U.S. Philips Corporation

Peter R Luyten

Jan A Den Hollander

Johannes J Van Vaals

Johannes H Den Boef

Jens D Jensen

Reurt P Van Stapele

A volume-selective magnetic resonance method for the determination of an MRI spectrum MR image, comprises a 90.degree. excitation pulse (p.sub.0) followed by two 180.degree. pulses (p.sub.1, p.sub.2,) the pulses (p.sub.0, p.sub.1, p.sub.2) being slice-selective. The magnetic resonance signal (SE) is sampled in the absence of magnetic field gradients and a spectrum is determined by way of Fourier transformation. In comparatively simple spin systems, J-refocusing is achieved for a specific choice of the echo time (TE), while only one J-coupling of more complex spin systems, comprising more than on J-coupling, is refocused by a specific choice of the echo time (TE). The method in accordance with the invention applies either a chemically selective 180.degree. pulse (p.sub.3) or a broadband 90.degree. pulse (p.sub.4) between the 180.degree. pulses (p.sub.1, p.sub.2). This causes J-refocusing to then occur, regardless the selected echo time (TE).

Volume-selective magnetic resonance imaging method and device

An improved MRI sequence for suppressing a signal from a chemical shift component avoids image artifacts due to relatively large rf fields inhomogeneities as may be caused by using linearly polarized rf fields by selectively inverting the chemical shift component by means of an adiabatic fast passage rf pulse prior to spin echo excitation.

Magnetic resonance method and device for suppressing a signal from a

An MRI method for spectroscopy utilizes a sequence which includes four RF electromagnetic pulses (p1, p2, p3, p4), three of which are spatially selective to generate a resonance signal (e) from a sub-volume of an object. The phase difference between the first and the second 90.degree. excitation pulse amounts to 90.degree.. The waiting period (dt1) between the first and the second pulse (p1, p2) is chosen so that the second pulse (p2) selectively resets the nuclear spins excited by the first non-selective pulse (p1) in the longitudinal direction. The selectively reset magnetization, for example of fat, is recalled, after the dephasing of the non-reset magnetization, for example of water, by the further pulses (p3, p4). A spectrum is determined from the resonance signal (e). In a modified version in which the phases of the first and the second pulse are the same, the sequence is used for shimming a local field around the sub-volume.

Method of determining a nuclear magnetization distribution of a

A magnetic resonance method for in vivo measurement of water-suppressed localized proton spectra, and device for performing the method, utilizes a frequency selective adiabatic fast passage pulse to achieve water suppression. Subsequent to a waiting period after the adiabatic pulse, during which selectively excited water magnetization has longitudinally relaxed until the longitudinal water magnetization has reached an amplitude of zero, an echo resonance signal in which water has been suppressed is generated by means of a volume-selective Hahn spin echo sequence. A spectrum is determined from the echo resonance signal by way of Fourier transformation. The method is particularly suitable for in vivo use in conjunction with surface coils where the rf electromagnetic field is liable to exhibit a substantial inhomogeneity. Comparatively small volumes can be measured by combination with a Hahn spin echo sequence, the overall examination time during in vivo measurement remaining within acceptable limits, for example during spectroscopic imaging.

Method of suppressing water resonance in a magnetic proton resonance

A method of heteronuclear decoupling in magnetic resonance spectroscopy and a device for determining a spectrum where spectra of a first type of nucleus which is spin-coupled to a second type of nucleus are decoupled inter alia in order to obtain a higher resolution. In inter alia phosphorous spectroscopy, during signal acquisition of resonance signals of the first type of nucleus, decoupling pulses are applied to the second type of nucleus, which decoupling pulses have been modulated in amplitude as well as in frequency or phase. The decoupling pulses need hardly be optimized. Very good decoupling is achieved, notably when use is made of surface coils for the transmitter and receiver coils exhibiting a substantial field inhomogeneity. When surface coils are used, suitable decoupling is achieved across a comparatively large volume.

Method of heteronuclear decoupling in magnetic resonance spectroscopy,

The measurement of localized spectra by means of stimulated echoes is known per se. Using three 90.degree. pulses, stimulated echoes are then generated; these pulses are selective or not. However, this technique it is not suitable for measuring good proton spectra of metabolites because the response of the non-bound protons is much greater than the response of the bound protons. In accordance with the invention, a fourth (spatially selective) 180.degree. refocusing pulse is added to a pulse sequence consisting of a 90.degree. non-spatially selective but frequency-selective pulse and two subsequent 90.degree. spatially selective pulses. Thus, a refocused stimulated echo is generated in which the response of the non-bound protons is suppressed and which contains only signals from the chemically bound protons. The proposed methods are particularly suitable for measurements on lactate because of the excellent spectral editing properties.

Volume-selective spectroscopy using refocused echoes

Using the method in accordance with the invention a layer of an object is selected by means of a cycle comprising a non-selective 90.degree. pulse, a dephasing gradient magnetic field, a non-selective 180.degree. pulse and a selective 90.degree. pulse in the presence of a similar gradient field. In the layer, a magnetization in the z-direction is obtained. Outside the object layer the transverse magnetization is totally dephased. By executing the cycle three times, during which the gradient directions of the three gradient fields used are mutually orthogonal, a 'cube-like' volume is selected. High-resolution images of spin density distributions and T1 or T2 distributions can thus be realized and location-dependent spectroscopy is also possible.

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Eindhoven, Netherlands

Peter R Luyten