Ratio Histogram Research Articles

ComEst: A completeness estimator of source extraction on astronomical imaging

The completeness of source detection is critical for analyzing the photometric and spatial properties of the population of interest observed by astronomical imaging. We present a software package $\mathtt{ComEst}$, which calculates the completeness of source detection on charge-coupled device (CCD) images of astronomical observations, especially for the optical and near-infrared (NIR) imaging of galaxies and point sources. The completeness estimator $\mathtt{ComEst}$ is designed for the source finder $\mathtt{SExtractor}$ used on the CCD images saved in the Flexible Image Transport System (FITS) format. Specifically, $\mathtt{ComEst}$ estimates the completeness of the source detection by deriving the detection rate of synthetic point sources and galaxies simulated on the observed CCD images. In order to capture any observational artifacts or noise properties while deriving the completeness, $\mathtt{ComEst}$ directly carries out the detection of simulated sources on the observed images. Given an observed CCD image saved in FITS format, $\mathtt{ComEst}$ derives the completeness of the source detection from end to end as a function of source flux (or magnitude) and CCD position. In addition, $\mathtt{ComEst}$ can also estimate the purity of the source detection by comparing the catalog of the detected sources to the input catalogs of the simulated sources. We run ComEst on the images from Blanco Cosmology Survey (BCS) and compare the derived completeness as a function of magnitude to the limiting magnitudes derived by using the Signal-to-Noise ratio (SNR) and number count histogram of the detected sources. $\mathtt{ComEst}$ is released as a Python package with an easy-to-use syntax and is publicly available at https://github.com/inonchiu/ComEst

Whole-Tumor Quantitative Apparent Diffusion Coefficient Histogram and Texture Analysis to Predict Gleason Score Upgrading in Intermediate-Risk 3 + 4 = 7 Prostate Cancer.

The objective of our study was to evaluate whole-lesion quantitative apparent diffusion coefficient (ADC) for the prediction of Gleason score (GS) upgrading in 3 + 4 = 7 prostate cancer. Fifty-four patients with GS 3 + 4 = 7 prostate cancer diagnosed at systematic transrectal ultrasound (TRUS)-guided biopsy underwent 3-T MRI and radical prostatectomy (RP) between 2012 and 2014. A blinded radiologist contoured dominant tumors on ADC maps using histopathologic correlation. The whole-lesion mean ADC, ADC ratio (normalized to peripheral zone), ADC histogram, and texture analysis were compared between tumors with GS upgrading and those without GS upgrading using multivariate ROC analyses and logistic regression modeling. Tumors were upgraded to GS 4 + 3 = 7 after RP in 26% (n = 14) of the 54 patients, and tumors were downgraded after RP in none of the patients. The mean ADC, ADC ratio, 10th-centile ADC, 25th-centile ADC, and 50th-centile ADC were similar between patients with GS 3 + 4 = 7 tumors (0.99 ± 0.22, 0.58 ± 0.15, 0.77 ± 0.31, 0.94 ± 0.28, and 1.15 ± 0.24, respectively) and patients with upgraded GS 4 + 3 = 7 tumors (1.02 ± 0.18, 0.55 ± 0.11, 0.71 ± 0.26, 0.89 ± 0.20, and 1.11 ± 0.16) (p > 0.05). Regression models combining texture features improved the prediction of GS upgrading. The combination of kurtosis, entropy, and skewness yielded an AUC of 0.76 (SE = 0.07) (p < 0.001), a sensitivity of 71%, and a specificity of 73%. The combination of kurtosis, heterogeneity, entropy, and skewness yielded an AUC of 0.77 (SE = 0.07) (p < 0.001), a sensitivity of 71%, and a specificity of 78%. In this study, whole-lesion mean ADC, ADC ratio, and ADC histogram analysis were not predictive of pathologic upgrading of GS 3 + 4 = 7 prostate cancer after RP. ADC texture analysis improved accuracy.

