Magnetic resonance angiography used to detect kinking in the iliac arteries in endurance athletes with claudication.

In endurance athletes, leg complaints upon maximal exercise caused by flow limitations in the iliac arteries are frequently encountered. We theorize that functional kinking of the vessels, which occurs especially during hip flexion, may be a cause for such flow limitations. Conventional diagnostic tests cannot demonstrate such kinkings. Using gadolinium-enhanced magnetic resonance angiography, a 3D dataset of the aorto-iliac arteries could be obtained with the hips flexed. An image processing procedure was developed using a new segmentation algorithm to be able to use standard surface rendering techniques to visualize the arteries with an improved 3D appearance. These techniques were applied in the current study in 42 endurance athletes with documented flow limitations in the iliac arteries. As a control group 16 national level competitive cyclists without flow limitations in the iliac arteries were studied. Forty-six affected legs were examined in 42 patients. In all patients and reference persons image quality was adequate and the segmentation algorithm could be applied. In 22 affected legs (48%) a kinking in the common iliac artery could be demonstrated, compared with one leg (3%) in the control group. In 13 affected legs (28%) a kinking in the external iliac artery could be demonstrated, compared with three legs (9%) in the control group. It can be concluded that flow limitations in the iliac arteries in endurance athletes are associated with kinkings in the common and/or the external iliac arteries. Magnetic resonance angiography with the hips flexed followed by this newly developed segmentation algorithm is effective to visualize and score these kinkings.

Motion of the proximal renal artery during the cardiac cycle.

In 48 hypertensive patients, the motion of the proximal renal artery during the cardiac cycle was quantified using two-dimensional quantitative flow (QF) measurements and automatic contour detection. Substantial translational motion was observed with an amplitude ranging from 1 to 4 mm. Since motion effectively reduces spatial resolution, the use of motion suppression techniques should be strongly considered for renal MR angiography. J. Magn. Reson. Imaging 2000;12:924-928.

Dealing with the subvoxel vessel position relative to the reconstruction voxel grid in 2D MR quantitative flow measurements.

A method is introduced that quantifies the error in 2D MR Quantitative Flow measurements induced by the position of the vessel relative to the reconstruction voxel grid, called the subvoxel vessel position. In this method, the vessel area and the volume flow rate are determined for all possible subvoxel vessel positions resulting in a mean value with standard deviation. Since the subvoxel vessel position in standard MR image reconstruction is completely arbitrary, the standard deviation can be considered as a measure of its random error contribution. Simulation studies and in vivo measurements show that our method can be used to quantify and subsequently eliminate this random error. It is further quantitatively shown that, for low noise levels, Fourier interpolation to a higher reconstruction matrix also decreases the random error. We conclude that the precision of a 2D MR Quantitative Flow measurement is improved either by using our method or by reconstruction to a higher matrix.

Flow limitations in the iliac arteries in endurance athletes. Current knowledge and directions for the future.

Pain and powerless feeling in the leg during cycling may indicate a serious problem that limits the performance in cyclists. Apart from the well-known muscular and neurological origin, such complaints can also be attributed to flow limitations in the iliac arteries caused by functional lesions (kinking and/or excessive length of vessels) and/or intravascular lesions (endofibrosis). Reliable insight in the prevalence is lacking. Most intravascular lesions (approximately 90%) are located in the external iliac artery. The diagnosis is frequently missed because physiotherapists and medical doctors are often unacquainted with the problem. The only finding in physical examination, discriminating for a vascular problem, is a bruit in the inguinal region with the thigh maximally flexed. Available diagnostic techniques are proven to be inadequate for this specific lesion, which has characteristics other than those of atherosclerotic lesions. Moreover, common techniques in a vascular laboratory do not incorporate the specific sport conditions necessary for provoking the complaints. Provocative testing on a bicycle ergometer with high intensity of exercise, combined with postexercise blood pressure measurements (at the ankle of both legs, or the ankle to arm pressure ratio) is used. Imaging techniques (echo-doppler, arterial digital subtraction angiography, magnetic resonance imaging and angiography) are necessary for proper classification of the problem. The application of specific provoking manoeuvres (hip flexion, psoas contraction, high-intensity exercise) in combination with these imaging techniques prove to be potentially valuable, although the diagnostic accuracy has to be established. Treatment should be tailored to the specific problems of the individual patient. Conservative treatment mainly indicates an advice to change sports activity. Surgical mobilization of the iliac arteries for functional lesions, and vascular reconstructions in case of intravascular lesions are possible, although long-term follow-up is lacking. Percutaneous transluminal angioplasty and intravascular stent are contra-indicated because of high risks for dissection and reactive intimal hyperplasia, respectively.

Venous signal suppression in 3D dynamic Gd-enhanced carotid artery imaging using the eigenimage filter.

A three-dimensional dynamic gadolinium-enhanced carotid artery imaging protocol with 10 sec per phase was evaluated with respect to the acquisition of an arterial-only phase after contrast bolus injection. Subsequently, the eigenimage filter was used to suppress any venous signal based on a difference in arterial and venous temporal enhancement patterns. From 63 consecutive scans of the carotid bifurcation, venous enhancement in the maximal arterial phase was found to be absent in 43%, weak in 19%, and strong in 38% of cases. Our eigenimage filter successfully suppressed the low signal veins in 100% and the high signal veins in 67% of cases. The number of acquired high-quality arterial-only images increased from 43% without to 87% with the use of the filter. In conclusion, even when a dynamic scan cannot resolve the short physiological delay between arterial and venous enhancement, the eigenimage filter can effectively be used to suppress the veins. Magn Reson Med 42:307-313, 1999.

Separation of haemodynamic flow waves measured by MR into forward and backward propagating components.

Physiological information on the action of the heart and on the reflection sites in the arterial system can be derived respectively from the forward and the backward propagating pressure or flow wave components. Earlier work on the separation of these components was exclusively based on invasive measurements of pressure or flow. In this study magnetic resonance (MR), which is a non-invasive imaging technique, was used to measure the blood flow waveform simultaneously at multiple positions along a vessel. Linear one dimensional transmission-line theory was used to separate the flow waves into forward and backward propagating components. First results, obtained from the thoracic aorta of five healthy male volunteers, consistently showed a negative reflection with a delay of about 100 ms between the foot of the forward and the foot of the backward propagating flow wave. Our model, consisting of a single vessel segment with constant diameter and wall properties, was validated by the excellent agreement between the vessel area as calculated from the flow data using the law of mass conservation and as directly measured with a different independent MR technique.