CT (computed tomography)

Massachusetts General Hospital Imaging provides CT (computed tomography) imaging services in a caring environment using the latest technology and radiation-dose-reduction techniques, and every scan is interpreted by a radiologist with specialty training.
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About This Procedure


Before your appointment for a CT, please print and complete the Patient Procedure Screening Form.

Massachusetts General Hospital Imaging provides CT exams on the Mass General main campus and at convenient community locations. No matter which facility you come to, our staff places priority on making your journey through the imaging process comfortable, safe, and successful. All images are read by a radiologist with specialty expertise in the area of the body being studied.

CT overview

  • A CT scanner rotates to take X-ray images from different angles all around your body. A computer puts these images together to form detailed, two-dimensional pictures.
  • CT provides clearer, more detailed pictures than traditional X-rays.
  • CT serves a wide range of purposes, such as diagnosing bone fractures and preparing for orthopedic surgery.
  • Exams typically take 15 minutes in total; the actual scanning takes just minutes.
  • Many exams involve contrast—a drink or injection that makes the images more informative.
  • If you are over 60 or have kidney disease, diabetes, lupus, or multiple myeloma, you'll need a blood test beforehand to make sure the contrast will be safe for you.
  • The technologist performing your exam will be nearby and able to talk to you throughout the scan.
  • CT exams require that you lie still in a confined space. But because the scanning time is so short, most people tolerate the experience well.
  • Every exam is interpreted by a radiologist with specialty expertise in the specific area of the body under study. A specialist is capable of seeing and understanding subtle things due to advanced training and singular focus.
  • We use the latest technology, and the capabilities of our state-of-the-art scanners play a key role in tailoring each exam to your specific needs and reducing radiation exposure.





What To Expect

What should I expect BEFORE my CT scan?

  • Medications: It is important for you to keep to your regular medication schedule. Please take all the medications that have been prescribed to you by your doctor. Just let our staff know what medications you have taken prior to your test.
  • Food and drink: You should not eat solid foods for two hours prior to your test. You may, however, drink plenty of fluids, such as water, broth, clear soups, juice, or black decaffeinated coffee or tea. We encourage you to drink plenty of fluids before your arrival to our center.
  • When to arrive: If you are having a CT scan of your abdomen or pelvis, you need to arrive one hour before your scheduled appointment. This is to allow time for you to drink barium sulfate before your exam and to ensure that the barium fluid completely coats your gastrointestinal tract. The barium helps to highlight body areas for the CT scan. If you are having a scan other than the abdomen you should arrive at your appointed time.
  • What to wear: You should dress in comfortable clothing. It might be necessary for you to change into a hospital gown if there is metal in your clothing, such as a bra or zipper, within the area of interest of your study. If you are wearing jewelry or anything else that might interfere with your scan, we will ask you to remove it. The CT scan is conducted in a very secure environment. It is best, however, if you leave valuable items at home.
  • Diabetic conditions: If you are an insulin-dependent diabetic, please continue to take your insulin as prescribed, but remember to drink extra fruit juices to make up for the fasting of solid foods for the 2-3 hour period that your stomach is empty. Patients who are taking diabetic medications should take the prescribed dose as normally done on that day, but discontinue the next doses for 48 hours AFTER their CT exam. Patients should notify their Primary Care Physician (PCP) that they were instructed to discontinue their medication for 48 hours. If you need a substitute medication, please consult your doctor.
  • Intravenous preparation: Many patients receive a contrast agent intravenously (IV) during their CT test. If your doctor or the radiologist has determined that this procedure will enhance your CT scan results, the technologist will place an IV in your arm or hand prior to going into the test. (Please see the section on "Contrast medium," below.)
CT Scan image

What will I experience DURING my CT scan?

  • Scanning: Your CT technologist will bring you into the CT scan room where you will lie down on the patient table. The technologist positions your body so that the area you are having scanned is in the middle of the large doughnut-shaped scanner ring which holds the x-ray tube and an electronic detector. The technologist leaves the room, but is in full view and communication with you through the observation window in the adjoining room.

    The scanner does not touch you, nor do you feel the x-rays. It does make some noise and the table you are lying on may move slightly to make adjustments for a better view. It is important for you to lie very still and at some points, you may be asked to briefly hold your breath as the picture is taken. During the scan, a thin beam of x-ray is focused on a specific part of your body. The x-ray tube moves very rapidly around this area, enabling multiple images to be made from different angles to create a cross-sectional picture. The x-ray beam information goes to the electronic detector and then into a computer, which analyzes the information and constructs an image for the radiologist to interpret.
  • Length of scan: Each CT scan is individualized and tailored to each patient's needs. In general, the actual image-taking is only about one minute and most examinations last approximately 15 minutes in total.
  • Contrast medium: A contrast medium, or contrast agent, highlights your organs and blood vessels and helps the radiologist see them better. The contrast agents in use today carry a low risk of allergic reaction and cause little discomfort for most people. If you are over 60 or have kidney disease, diabetes, lupus, or multiple myeloma, you’ll need a blood test beforehand to make sure the contrast will be safe for you.

    The high speed of our state-of-the art scanners means we are able to produce high-quality images using less contrast than in the past; contrast dilutes fairly quickly into your bloodstream, but our fast scanners take their pictures before the dilution occurs.

What should I expect AFTER my CT scan?

