Magnetic Resonance Imaging (MRI), despite being one of the most pivotal innovations of contemporary medicine, is markedly limited due to its safety, cost, and inability to discern micro-insults within the brain (Glover, 2011). In 1992, scientists introduced functional Magnetic Resonance Imaging (fMRI), a non-invasive technique intended to measure brain activity with unparalleled specificity (Soares, et al., 2016). Due to fMRI development, physicians may now monitor regional variances in blood flow and brain activity, enabling them to truly understand their patient’s overall feelings and functionality (Glover, 2011).
In essence, fMRI and MRI function similarly; both methods use the body’s natural magnetic properties to produce detailed images (Berger, 2002). Hydrogen nuclei, due to their magnetic properties and abundance in the body, prove to be ideal targets for fMRI (Jensen, 2014). In the presence of a strong magnetic field, the random and intrinsic spin of hydrogen atoms become aligned, creating a magnetic vector oriented along the axis of the fMRI scanner (Berger, 2002; Jensen, 2014). When additional energy in the form of radio waves is administered, the vector is deflected (Berger, 2002). As the radiofrequency source is switched off, nuclei return to their resting state, emitting various intensities of radio waves that are integrated into comprehensive cross-sectional images (Berger, 2002). This process is illustrated in Figure 1.
Figure 1: Hydrogen proton responses to magnetic fields. A) depicts a water molecule’s structure, containing two hydrogen protons (red circles). Hydrogen protons act like a magnet, containing one positive charge spinning on its axis (blue dotted line). B) portrays the randomized vector (blue arrow) alignment of hydrogen protons under no magnetic field. In the presence of the fMRI’s magnetic field (large black arrow), most hydrogen protons’ axes align to create a magnetic vector that an fMRI can measure. C) depicts hydrogen proton behaviour with radiofrequency (RF) waves. The magnetic vector is deflected and the protons absorb energy. When the RF waves are turned off, the protons return to a resting state and emit RF waves (Broadhouse, 2019).
Although fMRI and MRI are both valuable diagnostic tools, MRI only pictures anatomical structure and imparts no information about function (Vincent, et al., 2008). Studying function is imperative for many clinical conditions including bipolar disorder, where structurally the brain appears normal, yet symptoms are identified from behaviour (Vincent, et al., 2008; Demirci and Calhoun, 2009). fMRI detects function through neuronal activity using the Blood Oxygen Level Dependent (BOLD) signal (Demirci and Calhoun, 2009). By measuring the dynamics of cerebral blood flow, BOLD contrast examines the underlying physiology that may result in a psychiatric disorder (Demirci and Calhoun, 2009).
The basis of BOLD imaging is grounded in the fundamental understanding that neuronal activity requires oxygen (Vincent, et al., 2008). Therefore, metabolically active regions have higher proportions of oxygenated hemoglobin (OxyHb) to deoxygenated hemoglobin (deOxyHb) than surrounding latent tissue (Vincent, et al., 2008). However, as neuronal activity increases, OxyHb increases beyond metabolic demand, resulting in the decrease of deOxyHb concentration within tissues (Gore, 2003). This decrease directly influences the ability to image function due to OxyHb and deOxyHb having different magnetic qualities (Vincent, et al., 2008; Gore, 2003).
Structurally, OxyHb unlike deOxyHb, is found to have no unpaired electrons and is classified as weakly diamagnetic (Pauling and Coryell, 1936). However, when OxyHb becomes deOxyHb, four unpaired electrons per heme molecule are exposed, creating a paramagnetic molecule (Pauling and Coryell, 1936). As seen in Figure 2, when OxyHb replaces deOxyHB within neuronally active tissue, distortion within the local magnetic environment decreases (Gore, 2003). This results in greater field uniformity, enhancing image intensity, and allowing researchers to monitor real-time activity (Pauling and Coryell, 1936).
Figure 2: Schematic of BOLD signal in fMRI. OxyHb (pink cells), due to being diamagnetic, have a negligible interaction with the fMRI’s applied magnetic field. As a result, imaging OxyHb creates a magnetically uniform image with no distortions. fMRI signals within neurally active regions of the brain will therefore have higher contrast and be easier to view. deOxyHb (blue cells), are paramagnetic and are influenced by a magnetic field. Imaging deOxyHb will result in distortion of the magnetic field and cause the fMRI signal to decay faster. Using foundational knowledge of magnetism, physicians can accurately image the brain’s structure and function (Gore, 2003).
fMRI currently has a small, yet burgeoning role in clinical neuroimaging. Applications of fMRI include early diagnosis of psychiatric disease, predicting treatment response, and informing early treatment approaches. The ability to monitor neuronal activity can ultimately aid in the personalization of therapies, development of drugs, and our understanding of various disorders (Orringer, Vago and Golby, 2012).
