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Τετάρτη, 25 Ιουνίου 2014 03:00

Ultrasound Elastography for Musculoskeletal applications: an update according to the EFSUMB guidelines (Elena Drakonaki)

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Elena Drakonaki, MD, PhD, PostDoc, Consultant Radiologist

Introduction

Ultrasound Elastography (USE) is a recently developed method which allows the assessment of the mechanical properties of living tissue. Being the imaging equivalent of clinical palpation, the technique has opened new dimensions in clinical imaging by providing complementary information to B-mode and Doppler ultrasound [1,2]. Of all human tissues, disease in musculotendinous tissue directly affects its biomechanical properties. Therefore, since the introduction of USE into commercially available US systems, there has been a growing interest in the application of this technique for assessing the musculoskeletal system in the clinical practice [3].

There are several USE techniques available for clinical uses, depending on the way of stress application; the techniques commonly used in the clinical practice include Strain USE and Shear Wave USE [3]. Strain USE, also described as Compression Elastography, Sonoelastography, and Real-time Elastography employes manual compression of the tissue using the hand-held US transducer, resulting in axial tissue deformation, which is used to calculate the Young’s modulus (a physical quantity measuring elasticity). It is an indirect technique for the assessment of strain information which are displayed as a gray scale or color coded strain distribution map (“the elastogramon the screen as superimposed on the B-mode image. The elastogram is a relative image presenting the level of strain of each area compared to the remaining tissue in the ROI. Most systems also provide a semi-quantitative measurement of the relative strains between the area of interest and a reference area (usually fat).

Shear wave USE is based on shear waves which are generated when the conventional ultrasound waves interact with tissue and propagate perpendicular to the displacement caused by the ultrasound pulse. The velocity of shear waves can be used to evaluate tissue stiffness. In contrast to strain USE, no manual compression is required and the technique results in both qualitative colour coded elastograms and quantitative maps either of elasticity (in kPa) or of shear wave velocity (in cm/sec).

US Elastography for Tendons

Most of the experience on tendons comes from studies of the Achilles tendon. The asymptomatic Achilles tendons are usually hard (86-93%) or may contain small areas of mild softening in the tendon midportion which may not correspond to findings on B-modeUS [4-7]. The alterations found in asymptomatic tendons have been attributed to false positive findings or to early changes. Symptomatic Achilles tendons usually contain discrete softening, and only rarely (32%) may appear as stiff structures [4-7]. Therefore, only discrete soft areas should be considered as definitely abnormal in Achilles tendon USE. Completely ruptured and surgically repaired tendons appear as heterogenous structures with the sutured area displaying increased stiffness, as part of healing [8]. The overall correlation between US and USE findings is excellent (accuracy 97%), provided that mild softening is considered physiological and only distinct red areas are considered abnormal [4-7]. Compared to clinical findings, USE has a mean sensitivity of 93.7% and a specificity of 99.2% [4-7]. A recent study on cadavers showed that EUS could detect more histologically verified lesions in the Achilles tendon than B-modeUS (100% versus 85.7%), thus indicating that it is more sensitive than conventional imaging [9]. The inter- and intra-observer reproducibility of the USE has been found excellent for qualitative assessment of elastograms and poor (variation 29%-37%) forsemi-quantitative measurements (strain ratio) [4-7].

US Elastography for Muscles

Normal relaxed muscle appears as an inhomogeneous mosaic of intermediate or increased stiffness with scattered softer areas especially at the periphery or near boundaries. In inflammatory myopathies USE can show changes in muscle elasticity in correlation with elevated serum markers(increased stiffness due to fibrosis or as reduced stiffness, secondary to fatty infiltration) [10].A case report on the use of USE in congenital Bethlem myopathy detected changes not evident in conventional imaging, indicating that USE may have a role for depicting dystrophic changes earlier than US or MR [11]. ΕUS with can depict myofascial trigger points and detect changes in muscle elasticity in contracted muscle to establish the target of botulinum toxin injection [12, 13]. Based on the above data, it is suggested that USE has a role in diagnosing, guiding interventions and monitoring their results in dystrophic, myopathic and spastic muscle.