Relation between optical non-contact profilometry and AFM roughness parameters on coated papers with oil-filled nanoparticles

In parallel with the development of nanoparticle coatings for protection of paper substrates, detailed descriptions of the surface topography with micro- to nanoscale roughness features are needed. In this work, papers have been coated with poly(styrene-co-maleic anhydride) nanoparticles including different types of vegetable oils and the surface roughness was evaluated at 2000×2000μm2 to 0.2×0.2μm2 length scales by combining non-contact optical profilometry (NCP) and atomic force microscopy (AFM). The relationships between roughness data were studied for statistical roughness parameters, spatial roughness parameters and in the frequency domain. In order to compare AFM roughness more accurately, the original images were flattened to remove effects of the underlaying fibrous substrate and highlight features of the nanoparticle coating. More detailed information on the coating topography could be obtained by considering bearing ratio curves and histograms, where it was concluded that the oil-filled coatings form a rather thin and continuous coating that closely follows the shape of the cellulose fibers. The relation between statistical roughness parameters from NCP and AFM follows an exponential trend with relatively low coefficient of determination. The increase in surface roughness with length scale showed a transition point attributed to short- and long-range surface features. Therefore, the correlation length was used as a spatial roughness parameter that provides a successful extrapolation of the average roughness over different length scales in a double logarithmic diagram with very high coefficient of determination. Based on the power spectral density, it was difficult to exactly distinguish between the different types of SMI/oil coatings, as they include similar nanoscale features. The frequency roughness parameters were better suited for extrapolation than statistical roughness parameters but little less efficient than the spatial roughness parameters.

Evaluation of linearly-graded SiPMs for high resolution small-animal PET

The performance of a position-sensitive silicon photomultiplier (PS-SiPM), a linearly graded silicon photomultiplier (LG-SiPM), was evaluated for use as a high resolution small-animal PET detector. This SiPM utilizes a combined resistive /capacitive current divider and a double quenching resistor in every SiPM microcell for position estimation. In this paper, using a 6 × 6 array of 0.45 × 0.45 × 6 mm3 polished cerium-doped lutetium-yttrium oxyorthosilicate (LYSO) crystals, coupled to the center of the SiPM, we evaluated the detector performance, with a focus on applications in very high resolution small-animal PET. Measurements of signal-to-noise ratio, energy resolution and flood histogram quality were performed at different over-voltages (from ∼1.0 V to ∼7.5 V) and different temperatures (–6.5 °C, 0 °C, 10 °C and 20 °C) to find the optimal working conditions. The timing resolution was measured at an over-voltage of 3.0 V and at different temperatures. The results showed that all the crystals in the LYSO array could be clearly resolved, even at room temperature (20 °C). The best flood histogram quality was obtained at an over-voltage of ∼3.0 V and a temperature of –6.5 °C. Under these conditions, the average energy resolution, signal-to-noise ratio, and coincidence timing resolution were 22.3 ± 2.7%, 269.0 ± 24.2 and 828 ± 43 ps, respectively.

Aspect ratio histograms of 3D ellipsoids and 2D ellipses — Analytical relations and numerical examples

A typical way of characterizing rocks, composite materials, or human tissue is to extract aspect ratio histograms. A common assumption for this type of analysis is that the sample is composed of several grains or building elements that have a similar shape. Among various shapes, the ellipsoid is very common. In practice, such detailed analysis is performed on 2D cuts or slices through the material. It is intuitive that there is a difference between a 2D aspect ratio histogram and the corresponding 3D histogram. I have derived simple equations that can be used to transform from 3D to 2D and also from 2D to 3D, assuming that the two shortest axes in the ellipsoid were equal. For the general case, when all axes were different, an approximate equation was derived. All equations were compared with stochastic numerical simulations of cutting a 3D ellipsoid by an arbitrary random number of planes. It was determined that in the general case, the shortest aspect ratio would dominate the 2D histograms and that it was practically impossible to detect the highest aspect ratio from 2D planar cuts.

Tip-enhanced Raman spectroscopic imaging shows segregation within binary self-assembled thiol monolayers at ambient conditions.

