Fludeoxyglucose (18F) Karolinska: Uses, Dosage & Side Effects
A radioactive glucose analog used as a diagnostic tracer in PET/CT imaging for oncology, neurology, and cardiology
Fludeoxyglucose (18F) Karolinska is a radiopharmaceutical diagnostic agent used in positron emission tomography (PET) and PET/CT imaging. Commonly known as FDG or 18F-FDG, it is a radioactive analog of glucose that accumulates preferentially in tissues with high metabolic activity. After intravenous injection, FDG is taken up by cells through glucose transporters and becomes metabolically trapped, allowing the PET scanner to create detailed images of glucose metabolism throughout the body. It is the most widely used PET tracer in clinical practice, with established roles in oncology for cancer detection, staging, treatment monitoring, and recurrence detection; in neurology for evaluating brain metabolism in epilepsy, dementia, and movement disorders; and in cardiology for assessing myocardial viability in ischemic heart disease.
Quick Facts: Fludeoxyglucose (18F)
Key Takeaways
- Fludeoxyglucose (18F) is the most widely used PET tracer worldwide, enabling non-invasive imaging of glucose metabolism for the diagnosis, staging, and monitoring of cancer, neurological disorders, and cardiac conditions.
- The tracer is administered as an intravenous injection in a controlled nuclear medicine setting, with typical adult doses ranging from 100 to 400 MBq depending on the clinical indication and patient weight.
- Patients must fast for 4 to 6 hours before the scan and have blood glucose levels below 11 mmol/L (200 mg/dL) to ensure optimal image quality and diagnostic accuracy.
- Side effects are exceptionally rare; the primary consideration is the ionizing radiation dose, which is kept as low as reasonably achievable (ALARA principle) and is comparable to or less than a standard diagnostic CT scan.
- Fluorine-18 has a physical half-life of approximately 110 minutes, meaning that the radioactivity decays rapidly and is largely eliminated from the body within 24 hours through a combination of physical decay and renal excretion.
What Is Fludeoxyglucose (18F) Karolinska and What Is It Used For?
Fludeoxyglucose (18F), commonly abbreviated as FDG or 18F-FDG, is a radiopharmaceutical agent that serves as the cornerstone of modern positron emission tomography (PET) imaging. The designation "Karolinska" indicates that this particular formulation is produced by the radiopharmacy at Karolinska University Hospital, one of the leading academic medical centers in Europe. However, the active substance itself — fludeoxyglucose labeled with the positron-emitting radioisotope fluorine-18 — is chemically and functionally identical to FDG preparations used at nuclear medicine departments worldwide.
Chemically, fludeoxyglucose (18F) is 2-deoxy-2-[18F]fluoro-D-glucose. It is structurally nearly identical to naturally occurring glucose (deoxyglucose), with one key modification: a hydroxyl group at the 2-position of the glucose molecule has been replaced by a radioactive fluorine-18 atom. This seemingly small change has profound consequences for the molecule's behavior inside the body. Like normal glucose, FDG is transported into cells via glucose transporter proteins (primarily GLUT-1 and GLUT-3) and is phosphorylated by the enzyme hexokinase to form FDG-6-phosphate. However, unlike glucose-6-phosphate, FDG-6-phosphate cannot undergo further metabolism through glycolysis because it lacks the necessary hydroxyl group at the 2-position. As a result, FDG-6-phosphate becomes metabolically trapped inside the cell, accumulating in proportion to the cell's rate of glucose uptake and phosphorylation.
This metabolic trapping mechanism is the fundamental principle that makes FDG PET imaging possible. Tissues with high glucose metabolic rates — such as malignant tumors, active brain tissue, working cardiac muscle, and sites of infection or inflammation — accumulate more FDG than surrounding normal tissues. The fluorine-18 isotope is a positron emitter: it undergoes beta-plus decay, releasing a positron that travels a short distance (typically less than 2 millimeters) before annihilating with an electron. This annihilation event produces two gamma photons of 511 keV each, emitted in exactly opposite directions (180 degrees apart). The PET scanner consists of a ring of gamma-ray detectors that simultaneously detect these paired photons, a process known as coincidence detection. By analyzing millions of such coincidence events, sophisticated computer algorithms reconstruct detailed three-dimensional images showing the distribution of FDG throughout the body.
