Intraarterial gadolinium-enhanced 2D and 3D MR angiography: a preliminary study

PURPOSE: To evaluate, in phantom and canine models, intraarterial gadolinium-enhanced two-dimensional (2D) and three-dimensional (3D) magnetic resonance angiography (MRA). MATERIALS AND METHODS: The in vitro experiments examined gadodiamide solutions ranging in gadolinium (Gd) concentration from 0.1% to 100%. A spoiled gradient-recalled echo (SPGR) sequence was used with various repetition time/echo time (TR/TE) parameters. Signal was measured to determine which concentration yielded the highest signal. For in vivo experiments, pigtail catheters were placed in the abdominal aortae of two dogs. Intraarterial injections of 20-30 mL of 0.5%-25% Gd solutions were performed. We acquired images with use of 2D and 3D SPGR techniques. Depiction of the abdominal aortae and renal vessels was assessed qualitatively and quantitatively. RESULTS: Phantom experiments demonstrated that a 2%-6% solution of Gd produced the highest MR signal, depending on the imaging parameters. In the canine model, a 2% Gd solution was best for 2D techniques, whereas 7%-14% Gd solutions were optimal for 3D techniques. CONCLUSIONS: Intraarterial contrast material-enhanced 2D and 3D MRA can be successfully implemented with use of dilute Gd. Dilution permits the administration of more intraarterial injections per day, without exceeding the dose limit, compared with intravenous Gd-enhanced MRA. Intraarterial injections also limit scan synchronization and contrast material dispersion issues. This technique may have application in MR-guided endovascular procedures.     

Intraarterial versus IV gadolinium injections for MR angiography: quantitative and qualitative assessment of the infrainguinal arteries

OBJECTIVE: Our purpose was to quantitatively and qualitatively compare 3D intraarterial (IA) gadolinium-enhanced MR angiography (IA MRA) versus the standard of reference of MR angiography, 3D IV gadolinium-enhanced MR angiography (IV MRA), in patients with peripheral arterial occlusive disease (PAOD) for use during catheter-based MR-guided endovascular interventions. CONCLUSION: IA MRA provides image quality of the infrainguinal arteries in PAOD patients comparable to IV MRA with a significantly improved assessment of the infrapopliteal arteries due to reduced venous contamination. Further benefits of IA MRA include usage of only very low doses of gadolinium and simplified bolus timing.     

Using gadolinium-enhanced three-dimensional MR angiography to assess arterial inflow stenosis after kidney transplantation

OBJECTIVE: Our objective was to evaluate use of gadolinium-enhanced three-dimensional (3D) MR angiography in the assessment of suspected arterial inflow stenosis after kidney transplantation. SUBJECTS AND METHODS: Twenty-eight consecutive patients receiving kidney transplants (26 single-kidney transplants and two en block transplants) with suspected arterial inflow stenosis were examined with two MR angiography sequences: gadolinium-enhanced 3D fast spoiled gradient-recalled (SPGR) imaging and 3D phase-contrast imaging. Twenty-four of these patients then were examined using the gold standards: either digital subtraction angiography (DSA) (n = 23) or surgery (n = 1). MR angiography and DSA studies were independently and prospectively analyzed for the presence of arterial stenoses (mild [<50%], severe [50-90%], or critical [>90%]) in the iliac, anastomotic, and renal artery segments. Two independent observers retrospectively evaluated the MR angiography sequences for ability to detect or exclude significant (> or = 50%) arterial stenoses. RESULTS: In 22 single-kidney transplants, DSA showed eight significant stenoses in 66 arterial segments. MR angiograms adequately showed 66 of 66 segments (prospective observers) and 64 of 66 segments (each retrospective observer), which were subsequently evaluated. The sensitivity and specificity of MR angiography in revealing significant stenoses were 100% and 98% (prospective analysis), 88% and 98% (retrospective observer 1), and 86% and 100% (retrospective observer 2). Concordance between observers showed kappa values exceeding .85 for all comparisons except the analysis of phase-contrast series (kappa = .62). In one en block transplant, DSA showed that stenosis was greater than 90%, although it had been graded at less than 50% with MR angiography. CONCLUSION: Gadolinium-enhanced 3D MR angiography accurately evaluated arterial inflow in single-kidney transplants.     

