Acoustic Radiation Force Impulse (ARFI) of the pancreas.

Transcription

1 Acoustic Radiation Force Impulse (ARFI) of the pancreas. Poster No.: C-0686 Congress: ECR 2014 Type: Educational Exhibit Authors: S. Crosara, M. D'Onofrio, R. De Robertis, S. Canestrini, E. Demozzi, R. Pozzi Mucelli; Verona/IT Keywords: Tissue characterisation, Neoplasia, Experimental investigations, Diagnostic procedure, Ultrasound, Experimental, Elastography, Ultrasound physics, Pancreas, Abdomen DOI: /ecr2014/C-0686 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 12

2 Learning objectives The aim of the present study is to describe the pancreatic applications of ARFI, a new technique able to distinguish tissues on the basis of their stiffness. Background TECHNOLOGY Elastography is a new technique applied to US imaging [1]. The challenge of this new technique is to distinguish different tissues on the basis of their specific consistency (Fig. 1), reflected by the deformation generated in the tissue itself by an imparted force on the target organ [2,3]. ARFI imaging is able to qualitatively and quantitatively define the tissue stiffness with no need for an external compression, so reducing the interobesrver variability. It exploits short duration acoustic radiation forces to generate localized tissue displacements that are registered by the US scanner. Such displacements are related to the viscoelastic properties of local soft tissue [4]. ARFI has the advantage of being integrated into a conventional ultrasound system and therefore can be performed during a standard examination [5]. ARFI can be used in two different ways. One is qualitative, called Virtual Touch Tissue Imaging, which employs a short acoustic impulse of high intensity to deform the tissue elements and create a static map (elastogram) of the relative stiffness of the tissues included in the region of interest (ROI). The system is set up to use a hue chromatic (gray scale or red-green-blue) map. One limitation of this technique is that the complete chromatic spectrum encoding the tissue is applied to each elastographic record and indicates the grade of relative elasticity within the sample area, thus there is not an absolute chromatic scale of tissue stiffness. Another application (Fig. 2), called Virtual Touch Tissue Quantification, is quantitative: after the preliminary selection of a target ROI of fixed dimensions (10x15 mm) on a conventional US image, an acoustic push pulse departing from the probe is transmitted through the tissue by side of the target ROI and induces sound waves from the deformation of the tissue itself. A numeric value of the wave speed (meters/second) is then reported as a result of multiple measurements automatically made for that spatial location: the stiffer a tissue is, the greater the numerical value will be [6]. IMAGING INTERPRETATION According to preliminary results, the internal structure of the pancreas is normally uniformly iso/hyper-echoic compared to the liver. It appears as intermediately soft, Page 2 of 12

3 characterized by a homogeneous soft tissue area. The mean velocity value measured through the normal pancreatic parenchyma (Fig. 3) is approximately 1.40 m/s [7-9]. Embriologically the pancreas develops from two primordia, the dorsal and the ventral. The dorsal primordium can rise above the surrounding tissue as a band-shaped hypoechoic structure and should not be confused with local inflammation or a tumor. ARFI provides similar values in both parts of a healthy pancreas [9]. With advancing age, pancreatic echogenicity increases significantly, as a result of fat and connective tissue deposits; the elastographic image becomes heterogeneous and the velocity values becomes higher [9]. Images for this section: Page 3 of 12

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5 Fig. 1 Fig. 2 Page 5 of 12

