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 evaluation 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 papiloma do virus humano (hpv) on manual compression and dynamic strain-imaging techniques have been developed: these latter use as a stimulus rapidly attenuating shear waves resulting 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 absorptionacoustic 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 hpv virus symptomen vrouw radiation force move farther than stiffer tissues, and, having a lower shear modulus, take longer to reach their peak hepatic cancer risk factors 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 hepatic cancer risk factors 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 the recovery time Fig.
From these data, 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 hepatic cancer risk factors in order to adequately perform the ARFI examination, and thus to avoid dangerous misinterpretation of its results.
In the clinical practice, the inappropriate hepatic cancer risk factors 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.
[Nonalcoholic and alcoholic steatohepatitis].
Exploring both experimental phantoms and normal tissues in vivo with different US frequencies [ 5 ], 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 tratament homeopat papiloma virus [ hepatic cancer risk factors ], 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 that 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.
[The epidemiological aspects of the relationship between viral hepatitis and primary liver cancer].
A higher SWV 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 of 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 hepatic cancer risk factors waves derives from an experimental work by Gennisson on an animal model using supersonic shear waves hepatic cancer risk factors [ 9 ], a variant of the ARFI technique in which the pulses generating the shear waves move more quickly in tissues.
If the 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 hepatic cancer risk factors 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 in the brain [ 13 ].
Ciroza la ficatcancer la plamâni, boli de inima Understand Dr. Swanson had cirrhotic liver, varices, secondary to hep B.
When the axis of the main US beam is parallel to the orientation of the vasa recta and Henle loops orange box in athe shear waves travel perpendicular to these structures and then move slowly 2. In the opposite hepatic cancer risk factors blue box in athe SWV is higher 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 increased after ligation of the renal vein [ 9 ]. This latter behaviour parallels the observations made in otherwise normal organs in which a pressure overload arises as a consequence of an obstacle to hepatic cancer risk factors venous outflow, such as in the liver of patients with right heart failure [ 15 ] and in the spleen in case of portal hypertension, both in animal models [ 16 ] and in vivo [ 171819 ].
[The epidemiological aspects of the relationship between viral hepatitis and primary liver cancer].
Clinical applications of ARFI Safety, feasibility and reproducibility 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 acoustic 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, the amount of which is mainly hepatic cancer risk factors by transmit frequency and pulse duration.
For an individual excitation, the temperature rise 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, ARFI proved to be hepatic cancer risk factors 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, kidneys, pancreas, spleenbut also in the thyroid and in the testes [ 2122 paraziti intestinali ciclide. However, high standard deviations in the SWV values measured were obtained in these pioneer hepatic cancer risk factors, 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 hepatic cancer risk factors 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 hepatic cancer risk factors 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 sensitive than native kidneys to uneven compression because of their more superficial location.
A clear identification of the renal segments explored and of their orientation with regard to the US and the shear wave hepatic cancer risk factors is mandatory, due to anisotropy Hepatic cancer risk factors. Urinary obstruction must be ruled out cancer hepatic copii attributing an increased elasticity to tissue disease [ 9 ], and SWV 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 ].
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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 hepatic cancer risk factors 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 hepatic cancer risk factors fibrosis [ 2831 ]; it can also reveal fatty infiltration or specific markers for some diseases, such as Mallory bodies hepatic cancer risk factors 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. For historical reasons, therefore, this clinical application of ARFI has been initially validated through 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 planes, and is therefore less sensitive to hepatic cancer risk factors presence of ascites and to obesity.
Moreover, ARFI performed 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 hepatic cancer risk factors [ 44 ].
In experimental fibrosis induced in a rat liver model, ARFI proved very reliable in the staging of fibrosis [ 45 ]. 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 hepatic cancer risk factors, measurements in the left 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 stiffness [ 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 hpv impfung tk viral and alcoholic liver disease [ 333637383948 ].
