Current cardiac imaging techniques for detection of left ventricular mass

Estimation of left ventricular (LV) mass has both prognostic and therapeutic value independent of traditional risk factors. Unfortunately, LV mass evaluation has been underestimated in clinical practice. Assessment of LV mass can be performed by a number of imaging modalities. Despite inherent limitations, conventional echocardiography has fundamentally been established as most widely used diagnostic tool. 3-dimensional echocardiography (3DE) is now feasible, fast and accurate for LV mass evaluation. 3DE is also superior to conventional echocardiography in terms of LV mass assessment, especially in patients with abnormal LV geometry. Cardiovascular magnetic resonance (CMR) and cardiovascular computed tomography (CCT) are currently performed for LV mass assessment and also do not depend on cardiac geometry and display 3-dimensional data, as well. Therefore, CMR is being increasingly employed and is at the present standard of reference in the clinical setting. Although each method demonstrates advantages over another, there are also disadvantages to receive attention. Diagnostic accuracy of methods will also be increased with the introduction of more advanced systems. It is also likely that in the coming years new and more accurate diagnostic tests will become available. In particular, CMR and CCT have been intersecting hot topic between cardiology and radiology clinics. Thus, good communication and collaboration between two specialties is required for selection of an appropriate test

Feasibility and diagnostic power of transthoracic coronary Doppler for coronary flow velocity reserve in patients referred for myocardial perfusion imaging

<p>Abstract</p> <p>Background</p> <p>Myocardial perfusion imaging (MPI), using single photon emission computed tomography (SPECT) is a validated method for detecting coronary artery disease. Transthoracic Doppler echocardiography (TTDE) of flow at rest and during adenosine provocation has previously been evaluated in selected patient groups. We therefore wanted to compare the diagnostic ability of TTDE in the left anterior descending coronary artery (LAD) to that of MPI in an unselected population of patients with chest pain referred for MPI. Our hypothesis was that TTDE with high accuracy would identify healthy individuals and exclude them from the need for further studies, enabling invasive investigations to be reserved for patients with a high probability of disease.</p> <p>Methods</p> <p>Sixty-nine patients, 44 men and 25 women, age 61 ± 10 years (range 35–82), with a clinical suspicion of stress induced myocardial ischemia, were investigated. TTDE was performed at rest and during adenosine stress for myocardial scintigraphy.</p> <p>Results</p> <p>We found that coronary flow velocity reserve (CFVR) determined from diastolic measurements separated normal from abnormal MPI findings with statistical significance. TTDE identified coronary artery disease, defined from MPI, as reversible ischemia and/or permanent defect, with a sensitivity of 60% and a specificity of 79%. The positive predictive value was 43% and the negative predictive value was 88%. There was an overlap between groups which could be due to abnormal endothelial function in patients with normal myocardial perfusion having either hypertension or diabetes.</p> <p>Conclusion</p> <p>TTDE is an attractive non-invasive method to evaluate chest pain without the use of isotopes, but the diagnostic power is strongly dependent on the population investigated. Even in our heterogeneous clinical cardiac population, we found that CFVR>2 in the LAD excluded significant coronary artery disease detected by MPI.</p

Investigation of microbubble-cell interaction and development of an ultrasound delivery system

