Ultrasound Imaging - Report Example

Introduction Ultra sound imaging is a medical imaging technique whereby a part of the body is exposed to high frequency sound waves so as to produce images of the inside of the body. The techniques involved in ultrasound imaging do not use ionizing radiation but rather uses sound waves that are transmitted into the body by small probes. The waves then bounce back, generating an image of the inside of the body in real time. The images generated show the movement of internal organs of the body as well as their structures. Ultrasound imaging is a noninvasive medical test that plays an important role in diagnostic process and has numerous advantages over computerized tomography and magnetic resonance imaging (Nelson and Dolories 1998, 1243). Conventional imaging techniques are fuzzy and make it difficult to detect subtle and small tissue variations during diagnosis and staging of diseases (Fenster, Downey and Cardinal 2001, 67-68). They only show images in flat sections of the body. In the past few decades, there have been advances in real time imaging in the medical imaging industry in addressing the need for flexibility, reduced invasiveness, lower costs and increased precision (Poon and Robert 2006, 357). They include extended field of view and 3D ultrasound imaging. Underlying technology of EFOV The technology of real-time EFOV Was first described by Weng and his colleagues in 1997allows the generation of real-time sonograms with field of view that goes up to 60 cm without using any external sensor. The system allows parallel processing of numerous operations per second through the use of a programmable image processor board with multiple computer chips (Henrich 2003, 122). The system acquires numerous images in anatomically and spatially accurate fashion by detecting and correlating the internal landmarks of the structure under scan. In clinical practice, the scan plane is selected using a real-time probe. The sonographer enables the EFOV mode and then slides the probe along the surface of the skin in the direction of the real time scan plane. The real time image is monitored on the screen as the EFOV image is being acquired (Saurbrei 1999, 336). Underlying technology of 3D ultrasound imaging The technologies of 3D ultrasound imaging involve the use of conventional 1D ultrasound transducers in acquiring a series of 2D ultrasound images and through proper positioning and orientation, 3D images are produced. There are four 3D ultrasound imaging techniques: mechanical scanners, free-techniques without position sensing, free-hand techniques with position sensing and 2D arrays (Fenster, Downey and Cardinal 2001, 69, 70) The technology in mechanical scanners involves the use of a motorized mechanical apparatus that translates, tilts, or rotates a conventional transducer when scanning the anatomy. The acquired 2D ultrasound images after spanning a given volume of interest are then recorded by a computer. The 2D images are then stored either in original digital format in the memory of the ultrasound system’s computer or in an external computer memory. Using an external computer or the ultrasound machine’s computer, the 3D image reconstruction and viewing is carried out though the use of predefined geometric parameters that describe the position and orientation of the 2D images in a 3D image volume. The spatial or angular intervals between successful 2D images are adjusted to minimize the scanning time (Fenster, Downey and Cardinal 2001, 70-73). The free-hand scanning with position sensing techniques does not require a motorized fixture. Instead, they have a sensor, attached to the transducer, which measures its orientation and position. The operator holds and manipulates the transducer over the anatomy to be imaged. During this process, the acquired 2D images are stored together with their orientations and positions in the computer. 3D images are then constructed using this information. There must be appropriate spatial sampling done to ensure there is no significant gap since the locations of the 2D images acquired are not predefined (Fenster, Downey and Cardinal 2001, 75-77). Another 3D scanning technique is free-hand scanning without position sensing which involves the manipulation of the transducer over the patient when acquiring 2D images. 3D images are then reconstructed by assuming the predefined scanning geometry. The operator must be very careful in moving the transducer at a velocity that ensures the 2D images are obtained at regular spacing. Good 3D images are obtained if there is uniform motion of over the distance and angle in the area scanned (Fenster, Downey and Cardinal 2001, 78). 2D Arrays for dynamic 3D ultrasound forms the last 3D scanning technique which uses a transducer with a 2D array unlike the free hand scanning and mechanical approaches which uses a 1D array transducer. Here, the electronic scanning transmits a broad beam of ultrasound beam sweeping over the entire anatomy under examination. Multiple planes are displayed in real time from this volume through the processing of the detected returned echoes by the 2D array. The multiple planes can then be manipulated interactively to allow the exploration of the volume under investigation by the operator (Fenster, Downey and Cardinal 2001, 78-79). Operating principle of EFOV The activation of the EFOV option for the machines with EFOV ultrasound software allows the probe to be advanced slowly in a longitudinal direction in the same single plane