Quantification of elastic recoil after balloon angioplasty in the iliac arteries.

PURPOSE: Elastic recoil of the arterial wall has been shown to be responsible for a significant loss of luminal area after balloon angioplasty in the coronary arteries, but it has not been well studied in the peripheral arteries. Because elastic recoil depends on the presence of elastin in the arterial wall, and the amount of elastin varies by artery and proximity to the aorta, the importance of this response to angioplasty may be different in peripheral arteries. The purpose of this study is to document the degree of elastic recoil in the iliac arteries, and analyze variables that might influence the results. MATERIALS AND METHODS: A series of 19 patients with 25 iliac artery stenoses underwent balloon angioplasty followed by placement of a Palmaz stent with the same-sized angioplasty balloon. The minimum luminal diameter of the lesion was measured before treatment, immediately after balloon angioplasty, and again after stent placement. The arterial diameter after stent placement was defined as the diameter of the inflated balloon. The degree of recoil was correlated with nine variables: patient age and sex, lesion location and length, lesion severity (as percent stenosis), the balloon:artery ratio, and three factors related to lesion morphology--complex versus simple, eccentric versus concentric, and calcified versus noncalcified. RESULTS: Elastic recoil averaged 36% +/- 11% and ranged from 19% to 54% in this series of patients. The only variable that significantly influenced the degree of elastic recoil was the balloon:artery ratio (P =.039), which was directly related. CONCLUSION: Elastic recoil is a significant limitation of balloon angioplasty in the iliac arteries. This study illustrates the importance of techniques that limit recoil, such as vascular stents, in angioplasty of the iliac arteries.

Prevention of venous thromboembolic disease following primary total knee arthroplasty. A randomized, multicenter, open-label, parallel-group comparison of enoxaparin and warfarin.

BACKGROUND: Patients treated with total knee arthroplasty are at high risk for the development of venous thromboembolism postoperatively. This study compared the efficacy and safety of two common thromboprophylactic agents, enoxaparin (a low-molecular-weight heparin) and warfarin. METHODS: Three hundred and forty-nine patients were included in a prospective, randomized, multicenter, open-label, parallel-group clinical trial. Treatment with enoxaparin (30 mg, administered subcutaneously twice daily) or warfarin (adjusted to an international normalized ratio of 2 to 3) was initiated during the immediate postoperative period, within eight hours after the surgery, and was continued for four to fourteen days. Venous thromboembolism was defined as deep-vein thrombosis documented by contrast venography, symptomatic deep-vein thrombosis documented by lower-extremity ultrasonography, or symptomatic pulmonary embolism confirmed by a positive lung scan or pulmonary angiography. RESULTS: In the all-treated-patients group, eighty (45%) of the 176 warfarin-treated patients had venous thromboembolism: fifty-nine (34%) had distal deep-vein thrombosis; twenty (11%), proximal deep-vein thrombosis; and one (0.6%), pulmonary embolism. Venous thromboembolism developed in significantly fewer (p = 0.0001) enoxaparin-treated patients (forty-four of 173; 25%): forty-one (24%) had distal deep-vein thrombosis, three (2%) had proximal deep-vein thrombosis, and none had pulmonary embolism. The enoxaparin-treated patients also had a significantly lower prevalence of proximal deep-vein thrombosis (p = 0.002). The estimated odds for the development of venous thromboembolism were 2.52 times greater (95% confidence interval, 2.00 to 3.19) with warfarin than they were with enoxaparin. Major hemorrhage occurred in four warfarin-treated patients and nine enoxaparin-treated patients; with the numbers available, this difference was not significant (p = 0.17). Clinically important operative-site hemorrhage occurred in six (3%) of the warfarin-treated patients and twelve (7%) of the enoxaparin-treated patients (p = 0.15). CONCLUSIONS: A fixed 30-mg subcutaneous dose of enoxaparin, administered twice daily, with the first dose administered within eight hours after the completion of surgery, was significantly more effective than adjusted-dose warfarin in reducing the occurrence of asymptomatic venous thromboembolism, including proximal deep-vein thrombosis, in patients undergoing total knee arthroplasty. With the numbers available, there was no significant difference between groups with regard to the occurrence of major hemorrhagic complications; however, the rate of overall hemorrhagic complications was higher in the enoxaparin group.