Beyond a shadow of a doubt, fMRI has proven to be one of the most powerful tools in modern-day medicine. By offering insight into brain activity, fMRI has heralded a new age of imaging in neuroscience. With further research into fMRI, we can acquire additional information regarding the onset of cognitive disorders and provide more effective treatment for all patients.
References:
Berger, A., 2002. Magnetic resonance imaging. BMJ, 324(7328), p.35. https://doi.org/10.1136/bmj.324.7328.35.
Broadhouse, K.M., 2019. The Physics of MRI and How We Use It to Reveal the Mysteries of the Mind. Front. Young Minds, 7, p.23. https://doi.org/10.3389/frym.2019.00023.
Demirci, O. and Calhoun, V.D., 2009. Functional Magnetic Resonance Imaging – Implications for Detection of Schizophrenia. Eur Neurol Rev., 4(2), pp.103–106.
Glover, G.H., 2011. Overview of Functional Magnetic Resonance Imaging. Neurosurg Clin N Am, 22(2), pp.133–139. https://doi.org/10.1016/j.nec.2010.11.001.
Gore, J.C., 2003. Principles and practice of functional MRI of the human brain. J Clin Invest, 112(1), pp.4–9. https://doi.org/10.1172/JCI19010.
Jensen, E.C., 2014. Technical Review, Types of Imaging, Part 4—Magnetic Resonance Imaging. The Anatomical Record, 297(6), pp.973–978. https://doi.org/10.1002/ar.22927.
Orringer, D., Vago, D.R. and Golby, A.J., 2012. Clinical Applications and Future Directions of Functional MRI. Semin Neurol., 32(4), pp.466–475. https://doi.org/10.1055/s-0032-1331816.
Pauling, L. and Coryell, C.D., 1936. The Magnetic Properties and Structure of Hemoglobin, Oxyhemoglobin and Carbonmonoxyhemoglobin. Proc. N. A. S., 22, pp.210–216.
Soares, J.M., Magalhães, R., Moreira, P.S., Sousa, A., Ganz, E., Sampaio, A., Alves, V., Marques, P. and Sousa, N., 2016. A Hitchhiker’s Guide to Functional Magnetic Resonance Imaging. Frontiers in Neuroscience, 10, pp.1–35. https://doi.org/10.3389/fnins.2016.00515.
Vincent, K., Moore, J., Kennedy, S. and Tracey, I., 2008. Blood oxygenation level dependent functional magnetic resonance imaging: current and potential uses in obstetrics and gynaecology. BJOG, 116(2), pp.240–246. https://doi.org/10.1111/j.1471-0528.2008.01993.x.
Comments
9 Responses to “Learning How to Read Minds”
Hi iSci!
I came upon this topic while doing some reading on recent developments in neuroscience. MRI was a concept first introduced to us in RP4 of 1A24, but the actual physics behind MRI was something we did not fully explore. After some digging, I became really interested in this field of neuroscience and decided to share it with you all. fMRI is a new technology that could change the landscape of healthcare forever. fMRI is a more revealing adaptation of the MRI, yet it still has not even scratched the surface of its potential. During my reading, I found this topic’s fusion of neurobiology and the physics of magnetism highly intriguing. I hope you found my blog post interesting and if you have any feedback or suggestions I would love to hear them. Any and all comments are welcome. Thank you so much.
Have a great day!
Rith
Hello Rith,
I really enjoyed reading your blog post! I learned a lot about fMRIs from a neuroscience and physics context.
Here are a few of my suggestions:
1) Consider italicizing your figure captions to differentiate them from the rest of your text and make them stand out.
2) This is entirely up to you, but maybe shorten your figure captions as they seem a bit lengthy. Of course, that is just my personal opinion and they are also fine as is!
3) The first sentence of your fourth paragraph is a bit wordy, I would either reword it or split it up into two sentence. For example, you could rephrase it as: “The basis of BOLD imaging is grounded in the fundamental understanding that neuronal activity requires oxygen. Therefore, metabolically active regions have higher proportions of oxygenated hemoglobin (OxyHb) to deoxygenated hemoglobin (deOxyHb) than surrounding quiescent tissue (Vincent, et al., 2008).” (I just put a period after “oxygen” and split it into two sentences).
