High-Intensity Focused Ultrasound Therapy: an Overview for Radiologists

High-intensity focused ultrasound therapy is a novel, emerging, therapeutic modality that uses ultrasound waves, propagated through tissue media, as carriers of energy. This completely non-invasive technology has great potential for tumor ablation as well as hemostasis, thrombolysis and targeted drug/gene delivery. However, the application of this technology still has many drawbacks. It is expected that current obstacles to implementation will be resolved in the near future. In this review, we provide an overview of high-intensity focused ultrasound therapy from the basic physics to recent clinical studies with an interventional radiologist's perspective for the purpose of improving the general understanding of this cutting-edge technology as well as speculating on future developments.

Percutaneous Transportal Sclerotherapy with N-Butyl-2-Cyanoacrylate for Gastric Varices: Technique and Clinical Efficacy

OBJECTIVE: This study was deigned to evaluate the technique and clinical efficacy of the use of percutaneous transportal sclerotherapy with N-butyl-2-cyanoacrylate (NBCA) for patients with gastric varices. MATERIALS AND METHODS: Seven patients were treated by transportal sclerotherapy with the use of NBCA. For transportal sclerotherapy, portal vein catheterization was performed with a 6-Fr sheath by the transhepatic approach. A 5-Fr catheter was introduced into the afferent gastric vein and a microcatheter was advanced through the 5-Fr catheter into the varices. NBCA was injected through the microcatheter in the varices by use of the continuous single-column injection technique. After the procedure, postcontrast computed tomography (CT) was performed on the next day and then every six months. Gastroendoscopy was performed at one week, three months, and then every six months after the procedure. RESULTS: The technical success rate of the procedure was 88%. In six patients, gastric varices were successfully obliterated with 1-8 mL (mean, 5.4 mL) of a NBCA-Lipiodol mixture injected via a microcatheter. No complications related to the procedure were encountered. As seen on the follow-up endoscopy and CT imaging performed after six months, the presence of gastric varcies was not seen in any of the patients after treatment with the NBCA-Lipiodol mixture and the use of microcoils. Recurrence of gastric varices was not observed during the follow-up period. Worsening of esophageal varices occurred in four patients after transportal sclerotherapy. The serum albumin level increased, the ammonia level decreased and the prothrombin time increased at six months after the procedure (p < 0.05). CONCLUSION: Percutaneous transportal sclerotherapy with NBCA is useful to obliterate gastric varices if it is not possible to perform balloon-occluded retrograde transvenous obliteration.

Transarterial Embolization of an Inferior Genicular Artery Pseudoaneurysm with Arteriovenous Fistula after Arthroscopy

Arthroscopic meniscectomy of the knee is generally a safe and effective procedure with a low rate of vascular complications. We report here on a unique case of a 55-year-old man with a lateral inferior genicular artery pseudoaneurysm and a concomitant arteriovenous fistula that developed after arthroscopic meniscectomy; this was successfully treated with selective angiographic embolization. This case illustrates the effectiveness of an endovascular approach as a minimally invasive treatment for this uncommon complication that occurs after an arthroscopic procedure.

Glue Embolization of Aneurysm after Stenting in Canine Carotid Arteries - Technical Feasibility

PURPOSE: Coiling or infusion of embolic materials into a wide necked aneurysm can be performed with stenting. The purpose of our study is to assess the technical feasibility of aneurysm treatment with glue embolization after stenting. MATERIALS AND METHODS: We used four Wallstents for surgically repairing eight canine carotid aneurysms. After confirmation of the aneurysms on the angiogram, we introduced a 6-7 F guiding catheter in order to deploy the stents. After stenting, we passed a microcatheter into the aneurysm lumen through the stent mesh. 28% glue was slowly injected until the glue cast completely filled the lumen. We evaluated the passage of a microcatheter through the stent meshwork, formation of the glue cast and the stents' ability to protection for any leakage of glue. The follow-up angiogram was obtained for two dogs, one to three times until 8 weeks, and then we sacrificed the dogs and performed pathologic examinations. RESULTS: Stenting was successful in all cases except one in which the vessel was occluded because the stent was not completely expanded within the lumen. The microcatheter could not pass through the stent mesh in one aneurysm. The two week follow-up angiogram showed complete occlusion of the aneurysm and a patent carotid lumen in a case after successful stenting and glue embolization without distal migration of glue. Tungsten in the glue was noted to migrate out of aneurysm into the soft tissue of the neck. Histopathologic examination showed successful obliteration and stable organization of the aneurysmal lumen with ingrowth of fibroblasts and a foreign body reaction. In contrast, the aneurysms without the glue embolization being performed showed partially thrombosed aneurysmal lumens that became smaller and indistinct on the 8 week follow-up angiograms. Histopathologic examination showed a disorganized thrombus with numerous recanalizations. CONCLUSION: Glue embolization after stenting could be performed for aneurysm without distal migration of the glue or gluing of the catheter. This concept appears to be useful for applications to the further research and the treatment of aneurysm.

