CT (Computerised Tomography) Scan

CT (Computerised Tomography) Scan

What is a CT scan?

A CT scan, or computerised tomography, is a means of medical testing that combines a series of X-ray images and computer processing to create cross-sectional visuals of the inside of the body. X-ray images are taken at a variety of different angles that provide a detailed view of bones, organs, soft tissues and blood vessels.

This means of testing is a highly accurate way for medical professionals to quickly examine a person who may have serious internal injury or bodily trauma. A doctor can see just about the entire body using the technology of this visual imaging test. The highly-detailed images created provide much needed visual information that enables a medical doctor to accurately diagnose a problem, disease, injury or abnormality. In turn, the most effective means of treatment can be implemented, lowering the risk of further damage.

CT brain  scan showing Ischemic stroke (hypodensity at right frontal-parietal lobe)Key areas of the body a doctor may recommend a scan to gain a better perspective of include:

  • The head
  • The spine
  • The shoulders
  • The chest
  • The heart
  • The abdomen
  • The knees

The series of images taken during the testing procedure are combined using computerised software that creates cross-sections or slices to form detailed images of the inside of the body. Here, any abnormalities will be clearly shown and easily diagnosed. A 3-D image can be created of a particular area of the body for medical professionals to gain a clearer idea as to what may be malfunctioning or damaged, and make a more accurate diagnosis.

A CT scan is minimally invasive and is a completely painless experience. It can also be done relatively quickly, which can be very useful in time-sensitive medical situations.

Why would a CT scan be recommended?

As an imaging technique which can give medical professionals eyes on the inside of the body, CT scans have a variety of different uses, particularly when it comes to evaluating injuries and diagnosing diseases.

A CT scan may be recommended to:

  • Check for muscle disorders
  • Evaluate bone fractures and joint problems
  • Diagnose infections in the body
  • Diagnose conditions such as liver problems, emphysema, cancer or heart disease
  • Locate tumours or abnormal masses (growths), blood clots and build-up of fluid in the body
  • Assess internal structures and blood vessels, as well as internal injury and bleeding

A CT scan is also useful for:

  • Monitoring the effectiveness of specific treatments which may otherwise be complex to assess (such as those for heart disease, emphysema and cancer).
  • Use as a visual guide for biopsy, radiation therapy or surgical procedures

Preparing for a CT scan

If a medical professional has recommended a CT scan for you, he or she will prepare you for the testing procedure.

You may be asked to do the following ahead of your scan:

  • Remove some or all of your clothing. A hospital gown will be provided for you to wear instead.
  • Remove all metal objects. This will include any jewellery, eyewear (such as glasses), clothing and dentures. Metal objects will interfere with the imaging results of the scan.
  • Avoid eating or drinking liquids several hours (often 4 to 6 hours prior) before the scan is scheduled to take place.

Your doctor will likely explain how the scan works and the reasons why he or she feels that it is necessary based on the physical areas of concern or medically associated problems you are currently experiencing.

If your child is to go through a CT scan, the process may be considerably more difficult for them to understand, particularly if they are very young. An infant, or toddler may be lightly sedated so as to ensure that they remain calm and still during the scan process. In this way, a young child is more likely to feel like they have drifted off to sleep, instead of becoming fearful during the scanning process.

It is important that you or your child requiring a scan, remain still during the test. Any movement can distort or blur images and cause inaccurate results.

What happens during a CT scan?

Young male nurse preparing patient for CT scan test in examination room

A narrow X-ray beam is used to encircle the area of the body being analysed or assessed. During a scan, the beam will be used to provide a series of images, taken at different angles, that are then sent back to a computer. Technological software will then process the visuals and be sliced together to create a cross-sectional image of the inside of the body.

The process is repeated until enough images are produced to stack the scans, one on top of the other, forming the final 3-dimensional image (3-D visual). This visual essentially re-creates a 3-dimensional visual of your insides, such as an organ, set of bone structures or blood vessels. The visual can then be looked at from every angle to assess the nature of a medical problem or injury or diagnose a condition (if there is an abnormality present).

