Compléter Magnetic Resonance Imaging (MRI)Version en ligne - components of an MRI machine - how an MRI machine produces images par Zainab Nabeel 1 During MRI testing , the patient sits inside a surrounded by a field . Some mechanisms happen between the MRI machine and the patient's body causing ( radio - frequency ) signals to be released from the patient's body . The MRI machine captures these signals , producing an MRI image . Chemists have been using a technique called spectroscopy ( nuclear magnetic resonance spectroscopy ) since the 1950's to figure out the chemical composition of substances . In NMR spectroscopy , first a sample tube containing the substance is subjected to a strong field . Then , an RF transmitter sends a signal called an RF pulse into the sample . The same RF transmitter is used to detect signals from the sample afterwards . These signals are called decaying electromagnetic signals ( signals that decrease in with time ) . In NMR , we are interested in how strong these signals are at different magnetic field strengths to detect the presence of specific chemical groups . In MRI , we are interested in how fast the signals that belong to hydrogen atoms decay ( called T1 and T2 ) to detect local tissue properties . Nuclear Magnetic Resonance ( NMR ) gets its name because it is associated with the nucleus of atoms . MRI is an imaging technique that is based on the principles of and relies on the body's natural magnetic properties to produce images . Normally , hydrogen spin on their axes in random directions , however when the body is subjected to a magnetic field , the protons' axes will either align with the field or themselves against the field . Protons align in two different directions because of their different energy states . Protons that align with the field are in a lower energy state and protons that align against the field are in a higher energy state . There are usually a few more protons that align with the field than protons that align against the field . These are the protons used for producing an image . Once the magnetic field is applied , the MRI technician would use the RF placed near the body part being scanned to send RF . The extra protons mentioned earlier will absorb the energy of these pulses and that will cause them to flip on their , so they will become aligned the magnetic field . So , essentially these protons have moved to the energy state . When the RF pulses stop , these protons release the energy they absorbed and return to their previous alignments and lower energy states . In doing so , they emit a signal back to the RF coil , which gets turned into an electric that gets digitized by the scanner . That is how an image is produced using an MRI machine . It should be noted however that different shades of can be seen in MRI images . This is due to the varying signal strengths . The stronger the signal back to the coil , the lighter the shade will be . The strength of a signal corresponds to the number of present in the body part . The more protons , the stronger the signal will be .
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