Antenatal dexamethasone treatment transiently alters diastolic function in the mouse fetal heart.

Endogenous glucocorticoid action is important in the structural and functional maturation of the fetal heart. In fetal mice, although glucocorticoid concentrations are extremely low before E14.5, glucocorticoid receptor (GR) is expressed in the heart from E10.5. To investigate whether activation of cardiac GR prior to E14.5 induces precocious fetal heart maturation, we administered dexamethasone in the drinking water of pregnant dams from E12.5 to E15.5. To test the direct effects of glucocorticoids upon the cardiovascular system we used SMGRKO mice, with Sm22-Cre-mediated disruption of GR in cardiomyocytes and vascular smooth muscle. Contrary to expectations, echocardiography showed no advancement of functional maturation of the fetal heart. Moreover, litter size was decreased 2 days following cessation of antenatal glucocorticoid exposure, irrespective of fetal genotype. The myocardial performance index and E/A wave ratio, markers of fetal heart maturation, were not significantly affected by dexamethasone treatment in either genotype. Dexamethasone treatment transiently decreased the myocardial deceleration index (MDI; a marker of diastolic function), in control fetuses at E15.5, with recovery by E17.5, 2 days after cessation of treatment. MDI was lower in SMGRKO than in control fetuses and was unaffected by dexamethasone. The transient decrease in MDI was associated with repression of cardiac GR in control fetuses following dexamethasone treatment. Measurement of glucocorticoid levels in fetal tissue and hypothalamic corticotropin-releasing hormone (Crh) mRNA levels suggest complex and differential effects of dexamethasone treatment upon the hypothalamic-pituitary-adrenal axis between genotypes. These data suggest potentially detrimental and direct effects of antenatal glucocorticoid treatment upon fetal heart function.

Efficacy and safety of point-of-care ultrasound-guided intra-articular corticosteroid joint injections in patients with haemophilic arthropathy.

INTRODUCTION AND OBJECTIVES: Intra-articular corticosteroid injections are standard of care for managing joint pain secondary to osteoarthritis or rheumatoid arthritis but are rarely used in haemophilic arthropathy. We have introduced and evaluated the efficacy and safety of ultrasound-guided corticosteroid injections for pain relief in patients with haemophilic arthropathy. PATIENTS AND METHODS: Ultrasound-guided intra-articular injections performed on haemophilia patients at UCSD between March 2012 and January 2016 were analysed. Needle placement and injection (40 mg triamcinolone; 3-5 mL lidocaine) were performed with musculoskeletal ultrasound and Power Doppler. Analysis included patient demographics, joint-specific parameters such as tissue hypervascularity and effusions, pain relief, and procedure-associated complications. RESULTS: Forty-five injections (14 ankles, 13 elbows, 18 knees) were administered in 25 patients. Advanced arthropathy with hypervascularity and/or effusions was present in 91% and 61% of joints, respectively. Ninety-one per cent of injections resulted in pain relief which was significant in 84% (>30% reduction). Median pain score was reduced from 7 of 10 to 1 of 10 (P < 0.001), usually within 24 h. Median duration of pain relief was 8 weeks (range 1-16 weeks). Haemophilia B patients experienced longer periods of relief, and high Pettersson scores were associated with shorter duration of relief. There were no procedure-associated complications. Repeat ultrasound of eight joints within 4 weeks of injection demonstrated nearly complete resolution of hypervascularity. CONCLUSIONS: Point-of-care ultrasound enabled intra-articular corticosteroid injections that provided highly effective, safe, and relatively long-lasting pain relief in haemophilic arthropathy. This approach should be used to improve pain management in haemophilic arthropathy.

Duplicate publications and related problems in published papers on oral and maxillofacial surgery.

