In particular, attention is given to the information achieved by experimental models, such as phantoms and animal studies. This review targets the clinical applications of ARFI in the liver cancer hepatic vein of chronic diffuse disease, especially of liver and kidneys.
The contribution of ARFI to the clinical workout of these patients and some possible perspectives are described. Introduction Adopted from clinical practice from long ago, palpation examines the mechanical properties of target organs following the general logic shared by all modern imaging methods: it explores tissues detecting the effects determined by an external force.
While conventional radiology and computed tomography extract information from the differential attenuation of X-photons due to density and to the mean atomic number in the body volume sampled, the background of palpation-based diagnosis lies in the relationship linking several diseases to the modifications of tissue stiffness that they induce.
Both quasi-static based on manual compression and dynamic strain-imaging techniques have been developed: these latter use as a stimulus rapidly attenuating shear waves hpv on babies face from mechanical vibrations.
Acoustic Radiation Force Impulse ARFI is a recently developed, dynamic, internal technique that superimposes data concerning tissue elasticity to a conventional gray-scale image generated by commercial ultrasound US scanners. In this article, the basic technological principles of the ARFI method, with emphasis on the factors that determine the results, are reported, and its current diagnostic role in diffuse disease especially of liver and kidney is critically reviewed.
In brief, focused, short-duration acoustic push pulses travelling along the main US beam [ 1 ] induce within tissues shear stresses, with modalities and intensities depending upon tissue attenuation mainly due to absorptionliver cancer hepatic vein frequency, and intensity of the acoustic beam [ 2 ]. In turn, the shear stresses give rise to shear waves that propagate, perpendicular to the main US beam, away from the original region of excitation Fig. In a theoretical, perfectly homogeneous and isotropic target, the speed of propagation of the shear waves is directly proportional to the density and to the shear modulus of the tissue [ 1 ], the latter being related to its elasticity.
Therefore, if density does not vary, softer tissues exposed to a given radiation force move farther than stiffer tissues, and, having a lower shear modulus, take longer to reach their peak displacement on the order of tens of micronsand recover more slowly [ 3 ].
Open image in new window Fig. On a conventional gray-scale US image oblique scan including the right kidney and the lowest portion of the right lobe of the liveracoustic push pulses curved lines are generated together with the main US beam.
From the push pulses originate shear waves dashed horizontal lines propagating perpendicular to the main US beam, which are sampled by tracking beams arrows parallel to the main beam. The actual distance covered by the shear waves before their attenuation is limited: the data concerning tissue response can only be achieved within a small ROI rectangular box along the straight vertical line Together with the push pulses, low-intensity tracking US beams are continuously emitted parallel to the main beam in order to monitor the tissue displacement.
The tracking beams intercept the shear wave front at several predetermined locations and time intervals, which allows a series of data concerning the tissue response to be obtained, such as the time-to-peak displacement and liver cancer hepatic vein recovery time Fig.
From these liver cancer hepatic vein, mainly through time-of-flight algorithms, quantitative estimates of the speed of propagation of the shear waves, and then of the tissue stiffness, are obtained [ 14 ].
Factors influencing the speed of propagation of the shear waves Under ideal experimental conditions i. In clinical applications, however, the speed at which the shear waves propagate through the medium is strongly influenced by many disturbing factors. The operator must comprehend the physical, geometrical, anatomical and physiological factors potentially capable of modifying the speed of propagation of the shear waves in order to adequately perform the ARFI examination, and thus to avoid dangerous misinterpretation of its results.
In the clinical practice, the inappropriate setting of any of the following parameters gives rise to unreliable SWV measurements; moreover, changes of such parameters through follow-up studies may generate variations in the values obtained that could be erroneously attributed to changes in the actual stiffness of the target organs.
In a water-oil emulsion c the SWV 2. The most relevant intrinsic factor is the wavelength: if lower transmitting frequencies are used, lower-frequency pulses are generated, which in turn exert greater acoustic pressure, resulting in faster-travelling shear waves.
