Body Imaging at 7T?: Perspectives in 2012

Neil M. Rofsky, MD, FACR, FSCBTMR, FISMRM

In 1999, did you think you would use a 3T scanner for body imaging?

• 1) I was confident of this

• 2) I was unsure

• 3) I was very skeptical

• 4) I thought it was impossible

How would you characterize your current use of 3T for body imaging?

• 1) Interchangeably with 1.5T

• 2) Sparingly

• 3) Not at all

• 4) No access to a 3T in my practice

Starfruit at 7T

7T

• Unlike conventional 1.5T and 3T MR systems using a large volume built-in transmit body RF coil, 7 Tesla MRI at this point uses local transmit/receive RF coils

Umutlu,et al. Eur Radiol 2011; 21:841–849

Why 7T?

• SNR advantage

• Chemical separation

• Spectro

• Multipoint Dixon

• Na-23, O-17, P-31

• Unique contrast

• Susceptibility – brain, DWI?

• Fxnal blood flow

1H NMR spectra of subcutaneous fat (left) and tibial bone marrow (right) from a 26 year-old healthy male at 7 Tesla (7T).

Ren J et al. J. Lipid Res. 2008;49:2055-2062

So what?

• The ability to resolve protons adjacent to double bonds allows noninvasive estimation of the fatty acid composition of adipose tissue.

• Potential as an internal standard to quantify intramuscular lipids

• New insights into insulin sensitivity, diabetes, and obesity

Challenges: Images

• Artifacts

• Tissue susceptibility

• Chemical shift

• Signal heterogeneities

• Radiofrequency (RF) wavelength

• SAR

• Flip angle adjustments

• Echo train imaging

7T, 1H frequency = 298 MHz λ

• the radio frequency (RF) ��s in body

tissues are ≤ the object of interest resulting in non-uniform excitation and receive patterns due to complex RF field interferences.

300 cm

T2WI (TSE) at 7T

Umutlu,et al. Eur Radiol (2011) 21:841–849

16 channel transmit/receive array

Ladd et al. 2010 IEEE International Symposium on Biomedical Imaging Pages: 572-572

What # is optimal???? $$$$

7T Abdomen: T2WI

T2W, echo-train imaging: FSE, TSE

• Mult refocusing pulses

• SAR intensive

• Mitigate?

�� FAs

• Novel sequence design

T2W, echo-train imaging: FSE, TSE

1/100th reduction in SAR

Sarkar, et al. Radiology 2011; 259: 550-557.

T2W, echo-train imaging: FSE, TSE

1/100th reduction in SAR

Sarkar, et al. Radiology 2011; 259: 550-557.

*

Renal imaging at 7T (flat contrast)

T1WI GRE in phase T1WI GRE opposed phase

Umutlu,et al. Eur Radiol 2011; 21:841–849

Renal imaging at 7T (flat contrast)

T1WI GRE in phase T1WI GRE opposed phase

Umutlu,et al. Eur Radiol 2011; 21:841–849

add-on system for RF shimming integrated on the small signal side of the MR system

Renal imaging at 7T 2D FLASH

Umutlu,et al. Eur Radiol; 2011:841–849

L S

Prostate at 7T: Radiative Surface Coil

0.5 mm x 0.5 mm x 3 mm Raaijmakers et al. Mag Res in Medicine 66:1488–1497 (2011)

3T ERC 0.7x 0.7 x 2mm

7T: Patient acceptance

Mean grades < 3 (“very well tolerable”) except for exam duration at 7T.

Theyson, et al. Magn Reson Mater Phy (2008) 21:63–72

Conclusions

• Not useful for clinical in 2012

• Impossible??

• Niche applications??

• Stay tuned…..