Harmonic Imaging Method Research Articles

Ultrasound Tissue Harmonic Imaging based on Wavelet Correlation Analysis

In this paper, an ultrasound tissue harmonic imaging method based on wavelet transform has been proposed. Wavelet transform is utilized to analyze the correlation between mother wavelet and the received echoes. In order to obtain a better correlation, a new mother wavelet named ‘Tissue wavelet’ is constructed according to the KZK equation. The proposed method was validated by experiments performed on an ultrasound flow phantom. Results showed that the contrast and axial resolution have been improved effectively.

Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-Factor Lateral Mode Transmitters for Intravascular and Intracavity Applications

Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique that utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast-to-tissue ratio than second harmonic imaging methods. In this paper, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency intravascular ultrasound transducer was developed for concept validation, which achieved larger signal amplitude, better contrast-to-noise ratio (CNR), and pulselength compared to the previous work. A dual-frequency [Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral sizes of the microbubbles in a 200- [Formula: see text] tube were measured to be 269 and [Formula: see text], respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when the final transducer size requirements dictate design choices.

Prevalence of aneurysm of the interatrial septum in the general population and in patients with a recent episode of cryptogenetic ischemic stroke: a tissue harmonic imaging transthoracic ecocardiography study in 5.631 patients

Cerebral ischemia is among the principal causes of mortality and morbidity in industrialized countries being responsible of 10-12% of all deaths and of an elevated number of permanent disability. The cardio-embolic forms may be responsible of the 30-35% of cerebrovascular acute syndrome, nevertheless in a significant percentage of cases, especially among young people, cerebral ischemic episodes are not induced by these cardio-embolic forms: these cases are defined as cryptogenetic stroke/TIA. In these patients cardiac abnormalities represented by an aneurysm of the interatrial septum (ASA) and by a patent foramen ovale (PFO) have been frequently observed. The purpose of our prospective, study was to evaluate, through transthoracic echocardiography and tissue harmonic imaging (ETT-THI), the prevalence of ASA in the general population (group A) and the prevalence of ASA-FOP in a subgroup of patients with recent episode of cryptogenetic ischemic stroke/TIA (group B). We studied in a prospective manner from January 1 2003 to October 31t 2004 n. 5.631 patients. The presence of ASA was found in 3.2% of patients of group A, while in patients of group B we identified an ASA in 32% and a POF in 42% of the cases. Using a ETT-THI, our study shows in a wide range of a non selected population a prevalence of ASA greater than in previous studies. Such high prevalence in the general population of patients submitted to echocardiography and the higher frequency in subjects with recent cryptogenetic stroke, suggests to search carefully these abnormalities at the level of the interatrial septum using the harmonic imaging method.

Harmonic tracking of acoustic radiation force-induced displacements

Ultrasound-based elasticity imaging methods rely upon accurate estimates of tissue deformation to characterize the mechanical properties of soft tissues. These methods are corrupted by clutter, which can bias and/or increase variance in displacement estimates. Harmonic imaging methods are routinely used for clutter suppression and improved image quality in conventional B-mode ultrasound, but have not been utilized in ultrasound-based elasticity imaging methods. We introduce a novel, fully-sampled pulse-inversion harmonic method for tracking tissue displacements that corrects the loss in temporal sampling frequency associated with conventional pulse-inversion techniques. The method is implemented with acoustic radiation force impulse (ARFI) imaging to monitor the displacements induced by an impulsive acoustic radiation force excitation. Custom pulse sequences were implemented on a diagnostic ultrasound scanner to collect spatially-matched fundamental and harmonic information within a single acquisition. B-mode and ARFI images created from fundamental data collected at 4 MHz and 8 MHz are compared with 8-MHz harmonic images created using a band-pass filter approach and the fully sampled pulse-inversion method. In homogeneous, tissue-mimicking phantoms, where no visible clutter was observed, there was little difference in the axial displacements, estimated jitter, and normalized cross-correlation among the fundamental and harmonic tracking methods. The similarity of the lower- and higher-frequency methods suggests that any improvement resulting from the increased frequency of the harmonic components is negligible. The harmonic tracking methods demonstrated a marked improvement in B-mode and ARFI image quality of in vivo carotid arteries. Improved feature detection and decreased variance in estimated displacements were observed in the arterial walls of harmonic ARFI images, especially in the pulse-inversion harmonic ARFI images. Within the lumen, the harmonic tracking methods improved the discrimination of the blood–vessel interface, making it easier to visualize plaque boundaries. Improvements in harmonic ARFI images in vivo were consistent with suppressed clutter supported by improved contrast and contrast-to-noise ratio (CNR) in the matched harmonic B-mode images compared with the fundamental B-mode images. These results suggest that harmonic tracking methods can improve the clinical utility and diagnostic accuracy of ultrasound-based elasticity imaging methods.