As duplicate publication is unethical, our aim was to find out how common it is among published papers on oral and maxillofacial surgery. We used PubMed to identify index articles published in 2010 in the Journal of Oral and Maxillofacial Surgery, the British Journal of Oral and Maxillofacial Surgery, and the European Journal of Cranio-Maxillo-Facial Surgery, and searched for possible duplicate publications from 2008 to 2012 using the first or second and last authors' names. Suspected duplicates were categorised into "non-duplicate" (no overlap), "duplicate" (identical results and conclusions), or "salami-sliced" publications (part of the index article repeated or continued). Of the 589 index articles, 17 (3%) had some form of duplication, but specifically, we found 3 duplicate, and 15 salami-sliced publications. Most redundant articles originated from China (n=4), followed by Italy, Japan, and Germany (3 from each) and the United States and Denmark (2 each). Of the 18 redundant publications, 9 did not reference the related index article. Duplicate material is still being published, and salami-slicing is relatively common among publications on oral and maxillofacial surgery. Further research is required into the extent and impact of this finding.

A Protocol for Improved Measurement of Arterial Flow Rate in Preclinical Ultrasound.

PURPOSE: To describe a protocol for the measurement of blood flow rate in small animals and to compare flow rate measurements against measurements made using a transit time flowmeter. MATERIALS AND METHODS: Measurements were made in rat and mice using a Visualsonics Vevo 770 scanner. The flow rate in carotid and femoral arteries was calculated from the time-average maximum velocity and vessel diameter. A correction factor was applied to correct for the overestimation of velocity arising from geometric spectral broadening. Invasive flow rate measurements were made using a Transonics system. RESULTS: Measurements were achieved in rat carotid and femoral arteries and in mouse carotid arteries. Image quality in the mouse femoral artery was too poor to obtain diameter measurements. The applied correction factor in practice was 0.71-0.77. The diameter varied by 6-18% during the cardiac cycle. There was no overall difference in the flow rate measured using ultrasound and using transit-time flowmeters. The flow rates were comparable with those previously reported in the literature. There was wide variation in flow rates in the same artery in individual animals. Transit-time measurements were associated with changes of a factor of 10 during the typical 40 min measurement period, associated with probe movement, vessel spasm, vessel kinking and other effects. CONCLUSION: A protocol for the measurement of flow rate in arteries in small animals has been described and successfully used in rat carotid and femoral arteries and in mouse carotid arteries. The availability of a noninvasive procedure for flow rate measurement avoids the problems with changes in flow associated with an invasive procedure.

Contrast imaging ultrasound detects abnormalities in the marmoset ovary.

The development of a functional vascular tree within the primate ovary is critical for reproductive health. To determine the efficacy of contrast agents to image the microvascular environment within the primate ovary, contrast ultrasonography was performed in six reproductive-aged female common marmosets (Callithrix jacchus) during the late luteal phase of the cycle, following injection of Sonovue™. Regions of interest (ROIs), representing the corpus luteum (CL) and noncorpus luteum ovarian tissue (NCLOT), were selected during gray-scale B-mode ultrasound imaging. The magnitude of backscatter intensity of CL and NCLOT ROIs were calculated in XnView, post hoc: subsequent gamma-variate modeling was implemented in Matlab to determine perfusion parameters. Histological analysis of these ovaries revealed a total of 11 CL, nine of which were identified during contrast ultrasonography. The median enhancement ratio was significantly increased in the CL (5.54AU; 95% CI -2.21-68.71) compared to the NCLOT (2.82AU; 95% CI 2.73-15.06; P < 0.05). There was no difference in time parameters between the CL and NCLOT. An additional avascular ROI was identified in the ovary of Animal 5, both histologically and by ultrasonography. This cystic ROI displayed a markedly lower enhancement ratio (0.79AU) and higher time parameters than mean CL and NCLOT, including time to peak and time to wash out. These data demonstrate, for the first time, the ability of commercially available contrast agents, to differentiate structures within the nonhuman primate ovary. Contrast-enhanced ultrasonography has a promising future in reproductive medicine.

Probing microbubble targeting with atomic force microscopy.

