ployed. Early attempts in the 1960s used the clearancerate ofxenon-133 following intramuscular injection (1—3). A significantdisadvantageofthetechniquewastherequirement of multiple injections if more than onevascular territory was being investigated. Particulatetracer methods using radiolabeled albumin microspheres were described in the l970s. Although relativeregional perfusion can be acurately measured with thistechnique, its major disadvantage is the requirement ofarterial injection (4—6).The full potential of nuclearmedicine in evaluating vascular disease was not realizeduntil thallium became available. After i.v. injection, thefractional organ distribution of thallium approximatesfractional cardiac output. It was first suggested thatthallium could be used to quantify blood flow to thelower extremities in 1977 (7). Since that time, severalreports have been published regarding the use of thalhum in this setting (8—16).However, most reports werelimited by the technology available at the time. Assessment was done by probe counting or regional imagingwith comparison of intra- or inter-regional activity ratios. This made it difficult to detect disease when it waspresent at multiple levels or in both legs forlack of anabsolute reference standard. With a whole-body scanner, it is possible to measure thallium activity in thelegs relative to whole-body activity, which would avoidthe limitations ofregional imaging. There has been onlyone report using whole-body thallium scintigraphy toestablish normal values for lower extremity arterial flowduring exercise (14). However, this report did not investigate the effect of gender and age. Furthermore,normal values for gluteal activity were not reported. Anassessment of gluteal activity is especially importantsince ischemia in the distribution of the internal iliacartery can mimic arthritis and is not detectable by othernoninvasive tests of arterial disease. Finally, there havebeen no reports ofthe utility ofwhole-body imaging ofthallium redistribution 4 hr after its injection.

We conducted a prospective study ofthalhium wholebody scintigraphy in order to standardize the method

Whole-bodythalliumscintigraphycanbeusedto diagnoseandevaluateocclusivearterialdiseasein patientswith legclaudication.We performedexercise and redistributionscans in 36 healthy individuals and 17 patients with claudication. Regions of interest were drawn around the wholebody,aswellaseachbuttock,thigh,andcalf.Countsineachregionwereexpressedas a percentageof wholebody activity, as well as an interextremity activity ratio foreach level.Significantdifferencesdue to genderand agewere found. The sensitivityand specificityof the test inmen was 94% and 71%, respectively, using the criterionof percentageregionaluptakeand 81% and 90%, respectively,usinginterextremitycomparison.We condudethatexercise whole-body thallium imaging is a simple andaccurate test for the evaluationof suspectedocclusivearterialdiseaseinthelegs.

J NucI Med 1990; 31:1443—1449

he gold standard for the diagnosis of occlusivearterial disease in the legs is the arteriogram. An inference regarding function (or dysfunction) is made fromthe anatomy revealed by the arteriogram. However, thecorrelation between structure and function is not perfect. The arteriogram studies large vessels but does notprovide information about flow, which is also dependent upon such factors as level of exercise, collateralcirculation, and the presence of small vessel disease.Furthermore, the test is invasive, sometimes requireshospitalization, and carries a small risk of complication.

Radionuclide assessment of arterial disease providesphysiologic information, is simple to perform, relativelynoninvasive, quantifiable, and may be used for serialevaluation. Many different techniques have been em

ReceivedSept. 26, 1989; revision accepted Mar. 6, 1990.For reprints contact: George M. Segall, MD, Nuclear Medicine Service

(115),VeteransAdministrationMedicalCenter,PaloAlto,CA94304.

