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Vascular and Interventional Radiology |
1 From the Departments of Radiology (R.W., M.A., A.B.), Cardiology (S.G., A.G.), and Medical Physics (L.C.), Ospedale San Giovanni, 6500 Bellinzona, Switzerland. Received December 5, 2001; revision requested February 18, 2002; final revision received August 1; accepted August 8. Address correspondence to R.W. (e-mail: rolf.wyttenbach@bluewin.ch).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Fifty-six patients underwent MR angiography enhanced with either Gd-DOTA (28 patients) or Gd-BOPTA (28 patients). All arterial segments from the renal arteries to the distal run-off vessels were evaluated for disease severity. The sensitivity, specificity, and accuracy of MR angiography enhanced with both agents separately were evaluated with a paired t test; digital subtraction angiography was the reference standard. Interobserver variability was assessed by using the Cohen test.
RESULTS: Diagnostic MR angiograms were obtained in all 56 patients. Overall, sensitivity and specificity of Gd-DOTA–enhanced MR angiography were 96% and 93%, respectively, for observer 1 and 96% and 85%, respectively, for observer 2 (
= 0.82). Corresponding values for Gd-BOPTA–enhanced MR angiography were 94% and 93%, respectively, for observer 1 and 94% and 89%, respectively, for observer 2 ( = 0.78). No consistent differences between the two contrast materials in assessment of PAOD in the renal to popliteal arteries were observed. For assessment below the knee, specificity was slightly higher in the Gd-BOPTA group—91% and 84% for observers 1 and 2, respectively—than in the Gd-DOTA group—89% and 77%, respectively (P < .01). The number of nonassessable below-the-knee segments was significantly lower in the Gd-BOPTA group: nine of 299 segments versus 25 of 312 segments in the Gd-DOTA group (P < .01).
CONCLUSION: At MR angiography of the distal run-off vessels, Gd-BOPTA yielded higher specificity and a significantly smaller number of nonassessable segments than Gd-DOTA. The diagnostic accuracy of the two gadolinium chelates at peripheral MR angiography was comparable in the renal to popliteal arteries.
© RSNA, 2003
Index terms: Angiography, 92.122 • Arteries, stenosis and obstruction, 92.721 • Contrast media, comparative studies • Magnetic resonance (MR), contrast media, 922.12942, 922.12943 • Magnetic resonance (MR), vascular studies, 922.12942, 922.12943
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Three-dimensional contrast material–enhanced magnetic resonance (MR) angiography has gained widespread use for the assessment of virtually all vascular territories because it enables one to visualize vascular disease noninvasively (3–7). MR angiographic techniques have also proved to be robust, accurate, and reproducible for the assessment of peripheral arterial occlusive disease (8,9) by using a single injection of a conventional extracellular gadolinium chelate such as gadopentetate dimeglumine (Magnevist; Berlex Laboratories, Wayne, NJ) or gadoterate meglumine (Gd-DOTA, Dotarem; Guerbet, France). However, the accurate MR angiographic evaluation of vascular disease at the level of the distal run-off vessels of the lower limbs is challenging owing to signal-to-noise ratio and spatial resolution limitations.
Gadobenate dimeglumine (Gd-BOPTA, MultiHance; Bracco Diagnostics, Italy) is one of a new class of gadolinium chelates that have a weak protein interaction, which leads to an almost twofold increase in relaxivity compared with the relaxivity generated by conventional gadolinium chelates, which do not have a protein interaction (10). Gd-BOPTA, as compared with gadopentetate dimeglumine, has been shown to lead to more pronounced vascular enhancement of the more distal vessels (11). This property is potentially useful in peripheral contrast-enhanced MR angiography, especially in the calf vessels where inadequate vessel contrast is a major limitation.
