Ultrasonic imaging apparatus
View Patent ↗In an ultrasonic contrast imaging method in which signals specific to a contrast agent are extracted to form an image, imaging is performed with the following three well-balanced properties: frame rate, spatial resolution, and contrast-agent selectivity. A first chirp signal whose frequency increases with time and a second chirp signal obtained by inverting the first chirp signal about the time axis are used, and they are individually transmitted and received. A decoder having decode filters each adapted for a coded sequence, which is obtained when the chirp signal is decomposed into a pulse signal and a coded sequence, is provided. The decode filters are adapted for echo signals received in response to two chirp signals, respectively, and outputs of the two decode filters are input to a subtractor, whereby the difference therebetween is determined. Thus, contrast-agent selectivity is balanced with spatial resolution.
1. An ultrasonic imaging apparatus comprising:
a transmitter configured to transmit, to a test subject,
a first chirp signal with a frequency that increases monotonically with time, the first chirp signal produced as a convolution of a first pulse signal with a first coding signal, and pulse compression is performed according to the first coding signal, and
a second chirp signal with a frequency that decreases monotonically with time, the second chirp signal produced as a convolution of a second pulse signal with a second coding signal, and pulse compression is performed according to the second coding signal;
a receiver configured to receive, from the test subject, a first reception signal resulting from the first chirp signal and a second reception signal resulting from the second chirp signal;
a decoder that includes:
a first decode filter based on the first coding signal,
a second decode filter based on the second coding signal, and
the decoder being configured to convolve the first reception signal with the first decode filter to output a first convolution signal, and to convolve the second reception signal with the second decode filter to output a second convolution signal; and
a subtractor that performs subtraction processing in order to determine a difference between the first convolution signal and the second convolution signal.
2. The ultrasonic imaging apparatus according to claim 1 , wherein the second chirp signal is a signal obtained by inverting the first chirp signal about a time axis.
3. The ultrasonic imaging apparatus according to claim 1 , wherein the first decode filter is an auto-correlation function for the first coding signal, and the second decode filter is an auto-correlation function for the second coding signal.
4. The ultrasonic imaging apparatus according to claim 1 , wherein the first decode filter is a mismatched filter for the first coding signal, and the second decode filter is a mismatched filter for the second coding signal.
5. The ultrasonic imaging apparatus according to claim 1 , further comprising:
an adder configured to add the first convolution signal to the second convolution signal; and
a display configured to receive an output of the subtractor as a contrast signal, to receive an output of the adder as a tissue signal, and to display superimposed images of the signals.
6. The ultrasonic imaging apparatus according to claim 1 , wherein the first pulse signal and the second pulse signal have a same waveform.
7. The ultrasonic imaging apparatus according to claim 1 , wherein the bandwidth of the first reception signal is approximately equal to the bandwidth of the first convolution signal, and the bandwidth of the second reception signal is approximately equal to the bandwidth of the second convolution signal.
8. The ultrasonic imaging apparatus according to claim 1 , wherein the bandwidth of the first coding signal is wider than the bandwidth of the first reception signal, and the bandwidth of the second coding signal is wider than the bandwidth of the second reception signal.
9. The ultrasonic imaging apparatus according to claim 1 , wherein the bandwidth of the first coding signal is wider than the bandwidth of the first reception signal, and the bandwidth of the first reception signal is approximately equal to the bandwidth of the first convolution signal; and
wherein the bandwidth of the second coding signal is wider than the bandwidth of the second reception signal, and the bandwidth of the second reception signal is approximately equal to the bandwidth of the second convolution signal.