Conventional Harmonic Imaging Research Articles

Contrast-enhanced harmonic EUS with novel ultrasonographic contrast (Sonazoid) in the preoperative T-staging for pancreaticobiliary malignancies

Objective. Sonazoid is a new second-generation microbubble contrast for ultrasonography. In this pilot study, the diagnostic role of contrast-enhanced harmonic imaging endoscopic ultrasonography (CH-EUS) with Sonazoid was prospectively evaluated in preoperative T-staging of pancreaticobiliary malignancies. Patients and methods. Patients with suspected pancreaticobiliary malignancies underwent CH-EUS by a single examiner. After the lesions were observed carefully with conventional harmonic imaging EUS (H-EUS), CH-EUS was performed with intravenous injection of Sonazoid. A reviewer who was blinded reviewed the recordings of H-EUS and CH-EUS and assessed the T-staging. The accuracy of H-EUS and CH-EUS for T-staging was compared to the results of surgical histopathology in patients who underwent surgery. Result. Twenty-six patients underwent surgical resection and could be included in the study. The final diagnosis were pancreatic cancer in 11, bile duct cancer in 7, gallbladder cancer in 4 and ampullary cancer in 4. The overall accuracy of H-EUS and CH-EUS for T-staging were 69.2 (18/26) and 92.4% (24/26), respectively (p < 0.05). There were disagreement in six cases between H-EUS and CH-EUS. CH-EUS staged correctly in all of these six cases, whereas H-EUS misdiagnosed the depth of invasion in one case of gallbladder cancer and one case of ampullary cancer, and invasion of portal vein in two cases of pancreatic cancer and two cases of bile duct cancer. Conclusion. The depth of invasion of biliary cancer and vascular invasion of pancreatic and biliary cancer could be demonstrated more clearly with CH-EUS compared to H-EUS. CH-EUS has the potential to improve the diagnostic accuracy of preoperative T-staging of pancreaticobiliary malignancies.

Harmonic Imaging Using Multitone Nonlinear Coding

We present a new method that uses nonlinear properties of tissue to improve contrast-to-noise ratio. In our novel method, the acoustic source is activated with two tone-bursts (2.2 and 4.4 MHz), with specially designed polarization of the individual tone-burst. This new approach is called multitone nonlinear coding (MNC) because the choice of polarization of both tones (and their amplitudes), allowing optimization of the receiving properties, depends on the nonlinear properties of tissue. The calculations were done for two tone-bursts propagating in the tissue-like glossy medium with absorption of 7 Np/m · MHz. The method was experimentally verified by scanning the incident pulses propagating in soft tissue and by scanning the thread phantom immersed in water. The concept of the virtual fields was introduced to explain abilities and properties of pulse inversion and MNC and to compare the two methods. Comparison of the spatial field distribution obtained using MNC with the conventional harmonic imaging approach, in which the second harmonic is used to reconstruct the image, is presented. It was shown that, for the same peak pressure amplitude, the resulting mechanical index was about 40% lower for MNC, lateral resolution was 10% to 30% better and, what seems to be the most encouraging, the signal gain was up to eight times higher than pulse inversion. (E-mail: anowicki@ippt.gov.pl)

