Ultrasonographic evaluation of focal hepatic lesions: comparison of pulse inversion harmonic,tissue harmonic,and conventional imaging techniques.

A prospective study was performed to evaluate whether pulse inversion harmonic imaging and tissue harmonic imaging improve the lesion conspicuity and change ultrasonographic characteristics of focal hepatic lesions. Three radiologists evaluated 97 focal hepatic lesions by consensus: cirrhosis‐related nodules (n = 23), metastases (n = 23), hemangiomas (n = 27), and cysts (n = 24). In our study, pulse inversion harmonic imaging was judged superior to both tissue harmonic imaging and conventional imaging in conspicuity and overall quality for cirrhosis‐related nodules, metastases, and cysts (P < 0.05). Compared with conventional imaging, both pulse inversion harmonic imaging and tissue harmonic imaging provided better conspicuity, clearer internal echogenicity, and stronger through‐transmission of cysts (P < 0.05). Pulse inversion harmonic imaging was judged to be better in depicting internal morphology for cirrhosis‐related nodules and metastases than conventional imaging (P < 0.05). For hemangiomas, no statistically significant difference was found in all parameters except better posterior enhancement by tissue harmonic imaging than other techniques. In conclusion, pulse inversion harmonic imaging showed the best conspicuity and also enhanced characteristics of both cystic and solid hepatic lesions. Tissue harmonic imaging was judged superior to conventional imaging in evaluating cysts but was not beneficial for solid lesions. The results of this trial may be specific to the machine used for this study.     

组织谐波成像在胆囊病变超声诊断中的应用

目的通过常规基波成像（FI）和组织谐波显像（THI）技术对比,探讨超声自然组织谐波成像在胆囊病变中的应用价值。方法采用基波显像和组织谐波成像对63例胆囊病变患者进行对比观察。结果63例患者FI与THI图像对比分析,后者图像整体质量均得到明显改善。结论组织谐波成像能明显改善二维图像质量,有助于提高超声对胆囊病变的诊断准确率。     

组织谐频成像与基频成像在心脏声像图中的对比观察

目的:探讨组织谐频成像（THI）与常规基频成像（FI）的对比观察，研究THI改善声像图质量，增强图像的显现力。方法：对150例（标准受检100例、透声差受检50例）心脏（正常或异常）进行观察，分析两种检查的图像质量。结果：FI成像标准受检图像显示优良率81％，透声差受检图像显示优良率64％。THI成像标准受检图像显示优良率91％，透声差受检图像显示优良率88％。结论：无论标准受检或透声差受检THI的图像质量均较FI的图像质量明显改善，可提高诊断的准确性。     

Comparing differential tissue harmonic imaging with tissue harmonic and fundamental gray scale imaging of the liver.

OBJECTIVE: The purpose of this study was to compare fundamental gray scale sonography, tissue harmonic imaging (THI), and differential tissue harmonic imaging (DTHI) for depicting normal and abnormal livers. METHODS: The in vitro lateral resolution of DTHI, THI, and sonography was assessed in a phantom. Sagittal and transverse images of right and left hepatic lobes of 5 volunteers and 20 patients and images of 27 liver lesions were also acquired. Three independent blinded readers scored all randomized images for noise, detail resolution, image quality, and margin (for lesions) on a 7-point scale. Next, images from the same location obtained with all 3 modes were compared blindly side by side and rated by all readers. Contrast-to-noise ratios were calculated for the lesions, and the depth of penetration (centimeters) was determined for all images. RESULTS: In vitro, the lateral resolution of DTHI was significantly better than fundamental sonography (P = .009) and showed a trend toward significance versus THI (P = .06). In the far field, DTHI performed better than both modes (P < .04). In vivo, 450 images were scored, and for all parameters, DTHI and THI did better than sonography (P < .002). Differential tissue harmonic imaging scored significantly higher than THI with regard to detail resolution and image quality (P < .001). The average increase in penetration with THI and DTHI was around 0.6 cm relative to sonography (P < .0001). The contrast-to-noise ratio for DTHI showed a trend toward significance versus THI (P = .06). Side-by-side comparisons rated DTHI better than THI and sonography in 54% of the cases (P < .007). CONCLUSIONS: Tissue harmonic imaging and DTHI do better than fundamental sonography for hepatic imaging, with DTHI being rated the best of the 3 techniques.     

