Intraarterial Magnetic Resonance Research Articles

Perfusion Reduction at Transcatheter Intraarterial Perfusion MR Imaging: A Promising Intraprocedural Biomarker to Predict Transplant-Free Survival during Chemoembolization of Hepatocellular Carcinoma

To investigate the predictive value of transcatheter intraarterial perfusion (TRIP) magnetic resonance (MR) imaging-measured tumor perfusion changes during transarterial chemoembolization on transplant-free survival (TFS) in patients with unresectable hepatocellular carcinoma (HCC). This HIPAA-compliant prospective study was approved by the institutional review board. Written informed consent was obtained from all patients. Fifty-one consecutive adult patients with surgically unresectable single or multifocal measurable HCC and adequate laboratory parameters who underwent chemoembolization in a combined MR imaging-interventional radiology suite between February 2006 and June 2010 were studied. Tumor perfusion changes during chemoembolization were measured by using TRIP MR imaging with area under the time-signal intensity curve calculation. The end point of the study was TFS. The authors assessed the correlation between the percentage perfusion reduction in the tumor during chemoembolization and TFS by using univariate and multivariate analyses. Fifty patients (mean age, 61 years; 39 men aged 42-87 years [mean age, 61 years] and 11 women aged 49-83 years [mean age, 62 years]) were eligible for the analysis. Patients with 35%-85% intraprocedural tumor area under the time-signal intensity curve reduction (n = 32) showed significantly improved median TFS compared with patients with an area under the time-signal intensity curve reduction outside this range (n = 18) (16.6 months [95% confidence interval: 11.2, 22.0 months] vs 9.3 months [95% confidence interval: 6.6, 12.0 months], respectively; P = .046; hazard ratio: 0.46; 95% confidence interval: 0.21, 1.00). The cumulative TFS rates in the 35%-85% and less than 35% or more than 85% perfusion reduction groups at 1, 2, and 5 years after chemoembolization were 66.4%, 42.2%, and 28.2% versus 33.8%, 16.9%, and 0%, respectively. The study shows evidence of an association between intraprocedural tumor perfusion reduction during chemoembolization and TFS and suggests the utility of TRIP MR imaging- measured tumor perfusion reduction as an intraprocedural imaging biomarker during chemoembolization.

Coil-treated Aneurysms: Decision Making Regarding Additional Treatment Based on Findings of MR Angiography and Intraarterial DSA

To assess whether magnetic resonance (MR) angiography can be used as a noninvasive alternative to intraarterial digital subtraction angiography (DSA) to indicate additional treatment in the follow-up of patients with coil-treated intracranial aneurysms. This was an ethics committee-approved multicenter study. Consecutive patients who were scheduled for follow-up intraarterial DSA after coil placement were invited for additional MR angiography after providing written informed consent. Interventional neuroradiologists gave treatment advice (additional treatment, extended follow-up imaging, or discharge from follow-up) for each imaging modality. Agreement between treatment advices based on intraarterial DSA and MR angiographic findings and interobserver agreement were assessed with weighted κ statistics. Agreement between intraarterial DSA- and MR angiography-based treatment recommendations was substantial (κ = 0.73; 95% confidence interval [CI]: 0.66, 0.80). In 34 of the 310 patients (11%), the advice was additional treatment based on findings of both modalities. In six patients (2%), the advice based on intraarterial DSA findings was additional treatment, while that based on MR angiographic findings was extended follow-up imaging; therefore, none of these patients were discharged from follow-up on the basis of MR angiographic findings. In six other patients (2%), the advice based on MR angiographic findings was additional treatment, while that based on intraarterial DSA findings was extended follow-up imaging (four patients), discharge from follow-up (one patient), and noninterpretable DSA (one patient). Extended follow-up imaging was suggested for 37 patients (12%) after intraarterial DSA and for 49 patients (16%) after MR angiography (difference: 4%; 95% CI: -0.6%, 8.4%). Interobserver agreement was substantial for intraarterial DSA (κ = 0.73; 95% CI: 0.64, 0.82) and moderate for MR angiography (κ = 0.53; 95% CI: 0.36, 0.70). The overall proportion of patients advised to undergo additional treatment is similar based on intraarterial DSA and MR angiographic findings, with only few individual discrepancies. MR angiography can therefore be used for therapeutic decision making in the follow-up of patients with coil-treated aneurysms. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112608/-/DC1.