Prolonged enoxaparin therapy to prevent venous thromboembolism after primary hip or knee replacement. Enoxaparin Clinical Trial Group.

BACKGROUND: Patients undergoing hip or knee joint replacement are at risk for venous thromboembolic complications for up to twelve weeks postoperatively. We evaluated the efficacy and safety of a prolonged post-hospital regimen of enoxaparin, a low-molecular-weight heparin, in this patient population. METHODS: Following elective total hip or knee replacement, 968 patients received subcutaneous enoxaparin (30 mg twice daily) for seven to ten days, and 873 were then randomized to receive three weeks of double-blind outpatient treatment with either enoxaparin (40 mg once daily) or a placebo. The primary efficacy end point was the prevalence of objectively confirmed venous thromboembolism or symptomatic pulmonary embolism during the double-blind phase of treatment. RESULTS: Of the 873 randomized patients, 435 underwent elective total hip replacement and 438 underwent elective total knee replacement. Enoxaparin was superior to the placebo in reducing the prevalence of venous thromboembolism in patients treated with hip replacement: 8.0% (eighteen) of the 224 patients treated with enoxaparin had venous thromboembolism compared with 23.2% (forty-nine) of the 211 patients treated with the placebo (p < 0.001; odds ratio, 3.62; 95% confidence interval, 2.00 to 6.55; relative risk reduction, 65.5%). Enoxaparin had no significant benefit in the patients treated with knee replacement: thirty-eight (17.5%) of the 217 patients treated with enoxaparin had venous thromboembolism compared with forty-six (20.8%) of the 221 patients treated with the placebo (p = 0.380; odds ratio, 1.24; 95% confidence interval, 0.76 to 2.02; relative risk reduction, 15.9%). Symptomatic pulmonary embolism developed in three patients, one with a hip replacement and two with a knee replacement; all had received the placebo. There was no significant difference in the prevalence of hemorrhagic episodes or other types of toxicity between the enoxaparin and placebo-treated groups. CONCLUSIONS: Prolonging enoxaparin thromboprophylaxis following hip replacement for a total of four weeks provided therapeutic benefit, by reducing the prevalence of venous thromboembolism, without compromising safety. A similar benefit was not observed in patients treated with knee replacement.

Accuracy and safety of carbon dioxide inferior vena cavography.

PURPOSE: The purpose of this study was to assess the accuracy of carbon dioxide compared to iodinated contrast material for determining inferior vena cava (IVC) diameter prior to filter placement, and to assess the safety of CO2 when used for this purpose. PATIENTS AND METHODS: Consecutive patients undergoing inferior vena cavography prior to filter placement were prospectively evaluated with use of both CO2 and iodinated contrast material. The diameter of the IVC was measured and compared in the same four locations in each patient for both agents. The diameter was corrected for magnification and pin-cushion distortion. The ability of CO2 to correctly classify IVC diameter as < or =28 mm or >28 mm, based on the IVC diameter with iodinated contrast material, was determined. A consensus panel assessed renal vein visualization with CO2 and iodinated contrast material. Blood pressure and arterial oxygen saturation were measured immediately before and after CO2 injection. RESULTS: Among 30 patients, there was no significant difference in the measured diameter of the IVC with CO2 versus iodinated contrast material after correction for magnification and pin-cushion distortion. One of 30 patients (3.3%) in this study was misclassified as having an IVC < or =28 mm with CO2 when, in fact, the IVC diameter was >28 mm based on iodinated contrast material. This could be clinically significant for certain IVC filters. Forty-seven percent of renal veins identified on contrast venography were identified by CO2 vena cavography. There was no significant difference in the blood pressure or oxygen saturation values measured before and after CO2 injection. However, one patient with pulmonary artery hypertension did experience transient, symptomatic hypotension after CO2 injection. CONCLUSIONS: In most patients, CO2 vena cavography accurately evaluated IVC diameter prior to filter placement. In 3.3% of patients, the discrepancy in measurements between CO2 and iodinated contrast material could be clinically significant, depending on the type of filter placed. CO2 was less accurate than iodinated contrast material in identifying renal veins. Although CO2 vena cavography is safe in the majority of patients, it should be used with caution in patients with pulmonary hypertension.