Microbubble science is expanding beyond ultrasound imaging applications to biological targeting and drug/gene delivery. The characteristics of molecular targeting should be tested by a measurement system that can assess targeting efficacy and strength. Atomic force microscopy (AFM) is capable of piconewton force resolution, and is reported to measure the strength of single hydrogen bonds. An in-house targeted microbubble modified using the biotin-avidin chemistry and the CD31 antibody was used to probe cultures of Sk-Hep1 hepatic endothelial cells. We report that the targeted microbubbles provide a single distribution of adhesion forces with a median of 93pN. This interaction is assigned to the CD31 antibody-antigen unbinding event. Information on the distances between the interaction forces was obtained and could be important for future microbubble fabrication. In conclusion, the capability of single microbubbles to target cell lines was shown to be feasible with AFM.

Colour M-mode tissue Doppler imaging in healthy cats and cats with hypertrophic cardiomyopathy.

OBJECTIVES: To determine whether decreased diastolic and systolic myocardial velocity gradient between the endocardium and the epicardium exist in the left ventricle of cats with hypertrophic cardiomyopathy. METHODS: Myocardial velocity gradient and mean myocardial velocities were measured by colour M-mode tissue Doppler imaging in the left ventricular free wall of 20 normal cats and 17 cats with hypertrophic cardiomyopathy. RESULTS: The peak myocardial velocity gradient (sec(-1)) during the first (E1) (5.71+/-1.75 versus 11.38+/-3.1, P<0.001) and second phase (E2) (3.09+/-1.53 versus 7.02+/-3.1, P=0.005) of early diastole and also the maximum early diastolic myocardial velocity gradient (Emax) (6.12+/-2.1 versus 10.76+/-3.2, P<0.001) were reduced in cats with hypertrophic cardiomyopathy compared with normal cats. Peak myocardial velocity gradient during early systole (Se) was lower in affected cats than in normal cats (6.26+/-2.08 versus 8.67+/-2.83, P=0.006). Affected cats had a lower peak mean myocardial velocities (mm/s) during the two isovolumic periods (IVRb and IVCb) compared with normal cats (2.97+/-6.76 versus 12.74+/-5.5 and 22.28+/-9.96 versus 38.65+/-10.1, P<0.001, respectively). CLINICAL SIGNIFICANCE: This study shows that hypertrophic cardiomyopathy cats have decreased myocardial velocity gradient during both diastole and systole and also altered myocardial motion during the two isovolumic periods. Myocardial velocity gradients recorded by colour M-mode tissue Doppler imaging can discriminate between the healthy and diseased myocardium.

Nanomechanical probing of microbubbles using the atomic force microscope.

Atomic force microscopy (AFM) is a versatile mechanical nanosensor that can be used to quantify the mechanical properties of microbubbles (MBs) and the adhesion mechanisms of targeted MBs. Mechanical properties were investigated using AFM tipless cantilevers to microcompress the MBs. The range of compressive stiffness for biSphere was found to be between 1 and 10Nm(-1) using a cantilever with a spring constant of 0.6 Nm(-1). This stiffness was shown to decrease with the MB size in a non-linear fashion. It is also possible to calculate a theoretical Young's modulus of the shell. The adhesion properties of targeted lipid based MBs that use avidin-biotin chemistry for the attachment of targeting ligands were also studied. The MBs were attached to poly-L-lysine treated tipless cantilevers with spring constants ranging from 0.03 to 0.1 Nm(-1). This system interrogated individual cells with pulling cantilever distance of 15 microm, and scan rate at 0.2 Hz. The depth of contact was not larger than 0.4 microm. The targeted MBs provided a significantly larger adhesion to the cells compared to control ones. Average adhesion force was dependent on depth of contact. Analysis of the data demonstrated a single distribution of adhesion events with median at 89 pN, which is in agreement with the literature for such interactions. The nanointerrogation of MBs using AFM provides new insight into their mechanical properties, and should be of assistance to MB design and manufacture.

Nanointerrogation of ultrasonic contrast agent microbubbles using atomic force microscopy.

