Transcript Inversion Recovery

Beyond FLAIR: Expanding the Role
of Inversion Recovery in MR Imaging
of the Brain
Ali Batouli1
Michael Spearman1
Michael Goldberg1
Emmanuel Kanal2
1
Allegheny Health Network
2
University of Pittsburgh
Poster # EP-58
DISCLOSURES
• The authors have no disclosures
What is inversion recovery?
• Inversion Recovery (IR) pulses have the power to null
the signal from a desired background tissue to
accentuate underlying pathology
• This allows for greater contrast and improved
diagnostic accuracy
How does IR work?
• IR is a conventional spin echo sequence preceded by
a 180° inverting pulse
• The time between the 180° inverting pulse and the
90°-pulse is called the inversion time (TI)
Traditional Spin Echo:
{90°−180°−echo}
Inversion Recovery:
180° —
{90°−180°−echo}
Image modified from http://mri-q.com/what-is-ir.html © 2014 AD Elster, ELSTER LLC
How does IR work?
• Longitudinal magnetizations of different tissues are
separated based on intrinsic T1 relaxation times at the
start of signal acquisition
• The TI controls degree of separation of varying tissues
and hence image contrast
• Signal from any particular tissue can be nulled by
carefully choosing TI in relation to TR
FLAIR – nulled CSF signal
TR: 8,000-11,000 ms
TI: 2,000-2,600 ms
What are the traditional uses of
IR in imaging of the brain?
• T2 weighted Fluidattenuated inversion
recovery (FLAIR)
FLAIR
– Fluid is nulled to
highlight periventricular
and perisulcal pathology
– FLAIR improves MS
lesion detection in the
supratentorial brain by
7% compared to T2
Image from Woo et al. 2006
(Woo et al. 2006)
T2
What are newer uses of IR in
imaging of the brain?
• T2 weighted double
inversion recovery
(DIR)
– 2 inversion times
used to null CSF and
white matter
– DIR improved MS
lesion detection in
the infratentorial
brain by 56%
compared to FLAIR
(p=0.02) (Wattjesa et
al. 2007)
Figure from: Wattjes et al. 2007
PURPOSE
• Develop new partially T1 weighted MRI sequences
that utilize the power of inversion recovery to null
signal from gray matter (GM) and white matter (WM)
• Improve diagnosis of T1 hyperintense and enhancing
pathology at the gray white junction
Materials and Methods
• Siemens Avanto 1.5T MRI system
• Standard circular polarized head coil used on healthy
adult volunteer.
• Following variables were held constant:
– Echo time (TE) of 11 ms
– Receiver bandwith of 16 kHz
– Single excitation
– Slice thickness of 5 mm
– 29 sections
– 256 x 256 matrix size.
– Field of view: 220 mm
– Phase oversampling: 20%
Materials and Methods
• Multiple TR and TI times were chosen in order to
optimize white matter and gray matter signal nulling.
• White matter inversion recovery (WMIR) and Gray
matter inversion recovery (GMIR) sequences were
chosen at mild and moderate T1 weighting
• High fat signal was maintained on all sequences to
ensure high conspicuity of T1 hyperintense pathology
Results
• Four overall sequences were chosen
• Mild and moderate T1 weighted WMIR
• TR ranged from 1000-1700 ms
• TI ranged from 300-350 ms
• Mild and moderate T1 weighted GMIR
• TR ranged from 1000-2500 ms
• TI ranged from 350-630 ms
TI: 300-630
TE: 11
TR: 1000-2500
Times not to scale. TI, TE and TR in milliseconds.
Image modified from http://mri-q.com/what-is-ir.html
© 2014 AD Elster, ELSTER LLC
Results
• Four overall sequences were chosen
• Mild and moderate T1 weighted WMIR
• TR ranged from 1000-1700 ms
• TI ranged from 300-350 ms
• Mild and moderate T1 weighted GMIR
• TR ranged from 1000-2500 ms
• TI ranged from 350-630 ms
TI: 300-630
TE: 11
TR: 1000-2500
Times not to scale. TI, TE and TR in milliseconds.
Image modified from http://mri-q.com/what-is-ir.html
© 2014 AD Elster, ELSTER LLC
Results: Mildly T1 weighted WMIR
• TR 1700
TI 350
• Signal intensities:
• WM – 25
GM – 180
• Ratio of WM to GM: 14%
CSF – 250
Fat – 520
Ratio of WM to Fat: 5%
Results: Moderately T1 weighted WMIR
• TR 1000
TI 300
• Signal intensities:
• WM – 25
GM – 55
• Ratio of WM to GM: 45%
CSF – 65
Fat – 380
Ratio of WM to Fat: 7%
Results: Mildy T1 weighted GMIR
• TR 2500
TI 630
• Signal intensities:
• WM – 220
GM – 20
• Ratio of GM to WM: 9%
CSF – 205
Fat – 650
Ratio of GM to Fat: 4%
Results: Moderately T1 weighted GMIR
• TR 1000
TI 350
• Signal intensities:
• WM – 90
GM – 10
• Ratio of GM to WM: 14%
CSF – 60
Fat – 525
Ratio of GM to Fat: 2%
Results
• Substantial nulling of WM and GM signal was
achieved.
• Sequences had both mild and intermediate T1 and
T2 weighting, with the nulled tissue having near zero
signal
• Fat signal intensity was maintained
Conclusion
• Inversion recovery is a powerful tool that increases
image contrast by nulling background tissue
• T1 weighted GMIR and WMIR are new sequences
which may improve diagnosis of T1 hyperintense
pathology such as:
– Metastastic disease
– Small vascular malformations
• Further research is necessary to test these new
sequences
References
1. Hori M, Okubo T, Uozumi K, et al. T1-weighted fluid-attenuated inversion recovery at
low field strength: a viable alternative for T1-weighted intracranial imaging. AJNR
2003;24:648–51.
2. Lee JK, Choi HY, Lee SW, et al. Usefulness of T1-weighted image with fast inversion
recovery technique in intracranial lesions: comparison with T1-weighted spin echo
image. Clin Imaging 2000;24:263–69.
3. Wattjesa MP, Lutterbeya GG, Giesekea J,et al. Double Inversion Recovery Brain Imaging
at 3T: Diagnostic Value in the Detection of Multiple Sclerosis Lesions. AJNR
2007;28:54-59.
4. Qiana YF, Yua CL, Zhanga C, et al. MR T1-Weighted Inversion Recovery Imaging in
Detecting Brain Metastases: Could It Replace T1-Weighted Spin-Echo Imaging? AJNR
2008;29:701-704.
5. Melhem ER, Bert RJ, Walker RE. Usefulness of optimized gadolinium-enhanced fast
fluid-attenuated inversion recovery MR imaging in revealing lesions of the brain. AJR
Am J Roentgenol 1998;171:803–07.
6. Woo JH, Henry LP, Krejza J, Melhem ER. Detection of Simulated Multiple Sclerosis
Lesions on T2-weighted and FLAIR Images of the Brain: Observer Performance.
Radiology 2006 241:1, 206-212.
Thank You!