DOCUMENT RESUME

ED 292 657 SE 049 008

TITLE Magnetic Resonance Imaging. Statement, NationalInstitutes of Health Consensus Development Conference(Washington, D.C., October 26-28, 1987). Volume 6,Number 14, October 26, 1987.

INSTITUTION National Institutes of Health (DHHS), Bethesda,Md.

PUB DATE 87NOTE 12p.PUB TYPE Reports - Descriptive (141) -- Collected Works -

Conference Proceedings (021)

EDRS PRICE MF01/PC01 Plus Postage.DESCRIPTORS *Medicine; *Physics; *Radiology; Research and

Development; *Safety; Science and Society;*Technological Advancement

IDENTIFIERS *Magnetic Resonance Imaging

ABSTRACTMagnetic resonance imaging (MRI) is a new technique

that affords anatomic images in multiple planes and may provideinformation on tissue characterization. This document describes howMR images are obtained and discusses how they differ from thoseproduced by x-rays. The major portion of this report covers aconference held in October, 1987, which was designed to deal withsafety and efficacy of the MRI method. The report provides evidencethat was presented at the conference regarding the followingquestions: (1) are there contraindications to or risks of MRI? (2)what are the technological advantages and limitations (anddisadvant ges of MRI)? (3) what are the clinical indications for MRI,and how does it compare to other diagnostic modalities? and (4) whatare the directions for future research in MRI? (TW)

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MAGNETICRESONANCEIMAGING

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U.S. DEPARTMENT OF EDUCATIONOffice of Educational Research and Improvement

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National Institutes of HealthConsensus DevelopmentConference Statement

Volume 6 Number 14October 26, 1987

IN Introduction

IR Magnetic resonance imaging (11 sI) is"1 a new and innovative technique thatCfcv affords anatomic images in multiple

planes and may provide informationon tissue characterization. The firstmagnetic resonance image waspublished in 1973 by Lauterbur.Since that time, major technologicaladvances, together with increasingclinical and investigative interest inthe method, have been accompaniedby the development of equipmentthat is now clinically applicable toman, with potentially great benefitsin assessing pathophyrdologic states.

The MR images are obtained byplacing the patient or area ofinterest within a powerful, highlyuniform, static magnetic field.Magnetized protons (hydrogennuclei) within the-patient align likesmall magnets in this field.Radiofrequency pulses are thenutilized to create an oscillatingmagnetic field perpendicular to themain field, from which the nucleiabsorb energy and move out ofalignment with the static field, in astate of excitation. As the nucleireturn from excitation to theequilibrium state, a signal induced inthe receiver coil of the instrumentby the nuclear magnetization canthen be transformed by a series ofalgorithms into diagnostic images.Images based on different tissuecharacteristics can be obtained byvarying the number and sequence of

pulsed radiofrequency fields in orderto take advantage of magneticrelaxation properties of the tissues.

Magnetic resonance images differfrom those produced by x-rays: thelatter are associated with absorptionof x-ray energy, while MR imagesare based on proton density andproton relaxation dynamics. Thesevary according to the tissue underexamination and reflect its physicaland chemical properties.

In order to resolve issues regardingsafety and efficacy, the WarrenGrant Magnuson Clinical Center andthe Office of Medical Applications ofResearch of the National Institutesof Health (NIH) convened aconsensus conference on MI onOctober 26, 27, and 28, 1987. Theconference was cosponsored by theDivision of Research Resources, theNational Cancer Institute, theNational Heart, Lung, and BloodInstitute, the National Ins'dtute onAging, and the National Institute ofNeurological and CommunicativeDisorders and Stroke of the NIH;the Food and Drug Administration(FDA); and the National Institute ofMental Health.

At NIH, the ConsensusDevelopment Conference bringstogether investigators in thebiomedical sciences, clinicalinvestigators, practicing physicians,and consumer and special interestgroups to make r. scientific

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assessment of technologies, includingdrugs, devices, and procedures, andto seek agreement on their safetyand effectiveness.

During the first day-and-a-half ofthe meeting, a ConsensusDevelopment panel and members ofthe audience heard evidencepresented on the followingquestions:

Are there contraindications to orrisks of MRI?

What are the technologicaladvantages and limitations(disadvantages) of MRI?

What are the clinical indicationsfor MRI, and how does it compareto other diagnostic modalities?

What are the directions for futureresearch in MRI?

Members of the panel includedrepresentatives of internal medicine,neurology, neurosurgery, radiationoncology, radiology, clinicalepidemiology, surgery, the law, andthe hospital community.

The National Institutes of Healthurges that this summary statementbe posted, duplicated, anddistributed to interested staff.

BEST COPY AVAILABLE

The invited speakers includedphysicists, biomedical scientists,reproductive scientists, andradiologists with extensiveexperience in MRI in all of thesubspecialties of the field.

1.

Are there contraindications to orrisks of MRI?

