Effects of Beamforming Techniques on Quality of Ultrasound Computed Tomography Images.

Background: In body tissues, tumors generally have different speeds of sound (SOS) than normal tissues. In this respect, ultrasound computed tomography (UCT) can generate a cross-sectional SOS map as an innovative ultrasound imaging method. This technique can produce images with a resolution of millimeters and a high signal-to-noise ratio. Objective: This study aimed to improve UCT image quality without increasing breast cancer screening and diagnosis time. Material and Methods: In this analytical study, a ring-shaped UCT breast imaging system was simulated using the K-wave toolbox of MATLAB. The system has a 20 cm diameter and 256 ultrasonic piezoelectrics placed in the ring's circumference. Different beamforming techniques imaged two designed phantoms (i.e., resolution and contrast), and the resolution and contrast to noise ratio (CNR) were calculated. Results: The results of resolution phantom imaging without any beamforming showed that only bars with the value of 0.125 and 0.167 lp/mm were distinguishable, and the 0.1 bars were not recognizable in the imaging. In addition, increasing the number of transmitters led to no noticeable change in resolution for 0.125 and 0.167 lp/mm bars. In all beamforming techniques for imaging the contrast phantom, the CNR parameter up to an object with a diameter of 8 mm increases with increasing diameter without any change. Conclusion: The beamforming technique using three simultaneous transmitters improved the resolution by about 1 mm compared to the normal strategy. In addition to high-contrast images, beamforming with 9 simultaneous transmitters led to a preferable technique.

Pulsating Microbubble in a Micro-vessel and Mechanical Effect on Vessel Wall: A Simulation Study.

BACKGROUND: Microbubbles are widely used in diagnostic ultrasound applications as contrast agents. Recently, many studies have shown that microbubbles have good potential for the use in therapeutic applications such as drug and gene delivery and opening of blood- brain barrier locally and transiently. When microbubbles are located inside an elastic microvessel and activated by ultrasound, they oscillate and induce mechanical stresses on the vessel wall. However, the mechanical stresses have beneficial therapeutic effects, they may induce vessel damage if they are too high. Microstreaming-induced shear stress is one of the most important wall stresses. OBJECTIVE: The overall aim of this study is to simulate the interaction between confined bubble inside an elastic microvessel and ultrasound field and investigate the effective parameters on microstreaming-induced shear stress. MATERIAL AND METHODS: In this Simulation study, we conducted a 2D finite element simulation to study confined microbubble dynamics, also we investigated both acoustical and bubble material parameters on microbubble oscillation and wall stress. RESULTS: Based on our results, for acoustic parameters in the range of therapeutic applications, the maximum shear stress was lower than 4 kPa. Shear stress was approximately independent from shell viscosity whereas it decreased by increasing the shell stiffness. Moreover, shear stress showed an increasing trend with acoustic pressure. CONCLUSION: Beside the acoustical parameters, bubble properties have important effects on bubble behavior so that the softer and larger bubbles are more appropriate for therapeutic application as they can decrease the required frequency and acoustic pressure while inducing the same biological effects.

Leveraging deep neural networks to improve numerical and perceptual image quality in low-dose preclinical PET imaging.

The amount of radiotracer injected into laboratory animals is still the most daunting challenge facing translational PET studies. Since low-dose imaging is characterized by a higher level of noise, the quality of the reconstructed images leaves much to be desired. Being the most ubiquitous techniques in denoising applications, edge-aware denoising filters, and reconstruction-based techniques have drawn significant attention in low-count applications. However, for the last few years, much of the credit has gone to deep-learning (DL) methods, which provide more robust solutions to handle various conditions. Albeit being extensively explored in clinical studies, to the best of our knowledge, there is a lack of studies exploring the feasibility of DL-based image denoising in low-count small animal PET imaging. Therefore, herein, we investigated different DL frameworks to map low-dose small animal PET images to their full-dose equivalent with quality and visual similarity on a par with those of standard acquisition. The performance of the DL model was also compared to other well-established filters, including Gaussian smoothing, nonlocal means, and anisotropic diffusion. Visual inspection and quantitative assessment based on quality metrics proved the superior performance of the DL methods in low-count small animal PET studies, paving the way for a more detailed exploration of DL-assisted algorithms in this domain.