頸動脈プラーク病変における新生血管について―新画像法から―

Carotid artery stenosis should be discussed in relation to its frequency or after NASCET, ECST and ACAS surveys. We normally examine a patient's stenotic frequency through the narrow directions of angiography. It is possible that such evaluation is insufficient. The importance of the futures of a carotid artery wall, which is largely studied through ultrasound sonography, is well understood. The presence of ulceration, the surface condition and sonographic intensity of the plaque are routinely examined, but we focused on the existence of neovascularization in plaques, one of the pathological factors leading to plaque hemorrhage and rupture. This pathological process appears to be responsible for carotid artery stenosis, occlusion and artery-to-artery embolisms. Harmonic image is a contrast specific imaging modality that males use of the nonlinear properties of ultrasound contrast agents by transmitting at the fundamental frequency and receiving at multiples of these frequencies. Pulse inversion harmonic image (PIHI), using pulse inversion to eliminate and strengthen the harmonic frequency, is more effective than conventional harmonic imaging. We can detect a tissue perfusion by contrast sonographic imaging with PIHI. This method has already been reported on the clinical fields, e.g. in imaging cardiac infarction, liver tumors, brain tumors and cerebrovascular diseases. There are 2 routes of vascular wall feeding: diffusion through the endothelium, and diffusion through the vasa vasorum from the adventitious to the outer part of the medium. There is no neovascularization at the inner side of the carotid artery, but some plaques are associated with neovascularization in themselves, so an attempt was made to detect such plaques by the intermittent and real time contrast sonographic imaging method with PIHI. The evaluation of neovascularization by the intermittent method and its classification as Type I to IV, according to the distribution of neovascular vessels in the plaque, have already been reported. The real time contrast sonographic imaging method with PIHI has revealed some characteristics of neovascularization: 1. The newly formed vessels from the advantitia are larger than the ones from the endothelium. 2. There is some anastomosis between the neovasculatures. 3. The distribution of neovascular vessels is concentrated in an inner part of plaque. In addition, these vessels run in a spiral pattern. 4. Neovascular circulation is related to the pulsation of the carotid artery. 5. It seems that many newly formed vessels sprout from the endothelium.

Corona enhancement in ultrasonographical post-vascular phase images with microbubble contrast agent: A novel specific sign for hepatocellular carcinomas

In 1.5 Harmonic Imaging ultrasonography (1.5 HI US), images are obtained in a band intermediate between the fundamental and 2nd harmonic components, resulting in stronger contrast enhancement than in conventional harmonic imaging. We attempted to assess the hemodynamics of hepatocellular carcinomas (HCC) with special attention to blood drainage using 1.5 HI US. Forty-two HCC nodules, metastatic liver tumors and hepatic hemangiomas were studied. In contrast studies, intermittent ultrasound transmission was performed for a period of up to 45 sec after the injection of contrast agent, which was regarded as the vascular phase. The time point of 5 min later was specified as the post-vascular phase, and images were obtained by single manual transmission for comparison of contrast enhancement with surrounding hepatic parenchyma. In addition, histological examination was performed. 1.5 HI US clearly demonstrated the strong tumor vessels in most HCCs. Corona enhancement, in which the areas surrounding the tumor are enhanced, was observed in 71.4% (30/42) of HCC nodules during the post-vascular phase. This sign was not observed in any other tumors. Histological findings revealed that CD34-positive-endothelial cells were prominent in the surrounding area of HCC. In conclusion, 1.5 HI US is an effective tool for evaluating hemodynamics in both early- and post-vascular phase. Corona enhancement may be due to the trapping of contrast agent in the endothelial cells in the surround of HCC nodules and be a novel specific sign for HCC.

The Relationship between Subharmonic Generation and Quantity of Bubbles

Harmonic imaging is a prosperous technique to obtain a high quality ultrasonic image using harmonics in echoes from microbubbles, i.e., the collapse of microbubbles and subsequent harmonic emission are used for some imaging techniques, such as flash echo imaging. The mechanism of subharmonic generation is not figured out enough however it is considered that there are some relationships between the resonance and collapse of microbubble. On the other hand, subharmonic in echoes from microbubbles is expected to obtain higher contrast between tissue and blood flow than conventional harmonic imaging because it can be hardly detected from tissue. We observed echo signals and images of microbubbles through a microscope simultaneously and investigated the relationship between time-variation of each harmonics component and bubble's behavior. Our results showed clear inverse correlation between decrease of number of bubbles and subharmonic generation.

