A Computed Tomography Pulmonary Angiogram (CTPA) is a specialized imaging procedure using computed tomography technology. The scan captures detailed images of the pulmonary arteries, the blood vessels that transport blood from the heart to the lungs. By employing an intravenous contrast agent, the CTPA creates a visual map of blood flow, allowing identification of blockages or structural abnormalities.
Identifying the Need for a CT Pulmonary Angiogram
The primary reason a doctor orders a CTPA is to diagnose or rule out Pulmonary Embolism (PE). PE occurs when a blood clot, often originating in the legs, travels to the lungs and blocks blood flow in the pulmonary arteries. Due to the seriousness of this condition, the CTPA is the standard and most reliable imaging study for confirming or excluding PE.
Patients requiring this scan often present with symptoms suggesting a clot. These frequently include sharp chest pain that worsens when taking a deep breath (pleuritic chest pain). Other common signs are sudden shortness of breath, a rapid heart rate (tachycardia), or a drop in blood oxygen saturation.
The CTPA is also valuable for evaluating other lung blood vessel conditions. It assesses Pulmonary Hypertension (high blood pressure in the lungs) by measuring the size of the main pulmonary artery and the heart’s right chambers. The scan helps identify congenital problems, such as abnormal connections or narrowed segments (stenosis). Detailed images can also evaluate tumors or aneurysms affecting blood flow.
Essential Steps for Preparing for the Scan
Preparation focuses on safely administering the iodinated contrast material. Patients are typically asked to fast for about four hours before the scan to ensure the stomach is empty. This fasting minimizes the risk of nausea from the contrast injection and ensures the best image quality.
A laboratory blood test to check kidney function is mandatory before the procedure. The test measures creatinine levels to calculate the estimated Glomerular Filtration Rate (eGFR), which indicates how effectively the kidneys filter waste. Since the contrast agent is flushed through the kidneys, a reduced eGFR increases the risk of temporary contrast-induced nephropathy.
If a patient takes Metformin, they may be instructed to stop taking it on the day of the scan and for 48 hours afterward. This precaution prevents Metformin buildup in the bloodstream, which could cause lactic acidosis if temporary kidney strain occurs. The medical team provides specific instructions tailored to the patient’s kidney function and medication regimen.
Upon arrival, a healthcare professional establishes an intravenous (IV) line, usually in the arm, for injecting the contrast agent. Patients must discuss any history of allergic reactions to contrast dye, as a prior reaction is the greatest risk factor for a future event. Allergies to shellfish or iodine-containing antiseptics are generally not considered significant risk factors for a reaction to the modern, low-osmolality contrast used in CTPA.
What Happens During the CTPA Procedure
The CTPA procedure takes place in a dedicated imaging suite with a large, ring-shaped scanner. The patient lies flat on their back on a narrow table, usually with arms raised above their head. This position moves the shoulder girdle out of the imaging field, preventing artifacts that interfere with visualizing the pulmonary arteries.
The technologist operates the machine from an adjacent control room but maintains constant visual and verbal contact with the patient. Before the scan, the IV contrast agent is injected rapidly using an automated pump. This quick injection (bolus) is timed precisely using bolus tracking to ensure the scan captures the contrast at its highest concentration within the pulmonary arteries.
Immediately after the injection, the patient experiences several normal sensations, which the technologist explains beforehand. The most common is an intense, spreading warmth or flush felt throughout the body, particularly in the face and pelvic region. This warmth is a physiological response caused by the contrast agent’s rapid circulation and temporary vasodilation.
Many patients report a temporary metallic taste in their mouth, due to the contrast stimulating chemosensory pathways. It is also common to feel a strong urge to urinate as the contrast rapidly reaches the bladder, though this feeling is temporary and does not indicate a loss of bladder control. During the imaging phase, the patient is instructed to hold their breath for a short period, often less than 10 seconds. This breath-hold is crucial for preventing motion artifacts and ensuring clear images.
Post-Scan Care, Results, and Safety Considerations
Once imaging is complete, the technologist removes the IV line. The most important post-scan instruction is to significantly increase fluid intake for the remainder of the day. Drinking plenty of water helps the kidneys efficiently flush the iodinated contrast agent out of the system.
The patient is typically monitored briefly after the procedure for immediate adverse reactions. While immediate reactions are rare, delayed reactions, such as a mild skin rash or hives, can occur hours or days later. The radiology team provides contact information for patients to report any delayed symptoms.
Modern CT scanners utilize low radiation doses, and the benefit of a timely, accurate diagnosis for conditions like Pulmonary Embolism outweighs the risk from radiation exposure. Results are typically delivered in two stages: a preliminary finding communicated quickly to the ordering physician, followed by a final, detailed report from the radiologist, often available within 24 to 48 hours. Patients should consult with their ordering physician or the radiology team for personalized medical advice regarding preparation, risks, and results timeline.