I hope to use MRI methods to image species with extremely short transverse relaxation times (e.g., 7Li of lithium metal). I recently started using Bruker's microimaging system(Micro 2.5) and the Paravision software. I found that some built-in pulse sequences such as Flash, MSME, and RARE are effective for imaging high-sensitivity nuclei (1H), but may not be efficient for low-sensitivity species like 7Li with short T2 . Currently, I aim to perform a simple spin-echo imaging experiment and then perform phase encoding along the x and y axes without slice selection. Unfortunately, it seems that Paravision does not provide a simple way to customize pulse/gradient sequences. Therefore, my question is, can Paravision be used to customize imaging pulse sequences? I would like to control parameters such as pulse width, power, pulse spacing, and gradient amplitude, similar to what is possible with TopSpin.
In addition, I would greatly appreciate it if someone could provide information on how to program gradient pulses and process phase encoding data in TopSpin.
Hi Hongxin,
You can just about image Li0 using paravision with a MSME sequence, hard pulses, and short echo times. The best resolution is around 50 microns.
However, one would recommend using TopSpin, where it is possible to achieve less than 10 microns.
Gregory J Rees
Hi Gregory，
Sincerely thank you for generously sharing your experience. Today, I followed your advice and tried using the MSME sequence (p90=150us@150W, TE=2ms，slice = 5mm， Resolution = 1mm * 1mm), but still did not observe any signal. I noticed that the RF field strength of the coil is limited, resulting in longer hard pulse widths. Additionally, it is very challenging to reduce the TE to less than 1ms in Paravision. Considering that the T2 of Li0 is very short (
Hi Hongxin,
What about sequences adapted to short T2? In your case, I would recommend the ZTE sequence to avoid any trouble in trajectory measurement that you might encounter with UTE.
I would recommend starting with a single pulse to check your linewidth and then parametrize your ZTE experiment accordingly.
Best regards,
Maxime
Hi Hongxin,
Your P90 is very long (40 mm coil?). I tend to use a 10 mm coil and get 15 us @ 80 Watts. The T2 I get for Li0 is typically >4 ms as well. As Maxime notes it may be worth trying a ZTE experiment.
From my last Li0 images :
MSME, P90 15 us @ 80 W,
5x5 mm, 128x128
Tr = 500 ms
Echo spacing 3.838 ms
ns = 2048
offset = 240 ppm
bandwidth 50 kHz
Gregory J Rees
Hi Gregory,
You are right, we are using a 30mm coil, which results in a very long P90 (it might even be difficult to achieve a full 90° flip, I guess). Also, I noticed that the total duration of your experiment is approximately 36 hours, which really surprised me. Your detailed experimental parameters are extremely valuable to me! Additionally, I found that your offset can set to 240 ppm. Strangely, when I set the working chemical shift, its range is limited to (200, -200) ppm. How you achieved this?
Maxime Yon
Hi Maxime,
hank you for your very honest suggestions! In fact, I have tried ZTE and UTE initially but did not acquire the expected signal. On one hand, this is due to my unfamiliarity with the parameters for such pulses, and on the other hand, it might be due to insufficient sampling time. However, I noticed a rather strange phenomenon. When using UTE for sampling, a circular 2D image can be observed. At first, I thought this was my Li0 sample, but after modifying the FOV, I found that the circular image always occupies the same proportion of the frame. This means that this signal is inherently generated by the pulse sequence itself. Why is this happening?
Hi Hongxin,
UTE can give this kind of weird result when the trajectory is not well measured which is usually the case if you do it directly on your short T2 material.
ZTE is more robust since it does not require a trajectory measurement.
What is the result of a single pulse experiment in Paravision? That would help to define the ideal parameters for imaging...
Best,
Maxime
Hi Hongxin,
How are you imaging the metal if you cannot set your chemical shift beyond 200 ppm? As with Maxime - can you see it in the single pulse? There should be no limit on where you set the offset frequency.
As for the experimental time, yes it is very long, the skin depth and lack of Li0 signal usually mean you don't see much signal. I normally run mine over weekends.
You can also heat the sample up a bit, this allows for more Li diffusion, creating longer T2 times. This can help with signal-to-noise and echo times.
Best wishes, Greg
Gregory J Rees
Hi Greg,
This is really strange because when I set the working chemical shift to 250 ppm, the program throws an error (as shown in the picture). Could it be due to different software versions? (I am using Paravision 360). I utilized a bug in the program by directly setting the working frequency to the frequency corresponding to 250 ppm. This way, I can see the lithium metal signal in the onepulse results. Anyway, this is really confusing for me!
Hongxin
Hi Hongxin,
Weird, can toy change the working frequency to Li0?
I suspect it's in the coil settings. But yoy might need to email Bruker apps support for a fix.
Best Greg
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