What is the contribution of elastography to thyroid nodules evaluation?

Ultrasound elastography

Physicians have used palpation as a diagnostic examination to understand the elastic properties of pathology for a long time since they realized that tissue stiffness is closely related to its biological characteristics. US elastography provided new diagnostic information about elasticity comparing with the morphological feathers of traditional US, and thus expanded the scope of the application in clinic. US elastography is now widely used in the field of diagnosis and differential diagnosis of abnormality, evaluating the degree of fibrosis and assessment of treatment response for a range of diseases. The World Federation of Ultrasound Medicine and Biology divided elastographic techniques into strain elastography (SE), transient elastography and acoustic radiation force impulse (ARFI). The ARFI techniques can be further classified into point shear wave elastography (SWE), 2D SWE, and 3D SWE techniques. The SE measures the strain, while the shear wave-based techniques (including TE and ARFI techniques) measure the speed of shear waves in tissues. In this review, we discuss the various techniques separately based on their basic principles, clinical applications in various organs, and advantages and limitations and which might be most appropriate given that the majority of doctors have access to only one kind of machine.

TI-RADS Diagnostic Performance: Which Algorithm is Superior and How Elastography and 4D Vascularity Improve the Malignancy Risk Assessment

Given the increased prevalence of thyroid nodules in the general population (~50%), the real challenge resides in correctly recognizing the suspicious ones. This study proposes to compare four important Thyroid Imaging and Reporting Data Systems (TI-RADS) and evaluate the contribution of elastography and 4D Color Doppler assessment of vascularity in estimating the risk of malignancy. In the study, 133 nodules with histopathological examination were included. Of these, 35 (26.31%) proved to be malignant. All nodules were classified using the four selected systems and our proposed improved score. The American College of Radiology (ACR) and EU TI-RADS had good sensitivity (94.28%, 97.14%) and NPV (93.33%, 95.83%), but fairly poor specificity (31.81%, 23.46%) and PPV (35.48%, 31.19%), with an accuracy of 42.8% and 45.8%, respectively. Horvath TI-RADS had better accuracy of 66.9% and somewhat improved specificity (62.24%), but poorer sensitivity (80%). Russ’ French TI-RADS includes elastography in the risk assessment strategy. This classification proved superior in all aspects (Se: 91.42%, Sp:82.65%, NPV:96.42%, PPV:65.30%, and Acc of 84.96%). The mean strain ratio (SR) value for malignant lesions was 5.56, while the mean SR value for benign ones was significantly lower, 2.54 (p < 0.05). It also correlated well with the response variable: histopathological result (p < 0.001). Although, adding 4D vascularity to the French score generated a similar calculated accuracy and from a statistical point of view, the parameter itself proved beneficial for predicting the malignancy risk (p < 0.001) and may add important knowledge in uncertain situations. Advanced ultrasound techniques definitely improved the risk estimation and should be used more extensively.

Impact of imaging cross-section on visualization of thyroid microvessels using ultrasound: Pilot study