Intravascular ultrasound as an alternative to positive-contrast vena cavography prior to filter placement.

PURPOSE: In a nonconsecutive series of patients, intravascular ultrasound (IVUS) was investigated for safety and efficacy as an alternative to positive-contrast vena cavography for evaluating the inferior vena cava (IVC) prior to filter placement. MATERIALS AND METHODS: In a 6.5-year period, 30 patients (15 women, 15 men) ranging in age from 22 to 98 years old (mean, 56 years) underwent vena cava filter placement without conventional positive-contrast vena cavography, after IVUS evaluation of the IVC with use of a 6.2-F, 12.5- or 20-MHz monorail catheter system. The rationale for using IVUS included contraindications to iodinated contrast material in 14 patients with renal insufficiency and in four patients with previous life-threatening anaphylactoid reaction to iodinated contrast material; limitations to radiation exposure in four pregnant patients; and inability to otherwise image the IVC of eight morbidly obese patients who exceeded the weight limits of available angiographic equipment. IVUS completely replaced positive-contrast vena cavography, although not fluoroscopy in the four pregnant patients and in the 18 patients with contrast material contraindications. In two of the eight obese patients, IVUS was the only imaging modality. RESULTS: In all 30 patients, IVUS successfully determined the patency of the filter delivery route veins and the vena cava, the absence of thrombus, the location of renal veins, the absence of anatomical variants, and the vena cava diameter at the desired filter deployment level. Successful filter placement was confirmed in all 30 patients either with plain film alone (n = 12), IVUS alone (n = 3), computed tomography alone (n = 1), external ultrasound alone (n = 1), IVUS and another imaging modality (n = 10), or by combinations of other imaging modalities (n = 3). There were no complications. CONCLUSIONS: IVUS is a safe and effective alternative to conventional positive-contrast vena cavography for imaging the IVC prior to filter placement in patients with contraindications to iodinated contrast material or ionizing radiation.

Feasibility of three-dimensional intravascular ultrasonography: preliminary clinical studies.

The aim of this study was to demonstrate the clinical utility of reconstructed three-dimensional intravascular ultrasonography using a voxel-based volume rendering technique. Three-dimensional reconstruction of intravascular ultrasonographic data was performed in 12 patients with various vascular abnormalities during interventional radiology procedures. A stepping motor device was used to pull either a 12.5 or a 20 MHz catheter-based transducer through the lumen of a variety of vessels at a rate of 1.5 mm/s. Images were downloaded to a Life Imaging System for three-dimensional reconstruction. The value of three-dimensional ultrasonographic imaging was evaluated in comparison to conventional intravascular ultrasonography. A variety of abnormalities were demonstrated in reconstructed three-dimensional ultrasound imaging, including arterial atheroma and plaque, aneurysm and pseudoaneurysm, aortic dissection and stenosis (May-Thurner syndrome). The vascular branches and accessory vessels, as well as their relationships to each other, were easily demonstrated on three-dimensional imaging by selecting an appropriate angle, plane, and section of the image. The dimensions and shapes of the vascular lumen were determined in the longitudinal view. Three-dimensional information proved useful for determining the distribution and type of plaque in vessels. Reconstructed three-dimensional imaging allows for global evaluation of the dissection entry site, extent of the flap, and the false lumen of a pseudoaneurysm. Intravascular three-dimensional ultrasonography provides information complementary to that obtained with two-dimensional imaging. It supplies information about spatial relationships of anatomic structures that cannot be evaluated using conventional imaging methods.

US, CT, and MR evaluation of accessory renal arteries and proximal renal arterial branches.

