Overview of CT Orbit Scan
A CT orbit scan is a diagnostic imaging procedure specifically designed to examine the orbits, which are the bony cavities in the skull that house the eyes and their associated structures. This scan utilizes computed tomography (CT) technology to produce detailed cross-sectional images of the orbits, including the eye sockets, optic nerves, extraocular muscles, and surrounding soft tissues.
The primary aim of a CT orbit scan is to evaluate conditions affecting the eyes and surrounding areas. It is commonly used to diagnose and assess a variety of issues such as orbital fractures resulting from trauma, tumors or masses within the orbit, and inflammatory or infectious conditions like orbital cellulitis. The scan can also help in identifying abnormalities in the optic nerves and assessing conditions that might impact vision or eye movement.
The procedure involves the use of x-rays, which are processed by a computer to create detailed images of the orbit. These images provide valuable information for diagnosing disorders, planning treatments, and guiding surgical interventions. For instance, it can be instrumental in pre-surgical planning for orbital surgeries or in monitoring the progress of certain conditions.
What are some common uses of the procedure?
A CT scan of the orbit is employed for various diagnostic purposes, primarily focusing on the bony structures and soft tissues within the eye socket. One of the most common uses is to evaluate orbital fractures resulting from trauma, such as those caused by accidents or sports injuries. This imaging helps in assessing the extent of the fracture and any associated damage to the surrounding tissues.
The scan is also critical in identifying and characterizing tumors or masses located within the orbit. This includes both primary orbital tumors and metastatic lesions that have spread from other parts of the body. By providing detailed images of the orbit, the CT scan aids in determining the size, location, and extent of these growths, which is essential for treatment planning.
In addition to trauma and tumors, the CT orbit scan is used to investigate inflammatory or infectious conditions such as orbital cellulitis or abscesses. It can also help in diagnosing and evaluating conditions affecting the optic nerves, which are crucial for vision. For instance, it can be used to assess optic nerve compression or other abnormalities that might impact visual function.
Furthermore, the CT orbit scan can assist in the preoperative planning for orbital surgeries or in evaluating the results of previous treatments. It provides valuable insights into the anatomy of the orbit, which helps in the precise execution of surgical procedures or in monitoring the effectiveness of ongoing treatment. Overall, this scan is a key tool in diagnosing and managing a wide range of orbital and ocular conditions.
How should I prepare for a CT scan?
For a CT scan, wear comfortable, loose-fitting clothing. You may be required to change into a gown for the procedure. Metal objects, including jewelry, eyeglasses, dentures, and hairpins, can interfere with the CT images, so it is advisable to leave them at home or remove them before the exam. Some CT exams may also require the removal of hearing aids and removable dental work. Women should remove bras containing metal underwire, and you may need to remove any piercings if possible.
If your CT scan involves the use of contrast material, your doctor may instruct you to refrain from eating or drinking for a few hours before the exam. Inform your doctor about all medications you are taking and any allergies you have. If you have a known allergy to contrast material, your doctor may prescribe medications, usually a steroid, to reduce the risk of an allergic reaction. To avoid unnecessary delays, contact your doctor well in advance of the exam date.
Additionally, inform your doctor about any recent illnesses or other medical conditions, and whether you have a history of heart disease, asthma, diabetes, kidney disease, or thyroid problems, as these conditions may increase the risk of an adverse effect. The radiologist should also be informed if you have asthma, multiple myeloma, or any disorder of the heart, kidneys, or thyroid gland, or if you have diabetes, particularly if you are taking Metformin.
Women should always inform their physician and the CT technologist if there is any possibility that they may be pregnant. For more information, refer to the CT Safety During Pregnancy page.
What does the equipment look like?
The CT scanner is typically a large, donut-shaped machine with a short tunnel in the center. You will lie on a narrow table that slides in and out of this short tunnel. Surrounding you, the x-ray tube and electronic x-ray detectors are positioned opposite each other in a ring, called a gantry. The computer workstation that processes the imaging information is located in a separate control room. This is where the technologist operates the scanner and monitors your exam, maintaining direct visual contact with you. The technologist can hear and communicate with you using a speaker and microphone.
