European Radiology

, Volume 16, Issue 3, pp 685–691

Total-body 3D magnetic resonance angiography influences the management of patients with peripheral arterial occlusive disease

Authors

    • University Medical Center Hamburg-Eppendorf
  • Christoph U. Herborn
    • University Medical Center Hamburg-Eppendorf
  • Knut Kröger
    • Department of AngiologyUniversity Hospital Essen
  • Stefan G. Ruehm
    • Department of RadiologyDavid Geffen School of Medicine at UCLA
  • Jörg F. Debatin
    • University Medical Center Hamburg-Eppendorf
Vascular-Interventional

DOI: 10.1007/s00330-005-0001-8

Cite this article as:
Goyen, M., Herborn, C.U., Kröger, K. et al. Eur Radiol (2006) 16: 685. doi:10.1007/s00330-005-0001-8

Abstract

High-resolution total-body 3D MR angiography (MRA) has recently become available, revealing additional clinically relevant disease in patients with peripheral arterial occlusive disease (PAOD). However, the actual impact of total-body MRA on patient management in patients with PAOD has not been investigated so far. Two hundred forty-nine consecutive patients with angiographically proven PAOD were prospectively examined by means of contrast-enhanced total-body 3D MRA on a 1.5-T MR scanner. All correlative imaging studies performed within 60 days of total-body MRA were included in the efficacy analysis. Additional clinically relevant disease (luminal narrowing >50%, aneurysmal changes or dissections) was found in 73 segments (52 patients), including the renal arteries (36 segments), carotid arteries (28 segments), subclavian arteries (four segments) and abdominal aortic aneurysms (AAA) (five segments). Of the 73 segments, 36 were deemed necessary for further investigation by means of focused MRA examinations; the diagnosis was confirmed in all cases. Within the 60-day follow-up period, interventional or surgical therapy outside the peripheral arterial tree was performed in nine patients (11 segments), including carotid endatherectomy and renal artery angioplasty. The outlined total-body 3D MRA approach permits a comprehensive evaluation of the arterial system in patients with atherosclerosis and does indeed have an impact on patient management in patients with PAOD.

Keywords

AtherosclerosisMR angiographyPeripheral arterial occlusive diseasePatient management

Introduction

With more than 100,000 surgical procedures performed annually in the United States alone [1], peripheral arterial occlusive disease (PAOD) is well recognized as a major health problem. The disease interferes with activities of daily living, resulting in the loss of independence and economic productivity. The management of a patient with PAOD has to be planned in the context of the epidemiology of the disease and the apparent risk factors or markers that predict spontaneous deterioration [2]. It is obvious that the choice of the optimal therapeutic strategy for atherosclerosis, including surgical and percutaneous catheter-based interventions as well as pharmacologic treatment, depends on the accurate classification of atherosclerotic disease with regard to the location, extent, and severity of arterial involvement. Since atherosclerotic disease affects the entire arterial system, extended coverage allowing the concomitant assessment of the arterial system from the supra-aortic arteries to the distal runoff vessels appears desirable. For this purpose, several imaging modalities, including conventional catheter angiography, duplex ultrasound, as well as CT and MR angiography (MRA) are in clinical use. The lack of ionizing radiation and contrast agents void of any nephrotoxicity [3] in conjunction with high diagnostic accuracy have driven the rapid implementation of MRA as the modality of choice for assessing arterial disease in many centers throughout the world [47].

The implementation of stronger and faster gradient systems in combination with new MR contrast agents has laid the foundation for faster MR imaging [8, 9]. Employing the latest gradient generation, multiple 3D MRA data sets covering multiple vascular beds can be collected in rapid succession [10, 11]. Recently, high-resolution total-body 3D MRA has become available, permitting the accurate display of the arterial vasculature extending from the supra-aortic arteries to the lower extremity vessels [1214]. In contrast to imaging strategies focused on the peripheral vasculature alone, the total-body MRA approach documented additional clinically relevant disease in unsuspected arterial territories [15]. However, the impact of total-body MRA on patient management in patients with peripheral arterial occlusive disease has not been investigated so far.

