1.5 T vs 3.0 T
Updates to Article Attributes
Comparing 1.5T vs 3T MRI systems identifies a number of differences; a 3T system has
- increased signal to noise ratio (SNR)
- increased spatial resolution
- increased temporal resolution
- increased specific absorption rate (SAR)
- increased acoustic noise
Signal to noise ratio
Theoretically, signal is proportional to the square of the static field strength (B0) whereas noise increases linearly. This implies that, in a perfect system, SNR of a 3.0T system would be twice as good as at 1.5T. In reality, due to an increase in susceptibility effects in most tissues, the actual improvement is only in the 30-60% range (instead of 100%). With this increased SNR, the spatial resolution and/or acquisition time can be improved, depending on which is more important for the particular case.
Specific absorption rate (SAR)
SAR is defined as the amount of radiofrequency energy (joules) deposited in tissues (kg). The limit set by the FDA is an amount which results in an increase of 1-degree centigrade in any tissue 2. SAR is proportional to the static field (B0) squared, meaning that a 3.0T system deposits 4 times as much energy within tissue as a 1.5T system. Additionally, SAR is proportional to
- pulse duration and length
- pulse number
- slice number
- flip angle
The dependence of SAR on flip angle results in a relatively large amount of energy deposition for standard spin echo sequences since they use 90-degree flip angles. As a result, there is increased use of gradient echo sequences, which use smaller flip angles. Unfortunately, these latter sequences image T2* and not T2, and are therefore more susceptible to local field artefacts. These problems have largely been overcome with modern units.
Acoustic noise
Rapid gradient switching leads to an increase in the intensity of the acoustic noise, which requires better insulation of both the unit itself and the containing room.
-</ul><h4>Signal to noise ratio</h4><p>Theoretically, signal is proportional to the square of the static field strength (<a href="/articles/b0-1">B<sub>0</sub></a>) whereas noise increases linearly. This implies that, in a perfect system, SNR of a 3.0T system would be twice as good as at 1.5T. In reality, due to increase in susceptibility effects in most tissues, the actual improvement is only in the 30-60% range (instead of 100%). With this increased SNR, the spatial resolution and/or acquisition time can be improved, depending on which is more important for the particular case.</p><h4>Specific absorption rate (SAR)</h4><p>SAR is defined as the amount of <a href="/articles/radiofrequency-energy">radiofrequency energy</a> (joules) deposited in tissues (kg). The limit set by the FDA is an amount which results in an increase of 1-degree centigrade in any tissue <sup>2</sup>. SAR is proportional to the static field (B<sub>0</sub>) squared, meaning that a 3.0T system deposits 4 times as much energy within tissue as a 1.5T system. Additionally, SAR is proportional to</p><ul>- +</ul><h4>Signal to noise ratio</h4><p>Theoretically, signal is proportional to the square of the static field strength (<a href="/articles/b0-1">B<sub>0</sub></a>) whereas noise increases linearly. This implies that, in a perfect system, SNR of a 3.0T system would be twice as good as at 1.5T. In reality, due to an increase in susceptibility effects in most tissues, the actual improvement is only in the 30-60% range (instead of 100%). With this increased SNR, the spatial resolution and/or acquisition time can be improved, depending on which is more important for the particular case.</p><h4>Specific absorption rate (SAR)</h4><p>SAR is defined as the amount of <a href="/articles/radiofrequency-energy">radiofrequency energy</a> (joules) deposited in tissues (kg). The limit set by the FDA is an amount which results in an increase of 1-degree centigrade in any tissue <sup>2</sup>. SAR is proportional to the static field (B<sub>0</sub>) squared, meaning that a 3.0T system deposits 4 times as much energy within tissue as a 1.5T system. Additionally, SAR is proportional to</p><ul>
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