Lower Extremity MR Angiography: Universal Retrofitting of High-Field-Strength Systems with Stepping Kinematic Imaging Platforms桰nitial Experience1

¹ From the Department of Diagnostic Radiology, William Beaumont Hospital, 3601 W 13 Mile Rd, Royal Oak, MI 48073 (A.N.S., K.G.B.); Department of Radiology, Veterans Administration North Texas Healthcare System, Dallas, Tex (A.J.D.); and Department of Radiology, Barnes-Jewish Hospital, St Louis, Mo (V.R.N.). Received March 13, 2001; revision requested May 7; revision received June 13; accepted June 22. 

	ABSTRACT

Top ABSTRACT INTRODUCTION Materials and Methods Results Discussion REFERENCES

 
In 15 volunteers and 84 patients with clinically suspected peripheral vascular disease, a stepping kinematic imaging platform, a manual retrofit stepping magnetic resonance (MR) imaging table, was used with three high-field-strength MR imaging systems to perform multistation peripheral contrast material–enhanced MR angiography in the lower extremity with the existing system phased-array coil. Each examination was performed in less than 45 minutes. Mounting of the stepping kinematic imaging platform was quick and simple and allowed rapid repositioning of a patient relative to the phased-array coil and acquisition of high-spatial-resolution MR angiograms of the peripheral vasculature with use of one injection of MR imaging contrast agent.

　

Index terms: Arteries, extremities • Arteries, MR, 92.129412, 92.12942, 92.12943 • Arteries, stenosis or obstruction, 92.721 • Magnetic resonance (MR), vascular studies, 92.129412, 92.12942, 92.12943

	INTRODUCTION

Top ABSTRACT INTRODUCTION Materials and Methods Results Discussion REFERENCES

 
Development of magnetic resonance (MR) angiography during the past few years has considerably improved the evaluation of patients presenting with vascular disease, and MR angiography has become the modality of choice in many instances (1–3). Compared with conventional time-of-flight MR angiography, gadolinium-enhanced rapid MR angiography has been shown to substantially improve the diagnostic performance of MR angiography (4,5). Initial experience in the imaging of abdominal vessels was limited to one station or one anatomic region with one arterial phase (6–9). More recently, advances in pulse sequences along with improved hardware capabilities have dramatically reduced the imaging time to perform multiple measurements in one breath hold (10,11).

The conventional approach for MR angiography in multiple anatomic stations in a peripheral lower extremity evaluation requires imaging at each station with a separate injection of contrast material (12). With subtraction of precontrast mask images from corresponding postcontrast images, good background tissue and venous signal suppression can be obtained, which improves distal vessel visualization. However, the approach that is routinely used with conventional single-phase contrast-enhanced three-dimensional MR angiography for multistation imaging is time-consuming and requires multiple injections and patient repositioning.

Rapid imaging can allow multistation MR angiography and incremental stepping of the imaging table during the passage of one injection of contrast agent. A bolus tracking method, in which one bolus of contrast material was injected and tracked at different anatomic regions where imaging was performed at the bolus arrival, allowed visualization of the entire peripheral vascular tree (13). Following the demonstration of these capabilities for translating patients by Wang et al (13), Maki et al (14), and Ho et al (15), other investigators used this technique with a variety of imagers and methods (15–22) (Table 1). Rapid patient repositioning is the key to infusion tracking during multistation MR angiography.

fig.ommitted TABLE 1. Rapid MR Imaging with Bolus Tracking in Previous Studies

 
The purpose of this study was to evaluate a commercially available manual repositioning device, a stepping kinematic imaging platform, that can be rapidly retrofitted onto an MR imaging system in cases of peripheral vascular disease.

	Materials and Methods

Top ABSTRACT INTRODUCTION Materials and Methods Results Discussion REFERENCES

 
MR Angiographic Examinations
From February to December 2000, MR angiography was performed at 1.5 T with three systems: system 1, n = 89 (Vision; Siemens Medical Systems); system 2, n = 8 (Signa; GE Medical Systems); system 3, n = 2 (Eclipse; Picker International). The discrepant distribution of examinations between systems 1–3 was related to the greater number of referrals from facilities with MR imagers from only the one supplier.

