Lung CT: what the scan shows and when it is ordered

A referral for a computed tomography scan is often frightening: the mind immediately jumps to something serious. In fact, it is an ordinary way to examine the chest layer by layer, slice by slice. Let us explain what the doctor sees, why contrast is sometimes needed, and how tomography differs from X-ray.

What lung and chest CT is

Computed tomography is a method of layer-by-layer examination of the internal structure of the body: the machine takes a series of X-ray images from different points around the person, and the program assembles them into a three-dimensional model of tissue density. For the chest, this means that the doctor receives cross-sectional slices of the lungs, heart, major vessels, lymph nodes, and upper abdomen.

Referrals often contain the abbreviations CT of the chest organs and SCT of the chest organs — this is how computed tomography of the chest organs is designated. It is ordered after chest trauma, when a mass, inflammation, or blood clots are suspected, and also to check how treatment is progressing.

What tomography shows

Chest tomography is one of the best ways to examine soft tissues such as the heart and lungs. The report usually contains specific findings:

• pneumonia, inflammation, and scars in lung tissue;
• nodules, masses, cysts, enlarged lymph nodes;
• blood clots in the vessels of the lungs, fluid around the lungs or heart;
• dilation of the large airways and emphysema;
• changes in the aorta and other major vessels of the chest.

The slices also show oncological processes: lung cancer, metastases, esophageal tumors, lymphomas in the chest.

CT with and without contrast: what the difference is

Contrast is a dye that highlights specific areas inside the body and makes the image clearer. It may be given to drink, injected into a vein in the arm, or administered through the rectum; it is excreted in urine. Whether contrast is needed is decided by the doctor — it depends on the purpose of the examination.

If the dye is injected into a vein, kidney function may be checked beforehand with a blood test. If there was a previous reaction to contrast, the doctor will discuss preparation that will allow it to be administered more safely, and 4–6 hours before the examination you are asked not to eat or drink. During the injection, a feeling of warmth, a metallic taste in the mouth, and a sensation as if you are urinating occur; this passes within seconds.

CT, X-ray, and MRI: what is chosen for lung diagnostics

CT is built from many X-ray images from different points around the body and provides a layer-by-layer image. A nodule is sometimes noticed on a chest X-ray, after which the doctor may order a CT. The choice between CT, X-ray, and MRI is made by the doctor; ask why this particular method was chosen.

How the examination is performed and how to read the report

The entire procedure usually takes 10–20 minutes, and the scan itself takes from 30 seconds to several minutes. You lie on a narrow table that slides into the ring of the machine; you need to lie still, otherwise the image will be blurred, and at certain stages you are asked to breathe in, breathe out, or hold your breath. The specialist operates the machine from the next room and can hear you.

Tell them in advance if you are pregnant or cannot rule out pregnancy, are breastfeeding, are taking medications, or if you have asthma, diabetes, kidney or thyroid problems, an allergy, or have had a reaction to contrast. Before the scan, you will be asked to remove jewelry, clothing with zippers, a bra, and hairpins: metal interferes with the rays. If you have a fear of enclosed spaces, report this in advance.

If contrast was administered, after the procedure you are asked to wait at the clinic for up to 30 minutes. The images are reviewed by a radiologist, who writes a report for the referring doctor; results are usually ready in 1–2 weeks, sometimes up to 4 weeks. If you have not been notified within 4 weeks, call the referring doctor. Numbers marked HU are values on the Hounsfield scale, where zero corresponds to the density of water.

Limitations and contraindications of the method

Complications are rare, but an allergic reaction to contrast is possible: weakness, sweating, difficulty breathing, and in rare cases a severe body response requiring immediate help. In people with kidney disease, the dye can harm the kidneys; during pregnancy, chest CT is generally avoided, and if it is necessary, special precautions are taken.

Tomography involves ionizing radiation: the risk from a single scan is small, but it increases if there are many examinations, so the doctor weighs the benefit and the risk. There are also technical limits: the weight limit for machines is about 204 kg, and for newer models up to 308 kg; if you weigh more than 136 kg, report this in advance.

A referral for CT is not in itself a reason to call an ambulance. Dial 103 or 112 if, after contrast administration, increasing weakness, sweating, or difficulty breathing occurs.

This material is for reference and does not replace a doctor's consultation: discuss questions about your examination and its results with the doctor who referred you.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer