3D and 4D Ultrasound ? Principle. Machine. Application. Examination. Difference. References.

3D Ultrasound “Introduction” :- Medical US imaging has progressed steadily with advances in clinical applications and equipment performance, making it an indispensable tool in obstetrics and in the diagnosis and management of many diseases. With the continued improvement of the technology, miniaturization of the scanners, ultrasound imaging is expanding its role with new diagnostic and therapy guidance applications. Although many new areas of ultrasound imaging are under development and investigation, three-dimensional ultrasound (3D US) has generated great interest.

Continuo…:- Most ultrasounds are conventional 2D images. 2D ultrasound images are made up of a series of thin image 'slices', with only one slice being visible at any one time to create a 'flat' looking picture. During the late 1990's, 3D ultrasounds (also known as 'ultrasound holographs') started to become available in some ultrasound centers. However, 3D ultrasound machines are extremely expensive and are not widely accessible at this stage. Definition : 3D gives us a 3 dimensional image of whatever we are scanning. With a machine that can give 3D imaging, Using computer controls, the operator can manipulate the image and obtain views that might not be available using ordinary 2 dimensional sonography (2D). 

3D Principle “Physical Basics” :- 3D ultrasounds work by taking thousands of image 'slices' in a series (called a 'volume of echoes'). The volumes are then digitally stored and shaded to produce 3 dimensional images that look more life-like. 3D Images for fetal face and hand. 

(1) VOLUME ACQUISITION :- 3D US systems use two basic approaches: conventional 1D arrays producing 2D images, which are reconstructed into 3D images using knowledge of their relative positions, and 2D arrays generating real-time 3D images directly. Although the use of 2D arrays to produce real-time 3D ultrasound images is the most convenient, this technology is still costly, requiring specialized technology. Most 3D ultrasound systems available today use the first method, in which conventional ultrasound machines with 1D arrays are used to acquire 2D images and reconstruct them into 3D US images.

The following are the main methods used to produce a 3D image :- 1-Mechanical scanning mechanisms : coupled to conventional transducers provide 2D images with accurate relative positions and orientations, allowing accurate 3D reconstructions. With accurate knowledge of the relative positions and orientations, the sequence of 2D images can be reconstructed into a 3D image very efficiently. Various kinds of mechanical 3D assemblies have been developed, which can rotate or translate the transducer over the region to be examined. Because the geometry is predefined, the reconstructed 3D image is available immediately after the acquisition.

Two types of mechanical assemblies are currently available: integrated mechanisms, which are designed to accommodate the motor and transducer within the housing, and external fixtures, which are attached to the conventional ultrasound transducer . the integrated approach requires specially designed transducers and an ultrasound system capable of controlling them. These types of systems are the most popular and are used extensively in obstetrics and radiology. Diagrams showing the motorized tilting 3D US scanning approaches using conventional ultrasound transducers. The tilting mechanism may be contained in a specially designed housing or an external fixture attached to the conventional ultrasound transducer.

external assemblies are generally bulkier, they employ conventional ultrasound transducers and can be interfaced to any conventional ultrasound machine. The external fixture approach is very flexible and has been used for controlling the movement of the transducer to generate three basic types of motion (linear, fan, and rotation scanning). In addition to vascular imaging, this approach has been successful in 3D US-guided breast biopsy and brachytherapy.

2-Tracked free-hand : In this approach, the operator holds an assembly composed of the transducer and an attachment that provides information on the orientation and angulation of the transducer. To produce a 3D US image, the operator manipulates the assembly over the anatomy in the usual manner. The most successful approach for providing the geometrical information makes use of a six-degree of freedom magnetic positioning device. These types of systems are generally compatible with any ultrasound machine. These types of assemblies have been used successfully in many applications including obstetrics and vascular imaging.