Non-invasive, contrast-free microvascular imaging of human thyroids can be potentially beneficial in reducing the large number of benign biopsies of suspicious nodules. However, motion incurred by thyroid due to its proximity to the pulsating carotid artery significantly impacts the visualization of blood flow in small vessels. Singular value based spatiotemporal clutter filtering (SVD-STF) improves the performance of tissue rejection in the presence of motion. However, despite effective clutter filtering, motion in thyroid imaging can impact coherent integration of the Doppler ensemble and degrade the visualization of the underlying vasculature. Recently studies have demonstrated that motion correction using 2D normalized cross-correlation based speckle tracking can address this issue, however, only in-plane motion can be tracked and corrected. Given the natural anatomical orientation of the rigid trachea, thyroid and the pulsating carotid artery, we hypothesize that imaging of thyroid microvessels may be more reliable in the longitudinal view than in the transverse. Specifically, distal presence of rigid trachea can limit out-of-plane motion in the longitudinal view. We tested this hypothesis on 48 acquisitions obtained from 24 thyroid patients having at least one suspicious nodule. In each patient, ultrasound images of the thyroid were acquired in both longitudinal and transverse views. Compounded plane-wave imaging was used to acquire the ultrasound images at high frame-rate, which is important for contrast-free small vessel blood flow imaging. Thyroid motion was tracked using 2D normalized cross-correlation based speckle tracking. Tissue clutter was rejected using singular value decomposition based spatiotemporal clutter filtering. The clutter-filtered Doppler ensemble was motion corrected prior to slow-time power Doppler integration. Signal-to-noise and contrast-to-noise ratios were computed to assess the improvement in quality of the power Doppler images. Out-of-plane motion was detected by estimating normalized ensemble cross-correlation coefficient. The results demonstrated that motion associated with the thyroid due to the carotid artery was primarily in the lateral direction, which could be estimated and corrected using 2D speckle tracking. However, the motion in the transverse view displayed increased speckle decorrelation. The average ensemble cross-correlation coefficient of the thyroid ultrasound images were significantly higher (p < 0.05) in the longitudinal view than in the transverse view. The largest improvement in SNR and CNR of the estimated PD images upon motion correction was observed in the longitudinal view (12.95 ± 3.76 dB and 16.48 ± 4.6 dB) than in the transverse view (3.72 ± 0.894 dB and 6.217 ± 1.689 dB). These preliminary results show that motion encountered by the thyroid due to carotid pulsations can be effectively tracked and corrected in the longitudinal view relative to transverse, which is important for reliably visualizing the underlying blood flow.

Diagnostic Performance of Ultrasound Strain Elastography in Transverse and Longitudinal Views in Predicting Malignant Thyroid Nodules

Agreement between ultrasound strain elastography (SE) scores of transverse and longitudinal views of thyroid nodules was investigated, and the diagnostic performance of these scores in predicting thyroid malignancy was assessed. From December 2016 to February 2017, a total of 250 thyroid nodules in 232 patients (62 males and 188 females, mean age: 45 y [20-75 y]) were enrolled. Diagnostic agreement between SE scores obtained in different views was assessed. Sensitivity, specificity, area under the receiver operating characteristic curve (Az) of the SE score in different criteria (criterion 1, SE score ≥4 from any view is defined as suspicious; criterion 2, SE score ≥4 as in only transverse view; and criterion 3, SE score ≥4 only from longitudinal view) were evaluated. Diagnostic agreement between SE scores of different views was fair (κ = 0.227). The Az value for criterion 1 (0.770, 95% confidence interval [CI]: 0.713, 0.820) was the highest among the three criteria, significantly higher than that of criterion 2 (0.692, 95% CI: 0.631, 0.749) (p < 0.001), but not statistically significantly different from that of criterion 3 (0.768, 95% CI: 0.711, 0.819) (p = 0.909). However, the Az value for criterion 3 was higher than that for criterion 2 (p < 0.005). The results indicated that criterion 1 had high sensitivity (80.0%) and criterion 2 had high specificity (68.0%). Our study found that the agreement between SE scores of different views was fair. SE scores ≥4 in either view were most sensitive for predicting malignant thyroid nodules.

Diagnostic value of 3D power Doppler ultrasound in the characterization of thyroid nodules

Background/aim

This study aimed to evaluate the diagnostic value of vascular indices obtained using 3D power Doppler ultrasound (3D PDUS) in differentiation of benign and malignant thyroid nodules.

Materials and methods

Sixty-seven patients (56 female, 11 male, mean age 44.6) with 81 thyroid nodules exhibiting mixed (peripheral and central) vascularization patterns, with the largest diameter between 10 and 30 mm, were prospectively evaluated using 3D PDUS. Nodule volume, vascularization index (VI), flow index (FI), and vascularization flow index (VFI) were calculated using the Virtual Organ Computer-aided Analysis (VOCAL) software, and these indices were then compared with regard to the cytohistopathology-based diagnosis. The optimum cutoff values for the differentiation of benign and malignant nodules were identified, and diagnostic efficacy was calculated using receiver operating characteristic (ROC) analysis.