6 Fig. 3 Page 6 of 12

7 Findings and procedure details SOLID LESIONS As well known, pancreatic ductal adenocarcinoma is a firm mass, stiffer than the adjacent parenchyma [10], owing to the presence of fibrosis and marked desmoplasia, and therefore it is characterized by a higher wave velocity value (Fig. 4 and Fig. 5). A wide range of values results also from our personal experience and only few data have been reported in the literature. Our latest unpublished data identify a velocity cut-off value (4 m/ s) with 100% specificity and 100% positive predictive value (Tab) in diagnosing pancreatic ductal adenocarcinoma. Pancreatic stiffness measured by ARFI is reported to be high also in patients with chronic pancreatitis [11], thus making a differential diagnosis difficult. ARFI can also be applied in the detection of pancreatic lesions (Fig. 6), improving their conspicuity thanks to the stiffness difference between the lesion itself and the pancreatic gland. CYSTIC LESIONS ARFI has not been tested only in solid tissues evaluation [6,12-14]. Although mechanical waves (US) propagates through solids and shear waves are highly attenuated in fluids in which only longitudinal waves or shear wave reflection at the solid-fluid interface may be measured, the wide range of differences of fluids in vivo led to test ARFI also on fluids and different responses have been obtained according to their viscosity and the presence of suspended particles [15-18]. In the daily clinical practice, cystic masses are still characterized and classified at imaging on the basis of their morphology, architecture and vascularization (parietal thickness, the presence and vascularity of septa and parietal nodules, the presence of calcifications and communication with the main pancreatic duct) [17]. Nevertheless, the definitive diagnosis of pancreatic cystic lesions sometimes still requires an invasive analysis of the cystic content. Morover, fluids in vivo can be really different. The test of ARFI on fluids provided different responses according to viscosity: serous cystadenoma is characterized by simple fluid content (in wich the propagation speed of shear wave is always represented by the non-numerical value "XXXX/0") [16], whereas mucinous cystic lesions have high viscous and particle fluid content (in complex fluids, more viscous than water, numerical values are obtained) [16,18]. In accordance with pathologic descriptions of fluids contained in different pancreatic cystic lesions, their complex nature could be determined by the presence of mucin, as in mucinous cystic neoplasms (Fig. 7) and mucinous intraductal papillary tumors (Fig. 8), or as result of intralesional bleeding or necrosis, as may occur in pseudocyst. To distinguish mucinous cystic lesions (potentially malignant) from serous cystic lesions (mainly benign) and to confirm the datain the literature [17], the result "XXXX/0" was considered indicative of simple liquids Page 7 of 12

8 (comparable to water) (Fig. 9). To identify lesions containing complex fluids, and therefore potentially mucinous, two different methods of reading can be used in our experience [19]: 1. At least two numerical values obtained when performing 5 measurements; 2. The prevalence of numerical values obtained irrespective of the number of measurements. On the basis of the results obtained in our experience [19], ARFI imaging with Virtual Touch Tissue Quantification could be of additional value in the characterization of pancreatic cystic lesions by noninvasive fluid evaluation. The good sensitivity (68.8%) of the first reading method (at least 2 numerical values obtained when performing 5 measurements) and the excellent specificity (100%) of the second method (prevalence of numerical measurements) for the diagnosis of mucinous cystic neoplasms and intraductal papillary mucinous neoplasms (unpublished data) with Virtual Touch Tissue Quantification show how this technique could represent an important medium for characterization of mucinous pancreatic cystic lesions (potentially malignant) as well as diagnostic and therapeutic management. In particular, the first method of diagnosis can be used to exclude malignancy or to identify those patients eligible for follow-up. Because of its high specificity, the second method, can be used to confirm malignancy in those patients who are candidates for surgical resection. Images for this section: Fig. 4: Pancreatic ductal adenocarcinoma: at conventional B-mode ultrasonography (A) it appears as a solid hypoechoic lesion; Virtual Touch tissue imaging (B) and Virtual Touch tissue quantification (C) show it as a stiff lesion. Measurement performed on normal pancreatic parenchyma (D). Fig. 5: Pancreatic ductal adenocarcinoma: at conventional B-mode ultrasonography (A) it appears as a solid hypoechoic lesion; Virtual Touch tissue imaging (B) and Virtual Touch tissue quantification (C) show it as a stiff lesion. Page 8 of 12

9 Table 1: ARFI cut-off of 4 m/s can identify pancreatic ductal adenocarcinoma with: # Sensitivity = 57.9 % # Specificity = 100% # Positive predictive value = 100% # Negative predictive value = 22.6% # Accuracy = 62.5% Fig. 6: A lesion barely clear on the pancreatic gland background (A) increases its conspicuity if studied in the Virtual Touch tissue imaging region of interest (B). Page 9 of 12

