The Insane Engineering of MRI Machines

Introduction to Magnetic Resonance Imaging (MRI)

This section introduces the concept of MRI and how it has revolutionized medical diagnosis and treatment.

How MRIs Work

• MRIs can safely locate and identify tumors in various organs, allowing doctors to accurately implant life-saving stents to open blood vessels.

• Prior to MRIs, harmful ionizing x-rays or low-detailed ultrasounds were used for imaging in medicine.

• To image the body, MRI machines exploit a quantum property of hydrogen atoms called spin.

• Once the atoms are aligned in the machine's incredibly strong magnetic field, the machines give them a tiny nudge using a magnetic radiofrequency pulse.

The Engineering Behind MRIs

• Physicists and engineers had to discover and master principles of quantum mechanics, superconducting magnets, computer science, and mathematics to unlock the power of MRI machines.

• Spin is an innate property of particles just like mass and charge. It makes particles behave like tiny bar magnets.

• Coils inside the machine send pulses by simply applying an alternating current through its coils at a very specific frequency. These coils are placed as close to the patient as possible but still inside the MRI tube.

Advantages of MRIs

• MRIs have completely changed how we view and understand our bodies. It has never been easier to visualize organs with such high details.

• Capable of creating a 3D reconstruction of the body rather than a flat 2D image.

• MRIs provide safe, millimeter resolution imaging without any moving parts.

Conclusion

MRI machines have revolutionized medical diagnosis and treatment. They exploit the quantum properties of hydrogen atoms to create high-resolution images of the human body. MRI technology is a marvel of modern physics and engineering that has completely changed how we view and understand our bodies.

MRI Technology

This section explains how MRIs work and the technology behind them.

Achieving High Magnetic Fields

• Early MRIs used permanent magnets but only reached strengths of 0.5T .

• Electromagnets can be used to reach stronger magnetic fields, but standard electromagnets can’t produce a 1.5 tesla field.

• Superconducting coils are required to achieve higher magnetic fields .

• Superconductors have zero resistance at temperatures close to absolute zero, allowing an electric current to travel indefinitely in a loop of superconducting material .

Cooling the Superconducting Coil

• Helium was initially used as a refrigerant for cooling the superconducting coil .

• Modern MRI machines use vacuum-sealed chambers that hold liquid helium without letting it evaporate, eliminating the need for refilling and minimizing costs .

• These "Zero Boil off" machines use an electric refrigerant cycle like the one in your fridge but on steroids .

Nudging Hydrogen Atoms

• MRIs detect signals from the spiral decay pattern of hydrogen atoms after they have been "nudged" with a radiofrequency wave at 64 MHz or 128 MHz .

• Rotational frequency is dependent on something we control, the magnetic field strength.

• If we can apply a gradient to the magnetic field strength, we can selectively nudge atoms.

Energy Consumption

• The energy needed to run an MRI for a full year is equivalent to 25 four-person households, around 130,000 to 140,000 kWh per year .

• The most common superconducting material used in MRIs is Niobium-titanium and demand for high-resolution images is so large that 80% of all Nb-Ti extracted from earth goes into an MRI machine .

How MRI Works

In this section, the speaker explains how Magnetic Resonance Imaging (MRI) works by contrasting different types of tissues using two signal types: T1 relaxation and T2 decay. The technician can emphasize either signal type depending on what the doctor wants to image.

Contrast Between Tissues

• To form an image, we need a way of identifying different kinds of tissues by contrasting them using two different signal types.

• The first signal type deals with how quickly atoms re-align themselves with the large magnetic field after a nudging pulse, called T1 relaxation.

• The second measure comes from the physical reality of interaction between hydrogens, called T2 decay. Hydrogens in fat have different intrinsic characteristics and interactions than hydrogens in water which allows technicians to contrast the tissues.

Emphasizing Signal Types

• Technicians can emphasize the T1 signal by sending pulses rapidly and listening to the signal immediately as the dephasing effects of T2 do not have enough time to take place.

• They can emphasize T2 by sending pulses slowly and listening for longer, allowing dephasing to occur.

Creating Images

• MRIs use Fourier analysis to create images instead of sampling individual pixels.

• Any image can be deconstructed into a weighted average of simpler black and white stripes using Fourier analysis.

• MRIs exploit this concept physically by creating striped patterns through gradient coils that change the phase of rotating hydrogens in all directions and frequencies.

• By adding more patterns, an image starts to emerge for each 2D slice which is formed from a grid of rotating hydrogens where we color their phase in grayscale.

The Intricate Dance of Quantum Physics and Carefully Manipulated Gradients

This section discusses the complexity of MRI systems and how they have changed the world of medicine.

Development of MRIs

• MRIs are incredibly useful in the field due to their practicality and affordability.

• The complexity of MRI systems is hard to fathom, from superconducting wires to vacuum-sealed helium reserves to rapidly changing magnetic gradients.

• Combining these technologies together was a remarkable feat that allowed us to peer into our bodies.

Keysight Virtual Event for Engineers

• Developing something as complicated as an MRI requires the very best test and measurement equipment.

• Keysight puts the very best electronic measurement and testing tools into engineers' hands, holding another virtual event for engineers on May 16th.

• This fantastic free event is a rare opportunity to learn about electronics from experts. It will explore performance of batteries, DC-DC converters, and internet of things devices using live experiments such as testing different battery models at different temperatures to see how that affects device run times and testing DC-DC converter performance.

Live Q&A Session with Industry Experts

• There will be a live Q&A session allowing you to ask industry experts questions - an opportunity that does not come around very often.

• Everyone who registers for the event will be entered into a draw for Keysight’s massive gear giveaway where they are giving away 20 pieces of pro-grade test gear worth $300,000 - extremely valuable professional grade tools! You will get an extra entry if you share this event with your colleagues or friends on social media platforms like LinkedIn or Twitter using #KeysightVirtualEvent.