Technetium-99m

Mechanism of Action

Technetium-99m is a radioactive isotope that exerts its mechanism of action by gamma-ray emission in the target tissue or organ, which is then picked up and captured by a unique gamma camera for medical imaging.[6][7] 99mTc is combined with a specific ligand and forms complexes that can then bind to its target tissue or organ with high affinity.[1] When distributed throughout the body and localized to its target, 99mTc emits photons that can be captured for imaging with a SPECT or PET scan.[5][8] 

A PET scan further detects the target tissue or organ's metabolic or biochemical function and can reveal both normal and abnormal metabolic activity. SPECT imaging captures a three-dimensional image of the target area where the radioactive tracer is distributed. This enables the assessment and evaluation of the perfusion and function of specific tissues and organs, which can be more advantageous than anatomical diagnostic imaging techniques like computed tomography (CT) scans and magnetic resonance imaging (MRI), which may only provide insight into structural information.[9]

Administration

Technetium radiotracer may be administered via injection intravenously (IV) or orally.[10][7] After the specific radioactive isotope complex is administered, it accumulates in the target organ or tissue. Following localization to the target tissue within the body, gamma rays are emitted by the Tc-99m, which are then captured for diagnostic imaging.[1] 

Technetium-99m Sodium Pertechnetate 

• Brain scintigraphy (adult): 370 to 740 MBq (10 to 20 mCi)

• Thyroid scintigraphy (adult): 37 to 370 MBq (1 to 10 mCi)

• Salivary gland scintigraphy (adult): 37 to 185 MBq (1 to 5 mCi)

• Blood pooling scintigraphy (adult): 370 to 1110 MBq (10 to 30 mCi)

• Vesic-ureteral scintigraphy (adult): 18.5 to 37 MBq (0.5 to 1 mCi)

• Nasolacrimal drainage scintigraphy (adult): 3.70 MBq (0.1 mCi) 

• Brain scintigraphy (children): 5.2 to 10.4 MBq (140 to 280 µCi/kg) 

• Thyroid scintigraphy (children): 2.2 to 3.0 MBq (60 to 80 µCi/kg) 

• Blood pooling scintigraphy (children): 5.2 to 10.4 MBq (140 to 280 µCi/kg) 

• Vesic-ureteral scintigraphy (children): 18.5 to 37 MBq (0.5 to 1.0 mCi) [11]

Technetium 99m-methylene Diphosphonate 

• Skeletal scintigraphy(adult): 740 to 1110 MBq (20 to 30 mCi)

• Skeletal scintigraphy(children): 9 to 11 MBq/kg (0.2 to 0.3 mCi/kg)

Technetium Tc99m Exametazime

• Cerebral flow scintigraphy: 370 to 740 MBq (10 to 20 mCi)

• Leukocyte labeled scintigraphy: 259 to 925 MBq (7 to 25 mCi) [10]

Technetium Tc 99m Sestamibi 

• Myocardial perfusion scintigraphy 555 to 1110 MBq (15 to 30 mCi)

• Parathyroid surgery preparation: 740 to 925 MBq 

• Breast scintigraphy 740 to 1110 MBq (20 to 30 mCi) [7]

Technetium-99m Tilmanocept 

• Lymph node biopsy/scintigraphy: 18.5 MBq (0.5 mCi) [12]

Technetium-99m Macroaggregated Albumin 

• Lung scintigraphy: 37 to 148 MBq (1 to 4 mCi)

• Portovenous shunt: 37 to 111 MBq (1 to 3 mCi) [13]

Dosages may be modified depending on the patient and indications of imaging. Patients who receive the agent orally must fast for at least 6 hours before administration.

Adverse Effects

Technetium-99m is a widely used radioactive isotope in nuclear medicine, and adverse effects may occur following systemic administration. Effects may occur secondary to the 99mTc or can be to the specific radiopharmaceutical it is tagged to. The most commonly reported effects include hypersensitivity-like reactions such as rash, angioedema, fever, and anaphylaxis.[14] In cases of a severe hypersensitivity-type reaction, corticosteroids, antihistamines, and epinephrine should be available for prompt administration.[7] Patients may also experience a transient increase in blood pressure, seizures, arrhythmias, and syncope. When used for abdominal imaging, gastrointestinal symptoms such as abdominal pain and discomfort, nausea, vomiting, and diarrhea may also occur. Other adverse effects include transient arthritis if the joint is affected. 

