Technetium-99m is the workhorse of nuclear medicine. It is a radioactive substance injected in tiny amounts so a camera can watch organs at work rather than just photograph their shape. The same substance serves for heart, bone, thyroid, lung, kidney and cancer scans, because it can be attached to different carrier molecules that each seek out a particular tissue. Its usefulness comes from fading quickly, which also means it can’t be stockpiled and depends on a fragile worldwide supply.
How a Technetium-99m Scan Works
Hospitals make the tracer on site. They receive a shielded generator containing molybdenum-99, which steadily decays into technetium-99m. Staff rinse the generator with salt water to draw off fresh technetium-99m each day.1PubMed. Technetium-99m generator That liquid is then mixed with a ready-made “cold kit” holding the carrier molecule and the chemicals that make it stick.2International Atomic Energy Agency. Technetium-99m Radiopharmaceuticals: Manufacture of Kits Change the kit and you change where in the body the tracer goes, and so which organ the scan studies.
That kit step is why scan orders name a carrier next to the technetium, such as sestamibi, MDP or MAG3. What differs is how the body handles the carrier: bone-seeking molecules settle in areas of active bone, while others are filtered out by the kidneys.
The camera then picks up the signal. Technetium-99m gives off gamma rays at an energy that passes out of the body and suits gamma cameras well.3Journal of Nuclear Medicine. What Is Technetium-99m Used for in Medicine? The image shows function, such as blood flow or bone activity, wherever the tracer gathers or is missing.
At the appointment, you get an IV injection and often wait while the tracer reaches its target. The wait can be a few minutes or a few hours, depending on the scan. Then you lie still under or between camera heads that move close to your body. The camera gives off no radiation. The amounts are so small that allergic reactions and side effects are rare, and you usually feel nothing beyond the needle.
How Much Radiation You Get and How Fast It Fades
Technetium-99m has a half-life of about 6 hours, meaning half its radioactivity is gone every 6 hours.4Journal of Nuclear Medicine. What Is Technetium-99m Used for in Medicine? By 24 hours, about 94% of the injected activity has decayed.5Journal of Nuclear Medicine. What Is Technetium-99m Used for in Medicine? It also gives off only gamma rays, with no alpha or beta particles that would deposit energy in tissue without helping the picture.6Journal of Nuclear Medicine. What Is Technetium-99m Used for in Medicine? Nearly all the radiation it gives you is the same radiation that forms the image.
Your body also clears tracer physically, mostly through urine, so for many tracers the amount in you falls even faster. That is why the day of the scan is the main time for precautions, not the days after.
The total dose from a typical scan is closer to a CT scan than to a single plain X-ray.7Wikipedia. Technetium-99m The dose varies with the scan type and the amount injected. The dose is also spread according to where the tracer goes, with the bladder and the target organ often receiving the most. Staff choose the lowest activity that gives a clear picture.
A few practical steps help after the scan. Drinking fluids and urinating often helps clear tracer that leaves through the kidneys. Ask whether you should keep brief distance from infants or pregnant people for the rest of the day. Tell staff beforehand if you are pregnant or breastfeeding, since instructions may change. Radiation detectors at airports or borders can briefly pick up the tracer, so keep your appointment letter with you.
Heart Scans
The most common heart use is a nuclear stress test, often with a tracer named sestamibi. Sestamibi stays put in heart muscle after it is injected during stress rather than quickly shifting.8PubMed. Technetium-99m-sestamibi myocardial perfusion imaging in detection of coronary artery disease: comparison between initial (1-hour) and delayed (3-hour) postexercise images So pictures taken an hour or more later still reflect blood flow at the moment of stress. When the drug adenosine stands in for exercise, the test detects coronary artery disease well in women regardless of symptoms.9PubMed. Adenosine technetium-99m sestamibi myocardial perfusion SPECT in women: diagnostic efficacy in detection of coronary artery disease
A test day usually includes a rest scan and a stress scan, sometimes on the same day. Stress comes from a treadmill, or from a medicine if you can’t exercise. You may be told to avoid caffeine beforehand because it blocks adenosine-type drugs. The 3D scan used is called SPECT (single-photon emission computed tomography), a word you may see on your order.
