COMPARISON SWE to STRAIN ELASTOGRAPHY for THYROID NODULES

Abstract

Although elastography can enhance the differential diagnosis of thyroid nodules, its diagnostic performance is not ideal at present. Further improvements in the technique and creation of robust diagnostic criteria are necessary. The purpose of this study was to compare the usefulness of strain elastography and a new generation of elasticity imaging called supersonic shear wave elastography (SSWE) in differential evaluation of thyroid nodules. Six thyroid nodules in 4 patients were studied. SSWE yielded 1 true-positive and 5 true-negative results. Strain elastography yielded 5 false-positive results and 1 false-negative result. A novel finding appreciated with SSWE, were punctate foci of increased stiffness corresponding to microcalcifications in 4 nodules, some not visible on B-mode ultrasound, as opposed to soft, colloid-inspissated areas visible on B-mode ultrasound in 2 nodules. This preliminary paper indicates that SSWE may outperform strain elastography in differentiation of thyroid nodules with regard to their stiffness. SSWE showed the possibility of differentiation of high echogenic foci into microcalcifications and inspissated colloid, adding a new dimension to thyroid elastography. Further multicenter large-scale studies of thyroid nodules evaluating different elastographic methods are warranted.

Methods

During a few weeks trial time in 2010, four consecutive patients with single thyroid nodule (n = 1) and nodular goiter (n = 3) were evaluated. Approval for this study was obtained from the Ethics Committee of the Medical University of Warsaw, and all patients provided informed consent.

The Bmode and power Doppler ultrasound of whole thyroid and neck lymph nodes was performed. Six dominant thyroid nodules (in regard to B-mode and power Doppler ultrasound features) were evaluated with shear wave and strain elastography qualitatively and quantitatively as well as some with contrast-enhanced ultrasound (Sonovue (Bracco)). The examinations were performed with following scanner: AiXplorer (Supersonic Imagine Inc. France)—SSWE, Aplio XG (Toshiba, Japan)—strain elastography, Technos (Esaote, Italy)—contrast-enhanced ultrasound, with linear high-resolution transducers: 15–4MHz, 18–7MHz, and, 8–3MHz respectively. For strain elastography, we adopted qualitative scale of Rubaltelli et al. with threshold score of 2/3 and quantitative scale of Cantisani et al. with threshold thyroid tissue/nodule strain ratio of 2 measured with Elasto-Q (Toshiba). For shear wave elastography, we adopted quantitative scale of Sebag et al. with the threshold stiffness (mean elastic modulus) of thyroid nodule of 65 kPa.

The final diagnosis was based on clinical evaluation, multiple FNB, 1 year followup, or surgery.

Discussion

Supersonic shear weave elastography consists of the generation of remote radiation force by focused ultrasonic beams, the so-called “pushing beams,” a patented technology called “Sonic Touch”. Using Sonic Touch, ultrasound beams are successively focused at different depth in tissues. The source is moved at a speed that is higher than the speed of the shear waves that are generated. In this supersonic regime, shear waves are coherently summed in a “Mach cone” shape, which increases their amplitude and improves their propagation distance. For a fixed acoustic power at a given location, Sonic Touch increases shear wave generation efficiency by a factor of 4 to 8 compared to a nonsupersonic source. After generation of this shear wave, an ultrafast echographic imaging sequence is performed to acquire successive raw radiofrequency dots at a very high-frame rate (up to 20,000 frames per second). Based on Young’s modulus formula, the assessment of tissue elasticity can be derived from shear wave propagation speed. A color-coded image is displayed, which shows softer tissue in blue and stiffer tissue in red. Quantitative information is delivered; elasticity is expressed in kilo-Pascal (kPa).

This preliminary paper based on small number of cases indicates that SSWE indicated correctly thyroid nodules suspicious for cancer in contrast to strain elastography. False positives on strain elastography could be due to liquid or degenerative content of nodules.

However, imaging with SSWE, as a sensitive method of evaluation of stiffness of human tissue, the operator should be aware of physiological processes influencing the elasticity and easily apply a few rules to avoid artifacts (Figures 4, 5 and 6). Among well-known artifacts on SSWE that should be mentioned is the one that can be encountered in any region when the SSWE can be applied: the increased stiffness of the structures under externally applied pressure (Figures 4 and 5) that can be due to nonlinear elastic effects, well explained by theory.

Another artifact that can be encountered in thyroid SSWE is one of increased stiffness in the isthmus of the thyroid due to trachea (Figure 6). It can be avoided with imaging in paracoronal plane of the nodule that does not incorporate the trachea. However, it is important to state that these artifacts when properly interpreted do not hinder the accurate diagnosis.

