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Neonatal Brain: Regional Variability of in Vivo MR Imaging Relaxation Rates at 3.0 T—Initial Experience¹

¹ From the Imaging Division, Lawson Health Research Institute, London, Ontario, Canada (L.A.W., N.G., P.A.P., D.S.L., V.K.H., R.T.T.); Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada (L.A.W., N.G., P.A.P., R.T.T.); Departments of Nuclear Medicine (L.A.W.), Radiology (N.G., R.T.T.), and Maternal and Newborn Health (D.S.L., V.K.H.), St Joseph’s Health Care, 268 Grosvenor St, London, ON, Canada N6A 4V2; and Department of Neurology, Henry Ford Health Systems, Detroit, Mich (J.R.E.). Received November 3, 2003; revision requested January 27, 2004; final revision received July 30; accepted September 29. Supported by the Canadian Foundation for Innovation, the Ontario Innovation Trust, the Ontario Research and Development Corporation Fund, and the Canadian Natural Sciences and Engineering Research Council. J.R.E. supported in part by National Institute of Neurological Disorders and Stroke grant 1P01-NS23393. Address correspondence to L.A.W. (e-mail: lwilliams@lri.sjhc.london.on.ca).

PURPOSE: To retrospectively investigate regional in vivo magnetic resonance (MR) imaging transverse and longitudinal relaxation rates at 3.0 T in neonatal brain, the relationship between these rates, and their potential use for gray matter (GM) versus white matter (WM) tissue discrimination.

MATERIALS AND METHODS: Informed parental consent for performance of imaging procedures was obtained in each infant. Informed consent for retrospective image analysis was not required; ethics approval was obtained from institutional review board. At 3.0 T, R1 and R2 were measured in brain regions (frontal WM, posterior WM, periventricular WM, frontal GM, posterior GM, basal ganglia, and thalamus) in 13 infants with suspected neurologic abnormality (two term, 11 preterm). Maps of R1 and R2 were acquired with T1 by multiple readout pulses and segmented spin-echo echo-planar imaging sequences, respectively. Accuracy of R1 and R2 map acquisition methods was tested in phantoms by comparing them with inversion-recovery and spin-echo sequences, respectively. Statistical analysis included linear regression analysis to determine relationship between R1 and R2 and Wilcoxon signed rank test to investigate the potential for discrimination between GM and WM.

RESULTS: In phantoms, R1 values measured with T1 by multiple readout pulses sequence were 3%–8% lower than those measured with inversion recovery sequence, and R2 values measured with segmented echo-planar sequence were 1%–8% lower than those measured with spin-echo sequence. A strong correlation of 0.944 (P < .001) between R1 and R2 in neonatal brain was observed. For R2, relative differences between GM and WM were larger than were those for R1 (z = –2.366, P < .05). For frontal GM and frontal WM, (R2_GM – R2_WM)/R2_WM yielded 0.8 ± 0.2 (mean ± standard deviation) and (R1_GM – R1_WM)/R1_WM yielded 0.3 ± 0.09.

CONCLUSION: Results at 3.0 T indicate that R1 decreases with increasing field strength, while R2 values are similar to those reported at lower field strengths. For neonates, R2 image contrast may be more advantageous than R1 image contrast for differentiation between GM and WM.

© RSNA, 2005

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