State-of-the-art MR Imaging for Thoracic Diseases

Abstract

Since thoracic MR imaging was first used in a clinical setting, it has been suggested that MR imaging has limited clinical utility for thoracic diseases, especially lung diseases, in comparison with x-ray CT and positron emission tomography (PET)/CT. However, in many countries and states and for specific indications, MR imaging has recently become practicable. In addition, recently developed pulmonary MR imaging with ultra-short TE (UTE) and zero TE (ZTE) has enhanced the utility of MR imaging for thoracic diseases in routine clinical practice. Furthermore, MR imaging has been introduced as being capable of assessing pulmonary function. It should be borne in mind, however, that these applications have so far been academically and clinically used only for healthy volunteers, but not for patients with various pulmonary diseases in Japan or other countries. In 2020, the Fleischner Society published a new report, which provides consensus expert opinions regarding appropriate clinical indications of pulmonary MR imaging for not only oncologic but also pulmonary diseases. This review article presents a brief history of MR imaging for thoracic diseases regarding its technical aspects and major clinical indications in Japan 1) in terms of what is currently available, 2) promising but requiring further validation or evaluation, and 3) developments warranting research investigations in preclinical or patient studies. State-of-the-art MR imaging can non-invasively visualize lung structural and functional abnormalities without ionizing radiation and thus provide an alternative to CT. MR imaging is considered as a tool for providing unique information. Moreover, prospective, randomized, and multi-center trials should be conducted to directly compare MR imaging with conventional methods to determine whether the former has equal or superior clinical relevance. The results of these trials together with continued improvements are expected to update or modify recommendations for the use of MRI in near future.

Magnetic resonance imaging for lung cancer: a state-of-the-art review

“…PaulLauterbur,whoreceivedthe2003NobelPrizeinMedi-cinewithPeterMansfield,developedthefirstMRIscannerin the1970s.Inhomogeneityinmagneticsusceptibilitydueto airandsofttissueinterfaceswithinthelung,combinedwith motionandlowintrinsicprotondensity,hinderstheuseof MRIinthelungparenchyma [3][4][5][6][7][8][9][10][11].Moreover,differencesin susceptibilitytoartifactsinthelungparenchymaandchest wallmanifestasadarklineperpendiculartothefrequency encodingdirection.Therefore,thoracicMRIwasinitiallycon-sideredlessinformativethanCTfortheassessmentoflung parenchymaldiseasesandthoraciconcologicdiseasesin clinicalpractice [4,6,.Nonetheless,researchershave beentryingtoenhancetheutilityofMRIforlungcancerand mediastinaltumorsandforpulmonaryvasculardiseases [4,6,.…”

“…Intheearly1990s,spinecho(SE)sequenceswereusedfor clinicallungcancerMRI;however,reportspublishedbythe RadiologicDiagnosticOncologyGroupconcludedthatMRI withnon-electrocardiogram(ECG)-gatedT1-weightedSEim-aginghadlessutilitythanCTfortumor,lymphnode,and metastasis(TNM)staging [34].Sincethen,continuousand remarkabletechnicaladvancementshavebeenmade.Tech-niquessuchasturboorfastSEandgradient-recalled-echo (GRE)sequences,fastGREwithshortechotime(TE),in-and opposedphaseT1-weightedGRE,T1-andT2-weighted,short inversiontimeinversionrecovery(STIR),andturbospinecho (TSE)withthehalf-Fouriersingle-shotmethodwithandwithoutblack-bloodhavebeenusedinroutineclinicalpractice sincetheearly1990s [6,10,11,13,17,20,[24][25][26]29].Diffusion-weightedimaging(DWI)hasbeenusedincombination withsingle-shotecho-planarimaging(EPI)sequencesand thefat-suppressiontechniqueforoncologicevaluationsince theearly2000s [13,17,20,[24][25][26]29].Therefore,almostallMRI sequencesforthoraciconcologicaldiseaseswereestablished bythemid-2000s.Duringthesameperiod,theparallelimagingtechnique,aswellasfastGREwithshortTEorultrashort TE(UTE)andcontrastmediawereproposedfortime-resolved(or4D)contrast-enhanced(CE-)MRangiography,dy-namicCE(DCE-)MRI,andDCE-perfusionMRI;assessmentsof thesetechniqueshavedemonstratedthattheyareclinically relevantforthemanagementofpulmonarynodulesand massesandforTNMstaging [6,[10][11][12][13]16,17,20,[22][23][24][25][26][28][29][30][31].…”

“…Moreover,whenefficacywascomparedwiththatusing 18 FDG inPET/CT,theresultsweresatisfactory [88,93].Table4shows AsforCESTimaging,APT-weightedimagingappearstobe asusefulasDWIandFDG-PET/CTfordifferentiatingbetween malignantandbenignnodules [35].AlthoughADCsensitivity wassignificantlyhigherthanthatofmagnetizationtransfer ratioasymmetry(3.5ppm)andmaximumstandardizeduptakevalue(SUV max ),itsspecificitywassignificantlylower (P < 0.05) [35]. [11,117].Table6 [45,49,[118][119][120][121][122][123][124][125][126][127]showsthediagnostic performanceofthoracicMRIforlungcancerN-staging.STIR TheadvantagesanddisadvantagesofPET/CTandchestMRI forlungcancerstagingaresummarizedinTable8.…”

Magnetic Resonance Imaging for Guidance and Follow-up of Thoracic Needle Biopsies and Thermal Ablations

“…8 Functional imaging such as diffusion-weighted imaging (DWI) and dynamic postcontrast images may improve the diagnostic yield of needle biopsies. 9,10 The focus of this review article is to provide an overview of the currently available hardware for MR-guided thoracic interventions, to summarize the experience with MR-guided thoracic needle biopsies and thermal ablation published to date, and to identify scenarios in which MR guidance may be most advantageous.…”

“…Increased soft tissue resolution is another advantage of MR, especially for targeting lesions close to the neuroforamen and mediastinal structures, including the phrenic nerve 8. Functional imaging such as diffusion-weighted imaging (DWI) and dynamic postcontrast images may improve the diagnostic yield of needle biopsies 9,10…”