mri

How to Prepare for a CT Scan

/ Thomas Cohn, MD

ct scanA CT scan is a medical imaging tool widely used by medical professionals to gain better insight into afflicted areas of the body.  In this article, we’ll explain what a CT scan is, how it works, and how to best prepare for one.

For more information, read our blog on when CT scans, MRIs, and x-rays are useful in treating pain.

What is a CT Scan?

Computerized Tomography (CT) scans are a series of x-ray views taken of a body part at different angles. Computer processing of the views is used to create a cross-sectional picture of the scanned body part.  A number of “slices” (x-ray images) are taken, and the computer combines the images to create a 3-dimensional view of the region examined.  When the test was first introduced, the brain was the most common area examined by CT scan. Now, CT scans are used to examine many areas of the body.

When are CT Scans Helpful?

CT scans are x-ray images of a body region.  Therefore, radiation exposure does occur during these studies.  They are very fast to obtain and often provide very detailed information.  CT scans are often used when detailed information is needed rapidly to make a diagnosis and initiate treatment.  This makes them useful in acute illness, trauma, and brain injury where data needs to be collected fast and treatment cannot be delayed.  MRI scans may provide more detailed information, but can take a long time to obtain.  CT scans are also used in people who have metal implants in their bodies like pacemakers that can not placed in strong magnetic fields.

The risk of CT scans is similar to the risk associated with x-ray radiation.  This is generally a small risk if exposure is limited.  Frequent or multiple x-rays and CT scans can be a concern due to radiation and cancer.  Scans also should not be done during pregnancy due to possible radiation damage to the fetus.

How to Prepare for a CT Scan

Preparing for a CT scan depends on the area being scanned.  Since they are used in cases of trauma, often no special preparation is necessary.  Sometimes, a special contrast is needed to increase visualization of an area.  It may be swallowed, or injected in a vein or body cavity.  The scanning process is fast, and the scanner is fairly open, so claustrophobia is generally not an issue.  Most people will be required to wear a hospital gown for the scan so that clothing does not interfere with the imaging.

After the scan, a radiologist will interpret the results and report their findings to the doctor who ordered the scan (your physician).  Combining the results of the scan with clinical information (including patient history and physical examination) is critical.  Since the picture is only one part of the story, all the information needs to be combined to give an adequate explanation of the condition and the treatments that will work.

How to Prepare for an MRI Scan

/ Thomas Cohn, MD

MRIMagnetic Resonance Imaging (MRI) scans are one of the newer technologies that allow us to view the inner structures of the body.  The scanners use extremely powerful magnetics that align the hydrogen proton spins, which are present in water and most tissue, and create signals that can be detected and interpreted by computers into pictures of the body and its contents.

There is no radiation used, just a powerful magnet that forms a detailed picture of the tissues in the body.  The most common magnet used today is 1.5 Telsa, and that can give excellent detail of most body structures. However, the most sophisticated and experimental scanners are 5 times stronger and give us even more detailed information about the body.

Bodily Structures

MRI scans are used to give us detailed information about the tissues in the body.  They are commonly used to study all of the following structures:

  • The brain and nervous system
  • The spine
  • Muscles
  • Joints

It is a tool to give a physician more information to help define what is wrong and guide future treatment choices.  Since it only shows the structures, it still requires a physician to examine a patient to determine if what is seen correlates to symptoms presented by the patient.

Risk Factors

The risks of MRI scans are very low in general.  Since there is no radiation, they are often considered completely safe without any side effects.  MRI scans use very powerful magnets, therefore any magnetic metal can not be in close proximity of the scanner.  Since the early 1990’s, all metal objects used for implants have usually been made to be compatible for a MRI.  A few notable exceptions include:

  • Most pacemakers
  • Some ear implants
  • Heart valves
  • Implantable stimulators

If you have had surgery and an implant, notify the scanner personnel and they can check whether you may have problems.  Other metal such as bullets or metal fragments near the eye (from metal grinding work) may also be an issue.  The other main problem is if the noisy, closed space of the scanner can cause severe anxiety of people, preventing them from tolerating the scan, and support by the MRI staff or medication may help with the problem.

Preparing for a MRI Scan

There is very little preparation necessary for a MRI scan.  Know if you have any metal in your body, so the scanner radiologist can determine if a scan can be performed, and leave all metal jewelry outside the scanner room when changing for the scan.  A scan can often take an hour of time, and keeping still and relaxing during the scan will allow the best pictures to be obtained.   The results will be given to the ordering physicians usually within a day, and they will help you interpret the results.

Read our previous article on the differences between MRI scans, CT scans, and X-rays.

Are X-Rays, MRIs, & CT Scans Helpful in Treating Back Pain?

/ Thomas Cohn, MD

spine x-rayOne of the most common concerns of someone with low back pain is whether they need X-Rays or special scans such as a CT or MRI study.  Usually, the answer is no. Most low back pain will resolve in weeks to a month or two with conservative care.  For normal back conditions, imaging is not necessary to guide care and is needed only in a few circumstances. In this article, we will outline the three major imaging methods (X-Rays, MRIs, CTs) and discuss when each is recommended.

X-Rays

Plain X-rays of the lumbar spine can show all of the following:

  • Alignment and curvature
  • Disc space
  • Bones

X –rays are helpful when there is acute trauma to the spine and fractures are a concern.  In children, where scoliosis is suspected, plain films of the spine are also helpful.  In normal adults without the above 2 conditions, X-rays show very little information that is useful in managing low back pain.  Chiropractic films of curvature do not contribute to management decisions in back pain, and just expose one to unnecessary radiation.

MRI Scans

MRI scans of the lumbar spine can give good detailed information with regards to the following:

  • Bones
  • Discs
  • Ligaments
  • Nerves
  • Other abnormalities in this region

In reality, MRI scans are best for determining surgical or advanced conservative pain intervention.  If you have had a scan in the past, you probably wouldn’t need another one unless your physician suspects significant new changes such as cancer.

CT Scans

CT scans of the lumbar spine are very good at evaluating the bone structures, but are not as good when evaluating discs, muscles, and nerves.  They are used in cases of trauma, since a scan can be done quickly, in minutes.  CT scans are also used after surgery, or when the patient has implants that are not compatible with the magnets of an MRI scan.  These scans are also done only when significant changes are suspected and a surgery type intervention is being considered.

Rarely is imaging absolutely necessary in the management of low back pain.  Most low back pain heals rapidly with conservative treatment.  If the low back pain is not improving, then one should find a Physical Medicine and Rehabilitation specialist.