Computed Tomography (CT) Scan | Johns Hopkins Medicine

What You Need to Know

• A CT scan is a diagnostic imaging exam that uses X-ray technology to produce images of the inside of the body.
• A CT scan can show detailed images of any part of the body, including the bones, muscles, organs and blood vessels.
• CT scans can also be used for fluid or tissue biopsies, or as part of preparation for surgery or treatment.
• CT scans are frequently done with and without contrast agent to improve the radiologist’s ability to find any abnormalities.

What is a CT scan?

Computed tomography is commonly referred to as a CT scan. A CT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body. It shows detailed images of any part of the body, including the bones, muscles, fat, organs and blood vessels.

CT scans are more detailed than standard X-rays. In standard X-rays, a beam of energy is aimed at the body part being 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 regular X-ray, a lot of detail about internal organs and other structures is not available.

In CT, the X-ray beam moves in a circle around the body. This allows many different views of the same organ or structure and provides much greater detail. The X-ray information is sent to a computer that interprets the X-ray data and displays it in two-dimensional form on a monitor. Newer technology and computer software makes three-dimensional images possible.

CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. CT can also be used for a tissue or fluid biopsy.

Why are CT scans sometimes ordered with contrast?

CT scans may be done with or without contrast. Contrast refers to a substance taken by mouth or injected into an 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. Your doctor will notify you of this prior to the procedure.

You will need to let your doctor know if you have ever had a reaction to any contrast media and/or any kidney problems. A reported seafood allergy is not considered to be a contraindication for iodinated contrast. If you have any medical conditions or recent illnesses, inform your doctor.

How do I prepare for a CT scan?

If you are having a computed tomography angiography (CTA) or a virtual colonoscopy, you will be given specific instructions when you make your appointment.

PRECAUTIONS: If you are pregnant or think you may be pregnant, please check with your doctor before scheduling the exam.

CLOTHING: You may be asked to change into a patient gown. If so, a gown will be provided for you. Please remove all piercings and leave all jewelry and valuables at home.

CONTRAST MEDIA: Contrast may be indicated for your exam. The contrast media improves the radiologist’s ability to find structures that are abnormal and understand normal anatomy better.

• Some patients should not have an iodine-based contrast media. If you have problems with your kidney function, please inform your radiologist in advance. We may be able to perform the scan without the contrast media or find an alternate imaging exam.
• The most common type of CT scan with contrast is the double-contrast study, which will require you to drink a contrast media before your exam begins in addition to the IV contrast. The more contrast you are able to drink, the better the images are for the radiologist to visualize your digestive tract.

ALLERGY: Please inform the access center representative when you schedule your scan if you have had an allergic reaction to any contrast media. IV contrast will not be administered if you have had a severe or anaphylactic reaction to any contrast media in the past. Mild to moderate reactions warrant a plan that includes taking medication prior to the CT examination. These plans will be discussed with you in detail when you schedule your exam. Any known reactions to a contrast media should be discussed with your personal physician.

EAT/DRINK: If your study was ordered without contrast, you can eat, drink and take your prescribed medications prior to your exam.

If your doctor orders a CT scan with contrast, do not eat anything three hours prior to your CT scan. We encourage you to drink clear liquids. You may also take your prescribed medications prior to your exam.

DIABETICS: People with diabetes should eat a light breakfast or lunch three hours prior to the scan time. Depending on your oral medication for diabetes, you may be asked to discontinue use of the medication for 48 hours after the CT examination. Detailed instructions will be given following your examination.

MEDICATION: All patients can take their prescribed medications as usual.

The Newest CT: Faster Than a Heartbeat

A new CT scanner will change the management and outcomes of coronary artery disease. The CT scan captures images of the heart between beats, leading to clearer images to help detect anatomic and functional characteristics of coronary artery disease. This technology can also be used to help replace invasive tests to determine which patients with chest pain need intervention.

Read more

What are the risks of a CT scan?

If you are pregnant or think you may be pregnant, you should notify your health care provider.

The amount of radiation dose used in a CT scan is small. You may want to ask your doctor about the amount of radiation used during the CT procedure and the risks related to your particular situation.

