Ventilation-perfusion scintigraphy (V/Q)
The method is based on two components:
- Perfusion: intravenous administration of 99mTc-labeled microparticles that temporarily block pulmonary capillaries, allowing blood flow assessment.
- Ventilation: use of inhalation agents (133Xenon, 99mTc-DTPA, Krypton-81m, or Technegas) to assess airway patency.
Modern SPECT has practically replaced planar imaging, providing 3D visualization. In diagnosing pulmonary embolism, SPECT-V/Q accuracy is comparable to CT angiography, while radiation exposure can be significantly lower.
PET-CT in lung oncology
Positron emission tomography with 18F-FDG makes it possible to detect tumors based on their increased glucose metabolism.
Key capabilities:
- Lung cancer staging: lymph node assessment and metastasis detection.
- Nodule characterization: differentiation of malignancies measuring 8–10 mm or larger.
- 20% reduction in the number of unjustified thoracotomies.
To quantify radiotracer accumulation, the SUV (Standardized Uptake Value) is used.
Molecular imaging: 68Ga-DOTATATE
Specific ligands are used for neuroendocrine tumors. 68Ga-DOTATATE binds to somatostatin receptors, which is critical for diagnosing bronchial carcinoids.
The advantage of this method over 18F-FDG is that 68Ga-DOTATATE does not accumulate in inflamed tissues of atelectatic lung, allowing clear delineation of tumor borders.
Briefly: answers to topical questions
Which specific radiopharmaceuticals are used to assess pulmonary perfusion?
- Technetium-99m-labeled protein microparticles (99mTc) — administered intravenously, causing microembolization in the pulmonary vascular bed.
- Technetium-99m-labeled macroaggregated albumin (Tc-99m MAA) — transported to the lesser circulation and trapped in small pulmonary capillaries.
What is the biochemical mechanism of 18F-FDG accumulation in malignant lung tumors?
The mechanism involves increased glucose uptake and utilization by cells with activated glycolysis. The fluorinated glucose analogue is transported into the cell by glucose transporters and phosphorylated by hexokinase. After phosphorylation, FDG cannot be metabolized further, becomes trapped, and accumulates intracellularly, reflecting the high metabolic activity of the neoplasm.
What perfusion defect patterns (scintigraphic signs) are characteristic of pulmonary embolism?
- Multiple bilateral segmental perfusion defects — indicate chronic pulmonary embolism, but are not strictly specific.
- Segmental perfusion defect — a reliable sign on perfusion scintigraphy in patients with a normal chest X-ray and no history of pulmonary disease.
To remember PET: "Glucose — FDG — Metabolism — SUV". The higher the tumor metabolism, the brighter it appears on the PET scan.
Class and exam questions
What is SUV and how is it calculated?
This is the Standardized Uptake Value. It is calculated as the ratio of tracer activity in tissue to the injected dose divided by the patient's body weight.
Why is 68Ga-DOTATATE preferred over 18F-FDG for carcinoids?
68Ga-DOTATATE is specific to somatostatin receptors and does not accumulate in inflamed lung tissue, unlike 18F-FDG, which yields false-positive signals in atelectasis areas.
What is the role of SPECT-CT in diagnosing pulmonary embolism?
SPECT-CT is a high-precision first-line method that evaluates ventilation and perfusion with lower radiation exposure than standard CT angiography.
What else to study on this topic
- Physical principles of gamma cameras and SPECT systems.
- Comparative analysis of radiation doses for various imaging modalities.
- Mechanisms of radiopharmaceutical uptake by tumor cells.
- Patient preparation for PET imaging: glucose level control.
- Image interpretation features in the presence of concomitant inflammatory lung processes.
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Comprehensive study guide on "Lung Scintigraphy" and 2,199 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
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Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.