Myocardial perfusion imaging with contrast echocardiography

Contrast-enhanced ultrasonography of maternal and fetal blood flows in pregnant bitches

We evaluated the potential usefulness of CEUS to assess fetal-maternal circulation during pregnancy in dogs. Nine bitches were examined at 23, 30, and 45 days of gestation using an ultrasound machine (LOGIQ E9) and SonoVue^® contrast media as echo-signal enhancer. Qualitative and quantitative evaluation of contrast enhancement patterns of uterine artery and utero/placental vessels were performed on recorded images. Independently of the gestational periods, the qualitative evaluation showed the initial wash-in phase from the first appearance of the uterine artery to the rapid distribution in embryonic vesicles or placenta to the progressive washout, whilst there was no enhancement of either embryos or fetuses in any bitch. Independent of gestational age, parameters derived from quantitative analysis of time intensity-curves of contrast enhancement (peak intensity, time to peak, rise time, washout) did not vary between proximal placenta, distal placenta, and uterine artery. With the progression of gestation, AUC values did not change in both proximal and distal placenta, but in the uterine artery it was lower (P ≤ 0.05) at day 30 than at day 23 (464.8 ± 16.1 vs.596.4 ± 28.1, respectively). In conclusion, CEUS appears to safely permit evaluation of the maternal and fetal vessels in the first two third of gestation, without any clinically relevant adverse effects. Further studies in a larger number of bitches in different stages of pregnancy are needed to establish standard parameters for normal pregnancies that can be used to detect abnormalities of pregnancy.

Cardiac Imaging in the Diagnosis of Coronary Artery Disease

Coronary artery disease (CAD) continues to be a leading cause of morbidity and mortality worldwide. Although invasive coronary angiography has previously been the gold standard in establishing the diagnosis of CAD, there is a growing shift to more appropriately use the cardiac catheterization laboratory to perform interventional procedures once a diagnosis of CAD has been established by noninvasive imaging modalities rather than using it primarily as a diagnostic facility to confirm or refute CAD. With ongoing technological advancements, noninvasive imaging plays a pre-eminent role in not only diagnosing CAD but also informing the choice of appropriate therapies, establishing prognosis, all while containing costs and providing value-based care. Multiple imaging modalities are available to evaluate patients suspected of having coronary ischemia, such as stress electrocardiography, stress echocardiography, single-photon emission computed tomography myocardial perfusion imaging, positron emission tomography, coronary computed tomography (CT) angiography, and magnetic resonance imaging. These imaging modalities can variably provide functional and anatomical delineation of coronary stenoses and help guide appropriate therapy. This review will discuss their advantages and limitations and their usage in the diagnostic pathway for patients with CAD. We also discuss newer technologies such as CT fractional flow reserve, CT angiography with perfusion, whole-heart coronary magnetic resonance angiography with perfusion, which can provide both anatomical as well as functional information in the same test, thus obviating the need for multiple diagnostic tests to obtain a comprehensive assessment of both, plaque burden and downstream ischemia. Recognizing that clinicians have a multitude of tests to choose from, we provide an underpinning of the principles of ischemia detection by these various modalities, focusing on anatomy vs physiology, the database justifying their use, their prognostic capabilities and lastly, their appropriate and judicious use in this era of patient-centered, cost-effective imaging.

Comparison of Uterine Receptivity between Fertile and Unexplained Infertile Women by Assessment of Endometrial and Subendometrial Perfusion Using Contrast-Enhanced Ultrasound: Which Index is Better--Peak Intensity or Area under the Curve?

The goal of this study was to compare uterine receptivity between women with normal fertility and those with unexplained infertility during natural cycles by assessment of endometrial and subendometrial perfusion using contrast-enhanced ultrasound (CEUS). We wanted to determine the better index: peak intensity (PI) or area under the curve (AUC). Thirty women with unexplained infertility were recruited into the study group, and 30 women with normal fertility were recruited into the control group. All women underwent CEUS during the late proliferative phase, ovulation phase, and implantation window of a menstrual cycle. Endometrial PI, endometrial AUC, subendometrial PI and subendometrial AUC were analyzed. In the late proliferative phase, the control group had a significantly higher endometrial PI (p < 0.001) as well as subendometrial PI (p < 0.001) and AUC (p = 0.004) than the study group. In the ovulation phase, the control group had a significantly higher endometrial PI (p < 0.001) and AUC (p = 0.021), as well as subendometrial PI (p < 0.001) and AUC (p = 0.003). During the implantation window, there were no significant differences between the two groups. Only subendometrial PI underwent a significant periodic change during the menstrual cycle in both groups. This finding was further confirmed by evaluation of the microvessel density of endometria. In conclusion, CEUS can be used to assess endometrial and subendometrial perfusion to evaluate uterine receptivity. Subendometrial PI was the most sensitive index compared with endometrial PI, endometrial AUC and subendometrial AUC.

Real-time placental perfusion on contrast-enhanced ultrasound and parametric imaging analysis in rats at different gestation time and different portions of placenta

Objectives

To quantitatively analyze placental perfusion in a rat model at different gestation time and different portions of placenta by real-time contrast-enhanced ultrasound (CEUS) and parametric imaging analysis.