In modern clinical practice, PET scanners are almost always combined with computed tomography (CT) scanners in hybrid PET/CT systems. The CT component provides detailed anatomical information that is fused with the metabolic data from the PET scan, allowing physicians to precisely localize areas of abnormal FDG uptake within the body's anatomical structures. More recently, PET/MRI (magnetic resonance imaging) hybrid systems have also become available at specialized centers, offering superior soft tissue contrast compared to CT while eliminating additional ionizing radiation from the anatomical imaging component.
Oncology Applications
Oncology represents the primary clinical application of FDG PET/CT, accounting for approximately 80 to 90 percent of all FDG PET scans performed worldwide. The rationale for its use in cancer is based on the Warburg effect, a metabolic phenomenon first described by Nobel laureate Otto Warburg in the 1920s: most malignant tumor cells exhibit markedly increased rates of glucose uptake and glycolysis compared to normal cells, even in the presence of adequate oxygen supply. This metabolic hallmark of cancer translates directly into increased FDG uptake, making tumors visible on PET images as areas of intense tracer accumulation, often described as "hot spots."
FDG PET/CT is used across virtually all stages of cancer management. For initial diagnosis, it helps characterize suspicious lesions detected by other imaging methods such as CT or ultrasound, distinguishing malignant from benign processes in many cases. For staging, it provides a comprehensive whole-body survey that can detect metastatic spread to lymph nodes, bones, liver, lungs, and other organs, often revealing disease that is occult on conventional imaging. This information is critical for treatment planning, as it determines whether a patient is a candidate for curative surgery, requires systemic chemotherapy, or would benefit from radiation therapy. For treatment monitoring, interim FDG PET/CT scans performed during chemotherapy or immunotherapy can assess early metabolic response, allowing oncologists to modify treatment regimens promptly if the tumor is not responding. After completion of treatment, FDG PET/CT is used for restaging and surveillance to detect residual or recurrent disease.
The cancers for which FDG PET/CT has the strongest evidence base include lung cancer (both non-small cell and small cell), lymphoma (Hodgkin and non-Hodgkin), colorectal cancer, esophageal cancer, head and neck cancers, melanoma, breast cancer, thyroid cancer, and cervical cancer. It is also increasingly used in pancreatic cancer, ovarian cancer, and multiple myeloma. Standardized uptake value (SUV), particularly the maximum SUV (SUVmax), is a semi-quantitative parameter used to measure the intensity of FDG uptake and is widely used in clinical reporting and treatment response assessment criteria such as the Deauville criteria for lymphoma and PERCIST (PET Response Criteria in Solid Tumors).
Neurology Applications
In the brain, FDG PET provides unique functional information about regional cerebral glucose metabolism. The healthy brain is the largest consumer of glucose in the body, utilizing approximately 120 grams of glucose per day and accounting for roughly 20 percent of total body glucose consumption despite representing only about 2 percent of body weight. Different brain regions have characteristic patterns of glucose metabolism, and deviations from these normal patterns can indicate neurological disease.
FDG PET brain imaging is used in the evaluation of epilepsy, particularly for pre-surgical planning in patients with medically refractory focal epilepsy. The epileptogenic focus typically shows reduced glucose metabolism (hypometabolism) during the interictal period (between seizures), which helps localize the seizure origin and guide surgical resection. FDG PET is also valuable in the differential diagnosis of neurodegenerative dementias, where characteristic patterns of hypometabolism can help distinguish Alzheimer's disease (temporoparietal hypometabolism) from frontotemporal dementia (frontal and anterior temporal hypometabolism), dementia with Lewy bodies (occipital hypometabolism), and other forms of cognitive decline. Additional neurological applications include the evaluation of brain tumors, encephalitis, and movement disorders.
Cardiology Applications
In cardiology, FDG PET is used to assess myocardial viability in patients with ischemic heart disease and left ventricular dysfunction. When areas of the heart muscle have been damaged by coronary artery disease, it is clinically important to determine whether the dysfunctional myocardium is viable (still alive but "hibernating" due to reduced blood supply) or non-viable (irreversibly scarred). This distinction has significant therapeutic implications: viable myocardium can potentially recover function after revascularization procedures such as coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI), whereas non-viable scar tissue will not benefit from revascularization.
