Jukka Jauhiainen

Independent component analysis of nondeterministic fMRI signal sources

Neuronal activation can be separated from other signal sources of functional magnetic resonance imaging (fMRI) data by using independent component analysis (ICA). Without deliberate neuronal activity of the brain cortex, the fMRI signal is a stochastic sum of various physiological and artifact related signal sources. The ability of spatial-domain ICA to separate spontaneous physiological signal sources was evaluated in 15 anesthetized children known to present prominent vasomotor fluctuations in the functional cortices. ICA separated multiple clustered signal sources in the primary sensory areas in all of the subjects. The spatial distribution and frequency spectra of the signal sources correspond to the known properties of 0.03-Hz very-low-frequency vasomotor waves in fMRI data. In addition, ICA was able to separate major artery and sagittal sinus related signal sources in each subject. The characteristics of the blood vessel related signal sources were different from the parenchyma sources. ICA analysis of fMRI can be used for both assessing the statistical independence of brain signals and segmenting nondeterministic signal sources for further analysis.

Slow vasomotor fluctuation in fMRI of anesthetized child brain.

Signal intensity changes in fMRI during rest caused by vasomotor fluctuations were investigated in this work. Resting‐state baseline fluctuations were evaluated in 12 children anesthetized with thiopental. Five subjects had fluctuations related to subvoxel motion. In seven subjects without significant motion, slow signal fluctuation at 0.025–0.041 Hz near one or more primary sensory cortices was observed. In each subject the amplitude and frequency of the fluctuations were stable. It is hypothesized that thiopental, which reduces blood pressure and flow in the cortex, alters the feedback in neurovascular coupling leading to an increase in the magnitude and a reduction in the frequency of these fluctuations. The use of anesthesia in fMRI may provide new insight into neural connectivity and the coupling of blood flow and neural metabolism. Magn Reson Med 44:373–378, 2000.

Apparent diffusion coefficients and T2 relaxation time measurements to evaluate disc degeneration: A quantitative MR study of young patients with previous vertebral fracture

Purpose: To assess the suitability of apparent diffusion coefficient (ADC) measurements to evaluate degeneration processes of the vertebral disc and to compare the results with T2 relaxation time measurements in both degenerated and normal intervertebral discs. Material and Methods: Fourteen young patients (8.8-20.8 years old) who had had a vertebral compression fracture at least 1 year earlier, underwent MR studies with diffusion imaging in three orthogonal directions and T2 relaxation time measurements. ADC values and T2 relaxation times of both degenerated and normal intervertebral discs were compared to the values of 20 healthy young asymptomatic control subjects. Results: In the degenerated discs of patients, the ADCx and ADCy values were decreased compared to earlier determined values of healthy controls. ADC values in the z-direction in degenerated discs did not differ significantly from the values of controls. T2 relaxation times were shorter in the degenerated discs of patients compared to the values of controls. The greatest changes in both these values were observed in degenerated discs followed by discs with normal signal intensity adjacent to primary trauma area and secondary trauma area. Conclusion: We suggest that decreased ADC values reflect the lost integrity of the intervertebral disc. ADC measurements at MR may prove sensitive depicting of early degenerative changes in vertebral discs.

Sweating impairment in patients with multiple sclerosis

Objectives –  To measure sweating in patients with multiple sclerosis (MS).

Sympathetic skin responses in multiple sclerosis.

Objectives –  This study assessed the sympathetic skin responses (SSRs) and their correlation with brain lesion volumes in patients with multiple sclerosis (MS).

Apparent Diffusion Coefficient on Magnetic Resonance Imaging in Pons and in Corona Radiata and Relation with the Neurophysiologic Measurement and the Outcome in Very Preterm Infants

Background: New imaging techniques allow a detailed visualization of the brain and the findings possibly correlate with neurophysiologic measurements and neurosensory and motor outcomes. Postnatal clinical factors known to associate with neurologic disabilities may contribute to brain abnormalities not visible to the naked eye. Objectives: We evaluated whether quantitative measurement of organized water diffusion on MR imaging, apparent diffusion coefficient (ADC), relates to neurophysiologic function and to clinical risk factors and motor outcome in preterm infants. Methods: Diffusion-weighted imaging was successfully performed at term age on 30 infants born <32 weeks of gestation, birth weight <1,000 g. Infants with major destructive brain lesions were excluded from the final analysis (n = 2). ADC was calculated within regions of interest placed in pons and in white matter regions known to contain motor fibers. Brain stem auditory evoked potentials (BAEP) were registered at term age. Gross motor outcome was assessed using Griffiths Scales at 2 years of corrected age. Results: A positive correlation was found between ADC in the pons and the latency of wave III in BAEP (r = 0.619, p = 0.024). Need for inotrope support during the postnatal period and bronchopulmonary dysplasia associated with high ADC values in the pons and in the corona radiata. Infants with poor gross motor outcome had higher ADC in the corona radiata than infants with better outcome (mean = 1.343 vs. 1.197, p = 0.004). Conclusions: This is the first study to report a relationship between ADC and BAEP measurements in the pons. The study may add to the current knowledge about the relation between postnatal clinical factors and diffusion-weighted imaging when evaluating the high-risk infants.

MR perfusion, diffusion and BOLD imaging of methotrexate-exposed swine brain

To evaluate the methotrexate (MTX)‐exposed swine brain, functional magnetic resonance imaging (MRI), including perfusion, diffusion, and blood‐oxygen‐level‐dependent (BOLD) contrast imaging, was used.

Functional magnetic resonance imaging of swine brain during change in thiopental anesthesia into EEG burst-suppression level--a preliminary study.

Deepening anesthesia produces well known changes in electroencephalogram (EEG) and evoked potentials, differing in pathological and normal brain. Yet, it is not known how the T2*-weighted signal changes in the healthy brain during deepening anesthesia. We studied the effect of thiopental bolus on functional magnetic resonance imaging (fMRI) in the healthy brain using porcine model. In five pigs (2–3 months, 20–25 kg), the control bolus prior to fMRI resulted in a change into burst-suppression. After the recovery of continuous EEG, fMRI (4 min) was performed with a single bolus of thiopental (11.4-17.1 mg/kg) administered 1 min after the onset of imaging. This was repeated in four of five pigs. Positive (6-8%) or negative (-3 to -8%) signal intensity changes correlated to the thiopental bolus injection were seen in the group average fMRI response. Positive response was 1.6% and negative response 2.3% of the total brain region of interest (ROI) voxels. Responding voxels were distributed more prominently in the thalamic ROI (4.5%) than in the cortical ROI (2.2%). The group average of unthresholded voxel time courses showed that the net effect of thiopental bolus was a small (0.5%) but a clear positive change in the thalamic region, while variance changed in the global level. In conclusion, this study is the first to show that significant signal intensity changes occur in fMRI response during the sudden deepening of thiopental anesthesia. However, these responses are neither anatomically constant nor global in the healthy swine brain.