NUCLEAR MEDICINE: OVERVIEW Jiraporn Sriprapaporn, M.D. Division of Nuclear Medicine Department of Radiology Siriraj Hospital
What is Nuclear Medicine?Nuclear medicine is a medicalspecialty which uses very smallamount of a radioactivesubstance or a chemicalcompound labelled with aradioactive substance, called“radiopharmaceutical” or“radiotracers” to image or treatdiseases.
DIAGNOSTIC NUCLEAR MEDICINERadionuclide imaging Rdn. non-imagingPlanar gamma camera Uptake testsSPECT Absorption testsSPECT/CT Whole body counterPET Surface countingPET/CT Breath tests
NM at Siriraj Hospital Dx THYROID Rx NM IMAGING
THYROIDThyroid function tests In-vitro TFT: serum T3, T4, FT3*, FT4, TSH, Tg*, TgAb** In-vivo TFT: RAIU, thyroid scan, I-131 TBSRadionuclide therapy of thyroiddiseases Hyperthyroidism Differentiated thyroid cancer (DTC)
Anatomy2 lobes connecting with“isthmus”Anterior to 2nd-4th trachealrings- C5-T1 vertebraeThyroid tends to increaseweight with age (N=20g)Arteries: Superior, inferiorthyroid A.Veins: Superior, middle, &inferior thyroid V.
Thyroid Function Kondo T, et al. Nature Reviews Cancer 6, 292- 306 (April 2006)
Thyroid Hormone SynthesisIodide trapping - into follicular cells PeroxidaseOrganification - Tyrosine + I -inactive iodotyrosines: 3-monoiodotyrosine (MIT) & 3,5-diido tyrosine (DIT). incorporated into Tg &stored as colloid.Coupling MIT + DIT T3 DIT + DIT T4Proteolysis or release - proteolysis of Tg producesthe active hormones T4 & T4, then secreted into theblood.
Thyroid Function Tests IN-VITRO TFT IN-VIVO TFT
In-vitro TFTT3, FT3*T4, FT4TSH: primary hypothyroidism*Tg*: tumor marker of DTCTgAb** (thyroglobulin Ab)Antimicrosomal Ab (Thyroid peroxidase Ab-TPOAb)Thyroid stimulating hormone receptor Ab -TRAb Total form = bound form + free form
Patient PreparationRAIU & Thyroid scan: Discontinue Thyroid hormone medications > 2 wks Antithyroid drug > 1 wk ( for I-131)I-131 Total-body scan (TBS): Thyroid hormone: 50 ug OD for 4 wks & discontinued for 2 wks
RAIU: IndicationsEquivocal invitro TFTDDx hyperthyroidism vs subacutethyroiditisThyroid remnant evaluation (PO.)Pre RAI treatment for hyperthyroidism
Factors Interfering RAIUIodine load* Iodide-containing drugs eg. Amiodarone, KI in cough remedy, Betadine Previous contrast studies eg. CT, IVP 4-6 wks Sea food or iodine-containing food/supplements
24-hr. Radioactive Iodine Uptake Typical Curves of 24-hr Radioiodine Uptake%Uptake 80 Hyperthyroid Rapid Turnover Normal Hypothyroid 0 Hours after tracer dose I-131 24 hr Normal 24 hr RAIU = 15-45%
Rapid TurnoverIsaacson, et al.Rapid turnover of I-131 in subpopulations ofhyperthyroid patients: A retrospective dataanalysis. J Nucl Med. 2009; 50 (Supplement2):1304 [from NC, USA]N= 963 patientsOnly 4 % had rapid turnover.Uptake at 4 hr/ uptake at 24 hr > 1
Perchlorate Discharge TestAim: To identify organificationdefects, most commonly involving theperoxidase enzyme. DyshormonogenesisIndications: Enlarged thyroid gland with hypothyroid or elevated TSH Pendred’s syndrome: familial goiter and hearing loss
Perchlorate Discharge Test Discharge < 5% Normal, no org. defect Discharge > 5% Positive for org. defect
Thyroid scan & TBS will be discussedin the section of NM imaging.
