Ординатура / Офтальмология / Английские материалы / Ultrasonography of the Eye and Orbit 2nd edition_Coleman, Silverman, Lizzi_2006

Figure 3.1. The immersion B-scan tank used by Baum and Greenwood provided sector scans of both eyes.

About 5 gallons of water and a special fitted face mask were required. These B-scans began the evolution of

B-scan ultrasonography of the eye.

Figure 3.2. Purnell used the same General Precision scanner as Baum but used a simple goggle and latex cover to provide the immersion standoff necessary to conduct the ultrasound wave. Much of the early clinical data provided by B-scan was achieved by Purnell et al.

Coleman et al. (33), at the Riverside Research Institute, developed the first commercially available B-scan with simultaneous A-scan and a simplified hand-operated linear B-scan, using an immersion bath around the eye, created using a plastic surgical drape (Figures 3.4 and 3.5). Bronson and Turner (34) developed a handheld B-scanner, which was the first of many easily used contact B-scanners commercially available (Figure 3.6). These instruments led to the widespread use of ocular ultrasound. Fisher et al. (35) has made many clinically significant observations with this early instrument. Figure 3.7 shows the Sonomed

instrument, which was the first contact B-scan using an oscilloscope for more accurate morphic outlining. Coleman (36,37) presented an evaluation of the reliability of ocular and orbital diagnosis with A-, B-, and M-scan ultrasound and a systematic description of ocular and orbital diagnosis. Coleman, Lizzi, and Jack (38) published the first book on ultrasonic diagnosis of the eye and orbit. Coleman and Lizzi (39,40) and the Riverside Research Institute made many innovations, including the use of color monitoring and encoding, and isometric viewing. Also, Coleman, Silverman, and Rondeau worked with power spectrum analysis for tissue characterization, three-dimensional (3-D) ultrasound, and digital signal processing (I-scan) principles (56).

M-scan diagnosis, first described by Coleman and Weininger (41, 42, 43), has been used to study physiologic changes during accommodation and the magnetic properties of foreign bodies. It has also been used for examining the vascular and respiratory pulsations in ocular and orbital tumors. Silverman, Kruse, and Coleman (44) pioneered the use of swept-scan analysis for use in evaluating vascular flow in various ocular conditions. Color-flow Doppler (CFD) imaging of the orbital vessels was first described by Erickson et al. (45) in 1989.

Figure 3.3. The first contact B-scan transducer system as devised by Purnell, Sokollu, and Holasek. The instrument was never commercialized.

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Figure 3.4. The equipment console used by Coleman for clinical ultrasonic evaluation. Two separate interchangeable A-and B-scans were used with different frequencies and simultaneous oscilloscope displays. An electronic interval counter and color and isometric displays were used. The laboratory instrument developed at the Harkness Eye Institute by Coleman and Lizzi provided variable frequency examinations up to 35 MHz along with precise electronic interval measurements of axial optical dimensions. This equipment was more complex than required for routine clinical use. (see color image)

Figure 3.5. The first commercially available A- and B-scanner, developed by Coleman and Katz and marketed by Sonometrics Systems, Inc. Both A- and B-scan modes were observed simultaneously by the examiner, with a separate oscilloscope display available for photography of implementation of the M-mode. Bottom: Scanning in “immersion,” performed while the patient lies supine on an examination table. This reduces the patient's head movement and permits the examiner to observe the relationship of the transducer to the eye while also observing the scan display on the oscilloscope.

Figure 3.6. The Bronson Turner contact B-scan provided an inexpensive B-scan sector scanner that led to widespread use of the contact B-scan technique. The television raster lines altered the shape of the scans but provided a very inexpensive way to add gray scale.

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Figure 3.7. The contact B-scan unit with A-scan using an oscilloscope, developed by Katz and Coleman. The oscilloscope provided more accurate morphology and amplitude quantification.

