RF Receiver System

Abstract

A solution is created for a radio frequency (RF) receiver system 1 that provides MR information from an examination space of a magnetic resonance (MR) imaging system, by expanding the dynamic range of the radio frequency (RF) receiver system 1 for better imaging performance. The sigma-delta ADC of the RF receiver system operates in single-bit mode with an automatic gain control (AGC) circuit used to control the DAC feedback strength, thereby expanding the dynamic range of the receiver to match the MRI signal. The present invention also relates to a magnetic resonance (MR) imaging system, a method for expanding the dynamic range of a radio frequency (RF) receiver system, a software package for a magnetic resonance (MR) imaging system, a software package for upgrading a magnetic resonance (MR) imaging system, and a computer program product.

Description

[Technical Field]

[0001] The present invention relates to the field of magnetic resonance (MR) imaging. In particular, the present invention relates to a radio frequency (RF) receiver system for providing MR information from an examination space of a magnetic resonance (MR) imaging system. The present invention further relates to a magnetic resonance (MR) imaging system, a method for extending the dynamic range of a radio frequency (RF) receiver system of a magnetic resonance (MR) imaging system, a software package for a magnetic resonance (MR) imaging system, and a software package for upgrading a magnetic resonance (MR) imaging system. [Background technology]

[0002] The dynamic range of MRI signals exceeds that of commercially available ADCs. Various techniques have been developed to extend the dynamic range of ADCs by variable gain and / or compression in the signal conditioning prior to the ADC. For sigma-delta ADCs, traditional approaches use multi-bit feedback DACs or high-order loop filters to extend the dynamic range.

[0003] A multi-bit feedback DAC requires a corresponding multi-bit quantizer, which increases the ADC's complexity as well as the receiver's total power consumption. Because errors in the feedback DAC cannot be compensated for by the sigma-delta control loop, the multi-bit DAC must be highly linear so as not to impair the required high dynamic range and fidelity of the sampled signal. Single-bit sigma-delta ADCs are inherently linear, avoiding the implementation complexities associated with achieving a fully linear multi-bit feedback DAC. Increasing the order of the loop filter also incurs costs in terms of power consumption and chip area, and adds design complexity. Generally, the theoretical benefits of higher-order loop filters are only partially achieved due to their significant design complexity and sensitivity to errors.

[0004] European Patent Application No. 3565124 discloses an analog-to-digital converter based on a single-bit sigma-delta quantizer. This known analog-to-digital converter includes an auto-ranging function implemented in the range control circuit. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a radio frequency (RF) receiver system with an extended dynamic range. [Means for solving the problem]

[0006] According to the present invention, this object is addressed by the subject matter of the independent claims. Preferred embodiments of the invention are set out in the subclaims.

[0007] Thus, according to the present invention, there is provided a radio frequency (RF) receiver system for providing MR information from an examination space of a magnetic resonance (MR) imaging system, the RF receiver system including: at least one RF coil with at least one connection port for receiving an analog MR information signal; and at least one analog-to-digital converter (ADC) connected to the at least one connection port for converting the analog MR information signal into a digital MR information signal, whereby the at least one ADC is a single-bit sigma-delta ADC, the single-bit sigma-delta ADC including a loop filter, a quantizer unit for quantizing the analog MR information signal, and a variable output intensity feedback digital-to-analog converter (DAC) unit. The RF receiver system further includes a signal processing chain including a first digital downconverter that converts the digital MR information signal at the ADC sampling frequency to an intermediate sampling frequency; at least one automatic gain control (AGC) circuit located after the first DDC and operating at the intermediate sampling frequency, that tracks the temporal magnitude of the MRI signal and adjusts the gain of a digital-to-analog converter (DAC) unit (inside the ADC) accordingly; and at least one feedback control that operates at the intermediate sampling frequency and adjusts the DAC output strength as a function of the temporal magnitude of the MRI signal.