The purpose of the current study was to prospectively compare the diagnostic accuracy of single-injection, three-station MR angiography from the renal arteries to the distal run-off vessels performed by using a gadolinium chelate that has a higher relaxivity, Gd-BOPTA, with the diagnostic accuracy of this examination performed by using a standard gadolinium chelate, Gd-DOTA. DSA was the standard of reference.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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50%) of the iliac or femoropopliteal arteries demonstrated at Doppler US were enrolled in our prospective study. Among these 56 patients, 19 (34%) had diabetes mellitus; 46 (82%), a history of smoking; 40 (71%), hypercholesterolemia; and 37 (66%), hypertension. All patients underwent MR angiography and diagnostic DSA before percutaneous transluminal angioplasty. DSA served as the standard of reference. No age criteria were applied, and claustrophobia and/or standard contraindications to MR imaging were the only exclusion criteria. The patients were randomly assigned to two study groups of 28 subjects each: The patients in one group underwent Gd-DOTA–enhanced MR angiography, and those in the other group underwent Gd-BOPTA–enhanced MR angiography. The Gd-DOTA group included 17 men and 11 women with a mean age of 70.2 years (age range, 53–82 years), and the Gd-BOPTA group included 22 men and six women with a mean age of 64.4 years (age range, 35–89 years). There was no significant difference in mean age between the Gd-BOPTA and Gd-DOTA groups (P = .14, unpaired t test).
The maximum time between MR angiography and DSA was 4 weeks (average intervals of 7.9 days for the Gd-DOTA group and 6.8 days for the Gd-BOPTA group). Statistical testing revealed no difference between the two contrast material groups with regard to maximum time between MR angiography and DSA (P = .51, unpaired t test). There was also no significant difference between the Gd-BOPTA and Gd-DOTA groups with respect to either weight (P = .90, unpaired t test) or sex (P = .15, unpaired t test). All MR imaging examinations were performed in accordance with the guidelines of our institutional review board. Informed consent was obtained from all patients. All studies performed with Gd-BOPTA received additional approval for contrast material use and MR imaging from the Ministry of Health of Southern Switzerland, which is overseen by the National Ministry of Health.
MR Angiography
MR angiography was performed by using a conventional 1.5-T unit (Gyroscan ACS-NT PT 6000; Philips Medical Systems, Best, the Netherlands) with a gradient strength of 23 mT/m and a slew rate of 105 mT/m/msec. In all examinations, a body coil was used for signal transmission and reception. The MR angiographic examination consisted of four steps: (a) positioning the patient, (b) determining the vessel anatomy by performing three fast time-of-flight sequences, (c) performing a timing sequence to determine the time of arrival of the contrast material at the level of the abdominal aorta, and (d) performing infusion-tracking MR angiography with manual table movement.
The patients were placed in the supine feet-first position on the table, which was appropriately positioned for MR imaging of the abdomen and pelvis. In planning the imaging volume for MR angiography, we used sagittal maximum intensity projection (MIP) reconstructions generated by using a fast two-dimensional magnetization-prepared gradient-echo inflow technique (12/6.9 [repetition time msec/echo time msec], 50° flip angle, 256 x 128 matrix, 400-mm field of view) to obtain information about the anteroposterior course of the arteries. Three two-dimensional time-of-flight sequences were performed to encompass the peripheral vascular tree from the renal arteries to the distal run-off segments in a stack of 30 images (3.3-mm section thickness, 10-mm intersection gap) that covered approximately 40 cm each. The total time to acquire these three localizer images, including the time required for the two manual table movements and the MIP reconstructions, was approximately 3 minutes.
We determined the imaging delay time by performing a dynamic gradient-recalled-echo sequence with short repetition and echo times (13 and 0.8 msec, respectively). Forty-five consecutive transverse images (128 x 256 matrix, 420-mm field of view, 60° flip angle, 20-mm section thickness) were obtained at the same section position through the infrarenal aorta with a temporal resolution of 1.2 seconds. Caudal and cranial 80-mm-thick presaturation slabs were used to suppress the signal from inflowing venous or arterial blood. A test bolus of either 1 mL of Gd-DOTA or 1 mL of Gd-BOPTA and a subsequent flush of 30 mL of normal saline solution were administered through an antecubital vein at a flow rate of 1 mL/sec by using an MR imaging–compatible injector (Injektron 82 MRT; Medtron, Saarbrücken, Germany). A board-certified radiologist (R.W. or A.B.) then visually evaluated the images for the arrival of the contrast material in the abdominal aorta, which was depicted as an increase in signal intensity. We calculated the effective delay time for the MR angiographic sequence from the time of arrival of the gadolinium-based contrast material by adding 5 seconds to allow an even concentration of the agent in the acquired volume.
