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1.  Loss of echogenicity and onset of cavitation from echogenic liposomes: pulse repetition frequency independence 
Ultrasound in medicine & biology  2014;41(1):208-221.
Echogenic liposomes (ELIP) are being developed for the early detection and treatment of atherosclerotic lesions. An 80% loss of echogenicity of ELIP (Radhakrishnan et al. 2013) has been shown to be concomitant with the onset of stable and inertial cavitation. The ultrasound pressure amplitude at which this occurs is weakly dependent on pulse duration. Smith et al. (2007) have reported that the rapid fragmentation threshold of ELIP (based on changes in echogenicity) is dependent on the insonation pulse repetition frequency (PRF). The current study evaluates the relationship between loss of echogenicity and cavitation emissions from ELIP insonified by duplex Doppler pulses at four PRFs (1.25 kHz, 2.5 kHz, 5 kHz, and 8.33 kHz). Loss of echogenicity was evaluated on B-mode images of ELIP. Cavitation emissions from ELIP were recorded passively on a focused single-element transducer and a linear array. Emissions recorded by the linear array were beamformed and the spatial widths of stable and inertial cavitation emissions were compared to the calibrated azimuthal beamwidth of the Doppler pulse exceeding the stable and inertial cavitation thresholds. The inertial cavitation thresholds had a very weak dependence on PRF and stable cavitation thresholds were independent of PRF. The spatial widths of the cavitation emissions recorded by the passive cavitation imaging system agreed with the calibrated Doppler beamwidths. The results also show that 64%–79% loss of echogenicity can be used to classify the presence or absence of cavitation emissions with greater than 80% accuracy.
doi:10.1016/j.ultrasmedbio.2014.08.021
PMCID: PMC4258473  PMID: 25438849
stable cavitation; inertial cavitation; passive cavitation imaging; Doppler ultrasound; echogenic liposomes
2.  Three-Dimensional Echocardiography-based Prediction of Posterior Leaflet Resection 
Echocardiography (Mount Kisco, N.Y.)  2014;31(10):E300-E303.
Clinical long-term outcomes have shown that partial leaflet resection followed by ring annuloplasty is a reliable and reproducible surgical repair technique for treatment of mitral valve (MV) leaflet prolapse. We report a 61-year-old male for three-dimensional transesophageal echocardiography (3D TEE)-based virtual posterior leaflet resection and ring annuloplasty. Severe mitral regurgitation was found and computational evaluation demonstrated substantial leaflet malcoaptation and high stress concentration. Following virtual resection and ring annuloplasty, posterior leaflet prolapse markedly decreased, sufficient leaflet coaptation was restored, and high stress concentration disappeared. Virtual MV repair strategies using 3D TEE have the potential to help optimize MV repair.
doi:10.1111/echo.12717
PMCID: PMC4224973  PMID: 25109487
mitral valve; three-dimensional echocardiography; mitral valve repair; resection; computational evaluation
3.  Thrombolytic efficacy and enzymatic activity of rt-PA-loaded echogenic liposomes 
Echogenic liposomes (ELIP), that can encapsulate both recombinant tissue-type plasminogen activator (rt-PA) and microbubbles, are under development to improve the treatment of thrombo-occlusive disease. However, the enzymatic activity, thrombolytic efficacy, and stable cavitation activity generated by this agent has yet to be evaluated and compared to another established ultrasound- enhanced thrombolytic scheme. A spectrophoto-metric method was used to compare the enzymatic activity of the rt-PA incorporated into ELIP (t-ELIP) to that of rt-PA. An in vitro flow model was employed to measure the thrombolytic efficacy and dose of ultraharmonic emissions from stable cavitation for 120-kHz ultrasound exposure of three treatment schemes: rt-PA, rt-PA and the perfluoro-carbon-filled microbubble Definity®, and t-ELIP. The enzymatic activity of rt-PA incorporated into t-ELIP was 28 % that of rt-PA. Thrombolytic efficacy of t-ELIP or rt-PA and Definity® was equivalent when the dose of t-ELIP was adjusted to produce comparable enzymatic activity. Sustained bubble activity was nucleated from Definity but not from t-ELIP exposed to 120-kHz ultrasound. These results emphasize the advantages of encapsulating a thrombolytic and the importance of incorporating an insoluble gas required to promote sustained, stable cavitation activity.
doi:10.1007/s11239-015-1204-8
PMCID: PMC4477081  PMID: 25829338
Acute ischemic stroke; Ultrasound; Ultrasound contrast agents; Acoustic cavitation; Echogenic lipsomes
4.  Personalized Computational Modeling of Mitral Valve Prolapse: Virtual Leaflet Resection 
PLoS ONE  2015;10(6):e0130906.
