Computed Tomography (CT or CAT) Scan of the Chest
Computer tomography, also referred to as a CAT scan or CT scan is a non-invasive imaging diagnostic procedure, which uses computer technology and X-rays to produce axial or horizontal images 9also called slices) of the human body. The CAT scan essentially shows detailed images of the part of the body in question, including muscles, bones, organs, and fats. CT scans are in essence more detailed than the standard X-rays.
For standard x-rays, an energy beam is aimed to the part of the body being studies. A plate, usually placed behind the body, captures the variations of the beam as it passes through the skin, tissue, bone, or muscle. However, though you can get a lot of information about the internal organs and structures on a standard X-ray, a lot of detail is not availed.
The CT scan has the X-ray moving in a circle around the body. What this does is allow for many different views of the same structure or organ. Then, the information is sent to the computer, which will interpret the data and display the result on a 2-dimensional format on a computer monitor.
In essence, CT scans can be done with or without contrast – the substance taken orally or injected into an intravenous (IV) channel to help the particular part, tissue, or organ become more visible under the beams. In this case, contrast examinations often need you to keep away from taking food orally for a period of time before the procedure is done. Your doctor should notify you about this in due time.
Chest CT scans can offer a much-detailed information about the various structures and organs located inside the chest region, than standard X-rays would. Therefore, this is a more effective diagnostic procedure as it provides more information when it comes to injuries and diseases that are related to the thoracic (chest) organs.
CT scans on the chest can also be used to see the placement of needles in biopsy procedures for thoracic tumors or organs or during the withdrawal (aspiration) of fluid from the thoracic cavities. Such scans are essential for monitoring tumors as well as other conditions of the chest area before, during, and after treatment.
Reasons for CT scan of the Chest
The chest region contains vital organs of the cardiovascular and respiratory systems, plus the esophagus, which includes the hollow tube of muscle that extends from below the tongue to the stomach. For this reason, a chest CT scan can be used to assess the chest and the organs of the chest for tumors and other injuries, lesions, infections, bleeding, obstructions, unexplained chest pains, intrathoracic bleeding, as well as many other conditions, especially when the other forms of diagnosis and examination have proved ineffective (such as physical examinations and standard x-rays).
The CT scan performed of the chest can also be used for evaluating the effect of the various forms of treatment for thoracic tumors. Another use is offering guidance for biopsies or aspiration of the tissues located in the chest. Keep in mind that the doctor can recommend a CT scan for a variety of reasons, and it is best to trust his expertise.
Risk involved in CT scans
It is a good idea to ask your doctor amount of radiation that they use during the CT scan procedure as well as the risks involved when it comes to your particular situation. You may also want to keep an updated record of the previous history of exposure to radiation, including other previous CT scans, and other forms of x-rays so that you can inform your doctor before the procedure commences. The risks associated with radiation exposure are usually related to the cumulative amount of x-ray examinations and treatments over a period of time.
If you are actually pregnant, or you suspect that you are pregnant, it’s always good to inform your doctor. Exposing your body to radiation during pregnancy poses a risk for birth defects. When a contrast is used during the procedure, there is a risk for developing allergic reactions. In this case, let your doctor know if you have had an allergic reaction to any of the contrast media or any form of kidney problems. Reported seafood allergies are not considered contradictions to the iodinated contrast.
For patients with any form of kidney failure or kidney problems, be sure to notify the doctor. The reason for this is that sometimes the contrast media might cause kidney failure, especially for patients that are dehydrated or have underlying kidney problems. Patients who are currently under the diabetes prescription called metformin (Glucophage) or any of its derivatives, some forms of contrast poses a risk of a condition referred to as metabolic acidosis, which is a dangerous change to the blood pH.
There are several other risks that may arise depending on the particular state of your health. In this case, be sure to have a talk with your doctor and discuss all the concerns that you might have prior to the CT scan procedure.
Other conditions or factors might interfere with the accuracy of chest CT scans. Such factors include the following:
- Body Piercings on the chest
- Metallic objects placed within the chest like a pacemaker and surgical clips
- Barium in the esophagus from a recent barium examination
Preparation for a CT scan
In John Hopkins radiology center, patients who are yet to undergo a computed tomography angiography (CTA) scan are given a basic set of instructions when they make the appointment.