FDG PET myocardial viability assessment is typically performed in conjunction with a myocardial perfusion study. The classic pattern of "mismatch" — reduced blood flow (perfusion defect) combined with preserved FDG uptake (indicating viable, metabolically active cells) — identifies hibernating myocardium that is likely to recover after revascularization. FDG PET is also emerging as an important tool in the evaluation of cardiac sarcoidosis, infective endocarditis, and prosthetic valve infections, where abnormal FDG uptake indicates active inflammation or infection.
Infection and Inflammation Imaging
An expanding clinical application of FDG PET/CT is in the evaluation of infection and inflammation. Activated inflammatory cells, particularly neutrophils and macrophages, have markedly increased glucose metabolism, leading to intense FDG uptake at sites of active infection or inflammation. FDG PET/CT has proven valuable in the workup of fever of unknown origin (FUO), where it can identify the source of infection or inflammation in cases that remain elusive after conventional diagnostic workup. It is also used in the evaluation of vascular graft infections, prosthetic joint infections, osteomyelitis, and large vessel vasculitis such as giant cell arteritis and Takayasu arteritis.
FDG PET/CT is indicated across multiple medical specialties: (1) Oncology — cancer diagnosis, staging, treatment monitoring, and recurrence detection; (2) Neurology — epilepsy localization, dementia differential diagnosis, and brain tumor assessment; (3) Cardiology — myocardial viability assessment and cardiac inflammation evaluation; (4) Infectious disease — fever of unknown origin, vascular graft infection, and prosthetic joint infection workup.
What Should You Know Before Receiving Fludeoxyglucose (18F)?
Contraindications
There are very few absolute contraindications to fludeoxyglucose (18F) administration. The primary contraindication is known hypersensitivity to the active substance or to any of the excipients in the formulation. However, true allergic reactions to FDG are exceedingly rare, with only isolated case reports in the medical literature. This is because FDG is a simple glucose analog administered in trace quantities (typically micrograms), which is far below the threshold that would be expected to provoke an immune response in most individuals.
Pregnancy represents a relative contraindication. Because FDG contains ionizing radiation, it poses a potential risk to the developing fetus. Nuclear medicine procedures involving ionizing radiation should generally be avoided during pregnancy unless the expected clinical benefit to the mother clearly outweighs the potential risk to the fetus. In clinical scenarios where an FDG PET scan is deemed essential during pregnancy (for example, in the staging of a life-threatening cancer), the examination may be performed with appropriate dose optimization and shielding, but only after careful discussion between the referring clinician, the nuclear medicine physician, and the patient.
Uncontrolled hyperglycemia is a relative contraindication because elevated blood glucose levels compete with FDG for uptake by glucose transporters, reducing the sensitivity and diagnostic quality of the scan. Most centers require that the blood glucose level be below 11 mmol/L (200 mg/dL) at the time of injection, with some centers using a stricter threshold of 8.3 mmol/L (150 mg/dL) for optimal image quality. Patients with diabetes mellitus require special scheduling and preparation protocols to ensure adequate blood glucose control on the day of the scan.
Warnings and Precautions
Fludeoxyglucose (18F) is a radioactive substance. It must only be received, used, and administered by authorized persons in designated clinical settings (nuclear medicine departments). Appropriate radiation protection measures must be observed for the patient, healthcare workers, and the general public in accordance with national regulations and international guidelines (IAEA, ICRP).
As with all radiopharmaceuticals, the ALARA (As Low As Reasonably Achievable) principle should guide the selection of the administered activity. The dose of FDG should be the minimum necessary to obtain adequate diagnostic information. This is particularly important in pediatric patients and young adults, who have a longer remaining lifetime over which the stochastic effects of radiation exposure could potentially manifest.
Patients should be well hydrated before and after the FDG injection and should urinate frequently to minimize the radiation absorbed dose to the urinary bladder, which receives the highest radiation exposure from FDG due to renal excretion of the tracer. The bladder wall is the critical organ for FDG dosimetry, and frequent voiding can significantly reduce the absorbed dose.
