Acta Radiol OnlineFirst, published on July 15, 2015 as doi:10.1177/0284185115595657
Original Article
Comparison of CT and MR angiography in evaluation of peripheral arterial disease before endovascular intervention
Acta Radiologica 0(0) 1–10 ! The Foundation Acta Radiologica 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185115595657 acr.sagepub.com
Alessandro Cina, Carmine Di Stasi, Vittorio Semeraro, Riccardo Marano, Giancarlo Savino, Roberto Iezzi and Lorenzo Bonomo
Abstract Background: Multidetector computed tomography angiography (MDCTA) and magnetic resonance angiography (MRA) are accurate techniques for selecting patients with peripheral arterial disease for surgical and endovascular treatment. No studies in the literature have directly compared MDCTA and MRA to establish which one should be employed, in patients suitable for both techniques, before endovascular treatment. Purpose: To compare diagnostic performance of MDCTA vs MRA before endovascular intervention. Material and Methods: We prospectively compared MDCTA (64 slices scanner) and MRA (1.5 T scanner; 3D gadolinium-enhanced bolus-chase acquisition plus time resolved acquisition on calves) to stratify 35 patients according to the TASC II score and a runoff severity score. We also evaluated the accuracy of both techniques in each arterial segment. Selective angiography performed during the treatment was the standard of reference. Results: MDCTA and MRA accurately classify disease in the aorto-iliac (accuracy 0.92 for MDCTA and MRA) and femoro-popliteal (MDCTA 0.94, MRA 0.90) segments. MDCTA was more accurate in stratifying disease in the infrapopliteal segments (0.96 vs. 0.9) and in assessing the impairment of runoff arteries (0.92 vs. 0.85) at per-segment analysis. MDCTA showed a higher confidence and a shorter examination time. Conclusion: Our results suggest that MDCTA can be considered as a first-line investigation in patients being candidates for endovascular procedures when clinical history or duplex sonographic evaluation are indicative of severe impairment of the infrapopliteal segment.
Keywords Peripheral arterial disease, magnetic resonance angiography (MRA), multidetector computed tomography (MDCT), endovascular procedures, tibial arteries Date received: 3 February 2015; accepted: 20 June 2015
Introduction Multidetector computed tomography angiography (MDCTA) and magnetic resonance angiography (MRA) have replaced diagnostic conventional or catheter angiography in clinical practice (1), and has thus become the standard diagnostic modalities in selecting patients with peripheral arterial disease (PAD) for surgical or endovascular intervention (2). The reported values of sensitivity and specificity for MDCTA in identifying significant stenoses and occlusions are in the range of 92–97% and 93–98%, respectively, with summary estimates of 96% for
sensitivity and 95% for specificity in a recent metaanalysis (3). For MRA a sensitivity of 98% (range, 92–100%) and a specificity of 96% (range, 91–99%) was described (3–6).
Department of Radiological Sciences, ‘‘Agostino Gemelli’’ Hospital, Catholic University, Rome, Italy Corresponding author: Vittorio Semeraro, Department of Radiological Sciences, ‘‘Agostino Gemelli’’ Hospital, Catholic University, Rome, Italy. Email: [email protected]
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The use of MDCTA vs. MRA, however, has not been adequately investigated; currently a direct comparison of both techniques for peripheral arteries in the same population is not available in the literature. As a consequence, for patients without specific contraindications to MDCTA and MRA, no scientific evidence based guidelines have been proposed and the use of MDCTA rather than MRA is related to experience and protocols of single institutions. Until 5 years ago, MDCTA was preferentially employed when MRA was contraindicated in a particular patient (ferromagnetic devices, pace makers or stimulators, claustrophobia), and MRA was favored in patients with renal function impairment. In recent years, the risk of gadolinium-related systemic nephrogenic fibrosis (SNF) (7) in patients with renal impairment or already on hemodialysis has hindered selective use of MRA in this group of patients, thus questioning previous convictions (8). For adequate planning of the endovascular treatment, the accuracy of a technique in the assessment of significant stenoses and occlusions is not an exhaustive indicator. Complexity and length of the lesion and characteristics of inflow and infrapopliteal vessels should be taken into consideration when deciding whether endovascular therapy or surgery is indicated, as these parameters are important determinants of short- and long-term clinical outcome of the treatment offered. In 2000 a classification of the global arterial impairment of the iliac and femoro-popliteal district was proposed by the Trans Atlantic Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC) (9). The main purpose of this classification, revised in 2007 (1), was the attempt to identify criteria for selection of patients for the open vs. endovascular treatment according to evidence from the literature. A clear correlation between patient classification according to TASC and results and outcomes after surgical and endovascular therapy has been demonstrated, both for ilio-femoral (10,11) and infrapopliteal intervention (12,13). The TASC II classification, however, does not provide a focused evaluation of the arteries of the calves and feet; these arteries are involved in 40–50% of symptomatic patients (14) and in recent years have become a frequent target of selective and combined endovascular treatment. The primary objectives of this study were to assess the accuracy of MDCTA vs. MRA in identifying the degree of impairment of the peripheral arterial tree in patients with PAD as candidates for endovascular treatment and to evaluate the accuracy of both modalities in classifying patients according to the TASC II grading for aorto-iliac and femoro-popliteal and following an ‘‘ad hoc’’ score for infrapopliteal segments.
Secondary objectives of the study were the assessment of the degree of reliability of both techniques for the evaluation of the arterial tree and the analysis of time consumption of both techniques.