RATIONALE AND OBJECTIVES: The purpose of this study was to compare color Doppler ultrasound (US), computed tomographic (CT) angiography, and magnetic resonance (MR) angiography for the evaluation of accessory renal arteries and proximal branches of the main renal artery. MATERIALS AND METHODS: Fifty-six subjects who had undergone conventional arteriography of the renal arteries participated in a prospective comparison of Doppler US (45 patients), CT angiography (52 patients), and nonenhanced MR angiography (28 patients). Conventional arteriography depicted 28 accessory renal arteries and 21 proximal branches of the main renal artery within 2 cm of the aorta. RESULTS: US depicted five of 24 accessory renal arteries seen at arteriography but no proximal arterial branches. CT angiography depicted 24 of 26 accessory renal arteries and 13 of 17 proximal arterial branches, as well as 15 additional accessory renal arteries not seen at conventional arteriography. MR demonstrated 11 of 15 accessory arteries, as well as four additional accessory arteries not seen at conventional arteriography. MR did not depict any of nine proximal arterial branches seen at conventional arteriography. CONCLUSION: When compared with US or nonenhanced MR angiography, CT is the preferred method for evaluation of accessory renal arteries and proximal branches of the renal artery.

Renal artery stenosis: CT angiography--comparison of real-time volume-rendering and maximum intensity projection algorithms.

PURPOSE: To compare results of helical computed tomographic (CT) angiography with real-time interactive volume rendering (VR) to CT angiography with maximum intensity projection (MIP) for the detection of renal artery stenosis. MATERIALS AND METHODS: Twenty-five patients underwent both conventional and CT angiography of the renal arteries. Images were blindly reviewed after rendering with MIP and VR algorithms. MIP images were viewed in conjunction with axial CT images; VR models were evaluated in real time at the workstation without CT images. Findings in 50 main and 11 accessory renal arteries were categorized as normal or by degree of stenosis. RESULTS: All arteries depicted on conventional angiograms were visualized on MIP and VR images. Receiver operating characteristic (ROC) analysis for MIP and VIR images demonstrated excellent discrimination for the diagnosis of stenosis of at least 50% (area under the ROC curve, 0.96-0.99). Although sensitivity was not significantly different for VR and MIP (89% vs 94%, P > .1), specificity was greater with VR (99% vs 87%, P = .008 to .08). Stenosis of at least 50% was overestimated with CT angiography in four accessory renal arteries, but three accessory renal arteries not depicted at conventional angiography were depicted at CT angiography. CONCLUSION: In the evaluation of renal artery stenosis, CT angiography with VR is faster and more accurate than CT angiography with MIP. Accessory arteries not depicted with conventional angiography were depicted with both CT angiographic algorithms.

Carbon dioxide as a contrast agent to guide vascular interventional procedures.

OBJECTIVE: The purpose of this study was to assess the value and limitations of carbon dioxide (CO2) as a contrast agent to guide vascular interventional procedures. SUBJECTS AND METHODS: Twenty-two adults underwent 26 vascular interventional procedures (21 arterial, five venous). We aimed to use only CO2 if possible because these patients had renal insufficiency (n = 21; mean creatinine level, 2.8 mg/dl) or were allergic to contrast material (n = 1). Arterial procedures performed included renal angioplasty or stent (n = 6), iliac angioplasty or stent (n = 5), infrainguinal angioplasty (n = 5), arterial bypass graft angioplasty (n = 3), and thrombolysis (n = 2). Venous procedures included transjugular intrahepatic portosystemic shunt recanalization (n = 3), angioplasty of the venous anastomosis of a thigh dialysis graft (n = 1), and angioplasty of the inferior vena cava (n = 1). RESULTS: Twenty-five of the 26 procedures were successfully performed. Of the 26 procedures, eight required no iodinated contrast material and 11 required less than or equal to 20 ml of contrast material. CO2 proved to be inadequate for the remaining seven procedures. Iliac artery angioplasty or stent placement required an average of 9 ml of iodinated contrast material; infrainguinal angioplasty required an average of 22 ml of iodinated contrast material. CONCLUSION: CO2 can be successfully used as a contrast agent in a variety of vascular interventional procedures. Such procedures can usually be performed in the iliac and infrainguinal arteries using minimal supplemental iodinated contrast material. However, CO2 failed to provide satisfactory guidance in half of the intraabdominal procedures in our study.