Posterior leaflet prolapse following chordal elongation or rupture is one of the primary valvular diseases in patients with degenerative mitral valves (MVs). Quadrangular resection followed by ring annuloplasty is a reliable and reproducible surgical repair technique for treatment of posterior leaflet prolapse. Virtual MV repair simulation of leaflet resection in association with patient-specific 3D echocardiographic data can provide quantitative biomechanical and physiologic characteristics of pre- and post-resection MV function. We have developed a solid personalized computational simulation protocol to perform virtual MV repair using standard clinical guidelines of posterior leaflet resection with annuloplasty ring implantation. A virtual MV model was created using 3D echocardiographic data of a patient with posterior chordal rupture and severe mitral regurgitation. A quadrangle-shaped leaflet portion in the prolapsed posterior leaflet was removed, and virtual plication and suturing were performed. An annuloplasty ring of proper size was reconstructed and virtual ring annuloplasty was performed by superimposing the ring and the mitral annulus. Following the quadrangular resection and ring annuloplasty simulations, patient-specific annular motion and physiologic transvalvular pressure gradient were implemented and dynamic finite element simulation of MV function was performed. The pre-resection MV demonstrated a substantial lack of leaflet coaptation which directly correlated with the severe mitral regurgitation. Excessive stress concentration was found along the free marginal edge of the posterior leaflet involving the chordal rupture. Following the virtual resection and ring annuloplasty, the severity of the posterior leaflet prolapse markedly decreased. Excessive stress concentration disappeared over both anterior and posterior leaflets, and complete leaflet coaptation was effectively restored. This novel personalized virtual MV repair strategy has great potential to help with preoperative selection of the patient-specific optimal MV repair techniques, allow innovative surgical planning to expect improved efficacy of MV repair with more predictable outcomes, and ultimately provide more effective medical care for the patient.
doi:10.1371/journal.pone.0130906
PMCID: PMC4477933  PMID: 26103002
5.  Nitric oxide pre-treatment enhances atheroma component highlighting in vivo with ICAM-1 targeted echogenic liposomes 
Ultrasound in medicine & biology  2014;40(6):1167-1176.
We present an ultrasound technique to detect the inflammatory changes in developing atheroma. We used contrast enhanced ultrasound imaging (CEUS) with 1) ICAM-1 targeted microbubbles, a molecule of adhesion involved in the inflammatory processes into the lesions of atheroma in New Zealand White rabbits, 2) a pre-treatment with NO-loaded microbubbles and US activation at the site of the endothelium in order to enhance the permeability of the arterial wall and the penetration of the ICAM-1 targeted microbubbles. Following this procedure, the acoustic enhancement is increased by 1.2 fold. NO-ELIP pretreatment with ultrasound activation can potentially facilitate the subsequent penetration of targeted ELIP into the arterial wall, thus allowing improved detection of inflammatory changes in developing atheroma.
doi:10.1016/j.ultrasmedbio.2013.12.013
PMCID: PMC4011946  PMID: 24613216
Echogenic liposomes; intravascular ultrasound imaging; nitric oxide; atherosclerosis; molecular imaging
6.  Thrombolytic efficacy and enzymatic activity of rt-PA-loaded echogenic liposomes 
Echogenic liposomes (ELIP), that can encapsulate both recombinant tissue-type plasminogen activator (rt-PA) and microbubbles, are under development to improve the treatment of thrombo-occlusive disease. However, the enzymatic activity, thrombolytic efficacy, and stable cavitation activity generated by this agent has yet to be evaluated and compared to another established ultrasound-enhanced thrombolytic scheme. A spectrophotometric method was used to compare the enzymatic activity of the rt-PA incorporated into ELIP (t-ELIP) to that of rt-PA. An in vitro flow model was employed to measure the thrombolytic efficacy and dose of ultraharmonic emissions from stable cavitation for 120-kHz ultrasound exposure of three treatment schemes: rt-PA, rt-PA and the perfluorocarbon-filled microbubble Definity®, and t-ELIP. The enzymatic activity of rt-PA incorporated into t-ELIP was 28 % that of rt-PA. Thrombolytic efficacy of t-ELIP or rt-PA and Definity® was equivalent when the dose of t-ELIP was adjusted to produce comparable enzymatic activity. Sustained bubble activity was nucleated from Definity but not from t-ELIP exposed to 120-kHz ultrasound. These results emphasize the advantages of encapsulating a thrombolytic and the importance of incorporating an insoluble gas required to promote sustained, stable cavitation activity.
doi:10.1007/s11239-015-1204-8
PMCID: PMC4477081  PMID: 25829338
Acute ischemic stroke; Ultrasound; Ultrasound contrast agents; Acoustic cavitation; Echogenic lipsomes
7.  Calibration of the 1-MHz Sonitron ultrasound systems 
Ultrasound in medicine & biology  2010;36(10):1762-1766.
