Identification and characterization of tissues by T₂‐selective whole‐body proton NMR imaging

Abstract

T2-selective proton imaging at 10 MHz is based on a Carr-Purcell-Meiboom-Gill pulse sequence with at least 36 echoes and 2 tau greater than or equal to 6 ms employing the projection reconstruction technique. The transverse magnetization decay of the volume elements is multiexponential composed of up to three monoexponential T2 components. The T2 values are arranged in T2 histograms which are slice specific. T2 windows are defined in the T2 histogram and used for imaging and for selecting T2 values which are assigned to proton classes and tissues. Tissue characterization is based on the visualization of differences in T2 behavior. The T2 values are transformed into 256 gray levels or, by use of a red-green-blue lookup table, into a rainbow code. Two display techniques have been developed and implemented in the RWTH Aachen Magnetic Resonance Software System (RAMSES): (i) for nonselective T2 imaging with secondary T2 selection and encoding of molecular classes on the basis of T2 values; (ii) for T2-selective imaging by employing combined primary and secondary T2 selection and encoding particular tissues and variations therein. The tissues can be identified by selecting different classes of molecules, like water, lipids, and proteins, when shifting the primary T2 window on the T2 axis of the T2 histogram.

Regional 1H transverse magnetization studies in perfused rabbit kidney

“…The ability to resolve at least two components in kidney tissue TDCs with CPMG imaging techniques provides an opportunity to make pixel-by-pixel maps of apparent biexponential parameters (1)(2)(3)(4). Table 3 demonstrates that apparent TDC parameters may be converted to real two-site exchange model parameters.…”

“…Methods for obtaining spatially resolved in vivo 'H transverse relaxation decay curves are now available (1)(2)(3)(4)(5)(6)(7) and offer the potential for increasing tissue specificity with MRI. The degree to which the methods will actually improve tissue specificity depends, to a large extent, on determining appropriate models for interpreting the observed relaxation behavior.…”

Diffusion nuclear magnetic resonance imaging in experimental stroke. Correlation with cerebral metabolites.

“…T 2 was determined from the echoes of the first multiecho train with signal intensity above the noise level (NL) as NL=m+3s, using the software system RAMSES. 17 ' 18 The data were analyzed for biexponential behavior with a modified Marquardt algorithm. 19 For the determination of T, the theoretical signal intensity ratio Q™ was computed as follows…”

Contrast in solid-state NMR imaging Part IIa: Basic filters

“…Further selectivity is achieved by modulating the magnitude of the phase toggle: A Gaussian-shaped modulation results in a Gaussian excitation shape and removes sinc lobes in the excitation spectrum. The effect of several adjustments of the selective excitation sequence on the 19 …”