During the uptake phase (the approximately 60-minute period between FDG injection and image acquisition), patients should rest quietly in a warm, dimly lit room. Physical activity, talking, and reading should be minimized to reduce physiological FDG uptake in skeletal muscles, which could interfere with image interpretation. Cold environments should be avoided because they can activate brown adipose tissue, leading to prominent FDG uptake in characteristic anatomical locations (supraclavicular, paravertebral, mediastinal) that can complicate image interpretation and potentially obscure pathological findings.
Pregnancy and Breastfeeding
All radiopharmaceuticals, including FDG, deliver ionizing radiation to the fetus when administered during pregnancy. The radiation dose to the fetus from a standard FDG PET scan has been estimated at approximately 2 to 4 mGy for a typical adult dose, which is below the threshold generally considered to pose a significant risk of deterministic effects. However, as a precaution, FDG PET scans should be avoided during pregnancy unless the clinical benefit is judged to clearly outweigh the potential risk. If a scan is necessary, the administered activity should be minimized, and the patient should be instructed to hydrate vigorously and void frequently to reduce the radiation dose.
Women of childbearing potential should be asked about the possibility of pregnancy before any radiopharmaceutical administration. If there is any doubt, a pregnancy test should be performed before proceeding with the scan. For breastfeeding mothers, the European Association of Nuclear Medicine (EANM) and other guidelines recommend interrupting breastfeeding for at least 12 hours after FDG administration. Any breast milk expressed during this period should be discarded. Close contact between the mother and the infant should also be limited for several hours after the injection to minimize the infant's radiation exposure from external irradiation.
Pediatric Considerations
FDG PET/CT is increasingly used in pediatric oncology, particularly for the staging and treatment monitoring of lymphoma, neuroblastoma, bone sarcomas, and other childhood cancers. Special care must be taken to minimize the radiation dose in children, who are more radiosensitive than adults and have a longer remaining lifetime. Pediatric FDG doses are typically calculated on a weight-based formula recommended by the EANM Dosage Card, which significantly reduces the administered activity compared to adult protocols. Sedation may be required for young children who are unable to remain still during the scanning procedure. The fasting protocol may need to be modified for infants and young children, taking into account their higher baseline metabolic requirements and reduced glycogen reserves.
Before your FDG PET scan: (1) Fast for 4–6 hours (water is permitted); (2) Avoid strenuous exercise for 24 hours; (3) Inform the nuclear medicine team about all medications, especially insulin, corticosteroids, and recent chemotherapy; (4) Wear comfortable clothing without metal; (5) Arrive 15–30 minutes before your scheduled time; (6) Drink plenty of water and empty your bladder frequently after the injection.
How Does Fludeoxyglucose (18F) Interact with Other Drugs?
Unlike conventional pharmaceutical drugs that interact through receptor binding, enzyme inhibition, or metabolic competition at therapeutic concentrations, the interactions relevant to fludeoxyglucose (18F) are fundamentally different. Because FDG is administered in trace quantities (nanomolar to picomolar concentrations) and does not exert any pharmacological effect, the concern is not about adverse drug-drug reactions in the traditional sense. Rather, certain medications and physiological states can alter the biodistribution of FDG in the body, potentially leading to false-positive results, false-negative results, or suboptimal image quality that compromises diagnostic accuracy.
Understanding these interactions is essential for proper patient preparation and accurate image interpretation. The nuclear medicine physician and referring clinician should work together to optimize the timing of FDG PET scans in relation to the patient's medication schedule and treatment timeline.
