Popular posts from this blog
MRI Physics
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 ...
Electromagnetic Induction
Electromagnetic induction Electromagnetic induction is the induction of electric current via changing magnetic fields. Magnetic fields are generated by moving charges (equivalent to electrical current). Ampere’s law or Fleming’s right hand rule determines the magnitude and direction (i.e. clockwise or anti-clockwise) of the magnetic field with respect to the direction of the flow of current. That is, if you point your right thumb in the direction of the current, the magnetic field will follow the curve of your fingers. Changing magnetic fields can induce an electric current. When a magnet is moved in and out of a closed circuit, an oscillating current is produced which ceases the moment the magnet stops moving. This is explained by Faraday’s law of induction. The change in magnetic flux through a closed circuit induces an electromotive force (EMF) in the circuit. The EMF drives a current in the circuit. The laws of electromagnetic induction state that the in...
Comments
Post a Comment