For MR angiography, a three-dimensional gradient-recalled-echo technique (4.4/1.2, 35° flip angle, one signal acquired, no flow compensation, 10.50-cm imaging volume, 349.7-Hz bandwidth per millimeter) was used to acquire 35 3-mm-thick image sections that were reconstructed with a zero-fill algorithm (12) to produce 70 1.5-mm-thick sections. The images were obtained in 17 seconds with a 70% rectangular field of view of 450 x 315 mm and a matrix of 512 x 128, which resulted in a voxel size of 0.88 x 2.46 x 3 mm3 before interpolation. The calculated voxel size after interpolation was 0.44 x 1.23 x 1.5 mm3.
The three-dimensional MR angiographic sequence was carefully planned so that the coronal and sagittal MIP images obtained from the two-dimensional time-of-flight localizer sequences would include the renal arteries, abdominal aorta, iliac arteries, and upper and lower leg arteries.
The dynamic MR imaging sequence was performed before and during infusion of the contrast material. First, precontrast images were acquired at the level of the abdomen and pelvis. The table was then manually moved out of the imaging unit by 35 cm. To achieve reproducible and accurate table movements, we placed a mark at the gantry and three marks at the table, with 35 cm separating the two points, to designate three premeasured stops. The position of the first marking served as the initial (ie, zero) position. A second dynamic MR imaging sequence at the level of the upper legs was then performed. The table was subsequently pulled outward by 35 cm again, and the next imaging volume at the level of the lower legs was acquired. After reconstruction of the three imaging volumes, which took approximately 6 minutes, the patient was pushed back into the MR imaging unit in the initial position.
Next, an identical postcontrast MR imaging examination of the region including the abdomen, pelvis, and upper and lower legs was performed with the imaging delay time described earlier herein. An MR imaging–compatible injector (Injektron 82 MRT) was used to infuse 34 mL of either Gd-DOTA or Gd-BOPTA at a flow rate of 1 mL/sec and then a 30-mL saline flush at 1 mL/sec. The total acquisition time for the gadolinium-enhanced examination, including the table movement, was approximately 56 seconds. The total in-room time to complete the MR imaging examination, including patient positioning, was 30–35 minutes.
We completed the MR imaging protocol by performing a transverse T1-weighted fast field-echo sequence (151/1.36, 80° flip angle, 8-mm section thickness, 204 x 512 matrix, 375 x 262-mm field of view, one signal acquired, 30 sections, acquisition time of 22 seconds) after gadolinium-based contrast material administration to exclude partially thrombosed aneurysms of the abdominal aorta, which may be difficult to visualize on MR angiograms only.
After reconstruction of the postcontrast images, subtraction of pre- from postcontrast images of the corresponding anatomic regions was performed. All MR angiographic data sets were postprocessed on a workstation (Easy Vision, Volume View, version 4.3; Philips Medical Systems). Nine rotated MIP displays ranging from -90° to +90° images were rendered containing the first volume set (abdominal aorta and pelvis). In addition, targeted thin-slab MIP images of the renal arteries in the coronal and transverse planes were reconstructed. Six targeted MIP reconstructions were rotated at 20° intervals from -60° to +60° at the level of the upper legs. Thin-slab reconstructions were obtained, if necessary. Nine rotated MIP reconstructions of the third imaging volume (lower legs) ranging from -45° to +45° were rendered of the subtracted and nonsubtracted data sets. We also obtained targeted thin-slab MIP reconstructions of the subtracted and nonsubtracted data sets to improve visualization of the peripheral arteries. All postprocessing and documenting of image data on film were performed by an experienced radiologist (R.W.). The total postprocessing time was 15–20 minutes. There was no evidence of contrast material–related adverse reactions in either contrast material group.
