3D Doppler Ultrasound - Research Paper Example

Running Head: 3D Doppler Ultrasound 3D Doppler Ultrasound Ultrasound is a reasonably priced imaging modality widely used for the staging and diagnosis of various diseases and conditions. Over the years, ultrasounds have benefited largely from the breakthrough of technological advances thus becoming an indispensable imaging modality owing to its non-invasive nature and flexibility. Technological breakthrough in this field has led to advancement of ultrasonic imaging with the coming of the 3D ultrasound. This novel approach in ultrasound imaging is speedily achieving extensive use with numerous applications. Following the coming of the 3D ultrasound, the limitations that hindered 2Dimension viewing of 3Dimension anatomy by means of conventional ultrasound have now been alleviated. 2D viewing of 3D anatomy was virtually unviable for two reasons. First, the anatomy is in 3D while conventional ultrasound image is in 2D and for that reason, the diagnostician must integrate numerous images in his or her mind. Such a practice would be inefficient leading to variability and erroneous diagnoses. Second, the 2D ultrasound image has a thin plane at a random arbitrary angle in the body. It thus becomes hard to pinpoint the image plane and replicate later for follow-up studies. 3D surmounts the limitations of 2D ultrasound imaging as this study will show. The study will particularly describe the developments of a number of 3D Doppler ultrasound imaging systems using free-hand, mechanical and 2D array scanning techniques. Introduction In the 20 century, medical imaging entailed visualizing the interior body using 2D x-ray images. Presently, 2D images have gained vast popularity even though the 2D imaging cannot be done away with. However, it is critical to note that the 3D imaging has many advantages over the 2D imaging. The use of 3D gained popularity in the 1970s after the innovation of the computed tomography. It is the development of the 3D imaging that has eventually resulted to the invention of the MRI (magnetic resonance imaging). The development of 3D has been facilitated by the technological development especially in the last three decades. Prior to that, medical ultrasound was mostly employed by the cardiologists, gynecologists, and the obstetrics. Following 3D improving the quality of the images greatly, the use of the 3D has greatly increased efficiency in the medical field. More so, the 3D Doppler ultrasound provides vital information through which the blood flow information can be analyzed. Through the 3D Doppler ultrasound, medical practitioners have greatly improved their services since they can use it in cardiology and radiology effectively, and many roles are being derived for the 3D Doppler ultrasound. In addition, more effective use of the 3D imaging is being used in therapy and surgery. Following the Doppler ultrasound machine, a medical practitioner places a scanner that is held in the hand and linked to a computer. The machine then senses the blood sound waves in the arteries and the veins. The 3D Doppler ultrasound has many advantages that makes it a very critical tool in the medical field. Besides having many advantages, there is no known risk linked to the medical practice and takes about an hour for the medical process to be completed. This research paper focuses on the 3D Doppler ultrasound imaging system using free-hand, mechanical, and 2D array scanning techniques. More so, the limitations of the 3D ultrasound are also evaluated. 3D Doppler Ultrasound Techniques 3D Doppler ultrasound uses the conventional 1D ultrasound transducers in order to get a chain of 2D ultrasound images. The only difference that occurs between it and 2D ultrasound is the direction and positioning of the 2D images in 3D image volumes that are being evaluated. During the 3D Doppler imaging, three factors need to be considered. These are: The scanning technique should be controlled to limit the changes of the image being affected by some involuntary motions like breathing. The orientation or direction and location of the 2D images that have been acquired must be established to limit the chances of distortion that results to errors in analysis. The machines being used must be efficient and simple to in order to limit the chances of complicating the process. While carrying out the 3D Doppler ultrasound techniques, there are several scanning methods that may be used, these methods affect the image being acquired and have their respective advantages and disadvantages. Among the most popular scanning methods employed in the 3D Doppler ultrasound scanning include mechanical linear, articulated arms, image correlation, 2D arrays, magnetic sensor, free hand acoustic, rotational, and tilt. There are three main 3D Doppler ultrasound techniques, there are: Mechanical scanners Free hand scanning, and 2D array scanning techniques Mechanical Scanners This entails a situation whereby the medical practitioner scans the blood system by use of a motorized mechanical tool to tilt, rotate, and translate a conventional transducer in the process of acquiring the 2D chain of ultrasound images on the area of interest and storing the images in the computer. Since there are well laid scanning procedures that control the process, the direction and the position of respective 2D image is known precisely. Following the high level of technological advancement, the practitioner may store the 2D images acquired in a digital format of the computer system or a video within the ultrasound machine. Transformation of the 2D images may be carried out either within the ultra sound machine or by an external