Radiology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online before print April 26, 2006, 10.1148/radiol.2393041574
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
2393041574v1
239/3/901    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Huegli, R. W.
Right arrow Articles by Bilecen, D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Huegli, R. W.
Right arrow Articles by Bilecen, D.
(Radiology 2006;239:901-908.)
© RSNA, 2006

Vascular and Interventional Radiology

Intraarterial MR Angiography and DSA in Patients with Peripheral Arterial Occlusive Disease: Prospective Comparison1

Rolf W. Huegli, MD, Markus Aschwanden, MD, Georg Bongartz, MD, Kurt Jaeger, MD, Hans-Georg Heidecker, MD, Christoph Thalhammer, MD, Anja-Carina Schulte, PhD, Claus Hashagen, MD, Augustinus L. Jacob, MD and Deniz Bilecen, MD

1 From the Departments of Radiology (R.W.H., G.B., H.G.H., C.H., A.L.J., D.B.) and Angiology (M.A., K.J., C.T.), University Hospital of Basel, Petersgraben 4, 4031 Basel, Switzerland; and Biocenter, University of Basel, Basel, Switzerland (A.C.S.). Received September 10, 2004; revision requested November 18; final revision received July 25, 2005; final version accepted August 11. Address correspondence to R.W.H. (e-mail: rhuegli{at}uhbs.ch).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
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 narrowing ≤ 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.

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.

© RSNA, 2006


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Intraarterial digital subtraction angiography (DSA) is currently the reference standard in diagnostic angiography. This catheter-guided invasive technique enables therapeutic intervention in terms of percutaneous transluminal angioplasty (PTA), which is a well-accepted therapy in the treatment of stenosis and occlusion in patients with symptomatic peripheral arterial occlusive disease (PAOD). PAOD is a chronic and widespread clinical disease with an age-adjusted prevalence of approximately 12% (1). It is most often caused by atherosclerosis (2).

During the past decade, gadolinium-enhanced magnetic resonance (MR) angiography with intravenous injection has been developed to provide a noninvasive alternative to diagnostic intraarterial DSA in the evaluation of atherosclerosis (3–8). The major advantages of MR angiography over DSA are (a) absence of x-ray exposure for the patient and investigator, (b) lack of nephrotoxic iodinated contrast media administration and reduction of allergic reactions, (c) three-dimensional vascular delineation of the arterial tree, and (d) excellent bone and soft-tissue contrast.

These favorable properties of MR imaging encouraged researchers to extend their investigations from diagnostic MR angiography to include therapeutic MR imaging–guided endovascular interventions (9–16). However, for MR imaging–guided interventions, intraarterial injection of gadolinium-based contrast media is more advantageous than intravenous injection, since an introducer sheath and/or a selective catheter has already been placed in the vessel lumen and gadolinium-based contrast media can be injected rapidly. Additionally, phantom and animal studies showed that intraarterial MR angiography allowed a substantial gadolinium dosage reduction compared with that used for intravenous MR angiography, without loss of image quality (9,12,15); this is important, as repetitive contrast agent injections are required.

Thus, the potential of intraarterial MR angiography in MR imaging–guided endovascular interventions is currently a subject of growing research activity. The primary aim of these activities is the acquisition of catheter-guided intraarterial MR angiograms with high spatial resolution and appropriate arterial enhancement.

In accordance with the findings of fundamental phantom and animal studies (12,15,17), a low-dose injection protocol was recently developed and used with intraarterial MR angiography in humans; this technique was proved to be useful in the arterial flow conditions in the lower extremity in patients with PAOD (17).

As a next step toward interventional MR angiography, a comparative study of intraarterial MR angiography and intraarterial DSA in patients seems warranted to determine its diagnostic value. Intraarterial MR angiography would be the method of choice for image acquisition with regard to MR imaging–guided endovascular interventions, if it could be proved that intraarterial MR angiography is accurate in the diagnostic assessment of the arterial tree.

Thus, the purpose of this study was to prospectively evaluate the accuracy of intraarterial MR angiography in the depiction of significant stenoses and occlusions, with intraarterial DSA serving as the reference standard.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Subjects
Within a 6-month period in 2003, 20 patients (11 men; nine women; age range, 48–86 years; mean age, 69.5 years ± 11.2 [standard deviation]) were consecutively enrolled in this study. All patients had PAOD with intermittent claudication (Fontaine classification stage II). Patients were scheduled to undergo PTA with DSA guidance. Grading and location of stenoses were preevaluated with duplex sonography (ATL HDI 5000; Philips, Best, the Netherlands).

Inclusion criteria were stenoses of more than 50% or occlusions within either the iliac axis or the femoropopliteal axis that could be treated with PTA. Exclusion criteria were general contraindications to MR imaging (pacemakers, ferromagnetic implants, or claustrophobia). Table 1 summarizes the characteristics of the patient population. The local ethics committee at the University Hospital of Basel approved the study protocol, and informed consent was obtained from all patients.