Balloon-Occluded Retrograde Transvenous Obliteration for Gastric Variceal Bleeding: Its Feasibility Compared with Transjugular Intrahepatic Portosystemic Shunt

OBJECTIVE: To assess the feasibility of balloon-occluded retrograde transvenous obliteration (BRTO) in active gastric variceal bleeding, and to compare the findings with those of transjugular intrahepatic portosystemic shunt (TIPS). MATERIALS AND METHODS: Twenty-one patients with active gastric variceal bleeding due to liver cirrhosis were referred for radiological intervention. In 15 patients, contrast-enhanced CT scans demonstrated gastrorenal shunt, and the remaining six (Group 1) underwent TIPS. Seven of the 15 with gastrorenal shunt (Group 2) were also treated with TIPS, and the other eight (Group 3) underwent BRTO. All patients were followed up for 6 to 21 (mean, 14.4) months. For statistical inter-group comparison of immediate hemostasis, rebleeding and encephalopathy, Fisher's exact test was used. Changes in the Child-Pugh score before and after each procedure in each group were statistically analyzed by means of Wilcoxon's signed rank test. RESULTS: One patient in Group 1 died of sepsis, acute respiratory distress syndrome, and persistent bleeding three days after TIPS, while the remaining 20 survived the procedure with immediate hemostasis. Hepatic encephalopathy developed in four patients (one in Group 1, three in Group 2, and none in Group 3) ; one, in Group 2, died while in an hepatic coma 19 months after TIPS. Rebleeding occurred in one patient, also in Group 2. Except for transient fever in two Group-3 patients, no procedure-related complication occurred. In terms of immediate hemostasis, rebleeding and encephalopathy, there were no statistically significant differences between the groups (p > 0.05). In Group 3, the Child-Pugh score showed a significant decrease after the procedure (p = 0.02). CONCLUSION: BRTO can effectively control active gastric variceal bleeding, and because of immediate hemostasis, the absence of rebleeding, and improved liver function, is a good alternative to TIPS in patients in whom such bleeding, accompanied by gastrorenal shunt, occurs.

The Effectiveness of Percutaneous Transarterial Embolization for Arteriovenous Malformation

PURPOSE: To determine the effectiveness of percutaneous transarterial embolization for the treatment of arteriovenous malformation (AVM). MATERIALS AND METHODS: Seven patients with AVMs located in the kidney, liver, lung, chest wall, uterus and paraspinal region underwent angiography and percutaneous transarterial embolization. The embolic materials used were steel coil, gelfoam, contour emboli, and absolute alcohol; in some cases, more than one of these were employed. The analysed the angiographic findings and clinical status following embolization were assessed and analysed. RESULTS: The AVMs had tortuous, dilated feeding arteries (n=7) and veins with early venous drainage (n=6). In the hepatic AVM, a grape-like dilated vessel arose from the hepatic artery and was connected to the portal vein. In the uterine AVM, numerous dilated feeding arteries formed a honeycomb. In the feeding arteries of the chest wall AVM and in the nidus of the pulmonary AVM, aneurysms were present. In simple AVMs, the patient's symptoms were relieved by first embolization. Complex AVMs, however, required repeated embolizations for symptomatic relief. Although extensive, complex AVMs of the chest wall and uterus recurred after initial embolization, repeated treatment successfully improved the clinical status of such patients. The complications developing after emboliation were fever (n=3) and pain (n=3), but these were relieved by conservative care. CONCLUSION: Percutaneous transarterial embolization is a safe and effective therapeutic method for the treatment of AVM. In a case of inoperable complex AVM, repeated embolization is the only method for symptomatic relief and the maintenance of life.

