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however, detection by CT or MRI is often inconclusive.

Cr imagesare sometimesobscured by artifacts, arising

from complexbony structures of the skull base, whereas MRI has the inherent drawback of weak signal detection (signal void) from the bone cortex. Several studies have shown that planar bone scintigra phy is a useful technique for demonstrating skull bone invasion of head and neck tumors (1—5), but the specific localization of these lesions was often difficult to ascertain because of the complexity of the skull base. Brown et a!. (6) reported that the normal and abnormal transaxial anat omy of the face and skull could be clearly definedby

SPECT. Despite their significant results, at the time,

SPEC!'hadpoorspatialresolution.Thisproblemhasbeen greatly reduced with the introduction of three-detector SPECT' cameras equipped with fanbeam collimators. This instrumentation provides significantly better spatial resolu tion and imageclarity than previous SPEC!' models. Bone SPEC!' with @Tc-HMDPhas become an impor tant diagnostic tool. Yui et a!. (7) showed how bone SPEC!' can be successfully used in skull-base regions and has high sensitivity for bone lesions detection. Moreover, the sensitivityof this methodcan provideearlierdiagnosis of bone abnormalities.These findingsare often more con clusive than those obtained by CT', MRI or planar bone scintigraphy. Inaddition,201T1-Cl,a radionuclidethatdisplaysprefer ential accumulationin a variety of tumor types, is com monly used in SPECT tumor imaging. Several reports have demonstrated its efficacy in evaluating and localizing ma lignant tissue, especially in the lungs (8, 11 ), brain (9,10) and skull base (12,13). Thisstudywas undertakento providea reliablediagnos tic method for the early detection of skull-base invasion of head and neck tumors. To achieve our goal, we used si multaneousbone and tumor dual SPEC!' (S-SPECT)im a@igfor co-localizationof bone and tumor-specificradio nuclidesin patients with suspected skull-baseinvasion.

MATERIALS AND METhODS Preliminary Study Prior to clinical application, a preliminaryexamination of a dried skull was conducted to establish anatomical details of the skull base. A dried skull was first labeled by immersion for 1 hr in 4000 ml @“Tc-HMDPdiluted with physiological saline and sub

Skull-base invasions of head and neck tumors were examined by simultaneous bone and tumor dual-isotope SPECT (S

SPECT)with°°@rc-hydroxy-methy1ene-diphosphonate(°@rc

HMDP)[email protected],enessandreliabilftyof tumor diagnosis by this method was the primary interest in this study. Methods: Before S-SPECT imaging, a phantom expen ment using dned skull-bonespecimenswas pertormedto estab lishanatomicaldetailsofthe skullbasewiththeSPECT camera. Radionudidecrosstalk,windowwidthsandcontrolpatientswere also examined prior to S-SPECT imaging.Twenty patientswith

suspected tumor invasion of the skull base underwent

S-SPECT. Results: Preliminary expenments revealed that crosstalk effects could be disregarded with adequate window width and routine administrative doses of the radionudkies.

S-SPECTdetectedbonedestruc@onand the extentof tumor

invas@n for all 12 palients in whom skull-base invohiement was diagnosed by CT or MRI. For the three patients in whom CT or MRIrevealednotumorinvasion,theS-SPECTimagesdidnot show any abnormal accumulabon in similar regions. In the re maining five patients without CT and MRI confirmation of skull base invasion,the S-SPECT findings showed skull-baseabnor maiities in three. Tumor invasionwas confirmed surgicallyor by clinical follow-up. The remaining two patients had negative S-SPECT images.Conclusion: S-SPECT is an effectiveand reliable diagnostic technique for detecting tumor invasion in the complex bony regions of the skull base. Key Words: single-photon emission computed tomography; technetium-99m-HMDP; thallium-201-chlonde; skull base inva sion; head and neck tumors J NucI Med 1995; 36:1740-

alignant head and neck tumors are commonly known to invade the skull base. Although not all invasive patterns are direct, occasionally there is protrusion through the neurovascularforamina.In many cases, resorption or destruction of the surrounding bony regions is observed. Todate,thediagnosisoflesionsintheskullbasehavebeen limited to the use of CT and MRI. When the lesion is localized near the cortical regions of the skull-base bone,

ReceivedSept.13,1994;revisionacceptedJan.26,1995. Forcorrespondenceorreprintscont@ MitsutakaFukum@o,MD,Depait@,ent ofRadkilogy,KochiMedialSchool,Kohasu,Okoh.cho,NankOkU-City,Kochi783, Japan.