View this table:
[in this window]
[in a new window]

  		Table 1. Patient Characteristics

 
Intraarterial DSA
Patients were referred to the interventional unit of the radiology department to undergo DSA-guided PTA. Vascular access was obtained in either the ipsilateral antegrade or the contralateral retrograde crossover direction. Intraarterial DSA was performed by two authors (R.W.H. and A.L.J., with 3 and 12 years of experience in interventional radiology, respectively). Examinations were performed with a standard angiographic unit (Multistar; Siemens Medical Systems, Erlangen, Germany).

Numbers and sites of PTA in all patients are listed in Table 1. Follow-up intraarterial DSA of the arterial tree was performed at the end of PTA and served as the reference standard for intraarterial MR angiography.

A mean total of 100 mL (range, 50–160 mL) of iopromide (Ultravist 300; Schering, Berlin, Germany) was injected. In patients (n = 4) who underwent crossover angiography, the tip of the 6-F sheath (Radiofocus Glidecath; Terumo, Leuven, Belgium) was positioned at the level of the common femoral artery. The following flow rates (measured in milliliters per second) and total volumes (measured in milliliters) in a 1:1 dilution of saline and contrast material were applied with a power injector (Angiomat; Liebel Flarsheim, Cincinnati, Ohio) according to our standard protocol (18): femoral artery, 6 mL and 3 mL/sec; popliteal artery, 8 mL and 4 mL/sec; and calf, 15 mL and 5 mL/sec. In patients (n = 16) who underwent antegrade angiography, contrast material was manually injected over the side port of the 4-F introducer sheath (St Jude Medical, Minnetonka, Minn); a total of 9 mL of contrast material was injected in the femoral and crural regions, with saline-to–contrast media ratios of 1:1 and 1:2, respectively. The tip of the sheath was localized within the lumen of the proximal superficial femoral artery. No vasodilatation drugs were administered during intraarterial DSA. The number of projections was at the discretion of the angiographer. Intraarterial DSA data sets served as the reference standard.

After the intervention, patients were transferred from the DSA suite to the MR imaging suite on a stretcher. During transportation, the intraarterial sheath was continuously flushed with a mixture of 5000 IU of heparin (Liquemin; B. Braun Medical, Emmenbruecke, Switzerland) per liter in an isotonic saline solution at a flow rate of 1 mL/min to ensure patency of the system. Patient transportation to and from the MR tomograph, together with repositioning, took approximately 20 minutes. Data acquisition for intraarterial MR angiography was performed no more than 30 minutes after intraarterial DSA.

Intraarterial MR Angiography
All MR imaging was performed with a clinical whole-body 1.5-T unit (Magnetom Sonata; Siemens Medical Solutions, Erlangen, Germany) equipped with a high-performance gradient system operating at a gradient strength of 40 mT/m and a slew rate of 200 T/m/sec. A phased-array peripheral vascular coil was used for signal reception. Asymmetric sequential k-space acquisition was performed; k-space center was reached after 8 seconds. Patients were examined in the supine position, with the feet first in the MR imager.

Intraarterial MR angiography data sets were acquired by using a three-dimensional fast low-angle shot gradient-echo sequence with fat suppression. To cover the whole vascular tree of the lower extremity, MR data were acquired in two consecutive steps. The first acquisition covered the thigh station, and the second acquisition covered the calf station; there was a 10-cm image overlap. The interval between injections was approximately 5 minutes to allow image reconstruction and sufficient washout of contrast agent from the arterial blood. The average examination time for intraarterial MR angiography was approximately 10 minutes per patient.

An 80-mm slab and 48 partitions (1.7-mm section thickness) were acquired for each station. The slab was interpolated by using zero filling (a) to 64 partitions with an interpolated section thickness of 1.3 mm in the thigh station and (b) to 80 partitions with an interpolated section thickness of 1.0 mm in the calf station. Acquisition time was reduced with an 80% partial Fourier technique applied in both phase-encoding directions. All other MR angiographic parameters for the thigh and calf stations are listed in Table 2.


View this table:
[in this window]
[in a new window]

  		Table 2. Intraarterial MR Angiography Parameters

 
Commercially available gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany), which is distributed with a full-strength concentration of 500 mmol, was diluted with saline solution to obtain a concentration of 50 mmol. For each station, a 20-mL bolus of 500-mmol gadopentetate dimeglumine was administered; this resulted in a total dose of 2 mmol gadopentetate dimeglumine. The intraarterial devices were extended with a 20-cm-long plastic tube to enable comfortable access for gadopentetate dimeglumine administration. Prior to intraarterial gadopentetate dimeglumine administration, a native image of each station was acquired to allow digital mask subtraction. Intraarterial injection and MR angiography data acquisition started simultaneously. The bolus was administered manually at an injection rate of approximately 1 mL/sec.

