Published ahead of print on January 9, 2008
doi: 10.3174/ajnr.A0841
Assessment of the Language Laterality Index in Patients with Brain Tumor Using Functional MR Imaging: Effects of Thresholding, Task Selection, and Prior Surgery
I.M. Ruffa,b,
N.M. Petrovich Brennanb,
K.K. Peckb,
B.L. Houb,
V. Tabarc,
C.W. Brennanc and
A.I. Holodnyb
a Northwestern University Feinberg School of Medicine, Chicago, Ill
b Functional MRI Laboratory of the Department of Radiology, Memorial Sloan-Kettering Cancer Center, New York, NY
c Department of Neurosurgery, Memorial Sloan-Kettering Cancer Center, New York, NY
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Fig 1. The general LI curve starts near zero and rises as the significance (P value) increases as statistical stringency reveals the dominant hemisphere. The LI peaks at a value of +1 or –1 when either the left or the right hemisphere is dominant. At peak statistical stringency, no activated voxels survive and the curve drops back to zero.
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Fig 2. Lateralization changes as a function of statistical thresholding in patient 1. At r = 0.35, P < .026, language would be considered bilateral, but as the statistical threshold increases, the language task indicates left lateralization in the Broca area.
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Fig 3. Laterality index curves of controls performing the following: A, the verb-generation task. In all the control subjects, LI indicates complete left language lateralization in the Broca area across all P values. B, the letter task. All control subjects indicate left-hemispheric dominance in the Broca area except for control 4, whose fMRI suggests bilateral language representation at the highest 2 P values (P < .164 and P < .071), which are clinically insignificant. C, the category task. The individual laterality curves follow the expected pattern, except for control 1 and control 3. In control 1, the LI follows the normal trajectory from r = 0.25, P < .164 until r = 0.45, P < .002, where the LI curve then changes direction and becomes right-lateralized until it hits a peak of LI = –1 at r = 0.75, P < 8.86 x 10–11. fMRI in control 3 indicates bilaterality for language in the Broca area across the entire range of P values measured except for at an r value of 0.65 (P < .3.74 x 10–6) when this subject's fMRI suggests left dominance for language.
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Fig 4. Laterality index curves of patients with tumor without prior surgery performing the following: A, the verb-generation task. Some patients show bilateral language lateralization in the Broca area at clinically insignificant P values, but all the patients lateralize language to the left hemisphere in the Broca area at clinically significant P values (P < .05). B, the letter task. Six patients show bilateral language representation in the Broca area at less significant P values. Patient 9 lateralizes language to the right. Patient 3 lateralizes to the left at less significant P values and to the right at more stringent P values, C, the category task. Two patients have LI curves that lateralize to the left, and 2 patients lateralize language to the right in the Broca area. Both patients who show right-hemispheric dominance for language (patients 5 and 6) have tumors in the right hemisphere.
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Fig 5. Axial T2-weighted images with coregistered fMRI data in patient 3, from the patients with tumor without prior surgery category, performing the letter fluency task. The fMRI data are presented at different thresholds. At less stringent thresholds (r < 0.55), the language LI is bilateral, whereas at more stringent (r > 0.55) thresholds, the LI shifts to the right side. This right-handed patient showed signs of moderate aphasia preoperatively and mild aphasia and dysarthria postoperatively, clinically suggesting a significant left language component.
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Fig 6. Laterality index curves of patients with tumor with prior surgery performing the following: A, the verb-generation task. Both fMRIs in surgical patients who performed the verb task suggest left-lateralized language. B, the letter task. Patients with prior surgery lateralize language to the left. Patient 4 exhibits bilateral language until P < 4.16 x 10–5. C, the category task. Depending on the statistical threshold used, this patient could be considered right-dominant (from P < .164–3.17 x 10–4) or left-dominant (from P < 4.16 x 10–5 to 3.74 x 10–6).
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