MRI Or CT - What's the Difference?
differences
MRI
The difference between magnetic resonance tomography (MRT) or also known as magnetic resonance tomography and computed tomography (CT) lies, in addition to the respective field of application (different indications), above all in the physical basis or the functionality.
The MRI works - unlike the CT - as an X-ray independent examination method with strong magnetic fields as well as with electromagnetic waves and thereby creates very detailed Sectional images of the body or individual body parts or organs in any plane.
There is therefore no radiation exposure during an MRI examination.
The electromagnetic waves that are emitted by the MRI machine lead to Changes in position of protons in the body tissue, which fall back into a state of rest after switching off the waves. Signals are sent that are recorded by a coil in the device and converted into sectional images by a computer.
The patient lies as quietly as possible on his back on an examination table that is pushed into the cylindrical MRT device.
Depending on the proton content of the different types of body tissue, signals of different strengths also arise, so that information about the type of tissue, the tissue composition and also about possible tissue changes can be obtained.
In general, the MRI is suitable for Representation of almost all types of tissue in the body, however, the focus in diagnostics is on imaging Soft tissue (e.g. internal organs) and the central nervous system (brain and Spinal cord), less in the bony representation (Skeletal system).
A special form is that MR angiography, which are specially designed for the exact representation of the Vascular system serves.
Read more about the topic here Angiography
An MRI examination takes an average of 15-20 minutes, depending on the area of the body to be examined and the additional effort required from special preparations or the administration of Contrast media Etc.
Computed Tomography
In contrast, that works CT With X-rayswhich - unlike a conventional X-ray image - not only x-ray the patient from one direction, but are "scanned" from all directions by the tubular CT device, so that at the end a high-resolution cross-sectional image of the respective body area is created (CT determines "only" Cross-sectional images, MRT can take images in any plane).
During a CT examination, the patient is exposed to radiation.
During the examination, the patient lies on a couch in the supine position as calmly as possible in the CT device, while the device rotates in layers around the patient.
The principle of imaging is identical to the one conventional radiograph: the X-rays shine through the body, are - depending on the particular tissue they hit - absorbed or reflected to different degrees and then calculated by a computer to form a sectional view.
The examination usually only takes a few minutes (often only up to 10 minutes), depending on the part of the body being examined and the administration of a contrast agent that may be necessary.
The field of application of CT is - like MRI - broad, both bony structures, as well as Soft tissue can be represented, the former a better display quality in the CT finds than in the MRI.
What is better?
When asked which examination method is better than the other, can no blanket answer given, since both MRI and CT have their clear advantages and disadvantages depending on the question.
E.g. be recorded that the MRI with radiation-free magnetic fields works, but the CT does radiation-exposing x-raysso that the indication must be made precisely in order to be able to decide which procedure is more suitable (e.g. Avoiding harmful X-rays on CT in pregnant women).
Furthermore, a preference for an examination method is also dependent on the Questionthat is hidden behind the imaging: the MRI is particularly suitable for Soft tissue imaging, the CT especially for imaging bony structures. Depending on the question, one or the other method is the better choice.
An economic aspect can also play a role in the answer to the question “What is better?”: An MRT examination is usually much more expensive than a CT examination, so that costs can be saved if the desired structure is displayed be possible in both procedures.
MRI or CT of the head - which is better?
The question of whether an MRI or a CT is better for an examination of the head cannot be answered in general, but depends on the medical question.
In the vast majority of cases, an MRI scan is more informative. The brain in particular can be assessed much better with this examination.
For example, a stroke caused by a circulatory disorder shows up much earlier on an MRI than on a CT scan.
A stroke due to cerebral hemorrhage, on the other hand, can be detected early using CT.
Certain forms of cerebral haemorrhage can even be identified much better with CT than with MRI.
MRI is more suitable for assessing the remaining soft tissues of the head.
However, in some respects CT is clearly superior to MRI, so that in many cases the CT examination is justified as the method of choice. While an MRI takes 15-20 minutes, a CT can be performed in just a few seconds.
This aspect is particularly important in emergency situations, so that, for example, a CT of the head is definitely preferable to an MRI after an accident. This is supported by the further advantage that the CT shows bony structures better than the MRI. In order to determine or rule out injuries to the skull and facial bones, for example after a traffic accident, a CT is better than an MRI.