Major Interactions
| Substance | Effect on FDG Scan | Management |
|---|---|---|
| Blood glucose / Glucose infusion | Elevated blood glucose competes with FDG for uptake via GLUT transporters, reducing tumor and brain uptake. Can cause false-negative results. | Patient must fast 4–6 hours. Check blood glucose before injection; reschedule if >11 mmol/L. |
| Insulin | Exogenous insulin stimulates GLUT-4 mediated glucose uptake in skeletal muscle and adipose tissue, diverting FDG away from tumors and increasing background uptake. | Short-acting insulin should be given at least 4 hours before FDG injection. Insulin pumps may need adjustment per center protocol. |
| Colony-stimulating factors (G-CSF, GM-CSF) | Markedly increases FDG uptake in the bone marrow and spleen for up to 2–4 weeks, potentially obscuring bone marrow involvement by malignancy. | Schedule PET scan at least 2 weeks (preferably 4 weeks) after last G-CSF/GM-CSF dose. |
| Chemotherapy | Recent chemotherapy can cause a transient inflammatory response ("flare") that increases FDG uptake, or may suppress tumor metabolism causing false-negative results. | Schedule PET scan at least 2 weeks after chemotherapy, or 6 weeks after completion of a full regimen for restaging. |
| Radiation therapy | Post-radiation inflammatory changes can cause increased FDG uptake at the treatment site, mimicking residual or recurrent disease. | Schedule PET scan at least 8–12 weeks after completion of radiation therapy. |
Minor Interactions
| Substance | Effect on FDG Scan | Management |
|---|---|---|
| Corticosteroids | May reduce FDG uptake in inflammatory and some tumor tissues by suppressing glucose metabolism and reducing inflammation. | Note current steroid use in the clinical history. Consider impact on interpretation. |
| Metformin | Can cause diffusely increased FDG uptake in the intestinal wall, potentially obscuring abdominal pathology. | Some centers temporarily discontinue metformin 48 hours before scanning. Others note it in the report. |
| Benzodiazepines and sedatives | May reduce cortical brain FDG uptake, affecting neurological PET studies. | Avoid sedation before FDG injection for brain PET studies unless clinically necessary. |
| Erythropoietin (EPO) | Can increase bone marrow FDG uptake by stimulating erythropoiesis. | Note current EPO therapy in clinical history for the reporting physician. |
It is important for patients to provide their nuclear medicine team with a complete list of all current medications, recent treatments, and relevant medical history before the FDG PET scan. This information is essential for optimal patient preparation, scheduling, and accurate image interpretation. In most cases, medications do not need to be stopped; rather, the nuclear medicine physician will factor the medication effects into their interpretation of the scan results.
What Is the Correct Dosage of Fludeoxyglucose (18F)?
Unlike most pharmaceutical products where patients follow a fixed dosage regimen, fludeoxyglucose (18F) is administered exclusively by trained nuclear medicine professionals in specialized clinical facilities. The dose (referred to as "administered activity" and measured in megabecquerels, MBq) is tailored to each individual patient and clinical scenario. Several factors influence the choice of administered activity, including the patient's body weight, the type and sensitivity of the PET scanner being used, the specific imaging protocol (whole-body versus focused), and the clinical indication for the examination.
Adults
Standard Adult Dosage
The recommended administered activity for adult whole-body FDG PET/CT imaging typically ranges from 200 to 400 MBq (approximately 5 to 10 mCi), depending on the scanner generation and imaging protocol. Modern time-of-flight (TOF) PET/CT scanners with silicon photomultiplier (SiPM) detectors can produce high-quality diagnostic images with lower activities, often in the range of 1.5 to 2.5 MBq/kg body weight. Older bismuth germanate (BGO) detector-based scanners may require higher activities, typically 3 to 5 MBq/kg.
For cardiac FDG PET studies, the administered activity is generally similar or slightly higher than for oncological studies, typically in the range of 200 to 400 MBq. Neurological FDG PET brain studies may use somewhat lower activities, often 150 to 250 MBq, because the brain is a relatively small field of view and brain PET protocols are optimized for high count-rate imaging.
Children
Pediatric Dosage
Pediatric FDG doses are calculated on a weight-based formula to minimize radiation exposure while maintaining diagnostic image quality. The European Association of Nuclear Medicine (EANM) Paediatric Dosage Card recommends a baseline activity of approximately 14 MBq for a 3 kg child, scaled linearly with body weight up to a maximum of approximately 200 to 300 MBq for adolescents approaching adult weight. As a general guideline, pediatric activities correspond to approximately 3.7 MBq/kg with a minimum of 26 MBq (0.7 mCi). Modern PET scanners allow further dose reduction in pediatric patients through extended acquisition times and advanced image reconstruction algorithms.
Elderly
Elderly Patients
No specific dose adjustment is required for elderly patients based on age alone. The administered activity is determined by the same weight-based formula used for other adult patients. However, elderly patients may have impaired renal function, which can affect the excretion of FDG and result in slightly higher radiation exposure. Adequate hydration and frequent voiding remain especially important in this population to minimize bladder dose. Special attention should be given to patient comfort during the uptake phase, as elderly patients may find it difficult to remain immobile for extended periods.