Microbubbles have been used for several decades as ultrasound contrast agents in diagnostic ultrasound imaging. However, their application in gene therapy as delivery vehicles has only recently been realised. The presence of microbubbles in close proximity to cells during ultrasound insonation can increase the efficacy of drug or gene delivery by inducing formation of transient, non-lethal perforations in the cell membrane, a process termed sonoporation. In order to develop techniques for successful delivery of therapeutic agents, it is necessary to quantify the composition and physical characteristics of microbubbles in order to be able to determine how these affect the sonoporation process as required. Although several microbubbles are available commercially, the components of the shell of these proprietary microbubbles have not been disclosed. In order to study sonoporation and the possibility of delivering drugs and genes it became necessary to develop a formulation for in-house experimental microbubbles. These experimental in-house microbubbles have not been previously investigated with regard to their interaction with cells, their potential for sonoporation and / or their bioeffects. Characterisation of the in-house microbubbles was necessary prior to any attempts to use them as delivery vehicles in vitro, or indeed, in vivo. Confocal laser scanning microscopy (CLSM) was used in order to determine the size distribution of both in-house microbubbles and Definity® a commercially available contrast agent. Confocal imaging and 3-D reconstruction of in-house microbubbles indicated the structure, morphology and size-distribution of these membrane-bound microbodies. Microbubbles were later separated according to size using a density gradient. It was concluded that the distribution of sizes of the microbubbles was in part due to the multi-lamellar nature of the microbubble shell. Cells were initially cultured in Petri dishes and insonated in the presence and absence of in-house microbubbles, in order to assess any bioeffects emerging from the application of ultrasound alone or in the presence of the microbubble constructs. Cells were cultured subsequently on an acoustically-transparent Mylar membrane, which was then “sandwiched” between two acetal homopolymer (Derlin) rings and placed in a specially designed ultrasound tank. Ultimately, cells were grown in an OptiCell™, an acoustically-transparent parallel membrane environment, where delivery of molecules of various sizes, in the presence of both in-house and Definity® microbubbles was investigated. Sonoporation was achieved with insonication of SK Hep-1 cells with a “physiotherapy machine” applying a power of 2.54 W / cm2 for 2-3 secs in the presence of Definity® microbubbles and passage of Calcein, an impermeable molecule, into the cells was detected using flow cytometric analysis. In addition, expression of enhanced green fluorescent protein (EGFP) was also detected 24 hours after insonication of SK Hep-1 cells in the presence of Definity® microbubbles and a linearised plasmid pCS2, encoding EGFP, under the same ultrasonic conditions. Sonoporation was also investigated with the use of a diagnostic ultrasound scanner, since it is more clinically relevant. Although several acoustic and non-acoustic parameters were investigated, sufficient sonoporation was not attained using this scanner. The bioeffects of ultrasound on cells both in vivo and in vitro have been extensively investigated. However, the exact cellular mechanisms that are affected by the application of ultrasound waves are not understood. In this study, the effects of ultrasound on a number of pathways were investigated. Expression of Hsp70, a cell stress protein often associated with heat-shock, during application of continuous wave ultrasound, suggests that cells may undergo heat stress. During application of continuous wave ultrasound in the presence of Definity® microbubbles, expression of Hsp70 was shown to decrease compared to when ultrasound was applied in the absence of Definity® microbubbles. In addition, expression of HO-1, a protein associated with hypoxic pathways was also present during application of ultrasound in the absence of microbubbles. These results suggest that in the absence of ultrasound contrast agents, insonation can cause the expression of proteins associated with different forms of cell stress such as heat-shock and hypoxia, thus initiating the apoptotic process. In this thesis, it has been shown that the mean size of the in-house microbubbles is comparable to that of commercially available microbubbles such as Definity®. In addition, it has been shown that sonoporation and successful delivery of small molecules in the presence of Definity® microbubbles is achievable with the equipment and the specific system which was developed. This reinforces the promising role of in-house microbubbles as delivery vehicles for therapeutic agents. Finally, an investigation on the possible bioeffects of ultrasound in the presence and absence of ultrasound contrast agents, revealed that under acoustic conditions identical to those used for achieving sonoporation, cells experience stress, instigating pathways that could potentially lead to cell death

Industrial-Scale Manufacture of Oleosin 30G for Use as Contrast Agent in Echocardiography

In ultrasound sonography, microbubbles are used as contrasting agents to improve the effectiveness of ultrasound imaging. Monodisperse microbubbles are required to achieve the optimal image quality. In order to achieve a uniform size distribution, microbubbles are stabilized with surfactant molecules. One such molecule is Oleosin, an amphiphilic structural protein found in vascular plant oil bodies that contains one hydrophobic and two hydrophilic sections. Controlling the functionalization of microbubbles is a comprehensive and versatile process using recombinant technology to produce a genetically engineered form of Oleosin called Oleosin 30G. With the control of a microfluidic device, uniformly-sized and resonant microbubbles can be readily produced and stored in stable conditions up to one month. Currently, Oleosin microbubbles are limited to the lab-scale; however, through development of an integrated batch bioprocessing model, the overall product yield of Oleosin 30G can be increased to 7.39 kg/year to meet needs on the industrial-scale. An Oleosin-stabilized microbubble suspension as a contrast agent is in a strong position to take a competitive share of the current market, capitalizing on needs unmet by current market leader, Definity®. Based on market dynamics and process logistics, scaled-up production of Oleosin 30G for use as a contrast agent is expected to be both a useful and profitable venture