MRI is generally safe when used inaccordance with the performancecharacteristics approved by theFDA. Risks are primarily related tothe static and oscillating magneticfields used in MRI. These fields arecapable of producing adversebiologic effects at a sufficiently highexposure, but effects have not beenobserved at the levels currentlyemployed in clinical practice.

The most important known risk isthe projectile effect, which involvesthe forceful attraction offerromagnetic objects to the magnet.Caution also must be exercisedwhen there are ferromagneticobjects embedded in the patient,such as shrapnel, or implants suchas pacemaker wires. MRI should notbe performed on patients withcardiac pacmakers or aneurysmclips.

Biologic effects of static magneticfields, such as ECG changes in Twave amplitude and magnetohydro-dynamic flow efiects, are transient.In the short-term studies reportedthus far, these do not appear to behazardous at field strengths below 2tesla. A preliminary case - controlstudy of male workers exposed tomagnetic fields has shown no trendsindicating a dose-response effect,but the number of subjects wassmall and the followup period short.

Rapidly changing gradient fields caninduce electric currents inconductive tissues. Recent studies

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indicate no interference with cardiacfunction or nerve conduction at 2 to 7tesla. The exposure levels approved bythe FDA, which are below those thatwould induce neuromuscularstimulation, are believed to providea wide margin of safety in this respect.

Heating may occur in tissues as aresult of resistive losses due tocirculating currents fromradiofrequency coils. High-fieldscanners are more likely to causemeasurable temperature elevationsthan low-field devices. Although noadverse effects have been observedat FDA-approved absorption rates,care must be taken with patientswhose heat loss mechanisms areimpaired and with hyperpyrexicindividuals. Pulse sequences shouldbe modified to prevent excessiveheat buildup, particularly in warmand humid environments.

Caution must be exercised in theMRI examination of infants, patientsrequiring monitoring and life-supportsystems, and patients who arepregnant. Although there is noevidence that magnetic and electricfields associated with MRI interferewith human development, in vitrostudies and theoretical predictionsraise the question of whetherexposure might pose risks to thedeveloping embryo and fetus.Therefore, MRI, as with allinterventions in pregnancy, shouldbe used during the first trimesteronly when there are clear medicalindications and it offers a definiteadvantage over other tests.

2.

What are the technologicaladvantages and limitatiofis(disadvantages) of MRI?

Advantages

MRI provides information thatdiffers from other imaging

modalities. Its major technologicaladvantage is that it can characterizeand discriminate among tissuesusing their physical and biochemicalproperties (water, iron, fat, andextravascular blood and itsbreakdown products). Blood flow,cerebrospinal fluid flow, andcontraction and relaxation of organs,both physiologic and pathologic, canbe evaluated. Because calcium emitsno signal on spin echo images,tissues surrounded by bone, such asthe contents of the posterior fossaand the spine, can be imaged, andbeam hardening artifacts areavoided. MRI produces sectionalimages of equivalent resolution inany projection without moving thepatient. The ability to obtain imagesin multiple planes adds to itsversatility and diagnostic utility andoffers special advantages forradiation andlor surgical treatmentplanning. Excellent delineation ofanatomic structures results frominherent high levels of contrastresolution.

Para- and superparamagneticcontrast agents, which appear to berelatively nontoxic, will soon beavailable in the United States. Theseagents should permit evaluation ofthe integrity of the blood-brainbarrier, the reticulo-endothelialsystem, and the extratellular space.

MR image acquisition does not useionizing radiation, nor does itrequire iodinated contrast agents.Because it requires little patientpreparation and is noninvasive,patient acceptability is high.

Disadvantages

The relatively slow scan acquisitiontime results in artifacts due tobiological (physiological) motion, e.g.,cardiac, vascular, cerebrospinal fluidpulsation, respiratory excursion, andgastrointestinal peristalsis.Technological advances now

evolving, such as tine MRI,improved surface coils, respiratory,cardiac, and peripheral gating,chemical shift imaging, and fastscanning (gradient refocusedimages), may resolve many of theseproblems. Sonic patients,particularly acutely ill patients,cannot cooperate and moveirt,mtartifacts result. Patient throughputis slow compared with other imagingmodalities.

Because of the small bore of themagnet, some patients experienceclaustrophobia and have difficulty incooperating during the study. Someobese patients cannot be examined.

The strong static magnetic field,which interferes with the properfunctioning of the usual life-supportequipment, and the small bore of themagnet make it difficult orimpossible to examine some criticallyill patients. Patients with pacemakersand ferromagnetic appliances cannotbe studied. MRI units requireuare.ful siting and shielding.

While the appearance of calcium asa signal void provides someadvantages, it also limits the abilityto detect pathological calcification insoft tissues and tumors, andpathological changes in cortical boneare poorly depicted, using routinespin echo techniques. Other imagingsequences may permit visualizationof some of these lesions.

Presently, contrast agents toenhance the MR images are notapproved for general use in theUnited States. Greater technologicalexpertise is required for utilizationof MRI than for most other imagingmodalities. These factors limit thepresent application of MRI.

MRI equipment is expensive topurchase, maintain, and operate.Hardware and software are stillbeing developed.

