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Summary

Identification of myocardial viability in hypokineticsegments is important in patients with ischemic car-diomyopathy because systolic dysfunction improves withrevascularization. Positron emission tomography (PET)F-18 fluoro deoxyglucose (FDG) uptake has been demon-strated as an accurate indicator of metabolically active andthus viable myocardium. F-18 FDG single photon emis-sion computed tomography (SPECT) has recently beenintroduced and offers a technically easier and less costlyalternative to PET imaging for determination of myocar-dial viability. A body of literature demonstrates that F-18FDG SPECT can reliably be performed with SPECThardware equipped with 511-keV collimators, which pro-vides an accurate assessment of myocardial viability.F-18 FDG SPECT offers data similar to those offered byF-18 FDG PET and compares favorably with other imag-ing modalities, including rest-redistribution and stress-reinjection thallium-201 myocardial perfusion imaging,gated technetium 99m SPECT, and low-dose dobutamineechocardiography.

Background

“Myocardial viability” literally suggests the presenceof viable myocytes, but the term is most commonly usedto describe the presence of hibernating myocardium. Firstintroduced by Diamond et al1 and later established by

Rahimtoola,2 the term “myocardial hibernation” refers toa state in which severe coronary artery disease results inchronic systolic dysfunction of noninfarcted (ie, metabol-ically active) myocardial segments, which will recoverfunction after revascularization. Although myocardialischemia is frequently associated with stress-inducedregional systolic dysfunction, ischemic myocardium mostcommonly has normal resting wall motion and thickeningand thus is not hibernating.

The detection of hibernating myocardium in patientswith ischemic cardiomyopathy has great clinical signifi-cance. Although in this patient population medical ther-apy alone carries a grim prognosis with high morbidityand mortality rates,3,4 myocardial revascularizationimproves left ventricular regional and global systolicfunction,2,5-8 resulting in improved life quality,7,9

decreased subsequent cardiac events, and probably pro-longation of life expectancy.10-12 The potential benefitfrom revascularization, however, is associated with ahigh procedure-related complication event rate,13 neces-sitating an accurate and reliable assessment of myocar-dial viability. Several modalities have been introducedtoward this goal, including nuclear cardiology (eg, thal-lium-201 rest-redistribution, resting Tc-99m perfusionimaging, F-18 FDG SPECT, and F-18 FDG PET),echocardiography (dobutamine echocardiography), andrecently cardiac magnetic resonance imaging (MRI) (eg,dobutamine MRI, myocardial tagging, contrast-enhancedperfusion MRI).

Rationale for FDG Imaging

The pathophysiology underlying myocardial hiber-nation is not entirely understood. Clinical and experi-mental data have demonstrated that hibernatingmyocardium may have either normal or reduced coronaryblood flow.14 Whether chronic resting systolic dysfunc-tion is the result of chronic hypoperfusion or repeatedepisodes of ischemic insults (“stunning”) is a topic ofdebate.15 As resting metabolism is preserved, glucoseusage is normal or may even be increased. Glucoseuptake can be accurately measured with the use of FDG,

TECHNOLOGISTS’ SECTION

F-18 fluoro deoxyglucose SPECT for assessment of myocardial viability

James Fitzgerald, CNMT, RT(N),a J. Anthony Parker, MD, PhD,a and Peter G. Danias, MD, PhDb

From the Division of Nuclear Medicine,a Department of Radiology andCardiovascular Division,b Department of Medicine, Beth IsraelDeaconess Medical Center and Harvard Medical School, Boston,Mass.

Dr Danias is partially supported by the Clinical Investigator TrainingProgram, Beth Israel Deaconess Medical Center—Harvard/Massachusetts Institute of Technology Health Sciences andTechnology in collaboration with Pfizer Inc.

Reprint requests: Peter G. Danias, MD, PhD, Cardiovascular Division,Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston,MA 02215; pdanias@caregroup.harvard.edu.

