Background technology
In the medical ultrasonic technical field, thereby the method for utilizing Doppler effect to obtain spectrogram measurement blood flow velocity has obtained developing rapidly in recent years.
Ultrasonic Doppler technique is measured in the process of blood flow rate, and the continuous ultrasound doppler system sends ultrasound wave in tissue through probe, and receives the scatter echo that hemocyte causes.Due to the mobility of hemocyte, there is certain frequency shift (FS) between its scatter echo and transmitted wave, and the movement velocity of hemocyte is proportional to this frequency shift (FS), be to be Doppler effect.
Measure corresponding frequency deviation and can estimate endovascular blood circumstance.At pulse Doppler, measure in the process of blood flow rate, measuring system sends sound wave pulse according to certain time interval, and receive echo-signal between two subpulses, measure the phase contrast of echo and certain reference signal, this phase contrast is the same with the frequency deviation in continuous-wave doppler, and rate of change is proportional to the flowing velocity of blood flow.Processing continuously clinically is consistent with the method for pulse Doppler.
Echo-signal becomes the audio Doppler centered by 0 frequency, approximately several KHz of its bandwidth after processing through orthogonal modulation, filtering etc.The flow velocity of blood in human vas is unfixed, and diverse location has different speed.General angiocentric flow velocity is larger, and approaches 0 near the local flow velocity of blood vessel wall.Therefore Doppler signal frequency spectrum has certain width, wherein peak frequency is proportional to endovascular peak veloity,PV, mid frequency (prominent frequency) represents the flow tendency of vessel inner blood integral body, and the erythrocyte with this flow velocity accounts for maximum ratio in blood.Be subject to the impact of heart contraction and diastole, the Doppler signal frequency spectrum that system detects also changes thereupon.The different frequency composition of synchronization is modulated into to gray scale by watt level, obtain the spectrum line in this moment, carry out frequency spectrum calculating if repeatedly intercept Doppler signal by the certain hour interval, and show successively spectrum line by the time order, just obtained the Doppler signal sound spectrogram.
The peak frequency envelope curve extracts and obtains from sound spectrogram.Can obtain by connecting not the peak frequency of Doppler signal frequency spectrum in the same time, this profile amplitude is directly proportional to blood flow Peak Flow Rate in blood vessel.Described peak frequency is the basis of estimation average frequency and other Doppler parameter of calculating, therefore estimates that exactly peak frequency is in important significance in clinical application.
The method of initial estimation peak frequency envelope curve is: determine by the operator is manual in freeze frame, then calculate corresponding other parameters.This method shortcoming clearly, poor repeatability, precision is low, also can't do real-time estimation.
At present, the method for extracting the peak frequency envelope curve mainly contains two classes: a class is based on the processing method of image, as rim detection, and dimension modulation Z axis method etc., the shortcoming of these class methods is that amount of calculation is too large, is difficult to application under real-time conditions; Another kind of is to utilize the power spectral density integral curve, carries out the peak frequency estimation, accounts in actual applications dominant position, as percentage ratio method (PM), crosses threshold method (TCM), geometric method (GM) etc.
The percentage ratio method is to set the percentage ratio that peak frequency is signal plus noise power summation, calculates relatively simply, and still, it is difficult to definite stable percentage ratio to the signal to noise ratio sensitivity, and optimum percentage ratio in the same time is not inconsistent yet.Cross threshold method by setting threshold, find in a continuous n Frequency point at least the point of m power spectral value over this threshold value, the threshold value setting of this method is very crucial, and threshold value Maximum frequency curve bigger than normal is less than normal, the too small noise that easily detects of threshold value.Geometric method is to carry out the matching integrated power spectrum with three straight lines, and it does not need selected threshold, and still, it is larger to the dependency of spectrum peak, and utilizes the peak that FFT tries to achieve to have very large randomness, has affected the estimated accuracy of peak frequency.
