Volume coils
Updates to Article Attributes
Volume coils are the transmit and receive radiofrequency coils which are used to both transmit and receive the radiofrequency signal in MRI. Most MRI scanners have what is called a body coil – which is a volume coil built into the bore of the magnet which transmits the radiofrequency for most examinations. Certain types of imaging require additional smaller volume coils – such as in head and occasionally in extremity imaging (e.g. the knees).
Typical head imaging makes used of head coils, or birdcage coils (because of their appearance). Birdcage coils are an example of circularly polarised coils or quadrature excitation. Circularly polarised coils (in contrast to linearly polarised coils) add a second set of coils perpendicular to the first, driven with sinusoidal currents shifted by 90 degrees. This results in a rotational B1 field (hence circularly polarised). This system is more efficient, as non contributory counter-rotating fields are 180 degrees out of phase and cancel each other out, whereas the in sync subfields accumulate to produce the electromagnetic field.
Volume coils generally have a homogenous RF excitation across a large volume. This is important for transmission, but has the downside of receiving a lot of noise when the target region of interest is small.
-<p><strong>Volume coils</strong> are the <a title="Radiofrequency transmitter" href="/articles/radiofrequency-transmitter">transmit</a> and <a title="Radiofrequency receiver" href="/articles/radiofrequency-receiver">receive</a> <a title="Radiofrequency coils" href="/articles/radiofrequency-coils-1">radiofrequency coils</a> which are used to both transmit and receive the radiofrequency signal in MRI. Most MRI scanners have what is called a body coil – which is a volume coil built into the bore of the magnet which transmits the radiofrequency for most examinations. Certain types of imaging require additional smaller volume coils – such as in head and occasionally in extremity imaging (e.g. the knees).</p><p>Typical head imaging makes used of head coils, or birdcage coils (because of their appearance). Birdcage coils are an example of circularly polarised coils or quadrature excitation. Circularly polarised coils (in contrast to linearly polarised coils) add a second set of coils perpendicular to the first, driven with sinusoidal currents shifted by 90 degrees. This results in a rotational B<sub>1 </sub>field (hence circularly polarised). This system is more efficient, as non contributory counter-rotating fields are 180 degrees out of phase and cancel each other out, whereas the in sync subfields accumulate to produce the electromagnetic field.</p><p>Volume coils generally have a homogenous RF excitation across a large volume. This is important for transmission, but has the downside of receiving a lot of noise when the target region of interest is small.</p>- +<p><strong>Volume coils</strong> are the <a href="/articles/radiofrequency-transmitter">transmit</a> and <a href="/articles/radiofrequency-receiver">receive</a> <a href="/articles/radiofrequency-coils-1">radiofrequency coils</a> which are used to both transmit and receive the radiofrequency signal in MRI. Most MRI scanners have what is called a body coil – which is a volume coil built into the bore of the magnet which transmits the radiofrequency for most examinations. Certain types of imaging require additional smaller volume coils – such as in head and occasionally in extremity imaging (e.g. the knees).</p><p>Typical head imaging makes used of head coils, or birdcage coils (because of their appearance). Birdcage coils are an example of circularly polarised coils or quadrature excitation. Circularly polarised coils (in contrast to linearly polarised coils) add a second set of coils perpendicular to the first, driven with sinusoidal currents shifted by 90 degrees. This results in a rotational B<sub>1 </sub>field (hence circularly polarised). This system is more efficient, as non contributory counter-rotating fields are 180 degrees out of phase and cancel each other out, whereas the in sync subfields accumulate to produce the electromagnetic field.</p><p>Volume coils generally have a homogenous RF excitation across a large volume. This is important for transmission, but has the downside of receiving a lot of noise when the target region of interest is small.</p>
References changed:
- 1. Jerrold T. Bushberg, John M. Boone. The Essential Physics of Medical Imaging. (2011) <a href="https://books.google.co.uk/books?vid=ISBN9780781780575">ISBN: 9780781780575</a><span class="ref_v4"></span>
Tags changed:
- mri
- physics
Sections changed:
- Imaging Technology
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