History of Standardized Echography


Karl C. Ossoinig, MD
University of Iowa, USA


1.      Introduction


Standardized Echography” is a widely used ultrasonic diagnostic method in ophthalmology, which combines diagnostic A-scan, diagnostic B-scan, biometric A-scan and, at times, Doppler evaluations. Each of these applications is used for specific portions of the diagnostic effort according to each one’s optimal suitability:

Diagnostic B-scan is utilized for topographic evaluations such as the location of a lesion and its shape, insertions and relationship to neighboring structures, for an estimate of its dimensions across the sound beam, and for kinetic evaluations of some types of the lesion’s mobility and consistency. B-scan of 20-50 MHz is preferred for evaluations of the anterior eye segment, B-scan of 10 - 15 MHz is applied for the posterior eye segment, B-scan of 10 MHz is utilized for the orbit.

Diagnostic A-scan (8 MHz effective frequency, parallel beam) is applied for quantitative evaluations of a tissue’s structure, reflectivity and sound absorption, for some topographic evaluations such as the borders of orbital lesions or some peripheral insertions in the posterior eye segment, and for kinetic evaluations of a tissue’s vascularity, mobility and consistency.

Biometric A-scan (8 MHz effective frequency, parallel beam) serves precise measurements along the sound beam, for instance the maximal height of an intraocular tumor, the dimensions of an orbital mass lesion, the exact depth of a foreign body, the thickness of tissues such as the sclera, extraocular muscles and the optic nerve or the distension of its sheaths [103]. The same kind of biometric A-scan is used for most accurate and precise immersion axial eye length measurements for optimal IOL power calculations.

Pulsed Doppler (at least 9 MHz nominal frequency, preferably of a directional type) may be added for more specific evaluations of blood flow in larger vessels [49, 64].

For A-scans – in order to be diagnostically valid – one must use specifically (optimally) designed and standardized instrumentation [2, 75, 85, 205]. In addition to the instrumentation, all the examination techniques (A-scan, B-scan and Doppler) must also be specifically designed to allow for optimal results [1, 4, 8, 22, 35, 45, 46, 64, 138, 75, 150, 205]: a “Basic Examination” serves the detection of intraocular and (peri)orbital lesions; two types of “Quantitative Echography” help to evaluate structure, reflectivity, and sound absorption within a lesion; “Topographic Echography” reveals and documents the location, shape, borders and topographic relationships of lesions; various types of “Kinetic Echography” determine the vascularity, mobility and consistency of lesions.

Various types of “Echographic Tomography “ were introduced for immersion B-scan examinations [13, 15] when this B-scan method was still used for Standardized Echography: specific scanning techniques, i.e. transverse, longitudinal and axial scans are used with contact (posterior eye segment and orbit) and immersion (anterior eye segment) real-time B-scanning since the 1970's [75]. The fact that in Standardized Echography the A-scan instrumentation as well as all the examination techniques are optimally designed and standardized gives the method its name.

The primary goal of this optimal design of the A-scan instrumentation and of all examination techniques is a superior capacity for and efficacy in diagnosing, differentiating and measuring a great variety of normal and abnormal ocular tissues (anterior and posterior eye segment as well as orbit and periorbital region). The purpose of standardizing this design is to use a universal and optimal echographic language with superior, understandable, comparable and repeatable results.



2.      Historical Background 



The idea of Standardized Echography was conceived in 1963 in the II. Eye Department at the University of Vienna (Austria), when it became apparent to the author that even A-scan instruments with identical brand names produced very different results: while both intraocular and orbital tumors were successfully detected, measured and to some extent even differentiated by the author in the II.Eye Department as early as 1963 using the Kretz 7000 model, none of this was possible with the Kretz 7000 model purchased and used later the same year in the I. Eye Department at the University of Vienna.

This experience prompted phase I of the evolution of Standardized Echography which was undertaken in the 1960’s. Phase I  included extensive experimental and clinical investigations testing all those instrument parameters which influence the appearance and diagnostic value of the A-scan echograms and arriving at optimal choices for each of them to be standardized for all subsequent A-scan devices for Standardized Echography. During phase I  the author and his cooperators also undertook extensive experimental work with various biological materials including fixed and frozen tumor tissues and especially a variety of citrated blood samples to clarify the echo origin in living tissues, to reveal more acoustic criteria for the differential diagnosis of ocular and orbital lesions and to select a proper tissue model for setting the A-scan devices at the standardized Tissue Sensitivity [2, 4, 11, 18, 29, 33, 43, 205].