On the basis of these three kinds of methods, derive some and improved algorithm, cross threshold method (MTCM) as improved, mixing method (HM), improved geometric method (MGM), adaptive threshold method (ATM) and improved percentage ratio method (MPM) etc., improved to a certain extent the effect of algorithm, but large progress do not arranged.
The shortcoming of prior art: the accuracy of existing percentage ratio algorithm is subject to the restriction of signal noise ratio (snr) of image, and the accuracy of percentage ratio algorithm is not high.
Summary of the invention
Technical problem to be solved by this invention is: how the percentage ratio value of the signal to noise ratio of sound spectrogram picture and percentage ratio algorithm is associated, improve the accuracy of percentage ratio algorithm.
In an embodiment of the present invention, proposed the computational methods of peak frequency envelope curve, having comprised:
S1, the single spectral line of calculating sound spectrogram up has an energy accumulation from baseline and sum;
S2, judge whether sum is greater than first threshold; Be, get percent value and equal β, otherwise, get percent value and equal α, wherein β α;
S3, calculate single spectral line from baseline up to current some energy accumulation and sum1, judge whether sum1 is greater than the product of the percent value described in sum and S2, is, stops calculating sum1, get the point that current point is energy accumulation maximum on this spectrum line; Otherwise, calculate sum1, until sum1 is greater than the product of the percent value described in sum and S2;
S4, to being calculated by the root spectrum line on sound spectrogram, obtain the point of energy accumulation maximum on every spectrum line;
S5, the point that connects energy accumulation maximum on all spectrum lines of sound spectrogram forms the peak frequency envelope curve.
In addition, further embodiment of this invention also provides the accountant of peak frequency envelope curve, comprising:
Line gross energy computing unit, from baseline an energy accumulation up arranged for the single spectral line of calculating sound spectrogram and sum;
Whether the percent value determining unit, be greater than first threshold for judging described sum; Be, get percent value and equal β, otherwise, get percent value and equal α, wherein β α;
The computing unit of the point of energy accumulation maximum on line, for calculate single spectral line from baseline up to current some energy accumulation and sum1, judge that whether sum1 is greater than the product of sum and described percent value, is, stop calculating sum1, the point that current point is energy accumulation maximum on this spectrum line; Otherwise, calculate sum1, until sum1 is greater than the product of sum and described percent value;
The computing unit of the point of energy accumulation maximum on image, for to being calculated by the root spectrum line on sound spectrogram, obtain the point of energy accumulation maximum on every spectrum line;
Peak frequency envelope curve output unit, couple together for the point by energy accumulation maximum on all spectrum lines, forms the peak frequency envelope curve.
As can be seen from the above technical solutions, the embodiment of the present invention has the following advantages: the percentage ratio value of the signal to noise ratio of sound spectrogram picture and percentage ratio algorithm is associated, improved the accuracy of percentage ratio algorithm.
The specific embodiment
Below in conjunction with the Figure of description in the present invention, the technical scheme in invention is clearly and completely described, obviously, described embodiment is only the present invention's part embodiment, rather than whole embodiment.Embodiment based in the present invention, those of ordinary skills, not making under the creative work prerequisite the every other embodiment obtained, belong to the scope of protection of the invention.
embodiment mono-
In the present embodiment, referring to Fig. 1, the computational methods of peak frequency envelope curve comprise:
S1, the single spectral line of calculating sound spectrogram up has an energy accumulation from baseline and sum;
Sound spectrogram consists of the many spectrum lines of arranging according to time sequencing, and the point that all spectrum line upper frequencies are 0 forms baseline, and difference up represents different frequency values from baseline for every spectrum line, has different gray scales simultaneously, has represented different power.Be subject to the impact of heart contraction and diastole, the sound spectrogram of the Doppler signal that system detects also is rhythmic thereupon to be changed, as shown in Figure 5.
From baseline, a computational methods of energy accumulation sum is up arranged for calculating single spectral line on sound spectrogram, can obtain from prior art.
