1380014 ^ 六、發明說明： 【發明所屬之技術領域】 - 本發明係有關於一種超音波成像裝置及方法，尤指一 % 種可增加訊雜比以及改善成像深度者。1380014 ^ VI. Description of the Invention: [Technical Field of the Invention] - The present invention relates to an ultrasonic imaging apparatus and method, and more particularly to a model which can increase the signal-to-noise ratio and improve the imaging depth.
V 【先前技術】 ^ 超音波影像系統已廣泛地使用於生物醫學上的偵 測。目前超音波影像技術主要利用脈衝回波（pUl se-ech〇) 的方式來成像’其原理乃由發射端於每個陣列探頭元素 (array element)發射一短脈衝波（pulse)，藉由發射波束 成型（beamforming)調整每個頻道（channel)脈衝波之時間 延遲以及增益大小’將整個陣列信號聚焦於一條掃瞄線 (scan line)上的一個固定深度位置，之後藉由數位轉類比 裝置，將信號類比化’再藉由陣列探頭（Transducerarray) φ 將電信號轉化為超音波信號傳遞出去。於接收端部分’所V [Prior Art] ^ Ultrasonic imaging systems have been widely used in biomedical detection. At present, ultrasonic imaging technology mainly uses pulse echo (pUl se-ech〇) to image 'the principle is that the transmitting end emits a short pulse (pulse) in each array element, by transmitting Beamforming adjusts the time delay and gain magnitude of each channel pulse to focus the entire array signal on a fixed depth position on a scan line, followed by a digital to analog device. The signal is analogized and then converted into an ultrasonic signal by an array probe (Transducerarray) φ. At the receiving end section
欲觀察的組織藉由背散射（back_scattering)的方式回傳 , 仏唬，此時超音波系統藉由發射/接收切換裝置（T/R switch)，將接收信號導向接收端系統等候所回傳的信號， 首先陣列权頭先將機械波轉化成電信號，隨即每個頻道的 / #號經由放大、濾波以及類比轉數位裝置進行取樣，之後 母個頻C所取樣的數位信號進入動態聚焦（dynamic focusing)波束成型裝置，其原理乃根據此條掃瞄線上的每 個，間取樣點，動態地調整每個頻道信號的時間延遲以及 增益大小，並且將所有頻道的信號加總起來，之後藉由包 3 絡偵測器將聚焦後的信號強度取出。上述過程為一條掃晦 線的成像步驟，之後發射波束指向下一條掃瞄線重複上述 成像過程，所有掃瞄線所組合成的影像再經由掃瞄轉換裝 置（scan conversion)，將影像格式轉換成格狀式（grid)， 之後於顯示裝置展示影像》 目前超音波影像系統主要的限制之一在於穿透深声 以及訊雜比（signal-to-noise ratio, SNR)的不足，這兩 者之成因乃超音波於組織有訊號衣減（attenuati〇n)的現 象，考慮頻率相依（frequency dependent)之衰減現象，典 型的衰減係數值（attenuation coefficient)介於〇 5〜1 dB/MHz/cm，此值會隨著操作頻率以及成像深度變大而增 加，以中心頻率8MHz、衰減係數〇.6為例，在1〇公分^ 度之5虎較探頭表面之彳§號減少約9 6 dB，換句話說，如 果系統欲增加5公分的成像深度，則訊號強度或是訊雜比 需提高48 dB才能維持原深度的成像品質。頻率相依之衰 減現象在命頻系統更為嚴重’相較於上述低頻系統，高頻 超音波系統（頻率高於20MHz)擁有更佳的空間解析度，可 偵測更為細微的組織，由於訊號衰減程度隨頻率上升，因 此有限的穿透深度大大地限制了目前高頻系統的應用。 增加信號於人體内的穿透深度可藉由提高發射信號 強度來達成，而發射信號強度的提高可藉由調整脈衝波的 大小以及持續時間（duration)來完成，為了防止瞬間信號 功率過大造成人體不良的影響，脈衝波的大小必須限制， 無法毫無限制的增加，另一方面，增加脈衝波的持續時間 會造成訊號頻寬過小，影響影像的空間解析度，以上兩種 作法皆有其限制，無法有效地增加穿透深度以及訊雜比。 1380014 為了增加信號持續時間以及同時維持信號頻寬及保 有原本空間解析度的一個作法是發射展頻信號 (spread-spectrum)，稱為編碼激發（coded excitation) 系統，圖一 A及圖一 B分別為習知編碼激發系統架構示意 圖以及習知脈衝激發（pulsed excitation)系統架構示意 圖，一些展頻訊號如PN碼（pseudo random)、線性調頻碼 (linear FM or chirp)或是Barker碼，由於擁有較大的 時間頻寬乘積（time-bandwidth product)，可以藉由脈波The tissue to be observed is returned by back_scattering, 仏唬, at this time, the ultrasonic system directs the received signal to the receiving end system for waiting for the return by the T/R switch. Signal, first, the array head first converts the mechanical wave into an electrical signal, and then the /# number of each channel is sampled by the amplification, filtering, and analog-to-digital device, and then the digital signal sampled by the parent frequency C enters the dynamic focus (dynamic Focusing beamforming device, the principle is to dynamically adjust the time delay and gain of each channel signal according to each sampling point on the scanning line, and sum up the signals of all channels, then by The packet detector detects the intensity of the signal after focusing. The above process is an imaging step of a broom line, and then the transmitting beam is directed to the next scanning line to repeat the imaging process, and the images combined by all the scanning lines are converted into an image format by a scan conversion device. The grid is displayed on the display device. One of the main limitations of the current ultrasound imaging system is the penetration of deep sound and the lack of signal-to-noise ratio (SNR). The cause is that the ultrasonic wave is attenuated in the tissue, considering the frequency dependent attenuation phenomenon, the typical attenuation coefficient value is 〇5~1 dB/MHz/cm, This value increases with the operating frequency and the imaging depth. Taking the center frequency of 8MHz and the attenuation coefficient 〇.6 as an example, the number of tigers at 1〇cm^ is reduced by about 9 6 dB from the surface of the probe. In other words, if the system wants to increase the imaging depth by 5 cm, the signal strength or the signal-to-noise ratio needs to be increased by 48 dB to maintain the original depth of imaging quality. Frequency-dependent attenuation is more serious in the frequency-frequency system. Compared to the low-frequency system described above, the high-frequency ultrasonic system (frequency above 20MHz) has better spatial resolution and can detect finer tissue due to signal attenuation. As the frequency rises, the limited penetration depth greatly limits the application