Material and Methods Informed written consent from patients and approval of the study from the local ethical board were obtained. Inclusion criteria for the study were known PAD lasting for 6 months or longer, age > 18 years and clinical indication (eventually including previous Doppler US) for possible treatment; 219 patients were screened to be included in this study. Exclusion criteria were contraindications to endovascular treatment (30 patients); previous stent implantation in the target limb (29 patients); women of reproductive age (1 patient); and all the patients with contraindications to MDCTA (33 patients) and/or to MRA (Creatinine clearance < 40 mL/min; iodine allergy; claustrophobia; pace-makers, ferromagnetic implants, neurostimulators, 48 patients). For ethical reasons and to avoid time loss in performing both MDCTA and MRA in this study we excluded patients in whom the endovascular procedure was requested as an emergency treatment for ‘‘limb salvage’’ (52 patients). In 16 months, 35 consecutive patients (20 men, 15 women; mean age, 76 years; age range, 59–87 years) with PAD who were selected for possible treatment (Fontaine stage IIa n ¼ 8 patients, stage IIb n ¼ 7, stage III n ¼ 8, and stage IV n ¼ 12) were prospectively enrolled and underwent MDCTA, using 64-slice MDCT (LightSpeed VCT, GE Healthcare, Waukesha, WI, USA) and gadolinium-subtracted three-station bolus-chase MRA plus time resolved acquisition on the calves (Signa Echospeed 1.5 T, GE Healthcare), within 30 days before the endovascular treatment performed by DSA system (Integris Allura Xper FD 20, Philips, Eindhoven, The Netherlands).
Techniques of MDCTA, MRA, and DSA MDCTA scans were performed during i.v. administration of 100 mL of non-ionic iodinated contrast medium with a concentration of 400 mg I/mL (Iomeron, Bracco, Milan, Italy) by a double barrel injector at a rate of 3.5 mL/s through an 18-gauge i.v. cannula inserted into an antecubital vein. Contrast infusion was followed by an injection of 60 mL of saline at the same flow rate. The ‘‘smart prep’’ option of the scanner, with ROI localized on the supraceliac abdominal aorta, was employed to synchronize the scanning with peak arterial opacification. The MRA protocol consisted of a bolus chase three station subtracted acquisition during i.v.
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administration of 12 mL of gadolinium-based contrast agent (gadobenate dimeglumine, 529 mg/mL, Multihance, Bracco) by a double barrel injector at a rate of 1.5 mL/s through a 20-gauge i.v. cannula inserted into an antecubital vein. Contrast infusion was followed by injection of 20 mL of saline at the same flow rate. The automatic ‘‘bolus trigger’’ option of the scanner, with ROI localized on the supraceliac abdominal aorta, was employed to synchronize the scanning with peak arterial opacification. Sub-systolic thigh compression was employed to prevent venous contamination. On calves and feet, time resolved acquisition (TRICKS, GE Healthcare) were also employed after the standard acquisition by additional injection of 8 mL of the same contrast medium. Details of MDCTA and MRA techniques are reported in Table 1. The diagnostic selective DSA performed during the endovascular treatment was employed as the gold standard. Contrast agent injection (Omnipaque 350 mgI/mL, GE Healtcare) was performed by an automatic injector (4–10 mL/s according to the level of injection) via 4-6 Fr sheaths or 5 Fr selective diagnostic catheters by either retrograde or antegrade common femoral approach.
Image analysis Fourteen arterial segments per limb were evaluated on MDCTA, MRA and on the gold standard DSA when available: from aortic bifurcation to pedal (distal abdominal aorta, common iliac, external iliac, internal iliac, common femoral, profunda femoris, superficial femoral, popliteal, anterior tibial, tibio-peroneal trunk, posterior tibial, peroneal, dorsalis pedis, and lateral plantar). Each segment was blinded assessed at MDCTA and MRA for the degree of impairment (range, 1–4) following a score (Table 2) modified from a score proposed by Rutherford (15). To evaluate diagnostic reliability we adopted a score in the range of 1–3 (1, poor; 2, moderate; 3, good). Each aorto-iliac and femoro-popliteal district was stratified according to the TASC II classification (1), while the infrapopliteal district was classified according to the scheme described in Table 3, modified from the Rutherford angiographic runoff score (15). MDCTA and MRA images were analyzed at a workstation (Advantage Windows 4.3, GE Healthcare) by two different radiologists, one for MRA and one for MDCTA, blinded to DSA and MRA/MDCTA results. Assessment of stenoses and occlusions was performed on axial images plus MIP (with bone segmentation for MDCTA), volume rendering, and
multiplanar reconstructions. Stenosis quantification (diameter reduction) was performed by subjective criteria, with optional use of automatic vessel analysis tools. Since data of MDCTA and MRA were available to the interventional radiologist who performed the treatment, DSA runs for the study were analyzed by a different interventional radiologist unaware of MDCTA and MRA results on a dedicated workstation (Xcelera, Philips Medical Systems). The execution time and the time employed for reconstructions at the workstation were evaluated separately both for MDCTA and MRA.
Statistical analysis Variables employed to assess the primary objective of the study are ordinal, and a non-parametric inferential statistic was required. The Wilcoxon rank-sum test was employed to assess differences between MDCTA and MRA in the grading of impairment of arterial segments in the iliac, femoropopliteal, and infrapopliteal segments and for diagnostic confidence. Continuous variables, such as examination time, were expressed as mean and SD and the Student’s t-test was adopted to assess significant differences. All statistical tests were two-sided and a P value < 0.05 was considered statistically significant.
Results Thirty-five limbs with 330 arterial segments were studied on pre-treatment selective DSA and were available for the analysis of MDCTA vs MRA. The distribution of segments was: 54 iliac; 82 femoro-popliteal; and 194 below the knee. Significant stenoses or occlusions were detected at DSA in 128 segments. A per-segment analysis was performed to assess the accuracy of MDCTA vs. MRA in evaluating the exact degree of impairment of each segment and a pooled analysis was performed for iliac, femoro-popliteal, and infrapopliteal segments (Fig. 1). Overall accuracy of MDCTA was 0.94 (95% confidence interval [CI], 0.90–0.96) and accuracy for MRA was 0.92 (95% CI, 0.88–0.94) (P > 0.05). Accuracy for iliac segments was 0.98 for MDCTA (95% CI, 0.90–0.99) and 0.95 for MRA (95% CI, 0.84– 0.98) (P > 0.05). Accuracy for femoro-popliteal segments was 0.95 for MDCTA (95% CI, 0.88–0.98) and 0.91 for MRA (95% CI, 0.83–0.95) (P > 0.05). Accuracy for infrapopliteal segments was 0.92 for MDCTA (95% CI, 0.87–0.94) and 0.85 for MRA (95% CI, 0.79–0.89) (P ¼ 0.02).