S2, judge whether sum is greater than first threshold; Be, get percent value and equal β, otherwise, get percent value and equal α, wherein β α;
Described first threshold is an empirical value, according to experimental result, chooses, and preferably, described first threshold is 4000.
S3, calculate single spectral line from baseline up to current some energy accumulation and sum1, judge whether sum1 is greater than the product of the percent value described in sum and S2, is, stops calculating sum1, get the point that current point is energy accumulation maximum on this line; Otherwise, calculate sum1, until sum1 is greater than the product of the percent value described in sum and S2;
When sum1 is greater than the product of the percent value described in sum and S2, get the point of current point for energy accumulation maximum on this line.
S4, to being calculated by the root spectrum line on sound spectrogram, obtain the point of energy accumulation maximum on every spectrum line;
For every on sound spectrogram spectrum line, according to the described method of S1 to S3, calculate the point of energy accumulation maximum on this spectrum line.
S5, on all spectrum lines of connection sound spectrogram, the point of energy accumulation maximum, form the peak frequency envelope curve.Referring to Fig. 2, preferably, between described S1 and S2, also comprise S12:
Judge whether energy in the integral image zone and the ratio of T and theoretical ceiling capacity and M are less than the first empirical value;
To choose first group of percent value;
Otherwise, judge whether energy in grass energy and P and integral image zone and the ratio of T are less than the second empirical value; To choose first group of percent value; Otherwise, choose second group of percent value;
The α of described first group of percent value and β are greater than respectively α and the β of second group of percent value.
Described the first empirical value is chosen according to experimental result, and preferred the first empirical value is 0.07.
Energy in described grass energy and P, integral image zone and T, theoretical ceiling capacity and M, the explanation that its implication sees below.The characteristics of sound spectrogram are, under normal circumstances, variation between adjacent spectral line is slower, and single spectral line is due to the impact that is subject to speckle noise, the signal to noise ratio fluctuation meeting that statistics obtains is larger, if the image that the spectrum line of record in a period of time is formed is considered as a whole, can greatly reduce the fluctuation of signal to noise ratio, improve the system accuracy; In addition, because the situation that blood flow rate is slower is in the majority, most signals concentrate near baseline, and when the paradoxical expansion blood flow rate is accelerated, image peak signal just occurs away from b extent.Grass is defined as to 1/5 part on image top,, the part on each single spectral line top 1/5 all falls into the grass zone, in this part, generally the overwhelming majority all is full of by noise, or although signal is arranged, the ratio of signal is lower, the energy in this subregion and be grass energy and P.Energy in the computed image overall region and, be T.Theoretical ceiling capacity and M, refer to that on the hypothesis image, all points all have in the situation of ceiling capacity, institute have an energy accumulation with.Calculate described each regional energy and, by described zone, on corresponding each single spectral line, the addition of each point energy gets final product.The ratio of described P and T represents the contrast situation of noise and signal, and ratio is less, illustrates that the intensity difference of signal and noise is larger, more easily distinguishes.The ratio of T and M, the signal intensity of representative image integral body, ratio is larger, means that signal is stronger, and energy is higher, and ratio is little illustrates that the intensity of echo is low.
When the ratio of the energy in the integral image zone and T and theoretical ceiling capacity and M is less than the first empirical value 0.07, though perhaps this ratio be more than or equal to the first empirical value 0.07 when Dan Shi the ratio of the energy in grass energy and P and integral image zone and T is less than the second empirical value 0.018, the contrast of the signal band of key diagram picture and grass is comparatively clear, choose first group of percent value α and be 0.94 and β be 0.97;
When the ratio that the ratio of the energy in the integral image zone and T and theoretical ceiling capacity and M is greater than energy in the first empirical value 0.07 and grass energy and P and integral image zone and T is greater than the second empirical value 0.018, a little less than illustrating that image intensity signal, and the contrast of signal intensity and noise intensity is little, choose second group of percent value α and be 0.93 and β be 0.95.