1443Whole-BodyThalliumScintigraphy. Segallet al

Exercise Whole-Body Thaffium Scintigraphy

in the Diagnosis and Evaluation of Occlusive

Arterial Disease in the LegsGeorge M. Segall, Shelly E. Lennon, and C. Drew Stevick

Nuclear Medicine and VascularSurgery Services, VeteransAdministration Medical Center, Palo Alto, California andDepartment ofDiagnostic Radiology and Nuclear Medicine, Stanford UniversitySchool of Medicine,Stanford, California

Exercise durationGroup Age (mm)Peakhemodynamic

parametersheart

ratesys bp diabp

Group1A= healthymen;GroupI B = menwithsuspectedCAD;Group1C = healthywomen;andGroup2 = menwithclaudication.Asterisksindicatep valueforGroups1B,1C,or2 versusGroup1A: p < 0.05;@ p< 0.01;@ p < 0.001;and@ p < 0.0001.

ology, create a data base of normal values in patientsof differing age and sex, and then to use this data toexamine the sensitivity and specificity of the test inpaients with arterial disease.

MATERIALSANDMETHODSSubjects

Fifty-three individuals had whole-body thallium scans. Individuals who could exercise without development of legfatigue, pain, or cramps; who did not have a history of traumaor surgeryinvolvingthe legs;and who had an ankle-brachialindex (see below) 1.0 at rest, were used as normal controls.Group lÀwas comprised of 14 healthy men with an averageage of 37.8 ±8.3 yr who were recruitedfor the study. GrouplB included 10 men with an averageage of 61.8 ±7.5 yr andsuspectedcoronaryarterydiseasewho werereferredto nuclearmedicine for a thallium treadmill test and who agreed toundergo whole-body scintigraphy in addition to cardiac evaluation. Group 1Cwas composedof 12 healthy women withan average age of 34.8 ±9.6 yr who were also recruitedspecificallyfor this study.

Group 2 consisted of 17 patients, 16 men and 1 woman,with occlusivearterial diseasein the legs.The diagnosiswasmade only ifall ofthe following criteriawere met: 1)presenceof typical intermittent claudication; 2) diminished or absentpulseat the femoral,popliteal,or pedallevels;and 3)a restingankle-brachialindex <1.0. Nine patients had arteriographically documented large vessel disease. Three patients haddiabetes and six had multiple lesions. The average age of thisgroup was 66.3 ±5.4 yr.

Ankle-Brachial IndexDoppler-assistedmeasurementsof systolicblood pressure

at rest were obtained in all individuals before exercise. Measurements were taken with the patients supine. The anklebrachial index was derived by dividing the pressure measuredat the ankle by the pressuremeasuredin the antecubital fossa.Measurements at the ankle were taken over the posterior tibialor dorsalis pedis artery. The finding ofan ankle-brachial index<1.0 is highly suggestiveof functional arterial obstruction(11).

Exercise ProtocolAll patients performed symptom-limited treadmill exercise

with cardiac monitoring. Patients exercised according to theBruce protocol, or a low-level modification of the protocol.The test endpoint for individuals in Group 1 (controls) was

fatigue whereas all patients in Group 2 stopped exercisingbecauseof intermittent claudication.Duration of exercise,aswell as peak blood pressure and heart rate for both groups isshown in Table 1.

ScintigraphyTwo to 3 mCi of thailium-20l-chloride (@°‘Tl-chloride)

were injected at peak exercise, and patients were asked to walkfor an additional minute. Five minutes later they were placedsupine on the imaging table and whole-body scintigraphy wasperformed in the posterior projection. A few early patientsalso had anterior whole-body scintigrams. Scans were performed in a single-pass using a rectagularlarge field of viewgamma camera.A high-sensitivitylow-energycollimatorwasusedmostoftenin orderto maximizecounts,althougha highresolution low-energycollimator was occasionallyused forconvenience with equally good results. A 70—90keY windowwas used for acquisition. The scan speed was 40 cm/mm andall scans were completed in 5 mm. The total count wastypically, 150,000—250,000.Patients returned 4 hr after thaihum injection for redistribution imaging. No limitations wereplaced on diet or activity during the interim period.

