BB&T Contributing Editor

SAN DIEGO – The 2009 annual scientific meeting of the Society of Interventional Radiology (SIR; Fairfax, Virginia), held here in early March, provided a venue for leading physicians in this diverse specialty to present the latest developments in the field. Interventional radiology covers a wide variety of clinical applications in diagnosis and treatment of vascular disease, cancer, orthopedic disorders, urological disease, and neurological disease, and new developments in all of those areas were described at the SIR conference.

In spite of the slowdown in the economy, this year's conference was the largest of the past decade, indicating the robust demand for the services provided by interventionalists, which in turn is being driven by the trend toward increased patient preference for minimally invasive therapies. Important technology-based advances in cancer therapy were described that promise to enable more precise, targeted eradication of solid tumors, minimizing damage to adjoining healthy tissue and reducing treatment-related morbidity compared to open surgery.

In orthopedics, there also is strong momentum underlying the movement to less-invasive therapies, particularly for spinal disorders, which is creating growing demand for devices that can enable conversion of conventional surgery to minimally invasive procedures. Vascular therapy, which was one of the first areas in which interventional techniques were applied, is continuing to evolve, with advances including the use of drug-eluting stents for treating difficult peripheral lesions as well as the development of cell-based therapies for revascularization.

While there are clearly limits on the range of pathologies which can be addressed by interventional technologies, at least at their existing stage of development, the trend is toward a growing role for interventional radiology in healthcare.

Cancer management applications expand

The treatment of cancer represents a growing application for interventional radiology. Although total cancer incidence in the U.S. declined in 2008 compared to 2007 based on data from the American Cancer Society (Atlanta, Georgia), procedure volumes for cancer treatments are increasing in interventional radiology as applications expand to encompass a wider range of cancer types. The primary types of cancer treated with IR methods are liver, kidney and prostate cancer. Treatment modalities include a variety of percutaneous ablation techniques such as radiofrequency ablation (RFA), cryoablation, microwave ablation, and high-intensity focused ultrasound (HIFU) as well as transcatheter techniques including transarterial embolization and chemoembolization (TAE and TACE). Increasingly, those techniques are being employed in the treatment of other high-incidence cancer types including lung and breast cancer.

As shown in Table 1 on page 8, the number of new cases for the cancer types treated with IR techniques accounts for almost half of all new cases in the U.S., and over one-third of all cases worldwide. Prostate cancer, for example, is now treatable with a number of minimally invasive techniques employed by both interventional radiologists and urologists.

At the SIR conference, Dr. Gary Onik of the Center for Safer Prostate Cancer Therapy (Orlando, Florida) described the use of "male lumpectomy", or focused cryoablation therapy, for prostate cancer. Data from patient outcome studies performed by Onik over the past 12 years show that focal cryoablation is equivalent to other more invasive therapies including surgical (radical prostatectomy), radiation, and hormone therapy in terms of recurrence rates, but with reduced side effects such as incontinence and impotence.

Onik also described a 3-D mapping technique for diagnosis and staging of prostate cancer which improves accuracy and complements focal ablation treatment by enabling the tumor to be located more precisely and by detecting small tumor foci which can be missed by conventional transurethral ultrasound-guided (TRUS) biopsy. 3-D transperineal biopsy is performed using a sampling grid and ultrasound imaging to collect up to 50 biopsy cores, compared to 10-12 collected in a TRUS procedure.

The improved accuracy afforded by 3-D mapping is increasingly important as more options for treatment become available, enabling the optimum method to be selected for each patient. Onik has found that 3-D mapping can result in a significant change in therapeutic strategy versus that determined by TRUS. In some patients, watchful waiting can be employed rather than radical prostatectomy, while in others 3-D mapping shows more extensive cancer requiring more aggressive treatment than indicated by TRUS biopsy.

The combination of 3-D mapping with selective cryoablation provides a highly effective and less-invasive approach for prostate cancer treatment with reduced complications, even for those cases that now are treated with radical prostatectomy. Onik has demonstrated a 95% success rate for treatment of high-risk patients versus 45% for radical prostatectomy at 100 months, with 100% continence in the cryoablation group.

The two primary suppliers of cryoablation systems, Endocare (Irvine, California) and Galil Medical (Yokneam, Israel), are set to merge following the signing of an agreement in November of last year. The combined companies will account for more than 95% of the cryoablation market, and will have pro forma revenue of about $56 million. The company will be majority-owned by Endocare shareholders.