In summary, these two groups of percent value, according to different image situation choice for uses.
In the present embodiment, when T/M<0.07, choose first group of percent value α=0.94, β=0.97; When T/M >=0.07, and P/T<0.018 o'clock, first group of percent value α=0.94 chosen, β=0.97; And when T/M >=0.07, and P/T >=0.018 o'clock, choose second group of percent value α=0.93, β=0.95.
Referring to Fig. 2, preferably, between described S1 and S12, also comprise
S11, judge whether sum is greater than Second Threshold, is, carries out the S12 step; Otherwise, the peak frequency envelope curve is made as to baseline.
Described Second Threshold is also an empirical value, according to experimental result, selects, and in the present embodiment, described Second Threshold is 400.If sum is less than Second Threshold, illustrate that image signal energy is too small, the peak frequency envelope curve is made as baseline.
To sum up, according to the signal to noise ratio of sound spectrogram, by the selection of many groups percent value, can improve the accuracy of detection of improving the percentage ratio algorithm; The present invention can obtain peak frequency envelope curve more accurately.
embodiment bis-
Referring to Fig. 3, it should be noted that, the accountant of peak frequency envelope curve comprises:
Line gross energy computing unit 21, from baseline an energy accumulation up arranged for the single spectral line of calculating sound spectrogram and sum;
Whether percent value determining unit 22, be greater than first threshold for judging described sum; Be, get percent value and equal β, otherwise, get percent value and equal α, wherein β α;
The computing unit 23 of the point of energy accumulation maximum on line, for calculate single spectral line from baseline up to current some energy accumulation and sum1, judge that whether sum1 is greater than the product of sum and described percent value, is, stop calculating sum1, get the point of current point for energy accumulation maximum on this line; Otherwise, calculate sum1, until sum1 is greater than the product of sum and described percent value;
The computing unit 24 of the point of energy accumulation maximum on image, for to being calculated by the root spectrum line on sound spectrogram, obtain the point of energy accumulation maximum on every spectrum line;
Peak frequency envelope curve output unit 25, couple together for the point by energy accumulation maximum on all spectrum lines, forms the peak frequency envelope curve.
Referring to Fig. 4, it should be noted that, between described line gross energy computing unit 21 and percent value determining unit 22, also comprise: group is chosen unit 212, for judging energy in the integral image zone and the ratio of T and theoretical ceiling capacity and M, whether is less than the first empirical value; To choose first group of percent value; Otherwise, then judge whether energy in grass energy and P and integral image zone and the ratio of T are less than the second empirical value, be to choose first group of percent value; Otherwise, choose second group of percent value; The α of described first group of percent value and β are greater than respectively α and the β of second group of percent value.
Referring to Fig. 4, it should be noted that, online gross energy computing unit 21 and group are chosen unit 212
Between, also comprise:
Whether low-yield judging unit 211, be greater than Second Threshold for judging sum, is, carries out group and choose unit; Otherwise, the peak frequency envelope curve is made as to baseline.
For the disclosed device of embodiment, because it corresponds to the method disclosed in Example, so relevant part partly illustrates and gets final product referring to method.
The embodiment of the present invention has the following advantages:
The present invention associates the percentage ratio value of the signal to noise ratio of sound spectrogram picture and percentage ratio algorithm, has improved the accuracy of percentage ratio algorithm.Referring to Fig. 5, the carotid artery Doppler frequency spectrum signal that utilizes above-mentioned technology paired pulses Doppler ultrasound system to detect carries out the envelope extraction experiment, and its Maximum frequency curve, as shown in white curve in figure, has well been followed the tracks of the spectrum envelope of sound spectrogram.
The above computational methods to peak frequency envelope curve provided by the present invention and device are described in detail, for one of ordinary skill in the art, thought according to the embodiment of the present invention, all will change in specific embodiments and applications, in sum, this description should not be construed as limitation of the present invention.