Determination of Optimal Imaging Mode for Ultrasonographic Detection of Subdermal Contraceptive Rods: Comparison of Spatial Compound, Conventional, and Tissue Harmonic Imaging Methods

ObjectiveTo determine which mode of ultrasonography (US), among the conventional, spatial compound, and tissue-harmonic methods, exhibits the best performance for the detection of Implanon® with respect to generation of posterior acoustic shadowing (PAS).Materials and MethodsA total of 21 patients, referred for localization of impalpable Implanon®, underwent US, using the three modes with default settings (i.e., wide focal zone). Representative transverse images of the rods, according to each mode for all patients, were obtained. The resulting 63 images were reviewed by four observers. The observers provided a confidence score for the presence of PAS, using a five-point scale ranging from 1 (definitely absent) to 5 (definitely present), with scores of 4 or 5 for PAS being considered as detection. The average scores of PAS, obtained from the three different modes for each observer, were compared using one-way repeated measure ANOVA. The detection rates were compared using a weighted least square method.ResultsStatistically, the tissue harmonic mode was significantly superior to the other two modes, when comparing the average scores of PAS for all observers (p < 0.00-1). The detection rate was also highest for the tissue harmonic mode (p < 0.001).ConclusionTissue harmonic mode in uS appears to be the most suitable in detecting subdermal contraceptive implant rods.

J042043 金属中異質部の高調波画像化([J04204]超音波計測・解析法の新展開(4))

Conventional ultrasonic techniques are unable to detect material heterogeneities such as local plastic deformation or solidification boundaries of welds which have nearly same acoustic impedance with base materials. To solve this problem, higher harmonic imaging methods using immersion local resonance and backscattered waves are proposed and the validity of the method is demonstrated for local plastic deformation in thin plates and solidification boundaries of spots welds.

1081: Basic Research on Safety Assessment of Medical Ultrasound - The Problems in the Estimation of Safety Indexes

New type ultrasound diagnostic equipments with new functions like color Doppler imaging, harmonic imaging, 3 dimensional imaging etc. tend to irradiate higher intensity ultrasound with high frequency. Therefore the safety became important topic in medical ultrasound field. We measured the irradiated ultrasound pulse waveform, acoustic field and -12 dB output beam dimensions. The mechanical index MI, soft-tissue thermal index TIS and cranial-bone thermal index TIC were calculated from the results. The mechanical index can be calculated from attenuated peak-rarefactional acoustic pressure Pr,α divided by the square root of acoustic working frequency fawf. And they were divided by CMI. The soft-tissue thermal index can be calculated from the output power P multiplied by acoustic working frequency. And they were divided by CTIS1. In this case, CMI is defined as 1 MPa MHz-1/2 and CTIS1 is defined as 210 mW MHz in JIS T 0601-2-37: 2005 and IEC 62359 Ed. 1.0: 2005. Harmonic components with many different frequencies are generated by propagation of ultrasound in water and tissues or nonlinear behavior of micro bubble in the ultrasound diagnosis like tissue harmonic imaging or contrast harmonic imaging methods. These frequency components are different from the transmitting frequency and the fundamental frequency. Therefore it is difficult to determine the acoustic working frequency in the measured frequency spectrum for calculation of safety indexes by conventional definition. We will report about this important problem. New type ultrasound diagnostic equipments with new functions like color Doppler imaging, harmonic imaging, 3 dimensional imaging etc. tend to irradiate higher intensity ultrasound with high frequency. Therefore the safety became important topic in medical ultrasound field. We measured the irradiated ultrasound pulse waveform, acoustic field and -12 dB output beam dimensions. The mechanical index MI, soft-tissue thermal index TIS and cranial-bone thermal index TIC were calculated from the results. The mechanical index can be calculated from attenuated peak-rarefactional acoustic pressure Pr,α divided by the square root of acoustic working frequency fawf. And they were divided by CMI. The soft-tissue thermal index can be calculated from the output power P multiplied by acoustic working frequency. And they were divided by CTIS1. In this case, CMI is defined as 1 MPa MHz-1/2 and CTIS1 is defined as 210 mW MHz in JIS T 0601-2-37: 2005 and IEC 62359 Ed. 1.0: 2005. Harmonic components with many different frequencies are generated by propagation of ultrasound in water and tissues or nonlinear behavior of micro bubble in the ultrasound diagnosis like tissue harmonic imaging or contrast harmonic imaging methods. These frequency components are different from the transmitting frequency and the fundamental frequency. Therefore it is difficult to determine the acoustic working frequency in the measured frequency spectrum for calculation of safety indexes by conventional definition. We will report about this important problem.