3.

What are the clinical indicationsfor MRI, and how does it compareto other diagnostic modalities?

MRI is an evolving tchnology thatin most instances has been evaluatedby small descriptive studies ratherthan by large, carefully designed,prospective studies. Some of ourjudgments about the role of MRIrelative to other imaging modalitiesare based on less rigorouslydesigned studies than are desirable.For those clinical situations whereMRI can potentially replace otherprocedures, especially invasive ones,these judgments should be verifiedby additional prospective studies.Furthermore, when other new,costly, or invasive imagingmodalities are introduced in thefuture, considerable attention shouldbe paid initially to the types ofclinical problems that should bestudied first, to the need for singleor multi-institutional studies, to thetiming of the evaluations, to therequirements for interpretiveexpertise, and to the potentialsources of funding for suchevaluations. A consensus conferencemight be a suitable vehicle for suchdeliberations.

The panel took the position that thediagnostic capability of MRI relativeto those of its competing modalitieswas the most important endpoint tobe assessed at this time. It shouldbe recognized that an experimentalapproach that optimizes theattainment of diagnostic informationcannot readily provide simultaneousinformation on the effect of MRI onother indices such as patientmanagement and patient outcomes.Finally, it deserves emphasis thatthe panel focused on clinical efficacyand not on cost considerations.

The Brain

Brain. Tumors

MRI is a superb method of studyingbrain tumors because of theexcellent contrast resolution, easymultiplanar imaging, and absence of.artifacts. MRI and CT are roughlyequivalent for detection of mostbrain tumors. Because of theabsence of bone artifacts, as seen onCT, MRI is superior at the vertex,in the posterior fossa, near the wallsof the middle fossa, at the base ofthe skull, and in the orbit. CT issuperior to MRI for detection ofmeningioma but requires contrastenhancement. MRI performance willbe improved further by the use ofcontrast-enhancing agents.

Gliomas and metastases.Supratentorial gliomas andmetastases are detected by eitherMRI or CT. Secondary effects of thetumor, such as herniation,hydrocephalus, and volumedisplacement of adjacent tissues, aredisplayed well with both CT andMRI, although more anatomicinformation is available withmultiplanar MRI. Tumor boundariesin gliomas and metastases may beobscured by extensive edema.Contrast-enhanced CT currently isbetter than unenhanced MRI fordefining the gross margin betweentumor and edematous brain. Neithermethod is definitive in establishing atissue diagnosis: Calcification isbetter seen with CT. Contrast-enhanced CT better demonstratessubarachnoid spread from malignanttumors than MRI. MRI is especiallyeffective in the demonstration ofintratentorial tumors.

Meningiomas. The characteristichyperdense appearance of thesetumors on contrast-enhanced scansand the hyperostosis of underlyingbone allow superior detection byCT. MRI may provide more

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information than CT about theeffect of the tumor on adjacentstructures.

Acoustic Nan/mos. MRIdemonstrates smaller tumors betterthan CT, without the need forintrathecal air or contrast material,but larger tumors are well visualizedby both CT and MRI.

Pituitary Tumors. Both MRI andcontrast-enhanced CT are effectivein defininv pituitary tumors, butMRI may provide more informationabout the precise extent of thelesions and their.effect on adjacentstructures. Early studies suggestthat MRI may be superior fordetection of intrasellarmicroadenomas. MRI appears to besomewhat better in the diagnosis ofsome other suprasellar tumors,primarily because of its multiplanarcapabilities and the absence of boneartifacts.

Reexamination. The factors thatdictate the use of MRI or CT as theoriginal detection tool also apply tofollowup studies.

Nonneoplastic Disease

Any insult to the structural integrityof the brain associated withalteration in water content ormyelin can be reflected in abnormalsignal intensity on MRI. Thus, MRIis sensitive to the detection of awide variety of nonneoplasticprocesses affecting the brain. Inmany instances, the sensitivity ofMRI exceeds that of CT.

Ischemia. Within a few hours aftervascular occlusion, detection andlocalization of cerebral infarction ispossible with MRI, while CT (evenwith contrast enhancement) oftenyields equivocal or negative resultsin the first 24 to 48 hours. In thesubacute and chronic stages of

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stroke, MRI and CT provideequivalent information.

Hemorrhage. Within the first 24 to48 hours, acute intracranialhemorrhage, whether subarachnoid,intraparenchymal, or subdural, isnot easily detected with MRI but ismore reliably demonstrated on CT.The subacute hematoma (age 10 to20 days) is readily detected on MRI,while it may be much less conspicuouson CT. Thus, the two modalities havecomplementary roles in detection ofhemorrhageCT is more sensitive inacute hemorrhage, while MRI ismore sensitive in subacutehemorrhage. Unenhanced CT isoften the preferred initial study inpatients with stroke because of theclinical need to determine the,presence of hemorrhage.

Arteriovenous Malformations. MRIis exquisitely sensitive to flowingblood and has proven particularlyeffective in the detection andlocalization of vascularmalformations, including some"cryptic" malformations not evidenton cerebral arteriography.Arteriography remains necessary forthe pretherapeutic assessment ofsymptomatic malformations.