Administration Procedure
The FDG injection is given as a slow intravenous bolus, typically over 1 to 2 minutes, through a properly placed peripheral venous cannula. The injection site should be flushed with normal saline after administration to ensure that the full dose is delivered. Care should be taken to avoid paravenous injection (extravasation), which can result in suboptimal tracer delivery, degraded image quality, and potential local radiation dose to the injection site tissues.
After injection, the patient enters the uptake phase, a resting period of approximately 60 minutes (range 45 to 90 minutes depending on the protocol) during which FDG distributes throughout the body and is taken up by metabolically active tissues. During this phase, the patient should be positioned comfortably in a warm, quiet room, ideally with dimmed lighting. They should avoid physical activity, talking, chewing, and reading to minimize physiological muscle and brain cortex uptake that could complicate image interpretation.
Overdose
Pharmacological overdose in the traditional sense is not applicable to FDG because it is administered in trace quantities far below those that could cause any pharmacological effect. However, administration of an excessively high radioactive activity is a radiation safety concern. If an activity significantly higher than intended is inadvertently administered, the radiation absorbed dose to the patient can be reduced by promoting enhanced elimination through vigorous hydration and frequent voiding, and by maximizing the physical distance between the patient and others in the subsequent hours. The incident should be reported and managed according to institutional radiation safety protocols and applicable regulatory requirements.
What Are the Side Effects of Fludeoxyglucose (18F)?
Fludeoxyglucose (18F) has an extremely favorable safety profile. Because it is administered in trace quantities (nanomolar to picomolar concentrations) that are far below any pharmacologically active dose, it does not exert measurable physiological or pharmacological effects in the body. The glucose analog itself is identical to one of the body's most basic metabolic substrates, which contributes to its excellent tolerability. In decades of clinical use worldwide, with millions of doses administered annually, reports of adverse reactions directly attributable to FDG are exceedingly rare.
The principal safety consideration with FDG is the radiation exposure associated with the radioactive fluorine-18 isotope and, in the case of PET/CT, the additional radiation from the CT component. However, this radiation exposure is an inherent aspect of the diagnostic procedure rather than a "side effect" in the traditional pharmacological sense. The absorbed radiation doses are comparable to those from other widely used diagnostic imaging procedures and are carefully justified by the clinical benefit of the information obtained.
Very Common (>1/10)
- Radiation exposure (inherent to the procedure; effective dose approximately 5–7 mSv from FDG alone at standard adult activity)
- Minor discomfort at the injection site
- Temporary need to restrict contact with pregnant women and young children (radiation protection precaution)
Uncommon (1/1,000–1/100)
- Mild nausea or flushing during or shortly after injection
- Headache
- Transient sensation of warmth
- Anxiety related to the procedure (claustrophobia in the scanner)
Rare (<1/1,000)
- Allergic-type reactions (skin rash, urticaria, pruritus)
- Injection site extravasation with local tissue irritation
- Vasovagal reaction (fainting)
- Hypersensitivity reaction
Radiation Dosimetry
The radiation dose to patients from an FDG PET scan depends on the administered activity and the patient's body habitus. For a standard adult dose of 370 MBq (10 mCi), the estimated effective dose is approximately 7 mSv. The organs receiving the highest absorbed doses are the urinary bladder wall (approximately 73 mGy), the heart (approximately 22 mGy), and the brain (approximately 15 mGy). These values assume a standard voiding interval of 1 hour; frequent voiding can significantly reduce the bladder dose.
When the PET scan is combined with a diagnostic-quality CT scan (as in PET/CT), the total effective dose from the combined procedure is typically in the range of 15 to 25 mSv, depending on the CT protocol used. Low-dose CT protocols used primarily for attenuation correction and anatomical localization add approximately 2 to 5 mSv, while full diagnostic-quality CT protocols add 8 to 15 mSv or more. To put this in perspective, the average annual background radiation exposure is approximately 2.4 mSv, and a standard chest CT scan delivers approximately 7 mSv.