1740 TheJournalof NudearMediane•Vol.36 •No.10•October

Dual-Isotope SPECT of Skull-Base Invasion

of Head and Neck Tumors

Mitsutaka Fukumoto, Shoji Yoshida, Daisuke Yoshida and Seiji Kishimoto

Departments ofRadio1o@' and Otola,yngology, Kochi Medical Schoo4 Koch4 Japan

Bone

SPECTDiagnosisPositivePositiveTumor SPECTTumor

base.PositiveNegativeSkull contactingthe skull baseboneabnormality withnotumorinvasion. Possibilityof no20111uptake (falsenegative)or bony tumor.NegativePositivePatterninflammationaround Protrusionof is rare. tumorthroughthe neurovascuiarforaminawith invasion.NegativeNegativeSkull no baseis notinvolved.No tumorcontactwiththe skull base.

sequently dried with warm air to produce a phantom specimen. Bone SPECT was performed on the phantom skull and a control image of the skull base was obtained. The phantom image was compared with a bone SPECT image of the skull of a normal patient who had no symptoms of head and neck disease. Addi tionally, the neurovascularforaminaof the @‘Tc-HMDPlabeled

dry skull were filledwith smallcotton balls soaked with 20111Cl

(containing approximately 10—25MBq each), and S-SPECT was performed to determine the anatomical locations of the foramina by superimposingthem on the bone SPEC!' image. Crosstalkevaluation of the radionuclideswas examined in the rangeof 68—80keV to determine @“@Tcscattereffects on the 201'fl photopeak. The count per unit volume of 201@flmeasured from a homogeneous 2o―flaqueous solution (37.5 MBq/1 ml) was desig nated as variable A. In addition, a mixed aqueous solution con tamingequalvolumes of 2o―fl(37.5 MBq/1ml mixed solution)and @Tc(37.5 MBq/1ml mixed solution)was examined. In this case, the count per unit volume of @°‘T1of the above mixture was variable B. The crosstalk (CR) effect that @“Tchad on the 2o―fl window was approximated by the following formula:

CR=(B-A)/Ax 100(%).

The energy window width for S-SPECT was changed to 10%, 15%, 20% and 30% and the respective crosstalks were calculated. Because administered doses of radionuclides are different in clinical practice, @“Tccrosstalk in the energy window of 201'fl(at 10% window width) was also studied with a variety of mixed solutions. The radionuclides were combined in aqueous solutions with the proportionsof @‘@Tcto 201'flrangingfrom4:1 to 4:4 and subsequently examined for crosstalk. We chose these mixture ratios based on the results from single-isotope SPECT analysis of normal physiological distribution ratios of @“@Tc-HMDP( MBq, 4.5 hr) and 201iia (111MBq, 2.0 hr)obtained from the skull bases of normal individuals. Normal physiological distribution ratios in the range of 4:2 to 4:3 were observed in the preliminary clinical trials and were used for reference in the clinical studies. ClInIcal Study Following the preliminary studies, 20 patients (16 men, 4 women, aged 22 to 78 yr) with suspected skull-base tumor inva sion had S-SPECT. The imaging protocol was:

1. Intravenous injection of @“Tc-HMDP(555 MBq) with a 2. hr waiting time.
2. Whole-body planar bone scintigraphy was performed. 3. After bone scintigraphy, intravenous injection of 20111-Cl (111 MBq).
3. At 2 hr postinjection of 201'fl@ (4.5 hr postinjection of @‘@Tc-HMDP),S-SPED' of the skull base was performed.