AnalysisImages were acquired on computer in a 512 x 512 pixel

matrix. Only the posterior view was used for quantitativeanalysis. Rectangular regions of interest of equal size weredrawn around the whole body, buttocks, thighs, and calves(Fig. 1). No correction was made for background activity,whichwasnegligible.Total counts in each regionweredetermined by computer and expressed as a percentage of wholebodyactivity.Symmetryofactivity wasmeasuredby dividingthe average pixel value of any given region by the averagepixel value ofthe contralateralregion at the same level. Theseratios were determined for legsas well as buttocks, thighs, andcalves. The ratio was always derived by dividing the smallernumber by the larger number so that all values were less thanor equal to 1.0.

Statistical AnalysisValues are expressed as mean ±1 s.d. Student's unpaired

t-test was used for inter-group comparison. Probability (p)values <0.05 were considered significant.

RESULTS

Anterior and posterior whole-body images obtained5 mm after exercise in an individual with a normal scan

TABLE 1ExerciseData Accordingto Group(ValuesExpressedas mean±1 s.d.)

1A37.8 ±8.314.8 ±1.6180 ±11165 ±2073 ±101B61 .8±7.5―8.2 ±1.7@1 18 ±18@1 66 ±3581 ±16ic34.8

±9.61 1.5 ±3.1'178 ±11142 ±2(76 ±11266.3±5.4@―5.0±3.0@105±20―@163±4087±14@

1444 The Journalof NuclearMedicine•Vol. 31 •No. 9 •September1990

@n.

.-*.

A BA B FIGURE 2

Earlypost-exerciseanterior(A)andposterior(B)whole-bodyimagesofa manwitha normalstudy.Theglutealmusclesarenot well seenon the anteriorview and activity in the thigh andcalf musclesis significantlyattenuated by the long bones. Incontrast, muscle groups are clearly defined in the posteriorview.

show that different normal values must be establishedfor men and women.

Age is also an important factor. Men in Group lBwere on average 24 yr older than men in Group lA.Older men had slightly less thallium activity in thewhole leg than younger men, as well as lower overallthallium wash-out. There were also significant regional

differences between the two groups.Men with claudication had markedly lower values

for thallium activity in the leg and calfwhen comparedto either healthy younger or older men. These differences were highly significant. Furthermore, men withclaudication showed net gains in thallium activity in allregions of the leg in contradistinction to both controlgroups, which showed net decreases. These differenceswere also highly significant. Figure 3 shows an exampleof a typical scan in a man with claudication and signsof occlusive arterial disease.

FIGURE 1Early (A) and 4-hr (B) post-exerciseposteriorwhole-bodyimagesof a healthymanwithoutperipheralvasculardiseaseshowingtherectangularROlsaroundthewholebody,glutealregions, thighs, and calves used for quantitative analysis.Regionsat thesamelevelareequalinsize.

are shown in Figure 2. The gluteal region is not seenon the anterior view and the long bones cause a markedattenuation defect in the thigh and calf. In contrast, thegluteal, thigh, and calf regions are well demarcated onthe posterior view. Since the anterior view only provided limited information, it was abandoned after thefirst several individuals so that only the posterior viewwas acquired and used for analysis.

Regional thallium activity for all the individuals studied is shown in Table 2. Approximately one-quarter ofthe injected dose is distributed in the muscles of thelower extremities. Healthy women show significantlyless activity in the gluteal and thigh regions than healthymen, but have comparable calf values. This is true forboth early scans and scans done at 4 hr. Healthy womenalso show differences in regional wash-out when compared to healthy men, although the percent decrease intotal leg activity is not significantly different. The results

1445Whole-Body Thallium Scintigraphy •Segall et al

TABLE2RegionaIThallium Activity Expressed as aPercentageofWhole-Body

Activity(mean±1s.d.)GroupEarlyscan 4-hrscan% change

Group1A = healthymen,Group1B = menwith suspectedCAD;Group1C = healthywomen;andGroup2 = menwithclaudication.

Asterisks indicatep-valuefor Group 1B, 1C,or 2 versus Group1A.Poundsignsindicatep valuefor Group2 versusGrouplB.

