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Year : 2002  |  Volume : 12  |  Issue : 2  |  Page : 179-188
Three-dimensional contrast-enhanced magnetic resonance angiography-our priliminary experience


AMR Research Centre, Institute of Nuclear Medicine and Allied Sciences, Brig, Majumdar Road, Delhi-110054, India

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   Abstract 

Objectives: To evaluate the utility of gadolinium enhanced three dimensional magnetic resonance angiography for different vascular territories of the body in comparison to x-ray angiography and to present our preliminary experience in the optimal use of the technique. Materials and Methods: The study evaluated 30 consecutive patients who underwent contrast enhanced MR angiography for different indications. Contrast enhanced MRA was performed on 1.5 Tesla MR system (Magnetom Vision, Germany) using 3D-Flash sequences. Coronal dynamic MRa was performed after injection of the contrast bolus and the images obtained were reconstructed using maximum intensity projections. Twenty patients underwent DSA of 23 vascular territories after CE MRA. Five patients underwent surgery. All the studies were interpreted by two qualified radiologists in consensus. Results: CEMRA was 100 per cent sensitive in picking up aneurysmal and stenotic lesions. The specificity for complete occlusion and aneurysmal disease was also 100 percent, but for partial stenosis the specificity was 83.3 percent related to overestimation of stenosis. CEMRA offered a global view of vascular pathology precisely vessel stenosis, collateral formation and distal run-off, aneurysmal disease and the relation of different branches to the aneurysm from multiple projections. Conclusion: CEMRA should be considered an attractive and artifact-free advancement of MRA techniques, which besides surpassing the old unenhanced MRA techniques should tend to replace DSA for diagnostic purposes.

Keywords: Magnetic resonance (MR), angiography, contrast enhanced, carotids, peripheral vessels, aorta, renal arteries

How to cite this article:
Tripathi R P, Batra A, Taneja M, Kaushik S, Balwant, Kumaran S S. Three-dimensional contrast-enhanced magnetic resonance angiography-our priliminary experience. Indian J Radiol Imaging 2002;12:179-88

How to cite this URL:
Tripathi R P, Batra A, Taneja M, Kaushik S, Balwant, Kumaran S S. Three-dimensional contrast-enhanced magnetic resonance angiography-our priliminary experience. Indian J Radiol Imaging [serial online] 2002 [cited 2019 Nov 18];12:179-88. Available from: http://www.ijri.org/text.asp?2002/12/2/179/28440

   Introduction Top


X-ray angiography has long been considered the gold standard for demonstration of the body vasculature. However, the invasive nature of the investigation, the large amount of nephrotoxic contrast media involved and the use of ionizing radiation have always made a need felt for a non-invasive method for demonstration of vessels. Rapid advances in medical technology have made this possible in actual clinical practice through magnetic resonance angiography (MRA). The use of paramagnetic contrast and faster 3D gradient recalled echo techniques have provided a strong competitor to x-ray angiography as the first line of study for the various vascular territories of the body. The aim of this article is to present our preliminary experience and a brief overview of the application of contrast enhanced 3D MRA in imaging the different vessels of the body.


   Material & Methods Top


The study included 30 consecutive patients (21 men and nine women) with ages ranging from 20 to 68 years who underwent contrast enhanced MR angiography for different indications. MRI and contrast enhanced MRA was performed on 1.5 Tesla MR system (Magnetom Vision, Germany) with a gradient strengthof 25 mT/m. The contrast media used was Gadolinium - DTPA (Magnevist , Schering AG, Germany, 0.5mmol/ml), the dose varying from 0.1 mmol to 0.3mmol/kg in different patients. Initially after subject positioning and obtaining a localizer sequence, a 3D mask data set was acquired which later served for image subtraction from the contrast enhanced image data set to produce increased vessel to background contrast. The contrast was injected using an automated pressure injector (Medrad MR Spectrins) and each injection was followed by a saline flush. The transit time of contras to the region of interest from the injection site in the antecubital region was determined using the test-bolus technique. This was performed with a single section gradient recalled echo sequence which collected images at the site of interest following an injection of 2 ml test bolus of contrast, every 1 sec for 40 seconds. Using the appropriate scan delay, image acquisition was done at a time when maximum intensity of contrast was expected in the region of interest.