computer. This employs already set geometric parameters that set the position and direction of the 2D images in the 3D Doppler ultrasound image volume. The geometric parameters entail setting the 2D images at various angles with the objective of achieving certain objectives. Efficiency of this technique is achieved by using the minimal time to scan and testing the sample of the 3D images from the 3D image volume (Smith & Fenster, 2000). There are a number of scanning apparatus that are employed to translate the conventional transducer in order to achieve their required results. These apparatus differ in reference to their sizes and may range from small 3D probes that are employed during the scanning process to peripheral fixtures, mechanically holding the features of a conventional ultrasound system. According to Fenster et, al (2000), the 3D integrated probes are heavier and bigger than the conventional probes and are user friendly. However, the 3D integrated probes need the medical practitioners to buy particular ultrasound appliance for interfacing them. More so, the external apparatus are heavier compared to the integrated apparatus and can be enhanced to hold the transducer of whichever conventional ultrasound machines. This eventually saves the hospital the resources needed to purchase a unique 3D ultra sound machine. It is imperative to note that the imaging technique and the quality of the image produced by whichever conventional ultrasound machine can be attained in 3D. There are three principle mechanical scanners employed in the 3D Doppler ultrasound imaging, these are: Linear 3D scanners Tilt 3D scanners, and Rotational 3D scanners Linear 3D scanners This method of scanning entails a motorized driven mechanism that linearly translates the transducer on the skin of a patient with the 2D images being taken at certain preset intervals hence ensuring that the acquired images are parallel and homogeneously spaced. While carrying out the 3D scanning, it is critical to ensure that the translation speed and interval are varied with the objective of matching the sampling rate to the outline rate of the ultrasound machine and to equate the sampling interval to half the angular resolution of the transducer (Smith & Fenster, 2000). Through the use of the set standards, the 2D image is easily transformed to 3D ultrasound image. Through that reconstruction, the 3D images can be achieved immediately after the scanning process and thereafter optimization of the resolution. Since the 3D image is achieved using a chain of 2D images, the resolution attained is not expected to be isotropic. In case the reconstruction direction is parallel to the 2D images, then the 3D images acquired will be similar to the 2D images, however, when perpendicular direction, then it will be similar to the transducer’s angular resolution. It is imperative to note that, the 3D resolution is most horrible in the 3D direction of scanning, therefore, for the most favorable results are achieved when the transducer has a well-elevated resolution. It is worth noting that, linear scanning is widely employed in vascular imaging implication that uses the 3D colored Doppler ultrasound images and B- mode located in the carotid arteries (Guo & Fenster, 1996). Tilt 3D Scanners This scanning process involves the transducer being tilted by a motor while guaranteeing that the transducer face is parallel to the axis and at the same time, the 2D images are being taken at standard angular gap. That makes certain that the fan or overlapping images radial to axis are formed. Both an integrated 3D probe along with external fixture can form such type of motion. Whether employing the external fixture or the integrated 3D probe, the probe hosting remains at the same position on the skin of the sick individual. The formation of fan like images form a geometry whereby the large region obtained can be adjusted at certain angles to achieve the best results. (Downey, et, al, 1995a) The 3D tilt scanning results to compacting designs in either external fixtures or integrated 3D probes. The compacting is instrumental in enabling the physician to position and adjust the scanning machine with ease. Efficiency when using the 3D tilt scanners is achieved when the physician is able to select the optimal ultrasound frame rate, elevation interval, and scanning angle, hence using the minimal time. In the 3D tilt, the scanning can be made by the axis whereby the 2D images can be attained by a side linear transducer range that is normally parallel to the probe axis and eventually make a fan of 2D images that have the ability of spanning between 80o and 110o scanning angle. Besides the 3D tilt scanners being employed in the 3D Doppler ultrasound imaging, it is popularly used in prostrate imaging, cryosurgery, and various other medical practices. Rotational 3D Scanners This scanning process entails rotating the transducer using a motor at a fixed axis that normally bisects the transducer perpendicularly at minimal angle of 180o in order to get the required 2D images. The scanning geometry focuses on getting images from a conical volume relative to the axis. This can be achieved through both the external fixture and the integrated 3D probe. In this case, an isotropic 3D image resolution will not be achieved. This is based on the fact that the 2D images produced crisscross along the axis thereby meaning that the highest spatial sampling will close to the axis. In addition, the elevation resolution and the axis in the produced 2D images decreases as the distance from the transducer increases. The combined impact of these effects can result to the 3D image achieved to be complex. It is