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MRI or CT scan of the lungs - which is better?
CT is preferable to MRI for imaging studies of the lungs.
Changes, lung tumors or metastases can usually be visualized well. In the case of a pulmonary embolism (blockage of a pulmonary artery by a dissolved blood clot), CT imaging of the lungs is the method of choice.
An MRI examination can only be used if there is an intolerance to contrast media. Basically, however, it should be noted that imaging of the lungs (regardless of whether it is a CT or MRT) requires a justified indication and should not be done for every possible lung disease. In many cases, simpler examinations such as an X-ray or ultrasound are sufficient and sometimes even more informative.
Any abnormalities found in the X-ray can, if necessary, be further clarified with a subsequent CT examination.
Read more on the topic: MRI of the lungs
MRI or CT of the abdomen - which is better?
There is no general answer to whether an MRI or a CT scan of the abdomen is better. Depending on the indication or question, one examination method can be superior to the other or both are to be regarded as equivalent.
For a general examination, for example to find out whether a tumor disease has already spread to other organs (staging examination), CT is more suitable.
In contrast, MRI is preferred for the precise depiction of liver changes.
The representation of the biliary tract and pancreas is also more precise in the MRI.
For a targeted examination of changes or masses of the kidney, a CT is usually preferred.
An exception is the representation of the renal blood vessels. For this, the MRI vessel representation (MRT angiography) is the method of choice.
When examining organs in the pelvis such as the bladder, prostate or rectum, MRI is also preferred.
Abdominal wall defects (hernias) can also be seen better on MRI than on CT. In this case, however, a good physical examination and possibly an ultrasound are usually sufficient and complex imaging such as MRI can be dispensed with.
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MRI or CT of the cervical spine - which is better?
Whether an examination of the cervical spine should be carried out using CT or MRI depends on the question.
If there is a suspicion that a bony injury may be present, for example after a traffic accident, a CT examination should be performed. This is the best way to detect or exclude broken bones.
For all other questions that require precise imaging of the cervical spine, MRI is preferred. If there is a herniated disc in this area of the spine, an MRI should be performed instead of a CT. Because of the overlapping of the shoulders, the imaging of the intervertebral discs by the CT is often difficult.
Read more on the topic: MRI of the cervical spine
MRI or CT of the lumbar spine - which is better?
Imaging of the lumbar spine should generally only be carried out under strict indications.
If, for example, there is a well-founded suspicion that a herniated disc may be present, this can be confirmed or rejected by both an MRI and a CT scan. Which examination should be carried out depends on the accompanying circumstances.
A CT examination can usually be reached and carried out more quickly. However, especially in younger patients, due to the radiation exposure, CT should be avoided and MRI should be preferred. An MRI should also be preferred in patients who have already had surgery for a herniated disc and who develop symptoms again.
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MRI or CT of the heart - which is better?
The heart consists mainly of muscle tissue, which is why an MRI is much more suitable for imaging than a CT in most cases.
Even three-dimensional images can be generated using MRT images of all levels. This provides information about the size of the heart, the thickness of the heart walls and the structure of the heart valves, for example.
However, an MRI scan of the heart is only indicated in rare cases. There were other examination methods available, such as ultrasound, which were sufficient for the respective question or even more informative than MRI.
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MRI or CT scan for a herniated disc
Both MRI and CT are suitable for examining whether a patient has a herniated disc.
The MRI examination is only superior in the area of the lower cervical spine, since the CT is often more difficult to assess due to the overlapping of bones.
In principle, imaging of the spine should only be carried out if there is justified suspicion of a structural disease such as a herniated disc.
Before doing this, the doctor should conduct a detailed interview and physical examination.
A severe herniated disc sometimes causes symptoms of paralysis in addition to pain and abnormal sensations in an arm or leg.
In such a case, imaging by means of CT should be carried out as soon as possible, as this examination can be carried out more quickly and more easily than an MRI.
If only back pain is present, no imaging should be performed, but movement and, if necessary, special exercises should be prescribed.
However, there is also an indication where an MRI is justified and also better than CT. If a patient has had a herniated disc that has already been operated on and pain returns over time, an MRI can be used to differentiate whether the pain is caused by another herniated disc or by scarred changes.