 Beginning in 1964 the author also embarked in the development of B-scan instrumentation and techniques to augment the A-scans [3, 5, 7, 9, 10, 15, 16, 20, 35]. Progressively more efficient immersion B-scan devices with use of electromechanical guidance of the sound beam were developed by the author together with Kretztechnik. This cooperation resulted in the worldwide first commercially available A&B-scan unit [9, 13, 20, 25, 28, 29, 35] in 1966 (Kretztechnik 7900 S with the choice between a hand-guided probe or an automatic probe transport for B-scan tomography for immersion B-scanning incorporating the first commercially available standardized A-scan device) { not to be confused with a parallel development by W. Buschmann of an experimental unit for use with an arc-shaped array transducer for contact B-scanning bearing the same name, which, however, never became functional and therefore did not go into serial production }.

The A-scan part of the instrument's signal processing was standardized and served as prototype for the Kretztechnik 7200 MA [35, 40], which was developed by the author with Kretztechnik  during the late 1960's as a stand-alone standardized A-scan unit which was clearly improved over the 7900 S standardized A-scan device. The Kretz 7200 MA was the first fully standardized A-scan device [44, 205]. It went into serial production in 1970; it was the only A-scan instrument available for Standardized Echography throughout in the 1970’s and early 1980’s. About 500 of these units were put into use by 1980 worldwide. Some of these units are still in use today.

In 1970, the author temporarily dropped immersion B-scan from use in Standardized Echography as it had become sufficiently apparent that the B-scan information, though impressive to any audience or readership, did not add anything significant to the acoustic information obtained by the superior standardized A-scan, but rather lacked reliability in the display of peripheral intraocular and orbital lesions and took way too much time in a busy clinical practice to remain feasible. When the author moved to Iowa City in 1971, he for a year applied only standardized A-scan utilizing the Kretztechnik 7200 MA [35, 40, 38]. When Nathaniel R. Bronson introduced contact real-time B-scan in 1972 [34, 47], B-scan once again became an integral part of Standardized Echography [43, 44, 48, 49, 52, 55, 57, 64, 69,70].

Early on, the method of Standardized Echography actually was referred to as “Clinical Echo-ophthalmography”  [9, 29, 35, 40, 49, 55] since it did provide clinically extremely useful diagnoses already in those early years, in contrast to the experimental nature of  other investigators' A-scan or B-scan applications. However, the specific description of the method as "Clinical" was dropped by the author in the mid-1970s when it became apparent, that contact real-time B-scan used without (standardized) A-scan also gained clinical significance. After designing special standardized examination techniques, i.e. transverse, axial and longitudinal scans for the contact real-time B-scan method, the author renamed this combined A-scan / B-scan / Doppler method “Standardized Echography” [75].

Phase I was completed by 1971, when the first commercially available standardized A-scan unit, the Kretz 7200 MA was introduced and the author moved to the Eye Department at the University of Iowa in the USA.

Phase II of the evolution of Standardized Echography took place during the 1970's, 1980's and into the early 1990's. Because of the availability of standardized instrumentation phase II brought an explosion of clinical investigations resulting in a rapid expansion of Standardized Echography [39 - 201; 212, 213, 215, 217, 220, 223, 225]. Also, early during phase II, a breakthrough regarding tissue models had been achieved:  a solid tissue model for setting a standardized A-scan device at the (very high) standardized Tissue Sensitivity had been created by Peter Till to replace the previously used citrated blood samples [61, 68, 80, 91]. This solid tissue model continues to be an essential part of every fully standardized echography instrument; it is regularly furnished with fully standardized instruments upon their purchase.

Since the mid 1970's measurements of the extraocular muscles and the optic nerve  were added to the armamentarium of Standardized Echography and were perfected during the following years. The author designed the "30 degree test" [86, 87, 150] to distinguish between solid and fluid optic nerve sheath widening, and later on the even more important technique of "exercising " the optic nerve to distinguish between intracranial hypertension and optic nerve compression [150]. Differential diagnoses of diseases affecting the optic nerve and the extraocular muscles including the most frequent orbital condition, i.e., Graves' orbitopathy were all defined and secured in phase II.

All in all, the diagnostic capacity of Standardized Echography was largely extended during phase II so that it further excelled over other diagnostic procedures (Fig. …) in safely providing more than 75 different intraocular as well as more than 65 different (peri)orbital diagnoses.