5. Bone and tumor S-SPED' imageswere evaluated.

A three-detectorSPECT cameraequippedwith a fanbeamcol limator with 7.3 mm spatial resolution (FWHM, at the rotation center) was used for the preliminary and clinical studies. Each detector was rotated at 4°step angles (30-sec step inter vals). Fanbeamprojectiondata from 90 steps were acquiredover

15mmandcollectedon a 256x 256matrix.Thefanbeamprojec

tion datawere then converted to the parallel-beamprojectiondata on a 128 x 128 matrix, and SPECT images with 1.7 mm slice thickness were constructed by Butterworth and ramp filters for preprocessing and backprojection, respectively. Axial, coronal and sagittal images of bone and tumor SPECT were obtained simultaneously.Diagnosis of the skull-baseinvasionwas madeby

TABLE I

S-SPECT Resultsof Skull-Base Invasion

analysis ofboth kinds of images. Examples of positive or negative findings and a brief description of their significance are given for each radionuclidein Table 1.

RESULTS Preliminary Study Comparison of bone SPEC!' images obtained from the dried skull phantom and the normal control patient re

vealed no majordifferencesin skull-baseanatomicaldetails

(Fig. 1). Applicationof S-SPECT to the dry bone phantom

(labeled with @Tc-HMDP)containing 201'flQ labeled cotton balls in the neurovascular foramina made it possible to determine the locations of the foramina in S-SPECT images (Fig. 2). Results of the crosstalk study, in equal

doses of @‘@Tcand @°@‘fl,revealed slightly increased

crosstalk in the 1O%—20%window width, whereas in the

30% window width, greater than 30% crosstalk was ob

served (Table 2). When the mixture ratios of 9@―Tcto @°‘Tl

were changed, the crosstalk was slightly increased, except

when the mixture ratio of @‘@Tcto @°‘Tlwas 4:1 (Table 2).

ClinicalStudy

The results of S-SPECT evaluation of skull-base tumor

invasion and other modalities (CT, MRI and surgical find ings) are given in Table 3. For the patients with conclusive

Cr and MRI results of skull-basedestruction and tumor

invasion, S-SPECT also visualized abnormal tracer accu mulations in both the bone and tumor SPECT images.

In the three patients in whom Cl.' and MRI showed

noncontacting tumor at the skull base, S-SPED.' analysis

revealed no alterations in the bony anatomy of the skull

base and a complete separation of tumor from the bone.

The remainingfive patients displayed problematicsigns of

skull-base destruction. S-SPEC!' detected tumor invasion in three of five patients with inconclusive findings; surgery

later confirmed tumor invasion. In two patients with sus

pected skull-base invasions, S-SPED.' was negative and

surgery confirmed the S-SPECT results. Four typical cases of S-SPECT application are illustrated (Figs. 3—6).Al

Bone and Tumor SPECT at Skull Base •Fukumotoet al. (^) 1741

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FIGURE2. SPECTimagesof the @‘Tc-HMDP-iabaleddried

skull containingsmallcottonswabsin the majorneurovascularto ramina Cottonballslabeledwith @°iialsowere placedaroundthe CnStagab.

TABLE 2

CrosstalkStudyResults

WindowwklthCrosstalkratio30% 2.5%20% wkfth37% ± 2.1%15%width11%±2.2%1O%wklth7%±1.5% width18% ±

MixtureratioCrosstalkratio(@rc:@°111)(10% fixed)4:135%±5.2%4:220%±4.1%4:317%±3.1%4:411% width

Patient no. DiagnosisCT/MRIS-SPECT

in SkullBaseInvasion SPECTEvaluation1 biopsy)Bone SPECTTumor (ope, SCCPositivePositivePositiveInvasion(+)2 Maxillary ca SCCPositivePositivePositiveInvasion(+)3 Madllatyca AdenoPositivePositivePositiveInvasion(+)4Parotidca neuroblastomaObscurePositivePositiveInvasion(+)5 Nasal SCCPositivePositivePositiveInvasion(+)6 Nasalca SCCPositivePositivePositiveInvasion(+)7 Epiphatyngealca SCCPositivePositivePositiveInvasion(+)8 Epipharyngealca SCCPoabvePositivePositiveInvasion(+)9 Maxillaryca SCCPositivePositivePositrveInvasion(+)10 EpipharyngealCa SCCObscurePositivePositiveInvasion(+)11Epipharyngealca opPositivePositivePositiveInvasion(+)12 Chondrosarcoma. pre Invasion(—)13 MaxillarycaSCCNegativeNegativeNegativeNo lymphomaObscurePositiveNegativeInvasion(+)14 Maxillary Invasion(—)15 Maxillaryca SCCNegativeNegativeNegativeNo Residual(—)16Chondrosarcoma.postopObscurePositiveNegativeNo papillomaPositivePositiveNegativeInvasion(+)17 Palateinverted ca*PositivePositiveNegathfeInvasion(+)18 Undifferentiated Invasion(-)19 MmdllaiycaSCCNegativeNegativeNegativeNo SCCPositivePositivePositiveInvasion(+)20 E@pharyngealca