Phase segregation of coadsorbed thiol molecules on a gold surface was investigated with nanoscale chemical imaging using tip-enhanced Raman spectroscopy (TERS). Samples were prepared using mixed solutions containing thiophenol (PhS) and an oligomeric phenylene-ethynylene (OPE) thiol, with 10:1, 2:1, and 1:1 molar ratios. Phase segregation into domains with sizes from ≈30 to 240nm is observed with these molar ratios. A comparison of TERS images with different pixel sizes indicates that a pixel size bigger than 15nm is not reliable in defining nanodomains, because of undersampling. In this study, the formation of nanodomains was clearly evident based on the molecular fingerprints provided by TERS, while ambient scanning tunneling microscopy (STM) was not capable of discerning individual domains via their apparent height difference. TERS therefore allows to image nanodomains in binary self-assembled monolayers, which are invisible to methods solely relying on topographic or electron density characteristics of self-assembled monolayers. Moreover, TERS mapping provides statistical data to describe the distribution of molecules on the sample surface in a well-defined manner. Peak ratio histograms of selected TERS signals from samples prepared with different mixing ratios give a better understanding of the adsorption preference of the thiols studied, and the relationship of their mixing ratio in solution and adsorbed on the surface.

False positive and false negative diagnoses of prostate cancer at multi-parametric prostate MRI in active surveillance.

MP-MRI is a critical component in active surveillance (AS) of prostate cancer (PCa) because of a high negative predictive value for clinically significant tumours. This review illustrates pitfalls of MP-MRI and how to recognise and avoid them. The anterior fibromuscular stroma and central zone are low signal on T2W-MRI/apparent diffusion coefficient (ADC), resembling PCa. Location, progressive enhancement and low signal on b ≥1000 mm²/s echo-planar images (EPI) are differentiating features. BPH can mimic PCa. Glandular BPH shows increased T2W/ADC signal, cystic change and progressive enhancement; however, stromal BPH resembles transition zone (TZ) PCa. A rounded morphology, low T2 signal capsule and posterior/superior location favour stromal BPH. Acute/chronic prostatitis mimics PCa at MP-MRI, with differentiation mainly on clinical grounds. Visual analysis of diffusion-weighted MRI must include EPI and appropriate windowing of ADC. Quantitative ADC analysis is limited by lack of standardization; the ADC ratio and ADC histogram analysis are alternatives to mean values. DCE lacks standardisation and has limited utility in the TZ, where T2W/DWI are favoured. Targeted TRUS-guided biopsies of MR-detected lesions are challenging. Lesions detected on MP-MRI may not be perfectly targeted with TRUS and this must be considered when faced with a suspicious lesion on MP-MRI and a negative targeted TRUS biopsy histopathological result.Keypoints• Multi-parametric MRI plays a critical role in prostate cancer active surveillance.• Low T2W signal intensity structures appear dark on ADC, potentially simulating cancer.• Stromal BPH mimics cancer at DWI and DCE.• Long b value trace EPI should be reviewed• Targeted biopsy of MR-detected lesions using TRUS guidance may be challenging.

Handheld object detection and its related event analysis using ratio histogram and mixture of HMMs

This paper proposes a novel system to analyze human-object interaction events happening between hands and faces in real time. Two challenging problems in this event analysis must be addressed, i.e., there is no prior knowledge (like shape, color, size, and texture) about the handheld objects, and there are large spatial–temporal variations in event representation. For the first challenge, a novel ratio histogram is proposed to find important color bins to locate handheld objects and their trajectories via a code book technique. This scheme is different from other boosted methods which require very time-consuming estimations to search reliable body configurations. For the second challenge, a mixture of HMMs is proposed to describe an event not only from its dynamic context but also its multiplicity context. It can be performed in real time because an exhaustive search process is avoided to find possible interaction pairs between objects and body parts.