 Although the advent of CT and MRI reduced the need for Standardized Echography for orbital evaluations, Standardized Echography remained superior in many areas of orbital diagnoses, e.g., in Graves' orbitopathy, orbital myositis, inflammatory disease, evaluations of the optic nerve such as clarification of unilateral papilledema, optic nerve compression, optic neuritis, optic atrophy etc.,  further in the detection and localization of foreign bodies, especially organic ones, and in the differential diagnosis of orbital tumors. 

In 1984 the first combined standardized A-scan/B-scan instrument since the 7900 S unit of the 1960's became known as Ophthascan S (manufactured by Biophysic Medical, France). It was introduced at SIDUO X in St.Petersburg Beach, Florida [216]. Being the first digitized unit for Standardized Echography it had, however, some flaws (low image repetition hampering kinetic evaluations; poor high-frequency filtering rendering the A1sign worthless). A greatly advanced stand-alone standardized A-scan unit, the Mini-Ascan was developed subsequently by the author in cooperation with Biophysic Medical, France. This unit became available in the late 1980's. The Mini-A-scan offered a number of innovations that made operation faster, easier and more precise; its measuring resolution of 0.03 mm remained unparalleled until the year 2000, when the Cine-scan S was introduced during SIDUO XVIII. The Mini-A-scan was highly developed; its name contains an accidental understatement and was supposed to refer to its smaller size and lesser cost in comparison to a much more powerful digital A/B combination that was to follow instantly. The latter did not materialize, however, since Biophysic Medical was taken over by Alcon at that time. However, the previously so successful team of Biopysic Medical regrouped under the name of Biovision International (BVI) and, more recently, expanded to a combined US/French venture known as Quantel Medical/BVI (Bozeman, Mt, USA /Clermont-Fd / Paris, France). The cooperation of the author with Quantel Medical /BVI resulted in the development of progressively more sophisticated and advanced Standardized Echography instrumentation, i.e., the A/B system "B-scan S" (1994) and most recently its successor, the "Cine-scan S" (2000). The previous plan to create a superior A/B combination (see above) is finally being realized.

The great expansion of the applications and the increasing sophistication of Standardized Echography brought about in phase II not only enhanced this method over other diagnostic procedures but also incorporated a major obstacle for wider usage and faster spread of this unique method: it required lengthy training and major experience; it was time-consuming and for many applications difficult. 

The advent of the digital revolution and modern software applications led to phase III of the evolution of Standardized Echography beginning in the early 1990's and continuing at an ever faster pace. These technological advances began to systematically transform Standardized Echography into a quick and easy, and at the same time more objective, more reliable and more accurate method which in addition requires much less training and experience. An example is presented by the author in another contribution to SIDUO XVIII (see Ossoinig KC: "Computer-assisted Echographic Tissue Diagnoses: differentiation between retinal and membranous surfaces").  This rapidly developing user-friendly automation of differential diagnoses and measurements has begun to rejuvenate Standardized Echography preparing it for a much wider usage in the years to come.



3.   Phase I


During phase I of the evolution of Standardized Echography extensive experimental and clinical investigations were conducted to determine the optimal settings of each of the parameters of an A-scan instrument, which influence the appearance and diagnostic value of the A-scan echograms.

The results were usually optimal compromises between opposite requirements. For instance, the optimal frequency for the A-scan evaluations was found to be 8 MHz (effective, not just nominal, frequency). While higher frequencies would have been more desirable because of their greater resolution, they had to be ruled out because of their increased absorption in the ocular tissues. Thus 8 MHz was found to be the optimal compromise between resolution and penetration. Also, the 8 MHz frequency turned out to be optimal for the differentiation of tissue structures on the barely sub-macroscopical level. Higher frequencies become confusing by resolving too many microscopical elements.

The A-scan quality most productive in delivering diagnostically important information about tissues, is the amplitude of echo spikes. Echo signal amplitudes reveal internal structure, reflectivity, absorption and indirectly the vascularity and consistency of tissues. Amplitudes of echo signals are, however, influenced by a host of different instrument parameters and settings, especially the probe characteristics, the receiver bandwidth, the amplifier characteristics, the display height, the gain settings, and also to a great degree by the examination technique applied. If all of these parameters and the technique are optimized and standardized, tissue differentiation becomes successful to an astonishingly great degree.

There are other important steps of signal processing which are also indispensable for optimal diagnoses, e.g., the degree of high-frequency filtering (see Ossoinig KC: "Computer-assisted Echographic Tissue Diagnoses: differentiation between retinal and membranous surfaces" in the proceedings of SIDUO XVIII). 

