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Sonoelastography- An Emerging Imaging Technique

Sonoelastography is slowly emerging as a new non-invasive imaging technique which could potentially reduce unnecessary biopsies (taking a tissue sample). Sonal Shukla asks experts about its application and efficacy

Sonoelastography is a new ultrasound technique that evaluates the elasticity of any given tissue. It is a complimentary imaging technique to the other conventional ones, i.e. sonomammography and X ray mammography. It has been known that many cancers (breast, prostate, liver metastases, etc) appear as hard nodules and manual palpation (a method of feeling the lump with the fingers to determine its characteristics) is a standard practice to detect them. But many nodules elude palpation by virtue of their small size or their deep location within the body. Elastography is expected to overcome most of these difficulties because it combines the penetration depth and resolution of ultrasound with high sensitivity to stiffness contrast.

According to Dr JP Singh, Senior Consultant and HOD, Fortis Hospital, Noida, as the echogenicity and the mechanical attributes of the tissue are generally not correlated, it is expected that imaging tissue stiffness or strain will provide new information related to tissue structure and/or pathology. Shares Dr Mukund Joshi, Consultant Radiologist, Jaslok Hospital, Mumbai, "It is known that breast cancer tissue is harder than the surrounding normal tissue. Thus, elastography is a new technique that distinguishes between a benign lump from a cancer. This technique is now extensively used in diagnosing breast lumps." Recognising that this modality has been clinically validated as an accurate and reproducible technique that can provide significant diagnostic benefits in routine clinical applications, the technique uses mechanical compression to analyse the stiffness of different tissues.

The Technique

"Considering its usefulness, this modality will surely be available in many more centres in the next five years' - Dr Mukund Joshi Consultant Radiologist Jaslok Hospital Mumbai

"Sonoelastography has the potential to improve the accuracy of percutaneous biopsy and/or nodal dissection - Dr Sunita Dube Medical Director & CEO Aryan Hospital & Medical Center Mumbai

" Sonoelastography is only an adjunct to other methods of conventional imaging" - Dr Dibya Jyoti Konger Consultant Kokilaben Hospital and medical research Institute Mumbai

Fibrotic or cancerous lesions are usually considerably more resistant to compression than healthy tissue. Elastography relates to distortion of a mass to pressure. When tissues are deformed with force, the difference in distortion that occurs within the tissue is elasticity imaging. Elastographic images are obtained with an ultrasound linear array probe.

It is held on the breast and uniform pressure is applied over the area of interest. The ultrasound machine records two simultaneous images side by side. One image is like any other ultrasound image, while the other represents the elastogram. Both images are displayed side by side.

On the elastogram, the hard areas (cancer) appear darker while softer areas (benign) appear lighter. Also, on the measurements, a cancer is larger in diameter as compared to the basic ultrasound image which is obtained simultaneously, while a noncancerous lump is smaller in diameter. These findings enable a sonologist to differentitate between benign and malinant breast lumps.

"The technique has developed alongside conventional B-mode ultrasonography and is also attracting interest from companies seeking to apply it in combination with other imaging modalities such as MRI," says Dr Sunita Dube, Medical Director and CEO, Aryan Hospital and Med ical Center. This technique was first introduced in 1991. It is only in the last decade that elastography is universally used in the evaluation of breast masses. Researchers are also studying elastography for diagnosing prostate cancer, thyroid cancer cirrhosis of the liver (in which the liver characteristically hardens), skin abscess and heart irregularities, among other applications. In liver fibrosis, it is also being evaluated as follow up technique for evaluating various treatment modalities and natural disease progression. In musculoskeletal imaging, the real-time sonoelastography is being tried for diagnosis of tissue softening or tears of heel, elbow and shoulder tendons. "There are encouraging reports in three fields. Firstly, easier lesion detection (this is important for technique to get popular as ultrasound is quite operator dependent), secondly, lesion detection which are isoechoic to main organ but can be picked up on elastography because of differing strain properties with same echogenicity and thirdly, the strain pattern of detected lesion correlation with benignity or malignancy," shares Dr Singh.

Advantages of Sonoelastography

The technique is non-invasive in nature, does not involve radiation and once established will become adjunct to the ultrasound examination and will be done in same sitting. "It grades lesions with intermediate characteristics depending on its elasticity, improves sensitivity and specificity of conventional sonomammography for breast malignancy, aims at reducing negative biopsy rates, is not time consuming and is done at the same time as the sonomammography," says Dr Shrinivas Desai, Director- Department of Imaging and Interventional Radiology, Jaslok Hospital, Mumbai. It helps the clinician to plan the line of treatment for a given breast mass with greater ease. According to Dr Dibya Jyoti Konger, Consultant, Kokilaben Hospital and Medical Research Institute, Mumbai, this technique has a very high level of sensitivity and negative predictive value (upto 100 per cent). It may serve as a link bridging suscipicion and definite proof for malignancy.