crucial to note that this scanning procedure is very sensitive to the patient movement caused by the intersection of the 2D images crisscrossing at the middle of the 3D images. Any patient movement when the 2D images are being taken, therefore, results to different 3D images (Landry, et, al, 2004). Free- Hand Scanning This is better and effective scanning technique since there are no bulky apparatus such as motor fixtures that may inconvenience the physician. This process involves a sensor being connected to the transducer, the physician controls the elevation, and positioning as the 2D images are being stored in a computer. The stored information is then used to create 3D images. Spatial sampling is critical since the physician does not have a preset relative position. There are a number of free hand scanning techniques; these include acoustic sensing, image based sensing, articulated arms, and magnetic field sensing. The articulated arm 3D scanning entails a procedure in which the orientation and the position sensing can be done when mounting the ultrasound transducer on an arm like mechanical system that is composed of several joints. The physician can thereby control the transducer as the 2D images are being recorded. The performance of this technique is enhanced when the arms of the mechanical tool are kept as short as possible in order to take the best 2D images. Acoustic free hand 3D scanning uses a collection of three devices that produce sound and a microphone that collects the sounds. The position and orientation of the transducer collects the 2D image from the sound produced and image is determined by the speed of the sound. Free hand 3D scanning using magnetic field sensors employs a magnetic sensor that has six degrees of freedom. Different magnetic fields are created and the receiver that has three orthogonal coils evaluates the strength of the magnetic field, the three coils along with the strength of the magnetic field enable the 2D images to be collected. 2D Array Scanning Techniques In the above mentioned free hand mechanical scanning techniques, there must be the use of 2D images that are achieved from the conventional transducer, with 1D array being moved mechanically on the required part of the body. However, the 2D array scanning does not require the movement of the transducer as the electronic scanning can be done whereby an ultrasound beam can be swept over the patient or part being scanned (Shattuck, et, al, 1984). The 2D array produces a beam of ultrasound that moves on the surface of the individual in a truncated pyramid shape like with the returning echoes being detected by the 2D array that are subsequently processed to produce the 3D image. The main limitation when using this technique is the cost and the radiology emitted otherwise it has been used in echocardiology in which it has produced valuable results (Sohn, 1989). Limitations of 3D Doppler Ultrasound The 3D images achieved are produced from the 2D images gotten from the ultrasound transducer. The 3D images are worked on by the physician; consequently, the success of giving the patient the best intervention depends on the professionalism of the operator or physician and ability to collect the optimal 2D images. Converting the 2D images to 3D consumes a lot of time, mentally challenging, is subjective, and therefore if the 3D images achieved are not precise, then the patient may end up being given the wrong medication. Lastly, when the 2D are collected and processed to form the 3D images by a computer, the 2D images collected may be altered by the operator and result to wrong intervention. Lastly, taking the 2D images takes long than taking the magnetic resonance imaging or the CT. Conclusion The use of the 3D images for clinical intervention has many advantages and the greatest of them is that it is not invasive. The advantages have made the technique to gain popularity across the globe. Despite the few limitations, 3D Doppler ultrasound is very efficient when employed by a qualified and experienced physician. There is a high expectation that the 3D ultrasound image techniques will be improved and overcome the limitations that come along with transforming the 2D images into 3D images. The 3D Doppler Ultrasound images are not invasive and do not have known negative impact on the client. In the case of the 2D array scanning techniques, the operator needs to control the amount of the radiation reaching the patient since excess radiation can be harmful. References Downey, D. B, & Fenster, A. (1995). Vascular imaging with a three-dimensional power Doppler system. Am. J. Roentgenol, (165), 665–8. Fenster, A., Downey, D. B. & Cardinal, H. N. (2000).Three-dimensional ultrasound imaging. Phys. Med. Biol. 46 (2001) 67–99. Government of Western Australia Department of Health. (2009).Doppler Ultrasound. Retrieved from www.imagingpathways.health.wa.gov.au Guo, Z. & Fenster, A. (1996). Three-dimensional power Doppler imaging: a phantom study to quantify vessel stenosis Ultrasound Med. Biol., (22), 1059–69. Landry, A., Spence J.D., Fenster A. (2004). Measurement of carotid plaque volume by 3-dimensional ultrasound. Stroke, 35(4), 864-869. Shattuck, D. P., Weinshenker, M. D., Smith, S.W. & von Ramm, O. T. (1984) Explososcan: a parallel processing technique for high speed ultrasound imaging with linear phased arrays J. Acoust. Soc. Am. (75), 1273–82. Smith W. L. & Fenster, A. (2000). Optimum scan spacing for three-dimensional ultrasound by speckle statistics. Ultrasound Med. Biol. (26) 551–62. Sohn, C. (1989). A new diagnostic technique: three-dimensional ultrasound imaging Ultrasonics International ’89 Conf. Proc. 1148–53. Read More