Three-dimensional gadolinium-enhanced MR angiography of vascular complications after liver transplantation

OBJECTIVE: The goal of this study was to evaluate three-dimensional gadolinium-enhanced MR angiography as a tool for examination of liver transplant patients with potential vascular complications. MATERIALS AND METHODS: Thirty-eight consecutive three-dimensional gadolinium-enhanced MR angiograms were obtained in 34 patients. Results were retrospectively reviewed and correlated with conventional angiography in 20 of the 38 cases and sonography in 37 of the 38 cases. MR angiograms were evaluated for technical adequacy, vascular patency, and parenchymal abnormalities, and results were compared with angiography and sonography. Conventional angiography and surgery were used as gold standards when available. RESULTS: Thirty-four (90%) of 38 MR angiograms were technically adequate. Vascular abnormalities were identified in 20 patients, and 19 of these patients subsequently underwent angiography, surgery, or both. There were seven cases of hepatic artery thrombosis; all were detected with MR angiography with no false-positive or false-negative interpretations. Seven patients had moderate to severe hepatic artery stenosis (>50% narrowing as determined by conventional angiography). MR angiography revealed this stenosis in six of the seven patients, with one false-negative and three false-positive interpretations. Portal vein thrombosis was detected in three patients, and portal vein stenosis was detected in two patients. CONCLUSION: Three-dimensional gadolinium-enhanced MR angiography is useful in the examination of liver transplant patients and offers a noninvasive adjunct in patients with difficult or indeterminate sonographic examinations.     

Selection of patients with infrainguinal arterial occlusive disease for percutaneous transluminal angioplasty with duplex scanning

Aim:
To evaluate the role of duplex scanning in the selection of patients with infrainguinal arterial occlusive disease for percutaneous transluminal angioplasty (PTA). Material and Methods:
From January 1995 through May 2000, 702 patients (952 limbs), with chronic lower extremity ischemia due to infrainguinal atherosclerotic disease diagnosed by duplex scanning, were retrospectively studied. Diagnostic angiography (130 limbs) or infrainguinal PTA (108 limbs) was performed in 238 limbs. Two investigators retrospectively analyzed the duplex examinations and angiographies in a blinded manner and used similar criteria for the interpretation of lesions suitable or not suitable for PTA. Results:
The superficial femoral, popliteal and crural artery lesions were correctly selected for PTA in 85%, 66% and 32%, respectively. The accuracy, sensitivity, specificity, negative predictive value and positive predictive value of duplex scanning to appropriately categorize femoropopliteal lesions as suitable or unsuitable for PTA were 89%, 83%, 92%, 94% and 78%, respectively. The accuracy of duplex scanning for predicting the performance of infrainguinal PTA was 83%. Conclusion:
Duplex scanning has an important impact on the selection of treatment modalities in limbs with infrainguinal arterial occlusive disease. Femoropopliteal lesions can be reliably selected to PTA according to duplex scan findings.     

Angiographic characteristics of symptomatic recurrent disease after infrainguinal percutaneous transluminal angioplasty

Purpose: To evaluate the angiographic patterns of clinically manifest recurrent disease after infrainguinal percutaneous transluminal angioplasty (PTA) of stenoses and total occlusions. Methods: Among 326 infrainguinal PTAs on 263 consecutive patients, selective angiography was performed on 61 limbs of 52 patients 1–60 months after the primary intervention because of clinically suspected recurrent disease. Lesion-specific and patient-related factors were analyzed for 75 angiographically confirmed recurrent lesions in 57 limbs of 48 patients. Results: Recurrent disease was more frequently a stenosis when the original target lesion was a stenosis (92%, 44/48) than when the original lesion was a total occlusion (59%, 16/27; p < 0.001). When the original target lesion was a stenosis, the total length of the recurrent disease was longer than that of the original lesion [3.9 ± 3.9 cm (mean ± standard deviation) vs 2.8 ± 2.7 cm; p= 0.03], while in the subgroup of original total occlusions the length of the recurrent lesion was shorter than that of the original occlusion (7.1 ± 5.0 cm vs 9.9 ± 6.9 cm; p= 0.02). Half the restenoses (22/44) extended beyond one or both ends of the original stenosis and 38% (6/16) of the reocclusions extended beyond the distal end of the original occlusion. Conclusions: The type of recurrent disease depends on the original lesion type and the restenotic lesion frequently extends beyond one or both ends of the original target lesion.     

