Reliability of functional MR imaging with word-generation tasks for mapping Broca's area

Abstract

Background and purpose: Functional MR (fMR) imaging of word generation has been used to map Broca's area in some patients selected for craniotomy. The purpose of this study was to measure the reliability, precision, and accuracy of word-generation tasks to identify Broca's area.

Methods: The Brodmann areas activated during performance of word-generation tasks were tabulated in 34 consecutive patients referred for fMR imaging mapping of language areas. In patients performing two iterations of the letter word-generation tasks, test-retest reliability was quantified by using the concurrence ratio (CR), or the number of voxels activated by each iteration in proportion to the average number of voxels activated from both iterations of the task. Among patients who also underwent category or antonym word generation or both, the similarity of the activation from each task was assessed with the CR. In patients who underwent electrocortical stimulation (ECS) mapping of speech function during craniotomy while awake, the sites with speech function were compared with the locations of activation found during fMR imaging of word generation.

Results: In 31 of 34 patients, activation was identified in the inferior frontal gyri or middle frontal gyri or both in Brodmann areas 9, 44, 45, or 46, unilaterally or bilaterally, with one or more of the tasks. Activation was noted in the same gyri when the patient performed a second iteration of the letter word-generation task or second task. The CR for pixel precision in a single section averaged 49%. In patients who underwent craniotomy while awake, speech areas located with ECS coincided with areas of the brain activated during a word-generation task.

Conclusion: fMR imaging with word-generation tasks produces technically satisfactory maps of Broca's area, which localize the area accurately and reliably.

fig 1.

Sagittal (top right), axial (left), and coronal (bottom right) fMR images in patients performing word-generation tasks. A, Activation is evident in the pars triangularis and pars opercularis of the left inferior frontal gyrus (Brodmann areas 44 and 45) in a patient performing an LWG task. B, Activation also is evident in Brodmann areas 44 and 45 in a patient with an arteriovenous malformation in the right hemisphere who is performing an LWG task. C, Activation appears in Brodmann areas 9 and 46 in a patient with a tumor involving the inferior left frontal lobe who is performing a CWG task.

fig 2.

Sagittal (top right), axial (left), and coronal (bottom right) fMR images in a patient with a large left frontal tumor who is performing an LWG task. Activation is identified primarily in the right inferior frontal gyrus (Brodmann area 45)

fig 3.

Sagittal (top right), axial (left), and coronal (bottom right) activation images in two iterations of an LWG task. A and B, Patient with a left frontal tumor. Activation occurs in the same gyri between iterations, although with slightly different patterns. C and D, Patient with a left frontal tumor and right hemispheric activation.

fig 4.

Coronal fMR imaging images of two iterations of an LWG task in a patient with a left middle cerebral arteriovenous malformation. A, Activation in the first iteration. B, Activation in the second iteration, showing similar activation compared with A. C, Intersect map shows the voxels activated in the two iterations. The proportion of voxels in the intersect map compared with the average number of voxels in A and B (the CR) is 45%.

fig 5.

Sagittal (top right), axial (left), and coronal (bottom right) projections in a patient with a right frontal tumor. A, Activation from a CWG task. B, Activation from an LWG task.

fig 6.

Coronal images in a patient with a right frontoparietal arteriovenous malformation. A, Activation from an AWG task B, Activation from a CWG task. The activation patterns from the two variations of the word-generation task are similar. C, Intersect map shows the voxels activated by both versions of the task. The CR was 52%.

fig 7.

Comparison of intraoperative localization of speech function (ECS) and activation from the word-generation task (fMR imaging) in a patient with a left frontal-lobe glioma. Both activation and intraoperative localization of the speech mapping were classified as belonging to Brodmann areas 44 and 45. M indicates motor cortex; S, speech areas; T, tumor