For the year ended Dec. 31, 2008, Endocare reported cryoablation product sales of $45.14 million, down slightly from 2007. Endocare's domestic cryoablation procedures also dropped slightly from 9,373 in 2007 to 9,358 in 2008. To expand sales, the company is focusing on extending the range of applications to include kidney cancer ablation and treatment of metastatic bone cancer, the latter representing an opportunity of an estimated 100,000 patients per year who develop bone metastases, as well as lung and liver cancer.

In addition, a second-generation cryoablation technology, Near Critical Nitrogen technology, is under development that may allow smaller cryoablation probes to be developed, or conversely enable more rapid freezing to be achieved, shortening procedure time.

Christos Georgiades, MD, PhD, of Johns Hopkins Hospital (Baltimore), discussed the use of cryoablation for treatment of kidney cancer at the SIR meeting, providing an update on preliminary data presented at last year's conference. Georgiades has treated 84 patients with renal cancer using cryoablation, and by April had followed the patients for an average of three years. The latest data show that 98% of the patients have no evidence of disease. Of the two patients who developed recurrences, one has been re-treated, an option that is readily available with cryotherapy due to its minimal invasiveness and its ability to physically ablate all types of soft tissue.

Certain other treatment modalities, notably radiation and chemotherapy, can lose effectiveness with multiple uses as resistance develops. Georgiades has treated kidney tumors up to 10 cm in diameter with cryoablation, with a 100% response rate for those of 4 cm diameter or less and good results for larger tumors. Cryoablation is now the first line of treatment for patients with small kidney tumors at Johns Hopkins, replacing laparoscopic surgery, which can result in a multi-day hospital stay and a recovery period of two to four weeks, with an outpatient procedure.

Lung cancer represents a large potential market opportunity for cancer ablation technology, accounting for about 13% of all new cancer cases worldwide. The primary ablation modality in use for lung cancer at present is RFA, using systems such as the CoolTip RF from Covidien (Mansfield, Massachusetts) and the RF 3000 from Boston Scientific (Natick, Massachusetts).

At least 1,000 patients with lung tumors have now been treated with RFA in reported studies. As discussed by Terrance Healey, MD, of Massachusetts General Hospital (Boston), at the SIR conference, RFA therapy can result in an improved quality of life for inoperable lung cancer patients, and is effective in preventing recurrence particularly for tumors of 3 cm in diameter or less. Using the CoolTip RF system under PET-CT guidance, local progression of RFA-treated lung tumors was 28.8% in a study conducted by Healey.

Further improvement in response can be achieved by combining RFA with other therapies such as external beam radiation therapy. Tissues in an approximately 1 cm zone surrounding the region of complete RF ablation become more sensitive to other modalities even though they survive the initial treatment. Consequently, one new approach being evaluated in lung cancer is to first ablate the primary tumor with RFA, and then follow up with image-guided radiotherapy in the surrounding zone to kill any residual tumor cells in the margin. That approach can provide good local control of the primary tumor, although it is not considered a replacement for surgical resection since the adjoining lymph nodes are not resected as is typically done with surgery. For lung cancer with no nodal disease, however, the approach can be curative and allow the patient to avoid surgery and its associated morbidity.

A similar approach is being employed for liver cancer in which RFA is combined with chemotherapy using targeted agents such as Avastin from Genentech (South San Francisco, California) to eradicate residual tumor cells in the zone surrounding the region of RF ablation. Ablation is often the therapy of choice for liver cancer, since 80% to 90% of patients are ineligible for surgery when diagnosed.

Yet another novel approach combines RFA with heat-activated liposomal doxorubicin capsules for liver cancer treatment. The ThermoDox capsules, developed by Celsion (Columbia, Maryland), are engineered to release doxorubicin locally at temperatures above 39.5 C, and can be infused intravenously and activated locally via RFA.

As discussed by Bradford Wood, MD, of the National Institutes of Health (Bethesda, Maryland), at the SIR conference, a Phase III trial combining RFA and ThermoDox for the treatment of advanced liver cancer is now enrolling patients. ThermoDox also is being studied for use in conjunction with microwave treatment for breast cancer.

The newest interventional ablation technology, attracting a significant amount of attention at the SIR conference, is irreversible electroporation (IRE), which is being commercialized by AngioDynamics (Queensbury, New York) as the NanoKnife. The technology underlying the NanoKnife is not new, having been first demonstrated in the 1960s. It is already in use for treatment of skin cancer in Europe, where it is applied in concert with bleomycin to preferentially kill tumor cells. IRE is also commercially available for non-medical applications such as sterilization of surfaces.

