Radionuclide scanning: indications and possibilities

Radionuclide scanning is a set of imaging techniques that involves injecting very small amounts of radiopharmaceuticals into a patient and then recording their distribution within the body using a gamma camera or positron detectors. These techniques allow organ function and molecular processes to be visualized before anatomical changes appear, making them a complement to radiology and ultrasound. [1]

Key technologies include planar scintigraphy, single-photon emission computed tomography, and positron emission tomography. Hybrid systems combine these with computed tomography, improving the accuracy of lesion localization. The correct choice of technique depends on the clinical question: diagnosing pulmonary embolism, assessing myocardial perfusion, searching for metastases, assessing biliary function, and much more. [2]

The strength of nuclear medicine is its quantitative assessment of functions: renal filtration, bile excretion, myocardial blood flow, and tumor metabolic activity. This is important not only for diagnosis but also for monitoring therapy, making decisions about surgical intervention, and planning radiation therapy. [3]

International societies regularly update standards to standardize indications, preparation, protocols, and interpretation. Recent documents are available from the European Association of Nuclear Medicine, the Society of Nuclear Medicine and Molecular Imaging, the American College of Radiology, and specialized cardiac societies. [4]

Table 1. Main types of radionuclide imaging

Method	What does it measure?	Spatial resolution	When choosing
Scintigraphy	Distribution of radiopharmaceutical over time	Average	Organ function screening, rapid assessment
Single-photon emission computed tomography	Three-dimensional distribution of gamma quanta	Higher than planar scintigraphy	Myocardial perfusion, pulmonary ventilation and perfusion, bone lesions
Positron emission tomography	Anisotropic positron decay and annihilation	The highest among nuclear medicine methods	Oncology, inflammation, cardiology, neurology
Hybrid with computed tomography	Function plus anatomy	Combined data	Precise localization of foci, correction of weakening

Source: Quantitative Single Photon Emission Computed Tomography Handbook and Hybrid Imaging Handbook [5]

Principle, radiopharmaceuticals and physics of the method

Any radiopharmaceutical consists of a radioactive isotope and a carrier molecule that finds its "target": a receptor, membrane transporter, enzyme, or physiological pathway. For example, fluorodeoxyglucose targets glucose metabolism, while technetium methylene diphosphonate targets bone metabolism. Detectors record the radiation and construct maps of its distribution in time and space. [6]

Single-photon emission computed tomography (SPECT) and positron emission tomography (PET) allow for the acquisition of three-dimensional images and the calculation of semiquantitative and quantitative parameters. Current guidelines specifically address calibration, reconstruction, attenuation correction, and standardization of results between centers, which is particularly important for comparing studies within a single patient. [7]

Hybrid imaging systems combine functional data with computed tomography (CT) imaging. This simplifies anatomical referencing of lesions, reduces the incidence of false-positive findings, and increases physician confidence in interpretation. However, the addition of CT imaging increases the total radiation exposure, so appropriateness and optimization parameters are carefully observed. [8]

In recent years, the range of specialized drugs has expanded: ligands to prostate-specific membrane antigen for prostate cancer, somatostatin analogs for neuroendocrine tumors, labeled leukocytes for infections, and technetium complexes for biliary function. Separate protocols, doses, restrictions, and quality criteria have been developed for each molecule. [9]

Table 2. Examples of radiopharmaceuticals and typical tasks

Preparation	Target	Typical indications
Fluoride-18 based fluorodeoxyglucose	Glucose metabolism	Oncology, inflammation, fever of unknown genesis
Technetium methylene diphosphonate	Bone metabolism	Bone metastases, osteomyelitis, stress fractures
Ligands to prostate-specific membrane antigen based on gallium-68 or fluorine-18	Prostate cancer cells	Primary staging, biochemical relapse, selection for radioligand therapy
Gallium-68-dotatate or dota-tots	Somatostatin receptors	Neuroendocrine tumors
Technetium mebrofenin	Hepatobiliary function	Cholestasis, gallbladder dysfunction, bile leakage
Technetium macroglobulin albumin and xenon-133 or technetium aerosol	Ventilation and perfusion of the lungs	Pulmonary embolism

Sources: joint guidelines for prostate-specific membrane antigen, guidelines for somatostatin positron emission tomography, guidelines for hepatobiliary scintigraphy and ventilation-perfusion diagnostics. [10]

Indications

Oncology. Fluorodeoxyglucose positron emission tomography is used for staging, assessing treatment response, and detecting recurrence in many tumors. Prostate-specific membrane antigen (PSMA) ligands are specifically used for prostate cancer; they increase sensitivity at low PSA concentrations and help select patients for radioligand therapy. Somatostatin analogs are used for neuroendocrine tumors. [11]

