3D imaging is not very new, but up-and-coming applications for 3D MRI, CT and ultrasound are prompting more accurate diagnoses and enhanced healthcare.
The advent of new computer software and technology usually means improved care from institutions utilizing medical imaging equipment. 3D imaging is not exactly new, but up-and-coming applications for 3D MRI, CT and ultrasound are sure to increase the tools physicians' use to make more accurate diagnoses, and in turn and saving lives. From 3D magnetic resonance angiography to a virtual man to a 3D fetal face, each modality is trying to carve its own unique niche.
MRI and the heart
With the relatively new technique of MRA (magnetic resonance angiography), GE Medical Systems (GEMS of Waukesha, Wis.) has developed 3D MRA to view 3D volume sets of carotid arteries and peripheral vascular disease. Alfio Pennisi, M.D., of the South Jersey Radiology Associates (Voorhees, N.J.), has been using GEMS' high-field-strength 1.5 Tesla short-bore system since February to view carotid arteries in a completely different way.
A traditional contrast angiography study involves an invasive procedure of injecting iodine solution through a catheter inserted into an artery, with the accompanying small risk of iodine toxicity. A 3D MRA allows the injection to go into a vein and still see the arteries, and, if necessary, the veins.
GEMS uses the technique of acquiring a liptocentric case-based sampling, where the center of the volume that a technician wants to image is taken when the phase-encoding gradient is at its lowest point and the signal intensity is at its highest. It is a method of getting a sampling of the arterial data, while suppressing the venous data. This leaves more time, almost a minute, during the exam to view the vascular arterial anatomy, while suppressing the venous flow. The procedure alleviates the slight mortality risk that contrast angiography does.
The advantage of using a 3D volume set is that the original data set can be manipulated on the computer software to show the axial, sagittal and coronal planes, despite what plane the originals were taken in. A contrast arteriogram only can show one plane per contrast injection. Patients who need these exams often have nephrotoxicity and the contrast medium could pose a serious threat to the kidneys, says Pennisi. 3D MRA uses gadolinium, which is safer for patients.
"I anticipate this will replace, or at least significantly impact, the number of contrast arteriograms of the carotids that we will be doing in the future," says Pennisi, who has performed about 27 MRAs to date. "I think that in the future you're going to find that [in] carotid angiography, 3D MRA is going to be huge, and I think it is going to have a big impact on the way patients are managed in the future."
Pennisi also is using 3D MRA to view peripheral runoffs to diagnose peripheral vascular disease. A 3D MRA has the potential to replace ultrasound and the more invasive contrast angiography in diagnosing this disease. The study can be done in an outpatient setting with a special runoff coil designed by GEMS. Pennisi has done 26 such exams and has discovered that he essentially can "direct" an arteriogram by telling the angiographer exactly which vessel to inject contrast into, thereby lessening the length of the exam and risk to the patient. When compared with contrast arteriograms, 3D MRAs have been just as helpful to interventionalists, according to Pennisi.
There are some cons to this method as well. There might be venous contamination, but the arteries still can be seen well. It also is possible to overestimate a stenosis with this exam and miss certain types of stenosis, says Pennisi.
At St. Luke's Episcopal Hospital (Houston) and Texas Children's Hospital at the Texas Heart Institute (Houston), Scott Flamm, M.D., director, of MRI and cardiovascular MRI research, also has had success using 3D MRA for vascular studies.
"We have tried a number of techniques over the years, starting with the axial 2D time of flight, looking at the arterial supply from the abdomen all the way down to the toes, but now we can do it much more quickly using the contrast enhanced techniques," Flamm says. "I would hope that we would prove to be good enough and fast enough within the next year or two that we would be able to replace doing a diagnostic catheter angiogram and we could use this 3D MRA as a diagnostic and triage tool."
Flamm uses a Philips Medical Systems North America (Shelton, Conn.) Easy Efficient workstation to give patient MRI images depth and perception by applying 3D surface shading or 3D volume rendering. The reconstruction enhances the image to look like an actual structure in space, making it easy for other physicians and interventionalists to see where the stenosis is. In Flamm's experience, the 3D images have been a great help to interventionalists, since they can see exactly where the problem lies and they can do a more directed study.
"The field [of 3D medical imaging] is moving very quickly, but all of the techniques that we perform are quite manageable. You just really need knowledgeable people who are dedicated to doing very good work," says Flamm. "I really believe that it could be an overall cost saver to the hospital and to the healthcare system if we can integrate these studies appropriately," says Flamm.
