Ultrasound elastography in abdominal imaging

Transcription

1 Ultrasound elastography in abdominal imaging Olivier ucidarme Pitié Salpêtrière - UPMC Paris France Ultraschall Med. 013 Apr;34(): Ultraschall Med. 013 Jun;34(3): US elastography Ultraschall Med 017 Aug;38(4):e16-e47. Epub 017 Apr 13. Static/ Quasi Static Elastography - using an external Stress (alternative pushes) - using an internal stress (cardiac beats ) measure the strain and not the Young s modulus E (or shear elastic modulus of the tissue G) Stress s Strain Young s modulus E = stress/strain Qualitative assessment because stress is unknown US Elastography External alternative compressions Quasi-static Elastography Internal deformation (cardiac beats, breathing ) US elastography ShearWave Elastography - using an external push (Transient E, FibroScan ); NO image (1D) - using an internal US push (SWE / ARFI) Step 1: US impulsion Probe Step : Ultrafast imaging US push Shearwave nguyenthienhung.com Strain Elastography ( Hitachi Real-time Tissue Elastography HI-RTE ) Strain Elastography ( Philips Nanometer tissue strain tracking Elastography ) Estimation of the speed of the shearwave Young s modulus E= 3ρV c 1

2 External pressure (piston) No Image 1D Single Point Quantification US Elastography Shear-Wave Elastography Point SWE : ARFI Internal acoustic pressure Anatomical D image Single frame Acquisition D Color map SWE Real Time Acq. Point SWE = Acoustic Radiation Force impulse: ARFI quantification Shear-wave speed measurment US focused Impulse of 0.3s Measurment of the propagation of SW in a small volume of interest No elastogram, only a regional average of SW speed is measured in m/s Although ultrasound imaging is used to guide placement of the box, no elasticity images are produced Point Quantification Transient Elastography (Philips) Fibroscan (EchoSens) Virtual Touch Tissue Quantification Virtual Touch (Siemens) IQ (Siemens) ElastoPQ (Philips) Shear-wave speed measurment Shear-wave speed imaging SSI. SuperSonic Imagine Siemens (VTQ TM ), Philips (ElastoPQ TM ) Esaote, GE, Hitachi, and Samsung Point SWE = Acoustic Radiation Force impulse: ARFI quantification Shear-wave speed measurment US focused Impulse of 0.3s Measurment of the propagation of SW in a small volume of interest No elastogram, only a regional average of SW speed is measured in m/s Although ultrasound imaging is used to guide placement of the box, no elasticity images are produced D Shear wave elastography Shear-wave speed imaging Multiple pswe placing the ARFI focus (push) at multiple sequential locations detecting the shear wave arrival time at multiple lateral locations patches of small SW Speed values that may be mosaicked to create a large ROI D-SWE image displayed in color takes time + time needed for the transducer to cool = not real time kpa m/s E= 3ρV c E= 3V c 11.9 = 3* (1.99) D Shear wave elastography Shear-wave speed imaging m/s or kpa? Several focused US impulsions are generated at different depths along a line in a very short period of time creation of a plane SW travelling in a large surface area plane SW measured in real time by ultrafast imaging (plan waves) E maps are provided in almost real time after conversion in kpa B mode remains in close real time m/s is the unit of shear wave speed Vc, directly measured by the scanner For kpa (unit of elastic modulus), the scanner must convert the measured data using E = 3ρV c Based on many assumptions that are generally not valid nguyenthienhung.com