Intracranial Aneurysms Treated with Coil Placement: Test Characteristics of Follow-up MR Angiography—Multicenter Study

To determine the test characteristics of magnetic resonance (MR) angiography in the assessment of occlusion of aneurysms treated with coil placement. This was an ethics committee-approved multicenter study. written informed consent was obtained in 311 patients with 343 aneurysms, who had been treated with coil placement and were scheduled for routine follow-up with intraarterial digital subtraction angiography (DSA). Thirty-five patients participated two or three times. Either 3.0- or 1.5-T time-of-flight (TOF) and contrast material-enhanced MR angiography were performed in addition to intraarterial DSA. Aneurysm occlusion was evaluated by independent readers at DSA and MR angiography. The test characteristics of MR angiography were assessed by using DSA as the standard. The area under the receiver operating characteristic curve (AUC) was calculated for 3.0- versus 1.5-T MR angiography and for TOF versus contrast-enhanced MR angiography, and factors associated with discrepancies between MR angiography and DSA were assessed with logistic regression. Aneurysm assessments (n = 381) at DSA and MR angiography were compared. Incomplete occlusion was seen at DSA in 88 aneurysms (23%). Negative predictive value of MR angiography was 94% (95% confidence interval [CI]: 91%, 97%), positive predictive value was 69% (95% CI: 60%, 78%), sensitivity was 82% (95% CI: 72%, 89%), and specificity was 89% (95% CI: 85%, 93%). AUCs were similar for 3.0- (0.90 [95% CI: 0.86, 0.94]) and 1.5-T MR (0.87 [95% CI: 0.78, 0.95]) and for TOF MR (0.86 [95% CI: 0.81, 0.91]) versus contrast-enhanced MR (0.85 [95% CI: 0.80, 0.91]). A small residual lumen (odds ratio, 2.1 [95% CI: 1.1, 4.3]) and suboptimal projection at DSA (odds ratio, 5.5 [95% CI: 1.5, 21.0]) were independently associated with discordance between intraarterial DSA and MR angiography. Documentation of good diagnostic performance of TOF MR angiography at both 1.5 and 3.0 T in the current study represents an important step toward replacing intraarterial DSA with MR angiography in the follow-up of patients with aneurysms treated with coils.

Diagnostic pitfalls in postinterventional intraarterial magnetic resonance angiography after recanalization of femoropopliteal arterial occlusions

Magnetic resonance (MR)-guided vascular interventions are of increasing interest, and, with the use of contrast-enhanced techniques, intraarterial contrast-enhanced MR angiography (ia-ce-MRA) competes with intraarterial digital subtraction angiography (ia-DSA) for the diagnostic evaluation of the infrainguinal vessel tree. To assess the diagnostic value of ia-ce-MRA and high-resolution T1-weighted (hr-T1w) imaging compared to the gold-standard ia-DSA for residual stenosis and local dissections after femoropopliteal recanalization in patients with peripheral arterial occlusive disease (PAOD). Eight patients with PAOD and short vessel occlusion of their femoropopliteal arteries underwent recanalization and balloon positioning under DSA. Patients were transferred to a short-bore MR scanner. Percutaneous transluminal angioplasty (PTA) was accomplished under MR fluoroscopy. Pre- and postinterventional ia-ce three-dimensional (3D) gradient-echo MRA with gadopentate dimeglumine was performed using the intraarterial introducer sheath. Maximum intensity projections (MIP) and multiplanar reconstructions (MPR) were calculated from the data set. High-resolution T1w images of the angioplasty region before and after dilatation were acquired. Control ia-DSA images were obtained. The postinterventional angioplasty results for stenosis grading were comparable in ia-MRA and ia-DSA. Only two of five local dissections in ia-DSA were visualized with the ia-ce-MRA runs including MIPs and MPRs. To clearly depict dissection, hr-T1w images were needed. Grading of stenotic lesions with ia-ce-MRA after PTA is comparable to ia-DSA. Intraarterial ce-MRA with calculated MIPs and MPRs is only partially sufficient to visualize local dissections after PTA. High-resolution T1w images are required for precise diagnosis of dissections in magnetic resonance tomography.

