Abstract: The novel method of monitoring radio frequency ablation of cancer tissues by temperature mapping using magnetic resonance thermography, is described. The invention further provides a method of rapid cycling between radio frequency ablation signaling and magnetic resonance image collection that minimizes interference and allows accurate image gathering and effective tissue ablation. Furthermore, the invention provides a method of reducing destruction of healthy surrounding tissue while destroying tumor tissue by radio frequency ablation.

Abstract: After exciting magnetic resonance (60), a train of magnetic resonance echoes including echoes (70.sub.1, 70.sub.2, . . . ) is induced, e.g., with a series of refocusing pulses including pulses (72.sub.1, 72.sub.2, . . . ). The echoes are phase and frequency-encoded appropriately for generating at least first and second images (94, 98). The first image echoes are interleaved with the second image echoes, for example, odd-numbered echoes for the first image and even-numbered echoes for the second image. To select the effective first/second image echo time, the first/second image echo which follows resonance excitation by a time closest to the selected first/second image effective echo time is given the zero or minimum phase-encoding. Nearby echoes being encoded with low phase-encode angles. In this manner, the effective echo times of the first and second images are selected to have preselected relative contrasts of diagnostic interest.

Abstract: A plurality of radio frequency excitation pulses or shots (52) are applied, ten in the embodiment illustrated in FIGS. 4 and 5. Following each shot, sets of data lines are collected. In the first set, an early gradient echo (EGE1), a spin echo (SE1), and a late gradient echo (LGE1), are induced to form three corresponding data lines. Magnetization is inverted (56) and a second set of data lines are generated. In the illustrated embodiment, nine sets of data lines are generated in each repetition. Phase-encoding gradient pulses (86, 88) are applied to cause the early gradient echo, the spin echo, and the late gradient echo data lines of each set to fall offset by a third of k-space. Phase-encoding pulses (74) are applied before each set and stepped such that in half of the repetitions, the phase-encoding increases with each subsequent set. In the other half of the repetitions, the phase-encoding decreases for each subsequent set.

Abstract: A sequence controller (40) controls the pulses applied by the radio transmitter (24) and the gradient amplifiers (20) and gradient coils (22) such that each repetition includes a prepreparation sequence segment, such as a presaturation sequence segment and a magnetization transfer contrast correction (MTC) segment, and a plurality of image sequence segments. More specifically, each of the image sequence segments induce resonance, phase and frequency-encode the resonance, and generate one or more views of data, all within a corresponding one of a plurality of slabs or sub-regions (74.sub.1, 74.sub.2, . . .) of an image volume (72). More precisely to the preferred embodiment, the imaging sequence segments interleave the slabs such that resonance is not excited concurrently in adjacent slabs, without exciting resonance and collecting a view in a non-adjacent slab. The views are sorted (80) by slab and stored in corresponding slab data memories (82).

Abstract: A subject's respiratory cycle is monitored (70) and analyzed (74) to determine a probability table (76). The probability table is continuously updated to provide a dynamic indication of the center between most stationary and most moving halves or other characteristic points within the respiratory cycle. At the beginning of each repeat time (TR), as resonance is excited (40), the output of the respiratory monitor is checked (80) and a determination is made (82) whether the patient is currently in the most stationary half or the most moving half of the respiratory cycle. Data lines generated in one half of the respiratory cycle are phase-encoded (84, 88) to generate a data line in each of a plurality of segments of k-space on one side of the central, zero phase-encoding point. Echoes occurring during the other half of the respiratory cycle are phase-encoded to generate data lines in segments of k-space on an opposite side of the central phase-encode angle.

Abstract: A sequence control (40) causes a transmitter (24) and gradient amplifiers (20) to transmit appropriate radio frequency excitation and other pulses to induce magnetic resonance in selected dipoles and cause the magnetic resonance to be refocused into a series of echoes following each excitation. A receiver (38) converts each echo into a digital data line. Each data line is regridded (70) for uniformity in k-space (FIG. 4). The data lines are one-dimensionally Fourier transformed (72) in a frequency encode direction. The one-dimensionally Fourier transformed data lines are multiplied (80) with a phase correction vector. A phase correction vector determining system (82) determines a corresponding phase correction vector for each echo number or position following excitation from a series of calibration echoes. To compensate for a decrease in magnitude with echo position following excitation, the intensity of each data line is scaled (90) to a common magnitude.