Imaging techniques were adapted for different vascular regions [Table - 1]. The 3D-FLASH sequence was universally used with slice interpolation. Scanning was done on a body coil for large and on phased array coils for small areas of interest. The multistation technique was employed for visualization of larger length of the vessels as in the case of lower limbs. Imaging of the thoracic and abdominal vessels was done in a single breath hold.

Image data analysis and post-processing was performed on a parallel workstation (Magic view, Siemens). The source mask images obtained initially were subtracted from the contrast source images prior to maximum intensity projection (MIP) reconstruction. The final MIP images and the base images were interpreted by two qualified radiologists in consensus. Twenty patients underwent DSA of 23 vascular territories after CE MRA. Five patients underwent surgery. A comparison of CE MRA with DSA/ surgical findings was thus possible in 28 of the 34 studies.


   Results Top


There were 21 men and nine women in the study with a mean age of 35.5 years (range 20 to 68 years). A total of 34 contrast enhanced MRA studies were performed. All the patients tolerated the study well. No abnormal reaction or complication was noted. The mean average time for each study, which included the time for patient preparation, antecubital vein cannulation and subsequent acquisition of scout and mask images, was 40 minutes. The average table time of each patient was 15 minutes.

The various findings in the 34 studies are listed in Table 2 Digital subtraction / conventional angiography was considered the gold standard for reference. Comparison of CE MRA with DSA was possible in 23 of 34 studies. Surgical correlation was possible in five patients. Of the remaining six patients four were treated conservatively and two underwent surgery (lumbar sympathectomy for Buerger's disease) without undergoing an x-ray angiographic examination.

Of the 34 studies, 19 were for peripheral vessel disease, 11 for aortic disease and 4 for carotid disease evaluation. CEMRA was performed for 16 patients having peripheral vascular disease involving the lower limbs. Long segment irregularity of the vessel lumen suggesting diffuse atherosclerotic involvement [Figure - 1] was well seen in three patients. CEMRA picked up atherosclerotic plaques seen as filling defects producing irregularity of the vessel wall in three patients. Popliteal artery blocks with reformation

of distal vessels and run-off were well demonstrated and comparable with DSA [Figure - 2]. Of the segmental incomplete stenotic lesions involving the lower limb arteries, CE MRA picked up all the lesions (six studies) but overestimated stenosis in one study (16.67%, when compared to catheter angiography [Figure - 3]. MRA was at par with DSA in demonstrating collateral vessels and distal run-off in peripheral vascular disease. In the two patients having Buerger's disease, the involvement of medium sized arteries and the presence of corkscrew collaterals helped establish the diagnosis. CEMRA findings in the single case of superficial femoral artery aneurysm corroborated well with DSA [Figure - 4]. In both the cases of vascular malformations, CEMRA demonstrated the absence of any prominent arterial feeder corroborating with the DSA findings.

Atherosclerotic aneurysmal dilatations involving the arch of aorta and abdominal aorta were seen in four and three patients respectively. Associated findings included tortuosity of the aorta (five patients), ostial narrowing of the great vessels of the aortic arch (two patients) [Figure - 5] atherosclerotic plaques (four patients) [Figure - 5], occlusion of the superior mesenteric artery origin and formation of the Arc of Riolan (one patient).In a single patient of aortoarteritis, the irregular abdominal aorta, occlusion of the superior mesenteric artery and formation of the arc of Riolan was well seen [Figure - 6].

There was an excellent correlation between MRA and DSA in demonstrating aneurysmal dilatations. MRA could exactly define the extent and size of the aneurysm besides showing the relation of the arterial branches to the aneurysm. MRA in addition better demonstrated the origin of the various branches from different viewing angles in three of the eight patients having vascular aneurysms[Figure - 7].

Of the four cases referred for carotid evaluation, CEMRA demonstrated atherosclerotic plaques and irregular narrowing of the internal carotid artery (ICA) at the bifurcation of the common carotid artery (CCA) in two patients [Figure - 8] and complete occlusion of ICA in one patient. A large saccular aneurysm arising from the intracavernous portion of the ICA [Figure - 9] was seen in one patient. Ostial disease of the CCA at the aortic arch was seen in two patients one of whom had concomitant disease at the carotid bifurcation [Figure - 8]. DSA demonstrated similar finding in all patients having carotid disease except in single patient with ostial disease in whom selective catheterization of the left CCA failed. CE MRA was able to pick up all the findings demonstrated on DSA in all the studies; hence the sensitivity of CE MRA was 100%. The specificity of CEMRA varied for different lesions. For aneurysmal lesions and complete occlusion of arteries the specificity was 100%. In incomplete arterial stenosis, CEMRA overestimated stenosis in one of the six patients thus reducing the specificity to 83.3%.