Comparison of Doppler US and CT angiography for evaluation of renal artery stenosis.

RATIONALE AND OBJECTIVES: The authors compared Doppler ultrasound (US) with computed tomographic (CT) angiography in the evaluation of stenosis of the main renal artery. MATERIALS AND METHODS: Fifty-six patients who had undergone conventional angiography of the renal arteries participated in a prospective comparison of Doppler US (45 patients) and CT angiography (52 patients). US evaluation included both the main renal artery and segmental renal arteries. RESULTS: There were 27 main renal arteries with at least 50% stenosis in 20 patients. In 36 patients, there was no significant stenosis. All cases of main renal artery stenosis detected with Doppler US of the segmental arteries were also identified with Doppler US of the main renal artery. The by-artery sensitivity (63%) of US of the main renal artery was greater than that (33%) of US of the segmental arteries. CT angiography was more sensitive (96%) than Doppler US (63%) in the detection of stenosis, but the specificity of CT (88%) was similar to that of US (89%). The difference in the area under the receiver operating characteristic curve (AUC) between CT (AUC = 0.94) and US (AUC = 0.82) was statistically significant (P = .038). CONCLUSION: Doppler US of the main renal artery is more sensitive than Doppler US of segmental arteries in the detection of stenosis. CT angiography is more accurate than Doppler US in the evaluation of renal artery stenosis.

Malignant biliary duct obstruction: long-term experience with Gianturco stents and combined-modality radiation therapy.

PURPOSE: To evaluate the effect of combined-modality therapy including intraluminal iridium-192 on stent patency and survival in patients with malignant biliary obstruction treated with Gianturco stents. MATERIALS AND METHODS: Twenty-two patients with unresectable biliary obstruction caused by cholangiocarcinoma (n = 11) or by secondary extrahepatic bile duct malignant tumors (n = 11) were treated with percutaneous biliary drainage followed by intraluminal Ir-192 wire placement (mean dose, 25 Gy) before insertion of Gianturco metal stents. Eleven patients also received external-beam radiation therapy, and 13 patients received chemotherapy. Patency was defined as absence of jaundice or cholangitis that necessitated hospitalization, or as seen on hepatobiliary scans. Survival was determined from the time of stent insertion after brachytherapy. RESULTS: Patients with cholangiocarcinoma had extended mean stent patency of 19.5 months (range, 2-46 months) and mean survival of 22.6 months (range, 2-72 months). Patients with secondary malignant tumors had a mean patency of 4.8 months (range, 1.5-8 months) and a mean survival of 5.3 months (range, 2-9 months). CONCLUSION: Radiation therapy including intraluminal Ir-192 appears to extend stent patency and survival in patients with inoperable cholangiocarcinoma treated with Gianturco metal stents compared with patients with other extrahepatic bile duct malignant diseases and patients treated without combined-modality therapy in other studies.

Efficacy and safety of enoxaparin versus unfractionated heparin for prevention of deep venous thrombosis after elective knee arthroplasty. Enoxaparin Clinical Trial Group.

This study was a randomized, parallel-group, open-label clinical trial comparing the efficacy and safety of Enoxaparin, a low-molecular-weight heparin, and unfractionated heparin to prevent deep venous thrombosis after elective total knee arthroplasty. Four hundred fifty-three patients were randomized and received study medications. The primary efficacy evaluation was unilateral contrast venography done at the end of study or earlier if clinically indicated. The primary safety outcome was the incidence of bleeding episodes. Patients were assigned to 1 of 2 postoperative treatment groups: Enoxaparin 30 mg subcutaneous every 12 hours (228 patients), or unfractionated heparin 5000 units subcutaneous every 8 hours (225 patients). The incidence of proximal and distal deep venous thrombosis in the Enoxaparin group was 24.6% (56/228), and in the heparin group 34.2% (77/225). Three major hemorrhagic episodes were observed in each treatment group. Two cases of pulmonary embolism occurred in patients receiving heparin (1 fatal); no cases occurred in patients receiving Enoxaparin. This study showed that Enoxaparin administered postoperatively 30 mg every 12 hours is more effective and as safe as unfractionated heparin prophylaxis to prevent deep venous thrombosis in patients having elective total knee arthroplasty.