MR Angiogram Analysis
The arterial tree was divided into the following segments for analysis: renal artery, accessory renal artery, infrarenal aorta, common iliac artery, internal iliac artery, external iliac artery, common femoral artery, deep femoral artery, superficial femoral artery (divided into proximal, medium, and distal thirds), popliteal artery (divided into supra- and infragenicular segments), tibiofibular trunk, anterotibial artery, peroneal artery, and posterotibial artery. Each of these segments was divided into proximal and distal segments. The vessel segments that contained metallic stents were excluded from further analysis because of the associated artifacts known to be seen at contrast-enhanced MR angiography (13). Arterial segments that were not contained in the imaging volume were considered to be nondiagnostic.
All MR angiograms were reviewed independently by two board-certified radiologists (R.W., A.B.) with 10 and 12 years of experience, respectively. Both reviewers were blinded to the contrast material used at MR angiography and to the DSA results. All images were randomly evaluated 2 months after completion of the last MR imaging examination; the evaluations were performed during 1 week in five separate sessions of 10–12 examinations per session. The radiologist (R.W.) who was responsible for postprocessing the MR angiograms on the day of the image acquisitions was also one of the reviewers. To prevent this factor from having any influence, we displayed all images on film in a standardized manner, and the reviewers evaluated the images after a delay of at least 2 months (maximum of 10 months) after the MR examinations. Three-dimensional MR angiographic data sets were available on a workstation (Easy Vision) that permitted review of the source images and interactive reformations at the time of analysis, if necessary.
Analysis of the MR angiographic data was performed as follows: (a) All segments were assessed for the presence of stenotic or aneurysmal disease. The following four-point scale was used to grade stenotic or occlusive disease: 0 for normal vessel, 1 for irregularity of vessel wall with less than 10% luminal narrowing, 2 for stenosis involving 50% or less luminal narrowing; 3 for stenosis involving greater than 50% luminal narrowing, and 4 for occlusion. Only the most severe lesion in every segment was considered for analysis. Not all of the DSA images depicted all regions of the vascular tree; thus, only the vessel segments depicted at MR angiography for which there were corresponding segments depicted at conventional DSA were analyzed for comparison. (b) The image quality of MR angiograms obtained at the levels of the renal, pelvic, and upper and lower leg arteries was subjectively assessed by the two blinded independent radiologists (R.W., A.B.) by using a four-point scale: 1 for excellent, 2 for good, 3 for moderate, and 4 for poor image quality. The MR angiograms were assessed subjectively for vessel visibility, vessel-to-background contrast, and presence of artifacts.
DSA Image Analysis
We performed DSA in all patients by using a regular angiography unit (Integris V 3000; Philips Medical Systems) and a standard (ie, Seldinger) technique. In 40 patients, 20 of whom underwent Gd-BOPTA–enhanced MR angiography and 20 of whom underwent Gd-DOTA–enhanced MR angiography, a retrograde transfemoral approach was used by positioning a 4-F catheter (Omniflush; AngioDynamics, Queensbury, NY) at the level of the renal arteries. The first acquisition was performed from the level of the renal arteries to the distal tibial region by using an interactive bolus-chase technique. We injected 45 mL of sodium meglumine ioxaglate (Hexabrix; Guerbet, France) at a flow rate of 18 mL/sec by using a power injector (Angiomat 6000; Liebel-Flarsheim, Cincinnati, Ohio). At least two oblique supplementary views (right anterior oblique and left anterior oblique ±30°) of the pelvic arteries were obtained by injecting 15 mL of sodium meglumine ioxaglate at the same rate. If necessary, supplementary DSA images were acquired in the femoral, popliteal, and calf regions to improve the accuracy of the diagnosis. The total dose of sodium meglumine ioxaglate administered varied from 75 to 150 mL.
