Dr. Peter J. Fiester November 14, 2012 Define functional MRI. Briefly describe fmri image acquisition. Discuss relative functional neuroanatomy. Review clinical applications. Briefly discuss a few examples of research applications. MR images of the brain measuring brain activity during language, movement, sensory, sensation etc.. Increased neuronal activity fmri concept builds on the earlier MRI scanning technology and the discovery of properties of oxygen rich blood. i) changes in blood flow and blood oxygenation in the brain are closely linked to neural activity. BOLD blood oxygen level dependent signal Normal vascular response of the brain to activation Blood flow Oxyhemoglobin Oxygen extraction Deoxyhemoglobin Deoxyhemoglobin Signal EPI utilize gradient echo sequence. Gradient echo sequences are sensitive to local magnetic field inhomogeneities. Deoxyhemoglobin is paramagnetic and decreases T2*. Areas of increased neuronal activity (less deoxyhemoglobin) have increased signal. Images of the whole brain are acquired very fast over and over. TR 2 seconds (low resolution, fast acquisition). Present a task and measure how signal intensity in each voxel changes over time. Typically, the unwanted signal called the noise (from the scanner and random brain activity) is as big as the signal itself. To eliminate these, fmri studies repeat a stimulus presentation multiple times. The signal change is very low and cannot be directly detected. Therefore, advanced statistical methods (general linear model, for example) must be used to identify the voxels in which the signal varies according to the paradigm. 1
Acquistion time (Longer imaging time or higher field strength = greater signal to noise). Post processing techniques. To be useful to surgeons and clinicians in interpreting fmri images, we need to be familiar with the eloquent areas of the brain including major motor and sensory pathways and language centers. Patient preparation. Patient monitoring. Supplementary motor area (SMA) and premotor area are known to be activated by the motor task in addition to the primary motor area (M1). SMA is located on the midline surface of the hemisphere just anterior to the primary motor cortex leg representation. frontal expressive or motor area (Broca area). posterior receptive language center (Wernicke area). white matter fiber tract (arcuate fasciculus) interconnecting the two. (Fukunaga M, et al Electroencephalography and Clinical Neurophysiology(suppl.) 47: 265 269, 1996 Volume 1076, Issue 1, Brain Research. 3 March 2006, Pages 129 143 2
Figure 1. Image shows language processing areas of the brain, including Broca area (blue), located in Brodmann areas (BAs) 44 and 45; and Wernicke area (yellow), located in BAs 22, 37, 39, and 40. a.g. = angular gyrus, m.t.g. = middle temporal gyrus, p.o.... Broca s Aphasia effortful, nonfluent, monotonous, often agrammatic speech with phonemic paraphasias (eg, mook instead of book ) and articulatory deficits. Language comprehension is reasonably good, but speech production is impaired. Wernicke s Aphasia exhibit fluent, melodious, but empty speech that is often distorted by semantic paraphasias (eg, chair when table is meant) or neologisms, with poor language comprehension. Conduction aphasia fluent speech with phonemic paraphasias and self corrections with reasonably good comprehension. In particular, the repetition of long words and sentences is disrupted. Motor Language Sensory Visual, auditory Memory Higher cortical function Current primary clinical application of fmri is in presurgical planning for tumors or seizure focus. Tapping fingers and wiggling toes at same time. Foot motor task. 3
Figure 4a. Areas of activation for the verbal fluency verb generation paradigm. Figure 4b. Areas of activation for the verbal fluency verb generation paradigm. Figure 4c. Areas of activation for the verbal fluency verb generation paradigm. Figure 6a. Areas of activation for the verbal fluency verb generation paradigm. Figure 6b. Areas of activation for the verbal fluency verb generation paradigm. Figure 6c. Areas of activation for the verbal fluency verb generation paradigm. Dementias Dyslexia Autism ADHD Several more Define functional MRI. Briefly describe fmri image acquisition. Discuss relative functional neuroanatomy. ApoE4 subjects ApoE3 subjects Older adults at genetic risk for AD require more cognitive effort to achieve comparable performance on an episodic memory encoding task. Review clinical applications. Briefly discuss research applications. 4
Special thanks to Dr. Bennett for sharing some of the fmri images. 5