Contrast Pulse Sequencing Research Articles

Ferumoxytol-Enhanced 5D Multiphase Steady-State Imaging Using Rotating Cartesian K-Space With Low-Rank Reconstruction for Pediatric Congenital Heart Disease.

The rotating Cartesian k-space multiphase steady-state imaging with contrast (ROCK-MUSIC) pulse sequence enables acquisition of whole-heart, cardiac phase-resolved images in pediatric congenital heart disease (CHD) without reliance on the ventilator gating signal. Multidimensional reconstruction with low rank tensor (LRT) has shown promise for resolving complex cardiorespiratory motion. To enhance ROCK-MUSIC by resolving cardiorespiratory phases using LRT reconstruction and to enable semi-automatic hyperparameter tuning by developing an image quality scoring model. Retrospective. Thirty patients (45% female, age 2 days to 6.7 years) with CHD. 3-T, four-dimensional (4D) spoiled gradient recalled echo sequence. Eigenvector-based iTerative Self-consistent Parallel Imaging Reconstruction (ESPIRiT) served as the reference comparison for LRT reconstruction. A 4-point Likert scale was used for cardiac and vascular image quality scoring based on cardiac chamber definition, lumen signal uniformity, vascular margin clarity, and motion artifact. Ejection fraction and ventricular volumes were assessed in 16 patients. Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and edge sharpness were computed. Intraclass correlation coefficients, Wilcoxon signed-rank test, Bland-Altman. A P-value <0.05 was considered statistically significant. Relative to ESPIRiT, LRT images received significantly higher cardiac (2.81 ± 0.57 vs. 3.19 ± 0.54) and vascular (2.81 ± 0.60 vs. 3.36 ± 0.53) image quality scores. Image quality scoring with semi-automated hyperparameter tuning showed strong correlations (R2 = 0.748) among image quality, SNR, and septal sharpness. Comparison of ejection fraction and volumetry derived from ESPIRiT, and LRT showed no significant systematic difference (P = 0.32). Integration of low-rank reconstruction with ROCK-MUSIC acquisition may be feasible, and semi-automatic hyperparameter tuning could be effective for generating cardiorespiratory resolved images. 2 TECHNICAL EFFICACY: Stage 1.

Nonlinear simulation for contrast ultrasound imaging.

Contrast ultrasound (CUS) has received much interest because of its sensitivity enhancement for blood flow imaging. However, there is still a lack of nonlinear simulation method for CUS, as conventional simulators cannot deal with the microbubble acoustic nonlinearity. In this paper, a nonlinear simulation method of CUS is developed based on a combination strategy of the k-space pseudospectral method and Rayleigh-Plesset Marmottant model. Different contrast pulse sequence strategies as well as the radial modulation imaging are simulated and compared using the proposed method. For blood flow imaging, simulations under different scenarios such as power Doppler and ultrasound localization microscopy are also carried out. Furthermore, a face-to-face comparison is performed between simulations and phantom experiments to validate the proposed method.

Modulating Nonlinear Acoustic Response of Phospholipid-Coated Microbubbles with pH for Ultrasound Imaging.

Activatable microbubble contrast agents for contrast-enhanced ultrasound have a potential role for measuring physiologic and pathologic states in deep tissues, including tumor acidosis. In this study, we describe a novel observation of increased harmonic oscillation of phosphatidylcholine microbubbles (PC-MBs) in response to lower ambient pH using a clinical ultrasound scanner. MB echogenicity and nonlinear echoes were monitored at neutral and acidic pH using B-mode and Cadence contrast pulse sequencing (CPS), a harmonic imaging technique at 7.0 and 1.5 MHz. A 3-fold increase in harmonic signal intensity was observed when the pH of PC-MB suspensions was decreased from 7.4 to 5.5 to mimic normal and pathophysiological levels that can be encountered in vivo. This pH-mediated activation is tunable based on the chemical structure and length of phospholipids composing the MB shell. It is also reliant on the presence of phosphate groups, as the use of lipids without phosphate instead of phospholipids completely abrogated this phenomenon. The increased harmonic signal likely is the result of increased MB oscillation caused by a decrease of the interfacial tension induced at a lower pH, altering the lipid conformation. While relative signal changes are interpreted clinically as mostly related to blood flow, pH effects could be significant contributors, particularly when imaging tumors. While our observation can be used clinically, it requires further research to isolate the effect of pH from other variables. These findings could pave the way toward for the development of new smart ultrasound contrast agents that expand the clinical utility of contrast-enhanced ultrasound.

Cardiovascular magnetic resonance imaging for sequential assessment of cardiac fibrosis in mice: technical advancements and reverse translation.