Osteochondroma: an unusual cause of vascular disease in young adults.

Vascular complications such as pseudoaneurysm, arterial thrombosis, luminal stenosis due to extrinsic compression, deep venous thrombosis, and arteriovenous fistula are known complications of osteochondroma. The authors describe three cases of vascular injury caused by osteochondroma: popliteal artery impingement, popliteal artery pseudoaneurysm formation, and superficial femoral artery pseudoaneurysm with peripheral occlusion of the tibial and peroneal arteries due to embolization. Fifty-six cases of vascular complications due to osteochondroma from the English literature are also reviewed. This entity should be considered in young patients with evidence of peripheral vascular insufficiency or in patients with known osteochondroma who develop symptoms of local pain and swelling in the involved extremity.

Venography with carbon dioxide as a contrast agent.

PURPOSE: The purpose of this study was to evaluate the feasibility, safety, and potential role of carbon dioxide (CO2) as a contrast agent for venography. METHODS: Consecutive patients with contraindications to iodinated contrast agents or with unsatisfactory iodinated contrast studies underwent CO2 digital subtraction venography. The images were rated by three experienced angiographers. Image quality and complications were assessed. RESULTS: Over a 14-month period, 66 vein segments were studied in 21 patients. There was good correlation between experienced angiographers on CO2 image quality (Ri = 0.80) and good agreement on diagnosis (k = 0.62). In 91% of the vein segments evaluated with C02 there was interobserver agreement on the diagnosis. Upper extremity veins were adequately imaged with CO2 alone in all (6/6) patients with contraindications to iodinated contrast. Following suboptimal iodinated contrast studies in six patients, CO2 produced significantly better quality upper extremity central vein images (p < 0.05). Pain following injection into peripheral veins was the only CO2-related complication. Inferior vena cava (IVC) filters were successfully deployed with CO2 alone in 78% (7/9) of patients; two required iodinated contrast. CONCLUSIONS: Based upon initial experience, CO2 venography can be recommended in patients with contraindications to iodinated contrast or unsatisfactory iodinated contrast studies.

Arterial abnormalities following orthotopic liver transplantation: arteriographic findings and correlation with Doppler sonographic findings.

OBJECTIVE: We studied the findings on conventional arteriography in patients who had suspected graft ischemia after orthotopic liver transplantation to determine the value of a single Doppler signal in predicting these lesions. MATERIALS AND METHODS: We retrospectively reviewed selective visceral arteriograms with abnormal findings from 20 adults who had suspected graft ischemia after orthotopic liver transplantation and a single Doppler signal from the hepatic artery at the porta hepatis on sonograms obtained before arteriography. Arteriographic abnormalities were categorized according to morphology and location as follows: stenosis of recipient's hepatic artery, occlusion or stenosis of the transplanted extrahepatic artery, and occlusion or stenosis of the transplanted intrahepatic artery. RESULTS: Twenty-three arteriographic abnormalities were detected: four recipient celiac axis stenoses, seven extrahepatic occlusions, nine extrahepatic stenoses, and two occlusions and one stenosis of the transplanted intrahepatic artery. Six of the extrahepatic occlusions, two of the extrahepatic stenoses, and none of the recipient artery stenoses or the intrahepatic occlusions or stenoses were correctly diagnosed on the basis of Doppler findings. One patient with both an extrahepatic stenosis and an extrahepatic occlusion was thought to have an intrahepatic occlusion, and two patients with mild (< 50%) extrahepatic stenoses and one with an intrahepatic occlusion were thought to have an extrahepatic occlusion. CONCLUSION: A wide spectrum of abnormalities in the recipient's celiac axis or the transplanted arteries that may be associated with graft ischemia after orthotopic liver transplantation are often not detected or findings are misinterpreted on routine Doppler examination. In patients with suspected graft ischemia, visceral arteriography should be performed promptly to confirm the diagnosis and to allow early intervention.

Fallopian tube recanalization in an unrestricted patient population.

