PA Anatomy: Imaging Overview- MR

Magnetic resonance or MR uses magnetic properties of body tissues to generate images, and is related both to the presence and concentration of hydrogen atoms, and to the particular chemical compounds in which the hydrogen is located (this is mostly in water and in fat); in order for images to be obtained, the entire body must be in a very homogeneous high-intensity magnetic field, and usually the patient is on a movable table within a long narrow tube; imaging cannot be performed if the patient has certain types of metal objects in their body, like a pacemaker.

1) recognize each type of imaging and physical property--displays sections of the body, no overlap of structures but each image only shows a limited part of the body; physical property is tissue MAGNETIC/CHEMICAL properties; you can recognize MR as cortical bone will be very dark, and normal fat will be bright, unless 'fat suppression' is used (which decreases signal coming from fat); contrast used is called 'gadolinium'.

2) radiation--uses NO ionizing radiation, but does expose the body to a strong magnetic field.

3) technical factors are related to the PLANE of section and a variety of other settings that can be varied to highlight certain normal or abnormal processes; the commonest of these settings have to do with properties called 'T1' and 'T2'; in general, T1-weighted imaging displays water or edema as dark and T2-weighted imaging displays water or edema as bright.

4) WHITE areas are called 'high signal' and BLACK areas are called 'low signal'.

5) types of disease that are best displayed: soft tissues, such as tendons, cartilage, ligaments, fine internal structure of the central nervous system, internal structure of the uterus, breast tissue, blood vessels.

6) types of disease that are not well demonstrated: GI structures (which are moving during the relatively long imaging time), acute diseases (since imaging takes up to an hour), fine detail of bony structures.