3 Assumptions include that: m/s or kpa? ρ is always = 1 (not always true), there is no variation of the elastic modulus with the magnitude of applied force (push magnitude or probe pressure or portal). (In general, not true) there is no variation of the elastic modulus with the shear wave frequency In fact all tissues are viscoelastic, causing the tissue to become stiffer the faster it is strained, i. e., the higher the frequency there is no variation of the elastic modulus with direction (In general, not true) m/s = direct measurement and kpa indirect measurement In case of kpa: E or G? F 0 A ( 0 ) F A = E F A E = ( ) x F A = G F A G = x In case of kpa: E or G? V c may be converted to either Young s modulus E = 3ρV c or shear modulus G=E / (1+ ν) under the assumption that the tissue is incompressible ν = coef of Poisson (between 0 and 0.5): G=E / (1+ 0.5) = E/3 ρ is the density of the tissue. E and G are expressed in units of kilopascal (kpa) MRE literature: Stiffness data are provided for shear modulus G Ultrasound elastography literature : Stiffness data are provided for Young s modulus E E=3G MRE iver stiffness kpa (G) SWE liver stiffness 5-6 kpa (E) One more thing! SW speed will vary with a number of system factors: shear wave vibration frequency and bandwidth the different software method employed data should not be pooled when acquired using more than one system Stiffness thresholds for clinical use known for specific equipment should not be utilized for other equipment* * Dietrich CF et al. EFSUMB Guidelines Ultraschall in Med 017;38:e16-e47 iver examination procedure iver shear wave elastography (TE, pswe and D-SWE) General technical comments Patient preparation: Patient position: supine slight left oblique decubitus right arm up, max abduction - Optimize intercostal windows on right liver +++ homogeneous pattern + no shadowing - Using sufficient pressure on transducer to: open space + reduce attenuation + optimum coupling 3

4 ESFUMB guidelines* Patients should fast for a minimum of hours and rest for a minimum of 10 minutes before undergoing liver stiffness measurement with SWE Depth of measurement Quantification using the Q-Box : The depth range for the most reliable liver stiffness assessment using pswe and DSWE should be 3-5 cm from the probe surface and simultaneously 1- cm below the liver capsule ess than 8 cm in depth * Dietrich CF et al. EFSUMB Guidelines Ultraschall in Med 017;38:e16-e47 Wang CZ et al. Influence of measurement depth on the stiffness assessment of healthy liver with realtime shear wave elastography. Ultrasound Med Biol. 014 Mar;40(3):461-9 ESFUMB guidelines* The results with the lowest variability in comparing different pswe or D-SWE systems were obtained at a depth of 4 5 cm from the transducers (with convex transducers). Accordingly, this location is recommended if it is technically suitable. About respiration Better to avoid respiratory motion * Dietrich CF et al. EFSUMB Guidelines Ultraschall in Med 017;38:e16-e47 But About respiration ESFUMB guidelines* In Human: Free breathing SWE values were constantly 0 5% lower than Apnea ones (P < 0.001) In phantom: no differences between SWE measurements at rest and during motion patient breath-holding impacts liver stiffness Particularly if valsalva maneuver increase central venous pressure increase of the liver stiffness Measurement of liver stiffness by SWE should be performed through a right intercostal space in supine position, with the right arm in extension, during breath hold, avoiding deep inspiration prior to the breath hold. Measurement in the left liver lobe should be avoided * Dietrich CF et al. EFSUMB Guidelines Ultraschall in Med 017;38:e16-e47 4

5 Stiffness measurement of the liver Guidelines* for the clinical use of noninvasive tests for the evaluation of liver disease severity and prognosis from: the European Association for the Study of the iver (EAS) and the Asociación atino-americana para el Estudio del Hígado (AEH) the two clinically relevant endpoints in patients with viral hepatitis are: the detection of significant fibrosis (F) and the detection of cirrhosis (F4) iver Fibrosis Annual follow-up of the liver fibrosis progression Antiviral treatment US screening every 6 months intechopen.com preventionnotacure.blogspot.fr *European Association for Study of, Asociacion atinoamericanaparael Estudio del H. EAS-AEH Clinical Practice Guidelines: Non-invasive tests for evaluation of liver disease severity and prognosis. J Hepatol 015; 63: iver Fibrosis Stiffness & fibrosis Transcutaneous liver biopsy invasiveness, with potential severe complications in up to 1% of cases, sampling error, since the specimen represents only 1/ of the liver volume inter- and intraobserver variability at microscopic evaluation hepatoweb.com/informationbiopsiedufoie Stiffness correlates with the degree of fibrosis and indirectly with portal hypertension Imaging Rather good to identify F4 (cirrhosis) Not good for F1-F3 BedossaP, DargèreD, Paradis V. Samplingvariabilityof liverfibrosisin chronichepatitisc. Hepatology003;38: Healthy liver stiffness values Chronic liver diseases Range 95 th percentile System TE kpa 6.7 kpa Fibroscan TM pswe m/s VTQ TM - ElastoPQ TM D-SWE kpa 6. kpa SSI Significant (F) TE (kpa) pswe (m/s) D-SWE (kpa) Cirrhosis (F4) TE (kpa) pswe (m/s) D-SWE (kpa) * Dietrich CF et al. EFSUMB Guidelines Ultraschall in Med 017;38:e16-e47 5