over the area of interest. Meanwhile, the examination of the region of interest is carried out in real time. The EFOV machine’s computer calculates the motion of the transducer and reconstructs the sequential images in single large view without loss of resolution. The patient’s stability really matters in this method because it is sensitive to change in position. This can result in loss of image quality and produce artifacts (Saurbrei 1999, 336). Operating principle of 3D ultrasound The operating principle in 3D representation of the anatomy involves the placing of acquired 2D images in their respective positions and orientations in 3D image volume. Their pixel values are used in determining the voxel values of 3D image. There are two image reconstruction methods used in determining the 3D images. First is feature based reconstruction where the desired features of anatomical structures are determined and reconstructed into a 3D image. The surfaces of different structures are outlined and assigned different colours or shading. In order to enhance visibility, some of the features are eliminated and the resulting image is represented to the viewer in 3D. This approach reduces the content of the 3D image by representing few anatomical structures. The 3D image can be easily manipulated using inexpensive computer display hardware (Fenster, Downey and Cardinal 2001, 79). The second method of reconstructing images is the voxel based reconstruction. This approach uses a set of acquired 2D images in building a voxel-based image. This approach involves two steps. The first step is embedding the acquired images in the image volume by placing the image pixels at their correct 3D coordinates (x, y, z) based on the 2D coordinates (x, y) of the pixels at their 2D image, and the orientation and position of that image in respect to 3D coordinate axes. The voxel value of the 3D image point is calculated through interpolation as a weighted average of pixel values of its neighbours among the embedded 2D image pixels. For mechanically scanned images, 3D images are rapidly reconstructed by pre-computing the interpolation weights and placing them in a look-up table. This approach reserves all the information that was originally present in the acquired 2D images. The scanning process should be sampled adequately in order to generate large data files that depict the true anatomy. Since the original image is preserved, it is possible to process the 3D image several times using different rendering techniques or it to display features of interest (Fenster, Downey and Cardinal 2001, 80-81). Clinical examples of EFOV and their advantages over the conventional methods Annette and his colleagues did a clinical study to evaluate the usefulness of extended field of view (EFOV) imaging in obstetrics and determined the possible advantages it has over the other conventional methods. In this study, they selected pregnancies which were studied by both EFOV ultrasound and conventional B-mode. They subjectively compared the two techniques by judging their visualization as perceived by referring doctors and operators. They realized that EFOV imaging provided better visualization of the structures that were too large for the conventional B-mode to show in a single image i.e. the entire structure and the orientation in the uterus was shown. Besides, EFOV images were easily interpreted. However, the fetal movements limit EFOV imaging of the fetus. Due to the reliability of EFOV imaging method, it has been used in the visualization of the genital tract tumors, the uterus inn its entirety, and fetal structures throughout pregnancy. Besides, it also helped in the visualization of maternal or fetal complications in a single image. The EFOV imaging made it possible for the visualization and localization of retained placenta. The EFOV provided images of all myomas and their relationship to pregnancy in the study of genital pathology during pregnancy. Use of EFOV imaging made it easier to understand the topographical and dimensional relationship to uterus and birth canal as compared to the conventional methods (Henrich, et al. 2003, 121-127). Another study carried out by Hasan and Yucel evaluated the importance of extended field of view ultrasonography in superficial lesions. They evaluated a good number of patients who had superficial lesions on different parts of their bodies using both the EFOV ultrasonography and the traditional 2D ultrasonography. The EFOV is not considered as diagnostic, but rather helps in communicating findings, understanding spatial orientation or documenting the findings in a single image. In this study, the EFOV provided valuable additional information for the better documentation of the lesions. Unlike the traditional ultrasonography, EFOV depicts an abnormally as well as its relationship with the adjacent anatomic structures in a single image. EFOV image is distorted due to patient’s movement or surface irregularity. For such cases, the process must be repeated to obtain accurate information. The superficial lesions were documented successfully in a single image with EFOV imaging. In fact, the surrounding anatomical structures were also documented. They realized that it was far much easier to obtain a single EFOV image than combining two images of different parts of a large lesion. They concluded that EFOV sonography has greater accuracy and reliability than dual imaging ultrasonography. The EFOV images were considered helpful for spatial orientation, especially in