CT SCAN vs. MRI

Comparison between working principles of MRI and CT scan

CT Scan vs MRI – Computed tomography diagnostic imaging procedures use X-rays. These radiations are directed at the patient’s target organ or tissue from multiple orientations. The transducer transmits this information to a computer workstation where the slides are overlapped to form pictures of the tissues. 

Magnetic resonance imaging employs magnetic waves generated from solid magnets. These magnetic waves are projected on the patient’s body, which causes proton stimulation. As the radio waves are turned off, the resulting proton realigns with the magnetic fields and is detected by the MRI sensors. The information is transmitted to the computer system to generate pictures of the internal tissues and organs of the body.

CT scans and MRIs- Similarities

CT scans and MRI, both are medical diagnostic imaging procedures, that generate detailed three-dimensional anatomical pictures. Both of these non-invasive tests diagnose, detect, monitor, or treat a disease or injury. The basic principle behind both of the imaging techniques is more or less similar in the way that both of these require some radiations (in the case of CT scans, these are X- rays, and for MRI, these radiations are magnetic waves) that are directed on patient’s body and signals are received by a detector or transducer which transmits the information to a computer workstation, resulting in readable images.

The Mechanism Behind CT Scan 

In a CT scan, ionizing radiations are directed at the target internal organ of the body through different angles. The signals are detected with a built-in electronic detector which measures the resulting pattern of densities along a series of linear paths and transmits these signals to produce images. This technique involves scanning a particular organ or tissue of the body; hence, it is called a CT scan or computerized axial tomography.

 What does a CT Scan Show?

 CT scan is a better option when we need to detect the following problems;

1. 1. Bone deformities
2. 2. Joint problems
3. 3. Bone tumors
4. 4. Complex bone fractures 
5. 5. Cancer
6. 6. Emphysema
7. 7. Heart disease
8. 8. Liver masses
9. 9. Internal injuries (bleeding)
10. 10. Blood vessels or blood clotting
11.  

What does an MRI show?

Doctors recommend MRI when soft tissues of the body need to be examined in contrast to the surrounding tissue. MRI provides detailed information on soft tissues, which include, 

1. 1. Brain
2. 2. Tendons
3. 3. Muscles
4. 4. Ligaments
5. 5. Nerves
6. 6. Spinal cord

Instrumentation of a CT Scan

A CT scan device consists of a scanner, a table on which the patient is laid down, an X-ray machine, and a computer workstation to which the central CT is connected.

1. 1. CT Scanner- large doughnut-shaped structure in which a patient’s table goes in and out for scanning. 
2. 2. Patient table- It is a bed on which a patient is laid down, and this table moves inside the scanner. 
3. 3. X-ray tube – The X-ray tube converts electrical energy into photons. The X-ray beams are directed at the patient’s body while the tube is rotated around the table accordingly, targeting a particular tissue or organ.
4. 4. Detector – It is a built-in device of a CT scanner located at the lower half of the scanner. It captures the reflected X-rays from the patient’s body.
5. 5. Computer system- The signals are transmitted to the computer and converted into readable black and white pictures. Each image obtained in a CT scan represents a series of slices of the targeted tissue’s anatomy.
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Instrumentation of an MRI 

MRI instrumentation is the essential aspect of the generation of MRI images. Major instrumentation components include, 

1. 1. Magnetic system 
2. 2. Gradient system
3. 3. Computer system
4. 4. Radiofrequency system
5. 5. Data acquisition system
6.  

DICOM: It is the international standard used in medical imaging to process data. This system is involved in transmitting, storing, retrieving, and processing information.

Magnet:  It is a built-in component of a scanner. It provides a magnetic field throughout the process. 

Amplifier: It is the power supply that provides the gradient axis current. 

Four aspects involved in the assessment of gradient system performance are:

1. 1. Maximum gradient strength
2. 2. Slew rate or rise time
3. 3. Duty cycle
4. 4. Techniques to compensate for eddy currents produced during MRI
5.  

RF transmitter system:  RF transmitter system generates and broadcasts the RF pulses for the excitation of protons.

5 Benefits of MRI Over CT Scan

1. 1. MRIs use magnetic waves, and CT scan uses ionizing radiations, which are harmful penetrating radiations and can cause cancer if exposed repeatedly. 
2. 2. MRI can be employed to generate internal images of joints, head, legs, abdomen, etc.
3. 3. For scanning soft tissues, MRI provides more apparent contrast than CT scans
4. 4. MRI provides information on the internal soft tissues that CT scans cannot.
5. 5. To obtain pictures of herniated discs and torn ligaments, MRI is the preferred option.
6.  

CT scan and associated risk factors

A computed tomography procedure is not a painful diagnostic test. However, it may be risky for some people or under some conditions. 