Intraarterial MR angiography and DSA in patients with peripheral arterial occlusive disease: prospective comparison

PURPOSE: 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. MATERIALS AND METHODS: 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 narrowing50%) or vessel occlusions; 95% confidence intervals (CIs) were calculated for sensitivity and specificity. RESULTS: 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%). CONCLUSION: Intraarterial MR angiography is an accurate method used to depict significant stenoses and occlusions in lower extremity arteries with a low-dose injection protocol.     

Comparison of intraarterial and IV gadolinium-enhanced MR angiography with digital subtraction angiography for the detection of renal artery stenosis in pigs.

OBJECTIVE: Catheter-based intraarterial injections of gadolinium are useful during MR imaging-guided endovascular procedures to generate rapid vascular road maps. Using an animal model of renal artery stenosis, we tested the hypothesis that intraarterial gadolinium-enhanced MR angiography is as accurate as IV gadolinium-enhanced MR angiography and digital subtraction angiography (DSA). We also tested the hypothesis that intraarterial MR angiography uses less gadolinium than IV MR angiography. MATERIALS AND METHODS: We induced bilateral renal artery stenosis in five pigs. All pigs underwent comparative imaging with DSA, IV MR angiography, and aortic catheter-directed intraarterial MR angiography. For IV and intraarterial MR angiography, we used the same three-dimensional acquisition. We assessed differences in quantitative stenosis measurements among DSA, IV MR angiography, and intraarterial MR angiography using the Wilcoxon's signed rank test. RESULTS: Mean stenosis measurements (+/-SD) were as follows: DSA, 58% +/- 12%; IV MR angiography, 63% +/- 9.3%; and intraarterial MR angiography, 64% +/- 11%. There were no statistically significant differences in accuracy between DSA and IV MR angiography (p = 0.06), DSA and intraarterial MR angiography (p = 0.16), or IV and intraarterial MR angiography (p = 0.70). Intraarterial MR angiography used a mean gadolinium dose of 5.6 mL, compared with 9 mL for IV MR angiography. CONCLUSION: In swine, IV and intraarterial MR angiography have a similar accuracy for detecting renal artery stenosis. Intraarterial MR angiography uses smaller doses of injected gadolinium.     

Determination of optimal injection parameters for intraarterial gadolinium-enhanced MR angiography

PURPOSE: Rapid vascular depiction with use of a minimum of gadolinium (Gd) contrast agent will be required to generate road-map vascular images for magnetic resonance (MR) imaging-guided endovascular interventions. The objective of this study was to optimize intraarterial injections of MR contrast agent during magnetic resonance angiography (MRA), obtained during interventions, by determining the optimal Gd vascular concentration ([Gd]) for vessel depiction. MATERIALS AND METHODS: The authors derived theoretical expressions to estimate the [Gd] resulting in maximal signal in blood. A model was developed to account for flow dilution to estimate [Gd] given the injected Gd concentration, injection rate, and the blood flow rate. Experiments in four animals (three dogs, one pig) were conducted to verify this model with use of both time-resolved two-dimensional (2D) thick-slab and single-phase three-dimensional (3D) MRA acquisitions. The authors also determined the optimal [Gd] required for vessel depiction in animal models. RESULTS: The theoretical expressions yielded optimal [Gd] of 10.2 mmol/L in blood. The animal experiments used the flow dilution model and examined signal enhancement in the aorta and the renal and iliac arteries. Maximal enhancement occurred at [Gd] = 16.2 +/- 4.0 mmol/L (mean +/- SE). CONCLUSIONS: The theoretically predicted values for [Gd]optimal and the flow dilution model were successfully validated. The relationship between injected [Gd], injection rate, and blood flow rate permits rapid intraarterial administration of contrast material, using less overall contrast material than with standard intravenous Gd-enhanced MRA.     

