Biomedical subjects
Publications and source records attributed to Robert Turner.
Musically naïve subjects were scanned using functional magnetic resonance imaging (fMRI) before and after they had been taught to read music and play keyboard. When subjects played melodies from musical notation after training, activation was seen in a cluster of voxels within the right superior parietal cortex consistent with the view that music reading involves spatial sensorimotor mapping.
THE BASAL GANGLIA have important roles in somatic motor, oculomotor, limbic, and associative functions. These functions are represented in anatomically distinct territories in each basal ganglion nucleus. During surgery of the subthalamic nucleus for Parkinson's disease, the primary goal is to influence the physiology of the motor territory without affecting nonmotor areas. This article describes the use of movement-related cellular activity during single-unit microelectrode mapping to identify and to navigate within the motor territory of the subthalamic nucleus.
OBJECT: The objective of this study was to assess the feasibility and efficacy of treating spondylolisthesis-related spinal stenosis via unilateral approach bilateral decompression in which METRx-MD instrumentation is placed. METHODS: Eight consecutive patients with spinal stenosis underwent bilateral decompressions via a unilateral approach in which METRx-MD instrumentation was placed. The procedures were performed on an outpatient basis after induction of general anesthesia. The patients underwent preoperative and 3-month postoperative plain radiography in which flexion-extension x-ray films were obtained. Preoperative and postoperative magnetic resonance imaging was also performed. All radiographs and neuroimages were read by a single radiologist blinded to the clinical results. Eight vertebral levels in the eight patients were surgically decompressed (in one patient an additional level of nonspondylolisthesis-related stenosis was decompressed). The mean operative time was 92 minutes and the mean blood loss was 33 ml/level. Preoperatively stenosis was severe in five patients, moderate/severe in two, and moderate in one; postoperatively stenosis was absent in five, mild in two, and mild/moderate in one. Motion was detected on flexion-extension radiographs in three patients, but on early (3-month) postoperative radiographs there was no evidence of progression. CONCLUSIONS: By following the authors' procedure, minimally invasive bilateral decompression of acquired spinal stenosis associated with spondylolisthesis can be successfully performed on an outpatient basis, with reasonable operative times, minimal blood loss, and acceptable morbidity.
Echo-planar imaging with gradient echo allows whole-brain images to be rapidly acquired. However, its main limitation is that magnetic field inhomogeneities in regions of the brain close to bone and air-filled sinuses result in reduced signal-to-noise ratio and signal loss. In particular this is a problem for imaging the temporal lobes, and can therefore affect the results of some language-related studies. Decreasing the echo time (TE) increases the signal-to-noise ratio and reduces the amount of signal loss in susceptible regions. In this study we investigate the TE dependence of BOLD (blood oxygenation level-dependent) contrast and, in particular, how it is influenced in regions with susceptibility artifacts. We use a dual echo-time sequence to compare brain activations measured with two different TEs, TE = 40 ms and TE = 27 ms. The paradigm involves comparing famous faces to scrambled faces, a low-level control condition. It was chosen because famous faces have been repeatedly shown to activate the fusiform gyri and anterior temporal lobes in both PET and fMRI. Our results show that it is possible to detect robust activations at a lower TE in brain regions not affected by susceptibility artifacts (i.e., fusiform gyri), allowing for faster scanning times. However, although the amount of signal loss is reduced at the lower TE, this does not appear to be sufficient to recover the BOLD signal in regions affected by susceptibility artifacts (i.e., anterior temporal lobes).
Diffusion tensor imaging (DTI), a magnetic resonance imaging technique, is used to infer major axonal projections in the macaque and human brain. This study investigates the feasibility of using known macaque anatomical connectivity as a "gold-standard" for the evaluation of DTI tractography methods. Connectivity information is determined from the DTI data using fast marching tractography (FMT), a novel tract-tracing (tractography) method. We show for the first time that it is possible to determine, in an entirely noninvasive manner, anatomical connection pathways and maps of an anatomical connectivity metric in the macaque brain using a standard clinical scanner and that these pathways are consistent with known anatomy. Analogous human anatomical connectivity is also presented for the first time using the FMT method, and the results are compared. The current limitations of the methodology and possibilities available for further studies are discussed.
