Of today’s leading medical specialties, interventional radiology could well occupy center stage this year as innovations in medical device technology and enhancements to existing imaging modalities drive a rapidly growing array of minimally invasive new procedures that promise to dramatically improve outcomes as well as reduce costs. That is a remarkable accomplishment for a branch of radiology that was born in the mid-1970s, earned American Medical Association specialty recognition in 1992, and today numbers more than 5,000 practitioners worldwide, according to the Society of Cardiovascular and Interventional Radiology (SCVIR), Fairfax, VA.
Relying on MRI, CT, fluoroscopy, and ultrasound, interventional radiology activities now encompass a virtual alphabet of traditional and emerging procedures including:
- Balloon angioplasty
- Biliary drainage and stenting
- Central venous access
- Fallopian tube catheterization
- Gastrostomy tube placement
- Hemodialysis access maintenance
- Needle biopsy
- Transjugular intrahepatic portosystemic shunts (TIPS)
- Uterine artery (fibroid) embolization
- Varicocele embolization
- Vena cava filter placement
The frontiers of existing diagnostic imaging technology continue to expand as interventionists and device-makers create increasingly sophisticated enhancements to conventional equipment even as new catheter, balloon, and stent designs facilitate increasingly less invasive interventions. Indeed, minimally invasive interventions will likely characterize the field for years as hospitals, third-party payors, Medicare, and patients more fully realize the benefits of reduced morbidity, mortality, and cost as well as improved clinical outcome.
Experts acknowledge that as radiologists expand their traditional diagnostic and interventional domains from specific anatomic regions to organs and vessels throughout the body, decisions to determine which medical specialties will hold hegemony over particular procedures will have to be addressed to ensure quality and safety. Negotiation and cooperation between specialty societies as well as strong hospital credentialing and privileging committees will likely be necessary to ensure clinical collaboration rather than controversy and competition. Their goal will be to ensure that every hospital maintains a staff of appropriately qualified and experienced practitioners to meet clinical need. Achieving that goal may be difficult as new minimally invasive interventions enter territories dominated by cardiology, vascular surgery, gynecology, gastroenterology, and general surgery (see related article).
As minimally invasive diagnostic and therapeutic techniques proliferate, there are bound to be decreases in some of interventional radiology’s most traditional procedures and increases in others.
“Patients increasingly are being evaluated with noninvasive imaging — duplex ultrasound, magnetic resonance angiography (MRA) — and therefore, fewer diagnostic angiograms are being performed,” says David Sacks, MD, of Reading Hospital and Medical Center (Reading, PA), where he is head of interventional radiology.
It is an opinion shared by many interventionists. Mark H. Wholey, MD, of the Pittsburgh Vascular Institute and chief of radiology for Shadyside Hospital of the University of Pittsburgh Medical Center — who describes himself as a “100% cardiovascular interventional radiologist” — is among them.
“The introduction of 3-D computed tomographic angiography (CTA) and MRA could result in a 10% to 15% decline in diagnostic angiography in the next few years,” Wholey believes. “Depending on how sophisticated MRA becomes, activity could drop as much as 25% to 30%,” he predicts.
From his vantage point as chairman of the SCVIR Technology Assessment Committee and as a member of the group’s Standards of Practice Committee, Sacks perceives several emerging trends and new procedures.
“We are doing fewer biliary drainages than in the past because endoscopists are becoming increasingly skilled, therefore the procedures that people are doing today tend to be more technically difficult, as with patients whose cancers are higher up in the liver,” Sacks indicates.
To the relief of many interventionists, the number of lymphangiograms — often characterized as one of the most tedious and onerous of all procedures — is also dropping, according to Sacks. The image of “trying to thread a needle into a hair” comes to mind. He attributes the decline to improvements in CT and MRI, noting that the presence of metastatic disease in the lymph nodes now can be accurately confirmed noninvasively.
Far more dramatic than the declines, however, are emerging new procedures that are well suited to the interventional radiologist’s skills. Indeed, improvements in balloon, catheter, and stent designs in tandem with advances in real-time MRI, CT, ultrasound, and high-speed 3-D reconstruction and display capabilities are facilitating minimally invasive interventions from head to toe.
