From a hospital light box, we see a detail of a Magnetic Resonance Imaging (MRI) scan. Sections of a patient's skull and brain illustrate to doctors, potential abnormalities. Dyes used in X-ray and CT scans in the same way because both areas use X-rays (ionizing radiation). Agents work by blocking the X-ray photons from passing through the area where they locate and reach the X-ray film. This results in differing levels of density on the X-ray/CT film but the dyes have no direct physiologic impact on the tissue in the body. MRI contrast works by altering the local magnetic field in the tissue being examined. Normal and abnormal tissue will respond differently to this slight alteration, yielding differing signals. Varied signals are transferred to the images, visualizing many different types of tissue abnormalities and diseases.
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