Dr D Umashankar, Chief Radiologist, Padmashree Advanced Imaging Services, Bengaluru outlines the evolution of ultrasound technology and its growing implementation across different segments of healthcare
Because of constant improvements and better iterations of existing technologies and new developments, the overall costs of high-end ultrasound systems is lowered in comparison to other modalities which add to their cost – effectiveness and appeal to many hospitals.
Engineering advances
Early engineering advances in ultrasound were limited primarily by what could be done, economic factors are now in control. Iterative improvements that reduce vendors’ costs are sought after, with no technical achievement more prized than the one that cuts cost while at the same time offering design and upgrade flexibility, without any sacrifice in image quality. The miniaturisation of electronics is one of these improvements, and the replacement of hardware with software is another.
The impact of miniature, high-performance electronics is apparent in the appearance of the handheld ultrasound scanner. Manufacturers of these products want to put ultrasound in the hands of primary-care physicians and emergency medical personnel to enable quick screening or assessment of patients. It’s an ambitious goal that could change the practice of medicine. Meanwhile, conventional practitioners will benefit from the trend toward smaller, lighter, and easier-to-operate diagnostic equipment.
Increased spatial resolution from more sensitive transducer arrays and improved contrast agents could make diagnostic conclusions easier. Real-time volumetric scanning could reduce the need for operator skill, making ultrasound more reproducible and productive. Advanced computing platforms might even make automatic feature recognition possible, as lesions and tissues are outlined, measured, and compared to databases containing normal and abnormal ranges.
These technical advances form the basis for many of the recent trends you will read here.
Handheld/ point-of-care ultrasound
Improving ease of use has been an essential factor in the growth of ultrasound imaging, particularly as the demand for POC solutions has expanded. Adaptability is the key for this market segment that is moving radiology outside the walls of the imaging lab to first response scenes, the emergency department and even the patient’s bedside.
Two new innovations have come to the fore to address these issues. One of which is the introduction of touch – enabled ultrasound systems, which enhance mobility by sacrificing cumbersome keyboards. The other innovation happening is the emergence of using a customer android or an apple device as an ultrasound scanner. The Clarius ultrasound scanner is wireless and works with a mobile app that is compatible with most iOS and Android smart devices. With automated adjustments and an intuitive interface, the personal ultrasound device is designed to be carried around for quick exams and to guide procedures such as nerve blocks and targeted injections. Philips Healthcare also introduced Lumify, a mobile app-based ultrasound system. The concept turns any Android – based smart phone or tablet device into a hand-held, portable ultrasound system simply by plugging a Philips transducer into the device’s USB port and downloading the Lumify app. The transducer performs all of the acquisition functions and a portion of the image reconstruction processing, with the smart phone serving as the display screen and the connection link to the cloud storage archive.
Turning a consumer-grade smart phone into an ultrasound system provides hospitals, urgent care centers and doctor’s offices with a highly flexible point-of-care solution with a low total cost of ownership. These devices can perform scans of the gall bladder, abdomen and lungs, in addition to having OB/ GYN, vascular, superficial, musculoskeletal and soft tissue functionality.
The other innovation in some of the other manufactures devices, feature an all-touch control panel that combines the speed and flexibility of a soft user interface with the tactile feedback of
traditional keys. Etched markings for primary controls help the user easily locate key functions without looking away from the display monitor. Users can choose from several different exam presets with a single touch, including cardiovascular capabilities like continuous wave (CW) Doppler, and a series of emergency department-specific exams. Image optimisation is also a one-touch function. All these advances are bringing in a lot of excitement in the POC segment.
Wireless transducer
Siemens Healthcare introduced an ultrasound system with wireless transducers, the Acuson Freestyle. Completely untethered from the console, the product’s wireless transducer can reportedly be used to image from up to 10 feet away, and is built to endure any potential falls or mishaps. The system is targeted toward use in interventional applications such as in radiology and cardiology, and it can also be used to aid in vascular access procedures as well as needle visualisation. The system uses a proprietary 8 GHz ultra-wideband radio frequency to transmit data to the main console, and also includes Bluetooth wireless control.
