Final answer:
The Static Magnetic Field and the Radiofrequency Field are primarily responsible for providing the means for alignment of spinning protons in an MRI system, with the Static Magnetic Field causing initial alignment and the Radiofrequency Field perturbing and detecting the protons' relaxation.
Step-by-step explanation:
The MRI systems responsible for providing the means for alignment (net magnetization of spinning protons) are mainly the Static Magnetic Field and the Radiofrequency Field. The Static Magnetic Field, which is created by the large superconducting magnet within the MRI unit, typically measuring between 1 and 2 T in strength, is responsible for aligning the protons in the body.
The Radiofrequency Field is then used to perturb this alignment, which upon returning to its original state, allows for the capturing of detailed images. The Gradient Magnetic Field is also a key part of the MRI system but has a different role; it is utilized to create the spatial resolution needed to form an image by causing a slight variation in the magnetic field, allowing for the differentiation of signal location within the body.