J Nucl Cardiol 2000;7:382-7.Copyright © 2000 by the American Society of Nuclear Cardiology.1071-3581/2000/$12.00 + 0 43/8/107821doi:10.1067/mnc.2000.107821

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a glucose analog that traces the transmembranous trans-port and hexokinase-mediated phosphorylation of glu-cose.16 FDG-6 phosphate, the product of FDG phos-phorylation, cannot be dephosphorylated or furthermetabolized and is thus trapped in the myocardium.Accordingly, glucose uptake can be assessed by imagingFDG accumulation with PET or SPECT. The utility ofresting myocardial perfusion imaging with Tc-99magents or Tl-201 to assess resting myocardial blood flowhas been established. The combined assessment of flow(with a Tc-99m perfusion agent or Tl-201) and metabo-lism (with FDG imaging) can evaluate for the presence ofmyocardial viability (Figure 1).

The physiologic correlates of ischemia, hibernation,and infarction are presented in Table 1. The distinctivecharacteristic of hibernation is the normal (or slightlydecreased) resting blood flow in areas with normal (orhigh) glucose uptake (flow-metabolism mismatch). FDGPET and FDG SPECT are uniquely able to evaluate glu-cose uptake. Although conceptually the states of myocar-dial normality, ischemia, hibernation, and infarction rep-resent a cascade of gradually declining status, thestepwise evolution through these pathophysiologic statesis not necessary. For example, normal tissue may acutelyinfarct without gradual deterioration through intermedi-ate steps. In addition, these states commonly coexist witheach other, making their detection and accurate separa-tion difficult at times. FDG uptake imaging has thepotential to distinguish hibernating tissue, which recov-ers systolic function after revascularization, frominfarcted tissue, which does not improve function afterrevascularization, more clearly.

Practical Considerations

Several factors determine the extent of myocardialFDG uptake, including regional blood flow and oxygena-tion, serum glucose concentration, myocardial metabo-lism, and contractility. In the fasting state when blood-

insulin levels are low, free fatty acids are the main energysubstrate of the heart. In ischemic, hypoxic, and hiber-nating myocardium in particular during hyperinsulinemiaafter glucose loading, glucose becomes the main energysubstrate,17 and myocardial glucose uptake increases.Thus enhanced FDG uptake is seen in ischemic, hypoxic,and hibernating myocardium versus being seen in normalmyocardium. The FDG clearance from the blood pool israpid and other organs near the heart, such as the liver,intestine, and skeletal muscles take up proportionallysmaller amounts of FDG, resulting in a high target/back-ground ratio.17-19 FDG accumulates avidly in the brainand is excreted by way of the kidneys.

To maximize myocardial FDG uptake, hyperinsu-linemia is induced. For nondiabetic patients, the endoge-nous release of insulin after glucose loading (with theequivalent of 100 g of dextrose) is adequate. For diabeticpatients, oral glucose loading may have an unreliableeffect on the metabolic state, and thus hyperinsulinemiceuglycemic clamping20 is used to standardize metabolicconditions during the FDG study.21 For hyperinsuline-mic euglycemic clamping, insulin and glucose aresimultaneously infused, and serum glucose levels arefrequently determined to confirm a constant blood glu-cose level in the normoglycemic range. Intravenousinjection of 20 to 30 mCi (0.74 to 1.11 GBq) of a Tc-99m perfusion agent or 2.0 to 3.5 mCi (0.074 to 0.13GBq) Tl-201 is performed 30 minutes after glucose loador after establishment of the euglycemic hyperinsuline-mic clamping. Thirty minutes later, 5 to 10 mCi (0.185to 0.37 GBq) of F-18 FDG are also administered intra-venously. Imaging is performed 45 to 60 minutes afterinjection of FDG to allow for adequate FDG myocardialuptake. Because the emission energy of F-18 is higherthan that of Tc-99m or Tl-201, special attention must bedirected to radiation safety to ensure compliance withfederal regulations and the ALARA principle (ie, iso-lated or properly shielded rooms for injection and wait-ing after injection).22

Table 1. Blood flow, regional wall motion, and FDG uptake in various states, ranging from normality tomyocardial infarction

Blood flow Wall motion

After After FDGStress Rest revascularization Stress Rest revascularization uptake

Normal N N – N N – NIschemic A N N A N N NHibernating A N or A N A A N N or HInfarcted A A A A A A A

N, Normal; A, abnormal; H, high.