Trauma

In head trauma, MRI has provenuseful in the detection of all types ofintracranial hemorrhage, includinghemorrhagic contusions and shearinginjuries. During the first 1 to 3 daysafter injury, however, CT ispreferable not only becauseexamination time is shorter but alsobecause hemorrhage at this time ismore reliably demonstrated by CT.

Disorders of Myelination

Diseases associated withdemyelination or dysmyelination arereadily detected with MRI. MRI isrecognized as the preferred and

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most sensitive imaging technique forthe diagnosis of multiple sclerosis (MS),but MRI alone cannot establish adefinite diagnosis of MS in theabsence of strong clinical findings.Mid also exhibits greater sensitivityin the detection of radiation injuryto the brain than does CT. However,in the followup of patients afterradiation therapy or chemotherapyfor malignant intracranial neoplasm,neither MRI nor CT permitdifferentiation of late radiationinjury from recurrent tumor.

Dementia

The diagnosis of dementia requires aclinical neurological evaluation. Inthe assessment of dementia, eitherCT or MRI can be used todemonstrate remediable lesions.MRI demonstrates more lesions thanCT in patients with multi-infarctdementia. In older individuals,however, often without dementia,MRI also demonstrates high signalareas in white matter onT2-weighted images of uncertainclinical significance.

Infection

MRI demonstrates areas ofcerebritis and abscess formation in amanner similar to CT. White matteredema associated with inflammationis readily detected by MRI and mayallow earlier initiation of specifictreatment in certain illnesses suchas herpes simplex encephalitis.

Head and Neck

In the detection, localization, andtreatment planning of head andneck tumors, MRI offers anadvantage over CT due to itsmultiplanar capabilities, tissuecharacterization potential, and theabsence of bone and teeth artifacts.MRI affords ready distinction ofvessels from lymph nodes. MRI alsodepiLis the contents of the orbit.

The Spine

Surface coils constitute an integralpart of the MRI examination of thespine.

Tumors

MRI of the spinal canal has theadvantage over myelography ofdirect, noninvasive visualization ofthe spinal cord rather than merelyoutlining its margins. MRI is capableof demonstrating the entire spinalcord and of differentiating solidfrom cystic intramedullary tumors.Indications for myelography havedecreased considerably, and it maybecome obsolete in the future withthe wider availability of high-qualityMRI. An example of this is the useof MRI for the diagnosis andlocalization of acute spinal cordcompression. Intraduralextramedullary tumors are bestdemonstrated by MRI ormyelography.

Syringomyelia

MRI is the diagnostic method ofchoice and is considered to besuperior to both myelography andCT.

Degenerative Disc Disease

MRI is equivalent to CTmyelography in the evaluation ofherniated disc at the cervical andthoracic levels and is as good as orbetter than myelography. At thelumbar level, MRI is better than orequal to CT and is more accuratethan myelography. In spinalstenosis, MRI and CT are roughlyequivalent in diagnostic informationand less invasive than myelography.CT myel. : ihy provides thegreatest I ostic accuracy forcervical radiculopathy due tohypertrophk degenerative changes.

Trauma

When the patient's condition allows,MRI demonstrates the alteredrelationship between vertebralbodies, discs, spinal cord, and nerveroots. It is less applicable to thestudy of spinal stability and theintegrity of articular facets than CTor conventional radiography.

Congenital Disorders

Spinal cord abnormalities associatedwith congenital spinal dysraphismare most advantageously studied byMRI.

Infection

MRI and radionuclide scans aremore sensitive than CT for the earlydetection of osteomyelitis.

The great accuracy of both MRI andCT in defirjng spinal anatomicalchanges poses a particular challengeto clinicians. Correlative clinicalstudies to relate these changes withpatients' symptoms and outcome oftherapy are urgently needed.

The Cardiovascular System

MRI is particularly valuable as atechnique for imaging the heart andgreat vessels because flowing bloodproduces a unique signal. Therefore,no contrast medium is required todefine the cardiac chambers and thelumen and location of the greatvessels. Cardiac evaluation requireseither ECG gated MRI or tine MRI.

Ischentic Heart Disease

At the present time MRI has limitedusefulness in evaluating ischemicheart disease. It cannot substitutefor coronary arteriography indefining coronary artery anatomy. Itapparently can delineate infarctedmyocardium and adjacent residualviable myocardium. With

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paramagnetic contrast media it maybe possible to define regions ofacute scheinia. Gated MRI can beused to delineate scarring caused byprevious infarction, ventricularaneurysm, and chamber thrombi.

Cardiomyopathies

Gated mm defines the endocardialand epicardial surfaces, making itpossible to determine mural andseptal thickness, ventricular volume,and performance. Two-dimensionalechocardiography and radionuclidetechniques provide informationsimilar to MRI.

