Analysis of imaging axes significance in motion artifact suppression technique (MAST ™): MRI of turbulent flow and motion

Recently, a new technique has been demonstrated which effectively refocusses the dephasing effects of spins moving during application of MR imaging gradients. This paper presents an analysis of imaging axes significance in spin dephasing for motion occurring along the slice select, read and phase-encoding directions. A flow phantom under constant flow conditions in all experiments was used to provide complete spin dephasing when “traditional” imaging gradients were used. The MAST ™ technique was used to refocus along various combinations of imaging axes, and variable number of terms from the Taylor expansion of motion along them. Results indicate that motion along any imaging axis can be refocussed effectively when MAST gradients are used along only the slice select and read axis

In-plane flow velocity quantification along the phase encoding axis in MRI

In-plane flow quantification in MRI offers the potential for assessing vessel patency, and both volume flow rate and flow velocity. These techniques will have definite future impact on MR angiography. The method used in this paper employs motion artifact suppression technique (MAST ™) gradients to refocus spins travelling along any of the three imaging axes while encoding the velocity component along the phase encoding axis. 4,5,7,9 This method has several advantages over in-plane flow quantification along the read axis. 11,12 Primarily, flow voids due to complete spin dephasing can be eliminated (or reduced), wider velocity limits can be measured, and gradients can be designed which are sensitive to only velocity along the phase axis with no additional effect from higher order derivatives, or motion along the read axis. Flow phantom studies, carried out on 19 mm inside diameter glass tubes, have produced accurate results for flow rates ranging from 0.6 gallons per minute (GPM) to 2.5 GPM, corresponding to a mean velocity range from 13.2 cm/sec to 55.3 cm/sec. Reynolds numbers varied from 2,700 to 11,500. Errors were less than or equal to 8% over the range of flow rates studied

Automated segmentation of spinal diffusion tensor MR imaging

A novel automated segmentation technique is presented for the delineation of white matter and gray matter regions in diffusion tensor magnetic resonance imaging of the spine. The technique involves an automated method for the extraction of the spinal cord regions from the diffusion tensor imaging data and relies on the fuzzy means clustering approach, which is inherently robust. Experimental results obtained for the segmentation of in vitro spinal cord sections of varying ages from 48 to 80 years demonstrate the viability of the automated segmentation technique. Statistical comparison with manually delineated white matter regions indicates the potential of the automated technique for the investigation and analysis of white matter abnormalities in diffusion tensor magnetic resonance imaging of the spine

1H-magnetic resonance spectroscopy in amyotrophic lateral sclerosis

1H-magnetic resonance spectroscopy (MRS) is potentially a powerful tool for the investigation of the chemicals of the brain in vivo in health and disease. Levels of N-acetyl-aspartate (NAA) in the motor cortex and brainstem of patients with amyotrophic lateral sclerosis (ALS) have been reported to be reduced by up to 68%, and in one report the level of glutamate in the brainstem was increased by 58%. We studied levels of metabolites in the cerebral cortex and brainstem of 20 ALS patients and 14 age-matched controls with a 1.5 Tesla Picker magnet using MRS. We used the same spectra for determining both the area of the metabolite peaks expressed as a ratio of the area of the creatine (Cr) peak, and the absolute concentrations using the Provencher LC model. These produced different results. With the LC model, the NAA content of the motor cortex of ALS patients was reduced by 7.7% ( P=0.015), and that of the brainstem was reduced by 21.5% ( P=0.035), compared with controls. The degree of reduction of NAA was related to the severity of upper motor neuron abnormalities. No effect of treatment with anti-glutamate agents on NAA concentration could be detected. Concentrations of other metabolites were not affected in ALS. It appears that MRS is a technique that is still in development, and that further refinement is required before it can be used to understand disease mechanisms and investigate treatment in ALS

Subacute Pain after Traumatic Brain Injury Is Associated with Lower Insular N

Persistent pain is experienced by more than 50% of persons who sustain a traumatic brain injury (TBI), and more than 30% experience significant pain as early as 6 weeks after injury. Although neuropathic pain is a common consequence after CNS injuries, little attention has been given to neuropathic pain symptoms after TBI. Magnetic resonance spectroscopy (MRS) studies in subjects with TBI show decreased brain concentrations of N-acetylaspartate (NAA), a marker of neuronal density and viability. Although decreased brain NAA has been associated with neuropathic pain associated with spinal cord injury (SCI) and diabetes, this relationship has not been examined after TBI. The primary purpose of this study was to test the hypothesis that lower NAA concentrations in brain areas involved in pain perception and modulation would be associated with greater severity of neuropathic pain symptoms. Participants with TBI underwent volumetric MRS, pain and psychosocial interviews. Cluster analysis of the Neuropathic Pain Symptom Inventory subscores resulted in two TBI subgroups: The Moderate Neuropathic Pain (n = 17; 37.8%), with significantly (p = 0.038) lower insular NAA than the Low or no Neuropathic Pain group (n = 28; 62.2%), or age- and sex-matched controls (n = 45; p < 0.001). A hierarchical linear regression analysis controlling for age, sex, and time post-TBI showed that pain severity was significantly (F = 11.0; p < 0.001) predicted by a combination of lower insular NAA/Creatine (p < 0.001), lower right insular gray matter fractional volume (p < 0.001), female sex (p = 0.005), and older age (p = 0.039). These findings suggest that neuronal dysfunction in brain areas involved in pain processing is associated with pain after TBI