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Table 1. Technique for MDCTA and MRA examinations. MDCTA protocol Detector configuration Pitch Rotation time Table speed
64 1.25 mm 1.375 0.5 s 11 cm/s
Kv SFOV Filter mA
120 Large Standard Automatic
Aorto-iliac Body Oblique 3D TOF SPGR Smart Prep ZIPx2, ZIP 512 Minimum 20 83.33 Freq. 288, Phase 192 1 0.8 S-I 48 4 34
Femoro-popliteal Body Oblique 3D TOF SPGR
Calves and feet 8 channels phased array Oblique 3D TOF SPGR
ZIPx2, ZIP 512 Minimum 20 83.33 Freq. 320, Phase 192 1 0.8 S-I 48 3.6 32
ZIPx2, ZIP 512 Minimum 30 50 Freq. 256, Phase 512 1 0.6 S-I 48 2.8 38
Bolus-chase MRA protocol Coil Plane Sequence Triggering Options enabled TE Flip angle Bandwidth Acquisition timing NEX Phase FOV Frequency direction FOV Slice thickness Locations per slab
MRA time resolved protocol (TRICKS) Parameter Asset calibration Coil 8 channels phased array Plane Axial Sequence 2D GRADIENT ECHO Options enabled TE Flip angle Bandwidth Acquisition timing NEX Phase FOV Frequency direction FOV 48 Slice thickness 0 Locations per slab Acquisitions (n) 1
For infrapopliteal arteries, results of the standard MRA sequences plus time resolved acquisitions were also compared to standard acquisitions (Fig. 1). At per region analysis (Fig. 2) the accuracy for stratification of patients according to TASC classification was the same for MDCTA and MRA for the iliac region: 0.92 (95% CI, 0.66–0.98; P ¼ 0.43). In the femoro-popliteal region, MDCTA (accuracy, 0.94; 95% CI, 0.77–0.99)
Calves and feet 8 channels phased array Oblique 3D TRICKS ZIPx2, ZIP 512 Minimum 20 31,25 Freq. 512, Phase 256 1 0.75 Unswap 44 3 26 1 mask þ 9 post m.d.c.
stratification was slightly more accurate than MRA (accuracy, 0.9; 95% CI, 0.68–0.98) without significant statistical difference (P ¼ 0.08). Regarding the accuracy for the assessment of the infrapopliteal region, a difference at the statistical limit (P ¼ 0.04) was found between MDCTA (accuracy, 0.96; 95% CI, 0.84–0.99) and MRA (accuracy, 0.90; 95% CI, 0.76–0.96).
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Table 2. Score for assessment of single arterial segment impairment (modified from Rutherford). Score
Type of lesion
0 1 2
No >50% stenosis Single >50% stenosis Multiple >50% stenoses or Single 5 cm occlusion or Multiple 5 cm occlusion or total occlusion
3 4
Table 3. Score for impairment of infrapopliteal arterial district (modified from Rutherford).
Degree of impairment 1 2 3
4
Tibial trunks (ATA, PTA, PA) involved (number of vessel out of 3)*
Pedal trunks (Plantar and dorsalis pedis) involved (number of vessel out of 2)
1 stenosis/occlusion ! 2 stenosis/occlusion ! 1 stenosis/occlusion ! 3 stenosis/occlusion ! 2 stenosis/occlusion ! 1 stenosis/occlusion ! 3 stenosis/occlusion ! 2–3 stenosis/occlusion !
Patent Patent 1 stenosis/occlusion Patent 1 stenosis/occlusion 2 stenosis/occlusion 1 stenosis/occlusion 2 stenosis/occlusion
*Stenosis or occlusion of tibioperoneal trunk was considered as 2 vessells lesion. ATA, anterior tibial artery; PA, peroneal artery; PTA, posterior tibial artery.
The mean diagnostic confidence was 2.91 for MDCTA and 2.67 for MRA (P < 0.00001) (Fig. 3) with a difference particularly evident in the infrapopliteal arteries, while no significant differences were detected in iliac and femoro-popliteal segments. Since calcification can be depicted only at MDCTA and our primary purpose was to compare MDCTA to MRA, we did not perform a quantitative evaluation of the degree of calcification in our population, however, we reviewed all MDCTA examinations with a low or intermediate confidence score in infrapopliteal segments (grade 1 or 2 out of 3); we found diffuse calcifications in 13 out of 17 infrapopliteal arteries with a non-optimal confidence. Venous contamination limiting (confidence degree 1) an optimal evaluation of above the knee arteries was found in one limb at MDCT and in two limbs at MRA.
The mean scanning time (Fig. 4), interpreted as the overall occupation of the scanner, was 9 2 min for MDCTA and 33 4 min for MRA and the overall examination time was 29 4 min for MDCTA and 43 6 min for MRA, with a statistically significant advantage for MDCTA (P < 0.01).