musculoskeletal imaging; the evaluation of complex anatomic relationships between the bone structures and pathology of tissue areas (Yerli and Eksroglu 2009, 35-39). Kim and his colleagues, in their study, identified that EFOV imaging gives clearer images when compared with CT and MRI since in the real time scanning, the view of the anatomic plane is not restricted like in the conventional sonography. Thus, it is easier for the referring clinicians to understand the EFOV images than the conventional sonograms hence being able to use the scan results confidently without any need of confirmatory scans. Besides, the EFOV sonograms give images similar to those reconstructed in three dimensional through use of CT or MRI (Kim et al 2003, 392). Eugine, Middleton and Teefey (1999, 148) also recommends the use of EFOV in musculoskeletal imaging since there is no loss in the resolution of the images. Clinical examples of 3D ultrasound imaging and their advantages over the conventional methods In the clinical study carried out by Mehta, Azzouzi and Harmdy, they analyzed the use of 3D ultrasound systems in prostrate imaging and compared the results obtained with other conventional methods such as grey scale imaging in staging prostrate. They realized that 3D ultrasound imaging is able to achieve high performance as well as sensitivity which are essential in clinical practice, through the use of modern technologies and its adaptability to the ultrasound systems. In nephro-urologic system analysis, 3D ultrasound imaging serves as an outstanding method which combines volumetric and surface rendering, in giving remarkable details of the bladder’s internal surface of the bladder. This facilitates the detection process of the presence of polyps, tumors, or any other disorders of the bladder. This non-invasive method enables clinical practitioners to distinguish between the normal surfaces and the affected surfaces of the bladder. In addition, it shows changes that the surface undergoes as a result of aging and progression process of the disease. It is an effective method of visualizing ureteric jets and turmoral lesions. 3D reconstruction allows an accurate calculation of the urinary volume and transplanted kidney’s volume (Mehta, Azzouzi and Harmdy 2004, 339-349). Another clinical study which has been done with regard to 3D ultrasound imaging is in obstetric. In various studies, the ultrasound images of the fetus were constructed by emission of sound waves from a transducer placed on the mother’s stomach. As a beam of rays passes over the body under scan, a detailed scanned image is obtained. In comparison with 2D ultrasound images, the 3D ultrasound gave a clearer view of the dimensional structure of the fetus than the 2D ultrasound images. The 3D images created by layering of the numerous ultrasound images improves the doctor’s ability of identifying less obvious deformities like congenital heart abnormalities, cleft palate and down syndrome. It also gives a clearer view of the internal organs of the fetus and the relationship of the fetal abnormalities in their location relative to the mother. The obstetricians are able to monitor the blood flow, the movement of the fetus’ heart as well as the limbs for signs of abnormalities. Another significance of the 3D imaging in obstetrics is the view of the unborn child by the expectant mothers making them to remain healthier and calmer in the course of their pregnancy (n.n, n.d, 1). Conclusion 3D ultrasound imaging and EFOV are relative technologies that have been advanced in the real time imaging which allows physicians to view the anatomy and pathology as a volume and as a single image respectively. They have facilitated a rapid diagnosis and application of interventional techniques by enhancing the review of patient information interactively. The new imaging techniques have been applied in various clinical experiences and practices including obstetrics, gynecology, cardiology, musculoskeletal, modern studies among other applications. They have provided an easier understanding of the various clinical applications hence facilitating the clinical practice. Bibliography Eugine, C., Middleton, W & Teefey, S. “Extended Field of View Sonography Musculoskeletal Imaging.” Journal of Ultrasound Medicine 18(1999): 147-152 Fenster, A., Downey, D. & Cardinal, N. “Three Dimensional Ultrasound Imaging.” Journal of Physics in Medicine & Biology 46(2001): R67-R99 Henrich, W., et al. “Advantages of & Applications for Extended Field of View Ultrasound in Obstetrics.” Journal of Arch Gynecol Obstet 268(2003): 121-127 Kim, Hyung et al. “Extended Field of View Sonography: Advantages in Abdominal applications.” Journal of Ultrasound Medicine 22, (2003): 385-394 Mehta, S., Azzouzi, A. & Harmdy, F. “Three Dimensional Ultrasound and Prostate Cancer.” World Journal of Urol 22, (2004): 339-349 N,n “3D Obstetric Ultrasound Imaging.” (N.d): 1 Nelson, Thomas & Pretorius, Dolories. “Three Dimensional Ultrasound Imaging.” Journal of Ultrasound in Med. & Biol. 24, no. 9 (1998): 1243-1270 Poon, Tony & Rohling, Robert. “Three Dimensional Extended Field of View Ultrasound.” Journal of Ultrasound in Med. & Biol. 32, no. 3 (2006): 357-369 Saurbrei, Eric. “Extended Field of View Sonography: Utility in Clinical Practice.” Journal of Ultrasound Medicine 18(1999): 335-341 Yerli, Hasan & Eksroglu, Secil. “Extended Field of View Sonography: Evaluation of the Superficial Lesions.” Canadian Association of Radiologists Journal 60, no 1, (2009): 35-39 Read More