Clinical use of ultrasound tissue harmonic imaging.

The recent introduction of tissue harmonic imaging could resolve the problems related to ultrasound in technically difficult patients by providing a marked improvement in image quality. Tissue harmonics are generated during the transmit phase of the pulse-echo cycle, that is, while the transmitted pulse propagates through tissue. Tissue harmonic images are formed by utilizing the harmonic signals that are generated by tissue and by filtering out the fundamental echo signals that are generated by the transmitted acoustic energy. To achieve this, two processes could be used; one by using filters for fundamental and harmonic imaging and the second using two simultaneous pulses with a 180 degrees difference in phase. The introduction of harmonics allows increased penetration without a loss of detail, by obtaining a clearer image at depth with significantly less compromise to the image quality caused by the use of lower frequencies. This imaging mode could be used in different organs with a heightening of low-contrast lesions through artefact reduction, as well as by the induced greater intrinsic contrast sensitivity of the harmonic imaging mode.     

High-frame-rate tissue harmonic imaging enhances anatomic M-mode sections of the left ventricle in short-axis view.

BACKGROUND: High-frame-rate echocardiography (HFRE) and tissue harmonic imaging (THI) may improve image quality, thereby enabling anatomic M-mode sections of left ventricular (LV) wall segments to be visualized in various planes in the short-axis view. OBJECTIVES: The goals of this study were to compare image quality between HFRE and conventional-frame-rate echocardiography (CFRE) and between fundamental imaging (FI) and THI, and to obtain anatomic M-mode values of basal short-axis LV segments from healthy subjects for use in the evaluation of abnormal segments in patients with myocardial infarction (MI). METHODS AND RESULTS: The study included 28 healthy subjects and 15 patients with MI who underwent 2-dimensional echocardiography with an ultrasonographic system equipped with THI and anatomic M-mode. Left ventricular image cineloops at the basal short-axis view that were obtained with 3 combinations of imaging techniques (FI + CFRE, FI + HFRE, and THI + HFRE) were digitized and displayed side-by-side in random order for comparison by blinded readers. M-mode sections were done in 3 planes: anteroseptal-posterior, inferoseptal-lateral, and anterior-inferior basal segments. The THI + HFRE combination showed the best image quality with significant reduction in noise artifacts, resulting in a good signal-to-noise ratio and good tractability of all LV segments by anatomic M-mode. In healthy subjects, significant intersegmental differences existed in the diastolic and systolic thicknesses and in the percent systolic thickening of LV segments. In patients with MI, LV systolic thickening was significantly decreased in abnormal segments. No significant differences were noted in ejection fraction and fractional shortening among the 3 anatomic M-mode planes. CONCLUSION: High-frame-rate tissue harmonic imaging improved image quality, thereby allowing reproducible anatomic M-mode measurements in various planes in the short-axis view and providing a convenient objective evaluation of global and regional LV function.     

Detection of parenchymal abnormalities in acute pyelonephritis by pulse inversion harmonic imaging with or without microbubble ultrasonographic contrast agent: correlation with computed tomography.

The purpose of this study was to evaluate the ability of pulse inversion harmonic imaging with or without microbubble ultrasonographic contrast agent in depicting renal parenchymal changes in acute pyelonephritis. The study population included 30 patients with acute pyelonephritis and 10 healthy volunteers. Pulse inversion harmonic imaging with or without contrast agent was compared with conventional ultrasonography and tissue harmonic imaging in terms of detection and conspicuity of renal abnormalities. The detection and conspicuity of renal parenchymal abnormalities in acute pyelonephritis on tissue harmonic imaging, pulse inversion harmonic imaging, and contrast-enhanced pulse inversion harmonic imaging were significantly better than those on conventional ultrasonography. In 2 of 10 healthy volunteers all 4 techniques yielded false-positive diagnoses of parenchymal abnormalities. In conclusion, tissue harmonic imaging and pulse inversion harmonic imaging are sensitive techniques for depicting renal parenchymal lesions in acute pyelonephritis. Despite relatively lower specificities and negative predictive values, these techniques are thought to be useful for the depiction of subtle parenchymal changes in acute pyelonephritis.     

Qualitative and quantitative effects of harmonic echocardiographic imaging on endocardial edge definition and side-lobe artifacts.

