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Welcome to Radiological Assistance page. Here you can find some interesting fact about Radiology.

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MRI Physics

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THE BASIC PROCESS The way MR images are generated is complicated and is much harder to understand than plain radiography, CT and ultrasound. It has strong underpinnings in physics which must be understood before any real sense of 'how it works' is gained. What follows is a very abbreviated, 'broad strokes' description of the process. Essentially, the process can be broken down into four parts: 1. Preparation 2. Excitation 3. Spatial encoding 4. Signal acquisition Preparation The patient is placed in a static magnetic field produced by the magnet of the MR scanner. In living tissues there are a lot of hydrogen atoms included in water molecules or in many different other molecules. The proton, the nucleus of hydrogen, possesses an intrinsic magnetisation called spin. The spin magnetization vector precesses (rotates) around the magnetic field at a frequency called the Larmor frequency, which is proportional to the magnetic field intensity. The
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Echo Time

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ECHO TIME The echo time (TE) refers to the time between the application of the radiofrequency excitation pulse and the peak of the signal induced in the coil. It is measured in milliseconds. The amount of T2 relaxation is controlled by the TE.
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Relaxation

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Relaxation MRI image contrast is influenced by several characteristics of tissues and other materials including: T1, T2 and T2* relaxation as well as spin density, susceptibility effects and flow effects. This page and the following detailed pages on relaxation parameters will introduce properties and effects on imaging contrast, time and signal-to-noise ratio (SNR). Relaxation  is the process in which spins release the energy received from a radiofrequency pulse. T1 and T2 relaxation rates affect the SNR in an image. Improvement in the SNR is seen when the TR is increased significantly to about 3-5 T1 times. Changing the TR time will also affect the T1 weighting of the image and the acquisition time. T1 weighting occurs in a short TR spin echo sequence because of incomplete recovery of longitudinal magnetization. The effect of TR on SNR can be shown graphically by a T1 relaxation curve as illustrated in the exponential growth curve in figure 1. As the TR is increased to
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