The Induction of Hyperthermia in Rabbit Liver by means of Duplex Stainless Steel Thermoseeds

OBJECTIVE: To determine the heating characteristics of needle-shaped duplex stainless steel thermoseeds, and to evaluate their effectiveness in the induction of hyperthermia in rabbit liver. MATERIALS AND METHODS: Thermoseeds of the two different shapes, L-shaped for single doses of hyperthermia and I-shaped for in-vitro study and repeated hyperthermic induction, were prepared. For the in-vitro study, an I-shaped thermoseed 0.23 mm in diameter and 25 mm long was placed inside a plastic tube filled with water. Heat was applied for 30 minutes within an induction magnetic field, and during this time changes in temperature were recorded using three thermocouples. For the in-vivo study, fifteen New Zealand white rabbits were divided into five equal groups. An I-shaped or L-shaped thermoseed was inserted in each rabbit's liver, and then placed within the center of the magnetic induction coil during a 30-minute period of hyperthermia. The rabbits in the first group were sacrificed immediately after hyperthermia was induced once, while those in the other groups were sacrificed at 1, 3, and 7 days, respectively, also after one induction. The remaining three rabbits were sacrificed 4 days after three consecutive daily treatment sessions. The resected segments of liver were subsequently evaluated histopathologically for the extent of coagulation necrosis caused by heating of the thermoseed. RESULTS: The in-vitro study demonstrated that the temperature in the thermoseed, which was 25.9 degree C before heating and 54.8 degree C after heating, rose rapidly at first but progressively less rapidly as time elapsed. Light microscopic examination of the rabbits' livers revealed coagulation necrosis and infiltration by inflammatory cells around the insertion site of the thermoseed. The maximum diameter of coagulation necrosis was 2.81+/-1.68 mm, and this occurred in the rabbits that were sacrificed 7 days after heat induction. CONCLUSION: Needle-shaped duplex stainless steel thermoseeds show temperature-dependent-type heating characteristics, and in rabbit liver, induced coagulation necrosis of surrounding tissues after heat is applied for 30 minutes. These thermoseeds may thus be useful for the induction of interstitial hyperthermia.

Stent Assisted Coil Embolization of a Dissecting Aneurysm of the Vertebral Artery: A Case Involving a Patient with Hypoplasia of the Contralateral Vertebral Artery

A dissecting aneurysm of the vertebral artery may be treated conservatively, surgically, or using an endovascular approach. Proximal clipping, wrapping or trapping are surgical treatment methods, and endovascular treatment with coils and balloons is performed where a dissecting aneurysm is located near the midline or the appropriate surgical manipulation is difficult. As the contralateral vertebral artery of this patient was hypoplastic, the stent-assisted coil embolization technique was employed to preserve the ipsilateral vertebral artery. We describe a clinical case of dissecting aneurysm of the vertebral artery occurring in a patient in whom a hypoplastic contralateral vertebral artery was successfully treated.

Percutaneous Vertebroplasty in Osteoporotic Vertebral Body Compression Fracture

PURPOSE: To determine the clinical efficacy of percutaneous vertebroplasty in cases of painful and medically intractable osteoporotic vertebral compression fracture. MATERIALS AND METHODS: Ninety-eight patients (20 men and 78 women; mean age, 69 years) underwent 122 per-cutaneous vertebroplasty procedures for the treatment of osteoporotic vertical compression fracture. For the evaluation of bone mass, bone densitometry was performed in 45 patients, and to assess the recent evolution of the fracture, all 98 underwent MRI. Percutaneous vertebroplasty involves percutaneous transpedicular puncture of the involved vertebrae followed by the injection of a Polymethylmethacrylate(PMMA)-Barium mixture into the vertebral body. To assess leakage of the mixture into the epidural tissue, neural foramina, venous plexus and paravertebral tissue, we then immediately obtained a computerized tomographic (CT) scan, assessing the clinical efficacy of the procedure on the basis of time required for pain relief (defined as more than 60% reduction of initial pain), and time required for ambulation without significant pain. RESULTS: Percutaneous vertebroplasty was successful in all patients. Pain relief was accomplished within 1-5(mean, 1.8) days and early ambulation without significant pain was possible within 2 -15 (mean, 3.3) days. Post-procedural CT scanning revealed leakage of the PMMA-barium mixture into Paravertebral tissue(n=41), the paravertebral venous plexus (n=34) and epidural tissue (n=4). No neural foraminal leakage was identified, and no procedure-related complication requiring surgical treatment occurred. CONCLUSION: Percutaneous vertebroplasty is an effective new interventional procedure for the treatment of osteoporotic vertebral compression fracture. It relieves pain, provides early mobilization, and strengthens involved vertebral bodies.

