Head CT Scans
A CT Scan of the head utilizes special x-ray equipment to help in the assessment of head injuries, dizziness, severe headaches, and other symptoms of bleeding, aneurysm, brain tumors, and stroke. This can also help the physician to assess your sinuses, face, and skull or to develop a plan for radiation therapy in brain cancer treatment. In some emergency cases, the scan can reveal internal bleeding and injuries quickly enough to save lives.
If there’s a possibility that you’re pregnant, tell your doctor and be sure to discuss any recent medical conditions, illnesses, allergies, and medications you’re taking. Before the procedure, you will be instructed not to eat or drink anything for a few hours in advance. In case you have a known allergic reaction to contrast material, the doctor may prescribe some medications to reduce the impact of the allergy. These medications should be taken 12 hours before the exam. Leave all your jewelry at home, and wear comfortable loose clothing. You may be asked to wear a gown.
What’s Involved in the CT Scanning of the Head?
Computer tomography, commonly referred to as a CAT or CT scan is a diagnostic medical test that produces multiple pictures or images of the inside of the body just like the traditional x-rays.
The CT scan generates cross-sectional images which can be reformatted in multiple planes, and can even be used to generate 3-D images. The images can be printed on a film, viewed on a computer monitor, or transferred to a storage medium such as a DVD or CD.
In comparison to the traditional x-rays, CT images of various internal organs, blood vessels, soft tissue, and bones, have a much greater detail, especially of blood vessels and soft tissues. CT scanning also gives a much greater detail on head injuries, brain tumor, stroke, and other brain conditions than the regular radiographs (x-rays).
Common uses of CT scans
• Head CT scans are typically used to detect:
• Bleeding caused by a leaking or ruptured aneurysm in patients with a sudden severe headache
• Brain injury, bleeding, and skull fractures in patients with head injuries
• A stroke, particularly with the new technique referred to as Perfusion CT
• Bleeding or a blood clot within the brain shortly after symptoms of a stroke are recorded
• Enlarged ventricles (brain cavities) in patients with hydrocephalus
• Brain tumors
• Malfunctions or diseases of the skull
CT scanning is also used in:
• assessing the extent of soft tissue and bone damage in patients with facial trauma before surgical reconstruction.
• Determining whether inflammation of other changes have occurred in the paranasal sinuses
• Diagnosing diseases of the temporal bone located on the side of the skull, which might be the cause of hearing problems
• Planning radiation therapy for cancer of the brain and other tissues
• Assessing arteriovenous malfunctions or aneurysms through the CT angiography technique
How to prepare for a head scan
You should ideally wear loose fitting, comfortable clothing as you go to your exam. Before the procedure starts, you may be given a gown to wear.
Any metal objects including things like dentures, jewelry, hair pins, eyeglasses, etc. may affect the CT images and should therefore be removed before your exam or left at home altogether. You might also be asked to remove any removable dental work and hearing aids. If possible, you may be asked to remove any piercings. Women might also be asked to remove bras that contain metal underwire.
You will also be asked in advance not to drink or eat anything several hours beforehand, particularly if your exam involves the use of a contrast material. Make sure that you inform your doctor of any medications that you’re taking, and any allergies you might have. In case you have any known allergies to contrast dyes or material, your physician might prescribe some medications (mostly a steroid) to minimize the risk of developing an allergic reaction. You should take the medications as instructed, typically 12 hours before the administration of the contrast material. To prevent unnecessary delays, be sure to contact your physician before the exact time of the exam.
Don’t forget to let your doctor know any recent medical conditions or illnesses and whether you have a history of asthma, heart disease, kidney disease, diabetes, or thyroid problems. Any of these conditions will increase the risk of developing an unusual adverse effect. Your radiologists should also know if you have multiple myeloma, asthma, or any other disorder of the heart, thyroid gland, or kidneys, or if you have diabetes; especially if you’re taking Glucophage.
For women, you should always inform your CT technologist and your physician if there is any possibility that you may be pregnant.
What to expect
What does the equipment to look like?
