Wade 南非 佐藤摩彌 洋基 小布
以超音波彈性造影技術輔助診斷神經肌骨疼痛問題(Dr. Park, Korea)
ROLE OF ELASTOGRAPHY IN NEUROMUSCULOSKELETAL ULTRASOUND
Gi-Young ParkDepartment of Rehabilitation Medicine, Catholic University of
Daegu School of Medicine (Republic of Korea)Tissue hardness, the elasticity of the tissue identified on palpation,that is, deformability of the tissue, is determined by the structureand composition of the tissue. Tissue elasticity imaging consists ofeither an image of estimated elastic modulus or an image of strainin response to external force. The principles of tissue elasticityimaging are as follows. First, tissue compression produces strainand displacement within the tissue. Secondly, Strain is smaller inharder tissue than in softer tissue. Thirdly, we can estimate tissuehardness by measuring the tissue strain induced by compression.Many methods for tissue elasticity imaging are based on statictissue compression, which measure the strain distribution insidea body produced by relaxing or compressing a tissue. Therefore,tissue elasticity imaging does not directly represent tissue elasticitybut, rather, tissue displacement and strain. Diverse modalitiesmay be used for tissue elasticity imaging, the most powerfulbeing magnetic resonance elastography. Ultrasound elastographyimaging is possible for the evaluation of nearly every tissue and isone of the useful methods to quantify the strain of soft tissue. Asconventional ultrasonographic examination, freehand manipulationof the transducer and real-time visualization are required fora practical system of ultrasound elastography. Commercial ultrasoundscanners already offered real-time elastography and moreto follow. Ultrasound elastography provides information of tissuehardness, in addition to shape or vascularity, which is obtainedwith conventional ultrasonography. In clinical practice, ultrasoundelastography is not used independently but as a supplementaryrole for conventional ultrasonography. In the technical aspects ofultrasound elastographic examination, high quality of ultrasoundelastographic imaging is obtained with the transducer and lesionperpendicular to gravity and light contact using transducer thatdoes not distort the lesion. When excessive compression is applied,a false-negative finding may be observed because relationsof nonlinear properties of tissue elasticity are changed. When usingultrasound elastography, it is necessary to include a sufficientarea of surrounding normal tissue in the region of interest (ROI)correctly to determine the difference in hardness of the lesioncompared with the normal area. In color-scale elasticity images,the scale ranged from purple for tissue with greatest strain (softesttissue) to red for those with no strain (hardest tissue). Greenindicated average strain in the ROI. These color-scale elasticityimages are superimposed on the corresponding B-mode imagesso that the ultrasonographer can easily recognize the relationshipbetween strain distribution and the lesion on B-mode images. Ultrasoundelastography has potential for enhancing the specificity ofultrasound and mammography for breast cancer detection. Lesionsin the prostate, thyroid, pancreas, and lymph nodes have beeneffectively imaged using ultrasound elastography. The techniquemay also be possible in the evaluation of diffuse liver diseaseincluding cirrhosis and transplant rejection. Tissue elasticity notonly varies among different tissues, such as muscle, tendon, andnerve, but seems to reflect disease-induced changes in tissue properties.Therefore, ultrasound elastography is expected as meansfor providing novel diagnostic information for musculoskeletaldisease since the tissue hardness is closely related to its pathology.Tendons are particularly suitable for ultrasonographic examination.The dynamic imaging of ultrasonography can be used to assessthe level of tendon subluxation, and determine the severity of atendon injury, either partial or complete. We compared ultrasoundelastographic findings with gray-scale ultrasonographic findingsand evaluated the diagnostic value of ultrasound elastography fordetecting small full-thickness supraspinatus tendon tear. Ultrasoundelastography was obtained using free hand manipulation.For color-scale elastography, the diagnostic criterion indicative ofthe full-thickness tendon tear included a lesion with even elasticpattern (diffuse purple or mixed purple, blue or green) involvingthe full-thickness of supraspinatus tendon. Single-contrast shoulderarthrography was performed by the physiatrist and used as thereference standard for the full-thickness tendon tear. Our resultsindicate that ultrasound elastography showed higher accuracy thangray-scale ultrasonography in the diagnosis of small full-thicknesssupraspinatus tendon tear. Therefore, ultrasound elastographyshould be considered as an additional ultrasonographic methodfor evaluating small full-thickness supraspinatus tendon tear.Myofascial pain syndrome is a common type of musculoskeletalpain and characterized by trigger points, which are defined ashyperirritable spots within taut bands of skeletal muscle fibers.Myofascial taut band is considered a shortened or contracted musclefiber band with increased muscle tone. Therefore, myofascialtaut band have its higher stiffness compared to the surroundingmuscle fiber. Magnetic resonance elastography is a non-invasiveMR-based phase contrast imaging technique to image differencein tissue stiffness. Its findings suggest that the stiffness of thetaut bands in patients with upper trapezius myofascial pain maybe 50–100% greater than that of the nearby surrounding involvedmuscle or the controls. It may have a potential for objectivelycharacterizing myofascial taut bands that have been detectable onlyby the clinician’s palpation. Ultrasound elastography also showedincrease of stiffness in the taut band region of the affected uppertrapezius muscle relative to that of the unaffected side in patientswith myofacial pain syndrome. In the evaluation of peripheralnerve injury, ultrasound elastography is important not only to appreciatethe lesions but also to give more information about theentire nerve structure involved in trauma. In a case with mediansensory neuropathy after carpal tunnel steroid injection, focalhyperechoic area in the damaged median nerve was revealed ongray-scale ultrasonography. Ultrasound elastography showed thatthe stiffness of focal hyperechoic area in the median nerve (red oncolor-scale elastography) was greater than that of the surroundingnerve tissue (green on color-scale elastography). At 6 months afterinjection, pervious focal hyperechoic area in the median nervedisappeared and showed normal nerve echogenicity on follow-upultrasonography. In addition, even stiffness of the median nerve(green on color-scale elastography) was noted on follow-up ultrasoundelastography. This means that it changed from hard abnormaltissue to soft normal nerve tissue. Therefore, ultrasound elastographycan provide the precise information about serial structuralchanges of the injured peripheral nerve. Ultrasound elastographymay have potential for assessing the nature and consistency oflesions including hemorrhage, infection, edema, cyst, lipoma, andtumor. Recent study suggests that ultrasound elastography may beuseful in monitoring the severity of lymphedema. I consider thatultrasound elastography can provide us with more information inorder to get a precise diagnosis of neuromusculoskeletal disorders.However, ultrasound elastography is recommended as a mean ofassessment to complement the conventional ultrasonographicmethod. It is expected to be a new ultrasonographic techniquefor the diagnosis of neuromusculoskeletal disease such as tendontear, nerve injury, myofascial pain syndrome, and lyphedema etc.It may be widely used in the field of neuromusculoskeletal disease
for the near future.
