Lung health is essential for overall wellbeing. A key aspect of healthy lungs is their ability to efficiently transfer oxygen into the blood. This process relies on both the flow of air (ventilation) and the flow of blood (perfusion) through the lungs. While ventilation is about how well air moves in and out, perfusion refers to the movement of blood through the lungs’ fine network of blood vessels. Both are crucial, but today we’ll take a closer look at lung perfusion: what it is, when and why it’s measured, and how advanced imaging technologies are enhancing our understanding of it.

What is Lung Perfusion?

Lung perfusion describes the amount and distribution of blood flow within the lungs. After you breathe in, oxygen from the air reaches tiny air sacs called alveoli; at the same time, blood pumped from the heart flows through capillaries around these alveoli. Efficient gas exchange—and, ultimately, healthy oxygen levels in the body—depends on these two flows working in harmony.

Any mismatch between ventilation and perfusion (known as a “VQ mismatch”) may result in poor oxygenation and hint at underlying lung conditions.

When and Why is Lung Perfusion Measured?

Assessing lung perfusion is critical in diagnosing and managing a range of respiratory illnesses, including:

• Pulmonary Embolism (PE): Blood clots in the lungs block perfusion and can be life-threatening. Early detection is crucial.
• Chronic Thromboembolic Pulmonary Hypertension (CTEPH): Chronic blood clots can cause long-term increases in lung blood pressure.
• Chronic Obstructive Pulmonary Disease (COPD) and Asthma: These diseases affect both airflow and blood flow, and perfusion imaging can help pinpoint areas of poor lung function.
• Lung Cancer and Surgery Planning: Before surgery, doctors need to assess which regions of the lung are working best. This ensures enough healthy lung remains after surgery, minimizing post-operative complications.

Accurate perfusion imaging can reveal not only where blood flow is limited, but also how these limitations might impact a patient’s breathing and overall lung health.

How is Lung Perfusion Measured?

Historically, several tests have been used to evaluate lung perfusion:

1. Nuclear Medicine VQ Scan (Ventilation/Perfusion Scan)

This test uses radioactive tracers to assess both airflow and blood flow:

• Ventilation phase: The patient breathes in a gaseous tracer; images show where air is reaching in the lungs.
• Perfusion phase: A different tracer is injected into the blood; images reveal blood flow patterns. By comparing these images, doctors can spot mismatches between ventilation and perfusion, which can indicate the presence of a clot or other issue.

2. SPECT (Single Photon Emission Computed Tomography)

SPECT is an advanced nuclear VQ scan, producing 3D images of perfusion and ventilation with improved spatial detail compared to traditional scans. It’s considered the state-of-the-art for functional lung imaging, especially for detecting pulmonary embolism. However, limitations include the need for specialized equipment, radiotracers, and scheduling within nuclear medicine departments.

3. CT Pulmonary Angiography (CTPA)

CTPA can visualize larger blood vessels and is particularly useful for detecting major pulmonary emboli. It uses intravenous contrast dye to highlight vessel blockages, but doesn’t directly measure regional perfusion or ventilation.

4. Advanced Software Solutions—Like 4DMedical CT:VQ™

Emerging technology, such as 4DMedical’s CT:VQ* software, is revolutionizing perfusion imaging. CT:VQ™ extracts detailed information about both ventilation and perfusion from a standard, non-contrast CT scan—without the need for radiotracers or dyes. By analyzing the motion and density changes of lung tissue during breathing, CT:VQ provides both high-resolution, quantitative lung maps and overcomes many logistical hurdles present in nuclear scans.

*FDA clearance pending

The Future of Lung Perfusion Imaging

Advances in lung perfusion imaging are opening new routes for diagnosis and treatment of lung disease. At 4DMedical, our mission is to empower clinicians with accessible, precise, and actionable insights into lung function. With cutting-edge software like CT:VQ™, assessing both blood flow and ventilation will become not only faster and safer, but available to a wider range of healthcare providers and patients—without the need for specialized tracers or complex workflows. Innovations like these from 4DMedical will continue leading the way to improved diagnostic accuracy and better treatment decisions.