Cardiology. Single-photon emission computed tomography (SPECT) of myocardial perfusion and positron emission tomography with quantitative blood flow assessment help identify ischemia, assess myocardial viability, and stratify risk. Current guidelines detail protocols, stress agents, quality control, and reporting. [12]

Pulmonology. Ventilation-perfusion studies using single-photon emission computed tomography (SPECT) are the standard for diagnosing pulmonary embolism in patients with contraindications to contrast or with high sensitivity to breast dose. The addition of CT increases specificity and clarifies alternative diagnoses. [13]

Functional diagnostics of organs. Bone scintigraphy reveals areas of increased bone remodeling. The kidneys are assessed using diuretic renography and cortical scintigraphy, which allows for the differentiation of obstruction from dilation and the visualization of parenchymal scars. Hepatobiliary scintigraphy is helpful in the diagnosis of cholestasis, gallbladder dyskinesia, and postoperative leaks. [14]

Safety, radiation exposure, and special situations

Effective radiation doses for diagnostic nuclear medicine studies are typically comparable to those for computed tomography (CT) scans of organs and lower than those for many interventional procedures. In hybrid studies, the total dose is the sum of the contributions from the radiopharmaceutical and CT scans, which are taken into account during planning. The principles of justification and optimization are strictly adhered to. [15]

International commissions regularly update dose coefficients for commonly used drugs. The classic dataset is supplemented by publications with revised biokinetic models, including applications for calculating patient-specific estimates. This facilitates more precise potency selection, especially in children and in serial studies. [16]

Pregnancy is a relative contraindication to most diagnostic tests; the decision is made individually, taking into account the clinical urgency. During breastfeeding, the need for a break depends on the specific drug and its pharmacokinetics; iodine-131 is strictly prohibited, while for technetium complexes, a break may be brief or not required. Individual calculations and written notification to patients are practiced. [17]

Adverse reactions to radiopharmaceuticals are rare and usually mild. Typical non-radiological restrictions include hyperglycemia for fluorodeoxyglucose, caffeine consumption before stress tests, and violation of fasting protocols for gastrointestinal examinations. Proper preparation significantly improves diagnostic yield. [18]

Table 3. Typical effective doses

Study	Effective dose assessment
Technetium bone scintigraphy	About 3-4 millisieverts
Myocardial perfusion using single-photon emission computed tomography	On average, about 8 millisieverts with high variability
Fluorodeoxyglucose positron emission tomography plus low-dose computed tomography	Often 7-10 millisieverts, depending on the CT scan protocol
Ventilation-perfusion study of the lungs using single-photon emission computed tomography	Typically lower than CT pulmonary angiography, especially for the mammary gland

Sources: International dose codes and the European Multicentre Nuclear Cardiology Study. [19]

Table 4. Pregnancy and breastfeeding: general guidelines

Situation	Approach
Pregnancy	Consider alternatives without ionizing radiation, perform only according to strict indications
Breastfeeding: Technetium Complexes	Often, a minimal or no break is possible according to the tables for a specific drug.
Breastfeeding: Iodine-131	Complete contraindication, cessation of lactation
Personalization	Use of current dosage tables and calculations for a specific patient

Source: Radiation protection guidelines for patients and clinical recommendations. [20]

Patient preparation and how the procedure is performed

Preparation depends on the task. Fluorodeoxyglucose requires fasting for at least 6 hours, glycemic control, and no strenuous exercise the day before. For myocardial perfusion, caffeine should be avoided and, if possible, the temporary discontinuation of certain medications that interfere with the stress test should be discussed. For hepatobiliary scintigraphy, fasting for several hours is recommended, and for gastric emptying, a standardized test meal and a fixed imaging time are recommended. [21]

The process goes like this step-by-step. First, the indications and contraindications are confirmed, preparation is reviewed, the study procedure is explained, and informed consent is obtained. Then, the radiopharmaceutical is administered, the required time for distribution is maintained, imaging is performed using a gamma camera or positron emission scanner, and, if necessary, a CT scan is performed. The final data is reconstructed, quality checked, compared with clinical data, and a structured protocol is issued. [22]

Proper preparation is particularly critical in gastroenterology. To assess gastric emptying, a standardized test meal based on egg white proteins is used, with fixed recording points for up to 4 hours. Standardization allows for comparison of results between centers and dynamic monitoring. [23]

In renal medicine, protocols include fluid loading, sometimes a diuretic, and catheterization when indicated; these are detailed in joint guidelines. This allows for the differentiation of functional obstruction from minor dilation and the quantitative assessment of the contribution of each kidney. [24]

Table 5. Preparation for frequent examinations

Study	Basic training requirements
Fluorodeoxyglucose positron emission tomography	Fast for at least 6 hours, control glycemia, avoid strenuous exercise
Myocardial perfusion	Eliminate caffeine, discuss medications, wear comfortable clothes
Hepatobiliary scintigraphy	Fasting for several hours, clarification of analgesics and hormones
Gastric emptying	Standardized test food, fixed shooting intervals up to 4 hours
Diuretic renography	Hydration, clarification of diuretics and associated factors