If you are claustrophobic or tend to become anxious easily, tell your doctor ahead of time. You may be prescribed a mild sedative to take before the procedure to make you more comfortable.

What happens during a CT scan?

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, CT scans follow this process:

• You may be asked to change into a patient gown. If so, a gown will be provided for you. A locker will be provided to secure all personal belongings. Please remove all piercings and leave all jewelry and valuables at home.
• If you are to have a procedure done with contrast, an IV line will be started in the hand or arm for injection of the contrast media. For oral contrast, you will be given a liquid contrast preparation to swallow. In some situations, the contrast may be given rectally.
• You will lie on a scan table that slides into a large, circular opening of the scanning machine.
• 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. Speakers inside the scanner will enable the technologist to communicate with and hear you. You may have a call button so that you can let the technologist know if you have any problems during the procedure. The technologist will be watching you at all times and will be in constant communication.
• As the scanner begins to rotate around you, X-rays will pass through the body for short amounts of time. You will hear clicking sounds, which are normal.
• The X-rays absorbed by the body’s tissues will be detected by the scanner and transmitted to the computer. The computer will transform the information into an image to be interpreted by the radiologist.
• It is important that you remain very still during the procedure. You may be asked to hold your breath at various times during the procedure.
• If contrast media is used for your procedure, you may feel some effects when the contrast is injected into the IV line. These effects include a flushing sensation, a salty or metallic taste in the mouth, a brief headache, or nausea and/or vomiting. These effects usually last for a few moments.
• You should notify the technologist if you have any breathing difficulties, sweating, numbness or heart palpitations.
• When the procedure has been completed, you will be removed from the scanner.
• If an IV line was inserted for contrast administration, the line will be removed.
• While the CT procedure itself causes no pain, having to lie still for the length of the procedure might cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure, such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

What happens after a CT scan?

• If contrast media was used during your procedure, you may be monitored for a period of time for any side effects or reactions to the contrast, such as itching, swelling, rash or difficulty breathing.
• If you notice any pain, redness and/or swelling at the IV site after you return home following your procedure, you should notify your doctor, as this could indicate an infection or other type of reaction.
• There is typically no special type of care required after a CT scan. You may resume your usual diet and activities unless your doctor advises you differently.
• Your doctor may give you additional or alternate instructions after the procedure, depending on your particular situation.

What are some of the advances in CT technology?

Advances in CT technology include:

• High-resolution CT: This type of CT scan uses very thin slices (less than 0. 1 inches), which are effective in providing greater detail in certain conditions, such as lung disease.
• Helical or spiral CT: During this type of CT scan, both the patient and the X-ray beam move continuously, with the X-ray beam circling the patient. The images are obtained much more quickly than with standard CT scans. The resulting images have greater resolution and contrast, providing more detailed information. Multidetector-row helical CT scanners may be used to obtain information about calcium buildup inside the coronary arteries of the heart.
• Ultrafast CT (also called electron beam CT): This type of CT scan produces images very rapidly, thus creating a type of “movie” of moving parts of the body, such as the chambers and valves of the heart. This scan may also be used to obtain information about calcium buildup inside the coronary arteries of the heart, but the helical scanners are much more common.
• Computed tomographic angiography (CTA): Angiography (or arteriography) is an X-ray image of the blood vessels. A CT angiogram uses CT technology rather than standard X-rays or fluoroscopy to obtain images of blood vessels — for example, the coronary arteries of the heart.
• Combined positron emission tomography and CT (PET/CT): The combination of CT and positron emission tomography technologies into a single machine is referred to as PET/CT. PET/CT combines the ability of CT to provide detailed anatomy with that of PET to show cell function and metabolism in order to offer greater accuracy in the diagnosis and treatment of certain types of diseases, particularly cancer. PET/CT may also be used to evaluate conditions such as epilepsy, Alzheimer’s disease and coronary artery disease.

CT scan: MedlinePlus Medical Encyclopedia

A computed tomography (CT) scan is an imaging method that uses x-rays to create pictures of cross-sections of the body.