Often, a doctor will use a dye, known as contrast material (iodine or barium sulphate), just before a scan. This helps to highlight various areas of the body, such as tissues and easily shows up portions a doctor would like to assess more clearly. The contrast material appears white on the images produced and blocks X-rays, helping to provide emphasis where it is needed, and better enabling your doctor to better see what may be wrong.

You may be given contrast material ahead of your scan in one of three ways:

  • Injection: An injection can be administered through a vein in your arm if your urinary tract, gallbladder, liver or blood vessels are to be scanned. During the injection, you may experience a warm sensation and a metallic taste in your mouth.
  • Orally: A liquid containing contrast material, which is not typically pleasant to drink, may be given for you to swallow if your oesophagus or stomach is being scanned.
  • Enema: If your intestines are to be scanned, contrast material may be inserted in your rectum. You may experience bloating in the abdomen, which can be a little uncomfortable.

Once a scan has been completed, you will be given plenty of fluids to help your kidneys flush out the contrast material from your system (i.e. expel the substance from the body).

The duration of a scan can take anything from a few minutes up to about 30-minutes, depending on the nature of the scan and the machine used. Scans normally take place in a hospital or an outpatient facility (such as a radiology clinic).

If you are anxious at any point during the build-up to the scan or while inside the scanner, you doctor may administer a mild sedative to help you relax. Your technician may try and talk to you initially to help you feel calm.

What does the scanner look like and what will I be required to do?

The scanner is shaped like a large doughnut type of tunnel with the hole in the centre. A narrow, motorised table slides through this hole or opening in the centre. You will be required to lie down flat on this table. The table has straps and pillows which may be used to assist with keeping you in the best position for the test, and a cradle that will help to keep your head still during the scanning process.

Once you are laying down flat on your back (facing upwards) and settled into position, the table will be moved slowly into the doughnut shaped scanner. An X-ray tube and detectors will then be activated to rotate around you (you will not be moving at all). The rotation action is what is capturing images and will make clicking, buzzing and whirring sounds during the scanning process. Each rotation will create thin slices of visuals for the creation of cross-sectional images to be stacked together.

Medical team operating computers in CT scan lab for head sectionThe technologist conducting the scan will be positioned in another room next door so as not to interfere with the scanning process and skew the results. He or she is able to communicate with you via a built-in intercom. Your technologist can also see and hear you the entire time.

You will be asked to keep as still as possible throughout the scan. Any movement can disrupt the visuals created and cause blurring. Each image taken needs to be as clear and detailed as possible in order to be accurately assessed. From time to time your technologist may request that you hold our breath during the scan. This is not unusual and you need not panic. It may be that visuals need to be taken of a specific area and the rise and fall of your chest as you breathe may cause blurring. You will only need to hold your breath for a few seconds at a time. The table may move a few millimetres at a time during the process. You will remain perfectly still the entire time.

A scan can take place within a matter of minutes and up to half an hour, depending on the nature of your scan and what is needed for assessment. The entire process is painless and non-invasive. You will not be required to stay at a hospital facility.

Once the scan has been completed, you will be able to resume your normal day’s activity. Before departing, you will be advised about how long it will be before you can expect results. If you were given contrast material ahead of your scan, you will be advised to linger a little longer and given plenty of liquids to drink to help expel the material from your body. Once medical staff are satisfied that you are well enough and haven’t experienced any adverse reactions, you will be allowed to leave the hospital or radiology clinic. You may be asked to drink more fluids through the day or night to help your kidneys flush out all of the contrast material.

If you require medical care following your scan or you have already been admitted to hospital for any reason, you will be taken back to your ward (room) for monitoring. In most cases, where you are merely having a scan done, you will be allowed home shortly afterwards.

If a young child is being scanned, he or she will be sedated and positioned on the table for the test. A little one will ‘sleep through’ the entire scanning process and be taken to a recovery area afterwards to rest peacefully while the sedative wears off. Contrast material will be flushed out soon after the scan and if well enough, a young child will be allowed home.

Young lady laying still on a CT Scan bed (table)

Are there any risks involved?

Risk is usually minimal but your doctor or the technician conducting the scan will explain all potential factors ahead of the scanning procedure.

