127

The [18F]Fluorodeoxyglucose Method for theMeasurement of Local Cerebral Glucose

Utilization in Man

M. REIVICH,' D. KUHL,2 A. WOLF,3 J. GREENBERG,' M. PHELPS,2 T. IDO,3 V. CASELLA,3

J. FOWLER, 3 E. HOFFMAN,2 A. ALAVI,2 P. SOM,3 AND L. SOKOLOFF4

SUMMARY A method has been developed to measure local glucose consumption in the variousstructures of the brain in man with three-dimensional resolution. [18F]-2-deoxy-2-fluoro-D-gluco8e isused as a tracer for the exchange of glucose between plasma and brain and its phosphorylatdon byhexokinase in the tissue. A mathematical model and derived operational equation are used whichenable local cerebral glucose consumption to be calculated in terms of the following measurablevariables. An intravenous bolus of [I8F]-2-deoxy-2-fluoro-D-glucose is given and the arterial specificactivity monitored for a predetermined period of from 30 to 120 minutes. Starting at 30 minutes, theactivity in a series of sections through the brain is determined with three-dimensional resolution by anemission tomographic scanner. The method was used to measure local cerebral glucose consumptionin two normal volunteers. The values in gray matter structures range from 5.79 mg/100 g per minutein the cerebellar cortex to 10.27 in the visual cortex, whereas, in white matter structures, the valuesrange from 3.64 mg/100 g per minute in the corpus callosum to 4.22 in the occipital lobe. Averagevalues for gray matter, white matter, and whole brain metabolic rates, calculated as a weighted averagebased on the approximate volume of each structure, are 8.05, 3.80, and 5.90 mg/100 g per minute,respectively. The value of 5.9 mg/100 g per minute compares favorably with values previously reported.Ore Res 44: 127-137, 1979

THE ABILITY to measure regional cerebral bloodflow in man has greatly increased our understandingof cerebral hemodynamics, particularly in patho-physiological states. The ability to detect altera-tions in local cerebral metabolism in man would bevaluable in advancing our understanding of manydisorders of the brain. We have developed such atechnique which uses [18F]-2-deoxy-2-fluoro-D-glu-cose ([18F]-FDG).

The development of the Kety-Schmidt techniquefor the quantitative measurement of cerebral bloodflow in man made it possible to determine theaverage rates of glucose utilization in the brain asa whole from measurements of blood flow and thecerebral arteriovenous difference of glucose (Ketyand Schmidt, 1948). This method has added signifi-cantly to our knowledge of cerebral metabolism innormal and pathological states even though it pro-

From the 'Cerebrovascular Research Center, Department of Neurol-ogy, and the "Division of Nuclear Medicine, Department of Radiology,University of Pennsylvania School of Medicine, Philadelphia, Pennsyl-vania; the ^Department of Chemistry, BrooVhaven National Laboratory,Upton, New York; and the 4Laboratory of CerebraJ Metabolism, NationalInstitute of Mental Health, Bethesda, Maryland.

Presented in part at the 8th Cerebral Blood Flow Symposium inCopenhagen, Denmark, June 27-30, 1977.

Supported by U.S. Public Health Service Program Project Grant NS10939-05, Research Grant GM-16248, and ERDA Contract E(ll-l)-3399.

Present address for Drs. KuhJ, Phelps, and Hoffman: Division ofNuclear Medicine, UCLA School of Medicine, Los Angeles, California90024.

Address for reprints. Martin Reivich, M.D., Cerebrovascular ResearchCenter, 4th Floor, Piersol Building, Hospital of the University of Penn-sylvania, Philadelphia, Pennsylvania 19104.

Received February 15, 1978; accepted for publication July 25, 1978.

vides only an average value for the whole brain. Amethod to measure hemispheric cerebral glucoseuptake has been developed which also makes use ofblood flow and arteriovenous difference measure-ments (Meyer and Shinohara, 1970). Recently, thebasis for the use of uC-glucose for the measurementof regional cerebral glucose utilization has beenpublished (Raichle et al., 1978). However, no re-gional measurements have been reported as yet,and the method has not been applied to man.Because it is often not possible to detect regionalchanges in metabolism from measurements inmixed cerebral venous blood, and because manydisorders as well as many physiological changesaffecting the brain occur on a regional basis, itwould be useful to make regional measurements ofglucose utilization in the brain in man.

A method has been developed for the measure-ment of regional cerebral oxygen uptake (Ter-Po-gossian et al., 1970), but this technique has not beenused to obtain truly regional information withthree-dimensional resolution. The technique wehave developed for measuring the local cerebralmetabolic rate for glucose (LCMRgi) does give suchthree-dimensional information. Furthermore, glu-cose utilization is stoicbiometrically related to oxy-gen consumption in the aerobic state, except in afew situations such as starvation and insulin hypo-glycemia, and provides a measure of energy metab-olism in the anaerobic state as well.