Observation of targeted gold nanoparticles in nasopharyngeal tumour nude mice model through dual-energy computed tomography.

This study was performed to specify the efficiency of imaging nanoparticle concentration as contrast media in dual-energy computed tomography (DECT). Gold nanoparticles (AuNPs) and gold nanoparticles-conjugated folic acid through cysteamine (FA-Cya-AuNPs) were both considered as contrast agents. Characterization of NPs was performed using Dynamic Light Scattering (DLS) and zeta potential. The hemocompatibility of NPs was confirmed by different blood parameters such as white blood cell, red cell distribution width, hemoglobin, lymphocytes counts and haemolysis assay. DECT algorithm was confirmed using calibration phantom at different concentrations of NPs and tube potentials (80 and 140 kVp). Then, DECT was used to quantify the concentration of both AuNPs and FA-Cys-AuNPs in human nasopharyngeal cancer cells. Mice were injected with non-targeted AuNPs and targeted AuNps at a concentration of 3 × 103 µg/ml. Then, they were scanned with different tube potentials. The concentration of nanoparticles in the various organs of nude mice was measured through DECT imaging and inductively coupled plasma mass spectrometry (ICP-MS) analysis. The results of DECT images were compared with ICP-MS analysis and indicated that they were approximately similar. In sum, FA-Cys-AuNPs can be a proper candidate for targeted contrast media in DECT molecular scanning of human nasopharyngeal tumours.

Photoacoustic image improvement based on a combination of sparse coding and filtering.

SIGNIFICANCE: Photoacoustic imaging (PAI) has been greatly developed in a broad range of diagnostic applications. The efficiency of light to sound conversion in PAI is limited by the ubiquitous noise arising from the tissue background, leading to a low signal-to-noise ratio (SNR), and thus a poor quality of images. Frame averaging has been widely used to reduce the noise; however, it compromises the temporal resolution of PAI. AIM: We propose an approach for photoacoustic (PA) signal denoising based on a combination of low-pass filtering and sparse coding (LPFSC). APPROACH: LPFSC method is based on the fact that PA signal can be modeled as the sum of low frequency and sparse components, which allows for the reduction of noise levels using a hybrid alternating direction method of multipliers in an optimization process. RESULTS: LPFSC method was evaluated using in-silico and experimental phantoms. The results show a 26% improvement in the peak SNR of PA signal compared to the averaging method for in-silico data. On average, LPFSC method offers a 63% improvement in the image contrast-to-noise ratio and a 33% improvement in the structural similarity index compared to the averaging method for objects located at three different depths, ranging from 10 to 20 mm, in a porcine tissue phantom. CONCLUSIONS: The proposed method is an effective tool for PA signal denoising, whereas it ultimately improves the quality of reconstructed images, especially at higher depths, without limiting the image acquisition speed.

Performance evaluation of developed dedicated breast PET scanner and improvement of the spatial resolution by wobbling: a Monte Carlo study.

PURPOSE: Molecular imaging, particularly PET scanning, has become an important cancer diagnostic tool. Whole-body PET is not effective for local staging of cancer because of their declining efficiency in detecting small lesions. The preliminary results of the performance evaluation of designed dedicated breast PET scanner presented. METHODS AND MATERIALS: A new scanner is based on LYSO crystals coupled with SiPM, and it consists of 14 compact modules with a transaxial FOV of 180 mm in diameter. In this study, initial GATE simulation studies were performed to predict the spatial resolution, absolute sensitivity, noise equivalent count rate (NECR) and scatter fraction (SF) of the new design. Spatial wobbling acquisitions were also implemented. Finally, the obtained projections were reconstructed using analytical and iterative algorithms. RESULTS: The simulation results indicate that absolute sensitivity is 1.42% which is appropriate than other commercial breast PET systems. The calculated SF and NECR in our design are 20.6% and 21.8 kcps. The initial simulation results demonstrate the potential of this design for breast cancer detection. A small wobble motion to improve spatial resolution and contrast. CONCLUSION: The performance of the dedicated breast PET scanner is considered to be reasonable enough to support its use in breast cancer imaging.

