Radionuclide pulmonary ventilation/perfusion (V/Q) imaging plays a pivotal role in diagnosing pulmonary thromboembolism (PTE), a condition that can have serious implications if not identified promptly. With its non-invasive nature, V/Q imaging aids in screening, tracking, and evaluating treatment efficacy for both PTE and chronic thromboembolic pulmonary hypertension (CTEPH). However, discrepancies exist in imaging methodologies across hospitals in China, which can impact the consistency and reliability of diagnostic outcomes.
To address these variations, a working group conducted surveys and expert discussions across several nuclear medicine departments. This led to the development of an expert consensus aimed at standardizing the operational protocol for V/Q imaging. The objective of this consensus is to unify the examination processes, diagnostic methods, and precautionary measures involved in the clinical use of V/Q imaging procedures specific to PTE diagnosis.
A set of standard recommendations was articulated to streamline the imaging process and ensure high diagnostic quality. These guidelines provide clarity on the roles and requirements for implementing radionuclide V/Q imaging effectively. Among the highlighted protocols:
Recommendation 1: Use of 99mTc-Technegas is recommended for ventilation imaging. It is advised to wet the crucible with anhydrous ethanol to enhance Technegas generation efficiency. If Technegas is unavailable, alternatives such as 99mTc-DTPA aerosol can be used as a substitute (Consensus level: 100%).
Recommendation 2: Administer routine supplemental oxygen before pulmonary perfusion imaging to minimize the risk of false-positive images caused by vasospasm. The suggested flow rate is between 2-4 L/min for a duration of 5-10 minutes (Consensus level: 83.3%).
For pulmonary perfusion imaging, the group recommended administering a range of 200,000-700,000 radiopharmaceutical particles, with a target activity of 120-240 MBq (3-6 mCi). In cases involving severe pulmonary hypertension or right-to-left heart shunting, a reduced particle count of 100,000-200,000 is advisable (Consensus level: 83.3%).
Additionally, it is critical to gently agitate the suspension of 99mTc-macroaggregated human serum albumin (99mTc-MAA) prior to injection. The tracer should be injected slowly while the patient is in a supine position, ensuring continuous monitoring for any adverse reactions and careful avoidance of backflow into the syringe (Consensus level: 100%).
Specific guidelines are recommended for patients with allergic reactions. A routine skin test involving an injection of 0.1 ml of 99mTc-MAA should be performed prior to imaging. If the test yields no reaction, imaging can proceed, with emergency medications at the ready. However, if the test is positive, pulmonary perfusion imaging is contraindicated (Consensus level: 83.3%).
For special populations, such as pregnant women, a two-day imaging protocol is suggested if V/Q imaging is necessary. A dose reduction for lung perfusion imaging is advised, with a recommended dose of 50 MBq (1.35 mCi) of 99mTc-MAA (Consensus level: 100%).
When drafting reports, clarity is essential; ambiguous terminology such as "possible pulmonary embolism" should be avoided. Reports should convey definitive statements—either confirming or excluding the presence of pulmonary embolism, after thoroughly ruling out other potential causes. If clinical uncertainty persists, recommend correlating with clinical findings and other imaging modalities (Consensus level: 100%).
For patients diagnosed with CTEPH, toolsets for visual semi-quantitative analysis can function as adjuncts for efficacy measurements post-interventions like percutaneous pulmonary balloon angioplasty (BPA) or pulmonary endarterectomy (PEA). Where feasible, structured reporting is suggested to enhance the consistency and clarity in documenting segmental impairments (Consensus level: 100%).
The consensus statements established are designed to elevate the quality and reliability of radionuclide V/Q imaging in the clinical evaluation of pulmonary thromboembolism. By standardizing procedures and emphasizing clarity in diagnostic reporting, healthcare providers can improve patient outcomes and streamline clinical processes in the management of PTE. These guidelines form a robust foundation for further advancements in pulmonary imaging technologies and protocols in the future.