Results

Fifty-six of the 81 nodules included in this study were diagnosed as benign and 25 as malignant. Vascular indices in malignant nodules were significantly higher than those in benign nodules (P < 0.05). In benign nodules, the mean VI was 11.61 ± 6.88, mean FI was 39.75 ± 3.93, and mean VFI was 4.82 ± 2.94, compared to 18.64 ± 12.81, 41.82 ± 4.43, and 8.17 ± 6.37, respectively, in malignant nodules. The area under the curves (AUCs) was calculated as 0.68, 0.61, and 0.67 for VI, FI, and VFI, respectively. At optimal cutoff values of 10.2 for VI, 40.8 for FI, and 5.5 for VFI, the sensitivity and specificity were 72%/55.4%, 68%/57.1%, and 68%/67.9%, respectively.

Conclusion

3D PDUS can be useful in the characterization of thyroid nodules.

Validation and comparison of three newly-released Thyroid Imaging Reporting and Data Systems for cancer risk determination

PURPOSE

To validate and compare diagnostic value of three newly-released Thyroid Imaging Reporting and Data Systems (TIRADS) for cancer risk determination.

METHODS

Total 2031 patients with 2465 thyroid nodules were recruited for this study. Ultrasound (US) images were categorized based on three TIRADS editions established by Korean Society of Thyroid Radiology (KSThR), European Thyroid Association (ETA) and American College of Radiology (ACR). ROC curves were established to compare diagnostic value.

RESULTS

Total 1460 benign and 1005 malignant nodules were enrolled. The malignancy rates of each category in KSThR-TIRADS were 2.8%, 5.1%, 33.7% and 79.6%, respectively. For European-TIRADS, 0, 3.1, 22.8, and 73.5% of nodules categorized as 2 to 5 were malignant. Distribution of carcinomas among ACR-TIRADS categories was 0%, 2.3%, 7.5%, 40.1% and 81.4%, respectively. In terms of diagnostic value, KSThR-TIRADS had highest AUC (0.855) and specificity (87.4%), while lowest (71.4%) sensitivity. ACR-TIRADS showed best sensitivity (96.6%) with lowest specificity (52.9%) and the AUC (0.846) was slightly lower than KSThR-TIRADS. Total 56.1, 45.4, and 37.4% fine-needle aspiration biopsy (FNAB) were recommended by KSThR, ETA and ACR, revealing 42.8%, 44.5% and 53.6% malignant lesions, respectively. The rate of unnecessary FNAB was lowest with the ACR (17.3%), followed by ETA (25.2%) and KSThR (32.1%).

CONCLUSION

All these US models showed great value in predicting thyroid malignancy. Among them, KSThR-TIRADS showed the most effective diagnostic performance in specificity, while ACR-TIRADS yielded best sensitivity. As for FNAB criteria, ACR-TIRADS showed the lowest rate of unnecessary FNAB and highest rate of malignancy in FNAB.

Ultrasound elastography of the thyroid: principles and current status

Ultrasound (US) elastography has been introduced as a non-invasive technique for evaluating thyroid diseases. This paper presents a detailed description of the technical principles, peculiarities, and limitations of US elastography techniques, including strain elastography and shear-wave elastography. This review was conducted from a clinical perspective, and aimed to assess the usefulness of US elastography for thyroid diseases in specific clinical scenarios. Although its main focus is on thyroid nodules, the applications of US elastography for other thyroid diseases, such as diffuse thyroid diseases and thyroiditis, are also presented. Furthermore, unresolved questions and directions for future research are also discussed.

WFUMB Guidelines and Recommendations on the Clinical Use of Ultrasound Elastography: Part 4. Thyroid

The World Federation for Ultrasound in Medicine and Biology (WFUMB) has produced guidelines for the use of elastography techniques including basic science, breast and liver. Here we present elastography in thyroid diseases. For each available technique, procedure, reproducibility, results and limitations are analyzed and recommendations are given. Finally, recommendations are given based on the level of evidence of the published literature and on the WFUMB expert group's consensus. The document has a clinical perspective and is aimed at assessing the usefulness of elastography in the management of thyroid diseases.

