Radiology at the Movies
By Dan Harvey
Vol. 18 No. 12 P. 24
Cinematic 3D rendering produces stunning images, but is it more than just a good show?
Reactions of clinicians and medical students to images produced by a new visualization technique are often similar to the breathless responses of overwhelmed moviegoers emerging from the screening of a new animation film.
The new reconstruction technique, cinematic 3D rendering, provides eye-widening images in striking detail that take the viewer on a fantastic voyage into the interior of the human body. Compared with standard volume rendering, this advanced postprocessing 3D technique provides much more realistic images of high-density anatomical structures. The raw material, so to speak, comes from traditionally obtained CT data sets.
Cinematic 3D rendering was recently approved by the FDA for clinical use, says U. Joseph Schoepf, MD, of the department of radiology and radiological science at the Medical University of South Carolina (MUSC) in Charleston, South Carolina. He adds that the technique creates a more lifelike image than obtained with volume rendering or maximum intensity projection, which have served as the standard CT postprocessing techniques. A new and complex algorithm at the core of 3D rendering enhances the quality of the images.
"The first time I saw the images, I felt it was just like looking at an actual photograph of the interior anatomy," Schoepf says. "It was incomprehensible to me how you could turn a CT data set into something that realistic."
Suhny Abbara, MD, a professor of radiology and chief of the cardiothoracic imaging division at the University of Texas Southwestern in Dallas, explains the effect: "Three dimensions take volume rendering to where you have a higher degree of resolution, coloring, and light, all of which combine to make it lifelike," he says. "Cinematic 3D imaging goes one or two steps beyond surface rendering by assigning to tissues certain densities and colors. As such, it enables display of certain tissues in a way that makes more sense to the clinicians most interested in those tissues."
Schoepf sees the most immediate applications for the new technique as providing more information about complex anatomy or conditions and better surgical planning, including for cardiac procedures.
"Some cases are extremely complex, such as congenital heart disease. That would be a prime application for this," says Marwen Eid, MD, Schoepf's colleague at MUSC and, along with Schoepf, a coauthor of a recently published study of 3D rendering. In their study, Eid, Schoepf, and coauthors set out to conduct a comprehensive review of the 3D cinematic rendering technique. "Part of this involved assessing how it can be applied in the clinical setting and the main advantages it provides," Eid says.
The authors used the Siemens' imaging software platform syngo.via VB20—software than can be used with any scanner. For their purposes, they reconstructed CT source images with their own default settings. They used a slice thickness of 2 mm, with 1.5 mm increments, except for coronary CT angiography. For this, they used a slice thickness of 0.75 mm, with 0.5 mm increments. All CT angiography data were acquired after the intravenous injection of 50 to 80 mL nonionic, iodinated contrast media at a concentration of 300 to 370 mg J/mL, depending on the body region.
"The three most important domains we see right now include planning, teaching, and communication," Schoepf says.
For surgical planning benefits, Eid indicates that the new technique "would be an effective and less expensive alternative to 3D printing." Also, 3D rendering will provide a new tool for medical education as well as improving communication between physicians and patients and among different medical specialists.
Physician-patient consultation stands to gain by the ability to use cinematic 3D images to show a patient exactly what their pathology involves, better explain what treatment will entail, and potentially improve a patient's compliance. That is the area that most excites Abbara.
"Studies have revealed that compliance, especially for treatment of prevention of coronary artery disease, becomes enhanced if you share such images with the patients," he says. "Patients, who are typically 'blown away' when they see images of their own anatomy, will now be better able to understand, thanks to 3D rendering. As a communication tool, it may compel a patient to be much more compliant with medical therapy and lifestyle modification, which can prevent future events. That alone makes use of the technology quite valuable."
Eid says the technology fosters the "show-don't-tell" concept among physicians: "In vivid fashion, they can show the patient the pathology that is affecting them and how and why it is affecting them."
In addition, value as a medical education tool is evident. The images almost make it seem to students as if they are viewing a patient on an operating table. "At times, it can seem like a virtual dissection tool," Eid says.
How It Works
The earlier comparison to Hollywood cinema is not just hyperbole; the researchers who developed the new technique were inspired by what has been going on in recent years in the motion picture industry, where new computer animation technology has become much more lifelike.
It all has to do with light. Real-time lighting effects are complex, but cinematic rendering is capable of modeling elements such as shadows, ambient occlusion, multiscattering, and color transmittance. At the same time, it can combine these properties with features available in the most sophisticated camera technology, including aperture, exposure, and shutter speed.
Such capabilities are crucial to the effectiveness of the new technique. With cinematic rendering, tissues appear to interact with light, both reflection and absorption, which results in highly realistic imagery. Specifically, light mapping achieved through new computer algorithms produce the effect. Furthermore, users can manipulate the images and see anatomy from different viewpoints.