Validation of injection parameters for catheter-directed intraarterial gadolinium-enhanced MR angiography

RATIONALE AND OBJECTIVES: Catheter-directed intraarterial (IA) injections of gadolinium contrast agents may be used during endovascular interventions with magnetic resonance (MR) imaging guidance. Injection protocols require further validation. Using a flow phantom and swine, the authors aimed to (a) measure the optimal arterial gadolinium concentration ([Gd]) required for MR angiography and (b) validate a proposed IA injection protocol for gadolinium-enhanced MR angiography. MATERIALS AND METHODS: For in vitro experiments, the authors placed a catheter in the aorta of an aorto-renal-iliac flow phantom. Injected [Gd], injection rates, and aortic blood flow rates were varied independently for 36 separate IA gadolinium injections. The authors performed 2D and 3D MR angiography with a fast spoiled gradient-recalled echo sequence. For subsequent in vivo experiments, they selectively placed catheters within the aorta, renal artery, or common iliac artery of three pigs. Injection rate and injected [Gd] were varied. The authors performed 32 separate IA gadolinium injections for 2D MR angiography. Signal-to-noise ratios (SNRs) were compared for the various combinations of injection rate and injected [Gd]. RESULTS: In vitro, an arterial [Gd] of 2%-4% produced an optimal SNR for 2D MR angiography, and 3%-5% was best for 3D MR angiography. In swine, an arterial [Gd] of 1%-4% produced an optimal SNR. In the phantom and swine experiments, SNR was maintained at higher injection rates by inversely varying the injected [Gd]. CONCLUSION: Dilute arterial [Gd] is required for optimal IA gadolinium-enhanced MR angiography. To maintain an optimal SNR, injection rates and injected [Gd] should be varied inversely. The postulated injection protocol was validated.     

MR angiography of moyamoya disease before and after encephaloduroarteriosynangiosis

OBJECTIVE: Our purpose was to evaluate the usefulness of MR angiography in revealing moyamoya disease before and after encephaloduroarteriosynangiosis. SUBJECTS AND METHODS: Twenty-six patients (51 hemispheres) with angiographically confirmed moyamoya disease who underwent encephaloduroarteriosynangiosis were included in the study. Findings on preoperative MR angiography were compared with those on conventional angiography. Postoperative neurologic status was categorized as poor, fair, good, or excellent. Postoperative MR angiography was examined for the appearance of the superficial temporal artery, changes in moyamoya vessels, and transdural collateral vessels into the middle cerebral artery territory. RESULTS: Preoperative MR angiography revealed moyamoya disease in all patients (diagnostic accuracy, 100%). MR angiography correctly depicted the degree of internal carotid artery stenosis in 37 arteries (73%), moyamoya vessels in 33 hemispheres (65%), and the degree of stenosis in the middle, anterior, and posterior cerebral arteries in 125 (82%) of 153 arteries. After surgery, 39 hemispheres showed an excellent outcome, eight showed a good outcome, two a fair outcome, and two a poor outcome. On postoperative MR angiography, vascular supply to the middle cerebral artery territory via transdural collateral vessels increased in 28 hemispheres (55%) and decreased in four (8%). The size of the superficial temporal artery increased in 41 (80%) of 51 hemispheres. The extent of moyamoya vessels decreased in 27 hemispheres (53%) after surgery. CONCLUSION: MR angiography can show the changes in the superficial temporal artery and development of transdural collateral vessels after encephaloduroarteriosynangiosis. Because MR angiography is noninvasive, it is valuable for evaluating postoperative changes.     

Single-dose breath-hold gadolinium-enhanced three-dimensional MR angiography of the renal arteries

PURPOSE: To evaluate the quality of single-dose breath-hold three-dimensional (3D) magnetic resonance (MR) angiography of the renal arteries optimized with a 1-mL test bolus timing examination. MATERIALS AND METHODS: Three-dimensional spoiled gradient-echo imaging (3.8-4.2/1.3-1.7 [repetition time msec/echo time msec], 25 degrees-40 degrees flip angle) was performed in 60 patients after administration of gadopentetate dimeglumine (average dose, 0.11 mmol/kg). Synchronization of contrast material administration with data acquisition was achieved with a 1-mL test dose of contrast material to estimate patient circulation parameters. Image quality was assessed by using contrast-to-noise (CNR), relative vascular enhancement, and venous-to-arterial enhancement ratios and subjective scoring of arterial and venous enhancement. The effect of the contrast material injection rate and the influence of breath holding during the timing examination also were examined. RESULTS: Overall, of 60 studies, 58 were diagnostic and 56 demonstrated excellent arterial enhancement. Venous enhancement was seen in eight studies. The average aortic relative vascular enhancement (+/- SD) was 14.6 +/- 5.9, with an aorta-to-inferior vena cava (IVC) CNR of 69.7 +/- 43.9. The IVC-to-aorta venous-to-arterial enhancement ratio averaged 0.08 +/- 0.16. There was no significant difference in image quality based on injection rates or the performance of breath holding during the timing examination (P > .1). CONCLUSION: Breath-hold gadolinium-enhanced renal MR angiography free of venous enhancement can be performed consistently and reliably with 20 mL of contrast material when studies are synchronized to patient circulation time by using a timing examination.     