Valvular. Heart Disease

The recent development of tineMRI, which permits rapid dynamicimaging, makes it possible toevaluate ventricular performanceand to estimate the severity ofvalvular regurgitation. The relativevalues of 2-1) and Dopplerechocardiography, other noninvasivemethods, and the tine MRItechnique have yet to bedetermined.

Pericardial Disease

Gated MRI is being used to evaluatepericardial disease, butechocardiography remains theprocedure of choice because of lowercost, portability, and availability.

Intracardiac and ParacardiacMasses

MRI depicts the pericardium,cardiac chambers and walls, and thegreat vessels in the mediastinum.For imaging of intracardiac andparacardiac masses, MRI appears tobe superior to CT, althoughechocardiography remains theprimary screening procedure forintracardiac masses.

Congenital Heart Disease

MRI, through definition of thecardiac chambers, great vessels, andflow patterns, represents animportant noninvasive diagnosticimaging method in. congenital heartdisease. Because of the relativelylong times required for MRI, ECGgating or tine MRI is important tooptimize its value. Gated MRI iscapable of defining manymalformations of the cardiacchambers and the great vessels,such as transposition and pulmonaryatresia. Two-D and pulsed Dopplerechocardiography continue to be theprimary initial screening techniquesand provide information on pressureand flow in addition to cardiacanatomy.

Aorta

While CT has served as a screeningmethod in aortic dissection, theanatomic findings required forsurgery have been determinedprimarily by angiography. MRIpermits visualization of the aorticroot and detects intramuralhemorrhage, wall separation, andintimal flap. It may improve thescreening of suspected cases, but itis uncertain that it will obviate theneed for contrast angiography. Itpermits the distinction betweenaortic dissection and aneurysm ofthe thoracic and abdominal aorta.CT scanning has been accurate indelineating aortic size, change inaneurysm dimensions, and aorticaneurysmal bleeding. MRI has asimilar potential.

Thorax

Staging of BronchogenicCarcinoma

MRI is comparable to CT indiagnosing mediastinal adenopathy.The current interpretive criteria forMRI (as based on node size) are

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derived from and are identical tothose used for CT. MRI is superiorto unenhanced CT, however, inevaluating hilar masses, and isequivalent to enhanced CT. BecauseCT can evaluate the mediastinumand the upper abdomen as well asthe lungs and abdomen as part ofone examination, it is currently themethod of choice for stagingbronchogenic carcinoma.

Evaluation of Mediastinal Masses

MRI, because of its multiplanarimaging potential, providesinformation for determining theanatomic relationship betweenmediastinal masses and the greatvessels that is not always availablewith CT.

Evaluation of Parenchymal orHilar Masses

CT is used for the detection ofpulmonary nodules. In solitarypulmonary nodules, CT is preferredto MRI for assessing benignity.Because of the ability of MRI tovisualize flowing blood, it ispreferred to unenhanced CT fordetermining whether hilar orparenchymal masses are solid orvascular.

Liver

MRI is equivalent to contrast-enhanced CT in the detection ofpatients with metastases to the liverfrom carcinoma. The use ofiodinated contrast agents may beavoided with MRI. Cysts andhemangiomas, two common benignlesions, are relatively wellcharacterized by MRI.

Pancreas and Spleen

For evaluating lesions of thepancreas and spleen, CT is superiorto MRI.

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Kidney

Renal Masses

In detecting renal masses, MRI isapparently equivalent to CT, withspecific limitations noted below.Cysts and angiomyolipomas can becharacterized as with CT, andcomplicated cysts, containinghemorrhage, can be identified.

Benign tumors can be visualized butnot reliably distinguished frommalignant neoplasms.

Malignant tumors are identified andstaged as with CT, but the limitedability of MRI to detectcalcifications and define smalltumors is a drawback. MRI is usefulfor demonstrating vascular invasion.

Thus, MRI may be used in selectedcases when CT examination isequivocal or when iodinated contrastmaterial is contraindicated.

Renal Transplants

The normal corticomedullaryjunction of the kidney isdemonstrated with MRI. When thejunction is not visualized, thediagnosis of graft rejection can besuggested. Although MRI is useful,Doppler ultrasound appears to bemore sensitive and specific.

Adrenal Gland

MRI is equal to high resolution CTin visualizing the normal gland andin detecting lesions such ashyperplasia, adenoma, aldosteronoma,pheochromocytoma, and primarycarcinoma, as well as metastasis.Pheochromocytomas have an MRIintensity pattern that seems to becharacteristic. Furthermore, thediagnosis can be made without usingcontrast agents, to which patientssometimes react. Other lesionscannot be reliably characterized.

Female Pelvis

The uses of MRI in gynecologicdisease.are in the early stages ofinvestigation, but the ability of theexamination to depict anatmny inthree orthogonal planes aflids apotentially useful method of stagingtumors and selecting and planningthe treatment to be employed. MRIis not a screening modality and doesnot permit specific tissue diagnoses.

The application of MRI in high-riskobstetrical practice requires furtherexploration.