Examinations were performed in 15 healthy volunteers (13 men and two women; age range, 39–52 years; mean age, 43 years) and 84 patients (55 men and 29 women; age range, 40–78 years; mean age, 65 years) with clinically suspected peripheral vascular disease (eg, claudication, peripheral ulcers, Doppler ultrasonographic evidence of arterial disease). Informed consent approved by the human investigations committees of each institution was obtained from each volunteer prior to MR imaging.

The commercial version of a stepping kinematic imaging platform (SKIP; Magnetic Moments, Bloomfield, Mich) consists of three major parts: two lower platforms with a series of rollers and a top-sliding platform for moving patients. The posterior element of the phased-array receiver coil is placed between the two lower platforms (Fig 1a). The 6-foot-long (1.83 m) moving table is then placed on top of the posterior coil and lower platforms with rollers (Fig 1b). The 6-foot table, with a series of indents at fixed locations on the undersurface, slides smoothly over the rollers and locks into positions determined by using a spring-loaded plunger placed underneath the table. Three separate positions of this plunger allow the user to choose different table increments of 30, 40, or 48 cm. Patients are supine, with their feet entering the magnet bore. Contoured foam pads are used to immobilize and support the patient. The legs are elevated with the leg support pads to ensure a parallel course of the leg and abdominal vessels.

fig.ommitted Figure 1a. (a) Stepping kinematic imaging platform consists of two lower platforms (A, B) with a series of rollers that are placed on either side of the existing posterior element of the phased-array coil. (b) The top kinematic platform is placed onto the two lower platforms and posterior phased-array coil element. Three equally spaced wells (arrowheads) hold a spring-loaded plunger that allows the user to move the top kinematic platform in 30-, 40-, or 48-cm increments.

 

fig.ommitted Figure 1b. (a) Stepping kinematic imaging platform consists of two lower platforms (A, B) with a series of rollers that are placed on either side of the existing posterior element of the phased-array coil. (b) The top kinematic platform is placed onto the two lower platforms and posterior phased-array coil element. Three equally spaced wells (arrowheads) hold a spring-loaded plunger that allows the user to move the top kinematic platform in 30-, 40-, or 48-cm increments.

 
A coil-mount saddle is placed by attaching it to the lower stationary platform with pivot arms. This allows mounting of the existing phased-array coil at a fixed location within the magnet. The pivot of the anterior coil makes it ride smoothly over the anterior anatomy of the patient. This allows maximizing of the coil-filling factor, which in theory should maximize the signal-to-noise ratio. To extend the anatomic coverage, the posterior coil is displaced superiorly relative to the anterior coil element.

The region of interest to be evaluated is divided into either three or four stations. For a three-station study, the table increment is either 40 or 48 cm. For a four-station study, the table increment is 30 cm. The required anatomic coverage is accomplished by placing the plunger in the appropriate well. The total increment ranges from 120 to 144 cm. The overlap among stations is achieved by selecting an acquisition field of view larger than the table increment.

Positioning of the patient over the moving table is dependent on the area of interest that needs to be evaluated. Coverage can begin either from the chest or from the abdomen. To include the thorax, the distance from the sternal notch to the middle of the foot is measured. For most peripheral examinations, however, it is sufficient to begin imaging in the abdomen. In that case, the distance from the xiphoid to the middle of the foot is measured. On the basis of these distances, a table increment can be selected that allows imaging of the required anatomy. Finally, after the patient is placed supine on the table, we ensure that the proximal anatomy and the feet will be encompassed by the phased-array coil during imaging (Fig 2) by translating the kinematic platform with the patient to the different positions.

fig.ommitted Figure 2a. The location of the coil is shown with respect to the patient anatomy, which is centered at three stations: (a) legs, (b) thighs, and (c) abdomen. The anterior element of the phased-array coil is placed into a saddle, which is connected by using pivot arms. This allows the anterior coil element to move smoothly over the patient’s anterior surface anatomy. The flexible pivot also improves the coil-filling factor when the legs are imaged.