Read more on the topic: MRI for a herniated disc
MRI or CT scan for a brain tumor
In most cases, a brain tumor can be identified by both MRI and CT.
However, for a soft organ like the brain, MRI is superior in imaging.
The spread and delimitation of the tumor can often be shown well by this examination, which is of great importance in particular for the planning of the therapy (surgery or radiation).
In most cases, the MRI scan is performed with the simultaneous administration of a contrast medium through a venous access on the arm. Based on the accumulation behavior of the brain tumor, further important findings for diagnosis and therapy can be obtained.
MRI or CT scan for bleeding in the brain
If a patient is suspected of having a cerebral hemorrhage, imaging is necessary as soon as possible.
There are several reasons why CT is preferable to MRI.
On the one hand, the CT examination takes only a few seconds to minutes, while an MRI takes significantly longer and any necessary therapy would be delayed.
On the other hand, fresh cerebral hemorrhages can be seen much better with CT than with MRI. Even small bleeding can be recognized by the doctor who has been diagnosed with the CT and the source of the bleeding can often be determined immediately.
Learn more about the MRI for a stroke.
MRI or CT scan for headaches
In the case of a headache, imaging by means of MRI or CT should not be performed straight away.
In most cases, other methods can help diagnose the cause of the headache.
This primarily includes the medical consultation. Depending on the type of headache, accompanying symptoms or triggers, the type can often differentiate what the possible cause is and recommend therapy.
An MRI scan can only be considered if the doctor suspects that a brain disease is responsible for the headache, for example due to other symptoms such as abnormal sensations in the arms or legs.
An exception is a sudden, extremely severe headache that has never been felt before. One also speaks of an annihilation headache. This may be a sign of bleeding in the brain, which is best detected or ruled out with a CT scan as soon as possible.
Contrast media
The Contrast media in X-ray diagnostics, and thus also in CT, are usually either Contains iodine or barium sulfate, but there are also heavy noble gases (non-radioactive xenon), gaseous carbon dioxide , simple air or Mannitol solutions used, depending on which body region or which structures are to be displayed in the imaging.
In the MRI examination, iodine-free contrast media are used in principle back (no risk of allergic reaction): the most common use Agents containing gadolinium, manganese or iron oxide.
Advantages and disadvantages
The advantages of an MRT examination are primarily the lack of radiation exposure, the possibility of three-dimensional imaging, a high-quality display of soft tissue and a low level of dependency on the examiner as well as good reproducibility of the examination results.
The disadvantages of an MRI examination, on the other hand, are the high cost and time required, the more frequent occurrence of artifacts in imaging in contrast to CT, the susceptibility of the device and the imaging to metallic objects (absolute contraindication: pacemaker), the narrow tube, the Claustrophobia can trigger, the risk of blurring and the volume generated by the knocking noises of the device.
The advantages of a CT examination are the good resolution, the wide availability, the lower costs (in contrast to MRT) and the shorter examination time.
The disadvantages of the CT examination are almost limited to the radiation exposure that occurs (absolute contraindication: pregnancy).
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Differences in costs
Both MRI and CT are very expensive examinations, since the technical devices are very expensive to purchase and operate. The MRI is fundamentally more expensive than a CT, which is partly due to the lower availability and the greater examination effort.
The costs for a CT examination are calculated according to the doctors' fee schedule (GOÄ), whereby they depend on the body region shown and only cover the pure technical imaging, but not the associated advice and any additions such as e.g. the administration of contrast media.
The CT scan of the abdomen costs around € 151.55, that of the chest € 134.06 and that of the head € 116.57.
The MRI examination is also calculated according to the GOÄ and depends on the part of the body to be examined: an MRI of the abdomen, pelvis and head costs - without advice and additional costs - € 256, 46, an MRI of the chest area € 250.64 and the spine € 244.81.
It should be noted that the calculation according to the GOÄ only applies to private patients, the costs for the examination of statutory health insurance patients, on the other hand, are calculated according to the uniform assessment standard (EBM) and are usually somewhat lower.
If there is a justifiable indication for the MRI or CT examination, the costs are in most cases covered by the respective health insurance companies.
Read more on the subject at: Cost of an MRI examination.