Harmonic imaging is a new ultrasonographic technique that is designed to improve image quality by exploiting the spontaneous generation of higher frequencies as ultrasound propagates through tissue. We studied 51 difficult-to-image patients with blinded side-by-side cineloop evaluation of endocardial border definition by harmonic versus fundamental imaging. In addition, quantitative intensities from cavity versus wall were compared for harmonic versus fundamental imaging. Harmonic imaging improved left ventricular endocardial border delineation over fundamental imaging (superior: harmonic = 71.1%, fundamental = 18.7%; similar: 10.2%; P <.001). Quantitative analysis of 100 wall/cavity combinations demonstrated brighter wall segments and more strikingly darker cavities during harmonic imaging (cavity intensity on a 0 to 255 scale: fundamental = 15.6 +/- 8.6; harmonic = 6.0 +/- 5.3; P <.0001), which led to enhanced contrast between the wall and cavity (1.89 versus 1.19, P <.0001). Harmonic imaging reduces side-lobe artifacts, resulting in a darker cavity and brighter walls, thereby improving image contrast and endocardial delineation.     

超声组织谐波成像在腹部疾病中的诊断价值

目的探讨组织谐波成像在腹部疾病诊断中的临床应用价值.方法对120例腹部疾病患者分别进行传统超声及组织谐波成像,并保存相应的影像图片.然后采用双盲方法对上述影像图片进行评价分析.结果组织谐波成像图片评价明显优于传统超声成像,二者比较有明显差异.结论组织谐波成像可以提高图像的质量,有重要的临床应用价值.     

Characterization of a linear streak artifact with pulse inversion tissue harmonics in musculoskeletal sonography.

OBJECTIVE: To understand a linear artifact that projects deep to reflective structures that move rapidly while using tissue harmonic imaging with pulse inversion (PI) sonography. We hypothesize that this artifact is due to a cancellation error between firings in PI imaging, and it is, therefore, similar in generation to the twinkling artifact in color Doppler sonography. This artifact could be studied with the use of surfaces of different roughness to represent different rates of motion, in which roughness corresponds to spatial fluctuations in surface height. Given very slight variations in beam focusing as occurs with sonographic imaging arrays, these spatial fluctuations translate into temporal fluctuations in the received signal as would occur with tissue motion. METHODS: We scanned 4 different sandpaper grits and a smooth surface through a water path using fundamental and PI mode, 1- and 2-pulse techniques, respectively. The sandpaper and the smooth surface were scanned through a water path at mechanical indices of 0.1 to 0.7. Four independent images were subtracted pairwise to remove nonfluctuating signals. These noise pixels were counted and analyzed. RESULTS: Analysis of variance showed that the noise generated behind the different surfaces was highly significantly different. Two-tailed t tests generally showed significant differences in the quantity of noise between fundamental and harmonic imaging behind the roughest 3 grades of sandpaper. A multiple regression model showed significantly greater slopes for harmonic imaging for all grades of sandpaper and the smooth surface. CONCLUSIONS: The noise and, by extension, the linear streak artifact in musculoskeletal imaging are dependent on the mechanical index and are functions of sandpaper roughness. This would be equivalent to a subtraction error between 2 firings due to soft tissue motion, and the artifact may be a way to identify rapid soft tissue motion in PI images.     

Harmonic Imaging with Fresnel Beamforming in the Presence of Phase Aberration

Fresnel beamforming is a beamforming method with a delay profile similar in shape to a physical Fresnel lens. The advantage of Fresnel beamforming is the reduced channel count, which consists of four to eight transmit and two analog-to-digital receive channels. Fresnel beamforming was found to perform comparably to conventional delay-and-sum beamforming. However, the performance of Fresnel beamforming is highly dependent on focal errors. These focal errors result in high side-lobe levels and further reduce the performance of Fresnel beamforming in the presence of phase aberration. With the advantages of lower side-lobe levels and suppression of aberration effects, harmonic imaging offers an effective solution to the limitations of Fresnel beamforming. We describe the implementation of tissue harmonic imaging and pulse inversion harmonic imaging in Fresnel beamforming, followed by dual apodization with cross-correlation, to improve image quality. Compared with conventional delay-and-sum beamforming, experimental results indicated contrast-to-noise ratio improvements of 10%, 49% and 264% for Fresnel beamforming using tissue harmonic imaging in the cases of no aberrator, 5-mm pork aberrator and 12-mm pork aberrator, respectively. These improvements were 22%, 57% and 352% for Fresnel beamforming using pulse inversion harmonic imaging. Moreover, dual apodization with cross-correlation was found to further improve the contrast-to-noise ratios in all cases. Harmonic imaging was also found to narrow the lateral beamwidth and shorten the axial pulse length by at least 25% and 21%, respectively, for Fresnel beamforming at different aberration levels. These results suggest the effectiveness of harmonic imaging in improving image quality for Fresnel beamforming, especially in the presence of phase aberration. Even though this combination of Fresnel beamforming and harmonic imaging does not outperform delay-and-sum beamforming combined with harmonic imaging, it provides the benefits of reduced channel count and potentially reduced cost and size of ultrasound systems.     

