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

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

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?

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°*

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

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.

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

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

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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Skin T1 mapping at 1.5T, 3T, and 7T # 4451

Results: summary

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

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Skin T1 mapping at 1.5T, 3T, and 7T # 4451

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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Skin T1 mapping at 1.5T, 3T, and 7T # 4451

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:

jbarral@stanford.edu

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