These discussion points may include:

  • Ionising radiation exposure: During the scanning procedure, you will be exposed to a low dose of ionising radiation. As the scan is designed to pick up detailed visuals, this amount of radiation is greater than that of a normal X-ray. The amount of exposure, however, has not been seen to cause any long-term effect. Risk may increase if you have multiple scans during your lifetime. Any increased cancer risk and damage to your DNA due to the exposure is very small and the benefits of the scan outweigh the low amount of risk potential. Risk may be higher for young children as they are still growing, but machines and dosages of radiation are usually adjusted for children to minimise potential risks. A general rule of thumb is that the higher the number of portions of the body being examined, the higher the radiation dose and thus, the higher the potential risk. Newer machines in use require less scanning time, which in turn means less radiation exposure.
  • Pregnancy and an unborn baby: In most cases, a CT scan during pregnancy poses a very low risk of harm to an unborn baby. You should, however, advise your doctor of your pregnancy (should you not yet be showing). A doctor may opt for an alternative means of image testing, such as an ultrasound or MRI, if he or she feels it necessary to avoid radiation exposure altogether.
  • Adverse reactions to contrast material: It can happen that you experience an allergic reaction to the contrast material administered before a scan. Typically, an allergic reaction is mild and merely shows up as skin itchiness or a rash. Rarely is an adverse reaction more severe, or even life-threatening. If you’ve experienced contrast material (or reacted badly to iodine) before and had a bad reaction, notify your doctor ahead of time to ensure your own safety during the test. Sometimes a doctor may recommend allergy medication or steroids as a way to counteract potential adverse reactions.

What other things may lead to adverse side-effects?

If you are diabetic and take medications as part of your treatment plan, you should notify your doctor. It may be necessary for you to stop taking your medication just before the scan and temporarily for a short period following the test in order to avoid an interaction between your diabetes medication and the iodinated contrast used that could cause lactic acidosis (a build-up of lactate in the body). Your doctor will advise when it should be safe to resume taking your medication.

It rarely happens that contrast material affects the kidneys and causes problems. If you’ve had kidney problems in the past, you should advise your doctor well ahead of time before the test.

Results and patient follow-up

Doctor in hospital looking at results of a patient's CT scan

Scanned images will be stored as electronic data files for review and once compiled will be interpreted by a radiologist. A report will then be compiled and sent to your doctor, who will then contact you to discuss the findings in person.

Results are considered normal if the radiologist was not able to determine any abnormalities in the visuals. If any abnormalities are picked up, a radiologist, along with your doctor, may recommend further tests to help make an accurate diagnosis.

Can a CT scan help to diagnose chronic headaches or migraines?

A doctor may be able to make use of a CT scan to diagnose specific types of headaches and their root causes. This is very useful in formulating effective treatment measures.

If you suffer from headaches almost every day or you experienced a sudden and severe headache, a doctor may recommend a CT scan to assess what may be causing you such discomfort and pain. Migraines, however, are not likely to be diagnosed using a CT scan though.

Potential headache causes a doctor will be able to see can include:

  • An abscess or infection in the brain
  • Tumours in the brain
  • Fluid build-up (hydrocephalus)
  • Injury
  • A sinus blockage
  • An aneurysm (weakened artery in the brain) or bleeding in the brain

What is a CT angiogram?

CT scan angiogramA CT angiogram, or computed tomography angiogram also uses X-rays to provide detailed images of the inside of the body. This scanning test is usually recommended when it is necessary to focus on the functions of the heart, and blood vessels that link with the heart, lungs, kidneys, brain, neck, head and limbs (arms and legs).

If a doctor suspects that you may have narrowed blood vessels (stenosis) or potential blockages, such as the build-up of fatty tissue (plaque or cholesterol) or an aneurysm (bulge), this test may be strongly recommended to either rule out or diagnose a potential internal problem.

The testing process is much the same and can also include the administration of contrast material (typically through a vein in the arm or hand – IV). You may also be given a beta-blocker to slow down your heart rate if your heart and coronary arteries are the focal point of your test.

