THE MRI PROCESS
MRI is a non-invasive biomedical imaging technology that visualises tissues within the body. MRI is an interesting piece of physics that interacts with the body. As a technology it draws on the quantume mechanical properties embedded in corporeal matter - particularly hydrogen ions, also known as protons (H+). MRI brings together multiple aspects of our ontology. MRI interacts with the body through nuclear magnetic resonance and classical electrodynamics and thus physics allows us to connect to the abject. This brings us into contact with the body as a person, a patient, a member of a community, and as a cellular, molecular, atomic and subatomically composed entity.
The magnetic field of an MRI penetrates our materiality and requires both quantum mechanics and classical electrodynamics to work. MRI involves the phenomena of nuclear magnetic resonance (NMR) and the intrinsic subatomic properties of spin, angular momentum and magnetism possessed by atomic nuclei.
Protons within atomic nuclei are like tiny spinning magnets. The first stage of MRI involves the powerful MRI magnet which aligns the spin of the protons, lining them up like synchronised swimmers. Following this alignment, the protons are energised with radio frequency electromagnetic energy (RF photons) in the form of high-frequency RF pulses. This causes them to resonate.
As the protons absorb the RF energy, they wobble away from the magnet’s alignment to varying degrees depending on what material or substance they are in. When the RF signal is turned off the protons still resonate. Refocusing the magnet re-aligns the protons, causing them to re-emit the difference in RF as the NMR signal.
The time it takes for the protons to emit the signal is called relaxation time; it generally comes in two kinds of measurement: T1 and T2. The difference in relaxation time and proton density are essential factors in creating accurate MRI images. When the NMR signal is emitted it is detected in the scanner. These signals are converted into a digital biomedical image using the mathematics of signal analysis including a type of maths called Fourier transforms (FTs). This process is computational and mathematical where the wave properties of the NMR signal are used to figure out what kinds of matter/molecules are resonating where.
The body and its substances, molecules and atoms interact with the MRI system (magnet, RF signals and sensors/detection mechanisms) at the ‘body machine interface’. This interface is beyond (or within) the boundary of the skin. The magnet and RF signals are able to work across multiple scales of magnitude. By thinking about MRI in this way I was able to create sculptures that interact with MRI as if it were a body. Making sculptures with the body-machine interface in mind made it possible for my work to intersect, interact and intra-act with MRI. The analogue NMR signal being converted/processed/computationally interpreted into a digital biomedical image is perceived as the analogue-digital interface in my research (a non-scientific term).
An interface is the means by which interaction or communication is achieved or is a surface forming a common boundary between two or more bodies, spaces, or phases. Interface is a verb and a noun that entails action: to connect or become interfaced. In my making processes I consider the behaviour of corporeal matter at these interfaces and the types of connection, disconnection and reconnection that take place. Understanding what happens at the interfaces helps me decide how to develop practices that interact and interface with MRI on the molecular and mathematical levels.