Discussion As treatment options for lower extremity peripheral vascular disease have expanded, obtaining high quality diagnostic arterial images is mandatory. Understanding the location, severity, and complexity of occlusive disease is of paramount importance for accurately planning the most appropriate approach to revascularization; MDCTA and MRA have the potential to provide a panoramic and accurate vascular mapping (Figs. 5 and 6). The hypothetical advantages of MDCTA over MRA are the relatively short imaging time and lower cost (16). Covering a large volume over the whole vascular tree with sufficient intra-arterial contrast enhancement and minimal venous return remains a challenge for MRA, however, the time resolved acquisitions (17) and subsystolic calf compression, as demonstrated in the literature and by our experience can overcome this problem in most cases. MRA has some important advantages: it does not require iodinated contrast material and there is no radiation exposure. However, there are many contraindications for MRI including pacemakers, metal implants, claustrophobia, and the use of gadolinium contrast agents in patients with renal failure (8). For MDCTA, iodinated contrast agents are potentially nephrotoxic, but this adverse effect can be reduced by hydration and, although still under debate, administration of acetylcysteine (18). Another drawback of MDCTA may be that frequent use exposes a patient to large quantities of potentially carcinogenic ionizing radiation (19), however, the effective radiation dose of peripheral CTA for 16-detector row CT angiography is estimated in the range of 1.6–3.9 mSV and is lower than digital subtraction angiography (20). Fresh blood imaging (FBI) is an unenhanced MRA technique that can be useful particularly in patients with impaired renal function (21), but patients with PAD, especially those with severe stenoses in the lower leg and pedal vessels, frequently develop rest pain with resultant involuntary twitching that can significantly degrade image quality in fresh blood imaging which is exquisitely sensitive to even subtle movement. FBI-MR angiography moreover has high sensitivities only in the above the knee vessels (22). Nowadays 3.0 T peripheral CE-MR angiography is promising in clinical practice. More clinical studies
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Fig. 1. Per segment analysis of accuracy of MDCTA vs MRA (standard protocol þ tricks sequences on calves and feet and standard protocol alone) for assessment of the degree of impairment in each segment. (TOT ¼ total; ILI ¼ iliac; FP ¼ femoro-popliteal; IP ¼ infrapopliteal; ST ¼ standard protocol; TR ¼ tricks sequences).
Fig. 2. Per limb analysis of accuracy of MDCTA vs MRA to identify correct TASC classification (iliac and femoro-popliteal) and ‘‘ad hoc’’ infrapopliteal score. (ILI ¼ iliac; FP ¼ femoro-popliteal; IP ¼ infrapopliteal).
need to determine the clinical value and limitations of the peripheral MRA approach at 3.0 T for multisegmental PAD and diffused involvement of the runoff vessels. In a study comparing 3.0-T versus 1.5-T MRA van den Bosch HCet al. (23) reported a similar diagnostic performance, even if there was a significantly increased contrast-to-noise ratio for identical contrast agent dose at 3.0 T MRA. MDCTA, differently from MRA, can visualize calcified plaques providing useful data for the endovascular treatment and allowing advance selection of the best option for revascularization (PTA, cutting balloon, drug eluting balloon, laser or mechanical atherectomy, primary stenting, etc.); moreover the knowledge of the
presence of heavily calcified lesions can predict the treatment outcome (24). On the other hand, diffuse concentric calcification in the infrapopliteal vessels, often found in diabetic patients, due to the ‘‘blooming’’ of calcium with respect to the vessel’s lumen, makes the evaluation of stenosis on MDCTA very difficult (25). The use of dual source or dual-energy CT can overcome this limitation since it is possible to remove bones and intraluminal calcified plaques from angiography datasets on the basis of spectral differentiation separating iodine from calcium by this technique (26–29). However, dual-energy CT provides best results in arteries of the thigh; below the knee, plaque subtraction is less accurate and, thus far,
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Fig. 3. Per segment diagnostic confidence of MDCTA vs MRA. (TOT ¼ total; ILI ¼ iliac; FP ¼ femoro-popliteal; IP ¼ infrapopliteal).
Fig. 4. Comparative evaluation of time expense (min.) of MDCTA vs MRA.
no study has demonstrated any clear clinical advantage of dual-energy CT for peripheral artery applications. A published report comparing MDCTA and MRA for peripheral arterial disease is a randomized trial from Ouwendijk et al. (16) which was designed to evaluate the clinical utility, patient outcomes, and costs of MDCTA and MRA. The authors concluded that MDCTA has some advantages over MRA because of the higher diagnostic costs of MRA. Evaluation of accuracy of techniques was not a primary objective of this study and authors could not clearly demonstrate
that MDCTA more accurately depicts the extent and localization of disease. In a systematic review of literature published in 2007 (30), MRA seemed to be more specific than MDCTA, while in a more recent meta-analysis (3) no significant differences in the diagnostic performance were reported. The area of leg assessed affects diagnostic performance. In our study we found a higher accuracy for MDCTA in the assessment of impairment in infrapopliteal vessels; the superior spatial resolution allowed
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Fig. 5. Sixty-two years old diabetic man with left toe ulcer. Comparison of MIP MDCTA (A) and MRA (B) reconstructions. Only segments evaluated with the reference technique (DSA, C) were included in the study and evaluated at MDCTA and MRA (dashed box).
by MDCTA compared to MRA and the lower examination-time for MDCTA may explain this result. Our study has some limitations. We selected only patients who had indications for endovascular treatment, our results may not fully apply to the general population of patients suffering from PAD, including patients who are candidates for surgery. Finally an inter-observer variability analysis was not performed for MDCTA and MRA.
In conclusion, we can suggest the use of MDCTA as the first line investigation when clinical history (Fontaine III or IV) or previous imaging evaluation is indicative of diffuse steno-occlusive involvement of the infrapopliteal segment. The shorter execution time for MDCTA makes this technique more appropriate for patients with rest pain and limited compliance with prolonged immobilization. According to our experience additional time resolved sequences on calves and feet
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Fig. 6. Same case as Fig.5. Close up vision of infrapopliteal arteries. A good correlation is evident between MDCTA (A) and MRA (B) with respect to DSA (C). The focal stenosis of anterior tibial artery is correctly depicted by both techniques before endovascular treatment (D) (0.014’’ guidewire and dilation by 2.5 mm over the wire balloon).
should be part of the MRA protocol to improve diagnostic confidence in patients with suspected diffuse infrapopliteal involvement or in diabetic patients. Acknowledgements The authors thank Dr. L Ratnam for reviewing the paper for English language.