[0008] At any particular feedback DAC output strength, the single-bit ADC provides essentially linear digitization of the MRI signal. The intermediate sampling frequency must be high enough to track signal magnitude fluctuations and control the feedback output strength to avoid overflow in the sigma-delta control loop. It is preferably as low as possible to minimize DDC power consumption. Furthermore, the intermediate frequency is tied to a distinct MR imaging mode, which determines the interval at which the MR signal strength increases to a level that could cause ADC overload.

[0009] In an embodiment of the present invention, the signal processing chain further includes a numerically controlled oscillator (NCO) that provides the RF carrier frequency, and a digital signal processing circuit (DTC) that converts the quantized signal to a baseband sampling frequency (F Baseband ) and a first multiplier for frequency shifting the first signal to the second signal.

[0010] In another embodiment of the present invention, the signal processing chain further comprises at least a second DDC (DDC2), which has an intermediate sampling frequency (F AGC ) signal at baseband sampling frequency (F Baseband ) to convert.

[0011] In a further embodiment of the present invention, the signal processing chain includes a second multiplier located after the quantizer unit, which multiplies the digital MR information signal by a digital representation of the DAC gain to adjust the digital signal to compensate for the current DAC gain.

[0012] In another embodiment of the present invention, the DAC is a two-level DAC with high gain and low gain, and the signal processing chain further includes a calibration unit disposed after the quantizer unit, which adjusts the digital MR information signal according to the relative gain between the high state and the low state of the AGC.

[0013] In yet another embodiment of the present invention, the AGC is configured such that the DAC transitions to a high state when the signal magnitude is greater than a high threshold, and transitions to a low state when the signal magnitude is less than a low threshold.

[0014] In an embodiment of the present invention, the first DDC includes a high HDDC and a low LDDC. The high DDC and low DDC are disposed in a section of the signal processing chain having an intermediate sampling frequency and downconvert the high and low state signals of the AGC. The signal processing chain further includes a summator that combines the high and low state signals only after relative gain adjustment. The single-bit sigma-delta ADC further includes multipliers before the high DDC and low DDC, respectively, that frequency shift the quantized signal by the baseband sampling frequency using a numerically controlled oscillator.

[0015] In another aspect of the present invention, the above object is achieved by a magnetic resonance (MRI) imaging system comprising a main magnet generating a static magnetic field, a magnetic gradient coil system generating magnetic gradient fields superimposed on the static magnetic field, an examination space provided for positioning a subject of interest inside, at least one radio frequency receiver system as claimed in claims 1 to 3 for providing magnetic resonance information from the examination space, and a digital signal processing unit for processing digital MR information signals provided by the at least one RF receiver system.

[0016] In another aspect of the present invention, the above object is achieved by a method for extending the dynamic range of a radio frequency (RF) receiver system, the method comprising: providing the RF receiver system described above; receiving an analog MR information signal at at least one connection port of at least one RF coil in an RF receiver system; performing an analog-to-digital conversion of the analog MR information signal to a digital MR information signal within the RF receiver system; converting the digital MR information signal at the ADC sampling frequency to an intermediate sampling frequency by a first digital down-converter; tracking the magnitude of the digital MR information signal with an automatic gain control circuit; adjusting the DAC gain with respect to the magnitude of the digital MR information signal; frequency shifting the digital MR information signal at a baseband sampling frequency by a numerically controlled oscillator to provide an RF carrier frequency and a digital mixer; and converting the signal at the intermediate sampling frequency to a baseband sampling frequency by a second DDC.

[0017] In an embodiment of the present invention, the method further comprises: Multiplying the digital MR information signal by a digital representation of the DAC gain.

[0018] In another embodiment of the present invention, the method further comprises: providing a two-level DAC with high gain and low gain; providing a calibration circuit after the quantizer unit; and adjusting the digital MR information signal by a calibration circuit to a relative gain between a high gain state and a low gain state of the AGC.