For pediatric patients, radiation dose optimization is of paramount importance. Weight-adapted FDG activities, combined with low-dose CT protocols and advanced PET image reconstruction techniques (such as point spread function modeling and time-of-flight reconstruction), can significantly reduce the total radiation exposure while maintaining diagnostic quality. Total-body PET scanners, which have recently entered clinical use, can produce diagnostic-quality images with dramatically reduced FDG activities (as low as 10 to 20 percent of conventional doses), representing a significant advancement for pediatric nuclear medicine.
| Organ | Absorbed Dose (mGy) | Notes |
|---|---|---|
| Urinary bladder wall | 73 | Critical organ; reduced by frequent voiding |
| Heart | 22 | Due to high myocardial glucose metabolism |
| Brain | 15 | High cerebral glucose consumption |
| Kidneys | 8 | Renal excretion pathway |
| Liver | 6 | Hepatic glucose metabolism |
| Effective dose (whole body) | 7 mSv | Comparable to a diagnostic CT scan |
How Should Fludeoxyglucose (18F) Be Stored?
Fludeoxyglucose (18F) Karolinska is a radiopharmaceutical product that is produced, stored, transported, and administered exclusively within the nuclear medicine supply chain. Unlike conventional medications that patients may store at home, FDG never leaves the custody of authorized nuclear medicine professionals and radiation-qualified facilities. This section provides information about how the product is handled by healthcare professionals, as patients may be interested in understanding the quality and safety measures that apply to their tracer.
FDG should be stored at a temperature not exceeding 25°C, in its original container, within a lead-shielded storage unit designed for radioactive materials. The product should not be frozen. Storage must comply with national regulations and international guidelines for the safe handling of radioactive materials, including appropriate shielding, labeling, and inventory controls. Access to storage areas containing radioactive materials must be restricted to authorized personnel.
Due to the short physical half-life of fluorine-18 (109.77 minutes, or approximately 110 minutes), FDG has a limited shelf life. The product must be used within the time frame specified on the label, which is typically 12 hours from the time of production. After this period, the radioactive activity will have decayed to a level insufficient for diagnostic imaging. The radioactive concentration (MBq/mL) is calculated and calibrated at a specific reference time, and the nuclear medicine technologist must account for radioactive decay when drawing up the patient dose.
FDG is typically produced using a medical cyclotron, which accelerates protons to bombard oxygen-18-enriched water, producing fluorine-18 through a nuclear reaction. The fluorine-18 is then incorporated into the deoxyglucose molecule through an automated radiochemical synthesis process, followed by purification, quality control testing, and dispensing. Because of the short half-life, production and delivery logistics are time-critical: the cyclotron may be located on-site at the hospital (as at Karolinska University Hospital) or at a regional radiopharmacy that delivers the product by dedicated courier on the same day.
Unused FDG and any waste materials contaminated with the tracer are disposed of according to radioactive waste management protocols. Due to the short half-life, FDG waste can typically be stored for decay (approximately 10 half-lives, or about 20 hours) until the residual radioactivity falls below regulatory clearance levels, after which it can be disposed of as non-radioactive pharmaceutical waste.
What Does Fludeoxyglucose (18F) Karolinska Contain?
Fludeoxyglucose (18F) Karolinska is a clear, colorless to slightly yellow sterile solution for intravenous injection. The active substance is 2-deoxy-2-[18F]fluoro-D-glucose (fludeoxyglucose labeled with the radioactive isotope fluorine-18). The radioactive concentration at the time of calibration ranges from 450 to 11,250 MBq/mL, and the specific activity is very high, meaning that the total mass of fludeoxyglucose present in a patient dose is typically in the microgram range (often less than 50 micrograms). This extremely small mass is important because it means that FDG is administered in true tracer quantities that do not perturb the body's normal glucose metabolism or cause any pharmacological effect.