The NanoKnife was developed initially by Oncobionic, a company that was acquired by AngioDynamics in May 2008. IRE acts on cells not by heat or cold but rather by disrupting cell membranes, causing a metabolic imbalance that results in apoptosis (cell death). Cellular architecture is preserved, but the cells are no longer alive.

The NanoKnife system consists of a generator (essentially a large capacitor on wheels) and two or more needle electrodes ranging in diameter from 16 gauge to 19 gauge and 18 cm in length which are inserted percutaneously at the tumor site with a spacing of less than 3 cm. A series of very short (100 microsecond) electrical pulses are applied between the electrodes to the tissue, typically at a voltage of 1,500 to 3,000 volts. Eighty to 90 pulses are usually delivered in bursts of 10, requiring about 45 seconds to treat a spherical region of 2.5 cm in diameter. Multiple overlapping zones can be created to treat larger tumors. Cell death occurs rapidly, within 24 hours, and the dead tissue is subsequently cleared by natural processes in about 14 days.

Very sharp margins can be obtained between treated and untreated tissue regions, potentially making IRE more precise than RFA or cryotherapy. The pulsating voltage causes spasm, so patients are given muscle relaxants to paralyze the treated region. Particularly when treating areas around the heart, it is possible to induce arrhythmias, but that is being addressed by synchronizing the applied pulses with the heartbeat. So far, patients with pacemaker implants have not been treated with the NanoKnife.

In clinical studies performed so far, cancer types treated with the NanoKnife have included prostate, liver, kidney and lung. The technology has been shown to be safe in studies involving a total of 44 patients to date, and the NanoKnife has been cleared by the FDA for soft tissue ablation. A study now ongoing in Italy is employing the NanoKnife for prostate cancer treatment.

Randomized clinical trials comparing IRE to other accepted treatment modalities in specific cancer types will be needed to gain widespread acceptance, particularly in the U.S. One such trial was to begin in about a month, according to Ken Thomson, MD, of The Alfred Hospital (Melbourne, Australia), who has used the NanoKnife to treat a variety of cancer types including liver, kidney, and lung. In addition, as discussed by Stephen Kee, MD, of UCLA Medical Center (Los Angeles), at the conference, AngioDynamics has filed an IDE to begin trials in the U.S.

Advantages of the NanoKnife compared to other ablation technologies such as RFA, microwave and cryoablation include the lack of a heat-sink effect, since IRE does not depend on heating or cooling of tissue; the short treatment time of less than one minute; the ability to ablate large areas including the entire prostate gland; low levels of post-procedural pain; and rapid recovery.

A potential disadvantage is cost, since the disposable electrodes cost about $2,000 and the generator is priced at $400,000, while reimbursement for an entire ablation procedure using a competing technology such as cryoablation is only $1,200. Furthermore, efficacy of IRE in achieving tumor eradication with low recurrence rates equivalent to those for completing ablation modalities will need to be demonstrated.

Orthopedic interventions grow

Another growing application for interventional radiology is treatment of orthopedic disorders, particularly for disorders of the spine. As shown in Table 2 on page 10, about 1.3 million spinal surgery procedures are performed annually in the U.S. which can utilize minimally invasive techniques. At present, most of those procedures are performed via open surgery, although an increasing proportion of procedures for treating vertebral compression fractures are performed with interventional techniques such as vertebroplasty and kyphoplasty.

According to data from the National Center for Health Statistics, there were 47,000 kyphoplasty procedures and 18,000 vertebroplasty procedures performed in hospitals and ambulatory surgery centers in the U.S. in 2006. Some547,000 people suffered vertebral compression fractures in the U.S. in 2005, according to the National Osteoporosis Foundation (Washington), and the number of fractures is expected to increase as the population ages.

Although vertebroplasty was the first interventional technology to be widely employed, kyphoplasty is now the leading technology for interventional treatment of vertebral compression fractures. While a number of kyphoplasty technologies exist, the dominant product is the Kyphx family of balloon kyphoplasty devices from Kyphon (Fremont, California), a unit of Medtronic (Minneapolis).