Cardiovascular magnetic resonance (CMR) imaging has become an essential technique for the assessment of cardiac function and morphology, and is now routinely used to monitor disease progression and intervention efficacy in the clinic. Cardiac fibrosis is a common characteristic of numerous cardiovascular diseases and often precedes cardiac dysfunction and heart failure. Hence, the detection of cardiac fibrosis is important for both early diagnosis and the provision of guidance for interventions/therapies. Experimental mouse models with genetically and/or surgically induced disease have been widely used to understand mechanisms underlying cardiac fibrosis and to assess new treatment strategies. Improving the appropriate applications of CMR to mouse studies of cardiac fibrosis has the potential to generate new knowledge, and more accurately examine the safety and efficacy of antifibrotic therapies. In this review, we provide 1) a brief overview of different types of cardiac fibrosis, 2) general background on magnetic resonance imaging (MRI), 3) a summary of different CMR techniques used in mice for the assessment of cardiac fibrosis including experimental and technical considerations (contrast agents and pulse sequences), and 4) provide an overview of mouse studies that have serially monitored cardiac fibrosis during disease progression and/or therapeutic interventions. Clinically established CMR protocols have advanced mouse CMR for the detection of cardiac fibrosis, and there is hope that discovery studies in mice will identify new antifibrotic therapies for patients, highlighting the value of both reverse translation and bench-to-bedside research.

Numerical simulation method of nonlinear contrast-enhanced ultrasound imaging

&lt;sec&gt;Contrast-enhanced ultrasound imaging (CEUS) based on the acoustic nonlinearity of ultrasonic microbubble has received great attention in recent years. Compared with conventional linear ultrasound imaging, nonlinear CEUS can further improve the imaging resolution while overcoming the challenge of clutter filtering. Simulation, acting as an effective tool for research on new mechanisms and technologies of ultrasound imaging, has been a long-term focus of computational acoustics. In the community of biomedical ultrasound, common sound field simulation tools are mainly based on finite element method (FEM), analytical method, &lt;i&gt;k&lt;/i&gt;-space pseudospectral method and finite-difference time-domain method (FDTD), which are relatively mature solutions for simulating the nonlinear characteristics of tissue. However, it is still not trivial to simulate nonlinear CEUS by using the prevailing methods, as the nonlinearity of microbubble is often not considered.&lt;/sec&gt;&lt;sec&gt;In this paper, we propose a simulation method of nonlinear CEUS imaging that successfully combines the microbubble nonlinearity and classic &lt;i&gt;k&lt;/i&gt;-space pseudospectral method. Specifically, forced oscillation response of the microbubble is computed based on the modified Rayleigh-Plesset equation and such a nonlinear response is further dealt as an additional source for analyzing the nonlinear component propagation and CEUS imaging. To investigate the performance of the proposed method, B-mode images of single microbubble and clustered microbubbles are simulated based on plane wave imaging. The plane wave based CEUS imaging can thus be carried out with different compounding angles and different contrast pulse sequencing (CPS) strategies (pulse inversion, amplitude modulation, pulse inversion &amp; amplitude modulation, and probe element alternation). Different soft-tissue and mechanical parameters of the microbubble can be adjusted by using the proposed nonlinear simulation strategy, thus providing efficient solution for CEUS simulation. Such a method can evaluate the performances of different CPS strategies, and further contribute to the CEUS development.&lt;/sec&gt;

Ovarian contrast-enhanced ultrasonography and Doppler fluxometry in bitches during the postovulatory estrus and corpora lutea formation

The aim of the present study was to evaluate the vascularization features of canine ovaries during the follicular phase and the formation of the corpora lutea by using Doppler ultrasonography and Contrast-Enhanced Ultrasound (CEUS). Eight healthy bitches were enrolled in the study and were evaluated at five different timepoints (T1 – T5) of the estrous cycle established by vaginal cytology and serum progesterone concentration. Ultrasonographic examinations were performed by a single operator using the ACUSON S2000/SIEMENS machine equipped with a linear multifrequency transducer (9.0 MHz). Color-coded Doppler evaluation of the ovarian parenchyma was performed to investigate the aspects of the signal detection throughout the different timepoints. Pulsed-wave Doppler of the intraovarian arteries was performed to evaluate spectral waveform and doppler velocimetric parameters of Systolic Peak Velocity (SPV cm/s), End Diastolic Velocity (EDV cm/s), Resistivity Index (RI) and Pulsatility Index (PI). CEUS evaluation of the ovaries was performed using a vascular contrast agent (SonoVue®, Bracco, Sao Paulo, Brazil) and the CADENCE™ Contrast Pulse Sequencing (CPS, Siemens) software, in order to perform both qualitative and quantitative analysis. Perfusion parameters of pixel number, peak intensity (PPI in %), time to peak intensity (TTP in s), mean transit time (MTT in s) and area under the curve (AUC in %). Colour-coded Doppler evaluation demonstrated an increase in signal detection as cycle progressed, with blood flow initially detected with few coloured pixels and mainly at the ventral surface of the ovaries. Further on, the number of coloured pixels increased and spreading to the central region, resulting in a circular-like pattern around the corpora hemorrhagica. The spectral waveform was consistent at all timepoints. SPV (cm/s) and EDV (cm/s) presented a numeric trend and a slight statistical difference at all timepoints, whereas no difference was found for RI and PI. CEUS evaluation demonstrated an increase in pixel intensity across all the timepoints. Quantitative CEUS analysis revealed a statistical difference in PPI (%), MTT (s) and AUC (%) at T5. CEUS evaluation of the ovaries was feasible and demonstrated a marked increase in perfusion parameters in the late postovulatory period, demonstrating its applicability in the assessment of canine corpora lutea development.

