University of California

John C Hoenninger, Iii

Lawrence E Crooks

Mitsuaki A Arakawa

David A Feinberg

Jerome R Singer

John Van Heteren

James W Jones

Keiji Furui

Thomas McDermott

Jack H Zeilenga

A digital lowpass filter design for filtering nuclear magnetic resonance (NMR) signals in a magnetic resonance imaging (MRI) system supports multiple frequencies and is highly configurable without sacrificing speed and performance. The first FIR filter stage of a synchronized multirate digital filter is selected from a database of filter coefficient/parameter sets which are loaded at start time and used in place. Second (and later) FIR filter stages are fixed in the example. A large number of different filter frequencies can be selected rapidly without changing the parameterized filter program reducing the amount of time to start up the MRI system and allowing 'on-the-fly' filter changes in real-time between echoes and/or A/D samples. For example, filter preselection by the host can be performed in less than 100 .mu.s, and, one of several lowpass filters can be selected by the sequencer 'on-the-fly' with a latency of less than 10 .mu.s.

Multi-frequency digital low pass filter for magnetic resonance imaging

A control interface for a magnetic resonance imaging (MRI) system provides extended, improved linker syntax/techniques that maximize reuse of program segments, allow optimal compromise between detailed representation and efficient sequence program design and maintenance, and permit uniform application of the loop syntax to link commands for MRI sequencers with a wide range of hardware implementations. The control interface provides, among other features, generalized loops at the link level; loop symbols representing loop identity can be associated with scope and/or range (with some kind of limited grammar in the link command itself that supports identification of scope and/or range); parameter tables that can be associated with loop symbols (any given table can be associated with N loop symbols in order to provide multidimensional sequences); multiple levels of loop nesting; and directed limited syntax that provides limited grammar, and range and syntax checking and requires the user to explicitly enter information into the interface.

Control interface for an MRI system

A multi-rate sample MRI (magnetic resonance imaging) digital receiver maintains synchronization of digitally processed signals. This multi-rate sample data system is used to demodulate and filter a digitized MRI RF signal. A phase/timing relationship is established between the signal received and processed by the digital receiver, and the physical nuclear magnetic resonance (NMR) process the body being imaged is undergoing. Once established, the phase/timing relationship is maintained for the duration of the particular NMR experiment being performed. Special logic in the digital system ensures that the data output is synchronized with an external synchronous signal controlling data acquisition within the MRI system. Optimum signal processing is performed to minimize the time between the end of the acquisition control signal and the last output from the digital signal processing system.

Synchronized digital signal processor for MRI reception

A sequencer controller for nuclear magnetic resonance imaging includes a level-sensitive external gating arrangement. When a sequencer microcode WAIT instruction is executed, the gating arrangement operates differently depending on the level of the signal existing at the external gating input. If the external gating signal level is at one level, the gating arrangement causes the sequencer to wait until the external gating input changes level----thus permitting an external gating event (e.g., closure of a breath switch or the like) to interact with and control the timing of the NMR sequence. If the external gating signal is at a different level when the WAIT instruction is first executed, however, the sequencer does not 'wait' at all but instead ignores the WAIT instruction and goes to the next sequencer state. Such level sensitive external gating permits microcode sequences including WAIT instructions to be executed when external gating is desired and also when external gating is not desired, thus reducing the amount of code that needs to be maintained.

Microcode sequencer changing states in response to an external gating

An extremely fast and efficient Linker for a Magnetic Resonance Imaging (MRI) system Nuclear Magnetic Resonance (NMR) pulse control sequencer efficiently derives subsequent blocks of microcode to be loaded by using the contents of a memory buffer containing previously loaded microcode as a template, Most of the template is reused 'as is'. Only the relatively few field values in the microinstructions which change from one signal generation process, or cycle, to the next are replaced with new values. Offsets are tabulated of instructions which have associated multi-entry cycle indexed program change table (PCT) values. When further code is to be linked and loaded, the linker accesses the PCTs based on the table and to inserts new values into the appropriate instruction fields. The microcode memory image may be continuously maintained in a host memory buffer and re-edited successive times. The Fast Linker provided by the present invention is capable of continually loading microcode into a sequencer writable control store, and is fast enough to run under a time shared operating system at the same time a higher priority data acquisition and display process is executing.

