Continuing Education Activity

Technetium-99m (99mTc) is used for imaging and diagnostic purposes of organs and tissue. This activity describes the indications, actions, and contraindications of technetium-99m (99mTc) as a valuable agent in imaging and diagnostics. This activity will highlight the mechanism of action, adverse event profile, and other key factors pertinent to members of the interprofessional team in the imaging and diagnosis of patients with various disease states.

Objectives:

• Describe the typical imaging findings associated with technetium-99m (99mTc) use.
• Summarize the indications of technetium-99m (99mTc) use.
• Review the adverse effects of technetium-99m (99mTc).
• Outline some interprofessional team strategies for improving care coordination and communication to advance technetium-99m (99mTc) and improve outcomes.

Indications

Technetium-99m (99mTc) is a radionuclide isotope that is used primarily for imaging and diagnostic purposes.[1] It was isolated in 1938 from molybdenum-99 (Mo-99) decay and is the most common radioactive isotope tracer used for SPECT (single-photon emission computerized tomography) imaging of the brain, bones, lungs, kidneys, thyroid, heart, gall bladder, liver, spleen, bone marrow, salivary and lachrymal glands, blood pool, and sentinel nodes.[2][3] Technetium-99m is a more desirable radionuclide than other nuclear agents due to its short six-hour half-life, and the fact that it is not limited to a primary organ. 99mTc's short half-life accounts for less total radiation exposure to the patient.[3] Furthermore, the region of perfusion in an organ or tissue is evaluated by the uptake of the radiotracer, determining reversible or irreversible ischemia.[4] 

FDA Approved Technetium-99m Use

• Technetium-99m sodium pertechnetate - Used for diagnostic imaging of the thyroid, salivary gland, urinary bladder, vesicoureteral reflux, and nasolacrimal drainage imaging. Its use in the gastrointestinal tract is primarily for the diagnosis of Meckel's diverticulum(Meckel scintigraphy scan). 
• Technetium-99m sulfur colloid - Imaging of liver, spleen, and bone marrow - used for upper-gastrointestinal imaging assessing for reflux or gastric aspiration. It can also be useful to localize lymph nodes draining a malignant melanoma or breast cancer.
• Technetium-99m tetrofosmin - Cardiac perfusion imagining, assessing the function of the left ventricle, and determining coronary artery disease isolating ischemia and infarction
• Technetium-99m sestamibi - Cardiac perfusion imaging, assessing function, and localizing ischemia and infarction - also used for breast imaging.
• Technetium-99m tilmanocept - Used to localize lymph nodes drainage of primary tumors.
• Technetium-99m bicisate - Cerebral perfusion imagining used to localize the area of stroke.
• Technetium-99m exametazine - Used for imaging abdominal infections, inflammatory bowel disease, and brain perfusion.
• Technetium-99m pentetate - Imaging bone, kidney, and assessing pulmonary embolism
• Technetium-99m pyrophosphate -Imaging bone, gastrointestinal bleeding, and myocardial infarction
• Technetium-99m red blood cells - Localizing gastrointestinal bleeding.
• Technetium-99m succimer - Used for renal imaging.
• Technetium-99m methylene biphosphonate - Used for imaging bone.
• Technetium-99m macroaggregated albumin - Used to assess pulmonary perfusion.
• Technetium-99m mebrofenin - Used for hepatobiliary imaging.
• Technetium-99m medronate - Used for imaging bone.
• Technetium-99m mertiatide - Used for renal imaging.
• Technetium-99m oxidronate - Used for imaging bone

Mechanism of Action

Radioactive isotopes of technetium-99m (Tc) exert their effects by emitting gamma rays, which are then picked up by a gamma camera for imaging.[5][6] The radiotracers are not localized to a primary organ and distribute equally to multiple tissues. Once distributed, they emit photons that can be captured with for imaging with SPECT or PET.[4][7]

Administration

Technetium (Tc99m) radiotracer may be administered via injection intravenously or orally.[8][6]

Technetium-99m sodium pertechnetate 

• Brain scintigraphy (adult): 370 - 740MBq (10 - 20 mCi)
• Thryoid scintigraphy (adult): 37 - 370MBq (1 - 10 mCi)
• Salviary gland scintigraphy (adult): 37 - 185MBq (1 - 5 mCi)
• Blood pooling scintigraphy (adult): 370 - 1110 MBq (10 - 30 mCi)
• Vesic-ureteral scintigraphy (adult): 18.5 - 37MBq (0.5 - 1 mCi)
• Nasolacrimal drainage scintigraphy (adult): 3.70MBq (0.1 mCi) 