of current high frequency systems. Increasing the penetration depth of the signal in the human body can be achieved by increasing the intensity of the transmitted signal, and the improvement of the transmitted signal strength can be achieved by adjusting the magnitude and duration of the pulse wave, in order to prevent the transient signal power from being excessively large. The adverse effect, the size of the pulse wave must be limited, can not increase without limit, on the other hand, increasing the duration of the pulse wave will cause the signal bandwidth to be too small, affecting the spatial resolution of the image, both of which have their limitations. It is not possible to effectively increase the penetration depth and the signal-to-noise ratio. 1380014 In order to increase the signal duration and maintain the signal bandwidth and maintain the original spatial resolution, a spread-spectrum is transmitted, called a coded excitation system. Figure 1A and Figure 1B respectively. For a schematic diagram of a conventional coded excitation system architecture and a schematic diagram of a conventional pulsed excitation system architecture, some spread spectrum signals such as PN code (pseudo random), linear FM code (linear FM or chirp) or Barker code have Large time-bandwidth product, which can be pulsed
壓縮濾波器（pulse compression filter)將一長持續時間 的訊號壓縮成一短脈衝波，還原其空間解析度，脈波壓縮 遽波器主要分為匹配（matched f i 1 ter)以及非匹配遽波器 (mismatched filter)兩種，理論上，編碼激發系統所能達 到最大訊號強度或訊雜比增加的幅度約等於時間頻寬乘 積，以8MHz中心頻率、5MHz.頻寬，展頻信號長度為2〇微 秒為例，訊雜比增加了 20 dB，以上述計算衰減值為例， 可等效增加穿透深度達2公分’因此，編碼激發系統能夠 有效的增進訊號強度，-方面亦能夠維持良好的空間解析 度。 圖二A及圖二B均為f知編碼激發系統之架構示 圖。其中圖三A之脈波壓縮纽器係置於波束成型器之〕 而圖二B之脈越輯波器似於波束成型^ 於傳統脈衝激發^ ’編舰發超音波系統㈣有效的3 加穿透深度，提向系統訊雜比，其跟傳統 =差皮=展頻信號外，接收端需要有^ 縮^皮裔來回復其空間解析度。原則上，接 動悲聚焦波束成型之前，每個陣列頻道需自行先完成脈; 1380014 - 壓縮（如圖二A所示），如此才能正確壓縮成短脈衝信號， 如欲將脈波壓縮濾波器置於波束成型器之後，如圖二B所 示’則會造成展頻信號的壓縮錯誤，無法正確還原成短脈 • 衝信號，其成因乃因為動態聚焦之波束成型所致，圖三A及 - 圖三B分別為動態.聚焦以及固定聚焦之波束成型對於脈波 . 歷务目的效應示意圖，如圖三A及圖三B所示，假設單一散 射點位於發射聚焦位置，在接收端方面，由於動態聚焦之 波束成型裝置需對每個成像深度聚焦，因此所需要的延遲 • 時間曲線（亦即，每個陣列頻道對應的延遲時間）會隨深度 變化’如此將會造成信號加總（beamsum)之後的變形，造成 脈波壓縮濾波器的壓縮錯誤’反之而言，當波束成型裳置 為固定聚焦的情況下（亦即，對某深度聚焦），則每個成像 深度所對應延遲時間曲線一致，在此情況下，加總後的信 號會跟原發射波形一致，脈波壓縮濾波器能夠正確的還原 成短脈衝波。綜合上述討論，在沒有補償的情況下，脈波 壓縮濾波器只能夠置於動態聚焦波束成型裝置之前，才能 φ 正確地壓縮展頻信號。 但在動態聚焦的架構下，由於每個陣列頻道需配備脈 - 波壓縮遽波器，相較於傳統脈衝激發系統，編碼激發系統 ' · W硬體複雜度將大幅提高。以256個陣列探頭元素、展頻 信號長度20微秒、接收端系統取樣頻率4〇 MHz、以及脈 波壓縮遽波裔長度等於30微秒為例，則脈波壓縮渡波器所 需要的tap數目達1200個，因此，所有頻道全部之總_ 數目兩達307200個！如此龐大數目將大幅度提升系統複 雜度。 因此’如何研發出一種超音波成像裝置及方法，其可 1380014 增加訊雜比以及改善成像深度並減少系統複雜度，將是本 發明所欲積極探討之處。 【發明内容】 本發明提出一種超音波成像裝置及方法，其主要特性 為可增加訊雜比以及改善成像深度並減少系統複雜度。 本發明之一樣態為一種超音波成像裝置，包含有：一 發射單元，其係用以產生一編碼信號，並將該編碼信號加 以濾波、放大及聚焦；一換能器探頭，其與該發射單元耦 接，以做為聲壓與電之間的轉換器，其係為陣列多頻道結 構，並具有複數個發射及複數個接收頻道，以將該發射單 元之編碼信號，傳送至一物體，並接收該物體之回波信號； 一接收單元，其與該換能器探頭耦接，以接收該回波信號； 一波束成型單元，其與該接收單元耦接，以將該回波信號 加以放大、濾波並執行信號聚焦，以產生複數個掃瞄線或 波束；一脈波壓縮濾波單元，其與該波束成型單元耦接， 以壓縮該些掃瞄線或波束；以及一空間濾波器，其與該脈 波壓縮濾波單元耦接，以將該些掃瞄線或波束儲存，並結 合該些掃瞄線或波束，對選定之一影像區域進行濾波。 本發明之另一樣態為一種超音波成像方法，其包含下 列步驟： 利用一發射單元傳送一編碼信號，以將該編碼信號固 定聚焦於一深度，並藉由一換能器探頭發射； 利用一接收單元接收自該換能器探頭每個頻道接收的 回波信號，並完成聚焦，以得到複數個掃瞄線或波束； 7 1380014 ^ 利用一脈波壓縮濾波單元壓縮該些掃瞄線或波束；以 及 利用一空間濾波器結合該些掃瞄線或波束，根據所選 定之影像區域進行遽波。 藉此可增加超音波成像的訊雜比以及改善成像深度並 減少系統複雜度。 【實施方式】 •為充分瞭解本發明之特徵及功效，茲藉由下述具體之 實施例，並配合所附之圖式，對本發明做一詳細說明，說 明如後： 圖四為本發明之具體實施例的系統架構示意圖，請參 考圖四，本發明為一種超音波成像裝置1，包含有：一發 射單元2，其係用以產生一編碼信號，並將該編碼信號加 以濾波、放大及聚焦，其中該發射單元2包含波形產生器， 其可為雙極性（bipolar)以及單極性（unipolar)的波形產 _ 生器，而該編碼信號的波形可為任一個具有高時間頻寬乘 積之展頻信號，例如PN碼、線性/非線性調頻以及Barker 碼等；一換能器探頭3，其與該發射單元2耦接，以做為 聲壓與電之間的轉換器，其係為陣列多頻道結構，並具有 複數個發射頻道及複數個接收頻道，以將該發射單元2之 編碼信號，傳送至一物體4，並接收該物體4之回波信號， 其中該換能器探頭3係為一維或二維陣列結構；一接收單 元5，其與該換能器探頭3耦接，以接收該回波信號；一 波束成型單元6，其與該接收單元5耦接，以將該回波信 8 1380014 ' 號加以放大、濾波並執行信號聚焦，以產生複數個掃瞄線 或波束，其中該接收單元5内的信號聚焦係可固定聚焦於 一深度以產生一聚焦點或是可固定聚焦於複數個深度以產 生複數個聚焦點，且該些聚焦點之間的距離需大於或等於 該編碼信號的長度，另外前述之聚焦點可以跟該發射單元 2所設定之聚焦點相同或相異；一脈波壓縮濾波單元7(例 如，匹配濾波器或非匹配濾波器），其與該波束成型單元6 耦接，以壓縮該些掃瞄線或波束；以及一空間濾波器8， φ 其與該脈波壓縮濾波單元7耦接，以將該些掃瞄線或波束 儲存，並結合該些掃瞄線或波束，對選定之一影像區域進 行濾波。一般來說，為使能夠呈現特定影像區域之内容， 較佳係更包含一包絡偵測及掃描轉換單元9，其與該空間 濾波器8耦接，以對該影像區域進行包絡偵測及掃描轉 換，並且本發明可更包含一顯示裝置10，其與該包絡偵測 及掃描轉換單元9耦接，以顯示該影像區域之影像，其中 該影像區域之影像可為一維、二維或三維影像。 φ 圖五為本發明之具體實施例的方法步驟圖，請參考圖 五，本發明為一種超音波成像方法，首先利用一發射單元 傳送一編碼信號，以將該編碼信號固定聚焦於一深度，並 藉由一換能器探頭發射；接著利用一接收單元接收自該換 能器探頭每個頻道接收的回波信號，並完成聚焦，以得到 複數個掃瞄線或波束，其中該接收單元内的信號聚焦係可 固定聚焦於一深度以產生一聚焦點或是可固定聚焦於複數 個深度以產生複數個聚焦點，且該些聚焦點之間的距離需 大於或等於該編碼信號的長度；之後利用一脈波壓縮濾波 單元壓縮該些掃瞄線或波束；之後利用一空間濾波器結合 9 該些掃瞄線或波束，根據所選定之影像區域進行濾波；接 著利用該空間濾波器將該些掃瞄線或波束暫存；再來擷取 出欲施加濾波之影像區域；以及最後根據相對於該影像區 域所在之深度位置利用查表的方式決定該空間濾波器中之 係數，其中該係數可搭配該影像區域之訊雜比決定。 圖六為本發明之接收單元複數個固定聚焦深度與個別 接收聚焦區域示意圖，其係將影像劃分為數個子區域，每 個區域採用單一固定聚焦點，為了方便呈現，圖中以三個 子區域為例，如圖六所示，每個子區域都配以單一個聚焦 點，此聚焦點可於子區域之任意位置，不限於子區域之中 心點，為了避免子區域過多，造成脈波壓縮的錯誤（如同 動態聚焦對於脈波壓縮的效應），因此，各個子區域聚焦點 之間的距離，應不以小於發射編碼信號的長度為基準。 以下再針對本發明中各個主要元件做進一步說明，圖 七為本發明之波束成型單元架構圖，請參考圖七，由於每 個頻道的信號係經由個別的第一延遲器11以及第一乘法 器12，每個第一延遲器11的時間延遲量，則根據一預先 決定之聚焦點與個別陣列頻道之相對位置除以聲速決定， 而每個第一乘法器12所乘上的量，可以一致（即不施予權 重），或是傳統上所定義的視窗函數（window function)， 如Hamming、Gaussian等。