After MR imaging, patients were brought back to the interventional radiology unit for sheath removal, and either a sterile pressure bandage for antegrade puncture or an arterial puncture closure device (Angioseal; St Jude Medical) for retrograde crossover access was applied. Both intraarterial DSA and intraarterial MR angiography were well tolerated by all patients.

Image Analysis
For image analysis, the arterial vasculature of the investigated extremity was divided into femoropopliteal and infrapopliteal stations. Each station was marked on film hard copies prior to evaluation by a radiologist not involved in the readings (H.G.H., 1 year of experience in interventional radiology).

For intraarterial MR angiography, targeted maximum intensity projections (MIPs) were reconstructed from the subtracted images in anterior-posterior, left anterior oblique (reconstruction angle, 30°), and right anterior oblique (reconstruction angle, 30°) directions. In cases of venous overlay at MR angiography, additional reconstruction angles in left anterior oblique and right anterior oblique projections were used to enable visualization of all relevant arterial stenoses.

Intraarterial DSA images and MIPs were documented on film hard copies by using similar magnification factors. Furthermore, intraarterial DSA and intraarterial MR angiography data sets were available on a workstation, thus enabling review of the source images and interactive reformation at the time of interpretation. Intraarterial DSA served as the reference standard.

Intraarterial MR angiography and intraarterial DSA data sets were subjected to a prospective and masked analysis based on a station-by-station review. For lesion identification, the patient population was randomly divided into two subgroups of equal size. In one group, MR angiographic images were considered first for stenosis identification; in the other group, DSA images were considered first. All stenoses of more than 25% were numbered and marked on defined DSA and MR angiographic film hard copies. Eight weeks later, the remaining complementary MR angiograms and DSA film hard copies were also analyzed for stenosis identification. Subsequently, all MR angiograms and DSA film hard copies for each individual patient were correlated. Stenoses not tagged during one of the methods were identified and marked on corresponding images. A radiologist who was not involved in the reading (H.G.H.) performed the complete procedure, including lesion identification and tagging of film hard copies.

Angiograms were reviewed in consensus by two board-certified radiologists (R.W.H. and D.B., with 3 and 2 years of experience in interventional radiology, respectively) and two board-certified angiologists (M.A. and C.T., with 13 and 9 years of experience in angiology, respectively). In the first step, the review team interpreted all intraarterial DSA images; in the second step (6 weeks later), the same team analyzed all intraarterial MR angiographic images, which were arranged in a different order than the intraarterial DSA images. The readers were blinded to patients' names and clinical history and the results of other examinations.

All intraarterial MR angiographic reconstructed MIPs were assessed with regard to image quality (venous overlay and susceptibility artifacts). Intraarterial MR angiography and intraarterial DSA images were analyzed regarding the presence of arterial disease. During the readout, each vascular segment was assessed for the presence of (a) moderate stenoses (luminal narrowing ≤ 50%, (b) significant stenosis (luminal narrowing 51%–99%, and (c) occlusion (luminal narrowing of 100%).

Statistical Analysis
Overall sensitivity, specificity, accuracy, and positive and negative predictive values of intraarterial MR angiography in the characterization of significant stenoses or vessel occlusions at the femoropopliteal and infrapopliteal levels were determined, with intraarterial DSA serving as reference standard. We calculated 95% confidence intervals (CIs) for sensitivity and specificity.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Figures 1 and 2 demonstrate typical arterial delineation of femoropopliteal and infrapopliteal runoff on intraarterial MR angiograms compared with that on intraarterial DSA images.


Figure 1
View larger version (69K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1a: Coronal images in a 68-year-old man with left-sided lower leg claudication. (a) T1-weighted two-dimensional fast low-angle shot scout image of the thigh (repetition time msec/echo time msec, 8.5/4.0; flip angle, 35°; matrix, 256 x 256; field of view, 500 x 375 mm; voxel size, 2.6 x 2.0 x 2.0 mm; acquisition time, 20 seconds). (b) MIP of a mask-subtracted three-dimensional gradient-echo image of the distal superficial and proximal popliteal arteries obtained with low-dose intraarterial MR angiography (2.8/1.1; flip angle, 20°; matrix, 448 x 314; field of view, 380 x 380 mm; voxel size, 0.8 x 1.2 x 1.3 mm; number of partitions, 48; acquisition time, 27 seconds). Several moderate and significant stenoses are depicted. Note the lesion (arrow) that was underestimated as a moderate stenosis with intraarterial MR angiography. An eccentric lesion (arrowhead) in the distal femoral artery was rated correctly as a significant stenosis with both modalities. (c) Corresponding intraarterial DSA image shows the same lesion (arrow) and eccentric lesion (arrowhead) seen in b.