Invasion(—)tumor MaxillarycaSCCObscurePositiveNegativeNo

ongin).ca (parapharyngeal = carcinoma;adeno= adenocarcinoma;SCC =squamous-call carcinoma.

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Comparisonof WindowW@thto Crosstalk(@°11window)

CrosstalkEvaluationof Four MixtureRatios (@°i1window)

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FiGURE 1. Bone SPECT imagesof skull-baseregionsfrom a

@rc-HMDP-labeleddriedskull(A)andcontrolpatient(B).Corn

parison of anatomical structures revealed no major differences. No

mandibleis presentonthedriedskullspecimen.

TABLE 3

Assessment of Skull Base Invasion

I 742 TheJournalof NuclearMedicine•Vol.36 •No.10•October

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FIGURE4. (A)CTscans(bone-windowCTabove,contrast-en

hancedCTbelow)froma 66-yr-oldmanwithmaxillarycancerlocal

uzedinthe postero-lateralwallofthe maxillarysinusare negativefor skull-baseinvasion.(B)BoneSPECTrevealedhighaccumulationin

theskullbase(smallarrows);tumorSPECTwasnegativein this

area (largearrow).

DISCUSSION

Skull-base invasion of head and neck tumors signifi

cantly affect a patient's prognosis. Therefore, it is cx tremely important to detect the location and determine the

extent of tumor involvement in this region of the skull.

Otherclinicians (1—5)have reportedthatbone scintigraphy

was sufficientfor detecting head and neck tumorinvasions

at the skull bone. Unfortunately, the complex structureof

the skull base and lack of distinction between the numer

ous structure in this region are major limitations of bone scintigraphy. Brown et al. (6) distinguished between nor ma! and abnormal bony regions fairly distinctly by using

bone SPED.', but their findingswere limited by the spatial

resolution of the SPECT camera. Technological improve

ments have revolutionized SPECT imaging, making it

more accurateand reliablefor detecting tracerlocalization.

In many patients,extensive tumordevelopmentand skull-base destruction can be diagnosed accurately with CT or MRI. Yui et al. (7,13) reported that bone SPECT

could detect skull base abnormalities, even though CT or

FIGURE 3. (A) CT (above) and MRI (below) of a 67-yr-old womanwith epipharyngealsquamous-callcarcinomareveala con spicuous lesion on the rightside indicativeofskull-base invasion. (B)

S-SPECTshowsabnormalhigh @Fc-HMDPaccumulations(small

arrows) correspondingto tumor-positivesites (largearrows) in a regionjust bek)wthe rightforemenlacerum.

though the sample number was small, we performed sta

tistical analysis. S-SPECT sensitivity for detecting skull base tumor invasion was 93.3% (Table 4). S-SPEC!' bone image, on the other hand, had a sensitivity, specificity and accuracy of 100%, 60% and 90%, respectively (Table 4).

The sensitivity, specificity and accuracy of tumor

S-SPECF were 80%, 100% and 85%, respectively (Table 4). We found no accumulation of 201'fl in patients with malignant lymphoma, undifferentiated carcinoma or in verted papilloma.

A postoperative case of chondrosarcoma at the skull

base was of interest. Although the tumor was completely

removed, Cl' scans showed abnormalsoft-tissue density in

the skull base as a result of bone reinforcementtechniques

and postoperative changes (Fig. 6A). In this patient, CT

determination of residual abnormality or recurrent lesion

was not possible. S-SPECT, however, showed that bone

damage was a result of surgery, and tumor SPECT re

vealed the absence of malignanttissue (Fig. 6B).