Carcinoma of Endometrium

MRI shows promise as a means ofstaging as compared to physicalexamination or CT. The choice oftherapy may depend on tumorvolume, site, and depth ofmyometrial invasion, all of whichcan frequently be demonstrated byMRI.

Carcinoma of the Cervix

The value of MRI in staging cervicalcarcinoma lies in its ability todemonstrate the tumor directly,. tocalculate its volume, and to evaluateextension to adjacent organsaccurately. Although useful forstaging in selected cases, it has noapparent advantage over CT in thedetection of lymph node metastases.

In both endometrial and cervicalcarcinoma, the capacity of MRI todepict concomitant pelvic lesionsadds to its value.

Male Pelvis

Prostate

While it does not permit reliabledifferentiation of prostaticcarcinoma from benign prostatichypertrophy, MRI represents apromising method for staging the

extent of carcinomatous spreadoutside the capsule of the prostategland and appears to be equivalentto CT in this regard. Metastases toregional lymph nodes appear to bedetected by MRI and CT with equalefficacy.

Bladder

In staging bladder carcinoma, MRIcannot distinguish mucosal lesionsfrom those with superficial muscularinvasion, but it is effective instaging tumors that have invadedthe deep muscle layers, theperivesical fat, and adjacent organsand lymph nodes. While no largeprospective studies comparing MRIwith CT are available, preliminarydata indicate that tumor stagingwith MRI is as accurate as with CT.

Scrotum

In the scrotum, MRI permitsdistinction of intratesticular fromextratesticular lesions. It appears tohave no diagnostic advantage overultrasound, except when examiningthe painful scrotum.

Rectum

The staging of rectal neoplasms aswell as the differentiation ofrecurrent tumor from fibrosis in therectal wall represents, problems thatrequire further study.

Musculoskeletal System

Surface coils are essential foradequate examination of many areasin the musculoskeletal system.

Joints

MRI demonstrates the articularcartilages as well as adjacentmuscles and tendons. Because it isnoninvasive, MRI may be preferableto arthrography and arthroscopy inthe study of the knee. It is also

useful for evaluation of thetemporomandibular joint. The use ofMRI in the examination of otherjoints requires further evaluation.

Marrow Space

MRI reflects changes in the marrowspace by primary tumors andinfection. The local extent ofprimary bone tumors can be stagedbest by MRI. Metastatic tumor canbe demonstrated with MRI, whichapparently is more sensitive thanradionuclide bone scanning.

Aseptic Necrosis of Bone

MRI is superior to radionuclideimaging in the detection of the earlychanges. Preliminary data suggestthat MRI is better than CT.

Soft Tissue Tumors

MRI provides important informationregarding muscle, nerve, and vesselinvasion or entrapment in malignantsoft tissue tumors. A postoperativebaseline MRI study can be helpfulwhen the possibility of recurrencemust subsequently be evaluated.

Trauma

Because of the excellent contrastresolution of soft tissues, MRIdemonstrates muscle and ligamenttears and hematomas well. This maybe useful in following the evolutionof these lesions.

Contrast Media for MRI

Contrast agents are currently beingevaluated in laboratory and clinicalstudies. These agents, by alteringinherent tissue response to magneticfields, offer the promise of evengreater sensitivity for detection andimproved lesion characterization.They fall into two classes:paramagnetic materials, which havediagnostic properties similar to

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iodinated radiographic contrastagents, and even more potentsuperparamignetic materials, whichhave a wide area of effect.Gadolinium (Gd) DTPA appearssafer than iodinated contrast media.

Intravenous infusion of Gd-DTPAdemonstrates breakdown of theblood -brain barrier on Tl-weightedMRI studies, and such imagespermit improved definition of grossmargins of tumor, abscess, orinfirct. Outside the brain, the use ofcontrast-enhanced MRI may identifyareas of altered circulation due toinflammation, other soft tissueinjury, or neoplastic spread.

4.

Whet are the directions for futureresearch in MRI?

The role of MRI in the managementof the patient needs to be defined.What does it replace in existingdiagnostic algorithms? To what is itcomplementary? For example, willthe need for CT, ultrasound, andarteriography decrease? How doesthe information provided affectdiagnosis, staging, therapy, andpatient outcome? The answers tothese questions will require well-designed and well-conducted studiescomparing the efficacy of MRI withexisting diagnostic techniques.

Positron emission tomography (PET)can spatially image metabolicprocesses. To what extent is MRIcapable of fulfilling a similarfunction in regard to pH, blood flow,blood volume, and the metabolism ofoxygen and glucose? Similarly, PEThas been used to study neurotrans-mitters and their receptors; canMRI be applied for this purpose notonly to the central nervous systembut also to different membranereceptors in other organs?

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ININ=IMIL

Diagnostic imaging is concernedwith detection, localization, andtissue characterization. MRI hasbeen shown to be effective for allthree but offers special promise fortissue characterization. Futurepotential for MRI includesnonproton imaging, for example,phosphorus and sodium. Thecombination of imaging withlocalized in vivo spectroscopy mayyield fundamental informationregarding the metabolic status of aparticular organ or lesion. Forexample, phosphorus metaboliteconcentration may be measurable asa reflection of the state ofoxygenation of the myocardium orof tumors. In vitro spectroscopyoffers a method for examiningbiologic material of various types,for example, tissue fluids, pathologicspecimens, and cells in culture.

