe patient in one position. Active techniqueswhich require patient participationsuch as relaxation breathing, guidedimagery, or complex puzzle tasks, areuseful in relaxing children before MRI orperforming interventions such as intravenouscannulation and general anesthetic(GA) inductions.Successful use ofintravenous (IV) contrastIV cannulation is a major cause of anxietyin young patients presenting forMRI examination. Limiting the use of IVcontrast in pediatric examinations canoften mean the difference between asuccessful awake scan and a rebook forsedation. This requires the support ofthe radiologists to make decisions regardingwhether the benefits of contrast areworth the potential distress to the patient.Where contrast is necessary, it is oftenhelpful to separate the procedures ofIV placement and the MR exam by eitherplacing the cannula before the examinationor offering a break between thepre and post contrast scans. Manychildren respond well to being able tochoose an IV site. Active distractiontechniques can be helpful, and there areseveral aids available to assist with thepain, such as local anesthetic creams,ice, or nitrous oxide.Protocols and sequencesProtocol based scanning can be difficultin presenting pediatric patients, as therequired sequences differ dramaticallydepending upon pathology, patient age,compliance, and the clinical questionsbeing asked. It is often necessary for thetechnologist or radiologist to screen theexamination as it progresses and tailorthe sequences for the patient and pathology.A wide field-of-view scan can behelpful to obtain an overview to screenfor other pathologies, particularly inchildren who are difficult to examineclinically. Children can be unpredictablein how long they will remain still, so itis important to prioritize sequences withthe highest diagnostic yield such as T2,FLAIR, and diffusion. Scanning in multipleplanes or using 3D sequences canhelp delineate disorders as well as minimizethe chance of pathology beingmissed through partial voluming or interslicegap.Often it is necessary to modify a protocolor sequence when imaging childrenof different sizes or capabilities. It isimportant to strike a balance betweenoptimum image resolution and scan time.MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world 9

How-I-do-it4A4B4C4D4 Images of a 3-month-old child with a lipomatous tether of thespinal cord. The patient was scanned awake in a bean bag restraint(4A) using the 4-channel flex array (4B) positioned flat beneath.The high SNR afforded by this coil allowed high resolution thin sliceimaging and the addition of iPAT to reduce scan time. Siemens Timarchitecture allows flexibility to use coils in a number of orientations,or in combination with other coils, vital for imaging pediatricanatomy.10 MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world

How-I-do-itWhen modifying pulse sequences, thefollowing suggestions may be helpful:■ Select pulse sequences that closelymatch the FOV required and the coilbeing used. The less changes you needto make to a sequence, the less chancefor error.■ Concentrate on maintaining voxel sizeand signal-to-noise when changingfield-of-view or matrix size, and considerusing interpolation to maintain signaland resolution. The day optimizingthroughput (Dot) engines on the newerSiemens scanners can be used to automatemany of these decisions.■ Utilize recovery pulses, where available,to achieve reduction in TR timesand to collect the images in multipleconcatenations. When combined withinterleaving this dramatically reducesthe chance of crosstalk when usingminimal slice gaps.■ Use the shortest TE that will maintainimage contrast to boost signal andreduce image blur.Scanning techniquesCoil selectionNovel uses of MR coils are possible andoften necessary in pediatric imaging.Choosing a coil that closely matches theFOV you are imaging is important inextracting the maximum signal from yourpatients. Use of multichannel arrays isdesirable when available to take advantageof parallel imaging techniques (Fig. 4).Volume imaging3D imaging can be utilized in all areas ofthe body. The use of 3D sequences permitsreformatting, which can be helpful5A5B5 Volume imaging: Reformatting of 3D imaging is useful in the investigation of complex congenital conditions. The curved reformat ofthe T1-weighted MPRAGE sequence allows appreciation of the disorganised left cerebral cortex, and helped in identification of a region ofpolymicrogyria which was the seizure focus in this 12-year-old girl.MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world 11

How-I-do-it6A6B6C6D6E6F6 Motion correction – syngo BLADE can be used to provide a limited study in uncooperative patients (6A, 6B), but is particularly useful inimaging posterior fossa lesions in pediatric patients where complex and high flow from CSF and vascular structures cause artifacts that mayobscure some lesions (6C, 6D). High parallel imaging factors can also be utilised with multiple excitations to average out motion artifacts(6E None, 6F PAT3).12 MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world