[Thyroid cancers: from epidemiology to molecular biology]

Experts increasingly recognize the hypothesis of "over-diagnosis" as the main factor of the raising incidence of thyroid cancers (TC). The detection of multiple microtumors, mainly of a papillary type, at a sub-clinical stage, with the use of sensitive detection methods supports this hypothesis. However, the intensive management and monitoring of these cancers failed to reduce mortality. Environmental and other risk factors cannot provide a sufficient explanation, as previously thought. In this context, the use of improved tools is needed, and the most promising perspective lies in molecular biology applied to thyroid cancer for diagnosis, evaluation of prognosis and treatment. The next generation sequencing (NGS) has demonstrated its diagnostic performances in recent clinical trials. Its interest in cases with indeterminate cytology is demonstrated and should help better targeting surgical indications. Its promising prognostic and therapeutic applications must be confirmed by additional studies. The integration of NGS in current practice should have a real medical, economic and scientific impact. Indeed, the exponential increase in our knowledge of molecular mechanisms of thyroid tumorigenesis strengthens the will to "reclassify" these cancers into molecular rather than histological subtypes, in order to offer patients more specific and targeted treatment.

Thyroid nodules and differentiated thyroid cancer: update on the Brazilian consensus

Thyroid nodules are frequent findings, especially when sensitive imaging methods are used. Although thyroid cancer is relatively rare, its incidence is increasing, particularly in terms of small tumors, which have an uncertain clinical relevance. Most patients with differentiated thyroid cancer exhibit satisfactory clinical outcomes when treatment is appropriate, and their mortality rate is similar to that of the overall population. However, relapse occurs in a considerable fraction of these patients, and some patients stop responding to conventional treatment and eventually die from their disease. Therefore, the challenge is how to identify the individuals who require more aggressive disease management while sparing the majority of patients from unnecessary treatments and procedures. We have updated the Brazilian Consensus that was published in 2007, emphasizing the diagnostic and therapeutic advances that the participants, representing several Brazilian university centers, consider most relevant in clinical practice. The formulation of the present guidelines was based on the participants' experience and a review of the relevant literature.

Application of acoustic radiation force impulse imaging for the evaluation of focal liver lesion elasticity

BACKGROUND

Acoustic radiation force impulse (ARFI) imaging is a new elastography method for the evaluation of tissue stiffness. This study aims to evaluate the performance of ARFI in noninvasive assessment of the tissue stiffness of focal liver lesion (FLL) and to explore its potential value in the differential diagnosis of FLL.

METHODS

ARFI was performed in 140 patients with 154 FLLs, which included 28 hemangiomas (ANGIs), 14 focal nodular hyperplasias (FNHs), 61 hepatocellular carcinomas (HCCs), 39 metastases and 12 cholangiocellular carcinomas (CCCs). Virtual touch tissue quantification (VTTQ) values were obtained, analyzed and compared. The area under the receiver operating characteristic curve (AUROC) and optimal cut-off values were obtained using a receiver operating characteristic (ROC) curve analysis to assess diagnostic performance. All cases were definitively diagnosed using histopathology, CT, MRI or contrast-enhanced ultrasound.

RESULTS

The VTTQ median values of ANGI, FNH, HCC, metastasis and CCC were 1.30, 1.80, 2.52, 3.08 and 3.89 m/s, respectively. A significant increase in the VTTQ values of different lesions was observed: ANGI<FNH<HCC<InvalidTagstasis<CCC (P<0.001). The AUROC (95% CI) of VTTQ values was 0.94 (0.90-0.98) for ANGI, 0.91 (0.87-0.96) for malignant lesions and 0.87 (0.79-0.94) for CCC. The sensitivity and specificity for ANGI (86.5%, 89.3%, respectively), malignancy (81.3%, 92.9%, respectively), and CCC (91.7%, 72.5%, respectively) were associated with VTTQ cut-off values of 1.76, 2.22 and 3.00 m/s, respectively.

CONCLUSIONS

ARFI can accurately and objectively assess the elasticity of lesions by obtaining the shear wave elastic value of FLL with VTTQ. Therefore, ARFI is a novel, simple, noninvasive and useful diagnostic method for the characterization of FLL.