 

fig.ommitted   Figure 2b. The location of the coil is shown with respect to the patient anatomy, which is centered at three stations: (a) legs, (b) thighs, and (c) abdomen. The anterior element of the phased-array coil is placed into a saddle, which is connected by using pivot arms. This allows the anterior coil element to move smoothly over the patient’s anterior surface anatomy. The flexible pivot also improves the coil-filling factor when the legs are imaged.

 

fig.ommitted   Figure 2c. The location of the coil is shown with respect to the patient anatomy, which is centered at three stations: (a) legs, (b) thighs, and (c) abdomen. The anterior element of the phased-array coil is placed into a saddle, which is connected by using pivot arms. This allows the anterior coil element to move smoothly over the patient’s anterior surface anatomy. The flexible pivot also improves the coil-filling factor when the legs are imaged.

 
All MR angiographic examinations were performed by retrofitting a stepping kinematic imaging platform onto system 1–3 imagers, which were equipped with commercially available high-performance gradients. All patients were supine with their arms abducted over the head or adducted and supported close to the body with support straps. A standard intravenous catheter (96-inch low-pressure connecting tube) was inserted by using a 22-gauge catheter (Angiocath; Becton Dickinson, Sandy, Utah) needle at the antecubital fossa. With system 1, the contrast material was injected with a power injector (Spectris; Medrad, Indianola, Pa); with systems 2 and 3, the injection was performed manually. Patients were initially centered at the level of the abdomen (n = 91) or thorax (n = 8) inside the magnet bore.

A series of time-of-flight localizer images (systems 2 and 3, transverse; system 1, transverse and sagittal) were obtained at each station. On the basis of the localizer images, the three-dimensional imaging slab was placed coronally to cover the desired vascular area. The coverage was checked at each subsequent station to ensure inclusion of vessel territories at all three stations with a fixed single-slab position and thickness.

For dynamic gadolinium-enhanced MR angiography, a three-dimensional spoiled gradient-echo pulse sequence was used. With system 1, echo sampling was performed asymmetrically along both partition and phase-encoding directions; partition encoding was centered at three-eighths of the acquisition time, and linear encoding was centered along the phase direction. With system 2, an elliptic centered k-space acquisition scheme was used. With system 3, a standard three-dimensional gradient-echo pulse sequence with linear encoding along the phase and frequency direction was used. The imaging parameters used at all stations were identical (Table 2). Imaging was performed at the thorax or abdominal levels with a breath hold at deep inspiration.

fig.ommitted TABLE 2. Imaging Parameters at All Stations

 
In cases (n = 2) of possible vascular by-pass graft infection, transverse turbo short inversion time inversion-recovery imaging (system 1) was performed with the following pulse sequence parameters: repetition time msec/echo time msec/inversion time msec of 5,500/76/140–160; matrix, 132 x 256; field of view, 280 x 450 mm. Fifteen 7-mm-thick sections were acquired in a transverse orientation with an additional fat-saturation pulse to improve fat signal suppression.

Two distinct approaches have been used previously to image peripheral vessels, including a slow infusion rate (15) or a fast infusion rate (23–25) along with other optimal pulse sequence parameters. We used a combination of these two approaches: An initial higher infusion rate (1.5 mL/sec, 15-mL volume) was followed with a slow infusion rate (0.8 mL/sec, 23- or 33-mL volume) and then with a 15-mL saline flush at a rate of 1.5 mL/sec. The initial higher infusion rate concentrated the contrast material bolus to enhance the peak arterial signal, and the subsequent slow infusion rate helped maintain a higher plateau of arterial signal throughout the data acquisition. A 23-mL contrast material volume was used in patients with average (90 kg) body habitus, and a 33-mL volume was used in patients with above-average (>90 kg) body habitus.

Numerous methods have been published to estimate the bolus arrival time (26–29). We used a test bolus injection method, as described previously (29), at the level of the abdomen or thorax (first station). By measuring the bolus arrival time, the correct delay from the start of the injection to the start of imaging was estimated. With system 1, with the number of measurements set at three, a 4–5-second pause was introduced between successive measurements to allow table and patient translation. With systems 2 and 3, the slab location prescribed at the first station was used for imaging at subsequent stations. The prescan button was depressed during patient translation; subsequently, the scan button was depressed when the patient was translated to the next station.