F-18 FDG SPECT Imaging: Technique

F-18 FDG SPECT imaging requires a gamma cam-era with capability for dual-isotope imaging of Tc-99m(or Tl-201) and F-18 FDG. Because F-18 FDG has a rel-atively short half-life (109 minutes), decay correction iscommonly used during F-18 FDG data acquisition. Adual- or triple-headed camera system equipped with 511-keV–specific ultra-high energy general-purpose collima-tors23 and a thick (5/8 to 3/4 in) NaI(TI) crystal is used toimage the high-energy (511 keV) photons from thepositron-electron annihilation.24 Proper collimation with511-keV–specific collimators (rather than high-energycollimators) is critical for F-18 FDG SPECT to maintainadequate spatial resolution. Typical parameters for adual-headed system include a step-and-shoot acquisitionwith 64 azimuths (32 per head) over a 180° arc (45° rightanterior oblique projection to 45° left posterior obliqueprojection); azimuth duration of 60 seconds; and a matrixsize of 64 × 64 × 16. For Tc-99m imaging, an intrinsicTc-99m flood correction is used and dual energy win-dows (511 keV at 30% and 140 keV at 20%) are set upfor simultaneous F-18 FDG and Tc-99m acquisition.When Tl-201 is used for resting myocardial perfusionimaging, the acquisition windows are set to 73 keV at20% and 167 keV at 20% (for Tl-201) and 511 keV at30% (for F-18 FDG). As with any other nuclear cardiol-

ogy procedure, the raw data should be reviewed andprocessed while the patient is still in the nuclear labora-tory to ensure technically adequate acquisition (eg,absence of motion, artifacts). The reconstruction regionand ventricular coordinate system orientation from theTc-99m perfusion data are applied to analysis of the F-18FDG data. For Tc-99m perfusion images, typical pro-cessing parameters include a Butterworth filter with acutoff of 0.35 and an order of 4.0 for reconstruction.When Tl-201 is used for resting myocardial perfusionimaging, typical parameters include use of a Butterworthfilter with a cutoff of 0.30 and an order of 5.0 for recon-struction. For the F-18 FDG images, typical parametersinclude a Butterworth filter with a cutoff of 0.55, and anorder of 5.0. polar plots (bull’s-eye display) are con-structed with the short axis (and optionally the long axisat the apex) tomographic slices in a fashion similar to thatused for Tl-201 or Tc-99m SPECT myocardial perfusionimaging. Because the perfusion and metabolic images areacquired simultaneously and processed with identicalorientation, the images are exactly registered.

A hybrid PET-SPECT technique with a modifiedSPECT platform and coincidence detection has also beendescribed.25 An axial shield and filter combination thatlimits the angle of acceptance and filters most of the low-energy photons replaces the collimator. For thisapproach, a dual-headed camera with the camera heads

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Fitzgerald, Parker, and DaniasFDG SPECT for assessment of myocardial viability

Figure 1. FDG SPECT images of a patient with ischemic cardiomyopathy and significant viability. Short axis (SA), ver-tical long axis (VLA), and horizontal long axis (HLA) images of the heart show mismatched metabolism/flow defectswith FDG uptake in the distal anterior wall (white arrows), intraventricular septum (arrowheads), and inferior wall(black arrows), suggesting viability in these territories.

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opposed at 180° is equipped with a coincidence detectioncircuit. Transmission data (cesium 137 or barium 133)are used for attenuation correction. Typically transmis-sion data are obtained after the emission data; the headsrotate through 96 azimuths at 2 seconds/azimuth, and 3windows are used: 511 keV at 30% (F-18 FDG) and 310keV at 30% (Compton scatter) and either 662 keV at 20%(Cs-137) or 356 keV at 20% (Ba-133). A finer matrix (ie,128 × 128 × 16 or 256 × 256 × 16) is commonly used.The resting Tc-99m or Tl-201 myocardial perfusionimages are obtained with a conventional SPECTapproach as a separate acquisition. Appropriate qualitycontrol procedures should be performed routinely. Forcoincidence detection with SPECT equipment if nonuni-formity exceeds the manufacturer-specified upper limitfor emission data, a photopeak shift should be suspected,whereas for transmission data, current fluctuations of thehigh voltage supply unit should be suspected.