Materials and Methods

Sixty pregnant rats at different gestation time (15 dys,17 days and 20 days) were injected intravenously with microbubbles (5×10⁵ microbubbles /ml, 1.0 ml/kg), and cadence contrast pulse sequencing (transmission frequency of 7 MHz, mechanical index 0.18) was performed. Dynamic enhancement changes in placenta at different gestation time and different portions of placenta were measured and enhancement parameters analyzed with software. Correlation between enhancement parameters and average area densities of placenta vascular compartment was compared.

Results

The pattern and real-time sequence of enhancement in uterus and placenta were clearly depicted by CEUS. The time-to-peak enhancement was earlier in central portion than that in peripheral portion (12.30±6.33s vs 36.26±10.65 s, p = 0.005), and peak intensity of enhancement is much higher in central portion than that in peripheral portion (30.20±2.85 dB vs 20.95±6.25 dB, p = 0.000). The peak intensity of enhancement at day 15 (27.70±4.47 dB) was lower than that at day 17 (30.20±2.85 dB, p = 0.042) and at day 20 (31.85±4.41 dB, p = 0.015) of gestation. Significant correlation between average area densities of vascular compartment and the peak intensity of enhancement was identified in placenta at different gestation time (p<0.05). The average area densities of vascular compartment was higher in central portion than that in peripheral portion and has significant correlation with peak intensity of enhancement of the two potions (p<0.01).

Conclusion

CEUS is feasible to depict real-time sequence and quantitative parameters of perfusion in different portion of placenta at different gestational time in a rat model.

Comparison and evaluation of indicator dilution models for bolus of ultrasound contrast agents

Dynamic contrast-enhanced ultrasound (DCE-US) imaging is a promising diagnostic method, which enables the evaluation of tissue perfusion via different parameters. The mean transit time and time-to-peak parameters are the main time parameters and their values depend on the model used for the approximation of the noisy perfusion curves. In this paper, we described a new comparison of different perfusion models using a tissue mimicking phantom. The following models were compared: log-normal, lagged, Erlang, Gamma and the local density random walk model. We discovered that the mean-square error is not the best criterion for model evaluation. More important is the comparison between the estimated time perfusion parameters and the physical parameters of the developed tissue mimicking phantom. Based on the statistical analysis, we can suggest that for the DCE-US perfusion analysis more models should be used, excluding the log-normal model, which gives the highest error of mean transit time value.

Non-invasive imaging in coronary artery disease including anatomical and functional evaluation of ischaemia and viability assessment

Coronary artery disease has an important impact on the morbidity and mortality statistics and health economics worldwide. Diagnosis of coronary artery disease is important in risk stratification and guides further management. Invasive coronary angiography is the traditional method of imaging the coronary arteries and remains the gold standard. It detects luminal stenosis but provides little information about the vessel wall or plaques. Besides, not all anatomical lesions are functionally significant. This has lent itself to a wide variety of imaging techniques to identify and assess a flow-limiting stenosis. The approach to diagnosis of coronary artery disease is broadly based on anatomical and functional imaging. Coronary CT and MRI of coronary arteries provide an anatomical assessment of coronary stenosis. Coronary calcium score and coronary CT assess subclinical atherosclerosis by assessing the atherosclerotic plaque burden. The haemodynamic significance of a coronary artery stenosis can be assessed by stress radioisotope studies, stress echocardiography and stress MRI. The more recent literature also focuses on plaque assessment and identification of plaques that are likely to give rise to an acute coronary syndrome. There is an explosion of literature on the merits and limitations of the different imaging modalities. This review article will provide an overview of all the imaging modalities in the diagnosis of coronary artery disease.

Mapping microvasculature with acoustic angiography yields quantifiable differences between healthy and tumor-bearing tissue volumes in a rodent model

PURPOSE

To determine if the morphologies of microvessels could be extracted from contrast material-enhanced acoustic angiographic ultrasonographic (US) images and used as a quantitative basis for distinguishing healthy from diseased tissue.

MATERIALS AND METHODS

All studies were institutional animal care and use committee approved. Three-dimensional contrast-enhanced acoustic angiographic images were acquired in both healthy (n = 7) and tumor-bearing (n = 10) rats. High-spatial-resolution and high signal-to-noise acquisition was enabled by using a prototype dual-frequency US transducer (transmit at 4 MHz, receive at 30 MHz). A segmentation algorithm was utilized to extract microvessel structure from image data, and the distance metric (DM) and the sum of angles metric (SOAM), designed to distinguish different types of tortuosity, were applied to image data. The vessel populations extracted from tumor-bearing tissue volumes were compared against vessels extracted from tissue volumes in the same anatomic location within healthy control animals by using the two-sided Student t test.