In six patients, steady-state data acquisitions were acquired to depict the venous anatomy. A 30–45-second delay was used after the arterial-phase data were acquired in the leg. In the reverse direction, a measurement was obtained at the distal station (n = 5) first. When the patient was translated manually to the middle (thigh) station, and, subsequently, to the abdomen or pelvis station, the steady-state data acquisitions were performed to cover three stations (n = 5) or two stations (n = 1). The same pause (4–5 seconds) was used between measurements, to translate the patient to different stations.

Image Processing and Analysis
With system 1, a precontrast mask image was obtained at only the distal station. With systems 2 and 3, a precontrast mask image was obtained at all three stations. With use of pixel-by-pixel subtraction (image domain) between the pre- and postcontrast data for the same station, the resulting subtracted data were subjected to the maximum-intensity-projection algorithm. When necessary, targeted maximum intensity projection was performed to improve visualization of vascular anatomy. For presentation purposes with system 1, the edge definition was further improved by applying an image filter, which was applied to only the frontal maximum-intensity-projection images. Images from each examination were analyzed subjectively for image quality by one MR radiologist (K.G.B.) on the basis of (a) vascular signal-to-noise ratio and (b) vascular-to-background contrast. The images were graded as follows: grade 1, poor signal-to-noise ratio and vascular-to-background contrast in large vessels (aorta, iliac, and femoral) and small vessels (renal and infrapopliteal); grade 2, good signal-to-noise ratio, vascular-to-background contrast, or both in large vessels but poor in small vessels; and grade 3, excellent signal-to-noise ratio and vascular-to-background contrast in large and small vessels.

	Results

Top ABSTRACT INTRODUCTION Materials and Methods Results Discussion REFERENCES

 
Mounting of a stepping kinematic imaging platform onto an MR imaging table and positioning of the patient was accomplished in 5–10 minutes. All stations were imaged in all patients. The stop mechanism of the table was precise, which resulted in no misregistration of subtracted data sets. The images depicted minimal or no venous overlap from the abdominal or thoracic aorta to the middle of the foot, with excellent (grade 3) vascular signal-to-noise ratio and excellent (grade 3) vascular-to-background contrast in all volunteers (Fig 3) and in all patients, even when extensive occlusive disease or clinically important arteriovenous fistula was present (Fig 4).

fig.ommitted Figure 3a. Normal coronal MR angiograms were obtained with a stepping kinematic imaging platform retrofitted onto (a) system 1 (4.6/1.8 with 25° flip angle) and (b) system 2 (6.1/1.3 with 45° flip angle) with implementation of the existing body phased-array and torso-array coils, respectively.

 

fig.ommitted Figure 3b. Normal coronal MR angiograms were obtained with a stepping kinematic imaging platform retrofitted onto (a) system 1 (4.6/1.8 with 25° flip angle) and (b) system 2 (6.1/1.3 with 45° flip angle) with implementation of the existing body phased-array and torso-array coils, respectively.

 

fig.ommitted Figure 4a. Coronal MR angiograms (4.6/1.8 with 25° flip angle) in two patients demonstrate excellent vascular-to-background contrast and vascular signal-to-noise ratio despite the presence of (a) extensive femoral or popliteal occlusive disease (middle: upper and lower arrows, respectively) or (b) aortic and iliac (top, arrows) and femoral (middle, arrow) occlusions in a patient with a horseshoe kidney.

 

fig.ommitted Figure 4b. Coronal MR angiograms (4.6/1.8 with 25° flip angle) in two patients demonstrate excellent vascular-to-background contrast and vascular signal-to-noise ratio despite the presence of (a) extensive femoral or popliteal occlusive disease (middle: upper and lower arrows, respectively) or (b) aortic and iliac (top, arrows) and femoral (middle, arrow) occlusions in a patient with a horseshoe kidney.