頚動脈狭窄病変における新生血管の意義―Ｐｕｌｓｅ Ｉｎｖｅｒｓｉｏｎ Ｈａｒｍｏｎｉｃ Ｉｍａｇｉｎｇ法の下で超音波造影剤を使用―

The incidence of carotid artery stenosis is debatable based upon the findings of the NASCET, ECST and ACAS reports. We generally determine the incidence of stenosis in patients through the limited directions by angiographic methods. However, there are likely some shortcomings of this evaluation procedure with the pathogenesis of carotid artery stenosis. The importance of the carotid artery wall has recently been established. In general, these characteristics can be examined using ultrasound sonography. While the degree of ulceration, endothelial condition, lipid pool, thin cap and plaque intensity can ordinarily be examined, we are especially attempting to detect the existence of neovascularization in plaque. The importance of neovascularization in atherosclerosis has been recognized. Neovascularization is one of the pathological factors introducing plaque hemorrhage and rupture, which can result in carotid artery occlusion and artery-to-artery embolism. Pulse inversion harmonic image (PIHI) using pulse inversion to eliminate and strengthen the harmonic frequency is more effective than conventional harmonic imaging. We can detect a tissue perfusion by contrast sonographic imaging with PIHI, and its clinical application has already been reported. Consequently, we use this method to test for cardiac infarction, liver tumor, brain tumor and cerebrovascular diseases. We examined carotid artery wall perfusion (CAWP) and the rule of neovascularization within the plaque by this method. The routes of vascular wall feeding are as follows: 1) Luminal diffusion feeds the vascular wall from the endothelium to the inner part of the medium and 2) the vasa vasorum feeds it from the adventitia to the outer part of the medium. Consequently, neovascularization does not occur at the former vascular wall region. However, some plaque is resistant to neovascularization. As a result, we attempt to detect plaque using this method, and we have already described a classification of CAWP findings. Type I exhibits no perfusion and lack of neovascularization. Type II exhibits partial perfusion of CAWP that is indicative of mild neovascularization. Type III exhibits multiple perfusion of CAWP that is indicative of moderate neovascularization. Type IV exhibits general perfusion of CAWP that is indicative of neovascularization of the whole plaque. Type III and IV are usually observed in patients with intramural hemorrhage or artery-to-artery embolism. We propose the following mechanism for plaque development. The beginning of atherosclerosis→in some, neovascularization on the plaque development→The small neovasculature is vulnerable. Consequently, damage can occur by mechanical stimulation→then intramural hemorrhage can occur→resulting in the onset of ischemic symptoms as the development of stenosis or embolism. We intend to examine the incidence of carotid artery stenosis with or without neovascularization and carefully observe such patients because of the rapid development of plaque, plaque rupture, occlusion of main extracranial arteries and artery-to-artery embolism.

Improved myocardial contrast with second harmonic transient ultrasound response imaging in humans using intravenous perfluorocarbon-exposed sonicated dextrose albumin

Objectives. The objectives of this study were to determine whether a new method of ultrasound imaging (transient response imaging) could improve the myocardial contrast after intravenous injections of perfluorocarbon-exposed sonicated dextrose albumin microbubble contrast medium in humans.Background. We have shown in animals that very low doses of intravenous contrast medium can produce transient but significantly better myocardial contrast when diagnostic ultrasound pulses are interrupted (delivered only once per cardiac cycle) instead of conventional 25- to 30-Hz frame rate imaging.Methods. In 14 patients with normal rest wall motion, the peak myocardial contrast produced by transient response imaging was compared with that produced by conventional harmonic ultrasound imaging after injections of low doses (0.0025 to 0.01 ml/kg) of intravenous contrast medium. All studies were performed with second harmonic imaging (2.0 to 2.5 MHz-transmitted frequency). Blood pressure, oxygen saturation, respiratory rate and pulse were monitored before and after each injection.Results. The intravenous contrast medium in the doses given produced no hemodynamic changes and no significant side effects in any patients. Overall, the mean (± SD) anterior and posterior myocardial contrast produced was significantly greater with transient response imaging than with conventional harmonic ultrasound imaging (anterior: 37 ± 20 U transient response imaging vs. 18 ± 14 U conventional harmonic imaging, posterior: 17 ± 14 U transient response imaging vs. 5 ± 5 U conventional; p < 0.01). With the sample size of 14 patients, the study had 80% power to detect a tree difference of 18 U for anterior myocardial contrast and 90% power to detect a difference of 12 U for posterior contrast. Visually evident anterior or apical myocardial contrast was observed in 14 of 15 patients with transient response imaging but in only 7 patients with conventional harmonic imaging. Posterior or basal myocardial contrast was evident in 10 patients with transient response imaging but in only 1 patient with conventional harmonic imaging.Conclusions. Transient response imaging produces significantly better myocardial contrast than conventional harmonic imaging in humans and can be produced safely with minute quantities of intravenous perfluorocarbon.