How-I-do-itin reviewing and diagnosing complexcongenital conditions, and may reducethe number of 2D sequences performed.It allows for high resolution, no gapimaging which can be used to accuratelymeasure lesion size, and monitor changesin follow up imaging (Fig. 5).BLADERotating k-space techniques are utilisedin pediatric MR imaging to reduce artifactsfrom physiological motion in thebrain, as well as other body areas suchas the shoulder, chest, abdomen, andpelvis. It is particularly useful withyounger patients scanned at 3T wherecomplex and turbulent flow artifacts canmask pathology [11]. Recent studiesshow improvement in lesion conspicuityin the posterior fossa through reductionin pulsation artifacts [12]. Disadvantagesof BLADE include increased scantime, altered image contrast, increasedSAR, and reduction in sensitivity to somepathology, particularly haemorrhage[13]. Motion reduction with propellersequences can be utilized to obtain limiteddiagnostic information in movingpatients; however, their limitationsrestrict widespread use for correctingvoluntary patient motion in pediatricpatients (Fig. 6).Parallel imagingThe advent of parallel imaging techniquesand multiple element, phasedarray coils has transformed pediatricimaging in recent years, providing aboost in either signal or speed. Parallelimaging techniques combine signalsfrom several coil elements to produce animage with increased SNR, or allow partialsampling to reduce scan time. Theuse of parallel image acceleration andmultiple acquisitions can be used to averagemotion artifacts in pediatric imaging.Parallel imaging techniques can alsobe exploited to reduce the duration ofbreathhold imaging, allowing dynamiccapture of fast moving pediatricanatomy. Parallel imaging also reducesinhomogeneity artifacts such as seen indiffusion-weighted imaging [14].Time resolved angiographyWhen imaging arterio-venous malformationsand vascular shunts it is importantfor treatment and management to identifyfeeder vessels as well as the directionof blood flow. Rapid heart rates and highflow rates in children often make imagingof complex vasculature difficult withtraditional MR angiography techniques.Time resolved contrast-enhanced MRangiography (MRA) techniques can provideanatomical as well as functionalassessment of these vascular conditions[14].High field strengthimaging (3T)Higher field strengths offer the opportunityto address many of the difficultiesencountered with pediatric MR imaging.The increased SNR allows for smaller voxelsand increased resolution, or reducedaverages for increased speed. Parallelimaging factors can be increased furtherreducing scan time. Prolonged T1 timesfacilitate better background suppressionfor MRA and improved visualization ofparamagnetic contrast agents [5]. Theadvantages offered by higher fieldstrengths have lead to the viability ofseveral new techniques in pediatric MRI.Unfortunately, higher field strengthscan also present a number of challenges.The increased field strength leads togreater RF deposition, resulting inincreased heating (SAR), which can causesequence limitation in pediatric imaging.B 1 -field inhomogeneities, chemicalshift, motion artifacts and susceptibilityartifacts are more pronounced at higherfield strengths. However, there are anumber of new techniques, which offerpotential to mitigate against these difficulties.Prolonged T1 relaxation at higherfield strengths creates challenges inimage contrast, particularly in the neonatalbrain [5].Emerging techniquesin pediatric MRISWISusceptibility-weighted imaging is beingincreasingly utilized in pediatric patientsfor imaging trauma, vascular disease suchas haemorrhage, telangiectasia, and cavernousand venous angiomas, tumors andepilepsy imaging, as well as investigatingmetabolic disorders (Figs. 7, 8). The useof the phase images can be used to differentiatecalcification from haemhorrage inlesions [15].Parallel transmit technologyThe use of multiple coil elements totransmit part of the RF pulse results inshorter pulse durations, reductions inSAR, and corrections of patient-relatedinhomogeneities [16]. This addressessome major challenges of pediatric MRI,particularly at higher field strengths.Diffusion Tensor ImagingDTI has provided insights into connectivityand plasticity in the developing brain.It is now entering the clinical realm inthe assessment of traumatic brain injury,epilepsy and white matter disease [14].Arterial Spin LabelingASL provides functional information ofblood perfusion by magnetically tagginginflowing blood upstream from the regionof interest. Persistence of the ‘tag’ limitsits use in adults; however, this is of lessconcern in pediatric patients, due to fastflows and relatively short perfusion distances[5]. This technique offers thepotential to investigate regions of hypoandhyper-perfusion, in conditions suchas stroke or tumors, without the use ofintravenous contrast media; however,further validation is required to demonstratethe clinical utility of this techniquein pediatric patients [17].MR urographyMagnetic resonance urography providesboth anatomical and functional assessmentof the kidneys and urinary collectingsystem. The multi-planar capabilitiesMAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world 13