The present technique is based on the previouslydescribed (Sokoloff et al., 1977) [14C]-2-deoxyglu-

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cose ([MC]-DG) method for measuring LCMRg] au-toradiographically in animals. In this method,[UC]-DG is used as a tracer for the exchange ofglucose between plasma and brain and is phospho-rylated by hexokinase in the tissues. [HC]-DG isused because the labeled product, [uC]-deoxyglu-cose-6-phosphate, is essentially trapped in the tis-sue over the time course of the measurements. Amodel was designed based on the assumptions of asteady state for glucose consumption, a first-orderequilibration of the free [14C]-DG pool in the tissuewith the plasma level, and relative rates of phos-phorylation of [14C]-DG and glucose determined bytheir relative concentrations in the precursor poolsand their respective kinetic constants for the hexo-kinase reaction. The following operational equationbased on this model has been derived in terms ofdeterminable variables:

CT*(T) - k,*e

R =

L * > V - » l K - J|_Jo

meeting the requirements for external detectionand acceptable radiation dosimetry.

Because [18F]-FDG had not been synthesized pre-viously; a novel synthetic route to FDG, which wasused in the 18F labeling, was devised (Ido et al.,1978). [18F]-FDG as well as [HC]-FDG was used instudies to determine whether the former would bea suitable tracer for use in man.

Methods

RadiophannaceuticalsPSFJ-FDG

The direct fluorination of 3,4,6-tri-O-acetyl-D-glucal with high specific activity [18F]-fluorine (Ca-sella, V, Ido, T., and Wolf, A. P., unpublishedobservation) gave [18F]-3,4,6-tri-O-acetyl-2-deoxy-

(1)

Jowhere R = the calculated rate of glucose consump-tion per gram of tissue; Cr* = the concentration ofDG + DG-6-P0* in the tissue; Cp* and Cp = thearterial plasma concentrations of DG and glucose,respectively; ki*, k2*, and Its* are the rate constantsfor the transport from plasma to the tissue precur-sor pool, for the transport back from tissue toplasma, and for the phosphorylation of DG in thetissue, respectively; A = the ratio of the distributionvolume of DG in the tissue to that of glucose; <j> =the fraction of glucose that, once phosphorylated,continues down the glycolytic pathway; and Km*and Vniu* and Km and V ^ are the kinetic constantsof hexokinase for DG and glucose, respectively. Thelatter six constants can be combined into one con-stant, which has been designated the lumped con-stant (X-Vnuu,*.Km/$-VimU[.K1»*).

The extension of this method to man requires theuse of a tracer (radiopharmaceutical) that satisfiesthe following criteria: (1) The tracer must be takenup by the brain at a rate proportional to that ofglucose, and its metabolic products must remainwithin the tissue in a known form, as is the casewith DG. (2) The tracer must be labeled with a y-emitting radionuclide which is chemically stable invivo and which can be detected through the skullusing emission tomography. (3) The radiation ex-posure resulting from the use of this tracer must besafe.

A labeled analogue to DG which appears to sat-isfy these requirements is [18F]-FDG. Previous stud-ies had shown that FDG, like DG, is a good sub-strate for yeast hexokinase (Bessell et al., 1972).Furthermore, fluorine-18 decays by positron emis-sion, upon annihilation produces two 511-keV pho-tons, and has a short half-life (110 minutes), thereby

2-fluoro-D-glucopyranosyl fluoride, which was hy-drolyzed to [18F]-FDG (Ido et al., 1978). The radi-ochemical purity was >98% as determined by thinlayer chromatography on cellulose using isobutyricacid-ammonia-water (66:1:33), Rf = 0.67. Pharma-ceutical quality [18F]-FDG in isotonic saline for usein the human studies was sterilized by terminalMillipore (0.22 im) filtration. The preparation wascarried out according to a protocol that was dem-onstrated on three successive runs to yield a sterile,pyrogen-free product.* The specific activity! of[18F]-FDG at the end of synthesis (i.e., the timewhen preparation of injectible radiopharmaceuticalis completed) was 11 mCi/mg and 16 mCi/mg forthe two human studies.

FCJFDGD- (U[HC]} -glucose (from Amersham/Searle or

Schwarz/Mann) was converted to [uC]-3,4,6-tri-O-acetyl-D-glucal, which was then converted to [UC]-FDG by two methods. (1) Fluorination with trifluo-romethyl hypofluorite (CF3OF), according to themethod of Adamson et al. (1970), gave [UC]-FDGin >98% radiochemical purity as determined by thinlayer chromatography on silica gel with ethanol-ethyl acetate (1:1), R/= 0.67, with a specific activityof 1.35 mCi/mmol. (2) Fluorination with molecularfluorine as described above gave [UC]-FDG in 98%

* Tests for sterility and apyrogenicity were performed by South ShoreLaboratory, Islip, New York, and Leberco Laboratories, Roselle Park,New Jersey.

t The specific activity can be increased or decreased to suit therequirements of a particular study by changing the amount of lflF-Fj orsubstrate used in the synthesis.