F-18 FDG SPECT Imaging: Advantages andLimitations

F-18 FDG imaging is a direct physiologic correlateof myocardial metabolism and viability.26 The use of

widely available SPECT instrumentation for measure-ment of F-18 FDG uptake allows for acquisition of datathat previously required significantly more costly dedi-cated PET cameras. In addition, the simultaneous acqui-sition of F-18 FDG and Tc-99m perfusion data (metabo-lism and flow, respectively) offers the advantage ofexactly registered images. Because coincidence detectionmandates separate acquisition for flow and metabolismimaging, exact image registration is not possible withcoincidence detection that uses either modified SPECTor dedicated PET equipment.

Coincidence imaging with attenuation correction thatuses modified SPECT equipment has better spatial reso-lution and count sensitivity than the simultaneous acquisi-tion dual-isotope F-18 FDG SPECT with dedicated 511-keV collimators, similar to dedicated PET.25 However, theresolution of both these methods appears to be adequate toidentify regional myocardial metabolism and perfusion.Although tissue attenuation of a 511-keV photon is lessthan that of a 140-keV photon, there is considerablymore attenuation of the 2 coincidence 511-keV photonsthan the single 140-keV photon. Thus coincidence F-18FDG images of the heart are much more prone to attenu-ation artifacts than single photon F-18 FDG images and

Figure 2. Concordance between Tl-201 stress-redistribution-reinjection, PET, and FDG SPECT, showing absence ofviability in the apex because of previous myocardial infarction in the distribution of the left anterior descending coro-nary artery. For each technique, 4 radial long axis tomograms are displayed. Courtesy of Drs Srinivasan and Bacharach.

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even more prone to attenuation artifacts than Tc-99mimages. Attenuation correction is not needed for F-18FDG SPECT imaging with 511-keV collimators but isessential for coincidence detection with either modifiedSPECT or dedicated PET equipment.

Limitations of F-18 FDG SPECT imaging are pri-marily related to the logistic constraints of F-18 FDGimaging. The relatively high cost and short half-life of F-18 FDG make the commercial delivery and availabilityof F-18 FDG challenging. Because of the short half-lifeof F-18 FDG, decay correction is important for SPECTimaging. However, some systems do not provide decaycorrection for dual-isotope collection. Radiation expo-sure to personnel because of both F-18 FDG and Cs-137(or Ba-133) requires additional protective measures com-pared with Tl-201 or Tc-99m imaging. Furthermore inthe fasting state, myocardial uptake of glucose may below, is often inhomogeneous,16,19,27 and requires the useof glucose loading (or clamping). Glucose clamping inparticular is a tedious procedure that, if not performedmeticulously, may have a dramatic negative impact onpatient well-being and image quality. From the technicalpoint of view, the use of a 511-keV collimator necessaryfor dual-isotope F-18 FDG/Tc-99m or Tl-201 imagingdegrades the quality of the perfusion image. Finally, ithas been suggested that the resolution and counting sen-sitivity of F-18 FDG SPECT may be less than optimal.28

F-18 FDG SPECT Imaging: Comparison With OtherTechniques

All nuclear cardiology techniques have high sensi-tivity for assessment of myocardial viability.4,20,29 Ingeneral, good agreement is observed (Figure 2). In arecent pooled analysis, the sensitivity of various nuclearcardiology approaches was: Tl-201 rest-redistribution,86% (range 44% to 100%); resting Tc-99m perfusionimaging, 83% (range 73% to 100%); F-18 FDG SPECTimaging, 85% (range 80% to 89%); and PET, 88% (range71% to 100%).29 Specificity for these techniques is gen-erally lower and varies more. In the same review,29 thespecificity for F-18 FDG SPECT was 75% (range 66% to84%) compared with 54% (range 22% for 92%) for Tl -201 rest-redistribution and 69% (range 54% to 89%) forrest Tc-99m perfusion imaging.

