Final answer:
Myelography has become a rarely used diagnostic for Herniated Nucleus Pulposus (HNP) since MRI's noninvasive and advanced imaging capabilities, which include detailed two- and three-dimensional views of the spine, have largely replaced it.
Step-by-step explanation:
The diagnostic that is now rarely used for Herniated Nucleus Pulposus (HNP) since the availability of Magnetic Resonance Imaging (MRI) is myelography. Before the widespread use of MRI, myelography, which is an invasive procedure involving the injection of a contrast dye into the spinal canal, was commonly used to diagnose HNP. However, with the advent of MRI, a more advanced and noninvasive imaging technique, myelography has fallen out of favor due to MRI's superior ability to create detailed images of the body's soft tissues, including the spine and intervertebral discs, without exposure to ionizing radiation. Advanced imaging offered by MRI, including the ability to view two-dimensional and three-dimensional depictions of the spinal column, has revolutionized the field of diagnostic medicine for spinal conditions.