Radiologists and doctors will be on the lookout for other internal problems such as:

  • Pericarditis (a build-up of fluid around the heart)
  • Damage or injury to the heart valves
  • Dissection (tears) in the aorta (large blood vessel carrying blood from the heart to the remainder of the body)
  • Pulmonary embolism (blood clots in the lungs)
  • Abnormal blood vessels patterns (this could indicate tumours in the body)
  • Peripheral arterial disease (narrowing or arteries)

This scan is not as invasive as a standard angiogram which involves threading a catheter (thin tube) through an artery in your arm or leg and guiding it to your heart. A CT angiogram does not involve any tubes at all. If any abnormalities are discovered, however, more invasive testing procedures may be necessary. Your doctor will discuss any possibilities with you ahead of time to ensure you are as prepared as is necessary.

Results of the scan are usually ready within a day or two. Your doctor will contact you to discuss these in person and take any necessary next steps.

What is the difference between a CT scan and an MRI?

Medical technical assistant counselling patient and preparing radiological scan of the torso with magnetic resonance tomography (MRI)

An MRI (magnetic resonance imaging) scan is an entirely different imaging test to a CT scan. One distinct difference is that a CT scan uses radiation and an MRI scanning procedure does not.

A CT scanner takes multiple images, recording different levels of density in tissues, organs and bones using X-ray exposure. The average scanner today uses less radiation exposure than what most airline passengers are likely to experience on long haul flights across the globe. Newer scanners have been developed to decrease the image taking time and thus considerably reduce radiation exposure risk.

MRI scanners make use of very powerful magnetic fields and radio frequency pulses instead of radiation X-rays. These magnetic fields and pulses effectively produce highly detailed and clear images as well. Internal body structures, organs and tissues are also typical areas of interest during a scan. Sometimes images are significantly clearer on an MRI image result than on a CT.

An MRI scan does take a little more time than that of a CT and a patient will likely experience a bit more noise in the scanning process.

Both tests show up the same parts of the body, using different techniques. Your doctor will make a selection based on your specific symptoms and possible diagnosis needs.

The most distinctive differences (other than radiation) between the two testing methods are:

  • Uses: A CT is particularly useful for looking at bones and soft tissues. An MRI is very useful for detecting even the slightest of differences in the body’s soft tissues.
  • Cost of the test: A CT scan is normally less expensive than an MRI. If you have health insurance that covers the cost of scans, it is best to double check that you are fully covered before having either test done.
  • Testing time: A CT scan is typically done in a quicker period of time (sometimes within 5 minutes). The time necessary for either test does typically depend on the area/s of the body being assessed. An MRI can range from as little as 15 minutes up to 2 hours.
  • Patient comfort: Scanning machines are similar for both tests, in that you will need to lay flat on a table and be moved inside a round / doughnut shaped machine. A CT scanner, is more open than that of an MRI, so any fears about being in confined spaces is less intense than if you were experiencing an MRI (which is narrower and enclosed).
  • Adverse reactions: Allergic reactions are rare for both testing procedures but can happen, especially with those who have had problems with their kidneys or who are already treating conditions such as diabetes (this is related to the contrast material used). If a person is very dehydrated at the time of a scan, this could also lead to feeling unwell during and after a scan.
  • Limitations: Scanners are generally set at a specific size in most hospital and clinic facilities, and this may be limiting for an obese person (more than 300 pounds or 136 kilograms). If a CT is necessary, a larger patient may be sent to a facility that is equipped with a larger scanner that can handle their weight. In the case of an MRI, a larger person may be offered an open MRI machine as an alternative (if available). Metal objects, such as those implanted in the body, or even tattoos (some tattoo inks contain iron, which conducts electricity generated during the scan and may lead to burns) can prevent any person from being able to safely have an MRI.

When it comes to making a choice as to which scan is best, doctors will consider the following:

  • CT scan: Abdominal pain, particularly in emergency situations, emergency trauma (assessing blood and organ injury or bone fractures and the brain, especially when a stroke is suspected), and the chest (examining of lung tissue).
  • MRI scan: The spinal cord and nerves, the brain (when assessing causes of dementia, brain cancer or tumours, neurological diseases etc.) and joints (showing up ligaments and tendons more clearly).

Both scanner types are built to help medical professionals determine a problem source and help clarify a possible solution (course of action or treatment). Many factors will play a role in the choice of scan and depends largely on the objective of the test in the first place. Your doctor will select the test that best benefits you and allows for the most accurate diagnosis to be made.

 

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