Non-invasive modelling of ultrasound-induced temperature in tissues: a b-splines neural network solution

Efficient hyperthermia therapy session requires knowledge of the exact amount of heating needed at a particular tissue location and how it propagates around the area. Until now, ultrasound heating treatments are being monitored by Magnetic Resonance Imaging (MRI) which, besides raising the treatment instrumental cost, requires the presence of a team of clinicians and limits the hyperthermia ultrasound treatment area due to the space restrictions of an MRI examination procedure. This paper introduces a novel non-invasive modelling approach of ultrasound-induced temperature in tissue. This comes as a cost effective alternative to MRI techniques, capable of achieving a maximum temperature resolution of 0.26 degrees C, clearly inferior to the MRI gold standard resolution of 0.5 degrees C/cm(3). Furthermore, we propose an innovative modelling methodology, where various similar models are built and are further combined through an optimization procedure, that we call neural ensemble optimization (NEO). This combination mechanism is shown to be superior to more simple schemes such as simple averages or evolutionary strategy based techniques. (C), 2016 IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All Rights reserved

SMART IMAGE-GUIDED NEEDLE INSERTION FOR TISSUE BIOPSY

M.S

Possible Patient Early Diagnosis by Ultrasonic Noninvasive Estimation of Thermal Gradients into Tissues Based on Spectral Changes Modeling

To achieve a precise noninvasive temperature estimation, inside patient tissues, would open promising research fields, because its clinic results would provide early-diagnosis tools. In fact, detecting changes of thermal origin in ultrasonic echo spectra could be useful as an early complementary indicator of infections, inflammations, or cancer. But the effective clinic applications to diagnosis of thermometry ultrasonic techniques, proposed previously, require additional research. Before their implementations with ultrasonic probes and real-time electronic and processing systems, rigorous analyses must be still made over transient echotraces acquired from well-controlled biological and computational phantoms, to improve resolutions and evaluate clinic limitations. It must be based on computing improved signal-processing algorithms emulating tissues responses. Some related parameters in echo-traces reflected by semiregular scattering tissues must be carefully quantified to get a precise processing protocols definition. In this paper, approaches for non-invasive spectral ultrasonic detection are analyzed. Extensions of author's innovations for ultrasonic thermometry are shown and applied to computationally modeled echotraces from scattered biological phantoms, attaining high resolution (better than 0.1°C). Computer methods are provided for viability evaluation of thermal estimation from echoes with distinct noise levels, difficult to be interpreted, and its effectiveness is evaluated as possible diagnosis tool in scattered tissues like liver

Identification of the Elastic Modulus of an Organ Model Using Reactive Force and Ultrasound Image

制度:新 ; 報告番号:甲3418号 ; 学位の種類:博士(工学) ; 授与年月日:2011/7/28 ; 早大学位記番号:新574

Intraoperative Guidance for Pediatric Brain Surgery based on Optical Techniques

For most of the patients with brain tumors and/or epilepsy, surgical resection of brain lesions, when applicable, remains one of the optimal treatment options. The success of the surgery hinges on accurate demarcation of neoplastic and epileptogenic brain tissue. The primary goal of this PhD dissertation is to demonstrate the feasibility of using various optical techniques in conjunction with sophisticated signal processing algorithms to differentiate brain tumor and epileptogenic cortex from normal brain tissue intraoperatively. In this dissertation, a new tissue differentiation algorithm was developed to detect brain tumors in vivo using a probe-based diffuse reflectance spectroscopy system. The system as well as the algorithm were validated experimentally on 20 pediatric patients undergoing brain tumor surgery at Nicklaus Children’s Hospital. Based on the three indicative parameters, which reflect hemodynamic and structural characteristics, the new algorithm was able to differentiate brain tumors from the normal brain with a very high accuracy. The main drawbacks of the probe-based system were its high susceptibility to artifacts induced by hand motion and its interference to the surgical procedure. Therefore, a new optical measurement scheme and its companion spectral interpretation algorithm were devised. The new measurement scheme was evaluated both theoretically with Monte Carlo simulation and experimentally using optical phantoms, which confirms the system is capable of consistently acquiring total diffuse reflectance spectra and accurately converting them to the ratio of reduced scattering coefficient to absorption coefficient (µs’(λ)/µa(λ)). The spectral interpretation algorithm for µs’(λ)/µa(λ) was also validated based on Monte Carlo simulation. In addition, it has been demonstrated that the new measurement scheme and the spectral interpretation algorithm together are capable of detecting significant hemodynamic and scattering variations from the Wistar rats’ somatosensory cortex under forepaw stimulation. Finally, the feasibility of using dynamic intrinsic optical imaging to distinguish epileptogenic and normal cortex was validated in an in vivo study involving 11 pediatric patients with intractable epilepsy. Novel data analysis methods were devised and applied to the data from the study; identification of the epileptogenic cortex was achieved with a high accuracy