Successful drug and gene delivery across cellular membranes can lead to improved therapeutic outcomes. Recent studies have suggested that sonoporation may enhance drug and gene delivery across cellular membranes. The enhancement may be due to transient permeation of the membrane from cavitation or microstreaming effects of microbubbles exposed to ultrasound. Given limited acoustic pressure calibration and beam profile characterization of the Sonitron ultrasound systems in cellular bioeffects studies previously published, the objective of this work was to calibrate the acoustic output and explore the potential for standing waves in a cell-well plate. In this study three 1-MHz transducers driven by Sonitron ultrasound systems, which have been used in a number of sonoporation studies, were calibrated. Transducers with 10-mm, 6-mm and 20-mm diameter apertures (Sonitron 1000 and 2000, Rich-Mar, Inola, OK) were calibrated using PVDF needle hydrophones. Axial and transverse beam profiles were obtained, and the pressures were measured as a function of Sonitron intensity dial setting and duty cycle. The acoustic intensity was calculated and compared to the Sonitron intensity dial setting for duty cycles from 10 to 100%. Standing waves caused by reflections from the hydrophone holder were detected for each transducer. This observation may also have implications for in vitro sonoporation studies. Acoustic field characterization is an important first step in understanding the mechanisms of sonoporation and drug delivery across biomembranes.
doi:10.1016/j.ultrasmedbio.2010.05.020
PMCID: PMC4357174  PMID: 20800963
Sonoporation; Drug and Gene delivery; Transducer Calibration
8.  Subclinical Atherosclerosis and Obesity Phenotypes Among Mexican Americans 
Background
Data on the influence of obesity on atherosclerosis in Hispanics are inconsistent, possibly related to varying cardiometabolic risk among obese individuals. We aimed to determine the association of obesity and cardiometabolic risk with subclinical atherosclerosis in Mexican‐Americans.
Methods and Results
Participants (n=503) were drawn from the Cameron County Hispanic Cohort. Metabolic health was defined as <2 of the following: blood pressure ≥130/85; triglyceride ≥150 mg/dL; high‐density lipoprotein cholesterol <40 mg/dL (men) or <50 mg/dL (women); fasting glucose ≥100 mg/dL; homeostasis model assessment of insulin resistance value >5.13; or high‐sensitivity C‐reactive protein >3 mg/L. Carotid intima media thickness (cIMT) was measured. A high proportion of participants (77.8%) were metabolically unhealthy; they were more likely to be male, older, with fewer years of education, and less likely to meet daily recommendations regarding fruit and vegetable servings. One‐third (31.8%) had abnormal carotid ultrasound findings. After adjusting for covariates, mean cIMT varied across the obesity phenotypes (P=0.0001); there was no difference among the metabolically unhealthy regardless of whether they were obese or not. In multivariable analysis, after adjusting for covariates, cardiometabolic risk (P=0.0159), but not obesity (P=0.1446), was significantly associated with subclinical atherosclerosis.
Conclusions
In Mexican‐Americans, cardiometabolic risk has a greater effect on early atherosclerosis development than body mass index. Non‐obese but metabolically unhealthy participants had similar development of subclinical atherosclerosis as their obese counterparts. Interventions to maintain metabolic health among obese and non‐obese patients may be a more important goal than weight loss alone.
doi:10.1161/JAHA.114.001540
PMCID: PMC4392436  PMID: 25787312
atherosclerosis; carotid intima‐media thickness; obesity; population; risk factors
9.  Effect of Congenital Anomalies of the Papillary Muscles on Mitral Valve Function 
Parachute mitral valves (PMVs) and parachute-like asymmetric mitral valves (PLAMVs) are associated with congenital anomalies of the papillary muscles. Current imaging modalities cannot provide detailed biomechanical information. This study describes computational evaluation techniques based on three-dimensional (3D) echocardiographic data to determine the biomechanical and physiologic characteristics of PMVs and PLAMVs. The closing and opening mechanics of a normal mitral valve (MV), two types of PLAMV with different degrees of asymmetry, and a true PMV were investigated. MV geometric data in a patient with a normal MV was acquired from 3D echocardiography. The pathologic MVs were modeled by altering the configuration of the papillary muscles in the normal MV model. Dynamic finite element simulations of the normal MV, PLAMVs, and true PMV were performed. There was a strong correlation between the reduction of mitral orifice size and the degree of asymmetry of the papillary muscle location. The PLAMVs demonstrated decreased leaflet coaptation and tenting height. The true PMV revealed severely wrinkled leaflet deformation and narrowed interchordal spaces, leading to uneven leaflet coaptation. There were considerable decreases in leaflet coaptation and abnormal leaflet deformation corresponding to the anomalous location of the papillary muscle tips. This computational MV evaluation strategy provides a powerful tool to better understand biomechanical and pathophysiologic MV abnormalities.
doi:10.1007/s40846-015-0011-1
PMCID: PMC4342526  PMID: 25750606
Mitral valve; Parachute mitral valve; Parachute-like asymmetric mitral valve; Papillary muscle; Three-dimensional echocardiography; Computational simulation
10.  Mitral Valve Repair Using ePTFE Sutures for Ruptured Mitral Chordae Tendineae: A Computational Simulation Study 
Annals of biomedical engineering  2013;42(1):10.1007/s10439-013-0908-1.
