Totally Accessible MRI: A User’s Guide to Principles, Technology, and Applications PDF
Preview Totally Accessible MRI: A User’s Guide to Principles, Technology, and Applications
Totally Accessible MRI Totally Accessible MRI A User's Guide to Principles, Technology, and Applications Michael L. Lipton, MD, PhD With a Foreword by Emanuel Kanal, MD, FACR, FISMRM, AANG ~ Springer Michael L.Lipton, MD, PhD Associate ProfessorofClinicalRadiology, Psychiatry and BehavioralSciences Medical Director,MRI Services DirectorofRadiology Research AlbertEinstein College ofMedicine and Montefiore Medical Center Bronx, NY USA and Senior ResearchScientist The Centerfor Advanced Brain Imaging The NathanS.Kline Institutefor Psychiatric Research Orangeburg, NY USA ISBN:978-0-387-48895-0 e-ISBN: 978-0-387-48896-7 DOl:10.1007/978-0-387-48896-7 Libraryof CongressControlNumber:2007932970 ©2008SpringerScience+BusinessMedia,LLC All rightsreserved.Thisworkmaynotbe translatedor copiedinwholeorinpartwithoutthe writtenpermissionofthepublisher(SpringerScience+BusinessMedia,LLC,233SpringStreet, NewYork,NY 10013,USA),exceptfor briefexcerptsinconnectionwithreviewsorscholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation,computersoftware,or bysimilaror dissimilarmethodologynow knownor here- afterdevelopedisforbidden. Theuse inthis publicationoftradenames,trademarks,servicemarks,andsimilarterms,even iftheyarenotidentifiedassuch, isnotto be takenasan expressionofopinionasto whether or nottheyaresubjectto proprietaryrights. Whiletheadviceandinformationinthis bookarebelievedtobe trueandaccurateatthedate of going to press, neitherthe authors nor the editors northe publishercan acceptany legal responsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty, expressor implied,with respectto thematerialcontainedherein. Printedon acid-freepaper 987654321 springer.com Dedicated to the memory ofmy grandfathers: Samuel Parelman Samuel B. Lipton Meyer Light Herman Blitz Siegfried Rosenthal Stature ofcharacter and ethic, Unqualified love and support Justifiable pride in their enduring legacy Stand as an example for us all. May their memory be a blessing. Foreword BS"D Allmagnetic resonance technologists and allradiologistswhowork with magnetic resonance (MR) technology can be divided into two subgroups: (1) those who understand the underlying physics principles and how to apply them; and (2) those who do not. For so many patients and for so many diagnostic considerations, the difference between membership in these two groups is minimal. One can easilydiagnose avestibularschwannoma and accurately differentiate it from a cerebellopontine angle meningioma without being that well versed with many of the concepts underlying the creation of the MR images on which these tumors are depicted. One by rote can generate images of the pelvis that are quite diagnostic and aesthetically pleasing without really understanding the intricate interrelationships between the varyingimaging parameters used inthe generation ofthe obtainedimage contrast. There are certainsituations, however, for whichamore in-depth under- standing isrequired. For example:Seeingtissuesignaldisappearon ashort T1 inversion-recovery sequence yet recognizing that it does not have to originate from fat but maycomefrom methemoglobin or some othershort T1tissuemayprove clinicallyvitalfor arrivingat the correct diagnosis.For suchcircumstances,understandingtheunderlyingprinciplesthat governthe creationofthe imageand the contrastcontained thereiniscriticaland sets oneapart-anddistinctlyahead-ofthecompetition, whocannotmake this claim. In the two-plus decades during which I have taught my courses on MR physics entitled, "Clinical MR Physics: Understanding and Applying," I have had the good fortune to teach literally thousands of eager students. Among the most eager and most persistentwasDr. MichaelLipton. Never satisfied with a superficial understanding, he always asked for more and continually sought a deeper level of understanding of the underlying con- cepts in a never-ending effort to build upon and improve upon that which we already know. vii viii Foreword With thistext, Dr. Liptonattemptsto impartsome ofhisvastknowledge to one just starting out on ajourneytoward understanding this fascinating technology. In a clearly written and disarmingly informal style more remi- niscent ofconversationaltone thanformal lecture,Dr. Liptonbreaksdown many of the concepts involved in the clinical magnetic resonance imaging process into bite-sized pieces that are easy to swallowand digest. Steering clear of most mathematics and quantum mechanics and remaining firmly grounded in classical physics and explanations, Dr. Lipton sheds light on manytopicsthatcanbesodifficulttosomany.Bysodoing,heisattempting to modify the ratio of"understanders" to "rote performers" wefindin our MR society today. I hold this to be quite a commendable objective, and I applaudDr. Liptonforhisefforts. You, too, are tobecommended,because reading this book is clear evidence that you have taken your first steps in trying to switchcamps to the "understanders" group. With G-d's Help and through the assistance of Michael's pen, may you be granted the wisdom to attain your objectives and, more importantly, apply them to the benefit of the patients entrusted to your