 

Figure 1
View larger version (59K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1b: Coronal images in a 68-year-old man with left-sided lower leg claudication. (a) T1-weighted two-dimensional fast low-angle shot scout image of the thigh (repetition time msec/echo time msec, 8.5/4.0; flip angle, 35°; matrix, 256 x 256; field of view, 500 x 375 mm; voxel size, 2.6 x 2.0 x 2.0 mm; acquisition time, 20 seconds). (b) MIP of a mask-subtracted three-dimensional gradient-echo image of the distal superficial and proximal popliteal arteries obtained with low-dose intraarterial MR angiography (2.8/1.1; flip angle, 20°; matrix, 448 x 314; field of view, 380 x 380 mm; voxel size, 0.8 x 1.2 x 1.3 mm; number of partitions, 48; acquisition time, 27 seconds). Several moderate and significant stenoses are depicted. Note the lesion (arrow) that was underestimated as a moderate stenosis with intraarterial MR angiography. An eccentric lesion (arrowhead) in the distal femoral artery was rated correctly as a significant stenosis with both modalities. (c) Corresponding intraarterial DSA image shows the same lesion (arrow) and eccentric lesion (arrowhead) seen in b.

 

Figure 1
View larger version (57K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1c: Coronal images in a 68-year-old man with left-sided lower leg claudication. (a) T1-weighted two-dimensional fast low-angle shot scout image of the thigh (repetition time msec/echo time msec, 8.5/4.0; flip angle, 35°; matrix, 256 x 256; field of view, 500 x 375 mm; voxel size, 2.6 x 2.0 x 2.0 mm; acquisition time, 20 seconds). (b) MIP of a mask-subtracted three-dimensional gradient-echo image of the distal superficial and proximal popliteal arteries obtained with low-dose intraarterial MR angiography (2.8/1.1; flip angle, 20°; matrix, 448 x 314; field of view, 380 x 380 mm; voxel size, 0.8 x 1.2 x 1.3 mm; number of partitions, 48; acquisition time, 27 seconds). Several moderate and significant stenoses are depicted. Note the lesion (arrow) that was underestimated as a moderate stenosis with intraarterial MR angiography. An eccentric lesion (arrowhead) in the distal femoral artery was rated correctly as a significant stenosis with both modalities. (c) Corresponding intraarterial DSA image shows the same lesion (arrow) and eccentric lesion (arrowhead) seen in b.

 

Figure 2
View larger version (70K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2a: Images obtained in a 65-year-old woman with left-sided lower leg claudication show significant stenosis at the origin of the peroneal (arrowhead) and posterior tibial (straight arrow) arteries and collateralization extending from the tibioperoneal trunk to the peroneal artery and fading with vessel occlusion in the descending part of the anterior tibial artery (curved arrow). (a) Coronal MIP of a mask-subtracted three-dimensional gradient-echo image of the proximal calf arteries acquired with intraarterial MR angiography (3.5/1.3; flip angle, 20°; matrix, 448 x 307; field of view, 380 x 326 mm; voxel size, 0.8 x 1.1 x 1.0 mm; acquisition time, 33 seconds). (b, c) Corresponding intraarterial DSA images obtained in the early (b) and late (c) phases of the examination.

 

Figure 2
View larger version (81K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2b: Images obtained in a 65-year-old woman with left-sided lower leg claudication show significant stenosis at the origin of the peroneal (arrowhead) and posterior tibial (straight arrow) arteries and collateralization extending from the tibioperoneal trunk to the peroneal artery and fading with vessel occlusion in the descending part of the anterior tibial artery (curved arrow). (a) Coronal MIP of a mask-subtracted three-dimensional gradient-echo image of the proximal calf arteries acquired with intraarterial MR angiography (3.5/1.3; flip angle, 20°; matrix, 448 x 307; field of view, 380 x 326 mm; voxel size, 0.8 x 1.1 x 1.0 mm; acquisition time, 33 seconds). (b, c) Corresponding intraarterial DSA images obtained in the early (b) and late (c) phases of the examination.

 

Figure 2
View larger version (99K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2c: Images obtained in a 65-year-old woman with left-sided lower leg claudication show significant stenosis at the origin of the peroneal (arrowhead) and posterior tibial (straight arrow) arteries and collateralization extending from the tibioperoneal trunk to the peroneal artery and fading with vessel occlusion in the descending part of the anterior tibial artery (curved arrow). (a) Coronal MIP of a mask-subtracted three-dimensional gradient-echo image of the proximal calf arteries acquired with intraarterial MR angiography (3.5/1.3; flip angle, 20°; matrix, 448 x 307; field of view, 380 x 326 mm; voxel size, 0.8 x 1.1 x 1.0 mm; acquisition time, 33 seconds). (b, c) Corresponding intraarterial DSA images obtained in the early (b) and late (c) phases of the examination.