Further exploration of theapplications of MRI to the vascularsystem is required. It appears tohave promise as a means ofassessing peripheral venous diseasenoninvasively.

Although considerable developmentof equipment for MRI has occurred,there appear to be opportunities forenhancing both hardware andsoftware. Improving the techniquesof MRI includes the selection of theappropriate energy of the magnet,optimization of the magnetic fieldstrength in use, the fabrication ofefficient surface coils, the evaluationof new pulse sequences, and thedevelopment of computer softwareleading to the richer utilization ofthe available data.

Gadolinium DTPA has promise as acontrast agent for MRI. Thereshould be an active search for andan evaluation of other classes ofcontrast agents applicable to MRI.Paramagnetic-labeled pharmaceuticalsand monoclonal antibodies offer newopportunities for acquiring anatomic,

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physiologic, and pharmacologicinformation. For example, there aredisorders characterized byqualitatively or quantitativelyabnormal receptor sites that wouldlend themselves to study using theseagents.

It appears that MRI is a safemodality for imaging. Nevertheless,there must be continuinginvestigation of its secondary effectssuch as local heating of tissues. Thisis necessary as higher fieldstrengths and rapid imagingtechniques are more widely utilized.There is a need for long-termstudies of the potential somatic andgenetic effects of magneticresonance. These should considernot only the patient but also thoseindividuals exposed occupationally.

Conclusion

MRI is an innovative technique thatprovides images of the body in manydifferent planes and represents anextraordinary addition to ourdiagnostic armamentarium. Theimages generated vary according tothe tissues examined and reflecttheir physical and chemicalproperties. It is noninvasive, appearsto be relatively innocuous in clinicalapplication, and involves noexposure to ionizing radiation.

Even in the short period of its use,it has proved to be unusuallyrewarding in the detection,localization, and assessment ofextent and character of disease inthe central nervous, musculoskeletal,and cardiovascular systems. In thebrain, for example, it has a provencapacity to define some tumors andthe plaques of multiple sclerosisprovided by no other technique. It isa competing imaging method in theevaluation of many other organs.Additional prospective studiescomparing MRI with otherdiagnostic methods are essential in

those areas where the method hasshown promise but where its preciserole has not yet been defined. Thitconsensus development conferencedoes not purport to include all ofthe applications of MRI to thepediatric patient, a subject that willrequire separate consideration.

Although MRI can be used withoutcontrast media, the information itgenerates can be augmented bycontrast agents now beingintroduced.

The full potential of MRI has notbeen reache4, and continuingrefinement or equipment, contrastagents, and software may beanticipated. As higher magnetstrengths and rapid imagingsequences are investigated, furtherstudy of the long-term biologiceffects of magnetic fields isrequired.

Members of the ConsensusDevelopment Panel were:

Herbert L. Abrams, M.D., M.A.Panel and Conference ChairpersonProfessor of RadiologyStanford University School of MedicinePhilip H. Cook Professor of Radiology,

EmeritusHarvard Medical SchoolClinical Professor of RadiologyUniversity of California School of

Medicine at San FranciscoStanford University School of MedicineStanford, California

Alfred S. Berne, M.D.DirectorDepartment of Medical ImagingCrouse Irving Memorial HospitalSyracuse, New York

Gerald D. Dodd, M.D.Professor and HeadDivision of Diagnostic ImagingUniversity of Texas M.D. Anderson

HospitalHouston, Texas

Harold T. Dodge, M.D.Professor of MedicineUniversity of Washington School of

MedicineSeattle, Washington

Sid Gilman, M.D.Professor and ChairmanDepartment of NeurologyUniversity of MichiganAnn Arbor, Michigan

Samuel Hellman, M.D.Physician-in-ChiefMemorial Sloan-Kettering Cancer CenterNew York, New York

Charles A. Hufnagel, M.D.Professor of SurgeryUniformed Services University

of the Health Sciences Medical SchoolEmeritus Professor of SurgeryGeorgetown University School of

MedicineWashington, D.C.

Stephen A. Kieffer, M.D.Professor and ChairmanDepartment of RadiologyState University of New York

Health Science CenterSyracuse, New York

John A. Kirkpatrick, Jr., M.D.Radiologist-in-ChiefProfessor of RadiologyHarvard Medical SchoolChildren's HospitalBoston, Massachusetts

Don M. Long, M.D., Ph.D.Professor and ChairmanDepartment of NeurosurgeryJohns Hopkins University

School of MedicineBaltimore, Maryland

James J. McCort, M.D.Immediate Past PresidentRadiological Society of North AmericaChairmanDepartment of RadiologySanta Clara Valley Medical CenterSan Jose, California

Barbara J. McNeil, M.D., Ph.D.Professor of Radiology and Clinical

EpidemiologyHarvard Medical SchoolBrigham and Women's HospitalBoston, Massachusetts