The two sets of pictures are compared side by side, because one set alone cannot tell a narrowed artery from old scarring. Stress makes healthy arteries widen to deliver more blood, while a narrowed artery cannot widen enough, so the muscle it feeds receives less tracer. Areas that get less tracer under stress but fill at rest suggest a narrowed artery. Areas missing tracer in both suggest old damage. The results guide whether you need further tests such as angiography. Some heart centers are moving to PET scans with rubidium-82 instead of technetium-based scans.10PubMed Central. New Radionuclides and Technological Advances in SPECT and PET Scanners
When a medicine is used, an adenosine-type drug is given through the IV to widen the heart’s arteries. Many people feel flushing, chest tightness or breathlessness for a minute or two, and these effects fade quickly once the infusion stops. Staff monitor your heart rhythm and blood pressure throughout, and a reversing medicine is available if needed. Tell staff beforehand if you have asthma or severe lung disease, since that affects which drug they choose.
Bone Scans
A technetium-99m MDP whole-body bone scan is widely used to look for cancer that has spread to bone.11ScienceDirect / Journal of the Formosan Medical Association. High false negative rate of Tc-99m MDP whole-body bone scintigraphy in detecting skeletal metastases for patients with hepatoma It has limits. In people with liver cancer, nearly half of those with bone spread had at least one lesion the scan missed.12ScienceDirect / Journal of the Formosan Medical Association. High false negative rate of Tc-99m MDP whole-body bone scintigraphy in detecting skeletal metastases for patients with hepatoma So a normal bone scan doesn’t fully rule out bone spread in every cancer type, and doctors may add other imaging.
The tracer attaches to bone surfaces where new bone is being laid down, so brighter areas mark where bone is remodeling faster than usual. Because it detects activity, it can reveal a stress fracture or spread of cancer before changes become clear on an ordinary X-ray. Tracer that bone doesn’t take up is removed by the kidneys, which is why the pictures sharpen after the wait.
The appointment starts with an injection, then a wait of a few hours while the tracer settles in bone. The scan itself takes roughly 30 to 60 minutes lying still.
Bright “hot spots” aren’t always cancer. The tracer gathers wherever bone is actively repairing, so arthritis, old injuries and fractures also light up. Doctors look at the pattern as well as the brightness, since many scattered spots suggest something different from a single spot in a joint. A suspicious spot is often followed by a targeted X-ray, CT or MRI to see what is causing it.
Cancer Surgery and Sentinel Node Mapping
The sentinel lymph node is the first node that fluid from a tumor drains into. Technetium-99m mapping is the standard method for finding it in gynecological cancers.13PubMed Central. The role of technetium-99m isotope in sentinel lymph node identification in gynecological cancers In breast cancer, technetium-labelled sulfur colloid is used, alone or with blue dye.14PubMed Central. Intraoperative Injection of Technetium-99m Sulfur Colloid for Sentinel Lymph Node Biopsy in Breast Cancer Patients: A Single Institution Experience
The idea is that cancer cells spreading through lymph usually reach one node first, so testing that sentinel node tells you much about the nodes beyond it. Without mapping, a surgeon may remove many nodes to be safe, which carries more risk of swelling and numbness. The tracer helps the surgeon find the right node, which can be hard to locate by sight alone.
The tracer is injected near the tumor, sometimes the day before surgery or in the operating room. In surgery, a handheld probe beeps over the radioactive node. Removing just that node can spare patients a larger lymph node operation, and if it is clear, the cancer has likely not spread through lymph.
Some centers take pictures after the injection to show which nodes took up the tracer and where they lie, giving the surgeon a map. The images can reveal more than one sentinel node, or one in an unexpected area, such as under the arm and also elsewhere.
Thyroid, Lung, Kidney, Brain and Gut Scans
The thyroid absorbs technetium pertechnetate because it resembles iodide in size and charge.15PubMed Central. Thyroid uptake and scintigraphy using 99mTc pertechnetate: standardization in normal individuals A healthy thyroid takes up about 0.4% to 1.7% of the dose.16PubMed Central. Thyroid uptake and scintigraphy using 99mTc pertechnetate: standardization in normal individuals Higher or lower uptake on your report can point to an overactive or underactive gland. A single hot area may be a nodule making too much hormone, while a cold area gets further tests, since cold nodules are mostly not cancer. The scan is read alongside blood tests and an ultrasound.