Precautions
Should you be pregnant or suspect that you might be pregnant, please consult your doctor before you schedule your scan. Other options available for you will be discussed between you and your doctor.
Clothing
For clothing, keep in mind that you might be asked to change into an official patient gown. If this is the case, a gown will be provided to you. In addition, a locker will be assigned to ensure that your personal belongings are secured. Be sure to remove any form of piercings and leave all your valuables and jewelry at home.
Contrast Media
Most CT scans are usually done without a contrast media. The role of a contrast media is to improve the ability of the radiologist to view the images of the internal organs of the body.
Allergies
Make sure you inform the access center representatives if you have previously had any allergic reactions to contrast media, when you schedule the CT scan. Contrast IV will may not be administered to you if you have had an anaphylactic reaction in the past to any contrast media. If your allergy was mild and moderate during the previous use of contrast, then some medication will be administered prior to the chest CT scan. All of these plans will have to be discussed to you in detail in your appointment with our doctors for the exam. However, any known reactions to contrast media must be reported and discussed with your personal physician.
Food
You can eat and drink normally and even take your prescribed medications if your doctor decided to go with a CT scan without contrast. However, if your doctor ordered a CT scan with contrast, you are not supposed to eat and/or drink anything 3 hours prior to CT scan. Only clear liquids should be taken, and you may still take your prescribed medicine prior to the scan.
Diabetics
If you are a diabetic, you should eat a light meal three hours prior to the exam’s scheduled time. You might be asked to pause the use of medication for 48 hours after the scan, depending on the type of medication you use. At John Hopkins radiology center, you will be given detailed information on how to go about this, following your exam.
Medications
All patients may take the various forms of prescribed medicine as usual.
Don’t forget that based on your medical condition, the doctor might request a more specific preparation, which will be availed to you in detail.
CT scan Details: Procedure
CT scans can be performed on an outpatient basis and even as part of your stay in the hospital’s premises. The procedure will vary depending on the condition as well as the preferential aspects of your physician.
You might be asked to change into the patients’ gown, and this will be offered to you. In addition, a secure locker will be assigned to you where you can keep all of your personal items. Again, be sure to remove any forms of piercings and leave any valuables such as jewelry at home.
If your procedure involves the use of contrast, an intravenous (IV) line I started in the arm or hand for injection of the media. For the orally administered contrast, you will essentially be given a specially prepared liquid contrast preparation that you need to swallow. In some cases, the contrast can be given rectally.
Next, you will lie on the scan table, which slides into the large circular opening of the CT scanning machine. For comfort and preventing movement during the procedure, pillows and straps might be used. A technologist will be in the other room where the controls for the scanner are located. Nonetheless, you will be in a constant sight of the technologist via a window. You can communicate with the technologist via the speakers located inside the scanner. You also have a call button at your comfort to let them know if you are experiencing any problems as the procedure occurs. The technologist should be in constant communication with you, as they watch you every step of the procedure.
While the scanner starts to rotate around you, x-ray beams will be passing through the body for some amount of time. There are clicking sounds, which are very normal. The rays absorbed by your body tissue can be detected by the machine, and will be transmitted to the computer. This data will be translated into an image, and the radiologist can interpret it. More importantly, be sure to remain still throughout the procedure. You may also be asked to hold your breath several times during the procedure.
Contrast media may make you feel some effects when it is injected into the (IV) line. Such effects include a salty and metallic taste in your mouth, a flushing sensation, nausea or even vomiting, and a brief headache. The effects usually last for a short amount of time. Alert the technologist should you feel any form of breathing difficulties, numbness, sweating, or heart palpitations during the procedure.
Although the CT scan is not painful, the need to lie still for the entire procedure can be uncomfortable and even cause some pain, especially if you previously had an invasive procedure such as surgery or even an injury. In this case, the technologist will use all comfort measures possible and complete the procedure as quick as possible to minimize pain or discomfort.
How to prepare for a chest 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?
Benefits
– 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.
Risks
– 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.