Computationally Efficient System Matrix Calculation Techniques in Computed Tomography Iterative Reconstruction.

BACKGROUND: Relative to classical methods in computed tomography, iterative reconstruction techniques enable significantly improved image qualities and/or lowered patient doses. However, the computational speed is a major concern for these iterative techniques. In the present study, we present a method for fast system matrix calculation based on the line integral model (LIM) to speed up the computations without compromising the image quality. In addition, we develop a hybrid line-area integral model (AIM) that highlights the advantages of both LIM and AIMs. METHODS: The contributing detectors for a given pixel and a given projection view, and the length of corresponding intersection lines with pixels, are calculated using our proposed algorithm. For the hybrid method, the respective narrow-angle fan beam was modeled by multiple equally spaced lines. The computed system matrix was evaluated in the context of reconstruction using the simultaneous algebraic reconstruction technique (SART) as well as maximum likelihood expectation maximization (MLEM). RESULTS: The proposed LIM offers a considerable reduction in calculation times compared to the standard Siddon algorithm: 2.9 times faster. Differences in root mean square error and peak signal-to-noise ratio were not significant between the proposed LIM and the Siddon algorithm for both SART and MLEM reconstruction methods (P > 0.05). Meanwhile, the proposed hybrid method resulted in significantly improved image qualities relative to LIM and the Siddon algorithm (P < 0.05), though computations were 4.9 times more intensive than the proposed LIM. CONCLUSION: We have proposed two fast algorithms to calculate the system matrix. The first is based on LIM and was faster than the Siddon algorithm, with matched image quality, whereas the second method is a hybrid LIM-AIM that achieves significantly improved images though with its computational requirements.

Dual-energy CT imaging of nasopharyngeal cancer cells using multifunctional gold nanoparticles.

The purpose of this study is to measure the concentration of gold nanoparticles (AuNPs) attached to folic acid through cysteamin as the linker (FA-Cys-AuNPs) and AuNPs in KB human nasopharyngeal cancer cells using dual-energy CT (DECT). In this study, nanoparticles with a size of ∼15 nm were synthesized and characterised using UV-Vis, TEM, FTIR and ICP-OES analyses. The non-toxicity of nanoparticles was confirmed by MTT assay under various concentrations (40-100 µg/ml) and incubation times (6, 12 and 24 h). To develop an algorithm for revealing different concentrations of AuNPs in cells, a corresponding physical phantom filled with 0.5 ml vials containing FA-Cys-AuNPs was used. The CT scan was performed at two energy levels (80 and 140 kVp). One feature of DECT is material decomposition, which allows separation and identification of different elements. The values obtained from the DECT algorithm were compared with values quantitatively measured by ICP-OES. Cells were also incubated with AuNPs and FA-Cys-AuNPs at different concentrations and incubation times. Subsequently, by increasing the incubation time in the presence of FA-Cys-AuNPs, in comparison with AuNPs, DECT pixels were increased. Thus, FA-Cys-AuNPs could be a suitable candidate for targeted contrast agent in DECT molecular imaging of nasopharyngeal cancer cells.

Application of multi-wavelength technique for photoacoustic imaging to delineate tumor margins during maximum-safe resection of glioma: A preliminary simulation study.