A well-recognized problem with the echo-planar imaging (EPI) technique most commonly used for functional magnetic resonance imaging (fMRI) studies is geometric distortion caused by magnetic field inhomogeneity. This makes it difficult to achieve an accurate registration between a functional activation map calculated from an EPI time series and an undistorted, high resolution anatomical image. A correction method based on mapping the spatial distribution of field inhomogeneities can be used to reduce these distortions. This approach is attractive in its simplicity but requires postprocessing to improve the robustness of the acquired field map and reduce any secondary artifacts. Furthermore, the distribution of the internal magnetic field throughout the head is position dependent resulting in an interaction between distortion and head motion. Therefore, a single field map may not be sufficient to correct for the distortions throughout a whole fMRI time series. In this paper we present a quantitative evaluation of image distortion correction for fMRI at 2T. We assess (i) methods for the acquisition and calculation of field maps, (ii) the effect of image distortion correction on the coregistration between anatomical and functional images, and (iii) the interaction between distortion and head motion, assessing the feasibility of using field maps to reduce this effect. We propose that field maps with acceptable noise levels can be generated easily using a dual echo-time EPI sequence and demonstrate the importance of distortion correction for anatomical coregistration, even for small distortions. Using a dual echo-time series to generate a unique field map at each time point, we characterize the interaction between head motion and geometric distortion. However, we suggest that the variance between successively measured field maps introduces additional unwanted variance in the voxel time-series and is therefore not adequate to correct for time-varying distortions.
The draining vein problem is recognized as one of the most severe constraints on the spatial resolution of BOLD contrast fMRI, used widely in imaging neuroscience. Changes in blood oxygenation arising from local brain activity-related changes in blood flow propagate downstream in veins and can give rise to spurious activation at sites remote from neuronal activity. The geometry of the venous vasculature is quite regular in structure and is well depicted in photomicrographs. Quantitative analysis of this geometry, together with hydrodynamic considerations, permit upper bounds dependent on the area of cortical neuronal activity to be derived for the spatial extent of draining vein contamination. It is estimated that an activated cortical area of 100 mm(2) will generate an oxygenation change in venous blood that extends without dilution along the vein no more than 4.2 mm beyond the edge of the activated area. At greater distances along the draining vein this oxygenation change will be diluted. The model leads to a quantitative prediction of the functional form of this dilution.
OBJECT: The authors studied a consecutive series of patients with spinal stenosis in whom surgery was performed by a single surgeon who used a microscopic tubular retractor system (METRx-MD); patients underwent prospective evaluation involving radiography and magnetic resonance (MR) imaging. The objective was to assess the feasibility and surgery-related efficacy of performing unilateral-approach bilateral decompression and utilization of METRx-MD instrumentation in patients with spinal stenosis. METHODS: Seventeen consecutive patients with spinal stenosis underwent bilateral decompression; surgery was performed via a unilateral approach using METRx-MD instrumentation. The procedures were performed on an outpatient basis after induction of general anesthesia. Preoperative and 3-month follow-up plain radiographs with flexion-extension views were obtained. Preoperative and postoperative MR imaging was also performed. All studies were assessed by a single radiologist blinded to the clinical results. Twenty-two levels were surgically decompressed. The mean operative time was 90 minutes and the mean blood loss was 28 ml per level. Preoperatively stenosis was severe at 13 levels, moderate/severe at eight, and moderate at one. Postoperatively stenosis was absent at 13 levels, mild at seven, mild/moderate at one, and moderate at one. Preoperatively degenerative spondylolisthesis was documented in eight patients, with flexion-extension radiography revealing motion in three cases. On early (3-month) postoperative x-ray films there was no evidence of progression in any case. Grade I spondylolisthesis developed postoperatively in one patient, who remained asymptomatic. CONCLUSIONS: Minimally invasive bilateral decompression and instrumentation-assisted fusion can be successfully performed via a unilateral approach in patients with acquired spinal stenosis; the procedure can be undertaken on an outpatient basis, with reasonable operative times, minimal blood loss, and acceptable morbidity rates.