Ultrasound and photoacoustic methods for anatomic and functional imaging in image guided radiation therapy

(MATERIAL and METHODS) First, we define the physical principals and optimal protocols that provide contrast when imaging with US and the transducer properties contributing to resolution limits. The US field of view (FOV) was characterized to determine the optimal settings with regard to imaging depth, focal region, with and without harmonic imaging, and artifact identification. This will allow us to determine the minimum errors expected when registering multimodal volumes (CT, US, CBCT). Next, we designed an in-house integrated US manipulator and platform to relate CT, 3D-US and linear accelerator coordinate systems. To validate our platform, an agar-based phantom with measured densities and speed-of-sound consistent with tissues surrounding the bladder was fabricated. This phantom was rotated relative to the CT and US coordinate systems and imaged with both modalities. These CT and 3D-US images were imported into the treatment planning system, where US-to-US and US-to-CT images were co-registered and the registration matrix used to re-align the phantom relative to the linear accelerator. The measured precision in the phantom setup, which is defined by the standard deviation of the transformation matrix components, was consistent with and exceeding acceptable clinical patient re-alignments (2 mm). Statistical errors from US-US registrations for different patient orientations ranged from 0.06-1.66 mm for x, y, and z translational components, and 0.00-1.05 degrees for rotational components. Statistical errors from US-CT registrations were 0.23-1.18 mm for the x, y and z translational components, and 0.08-2.52 degrees for the rotational components. The high precision in the multimodal registrations suggest the ability to use US for patient positioning when targeting abdominal structures. We are now testing this on a dog patient to obtain both inter and intra-fractional positional errors. The objective of this experiment is to confirm Hill’s equation describing the relationship between hemoglobin saturation (SaO2) and the partial pressure of dissolved oxygen (pO2). The relationship is modeled as a sigmoidal curve that is a function of two parameters – the Hill coefficient, n, and the net association constant of HbO2, K (or pO2 at 50% SaO2). The goal is to noninvasively measure SaO2 in breast tumors in mice using photoacoustic computed tomographic (PCT) imaging and compare those measurements to a gold standard for pO2 using the OxyLite probe. First, a calibration study was performed to measure the SaO2 (co-oximeter) and pO2 (Oxylite probe) in blood using Hill’s equation (P50=23.2 mmHg and n=2.26). Next, non-invasive localized measurements of SaO2 in MDA-MD-231 and MCF7 breast tumors using PCT spectroscopic methods were compared to pO 2 levels using Oxylite probe. The fitted results for MCF7 and MDA-MD-231 data resulted in a P50 of 17.2 mmHg and 20.7 mmHg and a n of 1.76 and 1.63, respectively. The lower value of the P50 is consistent with tumors being more acidic than healthy tissue. Current work applying photon fluence corrections and image artifact reduction is expected to improve the quality of the results. In summary, this study demonstrates that photoacoustic imaging can be used to monitor tumor oxygenation, and its potential use to investigate the effectiveness of radiation therapy and the ability to adapt therapeutic protocols

Criteria for the design of tissue-mimicking phantoms for the standardization of biophotonic instrumentation

A lack of accepted standards and standardized phantoms suitable for the technical validation of biophotonic instrumentation hinders the reliability and reproducibility of its experimental outputs. In this Perspective, we discuss general criteria for the design of tissue-mimicking biophotonic phantoms, and use these criteria and state-of-the-art developments to critically review the literature on phantom materials and on the fabrication of phantoms. By focusing on representative examples of standardization in diffuse optical imaging and spectroscopy, fluorescence-guided surgery and photoacoustic imaging, we identify unmet needs in the development of phantoms and a set of criteria (leveraging characterization, collaboration, communication and commitment) for the standardization of biophotonic instrumentation

Multispectral image analysis in laparoscopy – A machine learning approach to live perfusion monitoring

Modern visceral surgery is often performed through small incisions. Compared to open surgery, these minimally invasive interventions result in smaller scars, fewer complications and a quicker recovery. While to the patients benefit, it has the drawback of limiting the physician’s perception largely to that of visual feedback through a camera mounted on a rod lens: the laparoscope. Conventional laparoscopes are limited by “imitating” the human eye. Multispectral cameras remove this arbitrary restriction of recording only red, green and blue colors. Instead, they capture many specific bands of light. Although these could help characterize important indications such as ischemia and early stage adenoma, the lack of powerful digital image processing prevents realizing the technique’s full potential. The primary objective of this thesis was to pioneer fluent functional multispectral imaging (MSI) in laparoscopy. The main technical obstacles were: (1) The lack of image analysis concepts that provide both high accuracy and speed. (2) Multispectral image recording is slow, typically ranging from seconds to minutes. (3) Obtaining a quantitative ground truth for the measurements is hard or even impossible. To overcome these hurdles and enable functional laparoscopy, for the first time in this field physical models are combined with powerful machine learning techniques. The physical model is employed to create highly accurate simulations, which in turn teach the algorithm to rapidly relate multispectral pixels to underlying functional changes. To reduce the domain shift introduced by learning from simulations, a novel transfer learning approach automatically adapts generic simulations to match almost arbitrary recordings of visceral tissue. In combination with the only available video-rate capable multispectral sensor, the method pioneers fluent perfusion monitoring with MSI. This system was carefully tested in a multistage process, involving in silico quantitative evaluations, tissue phantoms and a porcine study. Clinical applicability was ensured through in-patient recordings in the context of partial nephrectomy; in these, the novel system characterized ischemia live during the intervention. Verified against a fluorescence reference, the results indicate that fluent, non-invasive ischemia detection and monitoring is now possible. In conclusion, this thesis presents the first multispectral laparoscope capable of videorate functional analysis. The system was successfully evaluated in in-patient trials, and future work should be directed towards evaluation of the system in a larger study. Due to the broad applicability and the large potential clinical benefit of the presented functional estimation approach, I am confident the descendants of this system are an integral part of the next generation OR