How-I-do-it7A7B7 Images of a 1-month-old who presented with acute seizures. T2w, T1w and diffusion-weighted imaging were unremarkable. Susceptibilityweightedimaging (7A) shows increased venous drainage in the right temporal-parietal region. (7B) The same patient imaged 48 hours later afterseizure control with phenobarbital showing normalization of the cerebral flow. The sensitivity of syngo SWI is being increasingly utilized in thepediatric population.8A8B8 Venous angioma as imaged on syngo SWI (8A) and T2w sequences (8B). The ability to obtain this level of detail has allowed us to reduce ourreliance on intravenous contrast agents to delineate these lesions.14 MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world

How-I-do-it9A9B9C9D9 These images are of a patient with a pineal cyst causing obstruction of the cerebral aqueduct with associated enlargement of the lateral andthird ventricles. The sensitivity to flow of the T2w SPACE sequence can be used to demonstrate the obstruction in the pre surgical images (9A)as well as the increased retrograde flow through the foramen of Monro. The post surgical image (9B) shows the reduction in the size of the cystas well as the restored flow to the cerebral aqueduct. The 3D sequence can be easily reformatted to show the site of the fenestration of the thirdventricle (9C, 9D arrows). Third ventricultomies have been traditionally difficult to demonstrate with standard 2D and phase contrast imaging,however, with a single 3D acquisition we can now easily answer all of the questions of the neurosurgeon.MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world 15