care. Emanuel Kanal, MD, FACR, FISMRM, AANG Pittsburgh, Pennsylvania Why This Book? Nametipsascientiapotestasest[Knowledgeitselfispower]. -SirFrancis Bacon (OfHeresies, 1597) The pages thatfolloware, in averylarge part, an outgrowth of an intensive but accessible course in the physical basis and practical use of magnetic resonanceimaging(MRI) technology thatIhave had the privilege and plea- sure to present semiannually at Montefiore Medical Center/AlbertEinstein College ofMedicine since 1997.It isat the urging of numerous current and former students that I finally undertook to transform the contents of the course and itssyllabusinto acohesivewrittenwork. Myapproachinprepar- ingthis book has been to mirror the experience of the course, to the extent that ispossible giventhe restrictions of a one-sided conversation. The course remains oriented toward and open to anyone who wishes to understand MRI, from the ground up, asused in clinicalmedicine; it isnot merely a crash course to review for the radiology physics examinations. Whenthe study ofphysicsand technologyisbroachedamong clinicalradi- ologists, acommonrefrainis"why, beyondpassing our exams, do weneed to know it." The fact isthat most clinicalradiologists, simplybecause ofits seemingly overwhelming complexity and their heavy clinical workloads, remain largely in the dark with regard to the physical basis of the technol- ogythey wield.However,aswewillsee,alarge partofthe diagnosticpower ofMRIliesinunderstandingthe physical basis ofthe images you examine. Further, when, inevitably, images do not turn out asthey should, amodest awarenessofthe "innerworkings" ofMRIleaves the user poisedto under- stand and perhaps remedy the problem. I maintain that everything con- tained in these pages has direct importance and utility in clinical imaging. Nonetheless, asapart-timescientist, Ibelievethe materialisequallyuseful and importantfornonclinicians. The responsesofseveralgraduatestudents and faculty scientists who have attended the course looking for a rigorous but very approachable introduction have borne this out. In the interestofmakingthe materialasaccessible aspossible to aswide an audience as possible, I assume no specific background whatsoever on ix x WhyThisBook? the part of my students. (Attendees range from undergraduates to full professors but are predominately radiology residents.) Although it iscer- tainlytrue that mathematics isexquisitelywell-suitedfor expression ofthe concepts underlying MRI, I choose to take an entirely nonmathematical approach; onlyone equationneed be learned and recalled inorderto fully absorb the information. Where I do include equations, it isfor the benefit of those who find it a useful way to consolidate their understanding of concepts. Above all,thisbook isintendedfor users ofMRI; itisnot an exhaustive reference work and not apulse sequence developer's handbook. The book isdesigned to be read. Most importantly, however, I implore you to take the concepts detailed inthe followingpageswithyouasyoureviewclinical images,assessabnormalities, and confront artifacts and otherwise subopti- mal images. One thing I can virtually guarantee: when it comes to MRI, it is use it or lose it. Come join the users; the alternative doesn't sound very good! Michael L. Lipton, MD, PhD A User's Guide The scientistsoftoday think deeply instead ofclearly.One must be sane to think clearly,but one canthink deeply and be quite insane. -NikolaTesla (ModernMechanics andInventions,1934) We are forced to livewith[scientificadvances]whether wewant or not and try to make the best out ofit. -RichardR. Ernst (Nobel BanquetSpeech,1991) This book waswritten to be read. It is not a reference book but rather a conversationofsorts that you are invited tojoin. Our common goalwillbe a clear understanding of MRI. I begin at the beginning: the only prior knowledge requiredisofthe mostbasicconceptsofvectors-theiraddition and decomposition. A conciseexposition ofthis essential foundation topic isprovided in Appendix 1.With this smallbit of background in hand, the book canbe approached asaself-contained narrative,insequence, provid- ingacomprehensiveunderstandingofnuclear magnetic resonance (NMR) and basic and advanced MRI techniques. Alwayskeep clearlyinviewthat our goalisto understandessential prin- ciplesto the extent that they facilitate our understanding and enhance our application of clinicallyrelevant imagingtechniques. In order to maintain a readable narrative format, I have deliberately avoided specificliterature references for the myriad concepts and applications described in these pages.It goeswithout saying,however, that Icomeasanexpositor and not an originator of these concepts. As Dr. Emanuel Kanal once remarked to me (I paraphrase): As westruggle to understand this stuff,remember that someone figured it out the first time around! Those readers interested in morein-depth, specialized,ormathematicalapproachesmaywishtoconsult one of the sources listed in Appendix 4 and the original research cited in those references. I have divided the book into three parts. Part I covers the concepts of NMR, withoutcreatingan image, justanNMR signal.Thispartisimportant because it develops all of the concepts underlying image contrast that are xi
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