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With the advances in science being made, we have found many different, innovative ways to take a look inside the body without using the invasive techniques we employed in the past. Gone are the days of cutting off the top of the head to peer at the brain. Now, we can use specialised scanning techniques, such as a computerised axial…
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Jetzt kostenlos anmeldenWith the advances in science being made, we have found many different, innovative ways to take a look inside the body without using the invasive techniques we employed in the past. Gone are the days of cutting off the top of the head to peer at the brain. Now, we can use specialised scanning techniques, such as a computerised axial tomography (CAT) scan or the positron emission tomography (PET) scan.
Both use different, detailed techniques to get an image of what's happening inside your body and brain.
Fig. 1: CT and PET scans are used by medical professionals and researchers.
Despite PET and CAT scans both being scanning techniques, the way they gain insight into the body's internal state is different. Both expose you to some form of radiation. Before we identify the differences between the CAT scan and PET scan, let's quickly define tomography so we know what we're talking about.
Tomography is a technique used to produce an image of a cross-section of the human body (such as the brain) using waves. These waves penetrate the tissues and create three-dimensional images of the body section, based on how easily the waves pass through these tissues.
Generally, we can think of tomography as an imaging technique.
PET scans identify functional or dysfunctional high-activity and low-activity areas of the brain and body when scanning their internal state using a radioactive tracer that behaves similarly to glucose. PET scans identify areas of function and abnormalities by monitoring the metabolic rate and activity of cells; how your brain and body tissues use oxygen and glucose.
PET scans can identify blood flow based on these parameters, and then infer function and identify potential abnormalities based on this information.
Usually, a PET scan lasts around 30 minutes, so it's not a very fast scanning technique.
Before a PET scan, a doctor injects a tracing radioactive dye (called a radiotracer) into your arm, which is then absorbed into the bloodstream. It can take up to an hour for the dye to circulate to the right cells, significantly increasing the time needed for the procedure.
The radiotracer has a very similar structure to glucose, so when the body comes into contact with it, it treats it the same way. Glucose, as you know, is a form of sugar your body uses as fuel. Once an hour has passed, patients will enter the PET scanner, a tube-like machine which takes close to another hour to conduct.
The radiotracer gives off energy in the form of gamma rays which the PET scanner can detect. When dye builds up in a particular area, we can make educated assumptions about what functions and potential abnormalities are happening in those areas.
The dye used can change depending on what the technicians are trying to identify in your body. For instance, fluorodeoxysorbital (FDS) is one of the common dyes used, and it detects bacterial abnormalities, whereas another dye called Gallium-68 dotatate is used to detect neuroendocrine tumours.
These show up on scans/images as hot or cold areas:
Suppose one part of the brain is using more of the dye (believing it is glucose) during a memory task; we can assume that that area is related functionally to memory, as more blood is flowing to the area to fuel the activity. It will show up as red in comparison to other regions.
PET scans are used in cases of cancer. When someone has been confirmed to have cancer, their cancerous cells tend to consume more glucose than healthy cells. When it comes into contact with the dye, we can detect this activity with a PET scan.
It can help us identify certain disorders or diseases within the brain. Have a look at this PET scan of a healthy patient compared to a patient with Alzheimer's disease.
Fig. 2: PET scans reveal information on a healthy versus unhealthy brain.
We can see many active areas of the brain showing up red in the normal brain patient, but a lot of low activity, blue areas in the Alzheimer's patient, showing how the disease has affected the brain and its functions.
Raine et al. (1997) used a PET scan to identify brain abnormalities in murderers and found that they indeed did have lower activity in areas associated with controlling aggressive behaviours (such as the prefrontal cortex).
CAT scans use X-rays to create detailed images of the internal state of the body and brain. They can be used in conjunction with PET scans. A CAT scan can identify the differences between the various tissues, showing bone, soft tissues, and other internal structures.
CAT scans may also be referred to as CT scans, as they are the same thing. Most people now call CAT scans CT scans
Usually, a CAT scan lasts for around 10 to 20 minutes, although it can be as long as an hour if necessary.
A CAT scan works by sending x-ray beams through your body to capture an image of what's going on inside of you. The X-ray takes images from many different angles and produces cross-sections of images, known as slices. The computer then combines these angles and sections to provide a detailed image of the area of the body you're scanning.
As we mentioned above, a contrast dye can aid this process, although it is not required. The images are usually given in black and white, so dyes increase the contrast and resolution of the images. Overall, a CAT scan provides more detailed images than a normal X-ray.
CAT scans are used to identify disorders of the muscle and bone and detect other conditions such as cancer, heart disease, and so on. They can be used to monitor the progress of these diseases, identifying if the treatment is helping.
For example, if you have a tumour in your bone, a CAT scan can identify this and help diagnose the issue. It can identify the location of the tumour and then guide surgeons when operating to remove it, as it provides a detailed image of what is happening internally.
The image below depicts a CAT scan (CT scan) of a human brain. As you can see, it shows the different layers of the brain going from the base of the skull to the top.
Fig. 3: CT scan images of the human brain reveal information on the organ.
As we can see, the CAT and PET scan differences are quite evident in the two example photos we have given in the respective sections. Let's explore the differences between the two scanning techniques further.
CAT and PET scans produce different images and provide different functions, as a result. CAT scans differ from PET scans in a few ways, most notably in their use of X-rays to create images of the body and brain, although they may use a dye to gain more detail in their computerised images. Mainly, PET scans provide insight into brain and body function and possible sources of dysfunction, and CAT scans can identify areas of dysfunction by locating abnormalities.
CAT scans are usually faster than PET scans overall.
Fig. 4: Here we can see a composite of images resulting from brain scans using a.) CT, b.) PET, and c.) fMRI¹.
PET scans provide helpful information, but the technique has its issues.
First, let's explore the pros of PET scans.
Now, let's examine the cons of PET scans.
CAT scans provide helpful information, but the technique also has its issues.
First, let's highlight some of the pros of CAT scans.
Now, the cons of CAT scans.
A PET scan and a CAT scan can be combined to produce an even more detailed image of what's occurring internally.
A PET scan uses a tracing radioactive dye that requires one hour wait time to circulate around the body. The PET scan detects gamma rays emitted from this dye, creating an image of functional/dysfunctional areas based on the accumulation of this dye in high blood flow areas of the body and brain, indicating increased activity.
CAT scans use X-ray beams to create images of the body and brain (although they can also use a dye to increase the detail of their images). This happens at different angles to produce cross-sections of images, known as slices, combined into a computerised image. They do not require the dye.
Positron Emission Tomography (PET) scans and Computerised Axial Tomography (CAT) scans, also known as CT scans, are techniques used to assess and produce images of the internal state of the body and brain.
A PET scan and a CAT scan can be combined to produce an even more detailed image of what's occurring internally in the body.
CAT scans show a detailed, black and white image of the internal state of the body and brain. PET scans show functional areas of the body and brain by highlighting high activity areas in red/yellow, and low activity areas in blue/green.
Technically, PET scans provide more accurate information than CAT scans, as they show cellular activity within the tissues being analysed, which shows function/dysfunction. One of the most common dyes, fluorodeoxysorbital (FDS), is very similar to glucose and is treated as such in the body. Cancerous cells, for example, use more glucose than healthy cells, so more dye will accumulate in cancerous cells, which is detectable earlier than CAT scans.
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