Ultrasound Cerebral Perfusion Analysis Based on a Mathematical Model for Diminution Harmonic Imaging

Cerebral vascular diseases are detect- able by CT/MRI-based methods. Drawbacks of these methods are that they are expensive, time-consuming and intolerable to critically ill patients. Ultrasound, as an inexpensive bedside method, promises to become an alternative. Among other harmonic imaging methods, the diminution harmonic imaging (DHI) method is known, which determines perfusion-related parameters by analyzing ultrasound contrast agent (UCA) diminution kinetics based on constant UCA infusion. The shortcoming of DHI is that the used mathematical model can only determine these parameters by least squares fitting the model onto the data. In this work, the underlying mathematical model is further developed such that it becomes possible to directly calculate the parameters from the image data. Furthermore, the new model offers an improved way to estimate the spatial distribution of the destruction coefficient necessary for accurately determining the destruction power of the ultrasound pulse on the contrast agent. The direct calculation of the perfusion coefficient is much faster than the former fitting of the model. Perfusion as well as destruction coefficients are displayed as color-coded images. In an example, a region with perfusion deficits (as shown in a MR image of the same patient) is clearly identifiable. Displaying the parameters as color-coded images facilitates result interpretation for the diagnosing physician. The results are preliminary and still have to be validated, but they suggest that the new DHI model improves the significance of ultrasound as a diagnostic help.

Improved Monitoring of Intracranial Echo-guided Surgery: Reduction of Backscattering and Recognition of the Operating Part Using Microcapsule Vibration

In brain tumor surgery using the ultrasonic monitoring technique, surgical instruments such as microdissectors and suction tubes create imaging artifacts. In addition, recognition of the correct position of the suction tube tip under ultrasonic monitoring is difficult because conventional 2D ultrasound creates similar images regardless of the scanning position along the tube. The backscattering-like artifact from these surgical instruments is caused by ringing vibrations generated on the tube by the ultrasonic monitoring pulse. We have attempted to suppress this type of artifact in vivo using a suction tube covered with a high-attenuation heat-shrinkable coating devised on the basis of in vitro experiments, and confirmed that this was effective. To identify the position of the suction tip on the ultrasound image, 1.4-μm-radius microcapsules having a hard plastic shell were attached to the metal tube tip. The microcapsules vibrate in synchronization with the ultrasound monitoring pulse and regenerate harmonic signals, based on the same principle as contrast agents used in ultrasound imaging. By using the 2nd harmonic imaging method, the metal tube tip was found to be selectively emphasized on the ultrasound image. It is anticipated that these improvements will make intraoperative ultrasonic monitoring a more powerful tool for brain tumor surgery.

