Analytical tools for magnetic resonance imaging.

The purpose of this study was the development and testing of a method for unsupervised, automated brain segmentation. Two spin-echo sequences were used to obtain relaxation rates and proton-density maps from 1.5 T MR studies, with two axial data sets including the entire brain. Fifty normal subjects (age range, 16 to 76 years) were studied. A Three-dimensional (3D) spectrum of the tissue voxels was used for automatic segmentation of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) and for calculation of their volumes. Accuracy and reproducibility were tested with a three-compartment phantom simulating GM, WM, and CSF. In the normal subjects, a significant decrease of GM fractional volume and increased CSF volume with age were observed (P < 0.0001), with no significant changes in WM. This multispectral segmentation method permits reproducible, operator-independent volumetric measurements.

Section: Discussionmentioning

confidence: 99%

Unsupervised, automated segmentation of the normal brain using a multispectral relaxometric magnetic resonance approach

Alfano

Brunetti

Covelli

et al. 1997

“…Each histogram has a resolution of 1/256 of the maximum axis value. Histograms of inverse T1 and Tz were chosen as this space displayed, more clearly, normal tissue clusters and was reported to clearly separate pathology (23). The range of T2-l values selected for the T2-' axis of the histograms was 10 times larger than for T1-l because T2 values are less than Tl values.…”

Section: Methodsmentioning

confidence: 99%

A multispectral analysis of brain tissues

Fletcher

Barsotti

Hornak

1993

With the increasing use of three-dimensional MRI techniques it is becoming necessary to explore automated techniques for locating pathology in the volume images. The suitability of a specific technique to locate and identify healthy tissues of the brain was examined as a first step toward eventually identifying pathology in images. This technique, called multispectral image segmentation, is based on the classification of tissue types in an image according to their characteristics in various spectral regions. The spectral regions chosen for this study were the hydrogen spin-lattice relaxation time T1, spin-spin relaxation time T2, and spin density, rho. Single-echo, spin-echo magnetic resonance images of axial slices through the brain at the level of the lateral ventricles were recorded on a 1.5 Tesla imager from 20 volunteers ranging in age from 17 to 72 years. These images were used to calculate the T1, T2, and rho images used for the classification. Tissue classification was performed by locating clusters of pixels in a three-dimensional T1(-1)-T2(-1)-rho histogram. Gray matter, white matter, cerebrospinal fluid, meninges, muscle, and adipose tissues were readily classified in magnetic resonance images of the volunteers with a single set of T1, T2, and rho values. Cluster characteristics, such as size, shape, and location, provided information on the imaging procedure and tissue characteristics.

“…Then from [l] to [3], the constant -y20(kx + k,) is in the order of 1.8 X which is very small in comparison with other sources of experimental error. As a result, spin diffusion in imaging experiments is not a significant source of errors unless very strong gradients or samples with very long T, and very large diffusion constants are used.…”

Section: I41mentioning

confidence: 99%

Multiple field strength in vivo T₁ and T₂ for cerebrospinal fluid protons

Hopkins

Yeung²,

Bratton

1986

To estimate the feasibility of measuring in vivo CSF protein, oxygen, or other solutes through their effect on proton relaxation times, the T1 and T2 of CSF protons has been measured within the human lateral ventricles. T1 was measured at 6.25, 25.4, and 60.1 MHz with a two-point method. T2 was measured at 6.25 and 25.4 MHz using the CPMG sequence to acquire 8 echo images. The T1 was 4.3 s with no evidence of field dependence. The T2 was 2 s. Although these values approach those for water at the same temperature it is possible that the T1 is influenced by the normal oxygen concentration. Calculations based on the relaxivity of dissolved protein indicate that the use of these methods for the detection of elevated levels of CSF protein would be less sensitive than existing methods.