聚焦點可為單一聚焦，或如圖 六所示之多區域聚焦。 而前述之脈波壓縮濾波單元的功能為壓縮編碼信號， 回復其原有之空間解析度。一般來說，脈波壓縮濾波單元 可分為匹配濾波器以及非匹配濾波器兩種。匹配濾波器的 頻率響應乃為原編碼信號之頻譜的共軛複數，匹配濾波器 1380014 的優點是訊雜比的提升為理論上之最大值，且濾波器的長 度跟僅需跟原編碼信號的長度一致即可，缺點是壓縮後的 旁波瓣（sidelobe)有其一定的準位限制，影像的對比度會 受影響；相較而言，非匹配濾波器的頻率響應不同於原編 碼信號，能有效的壓抑旁波瓣，然而會因此犧牲一些訊雜 比，以及濾波器長度需要比原編碼信號長。 圖八為本發明之空間濾波器架構圖，請參考圖八，本 發明之空間濾波器8包含：一暫存器13，其與該脈波壓縮 濾波單元7耦接，以暫存該些掃瞄線或波束；一訊雜比估 計單元14，其與該暫存器1?耦接，並根據該些掃瞄線或 波束估計該影像區域内的訊雜比；一濾波裝置15，其與該 暫存器13耦接，並根據該些掃瞄線或波束對該影像區域進 行濾波，其中該濾波裝置15係為一維、二維或三維架構， 以分別對應所選定之一維、二維或三維影像區域；一記憶 體16,其儲存該空間濾波器8的係數；以及一查表裝置17, 其與該訊雜比估計單元14、該記憶體16及該濾波裝置15 耦接，以儲存該空間濾波器8的係數、該影像區域之訊雜 比以及該影像區域所在深度三者之間的對應關係，一般來 說，空間濾波器8的功能有二：一為補償接收單元因固定 聚焦所造成不佳的影像品質，二為改善脈波壓縮後信號可 能存在的旁波瓣，進而讓影像品質能逼近雙向動態聚焦的 影像品質。 圖九為本發明之訊雜比估計單元的訊雜比估計流程 圖，請參考圖九，由於濾波器係數的設計乃針對該影像區 域之所在深度，放置單一散射點，然後成像，此單一散射 點之影像稱為點擴散函數（point spread function, 1380014 PSF)，PSF的求得可藉由兩種方式：藉由實驗方式以及電 腦模擬方式。-旦取得PSF，則可根據此挪，設計最佳的 滤、波器係數。文獻中已有關於利用空間遽波器來改盖傳統 ‘ 脈衝激發超音波系統的影像品質，但並無用於編碼激發超 ’ 音波系統。這裡，本發明採用最小平方法（least_sqaures) _則來設計最佳”紐器騎’我們定義其價值函數 (cost function) E 為： E = fH(aQ + (l^a)I)f+x^(Cf~D) (1) 鲁其中’ f代表所欲求得之空間濾波器係數，其可為一維、 二維或三維架構；Q代表所欲最小化之旁波_域所形成 之摺積矩陣（convolution matrix);丨代表單位陣列 (identitymatrix)，即除了矩陣之對角線為i之外，其他 元素皆為0 ; α為一可調整之純量值，介於〇〜丨之間了入 為一純量值；C跟D定義為.兩者之間關係以=D，:所設 定影像區域賴定的值。根據上式，則最佳缝器係= 為： # /〇 = (« 0+Γ/ - a)I)~x CH(C(aQ+(l-a )1)1 CHy]D ⑵ 式（2)顯示最佳濾波器係數可隨著α而變。為了了解不门 α值的選擇對於濾波後影像的影響，目十為點擴散函數 (PSF)經過空間濾波器後的峰值功率（peak p〇wer)與旁波 瓣的關係波形圖。圖中上、下曲線分別對應一維及二^空 間濾波器，每條曲線上的值相對於式（2)中α值（介於〇 ι 之間）。此PSF位於11公分的位置，系統發射、接收分別 固定聚焦於12、15公分。一維濾波器係數的個數為^向 19個，二維濾波器在深度方向多了 5個。由圖十可知二濾 1380014 ' 波後的峰值與旁波瓣兩者之間存在妥協（trade-of f)的關 係，而兩者之間的關係等效於訊雜比與影像對比度之間的 關係，而對於二維濾波器而言，此關係尤甚明顯，由圖可 知，訊雜比與影像對比度兩者之間最佳的妥協位置乃位於 轉折點處（即a =0. 2的位置）。因此，根據圖十，我們可以 分析在不同影像訊雜比（尚未經過空間遽波器之前）的情況 下，每條曲線的轉折點，以便決定最佳α值以及式（2)最 佳濾波器。 φ 圖十一為不同深度所求得的一維空間濾波器示意 圖，以空間濾波器採用一維架構，共25個濾波器係數為 例，因此圖八_之暫存器需預先儲存至少25條掃瞄線，由 於空間濾波器會隨著深度而變化，因此每隔5公釐的位置 我們重新設計一組新的濾波器，如此根據前述之方式，我 們便可求得不同深度之一維空間濾波器。 為了驗證本案所提出的編碼激發超音波成像系統之 可行性，我們採用電腦模擬不同深度散射點之成像結果， φ 於深度10公分至17公分間，每0. 5公分放置一散射點。 模擬的參數如下所述：換能器探頭為256頻道之陣列架 構，中心頻率為5MHz，頻寬為2MHz，探頭元素間的間距為 0. 75倍的波長，探頭長度約為5. 76 cm，聲速為1540 m/s， 發射以及接收為單一固定聚焦點，分別聚焦於12以及15 公分，接收端信號的取樣頻率為40MHz。所發射的編碼信 號為偽線性調頻信號（pseudo-ch i rp)，此信號乃將線性調 頻信號手以兩元化，亦即當原線性調頻信號大於〇時，則 令為1 ;反之則令為0，所以此偽線性調頻信號為單極性信 號，此外，此偽線性調頻信號之掃瞄頻寬為3MHz，信號長 13 1380014 度為25微秒。脈波壓縮濾波器則採用非匹配濾波 遽波器能有效地將旁波瓣壓抑至預先^定的準位。请 波器則採用二維架構：每個濾波器在橫向（即跟換能== 平行的方向)有25個濾波器係數’縱向(即深度 碩 個係數’因此共7 5個渡波器係數。每隔5公釐的位I 3 們重新設計—組新的纽器，另外，為了驗證訊雜比估計 對於空間㈣器設計的重要性’我們於模擬中納 色雜訊。A pulse compression filter compresses a long duration signal into a short pulse wave to restore its spatial resolution. The pulse compression chopper is mainly divided into matched fi 1 ter and non-matched chopper ( Mismatched filter) In theory, the amplitude of the maximum signal strength or the increase of the signal-to-noise ratio of the coded excitation system is approximately equal to the time-frequency product, with a center frequency of 8MHz and a bandwidth of 5MHz. The length of the spread spectrum signal is 2〇 For example, the signal-to-noise ratio is increased by 20 dB. Taking the above-mentioned calculated attenuation value as an example, the penetration depth can be increased by up to 2 cm. Therefore, the coded excitation system can effectively improve the signal strength, and the aspect can also maintain good performance. Spatial resolution. Figure 2A and Figure 2B are diagrams showing the architecture of the coded excitation system. The pulse compression coupler in Figure 3A is placed in the beamformer] and the pulse of Figure 2B is similar to beamforming ^ in the traditional pulse excitation ^ 'The ship's ultrasonic system (4) effective 3 plus Penetration depth, to the system signal-to-noise ratio, in addition to the traditional = poor skin = spread spectrum signal, the receiving end needs to have a small body to restore its spatial resolution. In principle, before the sad focus beamforming, each array channel needs to complete the pulse first; 1380014 - compression (as shown in Figure 2A), so that it can be correctly compressed into a short pulse signal, if you want to compress the pulse compression filter After being placed in the beamformer, as shown in Figure 2B, it will cause a compression error of the spread spectrum signal, which cannot be correctly restored to a short pulse pulse signal. The cause of this is due to the beam shaping of dynamic focus. Figure 3A - Figure 3B shows the dynamic, focused and fixed-focus beamforming for the pulse wave. The effect of the calendar purpose is shown in Figure 3A and Figure 3B, assuming that a single scattering point is at the transmitting focus position, in terms of the receiving end, Since the dynamic focusing beamforming device needs to focus on each imaging depth, the required delay • time curve (ie, the delay time