Question

Q.7 MRI machine uses magnetic field to create detailed images of human soft organs. Can you
elaborate the basic concept of working of MRI scanner? How the strong magnetic field is
produced in MRI scanner to scan the organs? Discuss the role of radio waves in MRI machines?
Write down major parts used in MRI machine. What would happen if the north-pole end of a bar
magnet is held near a positively charged piece of plastic? Justify your answer. X-ray machine
and MRI machine do the same job of human organ scanning. Analyze both the machines and
discuss three merits and demerits of it.

Answer 1

a) The basic concept of working of MRI scanner: Magnetic resonance imaging (MRI) uses the body's natural magnetic properties to produce detailed images from any part of the body. It is often used for disease detection, diagnosis, and treatment monitoring. It is based on sophisticated technology that excites and detects the change in the direction of the rotational axis of protons found in the water that makes up living tissues.

MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field. When a radiofrequency current is then pulsed through the patient, the protons are stimulated, and spin out of equilibrium, straining against the pull of the magnetic field. When the radiofrequency field is turned off, the MRI sensors are able to detect the energy released as the protons realign with the magnetic field. The time it takes for the protons to realign with the magnetic field, as well as the amount of energy released, changes depending on the environment and the chemical nature of the molecules. Physicians are able to tell the difference between various types of tissues based on these magnetic properties. To obtain an MRI image, a patient is placed inside a large magnet and must remain very still during the imaging process in order not to blur the image. Contrast agents (often containing the element Gadolinium) may be given to a patient intravenously before or during the MRI to increase the speed at which protons realign with the magnetic field. The faster the protons realign, the brighter the image.

b) When the body is placed in a strong magnetic field, such as an MRI scanner, the protons' axes all line up. This uniform alignment creates a magnetic vector oriented along the axis of the MRI scanner.

c) The role of radio waves in MRI machines: When additional energy (in the form of a radio wave) is added to the magnetic field, the magnetic vector is deflected. The radio wave frequency (RF) that causes the hydrogen nuclei to resonate is dependent on the element sought (hydrogen in this case) and the strength of the magnetic field. When the radiofrequency source is switched off the magnetic vector returns to its resting state, and this causes a signal (also a radio wave) to be emitted. It is this signal which is used to create the MR images.

d) Major parts used in MRI machine:

• Magnet- The magnet is the most important and biggest part of the MRI device. It is this magnet that allows the MRI machine to produce high quality images.
• Gradient Coils- There are three different gradient coils. that are inside the MRI machine and are located within the main magnet. Each one of these produce three different magnetic fields that are each less strong than the main field. The gradient coils create a variable field (x, y, z) that can be increased or decreased to allow specific and different parts of the body to be scanned by altering and adjusting the main magnetic field.
• Radio Frequency (RF) coils- The basic function of the RF coils is to transmit radio frequency waves into the patient’s body.
• Patient Table- This component simply slides the patient into the MRI machine.
• Antenna/Computer System- The antenna is a very sensitive device that easily detects the RF signals emitted by a patient’s body while undergoing examination and feeds this information into the computer system.

e) If the north pole of a bar magnet is held near a stationary positively charge piece of plastic the plastic will neither be attracted nor be repelled, it will remain unaffected. First of all, when we take a plastic near to magnet it will remain unaffected because plastic is not a magnetic material. And also if we take stationary charged plastic near to the magnet it will remain unaffected because the charge is stationary so there won't be any magnetic field due to plastic and it will remain unaffected.

f) X-ray machine:

Merits: 1. Image Quality- Portable digital x-ray machines are equipped with high-tech features. This allows technologists to get high-quality images in a short time. The laser scanner of the imaging device does not make use of a film, and it consists of phosphor plates and cassettes that can be effectively deleted after usage. Technologists can also enhance the digital medical images that were taken out in the field, with the workstation connected to the portable unit.

2. Safety- Radiation exposure is one of the primary health concerns for both the patient and personnel in using traditional medical imaging equipments; however, studies show that there’s a significant reduction of radiation exposure in using portable radiology devices. The shield mounted on the front part of the portable X-ray device protects them from scattered radiation.

3. Speed- Radiograph examinations using mobile imaging equipments offer less processing speed and eliminate long wait-times. Portable X-ray machines can take less than 20 minutes. Moreover, the results are accessed in real-time and can be sent directly to the patient’s physician, which is usually done within an hour, allowing immediate diagnosis and start of the patient’s treatment.

Demerits:

1. X-rays makes our blood cells to have higher level of hydrogen peroxide which could cause cell damage.

2. a higher risk of getting cancer from X-rays.

3. The X-rays are able to change the base of the DNA causing a mutation.

MRI machine:

Merits: 1. Images may be acquired in multiple planes (axial, sagittal, coronal, or oblique) without repositioning the patient. CT images have only relatively recently been able to be reconstructed in multiple planes with the same spatial resolution.

2. Ability to image without the use of ionizing x-rays, in contradistinction to CT scanning.

3. MRI images demonstrate superior soft tissue contrast as compared to CT scans and plain radiographs making it the ideal examination of the brain, spine, joints, and other soft tissue body parts.

Demerits: 1. MRI scans are more expensive.

2. MRI scanning is not safe for patients with some metal implants and foreign bodies. Careful attention to safety measures is necessary to avoid serious injury to patients and staff, and this requires special MRI compatible equipment and stringent adherence to safety protocols .

3. MR image acquisition is noisy compared to CT.