X-ray. It uses radiation to make detailed pictures of the bones of your spine.
A technician uses a machine that sends X-ray beams through your body. It records a black-and-white image on a special film or computer. Bones, and other parts of your body that are thick or dense, show up white in the picture. Softer tissue, like fat or muscle, appear in shades of gray.
Your doctor can take separate X-rays that focus on the different parts of the spine, which is made up of 33 small bones called vertebrae.
X-rays are the most common tool used to "see" inside your body and take pictures of bones. While X-rays don't show as much detail as other imaging tests, they are often the tests doctors use at first to help them decide on your next steps.
Computed tomography (a CT scan) combines X-rays with computer technology to create a picture that shows a cross-section, or slice, of the bone.
For the most detailed pictures of the spine and all its parts, doctors often suggest magnetic resonance imaging (MRI). It uses powerful magnets, radio waves, and a computer -- not radiation. (WebMD)
How Do I Prepare for a Spinal X-ray?
Before your spinal X-ray, besides telling your doctor that you are or might be pregnant, let him know if you have an insulin pump or had any other types of X-rays recently.
You may need to remove your clothes and wear a gown during the test. Also, anything that's made of metal may show up on an X-ray, so remove things like these beforehand: