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An MRI scan and a CT scan are two different ways of looking inside the human body, and they can give us two very different pieces of information. So, what’s the difference between them, why are they used, and how do you read an MRI and a CT scan?
We’ll cover all that and more below.
How to read MRI results
MRIs can be a challenging thing to learn to understand but let’s try together. We have created a video tutorial for how to do this, here, to go along with our explanation below or you can take a look at the normal MRI of a male Lumbar Spine, abdomen or pelvis.
Explainer Video:
Explainer Article:
An MRI (Magnetic Resonance Imaging) scan is a method of taking pictures of the inside of your body using a magnetic field. This magnetic field interacts with the particles in your body to create detailed medical images of everything from the brain to the heart to the muscles. MRI scans are painless and non-invasive, which means that they can be performed on people of all ages. The process is also very safe, as no radiation is used.
The Different views of an MRI
MRI images can be taken in three different views or orientations to try to get a 360-degree picture of you:
- Sagittal or side view
The sagittal view of the MRI scan is a cross-sectional image of the body taken from the side profile view of the body.
- Coronal or front view
The coronal view is similar to a mirror image in that the right side of your body will be on the left side of the image.
- Axial or cross-sectional view
The axial view will also have the right side of your body on the left side of the image because the images are taken from the feet to the head.
What are MRI Slices?
MRI images are taken in small sections called slices. Each slice has a relatively thin width but covers the whole area in each particular view. The width can be varied depending on how strong the magnetic field is and how detailed an image needs to be.
These slides are taken as shown in each view to create a stack of slices that is called a series of slices. These slices are what you are looking at when you scroll through the different images captured by the scan. The slices will “flow” from one side of the stack to another, as you view it in any given way.
For example, from front-to-back and back-to-front when looking in the coronal or frontal view.
Understanding Your MRI
MRIs have many elements to them, such as intensity and sequences. Once you understand these elements, reading and understanding your MRI becomes much simpler.
What is “Intensity”?
The way the magnetic field interacts with you or the way the images are taken can be changed to give radiologists a slightly different perspective of the same view of images. This is known as the intensity.
For example, in most sequences, the soft tissue organs are gray in color and considered “isointense.” Something that is brighter (more white) will be called hyperintense, and something that is darker (more black) will be called hypointense.
MRI sequences
MRI sequences are a way to determine the composition of different areas of the body.
The most common MRI sequences are called T1-weighted imaging and T2-weighted imaging.
T1-weighted images/sequences
- These are good for looking at the “anatomy” of the body. The more “water” something has, the more “black” it looks. Organs are gray or isointense.
- Common colors of body parts:
-
- Cerebrospinal fluid, cysts, swelling/edema, bone bruises: black
- Fat: white
- Organs, muscle: gray
- Bone edges, lung: black
T2-weighted images/sequences
- These are good for looking at the “pathology” of the body. The more “water” something has, the more “white” it looks. Organs are gray or isointense. Tumors, swelling, bruising, and infections are usually bright and stand out.
- Common colors of body parts:
- Cerebrospinal fluid, cysts, swelling/edema, bone bruises, fat: white
- Organs, muscle: gray
- Bone edges, lung: black
STIR images/sequences
STIR (Short Tau Inversion Recovery) images make all the fat dark or black to help see everything else better, especially fluid, infection, and injuries.
FLAIR images/sequence
FLAIR (Fluid Attenuated Inversion Recovery) images make all of the water and cerebrospinal fluid black and helps to show brain diseases as bright.
Fat-saturated images
Any sequence can have fat saturation (usually called fat sat or FS) which will make the fat black.
Our expert radiologists at Mediphany can help you understand how to read your MRI. Would you like your images explained to you in a personalized video report?
How to read a CT scan
A CT scan is a type of imaging procedure that uses X-rays to create cross-sectional images, or slices, of the body. It provides more detail than an MRI and is useful for diagnosing and treating medical conditions.
A CT scan works by taking multiple X-ray images at one time from different angles and then combining them into one image. Links below are example of
Examples of CT Scans:
Explainer Video:
Explainer Article:
The Different views of a CT
Like an MRI, the same 3 different views or orientations are used to get an accurate 360-picture of you:
- Sagittal or side view
- Coronal or front view
- Axial or cross-sectional view
What are CT Slices?
Images are taken in small sections called slices. Each slice has a thin width but covers the whole area in each particular view. The width can be varied depending upon how strong the CT scanner is and how detailed an image needs to be.
These slices are what you are looking at when you move your mouse, scroll the mouse wheel, or use the arrow keys and see the images moving. They will “flow” through the stacks of slices in whichever view you are looking at to go from one side to the other. For example, from front-to-back and back-to-front when looking in the coronal or frontal view.
How does a CT scan work?
The way the X-rays interact with your body and its different tissues will provide the different colors seen in your images and help distinguish the different parts of your body (muscle vs. bone, liver vs. kidney, etc.). The denser an object in the body is, such as bone, the brighter/whiter the object will appear on the CT scan and vice versa. The relative “color” of each part of the body is correlated with a numbering scale called the Hounsfield scale and each part of the CT image will have a corresponding Hounsfield unit.
How is the Hounsfield scale measured?
By convention, pure water is given a Hounsfield unit of 0 and everything else is determined relative to that value. Some common examples are listed below, keeping in mind that the higher the Hounsfield unit, the brighter (whiter) the object, and vice versa. The Hounsfield scale usually ranges from -1000 to +3000. Parts of the body that are similar to each other in density and/or Hounsfield unit are called isodense. A part that is darker (lower Hounsfield unit) compared to another area (usually compared to soft tissue) is called hypodense, and a part that is brighter (higher Hounsfield unit) compared to another area (usually compared to soft tissue) is called hyperdense.
Examples with corresponding Hounsfield units:
- Air = -1000
- Lung = -500
- Fat = -100
- Water = 0
- Soft tissue (organs, muscle) = 30-60
- Bone = 700+
- Metal = 1500+
With the addition of intravenous contrast (contains iodine), anything that will have blood flow to it will increase the Hounsfield unit – become more hyperdense. This is done to help radiologists see diseases such as tumors that will have increased blood flow compared to the rest of the organ.
Our top priority at Mediphany is to give you the most accurate understanding of your CT and MRI images possible. Our expert radiologists are here to help.
Our MRI reading services will give you the peace of mind and confidence in your diagnosis and treatment plan.
Ask A Radiologist
If you have a question for one of the radiologists on our team please use the form below and we will do our best to get you an answer within 24 hours, free of charge!
*Note: This is intended to be educational service, and if you are seeking medical advice, please discuss with your doctor.
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