[0019] In yet another embodiment of the present invention, the method further comprises: providing a two-level DAC with high gain and low gain; providing a high HDDC and a low LDDC, the high DDC and the low DDC being disposed within a section of a single-bit sigma-delta ADC having an intermediate sampling frequency; shifting the digital MR information signal at a baseband sampling frequency by a numerically controlled oscillator before the high DDC and before the low DDC by a multiplier; down-converting the high-state signal and the low-state signal of the AGC by the high DDC and the low DDC; and combining the converted high-state and low-state signals after relative gain adjustment by a summator.

[0020] In another aspect of the present invention, the above object is achieved by a software package for a magnetic resonance (MR) imaging system, the software package including instructions for controlling a radio frequency (RF) receiver system in accordance with the above method.

[0021] In another aspect of the present invention, the above object is achieved by a software package for upgrading a magnetic resonance (MR) imaging system, the software package including instructions for controlling a radio frequency (RF) receiver system in accordance with the above method.

[0022] In yet another aspect of the present invention, the above object is achieved by a computer program product comprising instructions which, when executed by a computer, cause the computer to perform the steps according to the above method. That is, the computer program (product) of the present invention comprises instructions which, when executed by a computer, cause the computer to perform (the steps of) the method of the present invention. [Brief explanation of the drawings]

[0023] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, although such embodiments do not necessarily represent the full scope of the invention, and reference should therefore be made to the claims and this specification for interpreting the scope of the invention.

[0024] [Figure 1] FIG. 1 shows a schematic block diagram of a radio frequency (RF) receiver system according to an embodiment of the present invention. [Figure 2] FIG. 2 illustrates a schematic block diagram of a radio frequency (RF) receiver system with a two-level (high / low) DAC according to another embodiment of the present invention. [Figure 3] FIG. 3 shows a schematic diagram of the threshold values. [Figure 4]FIG. 4 illustrates, in accordance with another embodiment of the present invention, a block diagram of a radio frequency (RF) receiver system with a two-level (high / low) DAC in which high / low calibration is performed at an intermediate signal frequency. [Figure 5] FIG. 5 shows a flowchart of a method for extending the dynamic range of an ADC in a radio frequency (RF) receiver system in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows a schematic block diagram of a radio frequency (RF) receiver system according to an embodiment of the present invention. The RF receiver system 1 includes at least one RF coil with at least one connection port 2 for receiving an analog MR information signal. The RF receiver system 1 further includes a low noise amplifier LNA for amplifying the analog MR information signal. The amplified MR information signal is propagated to an analog-to-digital converter ADC. The ADC in this embodiment is an RF single-bit sigma-delta analog-to-digital converter with a variable output intensity feedback DAC. A loop filter LF, a quantizer unit QUANT, and a digital-to-analog converter DAC form a sigma-delta ADC control loop. The output intensity of the DAC is controlled by an ADC clock F ADCThe DAC gain must be sufficient to compensate for all signal levels at the LNA output during each period (i.e., greater than the maximum input). A high DAC output strength (or gain) allows it to track high signal magnitudes. A low DAC gain results in lower quantization noise and higher resolution for small signals, respectively. Thus, the DAC gain offers the possibility to shift the ADC's operating range with respect to the input signal strength, ideally keeping all other parameters (such as quantization and thermal noise) the same. However, it should be noted that when the input signal is high, a number of nonlinear effects begin to appear as the signal level inside the SDM increases, leading to a degradation of SNDR. Furthermore, the DAC gain setting introduces nonlinearities in ADC operation when the input signal is high, which is also observed as a decrease in SNDR. In this context, timely switching between low and high DAC gain is essential for proper operation. By increasing the DAC gain only during periods of high signal magnitude, the DR is extended only when necessary, minimizing the corresponding decrease in SNDR. This is particularly advantageous for MRI echo signals that are high for a limited duration, limiting the reduction in SNDR, which in practice is only slight.

