The term “3D imaging” refers to generation of a three-dimensional image using various modalities, generally obtained from summation or reconstruction of source two-dimensional images. The common modalities using this technique are magnetic resonance imaging (MRI) and computed tomography (CT).
|Legend. A 40-year-old-man presented with subarachnoid hemorrhage due to rupture of an aneurysm of his distal basilar artery at the origin of a duplicated superior cerebellar artery. These dilated superior cerebellar arteries provide supply to a right cerebellar hemisphere arteriovenous malformation, and the aneurysms have formed in response to the high blood flow in this region. The anatomy is difficult to determine from conventional angiography (Figures 1 and 2).|
Standard radiographs and ultrasound can also be reconstructed into 3D images, although less commonly. For MRI and CT, the 3D image is reconstructed from very thin axial images which are then “stacked,” and using various reconstruction paradigms, made into a seamless image that can then be viewed in three dimensions. The advantage of 3D imaging is that it permits greater understanding of the anatomy and pathology being investigated, as the images not only can be viewed from any direction, but the imaging anatomy becomes more “life-like” in that a volume is being studied, rather than a plane. The potential benefits are that subtle findings may become more apparent, thus increasing the accuracy of the imaging, and that any intervention, surgical or otherwise, is performed with a superior understanding of anatomic and pathologic relationships. In terms of the financial implications, the cost of 3D imaging is only marginally greater than that of the standard imaging. A CT performed with 3D technique is similar in cost to a similar routine CT without using a 3D protocol. The advantage is that with the greater amount of information provided, interventions can be performed more easily and more safely, hopefully decreasing the likelihood of complications and decreasing the time required in the planning and execution of a procedure.
|The relationship of the superior cerebellar arteries to the posteriorly projecting aneurysm and superiorly projecting aneurysm is much easier to understand with the three-dimensional reconstructions obtained from CT angiography (Figures 3-5). By rotating these CTA images, it can be seen that the superior cerebellar arteries arise from the junction of the neck of the aneurysm and the distal basilar artery for one aneurysm (Figure 6), and from the neck of the aneurysm itself for the other aneurysm (Figure 7). This information permitted the coiling of the aneurysms with a greater degree of understanding of the anatomy and hence greater safety than could have been achieved otherwise. Images courtesy of Jonathan Hartman, MD.|
This case study involves a 40-year-old man who presented to the hospital with intracranial hemorrhage, presumed to be from a ruptured cerebral aneurysm. As part of the workup, a standard CT of the head was performed, supplemented by CT angiography (CTA) of the intracranial arterial vasculature in order to identify and characterize the aneurysm. This allowed a noninvasive means of evaluating the aneurysm location, size, projection, and relationship to the adjacent arteries. During treatment of the aneurysm by endovascular coiling with platinum coils, the CT angiogram was instrumental in identifying a normal artery arising from the neck of the aneurysm, delineating the limit of where the coils could safely be placed in order to not block the normal vessel and cause a stroke. While conventional catheter-based angiography is generally considered the “gold standard” in evaluation of the vascular system, at times vessels can be obscured by superimposition on other vessels or, in this case, by superimposition on the aneurysm. Had the patient undergone open surgery with clipping of the aneurysm, the utility of the information would be the same, providing a depiction of the anatomy that is easily translated by the surgeon into a practical understanding of what to expect when the aneurysm is encountered.
As imaging technology and information processing continue to improve, 3D imaging will likely become increasingly important in planning surgery and other invasive procedures. It provides information equivalent or even superior to routine imaging and likely will replace much of what has in the past been obtained using conventional techniques; this is particularly true in the setting of vascular imaging, as conventional angiography is invasive, costly, and carries small but unavoidable risks. Furthermore, from the perspective of diagnosis, 3D imaging may provide increased accuracy and, for both radiologist and surgeon, allows a greater degree of certainty in evaluation and treatment.
Jonathan Hartman, MD, is assistant professor of radiology and director of neurointerventional radiology, UC Davis Medical Center, Sacramento, Calif.