Mitral valve repair using expanded polytetrafluoroethylene (ePTFE) sutures is an established and preferred interventional method to resolve the complex pathophysiologic problems associated with chordal rupture. We developed a novel computational evaluation protocol to determine the effect of the artificial sutures on restoring mitral valve function following valve repair. A virtual mitral valve was created using three-dimensional echocardiographic data in a patient with ruptured mitral chordae tendineae. Virtual repairs were designed by adding artificial sutures between the papillary muscles and the posterior leaflet where the native chordae were ruptured. Dynamic finite element simulations were performed to evaluate pre- and post-repair mitral valve function. Abnormal posterior leaflet prolapse and mitral regurgitation was clearly demonstrated in the mitral valve with ruptured chordae. Following virtual repair to reconstruct ruptured chordae, the severity of the posterior leaflet prolapse decreased and stress concentration was markedly reduced both in the leaflet tissue and the intact native chordae. Complete leaflet coaptation was restored when four or six sutures were utilized. Computational simulations provided quantitative information of functional improvement following mitral valve repair. This novel simulation strategy may provide a powerful tool for evaluation and prediction of interventional treatment for ruptured mitral chordae tendineae.
doi:10.1007/s10439-013-0908-1
PMCID: PMC3872503  PMID: 24072489
Mitral valve; Three-dimensional echocardiography; Mitral repair; Chordae tendineae; Simulation; Finite element
11.  Nitric Oxide Improves Molecular Imaging of Inflammatory Atheroma using Targeted Echogenic Immunoliposomes 
Atherosclerosis  2013;231(2):10.1016/j.atherosclerosis.2013.09.026.
Objective:
This study aimed to demonstrate whether pretreatment with nitric oxide (NO) loaded into echogenic immunoliposomes (ELIP) plus ultrasound, applied before injection of molecularly targeted ELIP can promote penetration of the targeted contrast agent and improve visualization of atheroma components.
Methods:
ELIP were prepared using the pressurization-freeze method. Atherosclerosis was induced in Yucatan miniswine by balloon denudation and a hyperlipidemic diet. The animals were randomized to receive anti-intercellular adhesion molecule-1 (ICAM-1) ELIP or immunoglobulin (IgG)-ELIP, and were subdivided to receive pretreatment with standard ELIP plus ultrasound, NO-loaded ELIP, or NO-loaded ELIP plus ultrasound. Intravascular ultrasound (IVUS) data were collected before and after treatment.
Results:
Pretreatment with standard ELIP plus ultrasound or NO-loaded ELIP without ultrasound resulted in 9.2 ± 0.7% and 9.2 ± 0.8% increase in mean gray scale values, respectively, compared to baseline (p<0.001 vs. control). Pretreatment with NO-loaded ELIP plus ultrasound activation resulted in a further increase in highlighting with a change in mean gray scale value to 14.7 ± 1.0% compared to baseline (p<0.001 vs. control). These differences were best appreciated when acoustic backscatter data values (RF signal) were used [22.7 ± 2.0% and 22.4 ± 2.2% increase in RF signals for pretreatment with standard ELIP plus ultrasound and NO-loaded ELIP without ultrasound respectively (p<0.001 vs. control), and 40.0 ± 2.9% increase in RF signal for pretreatment with NO-loaded ELIP plus ultrasound (p<0.001 vs. control)].
Conclusion:
NO-loaded ELIP plus ultrasound activation can facilitate anti-ICAM-1 conjugated ELIP delivery to inflammatory components in the arterial wall. This NO pretreatment strategy has potential to improve targeted molecular imaging of atheroma for eventual true tailored and personalized management of cardiovascular diseases.
doi:10.1016/j.atherosclerosis.2013.09.026
PMCID: PMC3871611  PMID: 24267236
Molecular Imaging; Atherosclerosis; Contrast Agent; Nitric Oxide; Ultrasound
12.  Therapeutic Time Window and Dose Dependence of Xenon Delivered via Echogenic Liposomes for Neuroprotection in Stroke 
CNS neuroscience & therapeutics  2013;19(10):773-784.
Aims
Neurologic impairment following ischemic injury complicates the quality of life for stroke survivors. Xenon (Xe) has favorable neuroprotective properties to modify stroke. Xe delivery is hampered by a lack of suitable administration strategies. We have developed Xe-containing echogenic liposomes (Xe-ELIP) for systemic Xe delivery. We investigated the time window for Xe-ELIP therapeutic effect and the most efficacious dose for neuroprotection. Molecular mechanisms for Xe neuroprotection were investigated.
Methods
Xe-ELIP were created by a previously developed pressurization-freezing method. Following right middle cerebral artery occlusion (2 hours), animals were treated with Xe-ELIP at 2, 3 or 5 hours to determine time window of therapeutic effect. The neuroprotectant dosage for optimal effect was evaluated 3 hours after stroke onset. Expression of brain-derived neurotrophic factor (BDNF), protein kinase B (Akt), and mitogen-activated protein kinases (MAPK) were determined.
Results
Xe-ELIP administration for up to 5 hours after stroke onset reduced infract size. Treatment groups given 7 and 14 mg/kg of Xe-ELIP reduced infarct size. Behavioral outcomes corresponded to changes in infarct volume. Xe-ELIP treatment reduced ischemic neuronal cell death via activation of both MAPK and Akt. Elevated BDNF expression was shown following Xe-ELIP delivery.