"You can make the computer show you exactly what you want to see," says Roy F. Riascos, MD, a professor and chief of neuroradiology with McGovern Medical School at The University of Texas Health Science Center at Houston and Memorial Hermann-Texas Medical Center. "Development of increasingly sophisticated software has gotten us to this point. Also, we get better and better as scanning techniques improve."
Cinematic rendering moves beyond the single raycasting principle found in standard volume rendering. Rather, it considers illumination rendered by billions of photons, which affect the targeted area in all directions. The scattered light is rendered along a single ray.
"Many photons create one pixel," Eid explains. "[Cinematic] rendering simulates the way that billions of photons [behave in] the volume being imaged, through a mathematical formula called the Monte Carlo simulation. Ultimately, it lends the images a lifelike appearance compared with volumetric rendering."
With the technique, Monte Carlo simulations generate a randomized subset of light paths with an adequate distribution. The final image is obtained via a progressive averaging of numerous Monte Carlo samples. These samples represent radiance at random positions with light scattered in random directions.
Schoepf describes the result as "the intuitive grasping of the complex imaging information." He adds that this technique can be applied with any scenario a clinician prefers. "For instance, at MUSC, our pediatric cardiologists are very enthusiastic about understanding the complex anatomy of a child with a congenital heart defect—particularly for surgical planning, when you can look into the lifelike rendition of a child's heart to plan that kind of surgery."
Riascos believes that cinematic rendering makes it possible to eliminate unnecessary procedures. "These, plus their risks in harming surrounding organs and unnecessary imaging procedures will be greatly reduced through the advanced surgical planning made possible," he says. "To me, that represents the most important advantage of this technique."
Also, he anticipates a positive impact on diagnosis. "Pathologies have become much easier to diagnose, in terms of location and surgical planning," Riascos says. "Now, with the [cinematic rendering] techniques, we will realize the huge benefit that the diagnosis is more accurate." The technique's benefit extends to postsurgical follow-up, he adds: "You can more accurately determine whether a lesion has grown."
Just Great Pictures?
As with any new technology, cinematic rendering is being closely scrutinized and its merits assessed. While observers are impressed with the resulting imaging quality, some are not completely sold on the idea that it represents an absolutely critical need.
For instance, Cynthia McCollough, PhD, director of the CT Clinical Innovation Center at Mayo Clinic, has expressed the opinion that no 3D image, no matter how lifelike, will ever take the place of the most basic of methods: a radiologist reading the individual 2D pictures from CT or MRI scans. McCollough has gone on record saying that, while 3D images help to summarize the layout of bones or blood vessels, they will not become "a standalone diagnostic tool anytime soon."
Also, Abbara raises a question about necessity. "I have yet to hear from anyone that this is a must-have application that solves a problem," he reports. "While I feel the images are truly awe inspiring, I am not yet convinced that it has added diagnostic or therapeutic value to the images. I haven't seen any particular problem that can be better addressed using cinematic vs standard volume rendered imaging."
Abbara often meets with colleagues throughout the nation, and he always asks them what they think is needed for CT. "No one has mentioned better CT rendering," he says. "I think that it is great that we have this, and I think that it is better that we can communicate what we see in such a vivid way. But, to me, this advancement does not appear to be driven by seeking an answer or fulfilling a need. Ideally, innovations are driven by an unanswered question or an outstanding need that exists."
But Schoepf responds by calling for time and patience before casting final judgment, as the intrinsic value of anything new is at first difficult to measure. "Take, for instance, something like virtual colonoscopy," he offers. "You do comparative trials, then, using that as a reference standard, you can easily determine performance metrics such as sensitivity, specificity, and overall accuracy. I think that is much more difficult with a novel visual technique such as cinematic rendering because you typically don't have an outside standard reference that you can use for comparison purposes. It proves to be a different animal, as far as other new applications. So, it is hard at first to quantify the additional value. Currently, we are in the business of trying to do just that."
Other challenges need to be addressed moving forward. For one, if clinical usage is to become widespread—even routine—higher speed rendering will be required. Also, development of monitor technology remains important, as this will support the 3D stereoscopics. Cinematic 3D images will also entail an increase in computer power. Other challenges involve improved rendering software and increased graphics processing.
More investigation into the accuracy of 3D rendering is necessary, as well, along with research that could properly assess the value of cinematic rendering compared with volume rendering. Such new information would be of particular importance to those surgeons who are ready to embrace cinematic 3D images.
Right now, researchers at MUSC are working on ways that will quantify the potential usefulness of the cinematic 3D rendering technique, Schoepf says. "Part of this involves measuring the confidence of a surgeon to perform an operation based on the preprocedure planning that comes out of using this technique," he says. The goal, he adds, is determining a measureable, quantifiable, incremental value over traditional techniques.
"You'll find that this will take researchers down the same pathways as before for other advancements," Schoepf says.
— Dan Harvey is a freelance writer based in Wilmington, Delaware.