An X-ray of the sacroiliac joint is a safe and painless test to visualise the area of the back where the spine joins with the pelvis (hip bones). The image is recorded on a special X-ray film. The X-ray image is black and white. Dense structures such as the bones, appear white and softer body tissues, such as the skin and muscles appear darker. The actual exposure time to radiation is usually less than a second, although the overall test may take 15-20 minutes.