In 16 patients, eight of whom underwent Gd-BOPTA–enhanced MR angiography and eight of whom underwent Gd-DOTA–enhanced MR angiography, an anterograde common femoral artery approach was used in single-leg DSA examinations. A 4-F introducer sheath (Cordis Europa, Roden, the Netherlands) was positioned in the common femoral artery, and multiple DSA images were obtained at the femoral, popliteal, and crural levels by using hand injections of 10 mL of sodium meglumine ioxaglate. The total dose administered was 40–60 mL.
A board-certified radiologist (M.A.) who has 20 years of experience and specializes in vascular interventions and was blinded to the MR angiographic results evaluated the DSA images by using a grading system identical to that used to evaluate the MR angiograms.
Statistical Analysis
The first objective parameter that we measured to assess differences between the two MR angiography groups (ie, Gd-DOTA and Gd-BOPTA groups) was the fraction of assessable segments with respect to the total number of arterial segments evaluated at DSA—in other words, the acceptability of each method. The sensitivity, specificity, and accuracy of MR angiography in the determination of 50% or less stenosis and greater than 50% stenosis, with DSA as the standard of reference, for each observer and with both contrast materials were computed by using a paired t test. Interobserver variability was analyzed by means of the Cohen test, in which a value greater than 0.75 corresponded to excellent agreement and a value between 0.50 and 0.75 corresponded to good agreement. We performed subjective blinded evaluation of image quality by computing the average of the scores assigned to each image by the reviewers and stratified according to anatomic level. We performed a paired t test to compare the scores between the two reviewers.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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At the level of the trifurcation arteries, a total of 611 segments—299 from the Gd-BOPTA group and 312 from the Gd-DOTA group—were assessed. DSA depicted 258 lesions—130 from the Gd-BOPTA group and 128 from the Gd-DOTA group—with 50% or less stenosis. DSA depicted 160 lesions—68 from the Gd-BOPTA group and 92 from the Gd-DOTA group—with greater than 50% stenosis. These 160 lesions included 121 occluded distal run-off segments—51 from the Gd-BOPTA group and 70 from the Gd-DOTA group.
MR Angiography
Reviewer 1.—Overall, reviewer 1 found that 10 (1.2%) of 806 segments in the Gd-BOPTA group (group 1) and 31 (3.8%) of 808 segments in the Gd-DOTA group (group 2) were not adequately depicted (P < .001) because of a poor signal-to-noise ratio or venous overlap. None of the vessel segments of interest was outside of the imaging volume. Therefore, subsequent analyses were based on the findings in 796 and 777 segments in the Gd-BOPTA and Gd-DOTA groups, respectively. Overall, reviewer 1 observed 519 and 529 segments in the Gd-BOPTA and Gd-DOTA groups, respectively, to have 50% or less stenosis. Reviewer 1 observed 161 segments in the Gd-BOPTA group, including 65 occluded segments, and 206 segments in the Gd-DOTA group, including 101 occluded segments, to have greater than 50% stenosis.
Reviewer 2.—Overall, reviewer 2 found that 10 (1.2%) of 806 segments in the Gd-BOPTA group and 27 (3.3%) of 808 segments in the Gd-DOTA group (P = .005) were not adequately depicted. Overall, reviewer 2 observed 548 and 530 segments in the Gd-BOPTA and Gd-DOTA groups, respectively, to have 50% or less stenosis. Reviewer 2 observed 186 segments in the Gd-BOPTA group, including 78 occluded segments, to have greater than 50% stenosis. This reviewer observed 251 segments in the Gd-DOTA group, including 116 occluded segments, to have greater than 50% stenosis. The performance values for MR angiographic discrimination between 50% or less and greater than 50% stenoses are shown in Table 1.
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= 0.78; 95% CI: 0.72, 0.84) and the Gd-DOTA group ( = 0.82; 95% CI: 0.78, 0.86). We observed no significant difference in interobserver agreement between the two contrast material groups at either overall assessment or anatomic region–based analysis (ie, of renal-pelvic and upper and lower leg arteries) (Table 2).