Key features of kyphoplasty include the creation of a cavity within the vertebral body, using bilateral balloon expansion in the case of the Kyphon technique, allowing low-pressure injection of cement which cures to provide internal support and stabilization of the fracture, as well as height restoration in patients whose spinal anatomy has become distorted as a result of a fracture. Due to the low pressure used for cement injection, leakage of cement into non-targeted areas, as has occurred in some vertebroplasty procedures, is minimized.

New developments in vertebroplasty technology, however, may revive physician interest in that technique. At the SIR conference, the DePuy Spine (Raynham, Massachusetts) unit of Johnson & Johnson (New Brunswick, New Jersey) exhibited the Confidence system, a vertebroplasty delivery system and cement which features much higher viscosity than prior-generation cements used for vertebroplasty. Introduced in mid-2008 in the U.S. market, Confidence was developed by Disc-O-Tech, a now-defunct Israeli company, acquired by Kyphon, and divested to DePuy as a condition of Medtronic's acquisition of Kyphon.

A study presented at the SIR conference by Bassem Georgy, MD, of UCSD Medical Center (San Diego), evaluated kyphoplasty vs. vertebroplasty using the Confidence system in a total of 75 patients and found equivalent leakage rates for the two systems. The results prompted Georgy to conclude that cavity creation as is performed in kyphoplasty may not play a role in limiting leakage. Rather, the use of a high-viscosity cement and matching delivery system is the key factor. With previous lower-viscosity cements, Georgy had experienced leakage rates of up to 40% compared to 12% for kyphoplasty.

Another new cement for use in treating vertebral compression fractures, Cerament, is under development by Bone Support AB (Lund, Sweden). The material is already cleared for use by the FDA as a bone void filler, and has the CE mark in Europe for use in vertebroplasty. A key advantage of Cerament is its partly bioabsorbable characteristic. The product consists of calcium sulphate hemihydrate and hydroxyl apatite mixed with a radiocontrast agent (Iohexol).

After injection, the contrast agent diffuses away and the calcium sulphate component bioabsorbs over a period of six months, to be replaced by in-growth of new bone. The resulting matrix has mechanical properties that closely match those of trabecular bone, minimizing the mismatch which results with the use of prior-generation cements and in principle reducing the risk of compression fractures in adjacent vertebrae. A study conducted by Paul Hatten, MD, of Indian River Radiology (Vero Beach, Florida) of 13 patients treated using Cerament found complete pain relief in all patients at six month follow-up, and to date no adjacent factures have occurred.

DFine (San Jose, California) exhibited the StabiliT Vertebral Augmentation System, a new kyphoplasty system that employs radiofrequency heating and an energy-responsive PMMA-based cement (StabiliT ER) to provide improved control over cement injection. In addition, the StabiliT system includes an osteotome device used to create a cavity in the fractured vertebral body which is then filled with cement. The system was introduced in mid-2008 in the U.S., and is available for investigational use in Europe.

The StabiliT ER cement is an ultra-high viscosity material, a key factor in providing improved control. Viscosity is six-fold to 12-fold higher than most vertebroplasty cements (excluding DePuy's Confidence), and three-fold to six-fold higher than the cement used for balloon kyphoplasty.

The SPACE study, an in vitro evaluation conducted by Kieran Murphy, MD, of University Health Network (Toronto), compared RF kyphoplasty performed with the StabiliT system to conventional vertebroplasty and balloon kyphoplasty in isolated vertebral bodies subjected to a mechanical load. Murphy found that the StabiliT system provides an extra margin of safety in controlling cement deposition and minimizing extravasation, and also found that height restoration was greatest for the StabiliT system at 52% compared to 43% for balloon kyphoplasty, a difference that was not significant, and 22% for conventional vertebroplasty, a difference that was significant.

Osseon Therapeutics (Santa Rosa, California) exhibited the Osseoflex steerable vertebroplasty device at the SIR conference. The system was introduced in late 2008, and consists of a delivery system with a curvable needle that facilitates access to the entire vertebral body during a procedure. The company also has developed Osseoperm, a high-viscosity PMMA cement.

The steerable needle enables a procedure to be performed with a single puncture, versus two punctures which are often required to access the entire vertebral body. As a result, procedure time is shortened by about half. So far, the Osseoflex system, which is priced at $2,395, has been used in about 130 patients. The company also has patented and developed a steerable RF ablation device and a steerable balloon.

Another steerable vertebroplasty device, the AVAflex, has been introduced by Cardinal Health (McGaw Park, Illinois). In addition to cement injection, the AVAflex device is approved for cavity creation, enabling physicians to code the procedure as a kyphoplasty if a cavity is created into which cement is injected.