corresponding to each array channel) will vary with depth 'this will result in signal summation (beamsum) After the deformation, causing the compression error of the pulse compression filter', conversely, when the beamforming is set to a fixed focus (ie, to a certain depth) Coke), then each imaging depth corresponding to the delay times of the curve, in this case, the summed signal will be consistent with the original transmit waveform, pulse compression filter can be reduced to the correct short pulse wave. Based on the above discussion, the pulse compression filter can only be placed in front of the dynamic focus beamforming device without compensation, in order to correctly compress the spread spectrum signal. However, under the dynamic focusing architecture, since each array channel needs to be equipped with a pulse-wave compression chopper, the hardware complexity of the coded excitation system will be greatly improved compared with the conventional pulse excitation system. Taking 256 array probe elements, spread spectrum signal length 20 microseconds, receiving system sampling frequency 4 〇 MHz, and pulse compression 遽 wave length equal to 30 microseconds as an example, the number of taps required for pulse compression converter Up to 1,200, so the total number of all channels is 307,200! Such a large number will greatly increase the system complexity. Therefore, how to develop an ultrasonic imaging device and method, which can increase the signal-to-noise ratio and improve the imaging depth and reduce the system complexity, will be actively explored by the present invention. SUMMARY OF THE INVENTION The present invention provides an ultrasonic imaging apparatus and method, the main features of which are to increase the signal-to-noise ratio, improve the imaging depth, and reduce system complexity. The present invention is an ultrasonic imaging apparatus comprising: a transmitting unit for generating an encoded signal and filtering, amplifying and focusing the encoded signal; a transducer probe, and the transmitting The unit is coupled to be a converter between sound pressure and electricity, which is an array multi-channel structure, and has a plurality of transmissions and a plurality of receiving channels for transmitting the encoded signals of the transmitting unit to an object. And receiving an echo signal of the object; a receiving unit coupled to the transducer probe to receive the echo signal; a beamforming unit coupled to the receiving unit to apply the echo signal Amplifying, filtering, and performing signal focusing to generate a plurality of scan lines or beams; a pulse compression filtering unit coupled to the beamforming unit to compress the scan lines or beams; and a spatial filter, It is coupled to the pulse compression filtering unit to store the scan lines or beams and combine the scan lines or beams to filter a selected one of the image regions. Another aspect of the present invention is an ultrasonic imaging method comprising the steps of: transmitting a coded signal by a transmitting unit to fix the coded signal to a depth and transmitting by a transducer probe; The receiving unit receives the echo signal received from each channel of the transducer probe and completes focusing to obtain a plurality of scanning lines or beams; 7 1380014 ^ compressing the scanning lines or beams by using a pulse compression filtering unit And using a spatial filter to combine the scan lines or beams to perform chopping according to the selected image area. This increases the signal-to-noise ratio of ultrasound imaging and improves imaging depth and system complexity. [Embodiment] In order to fully understand the features and functions of the present invention, the present invention will be described in detail by the following specific embodiments, and the accompanying drawings, For a schematic diagram of a system architecture of a specific embodiment, referring to FIG. 4, the present invention is an ultrasonic imaging apparatus 1 including: a transmitting unit 2 for generating an encoded signal, and filtering and amplifying the encoded signal. Focusing, wherein the transmitting unit 2 comprises a waveform generator, which can be a bipolar and unipolar waveform generator, and the waveform of the encoded signal can be any product having a high time bandwidth. a spread spectrum signal, such as a PN code, a linear/non-linear frequency modulation, and a Barker code, etc.; a transducer probe 3 coupled to the transmitting unit 2 as a converter between sound pressure and electricity, which is Array multi-channel structure, and having a plurality of transmission channels and a plurality of receiving channels, to transmit the encoded signal of the transmitting unit 2 to an