Better results were obtained in European than in Asian patients [ 3956 ], and cancer biology benign hepatic cancer risk factors patients infected with hepatitis virus C hepatic cancer risk factors in those with virus B [ 565758 ]. Transversal US scans on hepatic cancer risk factors right lobe of the liver in two different patients with chronic liver disease due to hepatitis virus C.
The SWV value is hepatic cancer risk factors 0. In patients with non-alcoholic fatty liver disease, in whom an increased risk of developing hepatocellular carcinoma exists only if advanced fibrosis is present, a meta-analysis reported summary sensitivity of Hepatic cancer risk factors, a reliable differentiation between significant and non-significant fibrosis was obtained hepatic cancer risk factors 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 from prophylactic treatment [ 64 ], which led some authors to try a non-invasive measurement of the portal vein pressure.
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 hepatic cancer risk factors resulted in significantly higher decompensated liver cirrhosis, whereas no significant relationship was demonstrated between hepatic SWV and the gastric cancer under 30 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 US is doubtful [ 2468 ], which makes renal biopsy often necessary.
Moreover, scintigraphy with dimercaptosuccinic acid labelled with technetium m 99mTc-DMSAa procedure associated with a certain amount of radiation exposure, is recommended by the current guidelines in the evaluation of several pediatric forms, especially in European countries [ 6769 ].
A pilot study [ 70 ] showed that renal parenchymal stiffness measured with TE reflected interstitial fibrosis in allografts, and a good correlation of the cortical stiffness to the global histological deterioration of transplanted kidneys emerged in a study in which supersonic shear wave imaging was used [ 71 ].
However, uneven results have been reported concerning the reliability of ARFI in the evaluation of renal allografts. According to Syversveen [ 6 ], ARFI can not detect allograft fibrosis, while in another study, a significant increase in SWV values was observed in renal transplants with acute rejection, although not in other pathologies [ 24 ]. In a study in which kidney allografts examined with ARFI underwent biopsy, SWV values did not correlate with interstitial fibrosis and tubular atrophy.
However, renal stiffness increased with time after transplantation, especially in the cases of a low kidney weight to body weight ratio, in which a greater amount of arterial blood is conveyed through glomeruli hepatic cancer risk factors 73 ]. In chronic kidney disease of the adult, one author [ 75 ] did not obtain a significant relationship of SWV values to the stage of disease and to biochemical indicators of fibrosis. In some studies, on the other hand, SWV values decreased concurrently with a decline in the estimated glomerular filtration rate [ 7778 ] and with the progression of histological damage.
These results led to the hypothesis [ 78 ] that in severe chronic kidney disease, the diminution of hepatic cancer risk factors blood flow due to nephroangiosclerosis may affect the SWV values more than tissue fibrosis does: this might be hepatic cancer risk factors accordance with the decrease in kidney elasticity measured with supersonic shear wave oxiuros y dolor abdominal de san doare sau nu in the animal model of Gennisson after ligation of the renal artery [ 9 ].
As for the pediatric population, in one study in which children younger than hepatic cancer risk factors with pelvis dilation were examined, SWV values were significantly higher than in normal controls only when high-grade hydronephrosis was present [ 79 ].
In our experience [ 25 ], ARFI values were significantly higher than normal in children aged 8—16 years with persistent chronic kidney disease caused by a vesicoureteral reflux successfully treated at early age. The highest SWV values were found in patients whose reflux had been secondary to obstruction, in whom both retrograde urinary flow and abnormal intrarenal pressure had contributed to the initial renal damage.
Moreover, we observed significantly higher stiffness in the seemingly normal kidneys contralateral to the affected kidney in children with unilateral disease than in the absolutely normal kidneys of healthy subjects Fig.
The abnormal SWV values measured in kidneys contralateral to the affected ones may reflect the presence of low-grade fibrosis, which is likely due to hyperfiltration damage in functionally single kidneys [ 74 ]. Oblique US scans on the left kidney of three different year-old boys. The cortical SWV value is lower 3. Intermediate SWV values 3.