What Is Computed Tomography Scan? CT Scan For Short.

All You Need To Know About Scanning of the Chest?

Computed tomography, better known as CT or CAT scan, is a diagnostic medical imaging test. Like traditional x-rays, it will generate a plurality of images or image inside the body.

Using various methods, including adjusting the radiation dose depending on the patient’s size and new software technology, the amount of radiation needed to perform a chest CT scan can be significantly reduced.

A low-dose chest CT scan produces images of sufficient quality to detect many lung diseases and abnormalities, using much less radiation than a normal chest CT scan—in some cases reducing the dose by 65 percent or more.

A low-dose chest CT scan is usually used to evaluate acquired and congenital lung abnormalities, such as pneumonia, interstitial lung disease, or tumor evaluation. Research is underway to further reduce radiation doses.

Depending on your medical problems and what information is required from the CT scan, the radiologist will determine which parameters should be used for scanning. If your child needs to undergo a CT scan, use appropriate low-dose pediatric settings.

Common Uses Of CT Scan.

A CT Scan becomes necessary when there is need to:

• Examine the abnormalities found on normal chest x-rays .
• Help diagnose the causes of clinical signs or symptoms of chest disease, such as coughing,shortness of breath, chest pain, or fever.
• Identify and evaluate the extent of tumors that occur in the chest, or tumors that have spread there from other parts of the body.
• Evaluate whether the tumors respond to treatment.
• Help plan radiation therapy.
• Evaluate chest injuries, including the heart, blood vessels, lungs, ribs, and spine.
• To evaluate abnormalities in the development of the chest, detected during ultrasound examination of the fetus.

Chest CT can demonstrate various lung disorders, such as:

• benign and malignant tumors.
• pneumonia.
• tuberculosis.
• bronchiectasis, cystic fibrosis.
• inflammation or other diseases of the pleura (the covering of the lungs).
• interstitial and chronic lung disease.
• congenital abnormalities.

CT scanning has recently been approved for screening asymptomatic people who have smoked a significant amount of cigarettes by the Centers for Medicare and Medicaid Services. See the Lung Cancer Screening page for more information.

A CT angiogram (CTA) may be performed to evaluate the blood vessels (arteries and veins) in the chest. This involves the rapid injection of an iodine-containing fluid (contrast material) into a vein while obtaining CT images. See the CT Angiography (CTA) page for more information.

How You Should Prepare For The Test?

What does the equipment look like?

The CT scanner is typically a large, donut-shaped machine with a short tunnel in the center. You will lie on a narrow examination table that slides in and out of this short tunnel. Rotating around you, the x-ray tube and electronic x-ray detectors are located opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate control room. This is where the technologist operates the scanner and monitors your exam in direct visual contact. The technologist will be able to hear and talk to you using a speaker and microphone.

How does the procedure work?

In many ways, computed tomography works the same way as other x-ray examinations. Different parts of the body absorb x-rays in different amounts. This difference allows the doctor to distinguish parts of the body from each other in an x-ray or CT image.

In a normal x-ray examination, a small amount of radiation is sent through the part of the body being examined. A special electronic image recording plate captures the image. On x-ray, the bones appear white. Soft tissues, such as the heart or liver, appear in shades of gray. The air seems to be black.

During CT scanning, several x-rays and electronic x-ray detectors rotate around you. They measure the amount of radiation absorbed by your entire body. Sometimes the viewing table moves during scanning, so that the x-ray beam moves in a spiral. A special computer program processes this large amount of data to create two-dimensional cross-sectional images of your body. These images are then displayed on the monitor. Computed tomography is sometimes compared to studying a loaf of bread by cutting it into thin slices. When image slices are reassembled using a computer program, the result is a very detailed, multidimensional representation of the inside of the body.

Improvements in detector technology allow almost all CT scanners to obtain multiple slices per revolution. These scanners, called multi-slices or multi-detector CT, allow you to get thinner slices in a shorter time. This results in more detail and additional viewing options.