Related tests include:

• Abdominal and pelvis CT scan
• Cranial or head CT scan
• Cervical, thoracic, and lumbosacral spine CT scan
• Orbit CT scan
• Chest CT scan
• CT angiogram

You will be asked to lie on a narrow table that slides into the center of the CT scanner.

Once you are inside the scanner, the machine’s x-ray beam rotates around you. Modern spiral scanners can perform the exam without stopping. There is very little noise.

A computer creates separate images of the body area, called slices. These images can be stored, viewed on a monitor, or copied to a disk. Three-dimensional models of the body area can be created by stacking the slices together.

You must stay still during the exam, because movement causes blurred images. You may be told to hold your breath for short periods of time.

Complete scans most often take only a few minutes. The newest scanners can image your entire body in less than 30 seconds.

Certain exams require a special dye, called contrast, to be delivered into your body before the test starts. Contrast helps certain areas show up better on the x-rays.

Let your health care provider know if you have ever had a reaction to contrast. You may need to take medicines before the test in order to avoid another reaction.

Contrast can be given several ways, depending on the type of CT being performed.

• It may be delivered through a vein (IV) in your hand or forearm.
• You might drink the contrast before your scan. When you drink the contrast depends on the type of exam being done. The contrast liquid may taste chalky, although some are flavored. The contrast passes out of your body through your stools.
• Rarely, the contrast may be given into your rectum using an enema.

If contrast is used, you may also be asked not to eat or drink anything for 4 to 6 hours before the test.

Before receiving IV contrast, tell your provider if you take the diabetes medicine metformin (Glucophage). People taking this medicine may need to stop temporarily. Also let your provider know if you have any problems with your kidneys. The IV contrast can worsen kidney function.

Find out if the CT machine has a weight limit if you weigh more than 300 pounds (135 kilograms). Too much weight can damage the scanner.

You will need to remove jewelry and wear a gown during the study.

Some people may have discomfort from lying on the hard table.

Contrast given through an IV may cause a slight burning feeling, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.

A CT scan creates detailed pictures of the body, including the brain, chest, spine, and abdomen. The test may be used to:

• Diagnose an infection
• Guide a doctor to the right area during a biopsy
• Identify masses and tumors, including cancer
• Study blood vessels

Results are considered normal if the organs and structures being examined are normal in appearance.

Abnormal results depend on the part of the body being studied. Talk to your provider about questions and concerns.

Risks of having CT scans include:

• Allergic reaction to the contrast dye
• Damage to kidney function from the contrast dye
• Exposure to radiation

CT scans expose you to more radiation than regular x-rays. Having many x-rays or CT scans over time may increase your risk for cancer. However, the risk from any one scan is small. You and your provider should weigh this risk against the value of the information that will come from a CT scan. Most new CT scan machines have the ability to reduce the radiation dose.

Some people have allergies to contrast dye. Let your provider know if you have ever had an allergic reaction to injected contrast dye.

• The most common type of contrast given into a vein contains iodine. If you have an iodine allergy, contrast may cause nausea or vomiting, sneezing, itching, or hives.
• If you absolutely must be given such contrast, your provider may give you antihistamines (such as Benadryl) or steroids before the test.
• Your kidneys help remove iodine from the body. You may need to receive extra fluids after the test to help flush iodine out of your body if you have diabetes or kidney disease.

Rarely, the dye may cause a life-threatening allergic response called anaphylaxis. If you have any trouble breathing during the test, tell the scanner operator immediately. Scanners come with an intercom and speakers, so the operator can hear you at all times.

CAT scan; Computed axial tomography scan; Computed tomography scan

• CT scan

Blankensteijn JD, Lely RJ. Computed tomography. In: Sidawy AN, Perler BA, eds. Rutherford’s Vascular Surgery and Endovascular Therapy. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 29.

Levine MS, Gore RM. Diagnostic imaging procedures in gastroenterology. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 124.

Van Thielen T, van den Hauwe L, Van Goethem JW, Parizel PM.Current status of imaging of the spine and anatomical features. In: Adam A, Dixon AK, Gillard JH, Schaefer-Prokop CM, eds. Grainger & Allison’s Diagnostic Radiology: A Textbook of Medical Imaging. 7th ed. Philadelphia, PA: Elsevier; 2021:chap 47.