Comparison of elastography methods in patients with pancreatic masses

Endoscopic ultrasonography (EUS) quantitative elastography methods are developed for non-invasive differentiation of pancreatic masses. First: To evaluate the diagnostic value of strain ratio (SR) and hue histogram (HH) in patients with pancreatic masses and to determine the cut-off value between pancreatic cancer and focal pancreatitis using a pancreatic tissue close to the mass as a reference area. Second: To calculate new variable HH ratio (HHR) in an attempt to improve sensitivity, specificity and accuracy of the method. In a prospective single center study, 149 patients were examined: 105 with the pancreatic masses and 44 controls using Pentax EUS linear probes in combination with Hitachi platforms. SR and HH were automatically calculated by machine software. Finally, two groups were formed: Pancreatic cancer group (58 patients) and focal pancreatitis group (47 patients). All statistical analysis has been made in SPSS 14.0 (SPSS Inc., Chicago, USA). Statistical analysis in our study showed that SR with a cut-off value of 7.59 reaches 100% sensitivity and 95% specificity with overall accuracy of 97% (confidence intervals [CI]: 92-97%) in detection of pancreatic cancer. Statistical analysis also showed that HH with a cut-off value of ≥86 reaches 100% sensitivity and just 45% specificity with overall accuracy of 66% (CI: 61-66%) in detection of pancreatic cancer. New variable HHR with cut-off ≥1.153 was slightly better with 98% sensitivity and 50% specificity, with overall accuracy of 69% (CI: 63-70%). SR showed significantly higher specificity compared with HH and HHR. More HH studies on Hitachi platforms are needed.

A Simple Capacitive Charge-Division Readout for Position-Sensitive Solid-State Photomultiplier Arrays

A capacitive charge-division readout method for reading out a 2 × 2 array of 5 mm × 5 mm position-sensitive solid-state photomultipliers (PS-SSPM) was designed and evaluated. Using this analog multiplexing method, the 20 signals (16 position, 4 timing) from the PS-SSPM array are reduced to 5 signals (4 position, 1 timing), allowing the PS-SSPM array to be treated as an individual large-area PS-SSPM module. A global positioning approach can now be used, instead of individual positioning for each PS-SSPM in the array, ensuring that the entire light signal is utilized. The signal-to-noise ratio (SNR) and flood histogram quality at different bias voltages (27.5 V to 32.0 V at 0.5 V intervals) and a fixed temperature of 0 °C were evaluated by coupling a 6 × 6 array of 1.3 mm × 1.3 mm × 20 mm polished LSO crystals to the center of the PS-SSPM array. The timing resolution was measured at a fixed bias voltage of 31.0 V and a fixed temperature of 0 °C. All the measurements were evaluated and compared using capacitors with different values and tolerances. Capacitor values ranged from 0.051 nf to 10 nf, and the capacitance tolerance ranged from 1% to 20%. The results show that better performance was achieved using capacitors with smaller values and better capacitance tolerance. Using 0.2 nf capacitors, the SNR, energy resolution and timing resolution were 24.3, 18.2% and 8.8 ns at a bias voltage 31.0 V, respectively. The flood histogram quality was also evaluated by using a 10 × 10 array of 1 mm × 1 mm × 10 mm polished LSO crystals and a 10 × 10 array of 0.7 mm × 0.7 mm × 20 mm unpolished LSO crystals to determine the smallest crystal size resolvable. These studies showed that the high spatial resolution of the PS-SSPM was preserved allowing for 0.7 mm crystals to be identified. These results show that the capacitive charge-division analog signal processing method can significantly reduce the number of electronic channels, from 20 to 5, while retaining the excellent performance of the detector.

Sensory innervation of the rat hind paw: morphometric comparison between sural and saphenous nerves.

Previous studies on dermatome mappings of the rat hind paws investigated the C‐fibers distribution and then assumed that the A‐fibers distributions resemble that of the C‐fibers. We investigated the morphometry of fascicles and myelinated fibers (A‐fibers) in the sural and saphenous nerves in young rats. Six 30‐day‐old female Wistar rats had their right and left sural and saphenous nerves prepared for light microscopy and morphometry. Comparisons were made between segments (proximal vs distal) and sides (left vs right) for the same nerves and between nerves (sural vs saphenous) from the same side and differences were considered if p&lt;0.05. Both the sural and saphenous nerves are longitudinally symmetrical on both sides. Both nerves also exhibited lateral symmetry. Also, no significant differences were found between nerves. Myelinated fibers and respective axons diameter, as the G ratio histograms are unimodal in both nerves, regardless of segments or sides. This indicates that the nerves investigated did not reach fully development in animals aged 30 days. The similar number of myelinated fibers, associated with their similar size in both sural and saphenous nerves suggests that the innervation territory for both nerves is equally distributed at the foot. This information is useful for studies of sensory neuropathies, in particular, studies of nerve regeneration.