   Discussion Top


Contrast enhanced three dimensional MRA allows a safe, quick and comprehensive evaluation of the body vasculature as opposed to the invasive technique of digital subtraction angiography. The previously described techniques of magnetic resonance angiography include time-of flight (TOF) MRA which is an inflow technique, phase contrast MRA which is based on phase shifts [1] caused by blood flow and magnitude contrast MRA (MC-MRA) in which flow compensated and de-phased data sets are combined to form an angiographic image. These techniques are possible without contrast; nevertheless they rely on velocity dependent inflow or phase shift effects and are afflicted with numerous drawbacks like long acquisition times, less spatial resolution and effects of in -plane saturation [2]. Besides, application of the venous presaturation slab results in failure to visualize retrograde flow. In imaging the thoracic aorta, ECG gating becomes crucial with these techniques which besides complicating the setup of an examination prolongs the acquisition time and often fails due to arrhythmias or weak ECG signals.

Three dimensional contrast enhanced MRA (3D-CEMRA) in contrast to the above described MRA techniques relies on the Tl shortening effects of paramagnetic contrast media and is flow independent. Artifacts due to flow turbulence, slow flow or in-plane flow are thus eliminated [3]. The development of high performance gradient systems and improved software now allow fast 3D gradient echo imaging with short acquisition times and increased spatial resolution. Cardiac gating is not required and the sequence can be acquired in a single breath hold.

The utility of contrast enhanced MRA is being evaluated for different regions of the body and based on the reported experience of various authors, the technique may gradually replace intra-arterial digital subtraction angiography (DSA) for diagnostic purposes. Various studies have found CE MRA equivalent or advantageous in delineating the abdominal aorta [4],[5], the renal vasculature [6],[7],[8], the peripheral lower limb vessels [9],[10], aortic aneurysms [4] and the carotid arteries [11],[12],[13].

In our study of 30 patients, CEMRA complemented with routine MR sequence served as the most convenient and single best investigation for evaluation of vascular disorders. The contrast dose used for CEMRA has been a matter of debate and various authors propose use of a higher dose (0.2-0.3 mmol/kg body weight) for better signal to noise ratio [7],[8]. Regulatory considerations allow for a maximal use of 0.3 - mmol/kg body weight / day for a single patient [5]. We universally used 0.1 - mmol/kg body weight (except for the distal leg arteries where 0.2-mmol/kgbody weight was used) and achieved good results. Besides being cost effective, use of the minimum dose required also allows for a second MRA study of a different region of the body.

Timing of contrast media injection is crucial for CE MRA studies. Delayed acquisition of image data produces venous opacification, which hampers adequate evaluation due to superimposition, while early acquisition before the arrival of contrast in the region of interest would produce a low contrast-noise ratio (CNR). The timing of injection of contrast media can be evaluated by either the test bolus technique or the automatic triggering method [14]. We used the test bolus technique as a routine for all our studies. Various techniques for evaluation of the entire length of the lower limb arteries as by CEMRA have been proposed [10],[15],[16],[17]. We performed these studies using the multistation technique.

CE MRA was extremely useful in evaluating and planning vascular intervention in lower limb vessels. CE MRA provided a ready road-map for interventional procedures which could be performed in the first sitting, allowing decisions regarding angioplasty balloon sizes besides reducing the amount of iodinated contrast used in DSA. In the 2 patients having tight common iliac stenosis, the preliminary CE MRA examination helped plan a brachial route for DSA. CEMRA could also help avoid an invasive DSA examination in patients having vascular disease not amenable to percutaneous vascular intervention such as Buergers disease and angiomatous malformation.