Predicting the acoustic response of an encapsulated microbubble to ultrasound requires an accurate assessment of the mechanical properties of the microbubble shell. Atomic force microscopy (AFM) provides an unprecedented spatial and force resolution of the order of Angstroms and subnanonewtons, respectively. It is introduced here as a means to interrogate microbubbles manufactured for ultrasonic imaging. The advantage of AFM over scanning electron microscopy (SEM) is that the microbubbles need not be subjected to a low temperature or low-pressure environment. The microbubbles were interrogated in a liquid environment, which could potentially be a simulated physiological environment. AFM was used in tapping mode imaging to reveal topographical detail of biSphere microbubbles. Because microbubbles are large objects compared with the overall size of usual AFM tips, a convolution between the AFM tip and the microbubble was typical of the acquired topographies. However, a part of the top half of the bubble was imaged with nanometer resolution, and roughness measurements are reported. Force-distance curves were captured using contact mode AFM. The range of stiffness or effective spring constant of biSphere was found to be between 1 and 6 N m(-1). In conclusion, the AFM is proposed here for the first time as a tool to image the surface of bubbles at the nanometer range in liquid and to perform reproducible measurements on the mechanical properties of individual microbubbles.

Manufacture and acoustical characterisation of a high-frequency contrast agent for targeting applications.

The aim of this study was to develop and acoustically to optimise an ultrasonic contrast agent for research imaging applications at 40 MHz. A range of liposomal dispersions were manufactured and the mean backscatter power was measured using a Boston Scientific ClearView Ultra intravascular scanner with a 40 MHz, 2.5 Fr Atlantis SR Plus catheter. The scanner had been modified to allow access to the unprocessed ultrasound data, which were digitised, and the mean backscatter power was calculated over a region-of-interest centred at 2 mm from the transducer. Mean backscatter power was normalised to the data collected from a water-air interface. The effects of sonication and rapid shaking on six liposomal samples were also studied and this indicated that both techniques significantly reduced the size of the liposomes within the dispersions. Maximum mean backscatter power was measured for sonicated liposomal dispersions with 60% by weight of phosphatidylethanolamine. Moreover, this dispersion had greater mean backscatter power than sheep blood at 40 MHz.

Pulsed tissue Doppler imaging in normal cats and cats with hypertrophic cardiomyopathy.

Myocardial motion was quantified in normal cats (n = 25) and cats with hypertrophic cardiomyopathy (HCM) (n = 23) using the pulsed tissue Doppler imaging (TDI) technique. A physiologic nonuniformity was documented in the myocardial motion of normal cats, which was detected as higher early diastolic velocities, acceleration, and deceleration in the interventricular septum compared with the left ventricular free wall (LVFW). HCM cats exhibited lower early diastolic velocities, acceleration, and deceleration and also prolonged isovolumic relaxation time compared with normal cats. These differences were detected mainly along the longitudinal axis of the heart. A cutoff value of E' in the LVFW along the longitudinal axis >7.2 cm/s discriminated normal from HCM cats with a sensitivity of 92% and a specificity of 87%. The physiologic nonuniformity of myocardial motion during diastole was lost in affected cats. Systolic impairment (decreased late-systolic velocities in most segments along the longitudinal axis and decreased early systolic acceleration in both mitral annular sites) was evident in HCM cats irrespective of the presence of left ventricular outflow tract obstruction and congestive heart failure. Postsystolic thickening was recorded in the LVFW along the longitudinal axis only in affected cats (n = 6) and was another finding indicative of systolic impairment in the HCM of this species. This study identified both diastolic and systolic impairment in cats with HCM compared with normal cats. The study also documents the normal physiologic nonhomogeneity in myocardial motion in cats and the subsequent loss of this feature in the HCM diseased state.

An in vitro study of a microbubble contrast agent using a clinical ultrasound imaging system.