Updated by: Jason Levy, MD, FSIR, Northside Radiology Associates, Atlanta, GA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

CT of the temporal bone

CT of the temporal bones is a non-invasive method for diagnosing the temporal bone, adjacent soft tissues and anatomical structures located in this area. The examination is carried out using x-rays, the results are displayed on the monitor screen in the form of layered images in three planes. Computed tomography allows you to determine the state of the smallest structures of the auditory canal, middle ear and make an accurate diagnosis. As a rule, it is prescribed in cases where other research methods have proved to be insufficiently informative.

Clinical Diagnostic Center specializes in diagnostic procedures. You can do a CT scan of the temporal bones at an affordable price in Nizhny Novgorod. The staff of our institution has the necessary qualifications to conduct such examinations. We invite you to sign up for a consultation and undergo computed tomography at any time convenient for you.

Purpose of CT of the temporal bones

Diagnosis of the condition of the temporal bones is of decisive importance for the detection of various pathologies and the establishment of many diagnoses. In this section of the cranium, blood vessels and nerve fibers are concentrated, on which the normal functioning of the masticatory, vestibular, and auditory apparatus depends. Conventional radiography or ultrasound very often does not give an idea of ​​the pathological changes in this area, but computed tomography of the temporal bones allows you to get a more detailed and clear picture.

This is the most informative and effective way to diagnose diseases at an early stage. Black-and-white images of organs and tissues displayed on the monitor screen can be enlarged, zoomed in, and any area can be accurately examined. The slice thickness is about 1 mm. These are optimal values ​​for examining the following structures:

• pyramids of the temporal bone
• cochlea, vestibule, anterior and posterior semicircular canal
• mastoid cells and antrum
• ossicles of the middle ear
• ear canal walls
• jugular fossa

The 3D-image obtained during the examination gives the most clear idea of ​​the anatomical structure of the patient’s organs. This is especially important when preparing for surgery for an inner ear implant.

Indications for CT of the temporal bones

CT of the temporal bones makes it possible to diagnose inflammatory, traumatic, tumor pathologies. Changes and diseases detected during the examination include:

• hematomas
• vascular pathologies
• arachnoiditis, encephalitis, abscess, pus between meninges
• damage to bones and soft tissues in the region of the temporal bone
• traumatic injuries (cracks, fractures)
• malformations of bones and inner ear
• Neoplasms located in the region of the temporal bones

CT scans of the temporal bones are usually prescribed by neurologists, ENT doctors, and neurosurgeons. The basis for the examination is the pathological changes identified during other types of diagnostics.

Indications for CT scan of the temporal bones:

• skull injuries with suspected fracture and soft tissue contusions in the temporal bone area
• inflammatory ear diseases (purulent otitis media, ethmoiditis, involvement of the meninges in the inflammatory process)
• vestibular disorders (dizziness, unsteadiness when walking)
• progressive hearing loss, ringing or tinnitus
• changes in the functioning of the facial nerve with the development of weakness of mimic muscles
• identified tumor processes

The doctor also prescribes a CT scan to examine the temporal bones in preparation for the operation to implant the electrode.

How a CT scan of the temporal bones works

The CT scanner is a large camera with a retractable bed. During the examination, the patient lies on the table of the tomograph. To avoid involuntary movements that can distort the scan results, during the examination, the head is fixed with a special pillow and straps.

During the scan, the table moves into the tomograph tunnel, while the patient’s head must be at the level of the radiation source. The waves reproduced by the device pass through the soft organic structures of the body and are displayed on the monitor in the form of images. The medical staff at this time is in the next room and monitors the progress of the procedure. The patient does not experience discomfort or pain.

CT of the temporal bones with contrast consists of several stages: first, a native scan is performed, then an iodine-containing preparation is injected. The final stage is rescanning to obtain contrast images. After taking images of the area under study, the doctor checks their clarity and detail.