CE MRA offers a global overview of the aortic arch, the descending thoracic aorta and their branches in patients of aortic aneurysm. The origins of different vessel branches in relation to the aneurysm are demonstrated which is an advantage over DSA due to the multi projectional capabilities of MRA. Considering the excellent correlation of CE MRA and DSA in the initial cases, one patient proceeded to surgery without undergoing DSA thus avoiding an invasive diagnostic procedure.

Routine MR imaging should always be complemented with CEMRA in aneurysmal disease. In a single case of pseudoaneurysm of the superficial femoral artery, besides delineating the size and extent of the aneurysm, CE MRA could better show the size and site of the neck of the pseudoaneurysm viewed from different projections. Routine MR imaging in addition revealed the exact compartmental location of the aneurysm besides demonstrating thrombosed regions of the aneurysm thus leading to a complete and accurate delineation of the aneurysm.

Many studies have reported the efficacy of CEMRA in the diagnosis of carotid disease [11],[12],[13]. Sardanelli et al [12] have reported a 100% sensitivity and specificity in the evaluation of carotid arteries by CEMRA using contrast FISP sequences. They also propose that when MRA and Doppler ultrasonography correlates, DSA may be avoided in patients having contraindications for the same. Moreover, aortic arch ostial disease frequently coexists with internal carotid artery disease. CE MRA can serve as an important screening investigation for disease at both these sites and provide a panoramic view showing both the aortic arch and the carotid bifurcation [13].

In our study, CEMRA was 100% sensitive in picking up stenotic lesions and aneurysmal lesions. The specificity of CEMRA was also 100% in complete occlusions and vascular aneurysms but in the case of partial stenosis, the specificity was only 83.3%. The latter occurred due to overestimation of stenosis. Overestimation of stenosis is a significant problem with MRA technique utilizing TOF techniques and is caused by signal loss due to turbulent flow [1]. CEMRA to a large extent is free from artifacts arising from such signal loss at the stenotic site, however, overestimation can occur due to certain degree of proton dephasing caused by flow [13].

CEMRA is not without potential disadvantages. Timing of contrast medium arrival in the region of interest is crucial for obtaining images in the arterial phase. For maximum contrast noise ratio, the image acquisition should be such that the center of the K space is filled during the presence of maximum contrast in the arteries. A delayed acquisition produces venous overlap while an earlier acquisition would produce a low CNR [5].

Inclusion of the whole volume of interest during planning is also important for CEMRA. Smaller volumes chosen may exclude tortuous or eccentrically placed arterial segments producing artifactual occlusions. Presence of T1 high signal intensity linear structures such as a methemoglobin containing sub-acute thrombus within a vessel may be missed on CEMRA since the thrombosed segment has similar intensity to contrast in the vessel and may mimic flow [18]. Long segments of vessels such as the lower limb arteries may be difficult to image with a single bolus injection although recently a moving bed infusion tracking peripheral MR angiography has been described [10].

As stressed by most authors, there is ample scope and need for conducting further studies to determine the clinical significance of CEMRA especially in thoracic aortic disease, carotid arteries, renal transplants and peripheral vascular disease.


   Conclusion Top


CEMRA should be considered an attractive and mostly artifact -free advancement of MRA techniques, which besides surpassing the old unenhanced MRA techniques should tend to replace DSA for diagnostic purposes.


   Acknowledgements Top


We would like to express our thanks to Mr. Sitaram for the preparation of the illustrations of this manuscript.

