Sample interview questions: Can you explain the concept of nuclear magnetic resonance imaging (MRI)?
Sample answer:
Nuclear magnetic resonance imaging (MRI) is a powerful imaging technique that utilizes the principles of nuclear physics to create detailed images of the human body. It is based on the phenomenon of nuclear magnetic resonance, which occurs when atomic nuclei with an odd number of protons or neutrons are placed in a strong magnetic field.
In the context of MRI, the atomic nuclei most commonly used are those of hydrogen, specifically the hydrogen nucleus, which consists of a single proton. When a patient undergoes an MRI scan, they are placed within a large, cylindrical magnet that generates a strong and uniform magnetic field. This magnetic field aligns the hydrogen nuclei in the body, effectively aligning their spins in the same direction.
To obtain an image, a second, smaller magnetic field, called the gradient field, is applied. This gradient field allows us to spatially encode the signals emitted by the hydrogen nuclei. When the gradient field is turned on, the hydrogen nuclei experience slightly different magnetic fields depending on their location in the body. As a result, they precess at different frequencies.
Radiofrequency pulses are then transmitted into the body. These pulses are carefully tuned to match the precession frequency of the hydrogen nuclei in a specific location. When the hydrogen nuclei absorb this energy, they temporarily move away from their aligned position and enter a higher energy state. This process is known as resonance.
After the radiofrequency pulse is turned off, the hydrogen nuclei gradually return to their original aligned state, releasing the energy they had absorbed. This energy is detected by a receiver coil, which surrounds the region of interest. The detected signals are then processed and used to construct an image of the body.
By manipulating the … Read full answer