Non-linear signal response functions and their effects on the statistical and noise cancellation properties of isotope ratio measurements by multi-collector plasma mass spectrometry

A nebulizer-centric response function model of the analytical inductively coupled argon plasma ion source was used to investigate the statistical frequency distributions and noise reduction factors of simultaneously measured flicker noise limited isotope ion signals and their ratios. The response function model was extended by assuming i) a single gaussian distributed random noise source (nebulizer gas pressure fluctuations) and ii) the isotope ion signal response is a parabolic function of the nebulizer gas pressure.Model calculations of ion signal and signal ratio histograms were obtained by applying the statistical method of translation to the non-linear response function model of the plasma. Histograms of Ni, Cu, Pr, Tl and Pb isotope ion signals measured using a multi-collector plasma mass spectrometer were, without exception, negative skew. Histograms of the corresponding isotope ratios of Ni, Cu, Tl and Pb were either positive or negative skew. There was a complete agreement between the measured and model calculated histogram skew properties.The nebulizer-centric response function model was also used to investigate the effect of non-linear response functions on the effectiveness of noise cancellation by signal division. An alternative noise correction procedure suitable for parabolic signal response functions was derived and applied to measurements of isotope ratios of Cu, Ni, Pb and Tl. The largest noise reduction factors were always obtained when the non-linearity of the response functions was taken into account by the isotope ratio calculation.Possible applications of the nebulizer-centric response function model to other types of analytical instrumentation, large amplitude signal noise sources (e.g., lasers, pumped nebulizers) and analytical error in isotope ratio measurements by multi-collector plasma mass spectrometry are discussed.

Changing Associations Between Cognitive Impairment and Imaging in Multiple Sclerosis as the Disease Progresses

The authors explored cross-sectional associations between MRI parameters (lesion metrics, brain volumes, magnetization transfer ratio histograms, and metabolite concentrations) and cognition in 61 patients who experienced clinically-isolated syndromes (CIS) 7 years earlier. IQ decline and poorer overall cognition were associated with T2 white-matter lesions, and slow information-processing with both T2 lesions and gray-matter atrophy. In a previous study of the same cohort, gray-matter atrophy measured shortly after CIS failed to predict development of cognitive impairment years later. Our findings suggest that gray-matter pathology, reflected by atrophy measurements, becomes increasingly important in determining cognition as MS progresses.

MTR and In-vivo 1H-MRS studies on mouse brain with parkinson’s disease

The aim of this study was to investigate whether the changes in the magnetization transfer ratio (MTR) histogram are related to specific characteristics of Parkinson’s disease (PD) and to investigate whether the MTR histogram parameters are associated with neurochemical dysfunction by performing in vivo proton magnetic resonance spectroscopy (1H-MRS). MTR and in vivo1H-MRS studies were performed on control mice (n = 10) and 1-methyl-1,2,3,6-tetrahydropyridine intoxicated mice (n = 10). All the MTR and in vivo1H-MRS experiments were performed on a 9.4 T MRI/MRS system (Bruker Biospin, Germany) using a standard head coil. The protondensity fast spin echo (FSE) images and the T2-weighted spin echo (SE) images were acquired with no gap. Outer volume suppression (OVS), combined with the ultra-short echo-time stimulated echo acquisition mode (STEAM), was used for the localized in-vivo1H-MRS. The quantitative analysis of metabolites was performed from the 1H spectra obtained in vivo on the striatum (ST) by using jMRUI (Lyon, France). The peak height of the MTR histograms in the PD model group was significantly lower than that in the control group (p < 0.05). The midbrain MTR values for volume were lower in the PD group than the control group(p < 0.05). The complex peak (Glx: glutamine+glutamate+ GABA)/creatine (Cr) ratio of the right ST in the PD group was significantly increased as compared to that of the control group. The present study revealed that the peak height of the MTR histogram was significantly decreased in the ST and substantia nigra, and a significant increase in the Glx/Cr ratio was found in the ST of the PD group, as compared with that of the control group. These findings could reflect the early phase of neuronal dysfunction of neurotransmitters.