Reduction of stent artifacts using high-frequency harmonic ultrasound imaging

Tissue harmonic imaging (THI) has been shown to improve medical ultrasound (US) image quality in the frequency range from 2 to 10 MHz and might, therefore, also be advantageous in high-frequency US applications, like US biomicroscopy and intravascular US (IVUS). In this study, we compared high-frequency THI (40 MHz) with fundamental imaging (20 and 40 MHz) with a distorting reflective metal stent in the near fields of both a spherically-focused US biomicroscopy transducer (aperture 8 mm, focal distance 13 mm) and an unfocused elliptical IVUS element. Hydrophone measurements of the harmonic beam (40 MHz) of both transducers showed relatively low signal strength in the near field compared with both (20 and 40 MHz) fundamental beams. For the focused transducer, THI suppressed the second stent echo up to 14 dB compared with fundamental imaging. No significant reduction in stent artifact imaging was observed for the unfocused IVUS element.     

组织谐波显像在输尿管结石检查中的应用

目的 探讨组织谐波显像对输尿管结石的诊断价值。方法 对169例输尿管结石患者进行基波显像和组织谐波显像对比观察。结果 组织谐波显像对输尿管内液区及结石病灶的边缘显示清晰，优于基波显像。结论 组织谐波显像能明显提高图像质量，使输尿管结石的阳性显示率和准确性明显提高。     

Optimal transmit phasing on tissue background suppression in contrast harmonic imaging

Ultrasonic harmonic imaging provides superior image quality than linear imaging and has become an important diagnostic tool in many clinical applications. Nevertheless, the contrast-to-tissue ratio (CTR) in harmonic imaging is generally limited by tissue background signal comprising both the leakage harmonic signal and the tissue harmonic signal. Harmonic leakage generally occurs when a wideband transmit pulse is used for better axial resolution. In addition, generation of tissue harmonic signal during acoustic propagation also decreases the CTR. In this paper, suppression of tissue background signal in harmonic imaging is studied by selecting an optimal phase of the transmit signal to achieve destructive cancellation between the tissue harmonic signal and the leakage harmonic signal. With the optimal suppression phase, our results indicate that the tissue signal can be significantly reduced at second harmonic band, whereas the harmonic amplitude from contrast agents shows negligible change with the selection of transmit phase. Consequently, about 5-dB CTR improvement can be achieved from effective reduction of tissue background amplitude in optimal transmit phasing.     

编码谐频成像在液腔的应用探讨

目的 探讨编码谐频在液性腔的应用价值。方法 对胆囊结石、胆囊息肉、胆总管结石和占位性病变、膀胱腔内血凝块、输尿管结石及卵巢囊腺瘤等疾病59例,分别用基频和谐频两种方式成像,对腔臂界面、腔液和腔内容物按清晰程度逐项对比。结果 谐频能够消除基频成像中旁瓣伪差干扰,提高图像清晰度。结论 编码谐频能客观、有效地提高液性腔的显示能力,获得更多的诊断信息。     

Contribution of tissue harmonic imaging and frequency compound imaging in interventional breast sonography.