Flamm foresees obtaining a 3D image of the heart and getting both morphological and functional information, and "true" 3D data sets that might show a beating heart in a single breath hold.
Siemens Medical Systems Inc.'s (Iselin, N.J.) 3D Virtuoso is a new diagnostic tool that is being used by The Methodist Hospital (Houston) for diagnosis and treatment of vascular disease. Michel Mawad, M.D., professor of
radiology, neurosurgery, neurology and ophthalmology at Baylor College of Medicine (Houston), and director of neuroradiology at The Methodist Hospital, is conducting a pilot study to explore the usefulness of 3D angiography and how it correlates with an MRI of the brain and functional imaging.
Mawad is studying patients with intercranial arteriovenous malformations (AVM) utilizing 3D MRI data sets of the brain with MRAs and 3D angiography. The main goal is to treat the malformation, but it is also to obtain information on the functionality of the cortex and to minimize the risk of endovascular treatment.
Siemens' 3D Virtuoso workstation allows
physicians to view vascular structures
in depth from any angle.
3D angiography "has brought new horizons to the evaluation and treatment of intercranial and vascular disease, such as artero-venous malformation and aneurysms," says Mawad. "In the case of aneurysm, it has really given us tremendous additional information that was not available with conventional two-dimensional angiography. The aneurysm can be seen easier in its relationship to the rest of the anatomy, so that physicians know the most effective way to treat it.
In studying AVM, Mawad can see the arteries that support the malformation, the presence of intranidal aneurysms, and differentiate between arteries and veins in the nidus.
Richard Ruoff, Siemens' product manager for angiography systems in the U.S., says that 3D imaging is becoming more popular in a clinical setting. There is immediate feedback from the scan, less inconvenience to the patient, and faster reconstruction times that allows for manipulation in post-processing. To date, Siemens has sold 70 systems for angiography.
3D MRI for breast imaging
A breakthrough in breast imaging that involves a core biopsy under MRI guidance could prove to be a lifesaver for many women. Diane Georgian-Smith, M.D., head of breast imaging at University of Washington (Seattle), has begun clinical use of this procedure in the last eight months and is pleased with the results. Because of MRI's extreme sensitivity, it is being used by Georgian-Smith to presurgically evaluate a tumor's extent. This method seems to be finding malignant tumors that cannot be detected by other modalities, thus changing surgical management. Georgian-Smith is looking for ways to do sampling to rule out false positives, and to place a marker by the tumor for surgery guidance to determine if the mass is malignant.
She is following studies in Germany that are using 3D as a screening test for asymptomatic high-risk women, such as those who have the breast cancer genes, BRCA 1 and 2. It is still investigational, but has potential because of the lack of radiation exposure to the patient. The studies hope to discover if MRI will, in fact, be useful in screening for breast cancer.
The future of MRI in breast cancer screening and treatment may include treatment ablation, where a probe might be placed in the tumor to destroy it by heat or freezing within the breast tissue, or a less invasive way to remove lesions without surgery.
3D CT expands
The use of 3D computed tomography has changed the way hospitals are interpreting exams. The University of Iowa Department of Radiology (Iowa City, Iowa) is using a Toshiba Aquilion multislice CT scanner and post-processing workstations for almost all of its exams, and it is creating 3D images for physicians to evaluate their patients. In an effort to better serve the physicians, Michael W. Vannier, M.D., professor and chairman, reviews all of the image sets and critiques the quality of the images weekly. He is trying to develop motion sequences that can be made available on a Web server, along with other images and files, for physicians to download from other locations. Vannier had the CT scanner moved to the ER recently in an effort to better serve both the patients and the hospital.
"In the emergency room, we think this multislice scanner, combined with the post-processing, may eliminate the need for almost all of what radiology did there in the past," he said. "It's going to have a change in everything that we do. We have to rewrite all of our protocols and ... it's not just the protocols by which you collect the images, but it's also the way you think about dealing with common problems that you encounter in everyday radiology," says Vannier.
Some patients requiring a colonoscopy for colorectal cancer screening will soon be able to take advantage of a new procedure called computed tomographic colonography (CTC). Ronald Bleday, M.D., assistant professor of surgery at Harvard Medical School, Boston, is using the new method himself and believes that every new physician should be made aware of it. A bowel prep is still necessary, but this less invasive procedure uses a CT to scan the abdomen and colon rather than a colonoscope. It is expected to be most useful in low- to medium-risk patients. The results of the exam need to be done by a radiology specialist because it is currently difficult to interpret.