[0026] The automatic gain control (AGC) circuit in Figure 1 tracks the magnitude of the detected signal and adjusts the DAC gain G accordingly. DAC At the same time, the digital representation of the DAC gain, G ADJ is used to adjust the digital signal to compensate for the current DAC gain. This compensation applies ADJ This is done by multiplying

[0027] The remainder of the circuitry comprises the range-adjusting receiver. The quantized signal is frequency-shifted to baseband in a digital mixer MIX. The required RF carrier frequency is generated by a numerically controlled oscillator NCO. The baseband signal is then low-pass filtered and decimated to baseband by a digital downconverter DDC. This mechanism auto-calibrates (equalizes) the digital data so that the switching points can be determined quickly and accurately enough to reconstruct a uniform bit stream representing the full dynamic range.

[0028] AGC is set to the intermediate frequency F AGC For this purpose, the DDC is divided into two parts, DDC1 and DDC2. DDC1 is ADC The signal is sampled at the intermediate sampling frequency F AGC Then, the DDC2 converts the signal to the baseband sampling frequency F BASEBAND Then convert it further.

[0029] FIG. 2 shows a schematic block diagram of a radio frequency (RF) receiver system with a two-level (high / low) DAC according to another embodiment of the present invention. In this embodiment, the DAC is a two-level DAC with high gain H and low gain L. A calibration circuit CAL adjusts the sampled signal according to the relative gain between the DAC's H and L states. CAL consists of a signed digital value that replaces the single-bit value output by QUANT in the H state. For example, a DAC with a nominal gain of 1.0 in the L state and a nominal gain of 5.0 in the H state actually has a relative gain of 4.9963. As a result, CAL generates the following value as a function of the gain state and the QUANT output: [Table 1]

[0030] To accurately determine the relative DAC gain, a calibration procedure is required. Alternatively, the DAC may be calibrated during manufacture, for example by laser trimming of resistors. The calibrated relative gain value needs to have sufficient accuracy over the entire dynamic range of the input signal, and thus necessarily requires a large number of bits. For example, MRI signals typically have a dynamic range of about 90 dB, and as a result, at least about (90 / 6.02) = about 15 bits are required to accurately represent the relative DAC gain. This significantly increases the DDC power consumption.

[0031] FIG. 3 schematically shows a diagram of the threshold values TH and TL. To avoid excessive transitions between the H state and the L state, AGC is implemented with hysteresis. This requires a high threshold value TH and a low threshold value TL. When the magnitude of the signal is greater than the high threshold (X > TH), the DAC transitions to the H state. When the magnitude of the signal is less than the low threshold (X < TL), the DAC transitions to the L state.

[0032] FIG. 4 schematically shows a block diagram of a radio frequency (RF) receiver system comprising a two-level (high / low) DAC in which high / low calibration is performed at an intermediate signal bandwidth according to another embodiment of the present invention. The DDC power consumption is proportional to both the number of bits required to represent the signal and the sampling frequency at which it operates. G ADJ To compensate the analog G DAC with sufficient accuracy necessarily requires a large number of bits. This increases the DDC power consumption required to downconvert to the baseband. By first converting the (unadjusted) signal to a low intermediate sampling frequency, the bit count at the high sampling frequency is reduced. Thus, FAGC provides a trade-off between the maximum signal bandwidth that the AGC can track and the power consumption of the DDC.

[0033] The unadjusted signal is F AGCSince the H-state signal is downconverted to 1, the H-state and L-state signals must be downconverted simultaneously, and the two are combined only after relative gain adjustment. This is performed by the high DDC (HDDC) and low DDC (LDDC) signal paths. The signal paths are summed by the summator SUM after calibration. Since the downconverted signal has become a multi-bit signal through digital processing before multiplication / mixing, calibration next requires multiplication MIX in the digital domain.

[0034] 5 shows a flowchart of a method for extending the dynamic range of an ADC in a radio frequency (RF) receiver system according to an embodiment of the present invention. The method begins with step 500, in which a radio frequency (RF) receiver system according to claim 1 is provided.