Conflict of interest None declared.
Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
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Original Article
Comparison of CT and MR angiography in evaluation of peripheral arterial disease before endovascular intervention
Acta Radiologica 0(0) 1–10 ! The Foundation Acta Radiologica 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0284185115595657 acr.sagepub.com
Alessandro Cina, Carmine Di Stasi, Vittorio Semeraro, Riccardo Marano, Giancarlo Savino, Roberto Iezzi and Lorenzo Bonomo
Abstract Background: Multidetector computed tomography angiography (MDCTA) and magnetic resonance angiography (MRA) are accurate techniques for selecting patients with peripheral arterial disease for surgical and endovascular treatment. No studies in the literature have directly compared MDCTA and MRA to establish which one should be employed, in patients suitable for both techniques, before endovascular treatment. Purpose: To compare diagnostic performance of MDCTA vs MRA before endovascular intervention. Material and Methods: We prospectively compared MDCTA (64 slices scanner) and MRA (1.5 T scanner; 3D gadolinium-enhanced bolus-chase acquisition plus time resolved acquisition on calves) to stratify 35 patients according to the TASC II score and a runoff severity score. We also evaluated the accuracy of both techniques in each arterial segment. Selective angiography performed during the treatment was the standard of reference. Results: MDCTA and MRA accurately classify disease in the aorto-iliac (accuracy 0.92 for MDCTA and MRA) and femoro-popliteal (MDCTA 0.94, MRA 0.90) segments. MDCTA was more accurate in stratifying disease in the infrapopliteal segments (0.96 vs. 0.9) and in assessing the impairment of runoff arteries (0.92 vs. 0.85) at per-segment analysis. MDCTA showed a higher confidence and a shorter examination time. Conclusion: Our results suggest that MDCTA can be considered as a first-line investigation in patients being candidates for endovascular procedures when clinical history or duplex sonographic evaluation are indicative of severe impairment of the infrapopliteal segment.
Keywords Peripheral arterial disease, magnetic resonance angiography (MRA), multidetector computed tomography (MDCT), endovascular procedures, tibial arteries Date received: 3 February 2015; accepted: 20 June 2015
Introduction Multidetector computed tomography angiography (MDCTA) and magnetic resonance angiography (MRA) have replaced diagnostic conventional or catheter angiography in clinical practice (1), and has thus become the standard diagnostic modalities in selecting patients with peripheral arterial disease (PAD) for surgical or endovascular intervention (2). The reported values of sensitivity and specificity for MDCTA in identifying significant stenoses and occlusions are in the range of 92–97% and 93–98%, respectively, with summary estimates of 96% for
sensitivity and 95% for specificity in a recent metaanalysis (3). For MRA a sensitivity of 98% (range, 92–100%) and a specificity of 96% (range, 91–99%) was described (3–6).
Department of Radiological Sciences, ‘‘Agostino Gemelli’’ Hospital, Catholic University, Rome, Italy Corresponding author: Vittorio Semeraro, Department of Radiological Sciences, ‘‘Agostino Gemelli’’ Hospital, Catholic University, Rome, Italy. Email: [email protected]
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The use of MDCTA vs. MRA, however, has not been adequately investigated; currently a direct comparison of both techniques for peripheral arteries in the same population is not available in the literature. As a consequence, for patients without specific contraindications to MDCTA and MRA, no scientific evidence based guidelines have been proposed and the use of MDCTA rather than MRA is related to experience and protocols of single institutions. Until 5 years ago, MDCTA was preferentially employed when MRA was contraindicated in a particular patient (ferromagnetic devices, pace makers or stimulators, claustrophobia), and MRA was favored in patients with renal function impairment. In recent years, the risk of gadolinium-related systemic nephrogenic fibrosis (SNF) (7) in patients with renal impairment or already on hemodialysis has hindered selective use of MRA in this group of patients, thus questioning previous convictions (8). For adequate planning of the endovascular treatment, the accuracy of a technique in the assessment of significant stenoses and occlusions is not an exhaustive indicator. Complexity and length of the lesion and characteristics of inflow and infrapopliteal vessels should be taken into consideration when deciding whether endovascular therapy or surgery is indicated, as these parameters are important determinants of short- and long-term clinical outcome of the treatment offered. In 2000 a classification of the global arterial impairment of the iliac and femoro-popliteal district was proposed by the Trans Atlantic Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC) (9). The main purpose of this classification, revised in 2007 (1), was the attempt to identify criteria for selection of patients for the open vs. endovascular treatment according to evidence from the literature. A clear correlation between patient classification according to TASC and results and outcomes after surgical and endovascular therapy has been demonstrated, both for ilio-femoral (10,11) and infrapopliteal intervention (12,13). The TASC II classification, however, does not provide a focused evaluation of the arteries of the calves and feet; these arteries are involved in 40–50% of symptomatic patients (14) and in recent years have become a frequent target of selective and combined endovascular treatment. The primary objectives of this study were to assess the accuracy of MDCTA vs. MRA in identifying the degree of impairment of the peripheral arterial tree in patients with PAD as candidates for endovascular treatment and to evaluate the accuracy of both modalities in classifying patients according to the TASC II grading for aorto-iliac and femoro-popliteal and following an ‘‘ad hoc’’ score for infrapopliteal segments.
Secondary objectives of the study were the assessment of the degree of reliability of both techniques for the evaluation of the arterial tree and the analysis of time consumption of both techniques.
