MRI Scanning

MRI Scanning

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Magnetic Resonance Imaging (MRI) Scanning

Magnetic Resonance Imaging (MRI) is arguably the most sophisticated imaging method used in clinical medicine. In recent years, MRI scans have become increasingly common, as costs decrease. MRI scans work as an imaging method due to the unique make-up of the human body. We are comprised entirely of cells which all contain water – principally made of hydrogen ions (H2O).

The magnet embedded within the MRI scanner can act on these positively charged hydrogen ions (H+ ions) and cause them to ‘spin’ in an identical manner. By varying the strength and direction of this magnetic field, we can change the direction of ‘spin’ of the protons, enabling us to build layers of detail. When the magnet is switched off, the protons will gradually return to their original state in a process known as precession. Fundamentally, the different tissue types within the body return at different rates and it is this that allows us to visualise and differentiate between the different tissues of the body.

Magnetic resonance imaging can produce highly sophisticated and highly detailed images of the human body. Generally speaking, MRI scanning is excellent for visualising soft tissue – and so it is often used in the detection of tumours, strokes and bleeds. It also can be used to visualise the functionality of suspected masses and tumours through IV, gadolinium-based agents.

MRI scans have many advantages. As stated previously, they provide excellent detail of the soft tissues of the body, and they do not cause any radiation exposure to the patient. MRI scans can create intricate images of the inside of the body, allowing doctors to diagnose and treat illnesses more effectively. Additionally, MRI scans are non-invasive, meaning patients are not subjected to any uncomfortable physical contact during the scan. MRI scans are also able to produce three-dimensional images, which can be rotated to allow doctors to observe the body from all angles.

Unfortunately, MRI scans have a few drawbacks. One of the major downsides is that MRI scans require a large amount of time to complete, usually averaging 35-45 minutes. This limits their use in trauma and emergency situations, where CT scanning is often preferred. Additionally, MRI scans come with a high price tag, making them the most expensive of all imaging modalities available.

When interpreting axial views of MRI scans, it is important to appreciate that the image is viewed from the feet upwards – and so the left-hand side of the image refers to the patient’s right (and vice versa). For these reasons, it is important to consult a medical professional before undergoing an MRI scan, as they can provide more information pertaining to the particular case.

At present, there are no known long lasting adverse effects from MRI scans. With the advent of technology, MRI scans continue to improve and become increasingly accessible in clinic. MRI scans provide doctors with a powerful tool in the detection, diagnosis and treatment of various medical conditions.

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging (MRI) is an advanced medical imaging technique used to create detailed images of organs, soft tissue, and other structures within the body. It works by using powerful magnets to align the protons of hydrogen ions in the body, which creates a rotating magnetic field, known as precession. This precession is detected by the scanner and a computer uses this information to create detailed images.

MRI scanning is an excellent method for imaging soft tissue, making it the superior choice to CT scanning for detecting tumours and other abnormalities. It also is more advantageous over CT in terms of radiation exposure, time consumption, and cost. However, the use of MRI has caused a renewed focus on safety in hospital and outpatient environments, since it has the potential to attract ferromagnetic objects and devices. As such, some medical and implantable devices such as cardiac pacemakers, heart monitors, defibrillators, and other battery-operated devices, are considered contraindications for MRI evaluation.

Interpreting a MRI Scan

The first step in interpreting a MRI scan is to determine the view of the scan. Like computed tomography, they typically produce three anatomical views: sagittal, coronal and axial (similar to the planes of the body). For the axial views, it is important to remember that the image is viewed from the feet upwards - and so the left-hand side of the image refers to the patient’s right (and vice versa).

The second step is to work out the weight of the image. The magnetic fields produced by the scanner can be manipulated to produce two distinct types of image - T1 weighted and T2 weighted. The resulting images will show different tissue types in different densities.

A T1 weighted image (white) will show fat, while a T2 weighted image (gray) will show protein rich fluid. In between these two weights is an intermediate T1 weighted image (gray), which will show spinal matter darker than a white T2 weighted image. These images will also vary depending on the amount of fat, bone and air present in the image. It can help to remember that a T2 weighted image shows water as white.

Clinical Relevance: Spinal Cord Compression

MRI scans can be used to assess the extent of cord compression when there is a suspicion of stenosis, disc herniation or cauda equina. The figure below shows a T2 weighted, sagittal MRI of the lumbar spine. The thecal sac is easily visible as the 1cm thick white band running posterior to the vertebral bodies. This is interupted at the L4/L5 level by a small round dark area, which is the herniation of the intervertebral disc into the central canal.

MRI scans offer a wide variety of uses and applications in the medical field, allowing for a more accurate diagnosis and treatment of conditions. The ability to detect soft tissue makes it a more suitable technique for detecting tumours and other abnormalities compared to CT. It also has the added benefit of no exposure to radiation, faster scanning times, and lower costs. The safety of MRI has become a major focus, since the potential attraction to ferromagnetic objects has to be taken into account. Interpreting a MRI scan requires understanding the weight of the scan to identify the different tissue types in the image.

Ultimately, MRI offers a great variety of benefits that are beneficial for medical diagnosis and treatment. By using powerful magnets to align and detect the protons from hydrogen ions, sophisticated images can be created. This, in combination with the numerous benefits such as time savings, cost savings, and non-exposure to radiation, makes MRI a viable option across many medical disciplines.

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