Contrast-enhanced ultrasound to detect active bleeding

Non-compressible internal hemorrhage (NCIH) is the most common cause of death in acute non-penetrating trauma. NCIH management requires accurate hematoma localization and evaluation for ongoing bleeding for risk stratification. The current standard point-of-care diagnostic tool, the focused assessment with sonography for trauma (FAST), detects free fluid in body cavities with conventional B-mode imaging. The FAST does not assess whether bleeding is ongoing, at which location(s), and to what extent. Here, we propose contrast-enhanced ultrasound (CEUS) techniques to better identify, localize, and quantify hemorrhage. We designed and fabricated a custom hemorrhage-mimicking phantom, comprising a perforated vessel and cavity to simulate active bleeding. Lumason contrast agents (UCAs) were introduced at clinically relevant concentrations (3.5×108 bubbles/ml). Conventional and contrast pulse sequence images were captured, and post-processed with bubble localization techniques (SVD clutter filter and bubble localization). The results showed contrast pulse sequences enabled a 2.2-fold increase in the number of microbubbles detected compared with conventional CEUS imaging, over a range of flow rates, concentrations, and localization processing parameters. Additionally, particle velocimetry enabled mapping of dynamic flow within the simulated bleeding site. Our findings indicate that CEUS combined with advanced image processing may enhance visualization of hemodynamics and improve non-invasive, real-time detection of active bleeding.

Calibration of concomitant field offsets using phase contrast MRI for asymmetric gradient coils.

Asymmetric gradient coils introduce zeroth- and first-order concomitant field terms, in addition to higher-order terms common to both asymmetric and symmetric gradients. Salient to compensation strategies is the accurate calibration of the concomitant field spatial offset parameters for asymmetric coils. A method that allows for one-time calibration of the offset parameters is described. A modified phase contrast pulse sequence with single-sided bipolar flow encoding is proposed to calibrate the offsets for asymmetric, transverse gradient coils. By fitting the measured phase offsets to different gradient amplitudes, the spatial offsets were calculated by fitting the phase variation. This was used for calibrating real-time pre-emphasis compensation of the zeroth- and first-order concomitant fields. Image quality improvement with the proposed corrections was demonstrated in phantom and healthy volunteers with non-Cartesian and Cartesian trajectory acquisitions. Concomitant field compensation using the calibrated offsets resulted in a residual phase error &lt;3% at the highest gradient amplitude and demonstrated substantial reduction of image blur and slice position/selection artifacts. The proposed implementation provides an accurate method for calibrating spatial offsets that can be used for real-time concomitant field compensation of zeroth and first-order terms, substantially reducing artifacts without retrospective correction or sequence specific waveform modifications.

Evaluation of Nonlinear Contrast Pulse Sequencing for Use in Super-Resolution Ultrasound Imaging.