Accurate margin delineation and safe maximal resection of glioma is one of the most challenging problems of neurosurgery, due to its close resemblance to normal brain parenchyma. However, different intraoperative visualization methods have been used for real-time intraoperative investigation of the borders of the resection cavity, each having advantages and limitations. This preliminary study was designed to simulate multi-wavelength photoacoustic imaging for brain tumor margin delineation for maximum safe resection of glioma. Since the photoacoustic signal is directly related to the amount of optical energy absorption by the endogenous tissue chromophores such as hemoglobin; it may be able to illustrate the critical structures such as tumor vessels during surgery. The simulation of the optical and acoustic part was done by using Monte-Carlo and k-wave toolbox, respectively. As our simulation results proved, at different wavelengths and depths, the amount of optical absorption for the blood layer is significantly different from others such as normal and tumoral tissues. Furthermore, experimental validation of our approach confirms that, by using multi-wavelengths proportional to the depth of the tumor margin during surgery, tumor margin can be differented using photoacoustic imaging at various depths. Photoacoustic imaging may be considered as a promising imaging modality which combines the spectral contrast of optical imaging as well as the spatial resolution of ultrasound imaging, and may be able to delineate the vascular-rich glioma margins at different depths of the resection cavity during surgery.

Targeted gold nanoparticles enable molecular CT imaging of head and neck cancer: An in vivo study.

The development of various cost-effective multifunctional contrast agent for specific targeting molecular imaging of tumors presents a great challenge. We report here the in vivo targeting imaging of folic acid (FA) gold nanoparticles (AuNPs) through cysteamine (Cys) linking for targeted of human nasopharyngeal head and neck cancer by computed tomography (CT). The toxicity of nanoparticles in kidney, heart, spleen, brain and liver was evaluated by H&E (hematoxylin and eosin) assay. We showed that the formed FA-Cys-AuNPs with an Au core size of ˜13 nm are non-cytotoxic in the particle concentration of 3 × 103 µg/ ml. The nude mice were scanned using a 64-slice CT scan with parameters (80 kVp, slice thickness: 0.625 mm, mAs: 200, pitch: 1). CT scan was performed before and after (Three and six hours) I.V (Intra Venous) injection of AuNPs and FA-Cys-AuNPs. The distribution of nanoparticles in the nude mice was evaluated by imaging and coupled plasma optical emission spectrometry (ICP-OES) analysis. The findings clearly illustrated that a small tumor, which is undetectable via computed tomography, is enhanced by X-ray attenuation and becomes visible (4.30-times) by the molecularly targeted AuNPs. It was further demonstrated that active tumor cells targeting (FA-Cys-AuNPs) is more specific and efficient (2.03-times) than passive targeting AuNPs. According to the results, FA-Cys-AuNPs can be employed as a promising contrast agent in CT scan imaging and maybe in radiotherapy that require enhanced radiation dose.

Folic acid-cysteamine modified gold nanoparticle as a nanoprobe for targeted computed tomography imaging of cancer cells.

Development of various cost-effective multifunctional nanoprobes for efficient targeted molecular imaging of tumors remains a great challenge in medicine. Herein, we report a simple method of forming folic acid-targeted multifunctional gold nanoparticles via cost-effective cysteamine as a template for tumor molecular computed tomography (CT) imaging technique. The formed multifunctional cysteamine-folic acid conjugated gold nanoparticles (FA-Cys-AuNPs) were characterized via different techniques. Colony assay, hematoxylin and eosin (H&E), MTT, and flow cytometry analysis were used to evaluate the cytocompatibility of the particles. We showed that the formed FA-Cys-AuNPs with an Au core size of ~15 nm are non-cytotoxic in a given concentration range and revealed greater X-ray attenuation intensity than iodine-based contrast agent under the same concentration of the active element. At 80 kVp, FA-Cys-AuNPs enable 1.77-times greater contrast per unit mass compared with iodine at a concentration of 2000 µg/ml, and importantly, the developed FA-Cys-AuNPs can be used as a contrast media for targeted CT imaging of folic acid receptor-expressing cancer cells in vitro. CT values of the targeted cells were 2-times higher than that of non-targeted cells at 80 kVp. These findings propose that the designed FA-Cys-AuNPs can be used as a promising contrast agent for molecular CT imaging. This data can be also considered for the application of gold nanostructures in radiation dose enhancement where nanoparticles with high X-ray attenuation are applied.