How-I-do-itof MRI are ideal for displaying complexcongenital anomalies of the genitourinarytract. This information can beused to predict outcome and selectpatients that are most likely to benefitfrom surgical intervention [18].MR enterographyCrohn’s disease is a serious and lifelongcondition affecting the digestive system.It affects primarily the ileum and coloncausing inflammation, ulceration andcan lead to abscess formation or fistulaeto other organs. Approximately 30% ofpatients with Crohn’s disease will presentbefore the age of 20. MRI providesthe ability to diagnose and monitor thiscondition as well as complications suchas peri-anal fistulae without exposingthe patient to radiation [19].ConclusionMagnetic resonance imaging referralsfor children continue to rise. The lack ofionizing radiation coupled with the highlevel of detail afforded by MR imaginghas made it the examination of choice fora growing number of pediatric presentations.Most children who require magneticresonance imaging will be examinedin specialist pediatric centers or hospitals;however, heightened pressure onspecialist centers has lead to many childrenbeing scanned in non-specialistfacilities where technologists may havelittle experience in pediatric imaging.These referrals need to be treated differentlyto standard adult imaging requestsin order to ensure diagnostic imagingwith minimal distress and interventionto the patient. There is no ‘one size fitsall’ approach to imaging children andpediatric MRI requires dedicated specialistknowledge, flexibility, and expertinput from the technologist. An awarenessof the challenges in pediatric MRIand experience in pediatric imagingtechniques is vital to successful examinationin this population. MRI in childrencan be extremely challenging physically,mentally, and emotionally, even for aseasoned pediatric technologist; however,these very challenges are also what makepediatric imaging such an interestingand rewarding field for MR technologists.AcknowledgmentsI would like to thank the patients andstaff of the Royal Children’s Hospital,Melbourne, for their inspiration, advice,and support in compiling this paper.References1 Machata AM, Willshke H, Kaban B, Prayer D,Marhofer P (2009) “ Effect of Brain MRI on BodyCore Temperature in Sedated Infants and Children”British Journal of Anaesthesia 102(3):385-9.2 Cohen MM, Cameron Cal B, Duncan PG (1990)“Pediatric Anesthesia Morbidity and Mortalityin the Perioperative Period” Anesthesia andAnalgesia 70”160-7.3 Homman H, Bornert P, Eggers H, Nehrke K, DosselO, Graesslin I (2011) “Toward individualised SARmodels and in vivo validation” Magnetic resonancein Medicine doi: 10.1002/mrm.22948.4 Serafini G, Ongaro C, Mori A, Rossi C, Cavalloro F,Tagliaferri C, Mencherini S, Braschi A (2005)“Anesthesia for MRI in the Pediatric Patient”Minerva Anesthesiology Jun 71(6) 361-6.5 Dagia C, Ditchfield M. (2008) “3T MRI inpaediatrics: Challenges and clinical applications”European Journal of Radiology doi:10.1016/j.ejrad.2008.05.019.6 Hussain HM, Barnes CE (2007) “Pediatric skeletaltrauma- Plain film to MRI” Applied Radiology36(8):24-33.7 Carter AJ, Greer ML, Gray SE, Ware, RS (2010)“Mock MRI: reducing the need for anaesthesia inchildren” Pediatric Radiology Aug;40(8):1368-74.8 de Amorim e Silva,C.T.J., Mackenzie,A.,Hallowell,L.M., Stewart, S.E., Ditchfield, M.R.(2006) “Practice MRI: Reducing the need for sedationand general anaesthesia in children undergoingMRI” Australasian Radiology 50(4),319-323.9 Hallowell, L.M., Stewart, S.E., de Amorim e Silva,C.T., Ditchfield, M.R. (2008) “Reviewing theprocess of preparing children for MRI” PediatricRadiology 38(3), 271-279.10 Gable S (2010) “Communicating effectivelywith children” University of Missouri, Columbia,Outreach and Extension information sheet.11 Vertinsky AT, et al. (2009) “Performance ofPROPELLER relative to standard FSE T2-weightedimaging in pediatric brain MRI” PediatricRadiology. Oct;39(10):1038-47.12 Von Kalle T, et al. (2010) “Diagnostic RelevantReduction of Motion Artifacts in the PosteriorFossa by syngo BLADE Imaging” MAGNETOMFlash 43(1/2010):6-11.13 Forbes KP, et al. (2003) “Brain Imaging in theUnsedated Pediatric Patient: Comparison ofPeriodically Rotated Overlapping Parallel Lineswith Enhanced Reconstruction and Single-ShotFast Spin-Echo Sequences” American Journal ofNeuroradiology 24:794-798.14 Shenoy-Bangle A, Nimkin K, Gee MS (2010)“Pediatric Imaging: Current and EmergentTrends” Journal of Postgrad Medicine 56:98-102.15 Zhen Wu, Sandeep Mittal, Karl Kish, Yingjian Yu,J. Hu, Mark Haake (2009) “Identification of Calcificationwith Magnetic Resonance Imaging UsingSusceptibility-Weighted Imaging: A Case Study”Journal of Magnetic Resonance Imaging 29(1):177-182.16 Wald LL, Adalsteinsson E (2009) “Parallel TransmitTechnology for High Field MRI” MAGNETOMFlash 40(1/2009):124-135.17 Chen J, et al. (2009) “Arterial Spin LabellingPerfusion MRI in Pediatric Arterial IschemicStroke- Initial Experiences” Journal of MagneticResonance Imaging February; 29(2) 282-290.18 Grattan-Smith JD, Jones R (2008) “Magneticresonance urography in Children” MagneticResonance Imaging Clinics of North America16 515-531.19 Sinha R (2009) “Role of MRI in Chron’s disease”Clinical Radiology 64 (4):341-352.ContactGlenn CahoonRoyal Children’s HospitalMelbourneAustraliaGlenn.Cahoon@rch.org.au*MR scanning has not been established as safe forimaging fetuses and infants under two years of age.The responsible physician must evaluate the benefitof the MRI examination in comparison to otherimaging procedures.16 MAGNETOM Flash · 2/2011 · www.siemens.com/magnetom-world