[Fat Bear Science] Why do we need to do CT or MRI after color Doppler ultrasound to diagnose some diseases? Can't one test do the job?

Doctor, I have a lot of lumps on my neck!

Go get a checkup first!

What tests do I need?

I need to have a blood test and then make an appointment for a CT scan and color ultrasound!

Why do we need to do color Doppler ultrasound after doing CT scan? Isn't that a duplicate examination?

Many patients are confused when they see the application form issued by the doctor. Why does the doctor issue two application forms for examinations? Is it an overcharge?

Coincidentally, these two days, Mr. Wang, 53, found that his waist hurt a lot after he got up. It got better after half an hour, but the waist pain reappeared after he got up the next day. He was worried and went to the hospital for a check-up.

Orthopedic doctors believe that there are many causes of low back pain, the most common of which are lumbar trauma, lumbar disc herniation, lumbar fracture, ankylosing spondylitis, etc. In orthopedic clinics, doctors often prescribe some radiological examinations for patients, mainly three types: X-ray examination, CT scan and magnetic resonance imaging (MRI). So, the question is, "Doctor, if I have a problem with my waist, which examination should I choose?"

Today, let’s talk about inspections.

Expert Profile

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Zhang Jiuquan

Director of the Department of Imaging, Affiliated Cancer Hospital of Chongqing University, Doctor of Medicine, Master's Supervisor, Associate Chief Physician, Associate Professor.

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Chen Pei

Nurse of the Ultrasound Medicine Department of the Affiliated Cancer Hospital of Chongqing University, leader of the hospital infection control group, and deputy leader of the nursing group.

She is good at nursing work such as ultrasound angiography and ultrasound interventional treatment.

Why is it necessary to do both color Doppler ultrasound and CT scan for thyroid examination?

Color Doppler ultrasound and CT are both imaging examinations. With the rapid development of medical imaging technology, both have their own strengths in diagnosing diseases. However, because the diagnostic principles of CT and color doppler ultrasound are different, they are two different examination methods:

CT scans human tissues through the use of radiation, and examines solid organs and bones such as the brain, chest, and abdomen. The advantages are clear, comprehensive, and cross-sectional imaging; the disadvantages are that there is a small amount of radiation, and it is not suitable for pregnant women. The price is higher than that of color Doppler ultrasound.

Color Doppler ultrasound uses modern technology to convert Doppler signals into color signals, and superimposes them with two-dimensional black and white sound and image images to achieve color blood flow imaging. As an important part of imaging diagnosis technology, ultrasound diagnosis technology has advantages over CT and magnetic resonance imaging. It can combine Doppler technology to monitor blood flow and direction, determine whether there are tumor lesions inside the organs and the blood supply status inside the tumor. In addition, in terms of cardiovascular, it can monitor hemodynamic changes in real time, determine blood flow speed and direction, etc., and has obvious advantages for congenital heart disease and vascular obstructive diseases. As a visual stethoscope for clinicians, color Doppler ultrasound can provide real-time guidance for clinicians at any time. Its advantages are convenience, safety, real-time, dynamic, radiation-free (can be used for pregnant women), and low price; its disadvantage is that it is easily affected by factors such as chest and abdominal gas and bones.

For example, when a patient with liver disease is found to have elevated alpha-fetoprotein, the doctor will usually issue an application for CT and color Doppler ultrasound at the same time. Why? Because with the improvement of technology, color Doppler ultrasound can not only detect small lesions inside the liver, but also clearly show the shape and location of the lesions and whether there are cancer thrombi in the hepatic vein or portal vein; while CT examination has a high spatial resolution and can detect tiny lesions with a diameter of about 1.0 cm, and the nature of the lesions can be determined by the enhancement pattern of the lesions.

However, as mentioned earlier, because color ultrasound and CT have different imaging methods and principles, the diagnostic information obtained may also be different. So which examination should clinicians believe in?

For example, color Doppler ultrasound found a high-echo lesion with a diameter of 8mm in the liver. Combined with the ultrasound manifestation of the lesion, it is likely to be a hemangioma. However, the patient is also a hepatitis B patient with a family history of liver cancer, so the clinician will be more cautious about the diagnosis of hemangioma. At this time, a CT enhanced scan is needed to determine whether it is a hemangioma based on the enhancement pattern of the nodule. This is why sometimes more than two imaging diagnoses are needed to make a clear diagnosis of the disease.