The Feasibility of CT-Guided Percutaneous Ethanol Injection Therapy for Hepatic Tumors

PURPOSE: To describe the technical features of CT-guided percutaneous ethanol injection therapy (PEIT) for hepatic tumors that are undetectable or inaccessible under ultrasound guidance, to analyze its short-term therapeutic results, and to discuss its feasibility and limitations with a review of the related literature. MATERIALS AND METHODS: During a 22-month period, 17 patients with 28 hepatic tumors (27 hepatocellular carcinomas and one metastasis) underwent 38 sessions of CT-guided PEIT. Follow-up CT scanning was also performed. All tumors were undetectable or inaccessible under ultrasound guidance. The quantity of ethanol injected depended on their maximum diameter, which was 0.9 -5.1 (mean, 2.2) cm. To determine the puncture site and direction of the needle, the graduated grid system was used. A 21 or 22-G PEIT needle was introduced into the tumor stepwise, with intermittent CT monitoring, and if the CT images obtained immediately after initial injection demonstrated incomplete perfusion, an additional dose of ethanol was administered. During the follow-up period of 28 -619 (mean, 261) days, three-phase spiral CT scans were obtained. We focused on whether or not a viable portion of ablated tumor was present, and if so, the interval during which the extent of viable portion had changed, as well as the CT findings which suggested a predisposition to incomplete ablation. RESULTS: PEIT was successfully performed in all patients. During each session, 3 -30 (mean, 12.1) mL of ethanol was injected for 35 -115 (mean, 85) mins, with 1 -7 (mean, 3.7) trials to determine the puncture site and needle direction. The follow-up CT results showed that 20 tumors (71.4%) contained no viable portion, that this portion had decreased in four (14.3%), and was unchanged or had increased in four (14.3%). In the eight tumors for which multiple sessions were required, follow-up CT showed that the viable portion was absent or had decreased in size in all except one. In five of the patients with a tumor containing a viable portion at follow- up CT, the procedure was incomplete because of unendurable pain (n = 2) or noncooperation (n = 3). A CT finding which suggested a predisposition to incomplete ablation was a poor margin (n = 3). Complications included severe pain (n = 6) and scanty peritoneal hemorrhage (n = 1). CONCLUSION: Despite several limitations of our study, the therapeutic results of CT-guided PEIT appeared to be similar to or slightly worse than those of well-established ultrasound-guided PEIT with the former procedure, however, intermittent CT monitoring indicates whether perfusion is complete, and for this reason, CT-guided PEIT is believed to be an effective treatment modality when a hepatic tumor is undetectable or inaccessible under ultrasound guidance.

Usefulness of "Double-catheter" Technique in GDC Treatment of Intracranial Wide-necked Aneurysm

Purpose: To describe two different methods of "double-catheter" techniques for the treatment of wide-necked intracranial aneurysms. MATERIALS AND METHODS: Using two microcatheters simultaneously, we treated two wide-necked ophthalmic aneurysms and one wide-necked basilar bifurcation aneurysm. In the two cases of ophthalmic aneurysms, the two microcatheters were placed in the aneurysm sac, thus allowing two coils to be braced across the aneurysmal neck before either was detached. In the case of the basilar bifurcation aneurysm, a microcatheter was placed in the posterior cerebral artery (PCA), and another within the aneurysm lumen. When making the first frame with a GDC, we tried to ensure that the frame of the coil and the microcatheter in the PCA did not over-lap. Then, through the microcatheter positioned at the PCA, angiography was performed and flow pattern and dye-disappearance time were evaluated. Subsequent coils were introduced, but in order to preserve PCA flow, not beyond the frame of the first coil. RESULTS: All three aneurysms were successfully embolized without parent artery compromise and the patients were discharged in good neurological condition. CONCLUSION: The "double-catheter" technique can provide a valuable option for treating wide-necked aneurysms, especially when 'balloon remodeling' is not feasible and/or the relationship between the aneurysmal neck and adjacent parent artery cannot be ascertained.