Materials and methods

From July 2002 to May 2004, total-body 3D MRA was performed on 249 consecutive patients (181 male, 68 female) aged between 43 and 87 years (mean age: 63.7 years). All patients were Caucasian. All patients were referred from the Department of Angiology for the MR-based assessment of angiographically documented PAOD (Fontaine grade IIb: 217 patients; grade III: 23 patients; grade IV: 9 patients). Two examinations were technically flawed (hardware failure) and hence excluded from the subsequent evaluation. Thus, the analysis was based on the total-body MRA examinations of 247 patients. The study was performed according to good clinical practice (GCP) rules following the approval of the local ethics committee. Written informed consent was obtained from all patients prior to enrollment. Vital signs and adverse reactions were monitored in all patients for up to 24 h following the MR examination.

MR imaging

All imaging was performed on a 1.5-T MR system (Magnetom Sonata, Siemens Medical Systems, Erlangen, Germany) equipped with a high-performance gradient system characterized by an amplitude of 40 mT/m and a slew rate of 200 mT/m/ms. All patients were placed feet first within the bore of the magnet and examined in the supine position on a fully MR-compatible rolling table platform (AngioSURF-system) that had been placed on the existing table top [16].

Total-body MRA is based on the acquisition of five slightly overlapping 3D data sets acquired in immediate succession. The first data set covers the aortic arch, supraaortic branch arteries and the thoracic aorta, while the second data set covers the abdominal aorta with its major branches, including the renal arteries. The third data set displays the pelvic arteries, and the last two data sets cover the arteries of the thighs and calves, respectively.

Based on a “moving vessel scout” and following determination of the contrast travel time with a test bolus, slightly overlapping data sets are collected using a fast low-angle shot (FLASH) 3D sequence (coronal acquisition; k-space sampling centric-elliptic; TR/TE: 2.1/0.7 ms, flip: 25°, 40 partitions interpolated by zero-filling to 64, FOV: 390×390 mm, matrix: 256×225, acquisition time: 12 s). The slice thickness was interpolated by zero-filling and varied between the stations: The true slice thickness for the first station was 2.4 mm (interpolated to 1.8×1.5×1.5 mm), for the second and third station 2.9 mm (interpolated to 1.7×1.5×1.8 mm), and for the two lower stations 1.9 mm (interpolated to 1.6×1.5×1.2 mm). A 2-cm overlap at each station's end results in a cranio-caudal coverage of 174 cm.

Gd-BOPTA (MultiHance, Bracco, Milan, Italy), a commercially available paramagnetic contrast agent, was administered at a weight-adjusted dose of 0.2 mmol/kg bw [17]. The agent was diluted with normal saline to a total volume of 60 ml. Contrast material was injected automatically (MR Spectris, Medrad, Pittsburgh, PA) using a biphasic protocol: the first half was injected at a rate of 1.3 ml/s, while the second half was administered at a rate of 0.7 ml/s, followed by a 20-ml saline flush.

Image and data analysis

For all patients the ‘in-room’ time, defined as the time span between the patient entering the MR room for positioning and the patient leaving the MR room, was determined. For image analysis, the arterial tree was divided into 30 segments: 1-2: right/left internal carotid arteries, 3-4: right/left common carotid arteries, 5: subclavian artery, 6: thoracic aorta, 7: suprarenal abdominal aorta, 8: infrarenal abdominal aorta, 9-10: right/left renal arteries, 11-12: right/left common iliac arteries, 13-14: right/left external iliac arteries, 15-16: right/left common femoral arteries, 17-18: proximal half of right/left superficial femoral arteries, 19-20: distal half of right/left superficial femoral arteries, 21-22: right/left popliteal arteries, 23-24: right/left tibio-peroneal trunk, 25-26: right/left anterior tibial arteries, 27-28: right/left peroneal arteries, and 29-30: right/left posterior tibial arteries.

Image quality was assessed by two experienced MR radiologists in consensus. The display of each arterial segment was characterized as either diagnostic or non-diagnostic. The display was considered diagnostic when the relevant vascular pathology could be reliably confirmed or excluded.

