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History
of Standardized Echography Karl
C. Ossoinig, MD 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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