Ta Tamerlan Saidov

Contrast-ultrasound dispersion imaging for prostate cancer localization by improved spatiotemporal similarity analysis

Angiogenesis plays a major role in prostate cancer growth. Despite extensive research on blood perfusion imaging aimed at angiogenesis detection, the diagnosis of prostate cancer still requires systematic biopsies. This may be due to the complex relationship between angiogenesis and microvascular perfusion. Analysis of ultrasound-contrast-agent dispersion kinetics, determined by multipath trajectories in the microcirculation, may provide better characterization of the microvascular architecture. We propose the physical rationale for dispersion estimation by an existing spatiotemporal similarity analysis. After an intravenous ultrasound-contrast-agent bolus injection, dispersion is estimated by coherence analysis among time-intensity curves measured at neighbor pixels. The accuracy of the method is increased by time-domain windowing and anisotropic spatial filtering for speckle regularization. The results in 12 patient data sets indicated superior agreement with histology (receiver operating characteristic curve area = 0.88) compared with those obtained by reported perfusion and dispersion analyses, providing a valuable contribution to prostate cancer localization.

Correspondence - Spatiotemporal correlation of ultrasound contrast agent dilution curves for angiogenesis localization by dispersion imaging

The major role of angiogenesis in cancer development has driven many researchers to investigate the prospects of noninvasive cancer imaging based on assessment of microvascular perfusion. The limited results so far may be caused by the complex and contradictory effects of angiogenesis on perfusion. Alternatively, assessment of ultrasound contrast agent dispersion kinetics, resulting from features such as density and tortuosity, has shown a promising potential to characterize angiogenic effects on the microvascular structure. This method, referred to as contrast-ultrasound dispersion imaging (CUDI), is based on contrast-enhanced ultrasound imaging after an intravenous contrast agent bolus injection. In this paper, we propose a new spatiotemporal correlation analysis to perform CUDI. We provide the rationale for indirect estimation of local dispersion by deriving the analytical relation between dispersion and the correlation coefficient among neighboring time-intensity curves obtained at each pixel. This robust analysis is inherently normalized and does not require curve-fitting. In a preliminary validation of the method for localization of prostate cancer, the results of this analysis show superior cancer localization performance (receiver operating characteristic curve area of 0.89) compared with those of previously reported CUDI implementations and perfusion estimation methods.

3D surface-based registration of ultrasound and histology in prostate cancer imaging

Several transrectal ultrasound (TRUS)-based techniques aiming at accurate localization of prostate cancer are emerging to improve diagnostics or to assist with focal therapy. However, precise validation prior to introduction into clinical practice is required. Histopathology after radical prostatectomy provides an excellent ground truth, but needs accurate registration with imaging. In this work, a 3D, surface-based, elastic registration method was developed to fuse TRUS images with histopathologic results. To maximize the applicability in clinical practice, no auxiliary sensors or dedicated hardware were used for the registration. The mean registration errors, measured in vitro and in vivo, were 1.5±0.2 and 2.1±0.5mm, respectively.

Crystallization of sodium sulfate on hydrophilic/hydrophobic surfaces during drying: An NMR study

Sodium sulfate is recognized as a salt with probably the most damaging capabilities when crystallizing in porous media. The three main crystalline phases which can be formed are thenardite (Na2SO4, anhydrous salt), decahydrate (Na2SO410H2O) and the thermodynamically metastable heptahydrate (Na2SO47H2O). In this study, using a setup in which nuclear magnetic resonance was combined with a digital microscope, we have investigated crystallization by the drying of sodium sulfate droplets on hydrophilic/hydrophobic surfaces in order to see, which crystalline phase is formed.

Delamination of Ançã limestone due to sodium sulfate under different environmental conditions as studied by nuclear magnetic resonance

Sodium sulfate is one of the most damaging and complex salts typically involved in the deterioration of our architectural heritage. One of the main difficulties is to determine which of its crystalline phases, that is, thenardite, mirabilite, or the metastable heptahydrate, will precipitate under certain conditions. Indeed, there is a significant range of temperature and relative humidity in which these phases can crystallize. Furthermore, one precipitated crystalline phase may under certain conditions transform to another one. Here, we show that nuclear magnetic resonance can be successfully used to non-destructively define the phase being precipitated. We investigate delamination of Ançã limestone due to sodium sulfate crystallization, a type of decay which is representative of those occurring in real constructions. The decay was achieved during isothermal drying of stone specimens under different environmental conditions. The work allowed concluding that both mirabilite and heptahydrate can be responsible for this type of decay in different conditions. The heptahydrate tends to crystallize when there is no previous presence of mirabilite crystals in the porous material.