CT scan results of the temporal bone

Deciphering the results of computed tomography of the temporal bones takes from 30 minutes to 1.5 hours. The radiologist describes the images obtained during the examination. When pathological changes are detected, a conclusion is made regarding their nature, causes and degree of localization.

The patient receives images on digital media or film, as well as a conclusion certified by the doctor’s signature. It should be understood that this conclusion is not a diagnosis. Making an accurate diagnosis and prescribing treatment is the responsibility of the attending physician.

Preparation for CT scan of the temporal bone

No special preparation is required for the appointment of tomography without contrast. If a CT scan with the introduction of a contrast agent is prescribed, it is necessary to refrain from eating for at least 6 hours and drink only clean water. Metal jewelry, hearing aid, dentures (removable) should be removed before the procedure.

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8.10. Measurement of mean value and standard deviation of intensity in space

____________________________________________________________________________________________

The functionality is available in an add-on module that is activated in the edition
“Pro” for a fee
________________________________________________________________________________________________

The VOI Sphere tool is similar to the ROI tools described in section 2. 17, but
measurements are performed in a space bounded by a sphere.

8.10.1 Building a sphere

____________________________________________________________________________________________

The functionality is available in an add-on module that is activated in the edition
“Pro” for a fee
________________________________________________________________________________________________

To draw a sphere, do the following:

1. Select the series to be measured, navigate to the image where you want to
   be the center of the sphere.

2. Activate the VOI sphere tool by clicking the button on the toolbar
   left, right or middle mouse button. For further work
   with the tool, use the button with which the tool was activated.
   See Section 1.14 for more information on tool management.

3. The VOI sphere can be built in two ways:

   • Move the cursor to the point where the center of the sphere should be.
     Click the mouse button. Set the desired sphere diameter by moving
     mouse. To complete the construction, click the mouse button;

   • click the mouse button at the point where the center should be
     sphere, and holding down the mouse button, set the desired diameter
     spheres. To fix the diameter of the sphere, release the mouse button.

4. To cancel an incomplete build, press the Esc button on your keyboard.

The following parameters are displayed next to the sphere:

• minimum intensity value;

• maximum intensity value;

• average intensity value;

• standard deviation;

The CT and PET windows display only the results for the corresponding series, in the window
CT+PET — for both series.

8.10.2 Location of the sphere in space

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The functionality is available in an add-on module that is activated in the edition
“Pro” for a fee
________________________________________________________________________________________________

The MIP window always displays all constructed spheres. In other windows
the image shows the line of intersection of the sphere with the image plane and the results
measurements. As you move away from the center of the sphere, the diameter of this circle decreases. If
sphere does not intersect with the image plane, then the measurement results for the sphere do not
displayed in this window.

If the center of the sphere is in the current image and the Sphere tool is activated
VOI” , then crosshairs are displayed in the center of the sphere and on its border.

8.10.3 Actions with the sphere

____________________________________________________________________________________________

The functionality is available in an add-on module that is activated in the edition
“Pro” for a fee
________________________________________________________________________________________________

To edit a sphere, do the following:

1. Navigate to the image that contains the center of the sphere. For this
   scroll through the slices until crosshairs appear in the center and on the border of the sphere.

2. To move the sphere, move the cursor over the crosshairs at its center, and while holding
   pressed left mouse button or the button that is currently activated
   tool, move the mouse. When hovering the cursor, the crosshair increases.

3. To change the radius, move the cursor over the crosshairs on the boundary, and while holding
   pressed left mouse button or the button that is currently activated
   tool, move the mouse. When hovering the cursor, the crosshair increases.

To move a block with measurement results, move the cursor over it and move
mouse while holding down the left mouse button or the button that is currently
tool is activated. For this, it is not necessary that the center of the sphere be on the current
image.

To remove a sphere, right-click on the corresponding block with
measurement results or on the crosshairs in the center or on the borders of the sphere and select
“Delete Object” command.

8.10.4 Rendering parameters

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The functionality is available in an add-on module that is activated in the edition
“Pro” for a fee
________________________________________________________________________________________________

To change the drawing parameters of the constructed sphere:

1. Place the cursor on the block with measurement results or on the crosshairs in the center or
   at the edge of the sphere.