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Glycogen storage disease type Ia (GSDIa) is caused by an inherited single-gene defect resulting in an impaired glycogen to glucose conversion pathway. Targeted ultrasound mediated delivery (USMD) of plasmid DNA to liver in conjunction with microbubbles may provide a potential treatment for GSDIa patients. As the success of USMD treatmentsis largely dependent on the accessibility of the targeted tissue bythe focused ultrasound beam, this study presents a quantitative approach to determine the acoustically accessible liver volume in GSDIapatients. Models of focused ultrasound beam profiles for transducers of varying aperture and focal lengths were applied to abdomen models reconstructed from suitable CT and MRI images. Transducer manipulations (simulating USMD treatment procedures) were implemented via transducer translations and 2D rotations with the intent of targetingand exposing the entire liver to ultrasound. Results indicate thatacoustically accessible liver volumes can be as large as 60% of theentire liver volume for GSDIa patients and on average 3 times largercompared to a normal group due to GSDIa patients’ increased liver size. Detailed descriptions of the evaluation algorithm, transducer-and abdomen models will be presented, together with implications forUSMD treatments of GSDIa patients and transducer designs for USMD applications.

Background: Inertial cavitation may cause hazardous bioeffects whileusing ultrasound and microbubble mediated thrombolysis. The purposeof this study was to investigate the influence of ultrasound pulselength and temporal bone on inertial cavitation thresholds within the brain utilizing transtemporal imaging transducers. Methods: A pig temporal bone overlaid with muscle tissue was placed over silastictubing containing a dilute microbubble infusion (0.5% Definity) within Phosphate Buffered Saline at 37 °C. A 1.6 MHz Philips iE33 two-dimensional probe (S5-1) imaged at incremental peak negative pressures. Broadband noise signals were recorded to characterize inertial cavitation using two 20 MHz passive cavitaion detectors (PCD). Backscattered RF signals were recorded by iE33. Results: About half of the acoustic pressure was attenuated by the temporal bone. Peak-negative-pressure thresholds of inertial cavitation were approximately equal to 0.51 and 0.31 MPa, 0.46 and 0.29 MPa for 5 and 20 microsecondspulse durations with and without bone, respectively. RF signals from the S5-1 correlated with inertial cavitation thresholds from the PCD. Conclusion: The threshold of inertial cavitation is influencedby ultrasound pulse length and temporal bone. RF signals can be used to characterize cavitation behavior for bone attenuation estimation and compensation.

Ultrasound mediated delivery (USMD) of novel therapeutic agents in the presence of microbubbles is a potentially safe and effective method for gene therapy offering many desired characteristics such as low toxicity, potential for repeated treatment, and organ specificity.In this study we tested the capability of USMD to improve gene expression in mice livers using glycogen storage disease Type Ia as a model disease under systemic administration of naked plasmid DNA. Image guided therapeutic ultrasound was used in two studies to provide therapeutic ultrasound to mice liver. In the first study involving wild type mice, control animals received naked plasmid DNA (pG6Pase 150 µg) via the tail vein followed by an infusion of Sonovue microbubbles, while the treated animals additionally received therapeutic ultrasound (1 MHz). Following the procedure, the animals were left to recover and subsequently sacrificed after 2 days when liver samples were extracted. RT-PCR assays using Taqman probes were performed on the samples to quantify mRNA expression. In addition, Western blot assays of FLAG-tagged glucose-6-phosphatase (G6Pase) were performed toevaluate protein expression. Ultrasound exposed animals showed a four-fold increase in G6Pase RNA in the liver, in comparison with control animals. Furthermore, results from Western blot analysis demonstrated a two-fold increased protein expression in ultrasound exposedanimals after two days (p<0.05). A second pilot study was performedwith G6Pase knockout mice, and the animals were monitored for correction of hypoglycemia over a period of 3 weeks prior to tissue analysis. The RT-PCR assays of samples from these animals demonstrated increased G6Pase RNA in the liver following ultrasound treatment. Theseresults demonstrate that ultrasound mediated delivery can increasegene expression of systemically injected naked pDNA in liver and also provide insight into the development of realistic approaches thatcan be translated into clinical practice.