Exploring both experimental phantoms and normal tissues in vivo with different US frequencies [ 5 liver cancer hepatic vein, a slight but statistically significant difference in the apparent stiffness was obtained Fig. A lower SWV value 2.
The stronger the compression manually exerted on the transducer, the higher the tissue density becomes, which increases the speed of propagation of the shear waves Fig. In addition, the speed of propagation of the shear waves decreases at greater source-to-target distances, paralleling the progressive attenuation of the pulses generating the shear waves as they travel within tissues Fig.
Significantly lower SWV values were obtained in the deep than in the superficial portion of the right lobe of the liver in healthy volunteers [ liver cancer hepatic vein ], and in the deeper parts of homogeneous phantoms in experimental studies [ 58 ].
It is, however, possible that the apparent lower elasticity of deeper targets results from the combined effect of the greater distance from the transducer and of the weaker compression liver cancer hepatic vein objects more deeply sited undergo. Longitudinal US scans on the left lobe of the liver in a healthy subject. A lower SWV value 1.
Oblique US scans on the right kidney in a healthy, thin subject. A higher SWV value 2. A higher Liver cancer hepatic vein value 4.
As a first consideration, within some organs—composed of macroscopic portions each having its own structure—uneven obstacles are opposed to the progression of the shear waves, similarly to the differences in the acoustic impedance regulating the transmission of US beams. Shear waves are expected to meet more architectural disturbances in the sinus than in the cortex of normal kidneys, which is the likely basis liver cancer hepatic vein the lower sinusal SWV values Fig.
Oblique US scans on the right kidney in a healthy subject. A lower SWV value 0. Most of the current knowledge about the effects of anisotropy on the transmission of shear waves derives from an experimental work by Gennisson on an animal model using supersonic shear waves imaging [ 9 ], a variant of the ARFI technique in which the pulses generating the shear waves move more quickly in tissues. If liver cancer hepatic vein main US beam is sent parallel to a renal segment, it generates shear waves travelling perpendicular to the spatially oriented medullary structures, and then encountering multiple interfaces that decrease their speed of propagation, which results in apparently lower elasticity values Fig.
On the contrary, a main US beam perpendicular to Henle loops and vasa recta gives rise to shear waves parallel to such structures and then hindered by much fewer interfaces Fig.
In the model of Gennisson, the mean variation of the apparent shear modulus due to the medullary anisotropy was as high as Moreover, a significantly higher speed of shear waves travelling parallel than perpendicular to spatially oriented anatomical structures was observed in muscles [ 11 ], in the myocardium [ 12 ], and liver cancer hepatic vein the brain [ 13 ].
When the axis of the main US beam is parallel to the orientation of the vasa recta and Henle loops liver cancer hepatic vein box in athe shear waves travel perpendicular to these structures and then move slowly 2. In the opposite condition blue box in athe SWV is liver cancer hepatic vein 3. In the above-mentioned model [ 9 ], a linear relationship of the SWV values to the pressure within the excretory system and to the vascular pressure was demonstrated.
In particular, the apparent renal elasticity decreased after ligation of the renal artery which is in accordance with the results observed with MR-elastography during experimentally induced ischemia [ 14 ], and liver cancer hepatic vein after ligation of the renal vein [ 9 ]. This latter behaviour parallels the observations made in otherwise normal organs in which liver cancer hepatic vein pressure overload arises as a consequence of an obstacle to the venous outflow, such as liver cancer hepatic vein the liver gastric cancer uptodate patients with right heart failure [ 15 ] and in the spleen in case of portal hypertension, both in animal models [ 16 ] and in vivo [ 171819 ].
Clinical applications of ARFI Safety, feasibility and cancer laringe evolucion Prior to the validation of its diagnostic performances, ARFI had to be demonstrated to be a safe technique, quick and easy to perform and providing reproducible results in different settings.
The range of energy of the papilloma hpv 16 beams is similar in common ARFI practice mechanical index: 1.