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radiochemical purity with a specific radioactivity of2.94 mCi/mmol.

Determination of Three-DimensionalDistribution of Activity in Brain

The three-dimensional distribution of 18F activityin the brain was quantified by radionuclide-com-puted tomography with a Mark IV scanner (Kuhlet al., 1977a). The instrument is a four-sided ar-rangement of 32 independent detectors which con-tinuously rotate as a unit, processing and displayingthe reconstructed data while the study progresses.Detection is by single photon counting. The accu-mulated data are processed by a Varian 620/i digitalcomputer, which makes corrections to equalize thedetector response and to compensate for photonattenuation in the head. An iterative reconstructiontechnique called Cumulative Additive Tangent Cor-rection is used to form the matrix of the distributionof activity for each cross-section of the head. Thecount distribution of the reconstructed section isthen converted to units of activity concentration byrelating it to the count distribution of a referencecylinder reconstruction for which the activity con-centration is known. Brain cross-sections at differ-ent levels are obtained by moving the subject's headfurther into or out of the scanner and then repeatingthe scan. The Mark IV scanner is a high-sensitivityinstrument with approximately uniform resolutionthroughout the section plane. The spatial resolutionin terms of full-width-at-half-maximum (FWHM)of the reconstructed image of a line source of 18F is1.7 cm in the center and 1.6 cm at the edges of thesection plane. Perpendicular to the section plane(i.e., section thickness), the FWHM is approxi-mately the same. Estimates of activity concentra-tion based on count summations in 2- by 2-cmregions of a section scan have a coefficient of vari-ation of approximately 5%. Accuracy and reproduc-ibility of these estimates are independent of locationin the scan field and independent of differences inneighboring activities (Kuhl et al., 1977).

Suitability of Biochemical Properties of FDGThe use of FDG to measure local cerebral glucose

utilization is based on the assumption that its bio-chemical properties are similar to those of DG. Theessential properties are: (1) it is transported andcompetes with glucose for phosphorylation by cer-ebral hexokinase to their respective hexose phos-phates; and (2) fluorodeoxyglucose phosphate, onceformed, is sufficiently slowly degraded that it canbe considered essentially trapped during the periodof measurement. This presumption was tested bytwo types of experiments.

To confirm that FDG is a substrate for hexoki-nase, [UC]-FDG was incubated with purified hexo-kinase and ATP in vitro, and the reaction productswere analyzed for evidence of [MC]-fluorodeoxyglu-cose phosphate formation. The reaction mixture

consisted of 33 mM Tris-chloride, 7 mM MgCl2, 7mM ATP, 8.3 mM [HC]-FDG (specific activity =0.38 juCi//unol), and 0.03 mg (4.2 U) of yeast hexo-kinase (Boehringer Manheim) at pH 7.8 in a finalvolume of 3.0 ml (Bessell and Thomas, 1973a). Theincubation was carried out for 20 minutes at 37°C,and 0.5-ml samples were removed at zero time andafter 10 and 20 minutes of incubation. The proteinin the samples was precipitated with 6% perchloricacid and removed by centrifugation. The perchloricacid was neutralized with K2CO3, and the precipi-tated KCIO4 was also removed by centrifugation.The supernatant solution was then evaporated todryness under vacuum, and the residue was redis-solved in 10 /J of water and chromatographed oncellulose MN 300 (Analtech, Inc.) thin layer chro-matographic plates in a solvent system consistingof isobutyric acid-ammonia-H2O (66:1:33,vol/vol/vol) (Ido et al., 1978). The plates were thendried and scanned for radioactivity with a Packardradiochromatogram scanner (Packard InstrumentCo.).

The suitability of [HC]-FDG as a tracer for cere-bral glucose consumption was further examined byusing it exactly as though it were [HC]-DG in atypical measurement of local cerebral glucose utili-zation by the [HC]-DG autoradiographic technique(Sokoloff et al., 1977). The experiment was carriedout in two normal, conscious, adult albino ratsweighing approximately 300 g. Approximately 10jiC\ of [UC]-FDG were administered as an intrave-nous pulse at zero time, and timed arterial bloodsamples were drawn during the subsequent 30 min-utes for assay of their plasma [14C]-FDG and glu-cose concentrations. At 30 minutes the rat wasdecapitated, and the brain was removed, frozen,and sectioned and autoradiographed as previouslydescribed (Reivich et al., 1969). Local cerebral glu-cose utilization was calculated from the measuredplasma and tissue MC concentrations as though thetracer used were [MC]-DG.

Calculation of the Radiation Dosimetry inMan Based on the Organ Distribution ofL18F]-FDG in Dogs

To calculate the absorbed radiation dose, prelim-inary distribution studies were performed in rats inwhich the time course of distribution of [UC]-DGwas determined. Six rats were killed at 1, 2, and 4hours after the intravenous injection of a bolus of[UC]-DG, and the activity in various organs wasassayed. This information allowed us to calculatethe biological half-life of DG in various organs andto choose an optimum time to study the distributionof FDG in the body. On the basis of these results,two dogs were studied 1 hour after an intravenousbolus injection of [18F]-FDG, and the distributionof 18F activity in various organs was determined(Gallagher et al., 1977).