Bone and Tumor SPECT at Skull Base •Fukumotoat al. 1743

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.4 ‘ scans from a 22-yr-oldwoman with nasalneuroblastomawere incondusivefor skull-baseinvasion.(B) S-SPECTrevealedpositivebonereactivityin the posteriornasal regionwith sometumor invasion(largearrows).A smallaccumula tion of tracer was Visualized I,, the right temporal bone in the bone SPECTimage(smallarrow).

MRI showed normal anatomy, when a tumor existed just

below or near the skull base. Their studies, however, used

single SPECT analysis of the radionuclide, and the rela tionships of bone with the tumor were inconclusive. In our study, a directcomparisonof tumorand bone

could be obtained by simultaneous visualization of both

radionuclides. Technetium-99m-HMDP is one of the most sensitive radiopharmaceuticals for detecting bone disease, and although false-positives are sometimes observed, con firmation can be achieved by examining the accumulation

of 201Tl-Clrelative to the false-positive site.

In this study, delayed 20111-Climages were suitable for

detecting malignant tumors because of delayed washout

observed in malignancies (8,15—17).Some studies using

@-°‘Tl-Clfoundthatonlytheearlyimagewas usedto obtain

the tumor SPECT image and that a delayed image was not

acquired (12, 18—21). This protocol is possible if positive

determination of the tumor as malignant can be made by

biopsy or other methods. When reactive inflammation has an effect on the skull

base regions, 201Tl-Clmay show high accumulations in the

inflamed areas in early images. In this situation, it is often difficult to determine whether these results reflect actual

FIGURE 6. (A) PreoperativeCT scanfrom a 37-yr-oldmanwith chondrosarcoma of the skull base dearly revealed skull-base in volvement. (B) Preoperative S-SPECT images were positive. The skullbasewasextensivelyinvaded(largearrows)withdestructionof

bonyregions.Postoperative5-SPECTrevealeda positivebone

SPECT as a result of reconstructivemeasuresin the skull base (smallarrow)and completeabsenceof @°iiaccumulationin the tumor SPECT, indicatingcomplete removal of malignant tissue.

invasion and changes in bone structureor an inflammatory

response. False-positive results can be avoided by analyz ing the delayed images. Thallium-201 Cl accumulations in inflammatory disease or benign lesions have been shown to decrease gradually with time, whereas delayed washout

was observed in malignanttumors (8,22). Examination of

the delayed image is an accurate method because it allows better differentiation between inflammatory and benign le sions from malignant lesions. In our study, we waited 2 hr before imaging, which appeared to be a suitable amount of time to permit contrast of the tumor from the surrounding tissues.

1744 The Journal of Nuclear Medicine•Vol. 36 •No. 10 •October 1995

SensitivitySpecificityAccuracyBone SPECT100%60%90%Tumor SPECT80%100%85%S-SPECT

detectabilityof skullbaseinvasion= 93.3%.

TABLE 4

Sensitivity, Specificity and Accuracy of Bone and Tumor SPECT

CONCLUSION

S-SPECT is a useful technique that provides a complete

anatomicaland physiological picture, detailingnormal and

abnormal tissues. Even when skull-base destruction was

evident on CT or MRI, S-SPECT clearly visualized the

lesion as well as changes in the bone that were undetect

able morphologicallyby CT or Mill. S-SPECT also proved

an extremely useful diagnostic tool for the detection of

silent or subclinical lesions and possible recurrent malig

nancies in instances when the CT or MRI results were

inconclusive.

ACKNOWLEDGMENTS

The authors thank Mr. Naoki Akagi, Kochi Medical School, for assistance with the SPECT camera and Mr. Patrick Nahirney for reviewing and preparingthe manuscript.

REFERENCES

1. AlexanderJM.Radionuclidebonescanninginthediagnosisoflesionsofthe maxillofacial region. I Oral Swg 1976;34:249—256. 2. Higashi 1, Sugimoto K, ShimuraA, Ctal. Technetium-99m bone imaging in the evaluation of cancer of the maxillofacial region. I Oral Sui@ 1979;37: 254—259.