Abstract: In a magnetic resonance imaging system, a read gradient scaler (102) scales the amplitude and width of read gradients (78, 82, 84). A sampling rate control (104) controls the sampling rate of the resonance signals received from corresponding magnetic resonance echoes (80 54, 86). For example, when the amplitude of the gradient pulse is doubled and its width halved, the sampling rate of the resultant magnetic resonance signal is doubled, e.g., from a bandwidth of 32 MHz to a bandwidth of 64 MHz. In this manner, some echoes are read-out over a longer period of time with a lower bandwidth to produce lower signal-to-noise data lines; whereas, other echoes are much shorter and are read-out more quickly, but with a lower signal-to-noise ratio.

Abstract: Magnetic resonance is excited (50) in first and second species dipoles of a subject in a temporally constant magnetic field. The resonance is refocused (52) to generate a spin echo (54) centered at a time when the first and second species resonance signals are in-phase. Gradients echoes (64, 68) are generated, centered at a time (2n+1).pi./.delta..omega. before and after the spin echo, where .delta..omega. is a difference between the first and second species resonance frequencies. In this manner, the first and second species signals are 180.degree. out-of-phase in the gradient echoes. The resonance is refocused (82) one or more times to generate additional spin and gradient echoes with different phase encodings (78). The sequence is repeated with yet more phase encodings, and magnetic resonance signals from the spin echo and the two gradient echoes are reconstructed (86) into a spin echo image (s.sub.0) and a pair of gradient echo images (s.sub.+1, s.sub.-1).

Abstract: An examination region (34) is divided into a multiplicity of slices, e.g. slices 1-20. The slices are divided up into groups or slabs, e.g., slabs I-V. A series of magnetization inversion pulses (70.sub.I- 70.sub.V) and slab select gradient pulses (74.sub.I -74.sub.V) are applied at regular intervals. At a duration after each slab inversion at which the magnetization of a material such as CSF is at a minimum or null (80) marks a center of a data acquisition period (84). A plurality of imaging sequences (82) are conducted in each data acquisition period. Each of the imaging sequences collects one or more data lines from each of the slices within the corresponding slab. This process is repeated cyclically until all of the data lines of each slice of each slab have been collected. The data lines are reconstructed (102) into an image representation which is stored in an image memory (104) for selective display on a video monitor (108).

Abstract: Magnets (12) create a temporally constant magnetic field through an examination region (14). Radio frequency coils (26, 34) and a transmitter (24) transmit radio frequency saturation pulses (52) and the resonance excitation and manipulation pulses of a magnetic resonance imaging sequence (72) into the examination region. Gradient amplifiers (20) and gradient coils (22, 32) create magnetic field gradients across the examination region for spatially focusing the saturation, for spoiling (62, 66, 70) residual transverse magnetization and for frequency and phase encoding in the magnetic resonance imaging sequence. A sequence controller (40) includes a saturation pulse controller (44) for generating the saturation pulse (52) and slice select gradients (58) and a steady state sequence controller (48) for generating the imaging sequence (72). The saturation is spectrally focused by limiting the frequency of the saturation pulse to selected frequencies.

Abstract: An RF pulse sequence (40, 42, 44) is applied to generate magnetic resonance in which a dipolar or bound spin system component of the magnetic resonance has a quadrature or 90.degree. phase offset from a Zeeman or free spin system component of the magnetic resonance. The resultant resonance signal is encoded with magnetic field gradients (50, 52, 54) and sampled during a dipolar spin system resonance echo (46). The process is repeated altering the relative phase of the three RF pulses (40', 42', 44') and of a digital radio frequency receiver (28) such that the sampled dipolar and Zeeman spin system components are again in quadrature, but 90.degree. offset in the opposite sense. The two resonance signals with their Zeeman components out of phase in the opposite sense are combined (64) such that the dipolar spin system components add and the Zeeman spin system components cancel.