10 Fig. 7: Mucinous cystic lesion: a pancreatic cystic lesion desplayed on conventional Bmode ultrasonography (A) and on Virtual Touch tissue imaging (B). Numerical values obtained at Virtual Touch tissue quantification (C) demonstrate the complex nature of the fluid content. Fig. 8: Intraductal papillary mucinous neoplasm: Numerical values obtained at Virtual Touch tissue quantification (A) demonstrate the complex nature of the fluid content. Diagnosis is confirmed by magnetic resonance cholangio-pancreatography (MRCP) (B). Fig. 9: Serous cystic lesion: Value X.XX m/s obtained at Virtual Touch tissue quantification (A) demonstrate the simple nature of the fluid content. Diagnosis is confirmed by MRI (B). Page 10 of 12

11 Conclusion ARFI is a promising technique for the differentiation of tissues: it can be useful in the diagnosis of pancreatic diseases and in choosing the correct patients management and follow-up. Personal information References 1. Piscaglia F, Salvatore V, Di Donato R, et al. Accuracy of Virtual Touch acoustic radiation force impulse (ARFI) imaging for the diagnosis of cirrhosis during liver ultrasonography. Ultraschall Med 2011;32(2): Hoyt K, Parker KJ, Rubens DJ, et al. Real-time shear velocity imaging using sonoelastographic techniques. Ultrasound Med Biol 2007;33: Nightingale K, Bentley R, Trahey G. Observations of tissue response to acoustic radiation force: opportunities for imaging. Ultrason Imaging 2002;24: Nightingale K, Soo MS, Nightingale R, et al. Acoustic radiation force impulse imaging: in vivo demonstration of clinical feasibility. Ultrasound Med Biol 2002;28: Shiina T, Nitta N, Ueno E, et al. Real time tissue elasticity imaging using the combined autocorrelation method. J Med Ultrasound 2002;29: Nightingale K, McAleavey S, Trahey G. Shear wave generation using acoustic radiation force: in vivo and ex vivo results. Ultrasound Med Biol 2003;29: Gallotti A, D'Onofrio M, Pozzi Mucelli R. Acoustic radiation force impulse (ARFI) technique in ultrasound with virtual touch tissue quantification of the upper abdomen. Radiol Med 2010;115: Mateen MA, Muheet KA, Mohan RJ, et al. Evaluation of ultrasound based acoustic radiation force impulse (ARFI) and esie touch so- noelastography for diagnosis of inflammatory pancreatic disease. JOP 2012;13: D'Onofrio M, Crosara S, De Robertis R, et al. Elastography of the pancreas. Eur J Radiol Uchida H, Hirooka Y, Itoh A, et al. Feasibility of tissue elastography using transcutaneous ultrasonography for the diagnosis of pancreatic diseases. Pancreas 2009;38: Yashima Y, Sasahira N, Isayama H, et al. Acoustic radiation force impulse elastography for noninvasive assessment of chronic pancreatitis. J Gastroenterol 2012;47: Page 11 of 12

12 12. Friedrich-Rust M, Wunder K, Kriener S, et al. Liver fibrosis in viral hepatitis: noninvasive assessment with acoustic radiation force impulse imaging versus transient elastography. Radiology 2009;252: Fahey BJ, Nightingale KR, Nelson RC, et al. Acoustic radiation force impulse imaging of the abdomen: demonstration of feasibility and utility. Ultrasound Med Biol 2005;31: Fahey BJ, Nelson RC, Bradway DP, et al. In vivo visualization of abdominal malignancies with acoustic radiation force elastography. Phys Med Biol 2008;53: D'Onofrio M, Gallotti A, Martone E, et al.solid appearance of pancreatic serous cystadenoma diagnosed as cystic at ultrasound acoustic radiation force impulse imaging. JOP 2009;10: D'Onofrio M, Gallotti A, Salvia R, et al. Acoustic radiation force impulse (ARFI) ultrasound imaging of pancreatic cystic lesions. Eur J Radiol 2011;80: Hutchins GF, Draganov PV. Cystic neoplasms of the pancreas: adiagnostic challenge. World J Gastroenterol 2009;15: D'Onofrio M, Gallotti A, Falconi, et al. Acoustic radiation force impulse imaging of pancreatic cystic lesions: preliminary results. Pancreas 2010;39: D'Onofrio, Crosara S, Canestrini S, et al.virtual analysis of pancreatic cystic lesion fluid content by ultrasound acoustic radiation force impulse quantification. J Ultrasound Med 2013;32: Page 12 of 12