thyroid

• Thyroid, Lymphatic, Inflammation, Endocrine


  • NMT 82
• Thyroid


  • 2 lobes (Right and Left)
  • 15-30gm
  • Isthmus - Thyroid tissue connecting Lobes
  • Highly Vascular Gland
  • One of the earliest NM Imaging Procedures
• Thyroid Function


  • Maintain basal metabolic rate
  • Metabolic rate regulated by two hormones - T3 (triiodothyronine) and T4 (thyroxine)
  • Hormones essential for sexual maturation and growth
• Five steps of hormone production

  1. Trapping of iodide by Thyroid

  2. Oxidation of I2 to I+

  3. Organification

  4. Condensation

  5. T3 and T4 formation
• T3 and T4 release

  • T3 and T4 released into circulation
  • 90% of T4 bound to TBG (inactive form)
• Thyroid Hormone production and Secretion


  1. Controlled by negative feedback mechanism

  2. TSH (Thyroid Stimulating Hormone) secreted by anterior pituitary gland

  3. Regulates thyroid Iodine uptake and release of hormones into circulation

  4. Low levels of hormone cause more TSH to be produced

  5. Stimulating thyroid gland to produce more T3 and T4
• Increased levels of hormones


  1. Signal pituitary to suppress TSH secretion

  2. Levels of hormones can affect the hypothalamus

  3. Secretes thyrotropin releasing factor (TRF)

  4. Stimulates pituitary gland to produce TSH
• Diseases that Effect the Thyroid


  • Hyperthyroidism - Thyroid produces excessive amounts of T4
  • Hypothyroidism - Decreased production of T4
  • Goiter - Enlarged thyroid due to iodine deficiency
• Hyperthyroidism


  Increased appetite, restlessness, hyperactivity
• Hypothyroidism


  Weight gain, lethargy, cold intolerance
• Add iodine to table salt
• Na-I 131


  • T1/2 = 8 days
  • 364 keV gamma; B-
• Na-I 123


  • T1/2 = 13.2 hrs
  • 159 keV gamma; no B-
• NaTcO4-


  Tc off the generator
• Na-I 131


  • Reactor produced
  • Fission or neutron capture
  • Non-carrier added
  • Clear, colorless
  • Stability achieved through alkaline pH (7.5 - 9.0)
  • Sodium ascorbate and thiosulfate
  • Shelf life = 4 weeks
  • Diagnostic and therapeutic purposes
  • Available in liquid or capsule form
• Na-I 123


  • Cyclotron produced
  • Clear, colorless
  • Stability achieved through alkaline pH (7.5 - 9.0)
  • Shelf life = 30 hrs
  • Diagnostic purposes
  • Available in liquid or capsule form
  • Radiopharmacist must check for I-124 and I-125 contaminants
• Sodium Iodide


  • Absorbed in intestine
  • Blood concentration peaks in 3 hours
  • 90% excreted by kidneys (urine)
  • 50% of dose excreted in 24 hrs
  • Sweat, saliva and all bodily fluids
• Thyroid Uptake and Scan


  1. Uptake - How much of the administered iodine is absorbed by the thyroid? Expressed as a % - Indicates the activity of the gland

  2. Scan - Images indicate the size, shape, location of nodules, hot/cold nodules
• Thyroid Uptake


  • Capsule placed in thyroid phantom
  • Activity in counts measured with thyroid probe
  • Take uptake measurement
  • Room background count
  • Capsule administered orally to patient
  • Uptake determined at 6h or 24h post administration
  • Background for patient - thigh
• Thyroid Scans performed 24 hours later
• Thyroid and Pertechnetate


  • Dose 10-20 mCi
  • Imaging performed 20 min PI
  • Trapped, not organified by thyroid
  • No uptake, only size and shape
  • Some nodules can be hot with TcO4- that are cold with iodine tracers
• Lymphatic System


  • Network of vessels through which lymph drains from the tissues into the blood
  • Lymph similar to plasma in composition
  • Produces monocytes and lymphocytes
  • Destroys aged red blood cells
  • Lymphatic capillaries unite to form ducts which supply lymph to the lymphnodes
• Lymphnodes


  • Small structures - 1 cm in diameter
  • Proximal ends of limbs in neck, groin, abdomen, thorax
  • Provide protection against bacterial infection by digestion of bacterial in lymphatic vessels
  • Can provide path for spread of metastasis
• Lymphnodes and Cancer


  • Provides paths for the spread of cancer from one part of the body to another
  • Lymphnode pathology is demonstrated by diminished or absent flow of lymph
  • Lymphodes are like a chain (Train-station)
• Lymphoscintigraphy