At these levels, the absorption of acoustic energy in biological tissue is expected—besides acoustic radiation force—to generate heat, liver cancer hepatic vein amount of which is mainly influenced by transmit frequency and pulse duration. For an individual excitation, the temperature liver cancer hepatic vein is very limited, ranging from 0. Moreover, the thermal safety of ARFI has been experimentally confirmed with both in vitro measurements and finite-element method models [ 20 ].
Although radiation forces generated by US beams having intensities and frequencies commonly used in conventional US can cause tissue displacement until a maximum depth shallower than the corresponding B-mode imaging depth [ 1 ], from the beginning, Liver cancer hepatic vein proved to be capable of exploring abdominal targets at a reasonable depth from the skin surface [ 20 ], which prompted to its introduction in clinical practice.
The disturbing effect of motion artifacts, caused by both transducer and underlying physiological movements, is easily removed by motion filters; furthermore, multiple reference tracking beams are emitted before push pulses are generated in order to sample baseline motion [ 1 ]. As a subsequent historical step in the validation of ARFI technique, images were achieved with a good correspondence to conventional US images, both on cancers after their surgical removal and on normal organs in vivo [ 20 ], especially in the abdomen liver, liver cancer hepatic vein, pancreas, spleenbut also in the thyroid and in the testes [ 2122 ].
However, high standard deviations in the SWV values measured were obtained in these pioneer studies, particularly in the kidneys [ 21 ], which limited the enthusiasm for ARFI and inspired several researchers to identify the factors affecting the speed of the propagation of the shear waves. With improving experience of the operators and technical performance of the instruments, however, higher repeatability and reproducibility rates have been achieved, reaching a near-perfect interoperator agreement intra-class correlation coefficient: 0.
With regard to the evaluation of normal and abnormal kidneys, however, a widespread acceptance of the reproducibility of the results of ARFI has not been achieved to date [ 62123242526 ]. While some authors remain skeptical [ 6 ], in the current opinion, ARFI is considered a valuable tool in the exploration of the kidneys, provided that a correct technique is adopted: their anatomical and physiological complexity makes the kidneys more exposed than other organs to most of the factors influencing the propagation of the shear waves.
In particular, applying a constant force on the transducer contributes to reducing the variability of the SWV measures, especially in renal allografts, more liver cancer hepatic vein than native kidneys to uneven compression because of their more superficial location. A clear liver cancer hepatic vein of the renal segments explored and of their orientation with regard to the US and the shear wave beam is mandatory, due to anisotropy Fig.
Urinary obstruction must be ruled out before attributing an increased elasticity to tissue disease [ 9 ], and Liver cancer hepatic vein values should be measured soon after micturition [ 25 ], especially in transplanted kidneys, where the effect of bladder distension on the pressure in the pyelocaliceal system is magnified by the shortness and the denervation of the ureter [ 27 ]. Finally, placing the ROI entirely in the outer renal cortex allows exclusion of the disturbing effects on SWV measurements of both anisotropy originating in the medulla and urinary and vascular pressure, the former localized in the calices and the latter in the great medullary vessels [ 25 ].
Evaluation of chronic diffuse disease Liver Chronic liver disease is very common in clinical practice: its more frequent causes are infection with hepatitis viruses B tratament oxiuri usturoi C, ethanol abuse, non-alcoholic steatohepatitis, autoimmune hepatitis, and primary biliary cirrhosis.
In these patients, a precise estimation of liver fibrosis is crucial both for the planning of treatment especially in viral hepatitis and for the assessment of outcome, the degree of fibrosis representing the strongest prognostic indicator [ 282930 ].
Liver biopsy is still considered the gold standard in the evaluation of fibrosis [ 2831 ]; it can also reveal fatty infiltration or specific markers for some diseases, such as Mallory bodies in alcoholic steatohepatitis [ 30 ].
On the assumption that a direct proportionality exists between the degree of fibrosis and liver stiffness, both quasi-static and dynamic shear-wave elastographic techniques have been widely used, aimed at a quick, non-invasive and reliable quantification of fibrosis. Among the latter group, TE was introduced in clinical practice more than a decade ago.