MRA image sets were further analyzed regarding the presence of vascular disease by the same readers. Thus, each vascular segment was assessed for the presence of stenoses with (1) luminal narrowing exceeding 50% on the basis of the most severe reduction of the arterial diameter compared with the most normal appearing segment proximal or distal to the area of arterial compromise, (2) vessel occlusion or (3) aneurysmal disease (documented by a maximum diameter of the thoracic/abdominal aorta >4.5 cm). Eyeball measurements on both the coronal source images and thin-slice MIPs (10 mm) were performed for grading the stenosis of each vascular segment.

Analysis was based on maximum intensity projections (MIP), available in 23 different projection angles from the right to left anterior oblique in steps of 5°, as well as multiplanar reformations viewed on a 3D workstation (Leonardo, Siemens, Erlangen, Germany). Arterial disease documented by total-body 3D MRA outside the peripheral tree was confirmed if deemed clinically necessary by the referring clinician. All imaging studies performed within 60 days of the respective total-body MRA examination were compared with the 3D MRA studies.

Results

For the 247 patients (7,410 segments), the examination rendered diagnostic image quality from the carotid arteries to the tibial vessels in 7,343 segments (99.2 %). Sixty-seven segments (0.8 %) in 29 examinations were rated non-diagnostic. Of these, 62 segments were located in the calves, where venous overlap and motion artifacts were the main reasons for the inability to confirm or exclude disease. Three arterial segments in the pelvis of one patient were not seen to good advantage due to the presence of oral contrast in the colon from a previous examination. Finally, two renal arteries in separate patients were not assessable due to severe venous overlap in conjunction with respiratory motion artifacts. The mean in-room time for all patients was 14.3 min and ranged between 15.8 and 13.6 min.

In the peripheral vascular tree total-body MRA documented pathology in 467 vascular segments in 243 patients: the two blinded readers found stenoses >50% in 319 segments, 145 occlusions, and 3 aneurysms (Table 1).
Table 1

Assessment of PAOD with total-body MR angiography by two blinded readers for 247 patients

Blood vessel

No. of segments with stenosis 50–99% (n=319)

No. of segments with occlusion (n=145)

No. of segments with aneurysm (n=3)

Common iliac art.

51

10

1

External iliac art.

49

7

0

Common femoral

26

9

0

Sup. fem art.

49

17

0

Popliteal artery

22

11

2

Tibioperoneal trunk

21

16

0

Ant.tibial art.

32

18

0

Peroneal art.

31

36

0

Post.tibial art.

38

21

0

Note: In all, 7,410 segments were evaluated, but 67 were excluded because of non-diagnostic image quality, which left 7,343 segments with diagnostic image quality

Outside the peripheral arterial tree, the two blinded readers depicted 73 unsuspected arterial pathologies (in 52 patients) on the total-body 3D MRA examinations that might have been relevant for subsequent patient management: Stenoses exhibiting luminal narrowing >50% were identified in 36 renal arteries (24 patients), 28 internal carotid arteries (22 patients), and 4 subclavian arteries (4 patients). Aneurysmal disease of the aorta, documented by a diameter >4.5 cm, was identified in five segments (five patients) (Table 2).
Table 2

Unsuspected arterial pathologies outside the peripheral arterial tree revealed by total-body MR angiography: 73 pathologies in 52 patients were detected

Blood vessel

No. of segments with stenosis 50–99% (n=68)

No. of segments with occlusion (n=0)

No. of segments with aneurysm (n=5)

Internal carotid art.

28

0

0

Subclavian art.

4

0

0

Renal art.