. or ‘ p < 0.05;@ or@ p < 0.01 ; @••or@ p < 0.001 ,@ or

#### p < 0.0001.

Figure 4 compares the frequency of abnormal findings on exercise whole-body scintigraphy using different“normal―values ofthallium activity. The graph depictsthe percentage ofpatients with claudication whose fractional whole-leg thallium uptake is <2 s.d.s below themean for either healthy young men or older men withsuspected coronary artery disease. Generally speaking,the test is more sensitive if young healthy men are usedto define normal values. Figure 5 depicts the specificityof the exam by comparing the two control groupsagainst one another. The specificity of the test is highin healthy young men when they are compared to oldermen with suspected coronary artery disease. The specificity of the test in older men is lower when they arecompared to healthy young men. Possible explanationsfor this difference include subclinical disease in oldermen as well as higher thallium delivery to the legs inhealthy young men who are able to exercise longer.

The same observations about the accuracy ofthe testare true ifone looks at individual regions as opposed tothe whole leg. Ifhealthy young men are used as controls,then 16/16 men with claudication have at least oneabnormal region on the early or 4-hr scan, or show atleast one region with abnormal distribution. However,

Gluteal1A9.2±0.98.7 ±0.8—4.9 ±5.0lB9.8±0.99.5 ±0.7―—3.4 ±6.0ic8.4±0.7W8.2 ±0.T—1.8 ±6.22##88±139.0±1.1##29±86Thigh1A11.4±0.810.7±0.7—5.8±4.4lB9.6±1.5@@9.5±1.3W—0.4±5.9@'ic10.0

±1.1••••9.2±0.9....—7.7 ±4.528.8±1.5@9.2 ±1.4@@‘5.3 ±7.0WCalf1A9.0

±0.67.9 ±0.4—11.5 ±4.8lB8.6±1.17.8 ±0.8—8.9 ±5.31C9.0±1.37.7 ±0.8—14.2 ±4.(2####61±1.5W####63 ±1.2W####68 ±10.1....Leg1A29.5±1.527.3±1.2—7.3±3.4lB28.1

±2.526.8 ±1.9—4.4 ±4.61C27.4±1.4'@25.2 ±1.1'@—8.1 ±3.92####237±2.4@###245 ±1.9....####40 ±4.3W

‘@

A B

FIGURE 3Early (A) and 4-hr (B) post-exercise posterior whole-bodyimagesof a manwith bilateralintermittentdaudication of thebuttocksandcalvesandsignsof occlusivearterialdisease.Decreased activity on the early scan is very apparent in theright calf, and to a lesserextent, in the left thigh. Quantitativeanalysisalsorevealsdecreasedactivityin the leftglutealregionon the early scan. The 4-hr imageshows some redistnbutionof activity to the left thigh and,questionably,the rightcalf. However, quantitative analysis indicates higher than normal redistributionto both thighs and both calves.

9/10 older men with suspected coronary artery diseasealso have one or more abnormalities (overall sensitivityand specificity of 100%and 10%,respectively). If oldermen are used as controls, then at least one regionalabnormality is detected in 15/16 patients with claudication and 10/14 healthy young men (overall sensitivityand specificity of 97% and 71 %, respectively).

Table 3 lists the frequency of normal results whenregional side-to-side thallium symmetry ratios are examined in the four groups ofpatients studied. Using an

empirically defined normal of 90% or greater, specificity is very high for healthy young men and women aswell as for older men without claudication. This findinghas also been observed by others (9,12). The sensitivityofthis method of analysis ranges from a low of 31% inthe thigh to a high of62% in the calf. The corresponding

1446 The Journalof NuclearMedicine•Vol. 31 •No. 9 •September1990

TABLE3Percentageof Individuals with Normal (90%)RegionalThallium

SymmetryRatiosGroupEarly

scan(%) 4-hrscan(%)

Group1A = healthymen;Group lB = menwith suspectedCAD;Group1C = healthywomen;andGroup2 = menwithdaudication.

