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| Result: Searchterm 'Slice'
found in 37 messages |
| Result Pages: 1 2 3 4 5 6 [7] 8 |
More Results:  Database (177) News Service (6) Resources (5) |
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Reader Mail
Wed. 12 Dec.07,
10:07
[Reply (1 of 2) to:
'double ir physic'
started by: 'soontorn siriserussa'
on Sun. 2 Dec.07]
 Category:
Sequences and Imaging Parameters
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| double ir physic |
Different types of double inversion recovery (DIR, 2IR) sequences are used to improve the suppression of blood signal (black blood technique) or to null the signals from two different tissue types (e.g. white matter and cerebrospinal fluid).
The black blood technique (used in cardiovascular MRI) works with two inversion pulses, where the first pulse is nonselective and the second pulse is slice-selective. TI is set to a value at which the signal of the recovering inverted blood is zero (http://www.mr-tip.com/serv1.php?type=db1&dbs=Double%20Inversion).
The second technique (also named gray matter only) is used in brain imaging to improve the detection of lesions, for example in the diagnostic of multiple sclerosis. Two 180° pulses with different TI are used to suppress two different types of tissue simultaneously.
Hope this helps
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|  View the whole thread | | |
Renate Bloemer
Mon. 13 Nov.06,
19:46
[Reply (1 of 3) to:
'MRA'
started by: 'Marco Costa'
on Sun. 22 Oct.06]
Category:
Protocols
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| MRA |
A test bolus helps to get the delay at which time the CE-MRA sequence has to be started. The sequence needed is a one-slice dynamic fast gradient echo sequence (if possible with fat suppression or subtraction) and a temporal resolution of 0.5 to 1.5 sec. This thick slice is placed over the vessel of interest and the dynamic is started simultaneous with a small (1-2ml) bolus of Gad.
In the follow up you can see at which time the bolus is visible. If it is not clear to differentiate, a ROI measurement will help. The starting time depends on the k-space filling. Around the peak of the highest intensity, the contrast information should be read out (with "centric" at the beginning of the sequence).
Centric k-space filling order means that the central lines of the k-space are filled in the first seconds after starting the scan. Depending on the equipment, there is more than one non-centric order, for example linear, where the central lines are filled in the middle of the scan time.
Hope this helps.
Renate Bloemer
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| | View the whole thread | | |
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
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| 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.
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| | 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
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Jorge Cazal
Mon. 13 Jun.05,
17:06
[Start of:
'Metalic particles into the cornea'
2 Replies]
Category:
Safety
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| Metalic particles into the cornea |
Dear Friends:
We are working in a Ophthalmology Department at Institut Universitari Dexeus-USP in Barcelona.
We received a patient who was treated for myopia some time ago using a LASIK technique ( Laser In situ Keratomileusis) as you probably know, cornea was sliced and lasered using a microkeratome however blade oscilation in the past eventually spread into the interface particles comming from steel inox blade´s.
Could this affect an MRI of Head, is this a contraindications, ( particles are microscopic/multiple and are interlamellar into cornea )
Thank you for your input
Kind Regards
Jorge Cazal;MD
Cornea & Refractive Surgery Unit
Institut Universitari Dexeus-Barcelona
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