Microcode linker/loader that generates microcode sequences for MRI

A local frequency generator employing a single crystal oscillator, latches and direct digital synthesizer circuits digitally produces all signals needed in the transmitter channel of a MRI system to generate MRI transmitter RF pulses. The local frequency generator is operable in both the single side band and double side band modes and has the capability of switching between the modes. The generator is constructed with a phase resetting capability for providing the plural output frequencies needed for making plural MRI slices.

MRI multi-frequency DSB and SSB RF synthesizer

A sequencer controller for nuclear magnetic resonance imaging includes a level-sensitive external gating arrangement. When a sequencer microcode WAIT instruction is executed, the gating arrangement operates differently depending on the level of the signal existing at the external gating input. If the external gating signal level is at one level, the gating arrangement causes the sequencer to wait until the external gating input changes level--thus permitting an external gating event (e.g., closure of a breath switch or the like) to interact with and control the timing of the NMR sequence. If the external gating signal is at a different level when the WAIT instruction is first executed, however, the sequencer does not 'wait' at all but instead ignores the WAIT instruction and goes to the next sequencer state. Such level sensitive external gating permits microcode sequences including WAIT instructions to be executed when external gating is desired and also when external gating is not desired, thus reducing the amount of code that needs to be maintained.

A microcoded pulse sequencer for real time control of a nuclear magnetic resonance (NMR) magnetic resonance imaging (MRI) system includes a microcode store which is continually loadable. Microinstructions are loaded into a one portion of the store while the sequencer executes micro-instructions out of another portion of the store. Means are provided to ensure that the sequencer never executes micro-instructions currently being loaded, and also ensures (through timing features) that the sequencer can never, over time, execute micro-instructions more rapidly than new micro-instructions can be loaded (i.e., so that the sequencer never 'runs out of' micro-instructions). Since the host processor and the microcode sequencer provide for continual loading of the sequencer store while the sequencer is running, the user/programmer may view the control store as an ideal virtual control store having an unlimited size. Programmers may now write NMR microcode sequences without concern for whether they will 'fit' into the physical memory space provided by sequencer store. In addition, reloading of the control store is completely transparent to ongoing NMR pulse sequences in the preferred embodiment and causes no troublesome image-degrading interruption of such sequences.

Continually loadable microcode store for MRI control sequencers

In a multi-slice magnetic resonance imaging system which employs a train of plural RF NMR nutation pulses, the frequency spectrum and/or magnetic gradient employed for succesive pulses is controlled so as to effect more nearly equal full-width-half-magnitude (FWHM) or other spatial dimensions of actual nuclei nutation variation versus distance curves for all of the slice selective nutation pulses. The result is a reduction of any 'gap' of non-imaged volume disposed between the succession of selected MRI slice volumes.

Contiguous slices in multi-slice MRI

An assembler/linker process utilizes predetermined control program segments ('templates' defining a sub-sequence of magnetic resonance imaging (MRI) states) together with predetermined program-change tables of MRI parameter values. At least some of the program segments are referenced by predetermined symbolic addresses and include pointer-references to corresponding ones of the table entries. The assembler/linker process machine replicates a predetermined set of such slice/specific program segments in a predetermined order while also simultaneously indexing corresponding symbolic addresses and referenced table entries in a predetermined sequence so as to maintain proper correspondence between slice-specific main programs and subroutines for each replicated program segment. In addition, certain of the replicated program segments may be defined having predetermined symbolic addresses which are not indexed thus further conserving the number of program instructions which need to be replicated and stored in the assembly/linkage process. A subset of slice-specific program segments can be further designated for replication as a unit before following program segments are utilized. A unique linker language level syntax is also provided for an ordered string of input digital data used to control the assembler/linker replication process.