Radiation dosimetry calculations were based on

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130 CIRCULATION RESEARCH VOL. 44, No. 1, JANUARY 1979

TABLE 1 Biological Half-Life of DG in the Rat

Organ tin (hr)

LungKidneyHeartLiverSpleenFatBrain

1 80.95.63.9

25217.2

the organ distribution at 60 minutes (Gallagher etal., 1977), and were calculated according to theMIRD* model, using the following assumptions: (1)after an intravenous injection of 1 mCi of [1BF]-FDG, kidneys, lungs, liver, brain, heart, spleen,ovaries, and bladder instantaneously and uniformlytake up the amounts of activity determined by thetissue distribution at 60 minutes in dogs; (2) theremainder of the activity is instantaneously anduniformly distributed throughout the whole body;and (3) the effective clearance half-time is 1.83hours (ti/2 of 18F) for all organs since, in most cases,it is rapid compared to the biological half-lives asdetermined in rats with [MC]-DG (Table 1).

Toxicity StudiesSix BNL strain adult mice were injected intra-

peritoneally with FDG, 14.3 mg/kg (1000 X humandose), at weekly intervals for 3 weeks (total of 3000X human dose), given food and water ad libitum,and observed over the 3-week period. A comparablegroup of six mice were injected intraperitoneallywith the same volume of sterile saline on the sameschedule, given food and water ad libitum, andobserved for 3 weeks. The mice were weighedweekly, and after 3 weeks were killed and theirinternal organs examined grossly and microscopi-cally.

Two adult female conditioned beagle dogs wereinjected intravenously with FDG, 0.72 mg/kg (50-X human dose), at weekly intervals for 3 weeks(total of 150 X human dose). Another adult femaleconditioned beagle received the same volume ofsterile saline intravenously. Baseline, 2-hour, 1-week, and 2-week blood and urine samples wereobtained for analysis. A few cerebrospinal fluidsamples were also collected. The following analyseswere performed: (1) Urine: physical and micro-scopic examination, electrolytes, creatinine, glu-cose, protein, urobilinogen, and osmolarity. (2)Blood: RBC, WBC, platelets, reticulocytes, differ-ential, hemoglobin, hematocrit, sedimentation rate,pro-time, osmolarity, electrolytes, glucose, urea ni-trogen, uric acid, creatinine, alkaline phosphatase,LDH, SGOT, SGPT, CPK, total protein, albumin,and total bilirubin. (3) Cerebrospinal fluid: glucose,protein, and chloride. At the end of 3 weeks the

• MIRD, Journal of Nuclear Medicine, Supplements 1-4 (1968, 1969,1970).

dogs were killed with an overdose of intravenouspentobarbital, and their internal organs were ex-amined grossly and microscopically.

Determination of Local Cerebral GlucoseConsumption in Man

Two normal male volunteers aged 26 and 24 werestudied after their informed consent was obtained.Each subject's brachial artery was catheterized per-cutaneously and an intravenous infusion of physi-ologic saline was started. The subject was madecomfortable in the Mark IV brain scanner, his headheld firmly in position with respect to the detectorsby a rigid foam head holder cast individually foreach subject. After a period of at least 30 minuteswas allowed for the subjects to attain a steadycontrol state, a bolus of [18F]-FDG (5.3 mCi in thefirst subject, 8.2 mCi in the second) was adminis-tered. The specific activities of the [18F]-FDG were8.9 and 8.8 mCi/mg, respectively, at the time ofinjection.

The [18F]-FDG method for determination of localcerebral glucose metabolism requires knowledge ofboth the arterial blood plasma glucose and [18F]-FDG concentrations as a function of time followingan intravenous bolus injection of [18F]-FDG. Theseconcentrations must be monitored from the time ofinjection of the [18F]-FDG until a time greater than30 minutes later, when the brain tissue 18F activityis quantitatively determined in three dimensions bymeans of a tomographic brain scan. Since theplasma glucose concentration is in a steady stateduring the time of the study (0-120 minutes), 2.0-ml blood samples were drawn from the arterialcatheter only every 10-15 minutes for glucose de-termination. The blood samples were centrifugedand a protein-free filtrate made from the separatedplasma by the Somogyi method (Somogyi, 1937).These samples were analyzed for glucose concentra-tion by an enzymatic technique (Saifer and Ger-stenfeld, 1958), using glucose oxidase (Glucostat,Worthington Biochemical Corp.) in barium-zinc fil-trates (Nelson, 1944).

