James MontgomeryMarch 29, 2010

Transsplenic Portal ScintigraphyMebrofenin vs. 99mTcO4

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Transsplenic Portal ScintigraphyTwo common radiopharmaceuticals for this

procedureNa99mTcO499mTc-Mebrofenin

Dose0.5 – 2.0 mCi in 0.2 – 0.5 mL volumeMuch smaller dose than PRPS (5 – 20 mCi)

Transsplenic Portal ScintigraphyNormal

Radioactivity travels from spleen and then seen in liver before the heart

127461PSS

See the radioactive isotope travel from the spleen through the shunt vessel to the vena cava

Activity in the heart before the liver125132

Technetium-99mThe first man-made element

Produced by atomic bombardment of Mo in 1937

Principal mode of decayIsometric transition – gamma ray emitter

Physical T1/26.02 hours

Principal photon energy140 keV

Production methodGenerator (Mo-99)

99mTc-MebrofeninLidocaine analog

Liver is the primary site of uptake and metabolism of lidocaine

High first pass extraction by the liver

Advantages of MebrofeninGives excellent images of the portal vein just

like 99mTcO4- but gives additional information…hepatic function

High first pass extraction by the liver>90% removed from blood pool on first pass

Will not pass through the liver to the heartRetained in the liver and gradually cleared into

the biliary systemHalf-time clearance rate of 19 minutesDogs with PSS have a conspicuously different

pattern from normal dogs

Advantages of MebrofeninEvaluate size and morphology of the liverAlso evaluate functionIn a normal dog, a static image at 5

minutes should have no activity anywhere except the liver and some residual in the spleen

Releasable at 1 hr

Comparison

TSPS - Mebrofenin

Hepatic Morphology

Sensitivity/SpecificityTSPSSensitivity

TSPSSpecificity

PRPSSensitivity

PRPSSpecificity

Single observer

100% 100% 100% 85.7%

Consensus 100% 100% 100% 95%

o Additionally, able to accurately determine shunt termination 97% of the timeo vs. 46% with PRPS

o Able to accurately determine number of shunt vessels 91% of the timeo vs. 71% with PRPS

o Cannot diagnose Microvascular Dysplasia

Portoazygous shunt

Portocaval or Splenocaval

Multiple acquired shunts

UTDo all of their TSPS with mebrofenin

$120

Hardly ever do US shunt huntsOnly for resident practice$210

CT those that are questionable with scintigraphy

Go to surgery based on scitigraphic results

NCSUAbdominal US

$262Abdominal CT

$537TSPS – pertechnetate

$163TSPS – mebrofenin

$220

Should we change our protocol?

ReferencesNuclear Medicine Short Course NotesMorandi F, et al. Transsplenic portal

scintigraphy using 99mTc-Mebrofenin in normal dogs. Veterinary Radiology & Ultrasound 2007(48):286-91.