 Future perspectives

There is limited data on USE for the evaluation of small tendon lesions and lateral epicondylitis. Regarding lateral epicondylitis, it was proved that USE has greater accuracy than conventional US and may allow localizing more focal lesions and more cases of collateral ligament and fascia involvement than US [14].  A study on patients with trigger finger showed increased stiffness of the A1 pulley and decrease in stiffness after corticosteroid injection [15]. An experimental study on animal digital tendons showed that lesions could only be partially detected by USE [16]. In plantar fascia, USE can detect age-related changes and also confirm the presence of fasciitis [17]. However, the clinical value of the technique in other than the Achilles tendons is still under evaluation. Regarding muscle disease, potential applications of USE include diagnosis of muscle atrophy and injury, however there is luck of sufficient data to establish the role of the technique in diseases other than muscle spasticity and dystrophy.

There are only limited data on the use of USE in inflammatory diseaseUSE can be of value to depict the presence of soft chronic bursitis, to evaluate patients with systemic sclerosis and differentiate the stiffer rheumatoid nodes from tophi [18-20]. Benign soft tissue lesions may display a variety of elastographic patterns ranging from soft to very hard, however, based on a small case series, there seems to be no pattern for lesion characterization [21].

Shear wave USE has not been extensively used for musculotendinous disease, but preliminary data show that the normal Achilles and patella tendons appear homogenously hard, with fewer fluctuant alterations than those evident with strain USE [authors’ unpublished data].

Technical considerations-artefacts

To minimize intra-observer variation and avoid transient temporal fluctuationsit is recommended to use several cine-loops and then select the best fit B-mode – elastogram image pairs for evaluation. Gel should be excluded from the ROI, as it influences the appearance of the elastogram. When examining protuberant masses or very superficial tissues, stand-off pads or caps applied to the probe can be employed to increase the distance between the probe and the skin and apply uniform compression over the entire lesion. Regarding the Achilles tendon, the reproducibility of transverse images is less than that of longitudinal images, because of artifacts at the borders of the image, so overlapping images should be acquired. The ROI of the elastogram should include the area of interest as well as an adequate amount of surrounding tissue, so that the tissue of interest occupies 25-50% of the ROI. For the Achilles tendon, the suggested standard size for longitudinal scans is a depth of 3 times the tendon and about ¾ of the screen and for transverse scans the paratenon should be included.

Several artefacts can be encountered using strain USE, which reduce the quality of the elastograms and should be excluded when measuring the strain ratio. These include changes at the edges of the elastogram and at the borders of thin structures, soft lines around calcifications, behind bone and at the interfaces between tissues. Cystic masses produce a characteristic pattern of stiffness (all colours) and pulsations caused by major vessels may result in artifacts.

Conclusion

The evidence so far seems very promising that USE can be used to assess the mechanical properties of musculoskeletal tissues in the clinical setting and as a research tool in the evaluation of musculotendinous disease. However, the amount of published literature at present is still very limited. The recent EFSUMB guidelines for the clinical use of USE conclude that there is enough evidence to recommend the use of the technique only for the Achilles tendon and spastic muscle and more experience is needed to expand the role of USE for other applications in the musculoskeletal system [22].

References

1.    Ophir J, Cespedes I, Ponnekanti H, Yazdi Y, Li X. Elastography: a quantitative method for imaging the elasticity of biological tissues. Ultrason Imaging 1991; 13:111–134

2.      Bamber J, Cosgrove D, Dietrich CF, et al EFSUMBguidelines and recommendations on the clinical use of ultrasound elastography. Part 1: Basic principles and technology. Ultraschall Med. 2013;34(2):169-84.

3.      Li YSnedeker JG. Elastography: modality-specific approaches, clinical applications, and research horizons. Skeletal Radiol.2011;40:389-97.

4.      Drakonaki EE, Allen GM, Wilson DJ. Real-time ultrasound elastography of the normal Achilles tendon: reproducibility and pattern description.Clin Radiol. 2009;64:1196-202.

5.      De Zordo T, Chem R, Smekal V, Feuchtner G, Reindl M, Fink C, et al. Real-time sonoelastography: findings in patients with symptomatic achilles tendons and comparison to healthy volunteers.Ultraschall Med. 2010;31:394-400.

