Dr Frank Gaillard et al.
MR spectrosopy (MRS) allows tissue to be interrogated for the presence and concentration of various metabolites. Grossman and Yousem said "If you need this to help you, go back to page 1; everything except Canavan has low NAA, high Choline" 1. This is perhaps a little harsh, however it is fair to say that MRS often does not add a great deal to an overall MR study but does increase specificity, and may help in improving our ability to predict histological grade.
Physics
The basic principle that enables MR spectroscopy (MRS) is the fact that the electron cloud around an atom shields the nucleus from the magnetic field to a greater or lesser degree. This naturally therefore results in slightly resonant frequencies, which in turn return a slightly different signal.
When we see spectra in general radiology practice, this is usually of protons, although phosphorus can also be targeted to examine ATP.
If raw signal was processed then the spectra would be dominated by water, which would make all other spectra invisible. Water suppression is therefore part of any MRS sequence, either via Inversion Recovery or Chemical shift selective (CHESS). If water suppression is not successful then a general slope to the base line can be demonstrated, changing the relative heights of peaks.
Magnetic resonance spectroscopy (MRS) is performed with a variety of pulse sequences. The simplest sequence consists of a 90 degree RF pulse without any gradients with reception of the signal by the RF coil immediately after the single RF pulse. Many sequences used for imaging can be used for spectroscopy also (such as the spin echo sequence). The important difference between an imaging sequence and a spectroscopy sequence is that for spectroscopy, a read out gradient is not used during the time the RF coil is receiving the signal from the person or object being examined. Instead of using the frequency information (provided by the read out or frequency gradient) to provide spatial or positional information, the frequency information is used to identify different chemical compounds. This is possible because the electron cloud surrounding different chemical compounds shields the resonant atoms of spectroscopic interest to varying degrees depending on the specific compound and the specific position in the compound. This electron shielding causes the observed resonance frequency of the atoms to slightly different and therefore identifiable with MRS.
MR spectrosopy (MRS) allows tissue to be interrogated for the presence and concentration of various metabolites. Grossman and Yousem said "If you need this to help you, go back to page 1; everything except Canavan has low NAA, high Choline" 1. This is perhaps a little harsh, however it is fair to say that MRS often does not add a great deal to an overall MR study but does increase specificity, and may help in improving our ability to predict histological grade.
Physics
The basic principle that enables MR spectroscopy (MRS) is the fact that the electron cloud around an atom shields the nucleus from the magnetic field to a greater or lesser degree. This naturally therefore results in slightly resonant frequencies, which in turn return a slightly different signal.
When we see spectra in general radiology practice, this is usually of protons, although phosphorus can also be targeted to examine ATP.
If raw signal was processed then the spectra would be dominated by water, which would make all other spectra invisible. Water suppression is therefore part of any MRS sequence, either via Inversion Recovery or Chemical shift selective (CHESS). If water suppression is not successful then a general slope to the base line can be demonstrated, changing the relative heights of peaks.
Magnetic resonance spectroscopy (MRS) is performed with a variety of pulse sequences. The simplest sequence consists of a 90 degree RF pulse without any gradients with reception of the signal by the RF coil immediately after the single RF pulse. Many sequences used for imaging can be used for spectroscopy also (such as the spin echo sequence). The important difference between an imaging sequence and a spectroscopy sequence is that for spectroscopy, a read out gradient is not used during the time the RF coil is receiving the signal from the person or object being examined. Instead of using the frequency information (provided by the read out or frequency gradient) to provide spatial or positional information, the frequency information is used to identify different chemical compounds. This is possible because the electron cloud surrounding different chemical compounds shields the resonant atoms of spectroscopic interest to varying degrees depending on the specific compound and the specific position in the compound. This electron shielding causes the observed resonance frequency of the atoms to slightly different and therefore identifiable with MRS.
The highly experienced team at Comprehensive Neurological Care Victoria includes Neurologists and a Neurophysiology Scientist. These specialist services are complimented by Neurophysiology diagnostic testing; EEG (Electroencephalography), NCS (Nerve Conduction Studies) and EMG (Electromyography)....
ReplyDeletehttps://cncvictoria.com.au/