Use of advanced echocardiography imaging techniques in the critically ill

Background: Critical care echocardiography has become standard of care in the ICU. New technologies have been developed and have shown potential clinical utility to elucidate myocardial dysfunction not seen with conventional imaging. We sought to determine the feasibility and potential clinical benefit of these techniques in common situations seen in the ICU. Hypothesis: Advanced echo techniques would be feasible in the majority of critically ill patients and have prognostic significance, clinical utility and diagnose cardiac abnormalities, potentially in a more sensitive manner than conventional techniques. Results: (a) Speckle tracking echocardiography (STE) Left ventricle and RV analysis with STE was feasibly in ~80% of patients. More dysfunction was found using STE vs conventional analysis. RV dysfunction assessed by STE held significant prognostic relevance in those with septic shock and highlighted subtle dysfunction induced by mechanical ventilation, both in animal and human studies. (b) 3D transthoracic echocardiography (3D TTE) Despite finding 3D TTE feasible in mechanically ventilated ICU patients (LV 72% and RV 55%), it lacked necessary low variability and high precision vs standard measures. (c) Myocardial contrast perfusion echocardiography (MCPE) Assessing acute coronary artery occlusion in the ICU patient is challenging. Troponin elevation, acute ECG changes, regional wall motion analysis on echo and overall clinical acumen often lack diagnostic capabilities. MCPE was found to be feasible in the critically ill and had better association predicting acute coronary artery occlusion vs clinical acumen alone. Conclusions: STE, 3D TTE and MCPE are feasible in the majority of ICU patients. STE may show dysfunction not recognised by conventional imaging. 3D TTE for volumetric analysis is likely not suitable for clinical use at this stage. MCPE may help guide interventions in acute coronary artery occlusion

Advanced design and experimental validation of MRI contrast agents for fluid pressure mapping using microbubbles

This work is related to monitoring fluid pressure using Magnetic Resonance Imaging or MRI and includes numerical simulations and experimental MRI. The nature of this study is such that techniques other than MRI have been extensively used to assess the contrast agent for its physical behaviour. These techniques include rheometry, light scattering, optical and scanning electron microscopy. Six MRI experiments in total were performed: The first two experiments use standard spin echo imaging techniques to test various lipid preparations which are then used as a contrast agent to pressure in a porous medium. The remaining experiments are performed using a fast imaging technique and investigate various improvements to the contrast agent which resulted in the development of an agent exhibiting an unprecedented level of sensitivity. A variety of lipid preparations are utilised throughout the experiments. Initial testing reveals that the DSPC lipid offers the greatest stability, although a fluorinated lipid is used in a later study for an improved synergy between the shell and gas microbubble components. Having assessed the microbubble stability, preparations are prepared as in the work previously published in the area. This preparation is tested in two porous media to investigate the sensitivity of the contrast agent to changes in pressure. A sensitivity of 20% signal change per bar is found in porous media although a drift of 11%h-1 is also observed. An improved preparation was then developed by using an alternative polysaccharide gel, gellan gum

Optimization of Oleosin 30G Production for Echocardiography

Provided they are uniform in size, monodisperse microbubbles behave as contrast agents to enhance echocardiographic imaging. Compounds like Oleosin 30G with surfactant-like properties help stabilize microbubbles - thereby ensuring their uniform size. Designed herein is an industrial-scale plant to produce medical-grade Oleosin 30G with a process consisting of three steps: 1) upstream production via recombinant E. coli in an integrated batch bioprocessing model, 2) downstream purification, and 3) processing by microfluidic manifolds. Ultimately Oleosin 30G-coated microbubbles are manufactured, ready for injection within one month. Owing to its unique properties and cost-effective production, Oleosin 30G has the potential to outcompete current market leader Definity®. Altogether, overall yield of Oleosin 30G constitutes 7.39 kg/year to provide for 100% market saturation. Financial analysis indicates pursuing Oleosin 30G for echocardiography applications is very profitable with a 296% return on investment and holds potential for production expansion should the market demand increase