New Imaging Technology and Transducers of Ultrasound - Research Paper Example

Extended Field-of- View Sonography Transducers of ultrasound are mobile and small when compared to those of computed tomography and magnetic resonance imaging. It is because of these properties that ultrasound can be used for viewing any part of the body in every position. However, one major limitation in this application is the small field of view, especially when high resolution linear arrays are used. the field of view excludes many identifiable landmarks. This limitation makes ultrasound a much inferior technology when compared to CT Scan or MRI. To overcome these disadvantages, a new imaging technology has been developed. This is known as extended field-of-view or EFOV. This new technology allows manual movement of the probe along the direction of the array of the transducer, thus facilitating panoramic images without any loss in resolution. The technology causes estimation of translation and rotation of the probe by comparing images which are successive during the movement of the probe (Kim et al, 2003). The technology also has a mechanism for no probe-position sensing. the images in this technology are transformed geometrically based on the position and motion of the probe and then entered into the EFOV image buffer. They are then combined with images which are obtained previously to produce EFOV image. Through this technology, it is possible to acquire and record panoramic images of length as much as 60 cm, thus providing opportunity to view anatomical structures of various topography This allows displaying of larger pathologic structures or organs in a single image itself, along with their surroundings. Thus EFOV technology has many clinical applications. Infact, many studies have reported the usefulness of this technology in imaging superficial small parts (Kim et al, 2003). Weng and colleagues were the first researchers to introduce extended field-of-view technology, in 1997. They widely applied this technology to many field of sonography (Kim et al, 2003). According to Cooperberg et al (2001), "through the magic of computer technology, extended field of view imaging is back! Extended field of view images can now be created very easily and conveniently, in real time. The convenience and accuracy of real-time imaging is maintained while important anatomical perspectives are added." In a pioneer study by Weng et al (1997), the researchers observed the benefits of extened field imaging that "combines the convenience of a real-time scanner with the spatial advantages of a static B-mode scanner and provides a panoramic image in real time without position sensors or cumbersome articulated arms." Their results revealed that this technology allowed viewing of large images with high preservation of resolution, as much as 60 cm long. The study detected measurement accuracy of more than 5 percent. the authors concluded that "in addition to providing a panoramic image to expand diagnostic capabilities, extended-field-of-view US provides a more easily interpretable image and is an effective cross-specialty communication tool. " In yet another study by Kim et al (2003), the researchers evaluated the benefits of EFOV in abdominal scanning. The study was conducted on 31 cases with intentions to evaluate abdominal structures. In the study, it was found that extended field of view imaging helped better display of spatial relationship between various normal structures in the abdomen and the lesions under study. The relationship was clear in a single image itself. This technology also allowed accurate quantification in measuring various volumes or sizes of the lesions and the organs. The authors of the study concluded that "extended field-of-view sonography provided the anatomic context of the lesion in its surroundings and allowed precise measurement and tracing of the extended and tubular structures and that the method has notable advantages and clinical applications." Thus extended filed-of-image allows easy viewing of large structures with their surrounding in a single image, increasing the scope of application of ultrasound. 3-D Ultrasound Since the advent of imaging technology over 5 decades ago, drastic changes have been occurring in the technology every decade. In 2D ultrasound technology alone, many improvements have occurred with reference to resolution, image quality, range of indications and availability. However, several limitations with 2D technology reduced the scope of its applications when compared to CT scanning and MR imaging. The most important limitation with 2D scanning is the dependence of the radiologist on noncontinuous series of representative sections of the internal organs to depict the anatomy. Other limitations include fixed imaging plane, lack of quantitative documentation of spatial relationship and irrational volume measurements because of reliance on 2-dimensional geometrical model, rather than 3-dimensional model. These limitations are overcome by 3D scanning technology (Lazebnik and Desser, 2007). 