 
   References Top

1.Saloner D. MRA: principles and display. In. Higgins CB. Hricak H. Helms CA. Eds. Magnetic resonance imaging of the body. Philadelphia: Lippencott-Raven Publishers, 1997; 1345-1368.  Back to cited text no. 1    
2.Prince MR. Body MR angiography with gadolinium contrast agents. MRI Clin North Am 1996; 4 (1): 11-24.  Back to cited text no. 2    
3.Prince MR. Gadolinium - enhanced MR aortography. Radiology 1994; 191: 155- 164.  Back to cited text no. 3  [PUBMED]  
4.Kelekis NL, Semelka RC, Worawattanakul S, Molina PL, Mauro MA. Magnetic Resonance imaging of the abdominal aorta and iliac vessels using combined 3-D gadolinium - enhanced MRA and gadolinium-enhanced fat-suppressed spoiled gradient echo sequences. Magnetic Resonance imaging. 1999; (17): 641-651.  Back to cited text no. 4    
5.Ruehm SG, Weishaupt D, Debatin JF. Contrast-enhanced MR angiography in patients with aortic occlusion (Leriche syndrome). Journal of Magnetic Resonance Imaging. 2000; 11:401-410.  Back to cited text no. 5    
6.Nelson HA, Gilfeather M, Holman JM, Nelson EW, Yoon H. Gadolinium - enhanced Breathhold three-dimensional time of flight renal MR angiography in the evaluation of potential renal donors, JVIR; 10:175-181.  Back to cited text no. 6    
7.Thornton J, O'Callaghan J, Walshe J, O'Brien E, Varghese JC, Lee MJ. Comparison of digital subtraction angiography with gadolinium-enhaned magnetic resonance angiography in the diagnosis of renal artery stenosis. Eur. Radiol, 1999; 9: 930- 934.  Back to cited text no. 7    
8.Johnson DBS, Lerner CA, Prince MR et al . Gadolinium - Enhanced Magnetic Resonance Angiography of Renal Transplants. Magnetic Resoance Imaging 1997; 15: 13-20.  Back to cited text no. 8    
9.Wasser MN Magnetic Resonance Angiography of peripheral vascular disease. Journal of Computer Assisted Tomography 1999; 23 (suppl. 1): S129-S133  Back to cited text no. 9    
10.Leiner T, Ho KYJAM, Nelemans PJ, de Haan MW, an Engelshoven JMA Three-dimensional contrast enhanced moving bed infusion tracking (MoBi-Track) peripheral MR angiography with flexible choice of imaging parameters for each field of view. Journal of Magnetic Resonance Imaging, 2000; 11:368-377.  Back to cited text no. 10    
11.Cloft HJ, Murphy KJ, Prince MR, Brunberg JA. 3D Gadolinium enhanced MR angiography of the carotid arteries. Magnetic Resonance Imaging 1996; 14: 593-600  Back to cited text no. 11  [PUBMED]  [FULLTEXT]
12.Sardanelli F, Zandrino F, Parodi RC, Caro GD. MR angiography of internal carotid arteries: breath-hold Gd-enhanced 3D fast imaging with steady precession versus unenhanced 2D and 3D Time of Flight Techniques. Journal of Computer assisted Tomography 1999; 23: 208-215.  Back to cited text no. 12    
13.Stone JA, Mukherji SK, Semelka R, Kelekis M, Neelon B and Castillo M. Contrast Enhanced 3D FISP MR angiography of the aortic arch ostia: Preliminary results. Journal of Computer Assisted Tomography 2000; 24: 369 - 374.  Back to cited text no. 13    
14.Maki JH, Chenevert TL, Prince MR. Contrast enhance MR angiography. Abd Imaging 1998; 23:469-484.  Back to cited text no. 14  [PUBMED]  [FULLTEXT]
15.Ho KYJAM, Leiner T, De Haan MW, Kessels AGH, Kitslaar PJEHM, van Engelshoven JMA. Peripheral vascular tree stenoses: evaluation with moving bed infusion tracking MR angiography. Radiology 1998; 206: 683-692.  Back to cited text no. 15    
16.Wang Y. Lee HM, Khilnani NM et al . Bolus - chase MR digital subtraction angiography in the lower extremity. Radiology 1998: 207, 263 - 2659.  Back to cited text no. 16    
17.Watanabe Y. Dohke M. Okumura A et al . Dynamic subtraction MR angiography: first pass imaging of the main arteries of the lower body. AJR 1998; 170: 352 - 360.  Back to cited text no. 17    
18.Insko EK, Siegelman ES, Stolpen AH. Subacute clot mimicking flow in a thrombosed arterial bypass graft on two-dimensional time of flight and three-dimensional contrast enhanced MRA. Journal of Magnetic Resonance Imaging 2000; 11: 192-194.  Back to cited text no. 18  [PUBMED]  [FULLTEXT]

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Correspondence Address:
R P Tripathi
AMR Research Centre, Institute of Nuclear Medicine and Allied Sciences, Brig, Majumdar Road, Delhi-110054
India
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Source of Support: None, Conflict of Interest: None


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    Figures

[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9]

    Tables

[Table - 1], [Table - 2], [Table - 3]

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