Supersonic shear wave elastography may add a new dimension to ultrasound evaluation of thyroid nodules in several ways, for example:

(a) improve general performance in elasticity differentiation of thyroid nodules over strain elastography due to its high reproducibility, independence of examiners skill and numeral scale of elasticity measurement in kPa;

(b) overcome the limitations of strain elastography=

  (i) nodules with liquid components or with degenerative changes;

  (ii) small nodules (very good spatial resolution of the technique);

  (iii) large nodules (possibility of subsequent determination of stiff regions even  of large nodules, without the need of visualizing the whole nodule on one image);

  (iv) multinodular goiter with no or scarce normal thyroid tissue as a reference;

(c) differentiation between soft-inspissated colloid and stiff microcalcifications;

(d) visualization of microcalcifications, even not visualized on B-mode imaging (may increase sensitivity and decrease specificity of thyroid cancer diagnosis);

(e) introduction of three-dimensional elastographic images to routine clinical practice and to national thyroid cancer databases, as this technique is

already available and enables rapid acquisition of 3D ultrasound and elastographic data. This would devoid diagnostic process and data archiving of image selection bias attributable to 2D ultrasound examination.

Further multicenter large scale studies of thyroid nodules evaluating different elastographic methods are warranted, including (a) investigation of developmental models of diseases that link biomechanical properties (elastography findings) with genetic, cellular, biochemical, and gross pathological changes; (b) comparison of accuracy of different elastographic methods; (c) establishment of optimal diagnostic elastographic criteria; (d) establishment of limitations of different elastographic methods in relation to evaluation of thyroid pathology.

PHÂN BIỆT ÁPXE và VIÊM MÔ TẾ BÀO - ÁPXE LẠNH

Abscess Evaluation

Brian Euerle, MD, RDMS

I. Introduction and Indications

Abscess and cellulitis are two of the most common soft-tissue infections seen in patients treated in emergency departments. Although they sometimes occur together, they are different disease processes requiring different treatments. An abscess is treated with incision and drainage and may not require antibiotics; cellulitis is treated with antibiotics alone.

It can be difficult to differentiate cellulitis from abscess based only on history and physical examination findings. Both processes may generally be characterized by warmth, erythema, tenderness, swelling, and induration. In some patients, an abscess is clearly evident because of obvious fluctuance and copious purulent drainage; however, this distinct presentation is not seen in the majority of cases. Because of the difficulty in diagnosis, the emergency physician might decide upon an inappropriate treatment, resulting in one of two possible errors. Incision and drainage might not be done in a patient with an abscess, or incision and drainage could be performed on a patient who has cellulitis but no abscess. Increased pain and poor patient outcome can result from either one of these errors.

Many researchers, including emergency physicians, have reported on the utility of ultrasound in the evaluation of abscesses and cellulitis. One group of emergency physicians found that soft-tissue ultrasound changed the management strategy for approximately half of their patients and concluded that ultrasound was useful because it could detect occult abscesses and avoid invasive procedures.

Ultrasound also allows many procedures to be done with greater safety. In the case of abscess drainage, ultrasound can locate adjacent structures such as large blood vessels and nerves that need to be avoided during the drainage procedure.

The use of bedside ultrasound can also help determine the treatment of a specific abscess based on its size and depth.
If an abscess is very small (smaller than 1 cm), the physician might choose treatment with antibiotics and warm compresses rather than incision and drainage.

Although the majority of abscesses are treated with incision and drainage, in certain cases, usually because of cosmesis, treatment with needle aspiration and antibiotics may be an option. Ozseker and colleagues found that ultrasound-guided aspiration and irrigation of breast abscesses was preferred to surgical drainage for abscesses with a diameter less than 3 cm. Ultrasound provides dynamic real-time guidance for needle aspiration, resulting in increased success.

II. Anatomy

The structures that are imaged in bedside ultrasound for abscess evaluation are primarily the skin, subcutaneous tissue, and fascia. The skin consists of two layers: the superficial epidermis and the deeper, thicker dermis. Subcutaneous tissue, located beneath the dermis, consists of connective tissue septa and fat lobules. Fascia, a deeper structure, is a dense, fibrous membrane.

III. Scanning Technique, Normal Findings and Common Variants

Equipment
It is important to select an appropriate transducer when using bedside ultrasound for abscess evaluation. Because most subcutaneous abscesses are relatively superficial, a high-frequency (7-12 MHz) linear array transducer is most useful. At times a deeper abscess may be beyond the range of the linear transducer and a lower frequency transducer must be used. In this situation, a lower frequency linear array transducer may be helpful. If this type of transducer is not available, a curvilinear transducer may be used.
Evaluation for peritonsillar abscess is a specialized application in which a high frequency intracavitary probe can be used.

Many emergency practitioners are familiar with the use of color Doppler ultrasound and this can be useful in abscess evaluation. One way in which Doppler can be helpful is by identifying large blood vessels that are adjacent to an abscess. Color Doppler can also be helpful in the evaluation of groin masses because it can help differentiate an abscess from a pseudoaneurysm. Power Doppler is a more advanced technique that is able to detect low velocity blood flow and movement. This can be used in abscess evaluation because it can identify hyperemia in the walls of abscesses and the surrounding tissues.