Maxwell J. Mehlman, J.D.Associate Professor and DirectorLaw-Medicine CenterCase Western Reserve UniversityCleveland, Ohio

Constance F. Row, F.A.C.H.E.PresidentCalvert Memorial HospitalPrince Frederick, Maryland

J. Sanford Schwartz, M.D.Associate Professor of MedicineSenior FellowLeonard Davis Institute of Health

EconomicsUniversity of PennsylvaniaPhiladelphia, Pennsylvania

Mentr,,ers of the Planning Committeewere:

John L. Doppman, M.D.Planning Committee ChairpersonDirector of Diagnostic RadiologyClinical CenterNational Institutes of HealthBethesda, Maryland

Herbert L. Abrams, k 1)., M.A.Panel and Conference ChairpersonProfessor of .RadiologyStanford University School of MedicinePhilip H. Cook Professor of Radiology,

EmeritusHarvard Medical SchoolClinical Professor. of RadiologyUniversity of California School of

Medicine at San FranciscoStanford University School of MedicineStanford, California

Edwin D. Becker, Ph.D.Associate Director for Research ServicesOffice of the DirectorNational Institutes of HealthBethesda, Maryland

Charles L. Coulter, Ph.D.HeadBiophysics SectionBiomedical Research Technology

ProgramDivision, of Research ResourcesNational Institutes of HealthBethesda, Maryland

Giovanni Di Chiro, M.D.ChiefNeuroimaging SectionDivision of Intramural ResearchNational Institute of Neurological and

Communicative Disorders and StrokeNational Institutes of HealthBethesda, Maryland

Andrew J. Dwyer, M.D.DirectorClinical MRIDepartment of RadiologyClinical CenterNational; Institutes of HealthBethesda, Maryland

Jerry M. ElliottProgram AnalystOffice of Medical Applications ofResearchNational Institutes of HealthBethesda, Maryland

Robert P. Friedland, M.D.ChiefBrain Aging and Dementia SectionLaboratory of NeurosciencesNational Institute on AgingNational Institutes of HealthBethesda, Maryland

Victor M. Houghton, M.D.ProfessorDepartment of RadiologyChiefNeuroradiology ResearchMedical College of WisconsinMilwaukee, Wisconsin

D.I. Houk, D. Phil., M.A.Physical'ScientistBiomedical Engineering andInstrumentation

Branch

Division 'of Research QlrvicesNational Institutes of rfealthBethesda, Miryland

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Gordon Johnson, M.D.Acting DirectorOffice of Health AffairsCenter for Devices and RadiologicalHealthFood and Drug AdministrationSilver Spring, Maryland

Stephen H. Koslow, Ph.D.ChiefNeuroscience Research BranchNational Institute of Mental HealthRockville, Maryland

Paul C. Lauterbur, Ph.D.ProfessorMedical Information S.ciesce and

ChemistryUnivers4 of Illinois at

Urbana-ChampaignUrbana, Illinois

Alexander R. Margulis, M.D.Professor and ChairmanDepartment of RadiologyUniversity of California at San FranciscoSan Francisco, California

Martin Rose, M.D.Former Chief Medical OfficerOffice of Medical Applications of

ResearchNational Institutes of HealthBethesda, Maryland

Francis F. Ruzicka, M.D.Chief Diagnostic Imaging Research

BranchRadiation Research ProgramDivision of Cancer TreatmentNational Cancer InstituteNational Institutes of HealthBethesda, Maryland

Michael J. BernsteinDirector of CommunicationsOffice of Medical Applications of

ResearchNational Institutes of HealthBethesda, Maryland

Colleen HenrichsenDeputy ChiefClinical Center CommunicationsNational Institutes of HealthBethesda, Maryland

The Conference was sponsored by

Warren Grant Magnuson CenterJohn L. Decker, M.D.Direct

Division of Research ResourcesBetty H. Pickett, Ph.D.Director

National Cancer InstituteVincent T. DeVita, Jr., M.D.Director

National Heart, Lung, and BloodInstitute

Claude !Ardent, M.D.Director

National Institute onT. Franklin Williams, M.D.Director

National Institute of Neurological andCommunicative Disorders and Stroke

Murray Goldstein, D.O.Director

Food and Drug AdministrationFrank E. Young, M.D.Commissioner

National Institute of Mental HealthFrederick K. Goodwin, M.D.Director

ce of Medical Applications ofesearch

William T. Friederald, M.D.Acting Director

*U. S. GOVERNMENT PRINTING OFFICE: 1988-207-026

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U.S. DEPARTMENT OF HEALTHBulk Rate

AND HUMAN SERVICESPostage and Fees Paid

Public Health ServicePHS/NIH/OD

Office of Medical Applications of ResearchPermit No. G291

Building 1, Room 216Bethesda, MD 20892

*046436EDUC RESOURCES INFO CIE ***NAIL INST OF EDUCATIONWASHINGTON, EC 202..)8

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Public Health Service National Institutes of Health

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