CONTRAST‐ENHANCED ENDOSCOPIC ULTRASONOGRAPHY IN THE DIAGNOSIS OF PANCREATO‐BILIARY DISEASES

In diagnostic imaging, techniques represented by computed tomography (CT) and magnetic resonance imaging (MRI), diagnosis by evaluation of plain images in combination with contrast‐enhanced images is considered important. Recently, the ultrasound contrast media that can be administered from peripheral veins have been developed, and their utility is reported not only for the circulatory organ area but also the digestive organ area, mainly for liver diseases. As for the pancreato‐biliary diseases, there often are the cases that visualization of the diseases itself is not easy by transabdominal ultrasonography, so, the evaluation of contrast‐enhanced ultrasonography remains difficult. In contrast, endoscopic ultrasonography (EUS) is thought to be one of the most valuable modality for those diseases.The mainstream of an operation method of EUS was mechanical radial type, but in late years, endoscopic ultrasonography of an electronic linear method and an electronic radial method have been developed. Because an electronic scan method was adopted, we get possible to apply technology of color Doppler flow imaging and power Doppler flow imaging and harmonic imaging methods to EUS.We would like to outline the usefulness of contrast‐enhanced color/power Doppler EUS and contrast‐enhanced harmonic EUS, moreover, tissue harmonic imaging and three dimensional imaging, on the basis of our experiences.

Value of new contrast harmonic technique for detecting tumor vascularity in hepatocellular carcinoma: Preliminary results.

To investigate the value of a new wide-band contrast harmonic imaging method in depicting intratumoral vascularity in hepatocellular carcinoma. Twenty-two patients with 28 hepatocellular carcinoma nodules evaluated with Contrast Harmonic Echo, a new wide-band harmonic imaging method, using Levovist(®) as a contrast-enhancing agent. Intermittent imaging was carried out in the early arterial phase for 10 to 40 seconds, in the late vascular phase for 1 to 2 minutes, and in the postvascular phase for 5 to 7 minutes. Subtraction images were obtained using the multishot method during the late vascular phase. The ability of Contrast Harmonic Echo imaging to detect vascularity in hepatocellular carcinoma was compared to that of unenhanced color Doppler imaging by analzing results obtained using dynamic CT as a gold standard. Contrast harmonic Echo imaging detected intratumoral vessels, tumor parenchymal stain, and perfusion defect in the early arterial phase, the late vascular phase, and the postvascular phase, respectively. In the late vascular phase, the subtraction image clearly delineated the tumor parenchymal strain. Intratumoral vascularity was detected in 25 (89%) of the hepatocellular carcinoma nodules by Contrast Harmonic Echo, compared with 15 (54%) when color Doppler imaging was used (p<0.05). The diagnostic sensitivity, specificity, and accuracy of Contrast Harmonic Echo were 96.1%, 100% and 96.4%, respectively, corresponding to results obtained using dynamic CT. Contrast Harmonic Echo imaging is superior to unenhanced color Doppler imaging in depicting intratumoral vessels and parenchymal stain, and agrees closely with results obtained with three-phase dynamic CT.

Medical diagnostic ultrasound transducer system and method for harmonic imaging

A transducer system and method for harmonic imaging is provided. At least one transducer element is provided. The transducer element comprises two stacked piezoelectric layers. Information from each of the layers is independently processed during one of a transmit event, a receive event, and both transmit and receive events. Information from the transducer element is provided to a filter. The filter isolates harmonic information for imaging. By providing a multi-layer transducer element with independent processing for each layer, a wide bandwidth transducer for harmonic imaging is provided. The null associated with most transducers at the second harmonic of a fundamental frequency is removed or lessened.

Medical diagnostic ultrasound system and method for harmonic imaging with an electrostatic transducer

A method and system for generating transmit pulses for use with an electrostatic transducer in harmonic imaging are provided. The excitation waveforms are pre-distorted to account for the non-linear output of the electrostatic transducer. Additionally, the force on a multiple element electrostatic transducer array is measured. A bias voltage is applied to the electrostatic transducer where the bias voltage is responsive to the measured force.

肝腫りゅう性病変の検出における超音波Ｎａｔｉｖｅ Ｔｉｓｓｕｅ Ｈａｒｍｏｎｉｃ Ｉｍａｇｉｎｇ法の有用性について

肝腫りゅう性病変の検出における超音波Ｎａｔｉｖｅ Ｔｉｓｓｕｅ Ｈａｒｍｏｎｉｃ Ｉｍａｇｉｎｇ法の有用性について