Shriram Sethuraman

Enhanced gene expression of systemically administered plasmid DNA in the liver with therapeutic ultrasound and microbubbles

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 livers. 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 microbubbles; the treated animals additionally received therapeutic ultrasound (1 MHz). Following the procedure, the animals were left to recover and were subsequently euthanized after 2 d and liver samples were extracted. Reverse transcription polymerase chain reaction (RT-PCR) assays were performed on the samples to quantify mRNA expression. In addition, Western blot assays of FLAG-tagged glucose-6-phosphatase (G6Pase) were performed to evaluate protein expression. Ultrasound-exposed animals showed a 4-fold increase in G6Pase RNA in the liver, in comparison with control animals. Furthermore, results from Western blot analysis demonstrated a 2-fold increased protein expression in ultrasound-exposed animals after two days ( p <; 0.05). A second pilot study was performed with G6Pase knockout mice, and the animals were monitored for correction of hypoglycemia over a period of 3 weeks before tissue analysis. The RT-PCR assays of samples from these animals demonstrated increased G6Pase RNA in the liver following ultrasound treatment. These results demonstrate that USMD can increase gene expression of systemically injected naked pDNA in the liver and also provide insight into the development of realistic approaches that can be translated into clinical practice.

Two‐Dimensional Real‐time Ultrasound Technique to Control Lesion Size during HIFU Therapy

The lack of accurate and low‐cost techniques for real‐time monitoring and feedback during ablative therapies such as HIFU has limited its widespread clinical adoption. A good ultrasound solution would enable a much more widespread usage of HIFU therapy. An acoustic radiation force (ARF) based technique for controlling the lesion size and its placement during HIFU therapy has been developed. A series of experiments were performed in excised bovine liver tissue to evaluate the proposed technique. The change in the ARF induced displacements during therapy at each spatial location was quantified by a unitless parameter, normalized displacement difference (NDD), defined as the difference between normalized displacement at the therapy endpoint and a reference determined from the data. The 2‐D displacement map (normalized to the value before therapy commenced) illustrated that displacements initially increased due to the temperature rise, reached a maximum, and then decreased with continuing therapy. Strong corr...

Gaussian mixture model based identification of arterial wall movement for computation of distension waveform.

This work proposes a novel Gaussian Mixture Model (GMM) based approach for accurate tracking of the arterial wall and subsequent computation of the distension waveform using Radio Frequency (RF) ultrasound signal. The approach was evaluated on ultrasound RF data acquired using a prototype ultrasound system from an artery mimicking flow phantom. The effectiveness of the proposed algorithm is demonstrated by comparing with existing wall tracking algorithms. The experimental results show that the proposed method provides 20% reduction in the error margin compared to the existing approaches in tracking the arterial wall movement. This approach coupled with ultrasound system can be used to estimate the arterial compliance parameters required for screening of cardiovascular related disorders.

A method for localized computation of Pulse Wave Velocity in carotid structure

Pulse Wave Velocity (PWV) promises to be a useful clinical marker for noninvasive diagnosis of atherosclerosis. This work demonstrates the ability to perform localized carotid PWV measurements from the distention waveform derived from the Radio Frequency (RF) ultrasound signal using a carotid phantom setup. The proposed system consists of low cost custom-built ultrasound probe and algorithms for envelope detection, arterial wall identification, echo tracking, distension waveform computation and PWV estimation. The method is proposed on a phantom data acquired using custom-built prototype non-imaging probe. The proposed approach is non-image based and can be seamlessly integrated into existing clinical ultrasound scanners.

Integrated ultrasound thermometry and multiphysics modeling for liver RF ablation monitoring: Ex vivo studies

Monitoring of radiofrequency ablation (RFA) is essential to ensure accurate treatment coverage of large liver tumors. Ultrasound is an excellent option for monitoring of ablations. Since ultrasound B-mode imaging lacks the ability to precisely estimate the extent of the lesion, there has been considerable effort and interest in other ultrasound based monitoring techniques. Ultrasound thermometry is one such technique that has the potential to monitor thermal ablations. However, drawback of the approach is its applicability only in sub-ablative temperatures. We attempt to overcome this limitation by integrating a predictive thermal model with ultrasound thermometry and extend its applicability to ablative temperatures. In this paper, we validate this integrated approach through ex vivo studies on bovine liver tissue. Specifically, sub-ablative temperature rise is measured using ultrasound thermometry in a plane distal to the metallic RFA tine. Independently, temperature distribution in the tissue is obtained from a COMSOL™-based multiphysics model (based on combining the Laplace and bio-heat transfer (BHTE) equation) customized for the ablation device geometry and boundary conditions. Subsequently, the experimentally determined ultrasound temperature estimates and the model temperature estimates are compared to estimate the local in situ unknown tissue properties. Finally, the adapted model is utilized during the ablation to estimate the ablation size. The thermal and electrical conductivity estimated using our approach for N=5 samples are 0.59±0.07 W/m/°C and 0.20±0.02 S/m respectively. Further, the lateral and axial lesion widths are 14.6 ±2.3 mm and 30.6±1.1 mm respectively and compare well with gross pathology estimates of 12.6±1.8 mm and 25.6±1.3 mm. In ex-vivo conditions devoid of blood perfusion effects, we have demonstrated the successful integration of the multiphysics model with the experimentally measured ultrasound backscatter data and the feasibility of the approach to monitor ablations.

Validating Ultrasound‐based HIFU Lesion‐size Monitoring Technique with MR Thermometry and Histology

In order to control and monitor HIFU lesions accurately and cost‐effectively in real‐time, we have developed an ultrasound‐based therapy monitoring technique using acoustic radiation force to track the change in tissue mechanical properties. We validate our method with concurrent MR thermometry and histology. Comparison studies have been completed on in‐vitro bovine liver samples. A single‐element 1.1 MHz focused transducer was used to deliver HIFU and produce acoustic radiation force (ARF). A 5 MHz single‐element transducer was placed co‐axially with the HIFU transducer to acquire the RF data, and track the tissue displacement induced by ARF. During therapy, the monitoring procedure was interleaved with HIFU. MR thermometry (Philips Panorama 1T system) and ultrasound monitoring were performed simultaneously. The tissue temperature and thermal dose (CEM43 = 240 mins) were computed from the MR thermometry data. The tissue displacement induced by the acoustic radiation force was calculated from the ultrasou...

Transrectal Array Configurations Optimized For Prostate HIFU Ablation

The objectives of this study were to evaluate and compare steering and ablation rates from several types of transrectal arrays operated at different frequencies for whole prostate ablation. Three‐dimensional acoustic and thermal modeling (Rayleigh‐Sommerfield and Penne’s BHTE) were performed. Treatment volumes up to 70cc and anterior‐posterior distances up to 6 cm were considered. The maximum transducer dimensions were constrained to 5 cm (along rectum) and 2.5 cm (elevation), and the channel count was limited to 256. Planar array configurations for truncated‐annular, 1/1.5D, and 2D random arrays were evaluated at 1, 2, and 4 MHz for capability to treat the entire prostate. The acoustic intensity at the surface was fixed at 10 W/cm2. The maximum temperature was restricted to 80° C. The volumetric ablation rate was computed to compare the treatment times amongst different configurations. The 1.5D Planar array at 1 MHz ablated the whole prostate in the shortest amount of time while maintaining adequate stee...