Machine generation of machine-executable state-change instructions for

An imaging NMR scanner generates multi-dimensional NMR spin echo responses from selected sub-volumes of an object. 90.degree. and 180.degree. r.f. nutation pulses are used together with a variable amplitude gradient between these nutation pulses to phase encode a second dimension in the spin echo response which is already phase-encoded in a first dimension by use of a magnetic gradient during signal readout. Two-dimensional Fourier transforms or multiple angle projection reconstruction processes are then used to generate an array of pixel value data signals representing a visual image of the point-by-point spatial distribution of nutated nuclei within the object. Image artifacts potentially caused by relatively moving elements of the object are avoided by selecting the spin echo generating sub-volumes to avoid the moving elements. High resolution images of sub-volumes of interest can be obtained by selection of a sub-volume of interest in conjunction with these reconstruction techniques. Solutions for possible aliasing artifacts are also presented as are three-dimensional reconstruction techniques using NMR spin echo responses from such selected sub-volumes.

Method and apparatus for rapid NMR imaging using multi-dimensional

An imaging NMR scanner obtains plural spin echo signals during each of successive measurement cycles permitting determination of the T2 parameter for each display pixel after but a single measurement sequence. The amplitude of the NMR spin echo responses is dependent on an 'a' machine parameter (the elapsed time between initiation of a given measurement cycle and the occurrence of the NMR response) and upon a 'b' machine parameter (the elapsed time between initiation of successive measurement cycles). These a and b machine time parameters are selectively controlled to enhance resultant image contrast between different types of tissue or other internal structures of an object under examination. Special phase control circuits ensure the repeatability of relative phasing between successive NMR responses from the same measured volume and/or of reference RF signals utilized to frequency translate and synchronously demodulate the NMR responses in the successive measurement cycles of a complete measurement sequence. Special sub-sequences of four measurement cycles are utilized to provide resultant combined spin echo measurements substantially independent of FID signal components.

Method and apparatus for rapid NMR imaging of nuclear parameters with an

Densities of resonant nuclei within elemental volumes along a line are measured using the nuclear magnetic resonance phenomenon called 'spin echo'. A first planar volume of nuclei is selectively excited to nutate spins by approximately 90.degree.. Thereafter a second planar volume of nuclei, transverse to the first planar volume, is selectively excited to nutate spins by approximately 180.degree.. The nuclei in the line volume common to both of the planar volumes thereafter generate characteristic spin echo signals. A magnetic gradient is established along this line volume during the spin echo read out so that the resultant spin echo signals can be processed to determine the respective densities of resonant nuclei along the line volume. Appropriate phasing of the excitations enables interference with the spin echo signals by the free induction decay to be eliminated. To enable rapid development, successive line volumes are read out which do not lie in previously excited planes.

Method and apparatus for rapid NMR imaging of nuclear densities within

Densities of resonant nuclei within elemental volumes along a line are measured using the nuclear magnetic resonance phenomenon called 'spin echo.' A first planar volume of nuclei is selectively excited to nutate spins by approximately 90.degree.. Thereafter a second planar volume of nuclei, transverse to the first planar volume, is selectively excited to nutate spins by approximately 180.degree.. The nuclei in the line volume common to both of the planar volumes thereafter generate characteristic spin echo signals. A magnetic gradient is established along this line volume during the spin echo read out so that the resultant spin echo signals can be processed to determine the respective densities of resonant nuclei along the line volume. Special pulsing sequences for rapidly effecting measurement of successive multiple line volumes and suitable apparatus for effecting such sequences are also described.

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Oakland, CA, United States of America

John C Hoenninger, Iii