40 years of Ultrasound Real-time Grayscale Diagnostics

In the last 40 years, Ultrasound technology has established itself globally as the most often used diagnostic procedure in medicine. For the entire medical field, a reliable and safe diagnosis without ultrasound imaging has become virtually inconceivable. The application does not put any strain on the patient and causes no side effects. In comparison to other imaging procedures, the exams are cost-efficient and can be performed quickly. As a result, Ultrasound technology has had a rapid and widespread acceptance in the medical field.

As early as 1955, J. Holmes first disclosed information on what is generally known as Compound Scanning, a development of D. Howry. In 1960, after thorough clinical evaluations in gynecology, the procedure was released for clinical use. The system's transducer is mechanically connected to an articulated arm. By means of position generators in its joints a true display of the ultrasound echoes is provided on the screen (Fig. [1]).

Fig. 1 Functioning principle of a Compound Scanner.

However, when utilized in clinical routine, it soon became clear that Compound Scanning had some significant limitations: The examination and generation of a complete image took several seconds or even minutes, which made the display of dynamic processes impossible. Aliasing errors due to movement and sound refraction or a non-alignment of the scanning system made clinical diagnoses difficult. In addition, the imaging techniques of that time enabled only the display of organ borders, but did not show their inner structures (Fig. [2]).

Fig. 2 Typical bistable (black & white) Compound image.

In 1965, R. Soldner reached a decisive breakthrough with the introduction of what is known as Real-time Imaging. In his research, R. Soldner, who was an engineer at Siemens Reiniger Werke in Erlangen (the forerunner of Siemens Medical Solutions), had concluded very quickly that although ultrasound imaging was able to provide valuable diagnostic information for all medical disciplines, the technological means provided, i.e. Compound Scanning, would not be successful in clinical routine.

The formation of the image and, thus, the entire examination, were too time-consuming to be successfully used in clinical surroundings. Additionally, multiple manual scans of the soft tissue would inevitably lead to image artifacts. The only solution was a quick single scan of the entire sectional plane at a high repetition rate. The development of real-time imaging had been at the forefront of R. Soldner's research from the very beginning. R. Soldner also discovered that the grayscale display in the ultrasound image was a definite advantage and virtually indispensable for the differentiation of organic tissue.

By 1963, he had already begun the clinical evaluation of a prototype of the legendary VIDOSON, the first real-time ultrasound system worldwide (Fig. [3], [4]). This evaluation took place at Würzburg University. Modern ultrasound real-time scanning with a grayscale display was born! The revolutionary automatic scanning technique of the VIDOSON made it possible to generate, for the first time, images of the human body in such short time intervals and fast sequences on a screen that not only stationary states could be displayed directly and immediately, but also inner organic movements could be directly observed, photographed or filmed. This solved the time and documentation problem, as well as eliminating the system-generated aliasing errors caused by body movement or misalignment.

Fig. 3 VIDOSON - Principle of automatic scanning.

Fig. 4 VIDOSON - 1966-model.

The new ultrasound system was first utilized in gynecology and obstetrics. There was no risk of damaging the fetus or causing hereditary defects, as there was with x-ray diagnostics. The diagnostic information, such as the position of the embryo and placenta within the uterus, the size of the fetal head, as well as the occurrence of twin pregnancies, was available at a very early stage. In addition, tumors and cysts could also be detected early with high accuracy.

In 1965, at a lecture given to the Münster Medical Society addressing the "New Possibilities in Ultrasound Diagnostics in Gynecology and Obstetrics", H.-J. Holländer, a young doctor from the Department of Gynecology at Münster University, provided the clinical breakthrough of this new scanning method (Fig. [5]).

Fig. 5 H.-J. Holländer 1965 at Münster University.

The news of the decisive diagnostic advantages of real-time imaging spread quickly and further clinical studies followed with a new VIDOSON version that featured a much improved image quality:

Higher lateral resolution, More detail recognition, Better tissue differentiation, More image contrast and a more stable image (Fig. 6).

Fig. 6 H.J. Holländer 1966 - 17 week-old twins.