The 2D images are then stored either in original digital format in the memory of the ultrasound system’s computer or in an external computer memory. Using an external computer or the ultrasound machine’s computer, the 3D image reconstruction and viewing is carried out though the use of predefined geometric parameters that describe the position and orientation of the 2D images in a 3D image volume. The spatial or angular intervals between successful 2D images are adjusted to minimize the scanning time (Fenster, Downey and Cardinal 2001, 70-73).

The free-hand scanning with position sensing techniques does not require a motorized fixture. Instead, they have a sensor, attached to the transducer, which measures its orientation and position. The operator holds and manipulates the transducer over the anatomy to be imaged. During this process, the acquired 2D images are stored together with their orientations and positions in the computer. 3D images are then constructed using this information. There must be appropriate spatial sampling done to ensure there is no significant gap since the locations of the 2D images acquired are not predefined (Fenster, Downey and Cardinal 2001, 75-77).

Another 3D scanning technique is free-hand scanning without position sensing which involves the manipulation of the transducer over the patient when acquiring 2D images. 3D images are then reconstructed by assuming the predefined scanning geometry. The operator must be very careful in moving the transducer at a velocity that ensures the 2D images are obtained at regular spacing. Good 3D images are obtained if there is uniform motion of over the distance and angle in the area scanned (Fenster, Downey and Cardinal 2001, 78).

2D Arrays for dynamic 3D ultrasound forms the last 3D scanning technique which uses a transducer with a 2D array unlike the free hand scanning and mechanical approaches which uses a 1D array transducer. Here, the electronic scanning transmits a broad beam of ultrasound beam sweeping over the entire anatomy under examination. Multiple planes are displayed in real time from this volume through the processing of the detected returned echoes by the 2D array. The multiple planes can then be manipulated interactively to allow the exploration of the volume under investigation by the operator (Fenster, Downey and Cardinal 2001, 78-79).

Operating principle of EFOV The activation of the EFOV option for the machines with EFOV ultrasound software allows the probe to be advanced slowly in a longitudinal direction in the same single plane over the area of interest. Meanwhile, the examination of the region of interest is carried out in real time. The EFOV machine’s computer calculates the motion of the transducer and reconstructs the sequential images in single large view without loss of resolution. The patient’s stability really matters in this method because it is sensitive to change in position.

This can result in loss of image quality and produce artifacts (Saurbrei 1999, 336). Operating principle of 3D ultrasound The operating principle in 3D representation of the anatomy involves the placing of acquired 2D images in their respective positions and orientations in 3D image volume. Their pixel values are used in determining the voxel values of 3D image. There are two image reconstruction methods used in determining the 3D images. First is feature based reconstruction where the desired features of anatomical structures are determined and reconstructed into a 3D image.

The surfaces of different structures are outlined and assigned different colours or shading. In order to enhance visibility, some of the features are eliminated and the resulting image is represented to the viewer in 3D. This approach reduces the content of the 3D image by representing few anatomical structures. The 3D image can be easily manipulated using inexpensive computer display hardware (Fenster, Downey and Cardinal 2001, 79). The second method of reconstructing images is the voxel based reconstruction.

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