Conclusion
This study demonstrates the therapeutic efficacy of Xe-ELIP administered within 5 hours after stroke onset with an optimal dosage range of 7–14 mg/kg for maximal neuroprotection.
doi:10.1111/cns.12159
PMCID: PMC3806289  PMID: 23981565
Stroke; Xenon; Neuroprotection; Liposomes; Cerebral ischemia
13.  Relationship between cavitation and loss of echogenicity from ultrasound contrast agents 
Physics in medicine and biology  2013;58(18):6541-6563.
Ultrasound contrast agents (UCAs) have the potential to nucleate cavitation and promote both beneficial and deleterious bioeffects in vivo. Previous studies have elucidated the pulse-duration dependent pressure amplitude threshold for rapid loss of echogenicity due to UCA fragmentation. Previous studies have demonstrated that UCA fragmentation was concomitant with inertial cavitation. The purpose of this study was to evaluate the relationship between stable and inertial cavitation thresholds and loss of echogenicity of UCAs as a function of pulse duration. Determining the relationship between cavitation thresholds and loss of echogenicity of UCAs would enable monitoring of cavitation based upon the on-screen echogenicity in clinical applications. Two lipid-shelled UCAs, echogenic liposomes (ELIP) and Definity®, were insonified by a clinical ultrasound scanner in duplex spectral Doppler mode at four pulse durations (“sample volumes”) in both a static system and a flow system. Cavitation emissions from the UCAs insonified by Doppler pulses were recorded using a passive cavitation detection system and stable and inertial cavitation thresholds ascertained. Loss of echogenicity from ELIP and Definity® was assessed within regions of interest on B-mode images. A numerical model based on UCA rupture predicted the functional form of the loss of echogenicity from ELIP and Definity®. Stable and inertial cavitation thresholds were found to have a weak dependence on pulse duration. Stable cavitation thresholds were lower than inertial cavitation thresholds. The power of cavitation emissions was an exponential function of the loss of echogenicity over the investigated range of acoustic pressures. Both ELIP and Definity® lost more than 80% echogenicity before the onset of stable or inertial cavitation. Once this level of echogenicity loss occurred, both stable and inertial cavitation were detected in the physiologic flow phantom. These results imply that stable and inertial cavitation are necessary in order to trigger complete loss of echogenicity acoustically from UCAs and this finding can be used when planning diagnostic and therapeutic applications.
doi:10.1088/0031-9155/58/18/6541
PMCID: PMC4170692  PMID: 24002637
cavitation thresholds; echogenic liposomes; echogenicity; passive cavitation detection; physiologic flow
15.  The Impact of Bubbles on Measurement of Drug Release from Echogenic Liposomes 
Ultrasonics sonochemistry  2012;20(4):1121-1130.
Echogenic liposomes (ELIP) encapsulate gas bubbles and drugs within lipid vesicles, but the mechanisms of ultrasound-mediated drug release from ELIP are not well understood. The effect of cavitation activity on drug release from ELIP was investigated in flowing solutions using two fluorescent molecules: a lipophilic drug (rosiglitazone) and a hydrophilic drug substitute (calcein). ELIP samples were exposed to pulsed Doppler ultrasound from a clinical diagnostic ultrasound scanner at pressures above and below the inertial and stable cavitation thresholds. Control samples were exposed to a surfactant, Triton X-100 (positive control), or to flow alone (negative control). Fluorescence techniques were used to detect release. Encapsulated microbubbles reduced the measured fluorescence intensity and this effect should be considered when assessing drug release from ELIP. The origin of this effect is not specific to ELIP. Release of rosiglitazone or calcein compared to the negative control was only observed with detergent treatment, but not with ultrasound exposure, despite the presence of stable and inertial cavitation activity. Release of rosiglitazone or calcein from ELIP exposed to diagnostic ultrasound was not observed, even in the presence of cavitation activity. Ultrasound-mediated drug delivery strategies with ELIP will thus rely on passage of the drug-loaded liposomes to target tissues.
doi:10.1016/j.ultsonch.2012.12.005
PMCID: PMC3632413  PMID: 23357288
Echogenic liposomes; pulsed Doppler ultrasound; drug release; cavitation; rosiglitazone; spectrofluorometric techniques
16.  Mitral valve function following ischemic cardiomyopathy: a biomechanical perspective 
Ischemic mitral valve (MV) is a common complication of pathologic remodeling of the left ventricle due to acute and chronic coronary artery diseases. It frequently represents the pathologic consequences of increased tethering forces and reduced coaptation of the MV leaflets. Ischemic MV function has been investigated from a biomechanical perspective using finite element-based computational MV evaluation techniques. A virtual 3D MV model was created utilizing 3D echocardiographic data in a patient with normal MV. Two types of ischemic MVs containing asymmetric medial-dominant or symmetric leaflet tenting were modeled by altering the configuration of the normal papillary muscle (PM) locations. Computational simulations of MV function were performed using dynamic finite element methods, and biomechanical information across the MV apparatus was evaluated. The ischemic MV with medial-dominant leaflet tenting demonstrated distinct large stress distributions in the posteromedial commissural region due to the medial PM displacement toward the apical-medial direction resulting in a lack of leaflet coaptation. In the ischemic MV with balanced leaflet tenting, mitral incompetency with incomplete leaflet coaptation was clearly identified all around the paracommissural regions. This computational MV evaluation strategy has the potential for improving diagnosis of ischemic mitral regurgitation and treatment of ischemic MVs.
doi:10.3233/BME-130777
PMCID: PMC4072029  PMID: 24211876
Mitral valve; ischemic mitral regurgitation; leaflet coaptation; echocardiography; finite element
17.  Telomere length in patients with systemic lupus erythematosus and its associations with carotid plaque 
Rheumatology (Oxford, England)  2013;52(6):1101-1108.
