THE LATEST IN ULTRASOUND - 3-DIMENSIONAL IMAGING - PART-II

Introduction: The three-dimensional (3D) reconstruction of ultrasound images has become a widespread option in ultrasound equipment. Specifi c softwares have become available and 3D reconstruction feasible since the early 1990s. particularly since 1994. Possible clinical applicati ons: Several clinical applications are feasible in all parenchymatous organs (mainly the liver and prostate), hollow viscera (e.g. the bladd er and gallbladder), peripheral vessels (supra-aortic trunks and limb vessels) and central (the aorta and iliac arteries) or cerebral vessel s. Moreover, tumoral vessels in parenchymatous organs can be reconstru cted, and even the fetus in the uterine cavity, with excellent detaili ng. The recent introduction of echocontrast agents and second harmonic imaging has permitted to study normal and abnormal peripheral, centra l and parenchymatous vessels, with similar patterns to those obtained with digital angiography. The spatial relationships between the vascul ar structures of the liver, kidney and placenta were studied with 3D u ltrasound angiograms. The applications of this new technique include t he analysis of vascular anatomy and the potential assessment of organ perfusion. The latest applications-intravascular studies: Some cathete rs with an ultrasound transducer in the tip have been tested for intra vascular studies. Just like conventional transducers, they provide two -dimensional (2D) images which are then postprocessed into longitudina l 3D or volume reconstructions. The former resemble angiographic image s and can be viewed 3D rotating the image along its longitudinal axis. Volume images, which are more complex and slower to obtain, can be ro tated on any spatial plane and provide rich detailing of the internal vascular lumen. The clinical importance of intravascular ultrasound wi th 3D volume reconstructions lies in the diagnosis of vascular conditi ons and the assessment and monitoring of intravascular interventional procedures-e.g. to detect inaccurate deployment of intravascular stent s and endoluminal grafts during the maneuver. Three-dimensional recons tructions involve geometric data rassembly and volumetric interpolatio n of a spatially related sequence of tomographic cross sections genera ted by an ultrasound catheter withdrawn at a constant rate through a v ascular segment of interest, resulting in the display of a straight se gment. Therefore particular care is needed and there are some useful h ints to avoid mistakes. Conclusions: Three dimensional reconstructions of B-mode and color Doppler images are no longer a work in progress a nd their clinical importance and possible applications are both establ ished and ever-increasing. On the other hand, independent of the diffe rent types of energy used, also computed tomography and magnetic reson ance 3D reconstructions are very useful from a clinical viewpoint and they have became an established routine technique for both these metho ds. It is very likely that 3D volume reconstructions in ultrasound wil l find numerous applications in the near future. They may help to incr ease the diagnostic confidence and to facilitate diagnosis, intraproce dure monitoring in interventional radiology and follow-up and also to reduce the number of invasive examinations with iodinated contrast age nts. This could result in cutting the cost and duration of the most ex pensive examinations. New, although invasive, applications can be hypo thesized for intravascular or intraluminal catheters with an ultrasoun d transducer inside. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.