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Steven Ford
Mon. 7 Mar.11,
15:24
[Reply (4 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
 Category:
Applications and Examinations
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| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
If some of the system are signal starved, it's most likely not due to gradient field strength and speed, but it can be related to that. Like everything else in MRI, it's complex and interdependent.
You're best advised to talk with the apps specialist from the systems that are under-performing, and learn from them what the bandwidth is, and also check the shim. Is the fat suppression OK, but the signal weak, or is the suppression bad also? Do you get a graphic output of the linear (gradient)shim corrrection on the various systems?
It is well worth the money that they might charge, if it comes to that, in order to optimize the use of the systems and for your own education. If the apps person does not know why the other machine works so well, there should be someone higher up in the organization who can shed some light on your question.
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Renate Semrau
Mon. 7 Mar.11,
15:11
[Reply (3 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
Category:
Applications and Examinations
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| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
Slew rate, rise time and/or duty cycle are specific parameters to describe the performance of the gradient amplifier. Amplifiers with higher performance allow a faster slew rate (shorter rise time). Stronger gradients allow to reduce echo time, increase the bandwidth and/or use a smaller FOV by influencing the SNR. To use same parameters on magnets with different gradient performance may not be recommended, or you have to adjust all parameters to the level of your magnet with the poorest performance.
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Elise Gough
Fri. 4 Mar.11,
13:56
[Reply (2 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
Category:
Applications and Examinations
|
| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
Thank you for your response. Our group is strict about FOV, thickness/gap parameters being the same across all magnets. One magnet has slew rate of 77, FRFSE T2, TE 85,TR 3500 Classic Fat supressed images which are pristine, vs magnets of 120 slew rate same parameters look signal starved. So gradient strength makes a speed difference, not an image quality difference?
Elise Gough RT(R)(CT)(MR)
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Robert Patten
Thu. 3 Mar.11,
22:08
[Start of:
'Building 3d Volumes from MRI DICOM'
4 Replies]
Category:
General
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| Building 3d Volumes from MRI DICOM |
I have a number of MRI and CTs since a bad accident. I am a Mechanical Engineer with an electrical, power and computer background.
I was able to render the CT to 3D using Onis (not sure if you've seen this program), but have been unable to manage it with any of the MRIs.
The MRIs were taken on a Phillips Intera 1.5T
I can render a volume but only (1) of the (3) 2D images are clear before it is rendered and the resulting 3D image is just noise. I've tried various software packages and spent a lot of time with the software. Perhaps I don't have the required image files.
Maybe someone knows the answer.
Thanks,
Bob
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Steven Ford
Thu. 3 Mar.11,
20:28
[Reply (1 of 8) to:
'6-1.5T MAGNETS, DIFFERING GRADIENTS'
started by: 'Elise Gough'
on Wed. 23 Feb.11]
Category:
Applications and Examinations
|
| 6-1.5T MAGNETS, DIFFERING GRADIENTS |
I assume that you mean a t2 fat suppressed sequence. Differing gradient strengths have only an indirect effect on these images. The fat saturation sequences require additional pulses which take time to execute; stronger gradient systems can execute these pulses faster.
If you see different results, it can be caused by a number of factors; if you can describe the differences, that would be helpful. Generally speaking, the quality of the magnet homogeneity makes a big difference. If the small FOV scans (wrist) look different from magnet to magnet, that's probably not the cause.
You should ask your MRI applications specialist about this, and pay attention to the TE and bandwidth. Are the FOV and number of steps the same?
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