Liver Tumors: Monitoring Embolization in Rabbits with VX2 Tumors—Transcatheter Intraarterial First-Pass Perfusion MR Imaging

To prospectively test the hypothesis that transcatheter intraarterial first-pass perfusion (TRIP) magnetic resonance (MR) imaging can depict serial reductions in rabbit liver tumor perfusion during transcatheter arterial embolization (TAE). All experiments had institutional animal care and use committee approval. In four rabbits implanted with eight VX2 liver tumors, catheters were positioned in the hepatic arteries with conventional angiographic guidance. After transfer to the MR imaging suite, serial TAE was performed, with approximately 0.5 million 40-120-microm embolic particles injected at each embolic stage. TRIP MR imaging was performed at baseline and after each subsequent embolic stage (10 minutes between stages). Serial TAE and TRIP MR imaging were repeated until stasis. The first-pass time course of signal enhancement was measured in both tumors and hepatic arteries. Tumor area under the curve (AUC) and maximum upslope (MUS) values, each normalized by arterial input, were measured to assess iterative perfusion reduction. Perfusion measurements across TAE stages were compared with paired t tests and linear regression. AUC decreased from a pre-TAE baseline of 0.408 (95% confidence interval [CI]: 0.330, 0.486) to 0.065 (95% CI: 0.046, 0.085) (P<.001) after TAE. MUS decreased from a pre-TAE baseline of 0.151 (95% CI: 0.121, 0.181) to 0.027 (95% CI: 0.022, 0.031) (P<.001) after TAE. Reductions to AUC and MUS after each embolic stage were statistically significant (P<.006 for each group of paired comparisons). AUC strongly correlated with MUS (r=0.966, P<.001). TRIP MR imaging can depict serial reductions in liver tumor perfusion during TAE. TRIP MR imaging offers the potential to target functional embolic end points during TAE.

Comparison of Transcatheter Intraarterial Perfusion MR Imaging and Fluorescent Microsphere Perfusion Measurements during Transcatheter Arterial Embolization of Rabbit Liver Tumors

Transcatheter intraarterial perfusion (TRIP) magnetic resonance (MR) imaging is clinically used in the interventional MR imaging setting to verify distribution of injected embolic or chemoembolic material during liver-directed transcatheter therapies and to monitor reductions in perfusion. The accuracy of this technique remains unknown. In the present study, rabbit VX2 liver tumors were used to test the hypothesis that TRIP MR imaging accurately measures changes in tumor perfusion during transcatheter arterial embolization (TAE), with injection of fluorescent microspheres used as the gold-standard technique. Five New Zealand White rabbits were used for this study (two donor rabbits and three with VX2 liver tumors). In three rabbits with implanted VX2 liver tumors, catheters were superselectively placed under digital subtraction angiographic guidance into the left hepatic artery supplying the targeted tumor. Fluorescent microspheres were injected into each rabbit's left ventricle before and after TAE. TRIP MR images were obtained at baseline and after embolizations for all rabbits with intraarterial injections of 2.5% gadopentetate dimeglumine solution. Linear regression was used to compare relative reductions in tumor perfusion between TRIP MR imaging and fluorescent microspheres. Results were considered statistically significant at a P value less than .05. There was good correlation between TRIP MR imaging and fluorescent microsphere measurements of reduction in tumor perfusion (r = 0.722, P < .012). TRIP MR imaging provides accurate semiquantitative measurement of perfusion reduction during TAE in rabbit liver tumors.

Comparison of Intraarterial MR Angiography at 3.0 T with X-ray Digital Subtraction Angiography for Detection of Renal Artery Stenosis in Swine

To compare the accuracy of catheter-directed intraarterial (IA) magnetic resonance (MR) angiography at 3.0 T with that of x-ray digital subtraction angiography (DSA) for the measurement of renal artery stenosis (RAS) in swine. Unilateral hemodynamically significant RAS (>50%) was induced surgically in six pigs with use of reverse cable ties. One to two weeks after surgery, each pig underwent x-ray DSA and MR angiography before and after percutaneous transluminal balloon angioplasty (PTA). X-ray DSA was performed before and after PTA of RAS by injection of iodinated contrast agent through a 5-F multiple-side hole angiographic catheter placed in the abdominal aorta under fluoroscopic guidance. MR angiography of RAS was performed before and after PTA of RAS on a 3.0-T clinical MR imager with use of gadolinium-based contrast agent. MR angiography and DSA images were analyzed with the full width at half maximum method. Percent stenosis measurements between x-ray DSA and MR angiography were compared with a paired t test and were correlated with linear regression and Bland Altman analysis (alpha = 0.05). Six cases of RAS were induced and imaged successfully with DSA and MR angiography techniques before and after PTA. On x-ray DSA, median stenoses was 64% (95% CI 57%-80%) before PTA and 20% (95% CI 5%-32%) after PTA. Corresponding MR angiography median stenosis measurement was 69% (95% CI 58%-80%) before PTA and 26% (95% CI 16%-36%) after PTA. A paired t test comparison did not show a difference between DSA and MR angiography (P = .16). RAS measurements on MR angiography correlated closely (P < .01) with DSA measurements (r(2) = 0.92). In swine, the accuracy of catheter-directed IA MR angiography with use of a clinical 3.0-T MR imaging unit for the measurement of RAS was similar to that of conventional x-ray DSA.