object 4, and receiving an echo signal of the object 4, wherein the The energy sensor probe 3 is a one-dimensional or two-dimensional array structure; a receiving unit 5 coupled to the transducer probe 3 to receive the echo signal; and a beamforming unit 6 coupled to the receiving unit 5 Connecting, the echo signal 8 1380014 ' is amplified, filtered and subjected to signal focusing to generate a plurality of scan lines or beams, wherein the signal focus in the receiving unit 5 can be fixedly focused on a depth to generate a The focus point may be fixedly focused on the plurality of depths to generate a plurality of focus points, and the distance between the focus points needs to be greater than or equal to the length of the coded signal, and the aforementioned focus point may be set with the transmitting unit 2 The focus points are the same or different; a pulse compression filtering unit 7 (for example, a matched filter or a non-matching filter) coupled to the beamforming unit 6 to compress the scan lines or beams; The spatial filter 8, φ is coupled to the pulse compression filtering unit 7 to store the scan lines or beams and combine the scan lines or beams to filter a selected image region. In general, in order to enable the content of a specific image area, an envelope detection and scan conversion unit 9 is further included, which is coupled to the spatial filter 8 to perform envelope detection and scanning on the image area. The present invention may further include a display device 10 coupled to the envelope detection and scan conversion unit 9 for displaying an image of the image region, wherein the image of the image region may be one-dimensional, two-dimensional or three-dimensional. image. φ FIG. 5 is a schematic diagram of a method according to a specific embodiment of the present invention. Referring to FIG. 5 , the present invention is an ultrasonic imaging method. First, a transmitting unit is used to transmit an encoded signal to fix the encoded signal to a depth. And transmitting by a transducer probe; then receiving, by a receiving unit, an echo signal received from each channel of the transducer probe, and performing focusing to obtain a plurality of scanning lines or beams, wherein the receiving unit is The signal focus system can be fixedly focused on a depth to generate a focus point or can be fixedly focused on a plurality of depths to generate a plurality of focus points, and the distance between the focus points needs to be greater than or equal to the length of the coded signal; And then compressing the scan lines or beams by using a pulse compression filtering unit; then combining the scan lines or beams with a spatial filter to filter according to the selected image region; and then using the spatial filter to Scanning lines or beams are temporarily stored; then the image area to be filtered is extracted; and finally, based on the image area Of the position determined using a table lookup of the coefficients of the spatial filter, where the coefficients may with to-noise ratio of the image area determined. 6 is a schematic diagram of a plurality of fixed focus depths and individual receiving focus areas of a receiving unit of the present invention, which divides an image into a plurality of sub-areas, each of which adopts a single fixed focus point. For convenience of presentation, three sub-areas are taken as an example. As shown in FIG. 6, each sub-area is provided with a single focus point, which can be anywhere in the sub-area, not limited to the center point of the sub-area, in order to avoid excessive sub-area, causing pulse wave compression errors ( As with the effect of dynamic focusing on pulse compression, therefore, the distance between the focus points of each sub-area should not be based on the length of the transmitted coded signal. The following further clarifies the main components of the present invention. FIG. 7 is a schematic diagram of the beamforming unit architecture of the present invention. Referring to FIG. 7, the signal of each channel is transmitted through the individual first delay 11 and the first multiplier. 