Evaluation of size, morphology, concentration, and surface effect of gold nanoparticles on X-ray attenuation in computed tomography.

Increasing attention has been focused on the use of nanostructures as contrast enhancement agents in medical imaging, especially in computed tomography (CT). To date, gold nanoparticles (GNPs) have been demonstrated to have great potential as contrast agents for CT imaging. This study was designed to evaluate any effect on X-ray attenuation that might result from employing GNPs with a variety of shapes, sizes, surface chemistries, and concentrations. Gold nanorods (GNRs) and spherical GNPs were synthesized for this application. X-ray attenuation was quantified by Hounsfield unit (HU) in CT. Our findings indicated that smaller spherical GNPs (13 nm) had higher X-ray attenuation than larger ones (60 nm) and GNRs with larger aspect ratio exhibited great effect on X-ray attenuation. Moreover, poly ethylene glycol (PEG) coating on GNRs declined X-ray attenuation as a result of limiting the aggregation of GNRs. We observed X-ray attenuation increased when mass concentration of GNPs was elevated. Overall, smaller spherical GNPs can be suggested as a better alternative to Omnipaque, a good contrast agent for CT imaging. This data can be also considered for the application of gold nanostructures in radiation dose enhancement where nanoparticles with high X-ray attenuation are applied.

A Nanotechnology-based Strategy to Increase the Efficiency of Cancer Diagnosis and Therapy: Folate-conjugated Gold Nanoparticles.

BACKGROUND: Gold nanoparticles (AuNPs), owing to their elegant physicochemical properties, have recently been introduced as promising theranostic nanoparticles. Folic acid is a necessary vitamin for cell proliferation. Accordingly, the surface functionalization of AuNP with folic acid may offer a great potential for the development of a strategy to increase the efficiency of cancer diagnosis and therapy based on the new nanotechnology. In this study, we have reviewed the recent progress made in the design and the biomedical application of various folate-conjugated gold nanoparticles (FAuNPs). METHODS: We performed a structured search in bibliographic databases and made a comprehensive list of relevant papers. The main subjects considered in this review included (1) methods for the preparation of F-AuNPs, (2) applications of F-AuNPs in computed tomography (CT), and (3) the use of F-AuNPs in targeted cancer therapy. RESULTS: As many as 96 papers were selected for the review. Accordingly, we explained the noncovalent and the covalent methods of fabricating the various types of F-AuNPs. Particular applications of F-AuNP in cancer diagnosis using the CT scan modality were described. In addition, the applications of F-AuNPs in targeted radiation therapy, chemotherapy, and hyperthermia were elucidated in depth. In the hyperthermia section, we presented certain extra explanations on F-AuNP-based laser, radiofrequency, and ultrasoundbased hyperthermia methods. CONCLUSION: This review identifies the important roles of F-AuNPs in current cancer studies that are being undertaken worldwide. The findings of this review confirm that F-AuNP is a new theranostic agent, which has a great potential for simultaneous cancer therapy and diagnosis.

Development and validation of an accurate GATE model for NeuroPET scanner.