Sources: practical parameters and specialized documents. [25]

How to read the results

Interpretation begins with data quality checks: motion, correct attenuation correction, and alignment of functional and anatomical volumes. Current guidelines for quantitative single-photon emission computed tomography (SPECT) describe metrics and control procedures that ensure reproducible conclusions. [26]

Each method has validated criteria. In the diagnosis of pulmonary embolism, identifying segmental ventilation-perfusion mismatches is key. In cardiology, standard perfusion maps, stress and rest curves, as well as quantitative indicators of blood flow and coronary reserve allow one to assess the severity of ischemia. [27]

In gastroenterology, interpretation is based on standardized norms for the percentage of emptying at given time points, while in the hepatobiliary system, gallbladder ejection fraction and passage time are calculated. Adherence to the protocol is critical, otherwise the indicators become incomparable. [28]

The clinical context and results of other studies are always taken into account. Hybrid complexes simplify differential diagnosis but require attention to superposition artifacts and dose limitations. Standardized reports help the clinician quickly understand the essence and make decisions. [29]

Table 6. Common artifacts and how to avoid them

Artifact	Cause	Prevention
Discrepancy between functional and anatomical data	Movement between the functional and computed tomography blocks	Fixation, short protocols, re-registration
False increase in accumulation in brown adipose tissue with fluorodeoxyglucose	Cold activation	Heat, pharmacological preparation according to indications
Attenuation correction errors	Inaccurate attenuation map	Control of compatibility and boundaries of organs
Extravasation of the drug	Extravascular administration	Careful venipuncture and observation

Sources: quantitative single-photon emission computed tomography manuals and practical guides. [30]

Key clinical scenarios

Myocardial perfusion. Single-photon emission computed tomography (SPECT) reveals reversible ischemia and irreversible perfusion defects, while positron emission tomography (PET) provides quantitative maps of blood flow and coronary reserve. This influences the choice of drug therapy, the need for revascularization, and prognosis. [31]

Pulmonary embolism. Ventilation-perfusion imaging using single-photon emission computed tomography (SPECT) is diagnostically effective, particularly in cases where contrast is contraindicated and in young women. The addition of CT improves specificity and identifies alternative causes of symptoms. [32]

Prostate cancer and neuroendocrine tumors. Prostate-specific membrane antigen (PSMA) ligands are sensitive to small lesions and are useful at low PSA concentrations. Somatostatin analogs provide high contrast in neuroendocrine tumors and aid in patient selection for radionuclide therapy. [33]

Kidneys and biliary system. Diuretic renography differentiates true obstruction from dilation, and cortical scintigraphy reveals parenchymal scarring. Hepatobiliary scintigraphy assesses gallbladder ejection fraction and aids in the diagnosis of leaks and dysfunction. [34]

Limitations and how to bypass them

Not all processes have a specific target. For example, fluorodeoxyglucose accumulation reflects metabolism and inflammation, so without clinical data and anatomical correlation, misinterpretations are possible. The solution is hybrid complexes, comparison with biochemistry, and repeat testing after therapy. [35]

Technical limitations include movement, metal implants, high body mass, and previous interventions. Modern quantitative single-photon emission computed tomography protocols and quality control standards help minimize their impact and maintain data comparability between centers. [36]

Dose load remains a focus of attention, particularly in children and during serial monitoring. Minimal sufficient activity, low-dose computed tomography protocols, the latest reconstruction algorithms, and personalized calculations based on current models are being used. [37]

Patient preparation is critical. Failure to adhere to fasting, caffeine, medication, or hydration regimens degrades quality and can completely alter interpretation. Therefore, protocols include separate reminders and checklists for each study. [38]

Questions and Answers

Is it painful and how long does it last?
The injection is usually well-tolerated, followed by a waiting period ranging from a few minutes to several hours, after which the images are taken. The total duration depends on the task: from 30 minutes to several hours. [39]

Can I have contact with children and pregnant women after the test?
Most medications do not require significant restrictions after diagnostic doses, but staff will provide individual recommendations regarding time and distance. Short-term restrictions may apply for some medications. [40]

What should be done with medications before myocardial perfusion and positron emission tomography?
The decision is individual. Caffeine withdrawal and temporary discontinuation of certain medications are often recommended; fasting and glucose control are important for fluorodeoxyglucose. [41]

How accurate are studies for pulmonary embolism?
Ventilation-perfusion single-photon emission computed tomography (SPECT) shows high sensitivity, and combining it with CT increases specificity and identifies alternative causes of symptoms. [42]

Isn't the "radioactive" substance dangerous?
The doses are small, carefully calculated, and comparable to other diagnostic methods. The benefits of a properly performed study usually outweigh the potential risks. [43]