 
Segments, Stenoses, and Occlusions
In 20 patients, a total of 40 stations were assessed. (Femoropopliteal and infrapopliteal stations were assessed in each patient.) The proximal 11 cm (sheet length) of the superficial femoral artery in the 16 patients with antegrade arterial access was not evaluated. Venous contamination was observed in five stations (12%) (femoropopliteal station, n = 1; infrapopliteal station, n = 4). Severe venous contamination partially hampered readout in two infrapopliteal stations (10%); thus, three stenoses seen at DSA could not be appreciated at MR angiography (Fig 3). Susceptibility artifacts occurred in one station (Fig 4). Stenoses not visualized in vessels with MR angiography because of artifacts or severe venous overlay were considered false-negative findings.


Figure 3
View larger version (123K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3: Coronal MIPs of a mask-subtracted three-dimensional gradient-echo image of the infrapopliteal arteries obtained with intraarterial MR angiography (3.5/1.3; flip angle, 20°; matrix, 448 x 307; field of view, 380 x 326 mm; voxel size, 0.8 x 1.1 x 1.0 mm; acquisition time, 33 seconds) in a 57-year-old woman with left-sided claudication symptoms (left image) and a 71-year-old man with right-sided claudication symptoms (right image). In the left image, intraarterial MR angiography reveals venous overlay that does not disturb the readout. Patent anterior tibial (arrowhead) and peroneal (arrow) arteries are seen; the peroneal artery is seen collateralizing on the distal tibial posterior artery. In the right image, severe venous contamination hampers the readout, with multiple stenoses visible in the anterior tibial artery (straight arrows). The peroneal artery (curved arrow) cannot be fully appreciated.

 

Figure 4
View larger version (138K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 4: Images in a 79-year-old woman with right-sided lower leg claudication who had undergone total knee replacement. Left: Coronal MIP of a mask-subtracted three-dimensional gradient-echo image of the knee obtained with low-dose intraarterial MR angiography (2.8/1.1; flip angle, 20°; matrix, 448 x 314; field of view, 380 x 380 mm; voxel size, 0.8 x 1.2 x 1.3 mm; acquisition time, 27 seconds) shows a short significant stenosis (arrow) in the popliteal artery at the level of the total knee arthroplasty. However, the lack of collateral vessels and the frank visualization of the vessel distal to the prosthesis indicate that there may not be any significant stenosis at the popliteal level. Right: Corresponding intraarterial DSA image with a lateral view of the knee and popliteal artery (inset) reveals a patent popliteal vessel (arrowheads) without stenoses.

 
A total of 163 stenoses were identified with intraarterial DSA in the lower extremity; 74 stenoses were identified at the femoropopliteal arteries, and 89 were identified at the infrapopliteal arteries. In the femoropopliteal axis, 50 (68%) stenoses were classified as moderate and 18 (24%) were classified as significant. Six (8%) vessel occlusions were found. In the infrapopliteal axis, 28 (31%) stenoses were classified as moderate and 39 (44%) were classified as significant. Twenty-two (25%) vessel occlusions were identified. The ratings of all stenoses in femoropopliteal and infrapopliteal arteries identified with intraarterial DSA and intraarterial MR angiography are listed in Table 3.


View this table:
[in this window]
[in a new window]

  		Table 3. Comparison of Intrarterial DSA and MR Angiography

 
In the femoropopliteal arteries, over- and underestimation rates were 7% (five of 74) and 3% (two of 74), respectively. In the infrapopliteal arteries over- and underestimation rates were 13% (12 of 89) and 4% (four of 89), respectively. Overall, 23 discrepancies (14.1%) in the evaluation of vascular lesions in the lower extremity were found. Of these discrepancies, 17 (10.4%) were overestimated with intraarterial MR angiography, whereas only six (3.7%) were underestimated. However, none of these 23 discrepancies was over- or underestimated by two grades (moderate stenosis classified as vessel occlusion or vice versa).

Comparisons
In the characterization of significant stenoses or occlusions in the lower extremity, sensitivity and specificity of intraarterial MR angiography were 93% (95% CI: 84%, 97%) and 86% (95% CI: 76%, 92%), respectively (Table 4). Overall, a positive predictive value of 88%, a negative predictive value of 92%, and an accuracy of 90% were determined.


