Standardized, Reproducible, High Resolution Global Measurements of T1 Relaxation Metrics in Cases of Multiple Sclerosis
Radhika Srinivasana,
Roland Henrya,
Daniel Pelletierb and
Sarah Nelsona
a Magnetic Resonance Science Center, the Department of Radiology, University of California, San Francisco and the University of California, San Francisco
b Multiple Sclerosis Center, Department of Neurology, University of California, San Francisco, San Francisco, CA
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FIG 1. Error ( T1/T1) (Appendix A, equation 5) in using different combinations of two flip angles to estimate T1 values. One of the flip angles was fixed at 40 degrees, and a TR of 27 was used. Vertical solid lines indicate the flip angle range that minimizes the error for a T1 value of 600 ms.
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FIG 2. Comparison of T1 values from spin-echo and spoiled gradient-echo methods for phantom with spin-echo T1 values in the range of 400 to 1900 ms.
A, This figure shows the T1 estimate derived from the spoiled gradient-echo method (ordinate) for phantoms with different spin-echo T1 values (abscissa). The latter were used as the standard to evaluate the accuracy of the spoiled gradient-echo T1 values. Points are the mean T1 values of a region of interest from the respective phantoms, and error bars represent SD. Solid line represents the ideal situation when the spoiled gradient-echo values are equal to the spin-echo T1 values. Dashed line shows a nonlinear fit through the T1 values estimated with the spoiled gradient-echo method.
B, Comparison of the T1 distribution from a single section for a normal control participant using the spin-echo (solid line) and spoiled gradient-echo (dashed line) methods.
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FIG 3. Percent deviation of T1 estimates from uniformity along the superior-inferior direction for uncorrected and corrected data. Negative values on the abscissa correspond to inferior section locations. The data were corrected for RF inhomogeneity by using a procedure outlined by Alfano et al (6). Considering that the average distance between the landmark position at niason and the center of the coil was 3 cm and that the size of the brain including the cerebellum is approximately 7 cm, the region of interest (ie, supratentorial brain volume) was contained within the homogeneous region of the head coil (solid lines).
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FIG 4. Procedure used to extract white matter and normal appearing white matter from T1 maps of study participants and patients.
A, T1 value of 1000.0 is used to threshold the T1 map.
B, White matter masks obtained by contouring the threshold T1 map.
C, The T1 distribution (solid line) obtained by applying the mask in B to the map in A. This distribution is fit to a Gaussian function (dot-dashed line) and converted into a probability distribution of T1 values.
D, White matter volume obtained by extracting pixels with T1 values within 90% probability (vertical lines in C).
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FIG 5. Results of the T1 map calculation and segmentation procedure from a normal control participant (upper panel) and a patient with relapsing-remitting multiple sclerosis (lower panel).
A, T1-weighted images.
B, T1 maps.
C, Segmentation into white matter.
D, Segmentation into gray matter.
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FIG 6. T1 distribution for a normal control participant (solid line), segmented into white matter (dashed line) and gray matter (dot-dashed line) components. Vertical solid lines represent the T1 range used to generate the white matter volume.
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FIG 7. Reproducibility of T1 measurements. T1 distribution for one control participant who underwent imaging multiple times with the 3D spoiled gradient-echo method. Solid line, session 1; dashed line, session 2.
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FIG 8. Comparison of T1 distributions between control participants (solid line) and all patients with multiple sclerosis (dashed line) in each respective subgroup. In each case, the histogram is normalized to the control population.
A, Control participants and patients with relapsing-remitting multiple sclerosis.
B, Control participants and patients with secondary progressive multiple sclerosis.
C, Control participants and patients with primary progressive multiple sclerosis.
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