The use of super-resolution ultrasound (SR-US) imaging greatly improves visualization of microvascular structures, but clinical adoption is limited by long imaging times. This method depends on detecting and localizing isolated microbubbles (MBs), forcing the use of a dilute contrast agent concentration. Contrast-enhanced ultrasound (CEUS) image acquisition times as long as minutes arise as the localization of thousands of MBs are acquired to form a complete SR-US image. In this article, we explore the use of nonlinear CEUS strategies using nonlinear fundamental contrast pulse sequencing (CPS) to increase the contrast-to-tissue ratio (CTR) and compare MB detection effectiveness to linear B-mode CEUS imaging. The CPS compositions of amplitude modulation (AM), pulse inversion (PI), and a combination of the two (AMPI) were studied. A simulation study combined the Rayleigh-Plesset-Marmottant (RPM) model of MB characteristics and a nonlinear tissue model using the k-Wave toolbox for MATLAB (MathWorks Inc., Natick, MA, USA). Validation was conducted using an in vitro flow phantom and in vivo in the rat hind-limb. Imaging was performed with a programmable US scanner (Vantage 256, Verasonics Inc., Kirkland, WA, USA) and customized to transmit a set of basis US pulses from which both B-mode US (frame rate (FR) of 800 Hz) and multiple nonlinear CPS compositions (FR of 200 Hz) could be assessed from identical in vitro and in vivo datasets using a near simultaneous method. The simulations suggest that MB characteristics, such as diameter and motion, help to predict which US imaging strategy will enhance MB detection. The in vitro and in vivo US imaging studies revealed that different subpopulations of polydisperse MB contrast agents were detected by linear imaging and by each different nonlinear CPS composition. The most effective single imaging strategy at a 200-Hz FR was found to be B-mode US imaging. However, a combination of B-mode US imaging with a nonlinear CPS imaging strategy was more effective in detecting MBs in vivo at all depths and was shown to shorten image acquisition time by an average of 33.3%-76.7% when combining one or more CPS sequences.

Faster super-resolution ultrasound imaging with a deep learning model for tissue decluttering and contrast agent localization

Super-resolution ultrasound (SR-US) imaging allows visualization of microvascular structures as small as tens of micrometers in diameter. However, use in the clinical setting has been impeded in part by ultrasound (US) acquisition times exceeding a breath-hold and by the need for extensive offline computation. Deep learning techniques have been shown to be effective in modeling the two more computationally intensive steps of microbubble (MB) contrast agent detection and localization. Performance gains by deep networks over conventional methods are more than two orders of magnitude and in addition the networks can localize overlapping MBs. The ability to separate overlapping MBs allows use of higher contrast agent concentrations and reduces US image acquisition time. Herein we propose a fully convolutional neural network (CNN) architecture to perform the operations of MB detection as well as localization in a single model. Termed SRUSnet, the network is based on the MobileNetV3 architecture modified for 3-D input data, minimal convergence time, and high-resolution data output using a flexible regression head. Also, we propose to combine linear B-mode US imaging and nonlinear contrast pulse sequencing (CPS) which has been shown to increase MB detection and further reduce the US image acquisition time. The network was trained with in silico data and tested on in vitro data from a tissue-mimicking flow phantom, and on in vivo data from the rat hind limb (N = 3). Images were collected with a programmable US system (Vantage 256, Verasonics Inc., Kirkland, WA) using an L11–4v linear array transducer. The network exceeded 99.9% detection accuracy on in silico data. The average localization accuracy was smaller than the resolution of a pixel (i.e. ). The average processing time on a Nvidia GeForce 2080Ti GPU was 64.5 ms for a 128 × 128-pixel image.

Use of contrast-enhanced ultrasound during preoperative evaluation of endometrial carcinoma

ObjectiveTo explore the clinical role of contrast-enhanced ultrasound (CEUS) in a preoperative evaluation of early endometrial carcinoma. MethodsThis study included 14 patients who underwent preoperative CEUS and contrast-enhanced magnetic resonance imaging (CEMRI) and were ultimately diagnosed with stage I endometrial carcinoma from December 2019 to December 2020. The parameters of the time-intensity curve (TIC) were compared with the endometrial carcinoma group, the invaded myometrium group, and the normal myometrium group. ResultsTIC parameters between the endometrial carcinoma group and the invaded myometrium group were similar. Compared with the normal myometrium group, the time to peak (TTP) was significantly shorter and the ascending slope (AS) was significantly higher in the endometrial carcinoma group. The TTP of the invaded myometrium group was shorter than that of the normal myometrium group and the peak intensity (PI) was higher than that of the normal myometrium group. We then compared the TIC parameters between the endometrial carcinoma group and the invaded myometrium group after adjusting for the normal myometrium group, and the results still did not show any difference. Of the 14 cases of endometrial carcinoma, 9 cases were diagnosed by CEMRI and were consistent with the pathology results, 1 case was underestimated, and 4 cases were overestimated; while 11 cases diagnosed were diagnosed by CEUS and were consistent with the pathology results, 1 case was underestimated, and 2 cases were overestimated. ConclusionsThe contrast pulse sequencing technique used in the CEUS examinations performed well in evaluating the extent of the endometrial carcinoma. Future studies with larger sample sizes are needed to determine the applicability and value of this new procedure during preoperative assessments of early endometrial carcinoma.

On the Development of a Novel Contrast Pulse Sequence for Polymer-Shelled Microbubbles.

