Name: mri scans: how body signals are formed
Uploaded: 2023-06-23T15:38:43.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Texas Essential Knowledge and Skills

High School

Chemistry

CHEM.14

CHEM.14.C

Magnetic Resonance Imaging

Magnetic resonance imaging, or MRI, is a non-invasive technique with wide applications in neuroradiology and musculoskeletal radiology.
While performing MRI, the patient is placed in a strong external magnetic field. It aligns the randomly oriented hydrogen nuclei of water in the patient&#39;s body in the direction of the field.
After this, an external radiofrequency pulse is applied, which is absorbed by the hydrogen nuclei, disturbing their alignment.
Once the pulse stops, these nuclei release the absorbed energy realigning with the magnetic field. These emitted signals are picked up by the MRI machine to generate a gray-scale image of the tissue.
The image contrast can be improved by the intravenous injection of gadolinium-based contrast agents. For example, in this image, bone metastasis is clearly visible when gadolinium is used.
Unlike CT and X-ray, MRI allows better visualization of soft tissue structures, such as the delicate spinal cord inside the vertebral column, brain anomalies, and ligament tears.
MRI has the advantage of providing anatomical details for all three planes: axial, sagittal, and coronal.

magnetic resonance imaging

Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which matter exposed to magnetic fields and radio waves was found to emit radio signals. In 1970, a physician and researcher named Raymond Damadian noticed that malignant (cancerous) tissue gave off different signals than normal body tissue. He applied for a patent for the first MRI scanning device in clinical use by the early 1980s. The early MRI scanners were crude, but advances in digital computing and electronics led to their advancement over any other technique for precise imaging, especially in discovering tumors. Compared to other diagnostic imaging techniques like computed tomography and X-ray, MRI does not expose patients to radiation.
The drawbacks of MRI scans include their much higher cost and patient discomfort with the procedure. The MRI scanner subjects the patient to such powerful electromagnets that the scan room must be shielded. The patient must be enclosed in a metal tube-like device for the duration of the scan, sometimes as long as thirty minutes, which can be uncomfortable and impractical for ill patients. The machine is also so noisy that, even with earplugs, patients can become anxious or fearful. These problems have been overcome somewhat with the development of &#34;open&#34;&#160;MRI scanning, which does not require the patient to be entirely enclosed in a metal tube. Patients with iron-containing metallic implants (internal sutures, some prosthetic devices, pacemakers and so on) cannot undergo MRI scanning because it can dislodge these implants.
Different images are formed depending on the time taken between the sequence of magnetic pulses and the receipt and interpretation of the signal. A T1-weighted image has fatty tissues appearing brighter due to their enhanced signal while suppressing water signals, making it appear darker. In contrast, the T2-weighted image shows an enhanced water signal. Further, using MRI contrast media or dyes, like gadolinium, helps improve the quality of the images. Usually injected into the patient&#39;s vein, the gadolinium contrast dyes contain strongly paramagnetic gadolinium (Gd), which has positive magnetic susceptibility. When placed in a magnetic field, it is not directly seen in the MRI result but helps shorten the T1 values in tissues, where it accumulates, which allows the tissues to appear brighter in T1-weighted images.
Functional MRIs (fMRI), which detect the concentration of blood flow in certain body parts, are increasingly being used to study the activity in parts of the brain during various body activities. This has helped scientists learn more about the locations of different brain functions and more about brain abnormalities and diseases. More recently, 4D flow MRI provides 3D blood flow images and hemodynamics, with the fourth dimension being time, allowing cardiovascular disease assessment through the 3D coverage of the anatomy and velocity.
This content is derived from <a href="https://openstax.org/books/anatomy-and-physiology/pages/1-7-medical-imaging">Openstax, Anatomy and Physiology, Section 1.7: Medical Imaging</a>

Magnetic resonance imaging (MRI) is a noninvasive medical imaging technique based on a phenomenon of nuclear physics discovered in the 1930s, in which ...

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JoVE Core

Anatomy and Physiology

Unit 1

Diagnostic Imaging Techniques

KEY TERMS AND CONCEPTS

mri scans: how body signals are formed

Magnetic resonance imaging, or MRI, is a noninvasive way to create detailed medical images. It uses strong magnetic fields and radio waves. When the body is exposed to them, it can emit radio signals that are used to build the image.

MRI became especially important after researchers saw that cancerous tissue gave off signals different from normal tissue. Raymond Damadian identified this difference in 1970 and later applied for a patent for the first MRI scanner used in clinical care. Early scanners were basic, but later digital computing and electronics made MRI much more precise, especially for finding tumors.

Unlike X-rays and computed tomography, MRI does not use radiation. It does have limits, though. The scan is expensive, and the patient must lie inside a metal tube-like scanner for as long as thirty minutes. The machine is also very noisy, which can make patients anxious. Open MRI systems were developed to reduce the feeling of being fully enclosed.

MRI uses powerful electromagnets, so the scan room must be shielded. Some people cannot have MRI scans if they have iron-containing metal implants, such as internal sutures, some prosthetic devices, or pacemakers. The magnetic field can move these implants and make the scan unsafe.

Different images can be made by changing the timing of magnetic pulses and signal detection. In a T1-weighted image, fatty tissues appear brighter because water signals are suppressed. In a T2-weighted image, water signals appear brighter. Doctors may also use contrast media, such as gadolinium, which is injected into a vein and helps tissues appear brighter on T1-weighted images.

MRI is also used to study body function, not just body structure. Functional MRI, or fMRI, measures blood flow changes in parts of the brain during different activities. This helps scientists map brain function and study brain abnormalities and disease. More recently, 4D flow MRI has been used to show 3D blood flow and hemodynamics over time, which helps assess cardiovascular disease.

MRI Scans: How Body Signals Are Formed

x-ray imaging

X-Ray Use in Medical Diagnosis

X-rays are a standard tool in medical diagnosis. They help doctors see bones, teeth, and some soft tissues without surgery. The first X-ray image showed Wilhelm Röntgen’s wife’s hand, and it opened a new way to look inside the body. Wilhelm Röntgen, a German physicist, discovered X-rays in 1895 while studying electrical current. He found that an invisible ray could pass through flesh but leave the bones outlined on a screen coated with a metal compound. His work led to the first durable record...

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Magnetic resonance imaging, or MRI, is a noninvasive way to create detailed medical images. It uses strong magnetic fields and radio waves. When the body is exposed to them, it can emit radio signals that are used to build the image. MRI became especially important after researchers saw that cancerous tissue gave off signals different from normal tissue. Raymond Damadian identified this difference in 1970 and later applied for a patent for the first MRI scanner used in clinical care. Early...

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overview of microscopy techniques

How Microscopes Reach Higher Resolution

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key terms and concepts

Learn how MRI uses magnets and radio waves to form body images, why T1 and T2 scans differ, and how fMRI helps study the brain and blood flow.

MRI Scans: How Body Signals Are Formed | JoVE K12

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JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

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MRI Scans: How Body Signals Are Formed

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