The excipients (inactive ingredients) in the formulation are pharmaceutical-grade substances that serve to maintain the solution's sterility, pH, osmolality, and stability. These typically include:
- Water for injections: The primary solvent, ensuring a sterile, pyrogen-free solution suitable for intravenous administration
- Sodium chloride: Adjusts the osmolality of the solution to approximate physiological levels, ensuring patient comfort upon injection
- Citrate or phosphate buffer: Maintains the solution pH within a physiologically acceptable range (typically pH 4.5 to 8.5), ensuring stability of the active substance and tolerability of the injection
The fluorine-18 isotope has a physical half-life of 109.77 minutes (approximately 110 minutes). It decays by positron emission (97%) and electron capture (3%) to stable oxygen-18. The maximum energy of the emitted positrons is 633 keV, and they travel a mean distance of approximately 0.6 mm in soft tissue before annihilating with an electron. The annihilation produces two 511 keV gamma photons emitted at 180 degrees, which are the photons detected by the PET scanner. After approximately 10 half-lives (about 18 to 20 hours), the radioactivity has decayed to less than 0.1% of its initial value, making the remaining product essentially non-radioactive.
Each batch of FDG undergoes rigorous quality control testing before release for clinical use. These tests include verification of radionuclidic purity (ensuring that fluorine-18 is the only radioactive isotope present), radiochemical purity (ensuring that the fluorine-18 is properly incorporated into the FDG molecule and not present as free fluoride), chemical purity (testing for the presence of the residual precursor and other synthesis byproducts), sterility testing, and bacterial endotoxin testing. The product must meet all quality specifications before it is approved for patient administration.
Frequently Asked Questions About Fludeoxyglucose (18F)
Fludeoxyglucose (18F), commonly known as FDG, is a radioactive tracer used in positron emission tomography (PET) and PET/CT imaging. It is used in oncology for cancer diagnosis, staging, monitoring treatment response, and detecting recurrence. In neurology, it evaluates brain metabolism in conditions such as epilepsy and dementia. In cardiology, it assesses myocardial viability in patients with coronary artery disease. It is also used in infectious disease and inflammation imaging.
Yes, FDG PET is generally considered safe. The radiation dose from a typical FDG PET scan is comparable to or less than that of a standard CT scan. Side effects directly from the FDG tracer are very rare and typically mild. The fluorine-18 isotope has a short physical half-life of approximately 110 minutes, meaning the radioactivity decays rapidly. Patients are advised to stay well hydrated and urinate frequently after the scan to reduce radiation exposure to the bladder.
Preparation typically involves fasting for 4 to 6 hours before the scan to ensure optimal FDG uptake. Only water is allowed during the fasting period. Blood glucose levels are checked before injection and should ideally be below 11 mmol/L (200 mg/dL). Diabetic patients may need special scheduling and insulin management. Strenuous exercise should be avoided for 24 hours before the scan to minimize muscle uptake. Patients should wear comfortable clothing and remove metal objects.
FDG PET scans are generally contraindicated during pregnancy due to the radiation exposure to the fetus. The scan should only be performed during pregnancy if the expected clinical benefit clearly outweighs the potential risk. For breastfeeding women, it is recommended to interrupt breastfeeding for at least 12 hours after the injection and to discard any expressed milk during this period. A nuclear medicine physician will discuss the specific risks and benefits with each patient.
The entire procedure typically takes 2 to 3 hours. After the FDG injection, there is a mandatory resting period of approximately 60 minutes (the uptake phase) during which the tracer distributes throughout the body. The patient should rest quietly in a warm, dimly lit room during this time. The actual PET scan itself takes approximately 20 to 30 minutes, depending on the area being imaged and the scanner type. Combined PET/CT scans may take slightly longer.
Several medications and substances can affect FDG biodistribution and image quality. Insulin and oral hypoglycemic agents can alter glucose metabolism and FDG uptake. Corticosteroids may reduce FDG uptake in inflammatory and tumor tissues. Colony-stimulating factors (G-CSF, GM-CSF) can increase bone marrow uptake for up to 2 to 4 weeks after administration. Chemotherapy drugs may temporarily alter FDG uptake patterns, so PET scans are typically scheduled at least 2 weeks after the last chemotherapy cycle. Patients should inform their nuclear medicine team about all current medications.
References
This article is based on the following international sources and evidence-based guidelines. All medical claims are supported by Level 1A evidence where available.
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Editorial Team
This article was written and reviewed by the iMedic Medical Editorial Team, which includes specialists in nuclear medicine, radiology, oncology, and clinical pharmacology. All content follows the GRADE evidence framework and is reviewed according to international medical standards.
iMedic Medical Editorial Team — specialists in nuclear medicine and diagnostic imaging with extensive clinical and academic experience in PET/CT imaging and radiopharmaceuticals.
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