Objective. To evaluate telomere length (TL) between patients with SLE and healthy controls and to test if TL is associated with carotid plaque.
Methods. A pilot study of 154 patients with SLE and 152 controls was performed from the SOLVABLE (Study of Lupus Vascular and Bone Long-Term Endpoints) cohort. Demographic and cardiovascular disease (CVD) factors were collected at baseline. The presence or absence of plaque was evaluated by B-mode US. Genomic DNA was isolated from whole peripheral blood. TL was quantified using real-time quantitative PCR.
Results. SLE women had a short TL compared with healthy controls (4.57 vs 5.44 kb, P = 0.03). SLE women showed shorter TL than controls across all age groups: <35 years (4.38 vs 6.37 kb), 35–44 years (4.52 vs 5.30 kb), 45–54 years (4.77 vs 5.68 kb) and ≥55 years (4.60 vs 4.71 kb). Among patients with SLE and carotid plaque there was a trend towards shorter TL at a younger age and it was significantly lower in the 35- to 44-year age group when compared with controls (P = 0.025). Multiple logistic regression analysis indicated a risk of carotid plaque with older age [odds ratio (OR) 1.09; 95% CI 1.06, 1.12] but not with TL (OR 1.05; 95% CI 0.97, 1.13).
Conclusion. SLE women had significantly shorter TL than controls. SLE women trended towards shorter TL at a younger age. When carotid plaque was identified, the younger SLE women had shorter TL. Only older age but not shorter TL was independently associated with carotid plaque. Additional studies are needed to confirm if TL is a novel biomarker for cardiovascular disease in SLE.
doi:10.1093/rheumatology/kes424
PMCID: PMC3651615  PMID: 23382361
systemic lupus erythematosus; cardiovascular disease; telomere length
18.  Adverse pregnancy outcomes and subsequent risk of cardiovascular disease in women with systemic lupus erythematosus 
Lupus Science & Medicine  2014;1(1):e000024.
Background/objective
Patients with systemic lupus erythematosus (SLE) are at increased risk for adverse pregnancy outcomes and cardiovascular disease (CVD). The objective of this exploratory study was to investigate the association between a history of adverse pregnancy outcomes and subsequent risk of subclinical CVD assessed by imaging studies and verified clinical CVD events in 129 women with SLE.
Methods
The occurrence of adverse pregnancy outcomes, specifically pre-eclampsia, preterm birth and low birth weight was ascertained by questionnaire. Subclinical CVD was assessed by coronary artery calcium (CAC) as measured by electron beam CT and carotid plaque measured by B mode ultrasound. Clinical CVD events were verified by medical record review. Logistic regression was used to estimate the association of pregnancy complications with occurrence of subclinical CVD and clinical CVD with a priori adjustment for age, which is associated with CVD and SLE disease duration as a measure of SLE disease burden.
Results
Fifty-six women reported at least one pregnancy complication while 73 had none. Twenty-six women had at least one pregnancy complicated by pre-eclampsia and were more likely to have a CAC score greater than or equal to 10 (adjusted OR=3.7; 95% CI 1.2 to 11.9), but the presence of plaque was not associated with this pregnancy complication, OR=1.1, (95% CI 0.4 to 2.8). Low birth weight and preterm birth were not associated with CAC or plaque.
Conclusions
Patients with SLE with a history of pre-eclampsia had a higher rate of subclinical CVD as measured by CAC score. Future studies are needed to confirm the relationship between adverse pregnancy outcomes and subsequent subclinical CVD and clinical CVD events.
doi:10.1136/lupus-2014-000024
PMCID: PMC4213826  PMID: 25379191
Cardiovascular Disease; Systemic Lupus Erythematosus; Pregnancy; Pre-eclampsia
19.  BROADBAND ATTENUATION MEASUREMENTS OF PHOSPHOLIPID-SHELLED ULTRASOUND CONTRAST AGENTS 
Ultrasound in medicine & biology  2013;40(2):410-421.