6.      De Zordo T, Fink C, Feuchtner GM, Smekal V, Reindl M, Klauser AS. Real-time sonoelastography findings in healthy Achilles tendons.AJR Am J Roentgenol. 2009;193:W134-8.

7.      KlauserAS, Faschingbauer R, Jaschke WR. Is sonoelastography of value in assessing tendons?Semin Musculoskelet Radiol. 2010;14:323-33.

8.      Tan S, Kudaş S, Ozcan AS, Ipek A, Karaoğlanoğlu M, Arslan H, Bozkurt M Real time sonoelastography of the Achilles tendon: pattern description in healthy subjects and patients with surgically repaired complete ruptures. Skeletal Radiol 2011 Dec 14

9.      KlauserAS, Myamoto H, Tamegger M et al. Achilles tendon assessed with sonoelastography: histologic agreement. Radiology 2013; DOI: 10.1148/radiol.13121936

10.  Botar-Jid C, Damian L, Dudea SM, Vasilescu D, Rednic S, Badea R. The contribution of ultrasonography and sonoelastography in assessment of myositis.Med Ultrason. 2010;12:120-6.

11.  Drakonaki EE, Allen GM. Magnetic resonance imaging, ultrasound and real-time ultrasound elastography of the thigh muscles in congenital muscle dystrophy.Skeletal Radiol. 2010;39:391-6.

12.  Sikdar S, Shah JP, Gebreab T, Yen RH, Gilliams E, Danoff J et al. Novel applications of ultrasound technology to visualize and characterize myofascialtrigger points and surrounding soft tissue.Arch Phys Med Rehabil. 2009;90:1829-38

13.  Vasilescu D, Vasilescu D, Dudea S, Botar-Jid C, Sfrângeu S, Cosma D.Sonoelastography contribution in cerebral palsy spasticity treatment assessment, preliminary report: a systematic review of the literature apropos of seven patients. Med Ultrason. 2010;12:306-10.

14.  Zordo T, Lill SR, Fink C, Feuchtner GM, Jaschke W, Bellmann-Weiler R, et al. Real-time sonoelastography of lateral epicondylitis: comparison of findings between patients and healthy volunteers.AJR Am J Roentgenol. 2009;193:180-5

15.  Miyamoto H, Miura T, Isayama H, Masuzaki R, Koike K, Ohe T. Stiffness of the first annular pulley in normal and trigger fingers.J Hand Surg Am. 2011;36:1486-91.

16.  Buck AR, Verstraete N, Li Y, Schweizer A, Snedeker JG, Buck FM. Detection of small tendon lesions by sonoelastographic visualization of strain profile differences: initial experiences. Skeletal Radiol. 2012;5 [epub ahead of print]

17.  Wu CH, Chang KV, Mio S et al. Sonoelastography of the plantar fascia. Radiology 2011; 259: 502–507

18.  Silvestri EGarlaschi GBartolini BMinetti GSchettini DD'Auria MCetal. Sonoelastography can help in the localization of soft tissue damage in polymyalgia rheumatica (PMR). Clin Exp Rheumatol. 2007;25:796.

19.  Iagnocco AKaloudi OPerella CBandinelli FRiccieri VVasile M, et al. Ultrasound elastography assessment of skin involvement in systemic sclerosis: lights and shadows. J Rheumatol. 2010;37:1688-91.

20.  Sconfienza LM, Silvestri E, Bartolini B, Garlaschi G, Cimmino MA. Sonoelastography may help in the differential diagnosis between rheumatoid nodules and tophi.Clin Exp Rheumatol. 2010;28:144-5.

21.  Bhatia KSRasalkar DDLee YPWong KTKing ADYuen YH et al. Real-time qualitative ultrasound elastography of miscellaneous non-nodal neck masses: applications and limitations.Ultrasound Med Biol. 2010;36:1644-52.

22.  Cosgrove D, Piscaglia F, Bamber J, et al. EFSUMBGuidelines and Recommendations on the Clinical Use of Ultrasound Elastography.Part 2: Clinical Applications. Ultraschall Med. 2013;19

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