  • Instructions: You have no restrictions after having a CT scan and can go about your normal activities. To help eliminate the contrast medium from your body, drink plenty of decaffeinated or non-alcoholic beverages. Water and juices also work well.
  • Exam results: All CT scans are read by a Mass General radiologist specialty trained in CT imaging and dedicated to the specific area of interest for your study. Rapid results are essential not only for your peace-of-mind, but also for your physician to begin planning your treatment immediately, if necessary. After the scan has been read the results are sent to your physician, who will discuss them with you.

Physician Resources

Screening Form

This form is available to provide to patients to complete and bring with them to their CT appointment.

CT with Anesthesia:
How to Prepare

This handout is available to give to patients ≥20 years to help them prepare for their CT.

CT with Anesthesia:
How to Order

Use this tip sheet to order and schedule CTs with anesthesia for patients ≥20 years.


Patient Education

CT in Depth

Learn more about CT common uses and safety.

Patient Handouts

Before your CT, please print and complete the Patient Procedure Screening Form.

CT in depth

What is a CT scan?

A CT (computed tomography) scan is a noninvasive medical test that uses special X-ray equipment to produce multiple images or pictures of the inside of the body and a computer to join them together in cross-sectional views of the area being studied. CT scans of internal organs, bone, soft tissue and blood vessels provide greater clarity than conventional X-ray exams.

Common uses

CT scanning is commonly used to diagnose problems such as cancers, cardiovascular disease, infectious disease, trauma and musculoskeletal disorders.


CT examinations improve health care and are an essential part of diagnosis and treatment planning. However, there are some risks associated with the level of radiation exposure during a CT and therefore the medical benefit of conducting the exam should always outweigh any risks involved. No direct data have shown that CT examinations are associated with an increased risk of cancer; extrapolations from studies of radiation exposure suggest there is a very small incremental risk.

At Mass General Imaging, we pay special attention to minimizing radiation exposure—without giving up image quality. Radiation reduction has long been a priority for our entire staff, including radiologists, the technologists who administer most exams, researchers, and equipment engineers. We use many strategies to reduce radiation exposure, from employing the latest technology to customizing exams for each patient.




  • Experts weigh risks of CT scans - 3/21/2013, Mass General

    Multiple studies have examined the benefits and risks of CT scans. Read the latest coverage on the issue in USA Today.

  • Safety: Children and CT Scans - 6/11/2012, Mass General

    Dushyant Sahani, MD, Director of CT at Massachusetts General Hospital Imaging, answers parents’ questions on the June 2012 study in The Lancet that found that children who get several CT scans have a slightly higher chance of brain cancer and leukemia in later life.

  • Thrall: Healthcare IT can help rads tackle radiation exposure - 9/20/2011, Clinical

    It's imperative that radiologists proactively find ways to keep radiation dose to a minimum, and healthcare IT can help, according to Dr. James H. Thrall, who spoke on the topic this week at the New York Medical Imaging Informatics Symposium.

  • Our experts share tips on reducing head-CT radiation - 8/3/2011, Clinical

    Continuing Mass General Imaging's leadership role in reducing CT radiation, radiologists from Mass General have co-authored a journal article summarizing methods for dose optimization in head CT scans.

  • Adaptive image filters lower CT radiation dose - 5/4/2010, Research

    Adaptive image filters can lower the patient radiation associated with chest and abdominal computed tomography (CT) scans while significantly improving image quality, according to a study by Mass General researchers.

  • Q&A: Look closer at CT scan cancer risks - 12/21/2009, Clinical

    In many cases, the benefits of these tests—in finding cancers, aneurysms or blood clots—far outweigh the relatively low risks of radiation.

  • Study looks at radiation exposure - 8/26/2009, Research

    As many as two-thirds of adults underwent a medical test in the last few years that exposed them to radiation and in some cases, a potentially higher risk of cancer, a study in five areas of the US suggests.

  • The value of CT scans - 3/12/2009, Clinical

    There is no reason to create obtrusive coverage policies that will block access to these lifesaving tools that are truly transforming care for millions of patients.


  • CT (computed tomography) slide show

    Images of Imaging: CT

    Get an inside look at CT exams at Mass General Imaging. Learn about CT technology, the professionals who guide patients through the exam process, and the specialty-trained radiologists who interpret every scan.

  • The Webster Center for Advanced Research and Education in Radiation

    Webster Center takes on radiation-dose reduction

    Dr. James H. Thrall, Department of Radiology chairman emeritus, discusses The Webster Center for Advanced Research and Education in Radiation, a unique research effort dedicated to reducing radiation dose for every exam Mass General Imaging performs.

  • Radiation reduction: Our ongoing objective

    Radiation reduction: Our ongoing commitment

    As CT (computed tomography) technology has transformed the practice of medicine, Mass General Imaging has dedicated itself to making sure each exam exposes the patient to the lowest achievable amount of radiation. Department of Radiology Chairman Emeritus James H. Thrall, MD, discusses our decade-long commitment—and our success—regarding this issue.

  • Decision tools support radiation-reduction efforts

    Decision tools support radiation-reduction efforts

    One effective way to reduce radiation exposure is to avoid unnecessary exams. That's why Mass General Imaging has been a leader in developing software tools that guide referring physicians by not only making sure the selected exam matches the patient's needs but also suggesting radiation-free alternatives when appropriate.

  • Imaging specialists, focused on you

    Imaging specialists, focused on you

    Each radiologist at Mass General Imaging is a specialist in a particular area of the body. Department of Radiology Chairman Emeritus James H. Thrall, MD, explains how patients benefit from the additional specialty training our physicians have completed.

Request an Appointment

Call to schedule an appointment 617-724-9729

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