Fusion
Fusion technology provides the ability to synchronise ultrasound imaging with computed tomography (CT) or magnetic resonance (MR) image, improving the detection of hard-to-find lesions.
The FDA cleared technology helps interventional radiologists and surgeons perform minimally invasive biopsies and other diagnostic and therapeutic procedures. through an intelligently integrated display of fused ultrasound and CT images. The system is available as an accessory, which can be retrofitted on most existing ultrasound machines.
This technology was developed in response to a clear need for simpler multi-modality imaging using ultrasound while minimising the number of CTs and hence improve patient safety by reducing radiation dose. By showing the clarity of CT with the real-time visualisation of ultrasound, users experience the benefits of both modalities simultaneously. The newer commercially available systems also incorporate a novel fully automated registration process which do not require special needles or new imaging equipment, preserving the customary work-flow and maximising the productivity of existing capital equipment. These devices were made to address the myriad challenges associated with working with CT and ultrasound images simultaneously. The older fusion systems require long and complex registration processes while the newer iteration eliminates this step through automated registration and system fusion, which is continuously updated throughout the procedure. The time required for registration drops to seconds. Moreover, clinical recommendations to reduce CT radiation doses heighten the importance of good ultrasound visualisation. With CT precisely overlaid on the ultrasound plane, deep and challenging lesions can be visualised and targeted efficiently.
The ability to see the target lesion clearly before, during and after a procedure means procedures can be reliably performed in ultrasound with real-time imaging, freeing up the CT suite for diagnostic imaging and mitigating exposure to ionising radiation for the patient and staff. Many of the first time users of this technology have called it a ” a game-changer.”
Shear wave elastography
SWE differs from traditional strain elastography, which relies on manual compressions by the examiner to assess tissue displacement. The SWE technique instead captures shear wave generation with patented Imaging technology to quantitatively measure the stiffness of local tissues. By being less dependent on an experienced operator, SWE can record elasticity more accurately than conventional elastography and produce a more objective, real-time colour-coded map to show tissue stiffness.
Currently it is widely used and studied in breast, liver, thyroid and musculoskeletal applications. Latest results from a multi-centre study, published in the Radiology and European Radiology journals, showed the technology improves breast ultrasound specificity when detecting breast lesions in patients. Other studies have demonstrated its exemplary utility in the detection of liver fibrosis and to differentiate it from the omnipresent diagnosis of fatty liver.
Shearwave elastography in liver
Liver disease is an important problem worldwide. Accurately diagnosing liver fibrosis and inflammatory activity are the most important factors for determining the stage of the disease, assessing the patient’s prognosis, and predicting treatment responses. This is true for a wide range of disorders, including viral hepatitis, alcoholic and non-alcoholic fatty liver disease, drug-induced liver injury, primary biliary cirrhosis, and autoimmune hepatitis.
Liver histologic analysis is still considered the reference standard in the assessment of liver fibrosis despite the intraobserver and interobserver variability in staging. Liver biopsy is a painful technique that is not well accepted by patients, has morbidity and mortality risks, and is not an ideal method for follow up of patients.
Thus, non-invasive methods for assessing liver fibrosis are of great clinical interest. In the last decade, techniques to non-invasively estimate the stage of liver fibrosis have become commercially available. They all have the capability to evaluate differences in the elastic properties of soft tissues by measuring tissue behaviour when a mechanical stress is applied. Ultrasound and magnetic resonance have been used for elasticity imaging. Magnetic resonance elastography, even though promising, has some disadvantages. It cannot be performed in a liver with an iron overload because of signal-to-noise limitations, the examination time is longer with respect to ultrasound elastography, and it is also a very costly procedure.
Shearwave elastography in breast
Mammography has been the standard of care for screening women for breast cancer since 30 years. However, it often fails to pick up lesions when used to image women with dense breasts who form about 40 per cent to 50 per cent of all women undergoing mammography. That dense breasts mask and miss cancer in mammography further compounds the clinical effectiveness of this modality as an accurate screening modality.
With the heightened focus on imaging women with dense breasts, interest is growing as well in other breast imaging modalities, including elastography ad other modalities like MRI and molecular breast imaging.
With strain elastrography, a malignant lesion appears larger than on conventional ultrasound, and a benign lesion appears smaller. However this technique is limited by operator dependence.
