Skin T1 mapping at 1.5T, 3T, and 7T
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Transcript of Skin T1 mapping at 1.5T, 3T, and 7T
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Skin T1 mapping at 1.5T, 3T, and 7T
Erik Gudmundson 2
Nikola Stikov 1
Maryam Etezadi-Amoli 1
Joëlle Barral 1
Peter Stoica 2
Dwight Nishimura 1
1 2
# 4451 Presentation: Thursday @ 2pm
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2Skin T1 mapping at 1.5T, 3T, and 7T # 4451
In a nutshell
Gold standard: 2D-Spin Echo Inversion Recovery
Model:
In vivo skin T1:
Affected by: temperature and perfusion
Fitting procedure: non-linear LS + grid search
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3Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Motivation & Goals
http://www.nlm.nih.gov
Epidermis ~ 100 μm
Dermis ~ 1 mm
Hypodermis (fat) ~ 1 cm
Barral JK, et al. Proc 16th ISMRM, p. 742, 2008
Define a T1 mapping gold standard methodology
Determine T1 of the different skin layers
For skin imaging, does increase in T1 at higher field strengths offset the SNR
gain?
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4Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Pulse sequence
http://www-mrsrl.stanford.edu/SpinBench
TIθ1 90°
TR
180°
* A selective pulse was used for Subject 1 and a non selective one for Subject 2. Transition bands decrease the effective flip angle when a selective pulse is used. In both cases, the effective flip angle at each location depends on T1 and T2.
2D Spin Echo Inversion Recovery SE-IR with a 8.64 ms Silver-Hoult adiabatic 180°*
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5Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Fitting procedure
The model is linear in a and b. This makes it possible to rewrite J so that an estimate of T1 is found through a 1D grid search over possible T1s
Generic model ‘ab’:
Find a, b, and T1 by minimizing
Stoica P and R Moses. Spectral Analysis of Signal, p. 151, 2005
Complex data
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6Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Protocol 1/2
1.5T, 3T and 7T
Receive-only @ 1.5T and 3TTransmit/Rc @ 1.5T and 7T
1 inch ∅
Calf immobilized
20C±2.5C*
68F±4F
Room temperature
*Variations between experiments. Temperature was stable within 1C for a
given experiment.
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7Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Protocol 2/2
TI = [50, 300, 1000, 2000] ms
We target T1s < 1000 ms.
Resolution: 117μm × 469μm × 2mm
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8Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Results: Example at 3T (1/3)
50 ms 300 ms 1000 ms 2000 msTI
Individual magnitude images
Dermis
Muscle
Hypodermis
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9Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Results: Example at 3T (2/3)SNR map @ TI = 2000 ms T1 map [ms]
Hypodermis
Muscle Dermis
Hypodermis
Muscle Dermis
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Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Results: Example at 3T (3/3)T1 histograms# pixels
ms
HypodermisMuscle* Dermis
*Muscle is not visible when a Tx/Rc coil is used
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Results: summary
Error bars indicate the standard deviation over the ROI, taken as 0.64xFWHM.
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Comparison with the literature
Richard S, et al. J Invest Dermatol 97:120-125, 1991 -- Gold GE, et al. AJR 183:343-351, 2004 -- Stanisz GJ, et al. MRM 54: 507-512, 2005
(used saturation recovery)
Muscle Hypodermis
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Conclusions
Barral JK, et al. Proc 16th ISMRM, p. 742, 2008
In the dermis, T1 mapping is still very challenging:
- short T2- presence of many structures- temperature differences
A 94 % increase in hypodermis T1 was observed from 1.5T to 7T. It translates to a 40% decrease in SNR efficiency for our skin protocol. It should therefore not offset the expected field-strength related SNR increase.
The fitting algorithm we proposed can be generalized to other relaxometry techniques.
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Skin T1 mapping at 1.5T, 3T, and 7T # 4451
Thank you!
Contact:
“Skin imaging at 7T” poster #1993, Wednesday @ 1:30 pm