 
In patients, renal artery stenosis, clinically important short-segment peripheral disease, long-segment occlusions with collateral vessels, graft patency or infection (Fig 5), and aneurysms could be detected, which allowed triage of patients to receive percutaneous interventional treatment with or without surgical intervention. Delayed steady-state or equilibrium-phase imaging in six patients allowed mapping of the saphenous veins without arterial contamination (Fig 6) (30).

fig.ommitted Figure 5. Left: Coronal maximum-intensity-projection images (4.6/1.8 with 25° flip angle) obtained at different stations. Right: Corresponding transverse fat-suppressed turbo short inversion time inversion-recovery images 5,500/76/140-160. MR angiograms were obtained in a patient with axillary-femoral (top), femoral-femoral(middle), and femoral-peroneal (middle and bottom) grafts; left femoral occlusive disease (middle); and infrapopliteal disease (bottom). Incidental left subclavian pseudoaneurysm (open arrow) and graft infection of old occluded graft (solid arrow) were depicted.

 

fig.ommitted Figure 6. Coronal three-dimensional maximum-intensity-projection images (4.6/1.8 with 25° flip angle), obtained at three stations, display the venous anatomy after the arterial first-pass data were subtracted from the steady-state data. The inferior vena cava (top, large arrow), iliac (top, small arrow), femoral (middle, curved arrow), and greater saphenous (middle, bottom, open arrows) veins are well delineated.

 

	Discussion

Top ABSTRACT INTRODUCTION Materials and Methods Results Discussion REFERENCES

 
Retrofitting of a stepping kinematic imaging platform onto an MR imaging system to allow manual control of table increments at multistation MR angiography and MR imaging has several advantages. First, this method does not necessitate use of any additional hardware or software modification to the imager. Standard imaging pulse sequences, such as three-dimensional breath-hold spoiled gradient-echo or fast low-angle shot pulse sequences, are already available on most imagers and can be used in this technique. Second, patients can be comfortably positioned with the existing phased-array coil. In obese patients, the main body coil can be used for signal reception. Currently, similar methods of imaging are provided by means of automatic movement of the existing MR table within the MR gantry. Such modifications require expensive hardware upgrades and a specialized coil for signal reception; these upgrades may not be readily available for all MR imaging systems.

In the literature, acquisition of a precontrast mask image is suggested at all imaging stations. When the mask image data are subtracted from the postcontrast image data, high-quality MR angiograms can be obtained that are similar to digital subtraction angiograms (13,29). In addition, use of a matrix with higher spatial resolution improves visualization of renal and distal small vessels. However, with use of a standard imager with a high-spatial-resolution imaging matrix and a phased-array coil for signal detection, the reconstruction time can be prohibitively long. With system 1 for example, with use of a phased-array coil with a 512 x 256 matrix and section interpolation, the processing time can be as long as 4–5 minutes per imaging station. In such circumstances, the subtraction technique may be avoided by not acquiring mask images at all stations.

Theoretically, use of a good fat-suppression pulse before acquisition of partition encodings can obviate subtraction. However, the shim procedure that is performed for one station might not be optimal for the next station. Adequate fat suppression becomes hard to achieve when the shim procedure is performed at the abdomen station and the same shim values are used for the leg station. To circumvent this problem, we acquired one precontrast image data set before arrival of the contrast material at the leg station and used it as the mask to be subtracted from the postcontrast image data set obtained at the same station.

There were several limitations in this study. We did not compare MR angiograms obtained without a stepping kinematic imaging platform with those obtained with a platform. Also, our findings were not compared with those obtained with a reference standard, such as conventional angiography. However, contrast-enhanced MR angiograms obtained both without and with a stepping table were compared in a meta-analysis by Koelemay et al (31). They found that diagnostic performance was improved with use of three-dimensional contrast-enhanced MR angiograms compared with two-dimensional time-of-flight MR angiograms and that contrast-enhanced MR angiograms are highly accurate in the assessment of vascular disease. In our study with a bolus-chase protocol, as described in the literature (26–29), we translated patients through the magnet bore with a commercially available stepping kinematic imaging platform to allow imaging at multiple vascular stations.