Shear Wave elastography imaging removes this anomaly. If results are concordant between strain and shear wave, then there is a high confidence that a positive result is accurate. In fact, this information achieves positive biopsy rates approaching 75 per cent. Considering that with mammography 80 per cent of biopsied lesions are benign, Ultrasound elastography can make a dramatic impact on reducing unnecessary biopsies.
Shearwave elastography in tendons
Shear-wave elastography provides an objective, quantitative assessment of tendon integrity and might be useful to guide treatment and develop new treatment approaches.
Insertion tendinopathies of the Achilles and patellar tendons are common orthopaedic diseases, especially among young athletes. While sonographic imaging has traditionally been used in these patients to assess morphologic changes via B-mode and perfusion changes via power Doppler, shear-wave elastography has recently been shown to be able to differentiate between symptomatic and asymptomatic tendons.
Diseased tendons are softer than normal tendons. This fact which is leveraged as an advantage to demonstrate the extent and stage of disease by using shearwave technology
Beyond assessing for the presence or absence of tendon pathology, shear-wave elastography yields quantitative data that can be correlated with clinical symptoms, Dirrichs said. The shear-wave elastography values correlated closely with clinical exam scores over the course of treatment for those patients whose symptoms had improved.
Contrast enhanced ultrasound
The field of diagnostic ultrasound is again on the cusp of major change. In the last decade, drug companies, ultrasound scanner manufacturers, and academic centres have invested manpower and funding in developing efficacious ultrasound contrast agents and new contrast-specific imaging modalities. Now, by bringing contrast media to the clinic, these efforts appear on the verge of success. As in MRI, CT, and conventional x-ray, the use of contrast media is changing the way ultrasound is performed, opening new and unique diagnostic opportunities.
Vascular enhancing ultrasound agents were first introduced by Gramiak and Shah in 1968, when they injected agitated saline into the ascending aorta and cardiac chambers during echocardiographic examinations. Strong echoes were produced within the heart, due to the acoustic mismatch between free air microbubbles in the saline and the surrounding blood. However, microbubbles produced by agitation are both large and unstable, diffusing into solution in less than 10 seconds.
Most vascular contrast agents are stabilised against dissolution and coalescence by the presence of additional materials at the gas-liquid interface. Air, sulfur hexafluoride, nitrogen, and perfluorochemicals are used as microbubble-filling gases, most newer agents use perfluorochemicals because of their low solubility in blood and high vapour pressure. By substituting different types of perfluorocarbon gases for air, the stability and plasma longevity of the agents have been markedly improved, usually lasting more than five minutes.
Several cardiac and vascular ultrasound contrast agents are commercially available.
Most agents also improve gray-scale visualisation of the flowing blood to such a degree that the tissue echogenicity increases (parenchymal enhancement). Microbubbles within the small vessels of an organ can thus provide a qualitative indication of perfusion.
Contrast should also be useful for evaluating vessels in a variety of organs, including those involved in renal, hepatic, and pancreatic transplants. If an area of ischemia or a stenosis is detected after contrast administration, the use of other more expensive imaging modalities, including CT and MRI, can often be avoided.
Contrast ultrasound in neurology
Transcranial Doppler (TCD) studies suffer from a poor signal – to – noise ratio and so contrast-enhanced TCD is receiving attention.
Contrast ultrasound in oncology
Contrast kinetics (i.e., the uptake and washout of contrast over time) may become important parameters in helping to differentiate benign from malignant tumours. In a published study on ultrasound contrast, they found that neovascular morphology (i.e., arterial-venous tumour vessel shunts) as well as contrast washout times were statistically significant in discriminating between malignant and benign lesions and also increased both sensitivity and specificity to 100 per cent. While such results are clearly limited by the number of cases, they still indicate that vascular ultrasound contrast agents could have a major role in the future diagnosis of breast cancer, and possibly other cancers.
Neoangiogenesis (creation of new blood vessels) is common to all malignant tumours, and these new vessels are usually abnormal-irregular in size, branching, and distribution, with flow in bizarre directions. Ultrasound alone cannot detect these small vessels but with the addition of ultrasound contrast media, they may be visualised. This has already been demonstrated in breast cancer and undoubtedly will move into other areas like ovarian cancer screening.