Principles of free-hand 3D ultrasound visualisation Principles of free-hand 3D ultrasound visualisation. By attaching a position sensor to the ultrasound probe, it is possible to simultaneously record the image and the position of the scan plane, so that the data can be explored in 3D. One of the major clinical advantages of recording US scans in this way is the ability to generate accurate estimates of the volumes of organs and other structures in the body. These volume measurements are used to determine the progression of certain diseases and their response to treatment.

3-Untracked free-hand : In this approach, the operator moves the transducer in a steady and regular motion, while 2-D images are digitized. Since the position and orientation of the transducer are not recorded, a linear or angular spacing between digitized images is assumed in reconstructing the 3D image. To avoid significant image distortions, the operator must be trained to move the transducer at a preselected linear or angular velocity. Nonetheless, geometric measurements such as distance or volume may be inaccurate and should not be made, limiting the utility of this approach to visualization of the anatomy only. Integration of this approach with any ultrasound system is easy and only requires software to reconstruct the series of 2D US images into a 3D image.

4- Real-time 3D with 2D arrays : Unlike the mechanical and free-hand 3D US systems, which use 1D arrays to produce a series of 2D images, systems using 2D arrays keep the transducer stationary and use electronic scanning to sweep an ultrasound beam over the volume-of-interest to produce 3D images in real time. The transducer is composed of a 2D phased array of elements, which are used to transmit a broad beam of ultrasound diverging away from the array and sweeping out pyramidal volumes. The returned echoes are detected by the 2D array and then processed to display in real time multiple planes from the volume or a volume-rendered view of the anatomy. The planes or the view can be chosen interactively to allow the user to view the desired region under investigation.

The diagram indicates how an ultrasonographic volume is acquired by a trans-abdominal volume scan. Allows the translation of the B-Mode probe and the acquisition of about 1024 transversal and parallel scan: by this way a volume is acquired. In this diagram can be seen the acquisition of volume using a vaginal scan.

The diagram on the left highlights the planes that the operator can choose in the volume acquired using the volumetric scan as seen in the photo on the right. This diagram shows the planes that can be selected by the operator within the volume acquired for computerized reformation in translation of the image.

This diagram shows the planes that can be selected by the operator within the volume acquired for computerized reformation in rotation.

(2) IMAGE RECONSTRUCTION :- The reconstruction algorithm uses the acquired 2D images and knowledge of their relative positions and orientations to place each in its correct location in the volume being reconstructed. With modern desktop computers, the reconstruction procedure can be carried out within a few seconds after all the 2D images have been acquired, or even during the image acquisition. Since the 3D image is built from acquired 2D images, the gray scale values of any voxels not sampled are determined by interpolation between the appropriate acquired images. Many algorithms have been developed to visualize and manipulate 3D images interactively.

IMAGE DISPLAY :- Although the quality and geometric accuracy of the 3D US image depend on the parameters and method of image acquisition, the 3D display technique often plays a dominant role in the physician's ability to obtain the desired information. Many 3D ultrasound display techniques have been employed, the two used most often are: Multi-planar reformatting :- This technique reformats the 3D data to a display of 2D planar surfaces.It is the most common visualization method used to view 3D ultrasound images. Because it provides 3D viewing by showing only 2D planes with 3D cues, just a small part of the complete 3D information can be viewed at any one time.

Volume rendering techniques (VR) :- An alternative technique used frequently to view 3D CT and MRI images makes use of volume-rendering approaches, in which the entire 3D image is viewed after it has been projected onto a 2D plane. Since the VR techniques project all 3D information onto a 2D plane, interpretation of complex images is difficult. Thus, this approach is not suited for viewing 3D B-mode ultrasound images with subtle contrast between different soft tissues. However, this approach has been used most successfully to view structures in which anatomical surfaces are clearly distinguishable, such as fetal structures surrounded by amniotic fluid, tissue/blood interfaces in the heart and large arteries.

Two multi-planar reformatting (MPR) approaches used to display a 3D US image of the prostate. Cube-view approach, in which the extracted planes are texture 'painted' on the faces of a polyhedron. Two volume rendered (VR) 3D US images showing the face and hand of a fetus.

