Summary of the article
What is a CT Scan ?
CT Scan allows you to view all the organs in slices and to reconstruct them in two or three dimensions. By rotating around the area to be explored, the X-ray tube emits a beam of photons that is received at the opposite end. The attenuation of the intensity of the rays after their passage through the body allows the images to be constructed using a computer. The acquisition is helical and continuous, it is done at the same time as the movement of the table.
The CT scan is widely used to analyze different types of tissues such as lungs, bones and joints, abdominal viscera and blood vessels. It allows to identify infectious lesions, abnormal vessels, cysts and lymph nodes, and tumors.
The scanner consists of a ring inside which the X-ray tube and sensors are located, and an examination table. Outside the room, separated by a leaded glass window, a control panel allows medical and paramedical professionals to program the image sequences and begin their interpretation.
How is a CT Scan performed ?
Depending on the organ to be studied, it takes 5 to 15 minutes to undergo a scan. Under the responsibility of the radiologist, you will be taken care of by a CT scan technician.
A preparation before the examination with the CT scan technician is necessary in order to verify that you do not have any contraindications, in particular to the injection of contrast product or in case of pregnancy.
After removing all metal objects, you will enter the room to be installed. You will lie down on the scanner table, remain still and hold your breath if asked to do so. The table moves while the images are being taken.
If the examination requires an injection of contrast medium, an infusion will be placed in your arm beforehand and you will be injected during the examination.
In an emergency, you can contact the handler with the bell and communicate via a microphone built into the machine.
Preparing for a CT Scan
Depending on the type of scan to be performed, you may be required to fast (not eat, drink or smoke for three hours before the scan), have a full bladder and/or drink a liter of water before the scan without urinating. If you have known allergies, you will have to take tablets on medical prescription, the day before the exam and the day of the exam to avoid any reaction.
On the day of the examination, please remember to present the following documents to the secretariat :
Your health insurance card ("carte vitale") and complementary health insurance card ("mutuelle")- Your prescription
- The contrast medium which has been prescribed when injected review.
- Your previous reports and images related to the condition which will allow a comparison and a better follow-up (X-ray, ultrasound, scanner, MRI...)
- Your blood test results
Preferably wear clothes that do not have zippers or snaps, avoid wearing jewelry and hairpins, otherwise you will have to remove them.
For your comfort and if you are not required to have a full bladder, remember to go to the bathroom beforehand to avoid any urges during the test.
Before entering the room, you will be asked about your medical history. It is important to mention :
- If you suffer from kidney failure or diabetes
- If you have ever had an allergy to an iodinated contrast medium
- If you are pregnant or have become pregnant
Contrast medium scanner
Certain CT scan indications require the injection of a contrast medium. The product used is based on iodine and allows the opacification of body parts to make them visible on the images.
The injection is a very common procedure in CT scans and is generally very well tolerated.
In most cases, you will be prescribed a creatinine test to check your kidney function. If you suffer from kidney failure, the injection will (unless absolutely necessary) canceled.
During the injection, you may feel a warm sensation throughout your body with more or less a strange metallic taste in your mouth. This will last on average less than a minute.
Generally well tolerated, there are some small risks associated with the injection :
- Hematoma caused by the placement of a peripheral venous voice. Without gravity, it will subside in a few days
- Subcutaneous leakage of the contrast product. This is due to the pressure during the injection and generally present no serious consequences.
- Nausea or vomiting.
- Urticaria which is more rare.
- A rare allergic reaction like eczema, asthma or cardio-respiratory disorders
- Nephrogenic systemic fibrosis, which occurs exceptionally in cases of renal insufficiency
These unpredictable reactions of intolerance to the contrast medium occur more frequently in patients with a history of allergies. They are generally transient and not serious.
Depending on the severity of the reaction, you will be given a treatment and referred for allergy screening.
For people at risk, an anti-histamine treatment may be prescribed by the attending physician or when the appointment is made.
In all cases (unless otherwise advised by your doctor), if you have been given a contrast agent, drink two liters of water after the examination. This will help to eliminate the medication quickly.
Image interpretation
The interpretation of images can be done at the end of the examination if a radiologist is able to analyze images immediately or later when a tele-radiology service is set up.
Before going home, the secretary will give you the report and the images, often burned on a CD. If it is not possible to print the results in this form or if the center has opted for tele-radiology, you will have access to your results online using a secure connection to a patient account.
What are the risks of a CT Scan ?
The photons generated by the X-ray tube have ionizing properties. The CT scan is therefore an irradiating imaging technique that can have effects on exposed cells, particularly in younger patients.
However, the very low doses received during a CT scan are largely acceptable and make the risk very low compared to the medical benefit. Thus, in the vast majority of cases, there is no reason to fear the appearance of determining effects. Random biological effects, on the other hand, are not known with certainty.
The risks associated with contrast medium injection are low : see Contrast medium scanner.
The major contraindication is pregnancy. It is therefore imperative to report any possible or current pregnancy so that precautions can be taken.
CT Scan categories
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