An Approach to Improving Efficacy of Cryosurgery: Numerical and Experimental (Using Gel Phantoms) Studies

Freezing and ablating using cryosurgery is becoming a promising surgical tool for the treatment of tumours. For improving the efficiency of the cryosurgical procedure, different approaches have been implemented till now. Most of these techniques have focussed on the freezing process, without giving adequate attention to the damage to the surrounding healthy tissue. In this study, a novel concept is proposed which achieves the desired freezing while protecting the surrounding healthy tissue through the use of low thermal conductivity liquid layer (perfluorocarbons) around the interface of the tumour. Numerical modelling has been done to determine the location of the ice fronts in the presence of this perfluorocarbon layer around the boundary of the tumour. It is noticed that this method leads to a higher ablation rate substantially reducing the surgical time. Also, an optimal offset, i.e. the minimum distance between the tip of the cryoprobe and the boundary of the tumour, is identified for a given tumour radius and active length which gives maximum tumour necrosis in minimum time. It is also observed that for a 2 mm increase in the active length of the cryoprobe, the decrease in optimal offset is approximately 1 mm. Furthermore, for the tumour with different radii (between 10 mm and 15 mm), with same active length of the cryoprobe, the time taken for complete ablation of the larger tumour is nearly 2.7 times the time taken for the smaller one for every 2.5 mm increase in the tumour radius. The results also reveal that there exists an optimal thickness of the perfluorohexane layer around the tumour interface. It is also seen that among perfluorohexane, octafluoropropane and water, perfluorohexane acts as the best substitute for the formation of an insulating layer around the tumour interface. Experiments have been performed to prepare pefluorocarbon (perfluorohexane and perfluorodecalin) emulsions in varied concentration (i.e. 30%, 50%, 70% and 90% (w/v)) through probe sonication. Further, this study reports the particle size, emulsion stability, functional group analysis, thermophysical properties of both perfluorodecalin and perfluorohexane emulsions. With regard to thermal conductivity, it is observed that perfluorodecalin emulsions possess a marginally lower thermal conductivity than perfluorohexane emulsions. It is interesting to note that during cryosurgery of gel phantom in the presence of low thermal conductivity perfluorodecalin emulsion (90% (w/v)), it is observed that the freezing front is not able to penetrate the gel while in its absence, there is a temperature of 4oC at the same thermocouple location of 10 mm (in the axial direction).Cryosurgery of glycine-containing gels is carried out in presence and absence of perfluorohexane layer, and the thermal history is measured using K-type thermocouples connected to a data acquisition system. The presence of glycine causes rapid freezing during cryosurgery with an ice ball depth of 16 mm, while with a perfluorohexane layer at this gel interface, this depth is 13 mm, indicating the ability of this layer to limit freezing. In this study, alumina has also been utilised for the preparation of adjuvant containing gel phantoms. After cryosurgery, it is clearly evident that a temperature decrease is observed in the alumina consisiting gel phantoms when compared to the agarose gel phantoms. It is also noticed that with the increase in insertion depth of the cryoprobe (from 1 to 1.5 cm), there is a decrease in temperature at each thermocouple location in the gel phantoms. This study also demonstrates that in the presence of perfluorohexane layer, when the alumina consisting gel phantoms are cryosurgically cooled; even with the increase in insertion depth, the thermocouple placed axially at 10 mm which is inside the perfluorohexane solution layer indicates a temperature of 25oC. However, in its absence, the temperature is found to be 5:47oC at the same position, suggesting that the freezing is limited within the gel. Furthermore, this work also proposes a new approach that utilises glycine-alumina emulsions as an adjuvant. After cryosurgery of glycine-alumina containing gel, a substantial temperature decrease is observed at all thermocouples placed nearer to the probe, thus indicating an enhancement in freezing. In conclusion, this study proposes novel approaches to improve the cryosurgical procedure through numerical modelling and experiments in gel phantoms, thus, providing newer approaches to improve the cryosurgical outcome