Advances in ultrasound

Historical perspective. From its modest beginnings in 1947, when Karl and Friederick Dussik attempted to use ultrasound to visualize the cerebral ventricles to modern rarefied applications like Acoustic Holography and Fusion Imaging, ultrasound has travelled a long way. If the greatness of an invention were to be measured by its effectiveness in alleviating human suffering and contributing to mankind’s well-being, ultrasound ranks very high in that select list. Building upon the principles discovered by Spallanzani in 1794, ultrasound saw the introduction of an immense variety of devices and techniques, for diverse applications in almost all branches of medicine- both in the diagnostic and therapeutic aspects. Ultrasound saw a continuous evolution of technology from A, B and M mode ultrasound to the modern Doppler Imaging, Contrast-enhanced ultrasound, US Elastography, 3D and 4D Imaging, High Intensity Focused Ultrasound (HIFU), Tissue Harmonic Imaging, Radiomic Ultrasound Analysis, Digital Beam Forming, Laparoscopic, Intravascular, Endoscopic and Intraoperative Ultrasound.

Advantages and limitations. As a major diagnostic modality, ultrasound had unique advantages and limitations. Its main advantages are its radiation-free nature, its unparalleled spatial and temporal resolution, its real-time capability, ability to visualize moving structure in the form of doppler, portability and lower cost. The main limitations are very few- the limited field of view, its operator dependence and difficulty in imaging structures behind bone or gas.

Recent advances. The advances in the field of ultrasound have been in several directions. Very high spatial resolution has always been a strong advantage of ultrasound, and resolution of even 0.1 mm can be achieved with conventional scanners. And recent advances, using ultrahigh frequency ultrasound using frequencies upto 3 Ghz have been used to achieve microscopic resolution in the submicron range- its applications include evaluating perfusion of tissues and visualizing plaques and vasa vasorum. Other advances includesuperb microvascular imaging, which can distinguish Doppler signals generated by low-velocity blood flow from those generated by tissue movement, was developed. Similar technology, such as high-definition color can display very small tumor vessels. Fusion imaging is a novel technology that accurately combines real-time US images with real-time CT or MRI volume data and displays them on the same monitor, side by side. This means that a clinician can visualize both registered multiplanar reconstruction (MPR) images on the same monitor to make diagnostic or procedural decisions in real time.Photoacoustic imaging (PAI) is an emerging modality that uses a combination of optical excitation and acoustic detection for visualizing vascular, functional, and molecular changes within living tissue. Molecular Ultrasound Imaging using Microbubbles and Nanobubbles is being developed to diagnose angiogenesis, inflammation, and thrombosis, and many intravascular targets, such as VEGFR2, integrins, and selectins, have been successfully visualized in vivo.

IVUS is a catheter-based imaging modality that provides high-resolution cross-sectional images of the coronary artery, enabling tomographic measurements of both the luminal and vessel areas. The axial resolution ranges between 100 to 200 µm and the lateral resolution is approximately 250 µm. There is also a newer iteration of IVUS called High Definition IVUS (HDi),which represents reinvention of the IVUS technology. It provides superior image quality, delivers axial resolution of 40 µm, and minimizes noise with greater depth of penetration.Ultrafast imaging describes image acquisition technologies with very high frame rate, typically in kilohertz range, with 2 major components: wide-field beam transmission and parallel receive beamforming. Shear wave elastography is one of the early clinical applications of ultrafast imaging.
Another notableadvance has been portable ultrasound. A major advance in the field of Doppler is Vector Flow Imaging. It achieves angle independent estimation of velocities and visualization of velocity vectors. The review of ultrasound technology will not be complete without the topic of therapeutic and theranosticultrasound for treatment-from uterine fibroids to essential tremor. Another advance has been in the realm of ultrasound-guided drug delivery with Sonoporation. The field of Artificial Intelligence is transforming medicine and ultrasound is no exception. There has been a continuous incorporation of Convolutional Neural Networks and other software in improving Computer aided diagnosis.

Applications. Ultrasound finds extensive application in almost all branches of medicine. It played a fundamental role in obstetric imaging right from conception till delivery and beyond and is used for monitoring fetal growth and detecting fetal and placental anomalies and assessing maternal well-being. Incardiology, Echo plays a vital role in real time functional and structural assessment of the heart. In oncology, ultrasonography is employed for three basic steps in the staging of neoplastic lesions: 1. detection of lesions, 2. diagnosis of their nature, 3.TNM staging. In neonatology, neurosonography is used for assessing the neonate’s brain through the open anterior fontanelle. 3/4D imaging have been utilized by clinicians to enhance the investigation and management of patients in areas as diverse as assessment of fetal growth and wellbeing, screening for fetal anomalies, prediction of pre-eclampsia and preterm birth, detection of ectopic gestation, evaluation of pelvic masses, screening for ovarian cancer and fertility management.And, of course, ultrasound is the workhorse in general medicine and surgery for assessment of the abdomen, pelvis and, increasingly, the chest. As doppler, it plays a crucial role in assessing the peripheral and central vascular conduits.

Conclusion. For the last few decades, ultrasound was strongly undervalued in clinical practice. Recent achievements have started to uncover its full diagnostic and therapeutic potential. Continued developments in this field will enhance the value of this modality even further.

At the MNJ Institute of Oncology, the premier Oncology Institute in Hyderabad, Ultrasound is extensively used, in conjunction with other modalities in detecting, staging and assessing the response of tumors to treatment. Extensive use is made of the conventional and high frequency ultrasound in anatomic and doppler examination of the various lesions. Also, ultrasound, along with CT is routinely used for image-guided FNAC and Biopsy.