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Compared with 69 segments in the Gd-BOPTA group that were reported to be occluded at DSA, 65 and 78 segments in the Gd-BOPTA group were reported by reviewers 1 and 2, respectively, to be occluded at MR angiography. Ninety-nine occluded segments in the Gd-DOTA group were identified at DSA, as compared with 101 and 116 occluded segments in this group that were identified by reviewers 1 and 2, respectively, at MR angiography.
Aneurysmal disease was identified at DSA in one segment in the Gd-BOPTA group and in three segments in the Gd-DOTA group. At MR angiography, aneurysmal changes in the Gd-BOPTA group were seen in two segments by reviewer 1 and in three segments by reviewer 2, whereas three segments with aneurysmal disease in the Gd-DOTA group were identified by both observers.
Diagnostic MR angiograms were obtained in all 56 patients and in both contrast material groups. Mean subjective, blinded image quality scores are categorized by reviewer, contrast material, and anatomic region and listed in Table 4.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The majority of contrast-enhanced MR angiographic examinations are conducted with conventional extracellular gadolinium chelates such as Gd-DOTA, gadopentetate dimeglumine, gadodiamide (Omniscan; Nycomed-Amersham, Norway), and gadoteridol (ProHance; Bracco Diagnostics, Milan, Italy). These paramagnetic chelates do not differ with respect to their mechanisms and characteristics of contrast enhancement, and all of them are characterized by the absence of protein-binding interactions.
Gd-BOPTA is one of a new group of gadolinium chelates that have a weak binding interaction with proteins, which results in a nearly twofold increase in the effectiveness of this agent for enhancement of the T1 relaxation of blood relative to that of standard gadolinium-based agents administered at the same dose (10,17). This weak and transient albumin-mediated relaxation enhancement facilitated by Gd-BOPTA may give this agent an advantage over standard gadolinium chelates in MR angiographic examinations.
Preliminary studies (18) to compare Gd-BOPTA with gadopentetate dimeglumine for MR angiography of the abdominal aorta have revealed a higher and longer vascular peak enhancement with use of Gd-BOPTA compared with that achieved with use of gadopentetate dimeglumine administered at the same dose and flow rate. Furthermore, Knopp and colleagues (11) observed stronger vascular enhancement with Gd-BOPTA than with gadopentetate dimeglumine in an intraindividual comparison study of MR angiography of the run-off vessels in which both agents were administered at a dose of 0.1 mmol per kilogram of body weight. In our opinion, it is interesting that the relative difference in vascular enhancement was more pronounced in the smaller, more distal vessels (11). To our knowledge, however, there has been no published prospective blinded study in which Gd-BOPTA was compared with a standard gadolinium-based compound—for example, Gd-DOTA—for peripheral MR angiography in patients who had peripheral arterial occlusive disease, with DSA as the standard of reference.
In the current study, we used a constant volume of 35 mL of contrast material regardless of the patient’s weight (19,20) instead of a weight-based dose of the two gadolinium chelates, as is generally done. The first-pass aortic concentration of a gadolinium-based contrast agent is not influenced by the individual’s weight and is directly proportional to the rate of infusion divided by the cardiac output (3). In order not to exceed a total dose of 0.25 mmol/kg, we reduced the injected volume of Gd-BOPTA in four patients who weighed less than 70 kg and in two patients in the Gd-DOTA group. Although 0.25 mmol/kg is considerably higher than the generally recommended dose of Gd-BOPTA of 0.1 mmol/kg, there were no contrast material–related complications in either group of patients in this study. However, in a more recent study (21), an even higher dose of Gd-BOPTA, 0.3 mmol/kg, was used at whole-body MR angiography without any contrast material–related complications. This higher dose reflects the current practice in MR angiographic protocols, in which a double (ie, 0.2 mmol/kg) or triple (ie, 0.3 mmol/kg) dose of a standard gadolinium chelate is administered, particularly for multistep peripheral MR angiography, which involves relatively long acquisition times and requires T1 shortening of blood.
