What influences the relative signal strength in proton density (PD) weighting?

The correct choice is influenced by the number of protons per unit volume in a tissue. Proton density weighting in MRI primarily measures the concentration of hydrogen protons within a specific tissue. Tissues that contain a higher density of protons, such as fat and water, will produce stronger signals compared to tissues with fewer protons, like air or dense calcium.

This intrinsic property of tissues plays a fundamental role in distinguishing between different types of tissues in MR images, making proton density a vital consideration in MR scans. The strength of the MR signal is directly related to how many protons are present to contribute to the signal, which is why the number of protons is a critical factor in proton density weighting.

Other factors, such as the strength of the magnetic field, duration of the RF pulse, and selected echo time, may impact overall image quality and characteristics but do not fundamentally define the proton density of the tissues. Instead, these factors primarily influence the timing and quality of the images produced rather than the inherent tissue signal related to proton density.