An X-ray is a picture taken from the inside of an object using high energy electromagnetic radiation with short wavelengths that can pass through items.
Being exposed to X-rays does carry risk of causing cancer many years or decades later, but the risk is thought to be very small. For example, an x-ray of your chest, limbs or teeth is equivalent to a few days worth of background radiation and has less than a 1 in 1 000 000 chance of causing cancer.
Most women feel some discomfort during a mammogram procedure which although varies from patient to patient. Some experience discomfort due to the compression but most women usually do tolerate the exam quite well.
Compression helps to spread out the normal fibro glandular (dense) tissue of the breast making it easier to see through the entire breast.
MRI (Magnetic Resonance Imaging) is a scan that uses magnetic fields and radio waves to produce a detailed image of the body's soft tissue.
There are no known side effect of MRI apart from reversible sensations experienced during the examination.
A CT scan is a combination of a series of x ray images taken at different angles. A computer is then employed to create images from the X-ray.
CT is employed after weighing the risk versus the benefit of carrying out the examination. It is done where the benefit is higher than the risk. Some diseases are shown more clearly by CT than MRI.