NeuroPET is a cylindrical full ring mobile PET/CT scanner for brain imaging that was developed by Photo Diagnostic Systems, Inc. The scanner has 7 modules, each with 3×4 detector blocks. The detectors have two layers of scintillator arrays with a half pixel pitch offset to realize two levels of depth of interaction. In this study, we evaluated the NeuroPET scanner modeled in the GATE simulation tool and analyzed the acquired data to better understand the contribution of inter-detector scattering (IDS). The results show that the average difference between simulated and measured data for a point-like source is 2.5%. The differences are 4.7% and 2.7% for NEMA line source in two data acquisition modes and 5.5% for peak NECR measurement. IDS evaluation indicated that the total fractions of the cross-layer crystal scatter (CLCS) and inter-layer crystal scatter (ILCS) events in singles detection mode are 1.98% and 7.98%, respectively. Approximately 90% of these CLCS events deposit most of their energy in the crystal layer other than the layer of first interaction. Additionally, no significant difference in ILCS fractions between the two layers (8.05% vs 7.35%) was observed. The simulation results demonstrate that ILCS events account for ∼79% of the total mis-positioned events.

Derivation of attenuation map for attenuation correction of PET data in the presence of nanoparticulate contrast agents using spectral CT imaging.

OBJECTIVE: Uptake value in quantitative PET imaging is biased due to the presence of CT contrast agents when using CT-based attenuation correction. Our aim was to examine spectral CT imaging to suppress inaccuracy of 511 keV attenuation map in the presence of multiple nanoparticulate contrast agents. METHODS: Using a simulation study we examined an image-based K-edge ratio method, in which two images acquired from energy windows located above and below the K-edge energy are divided by one another, to identify the exact location of all contrast agents. Multiple computerized phantom studies were conducted using a variety of NP contrast agents with different concentrations. The performance of the proposed methodology was compared to conventional single-kVp and dual-kVp methods using wide range of contrast agents with varying concentrations. RESULTS: The results demonstrate that both single-kVp and dual-kVp energy mapping approaches produce inaccurate attenuation maps at 511 keV in the presence of multiple simultaneous contrast agents. In contrast, the proposed method is capable of handling multiple simultaneous contrast agents, thus allowing suppression of 511 keV attenuation map inaccuracy. CONCLUSION: Attenuation map produced by spectral CT clearly outperforms conventional single-kVp and dual-kVp approaches in the generation of accurate attenuation maps in the presence of multiple contrast agents.

Organochlorine pesticides in soil under irrigated cotton farming systems in Vertisols of the Namoi Valley, north-western New South Wales, Australia.

Organochlorine pesticides (OCPs) such as DDT and DDE have been detected in the surface 0.2m of Vertisols in the lower Namoi Valley of north western New South Wales, Australia even though they have not been applied to crops since 1982. However, their presence in the deeper soil horizons has not been investigated. The objective of this study was to determine if OCPs were present to a depth of 1.2m in Vertisols under irrigated cotton farming systems in the lower Namoi Valley of New South Wales. Soil was sampled from the 0-1.2m depths in three sites, viz. the Australian Cotton Research Institute, ACRI, near Narrabri (149°36'E, 30°12'S), and two cotton farms near Wee Waa (149°27'E, 30°13'S) and Merah North (149°18'E, 30°12'S) in northern New South Wales, Australia. The OCPs detected and their metabolites were α-endosulfan, ß-endosulfan, endosulfan sulphate, DDD, DDE, DDT and endrin. The metabolite DDE, a breakdown product of DDT, was the most persistent OCP in all depths analysed. Endosulfan sulphate was the second most persistent followed by endrin>α-endosulfan>ß-endosulfan>DDT and DDD. DDT was sprayed extensively in the lower Namoi Valley up to the early 1980s and may explain the persistence of DDE in the majority of soil samples. Dicofol and Dieldrin, two OCPs previously undocumented in Vertisols were also detected. The movement of OCPs into the subsoil of Vertisols may occur when irrigation or rain transports soil colloids and organic matter via preferential flow systems into the deeper layers of a soil profile. Persistence of OCPs was closely correlated to soil organic carbon concentrations. The persistence in soil of OCP's applied to cotton crops grown more than two decades ago suggests that they could enter the food chain. Their presence at depths of 1.2m suggests that they could move into groundwater that may eventually be used for domestic and stock consumption.