Intraarterial MR Angiography and DSA in Patients with Peripheral Arterial Occlusive Disease: Prospective Comparison

To prospectively evaluate the accuracy of intraarterial magnetic resonance (MR) angiography in the depiction of significant stenoses and occlusions, with intraarterial digital subtraction angiography (DSA) serving as the reference standard. Approval of the local ethics committee and informed consent were obtained. Twenty patients (11 men; nine women; age range, 48-86 years; mean age, 69.5 years+/-11.2 [standard deviation]) with symptomatic peripheral arterial occlusive disease (PAOD) were prospectively enrolled. After percutaneous transluminal angioplasty (PTA), intraarterial MR angiography was performed in the thigh and the calf with a 1.5-T MR imager in two consecutive runs. Intraarterial MR angiography was performed with a low-dose injection protocol (ie, two 20-mL injections of a 50-mmol gadolinium-based contrast agent). Moderate stenoses (luminal narrowing<or=50%), significant stenoses (luminal narrowing 51%-99%), and occlusions (luminal narrowing of 100%) were identified on MR angiograms, which were compared with intraarterial DSA images. Intraarterial MR angiograms were analyzed for imaging artifacts. Sensitivity, specificity, accuracy, and positive and negative predictive values of intraarterial MR angiography with intraarterial DSA were determined for characterization of significant stenoses (>50%) or vessel occlusions; 95% confidence intervals (CIs) were calculated for sensitivity and specificity. Intraarterial DSA revealed 78 moderate stenoses, 57 significant stenoses, and 28 occlusions. Sensitivity, specificity, and accuracy of intraarterial MR angiography in the characterization of significant stenoses or occlusions were 92% (95% CI: 72%, 99%), 94% (95% CI: 82%, 98%), and 93%, respectively, in femoropopliteal arteries and 93% (95% CI: 83%, 98%), 71% (95% CI: 51%, 86%), and 86%, respectively, in infrapopliteal arteries. The main artifact observed with intraarterial MR angiography was venous contamination (12%). Intraarterial MR angiography is an accurate method used to depict significant stenoses and occlusions in lower extremity arteries with a low-dose injection protocol.

Magnetic Resonance-Guided Percutaneous Angioplasty of Femoral and Popliteal Artery Stenoses Using Real-Time Imaging and Intra-arterial Contrast-Enhanced Magnetic Resonance Angiography

The aim of this study was to demonstrate the possibility of performing magnetic resonance (MR)-guided interventional therapy for femoral and popliteal artery stenoses with commercially available materials supported by MR real-time imaging and intra-arterial MR angiography. A total of 15 patients suffering from symptomatic arterial occlusive disease of the lower limbs with 19 stenoses were included. Interventional intra-arterial digital subtraction angiography was performed before and after angioplasty on each patient as standard of reference. MR images were acquired on a 1.5-T MR scanner. A fast-low-angle shot (FLASH) 3D sequence was applied for a contrast enhanced MR-angiography (ceMRA). A total of 5 mL of diluted gadodiamide was injected via the arterial access. Maximum intensity projections (MIPs) were used as roadmaps and localizers for the interactive positioning of a continuously running 2D-FLASH sequence with a temporal solution of 2 images/second. The lesion was crossed by a balloon-catheter, which was mounted on a guidewire. The visibility was provided by the radiopaque markers on the balloon and was improved by injection of 1 mL of gadolinium into the balloon. Postinterventional control was performed by intra-arterial MR angiography and catheter angiography. Stenoses were localized by intra-arterial MR angiography. The guidewire/balloon combination was visible, and the balloon was placed correctly to cover the entire stenoses. Balloon dilation reduced the degree of stenosis by approximately 57% on average. No complications were observed. MR-guided balloon dilation of femoral and popliteal artery stenoses supported by real-time MR imaging and intra-arterial MR angiography is feasible with commercially available materials.

