Differences between CT and MRI

With the rapid development of medical technology, CT and MRI examinations have gradually become commonly used examination methods in hospitals. These two examinations can detect the specific imaging of the lesions, so as to understand the actual situation of the patient's diseased parts and facilitate doctors to carry out targeted treatment. However, what is the difference between the two? When going to the hospital for examination, in what cases do you need to choose CT and in what cases do you need to choose MRI?

Differences between CT and MRI

In clinical medicine, CT and MRI each have their own advantages. Generally speaking, there are the following differences between the two.

Different imaging principles

CT scan uses a tube to emit X-rays to penetrate the human body. Through the detection of the detector, the X-ray decay can be observed and the changes are finally converted into image information. MRI scan first allows the patient to completely enter the magnetic field, and then a radio frequency generator sends out radio frequency pulses. The radio frequency pulses will promote various relaxation times in various parts of the human body. Finally, all the detected data are sorted out and detailed calculations are performed to obtain the required image.

Radiation levels vary

CT scans are performed by computerized tomography using X-rays, which produces a small amount of radiation. Different scanning methods produce different amounts of radiation, such as CTA (CT angiography) and plain scans, which produce different levels of radiation. In addition, different parts of the body are exposed to different amounts of radiation. MRI scans directly place the human body into a magnetic field for testing, so they do not produce radiation.

Scanning speed varies

CT examinations are fast. With the gradual improvement of the imaging speed of 64-row and 320-row spiral CT and dual-source CT, even if enhanced CT of the head, face, neck, chest and abdomen is performed at the same time, it only takes a few minutes. A 1.5T MRI takes 10 to 20 minutes to image a part. The imaging speed is relatively slow and the requirements for body position are also relatively high. In addition, an enhanced MRI requires the injection of contrast agent in advance, which takes more time. Therefore, the number of people who can undergo MRI examinations every day is limited.

Different imaging parameters

In general, the imaging parameters and high soft tissue resolution of MRI are several times stronger than those of CT, especially the contrast of soft tissue is significantly higher than that of CT, and the structure of blood vessels can be fully displayed without the help of vascular contrast agents. Therefore, it has great advantages in examining tumors, lymph nodes, blood vessels and vascular structures. In recent years, the industry has developed new imaging technologies such as susceptibility imaging (SWI), magnetic resonance perfusion imaging (PWI), magnetic resonance diffusion tensor imaging (DTI) and magnetic resonance spectroscopy (MRS) for MRI.

Different resolution

Although the soft tissue resolution of MRI is higher than that of CT, the spatial resolution of CT is stronger than that of MRI. Therefore, CT is more suitable for bone tissue and chest-related examinations such as fractures, chest examinations, stones, cervical and lumbar spine diseases. In addition, CT imaging speed is relatively fast and is suitable for coronary artery CTA examinations. MRI is more suitable for the application of spine, cranial brain and spinal cord diseases.

Suitable for different groups of people

CT examinations are suitable for a wide range of people. Generally speaking, except for pregnant women, everyone else can have it. The MRI machine is like a large magnet. People with pacemakers, metal clothing, and insulin pumps in their bodies cannot have MRI-related examinations.

Advantages of CT and MRI

Advantages of CT

CT has good density resolution and is very suitable for lung and bone imaging. It is very intuitive to detect lung lesions. In addition, CT enhanced examination can more clearly show lesions in the mediastinum and changes in lymph nodes.

Advantages of NMR

MRI has a strong soft tissue resolution, so it can show soft tissue, nerves, and spinal cord more clearly, and the soft tissue contrast of MRI is significantly higher than that of CT. MRI emits signals from hydrogen nuclei, and the content of hydrogen nuclei from different tissues is also different, and due to the characteristics of hydrogen proton movement, the final signals are different. CT examination produces density differences between different tissues based on the thickness of human tissue and the tissue's absorption rate of X-rays. Since the X-ray absorption rates between soft tissues are similar, the soft tissue contrast of CT is significantly lower than that of MRI.

Normally, MRI cardiovascular imaging does not require contrast agent enhancement, while CT examinations require the injection of contrast agents into the body in advance for display.

Choice between CT and MRI

In clinical examinations, the examination method is mainly determined based on the patient's actual condition and the disease he suffers from. There are usually three options:

(1) If there is a problem with cerebral hemorrhage, it is best to do a brain CT scan immediately, which can clearly show whether there is any bleeding in the brain. In addition, a brain CTA examination can also be done to confirm the responsible blood vessel for the bleeding.

(2) If there is a problem with cerebral infarction, an MRI of the brain can be performed, which can clearly show the location of the cerebral infarction. If it is within the window period, thrombolytic treatment can be performed immediately.

(3) Generally speaking, if there is a fracture, CT and MRI can clearly show the specific location of the fracture. However, for relatively minor and fresh fractures, MRI can more clearly show the edematous fracture site, thereby determining whether the problem is serious.

CT and MRI examinations

As two common examination methods today, they have their own advantages and disadvantages, and they target very different items. In short, MRI is more suitable for ischemic lesions, while CT is more suitable for hemorrhagic lesions. If you really can't decide which examination method to choose, it is best to see a specialist first, and then choose the appropriate examination method based on your condition and the doctor's advice.