Modern CT scanners can scan large areas of the body in just a few seconds, and even faster in young children. This speed is useful for all patients. This is especially useful for children, the elderly, and the seriously ill-those who find it difficult to stay in place even for the short time it takes to get images.

For children, the CT scan technique will be adjusted to their size and area of interest in order to reduce the radiation dose.

Various CT scanning methods are used to obtain high-quality images at a lower radiation dose, including::

• Dose modulation, in which the radiation dose is continuously adjusted depending on the size of the patient at each location as the patient moves through the scanner.
• Noise management software for filtering unnecessary data
• Using screens (this method depends on the type of CT scanner used) external bismuth shields can be applied to the patient
• The x-ray tube can be turned off during part of its rotation.
  reduce the peak value of the voltage

Your radiologist will select the appropriate dose reduction method(s) to achieve the lowest possible dose required to answer the clinical question.

How is the procedure performed?

The technologist begins by positioning you on the CT exam table, usually lying flat on your back. Straps and pillows may be used to help you maintain the correct position and remain still during the exam.

If a contrast material is used, it will be injected into a vein shortly before scanning begins.

Next, the table will move quickly through the scanner to determine the correct starting position for the scans. Then, the table will move slowly through the machine as the actual CT scanning is performed. Depending on the type of CT scan, the machine may make several passes.

You may be asked to hold your breath during the scanning. Any motion, including breathing and body movements, can lead to artifacts on the images. This loss of image quality can resemble the blurring seen on a photograph taken of a moving object.

When the exam is complete, you will be asked to wait until the technologist verifies that the images are of high enough quality for accurate interpretation.

The actual CT scanning takes less than 30 seconds and the entire process, including exam preparation, is usually completed within 30 minutes.

Who interprets the results of a CT Scan?

A radiologist, a doctor specially trained to monitor and interpret x-ray examinations, will analyze the images. The radiologist will send an official report to the doctor who ordered the examination.

Additional exams may be required. If so, your doctor will explain why. Sometimes a follow-up examination is performed because a potential anomaly needs further assessment using additional views or special imaging techniques. You can also perform a follow-up examination to find out if there were any changes in the anomaly over time. Follow-up examinations are sometimes the best way to check whether the treatment is working, whether the abnormality is stable, or whether it has changed.

What are the benefits vs. risks of CT Scan?

Benefits of Computed Tomography

• CT is fast, which is important for patients who have trouble holding their breath.
• CT is widely available.
• CT scanning is painless, noninvasive and accurate.
• A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time.
• Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.
• CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives.
• CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.
• CT is less sensitive to patient movement than MRI.
• CT can be performed if you have an implanted medical device of any kind, unlike MRI.
• CT imaging provides real-time imaging, making it a good tool for guiding minimally invasive procedures such as needle biopsies and needle aspirations of many areas of the body, particularly the lungs, abdomen, pelvis and bones.
• A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.
• No radiation remains in a patient’s body after a CT examination.
• X-rays used in CT scans should have no immediate side effects.
• Low-dose CT scans of the chest use a lower dose of radiation than conventional chest CT.

Risks of Computed Tomography

• There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
• The effective radiation dose for this procedure varies. See the Radiation Dose in X-Ray and CT Exams page for more information about radiation dose.
• Women should always tell their doctor and x-ray or CT technologist if there is any chance they are pregnant. See the Safety in X-ray, Interventional Radiology and Nuclear Medicine Procedures page for more information about pregnancy and x-rays.
• CT scanning is, in general, not recommended for pregnant women unless medically necessary because of potential risk to the unborn baby.
• The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare, and radiology departments are well-equipped to deal with them.
• In some patients with reduced kidney function, the dye used in CT scanning may worsen kidney function.

What are the limitations of CT Scanning of the Chest?

A person who is very large may not fit in the opening of a conventional CT scanner , or may be above the weight limit—usually 450 pounds—for a moving table.

Magnetic resonance imaging (MRI) may be better than CT to detect certain types of soft tissue abnormalities.

Although the CT scan is very fast, movement from breathing or body movement during the scan may cause blurring of images.