View this table:
[in this window]
[in a new window]

  		Table 4. Sensitivity, Specificity, Positive Predictive Value, Negative Predictive Value, and Accuracy of Intraarterial MR Angiography in the Diagnosis of Significant Stenoses and Vessel Occlusions

 
Sensitivity for the diagnosis of significant lesions was similar in the femoropopliteal (92%; 95% CI: 72%, 99%) and infrapopliteal (93%; 95% CI: 83%, 98%) arteries. Specificity was high in the femoropopliteal arteries (94%; 95% CI: 82%, 98%) and moderate in the infrapopliteal arteries (71%; 95% CI: 51%, 86%). Positive predictive values were identical (both 88%) in the femoropopliteal and infrapopliteal arteries. The negative predictive value was higher in the femoropopliteal artery (96%) than in the infrapopliteal artery (83%). Accuracies in the femoropopliteal and infrapopliteal arteries were 93% and 86%, respectively.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
For characterization of significant stenosis or occlusion in the femoropopliteal arteries with intraarterial MR angiography, sensitivity and specificity were 92% and 94%, respectively. In the infrapopliteal arteries, sensitivity (93%) was comparable, but specificity (71%) was rather low. This might have been due to insufficient spatial resolution, especially in the partition direction. Refinement is warranted and might be achieved with faster imaging methods, such as parallel imaging (sensitivity encoding) (19) or keyhole (time-resolved imaging of contrast kinetics) (20) techniques. It also can be hypothesized that selective catheter placement may optimize contrast agent application in the lower leg and therefore enhance the diagnostic potential.

The overall values for sensitivity, specificity, and accuracy of intraarterial MR angiography were comparable with those of previously published intravenous gadolinium–enhanced MR angiography reports (4,21,22). Thus, it can be concluded that intraarterial and intravenous MR angiography examinations have similar diagnostic potential in the characterization of significant stenoses or occlusions. This is emphasized by the findings of an animal study, in which no significant differences in quantitative renal stenosis measurements between intraarterial MR angiography, intravenous MR angiography, and intraarterial DSA were reported (23).

Compared with the use of radiographic contrast agents, the use of MR contrast agents is not based on the visibility of the contrast agent itself but on its influence on the surrounding protons. Gadolinium-based MR contrast agents have a strong magnetic moment, which influences the relaxation of the surrounding blood protons as the contrast agent advances in the static magnetic field. Since gadolinium decreases both T1 and T2/T2* of blood, there is no linear dependence between signal intensity and gadolinium concentration as there is for radiographic contrast agents. There is, however, a rather broad concentration range for optimal contrast enhancement (24), which greatly depends on the applied MR sequence. Lower gadolinium concentrations will result in insufficient T1 shortening, while higher gadolinium concentrations will lead to a signal intensity decrease because the T2/T2*-dependent signal loss will override the T1-dependent signal gain.

Recently, an intraarterial MR angiography low-dose injection protocol was derived for visualization of the infrainguinal arteries in patients with PAOD (17). We applied this protocol in the current study. This protocol provides sufficient T1 shortening but excludes signal loss due to T2/T2*-dependent spin dephasing. It is also valid with the variable flow conditions in patients with PAOD.

There are typical image artifacts, such as venous contamination and susceptibility artifacts, that occur with intraarterial MR angiography but not with DSA. Venous overlay was observed in four infrapopliteal segments. This finding could not be attributed to imprecise bolus timing, since bolus injection and MR data acquisition started simultaneously. Also, a mask image of the respective station was acquired directly before contrast agent administration. Thus, it must be assumed that an accelerated arteriovenous transit time was responsible for early venous enhancement (25). This phenomenon is occasionally observed in steno-occlusive disease and is caused by a decreased arteriolar resistance that may shorten the pure arterial phase. Early venous contamination can be minimized either by using the cuff-compression technique, which prolongs the arterial transit time (26), or by using shorter acquisition times (20).

In addition, susceptibility artifacts due to ferromagnetic implants (eg, joint prosthesis) limit the diagnostic value of MR angiography in the respective region and were observed in one patient (Fig 4). Furthermore, shielding artifacts arising from vascular stent devices may also disturb the image quality of MR angiograms (27). To our knowledge, this inherent problem of MR imaging cannot be overcome by using refined imaging techniques. However, new concepts of material composition and stent design have the potential to reduce or eliminate these artifacts and may be available in the near future (28).

We used a low-dose injection protocol for intraarterial MR angiography that is valid for femoral flow conditions (17). Contrast media can be injected approximately 20 times before the Food and Drug Administration–approved limit is exceeded. Thus, this protocol seems to fulfill the requirements for an entire MR-guided interventional examination in most cases.

One limitation of this study was that diagnostic evaluation of intraarterial MR angiography was performed after PTA. The order of investigation reduced the number of significant stenoses detected in the femoropopliteal artery. We used this protocol so that patients would not be transported to the MR suite after they had undergone DSA-controlled arterial puncture and then transported back to the DSA suite to undergo PTA. The remaining significant stenoses in the femoropopliteal segments were detected after PTA or were not treated because of clinical considerations. Patients who underwent retrograde access and intervention in the ipsilateral iliac arteries underwent routine crossover angiography of the contralateral leg, without any interventions, if they were asymptomatic. In accordance with our treatment protocol, patients with PAOD at the calf level (Fontaine classification stage II) did not undergo infrapopliteal PTA.