• Brain scintigraphy (children): 5.2 - 10.4 MBq (140 - 280 µCi/kg)
• Thyroid scintigraphy (children): 2.2-3.0 MBq (60 - 80 µCi/kg)
• Blood pooling scintigraphy (children): 5.2-10.4 MBq (140-280 µCi/kg)
• Vesic-ureteral scintigraphy (children): 18.5 - 37 MBq (0.5-1.0 mCi)

Technetium 99m-methylene diphosphonate[8]

• Skeletal scintigraphy(adult): 740 - 1110 MBq (20 - 30 mCi)
• Skeletal scintigraphy(children):9 - 11 MBq/kg(0.2 - 0.3 mCi/kg)

Technetium Tc99m Exametazime

• Cerebral flow scintigraphy: 370-740 MBq (10-20mCi)
• Leukocyte labeled scintigraphy: 259 - 925 MBq (7-25mCi)

Technetium Tc 99m Sestamibi[6]

• Myocardial perfusion scintigraphy 555 MBq-1110 (15-30 mCi)
• Parathyroid surgery preparation: 740 - 925 MBq 
• Breast scintigraphy 740-1110 MBq (20 - 30 mCi)

Technetium-99m tilmanocept

• Lymph node biopsy/scintigraphy: 18.5 MBq(0.5 mCi)

Technetium-99m macroaggregated albumin 

• Lung scintigraphy: 37-148 MBq (1 - 4 mCi)
• Portovenous shunt: 37-111 MBq (1 -3 mCi)

Dosages may be modified depending on the patient and indications of imaging. Patients who receive the agent orally are to fast for a minimum of six hours before administration.

Adverse Effects

Most commonly, technetium-99m causes rash, angioedema, fever, and anaphylaxis due to hypersensitivity reactions. Patients may also experience a transient increase in blood pressure, seizures, arrhythmias, and syncope. When used in abdominal imaging, abdominal pain, vomiting, and diarrhea may occur. Patients may experience transient arthritis if the joint is affected.

Severe hypersensitivity type reactions may occur shortly following the administration of Technetium-99m. The administering nurse or physician should have corticosteroids and antihistamines at the ready in the event complications do arise.[6]

Adverse effects can be uniquely associated with either Tc-99m or the radiopharmaceutical it is tagged do. Tc99m MDP is more likely to manifest an adverse reaction as a skin rash.[9]

Contraindications

Technetium-99m (Tc99m) is labeled as pregnancy category C, as there are not enough adequate studies in pregnant women. Breastfeeding is a contraindication to its use as 10% of the agent may be excreted in breast milk during lactation.[10] Patients are advised to pump and discard breast milk or store up to 60-hours post-technetium-99m administration, and the recommendation is to formula feed.[11] Furthermore, a previously documented hypersensitivity reaction to Technetium-99m would be a contraindication to its use.

Monitoring

Technetium-99m (Tc99m) can be administered both in adults and children. Extra precautions should be taken with children as the pediatric population is at higher risk for radiation exposure compared to adults. In contrast, new mothers with exposure to technetium-99m agents at their workplace do not require special precautions other than the general protective care from radiation exposure.[11]

Toxicity

Technetium-99m has a photopeak of gamma-ray emission of 140.5 keV, making it a very minimal risk of toxicity.[3] The short six-hour half-life and rapid excretion from the body limit toxic effects and give enough time to perform its diagnostic imaging, all while limiting radiation exposure to the patient.[2][3] The kidneys excrete a portion of technetium-99m, so patients with impaired renal function require dosing modifications given their additional exposure to radiation.

Enhancing Healthcare Team Outcomes

Technetium-99m (99mTc) is a radionuclide nuclear agent that is FDA approved for diagnostic imaging of the brain, bone, lungs, kidneys, thyroid, heart, gall bladder, liver, spleen, bone marrow, salivary and lachrymal glands, blood pool, and sentinel nodes.  This agent should be used by an interprofessional team, which includes a radiologist, nurse, technologist, and physician specializing in their respective field. The handling of technetium-99m should only be done by trained healthcare professionals who are licensed and authorized to use radioactive agents. The clinician administering the radioactive isotope should be familiar with any acute life-threatening adverse effects such as hypersensitivity reactions that may occur during administration. 

Physicians should fully inform patients about preparatory instructions before imaging. The results of the imaging should be interpreted and reviewed by a radiologist or trained technologists. During pregnancy, patients should be counseled and provided information on the risks of administering technetium-99m as it is a pregnancy category C contraindication. Patients should receive clear explanations of radiation toxicity during pregnancy and avoidance of breastfeeding during pregnancy. The interprofessional team should counsel patients on the adverse effects of technetium-99m, and the early and late complications that may arise, and the severity of the complexity. Clear communication within an interprofessional team can minimize adverse effects and maximize the results of various diagnostic modalities to optimize patient care.