14). Images obtained after rest and exercise in normalindividuals are qualitatively similar, although muscleactivity is much higher after exercise. In patients withperipheral vascular disease, however, the images aredissimilar. Hamanaka et al. found that resting imagesin patients with peripheral vascular disease were notsignificantly different from normal controls whereaspost-exercise images showed significantly less fractionalleg activity (14). This situation is analogous to myocardial perfusion imaging where it is well known thatexercise is necessary to identify subcritical hemodynamically significant lesions.

The earliest studies of thallium scintigraphy employed intraextremity (gluteal-to-thigh, thigh-to-knee,thigh-to-calf, calf-to-ankle) and interextremity (thighto-thigh, calf-to-calf) ratios to evaluate limbs in healthyindividuals and patients with occlusive arterial disease(9,11,12).In thereportof Sederet al.,thediagnosticaccuracy for disease in the gluteal region and thigh was82% whereasthe accuracy for calf diseasewas 95%(12). The lower accuracy for proximal disease was dueto low sensitivity (75%), which the authors thoughtcould be explained by a balanced reduction in glutealand thigh activity in some patients. None of the previous reports using this kind of analysis stated whetherintraextremity or interextremity ratios could be usedseparately or which was more accurate.

The interpretation of exercise thallium whole-bodyscintigraphy using the criterion of interextremity symmetry is very appealing because the concept is intuitiveand it is easy to appreciate when reading a scan. Eightyone percent (13/16) of patients with claudication and

1001009256

10090

10069

100909238

1001009269

10090

10075

10090

10059

post-exercise 4-hour redistribution

100

90

00

@ 70

@ 60z

@ 50I-

@ 40U

@ 30

20

I0

L@ patients with claudicetloncompered to older men wUhsuspected CAD

petients with cleudicetion@ compered to heelthy young

men

Gluteal1AlB1C2

ThighlAlB1C2

Calf1AlBlC2

FIGURE 4Frequency of abnormal fractional whole-leg thallium activity inpatientswithclaudication,usingeitherhealthyyoungmenoroldermenwithsuspectedcoronaryarterydisease(CAD)forcomparison. Sensitivity is highest when healthy young menareusedto definenormal.

values are all lower for the 4-hr scans owing to redistribution ofthallium activity. Overall, 13/16 patients withclaudication (8 1%) have at least one region with interextremity asymmetry, whereas 0/10 healthy young men(0%), 2/ 12 healthyyoungwomen (17%), and 2/10 oldermen with suspected coronary artery disease (20%) haveone abnormality.

DISCUSSION

Previous studies of thallium scintigraphy for diagnosis ofocclusive arterial disease have compared imagesobtained at rest to those obtained after exercise (9,10,

FIGURE 5Frequencyof normal fractional whole-leg thallium activity intwocontrolgroupswhencomparedtooneanother.Specificityis highest when older men with suspected coronary arterydisease are used to define normal.

100

90

00

@ 70

@ 60z

@ 50

@ 40

0. 30

20

10

post -exerc ise 4-hour redistribution

healthy young mencompared to older menwith suspected CAD

1447Whole-Body Thallium Scintigraphy e Segall et al

older men with suspected@ CADcomporedto henithy

young men

signs of occlusive arterial disease in this study had atleast one region which showed asymmetric thalliumactivity. Furthermore, among the 26 healthy youngmen and women studied (Groups lÀand lC) only twowomen would have been misclassified as abnormal.The degree of asymmetry in these two women wasminimal. The side-to-side thallium activity ratio was

88% in the calf region in one, and 89% in the glutealregion in the other.