12. The amount of time delay of each first delay unit 11 is determined by dividing the relative position of a predetermined focus point and an individual array channel by the speed of sound, and the amount multiplied by each first multiplier 12 can be consistent. (ie, no weight is applied), or a window function that is traditionally defined, such as Hamming, Gaussian, and so on. The focus point can be a single focus, or multiple areas of focus as shown in Figure 6. The function of the aforementioned pulse compression filtering unit is to compress the encoded signal and restore its original spatial resolution. In general, the pulse compression filtering unit can be classified into a matched filter and a non-matched filter. The frequency response of the matched filter is the conjugate complex of the spectrum of the original coded signal. The advantage of the matched filter 1380014 is that the signal-to-noise ratio is increased to the theoretical maximum, and the length of the filter is only required to match the original coded signal. The length is the same. The disadvantage is that the compressed sidelobe has a certain level limit, and the contrast of the image will be affected. In comparison, the frequency response of the non-matching filter is different from the original coded signal. Effective suppression of side lobes, however, will sacrifice some signal-to-noise ratios, and the filter length needs to be longer than the original coded signal. FIG. 8 is a schematic diagram of a spatial filter architecture of the present invention. Referring to FIG. 8, the spatial filter 8 of the present invention includes: a temporary register 13 coupled to the pulse compression filtering unit 7 for temporarily storing the scans. Sight line or beam; a signal ratio estimation unit 14 coupled to the register 1?, and estimating a signal-to-noise ratio in the image area according to the scan lines or beams; a filtering device 15, The buffer 13 is coupled to the image area according to the scan lines or beams, wherein the filtering device 15 is a one-dimensional, two-dimensional or three-dimensional structure, respectively corresponding to the selected one dimension and two a memory or a three-dimensional image area; a memory 16 storing the coefficients of the spatial filter 8; and a look-up device 17 coupled to the signal-to-noise ratio estimating unit 14, the memory 16 and the filtering device 15, In order to store the correspondence between the coefficients of the spatial filter 8, the signal-to-noise ratio of the image region, and the depth of the image region, in general, the function of the spatial filter 8 is two: one is to compensate the receiving unit Poor image quality caused by fixed focus, the second The good pulse compression signal that may be present side lobes, thereby allowing the image quality can approximate the image quality of two-way dynamic focusing. FIG. 9 is a flowchart of the signal-to-noise ratio estimation of the signal-to-noise ratio estimating unit of the present invention. Referring to FIG. 9 , since the filter coefficient is designed for the depth of the image region, a single scattering point is placed, and then imaged, the single scattering The image of the point is called the point spread function (1380014 PSF). The PSF can be obtained in two ways: experimentally and by computer simulation. Once the PSF is obtained, the best filter and wave factor can be designed according to this. The use of spatial choppers to modify the image quality of conventional 'pulse-excited ultrasonic systems' has not been used in the literature, but is not used to encode excited super-sonic systems. Here, the present invention uses the least squares method (least_sqaures) _ to design the best "state ride". We define its cost function E as: E = fH(aQ + (l^a)I)f+x ^(Cf~D) (1) Lu where 'f represents the spatial filter coefficient to be obtained, which can be a one-dimensional, two-dimensional or three-dimensional structure; Q represents the fold formed by the sidewave_domain to be minimized Convolution matrix; 丨 represents the identity matrix (identitymatrix), that is, except that the diagonal of the matrix is i, all other elements are 0; α is an adjustable scalar value, between 〇~丨The input is a scalar value; C and D are defined as . The relationship between the two is = D,: the value of the set image area. According to the above formula, the optimal stitch system = is: # /〇= (« 0+Γ/ - a)I)~x CH(C(aQ+(la )1)1 CHy]D (2) Equation (2) shows that the optimal filter coefficient can be changed with α. The influence of the value selection on the filtered image is the waveform diagram of the peak power (peak p〇wer) and the side lobes after the point spread function (PSF) passes through the spatial filter. The upper and lower curves in the figure correspond to the waveforms. One And the 2^ spatial filter, the value on each curve is relative to the α value in equation (2) (between 〇ι). The PSF is located at 11 cm, and the system transmits and receives fixed focus on 12, 15 respectively. The number of one-dimensional filter coefficients is ^ to 19, and the two-dimensional filter is five more in the depth direction. It can be seen from Fig. 10 that there is a compromise between the peak of the wave and the side lobes of the 1380014' wave. (trade-of f) relationship, and the relationship between the two is