Ultrosonography is extremely important to the world of ophthalmology, especially when there is pathology that interferes with direct visualization of tissues, such as lid edema, tarsorrhaphies, corneal edema or opacification, hyphema, hypopion, miosis, pupillary membranes, dense cataracts or vitreous opacities. In these instances, ultrasound can accurately image various intraocular structures and help with the diagnosis of lens, vitreous, retina, choroid, and scleral diseases.
Additionally, even if the view through the globe is normal, ultrasound is useful in differentiating iris or ciliary body lesions, detachments, differentiating intraocular tumors, choroidal and retinal detachments, and disc drusen versus papilledema. Ultrasound is also very useful in characterizing different orbital tumors.
Ophthalmic ultrasound uses high frequency sound waves which, as they strike intraocular structures, are reflected back to the probe and converted into an electric signal. The signal is then reconstructed into an image on a monitor. The frequency of the sound waves is the number of oscillations per second measured in hertz (Hz). For sound to be considered ultrasound, it must have a frequency of greater than 20,000 oscillations per second, or 20KHz, which is inaudible to human ears. The higher the frequency, the shorter the wavelength and the shallower the tissue penetration. Many ophthalmic ultrasound devices are manufactured with frequencies of about 10 million oscillations per second, or 10 MHz.
Recently, high-resolution ophthalmic B-scan probes (ultrasound biomicroscopy or UBM) are manufactured with 20 to 50 MHz that penetrate only about 5 to 10 mm into the eye to allow detailed resolution of the anterior segment.
Below is a discussion of some of the B-scan devices on the market.
Nidek Echoscan US-4000
Nidek’s Echoscan US-4000 is a three-in-one unit including B-scan, biometry and pachymetry. The B-scan mode scans 400 lines over 60 degrees. There is no PC or external printer required. The internal thermal printer can immediately print B-scan images and can be attached to the patient’s medical record. The device has USB and LAN interfaces for data storage. There is a tiltable 8.4 inch XGA color LCD. (Image courtesy Nidek)
Quantel Aviso
Quantel’s Aviso™ platform has the capability for A and B-scan, as well as UBM for posterior pole and anterior segment diagnosis. The B-scan comes in 10 and 20 MHz. There is an eye diagram to aid in probe labelling. There is an unlimited number of scans per session. Post-processing image tools are included, such as measurement calipers, area and markers for quantification. Still images and video are accessible for direct editing and analyzing. There is automatic video recording of the last 40 seconds of examination. Also, there are various filters for tissue differentiation in B mode at all frequencies. The linear scanning UBM is a proprietary magnetic 50 MHz probe technology that enables the operator to visualize the structures behind the iris, such as the ciliary body and lens zonules. The probe is always perpendicular to the tissue interface of interest, which offers high signal intensity. The transducer scanning motion is controlled through magnetic field for quicker scanning and increased image resolution. There is also less vibration and the probe is lighter in weight. There is also a 25 MHz probe designed for anterior chamber imaging. (Image courtesy Quantel)
DGH 8000 B-Scan Scanmate
The DGH 8000 B-Scan Scanmate is a self-contained, portable multiple mode ultrasound imaging system that can interface with virtually any computer via a USB 2.0 port. User-friendly and intuitive, the Scanmate can take high-quality video and images quickly and easily. And various post-processing of images including gain adjustment, zoom without distortion, and contrast and image intensity variation helps ensure a better diagnosis and improve patient care quality. (Image courtesy DGH)
Ellex Eye Cubed
Eye Cubed™ from Ellex provides practitioners with customized configurations for both B-Scan and A-Scan modes, covering all diagnostic ultrasound needs for both the posterior and anterior segments. Its 40 MHz UBM B-Scan mode delivers accurate measurement and evaluation of the iris, angle and cilliary body, including sulcus-to-sulcus (ICL sizing) and IOL haptic placement, while the 10 MHz Posterior B-Scan mode allows practitioners views of the retina, choroid and sclera, as well as the vitreo retinal junction. Eye Cubed also offers advanced movie technology that can be reviewed frame-by-frame, and an image acquisition rate of up to 25 frames per second. (Image courtesy Ellex)
Accutome B-Scan Plus
The B-Scan Plus is a portable high definition B-scan with proprietary software that is DICOM compatible. This device has an axial resolution of 0.015mm. The probe design is sharp and focused due to the elimination of signal loss and can be plugged into any laptop or PC. This unit has the capability to zoom 2x without distortion of real-time or captured scans and has unlimited 34 second film loops. Information can be shared with adaptable document transfer via electronic medical records, email or printer. (Image courtesy Accutome)
Micro Medical Devices B-Scan Mobile USB Ophthalmic B-Scan
This device can be used with any PC and is capable of high resolution imaging that gives over 2000 sample points per line. There are adjustable size cine buffers with a maximum of 512 buffers to capture high quality images. The device has adjustable pulse power to improve penetration capabilities. With a pulse frequency of 12MHz/15MHz it has a 3 to 10 cm penetration depth. Structures in the eye can be measured with its dual calipers. The images and videos can be saved directly to the PC hard drive or can be printed. (Image courtesy Micro Medical)
Sonomed B-Scan Vu-Pad™
This device consists of a portable tablet with a multi-touch high-resolution screen that is 25 percent larger than some other portable ultrasound devices. It has video recording capability and image capture. Features include 12 or 20 MHz probes with focused introducers, a 256-ray scan, adjustable time-varied gain (TVG), baseline, log gain, and exponential gain (e-gain). The system uses linear calipers and an angle measurement tool. It operates with Microsoft Windows 8. (Image courtesy Sonomed)
Sonomed Master-Vu 5600 B-Scan
This probe is compatible with laptop, desktop or table PCs through a USB connection. It can capture both still image and video clips with an on-probe activation switch. There is a selectable simultaneous A-scan vector, measurement calipers for distance and angle measurements, continuous zoom and pan functions, near-mid-far gain, contrast and TVG controls. This device comes with a hard-shell padded carrying case, USB cable ad USB memory stick pre-loaded with the Master-Vu software that can be loaded onto multiple computers. (Image courtesy Sonomed)
Sonomed VuMAX HD
This unit is configurable as a B-scan, UBM or combination system with optional A-scan. The UBM feature provides angle detail for resolution of different structures at the angle and behind the iris for diagnosis of glaucoma-related concerns. The angle analysis tool comes with pattern recognition software that automatically identifies the iris root based on scleral spur reference to map out angle anatomy. There is a sulcus to sulcus scan setting that enables viewing of anatomical landmarks for ICL size. As well there is the proprietary eye tracking tool to confirm image alignment and apply built-in nomograms for proper sizing. The B-scan mode of the VuMAX HD allows imaging of the posterior segment using their proprietary Enhanced Focus Rendering. There are four present scan modes: orbit, vitreous body, retina surface and deep retina/choroid. (Image courtesy Sonomed)
Next month’s article will focus on A-scan devices, also extremely important in the ophthalmic world.