The problem of evaluating symmetry is the possiblepresence of bilateral disease causing a commensuratedegree ofdiminished thallium uptake. Others have alsocommented on the problems posed by bilateral diseasewith this kind ofanalysis (8). This is not a great problemif scintigraphy is merely used to screen for the presenceor absence of disease anywhere in the legs to establishthat symptoms are indeed due to claudication which isvascular in origin. In this situation, less than 20% ofpatients will be mistakenly classified as normal. However, the evaluation of symmetry will only detect themost severely diseased limb when both limbs are affected. To overcome this limitation, it is necessary tohave some measure of absolute thallium activity toincrease the sensitivity of the test. Regional fractionaluptake relative to whole-body thallium activity can beused for this purpose and is easy to measure.

There has only been one previous study which hasreported on the results of post-exercise whole-body

thallium scintigraphy for the diagnosis and evaluationof occlusive arterial disease (14). In that study, thecontrol group was comprised of ten subjects withoutsigns or symptoms of atherosclerosis or peripheral vascular disease whose average age was 39 yr. The numberof men and women was not specified. The reportedaverage regional fractional uptake post-exercise was12.26%±1.91%forthethighand6.58%±0.99%forthe calf. This compares to 9.6%—l1.4% for the thighand 8.6%—9.0%for the calf, depending on controlgroup, observed by us. The differences between the twostudies are probably due to patient selection as well astechnical factors. Hamanaka et al. did not reportwhether rectangular or irregular regions ofinterest wereused, whether the analysis was based on anterior and!or posterior whole-body images, or whether any background subtraction was employed (14). In any case, itunderscores the need for normative data to be developed in each laboratory.

It is interesting that healthy young men have higherfractional thallium uptake in the thigh, but lower fractional uptake in the gluteal region than older menwithout peripheral vascular disease. At first, we thoughtthis may be an artifact due to the occasional difficultyencountered in separating gluteal from thigh muscle,but careful redrawing of the regions of interest gave thesame results. It seems more likely that this difference isdue to an actual redistribution ofmuscle mass with age.

The definition of normal is a problem. It is probablybetter to use age-matched rather than healthy youngcontrols. However, using patients with suspected coronary artery disease as controls is not ideal since thesepatients may have subclinical peripheral vascular disease which is not evident because heart disease limitstheir exercise. This problem can be minimized by onlyusing individuals with normal cardiac thallium evaluations whose exercise endpoint is generalized fatiguerather than angina.

In summary, we believe that exercise thallium wholebody scintigraphy is a promising technique in evaluating patients with suspected occlusive arterial disease inthe legs. Laboratories interested in performing this testmay quickly and easily generate a normal data base byscanning patients referred for cardiac evaluation whohave no signs of heart disease. Only the posterior viewis required for analysis. Regional fractional thalliumuptake should be determined for early and 4-hr scans.Late imaging is helpful because significant redistribution is sometimes the only abnormal finding. Evaluation of symmetry is less sensitive, but significant asymmetry is highly specific.

Finally it should be pointed out that our values forsensitivity and specificity based on regional thalliumanalysis are for presence or absence ofdisease in a limb,without regards to actual location. All nine patients inthis study who had claudication and arteriographicallydocumented disease also had an abnormal thalliumscan. At this point, we can only conclude that exercisethallium whole-body scintigraphy may be a usefulscreening test in identifying patients with occlusivearterial disease. Demonstration that the test can be usedin conjunction with arteriography to evaluate the functional significance of anatomic disease and help selectpatients for revascularization requires further study.

REFERENCES

1. Lassen NA, Lindbjerg J, Munck 0. Measurement of bloodflow through skeletal muscle by intramuscular injection ofXe-133.Lancet1964;1:686—689.

2. AlpertJS, LarsenOA, LassenNA. Evaluationof arterialinsufficiencyof legs.A comparison of arteriography and theXe-133walkingtest.CardiovascRes1968;2:161—169.

3. Alpert JS,LarsenOA, LassenNA. Exerciseandintermittentclaudication.Bloodflowin the calf muscleduringwalkingstudiedbythe xenon-l33 clearancemethod. Circulation 1969;39:353—359.