Optimal insonation settings for contrast imaging are yet to be specified, mainly due to the lack of good understanding of the behaviour of the microbubbles. A satisfactory model that explains the behaviour of individual contrast agent scatterers has not yet been reported in the literature. An in vitro system based on a commercial scanner (ATL HDI3000) has been developed to investigate the backscatter of such agents. Suspensions of Definity were introduced in an anechoic tank. The frequency of transmitted ultrasound varied from 1 to 5 MHz, pulse period from 2 to 10 periods and peak negative acoustic pressure from 0.08 to 1.7 MPa. The backscatter at the fundamental and second harmonic frequency windows from the agent was normalized in terms of the corresponding components of backscatter from a blood mimicking fluid suspension. The agent provided a dominant resonance effect at 1.6 MHz transmit frequency. Second harmonic normalized backscatter averaged around 9 dB higher than the fundamental. The normalized fundamental backscatter intensity was linear with peak negative pressure. The second harmonic at resonance peaked at 0.5 MPa suggestive of bubble disruption above such pressure. The system proved capable of illustrating the ultrasonic behaviour of Definity in vitro, and the investigation suggested particular insonation conditions for optimal image enhancement using Definity.

Peak mean myocardial velocities and velocity gradients measured by color M-mode tissue Doppler imaging in healthy cats.

We sought to assess the feasibility of recording the myocardial velocity gradients (MVGs) and mean myocardial velocities (MMVs) measured by color M-mode tissue Doppler imaging (TDI) in the free wall of unsedated normal cats (n = 18) with a 7.4-MHz probe equipped to record TDI images. The peak MVG and MMV values during the different phases of the cardiac cycle corresponded to certain color velocity patterns occurring in the left ventricular free wall (LVFW). Biphasic shifts were recorded in the tracings of both the MVG and MMV during early diastole (E1 and E2) as well as during the isovolumic relaxation (IVR) and isovolumic contraction (IVC) phases. Stepwise regression analysis showed that age was the only significant predictor for the peak MVG values during the 2nd phase of early diastole (E2) (r = -0.79, r2 = 0.63, and P < .001). The peak late diastolic MVG values were associated positively with age (r = 0.50, r2 = 0.25, and P < .05). The peak MMV values showed a negative association with age during E2 (r = -0.71, r2 = 0.50, and P < .001) as well as during early systole (Se) (r = -0.55, r2 = 0.30, and P < .05) and late systole (SI) (r = -0.62, r2 = 0.39, and P < .01). A positive association was found between age and the peak MMV values during late diastole (r = 0.54, r2 =- 0.29, and P < .05). The MVG values showed cyclic variations consistent with wall thickness changes. The accuracy of velocity determination and the spatial resolution of the system used were validated with a phantom. To our knowledge, this study is the 1st report of the application of this technique to the myocardium of cats,providing insights into the physiology of myocardial motion. It provides reference ranges of the peak MVG and MMV values for future studies of feline myocardial diseases.

The behaviour of individual contrast agent microbubbles.

In recent years, our knowledge of the behaviour of ultrasonic microbubble contrast agents has improved substantially through in vitro experiments. However, there has been a tendency to use high concentrations of contrast agents in suspension, so that ultrasonic backscatter data are generated by a cloud of microbubbles. Such experiments involve a variety of assumptions with validity that is open to question. In addition, high concentrations of microbubbles cannot be used to understand the behaviour of individual microbubble scatterers. This paper proposes a technique that minimises the number of assumptions that need to be made to interpret in vitro experimental data. The basis of the technique is a dilute suspension of microbubbles that makes single scattering events distinguishable. A commercial scanner was used to collect radio frequency (RF) data from suspensions of two different contrast agents, Quantison and Definity. Backscatter data were collected over a range of acoustic pressures. It was found that Definity provided a constant number of scattering events per unit volume of suspension for almost all applied acoustic pressures. Quantison demonstrated an increasing number of scattering events per unit volume with increasing acoustic pressure. Below 0.6 MPa, Quantison scatterers were not individually detectable and provided levels of backscatter similar to those of a blood-mimicking fluid, which suggests that Quantison microbubbles had almost linear scattering behaviour. At acoustic pressures greater than 0.6 MPa, both agents appeared to provide echoes from free bubbles. The change in the number of scatterers per unit volume with acoustic pressure cannot be demonstrated using high concentrations of contrast agent.