The CT scanner is a distinctly shaped, large, boxlike machine short tunnel or hole at its center. You’ll lie down on a special, narrow examination table which slides in and out of the tunnel. The x-ray tube and an electronic x-ray detector will be rotating around you, and are located on opposite sides of each other in a ring-like structure called a Gantry.
In a separate room will be the computer workstation that processes the imaging information, and it’s where the technologist will be operating the scanner. The technologist will also be monitoring your examination in a direct visual contact and will in most cases be able to talk to you and hear you using a speaker and microphone.
How the procedure works
In a lot of ways, CT scanning works quite similarly to other x-ray examinations. Different parts of the body will absorb varying degrees of x-rays. This crucial difference in absorption rates allows body parts to be distinguished from each other on a CT electronic image or x-ray film.
Conventional x-ray exams have a small amount of radiation aimed at and passed through the target body part being examined, then an image is recorded on a special electronic image recording plate. On the x-ray, bones will appear white; soft tissue including organs like the liver or heart will show up in shades of grey; air appears black.
With CT scanning, a number of x-ray beams coupled with a set of x-ray detectors (electronic) rotate around you. In the process, they’ll measure the amount of radiation that’s absorbed in different parts of your body. At times, the examination table will move during the scan to ensure that the x-ray beam takes a spiral path. A specialized computer software is then used to process the large volume of data to create a 2-D cross-sectional images of your body, and then display them on a monitor.
You can think of CT imaging as observing a loaf of bread by first cutting it into many thin slices, such that when the image slices are reassembled through the computer software, the result into a very detailed multidimensional view of the loaf’s interior.
Recent advancements in refinements in detector technology allow almost all the modern CT scanners to get multiple image slices in just a single rotation. Such scanners are referred to as multi-detector CT or multi-slice CT, and allow for thinner image slices to be obtained in very short amount of time, which results into additional view capabilities and more detail.
The more modern CT scanners are so fast that they only need a few seconds to scan through large sections of your body. They’re even faster in small children. Such amounts of speeds are beneficial to all patients, but more so children, the critically ill, and the elderly, all of whom might have difficulty staying still, even for the brief amount of time required for images to be taken. The CT scanner technique can be adjusted for children to fit their size and area of interest, and minimize the dose of radiation.
Some CT exams may require the use of a contrast material to enhance the visibility of the area of interest.
CT scanning procedure
The technologist starts by positioning the patient on the CT examination table, often lying flat on their back. Pillows and straps might be used to help a patient maintain the correct posture and position as well as help them remain still during the exam.
Most scanners are fast enough to scan children without the need for sedation. In some special cases, the use of sedation may be required if the child cannot hold still. This is because motion leads to blurring of the image and degrades the quality of the examination, just as it affects conventional photographs.
Depending on the type of exam, if a contrast material is to be used, it’s either swallowed or injected via an intravenous line (IV). In some rare cases, it may also be administered by enema. Next, the table moves quickly through the scanner to find the correct position to start the scan. The table then moves slowly into the machine for the CT scanning to start. Based on the kind of CT scan required, the machine might take several passes.
You might be asked to momentarily hold your breath as the scan is performed. Any type of motion, whether body movements or breathing can cause artefacts on the final image. Such degradation of image quality resembles the blurring you will see on a photograph of a moving object.
Once the examination is complete, you’ll have to wait for a few minutes for the technologist to verify that the taken images are of high quality, enough for accurate interpretation. A head CT scan is usually completed within 10 minutes.
What can I expect to happen during and following the procedure?
In general, CT exams are easy, fast and painless. Using multidetector CT reduces how long a patient must lie still.
Although no pain is caused by the actual scanning process, needing to lie still for several minutes might result in some discomfort. The CT exam might be stressful for you, if you have chronic pain, are claustrophobic or have difficulty staying still. The nurse or technologist, under a physician’s direction, might offer some medication to you to help make the CT scanning procedure more tolerable.
If there is any intravenous contrast material utilized, you will feel a pinprick sensation when the needle gets inserted inside of your vein. Most likely you will have a flushed, warm sensation while the contrast materials are being injected and there will be a metallic taste inside of your mouth that will last for one to two minutes at most. You might have the feeling that you need to urinate; however, that will subside quickly and is a contrast effect.