3. Bergstedt HF, Linf MG. Facial bone scintigraphy. Act Rod Diag 1981;22: 609—618. 4. Baker HL, Woodbury DH, Krause Ci, Ctal. Evaluation of bone scan by scintigraphytodetectsubclinicalinvasionofthe mandibleby squamouscell carcinomaoftheoral cavity. Otolwy@golHeadNeckSuig 1983;90:327-336. 5. Gates GF, Goris ML Maxillaiy-facial abnormalities assessed by bone im aging.RathoIo@'j1976;121:677—682. 6. Brown ML, Keyes JW, Leonard PF, et al. Facial bone scanning by emis sion tomography. I NuciMed 1978;18:1184—1188. 7. Yui N, Togawa T, Kinoshita F, et al. Assessment ofskullbase involvement of nasopharyngeal carcinoma by bone SPEC!' using three detector system. Kaku Igaku 1992;29:37-47. 8. Tonami N, Shuke N, Yokoyama K, et al. Thallium-201single-photon emis sion computed tomography in the evaluation of suspected lung cancer. J Nuci Med 1989;30:997-1004. 9. Black KL, Hawkins PA, Kim KT, Becker DP, Lerner C, Marciano D. Use of thallium-201SPECT to quantitate malignancy grade of glioma. JNeuro siag1989;71:342—346. 10. Kim KT, Black KL, Marciano D, et al. Thallium-201 SPED' imaging of brain tumors: methods and results. I Nuci Med 1990;31:%5—969. 11. Matsuno S, Tanabe M, Kawasaki Y, et at. Effectivenessofplanar image and single-photon emission computed tomography of thallium-201 compared with gallium-67 in patients with primaty lung cancer. Eur I Nuci Med 1992;19:86—95. 12. Togawa T, Yui N, Kinoshita F, Shimada F, Omura K, Takemiya S. Visu alization ofnasopharyngealcarcinomawithTl-201 chloride and a three-head rotating gamma camera SPECT system. Ann NuciMed 1993;7:105—113. 13.Yui N, SekiyaN, AkiyamaY, et al. Single-photonemissioncomputed tomography in the diagnosis of skull base invasion of nasophaiyngeal car **cinoma. Kaku Igalat 1986;23:367-373.
4. Yui N, Kinoshita F, Akiyama Y, et al. ainiCal evaluation oftransaxial bone imaging with technetium-99m-phosphate compounds. Radio&sotopes1982;** 31:515—528. 15. Jinnouchi S, Hoshi H, Ohnishi T, et at. Thallium-201SPED' for predicting histologicaltypes of meningiomas.I NuciMed 1993;34:2091-2094. 16. Mahmoud El-Desouki. Thallium-201 thyroid imaging in differentiatingbe nignfrom malignantthyroidnodules.ClinNuciMed 1991;16:425-430. 17.OchiH, SawaH, Fukuda1, et a].Thallium-201-chloridethyroidscintigra phy to evaluate benign and/or malignant nodules: usefulness of the delayed scan. Cancer 1982;50:236-240. 18. Kaplan WD, Takvorian T, Morris JH, RumbaughCL, Connoly BT, Atkins HL. Thallium-201braintumor imaging;a comparative studywith pathologic correlation.I NuciMed 1987;28:47—52. 19. Schwartz RB, Caivaiho PA, Alexander E, Loeffler iS, Folkerth R, Holman BL. Radiation necrosis versus high-grade recurrent glioma: differentiation

A drawback of tumor SPEC!' using @°‘Tl-Clis no signif

icant accumulation of 201Tl-Cl in certain tumors in some

patients. Yui et al. (23) also reportedan absence of labeling

in the first two types of manifestations. On the other hand, Sehweil et al. (24) reported that detectability of mediastinal lymphoma using @°‘Tlwas 84.6%. They reported negative scans for patients with Hodgkin's and non-Hodgkin's lym

phoma. Nonaccumulation of 201'flis not a rare phenome

non in some types of malignanttumor.Furtherexamina

tion with regardsto cellular kinetics of each tumor type is

required. Tumors of squamous-cell variety, however, were de

tected in this study with high specificity and sensitivity,

indicatingthe usefulness of 201Tl-Clfor reliabledetection of

these types of tumors. Most malignant head and neck tu

mors are classified as squamous-cell carcinoma, which is

the basis for using S-SPECT in head and neck tumors.