equivalent to the relationship between the signal-to-noise ratio and image contrast, and for the two-dimensional filter, this relationship is particularly obvious, as can be seen from the figure, The best compromise between the odd ratio and the image contrast is at the turning point (ie, a = 0.2). Therefore, according to Figure 10, we can analyze the signal-to-noise ratio in different images (not yet subjected to spatial chopping). In the case of the device, the turning point of each curve, in order to determine the optimal alpha value and the optimal filter of equation (2). φ Figure 11 is a schematic diagram of the one-dimensional spatial filter obtained at different depths, with spatial filtering The device adopts a one-dimensional architecture with a total of 25 filter coefficients. Therefore, in Figure 8, the scratchpad needs to store at least 25 scan lines in advance. Since the spatial filter will vary with depth, we redesign a new set of filters every 5 mm. In the above way, we can find one-dimensional spatial filter with different depths. In order to verify the feasibility of the coded excitation ultrasonic imaging system proposed in this case, we use computer to simulate the imaging results of different depth scattering points, φ at depth 10 Place a scattering point every 0. 5 cm between centimeters and 17 cm. The simulation parameters are as follows: the transducer probe is a 256-channel array structure, the center frequency is 5 MHz, the bandwidth is 2 MHz, the distance between the probe elements is 0.75 times, and the probe length is about 5.76 cm. The sound velocity is 1540 m/s, and the transmission and reception are a single fixed focus, which are respectively focused on 12 and 15 cm, and the sampling frequency of the receiver signal is 40 MHz. The transmitted coded signal is a pseudo-chirp signal (pseudo-ch i rp), which is a binary signal to the chirp signal, that is, when the original chirp signal is greater than 〇, the command is 1; It is 0, so the pseudo-chirp signal is a unipolar signal. In addition, the pseudo-chirp signal has a scan bandwidth of 3 MHz and a signal length of 13 1380014 degrees of 25 microseconds. The pulse compression filter uses a non-matching filter. The chopper can effectively suppress the sidelobe to a predetermined level. The waver is a two-dimensional architecture: each filter has 25 filter coefficients in the lateral direction (ie, with the commutative == parallel direction) 'longitudinal (ie, the depth of the coefficient) so a total of 75 ferrite coefficients. Every 5 mm of I 3 redesigned - a new set of devices, in addition, in order to verify the importance of the signal-to-noise ratio estimation for the space (four) design 'we in the simulation nano-noise.
圖十二A及圖十展示了不同編碼激發系統之成像 結果，其中圖十二A比較了散射點於深度上的變化，而圖 十二B比較了位於17公分處散射點的橫向波束場強分佈 (beam Pattern)。圖中，標明” Dyp〇st，，的結果表發射固 定、接收動態聚焦後再加上單-脈波壓縮遽波器之架構； “Fxpost+niter”表雙向固定聚焦加上單一脈波壓縮濾 波器，並搭配㈣濾、波器之架構，所有空間渡波器係數的 決定乃基於前式中的α為1; “Fxpost+filter(adaptive)’，表雙向固定聚焦加上單一 脈波壓縮濾波器，並搭配空間濾波器之架構/然而空間濾 波器之係數根據訊雜比作動態的調整（即α非固定 值），GS”表發射、接收雙向動態聚焦之脈衝激發架構， 為理論上最佳的成像結果（實際上不可行，需假設物體不會 發生位移的理想狀態）。圖十二Α清楚證明了動態聚焦對於 脈波壓縮不良的效應，可發現壓縮後的結果造成準位的提 =(點線），相較之下，固定聚焦的架構雖不會造成脈波壓 縮錯誤（準位低於動態聚焦結果至少達如仙），然而空間濾 波器卻會對於訊號濾波後的大小有決定性的影響，特別的 14 曰 1380014 是，濾波器係數隨訊雜比作動態調整之結果（實線），相較 於沒有動態調整的結果（斷線），其濾波後強度之增加可達 20dB。圖十二B則更進一步驗證了本發明所提出架構的有 效性，可以發現固定聚焦搭配動態調整之濾波器係數（實線） 擁有較低的旁波瓣，最為接近雙向動態聚焦之理想情況（點 線），總括而言，圖十二A及圖十二B可以證明本發明所提 出的系統及方法可補償脈波壓縮濾波器置於波束成型之 後，使得影像品質逼近雙向動態聚焦的影像品質。 由以上所述可以清楚地明瞭，本發明係提供一種超音 波成像裝置及方法，其可增加訊雜比以及改善成像深度並 減少系統複雜度。 以上已將本發明專利申請案做一詳細說明，惟以上所 述者，僅為本發明專利申請案之較佳實施例而已，當不能 限定本發明專利申請案實施之範圍。即凡依本發明專利申 請案申請範圍所作之均等變化與修飾等，皆應仍屬本發明 專利申請案之專利涵蓋範圍内。 【圖式簡單說明】 圖一 A為習知編碼激發系統之架構示意圖。 圖一 B為習知脈衝激發系統之架構示意圖。 圖二A為習知編碼激發系統之架構示意圖，其中脈波壓 縮濾波器係置於波束成型器之前。 圖二B為習知編碼激發系統之架構示意圖，其中脈波壓 縮濾波器係置於波束成型器之後。 圖三A為動態聚焦之波束成型對於脈波壓縮的效應示 15 1380014 意圖。 圖三B為固定聚焦之波束成型對於脈波壓縮的效應示 意圖。 圖四為本發明之具體實施例的系統架構示意圖。 圖五為本發明之具體實施例的方法步驟圖。 圖六為本發明之接收單元複數個固定聚焦深度與個別 接收聚焦區域示意圖。 圖七為本發明之波束成型單元架構圖。 圖八為本發明之空間濾波器架構圖。 圖九為本發明之訊雜比估計單元的訊雜比估計流程圖。 圖十為點擴散函數經過空間濾波器後的峰值功率與旁 波瓣的關係波形圖。 圖十一為不同深度所求得的一維空間濾波器示意圖。 圖十二A為比較散射點於课度上的變化波形圖。 圖十二B為位於17公分處散射點的橫向波束場強分佈 圖。 