[0035] Next, in step 510, an analog MR information signal is received at at least one connection port of at least one RF coil in an RF receiver system.

[0036] Thereafter, in step 520, analog-to-digital conversion of the analog MR information signal to a digital MR information signal is performed within the RF receiver system.

[0037] In step 530, the ADC sampling frequency F ADC The digital MR information signal is converted to an intermediate sampling frequency F by a first digital down-converter DDC1. AGC is converted to

[0038] In step 540, the magnitude of the digital MR information signal is tracked with an automatic gain control AGC circuit.

[0039] Thereafter, in step 550, the DAC gain G is calculated relative to the magnitude of the digital MR information signal. DAC is adjusted.

[0040] In an embodiment of the present invention, the digital MR information signal is mixed at a baseband sampling frequency F by a numerically controlled oscillator NCO to provide an RF carrier frequency and a digital mixer MIX. Baseband Furthermore, in an implementation of the present invention, the intermediate sampling frequency F AGC The signal is converted to a baseband sampling frequency F by the second DDC (DDC2). Baseband It can be converted with.

[0041] While the present invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary, and not restrictive. The present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprises" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims are not to be construed as limiting the scope. Moreover, for the sake of clarity, not all elements in the drawings have been provided with reference signs. [Explanation of symbols]

[0042] Radio Frequency (RF) Receiver System 1 Connection Port 2 Low Noise Amplifier LNA Loop filter LF Quantizer unit QUANT Digital to Analog Converter DAC Sigma-Delta Modulator SDM Analog-to-Digital Converter (ADC) ADC Clock F ADC Intermediate sampling frequency F AGC Baseband sampling frequency F Baseband Automatic Gain Control AGC Digital Down Converter DDC Numerically Controlled Oscillator (NCO) First digital down converter DDC1 Second Digital Down Converter DDC2 Low state L High state H DAC gain G DAC Digital representation of DAC gain G ADJ Calibration circuit CAL Low Digital Down Converter LDDC High-speed digital down converter HDDC Low Threshold TL High Threshold TH SUM Mixer MIX

Claims

1. 1. An RF receiver system for providing magnetic resonance information from an examination space of a magnetic resonance imaging system, comprising: at least one RF coil having at least one connection port for receiving analog magnetic resonance information signals; at least one analog-to-digital converter (ADC) connected to the at least one connection port for converting the analog magnetic resonance information signal into a digital magnetic resonance information signal, whereby the at least one ADC is a single-bit sigma-delta ADC, the single-bit sigma-delta ADC including a loop filter, a quantizer unit for quantizing the analog magnetic resonance information signal, and a variable output intensity feedback digital-to-analog converter (DAC) unit; Including, the RF receiver system further includes a signal processing chain including a first digital downconverter for converting the digital magnetic resonance information signal at an ADC sampling frequency to an intermediate sampling frequency and at least a second digital downconverter for converting the intermediate sampling frequency signal to a baseband sampling frequency; at least one automatic gain control circuit located after the first digital downconverter, operating at the intermediate sampling frequency, tracking the temporal magnitude of the MRI signal and adjusting the gain of the DAC unit accordingly; at least one feedback control operating at the intermediate sampling frequency and adjusting a DAC output intensity as a function of the temporal magnitude of the MRI signal; 1. An RF receiver system comprising:

2. The signal processing chain further comprises: a numerically controlled oscillator providing an RF carrier frequency; a first multiplier for frequency shifting the quantized analog magnetic resonance information signal to the baseband sampling frequency; 10. The RF receiver system of claim 1, comprising:

3. 3. The RF receiver system of claim 1, wherein the signal processing chain further includes a second multiplier disposed after the quantizer unit, the second multiplier multiplying the digital magnetic resonance information signal by a digital representation of a DAC gain to adjust the digital magnetic resonance information signal to compensate for a current DAC gain.