The use of Doppler ultrasound in the eye and orbit had its start as a method to evaluate the hemodynamics of patients with cerebrovascular disease and its ophthalmic sequelae. The ophthalmic community was slow in adopting Doppler ultrasound as a diagnostic tool before the clinical availability of color Doppler imaging (CDI) in the late 1980s. Pioneers who used continuous wave Doppler evaluation of the orbital and ocular vasculature, such as Yamamoto and Ardouin (46, 47, 48, 49) in the 1970s, used stand-alone Doppler equipment (without B-scan control) that required extraordinarily careful interrogation of the eye and orbit. With the advent of duplex scanners, where a vector and Doppler gate could be positioned on a B-scan for localization, Doppler ultrasound became an important diagnostic tool in cardiovascular, peripheral vascular, and obstetrical ultrasound. The cost, availability, limited frequency range, and, possibly, higher power levels of such equipment ultimately limited Doppler use in the routine ophthalmic exam. The introduction of CDI changed this. Even with duplex Doppler, the identification of the relatively small and tortuous orbital and ocular vasculature had been problematic. With the superimposition of color flow information, rapid and correct identification of vessels became possible, and the diagnostic advantage of the technique began to outweigh the cost and access factors. Lieb et al. (50,51) were among the first to popularize the use of CDI studies for a range of ocular and orbital conditions.

Ophthalmic ultrasound can be divided into two phases during its half-century history. Initially, techniques and applications were described and perfected. In the second phase, advances in instrumentation and computer technology led to improved resolution and image quality as well as diagnostic and measurement accuracy.

Recent years have seen many improvements in the quality of images, as a result of higher frequencies of examinations, improved electronics and transducers, and, most important, computer power and software to allow 3-D scans (52), tissue characterization (53, 54, 55, 56, 57, 58), and other improved imaging techniques (59, 60, 61, 62). Measurement accuracy has significantly improved owing to higher frequencies and computer enhancement techniques, such as digital signal processing techniques, including deconvolution and analytic signal magnitude rectification of radiofrequency (RF) signals (63,64).

The most notable improvements in current ophthalmic ultrasound diagnosis have been with the high frequency B-scan. The ultrasound biomicroscope (UBM), introduced by Pavlin and Foster (59,60,65,66), was the first commercial instrument to take advantage of polyvinylidene fluoride (PVDF) film technology for high frequency scans. This instrument permitted numerous advances in anterior segment diagnosis, particularly in diagnosis of glaucoma, tumors, and trauma of the anterior segment. A different high frequency scanner (Figure 3.8), developed in our laboratory at Weill Medical College of Cornell University by Coleman et al.

(64,67), uses an arc scan to display the entire anterior segment and to align the transducer orthogonally with the anterior segment, to maximize accuracy of measurement for various applications,

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such as corneal mapping, preand post-LASIK surgery, physiologic studies of lens changes in accommodation, ciliary body and lens movement in presbyopia, and angle-to-angle and sulcus-to-sulcus measurements for intraocular lens powering and surgery.

Figure 3.8. An Artemis II high frequency scanner, developed by Ultralink LLC from technology devised at Cornell, for 50-MHz anterior segment imaging. This scanner provides orthogonal transducer alignment for viewing of the entire anterior segment by means of an arc scan. The definition is the current state-of-the-art for measurement of corneal thickness and anterior chamber dimension for both LASIK and intraocular lens surgery. In addition, it provides superb definition of intraocular pathology, such as intraocular tumors and ciliary body cysts.

Three-dimensional imaging of the eye was first described by Coleman et al. in 1987 but was not widely available until less expensive computer power and software became available. Three-dimensional imaging, as will be noted later, offers a significant advantage in measuring tumor volume for growth or regression posttreatment. It also provides a perspective for scanning that can aid interpretation of 2-D images, as well as interactive analysis of ultrasound images. Fisher et al. (61), working with Ophthalmic Technologies, Inc. (OTI), have developed a commercially available 3-D ultrasound system (Figure 3.9). Finger et al. (52) have also used this OTI scanner to examine intraocular tumors and to demonstrate the advantages of 3-D perspectives.

Figure 3.9. The OTI is a sector B- and A-scan system operating at 12 MHz or higher frequencies that provides

integrated 3-D scans with a contact system.

There are many new instruments available for not only 10-MHz scanning, but also 20to 30-MHz B-scanning. Many of our figures were taken with a Sonovision scanner (Figure 3.10), which is no longer commercially available,

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but provides the radiofrequency data necessary for our tissue characterization and parameter image analyses. We also use the Quantel Cinescan 20-MHz scanner (Figure 3.11) for evaluation of the posterior pole of the eye, as well as the vitreous. Figures throughout this chapter will have been produced using one of these four systems. A-scans, when shown, are always quantitative derivations from the radiofrequency, except for A-scans used in axial biometry.