The time course of the arterial plasma 18F activityfollowing the bolus injection was determined byperiodically drawing 2.5-ml samples, initially at 15-second intervals and then over progressively longerintervals, as seen in Figure 1. These samples werecentrifuged, and the plasma was assayed for 18Factivity in a Nal(Tl) well counter (Packard model3002). The activity was corrected for decay by ad-justing all values back to the time of injection.Standard samples containing ^Ga obtained from acylinder used to calibrate the detectors on the MarkIV scanner were counted along with the plasmasamples to provide a standard reference for effi-ciency correction between the Mark FV and the wellcounter (see below). The counts from these stan-dards also were corrected for decay back to the timeof injection.

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9 O 23

TIME IN MINUTES

FIGURE 1 Time course of arterial p8FJ-2-deoxy-2-flu-oro-D-glucose (psFJ-FDG) concentration in man follow-ing an intravenous bolus injection at time zero.

Thirty minutes after the injection of [18F]-FDG,the first scan was started. Each scan required 9-12minutes to complete, depending on the count rateobtained. Three and seven scans, respectively, wereobtained in the two subjects at +1, +2, and +4 cmin relation to the orbital-meatal line in the firstsubject and at - 1 , +1, +3, +4, +5, +6, and +7 cmin the second. Once the 18F concentration was de-termined in the section matrix by reconstruction, asdescribed above, the entire concentration distribu-tion was corrected for decay back to the time of[18F]-FDG injection. Immediately prior to thestudy, a section scan was made of a phantom cyl-inder containing a uniform concentration of "Ga inwater. MGa is a positron-emitting radionuclide froma commercially available ^Ga generator, and is anideal radionuclide for calibration for the positronemission of 18F. The data from the cylinder scanand the counting of a sample of the Ga solutionfrom the cylinder in the Nal(Tl) well counter allowone to determine the ratio of the efficiency of theMark IV scanner to that of the well counter used tocount the 18F activity in the plasma samples.

With the information concerning the arterial spe-cific activity of [18F]-FDG and the distribution of18F activity in the brain, it is possible to calculatethe rate of local cerebral glucose consumption usingEquation 1, where now C-f = the concentration ofFDG-6-PO* in the tissue; C£ = the arterial plasmaconcentration of FDG; k*, k*, and kf are the rateconstants for the transport from plasma to thetissue precursor pool, for the transport back fromtissue to plasma, and for the phosphorylation ofFDG in the tissue, respectively; X = the ratio of thedistribution volume of FDG in the tissue to that ofglucose; and Km and V ^ = the kinetic constantsof hexokinase for FDG.

C$ is obtained for each region of interest fromthe section scan; the time course of QJ and Cp aremeasured directly; the values of kf, k?, k|, and thelumped constant that were used are discussed belowunder Results. Thus we are able to calculate the

rate of glucose consumption, R, for any region ofthe brain.

Results

Biochemical Properties of FDGIncubation in vitro of [MC]-FDG with ATP and

purified hexokinase resulted in a time-dependent

• w ii ii a

DISTANCE (cm)

FIGURE 2 Thin-layer chromatographic analysis oftime-dependent transfer of radioactivity from f4CJ-FDGto a slower-moving compound with mobility like that ofp*C]fluorodeoxyglucose-6-phosphate during incubationin reaction mixture containing hexokinase and ATP.The composition of the reaction mixture and the chro-matographic procedures are described in Methods. Thetimes given in the figure represent the duration of incu-bation of the reaction mixture at 37° C. Incubation inabsence ofhexokinase or ATP resulted in no appearanceof slower-moving peak.

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132 CIRCULATION RESEARCH VOL. 44, No. 1, JANUARY 1979

[>«C]DEOXYGLUCOSE ["CjFLUORODEOXYGLUCOSE ["CjMETHYLGLUCOSE

FIGURE 3 Autoradiograms of brain sections from rats 30 minutes after an intravenous bolus injection of [**C]-DG,P4CJ-FDG, or p4C]-methy!glucose. Note the similarity of the autoradiograms from the rats receiving p4CJ-DG andfACJ-FDG and the lack of regional differentiation in the rat receiving p4C]-methylglucose, indicating that localmetabolism rather than blood flow and transport determines the local tissue concentration of UC at long intervalsafter a pulse of either f'CJ-DG or p*C]-FDG.

decrease in the chromatographic peak correspond-ing to [UC]-FDG and its partial replacement by aslower-moving peak (Fig. 2). No standard of fluo-rodeoxyglucose phosphate was available with whichto identify this slower peak positively as that of[14C]-fluorodeoxyglucose phosphate. Its mobility,however, was slower than that of both DG anddeoxyglucose-6-phosphate, and bore the same re-lationship to the mobility of [14C]-FDG as the mo-bility of deoxyglucose-6-phosphate did to that ofDG. Furthermore, its formation was fully depen-dent on the presence of ATP and hexokinase in theincubation mixture. The appearance of a labeledderivative of [UC]-FDG that was dependent on timeand on the presence of both hexokinase and ATP,and that corresponded to neither [HC]-DG nor[HC]-deoxyglucose-6-phosphate, was considered aspresumptive evidence that FDG is converted tofluorodeoxyglucose phosphate by hexokinase. Anunidentified radioactive contaminant present in theoriginal batch of [UC]-FDG used in these experi-ments, peak X in the chromatograms, was unaf-fected by the incubation procedure.

