What is CT Head / Brain Scan and what it shows?
Computed tomography (CT or CAT scan) is a noninvasive diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce horizontal, or axial, images of the body. A CT scan shows detailed images of any internal organs of the body, including the bones, muscles, fat, and organs. If doctor needs more detailed imaging than X – Ray he recommends for CT scans
In standard X-rays, a beam of energy is aimed at the body part which has to be studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle, and other tissue. While much information can be obtained from a standard X-ray, lot of details about internal organs and other structures is not available.
In computed tomography, the X-ray beam moves in a circle around the body which allows many different views of the same organ or structure. The X-ray information is sent to a computer that interprets the X-ray data and displays it in a two-dimensional (2D) form on a monitor.
CT scans may be done with or without “contrast”. Contrast refers to a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure.
Head / Brain CT scans can provide detailed information about brain tissue and brain structures than standard X-rays of the head / brain, thus providing more detailed information related to injuries and/or diseases of the brain.
Other procedures that may be used to diagnose brain disorders include X-rays, magnetic resonance imaging (MRI), positron emission tomography (PET), and cerebral arteriogram.
CT scans are frequently used to evaluate the brain / head disorders with symptoms such as headaches, weakness, seizures, confusion, etc to exclude a tumor, aneurysm or infection. They are also used as a follow up test for patients with strokes, bleeds or surgery. Below are a few common diagnoses that a Head / Brain CT scan detect.
Aneurysm – Aneurysms are ballooning of vessels that can cause rupturing. If blood leaks from the aneurysm patients describe the headache as a thunderclap and sharp/shooting pains. Patients can also have stroke-like symptoms with weakness, slurred speech and confusion. A Brain / Head CT scan is the first test done to evaluate for a bleed.
Tumors – Tumors can be primary (from brain tissue) or secondary (from other sites, eg breast cancer). These typically present with headaches, weakness, and seizures. Head CT scans can be done without or with IV contrast to detect tumors.
Bleeding – Hemorrhage, aka bleeding, in the brain can be from trauma, ruptured aneurysms or tumors that bleed. CT scans are very sensitive to recent bleeds (especially within a few hours).
Stroke – Stroke is also known as a “brain attack”. Stroke is a result of blocked artery that deprives a part of the brain of blood (pure blood supply from heart). This part of the brain loses it function and patients present with weakness, slurred speech, difficulty walking and on occasion, headaches. Head / Brain CT scan is the first test to detect a stroke or determine if the symptoms are caused by another factor such as a bleed or a tumor.
A CT scan of the brain will evaluate:
A CT scan of the brain will include parts of the sinuses. Though not used to primarily look for sinus disease, the brain CT can pick up thickening of the sinus tissue (mucosa) or fluid in the sinuses.
Brain CT scans can include parts of the orbits. It can pick up injury to the orbit and diseases of the orbits such as large tumors, bleeds, inflammation etc.
The skull is included in a brain CT scan and can detect bone tumors, infection and fractures. It can also detect bleeds in the space between the skull and brain (aka epidural and subdural bleeds).
The white and gray matter of the brain are well seen. CT scan can detect tumors, infection, bleeds, stroke and congenital defects. Part of the pituitary gland, optic nerves and upper brainstem are also evaluated. A “routine” head CT is done without contrast.
These are the fluid filled structures inside the brain that help circulate cerberospinal fluid. Tumors and bleeds can extend into these structures and cause blockage which can lead to headaches, confusion and problems with walking for example.
Anatomy of the Brain / Head
The central nervous system consists of the brain and spinal cord. The brain is an important organ that controls thought, memory, emotion, touch, motor skills, vision, respirations, temperature, hunger, and every process that regulates our body, even in sleep.
What are the different parts of the brain?
The brain can be divided into the cerebrum, brainstem, and cerebellum:
- Cerebrum. The cerebrum (supratentorial or front of brain) is composed of the right and left hemispheres. Functions of the cerebrum include: initiation of movement, coordination of movement, temperature, touch, vision, hearing, judgment, reasoning, problem solving, emotions, and learning.
- Brainstem. The brainstem (midline or middle of brain) includes the midbrain, the pons, and the medulla. Functions of this area include: movement of the eyes and mouth, relaying sensory messages (hot, pain, loud, etc.), hunger, respirations, consciousness, cardiac function, body temperature, involuntary muscle movements, sneezing, coughing, vomiting, and swallowing.
