Magnetic resonance imaging (MRI), ultrasound, and CT scans are diagnostic tools that most of us don’t fully understand. So, in this article, let's focus on CT.

What is a CT Scan? Slicing the Human Body for a Closer Look!

To put it simply, if an X-ray flattens the body for viewing, and ultrasound is like tapping a watermelon to check if it’s ripe, MRI is a shake and see approach, then CT is like slicing the body into thin slices for a detailed examination. And these slices can be less than 1 mm thick.

How Does a CT Work?

The process of CT imaging is quite complex. To avoid getting too technical, let’s explain it in simple terms: the machine emits X-rays that pass through the body and then produce an image on a processor.

Two Types of CT Scans:

• Plain CT Scan: You just lie on the CT machine, and the scan is completed in a few seconds.
• Contrast-enhanced CT Scan: This is done on top of the plain CT. A contrast agent (iodine-based) is injected into a vein. The iodine contrast travels through the bloodstream to various organs and tissues, allowing us to see them more clearly.

After injecting the iodine contrast, the abnormal tissues can be compared with surrounding normal tissues to identify any abnormalities.

To sum it up: contrast-enhanced CT shows more detail and clarity.

For a first-time patient, doctors may suggest a plain CT scan to understand the condition. If the plain CT reveals the abnormality and a definitive diagnosis can be made, then a contrast-enhanced CT may not be necessary. However, if the plain CT is unclear or inconclusive, a contrast-enhanced CT will be required.

It’s important to note that a small percentage of people may experience side effects from the iodine contrast. Therefore, it's crucial to carefully read the consent form for the contrast agent, drink plenty of water before and after the scan, and know that the contrast agent is usually excreted in the urine within 24 hours.

Is There Radiation from CT Scans? No Need to Worry if It’s Within Safe Limits

Since the CT machine emits X-rays that pass through the body, does this mean it is harmful? The potential harm from a CT scan mainly comes from the ionizing radiation produced by the X-rays. Ionizing radiation can damage certain large molecules in the body and harm cells, potentially damaging the body.

However, here’s the key: discussing radiation without considering the dosage is meaningless.

In fact, even without undergoing a CT scan, many things in everyday life expose us to radiation. Are you worried about these?

• Flying for 20 hours exposes you to 0.1 mSv of radiation.
• Smoking 20 cigarettes a day for a year exposes you to 0.5–2 mSv.
• Subway security checks expose passengers to less than 0.01 mSv per year.
• Natural background radiation that everyone receives annually is about 2 mSv.

According to the Diagnostic Reference Levels for Adults in X-ray Computed Tomography published by the government, the amount of radiation you receive during a CT scan of different parts of the body can be easily calculated.

Radiation Safety Standards in China

• The annual radiation limit for radiation workers is 50 mSv.
• The average annual radiation limit over five years is 20 mSv.

In other words, as long as the total radiation dose is controlled within safe limits, it is considered safe!

How Likely is a CT Scan to Cause Cancer?

Animal studies show that unless exposed to prolonged, high doses of radiation, the likelihood of cancer or bone marrow suppression is extremely low.

What about Marie Curie, who died of aplastic anemia (bone marrow suppression)? That was because she was exposed to radioactive materials daily, for a long time, in large amounts. It’s like having a constant CT scan.

So, don’t panic whenever you hear about radiation. The radiation from a single CT scan is safe and controllable.

What is CT Used For?

Some might ask, with such advanced technology available nowadays, why not just eliminate CT since it involves radiation? Well, that’s not possible.

First, when done under the guidance of a doctor, the radiation from CT scans is within safe limits. Second, CT has a broad range of applications, with unparalleled advantages in examining the head, lungs, limbs, and more.

Here are some common uses:

• Face and neck: CT can detect facial tumors, fractures, inflammations, and more, such as orbital diseases, sinus cancer, nasopharyngeal cancer, middle ear diseases, and thyroid or neck masses.
• Head: It’s the first choice for diagnosing head injuries, cerebral hemorrhage, stroke, vascular malformations, brain tumors, and developmental abnormalities. It’s especially effective for diagnosing acute stroke, cerebral hemorrhage, and head trauma.
• Chest: CT is used for diagnosing various tumors, tuberculosis, inflammations, bronchiectasis, lung abscesses, atelectasis, pneumothorax, fractures, esophageal foreign bodies, and various abnormalities in the lungs, pleura, and mediastinum.
• Abdomen and pelvis: It is mainly used for diagnosing diseases of the liver, gallbladder, pancreas, spleen, peritoneal cavity, retroperitoneal space, and the urinary and reproductive systems. It’s also useful for identifying the location and cause of intestinal obstruction and for assessing the extent of stomach or colon cancer invasion and distant metastasis.
• Skeletal system: CT can detect subtle fractures of the skull and spine, disc disease, spinal stenosis, bone tumors, bone tuberculosis, inflammations, and more. It can also create three-dimensional images and multi-planar reconstructions of the affected areas.

How to Minimize Exposure and Time During a CT Scan

• Remove metal objects: Before entering the CT room, the doctor will ask you to remove any metal items. Some women may even need to remove their bras. Wondering why? It’s simply because metal objects can interfere with the scan results, causing shadows that affect the doctor’s diagnosis—nothing more.
• Prepare in advance: For example, if you’re having a gastric CT scan, drinking more water beforehand can help fill the stomach and improve the imaging results.
• Work with the doctor to shorten scan time: During the scan, the doctor may ask you to hold your breath or take deep breaths. Be sure to follow these instructions, as it will reduce the scan time and minimize your exposure to radiation.

Of course, a CT scan is essentially still an X-ray machine, but with higher standards for radiation protection. Unless there’s a special need, unnecessary repeated scans are not recommended.

After the Scan, You Can Do These to Reduce Radiation Effects

After the scan, you can drink green tea and eat fresh fruits and vegetables like carrots, oranges, tomatoes, and apples. Foods like seaweed, kelp, and black fungus are also thought to have anti-radiation properties.

Special Considerations

• Pregnant women should avoid CT scans in the first 12 weeks. After that, the decision should be made based on the condition.
• Children should undergo low-dose CT scans.
• Patients with hyperthyroidism should be cautious when choosing contrast-enhanced CT.