Lower Extremity: Low-Dose Contrast Agent Intraarterial MR Angiography in Patients—Initial Results

Institutional review board approval and patient consent were obtained. A low-dose injection protocol for intraarterial three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography was derived from femoral flow phantom studies and prospectively evaluated in patients with peripheral arterial occlusive disease (PAOD). All MR angiograms were obtained at 1.5 T with a T1-weighted gradient-echo sequence. MR angiograms of a gadolinium dilution series (0.8-200.0 mmol/L) were acquired in a femoral phantom at different flow rates. Signal-to-noise ratios (SNRs) above the 75% threshold of the measured maximum were considered optimal. The lowest optimal concentration was injected intraarterially in nine patients to obtain 3D MR angiograms of the thigh and calf station. Contrast-to-noise ratios (CNRs) were calculated for four arterial segments. The low optimal concentration of 50 mmol/L (20-mL bolus volume), about 5% of the total permissible dose, showed SNRs larger than the 75% threshold in the phantom study. In patients, this concentration led to high-spatial-resolution angiograms with mean CNRs of 70.0 +/- 14.5 (+/- standard deviation) for the superficial femoral artery and 47.5 +/- 13.4 at the infrapopliteal level. Low-dose contrast agent intraarterial 3D MR angiography showed high arterial enhancement, enabling assessment of lower extremity arteries in patients with PAOD and multiple injections--a crucial precondition for MR-guided endovascular interventions.

Intraarterial Contrast Material–Enhanced Magnetic Resonance Angiography of the Aortoiliac System

In a period of 4 months, 10 patients were examined prospectively with intraarterial magnetic resonance (MR) angiography after digital subtraction angiography. Intraarterial MR angiography was performed with use of a 1.5-T MR imaging system. Contrast agent (gadodiamide) was injected with a conventional angiography catheter placed in the proximal abdominal aorta. The increase in vascular signal intensity was determined and the diagnostic value of the MR angiograms was scored according to a five-point scale by four investigators. The MR angiograms were judged good to excellent, and all were scored as diagnostic. In conclusion, this study shows that intraarterial MR angiography is feasible. Intraarterial MR angiography is appropriate to support MR-guided vascular intervention.

Renal embolization: feasibility of magnetic resonance-guidance using active catheter tracking and intraarterial magnetic resonance angiography.

Magnetic resonance (MR)-guidance of endovascular interventions offers various advantages, including the absence of ionizing radiation, excellent soft tissue contrast, and multiplanar and functional imaging capabilities. The objective of this study was to assess the feasibility of MR-guided renal embolization using active catheter tracking with automatic slice positioning and intraarterial contrast-enhanced MR angiography (MRA). MR-guided embolization of 16 kidneys was attempted in 15 pigs using real-time tracking of active 5-Fr. catheters. Embolization was monitored by selective intraarterial projection MRA. Intraarterial three-dimensional (3D) MRA was used for the assessment of embolization results. Additional pathologic correlation was available in 2 animals. The image quality of intraarterial 3D contrast-enhanced-MRA was rated by an independent radiologist who was not involved in the animal experiments. Active catheter tracking with automatic slice positioning allowed reliable catheter guidance and catheterization of the renal artery in all animals. Embolization was successful in all kidneys (11 left, 5 right), as verified by intraarterial 3D contrast-enhanced MRA (ce-MRA) and/or pathology. The image quality of intraarterial 3D ce-MRA was rated excellent in 10 animals, moderate in 4 animals, and poor in 1 animal. Renal embolization using active catheter tracking and intraarterial ce-MRA is feasible. Selective intraarterial ce-MRA allows the assessment of blood supply and organ perfusion before, during, and after therapeutic interventions, thereby complementing MR-guided endovascular interventions.

Experimental Approach to the Intra-arterial Magnetic Resonance Imaging Contrast Media (Gd-DTPA-Iodized Oil) and New Lipophilic Gadolinium Complex Combined with Iodized Oil

Experimental Approach to the Intra-arterial Magnetic Resonance Imaging Contrast Media (Gd-DTPA-Iodized Oil) and New Lipophilic Gadolinium Complex Combined with Iodized Oil

Cerebral venography with MR.

The authors describe a two-dimensional time-of-flight magnetic resonance (MR) angiography technique to create projection venograms of the head. The technique was applied to 27 healthy volunteers and 39 patients. The superior sagittal and straight sinuses, the internal cerebral veins, and the Galen vein were visualized in all the volunteers. Other veins were seen in a high percentage of subjects. Systematic comparison of digital subtraction angiography (DSA) after intraarterial contrast medium injection and MR venography in patients showed good correlation between the two techniques. MR venography proved helpful in identifying thrombosis or patency of cerebral veins and sinuses and showed collateral venous drainage and venous drainage from arteriovenous malformations. There was good correlation between conventional contrast angiography and MR venography. In conclusion, MR venography is considered reliable for showing the cerebral venous system and provides information additional to that of conventional spin-echo imaging.