OBJECTIVE: The purpose of this study was to retrospectively compare conventional imaging, frequency compound imaging (CI), and tissue harmonic imaging (THI) in interventional breast sonography. METHODS: Institutional Review Board approval and patient informed consent were not required. The authors reviewed 104 sonographically guided breast procedures in 83 patients. For each biopsy, 4 images obtained with conventional imaging, frequency CI at 10 and 14 MHz (CI10 and CI14), and THI were graded independently by 2 radiologists for lesion conspicuity, needle conspicuity, lesion and needle conspicuity, and overall image quality. Frequency CI at 10 MHz, CI14, and THI were compared with conventional imaging. Different clinical scenarios (fatty versus glandular background, fine needle versus core needle, and oblique versus horizontal needle direction) were evaluated. RESULTS: Statistical analysis showed that for overall image quality, CI10 was the best setting (odds ratios [OR], 3.67 and 7.48). For lesion conspicuity, CI14 (OR, 3.55) and THI (OR, 1.77) improved lesion visibility in a fatty background, whereas THI (OR, 0.26) was very limited in a glandular background. For needle conspicuity, no setting was better than conventional, whereas THI was the least valuable setting (OR, 0.011 and 0.049). For lesion and needle conspicuity, CI10 showed significantly better results than conventional for a dense background (P = .0268 and .4028; OR, 2.435 and 1.383) with 1 reviewer, whereas THI was the least valuable setting (OR, 0.014 and 0.042). CONCLUSIONS: Conventional imaging provided the best assessment of lesion and needle conspicuity. Frequency compounding is a useful setting for dense breast and for fine-needle aspiration. Tissue harmonic imaging has a role in the visualization of a lesion against a fatty background but is of limited value in needle visualization.     

Pulse compression for finite amplitude distortion based harmonic imaging using coded waveforms

Finite amplitude distortion based harmonic imaging has been used to reduce the image quality degradation produced by tissue inhomogeneities. Such harmonic signals are significantly lower than the linear components and are possibly too low compared to the dynamic range of the imaging system. To improve signal-to-noise ratio (SNR) without exceeding regulatory limits, coded excitation is explored. In addition, pulse compression schemes suitable for finite amplitude distortion based harmonic imaging are also developed. Note that due to the differences in harmonic generation, these compression schemes are different from those proposed for harmonic imaging using contrast agents. In this paper, simulation examples of SNR improvements by up to 8.2 dB are shown and the efficacy of the compression schemes is studied. Potential sources of performance degradation are also discussed.     

Imaging parameters on third harmonic transmit phasing for tissue harmonic generation

In third harmonic (3f0) transmit phasing, transmit waveforms comprising fundamental (f0) signal and 3f0 signal are used to generate both frequency-sum and frequency-difference components for manipulation of tissue harmonic amplitude. Nevertheless, the acoustic propagation of 3f0 transmit signal suffers from more severe attenuation and phase aberration than the f0 signal and hence degrades the performance of 3f0 transmit phasing. Besides, 3f0 transmit parameters such as aperture size and signal bandwidth are also influential in 3f0 transmit phasing. In this study, extensive simulations were performed to investigate the effects of these imaging parameters. Results indicate that the harmonic enhancement and suppression in 3f0 transmit phasing are compromised when the magnitude of frequency-difference component decreases in the presence of tissue attenuation and phase aberration. To compensate for the reduced frequency-difference component, a higher 3f0 transmit amplitude can be used. When the transmit parameters are concerned, a smaller 3f0 transmit aperture can provide more axially uniform harmonic enhancement and more effective suppression of harmonic amplitude. In addition, the spectral leakage signal also interferes with tissue harmonics and degrades the efficacy of 3f0 transmit phasing. Our results suggest that, in the method of 3f0 transmit phasing, the transmit amplitude, phase and aperture size of 3f0 signal should remain adjustable for optimization of clinical performance. Besides, multipulse sequences such as pulse inversion are also favorable for leakage removal in 3f0 transmit phasing.     

Tissue harmonic imaging techniques: Physical principles and clinical applications

Tissue harmonic imaging (THI) is a new gray-scale sonographic technique that improves image clarity. Harmonics form within the insonated tissue as a consequence of nonlinear sound propagation. Imaging with endogenously formed harmonics means that the distorting layer of the body wall is traversed only once by the harmonic beam--during echo reception. Both image contrast and lateral resolution are improved in harmonic mode compared with conventional (fundamental mode) sonography. This article summarizes the physics and various implementations of harmonic imaging mode, and reviews the clinical applications that have emerged to date.     

组织谐波显像诊断肝脏病变的临床应用

目的：探讨组织谐波显像对肝脏病变的诊断价值。方法：对比分析56个肝脏病灶的基波显像和组织谐波显像结果。结果：组织谐波显像对病灶的边界和内部回声等状况的显示均明显优于基波显像,对囊性病变尤其明显。结论：组织谐波显像能明显改善图像质量,提高诊断准确性。