Contrast agents are routinely used in ultrasound examinations. Nonlinear ultrasound imaging techniques have been developed over decades to enhance the contrast between the tissue and the blood pool after the injection of ultrasound contrast agents (UCAs). In this study, we introduce a new contrast pulse sequence, CPS4. The CPS4 combines pulse inversion (PI), subharmonic (SH), and ultraharmonic (UH) techniques to remove propagation distortion while capturing the unique SH and UH responses from UCAs. The novel CPS4 and conventional PI, SH, and UH techniques were used to detect the presence of a research-grade, thick-shell, polymer microbubble in a tissue-mimicking flow phantom. The contrast-to-tissue ratios (CTRs) obtained from the applications of all techniques were compared. The results show that the highest CTR of approximately 16 dB was obtained using CPS4, which was superior to the individual reference techniques: PI, SH, and UH techniques, in all scenarios considered in this study.

Efficacy and Safety of Clinical-Grade Human Vascular Endothelial Growth Factor-DΔNΔC Gene Therapy Containing Residual Replication-Competent Adenoviruses.

Biological bypass through induced angiogenesis by vascular endothelial growth factor D (VEGF-D) gene therapy (GT) is a new concept for the treatment of cardiac ischemia. Serotype 5 adenoviruses are used in the clinical trials for transferring the VEGF-D cDNA into the ischemic myocardium. However, the presence of replication-competent vectors in the adenovirus products is a widely recognized problem that may pose a potential safety risk to the treated patients. We compared three different VEGF-D GT production lots containing different levels of replication-competent adenoviruses (RCA) tested in 3 × 1010 viral particles (vp): <10 RCA (VEGF-D L-RCA1), 10-100 RCA (VEGF-D H-RCA2), and 100-200 RCA (VEGF-D H-RCA3), as measured by a novel droplet digital polymerase chain reaction (PCR) RCA assay in a preclinical rabbit model (n = 21). β-galactosidase encoding nonclinical-grade preparation was used as a nonangiogenic control. Each preparation was injected into the right semimembranosus muscle using dose of 1 × 1011 vp. Efficacy of the products was tested by the combination of contrast pulse sequencing ultrasound and modified Miles assay as well as quantifying the total cross-sectional area of capillaries. Safety, immunogenicity, toxicity, biodistribution, and shedding were assessed by general histology, serial measurements of C-reactive protein, white blood cell count and body temperature as well as using quantitative real-time PCR with primers targeted to the VEGF-D and replication-permitting E1 sequences. We found no significant differences in the efficacy or safety between the study groups. Most importantly, no detectable presence of RCA-specific E1 sequence was found in any samples tested, indicating that no detectable vector replication took place in vivo. We conclude that relatively low levels of RCA in adenoviral GT products may not be as important major safety issue as previously anticipated.

Microbubbles Cloaked with Hydrogels as Activatable Ultrasound Contrast Agents.

Microbubbles (MBs) are optimal ultrasound contrast agents because their unique acoustic response allows for exquisite sensitivity in vivo. This unique response is derived from MBs' elasticity that allows them to oscillate differently from surrounding tissues. While the main use of MBs in the clinic is for cardiac and perfusion imaging, imparting MBs with bioresponsive properties would expand their use to detect pathophysiologic changes. This can be achieved by damping MBs' oscillations to silence their signal and rescuing it when they encounter the biomarker of interest to improve detection and specificity of diseases such as deep vein thrombosis (DVT). Here, we demonstrate that conjugating perfluorobutane-filled MBs with hyaluronic acid (HA) and cross-linking HA with biodegradable linkers eliminates harmonic signal because of increased MB stiffness and decreased oscillation. In this proof-of-concept study, we used a reversible pH-sensitive cross-linker to establish and validate this targeted and activatable pH-sensitive MB (pH-MB) platform. Conjugation of HA to MBs and targeting of pH-MBs to CD44-positive cells were validated. Harmonic signal loss due to stiffening of pH-MBs' shell was confirmed using a clinical ultrasound scanner equipped with Cadence contrast pulse sequencing. pH-MBs imaged before and after acidification increased harmonic signal fivefold. Because the cleavage of the cross-linker we used is reversible, harmonic signal was silenced again when the acidic suspension was neutralized, confirming that harmonic signal is dependent on the cross-linked HA. The rate of rise and the magnitude of harmonic signal increase could be manipulated by varying the phospholipid composition and the number of HA cross-linkers, indicating that the platform can be tuned to the desired response needed. In this study, we established the feasibility of using targeted and activatable MBs and plan to apply this platform to aid in the diagnosis and management of patients with DVT and potentially other conditions.

Simultaneous Evalulation of Contrast Pulse Sequences for Super-Resolution Ultrasound Imaging - Preliminary In Vitro and In Vivo Results.