Let's go back to the beginning of the article. When a patient visits a doctor for a tumor in the front of the neck, the doctor usually prescribes a color Doppler ultrasound examination of the neck. The color Doppler ultrasound indicates a mass in the thyroid gland, and combined with the characteristics of the ultrasound, it is diagnosed as possible thyroid cancer. However, because the patient has many masses and the masses are large when palpated, the doctor will also prescribe a neck CT examination for the patient. Although the CT examination is not as sensitive as the color Doppler ultrasound for diagnosing thyroid tumors, due to the extremely high spatial resolution of CT, this can make up for the shortcomings of the color Doppler ultrasound that cannot fully explore, thereby accurately judging the range of tumor infiltration, etc.

All kinds of imaging examinations have their advantages and disadvantages. Only by grasping the advantages of various examinations, learning from each other's strengths and weaknesses, and finally providing doctors with more comprehensive information based on comprehensive information, can we provide important basis for subsequent diagnosis and treatment. Never think that the doctor has prescribed too many examinations for you!

For lower back pain, should I take an X-ray, CT scan or MRI?

Doctor, I have a problem with my waist. Which examination should I choose?

I believe that everyone is familiar with X-ray examinations. This type of examination is often the first choice for preliminary examinations because of its advantages of being quick, intuitive, and inexpensive. Lumbar X-ray examinations can be divided into lateral, hyperextension, hyperflexion, and bi-oblique positions. They are mainly used to observe the bone condition of the lumbar spine (such as lumbar fractures, lumbar tumors, spondylolysis, etc.) and the structure of the lumbar spine (such as changes in curvature, vertebral displacement or slippage, etc.). However, because X-ray examinations have their limitations, orthopedic doctors often recommend further examinations, such as CT or MRI.

CT examination is similar to X-ray examination in nature, but CT equipment can scan the human body 360 degrees without blind spots. Lumbar CT examination mainly observes the cross-section of the lumbar spine to understand the bone condition of the lumbar spine, the condition of the intervertebral disc protrusion, the condition of the intervertebral joints, etc. In addition, lumbar CT examination has two advantages.

First, CT scanning can achieve thin-layer reconstruction and decompose the cross-section of the lumbar spine into hundreds of images, which can better see small lesions, especially tiny fractures.

Second, after the scan is completed, the lumbar spine image can be reconstructed into a sagittal or coronal plane through image post-processing methods, and the lumbar spine image can be observed from different angles in multiple planes.

Doctor, is it enough to just do a lumbar spine CT scan and no other tests are needed?

This is not the correct understanding. Let me introduce the characteristics of lumbar spine magnetic resonance imaging.

Since magnetic resonance imaging has a high resolution for soft tissue imaging, lumbar MRI is better than lumbar CT in soft tissue imaging. Lumbar MRI can well observe the condition of the lumbar intervertebral disc. It can clearly show the morphology of the intervertebral disc and its relationship with the surrounding tissues such as the dura mater sac and nerve roots by comparing the cross-sectional images of the intervertebral disc with the sagittal images. It also has advantages in spinal cord lesions, inflammatory lesions, hemorrhagic lesions and lumbar muscle lesions. In addition, magnetic resonance imaging does not involve X-ray radiation, so it is a safer and more reliable examination. It is very good, but it has a disadvantage, which is that it is expensive.

Doctor, are there any contraindications for these tests? Can they be done at any time?

X-ray examination, CT examination, and MRI examination also have their corresponding contraindications. Let’s talk about CT first.

During CT examination, because X-rays cannot penetrate metal objects, obvious artifacts will be produced around metal objects. Therefore, patients who have had steel nails or plates inserted in their lumbar spine are not recommended to have lumbar CT as their first choice. As an examination with X-ray radiation, lumbar CT is also not recommended for pregnant women and children.

As for magnetic resonance imaging, since the examination is conducted in a huge magnetic field, patients with a history of metal implants (iron, cobalt, and nickel) must inform the doctor on duty before the examination and clarify the specific material composition of the implant. Lumbar magnetic resonance imaging is prohibited without knowing the surgical materials. In addition, since the aperture of magnetic resonance imaging machines is generally not very large, lumbar MRI is not recommended for patients with claustrophobia.

In summary, the three examinations of lumbar spine, X-ray, CT and MRI, cannot replace each other. Whether it is lumbar spine X-ray, CT or MRI, these three examinations have their own advantages and disadvantages. When seeing a doctor, the doctor needs to conduct a physical examination and combine the clinical symptoms to select the most appropriate corresponding examination for the patient.

Text/Fat Bear Photos/Partially from the Internet (Please contact us to delete if there is any infringement) Review/Department of Imaging and Department of Ultrasound Medicine

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