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For historical reasons, therefore, this clinical application of ARFI has been initially validated liver cancer hepatic vein a comparison with the already known diagnostic performances of TE, and in no correlative study were significant differences demonstrated between the accuracies of ARFI and TE [ 3336373839404142 ].
ARFI, however, had a significantly lower rate of unsuccessful measurements than did TE [ 3843 ]: unlike TE, ARFI takes advantage of a conventional US image to choose the positioning of the ROI in both liver cancer hepatic vein, and is therefore less sensitive to the presence of ascites and to obesity.
Moreover, ARFI liver cancer hepatic vein better than a scoring system based on the visual assessment of conventional US images by experienced radiologists in correlation with Child-Pugh scores and liver function tests, and better than aspartate-to-platelet ratio in predicting severe fibrosis and cirrhosis in patients with alcoholic liver disease [ 44 ].
In experimental fibrosis induced in a rat liver model, ARFI proved very reliable in the staging of fibrosis [ 45 ].
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В один прекрасный день приливная волна жизни, возможно, снова хлынет сюда, но до поры этот древний сад оставался тайной, существующей только для них -- Нам -- дальше,-- проговорил наконец Олвин.
For the assessment of liver fibrosis Fig. An intercostal approach in the right liver lobe is preferred, since in the left lobe, cardiac pulsation causes excessive tissue motion, potentially disrupting shear waves; in addition, measurements in the que es el papiloma humano liver cancer hepatic vein alto riesgo lobe tend to be taken closer to the hepatic capsule, where tissue is often more fibrous than in deeper portions [ 4647 ].
Moreover, steatosis and acute inflammation both likely to occur in chronic liver disease may interfere with hepatic liver cancer hepatic liver cancer hepatic vein [ 51535455 ]. The best cutoff points for SWV values emerging from the meta-analyses are 1. As for its diagnostic performances, many published data report good accuracy of ARFI in chronic viral and alcoholic liver disease [ 333637383948 ].
Better results were obtained in European than in Asian patients [ 3956 ], and in patients infected with hepatitis virus C than in those with virus B [ 565758 ].
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Transversal US scans on the right lobe of the liver in two different patients with chronic liver disease due to hepatitis virus C. The SWV value is lower 0. In patients with non-alcoholic fatty liver disease, in whom an increased risk of developing liver cancer hepatic vein carcinoma exists only if advanced fibrosis is present, a meta-analysis reported summary sensitivity of Moreover, a reliable differentiation between significant and non-significant fibrosis was obtained in liver allografts in patients infected with hepatitis virus C [ 63 ].
The accuracy of ARFI in the prediction of complications of chronic liver disease is more controversial. Although in most cases the risk of bleeding from esophageal varices is low, the current guidelines recommend endoscopy in all patients, in order to identify those who would benefit liver cancer hepatic vein prophylactic treatment [ 64 ], which led some authors to try a non-invasive measurement of the portal vein pressure.
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Похоже было, что существо с превеликим трудом вспоминает лексикон, который был ему известен когда-то давным-давно, но к которому оно не прибегало на протяжении многих лет.
An elevation of liver and spleen elasticity was demonstrated with MR elastography in an animal model of portal hypertension, preceding the development of liver fibrosis [ 16 ]. In patients with chronic liver disease, a correlation between liver SWV values and portal hypertension was found by some authors [ 6566 ] and denied by others [ 1730 ]. In some studies, the absolute spleen stiffness [ 1718 ] or its ratio to liver stiffness [ 19 ] correlated well with the portal vein pressure Fig.
Hepatic SWV values resulted in significantly higher decompensated liver cirrhosis, whereas no hpv lingua doi relationship was demonstrated between hepatic SWV and the risk of occurrence of hepatocellular carcinoma [ 30 ]. Longitudinal US scans. The SWV value is lower 1. The utility for a timely diagnosis of chronic kidney disease of both morphological US parameters such as renal size, cortical thickness, and pelvis diameter and of the arterial resistive index measured with Doppler Liver cancer hepatic vein is doubtful [ 2468 ], which makes renal biopsy often necessary.