Super-resolution ultrasound imaging (SR-US) has enabled a tenfold improvement in resolution of the microvasculature with clinical application in many disease processes such as cancer, diabetes and cardiovascular disease. Plane wave ultrasound (US) platforms in turn are capable of the very high frame rates needed to track microbubble (MB) contrast agents used in SR-US. Both B-mode US imaging and contrast enhanced US imaging (CEUS) have been effectively used in SR-US, with B-mode US having higher signal-to-noise ratio (SNR) and CEUS providing higher contrast-to-tissue ratio (CTR). Lengthy imaging time needed for SR-US to allow perfusion and MB detection is an impediment to clinical adoption. Both SNR and CTR improvements can enhance SR-US imaging by enhancing the detection of MBs thus reducing imaging time. This study simultaneously evaluated nonlinear contrast pulse sequences (CPS) employing different amplitude modulation (AM) and pulse inversion (PI) nonlinear CEUS imaging techniques as well as combinations of the two, (AMPI) with B-mode US imaging. The objective was to improve the detection rate of MB during SR-US. Imaging was performed in vitro and in vivo in the rat hind limb using a Vantage 256 research scanner (Verasonics Inc.). Comparisons of four CPS compositions with B-mode US imaging was made based on the number of MB detected and localized in SR-US images. The use of a PI nonlinear CEUS imaging strategy improved SR-US imaging by increasing the number of MB detected in a sequence of frames by an average of 28.3% and up to 52.6% over a B-mode US imaging strategy, which would decrease imaging time accordingly.

An Ultrasound Enhancing Agent with Nonlinear Acoustic Activity that Depends on the Presence of an Electric Field

The nonlinear acoustic properties of microbubble ultrasound enhancing agents have allowed for the development of subharmonic, second harmonic, and contrast-pulse sequence ultrasound imaging modes, which enhance the quality, reduce the noise, and improve the diagnostic capabilities of clinical ultrasound. This study details acoustic scattering responses of perfluorobutane (PFB) microbubbles, an un-nested perfluoropentane (PFP) nanoemulsion, and two nested PFP nanoemulsions—one comprising a negatively charged phospholipid bilayer and another comprising a zwitterionic phospholipid bilayer—when excited at 1 or 2.25 MHz over a peak negative pressure range of 200 kPa to 4 MPa in the absence and presence of a 1-Hz, 1-V/cm electric field. The only sample that exhibited an increase in nonlinear activity in the presence of an electric field at both excitation frequencies was the negatively charged nested PFP nanoemulsion; the most pronounced effect was observed at an excitation of 2.25 MHz. Interestingly, the application of an electric field not only increased the nonlinear acoustic activity of the negatively charged nested PFP nanoemulsion but increased it beyond that seen when the nanoemulsion is un-nested and on the same scale as PFB microbubbles.

Targeted Ultrasound Contrast Imaging of Tumor Vasculature With Positively Charged Microbubbles.

Molecular ultrasound imaging of tumor vasculature is being actively investigated with microbubble contrast agents targeted to neovasculature biomarkers. Yet, a universal method of targeting tumor vasculature independent of specific biomarkers, or in their absence, would be desirable. We report the use of electrostatic interaction to achieve adherence of microbubbles to tumor vasculature and resulting tumor delineation by ultrasound imaging. Microbubbles were prepared from decafluorobutane gas by amalgamation of aqueous micellar medium. Distearoyl phosphatidylcholine (DSPC) and polyethylene glycol (PEG)-stearate were used as microbubble shell-forming lipids; cationic lipid distearoyl trimethylammoniumpropane (DSTAP) was included to introduce positive electrostatic charge. Microbubbles were subjected to flotation in normal gravity, to remove larger particles. Murine colon adenocarcinoma tumor (MC38, J. Schlom, National Institutes of Health) was inoculated in the hind leg of C57BL/6 mice. Contrast ultrasound imaging was performed under isoflurane anesthesia, using a clinical imaging system in low power mode, with tissue signal suppression (contrast pulse sequencing, 7 MHz, 1 Hz; Mechanical Index, 0.2). The ultrasound probe was positioned to monitor the tumor and contralateral leg muscle; microbubble contrast signal was monitored for 30 minutes or more, after intravenous bolus administration of 2.10 microbubbles. Individual time point frames were extracted from ultrasound video recording and analyzed with ImageJ. Mean bubble diameter was ~1.6 to 2 μm; 99.9% were less than 5 μm, to prevent blocking blood flow in capillaries. For cationic DSTAP-carrying microbubbles, contrast signal was observed in the tumor beyond 30 minutes after injection. As the fraction of positively charged lipid in the bubble shell was increased, adherent contrast signal in the tumor also increased, but accumulation of DSTAP-microbubbles in the normal muscle increased as well. For bubbles with the highest positive charge tested, DSTAP-DSPC molar ratio 1:4, at 10 minutes after intravenous administration of microbubbles, the contrast signal difference between the tumor and normal muscle was 1.5 (P < 0.005). At 30 minutes, tumor/muscle contrast signal ratio improved and reached 2.1. For the DSTAP-DSPC 1:13 preparation, tumor/muscle signal ratio exceeded 3.6 at 10 minutes and reached 5.4 at 30 minutes. Microbubbles with DSTAP-DSPC ratio 1:22 were optimal for tumor targeting: at 10 minutes, tumor/muscle signal ratio was greater than 7 (P < 0.005); at 30 minutes, greater than 16 (P < 0.01), sufficient for tumor delineation. Cationic microbubbles are easy to prepare. They selectively accumulate in the tumor vasculature after intravenous administration. These microbubbles provide target-to-control contrast ratio that can exceed an order of magnitude. Adherent microbubbles delineate the tumor mass at extended time points, at 30 minutes and beyond. This may allow for an extension of the contrast ultrasound examination time. Overall, positively charged microbubbles could become a universal ultrasound contrast agent for cancer imaging.