Renal Artery Embolization Using a New Liquid Embolic Material Obtained by Partial Hydrolysis of Polyvinyl Acetate (Embol):Initial Experience in Six Patients

OBJECTIVE: To evaluate the therapeutic efficacy of a new liquid embolic materi-al,Embol, in embolization of the renal artery. MATERIALS AND METHODS: Embol is a new embolic material obtained by partial hydrolysis of polyvinyl acetate mixed in absolute ethanol and Iopromide 370 and manufactured by Schering Korea, Kyonggido, Korea. Six patients who underwent embolization of the renal artery using Embol were evaluated. Four were male and two were female and their ages ranged from 11 to 70 (mean, 53) years. Clinical and radiologic diagnoses referred for renal artery embolization were renal cell carcinoma (n = 3), renal angiomyolipoma (n = 2) and pseudoaneurysm of the renal artery (n = 1). After selective renal angiography, Embol was injected through various catheters, either with or without a balloon occlusion catheter. Changes in symptoms and blood chemistry which may have been related to renal artery embolization with Embol were analyzed. RESULTS: The six patients showed immediate total occlusion of their renal vas-cular lesions. One of the three in whom renal cell carcinoma was embolized with Embol underwent radical nephrectomy, and the specimen thus obtained revealed 40% tumor necrosis. In the two patients with angiomyolipomas, the tumors decreased in size and abdominal pain subsided. Bleeding from pseudoaneurysm of the renal artery was successfully controlled. Four patients showed symptoms of post-embolization syndrome, and one of these also showed increased levels of blood urea nitrogen and creatinine. One patient experienced transient hyperten-sion. CONCLUSION: Embol is easy to use, its radiopacity is adequate and it is a safe and effective embolic material which provides immediate and total occlusion of renal vascular lesions.

Usefulness of Flexible Covered Stent in Malignant Colorectal Obstruction

PURPOSE: To evaluate the usefulness of flexible covered stent in the treatment of acute colorectalobstruction secondary to colorectal carcinoma. MATERIALS AND METHODS: Flexible covered stents were placed in 11patients with clinical and radiologic signs of acute colonic obstruction secondary to colorectal carcinoma. Thepurposes of stent insertion were pre-operative bowel preparation in seven patients and palliative treatment infour. A fistula was present in two;in one this was between the proximal jejunum and colon, and the other wasrectovaginal. The usefulness of stent insertion for the purpose of preoperative bowel preparation was evaluatedaccording to the feasability and status of bowel preparation, as decided by the operator. Palliative treatment forthe relief of symptoms of acute bowel obstruction was evaluated according to the number and amount of defecation,bowel dilatation in simple abdomen radiography, and the presence of complications. RESULT: Bowel preparation forthe purpose of preoperative bowel cleansing was easy in seven patients;the fecal materials remaining in the colonpresented no problems during surgery. In one of four patients palliative treatment involved a colostomy;this wasdue to recurrent stent obstruction by fecal materials after three months, and in two other patients there wasstent obstruction after two and five months, respectively. The stent in one of four patients who underwentpalliative treatment was removed because of stent migration three days after insertion;the stents in two patientswith fistulas covered the fistulas successfully. Complications after stent insertion were anal pain in threepatients, anal bleeding in three and stent migration in one. CONCLUSION: The flexible covered stent was aneffective device for the relief of acute colonic obstruction secondary to malignant rectosigmoid neoplasia. Itallowed for single-stage operation and covered the fistula. We believe however that for further evaluation of theusefulness of this type of stent in long-term palliative treatment, a larger-scale study is needed.