During phase I the optimal design and the standardization of instrumentation and techniqes were accomplished in cooperation with Kretztechnik (Austria) through clinical and experimental research performed at the 2nd University Eye Clinic in Vienna (Austria) coupled with stepwise corrections and adjustments of a Kretz 7000 instrument.  This Kretz 7000 instrument became the prototype, first for  the Kretz 7900 S, and then for the Kretz 7200 MA [2, 9, 28, 29, 40, 43, 44, 75 and 205 ff] (see also chapter 2: Historical Background). This cooperation resulted in the following specific design criteria:

8 MHz (± 0.2 MHz) effective frequency with a 5 mm crystal diameter and a parallel beam; narrow-band receiver with maximal response at 8 MHz; S-shaped amplifier characteristic curve with a total dynamic range of 33 db (5%-95% spike height) with a specific distribution; very high standardized system sensitivity setting (Tissue Sensitivity) obtained with a solid tissue model; fixed ratio between vertical and horizontal screen display; and specific (incomplete) filtering of the high frequency oscillations. This design was found to be optimal in the 1960's and required no change since.

Standardized examination techniques for the A-scan method were developed at the same time and termed “Quantitative Echography”, “Topographic Echography”, and “Kinetic Echography” [1, 4, 8, 22, 35, 45, 46, 64, 138, 75, 150, 205]. Extensive experiments were undertaken by the author and his cooperators studying the effects of biological tissue structures on echographic displays 1, 4, 11, 18, 43, 205]. The purpose as well as the outcome of these studies helped to explain the different acoustic behavior of ocular and orbital, normal and abnormal tissues, and guided the instrument design for optimal visual acoustic tissue differentiation. 

Thus the groundwork for the clinical applications of Standardized Echography had been laid during phase I in the 1960s, when this method was still called “Clinical Echo-Ophthalmography” [9, 23, 29, 35, 40]. It was then that the basic principles for the diagnosis and differential diagnosis of intraocular and orbital lesions were set and many specific diagnoses were primed. These include:

retinal detachments vs. vitreous membranes and posterior vitreous detachments [3, 7, 16, 19, 35, 42]; choroidal detachments (serous vs. hemorrhagic) [3, 16, 22, 39]; retinopathia proliferans [38]; traumatic (hemorrhagic) retinal detachment [36]; asteroid hyalosis [7, 22]; choroidal melanomas [4, 16, 19, 20, 22, 35]; choroidal hemangiomas [41]; choroidal metastatic carcinomas [35]; disciform macula degeneration [22, 35, 41]; endophthalmitis [35]; (foreign bodies [3, 6, 16, 21, 35] and precise foreign body localization [5, 6, 7, 21], spherical foreign bodies [21], intrascleral foreign bodies [5, 6, 21]; retinoblastomas [22, 26, 35]; RLF [35]; posterior scleritis [35]; normal orbital tissues [10, 14]; detection of orbital tumors with 97% accuracy in 153 orbital cases (71 tumors) [12], which improved to 98.3% by 1969 in a total of 579 orbital patients (154 orbital tumors) [24]; cavernous hemangiomas [3, 16, 18, 19, 20, 25, 30, 35]; (pseudo)lymphomas [18, 19, 20, 25, 35]; orbital varix [30]; A-V fistulas [17, 19, 20, 30, 35]; dermoid cysts [3, 10, 16]; serous cysts [7, 19, 24, 25]; sphenoidal meningiomas [18, 19, 20, 35]; fibroneuroma [20]; orbital mucoceles [20, 24, 35]; remote orbital metastatic carcinomas [20,41]; maxillary/orbital carcinoma [37]; ethmoidal/orbital neoplasm [41]; scirrhous orbital metastatic carcinoma [27]; retrobulbar hematomas [7, 32]; optic nerve gliomas [3, 16, 20]; papilledema [35]; Graves' orbitopathy [31].

In essence, the author and his collaborators succeeded in laying the ground work for the method of Standardized Echography by making optimal standardized instrumentation and corresponding standardized examination techniques as well as acoustic criteria for the diagnosis and differential diagnosis of intraocular and (peri)orbital lesions available and by proving the effectiveness of the method through their clinical results.




3.   Phase II


Phase II lasted almost three decades from the 1970's well into the 1990's. It represents a time period of continuous expansion and consolidation of the usage of, the indications for, and the performance and clinical results of Standardized Echography. This was effected by (1) the availability of excellent standardized instrumentation and techniques and (2) by intensive training efforts by the pioneers of the method.