Evaluation of Sensory Pathways in Spinal Cord by Comparison of fMRI Methodologies

Introduction: Today, clinicians and neuroscientists need to have a comprehensive survey of neurological pathologies and injuries. For the First-time, SEEP contrast and Spin-Echo pulse sequences was used for functional imaging of the Lumbar spinal cord. This method used by several research groups for Spinal cord mapping, but other researchers tried to improve BOLD fMRI to Spinal cord imaging simultaneously. Here, we present a comparison between useful imaging methods and finally use of certain procedure for Spinal cord mapping with sensory stimulation. Materials and Methods: We planned two imaging protocols on Siemens 3T magnetom trio scanner: HASTE/SSFP, TE/TR: 76mS/6750mS for 9 sagittal slices with 2 mm thickness, FOV= 280×210mm, and Gradient Echo EPI, TE/TR: 30S/3000mS for 21 axial slices with 5mm thickness, FOV= 64×64mm. These image acquisition procedures performed on All 5 subjects (male, Age: 24.6±2.05), stimulated by 60g von Frey filament. Stimulations were used in the block design, 8 blocks with time 40.5 S for SE protocol and 42 S for GRE protocol and performed on right foot L4 dermatome. We entered each subject’s data sets into an individual first-level statistical analysis. Then we calculated signal changes in the mask that generated in the statistical analysis and amount of temporal Signal to Noise Ratio (tSNR). Other subjects group (5 males, Age 25.3±1.5) was imaged with same protocol as GE-EPI and T2W anatomic images (3D-FSE Isotropic, TR/TE:1500/430 ms, FOV= 256×60 mm, slice-thickness: 1mm). Data sets were processed with GLM and Finally, all first-level analysis results are entered in Higher-level analysis as group analysis and obtained statistical maps for spinal cord functions. Results: We observed different tSNR in two separated datasets, 2.619 ± 0.440 for SE-HASTE images and 4.901 ± 0.762 for GRE-EPI. After statistical analysis of images and obtaining signal change in the spinal cord. We comprised them and measured signal change was 1.737 ± 1.252 for SE-EPI and 2.554 ± 1.327 for GE-EPI. Based on these results we decided to use GE- EPI for spinal cord functional imaging. We stimulated L4 dermatome and this localized activation was observed in the T9-T1. The activation maps show ipsilateral synapse and tracks in the dorsal higher than ventral horn. Conclusion: At the first step evaluation of imaging methods show GRE-EPI can more efficient for Lumbar functional MRI and detection of BOLD signal change in the spinal cord. This research demonstrates the benefits of spinal cord fMRI for mapping of sensory stimulation. The resulting activity maps show primarily in ipsilateral dorsal regions and in some ventral regions, consistent with the spinal cord anatomy. These data also illustrate details of the sensory organization of the spinal cord, as well as anatomical detail of the spinous processes and positions of nerve roots.