Material and Methods Informed written consent from patients and approval of the study from the local ethical board were obtained. Inclusion criteria for the study were known PAD lasting for 6 months or longer, age > 18 years and clinical indication (eventually including previous Doppler US) for possible treatment; 219 patients were screened to be included in this study. Exclusion criteria were contraindications to endovascular treatment (30 patients); previous stent implantation in the target limb (29 patients); women of reproductive age (1 patient); and all the patients with contraindications to MDCTA (33 patients) and/or to MRA (Creatinine clearance < 40 mL/min; iodine allergy; claustrophobia; pace-makers, ferromagnetic implants, neurostimulators, 48 patients). For ethical reasons and to avoid time loss in performing both MDCTA and MRA in this study we excluded patients in whom the endovascular procedure was requested as an emergency treatment for ‘‘limb salvage’’ (52 patients). In 16 months, 35 consecutive patients (20 men, 15 women; mean age, 76 years; age range, 59–87 years) with PAD who were selected for possible treatment (Fontaine stage IIa n ¼ 8 patients, stage IIb n ¼ 7, stage III n ¼ 8, and stage IV n ¼ 12) were prospectively enrolled and underwent MDCTA, using 64-slice MDCT (LightSpeed VCT, GE Healthcare, Waukesha, WI, USA) and gadolinium-subtracted three-station bolus-chase MRA plus time resolved acquisition on the calves (Signa Echospeed 1.5 T, GE Healthcare), within 30 days before the endovascular treatment performed by DSA system (Integris Allura Xper FD 20, Philips, Eindhoven, The Netherlands).
Techniques of MDCTA, MRA, and DSA MDCTA scans were performed during i.v. administration of 100 mL of non-ionic iodinated contrast medium with a concentration of 400 mg I/mL (Iomeron, Bracco, Milan, Italy) by a double barrel injector at a rate of 3.5 mL/s through an 18-gauge i.v. cannula inserted into an antecubital vein. Contrast infusion was followed by an injection of 60 mL of saline at the same flow rate. The ‘‘smart prep’’ option of the scanner, with ROI localized on the supraceliac abdominal aorta, was employed to synchronize the scanning with peak arterial opacification. The MRA protocol consisted of a bolus chase three station subtracted acquisition during i.v.
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administration of 12 mL of gadolinium-based contrast agent (gadobenate dimeglumine, 529 mg/mL, Multihance, Bracco) by a double barrel injector at a rate of 1.5 mL/s through a 20-gauge i.v. cannula inserted into an antecubital vein. Contrast infusion was followed by injection of 20 mL of saline at the same flow rate. The automatic ‘‘bolus trigger’’ option of the scanner, with ROI localized on the supraceliac abdominal aorta, was employed to synchronize the scanning with peak arterial opacification. Sub-systolic thigh compression was employed to prevent venous contamination. On calves and feet, time resolved acquisition (TRICKS, GE Healthcare) were also employed after the standard acquisition by additional injection of 8 mL of the same contrast medium. Details of MDCTA and MRA techniques are reported in Table 1. The diagnostic selective DSA performed during the endovascular treatment was employed as the gold standard. Contrast agent injection (Omnipaque 350 mgI/mL, GE Healtcare) was performed by an automatic injector (4–10 mL/s according to the level of injection) via 4-6 Fr sheaths or 5 Fr selective diagnostic catheters by either retrograde or antegrade common femoral approach.
Image analysis Fourteen arterial segments per limb were evaluated on MDCTA, MRA and on the gold standard DSA when available: from aortic bifurcation to pedal (distal abdominal aorta, common iliac, external iliac, internal iliac, common femoral, profunda femoris, superficial femoral, popliteal, anterior tibial, tibio-peroneal trunk, posterior tibial, peroneal, dorsalis pedis, and lateral plantar). Each segment was blinded assessed at MDCTA and MRA for the degree of impairment (range, 1–4) following a score (Table 2) modified from a score proposed by Rutherford (15). To evaluate diagnostic reliability we adopted a score in the range of 1–3 (1, poor; 2, moderate; 3, good). Each aorto-iliac and femoro-popliteal district was stratified according to the TASC II classification (1), while the infrapopliteal district was classified according to the scheme described in Table 3, modified from the Rutherford angiographic runoff score (15). MDCTA and MRA images were analyzed at a workstation (Advantage Windows 4.3, GE Healthcare) by two different radiologists, one for MRA and one for MDCTA, blinded to DSA and MRA/MDCTA results. Assessment of stenoses and occlusions was performed on axial images plus MIP (with bone segmentation for MDCTA), volume rendering, and
multiplanar reconstructions. Stenosis quantification (diameter reduction) was performed by subjective criteria, with optional use of automatic vessel analysis tools. Since data of MDCTA and MRA were available to the interventional radiologist who performed the treatment, DSA runs for the study were analyzed by a different interventional radiologist unaware of MDCTA and MRA results on a dedicated workstation (Xcelera, Philips Medical Systems). The execution time and the time employed for reconstructions at the workstation were evaluated separately both for MDCTA and MRA.
Statistical analysis Variables employed to assess the primary objective of the study are ordinal, and a non-parametric inferential statistic was required. The Wilcoxon rank-sum test was employed to assess differences between MDCTA and MRA in the grading of impairment of arterial segments in the iliac, femoropopliteal, and infrapopliteal segments and for diagnostic confidence. Continuous variables, such as examination time, were expressed as mean and SD and the Student’s t-test was adopted to assess significant differences. All statistical tests were two-sided and a P value < 0.05 was considered statistically significant.
Results Thirty-five limbs with 330 arterial segments were studied on pre-treatment selective DSA and were available for the analysis of MDCTA vs MRA. The distribution of segments was: 54 iliac; 82 femoro-popliteal; and 194 below the knee. Significant stenoses or occlusions were detected at DSA in 128 segments. A per-segment analysis was performed to assess the accuracy of MDCTA vs. MRA in evaluating the exact degree of impairment of each segment and a pooled analysis was performed for iliac, femoro-popliteal, and infrapopliteal segments (Fig. 1). Overall accuracy of MDCTA was 0.94 (95% confidence interval [CI], 0.90–0.96) and accuracy for MRA was 0.92 (95% CI, 0.88–0.94) (P > 0.05). Accuracy for iliac segments was 0.98 for MDCTA (95% CI, 0.90–0.99) and 0.95 for MRA (95% CI, 0.84– 0.98) (P > 0.05). Accuracy for femoro-popliteal segments was 0.95 for MDCTA (95% CI, 0.88–0.98) and 0.91 for MRA (95% CI, 0.83–0.95) (P > 0.05). Accuracy for infrapopliteal segments was 0.92 for MDCTA (95% CI, 0.87–0.94) and 0.85 for MRA (95% CI, 0.79–0.89) (P ¼ 0.02).
