Differences

This shows you the differences between two versions of the page.

--- library:bandwidth [2025/03/31 19:39] – scott
+++ library:bandwidth [2025/03/31 20:18] (current) – scott
@@ Line 11: / Line 11: @@
   * Small FOV (13cm) bandwidth: 15-20 kHz
   * Large FOV (24+cm) bandwidth: 31+ kHz
-  * For FSE: keep Min TE around 8-12ms
+  * For FSE: Keep the Min TE around 8-12ms
 ==Siemens==
   * Bandwidth is reported as Hz/Pixel; hold the mouse over the drop down menu to see the # of pixels chemical shift
-  * Fat and water are ~220 Hz apart at 1.5T; try to keep the Hz/Pixel near 220, or # of pixel chemical shift close to 1-1.3
+  * Fat and water are ~220 Hz apart at 1.5T; try to keep the Hz/Pixel in 150-220, or # of pixel chemical shift close to 1-1.5
-  * Keep in mind how large the pixels are when adjusting FOV and Matrix, as the Hz/pixel will stay constant. Big pixels = larger artifacts
+  * Keep in mind how large the pixels are when adjusting FOV and Matrix, as the Hz/pixel will stay constant. Big pixels = big artifacts
 ====Bandwidth in Practice====
 {{:library:rbwchemshift_8_.gif|}}
+The images above are of a phantom made from tap water (outer circle) and olive oil (inner circle) with a T2 weighted FSE, with the frequency encoding direction set R/L. Bandwidth is increased from 10 kHz up to 63 kHz. Notice with low bandwidths the SNR is high, but the chemical shift artifact is significant. As bandwidth is increased, the SNR becomes worse, but the chemical shift is reduced. Looking closely at the top right corner, it is also apparent that some geometric distortion occurs with low bandwidths. As bandwidth increases from low to high, it is also noticeable that some T2 weighting is lost and the CNR between the olive oil and tap water is reduced. This is the to the high bandwidths shortening the echo spacing, and reducing the maximum TE's contributing to the CNR.
 {{:library:rbw_10-63khz_10_.gif|}}
+The images above are of an Axial T2 weighted FSE, with the bandwidth increased from 10 kHz to 63 kHz. Notice that the first low bandwidth (10 kHz) result in quite a blurry image; the echo spacing is long and the chemical shift artifact  is significant. As bandwidth is increased, note how the morphology of the extruded disc appears to change. Also note that the 'bulk' of the patient appears to move within the image; this is the effect of chemical shift across the entire image. Once the 63 kHz bandwidth is reached, the SNR is poor and zipper artifacts appear in the image.