By 1966, Münster University had proved that it was already possible to display a 12-week fetus and the fetal heart movement at 13 weeks' gestation. Furthermore, a measurement of the fetal head was possible at the beginning of the 13th week.

After the introduction of the VIDOSON system in gynecology, the number of pregnancy examinations using x-ray decreased by approximately 90% within the first years of its inception.

Soon after, interested colleagues from internal medicine departments began surfacing. In 1966, Gerhard Rettenmaier, scientific assistant at Erlangen Medical University, was asked to evaluate the usefulness of VIDOSON real-time imaging for the Department of Internal Medicine. His fundamental work on the diagnostics of the epigastric region is considered a milestone in the history of real-time sonography. In 1968, G. Rettenmaier gave his first well-acclaimed lecture on "Real-time sonography of the liver" at the Prague International Congress of Gastroenterology. In 1969, at the first ultrasound world-congress in Vienna, he reported on the intrahepatic echo patterns within the VIDOSON image and their diagnostic significance, as well as on the diagnostic interpretation of movement phenomena such as pulsation, respiratory movement and palpation effects, only possible with real-time ultrasound (Fig. [7]).

Fig. 7 G. Rettenmaier 1968 - liver metastases.

In these days, the ultrasound world was divided into two leagues: Compound-Scan vs. Real-time Imaging. Vivid discussions on the advantages or disadvantages of both procedures took place and lasted several years until real-time scanning would finally prevail.

H.-J. Holländer refers to these days as follows: "At the Vienna congress in 1969, I met Dr. Rettenmaier, the pioneer of VIDOSON ultrasound applications for internal medicine. He lectured on his findings about ultrasound reflections in the healthy or pathological liver. Afterwards he got into a heavy argument with the users of the Compound-technique with storage cathode-ray tube, who found the healthy liver hypoechoic, while Rettenmaier, by using the VIDOSON, had, on the contrary, detected an echo pattern in the healthy liver. He later said that the missing display of grayscale values was a "birth defect" of the storage cathode-ray tube technology, which was only eradicated in 1977 by a new grayscale technique for compound systems."

In 1973, J. Gehrke at Hammersmith Hospital, London, began to display two-dimensional heart images and added a new dimension to echocardiography with his first ECG-triggered VIDOSON images. At that time, the VIDOSON was the only system to display the entire heart in shades of grey.

The increasing success in real-time diagnostics attracted numerous volunteers who wanted to be taught the secrets of this new ultrasound technique by experienced colleagues. As a result, G. Rettenmeier, at the time chief of staff in Böblingen, and his colleague of many years, as well as co-author, K. Seitz, organized the first ultrasound training courses for interested users (Fig. [8]).

Fig. 8 G. Rettenmaier and K.-H. Seitz at an ultrasound training course.

As their experience grew, the content of the training courses increased until finally, a three-level training concept was put into practice. Employees from the Siemens ultrasound lab lectured on physical-technical basics. Since its inception, more than 1 000 colleagues from all over the world have been trained in Böblingen. In addition, it became the guideline for other numerous ultrasound training courses throughout Germany. Accordingly, many colleagues began to rely on ultrasound real-time imaging for routine clinical diagnoses and by 1980, more than 3 000 VIDOSON ultrasound systems had been installed.

Siemens has continued to develop other innovative high-tech systems for ultrasound diagnosis, such as the first worldwide electronic Linear Array (1969), the worldwide first annular array with dynamic focusing (1971) and the worldwide first fully digital ultrasound system (1980). Equally important was the development of Doppler systems for angiology and neurology applications, as well as phased-array systems for cardiology applications with a color-coded blood flow display.

Today's development trends in sonography are based upon the ever-improving technical capabilities in electronics. Users are offered increased diagnostic safety, as a result of better image resolution, while at the same time benefiting from improvements to their daily workflow. Furthermore, new fields of application for scientific research are also regularly being investigated. In the near future, more intelligent procedures will expand the use of ultrasound technology in ways that had previously been unimaginable, as well as leading to even more efficient systems.