Our three-station, single-injection MR angiographic strategy with manual table movement proved to be very robust and allowed the accurate display of arterial vessel segments from the renal arteries to the distal run-off vessels in all 56 patients. Diagnostic image quality was achieved in all studies.
The cut-off point used for statistical analysis in our study was stenosis involving a luminal reduction greater than 50%. Greater than 50% stenotic lesions were correctly identified on MR angiograms with overall sensitivity, specificity, and accuracy values in the 90% range. These results are comparable to those of previously reported studies (22). At the level of the renal and pelvic arteries, no significant difference in sensitivity, specificity, or accuracy between Gd-BOPTA– and Gd-DOTA–enhanced MR angiography was observed by either reviewer. In the femoral segments, sensitivity, specificity, and accuracy values exceeded 90% for both observers and with both contrast materials, but no consistent differences in these parameters between Gd-BOPTA– and Gd-DOTA–enhanced MR angiography were found by both observers in common. Both observers achieved significantly higher specificity values at the level of the tibial segments in the Gd-BOPTA group.
With regard to the number of tibial vessel segments that were not adequately depicted, both reviewers observed a significant, approximately threefold reduction in the number of nonassessable segments in the Gd-BOPTA group as compared with the number of nonassessable segments in the Gd-DOTA group. This finding may be explained by the higher relaxation enhancement achieved with Gd-BOPTA, which improves the signal-to-noise ratio; this is the major limitation of MR angiography of the peripheral run-off vessels when a quadrature body coil is used for signal reception, as in the current study. The relative number of inadequately depicted vessel segments in our study corresponds to known values in other studies (9). Since the integrity of distal run-off vessels is one of the most important factors in determining the outcome of femorodistal bypass surgery (23), an accurate evaluation of the distal run-off vessels is essential for treatment planning, particularly if vascular surgery is an option.
As known from single-station MR angiographic findings, overestimation of stenosis grade is more frequent than underestimation and should be regarded as a known limitation of MR angiography (24). In the current study, we observed no difference in the rate of stenosis grade overestimation between the two gadolinium chelate–enhanced MR angiographic examinations.
Furthermore, both observers agreed on the superior image quality of MR angiograms of the aortoiliac and tibial regions obtained by using Gd-BOPTA compared with the image quality of MR angiograms obtained by using Gd-DOTA. This difference was significant and also might be explained by the weak protein interaction of Gd-BOPTA, which yields improved overall vascular enhancement, as compared with the absence of a protein interaction with standard gadolinium chelates. Although stronger vascular enhancement results in higher contrast not only in the arterial tree but also in the venous phase (11), we did not observe a greater number of nonassessable distal run-off segments owing to venous overlap in the Gd-BOPTA group.
There were several limitations in this study. Because of hardware restrictions, we used manual table movement between the separate acquisitions before and after gadolinium-based contrast material administration. Manual positioning of the table may not be precise enough for subsequent subtraction of the data sets, particularly in the distal run-off segments where the arteries are very small. Furthermore, the reconstruction times between the pre- and postcontrast acquisitions were relatively long and thereby introduced another possibility for spatial misregistration caused by patient movement between the two acquisitions. This resulted in poor image quality of the subtracted data set at the level of the distal run-off vessels in some cases. To overcome this problem in these cases, a radiologist experienced in MR angiography performed additional postprocessing by using targeted subtracted and nonsubtracted MIP images with a reduced slab thickness parallel to the vessels of interest to eliminate the overlying fat signal. An additional advantage of evaluating nonsubtracted data sets is the preservation of anatomic information, which not only eliminates the potential for misinterpretation (15) but also is important to the vascular surgeon.
Future developments in peripheral MR angiography technology to improve image quality include the use of newer and faster MR imagers and a flexible choice of imaging parameters for each field of view. The use of automated table movement enables more precise patient positioning and therefore yields superior image quality of the subtracted data sets. Furthermore, the use of a dedicated peripheral multielement coil improves the signal-to-noise ratio and thus facilitates substantially improved visualization of the distal run-off arteries and the acquisition of higher spatial resolution images. In addition, three-dimensional MR angiographic data can be acquired in two passes, with the central k-space views acquired during the arterial bolus pass and the higher spatial-frequency k-space data acquired during subsequent recirculation of the contrast material. This technique facilitates a faster injection rate and has the potential to improve visualization of the distal run-off vessels (25).
