How to Read a CT Scan

Most of us have had a medical scan of some sort at some point in our lives. They’re used for everything from diagnosing acute illnesses, to replacements to invasive surgeries.

But what are the doctors and nurses actually looking at? how can they see the problem in that mess of black and white blobs? Well, today we’re going to learn how to understand what’s going on in those scans so you can identify and understand your own scans.

Before beginning, you should familiarise yourself with the anatomical planes by reading this article first.

CT Scan of the Lumbar Spine

The basic concept behind a CT Scan is that it can break the body into slices, like a loaf of bread that’s been sliced, revealing the inside of the loaf, the same applies to the body in a CT Scan. During the scan, the medical image will configure the scanner to only scan the desired area of the body. this will reduce the radiation dose to the patient. The scanner will then take a series of images that make up the slices, and then compile them into a black and white image that can be interpreted by the doctors.

To understand the scan, it is important to understand the anatomy of what we are looking at. In the case of the scan on the left, we are looking at a sagittal section of a lumbar spine. We can identify the body structures by their density, in this case, the brighter, or whiter the object, the denser it is. So the large white areas correspond to the bones of the spine. The grey area in the middle of the white areas is the spinal chord, and the vertical grey line on the left of the bones is the Aorta, or the major blood vessel that distributes blood throughout the body from the heart.

Identifying problems on the scan means interpreting and comparing what you see on the scan to your knowledge of the human anatomy, and what is considered normal for the patient. If you would like to understand the problems with this scan, you can read the case study here for a full explanation.

3D Reconstruction of Lumbar Spine

Because a CT Scan divides the body into slices, we can recombine those slices, using some fancy computer technology to reconstruct a virtual copy of the inside of the body so that doctors can better understand the internal structures and their relative positions. in this example, the above CT Scan of the lumbar spine has been reconstructed into a 3D model of showing the bones of the spine.

STEP ONE: Orientation

It is important when viewing a CT scan, particularly a physical printout, that you view the images in the correct orientation. There a few checks you can do to ensure you have the images orientated correctly, the most simple of which is the read the writing around the images. If they are backward or upside down, you have the scans the wrong way around. Another method is to look for the orientation markers that may sometimes accompany the scans. These will be either a capital L or R on one of the sides of the scan. these correspond to the left and right sides of the image relative to the patient.

STEP TWO: Identify Structures

The next step when viewing a CT Scan is to identify landmarks in the body that will assist you in orienting yourself to the images you are viewing. You can do this by examining all the images for a “wide shot” image that will lay out the location of the rest of the images. Once you have this worked out, you can move on the more detailed images. you should begin by identifying the bones that b=may be visible in the scan, these will be the brightest or whitest areas of the scan. Next, you need to identify the surrounding tissues and what they are likely to be. Muscle will appear as a neutral grey colour, while hollow spaces such as gasses will be black.

STEP THREE: Primary Scan

Now comes the fun part, meticulously looking through all the various areas of the image to find anything out of the ordinary. This is the point where a trained eye is essential in locating and identifying abnormal images. A trained radiographer or doctor will look for minute details in the connective tissues, muscle layers, bony structures and blood vessels. Unfortunately t this point it is difficult for the untrained person to understand what they are looking at and how to interpret the finer details of a CT image.

Reminder: Always remember, if you find something suspicious, consult your doctor or Always remember, if you find something suspicious, consult your doctor or healthcare professional. Do not make any decisions about your treatment based on your own evaluation of a scan. This article is intended to give you a better understanding of how CT scans work, and what it is you’re looking at, you will need years of experience and training to be able to accurately diagnose medical conditions based on a scan.


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