Contrast ultrasound dispersion imaging of different tumor types

Contrast-enhanced ultrasound imaging is a promising approach for prostate cancer detection by analysis of ultrasound-contrast-agent (UCA) transport kinetics. We have recently proposed the assessment of UCA dispersion kinetics as a valuable tool for characterizing prostate cancer microvascular architectures. To this end, a convective dispersion model is fitted to measured UCA time concentration curves. In this study, spatial coherence analysis is introduced as an alternative reliable method for estimation of UCA dispersion. An analytical monotonic relation between spatial coherence and UCA dispersion is derived. Coherence analysis is therefore proposed for classification of different tumor types. To this end, DU-145 and PC-3 human prostate cancer lines are studied in mice xenograft models. These models are investigated by coherence analysis, aiming at the characterization of their microvascular architecture. The results show a good correlation between microvascular density (MVD) and the obtained UCA dispersion (coherence) maps with p-value <; 0.01, suggesting contrast ultrasound dispersion imaging as a valuable non invasive option for characterization of MVD.

The thermodynamic and poromechanic crysallization pressure of sodium sulfate heptahydrate : an NMR study

Sodium sulfate is known as one of the most destructive salts leading to the deterioration of porous materials such as monuments, sculptures and civil engineering structures. While sodium sulfate crystals are growing in a porous material, a crystallization pressure will build up. In this study we compare two approaches for determining the crystallization pressure (i.e., a thermodynamic and a poromechanic). The thermodynamic pressure is related to the supersaturation of the crystals growing in a material, whereas the poromechanic pressure is related to the expansion of the material as a reaction to the crystal growth. In this study we have combined the non-destructive measurement of the concentration of the pore solution in a material by using Nuclear Magnetic Resonance (NMR) with an optical measurement of the dilation of the material during crystallization. This gives the possibility to simultaneously determine the crystallization pressure using both approaches. Here we have focused on the crystallization induced by cooling of a saturated fired-clay brick. In the experiments, first heptahydrate is formed which is supersaturated with respect to decahydrate and a transformation to decahydrate has to be induced. It was found that, for fired-clay brick, the thermodynamic crystallization pressure is larger than the poromechanic crystallization pressure. In a final equilibrium condition with no dynamical crystallization and a constant concentration, the thermodynamic and poromechanic crystallization pressure are equal. The highest crystallization pressure for sodium sulfate is obtained just after the transformation from heptahydrate into decahydrate.

Spatiotemporal methods for prostate cancer detection by contrast-ultrasound dispersion imaging

Prostate cancer is the most diagnosed form of cancer in men in western countries. The lack of reliable imaging solutions currently restricts treatment options to radical interventions. Reliable imaging of angiogenesis, which correlates with cancer aggressiveness, could enable efficient targeting of biopsies and focal therapies, but the complicated effects of angiogenesis on perfusion have prevented a breakthrough so far. As an alternative, contrast-ultrasound dispersion imaging (CUDI) has been proposed to obtain a better characterization of angiogenenic microvascular changes. CUDI makes use of dynamic contrast-enhanced ultrasound imaging after an intravenous contrast-agent bolus injection. Dispersion is estimated by spatiotemporal analysis of time-intensity curves (TICs) obtained at each pixel. Here we present an analytical framework for a dispersion analysis by estimation of the spatial TIC similarity. Data preprocessing is improved by a spatial Wiener deconvolution filter, which reduces the effects of the anisotropic spatial ultrasound resolution, and by TIC time windowing. In addition, we propose the TIC correlation coefficient as a new TIC similarity measure. A comparison of the resulting dispersion maps from 7 recordings with histology, obtained after radical prostatectomy, showed an increased spatial similarity in the presence of cancer in all patients. The cancer classification performance of CUDI was superior to all perfusion-related parameters and was improved by spatial filtering and windowing. Although an extended validation is required, these results confirm the promising value of CUDI for prostate cancer detection.

3D registration of histology and ultrasound data for validation of prostate cancer imaging

Several ultrasound (US) prostate cancer localization methods are emerging, opening opportunities for targeted biopsies and focal therapy. However, before any of these methods, like elastography or contrast-enhanced US, can be introduced into clinical practice, accurate validation is required. The current gold standard for validation is histological assessment of the prostate after radical prostatectomy. Therefore, a 3D registration of histological and US data is required. This task is complicated by misalignment between histology slices and ultrasound imaging planes, pressure caused by the adopted transrectal US probe, and deformation and volume change during fixation in formalin solution. In this work, we introduce a dedicated 3D algorithm, automatically registering histology and ultrasound data. Because there is no information available between histology slices, and internal landmarks are not consistently present in US images, registration is based on outer-contours shape only. A 3D surface model of the prostate in constructed, based on manually outlined contours in a transrectal sweep video and a longitudinal image. Also, a similar model is constructed from the histology slices, including cancerous areas marked by a pathologist. Registration of the models is then performed in three steps: affine registration, elastic surface registration, and internal registration. In-vitro validation of the algorithm was performed by inserting rubber wires into four prostate mimicking phantoms and applying probe pressure. The resulting registration accuracy was 1.6 mm, which is considerably smaller than the histology slicing resolution of 4 mm.