RAI Treatment for Thyroid DisordersHYPERTHYROIDISM Graves’ disease Toxic adenoma Multinodular toxic goiterTHYROID CANCER DTC
IndicationsFailed medical/surgical treatment-relapseSerious adverse effects of antithyroiddrugs: drug allergy, agranulocytosisInconvenience for frequent contactPoor socioeconomic problemsPresence of serious associated medicalillness eg. heart failure
Procedures for RAI TreatmentDiscontinue antithyroid drug for 5-7 daysMeasure 24 hr RAIUI-131 dose calculation for Rx dependingon gland size, RAIU, dose of I-131 (uCi)/gram thyroid tissue [100-200 uCi/gram]RAI Dose = [Thyroid mass (g) x 80-200 uCi/gm]/% uptake
Post RAI TreatmentSymptomatic-beta blockersAntithyroid drug: start after 7 days asrequired.Follow up q 1-2 monthsBlood test for T3, T4, TSH as requiredand when hypothyroid is suspected.Rx hypothyroid by replacement therapyRepeat RAI Rx 3-6 months interval
RAI Treatment for DTC Papillary thyroid carcinoma Follicular thyroid carcinoma Both are derived from follicular cells.
Treatment of DTCSurgery Near-total /total thyroidectomyRAI TreatmentHormonal treatment Suppressive dose of thyroid hormone (T4) to keep TSH 0.1-0.4 mIU/L.Long-term follow-upERT#
Revised ATA Guidelines for Differentiated Thyroid Cancerhttp://www.thyroid.org/professionals/publications/documents/ATA_Guidelines_DTC_2009.pdf
RAI TreatmentNo invasive properties or metas.100 mCiInvasive properties 150 mCiLN met 150 mCiLung met 150 mCiBone met 200 mCi
Patient PreparationFirst visit Evaluation of residual thyroid tissue (PO 7+ days without thyroid hormone at least 2 wks) • Thyroid scan • RAIU • (T4, TSH, Tg, TgAb) Schedule for admission after 4-6 weeks PO. without thyroid H med or prepare as I-131 TBS.
Follow-up of DTC Pts.Clinical history & physical examinationBlood Tests Thyroid hormones levels (TSH 0.1-0.4 mIU/L) Tumor marker ie. Tg (N < 1 ng/ml) & TgAb (N < 40 mIU/L) Calcium balance, CBCI-131 TBS at 6- 12 mo post Rx until negative* (*also other parameters are negative)Other investigations eg. CXR-yearly, Tl-201, Tc-99m MIBI scan, U/S, CT scan, MRIRepeat RAI Rx: at least 6-12 months interval
NUCLEAR MEDICINE IMAGING Jiraporn Sriprapaporn, M.D. Division of Nuclear Medicine Department of Radiology Siriraj Hospital
Scope of NM ImagingEndocrinology : Thyroid scan, Parathyroid scanCardiovascular system : Myocardial perfusion scan,Radionuclide venographyGenitourinary system : Renogram, Testicular scan,Radionuclide cystographyPulmonary system : Perfusion/ Ventilation lung scanSkeletal system : Bone scanGastrointestinal system : Liver scan, Hepatobiliary scan,GE reflux studyTumor imaging : Ga-67 scan for Lymphoma, I-131 scanfor pheochromocytoma, Tc-99m MIBI for parathyroidadenoma
Principle of NM Imaging Radiopharmaceutical Patient Gamma Camera Images
Radiopharmaceuticals A radioactive material ina form suitable foradministration to ahuman for the purposesof therapy or diagnosticinvestigation
RadiopharmaceuticalsRadioisotopes eg. I-131, Tc-99m A BRadiolabeled compounds eg. Tc-99mMDP for Bone scan, Tc-99m MAA forLung scan [distribution // compounds]1 Organ Many R’pharmaceuticals1 R’pharmaceutical Many organs
AtomsAtoms of all elements are composedof known p, n, & eNuclides containing same no. of p(atomic no. = Z) but different nIsotopes eg. I-123, I-131Isotopes have the same chemical butdifferent physical properties.