When we evaluate negative 201'fluptake SPECT images of

tumors, we must determine whether there was 201'flaccu

mulation in the tumor to avoid false-negative results. Thal

hum is believed to act as a potassium analog that can

stimulate the activity of the Na@-K@ATP-asedependent

pump of cell membranes, resulting in active transportof

20111 into the cytoplasm. Although thallium uptake is not identical to potassium (i.e.. 201'fl appears to bind to two sites on the enzyme), this process is also sensitive to

ouabain and sodium fluoride, which block the Na@-K@

pump (25). Delayed washout (or possibly prolonged up

take) in metastatic tissue may be reflective of the Na@-K@

ATP-ase activities of the tissue's constituent cells, a differ

ence that may explain the variation in thallium

accumulation in differenttumors (17,26).

The results of S-SPECT for detecting skull-base invasion

were 93.3%. It must be emphasized that the combinationof

bone and tumor SPED' imaging enabled considerably

higher detectability rates than either modality alone. Fur

thermore, if tumor detection by CF or MRI is possible, it can augment S-SPECT to evaluate the extent of bone in

volvement and localized reactive inflammation.For exam

ple, S-SPECTimagingmay indicatean abnormalityin a wider region of the skull base than CT or MRI. On the

other hand, S-SPECT imagingproved useful in localizing

skull-base invasions undetectable by both CT and MRI;

tumor invasion was later confirmed by surgery and ap

peared to be silent or subclinical in nature.

Bone and Tumor SPECT at Skull Base •Fukumotoat al. 1745

by using dual isotope SPECF with @°‘TIand @[email protected] ivdiol1991;12:1187—1192.

20. Ancri D, Basset JY. Diagnosis of cerebral metastasis by thaffium-201. Br Radio! 1980;53:443—453. 21.VanderwallHans,MurrayIPC,HuckstepRL, PhilipsRL.Theroleof scintigraphyin excludingmalignancyin bone. CliiiNuciMed 1993;18:551- 557. 22.TennvallJ,PalmerJ,CederquistE,etal.Scintigraphicevaluationand dynamicstudieswiththallium-201in thyroidlesionswith suspectedcancer. EurJ NuciMed 1981;6:295-300.
    23. Yui N, Kinoshita F, Shimada F. aink@1 evaluation ofhead and neck tumor scintigramwith @°‘Tl-chloride.Kaku Igaku 1979;16:221—227. 24. Sehweil AM, Mckillop JH, Milroy R, et al. Thallium-201scintigraphy in the staging of lung cance@r, breast cancer and lymphoma. Nuci Med Commun 1990;11:263—269.
    24. Britten iS, Blank M. Thallium activation of the (Na@-K@)activated AlP ase of the rabbit kidney. Biochem Biophys Acta 1968;159:160—166. 26. Sehweil AM, Mckillop JH, Milroy R, Wilson R, Abdel-Dayem HM, Omar @r.Mechanismof11-201uptakeintumors.EurJNuciMed1989;15:376-

Scatter

(Continuedfrom page 3A) radiation safety officers nod approvingly to committees assembled to

develop policy for this practice. I have met oncologists who will not

schedule patients for an office visit on the day ofa bone scan because they

are anxious about their own exposure to the radiation from the patient.

Although I do not argue with prudentradiationsafety procedures, regulatory agencies and radiation safety personnel have fostered the erroneous notion that all detectable radiation is dangerous, that regulatory limits indicate dangerous levels ofexposures and that risks exist at all levels ofexposure. This evolves into the notion that all detectable radiation is dangerous and represents meaningful risk and that some cancers are caused by any exposure above background. No mention is made that background

levels may vary in magnitude in various locales and that the incremental

background exposure in certain areas is many times the exposure received from certain occcupational activities. Despite intense scrutiny ofthese high background areas for many years, no adverse effect on the population has

been observed.

I wonder what the Martians think of all this?

Stanley J. Goldsmith, MD Editor-in-Chief The Journal ofNuclear Medicine October 1995

1746^ TheJournalof NuclearMedicine•Vol.36 •No. 10•October