Exciting new clinical possibilities arise from tissue – specific ultrasound contrast agents, which may improve the assessment of certain organs by improving the image contrast resolution through differential uptake.
Contrast ultrasound in cardiology
Other important clinical use of ultrasound contrast is in cardiology, where it will potentially compete with thallium nuclear scans. Myocardial imaging using ultrasound contrast agents provides an assessment of the coronary arteries and of the coronary blood flow reserve, as well as collateral blood flow that may exist.
Contrast ultrasound in infertility
Hysterocontrast salphingography (HyCoSy) was compared to established, more invasive techniques such as chromolaparoscopy and 91 per cent agreement was found. HyCoSy is rapidly becoming the screening test of choice to determine tubal patency.
Contrast ultrasound in paediatrics
Vesico – ureteral reflux (VUR) is a common problem in children. Reflux sonography, as an alternative to micturating cystography, detects or excludes VUR. This method detected VUR in children at the lowest cost.
Contrast ultrasound in drug delivery
Other concepts being explored include targeted drug delivery via contrast microbubbles. Tissue-specific ultrasound contrast agents are most often injected intravenously into the blood and taken up by specific tissues, such as the reticuloendothelial system, or they adhere to specific sites such as venous thrombosis.
The disadvantages of contrast agents are their cost and the requirement for an intravenous injection. Also, with more sensitive Doppler instrumentation, blood flow enhancement may not be as important as it has been in the past.
Laproscopic ultrasound
Laparoscopic ultrasound (LUS) is better than CT at detecting liver tumours, especially smaller ones, according to a study published in the August Archives of Surgery. The finding opens the door for expanded use of the technique in a wide variety of surgical procedures.
LUS detected every tumour seen on preoperative CT and found nearly 10 per cent that had been missed. Patients were upstaged by the use of ultrasound. This study points out that intra-operative ultrasound is better than anything else for detecting lesions.
LUS detected 9.5 per cent additional tumours in 20 per cent of patients. The lesions missed by CT were broken down by size: more than a quarter were smaller than 1 cm and none were greater than 3 cm. CT was more likely to miss tumours in the falciform ligament of the liver and along the liver’s periphery. The lesson here was to pay special attention to those areas where CT scan might be a little less effective.
Intravascular ultrasound
Drug-eluting stents have helped to significantly reduce in-stent restenosis and repeat revascularisation; however, percutaneous coronary intervention (PCI) of diffuse long coronary lesions remains difficult, as these have higher rates of in-stent restenosis and stent thrombosis than lesions that are shorter in length. Implantation of drug-eluting stents under IVUS guidance has been shown in four meta-analyses to be associated with reduced major adverse cardiac events, but the procedure’s effect on clinical outcomes remains uncertain due to the limited number of randomised trials with sufficient statistical power.
The authors also noted that the overall major adverse event rate was lower than they anticipated.
They concluded that among patients requiring long coronary stent implantation, the use of IVUS – guided everolimus – eluting stent implantation, compared with angiography – guided stent implantation, resulted in a significantly lower rate of the composite of major adverse cardiac events at one year.
Lung ultrasound
Lung ultrasound has been shown to be highly effective and safe for diagnosing pneumonia in children and a potential substitute for chest radiograph. Results are currently published in a reputed medical journal. WHO estimates three-quarters of the world’s population does not have access to radiography.
Ultrasound is portable, cost-saving and safer for children than an X-ray because it does not expose them to radiation. The results of this study could have a profound impact in the developing world where access to radiography is limited.
In the era of precision medicine, lung ultrasound may also be an ideal imaging option in children who are at higher risk for radiation-induced cancers or have received multiple radiographic or CT studies.
As more and more hand-held ultrasound machines come to market, lung ultrasound has the potential to become the preferred choice for the diagnosis of pneumonia in children. Further research is needed to investigate the impact of lung ultrasound on antibiotic use.
Conclusion
If the past is any indicator, these advances are only a sampling of what’s to come, as technologies are combined in new and creative ways. But it will always be the clinician’s skill and art that count most.