BOLD contrast fMRI of whole rodent tumour during air or carbogen breathing using echo-planar imaging at 1.5 T.

The aim of this study was to evaluate the feasibility of functional MR imaging (fMRI) at 1.5 T, exploiting blood oxygenation level-dependent (BOLD) contrast, for detecting changes in whole-tumour oxygenation induced by carbogen (5% CO2+95% O2) inhalation of the host. Adult WAG/Rij rats with rhabdomyosarcomas growing subcutaneously in the lower flank were imaged when tumours reached sizes between 1 and 11 cm3 (n=12). Air and carbogen were alternatively supplied at 2 l/min using a snout mask. Imaging was done on a 1.5-T MR scanner using a T2*-weighted gradient-echo, echo-planar imaging (GE-EPI) sequence. Analysis of the whole-tumour EPI images was based on statistical parametric maps. Voxels with and without signal intensity changes (SIC) were recorded. Significance thresholds were set at p<0.05, corrected for multiple comparisons. In continuous air breathing condition, 3 of 12 tumours showed significant negative SIC and 1 tumour had a clear-cut positive SIC. The remaining tumours showed very little or no change. When switching to carbogen breathing, the SIC were significantly positive in 10 of 12 tumours. Negative SIC were present in 4 tumours, of which three were simultaneously characterised by positive SIC. The overall analysis indicated that 6 of the 12 tumours could be considered as strong positive responders to carbogen. Our research demonstrates the applicability of fMRI GE-EPI at 1.5 T to study whole-tumour oxygenation non-invasively. The observed negative SIC during air condition may reflect the presence of transient hypoxia during these measurements. Selection of tumours on the basis of their individual response to carbogen is possible, indicating a role of such non-invasive measurements for using tailor-made treatments.

Brain areas involved in interlimb coordination: a distributed network.

Whereas behavioral studies have made significant contributions toward the identification of the principles governing the coordination of limb movements, little is known about the role of higher brain areas that are involved in interlimb coordination. Functional magnetic resonance imaging (fMRI) was used to reveal the brain areas activated during the cyclical coordination of ipsilateral wrist and foot movements. Six normal subjects performed five different tasks that were presented in a random order, i.e., isolated flexion-extension movements of the right wrist (WRIST) and right foot (FOOT), cyclical coordination of wrist and foot according to the isodirectional (ISODIR) and nonisodirectional (NON-ISODIR) mode, and rest (REST). All movements were auditory paced at 66 beats/min. During the coordination of both limb segments, a distributed network was identified showing activation levels in the supplementary motor area (SMA), cingulate motor cortex (CMC), premotor cortex (PMC), primary sensorimotor cortex (M1/S1), and cerebellum that exceeded the sum of the activations observed during the isolated limb movements. In addition, coordination of the limb movements in different directions was associated with extra activation of the SMA as compared to movements in the same direction. It is therefore concluded that the SMA is substantially involved in the coordination of the nonhomologous limbs as part of a distributed motor network. Accordingly, the long-standing exclusive association that has been made between this medial frontal area and bimanual (homologous) coordination needs to be abandoned and extended towards other forms of interlimb coordination (nonhomologous).

Intermediate short-term outcomes after brain computed tomography and magnetic resonance imaging in neurology outpatients.

OBJECTIVE: The purpose of this study was to assess and compare the impact of magnetic resonance imaging (MIR) and computed tomography (CT) on diagnostic and therapeutic decision making, taking into account the real cost of both techniques at the authors' institution. METHOD: Brain CT and routine and rapid MRI were compared, and case files were prepared with either the CT or the MRI findings. These files were separately presented to a neurologist, and different questions were asked about further management. The real cost of CT and MRI was calculated. A questionnaire was sent to the patients 3 months after imaging. RESULTS: More lesions were detected on MRI than on CT Routine and rapid AIRI were comparable. The analysis of the CT case files revealed an additional request for MRl in 33% of the patients. An analysis of the MRI case files revealed that 20% more technical examinations were requested after MRI than after CT In the majority of the patients (90%), neuroimaging had no impact on therapy except by means of reassurance of the physician. The scan was considered useful for therapeutic planning by excluding the presence of a space-occupying lesion. The real cost of the MP! strategy was 9% higher than that of the CT strategy. CONCLUSION: In this patient population, neuroimaging was normal in the majority of the patients. Undergoing an imaging examination was of benefit to the patients and improved their sense of well-being mainly by the reassurance they experienced, as reported by 91% of the patients. At the authors' institution, the real cost of MMI in this patient population was only slightly higher than the real cost of CT The statistical analysis favors the use of MRI as a 1st imaging examination.

The representation of shape in the context of visual object categorization tasks.

To investigate the role of human fusiform gyrus in shape processing, we determined the effect of shape degradation on BOLD contrast in this region with fMRI during three tasks requiring subjects to determine either whether two successively presented nonsense shapes had the same global orientation (OR task); whether two successively presented meaningful objects belonged to the same basic level category (CAT task); or whether two successively presented objects represented the same exemplar of a category (EX task). On the behavioral level, shape degradation by locally shifting the pixels constituting the lines of stimuli had no effect on performance in the OR task, while it was detrimental to performance in the CAT and EX tasks. In comparison to the OR task, both the CAT and EX tasks were associated with activations in the occipitotemporal and parietal cortex. When shape degradation was applied, activation in the middle fusiform gyrus was reduced in all tasks. The occurrence of this effect in the OR task indicates that it is independent of memory representations. The persistence of the effect in both tasks that showed a behavioral effect of degradation suggests that it does not reflect the amount of shape processing performed on the stimuli, but rather the specificity of the final perceptual representation that can be built from the shape information that is available. Other studies have shown effects of stimulus familiarity and task requirements in the fusiform gyrus, suggesting that there is no need to assume different modules for perceptual representation and representation in memory.