36

0

0

Aorta

0

0

5

Thrity-six of the 73 segments were deemed necessary for further investigation by means of focused MRA examinations: within 60 days after imaging, 16 patients had undergone a focused 3D MRA examination of the renal arteries (18 arteries with luminal narrowing >50%), confirming the diagnosis in all 18 cases in the 16 patients (Fig. 1, 2). In seven patients an angioplasty of the stenosed eight renal arteries was performed.
https://static-content.springer.com/image/art%3A10.1007%2Fs00330-005-0001-8/MediaObjects/330_2005_1_Fig1_HTML.jpg
Fig. 1

AngioSURF-based total-body 3D MR angiogram (ap-view) in a 63 year-old male patientwith PAOD and history of a femoro-popliteal bypass graft on the left leg. The 3D MRA examination shows diffuse atherosclerotic disease of the aorta and the peripheral vasculature. In addition, a moderate to severe stenosis of the right renal artery with slight poststenotic dilatation is depicted. Sequence parameters : FLASH 3D: TR/TE 2.1/0.7 ms, flip angle: 25°, 40 partitions interpolated by zero-filling to 64, slab thickness: 120 mm, slice thickness: 3.0 mm interpolated to 1.9 mm, FOV: 390×390 mm, matrix: 256×225 interpolated by zero-filling to 512×512, acq. time: 12 s per station

https://static-content.springer.com/image/art%3A10.1007%2Fs00330-005-0001-8/MediaObjects/330_2005_1_Fig2_HTML.jpg
Fig. 2

Contrast-enhanced renal MR angiogram of the same patient acquired 3 days after the total-body MRA examination. The examination confirms the moderate to severe stenosis of the right renal artery. Sequence parameters: FLASH 3D: TR/TE 3.0/1.0 ms, flip angle: 25°, 64 partitions, slab thickness: 120 mm, slice thickness: 2.8 mm interpolated to 1.4 mm, FOV: 309×380 mm, matrix: 208×512, and acq. time: 21 s

In 26 patients 28 internal carotid arterial stenoses were detected. To confirm the diagnosis, 15 patients were referred for a 3D MRA examination of the neck arteries confirming high-grade stenoses of the internal carotid artery in all 15 cases. In three patients carotid endatherectomy was performed within 60 days of the examination.

Of the five segments with aneurysmal disease (in four patients), four involved the infrarenal abdominal aorta, and one the thoracic aorta. The maximum diameter of the abdominal aortic aneurysms measured 4.8, 4.9, 5.0, and 5.3 cm, respectively. The thoracic aneurysm measured 5.2 cm. Within the 60-day follow-up period, three of the five patients were referred for a dedicated MRA examination of the abdominal aorta; the diagnosis was confirmed in all three cases.

Discussion

The outlined study clearly demonstrates in almost 250 patients with known PAOD the noteworthy influence of total-body MRA on subsequent patient management when additional relevant arterial disease outside the peripheral vascular tree was incidentally detected. In our study population interventional or surgical therapy outside the peripheral arterial tree was performed in as many as 9 patients (11 segments), including carotid endatherectomy (3 segments) and renal artery angioplasty (8 segments).

The contrast dose for total-body MRA is identical to that employed by most investigators for focused single-station as well as multi-station MRA examinations [18, 19] and remains well within the approved limits. To assure maximal arterial enhancement, Gd-BOPTA, a paramagnetic contrast agent with high intravascular relaxivity owing to some degree of weak albumin binding [20], was employed. As in many other previous investigations, Gd-BOPTA was used in an off-label manner.

The applied rolling table platform in conjunction with the ultrafast gradient system permits the rapid following of the contrast bolus through the different arterial stations. The examination time of less than 15 min is very short and exceeds by less than 10% the examination time required for single-station MRA examinations.

The diagnostic accuracy of contrast-enhanced three-dimensional MRA has been proven for virtually all vascular territories except the intracranial and coronary circulations. While the former is well depicted with time-of-flight and phase-contrast MRA techniques, which do not require the administration of any contrast agent [2123], MR display of the coronary arteries remains challenging [24, 25]. Encouraging results have recently been demonstrated based on the combined availability of navigator techniques [26] and intravascular contrast agents [27]. Reflecting the frequent presence of relevant arterial disease in these vascular territories, particularly in patients with PAOD, this intrinsic exclusion of the herein portrayed total-body approach must be considered a drawback.

With contrast-enhanced 3D MRA the select display of the arterial system is based on the presence of T1-shortening Gd-based contrast in the vascular territory under consideration during data acquisition [28]. Using the latest generation of high performance MR hardware, the acquisition time for a complete 3D data set can be reduced to merely 12 s. Thus, up to five 3D data sets can be collected within the short intraarterial contrast phase of slightly more than 60 s. The diagnostic accuracy of total-body MRA has been documented before [1015, 29]. Similarly, confirmatory studies performed in 36 segments in this study revealed no false positive or false negative examinations.

