Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2000-04-28
2003-05-06
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S437000, C600S453000, C600S455000
Reexamination Certificate
active
06558329
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to methods and apparatus which process data received from an ultrasound transducer in preparation for subsequent signal processing, such as, modulation recovery and scan conversion. More particularly, the present invention provides a single path for processing of data received from an ultrasound transducer, entirely in the digital domain, with an improved dynamic range.
FIG. 1
is a block diagram of an ultrasound system
100
. A transmit waveform generator
110
is coupled through a transmit/receive (T/R) switch
112
to a transducer array
114
, which includes an array of transducer elements. The T/R switch
112
typically has one switch element for each transducer element. The transmit waveform generator
110
receives transmit pulse timing sequences from a waveform timing generator
116
. The transducer array
114
, energized by the transmit waveform generator
110
, transmits ultrasound energy into a region of interest in a patient's body and receives reflected ultrasound energy, or echoes, from various structures and organs within the patient's body. As is known in the art, by appropriately delaying the pulses applied to each transducer element by the transmit waveform generator
110
, a steered and focused ultrasound beam is transmitted.
The transducer array
114
is coupled through the T/R switch
112
to a receive waveform generator
118
. Ultrasound echoes from a given point within the patient's body are received by the transducer elements at different times. The transducer elements convert the received ultrasound echoes to transducer signals which may be amplified, individually delayed and then summed by the receive waveform generator
118
to provide a waveform generator signal that represents the received ultrasound level along a desired receive line. The echoes exhibit a wide dynamic range of approximately 160 dB. Echoes from objects close to the transducer can produce a signal of 200 millivolts from the transducer, while echoes farther away from the transducer can produce a signal having an amplitude eight (8) orders of magnitude less. Any echo that cannot produce at least a 2 nano-volt response in the transducer array
114
can be lost in the noise.
The waveform generator signals are applied to a signal processor
124
which digitally processes the waveform generator signal for improved image quality and to perform such processing as color flow processing. As known in the art, the delays applied to the transducer signals may be varied during reception of ultrasound energy to effect dynamic focusing. The receive waveform generator
118
and the signal processor
124
form an ultrasound receiver
126
. The output of the signal processor
124
is supplied to a scan converter
128
which converts sector scan or other scan pattern signals to conventional raster scan display signals. The output of the scan converter
128
is supplied to a display unit
130
, which displays an image of the region of interest in the patient's body. In the case of a three-dimensional scan pattern, the scan converter
128
may be replaced by an image data buffer that stores the three-dimensional data set and a processor that converts the three-dimensional data set to a desired two-dimensional image.
A system controller
132
provides overall control of the system, including timing control. The system controller
132
typically includes a microprocessor operating under the control of control routines
134
stored in a memory
136
. The system controller also utilizes the memory
136
to store intermediate values, including system variables describing the operation of the ultrasound imaging system
100
. An external storage
138
, for example a floppy disk drive, a CD-ROM drive, a videotape unit, etc . . . , may be utilized for more permanent and/or transportable storage of data.
FIG. 2
is a block diagram of a single channel in a known ultrasound receiver. The ultrasound receiver shown herein is limited to a single receive channel so as to simplify explanation of the circuit. The elements within the dotted lines are repeated for each channel of the waveform generator, while the elements outside the dotted lines are global, serving the entire circuit.
Block
200
contains a representation of a signal produced by an element of a transducer array
114
(FIG.
1
). Basically, the signal from each element can be represented as a source voltage
210
(Es) having a resistance
212
(Rs) and a noise component
214
(e
n
). The signal is fed into a beamforming channel
205
. As noted above, each element of the transducer array
114
typically (but not necessarily) has a corresponding beamforming channel
205
.
The signal from each element is first amplified by amplifier
216
to bring the signal level up to an appropriate value. Subsequently, the signal is processed on two paths, one for digital processing (the “digital path,” elements
218
-
226
) and one for analog processing (the “analog path,” elements
232
and
234
).
Looking at the digital path, the signal
200
is first applied to a filter
218
, such as a harmonic filter or clipping filter. Filter
218
acts on the entire dynamic range of the signal
200
and prepares the signal for subsequent processing. In the case of the harmonic filter, echoes exhibiting a harmonic frequency of the fundamental transmitted frequency are extracted (or allowed to pass). The resultant signal is processed using so called “harmonic processing.”
The output of the filter
218
is applied to a variable gain amplifier
220
, which, in effect provides a window into the dynamic range of the signal
200
. In other words, the variable gain amplifier selects a portion of the dynamic range for subsequent processing. The portion of the signal
200
selected is varied based on the type of A/D converter used (121 dB wide for an 8 bit A/D converter and 133 dB wide for a 10 bit A/D converter at 40 MSPS sample rates) and the subsequent image processing to be applied to the signal
200
.
The digital processing path utilizes a pulse mode (as opposed to a continuous mode discussed hereinafter) in which pulses are transmitted, received, and processed on a cyclical basis. Most types of processing in this mode use a focused ultrasound signal. Areas outside the focus can be ignored, thereby limited the dynamic range of signals that need to be analyzed. The variable gain amplifier
220
limits the signal
200
to a defined dynamic range, without unacceptably affecting the resultant image.
The output of the variable gain amplifier
220
is filtered by a Nyquist filter
222
(in effect a low pass filter) to remove frequencies that can't be sampled by the A/D converter
224
. The highest frequency which can be accurately represented is one half of the sampling rate. Therefore, the Nyquist filter
222
is selected to match A/D converter
224
which converts the output of the Nyquist filter
222
into the digital domain. Current ultrasound systems employ an 8-bit or 10-bit converter.
After being converted into a digital signal, the output of the transducer array is processed through beamform logic
226
. Basically, the beamform logic
226
delays the digital output of each channel by a predetermined amount (based on the desired direction and focusing of the receive beam shape). One method of accomplishing this is to load the output into a register and after the predetermined time reading the register. Subsequently, the output of all of the channels are summed by summing logic
228
.
Each transmit event on the transducer array
114
(
FIG. 1
) starts a receive, process, delay and sum cycle in the receive waveform generator
118
. The resultant digital representation of the echo of each transmit event is submitted to digital processing
230
, such as signal demodulation and scan conversion.
As noted above, certain types of processing are currently performed in the analog domain. Perhaps the best example is Continuous Wave Doppler processing (CW processing). Doppler processing, in general, seeks to determin
Jaworski Francis J.
Jung William C.
Koninklijke Philips Electronics , N.V.
Vodopia John
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