Multiphase-multistep gadolinium-enhanced MR angiography of the abdominal aorta and runoff vessels

RATIONALE AND OBJECTIVES: To optimize three-dimensional gadolinium magnetic resonance angiography (3D-Gd-MRA) of the aorta and runoff vessels by addressing fundamentally different requirements for temporal and spatial resolution in a single semiautomated examination. METHODS: The technique was designed to obtain pure arterial-phase 3D-Gd-MR angiograms with adequate spatial resolution for each station while avoiding incomplete enhancement due to delayed filling vessels as well as venous overlay. During gadolinium-chelate infusion, a breath-held multiphase 3D-Gd-MRA scan was initiated in the aorta by automatic triggering, followed by automatic table movement. The acquisition was tailored to the vessels of interest by tilting of the 3D volumes. A spatial resolution of 1.7 x 1.2 x 0.8 mm in the calves was achieved by use of elliptical-centric k-space reordering. Signal-to-noise ratio was maximized with a 12-element peripheral vascular coil. Twelve patients with peripheral vascular disease were studied. RESULTS: In cases of aortic occlusive disease (n = 2), dissections (n = 3), or aneurysms (n = 4), substantially delayed fill-in of reconstituted arteries, false lumens, or aneurysmal segments occurred, which was detected only on the later 3D-Gd-MRA phase. High-resolution arterial-phase scans in the calves were obtained, with only one case of substantial venous overlay. Correlation to digital subtraction angiography revealed excellent agreement of pathological findings. CONCLUSIONS: Multiphase-multistep 3D-Gd-MRA reduces the limitations of standard 3D-Gd-MRA techniques with respect to anatomic coverage, spatial resolution, and nonuniform arterial vessel enhancement.     

Examination of susceptibility artifact in three-dimensional gadolinium-enhanced chest MR angiography

Signal loss that is sometimes found in the subclavian artery during chest MR angiography is thought to be caused by the susceptibility effect of highly concentrated contrast medium. In our research project, we examined the conditions under which signal loss occurs. We made vessel phantoms (artery phantom, vein phantom) that contained different concentrations of Gd-DTPA water solutions, and placed them in a 0.5 mmol/l Gd-DTPA water solution. We examined signal loss when the vein phantom was parallel to the magnetic field and when it was perpendicular to the magnetic field. We found that there was no signal loss in the artery phantom when the vein phantom was parallel to the magnetic field. In contrast, signal loss occurred in the artery phantom when the vein phantom was perpendicular to the magnetic field. The higher the concentration in the vein phantom, the closer the distance to the vessel phantom, and the longer the echo time (TE), the greater was the signal loss. Thus, the cause of signal loss in the subclavian artery was found to be the perpendicular orientation of the subclavian vein (through which the highly concentrated contrast medium flows) to the magnetic field. With the MRI devices currently in use, perpendicular orientation of the subclavian vein to the magnetic field cannot be avoided. Furthermore, the subclavian vein and subclavian artery are anatomically in close proximity to one another. These factors cause the susceptibility artifact, which is thought to result in signal loss in the subclavian artery.     

Intraarterial digital subtraction angiography in detection of hepatocellular carcinoma

To evaluate the usefulness of intraarterial digital subtraction angiography (IADSA) in hepatocellular carcinoma, IADSA was prospectively performed, combined with conventional film-screen angiography, in 40 patients in whom the tumor was histologically proven or highly suspected. Of the 16 main tumors less than 2 cm, IADSA detected 7 that were missed by film-screen angiography; 6 of these were less than 1 cm in size. With other diagnostic modalities including ultrasound; routine CT study, and CT after intraarterial Lipiodol injection, the detection rate of these tumors was low. IADSA's contribution is important in the detection of small hepatocellular carcinomas.