By Zara Haider
A sagittal MRI scan of a patient’s head
Fractured a leg? Most likely the doctor will issue an x-ray scan to get a better look at it. But, what if you injured a ligament, or had a concussion? Then you’ll have to go to a big room with a giant whirring machine to get an MRI scan.
MRI Machine
MRI or Magnetic Resonance Imaging is a machine that produces an image of soft tissue. Think of it like an x-ray for your organs and other boneless body parts.
It works by producing a strong magnetic field, which causes all the water molecules to align with it. A technician will then introduce a radiofrequency (rf) wave–perpendicular to the magnetic field– that disrupts the molecules and forces them to align with it.
Once the wave is shut off, the molecule realigns itself with the magnetic field. The speed in which they realign, along with the energy that they produce, is detected by the scanner and produces an image of various shades of gray.
An MRI technician preparing a patient for an MRI scan
The Science Behind the Images
Since water molecules are found throughout the body–in our bones, heart, kidneys, lungs, etc.–, their concentration of water in certain areas affects how fast the molecules move and how they appear on scans.
That’s how doctors can differentiate the heart from the lungs, and the lungs from the trachea!
There are 2 main sub-specialized scans that doctors can order: T1-weighted and T2-weighted scans. T1-weighted scans emphasize the details of organs and other body parts, while T2-weighted scans highlight pathological-related issues like tumors, cysts, lesions, and fluid build-up.
T-1 (left) vs T-2 (right) MRI scans depicting the brain
T1 and T2
The moment that the rf waves shuts off, the T1 and T2 relaxation periods start. T1 relaxation measures the time it takes for a water molecule to recover 63% (1- 1/e) of its initial alignment with the magnetic field along the longitudinal axis (z-axis). T2 relaxation measures the time it takes for a water molecule’s alignment in the transverse axis (xy-axis) to decay to 37% (1/e) of its initial value after an rf wave is applied.
This period of ‘relaxation’ is the transition of the molecules from an excited state, stimulated by the rf wave, to their normal state. Indeed, when a pulse of energy is exerted, the MRI scanner detects and interprets it into an image.
Body parts/fluids–usually watery-based ones like cerebrospinal fluid–detected with long T1 times appear dark whereas parts with short T1 times appear bright on T1-weighted scans. This means that cartilage, fats, and muscles are easily seen in those scans.
For T2-weighted scans, parts of the body with long T2 times appear bright, and the opposite is also true. This highlights fluids and foreign bodies.
Image Enhancements
Certains shades of gray, white or black can be hard to differentiate with the naked eye, even for a surgeon. So, how can doctors ensure a proper diagnosis for their patients?
Thanks to computer softwares like SUMA (Surface Mapping with AFNI, Analysis of Functional NeuroImages), MRI images can be processed and color-coded based on data points collected and analyzed by the software. This enhances the interpretability of MRI scans, making it easier for clinicians to understand and diagnose medical conditions.
A 3-D visualization of the brain produced by SUMA
Despite the growing integration of digital technologies and AI into medical diagnosis, they are quite costly. That’s why MRI technicians often utilize gadolinium-based contrast dyes (GBCAs), chemical enhancers.
GBCAs are intravenous drugs administered to patients by injection before the scan. The drug shortens the T1 and T2 relaxation periods, producing a stronger pulse of energy that refines the MRI machine’s image processing.
MRI machines are a feat in the world of biomedical engineering and a major advancement in healthcare. Without them, the rate of preventable deaths would skyrocket, causing widespread grief and loss for families. They’re indispensable tools for physicians managing severe cases. Until a revolutionary medical innovation that outperforms MRIs is developed, these magnetic machines will remain a staple in hospitals.
Citations:
AFNI, SUMA and FATCAT: v24.2.01. (n.d.). Afni.nimh.nih.gov. Retrieved July 17, 2024, from https://afni.nimh.nih.gov/pub/dist/doc/htmldoc/SUMA/cover.html#overview
Bashir, U. (2012, January 22). T2 relaxation . Radiopaedia. https://radiopaedia.org/articles/t2-relaxation?lang=us. Updated June 20, 2024.
JOHNS HOPKINS MEDICINE. (2024). Magnetic Resonance Imaging (MRI). Www.hopkinsmedicine.org. https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/magnetic-resonance-imaging-mri#:~:text=The%20strong%20magnetic%20field%20created
Jones, J. (2009, June 5). T1 relaxation time . Radiopaedia. https://radiopaedia.org/articles/t1-relaxation-time?lang=us. Updated April 8, 2023.
Llamas, M. (2018, August 6). Gadolinium-Based Contrast Agents. Drugwatch.com; DrugWatch. https://www.drugwatch.com/gadolinium/
T1 vs T2 MRI | T1and T2 MRI image comparison. (n.d.). MRIMaster. Retrieved July 17, 2024, from https://mrimaster.com/t1-vs-t2-mri/#:~:text=T1%20MRI%20highlights%20anatomy%2C%20provides
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