- Cerebellum. The cerebellum (infratentorial or back of brain) is located at the back of the head. Its function is to coordinate voluntary muscle movements and to maintain posture, balance, and equilibrium.
More specifically, other parts of the brain include the following:
- Pons. A deep part of the brain, located in the brainstem, the pons contains many of the control areas for eye and face movements, facial sensation, hearing, and equilibrium.
- Medulla. The lowest part of the brainstem, the medulla is the most vital part of the entire brain and contains important control centers for the heart and lungs.
- Spinal cord. A large bundle of nerve fibers located in the back that extends from the base of the brain to the lower back, the spinal cord carries messages to and from the brain and the rest of the body.
- Frontal lobe. The largest section of the brain located in the front of the head, the frontal lobe is involved in personality characteristics and movement.
- Parietal lobe. The middle part of the brain, the parietal lobe helps a person to identify objects and understand spatial relationships (where one’s body is compared to objects around the person). The parietal lobe is also involved in interpreting pain and touch in the body.
- Occipital lobe. The occipital lobe is the back part of the brain that is involved with vision.
- Temporal lobe. The sides of the brain, these temporal lobes are involved in memory, speech, and sense of smell.
Reasons for Head / Brain CT
A CT scan of the brain may be performed to assess the brain for tumors and other lesions, injuries, intracranial bleeding, structural anomalies such as hydrocephalus, infections, brain function or other conditions, particularly when another type of examination such as X-rays or physical examination are not conclusive.
A CT scan of the brain may also be used to evaluate the effects of treatment on brain tumors and to detect clots in the brain that may be responsible for strokes. Another use of brain CT is to provide guidance for brain surgery or biopsies of brain tissue.
There may be other reasons for your doctor to recommend a CT scan of the brain.
Your Brain CT Scan
A brain CT scan generally takes about 5 minutes or so to complete. If you are going for CT, remember to remove hair pins, piercings, earrings and necklaces as these metallic objects can interfere with the scan. Most scans are done without IV contrast but if your doctor is looking for a tumor or infection this may be done with contrast.
Risks of the procedure
You may want to know about the amount of radiation used during the CT procedure and the risks related to your particular situation. It is a good idea to keep a record of your past history of radiation exposure, such as previous CT scans and other types of X-rays, so that you can inform your doctor. Risks associated with radiation exposure may be related to the cumulative number of X-ray examinations and/or treatments over a long period of time.
If you are pregnant or suspect that you may be pregnant, you should tell your doctor. Radiation exposure during pregnancy may lead to birth defects. If it is necessary for you to have a CT of the brain, special precautions will be made to minimize the radiation exposure to the foetus.
Nursing mothers should wait 24 hours after contrast material is injected before resuming breastfeeding.
If contrast dye is used, there is a risk for allergic reaction to the dye. Patients who are allergic to or sensitive to medications should notify their doctor.
Patients with kidney failure or other kidney problems should notify their doctor. In some cases, the contrast dye can cause kidney failure. The effects of kidney disease and contrast agents have attracted increased attention over the last decade, as patients with kidney disease are more prone to kidney damage after contrast exposure.
There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.
Before the procedure
- If your procedure involves the use of contrast dye, you will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if something is not clear.
- Generally, there is no fasting requirement prior to a CT scan, unless a contrast dye is to be used. Your doctor will give you special instructions ahead of time if contrast is to be used and if you will need to withhold food and drink.
- Notify the technologist if you have ever had a reaction to any contrast dye, or if you are allergic to iodine.
- Notify the technologist if you are pregnant or suspect you may be pregnant.
- Based on your medical condition, your doctor may request other specific preparation.
During the procedure
CT scans may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician’s practices.
Generally, a CT scan of brain follows this process:
- You will be asked to remove any clothing, jewelry, or other objects that may interfere with the procedure, such as eyeglasses, hairpins, dentures, and possibly hearing aids.
- If it is important to remove cloths for Ct Scan, you will be given a gown to wear.
- If you are to have a procedure done with contrast, an intravenous (IV) line will be started in the hand or arm for injection of the contrast dye. For oral contrast, you will be given medication to swallow.
- You will lie on a scan table that slides into a large, circular opening of the scanning machine. Your head may be immobilized to prevent movement during the procedure.
- The technologist will be in another room where the scanner controls are located. However, you will be in constant sight of the technologist through a window The technologist will be watching you at all times and will be in constant communication.