Use of a phased-array torso surface coil integrated into the rolling AngioSURF table system translated into sufficient signal for high spatial resolution imaging. Thus, the voxel size amounted to 0.8×0.8×1.9 mm, enabling excellent delineation even of smaller vessels, such as the trifurcation arteries. The introduction of recently available parallel imaging techniques is likely to further improve both the acquisition time and spatial resolution of the examination [30]. Currently, the short acquisition time of merely 12 s per station is accomplished by gaining relatively thick slices and subsequent zero interpolation, which must be regarded as suboptimal. Recent studies have nicely shown the immense potential of parallel imaging in terms of increasing image quality for different vascular regions including the peripheral arteries [3133].

Beyond localizing and gauging the severity of a symptomatic arterial lesion, an optimized therapeutic strategy should be predicated upon other clinical factors, including the presence of concomitant arterial disease. This was the case in approximately 20% of the studied patients (52/247). This relatively high number is not surprising: it underscores the systemic nature of atherosclerosis. In fact, PAOD due to atherosclerosis is rarely an isolated disease process. Studies addressing the prevalence of coronary artery disease (CAD) in patients with PAOD show that patient history, clinical examination and ECG typically indicate a CAD presence of 40 to 60% of such patients, although this may often be asymptomatic as it is masked by exercise restrictions [33, 34].

Although weaker, the link between PAOD and renovascular disease is quite evident. Approximately one fourth of PAOD patients suffer from hypertension, and in these patients consideration should be given to the possibility of renal arterial compromise. Twenty-four patients (9%) revealed renal artery disease with a luminal narrowing exceeding 50%. In 16 of these patients, subsequent investigation deemed necessary for patient management confirmed the diagnosis.

There is ongoing controversy about the value of screening all patients with PAOD, symptomatic or not, for carotid disease and aortic aneurysms [35, 36]. Based on duplex sonography, carotid disease could be demonstrated in 26 to 50% of patients with PAOD [35, 37]. While some of these patients have a history of cerebral events or a carotid bruit, others must be considered ‘asymptomatic’ [38].

The management of patients with asymptomatic carotid artery stenosis is a highly controversial topic. While this study again confirms that claudicates are more likely to have significant but asymptomatic carotid disease compared to the general population, the treatment of asymptomatic carotid disease remains divisive [39, 40]. While more recent studies appear to demonstrate an unequivocal benefit associated with the treatment of such disease [41], the issue of yield versus cost remains unsettled [42].

When discussing the value of screening patients for abdominal aortic aneurysms (AAA), several points have to be considered: Firstly, for an unknown reason, the prevalence of abdominal aortic aneurysm has been increasing steadily over the past 40 years [43]. Secondly, AAAs are rarely symptomatic until they rupture, by which time the opportunity to intervene has usually been lost. The mortality rate of aneurysm rupture is in excess of 80 percent.

Selecting asymptomatic patients to screen for AAA remains a controversial topic with a wide range of recommendations [4447]. In random screening groups, the incidence of AAA is reported to be 2 to 3 percent, with 75 percent of the aneurysms found in individuals over the age of 60 years [48]. The likelihood of having AAA is increased in smokers, older individuals, males, and individuals who have CAD, PAOD [49, 50], or a first-order relative with aortic aneurysm [51]. As a result of being asymptomatic, life threatening, treatable and amendable to detection by noninvasive tests, screening for AAA in patients with PAOD may be an important way to eliminate a preventable source of mortality [52].

Noninvasiveness, three-dimensionality, extended coverage, and high contrast conspicuity are the main characteristics of total-body MRA that combine to allow a quick and comprehensive evaluation of the arterial system in patients with atherosclerosis. The technique is well suited for the assessment of the peripheral vasculature; in addition, it provides accurate data regarding the remainder of the arterial system and does indeed have an impact on patient management in patients with PAOD.

Copyright information

© Springer-Verlag 2005