Understanding the limitations of ultrasonic backscatter measurements from microbubble populations.

Despite over ten years of in vitro investigations of ultrasound contrast agents, the level of understanding of their behaviour in ultrasound fields is limited. Several problems associated with these investigations, particular to the nature of contrast agents, are discussed. Using a commercial scanner the RF normalized backscatter of two different contrast agents (Definity and Quantison) was measured at different suspension concentrations and acoustic pressures. Both contrast agents scattered ultrasound nonlinearly and the backscatter showed a dependence on acoustic pressure. In order to assess the average behaviour of the agents across the range of acoustic pressures and microbubble concentrations the experimental data were fitted to a theoretically acceptable model using nonlinear regression analysis. The analysis showed that both the backscatter and the attenuation of the Quantison suspensions displayed a higher order of dependence on acoustic pressure than the Definity suspensions. It was also discovered that Quantison microbubbles did not demonstrate uniform behaviour across the acoustic pressure range. At lower acoustic pressures the behaviour could not follow a model similar to that which predicted the behaviour at higher acoustic pressures, which was mainly due to the fact that free bubbles were released in a fashion dependent on acoustic pressure. The fact that two different populations of scatterers exist in the same suspensions makes the assessment of the behaviour of the particular agent impossible with the high concentrations that are commonly used. Very low concentration suspensions whereby single scattering events can be monitored should be more useful. In conclusion, the approach of using high microbubble concentrations in order to investigate the properties of ultrasonic contrast agents is limited in that the results of such studies cannot be used to understand the behaviour of single microbubbles.

The dependence of ultrasound contrast agents backscatter on acoustic pressure: theory versus experiment.

Experimental investigations have not fully explored the interaction between ultrasound beams and microbubble contrast agents. Moreover theoretical investigations have not solved the problem of the microbubble oscillation. A simple in-vitro system based on a commercial scanner (ATL UM9) was used to insonate (3 MHz transmission) diluted contrast suspensions of Definity and Quantison at different acoustic pressures (0.27-1.52 MPa). The experimental data were referred to a blood mimicking fluid in order to extract an estimate of their scattering cross-section. The results were compared with the solutions of the three main bubble oscillatidn models, Rayleigh-Plesset, Herring and Gilmore. Non-linear solutions of the above models were produced numerically using the Mathematica Package Software. The experiments showed that both agents provided a linear increase in scattering cross-section with increasing acoustic pressure. The thick shelled Quantison provided an increasing number of scatterers with increasing acoustic pressure, which proved that free bubbles leaked out of the shell. At high acoustic pressures both Quantison and Definity scattering cross-sections were almost identical, and were probably that of a free bubble. The Rayleigh-Plesset model provided a scattering cross-section almost independent of acoustic pressure. On the contrary the scattering cross-sections calculated by the Herring and Gilmore models solutions displayed a definite dependence on acoustic pressure of an order higher than one, which is slightly higher than the order of dependence exhibited by the experimental data. However, the increase of the experimentally measured scattering cross-section with acoustic pressure was sharper than the calculated one by the above two models. This is most probably due to the fact that the models simulated damped and not free bubble oscillations. In conclusion the Rayleigh-Plesset model was inadequate in describing the bubble oscillations even at small diagnostic acoustic pressures. The Herring and Gilmore models could simulate the dependence of the scattering cross-section of encapsulated microbubbles on acoustic pressure. However the contribution of free bubble oscillations has still to be modelled.

In vitro acoustic characterisation of four intravenous ultrasonic contrast agents at 30 MHz.

The acoustic properties of four ultrasonic contrast agents (Optison, Definity, SonoVue and Sonazoid) were studied at 30 MHz using a Boston Scientific ClearView Ultra intravascular ultrasound (US) scanner modified to allow access to the unprocessed US data. A range of contrast agent concentrations were studied using either saline or glucose as the diluent of choice. Mean backscatter power was measured over regions-of-interest (ROI) at distances of 1, 1.5, 2, 3, 4 and 5 mm from the centre of the intravascular probe and normalised to the US data collected from a standard glass reflector. For all of the agents, the mean backscatter power at 30 MHz varied in a linear manner with concentration between 0.01 million microbubbles/mL and 1 million microbubbles/mL. Furthermore, for two of the agents, mean backscatter enhancement was detectable at concentrations as low as 2 microbubbles/sample volume.