The aim of this study was to characterize the frequency-dependent acoustic attenuation of three phospholipid-shelled ultrasound contrast agents (UCAs): Definity, MicroMarker and echogenic liposomes. A broadband through-transmission technique allowed for measurement over 2 to 25 MHz with a single pair of transducers. Viscoelastic shell parameters of the UCAs were estimated using a linearized model developed by N. de Jong, L. Hoff, T. Skotland and N. Bom (Ultrasonics 1992; 30:95–103). The effect of diluent on the attenuation of these UCA suspensions was evaluated by performing attenuation measurements in 0.5% (w/v) bovine serum albumin and whole blood. Changes in attenuation and shell parameters of the UCAs were investigated at room temperature (25°C) and physiologic temperature (37°C). The attenuation of the UCAs diluted in 0.5% (w/v) bovine serum albumin was found to be identical to the attenuation of UCAs in whole blood. For each UCA, attenuation was higher at 37°C than at 25°C, underscoring the importance of conducting characterization studies at physiologic temperature. Echogenic liposomes exhibited a larger increase in attenuation at 37°C versus 25°C than either Definity or MicroMarker.
doi:10.1016/j.ultrasmedbio.2013.09.018
PMCID: PMC4026002  PMID: 24262056
Ultrasound contrast agents; Microbubbles; Broadband characterization; Size distribution; Polyvinylidene fluoride transducer; Echogenic liposomes; Definity; MicroMarker
20.  The effect of patient-specific annular motion on dynamic simulation of mitral valve function 
Journal of biomechanics  2013;46(6):1104-1112.
Most surgical procedures for patients with mitral regurgitation (MR) focus on optimization of annular dimension and shape utilizing ring annuloplasty to restore normal annular geometry, increase leaflet coaptation, and reduce regurgitation. Computational studies may provide insight on the effect of annular motion on mitral valve (MV) function through the incorporation of patient-specific MV apparatus geometry from clinical imaging modalities such as echocardiography. In the present study, we have developed a novel algorithm for modeling patient-specific annular motion across the cardiac cycle to further improve our virtual MV modeling and simulation strategy. The MV apparatus including the leaflets, annulus, and location of papillary muscle tips was identified using patient 3D echocardiography data at end diastole and peak systole and converted to virtual MV model. Dynamic annular motion was modeled by incorporating the ECG-gated time-varying scaled annular displacement across the cardiac cycle. We performed dynamic finite element (FE) simulation of two sets of patient data with respect to the presence of MR. Annular morphology, stress distribution across the leaflets and annulus, and contact stress distribution were determined to assess the effect of annular motion on MV function and leaflet coaptation. The effect of dynamic annular motion clearly demonstrated reduced regions with large stress values and provided an improved accuracy in determining the location of improper leaflet coaptation. This strategy has the potential to better quantitate the extent of pathologic MV and better evaluate functional restoration following MV repair.
doi:10.1016/j.jbiomech.2013.01.014
PMCID: PMC3629842  PMID: 23433464
Mitral valve; Finite element; Annular motion; Mitral regurgitation; Three-dimensional echocardiography
21.  Effect of leaflet-to-chordae contact interaction on computational mitral valve evaluation 
Background
Computational simulation using numerical analysis methods can help to assess the complex biomechanical and functional characteristics of the mitral valve (MV) apparatus. It is important to correctly determine physical contact interaction between the MV apparatus components during computational MV evaluation. We hypothesize that leaflet-to-chordae contact interaction plays an important role in computational MV evaluation, specifically in quantitating the degree of leaflet coaptation directly related to the severity of mitral regurgitation (MR). In this study, we have performed dynamic finite element simulations of MV function with and without leaflet-to-chordae contact interaction, and determined the effect of leaflet-to-chordae contact interaction on the computational MV evaluation.
Methods
Computational virtual MV models were created using the MV geometric data in a patient with normal MV without MR and another with pathologic MV with MR obtained from 3D echocardiography. Computational MV simulation with full contact interaction was specified to incorporate entire physically available contact interactions between the leaflets and chordae tendineae. Computational MV simulation without leaflet-to-chordae contact interaction was specified by defining the anterior and posterior leaflets as the only contact inclusion.
Results
Without leaflet-to-chordae contact interaction, the computational MV simulations demonstrated physically unrealistic contact interactions between the leaflets and chordae. With leaflet-to-chordae contact interaction, the anterior marginal chordae retained the proper contact with the posterior leaflet during the entire systole. The size of the non-contact region in the simulation with leaflet-to-chordae contact interaction was much larger than for the simulation with only leaflet-to-leaflet contact.
Conclusions
We have successfully demonstrated the effect of leaflet-to-chordae contact interaction on determining leaflet coaptation in computational dynamic MV evaluation. We found that physically realistic contact interactions between the leaflets and chordae should be considered to accurately quantitate leaflet coaptation for MV simulation. Computational evaluation of MV function that allows precise quantitation of leaflet coaptation has great potential to better quantitate the severity of MR.
doi:10.1186/1475-925X-13-31
PMCID: PMC3976553  PMID: 24649999
Mitral valve; Finite element; Contact interaction; Coaptation; Echocardiography
22.  Evaluation of Mitral Valve Dynamics 
JACC. Cardiovascular imaging  2013;6(2):263-268.