At the heart of phase II was indeed the intensive training of scores of ophthalmologists and ophthalmic technicians at the Universities of Vienna (Austria) and of  Iowa (USA), many of whom spread the method throughout the world by their teaching and training efforts of great numbers of their colleagues and who further improved and consolidated Standardized Echography through their own research and publications thus adding data to the already existing knowledge thereby confirming or enhancing the clinical usefulness and effectiveness of the method in the diagnosis and differential diagnosis of posterior as well as anterior eye segment lesions and of orbital and periorbital lesions, or by detailing acoustic differential criteria [50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 62, 66, 67, 71, 72, 73, 77, 79, 81, 83, 84, 86, 89, 90, 93, 95, 96, 98, 99, 100, 107, 110, 111, 112, 113, 114, 126, 128, 129, 131, 133, 137, 138, 139, 140, 142, 144, 145, 148, 149, 151, 153, 160, 165, 169, 171, 177, 180, 184, 185, 186, 188, 193, 194, 195, 198, 199, 201, 223, 225]; by designing flow charts for the differentiation of intraocular and (peri)orbital lesions [47, 48, 51, 64]; by adding new differential diagnoses to the widening spectrum of application of Standardized Echography [41, 46, 47, 48, 55, 56, 57, 60, 65, 69, 70, 76, 78, 82, 84, 87, 89, 92, 93, 94, 96, 97, 101, 102, 104, 105, 106, 108, 109, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 127, 130, 134, 135, 136, 141, 143, 147, 150, 152, 154, 156, 157, 158, 159, 161, 162, 163, 164, 166, 167, 168, 170, 172, 178, 179, 181, 182, 183, 187, 189, 190, 191, 192, 196, 212, 213, 215, 217, 220] and by providing statistically impressive results in larger patient populations for a variety of different disease processes [51, 56, 55, 58, 88, 89, 90, 93, 132, 146].

It is only fair to mention in this context at least the most important of these teachers and researchers emerging from those two training centers (in historic order): Peter Till, MD (Austria), Heinz Freyler, MD (Austria), Sandy F. Byrne, RDMS (USA),  Leroy McNutt, MD (USA), Philip Corboy, MD (USA), Roberto Sampaolesi, MD (Argentina), Barton L. Hodes, MD (USA), Frank Goes, MD (Belgium), Atsushi Sawada, MD (Japan), Brian Conner, MD (USA), Dwain Fuller, MD (USA), Barry Kerman, MD (USA), Francis Bigar, MD (Switzerland), Wolfgang Hauff, MD (Austria), Harold W. Skalka, MD, (USA), Celso Antonio de Carvalho, MD (Brazil), Alberto Betinjane, MD (Brazil), Samir Salomon, MD (Lebanon), H.John Shammas, MD (USA), Ingeborg Stenström, MD (Sweden), Alex Papic, MD (Chile), Eduardo Moragrega, MD (Mexico), Stephen Miller, MD (USA), Gary W. Abrams, MD (USA), Robin Bosanquet, MD (UK), Robert Levine, MD (USA), Giovanni Cennamo, MD (Italy), Roger P. Harrie, MD (USA), Ronald L. Green, MD (USA), Pier Enrico Gallenga, MD (Italy), Peter Bischoff, MD (Switzerland), Wichard AJ Van Heuven, MD (USA), Gerhard Hasenfratz, MD (Germany), Elisabeth Frieling, MD (Germany), William M. Hart Jr., MD, PhD (USA), Rainer Rochels, MD (Germany), Tom C. Fisher (USA), Richard A. Lewis, MD (USA), Daniele Doro, MD (Italy), Enrique Meerhoff, MD (Uruguay), Jan Schutterman, MD (Sweden), Amin Nasr, MD (Lebanon), Kamel Itani, MD (USA), T.Mohamed Matheen, MD (Saudi-Arabia), Ciro Tamburrelli, MD (Italy), Gustavo Tamayo, MD (Columbia), Jo Fukiyama, MD (Japan), Irene Landau, MD (Sweden), Gilberto Islas, MD (Mexico), Yuanyao Du, MD (China), Maren Schilling, MD (Germany), Nicola Rosa, MD (Italy), Christian Mardin, MD (Germany), Robert Cinefro, MD (USA), Eytan Z. Blumenthal, MD (Israel), Georg F. von Arx, MD (Switzerland), Mario de la Torre MD (Peru), Agostino La Rana, MD (Italy).


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