Real-time 4D :- 4D Ultrasound represents the difference between video and a still photograph. Through this technology, three-dimensional image is continuously updated, providing a "live action" view. The entirely digital platform and very fast processors cope with the large volume of data required to reconstruct 3D images again and again, giving the impression of a moving image. 4D Ultrasound takes multiple 2-dimensional ultrasound images, creates a 3-dimensional image and adds the element of time to the process. The result: live action images of any internal anatomy.

Available 3D/4D Ultrasound Machine :- The latest generation of ultrasound machines such as the GE Voluson 730 show moving images in real time and in three dimensions. GE Medical Systems' 4D Voluson 730 and Philips Medical Systems' Sonos 7500 Live 3D Echo platform, both real-time 3D systems, are on the market, and Siemens Medical Solutions' fourSight. GE strongly marketed the term "4D Ultrasound", whereas other companies that make ultrasound machines with similar capabilities marketed the terms "3D ultrasound", "Live 3D", and others. What makes the system unique is exclusive GE 4D technology. GE 4D Ultrasound represents the difference between video and a still photograph.

Built on a digital platform, the Voluson 730 System utilizes advanced signal processing technology to ensure optimal image quality for high-resolution 2D, volumetric 3D and real-time 4D imaging. The Voluson 730 is a whole body system with applications in Radiology, OB/GYN, Vascular, Urology & Cardiology. The GE Voluson machines produce the clearest images and the smoothest video. Most of the high quality sample images you see on the internet were taken with a GE Voluson machine.

3D/4D Clinical Application :- 3D US imaging is now readily available on most modern ultrasound systems. With its wide availability, investigators have reported on the utility of 3D US in a wide variety of applications. Any punctures or biopsies, interventional radiology, brachy-therapy, RF ablation, hook wire placement, cryogenic therapy and numerous other applications. 3D US in obstetrics :- The most extensive applications of 3D US have been in obstetrics due to its ability to provide information not readily available with 2D US imaging. Volume rendering(is the process of capturing ultrasound image information and compiling it into a three-dimensional image. ) coupled with MPR viewing of the fetal face and skeleton offers important views that enhance the compression of the ultrasound information.

These advantages include: Determine fetal age Analyze fetal development Evaluate multiple and/or high-risk pregnancies Detect fetal abnormalities Detect structural problem with uterus Detect placenta abnormalities Detect abnormal bleeding Determine ectopic pregnancy and other abnormalities of pregnancy Detect ovarian tumor/fibroids Locate the placenta

Chewing Firstwhinge Getlost Sleepy Smiling

3D image for fetal foot with six Toes. 3D image for fetus with cleft lip.

3D/4D Examination :- Risk :- 3D and 4D Ultrasound is believed to be a safe, non-invasive exam that utilizes sound waves to look inside the body. Despite extensive studies over 30 years ultrasound has not been shown to cause any harm. Examination Time :- 3D/4D ultrasound requires the same time as a traditional ultrasound - from 20 to 30 minutes, depending on a number of factors, such as the position of the baby. Preparation :- Does not require any special preparation.

Difference Summary :- A 2D ultrasound refers to a regular, black and white sonogram. This examination provides you with an outline of internal anatomy. A 3D ultrasound uses the same basic concept of a 2D ultrasound, but rather than take the image from a single angle, the sonographer takes a "volume" image. A 4D ultrasound (also referred to as "Live 3D") extends on the concept of a 3D ultrasound, but rather than taking a single volume image, multiple volume images are taken in rapid succession. The result of these images displayed in succession is a motion video .

References :- http://www.gehealthcare.com http://www.birth.com.au http://www.babybond.com http://www.obgynsono.com http://www.sufw.com.au http://www.mtauburnobgyn.com http://www.createhealth.org http://www.imagingeconomics.com http://mi.eng.cam.ac.uk Good luck…