Currently, the most common application for a stepping table is at MR angiography in the peripheral lower extremity to assess renal artery stenosis, peripheral vascular disease, or graft patency. The combined use of multistation MR angiography and MR imaging is also very useful in patients with graft infections. This method of imaging the run-off vessels is feasible and can be performed in one sitting and with one injection of MR contrast material; the patient does not need to be removed from the bore and repositioned to allow imaging at each station. Retrofitting of an MR imaging system by adding a stepping kinematic imaging platform for table stepping can provide a good alternative to an expensive upgrade with hardware, software, and dedicated peripheral vascular coils. With multistation rapid MR angiography, the future looks very promising. Further advances, such as independent slab positioning with custom shim and pulse sequence parameters, will further optimize signal-to-noise ratio and spatial resolution at each station. In the future, lower extremity MR venography may also supplement peripheral lower extremity MR angiography for mapping of the saphenous veins and may also supplement pulmonary MR angiography in patients suspected of having thromboembolic disease.

　

	REFERENCES

Top ABSTRACT INTRODUCTION Materials and Methods Results Discussion REFERENCES

 

1. Snidow JJ, Harris VJ, Trerotola SO, et al. Interpretations and treatment decisions based on MR angiography versus conventional arteriography in symptomatic lower extremity ischemia. J Vasc Interv Radiol 1995; 6:595-603.

2. Carpenter JP, Baum RA, Holland GA, Barker CF. Peripheral vascular surgery with magnetic resonance as the sole preoperative imaging modality. J Vasc Surg 1994; 20:861-871.

3. Grist TM. MRA of the abdominal aorta and lower extremities. J Magn Reson Imaging 2000; 11:32-43.

4. Poon E, Yucel EK, Pagan-Marin H, Kayne H. Iliac artery stenosis measurements: comparison of two-dimensional time-of-flight and three-dimensional dynamic gadolinium-enhanced MR angiography. AJR Am J Roentgenol 1997; 169:1139-1144.

5. Quinn SF, Sheley RC, Szumowski J, Shimakawa A. Evaluation of the iliac arteries: comparison of two-dimensional time-of-flight magnetic resonance angiography with cardiac compensated fast gradient recalled echo and contrast-enhanced three-dimensional time of flight magnetic resonance angiography. J Magn Reson Imaging 1997; 7:197-203.

6. Prince MR, Narasimham DL, Stanley JC, et al. Breath-hold gadolinium enhanced MR angiography of the abdominal aorta and its major branches. Radiology 1995; 197:785-792.

7. Leung DA, McKinnon GC, Davis CP, Pfammatter T, Krestin GP, Debatin JF. Breath-hold, contrast-enhanced, three-dimensional MR angiography. Radiology 1996; 200:569-571.

8. Holland GA, Dougherty L, Carpenter JP, et al. Breath-hold ultrafast three-dimensional gadolinium-enhanced MR angiography of the aorta and the renal and other visceral abdominal arteries. AJR Am J Roentgenol 1996; 166:971-981.

9. Shetty AN, Bis KG, Vrachliotis TG, et al. Contrast-enhanced 3D MRA with centric ordering in k-space: a preliminary clinical experience in imaging the abdominal aorta and renal and peripheral arterial vasculature. J Magn Reson Imaging 1998; 8:603-615.

10. Hoe LV, Jaegere TD, Bosmans H, Stockx L, et al. Breath-hold contrast-enhanced three-dimensional MR angiography of the abdomen: time-resolved imaging versus single-phase imaging. Radiology 2000; 214:149-156.

11. Korosec FR, Frayne R, Grist TM, Mistretta CA. Time resolved contrast-enhanced 3D MR angiography. Magn Reson Med 1996; 36:345-351.

12. Earls JP, Patel NH, Smith PA, DeSena S, Meissner MH. Gadolinium-enhanced three-dimensional MR angiography of the aorta and peripheral arteries: evaluation of a multistation examination using two gadopentetate dimeglumine infusions. AJR Am J Roentgenol 1998; 171:599-604.

13. Wang Y, Lee HM, Khilnani NM, Trost DW, Jagust MB, et al. Bolus-chase MR digital subtraction angiography in the lower extremity. Radiology 1998; 207:263-269.

14. Maki JH, Chenevert TL, Prince MR. Three-dimensional contrast-enhanced angiography. Top Magn Reson Imaging 1996; 8:322-344.