Another minor limitation was that the proximal segments of the superficial femoral artery were excluded from further evaluation because of insufficient retrograde filling at MR angiography when intraarterial contrast material was injected in the antegrade direction. One option to overcome this problem is to pull the antegrade introducer sheath back close to the arterial puncture site in the common femoral artery. To avoid loss of the arterial access, major bleeding, or both, during transportation from the interventional radiologic suite to the MR imager and back, we avoided retraction of the introducer sheath.

This study was performed with consensus reading of two experienced interventional radiologists and two angiologists. It might have been preferable to perform reading independently to allow assessment of inter- and intraobserver variability.

The results of this prospective study of catheter-guided intraarterial MR angiography with use of a low-dose injection protocol in patients with PAOD show good diagnostic image quality in the femoropopliteal arteries and reasonable diagnostic image quality in the infrapopliteal arteries. This protocol allows repetitive injection of contrast media before the total permissible dose is reached. These primary results hold promise that intraarterial MR angiography is a valuable building block toward future MR-guided endovascular interventions in patients; however, further studies are needed to optimize imaging techniques for intraarterial MR angiography.


   ACKNOWLEDGMENTS
 
We thank Tanja Haas, RT, and Philipp Madoerin, RT, for their effort and continuous support in MR imaging.


   FOOTNOTES
 

Abbreviations: CI = confidence interval • DSA = digital subtraction angiography • MIP = maximum intensity projection • PAOD = peripheral arterial occlusive disease • PTA = percutaneous transluminal angioplasty

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, R.W.H., H.G.H., D.B.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, R.W.H., D.B.; clinical studies, R.W.H., M.A., G.B., K.J., C.T., A.L.J.; statistical analysis, R.W.H., A.C.S., C.H.; and manuscript editing, all authors