F-18 FDG SPECT has been compared directly withPET in several studies,21,23,24,30,31 collectively evaluating766 myocardial segments in 125 patients for the presenceof myocardial viability. In these studies, F-18 FDGSPECT was shown to have sensitivity and specificitysimilar to PET for detecting myocardial viability.Hasegawa et al25 demonstrated that SPECT image qual-ity is only maintained when myocardial uptake of F-18

FDG is adequately high. Because coincidence detectionimaging offers superior spatial resolution, F-18 FDGcoincidence scanning with attenuation correction pro-vides images of superior resolution compared with non-coincidence F-18 FDG SPECT.

F-18 FDG SPECT compares favorably with Tl-201rest-redistribution imaging. Burt et al21 evaluated 20patients with F-18 FDG SPECT, F-18 FDG PET, anddelayed resting Tl-201 imaging. They showed that 13 of60 segments thought to be nonviable (based on resting 3-hour delayed Tl-201) were deemed viable by both PETand SPECT. Srinivasan et al32 reported on 28 patientswho were evaluated by PET, F-18 FDG SPECT, andstress-redistribution-reinjection Tl-201 imaging for pres-ence of myocardial viability. Of 137 segments that weredeemed nonviable by Tl-201 imaging, 59 (43%) werefound to be viable by PET, and of these, 52 (88%) werealso deemed viable by F-18 FDG SPECT. The lower sen-sitivity of Tl-201 imaging was attributed at least in part tothe increased diaphragmatic and soft-tissue attenuation towhich Tl-201 is more prone. Similar data were alsoreported by DePuey et al,33 who evaluated 23 patientswith F-18 FDG PET, gated SPECT with Tc-99m, anddelayed Tl-201 imaging. In this study, 58% of 41 vascu-lar territories were deemed viable by F-18 FDG SPECTbut only 22% by wall thickening (gated SPECT) and24% by delayed Tl-201. The major limitation of all thesestudies, however, is that the revascularization status ofthe patients was not reported and thus presence orabsence of viability was not conclusively confirmed. In adirect comparison of F-18 FDG SPECT and Tl-201stress-reinjection, Bax et al31 evaluated 17 patientsbefore and 3 months after revascularization. The sensitiv-ity of F-18 FDG SPECT and Tl-201 imaging were simi-lar (89% and 93%, respectively), but F-18 FDG SPECThad significantly higher specificity (77% versus 43% forF-18 FDG SPECT and Tl-201, respectively). The poten-tial incremental benefit of gated SPECT for assessmentof myocardial viability when Tc-99m agents are used asthe perfusion tracer has not been investigated.

F-18 FDG SPECT has also been shown to have sim-ilar sensitivity and specificity to low-dose dobutamineechocardiography.31,34 Cornel et al34 showed 87% agree-ment between the 2 tests, but 27% of the segments thatwere deemed viable by F-18 FDG SPECT did not havecontractile reserve by echocardiography. Bax et al31

reported higher sensitivity and specificity for F-18 FDGSPECT (89% and 77%, respectively) compared withdobutamine echocardiography (85% and 63% for sensi-tivity and specificity, respectively) for assessment ofmyocardial viability documented after revascularization.

Comparisons of newer imaging modalities, such ascardiac MRI, with F-18 FDG SPECT have not yet been

17. Saha GB, Maclntyre WJ, Brunken RC, et al. Present assessment ofmyocardial viability by nuclear imaging. Semin Nucl Med1996;26:315-35.

18. Gallagher BM, Fowler JS, Gutterson NI, MacGregor RR, Wan CN,Wolf AP. Metabolic trapping as a principle of radiopharmaceuticaldesign: some factors responsible for the biodistribution of [18F] 2-deoxy-2-fluoro-D-glucose. J Nucl Med 1978;19:1154-61.