Contrast agent stability: a continuous B-mode imaging approach.

The stability of contrast agents in suspensions with various dissolved gas levels has not been reported in the literature. An in vitro investigation has been carried out that studied the combined effect of varying the acoustic pressure along with degassing the suspension environment. In this study, the contrast agents were introduced into suspensions with different oxygen concentration levels, and their relative performance was assessed in terms of decay rate of their backscatter echoes. The partial pressures of oxygen in those solutions ranged between 1.5 and 26 kPa. Two IV and one arterial contrast agents were used: Definity, Quantison, and Myomap. It was found that Quantison and Myomap released free bubbles at high acoustic pressure that also dissolved faster in degassed suspensions. The backscatter decay for Definity did not depend on the air content of the suspensions. The destruction of bubbles was dependent on acoustic pressure. Different backscatter performance was observed by different populations of bubbles of the last two agents. The physical quantity of "overall backscatter" (OB) was defined as the integral of the decay rate over time of the backscatter of the contrast suspensions, and improved significantly the understanding of the behaviour of the agents. A quantitative analysis of the backscatter properties of contrast agents using a continuous imaging approach was difficult to achieve. This is due to the fact that the backscatter in the field of view is representative of a bubble population affected by the ultrasound (US) field, but this bubble population is not representative of the contrast suspension in the whole tank. Single frame insonation is suggested to avoid the effects of decay due to the ultrasonic field, and to measure a tank-representative backscatter. The definition of OB was useful, however, in understanding the behaviour of the agents.

An in vitro system for the study of ultrasound contrast agents using a commercial imaging system.

An in vitro system for the investigation of the behaviour of contrast microbubbles in an ultrasound field, that provides a full diagnostic range of settings, is yet to be presented in the literature. The evaluation of a good compromise of such a system is presented in this paper. It is based on (a) an HD13000 ATL scanner (Bothell, WA, USA) externally controlled by a PC and (b) on the use of well-defined reference materials. The suspensions of the reference ultrasonic scattering material are placed in an anechoic tank. The pulse length ranges from 2 to 10 cycles, the acoustic pressure from 0.08 to 1.8 MPa, the transmit frequency from 1 to 4.3 MHz, and the receive frequency from 1 to 8 MHz. The collection of 256 samples of RF data, at an offset distance from the transducer face, was performed at 20 MHz digitization rate, which corresponds to approximately 1 cm depth in water. Two particle suspensions are also presented for use as reference scatterers for contrast studies: (a) a suspension of Orgasol (ELF Atochem, Paris, France) particles (approximately 5 microm mean diameter) and (b) a suspension of Eccosphere (New Metals & Chemicals Ltd, Essex, UK) particles (approximately 50 microm mean diameter). A preliminary experiment with the contrast agent Definity (DuPont Pharmaceutical Co, Waltham, MA) showed that the above two materials are suitable for use as a reference for contrast backscatter.

An in vitro comparison of ultrasonic contrast agents in solutions with varying air levels.

The performance, in particular, the stability of ultrasound (US) contrast agents has yet to be assessed. An in vitro system has been set up to investigate the properties of ultrasonic contrast agents under different suspension conditions. This is designed to contribute to the optimal use of agents in clinical practice. In this study, the contrast agents were introduced into solutions of different oxygen concentration levels, as might be encountered in blood, and their relative performance was assessed in terms of decay in the solution environment. The partial pressures of oxygen in those solutions ranged between 1.5 and 26 kPa. Three IV and one arterial contrast agents were used: Levovist, DMP115, Quantison and Myomap. Levovist showed the highest sensitivity to oxygen concentration in the solution, and the other three proved tolerant for the above values of oxygen concentrations.