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Micheal D Phillips

Publications and source records attributed to Micheal D Phillips.

6 recordsLinked to original sources
PubMed2006

Functional pathway-defined MRI diffusion measures reveal increased transverse diffusivity of water in multiple sclerosis.

The diffusion properties of water are sensitive to microscopic changes in the white matter of multiple sclerosis (MS) patients. Typical MRI measures of disease burden in MS demonstrate modest to poor correlation with disability. Functional MRI and DTI-based fiber tracking were used to define the interhemispheric white matter pathway connecting bilateral supplementary motor areas (SMA) in 16 MS patients sand 16 control subjects. Fractional anisotropy (FA), mean diffusivity (MD), longitudinal (lambda(1)) and transverse diffusivity (lambda(2)) were measured along this pathway in all subjects. Mean FA was 0.587 +/- 0.032 for patients and 0.608 +/- 0.020 for controls (P < 0.02). Mean MD was (0.821 +/- 0.055) x 10(-3) mm(2) s(-1) for patients and (0.770 +/- 0.020) x 10(-3) mm(2) s(-1) for controls (P < 0.004). Mean lambda(1) values were (1.462 +/- 0.099) x 10(-3) mm(2) s(-1) for patients and (1.400 +/- 0.034) x 10(-3) mm(2) s(-1) for controls (P < 0.02). Mean lambda(2) values were (0.500 +/- 0.047) x 10(-3) mm(2) s(-1) for patients and (0.454 +/- 0.027) x 10(-3) mm(2) s(-1) for controls (P < 0.001). In addition, the correlation between the Multiple Sclerosis Functional Composite (MSFC) and transverse diffusivity was -0.341 (P < 0.05). The component test of the MSFC most related to the SMA pathway studied with our MRI method (Nine-hole Peg Test) showed significant correlation with transverse diffusivity (r = 0.392, P < 0.02), indicating that probing functional pathways with MRI measures can lead to a better reflection of disease status.

Adult↗
PubMed2006

Variability in RF-induced heating of a deep brain stimulation implant across MR systems.

PURPOSE: To compare the MRI-related heating per unit of specific absorption rate (SAR) profile of a conductive implant between two 1.5-Tesla/64 MHz MR systems using a transmit/receive (t/r) head coil configuration. MATERIALS AND METHODS: Deep brain stimulation (DBS) leads were configured within a gel-filled phantom of the human head and torso. Temperature variation at each of four contacts of the bilaterally-placed leads was monitored using fluoroptic thermometry. MRI was performed using the t/r head coils of two different-generation 1.5-Tesla MR systems from the same manufacturer. Temperature changes were normalized to SAR values for the head (DeltaT/SAR-H), and the slope of this DeltaT/SAR-H by time relationship was compared between the two scanners. RESULTS: The DeltaT/SAR-H for the implant ranged from 3.5 to 5.5 times higher on one MR system as compared to the other (P < 0.01) depending on the measurement site. CONCLUSION: The findings support previous observations that console-reported SAR does not constitute a reliable index of heating for elongated, conductive implants, such as the DBS hardware system tested. In contrast to our previous findings using a t/r body coil, the data presented here reveal marked differences between two MR systems using t/r head coils (the coil configuration was consistent with the implant manufacturer's imaging guidelines). J. Magn. Reson. Imaging 2006. (c) 2006 Wiley-Liss, Inc.

Body Temperature↗
PubMed2006

Parkinson disease: pattern of functional MR imaging activation during deep brain stimulation of subthalamic nucleus--initial experience.

PURPOSE: To prospectively determine the pattern of functional magnetic resonance (MR) imaging activation at 3 T produced by deep brain stimulation (DBS) of subthalamic nucleus (STN) for treatment of Parkinson disease and to determine the safety of DBS electrode stimulation during functional MR imaging at 3 T. MATERIALS AND METHODS: Informed consent was obtained from all subjects participating in the study, and the study protocol was approved by the institutional review board at the Cleveland Clinic Foundation and was HIPAA compliant. After extensive phantom safety testing of DBS lead systems, five patients (three men, two women; mean age, 49.4 years +/- 14.5 [standard deviation]; range, 31-74 years) with percutaneously extended bilateral DBS electrodes placed in the STN for treatment of Parkinson disease were examined at 3 T on the 1st or 2nd postoperative day. Imaging consisted of a three-dimensional anatomic data set with leads disconnected and a blood oxygen level-dependent functional MR image with a single lead connected to the external pulse generator in the MR imaging control room by using stimulation parameters previously determined to produce optimal stimulation for alleviation of symptoms. A total of nine leads were tested with the functional MR imaging protocol. Subjects underwent neurologic examination immediately before and after MR imaging. RESULTS: All five patients completed the study without change in their neurologic examination and with activation seen in eight of nine electrodes stimulated. Activation was seen in the ipsilateral basal ganglia in all subjects and ipsilateral thalamus in six of the electrodes tested. Two of the electrode stimulations demonstrated additional activation in the STN and/or substantia nigra region adjacent to the electrode tip. For three electrode stimulations, activation was seen in the contralateral superior cerebellum. CONCLUSION: Therapeutically effective DBS of STN can be performed safely during functional MR imaging at 3 T and produces a consistent pattern of ipsilateral activation of deep brain motor structures.

Adult↗
PubMed2002

Multiple sclerosis: low-frequency temporal blood oxygen level-dependent fluctuations indicate reduced functional connectivity initial results.

PURPOSE: To study the correlation of low-frequency blood oxygenation level-dependent (BOLD) fluctuations on magnetic resonance (MR) images obtained of the left- and right-hemisphere primary motor regions in healthy control subjects and patients with multiple sclerosis (MS). MATERIALS AND METHODS: Sixteen healthy volunteers and 20 patients with MS underwent MR imaging with a 1.5-T imager by using a protocol designed to monitor low-frequency BOLD fluctuations. Data for low-frequency BOLD fluctuations were acquired with subjects at rest and during continuous performance of a bilateral finger-tapping task. These data were low-pass filtered (<0.08 Hz), and cross correlations of all acquired pixels to a region of interest in the left precentral gyrus were calculated. Confidence levels were calculated from the cross correlations. The fraction of pixels in the right precentral gyrus above a confidence level of 95% for correlation with the left precentral gyrus was calculated for each subject. RESULTS: A plot of the fraction of the right precentral gyrus with high correlation with the left precentral gyrus for the finger-tapping state versus the resting state showed a clear discrimination between patients with MS and control subjects. Compared with control subjects, patients with MS generally had a smaller fraction of the pixels in the right precentral gyrus above the confidence level. This finding indicates that our method results in greater than 60% sensitivity and 100% specificity for discriminating patients with MS from control subjects. No significant correlation was found between clinical measures of MS disease and correlations of low-frequency BOLD fluctuations between left and right precentral gyri. CONCLUSION: On the basis of the connectivity measure of low-frequency BOLD fluctuations, patients with MS exhibited lower functional connectivity between right- and left-hemisphere primary motor cortices when compared with that in control subjects.

Adult↗