|
Magnetic
Resonance -
Technology
Information
Portal |
Welcome to MRI Technology • |
|
|
 | Info
Sheets |
| | | | | | | | | | | | | | | | | | | | | | | | |
 | Out-
side |
| | | | |
|
| | | | | |
| Result: Searchterm 'signal'
found in 52 messages |
| Result Pages: 1 2 3 4 5 6 7 8 9 [10] 11 |
More Results:  Database (369) News Service (50) Resources (8) |
|
|
ergun ahunbay
Tue. 2 Jan.07,
19:20
[Start of:
'Geometric distortion'
2 Replies]
 Category:
Artifacts
|
| Geometric distortion |
Dear Listers,
I have some questions about the image distortions in MRI:
1) Are the magnetic field inhomogeneities the only cause of image distortions? Does RF-inhomogeneities cause distortions or just signal inaccuracies?
2) Is it accurate to say that a spiral sequence would not have distortion due to magnetic field inhomogeneity(, but it would have blurring). Would there be image geometric distortions with a spiral imaging?
thank you very much in advance
|
|  View the whole thread | Reply to this thread
(login or register first) | |
Reader Mail
Mon. 30 Oct.06,
16:25
[Reply (1 of 2) to:
'interleaved slices and mean intensity difference in adjacent slices'
started by: 'Reader Mail'
on Wed. 4 Oct.06]
Category:
General
|
| interleaved slices and mean intensity difference in adjacent slices |
With interleaved slice acquisition for example in each TR first the odd slices, and then the even slices are acquired. Differences in signal intensity may occur by changes between these acquisitions (like movement), especially with a long TR. In particular, for fMRI sequences with interleaved slice acquisition a slice time correction is recommended to get accurate measurements.
However, I think "large" signal intensity differences with interleaved slices (except fMRI) are rarely seen with usual sequences and sufficient processing (interpolation) algorithms.
|
| | View the whole thread | | |
Jennifer Jackson
Fri. 21 Jul.06,
04:44
[Reply (1 of 2) to:
'Phase encoding'
started by: 'guillaume bierry'
on Fri. 7 Jul.06]
Category:
General
|
| Phase encoding |
Wow this is a long subject, First you have to under stand how the 3 main gradients are used. (slice select, Freq, then phase)
So you are use 1 of the gradients for your phase encoding. You need to fill the k-space which depends on you matrix. Lets assume you are using 256 (phase). In order to fill K-space you have to have 256 aquistions of the signal. Meaning for each picture (or slice) the signal must be acquire(sampled) 256 times each at a differnt amplitude to put it in a different Line of k-space.
Example- If you are performing a SE(spin echo) you have 1 TR period and 1 TE period (TE=is when the signal is sampled) so you will have to do the TR period 256 times to fill K-space with diffent amplitudes.
There is alot more that I left out. If this did not answer your question let me know
|
| | View the whole thread | | |
GONZALO SOLIS
Tue. 22 Nov.05,
05:35
[Start of:
'usmarine2tim2'
0 Reply]
Category:
Basics and Physics
|
| usmarine2tim2 |
Hello to all my fellow MR Technologists and / or students:
I have a few questions that I would greatly appreciate if someone could help me answer. The dead line is THIS Friday 25th 1000AM morning so please reply STAT
Please e mail me at USMARINE2TIM2@YAHOO.COM
1. . Breath hold duration of less than _________are
recommended when dealing with MR Arenal artery
scan?
a. 30sec
b. 25sec
c. 18sec
d. 8
2. . In renal angiography, what anatomical
landmark does the 3d slab need to cover just
anterior to?
a. Adrenal glands
b. Hepatic vein
c. Portal vein
d. Abdominal aorta
3. .What makes MRI a better choice than DSA for evaluation of a bilateral renal artery stenoses at the orgins of the renal arteries?
a. It is a noisier examination
b. The contrast used is less nephrotoxic than DSA
contrast
c. MRI has higher special resolution than DSA
4. Signal loss will result when further maturation of the clot produces which one of the following?
a. methemoglobin
b. hemosiderin
c. phagocytosis.
d. hemoglobin
5. .For cine gradient echo imaging with true FISP, which of the following statements is TRUE?
a. .images have better image contrast and acquisitions are faster than conventional cine gradient echo imaging
b. cine true FISP images can be performed on any MRI unit
c. to make true FISD images, intravenous gadolinium contrast is needed
d. .true FISP images cannot be used for breath- hold acquisitions because the sequence is too slow
6. Which one of the following statements is NOT
true about phase contrast imaging?
a. .phase contrast imaging is useful for measuring blood flow
b. .phase contrast images are ECG gated
c. .phase contrast images can be performed on most
scanners with cardiac imaging capabilities
d. phase contrast images required
intravenous gadolinium contrast
Thank you so much
Gonzalo RT (R) --future-Ã MR
God Bless
|
| | Reply to this thread
(login or register first) | |
tina muthana
Thu. 14 Apr.05,
22:44
[Start of:
'diffusion MRi'
1 Reply]
Category:
Basics and Physics
|
| diffusion MRi |
Hi
My name is Tina and I am currently studying Diffusion weighted MRI. I was wondering if anyone could elaborate on the effect of introducing a slice selection gradient along with the diffusion gradient on the signal attenuation. Also if there are any sites that could explain it, I would appreciate the information.
Thank you.
-TIna
|
| | View the whole thread | Reply to this thread
(login or register first) |
| |
| | Result Pages : 1 2 3 4 5 6 7 8 9 [10] 11 | |
|
| |
 | Look
Ups |
| |
|
MR-TIP.com uses cookies! By browsing MR-TIP.com, you agree to our use of cookies. | | | [last update: 2024-02-26 03:41:00] |
|
|
bottom
top