【主要元件符號說明】 1超音波成像裝置 2發射單元 3換能器探頭 4物體 5接收單元 6波束成型單元 7脈波壓縮濾波單元 1380014 8空間濾波器 9包絡偵測及掃描轉換單元 10顯示裝置 11第一延遲器 12第一乘法器 13暫存器 14訊雜比估計單元 15濾波裝置 16記憶體 17查表裝置Figure 12A and Figure 10 show the imaging results of different coded excitation systems. Figure 12A compares the variation of the scattering point in depth, while Figure 12B compares the lateral beam field strength of the scattering point at 17 cm. Beam pattern. In the figure, the result table of "Dyp〇st," is fixed, the dynamic focus is received, and the structure of the single-pulse compression chopper is added; the "Fxpost+niter" table is bidirectional fixed focus plus a single pulse compression filter. And with (4) filter, wave structure, the decision of all space waver coefficients is based on α in the previous formula is 1; "Fxpost+filter(adaptive)', table bidirectional fixed focus plus single pulse compression filter And with the structure of the spatial filter / however, the coefficient of the spatial filter is dynamically adjusted according to the signal ratio (ie, α non-fixed value), the GS" table transmits and receives the bidirectional dynamic focus pulse excitation architecture, which is theoretically the best. The imaging result (actually not feasible, it is necessary to assume that the object will not be displaced in an ideal state). Figure 12 shows clearly the effect of dynamic focusing on poor pulse compression, and it can be found that the result of compression causes the level of correction = (dotted line), in contrast, the fixed-focus architecture does not cause pulse compression errors (the level is lower than the dynamic focus result is at least as good as the fairy), but the spatial filter will be for the signal The size of the wave has a decisive influence. The special 14 曰 1380014 is the result of the dynamic adjustment of the filter coefficient with the signal-to-noise ratio (solid line), compared to the result without dynamic adjustment (broken line), the filtered intensity The increase can reach 20dB. Figure 12B further verifies the effectiveness of the proposed architecture of the present invention. It can be found that the fixed focus with the dynamic adjustment of the filter coefficient (solid line) has a lower side lobes, the closest to the two-way The ideal situation of dynamic focus (dotted line), in summary, Figure 12A and Figure 12B can prove that the system and method proposed by the present invention can compensate the pulse compression filter after beamforming, so that the image quality is approached Image quality of bidirectional dynamic focusing. It is clear from the above that the present invention provides an ultrasonic imaging apparatus and method which can increase the signal to noise ratio and improve the imaging depth and reduce the system complexity. The application is described in detail, but the above is only the preferred embodiment of the patent application of the present invention. The scope of the application of the patent application is that the equivalent changes and modifications of the scope of application of the patent application of the present invention should remain within the scope of the patent application of the patent application of the present invention. [Simplified illustration] Figure 1A Schematic diagram of the structure of a conventional coded excitation system is shown in Figure 1. Figure B is a schematic diagram of the structure of a conventional pulse excitation system. Figure 2A is a schematic diagram of a conventional coded excitation system in which a pulse compression filter is placed before the beamformer. Figure 2B is a schematic diagram of the architecture of a conventional coded excitation system in which a pulse compression filter is placed behind a beamformer. Figure 3A shows the effect of beamforming for dynamic focusing on pulse compression 15 1380014. Schematic diagram of the effect of beamforming for fixed focus on pulse compression. Figure 4 is a schematic diagram of the system architecture of a specific embodiment of the present invention. Figure 5 is a process step diagram of a specific embodiment of the present invention. Figure 6 is a schematic diagram of a plurality of fixed focus depths and individual received focus areas of the receiving unit of the present invention. Figure 7 is a diagram of the beam forming unit architecture of the present invention. FIG. 8 is a structural diagram of a spatial filter of the present invention. FIG. 9 is a flowchart of the signal-to-noise ratio estimation of the signal-to-noise ratio estimating unit of the present invention. Figure 10 is a waveform diagram showing the relationship between the peak power and the sidelobe of the point spread function after passing through the spatial filter. Figure 11 is a schematic diagram of a one-dimensional spatial filter obtained at different depths. Figure 12A is a waveform diagram showing the variation of the scattering point in the degree. Figure 12B shows the transverse beam field strength distribution at the scattering point at 17 cm. [Main component symbol description] 1 ultrasonic imaging device 2 transmitting unit 3 transducer probe 4 object 5 receiving unit 6 beam forming unit 7 pulse compression filtering unit 1380014 8 spatial filter 9 envelope detecting and scanning converting unit 10 display device 11 first retarder 12 first multiplier 13 register 14 signal ratio estimation unit 15 filter device 16 memory 17 table lookup device