The plain film x ray is the most common radiological diagnostic tool used today. The three main principles when using x rays include: the ability to create electromagnetic radiation at the required wavelength, the ability to focus the radiation onto specific areas and finally the ability of the radiation to be detected once it has travelled through the patient.
X rays can be absorbed in different ways depending on the nature of the tissue. High density tissue like bone will absorb the x rays more and therefore will appear white on an x ray. Low density tissue like organs such as the lungs will not absorb many x rays and hence will appear black on the x ray.
CT or computerized tomography scanning is common medical practice today. CT scans are created by using a series of X rays and firing these rays at the patient at different angles. As with plain film X ray the high-density tissue absorbs more radiation whereas the low-density tissue does not absorb as much. Due to the firing of X rays at different angles, a 3d image can be made using a computer. Often contrast is added to better visualise certain regions of the body such as the cardiovascular system. Unlike a plain film x ray, the CT image will be in the transverse plane as if we are looking up a patient’s feet who is lying down.
While X rays and CT scans are very good at visualising high density tissue, magnetic resonance imaging or MRI is better at visualising soft tissues. Therefore, it is very good at being able to detect certain soft tissue masses and tumours. Images with an MRI can be presented in the sagittal, coronal or transverse plane.
Depending on the weighting of the image different soft tissue structures appear bright and dark on an MRI. T1 weighted images are ones where the fat appears bright, but fluid appears dark. T2 images on the other hand represent fluid as bright and fat as dark.
Learn more about the different types of imaging in this section about imaging modalities- X rays, CT scans and MRI scans.