6 Stiffness measurement of the liver cut-off values to evaluate the presence and severity of liver fibrosis depend upon the different elastography techniques used the etiology of the underlying liver disease Significant (F) Cirrhosis (F4) Chronic liver diseases Hep C Hep B OH NAFD/NASH TE (kpa) > > > >7.9 (M) 7. (X) pswe (m/s) > >1.35 D-SWE (kpa) >7.1 > TE (kpa) >11-15 > > >9.3 (F3) pswe (m/s) > >1.87 D-SWE (kpa) >13.4 > Herrmann E, de édinghen V, Cassinotto C, et al: Hepatology. 017 Mar 31. [Epub ahead of print] Dietrich CF et al. EFSUMB Guidelines Ultraschall in Med 017;38:e16-e47 iver fibrosis No significant difference in diagnostic accuracy was found between the three elastography methods (pswe, D-SWE and TE) for the diagnosis of significant and advanced fibrosis and liver cirrhosis * *Cassinotto C, Boursier J, De edinghen V et al. Hepatology 016; 63: *CassinottoC, apuyadeb, MouriesA et al. J Hepatol014; 61: *Ferraioli G, Tinelli C, Dal Bello B et al. Hepatology 01; 56: *BotaS, HerknerH, SporeaI et al. iver Int013; 33: EFSUMB guidelines In chronic viral hepatitis C and B TE and pswe (VTQ ) and D-SWE (SSI) can be used as the first-line assessment for the severity of liver fibrosis In alcoholic liver disease: TE can be used to exclude cirrhosis if acute alcoholic hepatitis is not present there is still insufficient evidence to evaluate the role of pswe or D-SWE Role of SWE during HCV treatment in patients undergoing antiviral therapies liver stiffness rapidly declines during treatment, even in patients with advanced fibrosis and cirrhosis This decline appears to reflect the reduction in liver inflammation, restoration of liver function and the decrease in portal pressure, like an effect of HCV eradication Portal hypertension In viral cirrhosis, TE > 1 kpa predicts clinical decompensation of portal hypertension * A combination of a Young s modulus value < 0 kpa and a platelet count of > 150 G/ rules out varices needing treatment and endoscopy can be safely avoided ** For pswe and S-SWE reliable cut-offs are not available yet *RobicMA, ProcopetB, MetivierS et al. J Hepatol011; 55: **de Franchis R, Baveno VIF. J Hepatol 015; 63:

7 FNH : 30.5 kpa Focal liver lesion D-SWE Elasticité en Kpa (Moyenne ± SD) Adenoma 9,4±4,3 Hemangioma 13,8±5,5 FNH 33±14,7 HCC 14,86±10 Metastases 8,8±16 Cholangiocarcinoma 56,9±5,6 Adenoma : 9.4 kpa Conclusion TE, pswe and D-SWE grossly equivalent to assess liver fibrosis validated techniques : TE > pswe > D-SWE earning curve : D-SWE > pswe > TE Probably interesting for portal hypertension and followup during treatment of viral hepatitis Characterization of FF remains under development and cannot yet be recommended in clinical practice And also in abdomen : T, spleen, Kidney, prostate Guibal A, et al. Eur Radiol. 013 Apr;3(4): Gracias Olivier.lucidarme@aphp.fr 7