After you have entered the CT scanner, there might be special light lines projected onto your body. These are used to make sure your body is positioned properly. With a modern CT scanner, all you will hear are slight whirring, clicking and buzzing noises as the internal parts of the CT scanner, which usually are not visible to you, are revolving around you throughout the imaging process.
During your CT scan, you will be alone inside of the exam room, unless it is a special situation. For example, at times, a parent who has a lead shield on might remain with their child in the room. However, the technologist can hear, see, and speak to use through the built-in intercom system at all times.
A parent might be allowed inside of the room with a pediatric patient but will have to wear a lead apron so that radiation exposure is minimized.
After the CT exam is complete, the technologist will remove the intravenous line that was used for injecting the contrast material, and a small dressing will be placed over the tiny hole that the needle made to cover it. You can then resume your regular activities.
Who interprets my exam results and how will I receive them?
A radiologist who has expertise in interpreting and supervising radiology exams will analyze your images and then an official report will be sent to your primary physician or the physician who referred you for a CT exam. Your physician will discuss your results with you.
It might be necessary to have follow-up exams. Your physician will explain exactly why another exam has been requested. At times a follow-up exam is conducted because there is a potential abnormality that needs to be evaluated further with a special imaging technique or additional views. A follow-up exam might also be necessary in order to monitor any changes in a known abnormality over time. Some the best way to know whether a treatment is working or not or a finding is stable or has changed over time is through follow-up exams.
What are a CT scan’s benefits and risks?
– A CT scan is accurate, noninvasive and painless.
– One major advantage that a CT has is its capability to image blood vessels, soft tissue, and bone simultaneously.
– CT scanning, unlike conventional x-rays, provides images that are very detailed of many kinds of tissue in addition to the blood vessels, bones, and lungs.
– CT exams are simple and fast; in an emergency situation, they are able to reveal bleeding and internal injuries quickly enough to help save a life.
– It has been shown that CT is a cost-effective imaging tool for a broad array of various clinical issues.
– CT is less sensitive compared to MRI to patient movement.
– Unlike MRI, a CT scan may be performed even if you have any kind of implanted medical device.
– A diagnosis that is determined by a CT scan might eliminate the need for surgical biopsy and exploratory surgery.
– Following a CT exam, no radiation stays inside of the patient’s body.
– There should be no immediate side effects to the X-rays that are used in CT scans.
– There always is a slight chance of cancer due to radiation exposure. However, the benefit of receiving an accurate diagnosis from the scan far outweighs any risk involved.
– The effective dose of radiation for the procedure does vary.
– Women always should inform their physician and CT or x-ray technologist if there is a possibility they are pregnant.
– In general, CT scanning is not recommended for a woman who is pregnant, unless it is medically necessary due to the potential risk for the baby. However, with head CT scanning, this risk is minimal.
– Intravenous contrast manufacturers indicate that a baby should not be breastfed by the mother for 24-48 hours after being given contrast medium. However, both the European Society of Urogenital Radiology and American College of Radiology (ACR) have noted that available data suggests it is safe to breastfeed after intravenous contrast has been received. Please consult ACR’s Manual on Contrast Media along with its references for further information.
– The risk is extremely rare o serious reaction to any contrast materials containing iodine, and radiology departments are very well-equipped to handle them.
– Since children are more sensitive to the effects of radiation, they only should have a CT exam if it is essential for a diagnosis to be made, and repeated CT exams should not be done unless they are absolutely necessary. The lose-dose technique should always be done in any CT scans performed on children.
– What limitations does CT Scanning of the Head have?
A very large person might not fit inside of the opening on a conventional CT scanner or might be over the moving table’s weight limit – which is usually 450 pounds.
When compared with MRI imaging, on CT scans the precise soft tissue details (especially of the brain and its disease processes) are not as visible. The CT scan is not very sensitive when it comes to detecting meninges inflammation – which is the membranes that cover the brain.