How does the procedure work?
A CT scan operates similarly to other x-ray exams, relying on the differential absorption of x-rays by various body parts. This difference allows doctors to distinguish between different body structures on an x-ray or CT image. During a conventional x-ray exam, a small amount of radiation is directed through the body part under examination, with a special electronic image recording plate capturing the resulting image. On an x-ray, bones appear white, soft tissues such as the heart or liver show up in shades of gray, and air appears black.
In contrast, CT scanning employs multiple x-ray beams and electronic x-ray detectors that rotate around the patient, measuring the radiation absorbed throughout the body. Occasionally, the exam table will move during the scan. A specialized computer program processes the large volume of data to create two-dimensional cross-sectional images of the body, which are then displayed on a computer monitor. CT imaging is often compared to slicing a loaf of bread into thin slices and then examining each slice; when the computer reassembles these image slices, it provides a highly detailed multidimensional view of the body's interior.
Most modern CT scanners can obtain multiple slices in a single rotation, known as multi-slice (multidetector) CT scanners, which capture thinner slices in less time, resulting in more detailed images. These advanced CT scanners can image large sections of the body in mere seconds, and even faster in small children. This speed benefits all patients, especially those who find it challenging to remain still, such as children, the elderly, and critically ill individuals.
For pediatric patients, radiologists adjust the CT scanner techniques to their size and the area of interest, thereby reducing the radiation dose. Some CT exams also use a contrast material to enhance the visibility of the body area under examination.
How is the procedure performed?
The technologist begins by positioning you on the CT exam table, typically lying flat on your back. Straps and pillows may be used to help you maintain the correct position and remain still during the exam. Many modern CT scanners are fast enough to scan children without the need for sedation; however, in special cases where children cannot hold still, sedation may be necessary. Motion during the scan can cause blurring of the images and degrade image quality, similar to how it affects photographs.
Depending on the type of exam, contrast material may be used. If required, the contrast material will be swallowed, injected through an intravenous line (IV), or, rarely, administered by enema. Once you are positioned, the table will move quickly through the scanner to determine the correct starting position for the scans. The table will then move slowly through the machine for the actual CT scan. Depending on the specific type of CT scan, the machine may make several passes.
The technologist may ask you to hold your breath during the scanning process. Any motion, including breathing and body movements, can lead to artifacts on the images, causing a loss of image quality that resembles the blurring seen in photographs of moving objects. When the exam is complete, the technologist will ask you to wait until they verify that the images are of high enough quality for accurate interpretation by the radiologist.
A CT scan of the usually takes about 10-45 minutes to complete.
What will I experience during and after the procedure?
CT exams are generally painless, fast, and easy, with multidetector CT reducing the amount of time you need to lie still. Although the scanning itself causes no pain, there may be some discomfort from having to remain still for several minutes. If you have difficulty staying still, are claustrophobic, or have chronic pain, you may find the CT exam stressful. The technologist or nurse, under the direction of a physician, may offer you medication to help you tolerate the procedure.
If the exam uses iodinated contrast material, your doctor will screen you for chronic or acute kidney disease. The contrast material may be administered intravenously, so you will feel a pin prick when the nurse inserts the needle into your vein. As the contrast is injected, you might feel warm or flushed, and you may experience a metallic taste in your mouth. These sensations are normal and will pass quickly. You might also feel a need to urinate, but this is only a side effect of the contrast injection and will subside rapidly.
Upon entering the CT scanner, you may see special light lines projected onto your body, which help ensure that you are in the correct position on the exam table. With modern CT scanners, you may hear slight buzzing, clicking, and whirring sounds as the internal parts of the CT scanner revolve around you during the imaging process.
During the CT scan, you will be alone in the exam room unless there are special circumstances, such as a parent wearing a lead shield staying in the room with their child. However, the technologist will always be able to see, hear, and speak with you through a built-in intercom system. For pediatric patients, a parent may be allowed in the room but may need to wear a lead apron to minimize radiation exposure.