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Criqui MH, Fronek A, Barrett-Connor E, Klauber MR, Gabriel S, Goodman D. The prevalence of peripheral arterial disease in a defined population. Circulation 1985;71:510–515.[Abstract/Free Full Text]
  2. Mohler ER 3rd. Peripheral arterial disease: identification and implications. Arch Intern Med 2003;163:2306–2314.[Abstract/Free Full Text]
  3. Kreitner KF, Kalden P, Neufang A, et al. Diabetes and peripheral arterial occlusive disease: prospective comparison of contrast-enhanced three-dimensional MR angiography with conventional digital subtraction angiography. AJR Am J Roentgenol 2000;174:171–179.[Abstract/Free Full Text]
  4. Loewe C, Schoder M, Rand T, et al. Peripheral vascular occlusive disease: evaluation with contrast-enhanced moving-bed MR angiography versus digital subtraction angiography in 106 patients. AJR Am J Roentgenol 2002;179:1013–1021.[Abstract/Free Full Text]
  5. Goyen M, Ruehm SG, Debatin JF. MR angiography for assessment of peripheral vascular disease. Radiol Clin North Am 2002;40:835–846.[CrossRef][Medline]
  6. Winterer JT, Schaefer O, Uhrmeister P, et al. Contrast enhanced MR angiography in the assessment of relevant stenoses in occlusive disease of the pelvic and lower limb arteries: diagnostic value of a two-step examination protocol in comparison to conventional DSA. Eur J Radiol 2002;41:153–160.[CrossRef][Medline]
  7. Prince MR, Narasimham DL, Stanley JC, et al. Breath-hold gadolinium-enhanced MR angiography of the abdominal aorta and its major branches. Radiology 1995;197:785–792.[Abstract/Free Full Text]
  8. Rofsky NM, Adelman MA. MR angiography in the evaluation of atherosclerotic peripheral vascular disease. Radiology 2000;214:325–338.[Abstract/Free Full Text]
  9. Frayne R, Omary RA, Unal O, Strother CM. Determination of optimal injection parameters for intraarterial gadolinium-enhanced MR angiography. J Vasc Interv Radiol 2000;11:1277–1284.[Medline]
  10. Omary RA, Frayne R, Unal O, Grist TM, Strother CM. Intraarterial gadolinium-enhanced 2D and 3D MR angiography: a preliminary study. J Vasc Interv Radiol 1999;10:1315–1321.[Medline]
  11. Omary RA, Frayne R, Unal O, et al. MR-guided angioplasty of renal artery stenosis in a pig model: a feasibility study. J Vasc Interv Radiol 2000;11:373–381.[Medline]
  12. Omary RA, Henseler KP, Unal O, et al. Validation of injection parameters for catheter-directed intraarterial gadolinium-enhanced MR angiography. Acad Radiol 2002;9:172–185.[CrossRef][Medline]
  13. Omary RA, Unal O, Koscielski DS, et al. Real-time MR imaging-guided passive catheter tracking with use of gadolinium-filled catheters. J Vasc Interv Radiol 2000;11:1079–1085.[Medline]
  14. Strother CM, Unal O, Frayne R, et al. Endovascular treatment of experimental canine aneurysms: feasibility with MR imaging guidance. Radiology 2000;215:516–519.[Abstract/Free Full Text]
  15. Hwang KP, Green JD, Li D, et al. Minimizing contrast agent dose during intraarterial gadolinium-enhanced MR angiography: in vitro assessment. J Magn Reson Imaging 2002;15:55–61.[CrossRef][Medline]
  16. Serfaty JM, Yang X, Aksit P, Quick HH, Solaiyappan M, Atalar E. Toward MRI-guided coronary catheterization: visualization of guiding catheters, guidewires, and anatomy in real time. J Magn Reson Imaging 2000;12:590–594.[CrossRef][Medline]
  17. Bilecen D, Schulte AC, Heidecker HG, et al. Lower extremity: low-dose contrast agent intraarterial MR angiography in patients—initial results. Radiology 2005;234:250–255.[Abstract/Free Full Text]
  18. Jacob AL, Stock KW, Proske M, Steinbrich W. Lower extremity angiography: improved image quality and outflow vessel detection with bilaterally antegrade selective digital subtraction angiography—a blinded prospective intraindividual comparison with aortic flush digital subtraction angiography. Invest Radiol 1996;31:184–193.[CrossRef][Medline]
  19. Pruessmann KP, Weiger M, Scheidegger MB, Boesiger P. SENSE: sensitivity encoding for fast MRI. Magn Reson Med 1999;42:952–962.[CrossRef][Medline]
  20. Korosec FR, Frayne R, Grist TM, Mistretta CA. Time-resolved contrast-enhanced 3D MR angiography. Magn Reson Med 1996;36:345–351.[Medline]
  21. Ho KY, Leiner T, de Haan MW, Kessels AG, Kitslaar PJ, van Engelshoven JM. Peripheral vascular tree stenoses: evaluation with moving-bed infusion-tracking MR angiography. Radiology 1998;206:683–692.[Abstract/Free Full Text]
  22. Meaney JF, Ridgway JP, Chakraverty S, et al. Stepping-table gadolinium-enhanced digital subtraction MR angiography of the aorta and lower extremity arteries: preliminary experience. Radiology 1999;211:59–67.[Abstract/Free Full Text]
  23. Omary RA, Henseler KP, Unal O, et al. Comparison of intraarterial and IV gadolinium-enhanced MR angiography with digital subtraction angiography for the detection of renal artery stenosis in pigs. AJR Am J Roentgenol 2002;178:119–123.[Abstract/Free Full Text]
  24. Bos C, Smits HF, Bakker CJ, Viergever MA. Selective contrast-enhanced MR angiography. Magn Reson Med 2000;44:575–582.[CrossRef][Medline]
  25. Guyton A, Hall J. Local control of blood flow by tissue and humeral regulation. New York, NY: Saunders, 2000.
  26. Bilecen D, Schulte AC, Bongartz G, Heidecker HG, Aschwanden M, Jager KA. Infragenual cuff-compression reduces venous contamination in contrast-enhanced MR angiography of the calf. J Magn Reson Imaging 2004;20:347–351.[CrossRef][Medline]
  27. Wang Y, Truong TN, Yen C, et al. Quantitative evaluation of susceptibility and shielding effects of nitinol, platinum, cobalt-alloy, and stainless steel stents. Magn Reson Med 2003;49:972–976.[CrossRef][Medline]
  28. Buecker A, Spuentrup E, Ruebben A, Gunther RW. Artifact-free in-stent lumen visualization by standard magnetic resonance angiography using a new metallic magnetic resonance imaging stent. Circulation 2002;105:1772–1775.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 RadiologyHome page
D. R. Hadizadeh, J. Gieseke, S. H. Lohmaier, K. Wilhelm, J. Boschewitz, F. Verrel, H. H. Schild, and W. A. Willinek
Peripheral MR Angiography with Blood Pool Contrast Agent: Prospective Intraindividual Comparative Study of High-Spatial-Resolution Steady-State MR Angiography versus Standard-Resolution First-Pass MR Angiography and DSA
Radiology, September 3, 2008; (2008) 2492072033.
[Abstract] [Full Text]

Home page
 Am. J. Roentgenol.Home page
H. Ersoy and F. J. Rybicki
MR Angiography of the Lower Extremities
Am. J. Roentgenol., June 1, 2008; 190(6): 1675 - 1684.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
2393041574v1
239/3/901    most recent
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Huegli, R. W.
Right arrow Articles by Bilecen, D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Huegli, R. W.
Right arrow Articles by Bilecen, D.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
RADIOLOGY RADIOGRAPHICS RSNA JOURNALS ONLINE