Overall, your blog post was well-written and integrated various scientific disciplines well. I hope my suggestions can be useful for you!
Happy editing!
Sakina
Hi Sakina,
Thank you for the precise comments! I have implemented them all into my final draft.
Rith
Hi Rith,
Amazing work! You did an excellent job describing the physics at work behind this fundamental technique in neuroscience. I found the application of fMRI to the early detection of illnesses especially interesting.
I notice that your post is a bit on the lengthy side, and I think it could be more concise while still communicating all of the same points through the use of more direct phrasing. I’ll highlight a few examples of this – feel free to take or leave any of them as you choose, and perhaps devote a read-through of your post to catching similar instances where you could cut down on words.
P1S2: “a non-invasive technique intended to measure brain activity with unparalleled specificity” > “a non-invasive technique which measures brain activity with unparalleled specificity”
P1S3: “physicians now have the ability to monitor regional variances” > “physicians may now monitor regional variances”
P2S1: “At their core, fMRI and MRI function in similar fashions” > “In essence, fMRI and MRI function similarly”
P3S1+2: “Although fMRI and MRI are both incredibly useful diagnostic tools, MRI only pictures anatomical structure and imparts no information about function (Vincent, et al., 2008). Studying function is imperative for many clinical conditions including bipolar disorder, where structurally the brain appears normal, yet symptoms are identified using function” becomes somewhat repetitive with the triple mention of function – perhaps experiment with combining these two sentences to eliminate one or two of these and for a more seamless transition. The word “incredibly” at the beginning might also be removed – the point comes across regardless!
I hope these suggestions are helpful to you! Once again, amazing work – thank you very much for a fascinating read.
Best,
Maya
Hi Maya,
Thank you very much for your feedback! For your final comment, I changed the last “function” to “behaviour” because that phrasing conveys my point more effectively. Your suggestions were all great nevertheless.
Rith
Hey Rith,
This is an awesome blog post! I had the pleasure of doing some research into fMRI imaging last semester for one of my blog posts, so I was very excited to read your post and learn about it in even more depth. I absolutely loved how seamlessly you integrated the physics concepts along with biology ones, and thought it was very well-written and easy to understand. I just have a few small edits that I hope will make your post even better:
– in your second paragraph I would recommend adjusting the grammar in the third sentence to: “In the presence of a strong magnetic field, the random (and) intrinsic spin of hydrogen atoms (become) aligned, creating a…” to improve the readability
– in the third paragraph you mention that Bipolar disorder is identified through ‘function’, but you never explain exactly how ‘function’ is defined. Is it measured through brain activity?
– in the fourth paragraph I was wondering what exactly quiescent tissue is? This term may not be commonly known and could use a definition
– in the same paragraph, “resulting in deOxyHb concentration within tissues to decrease” might make more sense if written as “resulting in the decrease of deOxyHb concentration within tissues”
Overall, I think you did an excellent job, and I wish you the best of luck with your edits!
Cheers,
Katherine G
Hi Katherine,
Fantastic feedback. I incorporated all of your suggestions into my final draft. For your second point, I replaced that “function” with “behaviour” because it is a more accurate representation of what I am trying to convey. Thank you for the help.
Rith
Hi Rith,
Great job on this blog post! I thought you made this topic of fMRI imaging super accessible, as this is something I personally have found to be pretty confusing in the past. However, I found you were able to go into good depth without making it too confusing for the reader. I only have a few small suggestions for you.
– Your first sentence has some information that seems like it should have a citation. If you don’t want to cite the very first sentence, you could consider adding a more general overview of your topic to begin with.
– If word count permits, it could be interesting to also mention some downfalls of fMRI, if any. The thing that came to my mind was that this might be more costly than other diagnostic methods.
Overall I really enjoyed reading your post and I look forward to reading your final edits.
Maia
Hi Maia,
Thank you for your comments. I added a citation for my first sentence. For your second point, I did not mention the drawbacks of fMRI because I didn’t feel it was necessary to explain. The benefits of fMRI greatly outweigh the pitfalls. Namely, fMRI is non-invasive, relatively low cost, generally available for patients, and has high resolution. fMRI may have small negatives, but in the grand scheme of things, I thought they were inconsequential. You still make a great point though so thank you for the suggestion.
Rith