Physical PropertiesPhysical half lifeType of radiation emittedEnergy of radiation emittedPhysical property is characteristic of each radioisotope.!
Source of Production of RadionuclidesReactorRadionuclides contain excess neutron.CyclotronRadionuclides contain deficient neutron.Generator
Radionuclides Used in NMRadionuclides used in NM emit beta or gamma radiation Beta minus particles easily absorbed in tissue suitable for therapy Gamma rays more readily transmitted through tissue, allow external measurement & imaging by gamma camera Beta plus particles allow PET imaging following the "annihilation"
Positron-emitting RadionuclidesRadionuclides T1/2 C-11 20 min. N-13 10 min. O-15 2 min. F-18 110 min. Ga-68 68 min. Rb-82 75 sec
Ideal Properties of Radioisotopes Cheap Available Pure gamma emitter Optimal gamma energy (100-200 keV) * 140 Optimal half life *6 hr Safe Chemically active* Tc-99m is the most ideal agent !
Specific Uptake of Tc-99m Thyroid gland Salivary glands Gastric mucosa Choroid plexus
InstrumentsPlanar gamma cameraSPECT or SPET =Single Photon Emission(Computed) TomographySPECT/CTPET = PositronEmissionTomographyPET/CT
PET & PET/CT Imaging PET:Metabolic imaging Using positron emitter radionuclides Biological tracers (C-N- O-F) More sensitive Better image Whole body evaluation
Advantages of NM Studies Functional* Sensitive Quantitative Very safe Not too expensive Minimally invasive Low radiation exposure Screening Follow-up
Disadvantages of NM Studies Not widely available Give minimal radiation Generally non-specific Require NM instrument & radiopharmaceuticals Relatively more expensive than routine X-ray or U/S
Radiation ProtectionTo decrease radiation doses from unselaed sources of radionuclides by ……..1. shielding & avoiding contamination2. increasing distance from the source3. limiting time of exposure
Important TopicsWhich organ imaging?Uses or indications?Which R’pharm can be used? Route?What is the mechanism of uptake?What is the appropriate pt preparation?Technique of imaging procedure Imaging acquisition protocol (positioning-views) (Processing) & Image displayInterpretation Normal: Normal distribution? Abnormal: DDx?
Mechanisms of Localization1. Capillary blockade: Tc-99m MAA lung scan2. Diffusion : Tc-99m DTPA brain scan3. Sequestration : Ht. denatured RBC , labelled plt.4. Phagocytosis : Tc-99m sulfur colloid liver scan5. Active transport : Iodide, pertechnetate, Tl, OIH, IodoCH, IDA6. Compartmental localization : labelled RBC, SC for GI studies7. Physicochemical adsorption : Tc-99m MDP bone scan8. Ag-Ab reaction : labelled MoAb9. Others and unknown
Imaging TechniquesStatic vs dynamic imagingPlanar vs SPECT imagingWhole-body imagingImaging views: anterior, posterior,RAO, LAP, RPO, LPO, LL, RLMarkers: hot & cold
Image DisplayBlack on whiteWhite on blackColorsAdjust intensity !!Not too dark and not too light !!
Practical IssuesRadiation protection at all timesPrepare yourself about the tests before hands.Check the indications, appropriate?Any precaution or specific patient preparation required?Patient history taking & making note (LAB)Relevant physical examinationDouble check for correct dose preparationCorrect R’pharm administrationCheck the images before the patient leaveCheck the quality and quantity of the films and report paperimagesAsk the attending staff if you feel uncertain.Read the scan when it’s done.