Additional new biomaterials for use in treating vertebral compression fractures as well as for osteoplasty, including prophylactic augmentation of bones, include a new nanocrystalline calcium phosphate material from ETEX (Cambridge, Massachusetts) and Cortoss, a high-strength composite from Orthovita (Malvern, Pennsylvania) engineered to mimic the characteristics of human cortical bone.

The ETEX biomaterial is a mixture of carboxymethyl cellulose and calcium phosphate that exhibits improved resistance to leakage compared to PMMA, and that provides the potential for incorporation of agents such as parathyroid hormone (PTH) to stimulate bone re-growth. In animal studies described by Murphy at the SIR conference, stimulation of bone growth using the ETEX biomaterial loaded with PTH has been demonstrated. A further advantage of the ETEX material is the lack of heat generation which occurs with PMMA-based cements as they cure.

While some physicians believe the local heating can have a therapeutic effect by ablating nerves in the vertebra to alleviate pain, Murphy believes preservation of the nerves is preferable, and that the stabilization of fractures achieved with a properly applied, biocompatible cement is sufficient to eliminate pain.

A new technology for minimally invasive treatment of degenerated spinal discs is under development by ActiveO (Salt Lake City). The AO-1000 device from ActiveO employs ozone injection into herniated lumbar discs to reduce intradisc pressures and disc volume. The system consists of a miniaturized ozone generator housed in a syringe, with an attached needle enabling ozone injection under image guidance. Ozone acts on the disc to break down proteoglycans and remove water, resulting in shrinkage of the disc and reduced internal pressure.

A review of numerous published studies of ozone treatment of herniated discs, including data on 8,000 patients, was discussed by Murphy at the conference. The studies showed an 80% probability of improvement (pain reduction) in the treated patients, and clinically significant reductions in pain scores with no serious lasting complications. Recovery times are significantly shorter compared to surgical discectomy.

The ActiveO product is now undergoing clinical trials in the U.S., and Murphy expects the device to be on the market in about 18 months. More than 20,000 patients with herniated discs have been treated with ozone injections in Europe over the past 15 years.

Less-invasive technologies providing alternatives for spinal fusion are also advancing, enabling interventional radiologists to address the large patient population with degenerative disc disease who are now treated primarily with open surgery. Interventional Spine (Irvine, California) exhibited the PERPOS PLS percutaneous transfacet-pedicular compression system for the first time at the SIR conference.

The PERPOS system is used for posterior stabilization during a lumbar spine fusion procedure, and consists of an instrument kit which includes the Teleport Tissue Retractor to provide access to the spine through a single 15 mm incision, and devices for drilling and tapping of the facet. The company's BONE-LOK implants are then inserted, which are one-size-fits-all devices that size to the appropriate length in vivo.

A second-generation device, the PercuDyn System, is on the market outside the U.S. and undergoing clinical trials in the U.S. The PercuDyn system is a percutaneous device for supporting spinal facets without fusion, avoiding significant alternation of the spinal anatomy and providing relief from back pain.

A study presented at the SIR conference by Juan Dipp, MD, of Hospital Y Centro Medico Del Prado (Tijuana, Mexico), described results in 34 patients treated with the PercuDyn System for lumbar pain. Pain relief was achieved in all patients, with a recovery time of 4-6 hours and a procedure time of only 15 minutes per level. Between one and three levels were treated, all on an outpatient basis. The Interventional Spine devices are priced competitively with the rod and screw systems employed for open spinal fusion, and have been implanted in between 5,000 and 6,000 patients in the U.S. over the past eight or nine years.

Advances in vascular therapy

Minimally invasive therapies for vascular disease are advancing on multiple fronts, including new technologies for treatment of critical limb ischemia, new miniaturized stents for treatment of cerebral aneurysms, endovascular stent-grafts for an expanding range of indications, and evolving therapies for vascular thrombosis including treatment of deep vein thrombosis. Critical limb ischemia is a significant health issue worldwide, as shown in Table 3, accounting for almost a quarter of a million amputations in the U.S. and Europe annually.

Many CLI patients are not candidates for surgical bypass, and as a result interventional radiology-based therapies are now the first line of treatment for the condition. However, interventional treatment with angioplasty and bare metal stents, while heavily relied upon for CLI patients, is far from an ideal therapeutic modality, with recurrence rates ranging from 41-66%.