19. Cook G J, Fogelman I, Maisey MN. Normal physiological and benignpathological variants of 18-fluoro-2-deoxyglucose positron-emissiontomography scanning: potential for error in interpretation. Semin NuclMed 1996;26:308-14.

20. Bax JJ, Cornel JH, Visser FC, et al. Prediction of improvement of con-tractile function in patients with ischemic ventricular dysfunction afterrevascularization by fluorine-18 fluorodeoxyglucose single-photonemission computed tomography. J Am Coll Cardiol 1997;30:377-83.

21. Burt RW, Perkins OW, Oppenheim BE, et al. Direct comparison of flu-orine-18-FDG SPECT, fluorine-18-FDG PET and rest thallium-201SPECT for detection of myocardial viability. J Nucl Med 1995;36:176-9.

22. NRC Rules and Regulations, 10 C.F.R. Sect.10.1003 (1999).23. Chen EQ, Maclntyre WJ, Go RT, et al. Myocardial viability studies

using fluorine-18-FDG SPECT: a comparison with fluorine-18-FDGPET. J Nucl Med 1997;38:582-6.

24. Martin WH, Delbeke D, Patton JA, et al. FDG-SPECT: correlation withFDG-PET. J Nucl Med 1995;36:988-95.

25. Hasegawa S, Uehara T, Yamaguchi H, et al. Validity of 18F-fluo-rodeoxyglucose imaging with a dual-head coincidence gamma camerafor detection of myocardial viability. J Nucl Med 1999;40:1884-92.

26. Phelps ME, Hoffman EJ, Selin C, et al. Investigation of [18F]2-fluoro-2-deoxyglucose for the measure of myocardial glucose metabolism. JNucl Med 1978;19:1311-9.

27. Hicks RJ, Herman WH, Kalff V, et al. Quantitative evaluation ofregional substrate metabolism in the human heart by positron emissiontomography. J Am Coll Cardiol 1991;18:101-11.

28. Bax JJ, Wijns W. Fluorodeoxyglucose imaging to assess myocardialviability: PET, SPECT or gamma camera coincidence imaging? [edito-rial]. J Nucl Med 1999;40:1893-5.

29. Bax JJ, Wijns W, Cornel JH, Visser FC, Boersma E, Fioretti PM.Accuracy of currently available techniques for prediction of functionalrecovery after revascularization in patients with left ventricular dys-function due to chronic coronary artery disease: comparison of pooleddata. J Am Coll Cardiol 1997;30:1451-60.

30. Bax JJ, Visser FC, Blanksma PK, et al. Comparison of myocardialuptake of fluorine-18-fluorodeoxyglucose imaged with PET andSPECT in dyssynergic myocardium. J Nucl Med 1996;37:1631-6.

31. Bax JJ, Cornel JH, Visser FC, et al. Prediction of recovery of myocar-dial dysfunction after revascularization. Comparison of fluorine-18 flu-orodeoxyglucose/thallium-201 SPECT, thallium-201 stress-reinjectionSPECT and dobutamine echocardiography. J Am Coll Cardiol1996;28:558-64.

32. Srinivasan G, Kitsiou AN, Bacharach SL, Bartlett ML, Miller-Davis C,Dilsizian V. [18F]fluorodeoxyglucose single photon emission com-puted tomography: can it replace PET and thallium SPECT for theassessment of myocardial viability? Circulation 1998;97:843-50.

33. DePuey EG, Ghesani M, Schwartz M, Friedman M, Nichols K,Salensky H. Comparative performance of gated perfusion SPECT wallthickening, delayed thallium uptake, and F-18 fluorodeoxyglucoseSPECT in detecting myocardial viability. J Nucl Cardiol 1999;6:418-28.

34. Cornel JH, Bax JJ, Elhendy A, et al. Agreement and disagreementbetween “metabolic viability” and “contractile reserve” in akineticmyocardium. J Nucl Cardiol 1999;6:383-8.

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reported. The relative advantages and disadvantages ofthese technologies for assessment of myocardial viabilityremain to be investigated.

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