The autoradiographs obtained from sections ofthe brains of the two rats administered [HC]-FDGwere identical in character to those obtained with[MC]-DG and entirely different from those seenwith 3-O-methyl-[MC]glucose, which is not phos-phorylated by hexokinase (Fig. 3). Indeed, whenlocal cerebral glucose utilization was calculated inthis experiment with the same rate constants andlumped constant determined for [MC]-DG, the val-ues obtained for the local rates of glucose metabo-lism for various structures were distributed simi-larly (r = 0.989, P < 0.001) and were only moder-ately lower than those obtained with [UC]-DG(Table 2). These results indicate that FDG is essen-tially as suitable a tracer for the technique as DG,but is probably associated with a lumped constantsomewhat lower than that of [UC]-DG.

The exact value for this constant will have to bedetermined in man, but for these studies a value

TABLE 2Rat

Local Cerebral Glucose Metabolism in the

Structure

Visual cortexAuditory cortexLateral geniculateSuperior oliveLateral lemniscusInferior colliculusSuperior colliculus

Internal capsuleCerebellar white matter

[I4C]-DG (8 rata)(mg/lOOgper min)

Gray matter

20.329.316.926.520.536.518.0

White matter

5,-9-6.7

[14C]-FDG (2 rata)(mg/lOOgper min)

17.021.014.021.517.927.413.2

5.56.1

17.9% lower than that determined for DG in themonkey has been used, since on the average thevalues of regional glucose consumption obtainedwith FDG were 17.9 ± 2.5% (SE) lower than thoseobtained with DG (Table 2). The value of thelumped constant for DG in the awake monkey is0.344 ± 0.036 (SE) (Sokoloff, unpublished observa-tions). Therefore, a value of 0.282 was used in thepresent study.

The values of kf, kj, and kf for FDG will alsohave to be determined. However, since Equation 1is relatively insensitive to changes in these values,and since there was only a 17.9% difference in thecalculated values of regional glucose consumptionin toto, the values for these constants previouslydetermined for DG in rats (Sokoloff et al., 1977)were used (Table 3).

Organ Distribution of DG and Radiation Dose

The radiation doses to selected organs were cal-culated as described under Methods from previ-ously reported tissue distribution data for dogs

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LOCAL CEREBRAL GLUCOSE UTILIZATION IN MAN/Reivich et al. 133

TABLE 3 Values of Rate Constants for DG in theNormal Awake Rat

Rate constants(nun"1)

k,* k,' k,"

Giey matter 0.189 ± 0.012White matter 0.079 ± 0.008

0.245 ± 0.0400.133 ± 0.046

0.052 ± 0.0100.020 ± 0.020

Results are expressed as mean ± SE.From Sokoloff et al (1977)

TABLE 4 Radiation Dosmetry for 'eFDG in ManOrgan

Whole bodyOvariesLiverKidneysLungsBrainHeartSpleenBladder

Dose (mrad/mCi)

436367776766

147185289

(Gallagher et al., 1977). The calculated absorbedradiation doses to these organs in man are shownin Table 4.

Toxicity StudiesMice injected with FDG (14.3 mg/kg X 3) suf-

fered no immediate or long-term effects. Theirweight remained stable and did not differ signifi-cantly from that of the controls (see Table 5). Nogross or microscopic abnormalities were present inthe brain, heart, spleen, liver, kidneys, or lungs.

The dogs injected with FDG (0.72 mg/kg X 3)showed no clinical signs or symptoms of adverseeffects. No significant abnormalities were detectedin the blood, urine, or cerebrospinal fluid analyses,and no significant gross or microscopic abnormali-ties were present in the brain, heart, spleen, liver,kidneys, lungs, ovaries, or intestines.

The injected dose in man is approximately 1 mgof [18F]-FDG (0.014 mgAg), a factor of 150 timesless than the total dose administered without effectto dogs, a factor of 3000 times less than the totaldose administered without effect to mice, and afactor of 43,000 times below the LD50 for rats pre-viously reported (Bessell et al., 1973).

Local Cerebral Glucose Consumption in ManThe arterial [18F]-FDG concentration curve from

one of the subjects is shown in Figure 1. This curve

has been corrected for isotope decay back to thetime of injection of the bolus of [18F]-FDG.

Representative section scans from one subjectare shown in Figure 4. The level at which thesescans were performed is indicated in relation to theorbito-meatal line on a rectilinear scan of the sub-ject's head.

In Figure 5 the individual scans are shown alongwith an illustration of a slice through the humanbrain at approximately the same level. Indicatedare representative values for the calculated regionalrate of glucose utilization in mg/min per lOOg ofbrain.

In Table 6 are the calculated values of localglucose consumption for various cerebral structuresin the two subjects.