Adverse effects associated with 99mTc sestamibi include pain or discomfort of the breasts (mastalgia), distortion in taste sensations (dysgeusia), angina pectoris, chest pain or discomfort, and ST-segment electrocardiogram (ECG) changes. Proton pump inhibitors (PPI) should also be held for 72 hours before diagnostic myocardial perfusion imaging with 99mTc sestamibi as these drugs may lower the effect of the radioactive agent. Mortality has also been reported in patients with severe pulmonary hypertension and 99mTc macroaggregated albumin use.[15]

Contraindications

Technetium-99m is labeled as pregnancy category C due to insufficient studies on pregnant women. Breastfeeding is a contraindication to its use as 10% of the agent may be excreted in breast milk during lactation.[16] Patients are advised to pump and discard breast milk for up to 60 hours post-99mTc administration, and the recommendation is to formula feed the infant.[17] Furthermore, a previously documented hypersensitivity reaction to 99mTc is a contraindication. Patients with severe pulmonary hypertension are contraindicated to receive 99mTc macroaggregated albumin for lung imaging. Hypersensitivity albumin is also a contradiction to 99mTc macroaggregated albumin.

Monitoring

Technetium-99m can be administered to both adults and children. Extra precautions are necessary with children as the pediatric population is at higher risk for radiation exposure than adults. In contrast, new mothers exposed to 99mTc agents at their workplace do not require special precautions other than general protective care from radiation exposure.[17] Patients with suspected or known CAD who undergo myocardial perfusion testing using 99mTc sestamibi require cardiac event monitoring during diagnosis.[18] 

Toxicity

Technetium-99m has a photopeak of gamma-ray emission of 140.5 keV, meaning it has a very minimal risk of toxicity.[4] 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.[3][4] The kidneys excrete a portion of 99mTc, so patients with impaired renal function require dosing modifications to minimize their additional radiation exposure.

Enhancing Healthcare Team Outcomes

Technetium-99m is a radionuclide nuclear agent that is FDA-approved for diagnostic imaging of various organs of the human body, which include the brain, bone, lungs, kidneys, thyroid, heart, gall bladder, liver, spleen, bone marrow, salivary and lachrymal glands, blood pool, and sentinel nodes. Patient-centered care is an essential element of medical practice that involves a collaborative approach among healthcare professionals to improve outcomes and patient safety and enhance team performance. The use of 99mTc should be utilized by an interprofessional team, which includes a nuclear medicine specialist, radiologist, nurse, technologist, and clinician specializing in their respective field. 

Professionals trained to administer 99mTc are referred to as nuclear medicine technologists. They should be fully trained and specialized in radiation safety, dosimetry, and imaging techniques and able to perform their roles competently. They should also be familiar with the preparation of the kit before administration and any acute life-threatening adverse effects, such as hypersensitivity reactions that may occur during administration. If hypersensitivity or anaphylaxis occurs, the healthcare team should be fully prepared and equipped with prompt interventions such as corticosteroids and antihistamines. Patients with a history of CAD undergoing myocardial perfusion testing with 99mTc sestamibi must have continuous cardiac monitoring during the diagnostic evaluation. The procedure should be conducted where appropriate treatment is available during a cardiac emergency. 

Nuclear medicine technologists should also coordinate with the primary team and specialist who interpret the imaging studies to ensure timely diagnostic intervention is executed to prevent further delay of care. Clinicians interpreting the radionuclide scan should have expertise in nuclear medicine imaging and the interpretation of 99mTc studies. Interprofessional communication and coordination are crucial in optimizing patient-centered care using 99mTc. The technologist should coordinate with the primary team to provide accurate information to the clinician regarding the preparation of the kit and administration of the radiopharmaceutical. The primary team should further thoroughly inform patients about preparatory instructions before imaging, the benefits and risks of the imaging study, and the expected outcomes.

The interprofessional team should confirm the kit is appropriately labeled with the radiopharmaceutical's expiration date and that the appropriate radiation safety measures are in place to prevent any harm to the patient. Patients should be counseled and provided information on the risks of administering 99mTc during pregnancy, as it is a pregnancy category C contraindication. Patients should receive clear explanations of radiation toxicity and avoidance of breastfeeding during pregnancy. 

Effective communication and care coordination is essential to optimize diagnostic imaging using 99mTc. Nursing staff should communicate routinely with the nuclear medicine technologist and primary team to ensure that the patient scheduled for the nuclear imaging study is well-prepared. The healthcare team should also counsel patients on the adverse effects of 99mTc, the early and late complications that may arise, and their severity. Coordinated activity within an interprofessional team can minimize adverse effects and optimize the results of the diagnostic modalities when using 99mTc in nuclear medicine imaging studies. Collaborative efforts from physicians, nuclear technologists, nurses, nuclear pharmacists, and other health professionals involved in the administration of 99mTc should demonstrate specific skills, strategies, ethics, and interprofessional communication to provide optimal care to the patient. Care coordination and ethical practice are crucial in enhancing diagnostic quality, outcomes, patient safety, and team performance.