PURPOSE: To review the effectiveness of fallopian tube recanalization (FTR) when performed without restriction based on history or tubal condition. MATERIALS AND METHODS: From October 1989 to July 1992 in 37 consecutive women, aged 22-44 years (mean, 35 years), 42 FTRs were performed (five patients each underwent two FTRs). Water-soluble contrast material and selective ostial salpingography and/or microcatheter technique were used exclusively. Eighty tubes were evaluated, since four patients had previously undergone unilateral salpingectomy. Sixty-three tubes (79%) were occluded at the outset of the procedure. RESULTS: Complete recanalization was achieved in 45 of 63 (71%) occlusions. Adhesions were present in 25 of 80 (31%) tubes, salpingitis isthmica nodosa in 12 (15%), and hydrosalpinx in nine (11%). The 42 procedures resulted in 14 (33%) conceptions, nine (64%) of which involved pathologic tubes. Eleven intrauterine pregnancies resulted in five spontaneous first-trimester abortions, five full-term deliveries, and one continuing pregnancy. CONCLUSION: Favorable conception and live birth rates can be achieved with FTR, despite a high prevalence of tubal disease.

Cost containment in the use of low-osmolar contrast agents: effect of guidelines, monitoring, and feedback mechanisms.

PURPOSE: To describe a program for controlling intravenous use of low-osmolar contrast agents (LOCAs). MATERIALS AND METHODS: The department of radiology at the authors' institution adopted a policy of selective use of intravenously administered LOCAs. Clinical indications for LOCA use were specified after consultation with the administration, risk managers, legal department, and ethics committee of the hospital. The guidelines were then publicized throughout the department and hospital, and a contrast agent data form was developed to collect data on all cases. Monitoring mechanisms were instituted. RESULTS: Over the next 23 months, 11,373 patients received intravenous iodinated contrast agents, of whom 28.1% were deemed to be at high risk and were given LOCAs. Monthly tracking showed no evidence of a trend toward increasing use of LOCAs. CONCLUSION: Clear definition of use guidelines, close monitoring, and feedback can stabilize LOCA use at acceptably low levels.

Filter wheel equalization in DSA: simulation results.

Digital subtraction angiography (DSA) is a valuable and frequently used diagnostic technique which allows the evaluation of vascular anatomy and pathology. In order to improve the utility and diagnostic performance of DSA, a filter wheel system is presented which can provide mechanically simple, rapidly adaptable, and clinically practical radiographic equalization to DSA images. The filter wheel equalization system consists of a series of computer-driven filter wheels, mounted between the x-ray tube and collimator. Each wheel has an annular area of attenuator material which intersects the x-ray beam and carries a rotationally varying compensation pattern on it. Rotation of the filter wheel modulates the attenuator pattern in the x-ray field under computer control, in a manner designed to increase the x-ray exposure to underexposed areas in the image. A system with eight wheels has 10(19) possible equalization patterns. The compensation patterns are removed in the subtracted DSA images. Computer simulation techniques were used to evaluate various design scenarios for the filter wheel system, using a data base of 191 clinical DSA mask images. For a practical implementation of the filter wheel system, an improvement in the signal to noise ratio of 23%, averaged over the image, was found.

Hemodynamics of failing dialysis grafts.

Pressures were measured in the graft and the central vein during 104 consecutive angiographic examinations of failing hemodialysis grafts. Stenosis severity greater than 40% led to a statistically significant rise in graft pressure. In grafts in which all stenoses were of 40% or less severity, the systolic pressures in the venous and arterial limbs of the grafts were 31% +/- 16 and 45% +/- 17, respectively, of systemic systolic pressure. In grafts in which the highest grade of stenosis was greater than 40%, pressures in the venous and arterial limbs of the grafts were 53% +/- 25 and 75% +/- 24, respectively, of systemic systolic pressure. Graft thrombosis tended to occur at a higher degree of lumen reduction (but at similar pressures) with central vein stenoses compared with venous anastomotic stenoses. Dialysis graft pressures can help determine the hemodynamic importance of stenoses and the need for intervention. Percutaneous intervention should achieve arterial and venous limb pressures of less than 50% and 33% of systemic pressure, respectively.