Sacks and his associates describe percutaneous vertebroplasty for the treatment of osteoporosis-related compression fractures of the spine as an exciting new interventional procedure that is gaining acceptance. A biopsy needle is placed into the vertebral body and bone cement is then injected to stabilize and strengthen the compressed bone.
“People usually have relief from pain within 24 hours or less,” Sacks indicates, in contrast to standard therapy that consists of analgesics, weeks of bed rest, physical therapy, and back braces. “The procedure can usually be done on an outpatient basis in less than an hour for both benign and malignant spinal compression fractures,” he added.
Fibroid arterial embolization represents new ground for interventional radiologists. Many women with symptoms of uterine fibroids do not consider hysterectomy an option. Fibroid tumors are far more sensitive to being deprived of blood flow than normal uterine tissue, Sacks explains.
“When you deprive the uterus of blood flow, you have an almost selective effect on fibroids,” he explains. “The uterus in general remains unharmed and the fibroids begin to shrink away.” Approximately 4,000 fibroid embolizations have been performed nationwide with relief of uterine bleeding, cramping, and pain 80% to 90% of the time.
Sacks notes that chemoembolization of liver tumors is also a growing area of interest. A catheter is guided into the tumor and particles of sponge are introduced in combination with chemotherapy agents. The resulting emboli cause the blood flow to slow in the liver, trapping the cytotoxic agents within the tumor.
“This technique has shown definite effectiveness in treating primary liver tumors and it is promising but unproven for the treatment of metastatic liver tumors,” he notes.
The treatment of stroke with catheter-directed thrombolytics is another new procedure that shows significant promise. Unlike the conventional intravenous administration of tissue plasminogen activator (TPA), which dilutes before reaching a clot, the placement of a catheter into the thrombus with imaging-based guidance can substantially speed up clot dissolution and improve the chance of recovery, experts say.
Studies of intravenous TPA therapy for stroke demonstrate that the greatest benefits are achieved only if treatment begins within 3 hours of symptom onset — an unlikely scenario for most patients. The Journal of the American Medical Association recently published results of the PROACT study showing that significant improvements were achieved in stroke symptoms if patients were treated with catheter-directed drug administration within a 6-hour window.(1)
“Doubling the time window increases the number of patients who qualify by more than double,” Sacks explains, “because it is very hard to get to the emergency room within 2 hours. That leaves 1 hour for ER staff evaluation, a trip to radiology for a CT scan to ensure that a clot is present rather than a hemorrhage, and return to the ER for treatment. I estimate that five times more patients will qualify for treatment with intra-arterial drug as opposed to intravenous drug,” he says.
Radiofrequency (RF) interstitial thermal ablation under real-time MRI guidance is a relatively new area for interventional radiology, according to Jonathan S. Lewin, MD, associate professor of radiology, oncology, and neurological surgery and Vice-Chairman for Research and Academic Affairs at Case Western Reserve University (Cleveland). He is also director of MRI at University Hospitals of Cleveland.
Over the last 4 years, Lewin and his colleagues have successfully utilized interventional MRI for guiding RF tumor ablations in the liver, kidney, retroperitoneum, bone, and other sites.
“Using a fairly standard open magnet and some interventional accessories, we percutaneously place an electrode directly into the tumor and use an RF generator to heat it and the surrounding tissue. The key,” Lewin explains, “is that MRI is intrinsically sensitive to temperature and to the changes that accompany tissue necrosis. As treatment progresses, real-time MRI enables me to tailor the thermal lesion to the size and shape of the tumor.”
One of Lewin’s interventional systems is located within the hospital MRI center and is generally used to scan claustrophobic patients. An afternoon procedure slot has enabled him to perform about 400 interventional procedures — including biopsies, drainages, and injections — under real-time MRI guidance. Lewin reports that a colleague in musculoskeletal radiology also utilizes the system at least weekly to do piriformis injections for the treatment of nondiscogenic sciatica.