Scanning Technique

It is helpful to begin scanning a short distance away from the area of interest to gain an appreciation of the appearance of the normal, uninvolved anatomy. It may also be helpful to view the contralateral side of the patient’s body to obtain information about the normal appearance of structures.

Next, slide the probe over the extent of the abscess or cellulitis, maintaining the same orientation. Once the area has been visualized appropriately, rotate the transducer 90 degrees and repeat the process. If an abscess is present, place a gloved finger of the nondominant hand on the point of maximal fluctuance or “point” of the abscess. Then slide the transducer so that its mid-point is located against the finger. This can help you correlate the image on the screen with the anatomy and help plan the site of the incision. Body markings can also be used to indicate the extent of the abscess or location of the incision.

Once the presence of an abscess is confirmed, set the ultrasound probe aside and proceed with the incision and drainage. Another option is to incise the area while observing in real time under ultrasound. This technique may be helpful for deep or small collections, but it generally is not necessary.

It may be helpful to repeat the ultrasound examination after incision and drainage to assess the success of the procedure and locate undrained collections of purulence.

Normal Findings

With the equipment that is typically used for bedside ultrasonography, the epidermis and dermis cannot be differentiated. They appear together as a thin, hyperechoic layer. The subcutaneous layer appears hypoechoic on ultrasound, with two components: hypoechoic fat interspersed with hyperechoic linear echoes running mostly parallel to the skin, which represent connective tissue septa (Figure 1). Veins and nerves may be visualized within the subcutaneous layer.

Fascia appears as a linear hyperechoic layer. Its thickness may vary depending on the location.

Figure 1: Normal skin, subcutaneous tissue, and fascia.

IV. Pathology

On ultrasound an abscess is a spherical or oblong shaped structure that is largely anechoic or hypoechoic (Figure 2). However, as opposed to a simple cyst that will be uniformly anechoic throughout, an abscess will contain hyperechoic debris. This feature can be used to differentiate an abscess from a cyst. The walls of the abscess cavity may be distinct and hyperechoic, or may have a ragged appearance and intermix with the adjacent tissue. Because of the anechoic nature of the abscess, posterior acoustic enhancement may be seen. Dynamic scanning, achieved with gentle compression of the probe, may cause the contents of the abscess to swirl, which can be diagnostic of an abscess. Hyperechoic foci of air may be seen in necrotizing fasciitis.

Figure 2: Abscess containing hyperechoic debris.

The ultrasound appearance of cellulitis may vary depending on the stage and severity. The initial appearance may be generalized swelling and increased echogenicity of the skin and subcutaneous tissues. As cellulitis progresses and the amount of subcutaneous fluid increases, hyperechoic fat lobules become separated by hypechoic fluid-filled areas. This later stage of cellulitis is most typical and has been described as having a cobblestone appearance (Figure 3)

Figure 3: Cobblestone appearance of advanced cellulitis.

V. Pearls and Pitfalls Abscess and cellulitis are two common soft-tissue infections that can appear similar on physical examination. Bedside ultrasound can be very helpful in differentiating cellulitis from abscess. Ultrasound is effective at identifying occult abscesses in emergency department patients initially suspected of having cellulitis. On ultrasound imaging, an abscess appears as a spherical or oblong anechoic or hypoechoic collection containing hyperchoic debris.

Cold Abscess

from www.e-radiography.net

Definition
A cold abscess is an abscess that commonly accompanies tuberculosis. It develops so slowly that there is little inflammation, and it becomes painful only when there is pressure on the surrounding area. This type of abscess may appear anywhere on the body, but it is most commonly found on the spine, hips, lymph nodes, or in the genital region.

Radiographic Appearance
Radiologicaly there may be erosion of bone local to the abscess, or evidence of organ compression.
A sinogram will demonstrate the extent of the abscess.

Plain radiographs occasionally show a blurring or indistinctness of the lateral margins of the psoas muscle but, in general, are not as helpful as other techniques. Ultrasonography is useful in showing enlarged psoas muscle with hypoechogenic masses, however it is not as accurate as a CT scan in showing the abscess. MRI is advantageous because multiple processes can be evaluated.

Pathology
Although primary psoas abscess is very rare in children of "developed" countries, it is not rare in tropic and sub-tropical "third world" countries with poor socioeconomic conditions. Staphylococcus aureus is the most frequent type of infection seen in these environments, with almost all children presenting with the triad of pyrexia, flank pain and hip symptoms.
Psoas abscess can be a secondary problem associated with tuberculous spondylitis or in relation to inflammatory bowel disease (1). More recently, in the United States, psoas abscesses have been seen secondary to transperitoneal low-velocity gunshot wounds to the spine (3), or gastrointestinal or genitourinary trauma (2). Primary psoas abscess can be seen in patients with sickle cell disease, intravenous drug users, immunocompromised individuals or individuals positive for HIV.

Treatment:
Drainage of the abscess by CT-guided percutaneous catheter has been recommended by some, while surgical drainage is recommended by others, especially when percutaneous catheter drainage is not successful, followed by appropriate antibiotic therapy.