  1. Injections of sulfur colloid around the affected nipple - finds first lymphnode in the chain for biopsy

  2. Filtered Sulfur Colloid (Small particles) (500µCi)
• 99mTc Sulfur Colloid


  • Filtered is preferred
  • Unfiltered can get trapped at injection site
  • Dose 200 uCi for same day imaging, 1 mCi for next day imaging
  • Administered in a small volume 0.2 ml
  • 1-4 injections
  • Sentinal node localization for breast cancer, melanoma
  • Pre-op workup
• SC preparation


  1. Tc-sulfur colloid formed

  2. Precipitation of colloid

  3. 99mTc + sodium thiosulfate

  4. Heat to 100 degrees for 4-10 minutes

  5. pH buffer (acid)

  6. Gelatin (protect the colloid)

  7. EDTA chelate (remove excess Al+3)
• SC preparation


  • Particle size 0.1 - 1.0 um
  • Average 0.3 um
  • No reducing agent
• Lymphoseek


  • Recently FDA approved
  • 99mTc Tilmanocept
  • Indication - Lymphatic mapping, Sentinal node identification in breast ca. and melanoma
  • Patient dose: 0.5 mCi
  • Volume: 0.1 ml /single injection, 0.5 ml / multiple injection or syringes, 1.0 ml in multiple syringes
  • 7 nm particle size
  • More rapid, improved injection site clearance than sulfur colloid
• Tumors


  • Appear in different parts of the body as a result of proliferation of abnormal cells
  • Benign or Malignant
  • Characteristics we can Image - Metabolic activity, blood flow, vascular permeability, tumor associated antigens
  • Now - Typically Imaged with PET/CT
• Ga67 Citrate


  • Various Tumor Detection and Sarcoidosis
  • 10 mCi
  • Medium to High Energy collimator
  • Energy 93,184, 300, 393 keV
  • T1/2= 78 hours
  • Secreted by large intestine
  • Increase activity in bowel
  • Peaks used for imaging - 93, 185
  • Gallium resembles Iron - different oxidation state
  • Transferrin Analog
• Gallium 67


  • Solution contains sodium citrate, sodium chloride, benzyl alcohol (preservative)
  • pH is adjusted 5-8
  • Ga67 binds to serum protein transferrin (found in plasma)
  • Normal biodistribution - Liver, spleen, bone
  • Localizes in sites of infections, inflammation and certain tumors
• Ga-67 Uptake


  • Tumors, Infection, Inflammation
  • Osteomyelitis, Sepsis, Abcesses, Lung Inflammation
  • Transferrin specific receptors on tumor cells
  • During Inflammatory process, lactoferrin released by Leukocytes
  • Due to excretion by the bowel, NOT ideal for abdominal studies
  • Laxatives may be required for prep
• Sarcoidosis/Infection


  • Clinical indication - Inflammation/Infection/Tumor imaging
  • Dose 6 to 10mCi
  • Images taken 24-72 hours after injection
  • "Panda Sign" - Sarcoidosis Imaging
• In111 Labeled Leukocytes


  • Leukocytes = White blood cells
  • In 111 oxine is lipophilic - crosses lipid bilayer of cell membranes
  • Inside the cell, the In111 gets broken down and trapped in the cell
  • Used to image infection
  • Normal biodistribution - Spleen, liver, bone marrow
• In111 Labeled Leukocytes


  1. Blood is drawn from the patient (30 to 50ml) with large bore needle - Syringe containing heparin

  2. Blood is centrifuged to separate the WBC's from RBC's

  3. WBC's are then labeled with 200 to 500µCi In111

  4. Reinjected into the patient

  5. Imaged
• 111-In WBC's


  • WBC's separated from whole blood by sedimentation, centrifugation, washing
  • Hetastarch - Increases rate of sedimentation
  • Labeling is performed in saline, not plasma
  • Plasma contains albumins (transferrin) which will interfere with tagging efficiency
  • In111 affinity of transferrin is greater
  • Labeling will occur in all cells and alter biodistribution
  • Damaged cells will also alter biodistribution
• Leukocyte Labeling


  1. Blood withdrawn from patient with Large Bore Needle

  2. Filled with ACD (anticoagulant solution)

  3. WBC's isolated via centrifuge

  4. Hetastarch used to settle RBC's

  5. In111 Oxine added to leukocytes

  6. Labeling takes approximately 2 hours

  7. Strict Aseptic technique

  8. Reinjected back into patient

  9. Labeling Efficiency 70-90%
• Technical Considerations


  • Separation of WBC's is imperative
  • If platelets are tagged along with WBC's, false positive can occur
  • Platelets concentrate in sites of thrombosis rather than infection
  • MUST utilize safe blood precautions
• 111-In WBC's


  • Mixture of neutrophils, lymphocytes, monocytes
  • 10^8 cells
  • Biodistribution - 50% liver, 11% spleen, 8% lungs