doi:10.1016/j.jcmg.2012.10.017
PMCID: PMC3629823  PMID: 23489540
23.  Lipid complex of apolipoprotein A-I mimetic peptide 4F is a novel platform for Paraoxonase-1 binding and enhancing its activity and stability 
High density lipoprotein (HDL) associated paraoxonase-1 (PON1) is crucial for the anti-oxidant, anti-inflammatory, and anti-atherogenic properties of HDL. Discoidal apolipoprotein (apo)A-I:1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) complex has been shown to be the most effective in binding PON1, stabilizing it, and enhancing its lactonase and inhibitory activity of low density lipoprotein oxidation. Based on our earlier study demonstrating that apoA-I mimetic peptide 4F forms discoidal complex with 1,2-dimyristoyl-sn-glycero-3-phosphocholine, we hypothesized that lipid complexes of 4F would be able to bind PON1 and enhance its activity and stability. To test our hypothesis, we have expressed and purified a recombinant PON1 (rPON1) and studied its interaction with 4F:POPC complex. Our studies show significant increase, compared to the control, in the paraoxonase activity and stability of rPON1 in the presence of 4F:POPC complex. We propose that 4F:POPC complex is a novel platform for PON1 binding, increasing its stability, and enhancing its enzyme activity. We propose a structural model for the 4F:POPC:PON1 ternary complex that is consistent with our results and published observations.
doi:10.1016/j.bbrc.2012.11.128
PMCID: PMC3555693  PMID: 23261466
High density lipoprotein; Peptide; Amphipathic helix; Apolipoprotein A-I; Lipid; Paraoxonase-1
24.  HIGH PREVALENCE OF SUBCLINICAL ATHEROSCLEROSIS BY CAROTID ULTRASOUND AMONG MEXICAN AMERICANS: DISCORDANCE WITH 10-YEAR RISK ASSESSMENT USING THE FRAMINGHAM RISK SCORE 
Echocardiography (Mount Kisco, N.Y.)  2012;29(10):1224-1232.
Background
Framingham Risk Scores (FRS) were validated in a mostly Caucasian population. Evaluation of subclinical atherosclerosis by carotid ultrasound may improve ascertainment of risk in non-White populations. This study aimed to evaluate carotid intima-media thickness (cIMT) and carotid plaquing among Mexican Americans, and to correlate these markers with coronary risk factors and the FRS.
Methods/Results
Participants (n=141) were drawn from the Cameron County Hispanic Cohort. Carotid artery ultrasound was performed and cIMT measured. Carotid plaque was defined as areas of thickening >50% of the thickness of the surrounding walls. Mean age was 53.1±11.7 years (73.8% female). Most were overweight or obese (88.7%) and more than half (53.2%) had the metabolic syndrome. One third (34.8%) had abnormal carotid ultrasound findings (either cIMT ≥75th percentile for gender and age or presence of plaque). Among those with abnormal carotid ultrasound, the majority were classified as being at low 10-year risk for cardiovascular events. Carotid ultrasound reclassified nearly a third of the cohort as being at high risk. This discordance between 10-year FRS and carotid ultrasound was noted whether risk was assessed for hard coronary events or global risk. Concordance between FRS and carotid ultrasound findings was best when long-term (30-year) risk was assessed and no subject with an abnormal carotid ultrasound was categorized as low risk by the 30-year FRS algorithm.
Conclusions
Integration of carotid ultrasound findings to coronary risk assessments and use of longer term prediction models may provide better risk assessment in this minority population, with earlier initiation of appropriate therapies.
doi:10.1111/j.1540-8175.2012.01774.x
PMCID: PMC3687003  PMID: 22747630
Carotid ultrasound; Subclinical atherosclerosis; Framingham risk score; Minority population; Risk assessment
25.  Nitric oxide-loaded echogenic liposomes for treatment of vasospasm following subarachnoid hemorrhage 
Delayed cerebral vasospasm following subarachnoid hemorrhage causes severe ischemic neurologic deficits leading to permanent neurologic dysfunction or death. Reduced intravascular and perivascular nitric oxide (NO) availability is a primary pathophysiology of cerebral vasospasm. In this study, we evaluated NO-loaded echogenic liposomes (NO-ELIP) for ultrasound-facilitated NO delivery to produce vasodilation for treatment of vasospasm following subarachnoid hemorrhage. We investigated the vasodilative effects of NO released from NO-ELIP both ex vivo and in vivo. Liposomes containing phospholipids and cholesterol were prepared, and NO was encapsulated. The encapsulation and release of NO from NO-ELIP were determined by the syringe/vacuum method and ultrasound imaging. The ex vivo vasodilative effect of NO-ELIP was investigated using rabbit carotid arteries. Arterial vasodilation was clearly observed with NO-ELIP exposed to Doppler ultrasound whereas there was little vasodilative effect without exposure to Doppler ultrasound in the presence of red blood cells. Penetration of NO into the arterial wall was determined by fluorescent microscopy. The vasodilative effects of intravenously administered NO-ELIP in vivo were determined in a rat subarachnoid hemorrhage model. NO-ELIP with ultrasound activation over the carotid artery demonstrated effective arterial vasodilation in vivo resulting in improved neurologic function. This novel methodology for ultrasound-controlled delivery of NO has the potential for therapeutic treatment of vasospasm following subarachnoid hemorrhage. This ultrasound-controlled release strategy provides a new avenue for targeted bioactive gas and therapeutic delivery for improved stroke treatment.
doi:10.2147/IJN.S48856
PMCID: PMC3873237  PMID: 24379666
vasospasm; vasodilation; subarachnoid hemorrhage; nitric oxide; liposomes; ultrasound

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