RESULTS

Metrics of microvascular tortuosity were significantly higher in the tumor population. The average DM of the tumor population (1.34 ± 0.40 [standard deviation]) was 23.76% higher than that of the control population (1.08 ± 0.08) (P < .0001), while the average SOAM (22.53 ± 7.82) was 50.73% higher than that of the control population (14.95 ± 4.83) (P < .0001). The DM and SOAM metrics for the control and tumor populations were significantly different when all vessels were pooled between the two animal populations. In addition, each animal in the tumor population had significantly different DM and SOAM metrics relative to the control population (P < .05 for all; P value ranges for DM, 3.89 × 10(-)(7) to 5.63 × 10(-)(3); and those for SOAM, 2.42 × 10(-)(12) to 1.57 × 10(-)(3)).

CONCLUSION

Vascular network quantification by using high-spatial-resolution acoustic angiographic images is feasible. Data suggest that the angiogenic processes associated with tumor development in the models studied result in higher instances of vessel tortuosity near the tumor site.

Retrograde perfusion and filling of mouse coronary vasculature as preparation for micro computed tomography imaging

Visualization of the vasculature is becoming increasingly important for understanding many different disease states. While several techniques exist for imaging vasculature, few are able to visualize the vascular network as a whole while extending to a resolution that includes the smaller vessels. Additionally, many vascular casting techniques destroy the surrounding tissue, preventing further analysis of the sample. One method which circumvents these issues is micro-Computed Tomography (μCT). μCT imaging can scan at resolutions <10 microns, is capable of producing 3D reconstructions of the vascular network, and leaves the tissue intact for subsequent analysis (e.g., histology and morphometry). However, imaging vessels by ex vivo μCT methods requires that the vessels be filled with a radiopaque compound. As such, the accurate representation of vasculature produced by μCT imaging is contingent upon reliable and complete filling of the vessels. In this protocol, we describe a technique for filling mouse coronary vessels in preparation for μCT imaging. Two predominate techniques exist for filling the coronary vasculature: in vivo via cannulation and retrograde perfusion of the aorta (or a branch off the aortic arch), or ex vivo via a Langendorff perfusion system. Here we describe an in vivo aortic cannulation method which has been specifically designed to ensure filling of all vessels. We use a low viscosity radiopaque compound called Microfil which can perfuse through the smallest vessels to fill all the capillaries, as well as both the arterial and venous sides of the vascular network. Vessels are perfused with buffer using a pressurized perfusion system, and then filled with Microfil. To ensure that Microfil fills the small higher resistance vessels, we ligate the large branches emanating from the aorta, which diverts the Microfil into the coronaries. Once filling is complete, to prevent the elastic nature of cardiac tissue from squeezing Microfil out of some vessels, we ligate accessible major vascular exit points immediately after filling. Therefore, our technique is optimized for complete filling and maximum retention of the filling agent, enabling visualization of the complete coronary vascular network--arteries, capillaries, and veins alike.

A pilot study to assess markers of renal damage in the rodent kidney after exposure to 7 MHz ultrasound pulse sequences designed to cause microbubble translation and disruption

Acoustic radiation force has been proposed as a mechanism to enhance microbubble concentration for therapeutic and molecular imaging applications. It is hypothesized that once microbubbles are localized, bursting them with acoustic pressure could result in local drug delivery. It is known that low-frequency, high-amplitude acoustic energy combined with cavitation nuclei can result in bioeffects. However, little is known about the bioeffects potential of acoustic parameters involved in radiation force and microbubble destruction pulse sequences applied at higher frequencies. In this pilot study, rat kidneys are exposed to high-duty cycle, low-amplitude pulse sequences known to cause substantial bubble translation due to radiation force, as well as high-amplitude short pulse sequences known to cause microbubble destruction. Both studies are performed at 7 MHz on a clinical ultrasound system, and implemented in three-dimensions (3-D) for entire kidney exposure. Analysis of biomarkers of renal injury and renal histopathology indicate that there was no significant renal damage due to these ultrasound parameters in conjunction with microbubbles within the study group.

Microvascular coronary dysfunction in women: pathophysiology, diagnosis, and management

Women exhibit a greater symptom burden, more functional disability, and a higher prevalence of no obstructive coronary artery disease compared to men when evaluated for signs and symptoms of myocardial ischemia. Microvascular coronary dysfunction (MCD), defined as limited coronary flow reserve and/or coronary endothelial dysfunction, is the predominant etiologic mechanism of ischemia in women with the triad of persistent chest pain, no obstructive coronary artery disease, and ischemia evidenced by stress testing. Evidence shows that approximately 50% of these patients have physiological evidence of MCD. MCD is associated with a 2.5% annual major adverse event rate that includes death, nonfatal myocardial infarction, nonfatal stroke, and congestive heart failure. Although tests such as adenosine stress cardiac magnetic resonance imaging may be a useful noninvasive method to predict subendocardial ischemia, the gold standard test to diagnose MCD is an invasive coronary reactivity testing. Early identification of MCD by coronary reactivity testing may be beneficial in prognostication and stratifying these patients for optimal medical therapy. Currently, understanding of MCD pathophysiology can be used to guide diagnosis and therapy. Continued research in MCD is needed to further advance our understanding.