DiscussionFDG was chosen as a tracer for this method

because it could be labeled with a positron emitter(18F) which could be detected externally, and be-cause previous studies had demonstrated that DGwas a suitable tracer for glucose metabolism in thebrain (Sokoloff et al., 1977). DG differs from glucosein that a hydrogen atom replaces the hydroxylgroup at the second carbon atom of the molecule.DG has been shown to enter tissues and cells rapidly(Wick et al., 1955), to be phosphorylated by brainhexokinase to DG-6-PO4 (Sols and Crane, 1954),and not to be further metabolized (Sols and Crane,1954; Tower, 1958; Bachelard, 1971; Horton et al.,1973). DG-6-PO4 is not a substrate for either phos-phohexose isomerase or glucose-6-phosphate dehy-drogenase (Sols and Crane, 1954). It is transportedfrom the blood into the brain by the same saturablecarrier mechanism that transports glucose (Bache-lard, 1971; Horton et al., 1973; Bidder, 1968). Onceit is phosphorylated to DG-6-PO4 it remains in thetissue in that form. It is essentially "trapped" in thelocation at which it is phosphorylated, since thehalf-life of DG-6-PO4 is approximately 8 hours ingray matter and 10 hours in white matter (Sokoloffet al., 1977). The activity of glucose-6-phosphatase,an enzyme that might be expected to hydrolyzedeoxyglucose-6-phosphate, is reported to be verylow in mammalian brain (Hers and DeDuve, 1950;Raggi et al., 1960; Prasannan and Subrahmanyan,1968). It has been shown that deoxyglucose-6-phos-phatase activity in the brain is negligible in relationto this technique (Sokoloff et al., 1977). These char-acteristics made DG a suitable candidate for thedevelopment of an autoradiographic technique for

TABLE 5 Mice:

ControlExperimental

WeightAgent

SalineFDG

ig)Baseline

28.57 ± 2.7429.43 ± 1.07

1 Week

29.98 ± 3.1730.32 ± 1.23

2 Weeks

31.35 ±2.1830.80 ± 0.98

3 Weeks

32.90 ± 2.9930.85 ± 1.05

Results are expressed as mean ± SE.From Som, P., and Atkins, H. IND application #13483 (unpublished observations).

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134 CIRCULATION RESEARCH VOL. 44, No. 1, JANUARY 1979

[l8F-]2-DE0XY-2-FLU0R0-D-GLUCOSE

0. M. + 6 cm 0. M. + 5 cm

* * • %&• -

0.M.+ 4 cm O.M. + 3 cm

FIGURE 4 Section scans of the head beginning 30 minutes after an intravenous bolus injection of fsF]-FDG. Thelevel of each scan is indicated in relation to the orbito-meatal (O.M.) line on a rectilinear scan of the subject's head.A = anterior, P = posterior, L = left, and R = right.

the measurement of local cerebral glucose metabo-lism in animals. It should be noted that DG insufficiently high concentrations inhibits the trans-port and utilization of glucose (Tower, 1958), partlybecause of a depletion of available ATP for thehexose-catalyzed phosphorylation of glucose, butmainly by competitive inhibition of phosphohexo-kinase isomerase by deoxyglucose-6-phosphate.Therefore, DG must be used in trace amounts so asto have no effect on glucose metabolism. DG hasbeen successfully used in animals to measure localcerebral glucose utilization in various states of an-esthesia (Shapiro et al., 1975), in awake animals(Sokoloff et al., 1977), during induced seizures (Ken-nedy et al., 1975), and following middle cerebralartery occlusion in the cat (Ginsberg et al., 1977).

The substitution of a fluorine atom for a hydro-gen atom on the second carbon (C-2) of the DGmolecule does not alter its metabolic fate signifi-cantly. It has been demonstrated previously thatFDG is phosphorylated by hexokinase to 2-deoxy-2-fluoro-D-glucose phosphate (Bessell et al., 1972),and that this compound is a relatively poor sub-strate for glucose-6-phosphate dehydrogenase (Bes-sell and Thomas, 1973b). It should be noted thatmodification of the glucose molecule at C-2 (i.e., 2-

DG and 2-FDG) does interfere with its ability toundergo active transport (Barnett and Munday,1972), but since brain glucose transport is a carrier-mediated process, it is not necessary that the sub-strate possess the structure required for activetransport. It has been shown (Bachelard, 1971) thatglucose and DG share the same transport systemsfacilitating entry across the blood-brain barrier,thus demonstrating that this structural modifica-tion at C-2 does not interfere with carrier-mediatedtransport, although it does interfere with activetransport.

Although there is some evidence suggesting thatFDG is a nonreversible inhibitor of glucose phos-phorylation (Coe, 1972), this is not likely to causea significant effect on glucose metabolism in thepresent method, in which FDG is used in traceramounts. It is estimated that the peak concentra-tion of FDG in the brain is 0.3 /IM, which is approx-imately l/3000th of the concentration found toproduce 33% inhibition in vitro (Coe, 1972). At thisconcentration, the amount of inhibition presentwould be expected to be negligible.