For the scan, pertechnetate is given by injection and pictures are taken after a short wait of around twenty minutes. Tell staff about thyroid medicines and recent iodine exposure, such as contrast from a CT, because these can change how the scan is read.
For lung perfusion scans, tiny albumin particles labelled with technetium lodge briefly in lung capillaries.17PubMed Central. Lung perfusion imaging in nuclear medicine with 99mTc: a comprehensive survey of radiopharmaceuticals About 98% of the tracer lands in the lungs right after injection, mapping blood flow.18PubMed Central. Lung perfusion imaging in nuclear medicine with 99mTc: a comprehensive survey of radiopharmaceuticals Areas without tracer can reveal a clot blocking flow. A clear scan with even tracer throughout makes a clot unlikely. Missing patches need to be compared with the breathing images or a chest X-ray, because other lung conditions can also reduce blood flow in an area.
That breathing part shows where air reaches the lungs, using a gas or fine aerosol. A patch with normal air flow but missing blood flow fits a clot, while a patch missing both fits a lung disease. This matching is what separates clots from other causes of breathlessness. The scan uses no iodine contrast, which helps people with kidney problems or contrast allergy, and it is often chosen in pregnancy.
In children, the kidney tracer MAG3 can measure each kidney’s share of function as accurately as DMSA.19PubMed. Renal cortical imaging in children: 99mTc MAG3 versus 99mTc DMSA Brain blood-flow scans with technetium tracers are an accepted confirmatory test for brain death.20Diagnostic Radiation Physics Services. Brain Perfusion SPECT: HMPAO and ECD Imaging Pertechnetate also collects in stomach lining, so the Meckel scan finds misplaced stomach tissue in the gut that can cause bleeding.21PubMed Central. Bleeding Meckel’s Diverticulum in a 33-Year-Old Female Diagnosed with Video Capsule Endoscopy and a Technetium-99 m Pertechnetate Scan with a Favorable Response to H2 Blocker and PPI It is used when children have unexplained gut bleeding.22PubMed. The utility of technetium 99m pertechnetate scintigraphy in the evaluation of patients with Meckel’s diverticulum
Scans for Children
Children’s doses are calculated from body weight, with a set minimum so the image is still readable.23Diagnostic Radiation Physics Services. Pediatric Nuclear Medicine Dosing Explained Children are more sensitive to radiation and have longer lives for effects to appear.24Diagnostic Radiation Physics Services. Pediatric Nuclear Medicine Dosing Explained So the aim is the smallest dose that gives a clear picture.25Diagnostic Radiation Physics Services. Pediatric Nuclear Medicine Dosing Explained You can ask staff how the dose was chosen for your child’s weight.
A nuclear scan can show how an organ works without surgery, which is valuable when a child’s problem isn’t visible on other tests. Common reasons include scarring from kidney infection, urine drainage problems and bone pain with no clear cause.
Preparing helps. Explain the needle and the need to lie still, and bring comfort items or videos. Pictures can take a long time and movement blurs them, so staff may use a calm room, swaddling or distraction. Parents can usually stay with the child, though they may be asked to wear a lead apron or limit time close to the child afterward. Some centers offer sedation, but it is only used when truly needed, and you will be told about fasting beforehand.
Why Technetium-99m Sometimes Runs Short
Because of its 6-hour half-life, technetium-99m must be made close to when it’s used. The generators keep producing for about a week or so before they weaken, which is why deliveries are scheduled.
The parent molybdenum-99 comes from a handful of reactors worldwide.26MU Research Reactor. Reliability in a challenged global supply chain An unplanned outage at one, during maintenance at others, causes far-reaching shortages.27MU Research Reactor. Reliability in a challenged global supply chain These reactors are old and need regular shutdowns, and production runs continuously, so there is little spare capacity to cover a gap. Past reactor closures have left countries like the U.S. at risk while new suppliers came online.28Chemical & Engineering News. Severe shortages possible for key medical isotopes
There are new ways to make it. Hospital cyclotrons can now make technetium-99m directly without a reactor.29PubMed Central. Innovative Target for Production of Technetium-99m by Biomedical Cyclotron This has become a commercially workable option for regional supply.30Physics Procedia. Direct Production of 99mTc via 100Mo(p,2n) on Small Medical Cyclotrons
For you, a shortage may mean your scan is rescheduled or prioritized by urgency, or that your doctor switches to another test such as PET or CT.