1. 1. Risk to unborn babies: Although the radiations of CT scans are of a shallow dose, that does not harm humans. However, if a woman is pregnant, she might inform her doctor of her so that her doctor can recommend alternative diagnostic techniques like magnetic resonance imaging or ultrasound because ionizing radiations are more harmful to unborn babies than magnetic radiations and ultrasonic waves.

2. 2. Exposure to radiations: CT scan imaging involves brief exposure to ionizing radiations. In a CT scan, detailed information about a target tissue is obtained from different angles. Therefore, CT involves a comparatively high dose of ionizing radiation than standard X- rays. Since your body is exposed to a high dose of ionizing radiation, frequent CT scans may lead to cancer.
3.  

Experts in this field chose a minimal radiation dose to get information about the target tissue. 

3. 3. Reactions to contrast material: In some instances, your doctor may recommend that you receive a special dye called contrast material. Contrast material is a special dye. Certain patients are asked to drink it before the CT scan, and it can be inserted into the rectum before the procedure or injected into veins according to the part examined. 
4.  

Risks associated with MRI

Magnetic resonance images are obtained without ionizing radiation, which is harmful radiation. MRI uses magnetic waves instead. However, a magnetic resonance environment constitutes radiofrequency energy, a pulsed magnetic field, and static magnetic field. Each of these constituents has some specific health concerns, which include,

1. 1. Magnetic field: Static and strong magnetic solid fields attract metallic objects, such as keys, cell phones, and large items like floor buffers and oxygen tanks. If these objects become projectile and come into the MR environment, they may cause injury to the medical practitioners or patients. Hence, It is essential to screen people and objects entering the MRI room, to ensure that the MR environment is free of magnetic objects.

2. 2. Pulsed magnetic field: It is the magnetic field that alters with time. These altering magnetic fields result in unbearable loud noises, and if the practitioners or patients are not equipped with adequate noise-canceling devices, it may lead to hearing problems. Other concerns associated with pulsed magnetic fields are twitching sensations due to nerves or peripheral muscle stimulation. 

3. 3. Radiofrequency energy: The energy generated during the MRI process is relatively high that it causes heating of the body, and during lengthy MRI procedures, the heating effect is much higher.

4. 4. People with implants, artificial joints, intrauterine devices, pacemakers, etc., are not allowed for MRI because they have metallic substances which will become projectile for MR.

Which is cheaper, MRI or CT scan?

The cost of an MRI is more than a CT scan. MRI and computed tomography (CT) are diagnostic imaging procedures, MRI is based on magnetic radiation, and CT scan works through ionizing radiations. However, MRI is costlier than a CT scan as the price of an MRI is more or less double that of a CT scan. On average, CT scans cost around ₹ 3000, while MRI costs you around ₹ 6500.

Frequently Asked Questions

Which is better, MRI or CT scan?

Both techniques possess their significance, but when it comes to safety, MRI is safer than CT scans as in MRI, we are not exposed to high ionising radiation. These can lead to cancer. 

• 1. If you are considering money over safety, we can say MRI is relatively costlier than a CT scan. 
• 2. For pregnant ladies, it is advised to get an alternative for CT scans as these 
• 3.If a doctor wants to examine blood vessels, blood clotting, and complex parts of the body like bones and joints, he will ask for a CT scan over MRI
• 4. If a doctor wants to examine brain tissues, soft tissue contrast like fats, muscles, etc., she will ask for MRI rather than a CT scan
• 5. If time is your concern, a CT scan takes less time than MRI.
• 6. When we want more clarity and detailing in the images, we must go for an MRI.
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What is MRI best used for?

When the physician wants more clarity and detail in the images, he will ask for an MRI. 

What are the risk factors associated with MRI? 

Magnetic resonance images are obtained without ionizing radiation, which is harmful radiation. MRI uses magnetic waves instead. However, a magnetic resonance environment constitutes radiofrequency energy, a pulsed magnetic field, and a static magnetic field. Each of these constituents has some specific health concerns, which include,

1. 1. Magnetic field: Static and magnetic solid fields attract metallic objects, such as keys, cell phones, and large items like floor buffers and oxygen tanks. If these objects become projectile and come into the MR environment, they may cause injury to the medical practitioners or patients. Hence, It is essential to screen people and objects entering the MRI room, to ensure that the MR environment is free of magnetic objects. 

2. 2. Pulsed magnetic field: It is the magnetic field that alters with time. These altering magnetic fields result in unbearable loud noises, and if the practitioners or patients are not equipped with adequate noise-canceling devices, it may lead to hearing problems. Other concerns associated with pulsed magnetic fields are twitching sensations due to nerves or peripheral muscle stimulation. 

1. 3. Radiofrequency energy: The energy generated during the MRI process is relatively high that it causes heating of the body, and during lengthy MRI procedures, the heating effect is much high.
2. 4. 4. People with implants, artificial joints, intrauterine devices, pacemakers, etc., are not allowed for MRI because they have metallic substances which will become projectile for MRI.

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