At the SIR conference, Dimitri Karnabatidis, MD, PhD, of Patras University Hospital (Rion, Greece), described promising results in a single-center trial involving 103 patients treated for CLI with drug-eluting stents. The stent used in the study was the Cypher sirolimus-eluting stent from Cordis (Miami Lakes, Florida), which is CE-marked for below-the-knee use in Europe. The stents were implanted in the infrapopliteal artery, and patient outcome was compared to a control group receiving bare-metal stents.

While patient survival and limb salvage did not differ between the groups at three-year follow-up, patency was five-fold higher in the drug-eluting stent group, in-stent restenosis was 40% less, and repeat procedures were 2.5 times less (87% of patients in the drug-eluting stent group did not require repeat revascularization vs. 67% in the bare-metal stent group).

Stent fractures have been an issue with use of drug-eluting stents in the lower leg, where the devices are exposed to greater mechanical stresses than in the coronary arteries. A follow-on study by Karnabatidis evaluated the incidence of stent fractures in CLI patients with Cypher stents implanted in the infrapopliteal arteries. Although a low (0.3%) rate of fractures was observed, along with a 3% incidence of stent compressions, the re-intervention rate for patients with fractured or compressed stents was significantly higher at 41.7% compared to 19.4% for patients without stent fractures or compressions.

Another new development which may have long-term applications for patients with peripheral artery disease, who often progress to CLI, was presented at SIR by Dara Kraitchman, MD, of Johns Hopkins. Peripheral artery disease affects between 8 and 12 million individuals in the U.S.

Kraitchman is studying the use of stem cell therapy for revascularization in patients with CLI who are not candidates for bypass surgery. Stem cell therapy has shown some degree of promise in early-stage studies, but progress has been slowed by a lack of effective technologies to characterize the behavior and survival of implanted cells in-vivo. In addition, human studies of cell therapies have been limited mainly to use of autologous cells in order to avoid issues with immune rejection of cell implants.

Kraitchman described a new approach which involves encapsulation of stem cells in an alginate bubble. An alginate/poly-L-lysine construct has been developed that also contains an X-ray contrast agent (perfluorocatyl bromide) that makes the capsule visible on a CT scan. Kraitchman also has performed genetic engineering on the implanted cells to incorporate a luciferase gene to produce luminescence in the presence of a substrate when the cells are metabolically active. The technology consequently enables implanted cells to be localized in-vivo via non-invasive imaging as well as to verify that they are viable. In addition, it enables allogeneic cells to be used since the capsule shields the implanted cells from the recipient's immune system, avoiding rejection.

So far, studies have been confined to implants of allogeneic stem cells in rabbits. To enable the same technique to be used in human studies, it will be necessary to target injection of the luminescence substrate using CT guidance in order to achieve a sufficiently intense light output. Kraitchman estimates that a 150-fold increase in concentration will be needed compared to that being used in animals. Encapsulation does, however, limit the potential applications of cell therapy, since encapsulated cells cannot expand in vivo to form new structures such as blood vessels.

For revascularization in patients with PAD or CLI, the implanted cells serve as generators of blood vessel growth factors, stimulating angiogenesis in the surrounding tissue, while not directly participating in blood vessel formation. In other applications such as heart muscle regeneration, it will be necessary to develop techniques to dissolve the alginate capsule in vivo after implantation.

Evaluation of a new intracranial stent, the SILK stent developed by Balt Extrusion (Montmorency, France), was described by Veronica Crisotomo, MD, of Minimally Invasive Surgery Centre Jesus Uson (Caceres, Spain). A similar device, the Pipeline Neuroendovascular Device, is being developed by Chestnut Medical Technologies (Menlo Park, California).

The Balt SILK stent is a next-generation version of the company's LEO stent family, and is a braided nitinol device designed to seal wide-neck aneurysms. Sealing of wide neck aneurysms in the cerebral vessels remains a challenging application even for surgeons. The SILK stent is designed to cover the aneurysm with a tight metal mesh while also conforming to the adjacent vessel, resulting in thrombosis of the aneurysm without the need for coils or other embolic agents.

A study conducted by Crisotomo in sheep evaluated thrombogenecity and biocompatibility in 20 stents implanted in eight animals, comparing the new SILK stent to the LEO. Equivalent patency was achieved at 90 days, with one stent from each group found to be occluded. The SILK stent exhibited poor fluoroscopic visibility due to its nitinol construction, but Chestnut has added X-ray markers to improve visibility in preparation for moving into clinical studies

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