In conclusion, as compared with DSA, the described contrast-enhanced peripheral MR angiographic examination had high diagnostic accuracy with use of both contrast materials. In the distal run-off vessels, the specificity of Gd-BOPTA–enhanced peripheral MR angiography was higher and the number of nonassessable segments was significantly lower, as compared with these findings at Gd-DOTA–enhanced MR angiography. The two gadolinium chelates had a comparable diagnostic performance from the level of the aortoiliac region to the popliteal segments. Therefore, peripheral MR angiography enhanced with Gd-BOPTA yielded improved vascular enhancement compared with MR angiography enhanced with standard gadolinium-based materials, especially in the distal run-off vessels, presumably because of the weak protein interaction of this agent. This property is essential for the evaluation of the distal-off segments, which is important for treatment planning, especially when vascular surgery may be an option. Further investigations are needed to determine the clinical importance of this agent in peripheral MR angiography performed with rapidly developing imaging techniques.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, R.W., M.A., A.G.; study concepts, R.W., M.A., A.B.; study design, R.W., M.A., A.B., A.G.; literature research, R.W., S.G.; clinical studies, R.W., M.A., A.B.; data acquisition, S.G., R.W., A.B.; data analysis/interpretation, M.A., R.W., A.B., S.G.; statistical analysis, L.C., R.W., S.G.; manuscript preparation, R.W., S.G.; manuscript definition of intellectual content, R.W., S.G., M.A., A.G.; manuscript editing, R.W., L.C., S.G.; manuscript revision/review and final version approval, all authors.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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 F. Pediconi, C. Catalano, R. Occhiato, F. Venditti, F. Fraioli, A. Napoli, M. A. Kirchin, and R. Passariello Breast Lesion Detection and Characterization at Contrast-enhanced MR Mammography: Gadobenate Dimeglumine versus Gadopentetate Dimeglumine Radiology, October 1, 2005; 237(1): 45 - 56. [Abstract] [Full Text] [PDF]
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N. Anzalone, F. Scomazzoni, R. Castellano, L. Strada, C. Righi, L. S. Politi, M. A. Kirchin, R. Chiesa, and G. Scotti Carotid Artery Stenosis: Intraindividual Correlations of 3D Time-of-Flight MR Angiography, Contrast-enhanced MR Angiography, Conventional DSA, and Rotational Angiography for Detection and Grading Radiology, July 1, 2005; 236(1): 204 - 213. [Abstract] [Full Text] [PDF]
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F. Sardanelli, A. Iozzelli, A. Fausto, A. Carriero, and M. A. Kirchin Gadobenate Dimeglumine-enhanced MR Imaging Breast Vascular Maps: Association between Invasive Cancer and Ipsilateral Increased Vascularity Radiology, June 1, 2005; 235(3): 791 - 797. [Abstract] [Full Text] [PDF]
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M. Prokop, G. Schneider, A. Vanzulli, M. Goyen, S. G. Ruehm, P. Douek, M. Dapra, G. Pirovano, M. A. Kirchin, and A. Spinazzi Contrast-enhanced MR Angiography of the Renal Arteries: Blinded Multicenter Crossover Comparison of Gadobenate Dimeglumine and Gadopentetate Dimeglumine Radiology, February 1, 2005; 234(2): 399 - 408. [Abstract] [Full Text] [PDF]
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F. M. Vogt, W. Ajaj, P. Hunold, C. U. Herborn, H. H. Quick, J. F. Debatin, and S. G. Ruehm Venous Compression at High-Spatial-Resolution Three-dimensional MR Angiography of Peripheral Arteries Radiology, December 1, 2004; 233(3): 913 - 920. [Abstract] [Full Text] [PDF]
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50% versus >50% Stenosis at MR Angiography