Non-invasive quantification of liver fat content by different Gradient Echo MRI sequences in patients with Non-Alcoholic Fatty Liver Disease (NAFLD)

Introduction: Non-invasive quantification of liver fat by Gradient echo (GRE) Technique is an interesting issue in quantitative MRI. Despite the numerous advantages of this technique, fat measurement maybe biased by confounding and effects. The aim of this study was to evaluate the GRE pulse sequences with different and weighting for liver fat quantification in patients with Non-Alcoholic Fatty Liver Disease (NAFLD). Materials and Methods: This prospective, cross-sectional study was performed on 30 NAFLD-patients. Sixteen GRE protocols with different weighting contrast were performed with Siemens 1.5 Tesla with four Echo Times ( . For each sequence, TR or flip angle was changed and other scan parameters were fixed.To assessment of signal intensity changes, Regions of Interest (ROIs) which placed on images were copied into other images. 48 fat indexes were calculated based on three equations (Equ 1-3). ( ) (1) (2) ( (3); = ln ( Where is the time difference between and .Correlation between biopsy findings and MRI were performed using Pearson coefficient at the significant level of 1%. Results:Mean fat indexes which obtained from equation 3 have the maximum values in comparison to the other fat indexes. The maximum fat index was 23.58% which related to heavily weighted contrast pulse sequence (sequence 4 TR=50msec, α= defined by equation 3. The minimum fat index was -2.49% which correspond to the minimal weighted pulse sequence (sequence 13TR=200msec, α= defined by equation 2.Relationship between calculated fat indexes and flip angle reveals that, these indexes increased with flip angle especially at low angles. Increasing TR parameter decline fat indexes gradually.Correlational analysis between measured fat indexes and biopsy findings indicate that fat indexes calculated by equation 1 and 3 have slightly stronger correlatecpmpared to resulted data from equation 2. Conclusion:In general, the relaxation effects more critical than in fat quantification. Diagnostic accuracy of First dual GRE and Triple GRE techniques are better than Second dual GRE. There was no significant difference between First dual GRE and Triple GRE technique. In fat quantification with GRE techniques maybe the third and fourth echoes are unnecessary. Findings suggest that flip angle could be a major factor, if not the only one, causing the overestimation of measured fat content. Consequently, GRE techniques for fat quantification are more desirable with lower flip angle.

Abstract 2196: Noninvasive description of natural tumor evolution

Abstract Background: Our goal is to investigate how quantitative parameters of Contrast Enhanced Ultrasound (CEUS) and Shear Wave Elastography (SWE) change during tumor growth and link them with morphological and histological indexes. Methods: An ectopic model of murine colorectal carcinoma (CT26) was implanted in 46 mice (BALB/c ) at Day 0. On 5 subsequent days, data were acquired from subsets of these mice (D7, n=8 ; D10, n=9 ; D14, n=10 ; D16, n=9, D17, n=10) by scanning each tumor along its major, longitudinal axis in vivo to obtain conventional B-mode, SWE (SSI, Aixplorer, SL15-4 probe) and dynamic CEUS (Sequoia 512, 7-14 MHz probe, cadence contrast pulse sequencing) data. The ellipsoidal volume of each tumor was estimated from measurements of the width and thickness of the largest plane along the longitudinal and transversal plane using B-mode display on the Aixplorer device. Quantitative maps of tissue elasticity distribution in the tumor were obtained from SWE data. Average values and standard deviation of SWE data were calculated within regions selected to outline the tumor cross section on B-mode images. CEUS was performed after a syringe-pump-controlled bolus injection in the caudal vein of 40 μL of SonoVue (Bracco Suisse, Geneva, Switzerland) in a weight-adjusted volume of 0.5 mL/kg. A lognormal model was fit to the time intensity curve inside the tumor to estimate parameters related to microvascular volume and flow. All tumors imaged on a given day were excised and marked to conserve orientation and approximate position relative to the US imaging plane. Tumors were frozen with liquid nitrogen in an Optimal Cutting Temperature compound cube and stored at -80°C. Results: Significance of correlations were evaluated using the non-parametric Spearman correlation coefficient (RS). Average SWE parameters were not significantly correlated with the CEUS parameters (p &amp;gt; 0.03). Standard deviation of SWE in the tumor was well correlated with tumor volume (RS = 0.65 [p&amp;lt;6x10^-7]). For CEUS only the Time To Peak and Latency Time correlated with tumor volume (RS = 0.62 [p&amp;lt;4x10^-6] and RS = -0.72 [p&amp;lt;2x10^-8], respectively). Correlation with histological assessment of tumor microstructure is still in the process of analysis. Conclusions: These preliminary results probe the relationship between tumor volume, functional-flow and elastic properties in tumors. Both CEUS and SWE parameters were found that correlate with tumor growth and thus, appear to be sensitive to changes occurring during tumor development. Histological analysis of tumor microstructure is underway to more fully probe this point. Lack of correlation between SWE and CEUS parameters suggests that they provide complementary information. Better understanding of the sensitivity of these non invasive parameters to tumor growth changes will contribute to their eventual integration in procedures of tumor response criteria in clinical practice. Citation Format: Jerome Griffon, Delphine Le Guillou-Buffello, Oumeima Laifa, Lori Bridal, Michele Lamuraglia. Noninvasive description of natural tumor evolution [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2196.