An affine invariant relative attitude relationship descriptor for shape matching based on ratio histograms

A novel shape descriptor, named as ratio histograms (R-histogram), is proposed to represent the relative attitude relationship between two independent shapes. For a pair of two shapes, the shapes are treated as the longitudinal segments parallel to the line connecting centroids of the two shapes, and the R-histogram is composed of the length ratios of collinear longitudinal segments. R-histogram is theoretically affine invariant due to collinear distance invariance of the affine transformation. In addition, as the computation of the length ratio weakens the noise contribution, R-histogram is robust to noise. Based on the R-histogram, the shape-matching algorithm includes two major phases: preprocessing and matching. The first phase, which can be processed off-line, is trying to obtain the R-histograms of all original shape pairs. In the second phase, for each transformed shape pair, its R-histogram is computed and the candidate matched shape pair with minimal R-histogram matching error is found. Subsequently, a voting strategy, which further improves the accuracy of shape matching, is adopted for the candidate corresponding shape pairs. Experimental results demonstrate that the proposed R-histogram is robust and efficient.

The use of exit detector sinograms to detect anatomical variations for patients extending beyond the TomoTherapy field of view: A feasibility study

This work describes an independent method to use the TomoTherapy Hi-ART megavoltage CT imaging system for daily monitoring of anatomical changes of cancer patients whose anatomy extends beyond the imaging field of view. The imaging detector response to changes in attenuating media was measured using water-equivalent plastic. Weight loss was simulated using an anthropomorphic phantom and determining the system's ability to detect the weight loss. Layers of tissue-equivalent bolus were added to an anthropomorphic pelvis phantom and CT simulations of the phantom were conducted, one in which the phantom and bolus were both within the TomoTherapy imaging field of view, and another in which the couch was raised so that the bolus was outside the field of view. Gynecological treatment plans were developed using the TomoTherapy treatment planning system, and successive fractions of the plan were then delivered to the phantom. Weight loss was simulated by removing a 0.5 cm layer of bolus following each fraction. The exit detector sinograms were obtained from each fraction, and ratios of sinograms were calculated relative to a reference sinogram for which all bolus was in place. Histograms of ratio sinograms were determined and used to correlate with simulated weight loss. Exit detector sinograms and ratio histograms were also retrospectively analyzed for five patients all of whose anatomies extended beyond the imaging field of view and all of whom experienced weight variations exceeding 10% during treatment. Exit detector signal is well correlated to changes in attenuator thickness as demonstrated in both slab and anthropomorphic phantom geometries. Measured and expected signal increases agreed to within less than 2% for simulated weight loss on the anthropomorphic phantom. Exit detector signals for pelvic patients with significant weight loss variations were consistent with phantom measurements. The analysis of the ratio sinograms for the phantom measurements and real patients indicated that exit detector sinograms can be used to detect relative changes in patient anatomy for each fraction as a means of in vivo quality assurance.

Pulse modulated microwave and infrared thermography for superficial hyperthermia

A 3D temperature field distribution of biological tissue for superficial hyperthermia using a pulse modulated microwave (PMMW) was presented. A 3D sliced homogeneous phantom was radiated by the PMMW and an infrared thermal imager was applied to image temperature distribution throughout the phantom. The period of the PMMW is 3 s and the output power is 35 W. The temperature rises by at least 3 °C in the phantom when the duty cycle varies from 1/3, 1/2, 2/3 to 1 (denoted by scenarios 1–4). Both the accumulative temperature-volume histogram and the relative depth-area ratio histogram show that the maximum temperature rise (MTR) is 6.6 and 8 °C in scenarios 2 and 3, and they are superior to scenarios 1 and 4. Furthermore, the PMMW can control temperature field distribution of biological tissue. It provides both preliminary basis for thermal volume control and new technology for temperature control and monitor in superficial hyperthermia.