A direct comparison of the use of these twotracers (DG and FDG) for the determination oflocal cerebral glucose consumption by the autora-

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LOCAL CEREBRAL GLUCOSE UTILIZATION IN MAN/Reivich et al. 13S

Cingulofe8.07

Parietalwhite

Parietalcortex

Cingulategyrus

Head ofcaudate

Corpus'callosum

cipitalwhite

Corpuscallosum

InsulaThalamus

Visualcortex

Head ofcaudate

Thalamus

Cerebellum

Visualcortex

FIGURE 5 Section scans of the head and photograph of a slice through the human brain at approximately the samelevel. The numbers represent the local cerebral metabolic rate for glucose in mg/100 g per minute in the structurelabeled: (A) scan at OM. + 6 cm level; (B) scan at O.M. + 5 cm level; (C) scan at O.M. + 4 cm level; and (D) scan atOM. + 3 cm level.

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136 CIRCULATION RESEARCH VOL. 44, No. 1, JANUARY 1979

TABLE 6 Local Cerebral Glucose Metabolism in Man TABLE 8 Comparison of Local Cerebral GlucoseMetabolism in Primates

(mg/100 g per min)

Subject 1 Subject 2

Visual cortexThai am usFrontal cortexSensory-motor cortexParietal cortexTemporal cortexHippocampusCaudate nucleusPutamenAmygdalaCerebellum

Frontal white matterParietal white matterOccipital white matterCorpus callosum

Gray matter

11.248.798.158.176.02

6.476.09

White matter

2.373.884.693.22

9.306.068.438.757.658.125.857.236.746.235.79

4.913.543.764.05

diographic technique in the rat gave comparableresults. The correlation between the two sets ofdata for 10 different structures in the brain wasexcellent (r = 0.989). There was a small but sys-tematic difference between the values obtained withthe two tracers, those obtained with FDG beinglower. This is probably due to a slightly lower valuefor the lumped constant for FDG compared to DG.The exact value for this constant will have to bedetermined for man, but for the present a value17.9% lower than that determined for DG in theawake monkey has been used.

With this value of the lumped constant and thevalues of the kinetic constants in Table 3, we wereable to calculate values for local cerebral glucoseutilization for various structures in the brain ofnormal man.

It should be noted that the value of the lumpedconstant may be altered in diseased brain tissue,and it must therefore be evaluated before localcerebral metabolic rates can be quantified in suchconditions. The operational equation is relativelyinsensitive to changes in the kinetic constants forFDG (i.e., kf, kj, and k£), which influence the rate

TABLE 7 Values of Average Brain Metabolic Rate forGlucose in Man from Literature

CMR*(mg/100 g brain tissue per nun)

Scheinberg and Stead, 1949Novack et al., 1953Gottstein et al., 1963Cohen et al., 1967Takeshita et al., 1972

Present study

6.04 ± 0.246.5 ± 1.25.30 ± 0.964.48 ± 0.295.57 ± 0.79

5.9

(mg/100 g per min)

Man Monkey*

Visual cortexThalamusFrontal cortexSensory-motor cortexParietal cortexTemporal cortexHippocampusCaudate nucleusPutamenAmygdalaCerebellum

Subcortical white matter

10.277.428.298.466.848.125.856.856.426.235.79

3.80

8.737.107.768.098.428.266.168.66

10.566.918.61

2.12

Results are expressed as mean ± SE.

' From Reivich et al. (unpublished observations).

of clearance of unmetabolized FDG, and thereforethe effect of disease states on these parameters willprobably only negligibly affect the calculated valuesfor local cerebral metabolic rate. However, thissupposition will have to be demonstrated before themethod is used under such conditions.

There are no local cerebral glucose data availablefor man with which to compare the present results.However, an average value for cerebral glucoseconsumption can be calculated from our data andcompared with such values in the literature. Thevalue calculated was a weighted average based onthe approximate volume of each structure mea-sured. This gave an average gray matter value of8.05 mg/lOOg per minute, an average white mattervalue of 3.80 mg/lOOg per minute, and an averagewhole brain value of 5.9 mg/lOOg per minute. Thelast figure compares favorably with values in theliterature (Table 7). Regional values of cerebralglucose consumption are available in other awakeprimates with which these data can be compared(Table 8). There is good agreement between thevalues for various regions of the brain (r = 0.581; n= 12; P < 0.05).

On the basis of these studies, we feel that FDG isa suitable tracer for the measurement of localcerebral glucose metabolism, and that the samemodel that was used for DG can be applied to FDG.This has enabled us to measure quantitatively localcerebral glucose metabolism in man for the firsttime (Reivich et al., 1977). The method has sincebeen applied to make qualitative measurements inpatients with cerebrovascular disease (Kuhl et al.,1977b).

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Alavi, P Som and L SokoloffM Reivich, D Kuhl, A Wolf, J Greenberg, M Phelps, T Ido, V Casella, J Fowler, E Hoffman, A

utilization in man.The [18F]fluorodeoxyglucose method for the measurement of local cerebral glucose

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