Why don't you solve the aliasing problemen by adding a massive gradient that de-phase all the spins wherever you don't want any signal? Then you will maintain the NSA (i.e. SNR) and the spatial resolution. What am I missing?

Increasing FOV by adding wrap to avoid alliasing I guess. What would be the difference between matrix size and FOV ?

decreasing FOV leads to increased SNR?? is this what is happening in practice while changing the parameter on the machine?

@braciole7667

3 ай бұрын

Decrease fov , decrease in snr . Increase fov, increase snr.

@yosef8101

3 ай бұрын

@@braciole7667 yeah, my mistake

How many samples can you acquire at TE realistically ?

@spdn

7 жыл бұрын

mriquestions.com/frequency-wrap-around.html In most modern MR scanners, the MR signal is sampled 512-1024 times per echo (even though the display resolution in the frequency-encode direction is usually taken to be 256). In other words, the Nyquist sampling rate is 2-4 times the highest frequency in the signal. Because this task is accomplished by merely increasing the digitizing rate of the sampling circuitry, it imposes essentially no time penalty and occurs "invisibly".

01:25 I am a cardiologist and I agree :)

Thanks, well explained

Bandwidth and sampling rate are not the same thing. It's confusing when Dr. Lipton talks about bandwidth and means sampling rate.

@alienzenx

3 жыл бұрын

Thanks, I was really confused by this.

He does not seem to express a clear distinction or delineation between SEND BANDWIDTH/LARMOUR FREQUENCY BEING SENT, AS OPPOSE TO AND IN RELATIONSHIP TO THE RECEIVE BANDWIDTH. Where is the SEND bandwidth IN RELATIONSHIP to the receive bandwidth. Perhaps he expresses this in his other lecture...I'll check. Thanks so much

@jacobvandijk6525

2 жыл бұрын

I noticed that in his video on slice-selection (#21, after 30 min.) dr. Lipton doesn't use the word 'bandwidth' in connection to an RF-pulse. So for him bandwidth (BW) is only related to sampling. He could have distinguished between a spectral BW of the RF-pulse and a sampling BW.

I don't understand how he seems to be equating BW with sampling rate... Isn't BW the range of frequencies we want to sample and not a rate? I understand that BW and rate are related due to the Nyquist Theorem because we have to sample at least as often as 2X the highest frequency in the BW... therefore say the BW is 10, this would mean that 5 is the highest frequency in the BW so the sampling rate must be 10 (2*5). So in that sense, BW is equal to sampling rate but only due to the math and not conceptually

Overall this is a good course but I can’t recommend this particular video. There are multiple black pearls that will only confuse you. Look elsewhere to understand the concept of receiver bandwidth.

Confusing 😒

@jacobvandijk6525

2 жыл бұрын

Lack of equations. Just talk.