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Table 1. Technique for MDCTA and MRA examinations. MDCTA protocol Detector configuration Pitch Rotation time Table speed
64 1.25 mm 1.375 0.5 s 11 cm/s
Kv SFOV Filter mA
120 Large Standard Automatic
Aorto-iliac Body Oblique 3D TOF SPGR Smart Prep ZIPx2, ZIP 512 Minimum 20 83.33 Freq. 288, Phase 192 1 0.8 S-I 48 4 34
Femoro-popliteal Body Oblique 3D TOF SPGR
Calves and feet 8 channels phased array Oblique 3D TOF SPGR
ZIPx2, ZIP 512 Minimum 20 83.33 Freq. 320, Phase 192 1 0.8 S-I 48 3.6 32
ZIPx2, ZIP 512 Minimum 30 50 Freq. 256, Phase 512 1 0.6 S-I 48 2.8 38
Bolus-chase MRA protocol Coil Plane Sequence Triggering Options enabled TE Flip angle Bandwidth Acquisition timing NEX Phase FOV Frequency direction FOV Slice thickness Locations per slab
MRA time resolved protocol (TRICKS) Parameter Asset calibration Coil 8 channels phased array Plane Axial Sequence 2D GRADIENT ECHO Options enabled TE Flip angle Bandwidth Acquisition timing NEX Phase FOV Frequency direction FOV 48 Slice thickness 0 Locations per slab Acquisitions (n) 1
For infrapopliteal arteries, results of the standard MRA sequences plus time resolved acquisitions were also compared to standard acquisitions (Fig. 1). At per region analysis (Fig. 2) the accuracy for stratification of patients according to TASC classification was the same for MDCTA and MRA for the iliac region: 0.92 (95% CI, 0.66–0.98; P ¼ 0.43). In the femoro-popliteal region, MDCTA (accuracy, 0.94; 95% CI, 0.77–0.99)
Calves and feet 8 channels phased array Oblique 3D TRICKS ZIPx2, ZIP 512 Minimum 20 31,25 Freq. 512, Phase 256 1 0.75 Unswap 44 3 26 1 mask þ 9 post m.d.c.
stratification was slightly more accurate than MRA (accuracy, 0.9; 95% CI, 0.68–0.98) without significant statistical difference (P ¼ 0.08). Regarding the accuracy for the assessment of the infrapopliteal region, a difference at the statistical limit (P ¼ 0.04) was found between MDCTA (accuracy, 0.96; 95% CI, 0.84–0.99) and MRA (accuracy, 0.90; 95% CI, 0.76–0.96).
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Table 2. Score for assessment of single arterial segment impairment (modified from Rutherford). Score
Type of lesion
0 1 2
No >50% stenosis Single >50% stenosis Multiple >50% stenoses or Single 5 cm occlusion or Multiple 5 cm occlusion or total occlusion
3 4
Table 3. Score for impairment of infrapopliteal arterial district (modified from Rutherford).
Degree of impairment 1 2 3
4
Tibial trunks (ATA, PTA, PA) involved (number of vessel out of 3)*
Pedal trunks (Plantar and dorsalis pedis) involved (number of vessel out of 2)
1 stenosis/occlusion ! 2 stenosis/occlusion ! 1 stenosis/occlusion ! 3 stenosis/occlusion ! 2 stenosis/occlusion ! 1 stenosis/occlusion ! 3 stenosis/occlusion ! 2–3 stenosis/occlusion !
Patent Patent 1 stenosis/occlusion Patent 1 stenosis/occlusion 2 stenosis/occlusion 1 stenosis/occlusion 2 stenosis/occlusion
*Stenosis or occlusion of tibioperoneal trunk was considered as 2 vessells lesion. ATA, anterior tibial artery; PA, peroneal artery; PTA, posterior tibial artery.
The mean diagnostic confidence was 2.91 for MDCTA and 2.67 for MRA (P < 0.00001) (Fig. 3) with a difference particularly evident in the infrapopliteal arteries, while no significant differences were detected in iliac and femoro-popliteal segments. Since calcification can be depicted only at MDCTA and our primary purpose was to compare MDCTA to MRA, we did not perform a quantitative evaluation of the degree of calcification in our population, however, we reviewed all MDCTA examinations with a low or intermediate confidence score in infrapopliteal segments (grade 1 or 2 out of 3); we found diffuse calcifications in 13 out of 17 infrapopliteal arteries with a non-optimal confidence. Venous contamination limiting (confidence degree 1) an optimal evaluation of above the knee arteries was found in one limb at MDCT and in two limbs at MRA.
The mean scanning time (Fig. 4), interpreted as the overall occupation of the scanner, was 9 2 min for MDCTA and 33 4 min for MRA and the overall examination time was 29 4 min for MDCTA and 43 6 min for MRA, with a statistically significant advantage for MDCTA (P < 0.01).
