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1. 2. # 4451 Presentation: Thursday @ 2pm. Skin T1 mapping at 1.5T, 3T, and 7T. Joëlle Barral 1. Peter Stoica 2. Dwight Nishimura 1. Nikola Stikov 1. Maryam Etezadi-Amoli 1. Erik Gudmundson 2. In a nutshell. In vivo skin T1 :.

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Skin T1 mapping at 1.5T, 3T, and 7T

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Skin t1 mapping at 1 5t 3t and 7t

1

2

# 4451

Presentation: Thursday @ 2pm

Skin T1 mapping at 1.5T, 3T, and 7T

Joëlle

Barral 1

Peter

Stoica 2

Dwight

Nishimura 1

Nikola

Stikov 1

Maryam

Etezadi-Amoli 1

Erik

Gudmundson 2


In a nutshell

In a nutshell

  • In vivo skin T1:

  • Affected by: temperature and perfusion

  • Gold standard: 2D-Spin Echo Inversion Recovery

  • Model:

  • Fitting procedure: non-linear LS + grid search


Motivation goals

Epidermis ~ 100 μm

Dermis ~ 1 mm

Hypodermis (fat) ~ 1 cm

Motivation & Goals

For skin imaging, does increase in T1 at higher field strengths offset the SNR gain?

  • Define a T1 mapping gold standard methodology

  • Determine T1 of the different skin layers

http://www.nlm.nih.gov

Barral JK, et al. Proc 16th ISMRM, p. 742, 2008


Pulse sequence

Pulse sequence

2D Spin Echo Inversion Recovery SE-IR with a 8.64 ms Silver-Hoult adiabatic 180°*

θ1

90°

180°

TI

TR

* 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.

http://www-mrsrl.stanford.edu/SpinBench


Fitting procedure

Fitting procedure

Generic model ‘ab’:

Complex data

Find a, b, and T1 by minimizing

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

Stoica P and R Moses. Spectral Analysis of Signal, p. 151, 2005


Protocol 1 2

20C±2.5C*

68F±4F

1.5T, 3T and 7T

Calf immobilized

Room temperature

Protocol 1/2

Receive-only @ 1.5T and 3TTransmit/Rc @ 1.5T and 7T

1 inch ∅

*Variations between experiments. Temperature was stable within 1C for a given experiment.


Protocol 2 2

Protocol 2/2

We target T1s < 1000 ms.

TI = [50, 300, 1000, 2000] ms

Resolution: 117μm × 469μm × 2mm


Results example at 3t 1 3

Results: Example at 3T (1/3)

Individual magnitude images

TI

50 ms

300 ms

1000 ms

2000 ms

Muscle

Hypodermis

Dermis


Results example at 3t 2 3

Results: Example at 3T (2/3)

SNR map @ TI = 2000 ms

T1 map [ms]

Muscle

Muscle

Dermis

Dermis

Hypodermis

Hypodermis


Results example at 3t 3 3

Results: Example at 3T (3/3)

T1 histograms

# pixels

ms

Muscle*

Hypodermis

Dermis

*Muscle is not visible when a Tx/Rc coil is used


Results summary

Results: summary

Error bars indicate the standard deviation over the ROI, taken as 0.64xFWHM.


Comparison with the literature

Comparison with the literature

Muscle

Hypodermis

(used saturation recovery)

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


Conclusions

Conclusions

  • 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.

Barral JK, et al. Proc 16th ISMRM, p. 742, 2008


Thank you

Thank you!

Contact:

jbarral@stanford.edu

“Skin imaging at 7T” poster #1993, Wednesday @ 1:30 pm


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