After the CT exam, the technologist will remove your intravenous line and cover the tiny hole made by the needle with a small dressing. You can return to your normal activities immediately.
Who interprets the results and how do I get them?
A radiologist, a doctor specially trained to supervise and interpret radiology exams, will analyze the images from your CT scan. After analyzing the images, the radiologist will send an official report to the doctor who ordered the exam. Your doctor will then review the results with you and explain any findings.
In some cases, you may need a follow-up exam. If so, your doctor will explain the reason for this additional examination. A follow-up exam might be necessary to further evaluate a potential issue with more views or a special imaging technique, or to monitor any changes in a condition over time. Follow-up exams are often the best way to determine if treatment is effective or if a problem requires further attention.
Benefits
CT scanning offers numerous benefits, making it a valuable tool in medical imaging. It is a painless, noninvasive, and accurate procedure. One major advantage of CT scanning is its ability to image bone, soft tissue, and blood vessels simultaneously. Unlike conventional x-rays, CT scans provide highly detailed images of various types of tissue, including the lungs, bones, and blood vessels. The process is fast and simple, which is particularly beneficial in emergency cases where internal injuries and bleeding need to be identified quickly to help save lives.
CT scanning is also a cost-effective imaging tool for a wide range of clinical problems. It is less sensitive to patient movement compared to MRI, and unlike MRI, having an implanted medical device does not prevent you from undergoing a CT scan. Additionally, a diagnosis determined by CT scanning can eliminate the need for exploratory surgery and surgical biopsy.
No radiation remains in a patient's body after a CT exam, and the x-rays used for CT scanning should have no immediate side effects. These benefits highlight why CT scanning is a preferred choice in many medical scenarios.
Risks
There is always a slight risk of cancer associated with excessive exposure to radiation from CT scans. However, the benefit of obtaining an accurate diagnosis generally outweighs this risk. The radiation dose for CT procedures can vary; detailed information about radiation dose is available on the Radiation Dose page.
Women should inform their doctor and the CT technologist if there is any possibility of pregnancy, as CT scanning is generally not recommended for pregnant women unless absolutely necessary due to potential risks to the developing baby. The risk is minimal for head CT scans, but caution is advised. For more information on pregnancy and x-rays, refer to the Radiation Safety page.
If IV contrast material is used during the scan, manufacturers recommend that breastfeeding mothers avoid nursing for 24-48 hours afterward. However, the American College of Radiology (ACR) Manual on Contrast Media reports that the amount of contrast absorbed by an infant during breastfeeding is extremely low. For further details, consult the ACR Manual on Contrast Media and its references.
The risk of a serious allergic reaction to iodine-based contrast materials is extremely rare, and radiology departments are well-prepared to handle such reactions.
Children are more sensitive to radiation, so CT scans should be performed only when essential for diagnosis. They should not undergo repeated CT exams unless necessary, and CT scans in children should be conducted using low-dose techniques to minimize radiation exposure.
What are the limitations of Orbit CT?
CT scans of the orbit, while highly effective in many diagnostic scenarios, have some limitations. One primary limitation is their reduced sensitivity in detecting certain types of soft tissue abnormalities compared to other imaging modalities like magnetic resonance imaging (MRI). MRI is often better suited for visualizing detailed soft tissue structures, which can be critical when evaluating some orbital conditions.
Another limitation is related to image quality affected by patient movement. Any motion during the scan can lead to image blurring, which may obscure fine details necessary for accurate diagnosis. This is particularly challenging when imaging children or individuals who have difficulty staying still.
CT scans also involve exposure to ionizing radiation, which, while generally low, is a consideration for repeated imaging or in sensitive populations. Although modern techniques aim to minimize radiation doses, this remains a factor to consider, especially in pediatric cases or when multiple scans are needed.
In some instances, CT scans may not provide sufficient detail for comprehensive assessment of certain orbital pathologies, necessitating additional imaging studies or follow-up with other diagnostic tools to obtain a complete evaluation.