It serves as an accurate tool at monitoring medical therapy in liver cirrhosis and has been found to be more precise than other tools like Fibromax. Dr Dube says, "Sonoelastography has the potential to improve the accuracy of percutaneous biopsy and/or nodal dissection. It may also increase the accuracy of postoperative imaging follow-up, especially when metastatic deposits cause lymph nodes to harden before they become larger." This technique may obviate many biopsies of benign lesions and reduce the cost and discomfort of diagnosing breast cancer. Over the last few years, elastographic image quality has improved, along with the sharpness of margins and the resolution within the interior of hard lesions.

Perfection Re-defined!

There is no imaging technique which is flawless or perfect till today, and sonoelastography is no exception to that. Clinical challenges to this technique are in establishing precision at establishing exact cut-off to distinguish between malignant and benign tumours in various body tissues. Being an evolving technique, standardisation of elastograms, quantification and reproducibility are still being perfected. On the technology front, creating uniform vibration fields throughout the region of interest, overcoming tradeoffs between grayscale resolution versus stiffness estimation, computing speeds can always be improved. In addition, the long learning curve and operator dependency are important factors in any ultrasound compared to other imaging modalities.

Despite its potential, the elastographic technique is labour intensive and time consuming, requiring 30-40 minutes for off-line computer processing. "For sonoelastography to become adopted widely, image acquisition and reconstruction algorithms need to be improved," shares Dr Dube. According to experts, investigators in future studies also need to analyse inter and intraobserver variability, better understanding of the mechanical properties of tissue, the stiffness differential between tumour and normal tissue needed, to provide image contrast, and the development of alternative vibration techniques to generate higher frequency shearwaves at depth. "As of now, the areas where it can be useful have been identified but the extent and its due role as replacement or adjunct to guiding biopsy will need to be established over time," says Dr Singh.

Experts caution that however, elastography cannot be relied upon alone to evaluate the pathology. "It is an emerging and effective technique and is here to stay. However, it is to be understood that it is only an adjunct to other methods of conventional imaging and aimed to complement and improve diagnostic precision and not to replace any modality," opines Dr Konger.

Indian Scenario

There is no imaging technique which is flawless or perfect till today, and sonoelastography is no exception to that

This technique is well established in England, Europe and the USA. Dr Bill Svensson in the UK has been considered as one of the pioneers in popularising this technique for breast lumps. "In Europe, trials are underway for establishing the effectiveness of technique and reproducibility of results. The technique has its advantages, but there is still a long way before it enters the mainstream primary diagnostic procedure," says Dr Singh. India's first sonoelastography was launched three years ago; however, there are hardly any centres that have been practicing this technique.

Dr Joshi established this modality in India about four years ago. Jaslok Hospital in Mumbai has state-of-the-art equipment and has been utilising elastography for the last two years. Recently, the hospital has also acquired automated breast volume imaging ultrasound machine, the only of its kind in the country, which further assists in the diagnosis of breast cancer immensely. The other centres in India having this are in Hyderabad, Chennai, Amritsar and at the AIIMS, New Delhi. "As of now, the expertise in India or for that matter world over is limited. However considering its usefulness, this modality will surely be available in many more centres in the next five years," says Dr Joshi. The current cost varies between five and seven thousand rupees per examination.

Beyond the Present

The ease of availability and application, non invasive nature of this technique are set to make it increasingly popular among radiologist, believe Dr Desai. With new technologies based on ultrasound on the verge of practical usefulness, the practice of breast ultrasound will be revolutiolised if sonologists embrace them, believe Dr Dube. Integrating ultrasound breast imaging with new non-ultrasound technologies is important as are programmes to train and accredit as many professionals as possible. Experts like Dr Joshi are hopeful that sooner or later this technique will get popular in the Indian scenario, especially since the awareness for breast cancer is increasing by leaps and bounds. Also, it is an established fact that breast cancer is significantly increasing in the country with urbanisation of our population. "As the technique gets established with few clear-cut indications and established usefulness in mainstream, it will become popular, but the jury is still not out for the role it will finally play," concludes Dr Singh.

sonal.shukla@expressindia.com