By Isaac Levine, Ryan Morrison, Shivam Kaushik, and Deepak Iyer
Since the 1920s, when it was first used as a treatment for arthritis and gastric ulcers, ultrasound (US) technology has come a long way1. In 1947, neurologist Dr. Karl Dussik pioneered its use as a diagnostic tool in his attempts to image the cerebral ventricles2. In 1949, Dr. George Ludwig successfully imaged gallstones embedded in soft tissue, and seven years later Dr. Ian Donald used the one-dimensional A-mode to measure the diameter of the fetal head. In 1950s, Brown introduce a “two dimensional compound scanner” which enabled clinicians to visualize tissue density, an advancement widely considered crucial to US’s future medical usefulness.
Commercial use of US was launched in the 1960s with the advent of B mode devices, and in the 1970s gray-scale and real-time scanners were introduced. Doppler technology, commonly used to assess blood circulation and flow, was added to the growing ultrasound toolbox in the 1980s, and since then the technology has continued to advance, with 3D image processing and small handheld units increasingly being used at the bedside2.
The first documented US guidance in interventional radiology appeared in the early 1970s, used for renal and hepatic biopsies and drainage of abscesses. It wasn’t until the later part of that decade, and into the early 1980s with the introduction of real-time imaging that interventional use of US really took off. In 1983, US was successfully used for in-utero hydrocephalus shunting, and soon it had been applied to pericardiocentesis, soft tissue ablation, transhepatic cholangiography, cholecystostomy, gastrostomy, nephrostomy, and arterial and venous catheterization, and much else besides3. Since then, the role of US in interventional procedures has only grown, and it is currently recognized as a key component of the IR armamentarium in a wide range of roles.
The miniaturization of ultrasound system electronic hardware has unlocked the ability to turn a large, heavy hospital-based cart into a transducer plus system that fits entirely in the palm of your hand. These hand-held devices enable true point-of-care ultrasound at a fraction of the cost of a cart-based system. Image quality is sacrificed for portability; however, with continuous improvement, these devices may one day have equivalent image quality to that of a cart-based system. As the cost of these devices drops below thousands of dollars, they may also one day replace the stethoscope as a quick and easy way to examine vital functions of patients.
Therapeutic ultrasound products that use high intensity focused ultrasound (HIFU) to cause tissue destruction via thermal effects and cavitation are now available as alternatives to radiation treatment. Magnetic resonance (MR) guided HIFU has been around for many years and has successfully treated a wide variety of pathologic tissue types. New products are now hitting the market that utilize real-time ultrasound monitoring to track tissue changes in order to only ablate specific tissues of interest.
Artificial intelligence algorithms are starting to make their way into ultrasound imaging. One of the first commercially available products is an echocardiogram algorithm which allows for fast measurement of cardiac parameters such as heart chamber diameters. This can significantly improve the speed which an echocardiogram can be performed and may also improve the accuracy of measured parameters.
Advances in material science have modified the traditional polycrystalline ceramic material such as PZT (lead-zirconate-titanate) to new, highly efficient materials such as PMN-PT (lead magnesium niobite/lead titanate) PZN-PT (lead zirconate niobite/lead titanate). These materials result in a significant increase in penetration, resolution, and sensitivity in imaging performance.
By cutting ultrasound piezoelectric crystal in three different rows of elements, two focal zones are established at different depths. Clinically, this translates to very high-resolution signals at more than one depth meaning the overall ultrasound image will be extremely high-resolution.
The ability to merge real-time ultrasound with a previous MR, CT, or PET scan allows for an even more powerful diagnostic visualization tool. Extremely precise motion tracking of the ultrasound transducer unlocks the ability to fuse the multiple modality images together. Clinicians can visualize the best aspects of all the imaging modalities in one synchronized image.
Novel manufacturing techniques allow for the ultrasound sensor to be attached to an application specific integrated circuit (ASIC) which moves much of the systems’ electronics into the handle of the transducer. Much of the beamforming of the ultrasound wave now happens inside of the handle of the transducer. What this means is that a transducer can now have tens of thousands of individual elements in a 2D array versus the typical 128 elements of a traditional transducer. Clinically, what this enables is high-resolution, real time visualization of the X, Y, and Z planes at the same exact time and also the rendering of a 3D ultrasound image without the use of a motorized transducer.
Ultrasound transducers come in a wide variety of sizes and shapes to best fit the clinical application they are used in. The typical linear or curvilinear transducer has evolved into intravascular, transesophageal, transrectal, and transvaginal transducers for high fidelity imaging of the anatomy of interest. Intravascular Ultrasound (IVUS) features an ultrasound transducer on an intravascular disposable catheter, which is used heavily in Interventional Radiology procedures to monitor stenosis of vessels among other things. Transesophageal echocardiography (TEE) is often used to monitor heart valves, upper aortic dissections and tears, or congenital heart defects by providing a 3D image of the heart. Transrectal and transvaginal probes can provide images of male and female anatomy that are not possible with traditional probes such as high-resolution imaging of the prostate.
Since the 1960s ultrasound imaging systems have been widely distributed and used across the world. By the 2000s there were portable stations and by the 2010s advances in technology allowed for wireless imaging transducers to be paired with portable PC tablets. These developments point to improved workflow to make the healthcare system more efficient for patients and physicians through fewer keystrokes and automatic lesion seg4.
Artificial intelligence integration into ultrasound workstations allow for automation for certain tasks such as having voice recognition and hands free control of instrumentation.
Ultrasound is a noninvasive procedure in terms of radiation dosage so patients typically have no adverse outcomes. Complications arise due to image quality and user error.
Evidence on trends show an increase in ultrasound usage in lower and middle income countries. Usage of ultrasound across countries has increased by 24% since 2010 from 50 to 62 countries across the globe5. The World Health Organization (WHO) highlights the impact of ultrasound technology along with its importance in healthcare. There is a goal of establishing 90% of imaging needs in the primary care setting with ultrasound technology along with a WHO manual of usage.
1. Kane D, Grassi W, Sturrock R, Balint PV. A brief history of musculoskeletal ultrasound: ‘From bats and ships to babies and hips’. Rheumatology (Oxford). 2004;43(7):931-933.
2. Thomas A, Banerjee AK. The history of radiology. First edition. ed. Oxford, United Kingdom: Oxford University Press; 2013.
3. McGahan JP. The history of interventional ultrasound. J Ultrasound Med. 2004;23(6):727-741.
4. Fornell D. 5 Key Trends in New Ultrasound Technology. Imaging Technology News. 2019. Published February 7, 2019.
5. Stewart KA, Navarro SM, Kambala S, et al. Trends in Ultrasound Use in Low and Middle Income Countries: A Systematic Review. Int J MCH AIDS. 2020;9(1):103-120.