Lewin installed a second interventional MRI suite in an operating room (OR). It meets all hospital OR specifications.
“The only difference is a 0.2-T open MR imager in the middle of the room and a prototype table that doubles for conventional surgery as well as scanning,” he says. “We have done about 45 neurosurgical procedures to date, and although it is not really an interventional radiology technology, it is a tremendous leap forward in intraoperative imaging. That type of room costs about $1.5 million to build.”
FURTHER MR APPLICATIONS
In addition to his tumor ablation work, Lewin has applied interventional MRI technology to sclerotherapy for low-flow vascular malformations for more than 2 years.
“I essentially use MRI to guide a needle into a low-flow vascular malformation,” he explains. “Then I inject a sclerosing agent, which causes the abnormal vessels to clot off and essentially fibrose down. Although other imaging modalities are also used, MRI with contrast is particularly well suited for this procedure. Because of the very high vascular conspicuity of MRI, I can inject gadolinium very precisely and see exactly how thoroughly I have closed down a malformation’s various feeders.
“Unlike when using fluoroscopy, I can also see the different components of the lesion before I puncture them,” he adds, “and we avoid exposure to ionizing radiation.”
The interventional MRI project at University Hospitals of Cleveland began in 1993; Lewin’s group has collaborated extensively with one manufacturer to develop an FDA-approved interventional package and with another company to develop an MR-compatible RF generator.
“When tumors are ablated, patients clearly prefer a percutaneous, same-day outpatient procedure rather than a larger surgical operation,” Lewin says. “Some data suggest that we may be able to obtain cure rates similar to those of surgery, but that will require ongoing investigation and larger clinical trials.”
Lewin and other interventionists also point to successes in treating intracranial aneurysms with a recently approved embolization technology in which detachable coils are introduced intravascularly with microcatheters as opposed to an open craniotomy.
“It is a tremendous technology that has really changed the way cerebral aneurysms are treated at most large centers,” he comments, “even though it has been around only a few years.”
IMAGING OPTIMIZES PLACEMENT
Sacks and Lewin also point to a growing trend in the amount of venous access work being done by interventional radiologists. More than simply starting intravenous lines, procedures include difficult peripherally inserted central catheter (PICC) line placements, implantable chemotherapy ports, and the insertion of tunnel catheters for chemotherapy or hyperalimentation, procedures historically performed by surgeons in the OR.
Sacks and other interventionists attribute the increase to superb imaging that results in optimal placement, which in turn reduces complications and increases the chances that catheters and ports will remain functional for a longer period of time. Interventional radiologists can also provide alternative routes of venous access such as percutaneously through the liver or through the back.
“Now that aortic stent grafts have been approved, I think that many hospitals will soon design angiographic rooms that can be used as surgical suites to place stent grafts,” Sacks predicts. “Many facilities are buying high-quality C-arms to use in the OR. Although those C-arms are of much better quality than in the past, they still are not going to offer the same imaging quality that you get in high-end angiographic rooms.”
According to Sacks, some hospitals are already designing their angiographic rooms to meet OR specifications, including requirements for air exchanges, positive pressure, air filtration, suction devices, oxygen lines, and anesthesia lines.
“The angiographic room 5 years from now will probably also switch to flat-field technology,” he hints. “Image intensifiers will probably become flat-field like laptop computer displays, possibly reducing maintenance while making them lighter and more versatile.”
While many of the new interventional radiology procedures should be performed in a hospital, a growing number may soon become available in outpatient clinics and freestanding centers. Lewin points out that even MRI-guided tumor ablation can be done outside the hospital, although he concedes that it is wise to be geographically close to one in case of complications. Biopsies, chemoablations, sclerotherapies, piriformis injections, and other procedures, however, can easily be performed off-site.
“Private practice or university-affiliated outpatient centers could easily be performing many of these procedures,” he says. There are growing concerns, however, that the use of new clinical procedures may be expanding too rapidly because of market forces and financial incentives rather than best practices considerations.