4. Siegel ME, Giargiana FA, Rhodes BA, White RI, WagnerHN. Effect ofreactive hyperemia on the distribution of radioactive microspheres in patients with peripheral vascular disease.Am JRoenigenol1973;118:814—819.

5. Rhodes BA, Greyson ND, Siegel ME, et al. The distributionofradioactive microspheres after intra-arterial injection in thelegsofpatients with peripheral vasculardisease.Am J Roentgenol1973;118:820—826.

6. SiegelME, Giargiana FA, White RI, Friedman BH, WagnerHN. Peripheralvascularperfusion scanning.Correlation with

1448 The Journalof Nudear Medicinee Vol. 31 •No. 9@ September1990

the arteriogram and clinical assessment in the patient withperipheral vasculardisease.Am J Roenigenol 1975; 125:628—633.

7. StraussHW, KarrisonK, PittB.Thallium-201:noninvasivedetermination from the regional distribution of cardiac output.JNuclMed 1977;18:1167—1170.

8. Christenson J, Larsson I, Svensson SE, Westling H. Distribution of intravenously injected thallium-20l in the legsduring walking.Eur J Nuci Med 1977;2:85—88.

9. Siegel ME, Siemsen JK. A new noninvasive approach toperipheral vascular disease: thallium-20l leg scans. Am JRoenigenol 1978; 131:827—830.

10.GlassEC,DeNardoGL. Abnormalperipheraldistributionofthallium-20l due to arteriosclerosis. Am J Roenigenol 1978;131:718—720.

11. Siegel ME, StewartCA. Thallium-20l peripheralperfusionscans: feasibility of single-dose, single-day, rest, and stressstudy.AJR1981;136:1179—1183.

12. Seder iS, Botvinick EH, Rahimtoola SH, Goldstone J, Price

DC. Detectingand localizingperipheralarterialdisease:assessmentof@°Tlscintigraphy.AJR 1981; 137:373—380.

13. Burt R, Mullinix F, Schauwecker D, Richmond B. Leg perfusion evaluated by delayed administration of thallium-20l.Radiology 1984; 151:219—224.

14. Hamanaka D, Odori 1, Maeda H, Ishii Y, Hayakawa K,Torizuka K. A quantitative assessmentof scintigraphyof thelegs using 201fl EurfNuclMed 1984; 9:12—16.

15. Chevreaud C, Thouvenot P. Lapeyre G, Laurens M-H, Renard C. Thallium-20l muscle scintigraphy:application to themanagement of patients with arterial occlusive disease. Angiology 1987;38:309—314.

16. Oshima M, Akanabe H, Sakuma Sadayuki, Yano T, Nishikimi N, Shionoya S. Quantification of leg muscle perfusionusingthallium-201 singlephoton emission computed tomography. JNuclMed 1989; 30:458—465.

17. Sumner DS. Management of segmental arterial pressure: In:Rutherford RB, ed. Vascularsurgery. Philadelphia: WB Saunders;1984:109—135.

1449Whole-Body Thallium Scintigraphy •Segall et al

Erratum

Due to a production error, Equations 3—4in “LeftVentricular Volume Calculation Using a Count-BasedRatio Method Applied to Multigated Radionuclide Angiography―by Massardo et al. in the April issue of theJournal were printed incorrectly. The correct equationsare as follows:

The constant of proportionality is eliminated by takingthe ratio R = Ct/Nm, which from Equations 1 and 2 isas follows:

(@)D3 (!)D2CIKVI V1 6 6

R - N KV@@ V@1 M2D M2 (3)

It is clear that R is a dimensionless quantity that isequal to the number of reference volumes contained inthe entire spherical volume.

Equation 3 may be solved for D as follows:

D =@ (4)

The volume of the sphere is:

V1=@ D3,

hence from Equation 4,

V@=@ [ \/@@]