Magnetic resonance imaging system

Claim 2

A magnetic resonance imaging system for applying an RF field and slicing, phase encoding, and read-out gradient fields to an object to be examined which is placed in a homogeneous static field in a predetermined sequence, receiving a magnetic resonance signal from a region of interest in the object, causing a synchronous detection circuit to detect the magnetic resonance signal by using a predetermined reference wave, and sampling a detection output from said synchronous detection circuit, thereby acquiring magnetic resonance signal data and obtaining diagnostic data, said magnetic resonance imaging system comprising reference wave control means for shifting a frequency and phase of the reference wave, by predetermined amounts, from a frequency and phase of a magnetic resonance signal when the phase encoding and read-out gradient fields are zero.

Claim 3

A system according to claim 1, further comprising means for increasing gradient strengths of the phase encoding and read-out gradient fields to values larger than gradient strength before the shift operation.

Claim 4

A magnetic resonance imaging system for applying an RF field and slicing, phase encoding, and read-out gradient fields to an object to be examined which is placed in a homogeneous static field in a predetermined sequence, receiving a magnetic resonance signal from a region of interest in the object through a probe, causing a synchronous detection circuit to detect the magnetic resonance signal by using a predetermined reference wave, and sampling a detection output from said synchronous detection circuit, thereby acquiring magnetic resonance signal data and obtaining diagnostic data, said magnetic resonance imaging system comprising: sequence control means for executing a sequence to acquire all data needed for an image reconstruction of a slice portion which is excited by said RF field, within a period of relaxing magnetization in the slice portion due to relaxation of transverse magnetization; frequency control means, controlled by said sequence control means, for shifting a frequency of the reference wave, by a predetermined amount, from a frequency of a magnetic resonance signal when the phase encoding and read-out gradient fields are zero, and for switching polarities of a frequency shift value in synchronism with the switching of the read-out gradient; and phase control means, controlled by said sequence control means, for shifting a phase of the reference wave, by a predetermined amount, from a phase of a magnetic resonance signal when the phase encoding and read-out gradient fields are zero, and for changing gradually a phase shift value in synchronism with the switching of the read-out gradient.

Claim 5

A magnetic resonance imaging system for applying an RF field and slicing, phase encoding, and read-out gradient fields to an object to be examined which is placed in a homogeneous static field in a predetermined sequence, receiving a magnetic resonance signal from a region of interest in the object through a probe, causing a synchronous detection circuit to detect the magnetic resonance signal by using a predetermined reference wave, and sampling a detection output from said synchronous detection circuit, thereby acquiring magnetic resonance signal data and obtaining diagnostic data, said magnetic resonance imaging system comprising: sequence control means for executing a sequence to acquire all data needed for an image reconstruction of a slice portion which is excited by said RF field, within a period of relaxing magnetization in the slice portion due to relaxation of transverse magnetization; frequency control means, controlled by said sequence control means, for shifting a frequency of the reference wave, by a predetermined amount, from a frequency of a magnetic resonance signal when the phase encoding and read-out gradient fields are zero, and for switching polarities of a frequency shift value in synchronism with the switching of the read-out gradient; and phase control means, controlled by said sequence control means, for shifting a phase of the reference wave, by a predetermined amount, from a phase of a magnetic resonance signal when the phase encoding and read-out gradient fields are zero, and for changing gradually a phase shift value in synchronism with the switching of the read-out gradient.

Claim 6

A system according to claim 3, wherein said frequency control means includes SSB generating means for mixing a frequency signal having a frequency of a magnetic resonance signal obtained when the phase encoding and read-out gradient fields are zero with a shifting frequency signal having a frequency corresponding to the frequency shift value, and for generating an SSB signal with a additive frequency of both frequencies.

Claim 7

A system according to claim 3, wherein said frequency control means includes phase correcting means for compensating for phase continuity with reference to switching polarities of the frequency shift value.

Claim 8

A system according to claim 3, wherein said sequence control means includes means for generating the encoding gradient field in a narrow pulsed form on each switching period of the read-out gradient field.

Claim 9

A system according to claim 3, further comprising synchronous control means for controlling a center of a tuning frequency of said probe in synchronism with the switching of the read-out gradient.

Claim 10

A system according to claim 7, wherein said probe has coil means used for at least receiving the magnetic resonance signal, and said synchronous control means includes a variable capacitor device connected to said coil means.

Claim 11

A system according to claim 7, wherein said variable capacitor device is a variable capacitance diode.

Claim 12

A system according to claim 7, wherein said probe has coil means used for both transmitting the RF signal and receiving the magnetic resonance signal, and said synchronous control means includes a variable capacitance diode connected to said coil means and a PIN diode for protecting said variable capacitance diode when the RF signal is transmitted.

Claim 13

A system according to claim 3, wherein said probe has coil means used for both transmitting the RF signal and receiving the magnetic resonance signal, and means for lowering a Q of the probe to such an extent that amplitude and phase changes caused by frequency changes in a reference wave can be ignored.

Claim 14

A system according to claim 3, wherein said probe is exclusively used for receiving the magnetic resonance signal and has a Q which is so low that amplitude and phase changes caused by frequency changes in a reference wave can be ignored.