Discussion As treatment options for lower extremity peripheral vascular disease have expanded, obtaining high quality diagnostic arterial images is mandatory. Understanding the location, severity, and complexity of occlusive disease is of paramount importance for accurately planning the most appropriate approach to revascularization; MDCTA and MRA have the potential to provide a panoramic and accurate vascular mapping (Figs. 5 and 6). The hypothetical advantages of MDCTA over MRA are the relatively short imaging time and lower cost (16). Covering a large volume over the whole vascular tree with sufficient intra-arterial contrast enhancement and minimal venous return remains a challenge for MRA, however, the time resolved acquisitions (17) and subsystolic calf compression, as demonstrated in the literature and by our experience can overcome this problem in most cases. MRA has some important advantages: it does not require iodinated contrast material and there is no radiation exposure. However, there are many contraindications for MRI including pacemakers, metal implants, claustrophobia, and the use of gadolinium contrast agents in patients with renal failure (8). For MDCTA, iodinated contrast agents are potentially nephrotoxic, but this adverse effect can be reduced by hydration and, although still under debate, administration of acetylcysteine (18). Another drawback of MDCTA may be that frequent use exposes a patient to large quantities of potentially carcinogenic ionizing radiation (19), however, the effective radiation dose of peripheral CTA for 16-detector row CT angiography is estimated in the range of 1.6–3.9 mSV and is lower than digital subtraction angiography (20). Fresh blood imaging (FBI) is an unenhanced MRA technique that can be useful particularly in patients with impaired renal function (21), but patients with PAD, especially those with severe stenoses in the lower leg and pedal vessels, frequently develop rest pain with resultant involuntary twitching that can significantly degrade image quality in fresh blood imaging which is exquisitely sensitive to even subtle movement. FBI-MR angiography moreover has high sensitivities only in the above the knee vessels (22). Nowadays 3.0 T peripheral CE-MR angiography is promising in clinical practice. More clinical studies
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Fig. 1. Per segment analysis of accuracy of MDCTA vs MRA (standard protocol þ tricks sequences on calves and feet and standard protocol alone) for assessment of the degree of impairment in each segment. (TOT ¼ total; ILI ¼ iliac; FP ¼ femoro-popliteal; IP ¼ infrapopliteal; ST ¼ standard protocol; TR ¼ tricks sequences).
Fig. 2. Per limb analysis of accuracy of MDCTA vs MRA to identify correct TASC classification (iliac and femoro-popliteal) and ‘‘ad hoc’’ infrapopliteal score. (ILI ¼ iliac; FP ¼ femoro-popliteal; IP ¼ infrapopliteal).
need to determine the clinical value and limitations of the peripheral MRA approach at 3.0 T for multisegmental PAD and diffused involvement of the runoff vessels. In a study comparing 3.0-T versus 1.5-T MRA van den Bosch HCet al. (23) reported a similar diagnostic performance, even if there was a significantly increased contrast-to-noise ratio for identical contrast agent dose at 3.0 T MRA. MDCTA, differently from MRA, can visualize calcified plaques providing useful data for the endovascular treatment and allowing advance selection of the best option for revascularization (PTA, cutting balloon, drug eluting balloon, laser or mechanical atherectomy, primary stenting, etc.); moreover the knowledge of the
presence of heavily calcified lesions can predict the treatment outcome (24). On the other hand, diffuse concentric calcification in the infrapopliteal vessels, often found in diabetic patients, due to the ‘‘blooming’’ of calcium with respect to the vessel’s lumen, makes the evaluation of stenosis on MDCTA very difficult (25). The use of dual source or dual-energy CT can overcome this limitation since it is possible to remove bones and intraluminal calcified plaques from angiography datasets on the basis of spectral differentiation separating iodine from calcium by this technique (26–29). However, dual-energy CT provides best results in arteries of the thigh; below the knee, plaque subtraction is less accurate and, thus far,
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Fig. 3. Per segment diagnostic confidence of MDCTA vs MRA. (TOT ¼ total; ILI ¼ iliac; FP ¼ femoro-popliteal; IP ¼ infrapopliteal).
Fig. 4. Comparative evaluation of time expense (min.) of MDCTA vs MRA.
no study has demonstrated any clear clinical advantage of dual-energy CT for peripheral artery applications. A published report comparing MDCTA and MRA for peripheral arterial disease is a randomized trial from Ouwendijk et al. (16) which was designed to evaluate the clinical utility, patient outcomes, and costs of MDCTA and MRA. The authors concluded that MDCTA has some advantages over MRA because of the higher diagnostic costs of MRA. Evaluation of accuracy of techniques was not a primary objective of this study and authors could not clearly demonstrate
that MDCTA more accurately depicts the extent and localization of disease. In a systematic review of literature published in 2007 (30), MRA seemed to be more specific than MDCTA, while in a more recent meta-analysis (3) no significant differences in the diagnostic performance were reported. The area of leg assessed affects diagnostic performance. In our study we found a higher accuracy for MDCTA in the assessment of impairment in infrapopliteal vessels; the superior spatial resolution allowed
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Fig. 5. Sixty-two years old diabetic man with left toe ulcer. Comparison of MIP MDCTA (A) and MRA (B) reconstructions. Only segments evaluated with the reference technique (DSA, C) were included in the study and evaluated at MDCTA and MRA (dashed box).
by MDCTA compared to MRA and the lower examination-time for MDCTA may explain this result. Our study has some limitations. We selected only patients who had indications for endovascular treatment, our results may not fully apply to the general population of patients suffering from PAD, including patients who are candidates for surgery. Finally an inter-observer variability analysis was not performed for MDCTA and MRA.
In conclusion, we can suggest the use of MDCTA as the first line investigation when clinical history (Fontaine III or IV) or previous imaging evaluation is indicative of diffuse steno-occlusive involvement of the infrapopliteal segment. The shorter execution time for MDCTA makes this technique more appropriate for patients with rest pain and limited compliance with prolonged immobilization. According to our experience additional time resolved sequences on calves and feet
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Fig. 6. Same case as Fig.5. Close up vision of infrapopliteal arteries. A good correlation is evident between MDCTA (A) and MRA (B) with respect to DSA (C). The focal stenosis of anterior tibial artery is correctly depicted by both techniques before endovascular treatment (D) (0.014’’ guidewire and dilation by 2.5 mm over the wire balloon).
should be part of the MRA protocol to improve diagnostic confidence in patients with suspected diffuse infrapopliteal involvement or in diabetic patients. Acknowledgements The authors thank Dr. L Ratnam for reviewing the paper for English language.
Conflict of interest None declared.
Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
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