The growth in interventional procedures, according to Wholey, is being fueled by the rapid growth of minimally invasive techniques to manage vascular diseases. Cardiologists — who control the majority of patient volumes — have taken an especially serious interest in interventional peripheral procedures. Moreover, cardiologists and vascular surgeons are vitally interested in the minimally invasive management of abdominal aortic aneurysms with the new endoluminal aortic stent grafts and in the possible prevention of strokes with carotid stents rather than carotid endarterectomy.
“There is growing literature and a significant amount of data that would indicate that stenting — as done in the coronary arteries — can now be done for the carotids,” Wholey explains. “Approximately 10,000 procedures have been done worldwide and at least the early published morbidity and mortality figures — although they are only from registry and nonrandomized trials — suggest that this procedure may be as effective as and perhaps in some situations be superior to surgery.”
CAROTID STENTING CONTROVERSY
Carotid stenting is controversial, however, because many experts are concerned that it is being offered as a routine clinical procedure by a growing number of practitioners in the absence of appropriate randomized clinical trials. The American Heart Association and SCVIR officially consider carotid stenting an investigational technique that should be performed almost exclusively in the setting of research trials, Sacks says.
“It is unfortunately being offered very frequently as part of clinical care despite the fact that Medicare specifically excludes payment for angioplasty or stenting of the carotid bifurcation for routine clinical use. If you incorrectly call it something else, however, such as brachiocephalic angioplasty, it becomes payable,” he indicates.
A large, randomized clinical trial comparing carotid stenting with endarterectomy will soon begin. Wholey, one of the principal investigators in that National Institutes of Health-sponsored multicenter clinical trial, agrees that more research must be done before drawing conclusions that could alter the gold standard for stroke prevention.
The experts acknowledge that although ultrasound and CT fluoroscopy have continued to improve technically, the types of procedures they support have not really changed much based on technological advances. The advent of the multislice CT scanner may prove to be an exception, according to Lewin.
“It is a quantum leap of sorts in CT technology,” he indicates. “It allows us to do a bolus scan of the whole body in a breath-hold — a whole chest-abdomen-pelvis scan can now be done in 23 seconds. The resolution is incredible and one can do 3-D reformatting with wonderful image quality. Although it has not made the leap into intervention yet, it is clearly possible that it can have some impact on interventional procedures,” he states.
As is almost always the case, many of the new procedures reach clinical practice well ahead of the new reimbursement codes needed to support proliferation. Lewin, vice-chairman of the Intervention Study Group of the International Society of Magnetic Resonance in Medicine (ISMRM), points out that ISMRM and the American Society of Neuroradiology are working with the Health Care Financing Administration to come up with the necessary codes.
“I may spend an hour helping to determine the place to scan, helping to conduct the scan, helping to interpret it, and helping the neurosurgeon plan where further surgery may be needed,” Lewin says. “I will be reimbursed only for interpreting a standard MRI of the head with contrast because there are no billing codes for ‘intra-operative consultation for MRI.’ No codes exist for many of the interventional MRI procedures we do, so we bill them as best as we can,” he adds. “Consequently, I believe we are significantly under-reimbursed for some of our new procedures.”
Wholey is more blunt in his assessment: “The problem is that insurers are having more to say about the control of the patient and the choice of the physician,” he says. “They do not have front-edge technology assessment teams. Rather, they have clerks and primary care physicians making decisions on the treatment of aneurysms. They would rather subject a patient to aneurysmectomy — a major surgery with all its morbidity and 6 months of recovery time — rather than reimburse for noninvasive therapy at the outset and avoid a lengthy appeals process. It borders on the criminal in some cases.”
Nevertheless, the field of interventional radiology is poised to continue growing in terms of procedures as well as practitioners. While friction between interventional radiologists and other specialists may be inevitable as the groups decide who should perform which procedures, many experts believe that training, experience, skill, and mutual respect will ensure that quality care and clinical outcome remain everyone’s concern.
Sheldon M. Stern is a freelance medical writer in Irvine, Calif, and a contributing writer for Decisions in Axis Imaging News.