3-D Ultrasound is a type of medical ultrasound technique that is often used to evaluate fetus in pregnancy. The conventional scanning method that is commonly used for medical and obstetric purposes is 2-D scanning in which the sound waves are sent straight down and the reflected sound waves are used for image construction (Lazebnik and Desser, 2007). In 3-D scanning, the sound waves are sent in different angles and a sophisticated computer program is used to reconstruct a 3-dimensional volume image using the reflected echoes, thus allowing one to gauge not only the height and width of the organs but also the depth. Thus 3D ultrasound is also known as volumetric ultrasound. However, no movement is shown in the images (Lazebnik and Desser, 2007). Pioneers in the development of 3D Ultrasound are Stephen Smith and Olaf von Ramm from the Duke University in 1980s. 3D technology is currently used mainly in obstetric scanning to evaluate fetal organs (Lazebnik and Desser, 2007). 3D technology has several advantages. The sonographer is able to scan the region of interest using volume transducer with a single sweep itself, unlike 2D ultrasound. The sonographer does not need to acquire series of multiple images and thus the scanning time is drastically reduced. Thus this technology is easily applied from cranial ultrasound of neonates because images can be taken in a sweep and the patient does not have to be sedated. The volumes of 3D ultrasound can be processed even after acquisition as in CT imaging to obtain different views and also to ascertain troubleshoot questions. Classical examples which will need such application are fibroid uteri and multinodular fibroid glands which are much easier to evaluate when looked in multiple planes at the same time. Another major advantage of post processing is teleradiology, because the reader already has all the necessary information of the volume that is scanned and thus remote interpretation is possible. As far as abdominal imaging is concerned, 3D ultrasound is useful for estimation of volumes of gall bladder, liver masses and gall stones (Lazebnik and Desser, 2007). 3D ultrasound has applications in cardiovascular scanning also. The technology allows quantification of the volume of the plaque and direct visualization of arterial atherosclerosis. According to a study by Landry, Spence and Fenster (2005), carotid plaque volume and characterization can be successfully quantified using 3D technology. Some studies have also used 3D technology for aortic artery plaque characterization. Addition of color doppler to 3D ultrasound helps in the evaluation and grading of stenotic lesions and flow dynamics. Since 3D technology allows reformation of volumetric data in order to visualize flow in a plane parallel to the vessel that is interrogated, the inter-observer variability is very low and it is a big advantage in the field of cardiovascular studies. Since the contraction motion of the heart is basically 3 dimensional, 3D imaging of heart has several advantages. Accoridng to Unsgaard et al (2005), unlike 2D echocardiography that requires assumption of "simplified geometric model of ventricular shape, 3D echocardiography allows direct evaluation of ventricle segmentation. According to Chan et al (2004), 3D echocardiography allows visualization of an entire valve at any given point of time, through out the cardiac cycle (Lazebnik and Desser, 2007). 3D ultrasound has has applications in interventional sonology, both in operative interventions and minimally invasive procedures. 3D ultrasound is also associated with several limitations, Fundamentally, it is not different from 2D ultrasound. Since acoustic impedance differences, the actual source of contrast is identical, contrast limitations still apply. The user interfaces of 3D ultrasound are complex and infact quite challenging to master. It is also difficult to determine image orientation because of lack of standardized display convention. Interpretation of common artifacts is difficult and at the same time, 3D scanning introduces new artifacts because of lack of standardized view (Lazebnik and Desser, 2007). Thus 3D ultrasound enhances the application of sonology by allowed 3-dimensional view of organs. References Chan KL, Liu X, Ascah KJ, et al. (2005). Comparison of real-time 3-dimensional echocardiography with conventional 2-dimensional echocardiography in the assessment of structural heart disease. J Am Soc Echocardiogr., 17(9), 976-980. Cooperberg, P.L., Barberie, J.J., Wong, T., Fix, C. (2001). Extended field-of-view ultrasound. Semin Ultrasound CT MR 2001; 22:65–77. Kim, S.H., Choi, B.I., Kim, K.W., et al. (2003). Extended Field-of-View Sonography: Advantages in Abdominal Applications. J Ultrasound Med., 22, 385-394. Lazebnik, R.S., and Desser, T.S. (2007). Clinical 3D ultrasound imaging: beyond obstetrical applications. Diagnostic Imaging: Continuing Medical Education, 1-6. Landry, A., Spence, J.D., Fenster, A. (2005). Quantification of carotid plaque volume measurements using 3D ultrasound imaging. Ultrasound Med Biol., 31(6):751-762 Unsgaard, G., Selbekk, T., Brostrup Muller, T, et al. (2005). Ability of navigated 3D ultrasound to delineate gliomas and metastases —comparison of image interpretations with histopathology. Acta Neurochir (Wien), 147(12), 1259-1269. Weng, L., Tirumalai, A.P., Lowery, C.M., et al. (1997). US extended-field-of-view imaging technology. Radiology, 203, 877 –880. Read More