Endoscopic ultrasound elastography.

Endoscopic ultrasound (EUS) is a reference technique for diagnosing and staging several different diseases. EUS-guided biopsies and fine needle aspirations are used to improve diagnostic performance of cases where a definitive diagnosis cannot be obtained through conventional EUS. However, EUS-guided tissue sampling requires experience and is associated with a low but not negligible risk of complications. EUS elastography is a non-invasive method that can be used in combination with conventional EUS and has the potential for improving the diagnostic accuracy and reducing the need for EUS-guided tissue sampling in several situations. Elastography measures tissue stiffness by evaluating changes in the EUS image before and after the application of slight pressure to the target tissue by the ultrasonography probe. Pathologic processes such as cancerization and fibrosis alter tissue elasticity and therefore induce changes in elastographic appearance. Qualitative elastography depicts tissue stiffness using different colors, whereas quantitative elastography renders numerical results expressed as a strain ratio or hue histogram mean. EUS elastography has been proven to differentiate between benign and malignant solid pancreatic masses, as well as between benign and malignant lymph nodes with a high accuracy. Studies have also demonstrated that the early changes of chronic pancreatitis can be distinguished from normal pancreatic tissues under EUS elastography. In this article, we review the technical aspects and current clinical applications of qualitative and quantitative EUS elastography and emphasize the potential additional indications that need to be evaluated in future clinical studies.

Endoscopic ultrasound elastography

Endoscopic ultrasound (EUS) is a reference technique for diagnosing and staging several different diseases. EUS-guided biopsies and fine needle aspirations are used to improve diagnostic performance of cases where a definitive diagnosis cannot be obtained through conventional EUS. However, EUS-guided tissue sampling requires experience and is associated with a low but not negligible risk of complications. EUS elastography is a non-invasive method that can be used in combination with conventional EUS and has the potential for improving the diagnostic accuracy and reducing the need for EUS-guided tissue sampling in several situations. Elastography measures tissue stiffness by evaluating changes in the EUS image before and after the application of slight pressure to the target tissue by the ultrasonography probe. Pathologic processes such as cancerization and fibrosis alter tissue elasticity and therefore induce changes in elastographic appearance. Qualitative elastography depicts tissue stiffness using different colors, whereas quantitative elastography renders numerical results expressed as a strain ratio or hue histogram mean. EUS elastography has been proven to differentiate between benign and malignant solid pancreatic masses, as well as between benign and malignant lymph nodes with a high accuracy. Studies have also demonstrated that the early changes of chronic pancreatitis can be distinguished from normal pancreatic tissues under EUS elastography. In this article, we review the technical aspects and current clinical applications of qualitative and quantitative EUS elastography and emphasize the potential additional indications that need to be evaluated in future clinical studies.

Últimos avances sobre los tumores pancreáticos

Pancreatic cancer (PC) continues to have a poor prognosis. New epidemiological trials have suggested that there may be protective factors, such as aspirin or oleic acid intake. The main diagnostic tool for PC is endoscopic ultrasound (EUS), and new EUSrelated technologies have appeared, such as quantitative elastography (strain ratio and hue histogram analysis), intravenous contrasts, and the new procore needles to help in the differential diagnosis with other diseases (mainly chronic pancreatitis). In the next few years, intratumoral confocal endomicroscopy will be used for the diagnosis of PC and cystic tumors, by inserting a miniprobe inside the 19G needle of the echoendoscope.Notable therapeutic developments are studies on the safety, feasibility and accuracy of intratumoral gemcitabine administration by EUS-fine needle injection in the treatment of locally advanced PC. In the treatment of cystic tumors of the pancreas, mainly intraductal papillary mucinous neoplasms (IPMN), most studies aim to optimize follow up by assessing predictive factors of malignant transformation and evaluating the natural history of this neoplasm.