"It is not something that you can just take a course in and become good at. It is something that requires a fair amount of experience in interpreting, so it is something that, at least initially, medium to larger radiology departments should pick who should be the one to do this. On the clinical side, surgeons or gastroenterologists who have the patients who would benefit from this exam need to be taught when to use it and what's the proper use of it," Bleday says.
Rensselaer Polytechnic Institute's Visible Photographic Man (VIP-Man) mimics the effects of radiation on the most sensitive parts of the human body, such as the skin, lens of the eye and optic nerve.
The study done at Harvard found that, of the patients who had surgery or colonoscopy, their CTC results regarding the cancer stage and size correlated with the pathological findings.
Bleday is organizing quality control and training radiologists to read the results of the exam, and expects it will be a couple of years before a necessary multi-institutional study is done. The procedure will be even more effective when oncology protocols catch up with the imaging, he says.
New applications could include staging colon cancer pre-operatively. Bleday has done a small study that determined whether the cancer invaded the colonic wall or if there were associated lymph nodes. He hopes that his research will help with pre-operative staging of colon and rectal cancer, screening obstructing lesions upstream, and determining where the risks and benefits are to the general population.
Contrast in volume ultrasound
The newest dimension of ultrasound is to collect information in a volume set. Barry Goldberg, M.D., director of diagnostic ultrasound at Thomas Jefferson University Hospital (Philadelphia), is exploring how ultrasound images parts of the body, with regard to how effective contrast agents are in ultrasound. Goldberg believes that by using 3D ultrasound, valuable information can be collected on vascularity of tumors to present a clearer picture of abnormalities. By using contrast agents to enhance ultrasound, he is able to see smaller vessels and can study the pathways of vessels that are normally out of plane with 2D ultrasound, allowing for improved analysis of vascularity. This should help differentiate benign and malignant tumors. Human trials to view breast tumors have been ongoing for three years, and in the last year, liver and renal tumors have been viewed as well.
"We feel that in the future, with new technologies, evaluating over time the effectiveness of treatment is going to be very important, and being able to study the volume, is going to be key," says Goldberg.
The virtual human and radiation
At Rensselaer Polytechnic Institute (Troy, N.Y.), George Xu, assistant professor of nuclear engineering and engineering physics, has used original CT, MRI and photo images and data from the National Library of Medicine to create the Visible Photographic Man (VIP-Man), a 3D virtual man that mimics the effects of radiation on the most sensitive parts of the human body: the skin, lens of the eye, optic nerve, GI-tract mucus membranes and bone marrow.
The images come from an undertaking called The Human Project, in which male and female cadavers are scanned by CT and MRI units, creating images never before possible, explains Xu. The photos, as well as CT and MRI scans, were used to form a composite man.
In radiation therapy, a tumor is viewed with CT and MRI images, which recently have been coupled to computer codes that specify how much radiation is necessary and how to deliver it, says Xu. The VIP-Man project uses a whole-body image rather than MRI and CT scans alone and pairs the image with "Monte Carlo calculations" — a type of computer simulation that uses random numbers to come up with a result — to discover how much radiation would affect the surrounding sensitive areas. Xu speculates that the model would be of most interest to hospitals providing radiotherapy to patients and radiation risk assessment organizations for use with nuclear energy powerplant workers and X-ray technicians.
The VIP-Man is already being tested with radio-oncologists at Albany (New York) Medical Center. For their final thesis project, two of Xu's graduate students used VIP-Man as a patient. The students used traditional calculations for figuring radiation dosage and Xu used VIP-Man and the computer code calculations. Then they compared results.
"We are finding that the results are quite different. Now, whether that is clinically solvent, we don't know yet, but the results are very different. It is clear to us that if they can somehow use the method we developed, they can improve the radiation treatment of patients, there is no question about it." says Xu.
Xu hopes that Albany Medical Center will use the new technology on a routine basis in the next few years, especially since patients will benefit from more accurate treatment.
Benefits to all
3D imaging has many benefits for the medical community as well as the patient community. Goldberg sees more companies getting involved in 3D technology. "I think that [3D imaging] will be an important component. It depends on how rapidly 3D comes along, and [how] the technology advances … I would predict that all machines in the future would have 3D capabilities," he says. This can only mean more efficient hospitals and clinics, more accurate diagnosis by the physician and ultimately, better care for the patient.
