COLOR DOPPLER IMAGING OF THE EYE AND ORBIT
Section snippets
PHYSICAL BACKGROUND AND IMAGING DEVICES
Continuous wave Doppler, duplex scanning, and CDI are all based on the physical principles of the Doppler effect, named after C. J. Doppler (1803–1853).36, 49, 61, 81, 87 Movement of a reflector with respect to the sound source results in a change of wavelength. Because the velocity of sound is constant, the change in wavelength corresponds to a change in frequency. The magnitude of the change of frequency depends on (1) the wave velocity in the medium (C), and (2) the relative velocities of
EXAMINATION TECHNIQUE
The orbital examination can be performed with many commercially available CDI devices with high-frequency transducers. We use the QAD 1 and QAD 2000 ultrasound scanner (Quantum-Siemens Medical Systems, Issaquah, WA) with a 7.5-MHz linear phased array transducer. The ultrasound transducer is applied to the closed eyelids using sterile ophthalmic methylcellulose as a coupling gel. During the examination, the patient is in a supine position and care is taken not to apply pressure to the eye to
SAFETY
As with all new imaging modalities, safety issues should be considered using CDI on the eye and orbit. With the instruments used for our studies, the estimated in situ peak temporal average intensities at 4.2-cm depth in the color imaging mode (provided by Quantum-Siemens, Medical Systems) are 7 mW/cm2 for the 7.5-MHz transducer. When spectrum analysis is performed, the in situ peak temporal average intensity is approximately 71 mW/cm2. In the spectrum analysis mode, the in situ peak temporal
INDICATIONS
CDI is widely used as a well-accepted imaging technique in many medical specialties.17, 21, 30, 41, 51, 56 Its main indications are the evaluation of arterial and venous disorders of the extremities, abdomen, thorax3, 4, 11, 20, 28, 32, 37, 38, 39, 45, 62, 69, 84 and the extracranial cerebral vasculatures (color Fig. 2).8, 14, 30, 38, 42, 54, 55, 68, 77, 78, 91 Further indications are the evaluation of hemodialysis shunts, monitoring of transplanted kidneys,31, 33 cardiac applications,12, 22, 29
NORMAL ORBITAL VASCULATURE
A horizontal section through the eye and orbit at the level of the optic nerve allows the display of the CRA and the accompanying CRV. The CRA and CRV can be identified within the anterior 2 to 12 mm of the optic nerve shadow (color Fig. 3). It is possible to follow the CRA and in many instances its entrance into the optic nerve is seen 10 to 13 mm behind the globe. Because the flow of the CRA toward the transducer is displayed in red color, it may easily be distinguished from the CRV, which
INTRAOCULAR TUMORS
Effective vasculature is essential for all tumor growth. It is formed by newly sprouted, ingrowing vessels and by incorporation of existing host vessels into the tumor mass.66 Other than the qualitative information provided by intravenous fluorescein angiography, dynamic CT, and flow-related MR imaging pulse sequences, to date, no technique is available to assess tumor-associated blood flow in the eye and orbit. Although most intraocular tumors can be diagnosed clinically, additional imaging
ORBITAL TUMORS AND VASCULAR LESIONS
Doppler signals can be detected in most orbital tumors. In cavernous hemangiomas, however, the speed of flowing blood is usually so low and stagnant that the flow velocities are below the detection level. In other lesions, particularly malignant tumors, significant vascularity can be seen within the tumor (color Fig. 8). In rare instances benign orbital tumors, such as cavernous hemangiomas, may cause visual loss by compressing the optic nerve and its blood supply. Because CDI not only shows
CCSF
Various diagnostic modalities can be used to evaluate CCSF or dural cavernous arteriovenous malformations, including A- and B-scan ultrasonography,60, 67 orbital and cranial CT,34 carotid angiography, MR imaging,73 and orbital venography.86
In these patients, CDI clearly demonstrates the dilated, arterialized SOV with high velocity blood flow toward the transducer, indicative of a CCSF (color Fig. 9). CDI further depicts the high preseptal vascularity and the thickened extraocular muscles
RETINAL VASCULAR DISEASES
CDI in patients with CRA occlusions may reveal either absence or marked decreased flow in the artery. The maximum systolic amplitude is low and flow during diastole is also decreased (Fig. 10). Also, in CRA occlusions, massive calcifications of the vessel walls of the retinal bulbi vessels as well as calcific plaques can be detected. In patients with ischemic CRV occlusions a very characteristic Doppler spectral pattern can be seen. Flow in the CRA during systole is decreased, the peak systole
SUMMARY
Since the development of A- and B-scan ultrasound technique in the 1950s, significant progress in ophthalmic ultrasound has appeared. As the technology advances and ultrasound systems improve their ability to acquire and detect ultrasonic signals and to analyze them in terms of a spatial resolution and frequency distribution, there is no doubt that the extent of clinical applications will expand accordingly. Nevertheless, the fundamental physical restrictions of ultrasonography and Doppler will
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Address reprint requests to Wolfgang E. Lieb, MD, Department of Ophthalmology, Julius-Maximilians University, Josef-Schneider Strasse 11, 97080 Wuerzburg, Germany
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Department of Ophthalmology, Julius-Maximilians University, Wuerzburg, Germany