4. the DAC unit is a two-level DAC unit with high gain and low gain; 3. The RF receiver system of claim 1, wherein the signal processing chain further includes a calibration unit disposed after the quantizer unit, and the calibration unit adjusts the digital magnetic resonance information signal according to a relative gain between a high state and a low state of the automatic gain control circuit.

5. 3. The RF receiver system of claim 1, wherein the automatic gain control circuit is configured to transition the DAC unit to a high state when the signal magnitude is greater than a high threshold, and to transition the DAC unit to a low state when the signal magnitude is less than a low threshold.

6. the first digital downconverter includes a high digital downconverter and a low digital downconverter, the high digital downconverter and the low digital downconverter being disposed in a section of the signal processing chain having the intermediate sampling frequency and downconverting a high state signal and a low state signal of the automatic gain control circuit; and the single-bit sigma-delta ADC further includes: a summator that combines the high state signal and the low state signal only after a relative gain adjustment, the signal processing chain further comprising:

6. The RF receiver system of claim 5, further comprising a multiplier before the high digital downconverter and before the low digital downconverter, for frequency shifting the quantized analog magnetic resonance information signal to the baseband sampling frequency by a numerically controlled oscillator.

7. a main magnet that generates a static magnetic field; a magnetic gradient coil system for generating gradient magnetic fields superimposed on the static magnetic field; an examination space provided for positioning a subject of interest therein; - at least one RF receiver system according to any one of claims 1 to 6 for providing magnetic resonance information from the examination space; a digital signal processing unit for processing digital magnetic resonance information signals provided by said at least one RF receiver system; 1. A magnetic resonance imaging system comprising:

8. 1. A method for extending the dynamic range of an RF receiver system, comprising: Providing an RF receiver system according to claim 1; receiving an analog magnetic resonance information signal at the at least one connection port of the at least one RF coil in the RF receiver system; performing an analog-to-digital conversion of the analog magnetic resonance information signal into a digital magnetic resonance information signal within the RF receiver system; converting the digital magnetic resonance information signal at an ADC sampling frequency to an intermediate sampling frequency by a first digital down-converter; tracking the magnitude of the digital magnetic resonance information signal with the automatic gain control circuit; adjusting the gain of the DAC unit with respect to the magnitude of the digital magnetic resonance information signal; frequency shifting the digital magnetic resonance information signal at a baseband sampling frequency by a numerically controlled oscillator to provide an RF carrier frequency and a digital mixer; converting the digital magnetic resonance information signal at the intermediate sampling frequency to a baseband sampling frequency by the second digital down-converter; A method comprising:

9. 9. The method of claim 8, further comprising the step of multiplying the digital magnetic resonance information signal by a digital representation of a DAC gain.

10. providing a high gain and low gain two level digital to analog converter unit; providing a calibration circuit after the quantizer unit; adjusting the digital magnetic resonance information signal with the calibration circuit at a relative gain between a high gain state and a low gain state of the automatic gain control circuit; The method of claim 8 further comprising:

11. providing a high gain and low gain two level digital to analog converter; providing a high digital down-converter and a low digital down-converter, the high digital down-converter and the low digital down-converter being disposed within a section of the single-bit sigma-delta ADC having the intermediate sampling frequency; shifting the digital magnetic resonance information signal at the baseband sampling frequency by the numerically controlled oscillator before the high digital down-converter and before the low digital down-converter by multipliers, respectively; downconverting the high-state signal and the low-state signal of the automatic gain control circuit by the high digital downconverter and the low digital downconverter; combining the converted high-state signal and the converted low-state signal after relative gain adjustment by a summator; The method of claim 8 further comprising:

12. A software package for a magnetic resonance imaging system, comprising instructions for controlling an RF receiver system according to the method of any one of claims 8 to 11.

13. A software package for upgrading a magnetic resonance imaging system, comprising instructions for controlling an RF receiver system according to the method of any one of claims 8 to 11.

14. A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of claims 8 to 11.

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