15. Ho KYJAM, Leiner T, de Haan MW, van Engelshoven JMA. Gadolinium optimized tracking technique: a new MRA technique for imaging the peripheral vascular tree from aorta to the foot using one bolus of gadolinium (abstr) In: Proceedings of the Fifth Meeting of the International Society for Magnetic Resonance in Medicine. Berkeley, Calif: International Society for Magnetic Resonance in Medicine, 1997; 203.

16. Ho KYJAM, Leiner T, de Haan MW, Lessels AGH, Kitslaar PJEHM, van Engelshoven JMA. Peripheral vascular tree stenoses: evaluation with moving-bed infusion-tracking MR angiography. Radiology 1998; 206:683-692.

17. Earls JP, DeSena S, Bluemke DA. Gadolinium-enhanced three-dimensional MR angiography of the entire aorta and iliac arteries with dynamic manual table translation. Radiology 1998; 209:844-849.

18. Meaney JFM, Ridgway JP, Chakraverty S, et al. Stepping-table gadolinium enhanced digital subtraction MR angiography of the aorta and lower extremity arteries: preliminary experience. Radiology 1999; 211:59-67.

19. Leiner T, Ho KYJMA, van Engelshoven JMA. Contrast-enhanced MR angiography from the aortic arch to the ankle including the renal arteries in 2 times 2 minutes (abstr) In: Proceedings of the Seventh Meeting of the International Society for Magnetic Resonance in Medicine. Berkeley, Calif: International Society for Magnetic Resonance in Medicine, 1999; 1226.

20. Bis KG, Shetty AN. Multistation MRA and MRI with SKIP (Stepping Kinematic Imaging Platform) (abstr). Radiology 2000; 214:610.

21. Busch HP, Hoffmann HG, Metzner CH, Oettinger W. MRA of the vessels of the pelvis and legs with automatic table movement (MoBI-Track): results in 100 patients. Medicamundi 1999; 43:25-34.

22. Janka R, Fellner F, Requardt M, Fellner C, et al. Contrast enhanced MRA of peripheral arteries with automatic floating table. Rontgenpraxis 1999; 52:15-18.

23. Strouse PJ, Prince MR, Chenevert TL, et al. Effect of the rate of gadopentetate dimeglumine administration on abdominal vascular and soft tissue MR imaging enhancement patterns. Radiology 1996; 201:809-816.

24. Shetty AN, Bis KG, Kirsch M, Weintraub J, Laub G. Contrast-enhanced breath-hold three-dimensional magnetic resonance angiography in the evaluation of renal arteries: optimization of technique and pitfalls. J Magn Reson Imaging 2000; 12:912-923.

25. Kopka L, Vosshenrich R, Rodenwaldt J, Grabbe E. Difference in injection rates on contrast-enhanced breath-hold three-dimensional MR angiography. AJR Am J Roentgenol 1998; 170:345-348.

26. Willman AH, Riederer SJ, King BF, et al. Fluoroscopically triggered contrast-enhanced three-dimensional MR angiography with elliptical centric view order: application to the renal arteries. Radiology 1997; 205:137-146.

27. Prince MR, Chenevert TL, Foo TKF, et al. Contrast-enhanced abdominal MR aortography: optimization of imaging delay time by automating the detection of contrast material arrival in the aorta. Radiology 1997; 203:109-114.

28. Ho VB, Foo TKF. Optimization of gadolinium-enhanced magnetic resonance angiography using an automated bolus detection algorithm (MR SmartPrep). Invest Radiol 1998; 33:515-523.

29. Lee VS, Rofsky NM, Krinsky GA, Stemerman DH, Weinreb JC. Single-dose breath-hold gadolinium-enhanced three-dimensional MR angiography of the renal arteries. Radiology 1999; 211:69-78.

30. Lebowitz JA, Rofsky NM, Krinsky G, Weinreb JC. Gadolinium-enhanced MR venography with subtraction technique. AJR Am J Roentgenol 1997; 169:755-758.

31. Koelemay MJW, Lijmer JG, Stoker J, Legemate DA, Bossuyt PMM. Magnetic resonance angiography for the evaluation of lower extremity arterial disease: a meta-analysis. JAMA 2001; 285:1338-1345.